WO2003036335A2

WO2003036335A2 - Polarization multiplexer/demultiplexer for optical array processors

Info

Publication number: WO2003036335A2
Application number: PCT/IL2002/000852
Authority: WO
Inventors: Haim Eder; Yoav Yadin; Koby Scheuer; Moti Margalit
Original assignee: Lambda Crossing Ltd.
Priority date: 2001-10-25
Filing date: 2002-10-24
Publication date: 2003-05-01
Also published as: AU2002347569A1; WO2003036335A3

Abstract

An optical device and method are presented for adjusting a polarization condition of multi-channel light associated with an optical processor system (30) that has a plurality of processing units (PU) for processing linearly polarized light. The device comprises a polarization splitting/combining element (14), which may comprise a prism assembly or a birefrigerent crystal and first and second collimator arrays (12, 16). The first collimator array (12) is accommodated between a multi-channel light transmission system (20) and the polarization splitting/combining element (14). The second collimator array (16) is accommodated between the polarization splitting/combining element (14) and the optical processor system (30). The polarization splitting/combining element (14) is has predetermined dimensions and orientation to demultiplex into light of orthogonal linear polirizations light from the transmission system or multiplex into a randomly polarized light beam light from the optical processor system.

Description

POLARIZATION CONDITIONER FOR OPTICAL ARRAY PROCESSORS

FIELD OF THE INVENTION

This invention is in the field of optical devices and relates to a device for adjusting the polarization condition of multi-channel tight propagating to or from an optical processor system.

BACKGROUND OF THE INVENTION

Various optical processes are generally polarization dependent, hi integrated optics, for example, it is often simpler to optimize the device to operate at one specific linear polarization of input signal.

There is a large number of optical systems that receive light signals from and output processed signals to optical fibers. Depending on its type, the system may have one or more inputs and one or more outputs. In certain systems, an input port may also serve as an output port, in which case the signal flows through the fiber coupled thereto in both directions.

In general, however, signals arriving over a fiber, especially a communication fiber, having a considerable length, are randomly polarized. Placing a polarizer (polarization rotator or converter) at the input of an optical device would result in undesirable loss of power. A solution known in the art is to split the incoming randomly polarized tight signal into two tight components of orthogonal polarizations, process each of the two components separately by means of a pair of polarization optimized optical processing units of a similar function, and then combine each pair of the output signals to produce a single randomly polarized output signal. There are transmission systems in which multiple fibers run in parallel along a cable. For example, optical transmission systems that are based on wavelength division multiplexing (WDM), e.g., add and drop multiplexers, switching devices, tunable filters, etc., achieve high information capacities by aggregating many optical channels onto a signal strand of optical fiber. These systems thus involve inputting and outputting a plurality of optical fibers which are usually realized as co-planar light guides. To process multi-channel signals, processor systems including an array of processing units, each for processing a corresponding one of the channels, can be used (e.g. WO 0073842, US 2002/0097957). Such an array device is inherently more economical to fabricate, compared to an equivalent number of discrete processors.

SUMMARY OF THE INVENTION

There is a need in the art to facilitate the polarization independent processing of a plurality of light signals by providing a novel optical device and method enabling a polarization-conditioning coupling of light signals into and/or out of an optical processor system. The device of the present invention can be economically fabricated as a single assembly and can be easily coupled between such an optical processor system and a transmission system carrying multi-channel light.

The present invention provides a polarization adjusting device that may be coupled, at one end, to a transmission system having an array of N light-guides (e.g., fibers) carrying N randomly polarized light signals, respectively, and at the other end - to 2N light-paths (e.g., arranged in one or two linear arrays) and carrying linearly polarized light signals. The 2N tight-paths may be associated with an optical processor system, being ports of processing units therein, or they may be light-guides that couple to such processor units. For signals flowing from the N-array to the 2N- array (which become input signals to the optical processor system) the device of the invention acts as a polarization splitter, while for signals flowing from the 2N-array to the N-array (which are output signals from the processor system) the device of the invention acts as a polarization combiner. In the case of bi-directional processors, the device acts as both a splitter and combiner. In its basic configurations, the device of the present invention comprises a single polarization sptitting/combining element for transmitting N-channel tight between a transmission system and an optical processor system, a first collimator array of N collimators, and a second collimator array of 2N collimators. The first array is designed and disposed so that the light emanating from each collimator forms a collimated beam, and all such beams are substantially parallel to one another. The polarization sptitting/combining element is designed and disposed so as to intercept all the collimated beams and so that each beam is split into a pair of collimated beams with mutually orthogonal directions of linear polarization. All pairs of beams are polarized along the same set of orthogonal directions and all beams polarized in any one direction are mutually parallel. Preferably, the construction is such that all the linearly polarized beams are mutually parallel, that is - the array of beams of one linear polarization is parallel to the array of beams of the other linear polarization. The second collimator array is designed and disposed so that each collimator focuses a corresponding polarized beam onto a corresponding one of 2N tight-paths (e.g., a corresponding port of an optical processor system). In some configurations, the 2N tight-paths may consist physically or logically of two linear arrays, e.g., for two linear polarizations, respectively, and in some configurations - of more than two linear arrays. There is thus provided according to one aspect of the present invention an optical device for adjusting a polarization condition of multi-channel light associated with an optical processor system that has a plurality of processing units for processing linearly polarized light, the device comprising:

- a polarization sptitting/combining element for accommodating between the optical processor system and a light transmission system, the polarization sptitting/combining element having predetermined dimensions and orientation to cany out at least one of the following: concurrently receiving all randomly polarized light beams of the multi-channel tight coming from the transmission system and producing from each of the received beams a pair of tight components of orthogonal linear polarizations; and concurrently receiving all tinearly polarized light components of the multi-channel tight coming from the optical processor system and for each channel combining a pair of orthogonally polarized light components into a randomly polarized light beam; - a first array of coltimators for accommodating between the multi-channel transmission system and the polarization sptitting/combinii g element, the collimators of the first array being optically coupled to light guides, respectively, of the transmission system, to produce collimated beams substantially parallel to each other; and - a second array of collimators for accommodating between the polarization sptitting/combining element and the optical processor system, each collimator of the second array being in the path of a respective one of the linearly polarized tight components and optically coupled to a corresponding one of the processing units. The polarization sptitting/combining element may be of any known type, based on diverse physical principles. Two specific types are used in embodiments disclosed herein: One type comprises a cubic beam splitter/combiner, which may be formed from of a pair of right-angle prisms with their diagonal facets coupled by a thin polarizing layer. The two linearly polarized light components of each pair emerge in mutually orthogonal directions. In this case, in order to make the orthogonal polarized tight components parallel to each other as might be desired, a light deflector element (e.g., a right-angle prism) is used, being disposed in the path of all tight components of one of the two linear polarizations, so as to redirect them in the direction of the tight components of the other linear polarization. The other type of polarization sptitting/combining element, specifically disclosed, comprises a birefringent medium (crystal).

Several configurations of the invented device are possible, some of which are disclosed herein. These may generally be divided into two groups: The first group configurations provide the propagation axes of all polarized light components lying in the same plane, which is usually also the plane in which the unpolarized beams tie. Such configurations are particularly suitable for coupling the polarization adjusting device to a single planar processor system. The second group configurations provide the propagation axes of all tight components of one linear polarization lying in a plane different from, though preferably parallel to, the plane of propagation of the axes of light components of the other polarization. Those configurations of the first group, in which the polarization sptitting/combining element is based on a birefringent medium may be further divided into those in which orthogonally polarized light components of each pair emerge adjacent to each other and those in which all light components polarized in one direction emerge spatially separate from the light components polarized in the other direction.

For specific applications, where all the processing units operate with the same linear polarization of tight, the polarization adjusting device of the invention also includes a polarization rotator assembly (e.g., including one or a plurality of half- wave plates), which is designed and disposed in the path of all the tight components of one linear polarization so as to apply a 90 degree rotation to the plane of polarization of these light components.

The polarization adjusting device of the invention may include a front coupling section, which comprises an array of tight guides, one end of each being at the focal plane of a corresponding collimator in the first array, and the other end of each being directly coupled to a corresponding light guide in the transmission system.

The invention may include a back coupling section (also called delivery section), which comprises an array of tight guiding fibers, one end of each being at the focal plane of a corresponding collimator of the second array and the other end of each being optically coupled to a corresponding port of the processor system. The back coupling section serves to geometrically match the arrangement of the points of convergence to the arrangement of the ports of the processor system. In some configurations, the delivery section may also serve as a polarization rotator, by making half the tight guides therein of polarization maintaining fiber sections, each twisted by 90 degrees. In another aspect, the invention is of a system for processing multi-channel light, the system comprising:

- an optical processor system having a plurality of processing units, each pair of for processing units being operable to process linearly polarized light of a corresponding one of the multiple channels; and

- an optical device for adjusting a polarization condition of the multi-channel tight, said optical device being accommodated between the optical processor system and a tight transmission system for transmitting randomly polarized multi-channel light, and comprising a polarization sptitting/combining element; a first array of collimators accommodated between the multi-channel transmission system and the polarization sptitting/combining element such that each first collimator is optically coupled to a corresponding one of tight guides of the transmission system; and a second array of collimators accommodated between the optical processor system and the polarization sptitting/combining element such that each second collimator is optically coupled to a respective one of the processing units, the optical device carrying out at least one of the following:

- concurrently transmitting all the multiple channels of input light of random polarization from the transmission system to the optical processor, while producing from each of the received randomly polarized channels a pair of linearly polarized tight components, and directing the linearly polarized light components into the processing units, respectively;

- concurrently transmitting all the multi-channel linearly polarized light components from the processing units, while for each tight channel combining a pair of the orthogonally polarized tight components into a randomly polarized tight beam, and directing the randomly polarized light beams into the multi-channel transmission system.

The system may have many configurations, wherein input- and output ports of processing units are variously associated with signal supply light guides and signal detivery light guides, respectively, in the various transmission systems. Generally, all processing units are logically grouped in pairs, each pair of processing units serving for processing a corresponding one of the tight channels (e.g., wavelength band) wherein the two units of each pair may be designed to process light of the same linear polarization or of the orthogonal linear polarizations, respectively. Each pair of input ports of the processor system is coupled through a polarization adjusting device to a corresponding supply tight guide, and/or each pair of output ports is coupled through a polarization adjusting device to a corresponding delivery tight guide.

According to yet another aspect of the present invention, there is provided a method for adjusting a polarization condition of multi-channel tight to be processed by an optical processor system having a plurality of processing units for processing linearly polarized light, the method comprising:

- passing multi-channel randomly polarized tight through a first collimator arra thereby producing a plurality of substantially parallel randomly polarized tight beams, each of a corresponding one of the multiple channels; - passing all the randomly polarized beams through a common polarization splitting combining element that splits each of the randomly polarized beams into two tight components of orthogonal polarizations, respectively;

- passing all the linearly polarized light components through a second collimator array to thereby direct each of the linearly polarized tight components to a corresponding one of ports of the processor system.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic block diagram of an optical system utilizing the optical device according to the invention;

Figs. 2A and 2B show top and side views of the optical device according to two embodiments of the invention, respectively, that utilize a cubic beam splitter/combiner and a polarization rotator; Fig. 3 shows top and side views of the device according to another embodiment of the invention that utilizes a birefringent crystal and a polarization rotator;

Fig. 4 shows top and side views of the device according to yet another embodiment of the invention that utilizes a birefringent crystal and a polarization rotator;

Fig. 5 shows top and side views of a modified version of the embodiment of Fig. 4;

Fig. 6 shows top- and side views of an example of a coupling section suitable to be used in the device according to the invention; and

Fig. 7 shows top and side views of another example of a coupling section suitable to be used in the device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1, there is schematically illustrated a system 1 designed foi^¬ processing multi-channel light. The system 1 comprises an optical processor system 30 including a plurality of processing units PU, and a tight transmission system 20 in the form of a fiber array each for transmitting a respective one of the multiple channels (e.g., a specific wavelength band different from that of the other channels), and utilizes a polarization adjusting device 10 according to the invention. Generally, the polarization adjusting device according to the invention is designed to adjust a polarization condition of multi-channel tight that come from the transmission system and is to be processed by the optical processor system, to adjust a polarization condition of multi-channel tight processed by the optical processor system and to be transmitted through a transmission system, or to adjust both the polarization condition of tight to be processed and the processed light to be further transmitted. This enables polarization independent operation of the entire system 1.

In the present example of Fig. 1, the system 1 is designed for using the device 10 for adjusting the polarization condition of the input multi-channel light propagating from the fibers 20 towards the optical processor system 30. It should, however, be understood that the same device 10 can be used for adjusting the polarization condition of the output of the processor(s) 30 prior to entering the fiber array 20, provided the processor units have bi-directional ports. Alternatively, an additional similar polarization adjusting device and an output multi-fiber transmission system can be used at the output of the processor system 30.

The optical processor system 30 may be of the kind capable of separately processing light of different linear polarizations, in which case the processor units include a corresponding number of processing units' pairs (corresponding to the number of input fibers in the array 20), wherein each pair of processing units is for processing a corresponding one of multiple tight channels, and the processing units of each pair operate with the orthogonal polarizations, respectively. Alternatively, the optical processor system 30 may be of the kind capable of processing only light of a specific linear polarization.

The polarization adjusting device 10 is thus disposed between the end face of the transmission system 20 in the form of array of N fibers or tight guides, and the end faces of the processor units PU of the processor system 30. The array of tight guides 20 is usually linear, i.e. lying in a single plane, and the embodiments of the invented device described herein are adapted to such a linear array, til general, however, the polarization adjusting device 10 may be configured for any arrangement of tight guides, including a non-planar arrangement, with minor modifications. The optical processor system 30 has multiple processing units (optical functional elements, such as filters, switches, etc.), each unit having input and output ports or a bi-directional port, through which light signals may be both input and output. The polarization adjusting device 10 may be coupled to a plurality of such ports, whether they all be input ports, output ports or bi-directional ports, or whether they include ports of various functions. In any case, there is a separate tight path between any one of the N tight guides in the transmission system and a corresponding pair of ports on the processor system. Any such path that is coupled to input ports carries light signals supplied from the transmission system to the optical processor system and is considered an input path; any such path that is coupled to output ports carries light signals delivered from the optical processor system to the transmission system and is considered an output path; finally any such path that is coupled to bidirectional ports carries tight signals in both directions and is considered a bidirectional path. All ports are assumed to form one or more regular arrays on a corresponding end face of the processor system. The optical processor system 30 may be realized in a planar lightwave circuit (PLC) technique, which has an inherent advantage in integration of complex optical functions. Many configurations of the processor system are possible, reflecting its type, the relation between input- and output ports and the number of processing units therein; the relation between such processor system configurations and configurations of the polarization adjusting device 10 will be discussed by specific examples further below, the relations with other configurations being readily deducible by persons knowledgeable in the art. hi some systems, a plurality of such polarization adjusting devices may be utilized. It will be appreciated that the polarization adjusting device of the invention is also applicable in other optical systems, generally characterized by one or more arrays of guides of randomly polarized tight on one side, and one or more arrays of guides of linearly polarized light on the other side, where the invented devices serve to condition or adjust the polarizations between them.

The polarization adjusting device 10 basically comprises a single polarization sptitting/combining element (PSCE) 14, a first collimator array 12 which is an array of N collimators disposed to one side 13 of the PSCE, and a second collimator array 16 which is an array of 2N collimators disposed to the other side(s) 17 of the PSCE. The PSCE 14 can thus be simultaneously applied to a plurality of randomly polarized light beams coming from the plurality of fibers 20, and/or be simultaneously applied to a plurality of pairs of specifically polarized tight components emerging from the optical processor 30. Considering bi-directional light propagation through the system 1, the PSCE 14 functions as both the polarization splitter and combiner. The PSCE 14, in its one operational mode, functions as a polarization splitter: receives N collimated, randomly polarized and mutually parallel light beams entering the PSCE through its face 13, and produces 2N linearly polarized light components emerging from the PSCE at its side(s) 17. The tight components of each pair entering the processor system 30 may be of the same linear polarization, or of the orthogonal linear polarizations, in which case a polarization rotator assembly 15 (e.g., utilizing a half-wave plate) is used at the output of the PSCE 14. In the other operational mode of the PSCE 14, it functions as a polarization combiner: it receives 2N collimated light components entering the PSCE through its face 17, and produces N randomly polarized beam to enter N fibers, respectively, hi other words, for any such beams in input paths, the PSCE functions as a polarization sptitter. For beams in output paths, it functions as a polarization combiner, and for beams in bi-directional paths, the PSCE functions as both a splitter and a combiner. For brevity, the descriptions that follow are in terms of an input path; the functions of the devices in an output path, or a bidirectional path, should be readily understood.

It should be understood that the provision of the polarization rotation assembly 15, which causes the plane of polarization of tight passing therethrough to rotate by 90 degrees is optional, being used in cases when all the processing units in the optical processor system 30 are of the kind operating with tight of one specific linear polarization. Various types and configurations of the PSCE are discussed in the sequel.

The array of N collimators 12 consists of a narrow transparent block, one face of which is to be attached to the end face of the fiber array 20 and the other face is to be covered with or foπned into an array of positive lenslets, each to function as a collimator. The lenslets may be based on diffraction or on refraction; in the latter case they may be of the shaped type or of the graded index type. Such lenslets arrays are known in the art and are readily available in the market (for example WO056076, US 2002/0097956, US 2001/0024548), and therefore need not be described in detail.

The lenslets arrangement is preferably such that its center-to-center spacing is identical to that of the light guides in the array 20 and their mode field diameter is matched to that of the light guides. The optical width of the block is determined by the focal length of the lenslets. This optical width may consist entirely of solid transparent material, in which case the two faces are coupled by contact (possibly by means of an optical adhesive), or, preferably, the width includes an air gap.

Also optionally provided in the polarization adjusting device 10 is a front coupling section 11, consisting of a short array of tight guides, to be termed "coupling tight guides". The coupling section 11 is by its one end attached to the face (left face) of the collimator array 12 with identical center-to-center spacing, so that the tight guides are on-axis with their corresponding lenslets; and at the other end, is attachable to the end of the fiber array 20 so that the corresponding tight guides in the coupling section 11 and fiber array 20 directly couple, that is - butt-couple, with each other. The coupling section 11 then optically forms an extension of the fiber array 20. The provision of the coupling section 11 facilitates the alignment precision required during coupling to the tight guide array 20 and ensures that the resultant collimated beams emerge normal to the end surface of the block. In any case, the back foci of the lenslets ideally tie at the centers of the end facets of the respective tight guides; preferably the mode field diameter of the lenslets matches that of the light guides. The first collimator array 12 is positioned in relation to the PSCE 14 so that all the collimated beams, which preferably travel through air, normally enter the PSCE's left face; the distance between these two elements is not critical.

The second collimator array (of 2N collimators) 16 is essentially similar to that described hereabove, however, it is subject to a variety of configurations, which depend on the configurations of the PSCE 14 and of the processor system 30. In general, this array, which could possibly consist of a plurality of linear sections and thus constitute a plurality of arrays, is optically coupled either directly to the ports of the optical processor system 30 or to an optional delivery section 18, to be described below.

Reference is made to Figs. 2A and 2B schematically illustrating two practical embodiments, respectively, of the polarization adjusting device according to the invention. In each of these figures, the upper drawing is to be considered a top view and the lower drawing - a sideview. Polarization splitting and combining elements 114A and 114B of these examples, respectively, utilize a beam sptitting/combining cube having a polarization sptitting/combining surface, and differ from each other in the orientation of this surface with respect to input light beams.

The PSCE 114A thus comprises the beam sptitting/combining cube 22 having a polarization sptitting/combining surface 22A, and preferably also comprises a light deflector element 24 (e.g., a right-angle reflector prism) attached or located close to a facet 28 of the cube 22. The provision of the deflector element simplifies the entire system construction by producing substantially parallel tight component output from the PSCE. The beam sptitting/combining cube 22 preferably consists of two right- angle prisms joined at their diagonal facets by a thin polarizing film presenting the surface 22A. The PSCE 114A operates in the following manner. Each of the substantially parallel, randomly polarized beams 25, emanating from the first collimator array 12, enters the cube 22 from its facet 26 and is split at the surface 22 A into two mutually orthogonal polarization components: first polarization component 25A passes through the surface 22A and proceeds in the same direction as the input tight beam 25 to emerge through the facet 27 of the cube 22, while the second polarization component 25B undergoes a 90 degree deflection at the surface 22A in a direction along an axis lying in the same plane as the incoming beam 25 and emerges through the facet 28 of the cube 22. The second polarization component 25B is then deflected by the prism 24 into the original direction (that of the input beam 25), to thereby emerge parallel to the first component 25A. As a result, the polarized light components 25A and 25B propagate in the same plane (that of the incoming beams 25), with one group of polarization components lying beside the other. This embodiment is particularly useful for convenient direct coupling to a planar processor system. It should be noted that the deflection (prism 24) may alternatively be applied to the first polarization component 25A (e.g., that passing through the polarization sptitting/combining surface), so that both components 25A and 25B emerge from the polarization adjusting device normal to the original direction of the input light propagation. It should also be noted that the provision of the light deflector element is optional, and in certain configurations, the beams of the second group 25B may be allowed to emerge from the PSCE in an orthogonal direction with respect to those of the first group, depending on the processor system configuration.

Further optionally provided in the PSCE 114A (and in PSCE 114B of Fig, 2B) is a polarization rotating assembly (e.g., a half-wave plate) 15, which, in the present example, is located in the optical path of the tight components 25B, being attached or located close to the respective facet of the prism 24, but which generally can be accommodated in the optical path of either one of the tight components' groups 25A and 25B. It should be understood that the polarization rotating assembly may be associated with facet 27 of the cube. The polarization rotating assembly may be located in the path of light components 25A upstream of the deflector element. The polarization rotating assembly causes 90 degree polarization rotation of tight passing merethrough, and thus the tight components of the two groups become of the same linear polarization. It is noted that with this option, when the PSCE functions as a combiner, all the polarized beams emerging from the optical processor system are assumed to be identically polarized and the use of the polarization rotator causes the polarization of the two groups to become mutually orthogonal, to be then appropriately combined by the cube 22.

In the example of Fig. 2B, a beam stilting/combining cube 22', namely its polarization sptitting/combining surface 22A', is oriented with respect to the incoming beams 25 such that the second group of beams 25B is deflected out of the plane of the incoming beams. As a result, considering the use of the light deflector element 24', the light components of the first and second groups 25A and 25B propagate in two spaced-apart parallel planes, one on top of the other. This embodiment has the advantage of a smaller cube 22' and smaller right-angle prism 24', but requires the appropriate orientation of the input ports of the processor system for different linear polarizations (so as to be at two different heights) or the use of a suitable delivery section (to be described below).

Reference is now made to Figs. 3, 4 and 5 that depict three more embodiments, respectively, of the polarization adjusting device, in which a PSCE is typified by a birefringent medium (typically a birefringent crystal), for example made of Yttrium Vanadate (YVO₄). Similarly, in each of these figures, the upper drawing is to be considered a top view, and the lower drawing - a sideview. The advantage of these embodiments over those of Figs. 2A and 2B is the simplicity of assembly.

In a PSCE 214 of Fig. 3, a birefringent crystal 32 is oriented with respect to input beams 25 so that each beam 25 entering the crystal from its facet 32A is split as follows: One polarization component (TE) 33 proceeds through the crystal along the same line as the entering beam; the other component (TM) 34 is refracted in the extraordinary mode, proceeding through the crystal upward at some angle to the original direction, and upon emerging from the facet 32B, it is refracted back to the original direction (that of the input beam 25). As a result, all the TM components 34 emerge at a plane 35A that is a certain distance above a plane 35B of the TE components 33; the effect is similar to that of the embodiment of Fig. 2B. Here again, a polarization rotating assembly 15 may optionally be used (depending on the type of processing units of the optical processor system) being attached or located close to the facet 32B of the crystal within a respective location so as to be in the path of one of the polarization groups.

In a PSCE 314 of Fig. 4, a birefringent crystal 32' is oriented so that the extraordinary refraction is effected in the plane of the array of incoming beams 25 (here - the horizontal plane). The length of the crystal 32' is preferably such that the ordinary and extraordinary beam components 33 and 34 reach the facet 32B of the crystal in an interleaved fashion. The effect is the emergence of 2N parallel beams 33 and 34 of orthogonal polarizations in a common plane. It is noted that the center- to-center distances of these beams are half those of the incoming beams; thus the lenslets of the matching second collimator array (not shown in Fig. 4) must be designed so that the beams are sufficiently narrow to avoid overlaps. A polarization rotating assembly 15' may optionally be provided, being attached or located close to the respective facet of the crystal. For example, the polarization rotating assembly 15' may be in the form of a half-wave patterned so as to have holes or slots at alternate emerging beam positions; thus beams with one polarization plane will undergo rotation of polarization, while the others will remain unaffected. This allows the direct coupling of the second collimator array (16 in Fig. 1) to a planar optical processor system, if the corresponding ports on the latter are linearly arranged, with the same center-to-center distances. Otherwise, a special delivery section, to be described below, is used. Fig. 5 depicts a polarization adjusting device, which is generally similar to that of Fig. 4, but differs therefrom in that the length of a birefringent crystal 32" is extended so that the two groups of polarization components emerge from the crystal 32" totally spatially separated (rather than interleaved, as in Fig. 4). The effect is similar to that of the embodiment of Fig. 2A (one group of beams on top of the other), albeit with a greater length of the device. Here, again, a single polarization rotating element (e.g., half-wave plate) 15 may be placed in the path of one of the two groups of beams.

For each of the embodiments described hereabove, there is provided a matching second collimator array (16 in Fig. 1), of 2N collimator lenslets, whereby each lenslet is placed at the expected path of the corresponding polarized beam. For some configurations of some of the embodiments, the second collimator array may consist of two separate arrays, or assemblies, (one for each group of beams of like polarization direction) or a single array that is configured in two segments or two rows. Generally speaking, the second collimator array 16 is optically coupled to the corresponding ports on the processor system, so that each light component is coupled into a corresponding port of the processor system (corresponding processing unit). In some cases, the collimator array (or any sub-array thereof) may be physically attached to a facet of the processor system, if the latter is also suitably configured, so that each tight component is focused onto the corresponding port, i.e. - on the end face of a corresponding tight-guide on the processor system; preferably the mode field diameter of the lenslets matches that of the ports. In general, however, there may be required an intervening back coupling section (also called delivery section) 18 that converts between the geometric arrangement of the collimator lenslets and that of the corresponding ports on the processor system. Such a delivery section generally consists of 2N fibers, one end of each fiber positioned at the focus of a corresponding lenslet and the other end coupled to the corresponding port; the latter coupling is preferably of the butt-coupling type, to be also referred to as direct coupling. In addition to the geometric re-configuration function, and in common with the front coupling section (11 in Fig. 1), the back coupling section 18 thus also serves to ease the precision required in aligning the polarization adjusting device with the optical processor system. The fibers are preferably of the polarization mamtaining type. Optionally, half of these fibers are twisted by ninety degrees, thus functioning as polarization rotators, instead of the half-wave plate, mentioned hereabove.

Figs. 6 and 7 show schematically two specific examples of back coupling (i.e. delivery-) section 18. Again, the upper drawing in each figure is to be considered a top view and the lower drawing - a side view. In each of these drawings, lines 38 between the second collimator array 16, on the left, and a processor system 30, on the right, represent light-guiding fibers. In practice, however, the fibers are not necessarily configured along straight lines. The example of Fig. 6 is suitable for the polarization adjusting devices of Figs. 2B and 3 and, as clearly seen in the drawings, the light components of different polarizations and emerging at the two planes are directed to two corresponding sections, respectively, of the single planar processor system 30. The example of Fig. 7 is suitable for the polarization adjusting device of Fig. 4 and, as clearly seen in the drawings, the tight components of different polarizations and emerging at alternate positions along the 2N array of lenslets are, again, directed to corresponding sections of the single planar processor system 30. Other embodiments and configurations of the back coupling section are possible - to match various configurations of the second collimator array and of the processor; these should be obvious to a practitioner in the art.

Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore exemplified without departing from its scope defined in and by the appended claims.

Claims

CLAIMS:

1. An optical device for adjusting a polarization condition of multi-channel tight associated with an optical processor system that has a plurality of processing units for processing linearly polarized tight, the device comprising: - a polarization sptitting/combining element for accommodating between the optical processor system and a tight transmission system, the polarization sptitting/combining element having predetermined dimensions and orientation to carry out at least one of the following: concurrently receiving all randomly polarized light beams of the multi-channel tight coming from the transmission system and producing from each of the received beams a pair of tight components of orthogonal linear polarizations; and concurrently receiving all linearly polarized tight components of the multi-channel tight coming from the optical processor system and for each channel combining a pair of orthogonally polarized light components into a randomly polarized tight beam;

- a first array of collimators for accommodating between the multi-channel transmission system and the polarization sptitting/combining element, the collimators of the first array being optically coupled to tight guides, respectively, of the transmission system, to produce collimated beams substantially parallel to each other; and

- a second array of collimators for accommodating between the polarization sptitting/combining element and the optical processor system, each collimator of the second array being in the path of a respective one of the linearly polarized tight components and optically coupled to a corresponding one of the processing units.

2. The device of Claim 1, comprising a polarization rotator assembly accommodated in optical paths of the light components of one linear polarization, and operating to apply thereto a 90 degree polarization rotation.

3. The device of Claim 1, wherein said beam sptitting/combining element is a cubic beam splitter/combiner having a polarization sptitt g/combining surface allowing passage therethrough of tight of one linear polarization and applying a 90 degree deflection to light of the other linear polarization, the light components of the orthogonal linear polarizations thereby emerging from two different facets, respectively, of the beam splitter/combiner.

4. The device of Claim 3, wherein said polarization splitter/combiner is formed by two right-angle prisms are joined at their diagonal facets by a thin polarizing layer presenting said polarization sptitting/combining surface.

5. The device of Claim 3, comprising a tight deflector assembly accommodated in an optical path of light components emerging from the cubic beam splitter/combiner through its one facet, and deflecting the respective light components in a direction substantially parallel to a direction of propagation of the tight components emerging through the other facet of the beam splitter/combiner, propagation axes of all the linearly polarized tight components being thereby substantially parallel to each other.

6. The device of Claim 5, wherein the propagation axes of all the linearly polarized tight components are parallel to the propagation axes of the randomly polarized collimated light beams.

7. The device of Claim 5, comprising a polarization rotator assembly accommodated in optical paths of the light components deflected by the tight deflection assembly and operating to apply a 90 degree polarization rotation to said deflected tight components.

8. The device of Claim 5, wherein said light deflector assembly comprises a right- angle prism attached or located close to the respective one of said two facets of the beam splitter/combiner, and oriented such that a diagonal facet of the deflecting right- angle prism is substantially parallel to the polarization sptitting/combining surface of the cubic splitter/combiner.

9. The device of Claim 6, wherein the orientation of the sptitting/polarizing surface with respect to a plane of propagation of the randomly polarized beams is such that the deflection of tight components of one polarization results in that the tight components of two orthogonal polarizations propagate in two spaced-apart parallel planes, respectively.

10. The device of Claim 6, wherein the orientation of the sptitting/polarizing surface with respect to a plane of propagation of the randomly polarized beams is such that the deflection of light components of one polarization results in that the tight components of two orthogonal polarizations propagate in a common plane, with all the tight components of one polarization being spaced apart from all the tight components of the other polarization.

11. The device of Claim 1, wherein said beam sptitting/combining element comprises a birefringent medium that directs the two orthogonal polarization components of each of the randomly polarized beams along two spatially separated paths, respectively.

12. The device of Claim 11, wherein a tight path defined by the birefringent medium is such that the tight components of the orthogonal polarizations emerge from the medium in an interleaved fashion.

13. The device of Claim 11, wherein a tight path defined by the birefringent medium is such that all the light components of one polarization are spaced-apart from all the tight components of the other polarization.

14. The device of Claim 11, comprising a polarization rotator assembly accommodated in optical paths of the tight components of one linear polarization, and operating to apply thereto a 90 degree polarization rotation.

15. The device of Claim 12, comprising a polarization rotator assembly having a plurality of spaced-apart polarization rotating regions accommodated in optical paths of the tight components of one linear polarization, respectively, and operating to apply thereto a 90 degree polarization rotation.

16. The device of Claim 1, wherein said first array of collimators is attachable to the transmission system so that the mode field diameter of each collimator matches that of the corresponding tight guide.

17. The device of Claim 1, comprising a front coupling section including a plurality of coupling tight guides, the front coupling section being attached to said first array of collimators such that each of said coupling tight guides is by its first end optically coupled to a corresponding one of the collimators; and by its second end is directly coupled to a corresponding one of the tight guides of the transmission system.

18. The device of Claim 1, wherein said second array of collimators is attached to the optical processor system so that the mode field diameter of each collimator optically matches that of the corresponding port of the processor system.

19. The device of Claim 1, comprising a back coupling section including a plurality of light guiding fibers and being attached to said second array of collimators, so that each of said fibers is by its one end optically coupled to a corresponding one of the collimators; and by its other end is directly coupled to a corresponding port of the processor system.

20. The device of Claim 19, wherein said light guiding fibers are polarization maintaining fibers.

21. The device of Claim 19, wherein the light guiding fiber is twisted so that the direction of polarization of tight coupled into it at one end is orthogonal to that of tight coupled out of it at the other end.

22. A system for processing multi-channel tight, the system comprising:

- the optical device constructed according to Claim 1 for adjusting a polarization condition of the multi-channel light, said optical device being accommodated between the optical processor system and a tight transmission system for transmitting randomly polarized multi-channel tight, and comprising a polarization sptitting/combining element; a first array of collimators accommodated between the multi-channel transmission system and the polarization sptitting/combining element such that each first collimator is optically coupled to a corresponding one of tight guides of the transmission system; and a second array of collimators accommodated between the optical processor system and the polarization sptitting/combining element such that each second collimator is optically coupled to a respective one of the processing units, the optical device carrying out at least one of the following:

- concurrently transmitting all the multiple channels of input tight of random polarization from the transmission system to the optical processor, while producing from each of the received randomly polarized channels a pair of linearly polarized tight components, and directing the linearly polarized tight components into the processing units, respectively;

- concurrently transmitting all the multi-channel linearly polarized tight components from the processing units, while for each tight channel combining a pair of the orthogonally polarized tight components into a randomly polarized light beam, and directing the randomly polarized tight beams into the multi-channel transmission system.

23. The system of Claim 22, wherein the two processing units of each pair operate with light of the same linear polarization.

24. The system of Claim 22, wherein the two processing units of each pair operate with orthogonal polarization of tight, respectively.

25. The system according to Claim 24, wherein said optical device for adjusting the polarization condition of the multi-channel tight comprises a polarization rotator assembly.

26. The system according to Claim 22, wherein said polarization sptitting/combining element is a cubic beam splitter/combiner comprising a polarization sptitting/combining surface.

27. The system according to Claim 22, wherein said polarization sptitting/combining element comprises a birefringent medium.

28. The system according to Claim 22, wherein said optical device for adjusting the polarization condition of the multi-channel tight comprises a tight coupling section accommodated between the hght transmission system and the first array of collimators.

29. The system according to Claim 22, wherein said optical device for adjusting the polarization condition of the multi-channel tight comprises a light coupling section accommodated between the second array of collimators and the optical processing system.

30. The system according to Claim 29, wherein said coupling section comprises a plurality of fibers each of the polarization maintaining type.

31. The system according to Claim 29, wherein said coupling section operates as a polarization rotator.

32. The system according to Claim 31, wherein said coupling section comprises a pluratity of fibers, half of said fibers being twisted by 90 degrees.

33. A method for adjusting a polarization condition of multi-channel light to be processed by an optical processor system having a plurality of processing units for processing linearly polarized tight, the method comprising:

- passing multi-channel randomly polarized light through a first collimator array, thereby producing a pluratity of substantially parallel randomly polarized light beams, each of a corresponding one of the multiple channels;

- passing all the randomly polarized beams through a common polarization splitting combining element that splits each of the randomly polarized beams into two light components of orthogonal polarizations, respectively; - passing all the linearly polarized light components through a second collimator array to thereby direct each of the linearly polarized tight components to a corresponding one of ports of the processor system.