WO2000048029A1

WO2000048029A1 - Compact multiple port optical isolator

Info

Publication number: WO2000048029A1
Application number: PCT/US2000/001254
Authority: WO
Inventors: Ping Xie; Yonglin Huang
Original assignee: New Focus, Inc.
Priority date: 1999-02-11
Filing date: 2000-01-19
Publication date: 2000-08-17
Also published as: AU2415900A

Abstract

Disclosed is a multiple port optical fiber faraday isolator for isolating multiple spatially separate optical signals. First and second beam benders are used to minimize the size of the device. One embodiment uses lenses (202, 204) for the beam benders and these are positioned either side of the optical isolator core (210), with the convergence point of spatially separated signals located at the isolator core. In another embodiment the first and second beam benders both comprise two birefringent wedge pairs (730a-d, 740a-d), and are located between two isolator cores (726, 746).

Description

COMPACT MULTIPLE PORT OPTICAL ISOLATOR

BACKGROUND OF THE INVENTION

This application claims priority to United States Provisional Patent Application serial number 60/120,006, entitled "Compact Optical Isolator Arrays", filed February 11 , 1999.

An optical isolator transmits optical signals in one direction but blocks optical signals propagating in the opposite direction. Optical isolators find use, among other areas, in fiber optic networks at the output of laser diodes coupled to optical fibers in a fiber optic network. Laser diodes can be quite sensitive to optical signal reflections from other optical elements downstream of the laser diodes. Optical signal reflections may cause a shift in output wavelength of a laser diode, or output power loss. Optical isolators are used to block such reflections, effectively isolating laser diodes from perturbations due to downstream optical elements.

Further, it is desirable, in an optical isolator device for an optical fiber communication network, that the isolator be polarization insensitive. Generally, a light beam propagated through an ordinary optical fiber has an arbitrary polarization. Moreover, the polarization state changes due to the factors including varying ambient temperature and deformation of the fiber. For polarization insensitive optical isolator devices, reference may be made to, for example, United States Patent Nos. 4,548,478, issued October 22, 1985 and 4,239,329, issued December 16, 1980. These documents, and all other documents cited to herein are incorporated by reference as if reproduced fully herein.

A single optical isolator device disclosed in the above U.S. Patent No. 4,548,478 is disclosed as having a first birefringent crystal wedge for splitting an incident light beam into an ordinary ray and an extraordinary ray, a Faraday rotator for rotating the polarization direction of the two rays from the first crystal wedge by 45 degrees, and a second birefringent crystal wedge for combining the two polarization components that have passed the Faraday rotator. When a reflection of the output beam of the isolator device is propagated through the device in the opposite direction, the relation between the polarizations is reversed in the first crystal wedge. As a result, the forward and reverse beams do not follow the same optical path, thus isolation is achieved. This kind of isolator device is free from changes in loss caused by the changes in the polarization of the input beam since light in the isolator device moves in a constant manner without regard to the polarization orientation of the input beam.

To enhance the isolation, a series of birefringent wedges interposed with non-reciprocal Faraday rotators can be placed in series. For example, a first birefringent crystal plate, a Faraday rotator, a second birefringent crystal plate, a Faraday rotator and a third birefringent crystal plate may be sequentially arranged in this order, as disclosed in Summaries of 1991 Spring Conference of The Institute of Electronics, Information and Communication Engineers, pp. 4-125.

The isolator device of U.S. Patent No. 4,239,329 is, in principle, the same as the above-stated isolator device except that the birefringent crystal wedges are replaced by birefrigent walk-off crystals and an additional reciprocal polarization rotator is also added. In operation, the light from one optical fiber is separated into ordinary and extraordinary ray by a first birefrigent crystal member. Both rays are subjected to a total of 90° polarization rotation by transmitting in a forward direction through a Faraday rotator having an angle of polarization rotation of 45° and through a reciprocal polarization rotator having an angle of polarization rotation of 45°. The ordinary and extra-ordinary rays may then be recombined at the second birefringent crystal member. In the reverse direction, the relation between the polarization components is reversed in the first crystal member. The forward and reverse beams do not follow the same optical path, thus isolation is achieved.

Optical isolators have become ubiquitous in modern fiber optic networks, particularly in telecommunications networks, because of their role in reducing laser diode output wavelength drift and signal power loss. As the complexity of these networks has increased, the number of laser diodes in a given network has also increased. Accordingly, the need for large numbers of optical isolators in a given network or optical circuit has also increased

However, a single optical isolator may be expensive and the costs of optical isolators for a particular network can be quite high. Furthermore, the number of devices can increase system complexity and raise system costs. Attempts have been made to resolve these problems. For example, United States Patent No. 5,706,371 to Pan discloses an optical isolator array. This document, and all other documents referred to herein are incorporated by reference as if reproduced fully herein. The array is disclosed as having a substrate with parallel grooves and a groove perpendicular to the parallel grooves to separate them. First sleeves each holding an end section of a first optical fiber and a first collimating element may be fixed in the parallel grooves on one side of the perpendicular groove. Second sleeves each holding an end section of a second optical fiber and a second collimating element may be fixed in the parallel grooves on the other side of the perpendicular groove. An optical isolator core subassembly having first and second strips of birefringent polarizer material, and a strip of Faraday rotator material between the first and second strips of birefringent polarizer materials is fixed in the perpendicular groove. Each optical isolator is disclosed as being formed by a first sleeve, first collimating lens, the optical isolator core subassembly, the second collimating lens and the second sleeve in a parallel groove between a first optical fiber and a second optical fiber having end sections held respectively in the first and second sleeves.

However, this approach simply puts each individual isolator side by side and then packages them to form an array. If more isolators are needed, the dimensions of the crystal core must be enlarged. Therefore, the optical footprint (or size) of the array is still approximately the same as if individual optical isolators were being used, with a minimal savings of materials. Additionally, alignment costs are not reduced with this design compared with individual optical isolators. Therefore, this design is not very satisfactory due to the optical footprint and cost considerations.

There is therefore a need for apparatus and methods to solve the above mentioned problems.

SUMMARY OF THE INVENTION

In an aspect, the invention relates to an optical isolator array for optically isolating at least one optical signal comprising a first beam bender; a first optical isolator core optically coupled to the beam bender; a second beam bender, optically coupled to the first optical isolator core; and the second beam bender located on a side of the optical isolator core opposite from the first beam bender, wherein the first beam bender, first optical isolator core, and second beam bender all are located along a propagation path of an optical signal propagating through the optical isolator array. In another aspect, the invention relates to a method of isolating an optical signal comprising providing an optical isolator array comprising one or more isolator stages, wherein each isolator stage comprises an optical isolator core optically coupled to a set of optical signals; inserting an optical signal into the optical isolator array; and optically isolating the optical signal. In yet another aspect, the invention relates to a method of optically isolating multiple spatially separate optical signals comprising generating a set of optical signals propagating along propagation paths; converging the propagation paths thereby converging the set of optical signals; and propagating the set of optical signals through at least one optical isolator core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of an optical isolator array according to the invention. FIG. 2 shows a side view of a single stage optical isolator array according to the invention.

FIG. 3 shows a side view of a two stage optical isolator array according to the invention.

FIG. 4 shows a side view of a two stage optical isolator array according to the invention, having a different configuration.

FIG. 5 shows a side view of an optical isolator array, according to the invention, that incorporates birefringent walk-off crystals.

FIG. 6 shows a side view of a two stage optical isolator array, according to the invention, that incorporates birefringent walk-off crystals. FIGS. 7A-B show a top and side view of another embodiment of an optical isolator array according to the invention.

FIGS. 7C-D show a cross-sectional view of an optical isolator array according to the invention, with the relative spatial positions of the polarization components indicated. FIGS. 8A-B shows a top and side view of a multiple stage optical isolator array according to the invention. DETAILED DESCRIPTION OF THE INVENTION An optical isolator is typically comprised of a subassembly of an isolator core, an input fiber assembly, and an output fiber assembly. A free space isolator comprises only an isolator core subassembly. An optical isolator array is disclosed in the present invention. Optical isolator arrays according to the invention comprise a set of converging optical signals, and a single optical isolator core through which all the optical signals pass. In a preferable embodiment, the set of optical signals comprise optical signals that are spatially separate In a preferable embodiment, the optical signals are caused to converge by beam benders that turn the optical signals propagating through them through a determinable angle. The angle is determined by factors including, but not limited to, the angle of incidence, and the direction of propagation.

In another aspect of the invention, beam benders, of which the inventive optical array is comprised, are used to bend optical signals to converge to at least one focal point, permitting shared use of a single optical device by at least one, preferably two or more, optical signals.

The invention is generally illustrated in FIG. 1. FIG. 1 shows a set of converging optical signals 102 with convergence point 104. This is a set of interest, i.e. a set of converging optical signals that are desired to be isolated; and may be a sub-set of a larger set of optical signals being processed as part of a larger optical circuit. Also shown are is a representation of an optical isolator cores that may be placed at positions 106, 108 and 110. At each of positions 106, 108 and 110, the optical isolator core is placed so that each individual signal of the set of converging optical signals passes through a single optical isolator core. The action of an optical isolator core on the set of converging optical signals as shown creates the inventive optical isolator array. Particular advantages of the invention may be seen by inspecting the relative size of the optical isolator core at positions 106, 108 and 110 that is needed to include all of the converging optical signals. For example, the optical isolator core at position 106 needs to be spatially the largest optical isolator core, followed by the optical isolator cores at positions 108 and 110, respectively. The closer that an optical isolator core, according to the invention, is located to convergence point 104, the more economical the inventive optical isolator array will be. This is because the distance between the converging optical signals decreases, permitting use of a smaller optical isolator core in the inventive optical isolator array. Therefore, by manipulating the positioning of the optical isolator core element, it is possible to reduce hardware cost by using smaller optical elements. In a preferable embodiment, the optical isolator core is located at or near a convergence point of propagation paths of optical signals propagating through the optical isolator array.

Another preferable method for reducing costs of hardware or optical elements, according to the invention, is by changing the focusing, collimation, or convergence/divergence of sets of optical signals. In this way, the relatively expensive optical isolator cores may be spatially located in such a fashion as to minimize their cost, such as at a convergence point, or at a point where the set of optical signals has been collimated.

In a preferable embodiment, changing the focusing, collimation, or convergence/divergence of sets of optical signals may be accomplished by using one or more beam benders. Preferable beam benders according to the invention may be based on either polarization insensitive beam turning, for example through a lens or polarization sensitive turning, for example through a birefringent prism system.

In another embodiment, alignment of multiple sets of optical signals propagating through the inventive optical isolator array may be achievable simultaneously. For example, by aligning only one or two signals across the optical isolator array, the remaining signals may be isolated and aligned. This particular advantage of the invention may be achieved by mounting input fiber arrays and output fiber arrays in precisely fabricated grooves or bores in mounting pieces such that the relative position of the input fiber arrays, carrying the input optical signals, matches that of the output fiber arrays, carrying the output optical signals. This reduces alignment time, and increases output yields.

Polarization sensitive angle turning may be preferably achieved by having an optical signal be incident upon a birefringent crystal at an angle with respect to the crystal's c axis. Beams with different polarization vectors may experience different angles of refraction because of the difference in index of refraction in beam bender birefringent crystals. In alternate embodiments of the invention, the polarization sensitive beam bender comprises a Wollaston, Rochon, or modified Wollaston or Rochon prism, a Senarmont prism or other polarization dependent angle turning optical elements. These prisms produce separate beam pathways by refractive separation of a beams transmitted through the prism at polarization vector dependent angles. In another aspect of the invention, optical isolator cores along the optical isolator array may be optically coupled in series to increase the degree of isolation by forming a single or multiple stage isolator. For example, a two-stage isolator array may comprise two isolator cores with total isolation twice that of each individual isolator core. It is a particular advantage of the invention that significant increases in optical isolation may be achieved for a number of optical signals at a lesser increase in component cost as compared to conventional isolators.

Suitable materials and designs useful in making optical isolator arrays according to the invention are disclosed in U.S. Patent Application Serial No. 09/135,083, filed August 17, 1998, [Attorney Docket No. 10629.725], and U.S. Patent Application Serial No. 09/186,751 , filed November 5, 1998, [Attorney Docket No. 10629.729], both of which are incorporated herein by reference. A number of different optical isolator core arrangements may be usable in the practice of the invention. Functionally, optical isolator cores may be arranged such that a pair of polarizers sandwich a non-reciprocal (i.e. Faraday) rotator. Suitable polarizers comprise birefringent wedges, birefringent walk-off crystals, Wollaston prisms, Rochon prisms and the like. Suitable non-reciprocal rotators comprise latching Faraday garnet (doesn't require a magnet) and non-latching garnet (usually requires a magnet). One arrangement according to the invention comprises a pair of birefringent wedges sandwiching a non-reciprocal rotator. Another arrangement is shown in FIG. 5, discussed below, which uses a pair of birefringent walk-off crystals that sandwich a non-reciprocal rotator and a reciprocal rotator. Polarization insensitive turning may be achieved, in part, by propagating an optical signal through, for example, a polarization insensitive beam bender such as a lens, at a distance from the lens' principal axis. A wide variety of lenses may be useful in the practice of the invention, including, but not limited to, GRIN lenses, asperic lenses, plano-convex lenses, ball lenses, and the like. This embodiment is illustrated in FIG. 2, wherein two lenses are used to converge and then collimate a set of input optical signals. Optical isolator array 200, as shown in FIG. 2, includes first beam bender 202, second beam bender 204, and optical isolator core 206. Optical isolator core 206 includes first birefringent wedge 208, second birefringent wedge 212, and non-reciprocal rotator 210.

First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 206, along a propagation path of input optical signals 214 and output optical signals 218. In optical isolator core 206, first birefringent wedge 208 and second birefringent wedge 212 are located on either side of non-reciprocal rotator 210, along a propagation path of input optical signals 214 and output optical signals 218.

In operation, input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 216. The set of converging optical signals 216 then propagates through optical isolator core 206. As each optical signal propagates through birefringent wedge 208, it will be decomposed into two perpendicular polarization components with different propagation orientations. Non-reciprocal rotator 210 rotates the polarization direction of both polarization components by 45 degrees. Upon propagating through second birefringent wedge 212, both polarization components will be bent to propagate along the same optical path. Further discussion of optical isolator core 206's operation may be found in U.S. Patent No. 4,548,478 to Shirasaki, hereby incorporated by reference in its entirety. Next, the optical signals emerging from optical isolator core 206 are collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218. When input optical signals 214 are coming from optical fibers, first beam bender 202 may serve two functions. First, it collimates the optical signal from each individual fiber. Second, it causes convergence of the set of converging optical signals 216. Similarly, second beam bender 204 serves two functions. First, it causes a set of diverging optical signals to become collimated. Second, it focuses each collimated optical signal into its respective receiving fiber to enhance the coupling efficiency. In other words, because first beam bender 202 may have modified the beam profile of the optical signals, second beam bender 204 may serve to correct the beam profile of output optical signals 218 back to be substantially the same as that of input optical signals 214. This enhances fiber to fiber coupling efficiency. Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 200. This effect produces optical isolation. The impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc.

The type of optical isolator core used in optical isolator array 200 is usually not polarization mode dispersion free (PMD-free), as in the case of a single isolator built with that core, because of the use of the brirefringent wedges. To reduce or eliminate PMD in a conventional manner, a compensation plate may be used. Such a compensation plate may include a birefringent plate that possesses an optical path difference or differential group velocity delay between its two polarization eigenstates. If the plate is designed to have the same amount of PMD but in opposite sign with respect to the isolator core, PMD of the combined isolator core and compensation plate will be eliminated or substantially reduced. However, additional compensation plate adds alignment complexity and cost to the optical isolator array.

PMD-free, or substantially PMD-free, optical isolator array 300, which is configured such that a compensation plate is not needed, is shown in FIG. 3. Optical isolator array 300 possesses an additional advantage over optical isolator array 200 in that it is a multiple stage optical isolator array. PMD- free, or substantially PMD-free, operation may be achieved by adding a second optical isolator core based on birefringent wedges having an opposite sign PMD as compared to the first optical isolator core that is also based on birefringent wedges. An example of a PMD compensated isolator device is disclosed in U.S. Patent No. 5,557,692. Optical isolator array 300 includes first beam bender 202, second beam bender 204, optical isolator core 206 and second optical isolator core 302. Optical isolator core 206 includes first birefringent wedge 208, second birefringent wedge 212, and non-reciprocal rotator 210. Second optical isolator core 302 includes third birefringent wedge 304, fourth birefringent wedge 308, and second non-reciprocal rotator 306.

First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 206, along a propagation path of input optical signals 214 and output optical signals 218. In optical isolator core 206, first birefringent wedge 208 and second birefringent wedge 212 are located on either side of non-reciprocal rotator 210, along a propagation path of input optical signals 214 and output optical signals 218. Second optical isolator core 302 is located between optical isolator core 206 and second beam bender 204, along a propagation path of input optical signals 214 and output optical signals 218. In second optical isolator core 302, third birefringent wedge 304 and fourth birefringent wedge 308 are located on either side of second non-reciprocal rotator 306, along a propagation path of input optical signals 214 and output optical signals 218.

In operation, input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 216. The set of converging optical signals 216 then propagates through optical isolator core 206. The operation of optical isolator core 206 has been generally described above. Next, the optical signals emerging from optical isolator core 206 propagate through second optical isolator core 302, for a second stage of optical isolation. The optical signals are then collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218.

Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 300. This effect produces optical isolation. Further discussion of optical isolator core 206's operation or second optical isolator core 302's operation may be found in U.S. Patent No. 4,548,478 to Shirasaki, The impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc.

FIG. 4 shows an alternative arrangement to multiple stage optical isolator array 300. In this embodiment, the beam benders are located between the optical isolator cores, instead of the other way around. Optical isolator array 400 includes first beam bender 202, second beam bender 204, optical isolator core 206 and second optical isolator core 302. Optical isolator core 206 includes first birefringent wedge 208, second birefringent wedge 212, and non-reciprocal rotator 210. Second optical isolator core 302 includes third birefringent wedge 304, fourth birefringent wedge 308, and second non-reciprocal rotator 306.

First beam bender 202 and second beam bender 204 are located between optical isolator core 206 and second optical isolator core 302, along a propagation path of input optical signals 214 and output optical signals 218. In optical isolator core 206, first birefringent wedge 208 and second birefringent wedge 212 are located on either side of non-reciprocal rotator 210, along a propagation path of input optical signals 214 and output optical signals 218. In second optical isolator core 302, third birefringent wedge 304 and fourth birefringent wedge 308 are located on either side of second non-reciprocal rotator 306, along a propagation path of input optical signals 214 and output optical signals 218.

In operation, input optical signals 214 propagate through optical isolator core 206. The operation of optical isolator core 206 has been generally described above. The optical signals then pass through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 416. The set of converging optical signals 216 then propagates through convergence point 418, after which they diverge and are collimated by second beam bender 204. Next, the optical signals propagate through second optical isolator core 302, for a second stage of optical isolation and are outputted from the optical isolator array as output optical signals 218.

Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 400. This effect produces optical isolation. The advantages of optical isolator array 400 are similar to those of optical isolator array 300, in that optical isolator array 400 operates with a greater degree of isolation, and with low cost compared to conventional isolators. Further, use of two isolator cores having opposite PMD relative to one another may result in substantially PMD-free operation.

FIG. 5 shows an embodiment of optical isolator array 500, according to the invention. Optical isolator array 500 includes a new configuration of optical isolator cores, based on a pair of birefringent walk-off crystals, rather than birefringent wedges. Further, optical isolator array 500 achieves substantially PMD-free operation in a different manner to the manner previously discussed in the description of the birefringent wedge embodiments. Optical isolator array 500 includes first beam bender 202, second beam bender 204, and optical isolator core 506. Optical isolator core 506 includes first birefringent walk-off crystal 502, second birefringent walk-off crystal 504, reciprocal rotator 508, and non-reciprocal rotator 210. First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 506, along a propagation path of input optical signals 214 and output optical signals 218. In optical isolator core 506, first birefringent walk-off crystal 502 and second birefringent walk-off crystal 504 are located on either side of non-reciprocal rotator 210 and reciprocal rotator 508, along a propagation path of input optical signals 214 and output optical signals 218. Non-reciprocal rotators include Faraday rotators; reciprocal rotators include half-wave plates.

In operation, input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 216. The set of converging optical signals 216 then propagates through optical isolator core 506. In optical isolator core 506, first birefringent walk-off crystal 502 spatially separates the components of input optical signals 214 that are polarized perpendicularly to each other. Conversely, second birefringent walk-off crystal 504 spatially recombines the components, meaning that the inventive optical isolator arrays are inherently polarization insensitive and are useful in, among other uses, telecommunications applications. The optical axes of first birefringent walk-off crystal 502 and second birefringent walk-off crystal 504 are positioned such that the ordinary component is not laterally displaced during propagation through the inventive optical isolator arrays. However, the extraordinary component is displaced in one direction by the first birefringent walk-off crystal 502 (for example, up), and in the other direction direction by the second birefringent walk-off crystal 504 (for example, down). Such an arrangement of the birefringent walk-off crystals promotes PMD-free, or substantially PMD-free, operation may be achieved without introducing an additional compensation plate. A further advantage is that single stage PMD-free, or substantially PMD-free, operation may be achieved as compared to birefringent wedge-based optical isolator cores.

However, the size of the birefringent crystals is usually significantly greater than that of birefringent wedges, thus potentially adding to the component cost of this embodiment of the inventive optical isolator array as compared to the birefringent wedge embodiments. Additionally, use of birefringent crystals necessitates the use of reciprocal rotators or a third birefringent crystal for recombining two perpendicular polarization beams. Such a configuration adds costs versus a birefringent wedge embodiment that does not necessarily require use of a reciprocal rotator to achieve substantially PMD-free performance.

The optical signals emerging from optical isolator core 506 are collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218. Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 500. This effect produces optical isolation. Further discussion of optical isolator core 506's operation may be found in U.S. Patent No.

4,239,329, to Matsumoto, hereby incorporated by reference in its entirety. The impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc.

Optical isolator array 600 is another example of a multiple stage optical isolator array. Optical isolator array 600 is constructed with optical isolator cores that use birefringent walk-off crystals, similarly to optical isolator array 500, described above. Optical isolator array 600 includes includes first beam bender 202, second beam bender 204, optical isolator core 506 and second optical isolator core 602. Optical isolator core 506 includes first birefringent walk-off crystal 502, second birefringent walk-off crystal 504, reciprocal rotator 508, and non-reciprocal rotator 210. Second optical isolator core 602 includes third birefringent walk-off crystal 604, fourth birefringent walk-off crystal 608, second reciprocal rotator 610, and second non-reciprocal rotator 606.

First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 506, along a propagation path of input optical signals 214 and output optical signals 218. In optical isolator core 506, first birefringent walk-off crystal 502 and second birefringent walk-off crystal 504 are located on either side of non-reciprocal rotator 210 and reciprocal rotator 508, along a propagation path of input optical signals 214 and output optical signals 218. Second optical isolator core 602 is located between optical isolator core 506 and second beam bender 204, along a propagation path of input optical signals 214 and output optical signals 218. In second optical isolator core 602, third birefringent walk-off crystal 604 and fourth birefringent walk-off crystal 608 are located on either side of second non-reciprocal rotator 606 and reciprocal rotator 610, along a propagation path of input optical signals 214 and output optical signals 218.

In operation, input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals. The set of converging optical signals then propagates through optical isolator core 506. Next, the optical signals emerging from optical isolator core 506 propagate through second optical isolator core 602, for a second stage of optical isolation. The optical signals are then collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218. Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 600. This effect produces optical isolation. The impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc. Of course, additional stages of optical isolation may be added to optical isolator core 600 to increase the amount of optical isolation delivered by optical isolator core 600.

FIGS. 7A-B show top and side views of an embodiment of an inventive optical isolator array. The optical isolator core shown in FIGS. 7A- B show beam benders comprising modified Wollaston prisms. Conventional Wollaston prisms are formed by two birefringent wedges. In such prisms, the optical axes of each birefringent wedge are substantially perpendicular to one another and one of the optical axes is perpendicular to the direction of wedge interface. Conventional Wollaston and Rochon prisms are discussed further in Hecht, Optics 292 & 329 (1987) (2d. ed. Addison- Wesley). In contrast, in a modified Wollaston prism the optical axis of each of its wedges are oriented perpendicularly to each other and 45 degrees in a plane that is normal to the normal incidence direction with respect to the optical axis in a conventional Wollaston prism. Similarly, in a modified Rochon prism, the optical axis of one of the wedges is oriented normal to the first interface, which is the same as in a conventional Rochon prism. The first interface is normal to the normal incidence of the optical signal. However, the optical axis in the other wedge is oriented 45 degrees in the second interface (the second interface being parallel to the first interface and at the opposite end of the modified Rochon prism) with respect to the optical axis orientation the wedge would possess in a conventional Rochon prism.

FIGS. 7A-B show a view of optical isolator array 700, according to the invention. Optical isolator core need not have each of its component elements physically coupled, so long as they are optically coupled. For example, an optical isolation core of optical isolator array 700 comprises two polarizers (first beam displacer/combiner 722 and second beam displacer/combiner 750, discussed below), and two non-reciprocal rotators (first nonreciprocal rotator 726 and second nonreciprocal rotator 746). Optical isolator array 700 includes first optical port 702, third optical port 704, second optical port 706, fourth optical port 708, first imaging element 770, second imaging element 772, first beam displacer/combiner 722, first nonreciprocal rotator 726, first beam benders 730A-D, second beam benders 740A-D, second nonreciprocal rotator 746, and second beam displacer/combiner 750.

Optical isolator array 700 possesses a longitudinal axis, along which the various optical components are distributed, and a proximal and distal end. First optical port 702, and third optical port 704 are located at a proximal end, and second optical port 706 and fourth optical port 708 are located at a distal end of the optical isolator array.

In preferable embodiments, the first, second, third and fourth optical ports may comprise integrated optical circuits or optical fibers. First imaging element 770 may be preferably located on the optical path between the first and third optical ports and the first beam displacer/combiner. Second imaging element 772 may be preferably located on the optical path between the second and fourth optical ports and the second beam displacer/combiner. Such arrangements result in the first, and third optical ports on the proximal side and the second and fourth optical ports on the distal side being conjugate images of each other. In a preferable embodiment, the first or second imaging element may be a collimating lens. In a more preferable embodiment, the imaging element may be a Grin lens. First beam displacer/combiner 722 is optically coupled distally to the first and third optical ports. In a preferable embodiment, the first beam displacer/combiner is a birefringent crystal. In a more preferable embodiment, the first beam displacer/combiner comprises Yttrium Orthovanadate, calcite, rutile or alpha-BBO. First nonreciprocal rotator 726 comprises a nonreciprocal Faraday polarization rotator and is optically coupled distally from the first beam displacer/combiner. In a preferable embodiment, first nonreciprocal rotator 726 comprises yttrium-iron-garnet (YIG), or Bi-added thick film crystals. The Bi-added thick film crystals preferably comprise a combination of (YbTbBi)₃Fe₅O₁₂ and (GdBi)₃(FeAIGa)₅O₁₂₎ or of Y.I. G. and Y_3xBi_xFe₅O₁₂. First beam benders 730A-D comprise two pairs (i.e. four) of birefringent wedges that are optically coupled distally to the first nonreciprocal rotators and to each other. In a more preferable embodiment, the first beam benders comprise one or more prisms. In a still more preferable embodiment, the first beam benders comprises a set of Wollaston, Rochon or modified Wollaston or Rochon prisms. In the following discussion, the beam benders may comprise modified Wollaston prisms. The beam benders, which are indicated in optical isolator array 400 by the pairs of beam benders 730A-B, 730C-D, 740A-B, and 740C-D, are stacked in the embodiment as shown. The arrangement of beam benders 730A-B and 730C-D is identical, except that they are rotated by 180 degrees with respect to the optical isolator array's longitudinal axis. Similarly, beam benders 740A-B and 740C-D are identical, except for their 180 degrees rotation with respect to the optical isolator array's longitudinal axis. Thus, beam benders 730C-D are stacked on top of beam benders 730C-D, to form a stacked set of beam benders. Likewise beam benders 740C-D are stacked on top of beam benders 740A- B to form a stacked set of beam benders. The effect of these stacked sets of beam benders is to permit angle turning of both the top and bottom components that are orthogonal to each other in the same direction without having to change their orientation.

There is a complete gap 736, defined by the first beam benders 730A-D, and the second beam benders 740A-D that is located distally from first beam benders 730A-D. The first and second beam benders are therefore spaced apart from one another.

Second nonreciprocal rotator 746 comprises a nonreciprocal Faraday polarization rotator and is optically coupled distally from the second beam benders. In a preferable embodiment, the second nonreciprocal rotators comprise yttrium-iron-garnet (YIG), or Bi-added thick film crystals. The Bi- added thick film crystals comprise a combination of (YbTbBi)₃Fe₅O₁₂ and (GdBi)₃(FeAIGa)₅O₁₂, or of YIG and Y_3xBi_xFe₅O₁₂. Second beam displacer/combiner 750 is optically coupled distally from the second nonreciprocal rotators and proximally from the second optical port.

In operation, arbitrarily polarized light from first optical port 702 and exits first imaging element 770 at a slight angle to the longitudinal axis of first imaging element 770. The arbitrarily polarized light then enters first beam displacer/combiner 722, which acts as a polarization sensitive beam displacement plate. The arbitrarily polarized light is decomposed into two orthogonal polarization components. Within the first beam displacer/combiner, the first component is an ordinary light ray (O-ray) and the other component is an extraordinary light ray (E-ray). The E-ray walks off vertically from the O-ray through the first beam displacer/combiner, with the result that there is a top and bottom component. The components then enter first nonreciprocal rotator 726. In a preferable embodiment, first nonreciprocal rotator 726 rotates by 45 degrees clockwise both the top and bottom components of light passing through it from first optical port 702 to second optical port 706. In another preferred embodiment, the relative directions of rotation imparted by first nonreciprocal rotator 726 and second nonreciprocal rotator 746 may be respectively reversed.

Upon exiting the first nonreciprocal rotators, the components enter first beam benders 730A-D. The first beam benders turn both polarization components towards the longitudinal axis of the optical isolator array without changing their polarization orientation. The components then exit the first beam bender and transit complete gap 736. The components next pass through second beam benders 740A-D, which bend the components such that their propagation directions are changed. The first and second beam benders and the complete gap are adjusted so as to achieve alignment of the components with the longitudinal axis of the second imaging element and/or second optical port 706, as discussed above. The components then enter second nonreciprocal rotator 746. In a preferable embodiment, second nonreciprocal rotator 746 rotates by 45 degrees clockwise both top and bottom components of light passing through it from first optical port 702 to second optical port 706. The components then pass through second beam displacer/combiner 750, where the beams are recombined. The recombined light beam then passes through second optical port 706 via second imaging element 772. Arbitrarily polarized light reflected back through optical port 706 will travel along a different path as it will be refracted at the interface between beam benders 740D and 740C, and at the interface between beam benders 740A and 740B. This refraction effectively isolates the signal passing from first optical port 702 to second optical port 706.

A particular advantage of optical isolator array 700, as indeed of all the optical isolator arrays according to the invention, is that the inventive optical isolator arrays are capable of simultaneously isolating optical signals propagating through the optical isolator array. This simultaneous optical isolation feature is highly desirable, as it permits design of optical circuits possessing smaller optical footprints and lower costs as compared with conventional optical isolator core designs. For example, two or more signals may be isolated by passing the signals through a single isolator array according to the invention. The operation of optical isolator array 700 is illustrated in the cross sectional schematic representations shown in FIGS. 7C-D. FIG. 7C shows how the two orthogonal components of unpolarized light entering at first optical port 702 are manipulated so as to arrive at second optical port 706. The two unpolarized orthogonal components are shown at cross section A- A, as they exit first imaging element 770 and enter the first beam displacer/combiner. At cross-section B-B, upon exiting first beam displacer/combiner 722, the top component is shown as being walked off vertically from the bottom component, and both the top and bottom components are shown as being shifted equidistantly in the same direction - - to the left of the cross-section of the optical isolator array - due to action of first imaging element 770. At cross-section C-C, upon exiting first nonreciprocal rotator 726, the polarization of the top and bottom component are shown as being rotated 45 degrees clockwise. At cross-section D-D, upon exiting beam benders 740A-D, both of the components are unchanged in polarization orientation, but their spatial position and their propagation direction have been changed. At cross-section E-E, upon exiting second nonreciprocal rotator 746, the polarization of both the top and bottom components is shown as being rotated 45 degrees clockwise. At cross- section F-F, upon exiting second beam displacer/combiner 750, the two components are recombined to exit at second optical port 706. Arbitrarily polarized light reflected back through second optical port 706 (e.g. part of an optical signal reflected from a component downstream of the optical isolator array) will travel along a different path as it will be refracted at the interface between beam benders 740D and 740C, and at the interface between beam benders 740A and 740B. This refraction effectively isolates the signal passing from first optical port 702 to second optical port 706. First beam displacer/combiner 722 also promotes isolation of the optical signal. FIG. 7D shows how the two orthogonal components of unpolarized light entering at fourth optical port 708 are manipulated so as to arrive at third optical port 704. The two unpolarized orthogonal components are shown at cross section F-F, as they exit second imaging element 772 and enter second beam displacer/combiner 750. At cross-section E-E, upon exiting second beam displacer/combiner 750, the bottom component is shown as being walked off vertically from the top component, and both the top and bottom components are shown as being shifted equidistantly in the same direction - to the right of the cross-section of the optical isolator array - due to the action of second imaging element 772. At cross-section D-D, upon exiting second nonreciprocal rotator 746, the polarization of the top and bottom component are shown as being rotated 45 degrees clockwise. At cross-section C-C, upon exiting beam benders 730A-D, both of the components are unchanged in polarization orientation, but their spatial position and their propagation direction have been changed. At cross- section B-B, upon exiting first nonreciprocal rotator 726, the polarization of both the top and bottom components is shown as being rotated 45 degrees clockwise. At cross-section A-A, upon exiting first beam displacer/combiner 722, the two components are recombined to exit at third optical port 704. Arbitrarily polarized light reflected back through third optical port 704 (e.g. part of an optical signal reflected from a component downstream of the optical isolator array) will travel along a different path as it will be refracted at the interface between beam benders 730D and 730C, and at the interface between beam benders 730A and 730B. This refraction effectively isolates the signal passing from fourth optical port 708 to third optical port 704. Second beam displacer/combiner 750 also promotes isolation of the optical signal.

FIGS. 8A-B show top and side elevations of another optical isolator array according to the invention, in a multiple stage optical isolator array configuration, with a different configuration of optical isolator cores and beam benders. As noted above, it is an advantage of the invention that multiple stages of optical isolation may be achieved simultaneously across a number of different optical signals. Further, the addition of end portions with beam displacer/combiners and non-reciprocal rotators provides for polarization of normal light beams that varies depending on the propagation direction of the incoming light beam. This allows optical isolator arrays to be built that isolate input signals with arbitrary polarization orientation and arbitrary degrees of polarization. Multiple stage optical isolator array 800 includes: first optical port 802, third optical port 804, second optical port 806, fourth optical port 822, fifth optical port 820, and sixth optical port 824, first end portion 870, center portion 880, and second end portion 890. First end portion 870 includes first beam displacer/combiner 810, first nonreciprocal rotator 826A, and first reciprocal rotator 827. Center portion 880 includes first imaging element 830, beam bender 808, 812, and second imaging element 832. Second end portion 890 includes second nonreciprocal rotator 836A, second reciprocal rotator 837, and second beam displacer/combiner 840.

The components of the optical isolator array 800 are laid out along a longitudinal axis. First end portion 870 is optically coupled distally to the first and third optical ports, and is located in an opposing relationship to second end portion 890. First beam displacer/combiner 810 is optically coupled distally to the first, third, and fifth optical ports 802, 804, and 820. In a preferable embodiment, first beam displacer/combiner 810 is a birefringent crystal. In a more preferable embodiment, first beam displacer/combiner 810 comprises Yttrium Orthovanadate, calcite, rutile or alpha-BBO (barium borate). First nonreciprocal rotator 826A comprises nonreciprocal Faraday polarization rotators and are optically coupled distally from first beam displacer/combiner 810. In a preferable embodiment, first nonreciprocal rotators 826A-B comprise yttrium-iron-garnet (YIG), or Bi-added thick film crystals. The Bi-added thick film crystals preferably comprise a combination of (BiTb)₃(FeGa)₅O₁₂, (YbTbBi)₃Fe₅O₁₂ and (GdBi)₃(FeAIGa)₅O₁₂, or of YIG and Y_3xBi_xFe₅O₁₂. Optically coupled on a side of first non-reciprocal rotator 826A opposite from first beam displacer/combiner 810 is reciprocal rotator 827, which is preferably a half-wave plate.

Optically coupled distally to first end portion 870 is center portion 880. Included in center portion 880 are walk-off crystals 828 and 834, imaging elements 830 and 808, together with complete gap 812. Walk-off crystal 828 is optically coupled distally to first reciprocal rotator 827. Imaging element 830 is optically coupled to walk-off crystal 828. Imaging element 832 is optically coupled, across complete gap 812, to imaging element 830, thus defining complete gap 812. In a preferable embodiment, either or both of the imaging elements comprise aspheric lenses. Each of the imaging elements 830, 832 has a common focal point 852. Walk-off crystal 834 is optically coupled to imaging element 832.

Optically coupled distally to center portion 880 is second end portion 890. Second end portion 890 comprises second reciprocal rotator 837, which is optically coupled to second nonreciprocal rotator 836A, which is in turn optically coupled to walk-off crystal 834. Second nonreciprocal rotator 836A may comprise a nonreciprocal Faraday polarization rotator. In a preferable embodiment, second nonreciprocal rotator 836A comprises yttrium-iron-garnet (YIG), or Bi-added thick film crystals. The Bi-added thick film crystals preferably comprise a combination of (YbTbBi)₃Fe₅O₁₂ and (GdBi)₃(FeAIGa)₅O₁₂, or of YIG and Y_3xBi_xFe₅O₁₂. Reciprocal rotator 837 preferably comprises a half-wave plate. Second beam displacer/combiner 840 is optically coupled distally from second nonreciprocal rotator 836A and proximally from second optical port 806, fourth optical port 822, and sixth optical port 824. In operation, arbitrarily polarized polarized light from first optical port 802 enters first beam displacer/combiner 810, which acts as a polarization sensitive beam displacement plate. The arbitrarily polarized light is decomposed into two rays with orthogonal polarization vectors. Within first beam displacer/combiner 810, the first ray is an ordinary light ray (O-ray) and the other ray is an extraordinary light ray (E-ray). The E-ray walks off vertically from the O-ray through first beam displacer/combiner 810, with the result that there is a top and bottom ray, relative to the longitudinal axis. The rays then enter first nonreciprocal rotator 826A. In a preferable embodiment, first nonreciprocal rotator 826A rotates by 45 degrees clockwise a ray of light passing through it from first optical port 802 to second optical port 806. In another preferable embodiment, first nonreciprocal rotator 826A rotates by 45 degrees counter clockwise a ray of light passing through it from first optical port 802 to second optical port 806. The rays then enter first reciprocal rotator 827. In a preferable embodiment, first reciprocal rotator 827 rotates by 45 degrees clockwise a ray of light passing through it from first optical port 802 to second optical port 806. In another preferable embodiment, first reciprocal rotator 827 rotates by 45 degrees counter clockwise a ray of light passing through it from first optical port 802 to second optical port 806.

Upon exiting first reciprocal rotator 827, the polarization orientation of both rays have been rotated 90 degrees and are still orthogonal to each other before entering walk-off crystal 828. As they propagate through walk- off crystal 828, the rays are recombined. The recombined rays next enter imaging element 830. Imaging element 830 bends distally propagating light from optical port 802 and collimates the beam in the process. At this point, the rays have passed through the first stage of the multiple stage optical isolator array 800. Any reflected light propagating in a proximal direction along the path of the rays will be refracted away from the path, as shown in FIG. 8B. Relevant further discussion of optical isolation may be found in U.S. Patent No. 4,239,329, to Matsumoto, hereby incorporated by reference in its entirety. The arrangement, as described so far, provides sufficient isolation to function as an independent optical isolator array. In a preferred embodiment, the first stage of multiple stage optical isolator array 800 provides about 30 dB of optical isolation.

If additional isolation is desired, further stages of optical isolator cores according to the invention may be added. In the embodiment as shown, the isolator stages are coupled across complete gap 812. Light propagating across complete gap 812 enters imaging element 832. Imaging element 832 performs a symmetrical function to imaging element 830 in bending distally propagating light to a path parallel to the longitudinal axis.

In an embodiment of the invention the imaging elements 830, 832 may alternately comprise one or more collimating lenses and prisms in series to collimate and bend the light. The lenses may have uniform index of refraction or may be fabricated with a graded index of refraction. In a preferable embodiment, the lens are fabricated with graded indices of refraction, e.g. GRIN lenses.

Collimated, arbitrarily polarized light exiting through imaging element 832 then enters walk-off crystal 834, where the E-ray is walked off, while the propagation of the O-ray is unchanged. The rays then enter second reciprocal rotator 837. In a preferable embodiment, second reciprocal rotator 837 rotates by 45 degrees counterclockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806. In another preferable embodiment, second reciprocal rotator 837 rotates by 45 degrees clockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806.

The rays then enter second nonreciprocal rotator 836A. In a preferable embodiment, second nonreciprocal rotator 836A rotates by 45 degrees counterclockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806. In another preferable embodiment, second nonreciprocal rotator 836A rotates by 45 degrees clockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806. The rays then pass through second beam displacer/combiner 840, where the rays are recombined. The recombined light beam then passes through second optical port 806.

At this point, the rays have passed through a second stage of the multiple stage optical isolator array 800. Any reflected light propagating in a proximal direction along the path of the rays will be refracted away from the path, as shown in FIG. 8B. The arrangement, as described so far, provides sufficient isolation to function as an independent optical isolator array. In a preferable embodiment, the second stage of multiple stage optical isolator array 800 provides about 30 dB of optical isolation. In another preferable embodiment, the two stages of optical isolation shown in optical isolator array 800 provide about 60 dB of optical isolation. As can be seen in the figure, multiple signals may be isolated simultaneously using the same primary structure. The number of signals that may be simultaneously optically isolated using multiple stage optical isolator array 800 is limited primarily by the required spacing between the various optical ports. In certain embodiments, the spacing between the optical port locations may be adjusted by increasing or shortening the length of complete gap 812.

In another aspect of the invention, thermally expanded core (TEC) fibers may be used to reduce alignment sensitivity. In another aspect of the invention, the inventive optical isolator array may be used in telecommunications systems such as wavelength division multiplexers and EDFA's.

It will be apparent to those skilled in the art that various modifications and variations can be made in the isolator array, systems and methods of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

CLAIMSWhat Is Claimed Is:

1. An optical isolator array for optically isolating at least one optical signal comprising: a first beam bender; a first optical isolator core optically coupled to the first beam bender; a second beam bender, optically coupled to the first optical isolator core; and the second beam bender located on a side of the optical isolator core opposite from the first beam bender, wherein the first beam bender, first optical isolator core, and second beam bender all are located along a propagation path of an optical signal propagating through the optical isolator array.

2. The optical isolator array of claim 1 , wherein the first optical isolator core comprises a nonreciprocal rotator; and a first polarizer optically coupled to the nonreciprocal rotator; a second polarizer optically coupled to the nonreciprocal rotator; and the second polarizer located on a side of the nonreciprocal rotator opposite from the first polarizer, wherein the first polarizer, the nonreciprocal rotator, and second polarizer all are located along a propagation path of an optical signal propagating through the optical isolator array.

3. The optical isolator array of claim 2, wherein the first polarizer or the second polarizer comprises a birefringent wedge, a birefringent walk-off crystal, a Wollaston prism, or a Rochon prism.

4. The optical isolator array of claim 3, wherein both the first polarizer and the second polarizer comprise a birefringent wedge.

5. The optical isolator array of claim 3, wherein both the first polarizer and the second polarizer comprise a birefringent walk-off crystal.

6. The optical isolator array of claim 2, wherein the nonreciprocal rotator comprises latching Faraday garnet or non-latching garnet.

7. The optical isolator array of claim 1 , wherein the first beam bender or the second beam bender comprise a polarization sensitive beam bender or a polarization insensitive beam bender.

8. The optical isolator array of claim 7, wherein the polarization sensitive beam bender comprises a Wollaston prism, a Rochon prism, a modified

Wollaston prism, a modified Rochon prism, a Senarmont prism, or two pairs of birefringent wedges.

9. The optical isolator array of claim 7, wherein the polarization insensitive beam bender comprises a GRIN lens, an aspheric lens, a planoconvex lenses, or a ball lens.

10. The optical isolator array of claim 1 , wherein the first optical isolator core is located at or near a convergence point of propagation paths of optical signals propagating through the optical isolator array.

11. The optical isolator array of claim 1 , wherein the optical isolator array is configured in a substantially polarization mode dispersion free configuration.

12. The optical isolator array of claim 11 , wherein the optical isolator array comprises a birefringent compensation plate, and wherein the optical isolator array is substantially polarization mode dispersion free.

13. The optical isolator array of claim 11 , wherein the optical isolator array comprises two optical isolator cores, and the two optical isolator cores possessing opposite sign polarization mode dispersion with respect to each other, and wherein the optical isolator array is substantially polarization mode dispersion free.

14. The optical isolator array of claim 1 , comprising two or more optical isolator cores.

15. The optical isolator array of claim 1 , further comprising a mounting piece, the mounting piece supporting an input fiber array or an output fiber array, wherein aligning one or two fibers in the input fiber array or the output fiber array aligns the remaining fibers in the input fiber array or the output fiber array, respectively.

16. The optical isolator array of claim 1 , further comprising: a second beam bender, optically coupled to the first optical isolator core, and; a second optical isolator core; optically coupled to the first optical isolator core; and the first beam bender and the second beam bender located between the first optical isolator core and the second optical isolator core, wherein the first optical isolator core, first beam bender, second beam bender, and second optical isolator core all are located along a propagation path of an optical signal propagating through the optical isolator array.

17. The optical isolator array of claim 16, wherein the first optical isolator core or the second optical isolator core comprises a nonreciprocal rotator; and a first polarizer optically coupled to the nonreciprocal rotator.

18. The optical isolator array of claim 17, wherein the first optical isolator core or the second optical isolator core further comprises a second polarizer optically coupled to the nonreciprocal rotator, and the second polarizer located on a side of the nonreciprocal rotator opposite from the first polarizer or the second polarizer, respectively, wherein the first polarizer, first or second optical isolator core, and second polarizer all are located along a propagation path of an optical signal propagating through the optical isolator array.

19. The optical isolator array of claim 18, wherein the first polarizer or the second polarizer comprises a birefringent wedge, a birefringent walk-off crystal, a Wollaston prism, or a Rochon prism.

20. The optical isolator array of claim 18, wherein both the first polarizer and the second polarizer comprise a birefringent wedge.

21. The optical isolator array of claim 20, wherein both the first polarizer and the second polarizer comprise a birefringent walk-off crystal.

22. The optical isolator array of claim 17, wherein the nonreciprocal rotator comprises latching Faraday garnet or non-latching garnet.

23. The optical isolator array of claim 16, wherein the first beam bender or the second beam bender comprise a polarization sensitive beam bender or a polarization insensitive beam bender.

24. The optical isolator array of claim 23, wherein the polarization sensitive beam bender comprises a Wollaston prism, a Rochon prism, a modified Wollaston prism, a modified Rochon prism, or a Senarmont prism.

25. The optical isolator array of claim 23, wherein the polarization insensitive beam bender comprises a GRIN lens, an aspheric lens, a planoconvex lenses, or a ball lens.

26. A telecommunications system comprising the optical isolator array of claim 1.

27. A wavelength division multiplexer comprising the optical isolator array of claim 1.

28. An erbium-doped fiber amplifier comprising the optical isolator array of claim 1.

29. A method of isolating an optical signal comprising: providing an optical isolator array comprising one or more isolator stages, wherein each isolator stage comprises an optical isolator core optically coupled to a set of optical signals; inserting an optical signal into the optical isolator array; and optically isolating the optical signal.

30. The method of claim 29, wherein the optical isolator core comprises a nonreciprocal rotator; and a first polarizer optically coupled to the nonreciprocal rotator; a second polarizer optically coupled to the nonreciprocal rotator; and the second polarizer located on a side of the nonreciprocal rotator opposite from the first polarizer, wherein the first polarizer, the nonreciprocal rotator, and the second polarizer all are located along a propagation path of an optical signal propagating through the optical isolator array.

31. The method of claim 30, wherein the polarizer comprises a birefringent wedge, a birefringent walk-off crystal, a Wollaston prism, or a Rochon prism.

32. The method of claim 30, wherein the nonreciprocal rotator comprises latching Faraday garnet or non-latching garnet.

33. A method of aligning an optical isolator array, comprising providing the optical isolator array of claim 1 , wherein the optical isolator array further comprises a mounting piece, the mounting piece supporting a fiber array that comprises two or more optical fibers, and aligning at least one fiber in the fiber array with respect to the optical isolator array, wherein one or more remaining fibers in the fiber array are also aligned with respect to the optical isolator array.

34. A method of optically isolating multiple spatially separate optical signals comprising: generating a set of optical signals propagating along propagation paths; converging the propagation paths thereby converging the set of optical signals; and propagating the set of optical signals through at least one optical isolator core.

35. The method of claim 34, wherein the set of optical signals comprise optical signals that are spatially separate.

36. The method of claim 34, wherein the set of optical signals are caused to converge by beam benders that turn the propagation paths through a determinable angle.

37. The method of claim 34, wherein the at least one optical isolator core is spatially located at a convergence point of the propagation paths.

38. The method of claim 34, wherein the at least one optical isolator core is spatially located at a point other than a convergence point of the propagation paths.