WO2014036842A1

WO2014036842A1 - Tunable laser for outputting non-polarized light

Info

Publication number: WO2014036842A1
Application number: PCT/CN2013/076160
Authority: WO
Inventors: 高培良
Original assignee: 天津奇谱光电技术有限公司
Priority date: 2012-09-05
Filing date: 2013-05-23
Publication date: 2014-03-13
Also published as: CN102820611A; CN102820611B

Abstract

A tunable laser for outputting non-polarized light comprises a first reflection mirror (72), a broadband laser gain medium (76), a tunable Fabry-Perot filter (400), a tunable acoustooptic filter (500), a second reflection mirror (84), a third reflection mirror (86), and a laser control circuit (88). A broadband light beam sent by the broadband laser gain medium (76) is filtered by the tunable Fabry-Perot filter (400) and then is filtered by the tunable acoustooptic filter (500). A first-grade diffraction light beam of the tunable acoustooptic filter (500) is divided into two beams of polarized light with polarization states perpendicular to each other, and a zero-grade diffraction light beam of the tunable acoustooptic filter (500) serves as an output light beam of the laser. The tunable laser for outputting non-polarized light implements continuous, rapid and precise tuning on the output light of the laser in a wide spectral range, has characteristics of absence of mechanical movement parts, high electronic tuning speed, stable and reliable performance, small sizes, easiness in mounting and production and the like, and can be widely applied in the fields of lasers, optical testing, optical fiber communications, biological and medical instruments, optical fiber sensor networks and the like.

Description

Tunable laser with non-polarized light output

The invention belongs to the field of optoelectronic technology, in particular to a tunable laser with unpolarized light output.

Background technique

Due to its high spectral resolution over a large spectral range, gratings are widely used in a variety of tunable lasers. The problem is that: Due to the need to use a precision stepper motor to drive the grating for scanning, tunable lasers using such techniques are relatively large in size, susceptible to mechanical shock, and expensive.

The traditional optical Fabry-Perot etalon is a filter element fabricated using the principle of multi-beam interference. There are two main types: one is air-spaced and the other is optical glass-spaced. The multi-wavelength interference effect of the Fabry-Perot cavity formed by the high reflectivity of the multilayer dielectric film on the two light-passing surfaces enables multi-wavelength narrow-band filtering output over a wide spectral range, and has stable performance. It has wide optical aperture, high optical power destruction threshold, simple structure and low cost. Therefore, it is widely used in various types of lasers, optical measuring instruments and optical fiber communication devices.

The tuning function of the transmitted optical frequency can be achieved using a conventional optical Fabry-Perot etalon. For air-spaced Fabry-Perot etalons, tuning can be done by changing the angle of incidence of the light, but the tuning range of this method is small; it is also possible to change the Fabry by mechanical means (such as stepper motors). The cavity length of the Perot etalon is tuned. This method can achieve a large tuning range, but the tuning accuracy is low, and the precision of the mechanical components is high and the stability is not good. In addition, the PZT piezoelectric ceramic (lead zirconate titanate) technology can improve the tuning accuracy and speed by changing the cavity length of the Fabry-Perot etalon, but it is not easy to miniaturize and the drive circuit is complicated. Changing the temperature of the etalon can also achieve a wider range of tuning, but the disadvantage of this method is that it is slow. At the same time, the filter output characteristic of a single Fabry-Perot etalon is a multimode output with an optical frequency interval of free spectral range.

The Acousto-Optical Tunable Filter (AOTF) is a solid-state, electronically tunable bandpass spectral filter that uses anisotropic acousto-optic interactions. The advancement of crystal growth technology and high-frequency piezoelectric transducer technology has greatly improved the acousto-optic originals, making the AOTF technology mature and entering the industrial application from the laboratory. AOTF implementations typically employ anisotropic birefringent acousto-optic (AO) media with high-speed tuning capabilities, proven long-term stability, and low cost.

The principle of operation of an acousto-optic filter is based on a phenomenon called Bragg diffraction, in which the direction of the diffracted light depends on the wavelength of the acoustic wave. Compared with traditional technologies, AOTF provides continuous and fast adjustment capability, but to achieve a narrow filter spectral bandwidth, it is generally required that the size of the acousto-optic crystal is relatively large. There are two types of acousto-optic filters: collinear and non-collinear, where non-collinear non-paraxial filters with high RF frequencies can achieve narrowband optical frequency tuning, but it is almost impossible to do It has the same narrowband filtering function as the Fabry-Perot etalon. Therefore, it is difficult to achieve narrowband output with a tunable laser using only an acousto-optic filter.

Summary of the invention

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the deficiencies of the prior art and to provide a tunable laser having high stability, high precision, high speed, inorganic mechanical moving parts, electronic tuning, and unpolarized light output in a large spectral range.

The present invention solves the prior art problem by adopting the following technical solutions:

A tunable laser of unpolarized light output, comprising a first mirror, a broadband laser gain medium, a tunable Fabry-Perot filter, a tunable acousto-optic filter, a second mirror, a third mirror, and a laser control circuit; the first mirror and the second mirror constitute a first laser resonator cavity, the first mirror and the third mirror constitute a second laser resonator cavity; the wideband beam emitted by the broadband laser gain medium passes the tunable method After filtering the Brill-Perot filter, it is filtered by a tunable acousto-optic filter, and the first-order diffracted beam is split into two polarized lights whose polarization states are perpendicular to each other, and the S-state polarized beam is reflected by the second mirror and is A laser oscillation is formed in a laser resonator cavity, and the P-state polarized beam is reflected by the third mirror and forms a laser oscillation in the second laser resonator cavity. The zero-order diffracted beam of the tunable acousto-optic filter is used as the output beam of the laser. The laser control circuit is connected to the broadband laser gain medium, the tunable Fabry-Perot filter and the tunable acousto-optic filter respectively to achieve excitation Tunable output control function.

Moreover, the first mirror, the second mirror, and the third mirror are one of three types of mirrors: a plane mirror, a concave mirror, and a convex mirror.

Moreover, the tunable Fabry-Perot filter includes a first liquid crystal cell, a second liquid crystal cell, and a tunable Fabry-Perot filter driving circuit, which are sequentially mounted in front and rear, and two liquid crystal cells are The first optically transparent material, the liquid crystal material and the second optically transparent material are sequentially mounted together, and the second optically transparent material of the first liquid crystal cell is mounted together with the first optically transparent material of the second liquid crystal cell. The first optically transparent material of the first liquid crystal cell is provided with a high-reflectivity multilayer dielectric film to form a first mirror, and the second optically transparent material of the second liquid crystal cell is provided with a high-reflectivity multilayer dielectric film to form a second a mirror, the optical axes of the liquid crystal materials in the two liquid crystal cells are perpendicular to each other and disposed in a Fabry-Perot cavity composed of the first mirror and the second mirror, the tunable Fabry-Perot The driving circuit of the filter is connected to the two liquid crystal cells and the tuning function of the filter is realized by controlling the effective refractive index of the liquid crystal material, and the driving circuit and the laser of the tunable Fabry-Perot filter Circuit is connected.

Moreover, the high-reflectivity multilayer dielectric film on the first optically transparent material of the first liquid crystal cell is disposed outside the first optically transparent material, and the inner side of the first optically transparent material is sequentially disposed from the inside to the outside. An optical antireflection film and a transparent electrode; an outer side of the second optically transparent material of the first liquid crystal cell is an optically polished surface, and an inner side of the second optically transparent material is provided with an optical antireflection film, a transparent electrode and a non-infrared from the inside to the outside. a film of a conductive material covering a portion other than the clear aperture and a channel approximately 1 mm wide connected to the edge of the second sheet of optically transparent material for An outlet for the excess liquid crystal material is provided, and a cavity is formed with the inner side of the first optically transparent material for providing a liquid crystal material, and the transparent electrode is connected to a driving circuit of the tunable Fabry-Perot filter.

Moreover, the high-reflectivity multilayer dielectric film on the first optically transparent material of the first liquid crystal cell is disposed inside the first optically transparent material, and the transparent electrode is disposed inside the high-reflectivity multilayer dielectric film. An optical antireflection film is disposed on an outer side of the first optically transparent material; an outer side of the second optically transparent material of the first liquid crystal cell is an optically polished surface, and an inner side of the second optically transparent material is optically enhanced from the inside to the outside. a film, a transparent electrode, and a film of a non-conductive material covering a portion other than the clear aperture and a channel approximately 1 mm wide connected to the edge of the second sheet of optically transparent material for providing excess liquid crystal material An outlet, and a cavity formed inside the first piece of optically transparent material for providing a liquid crystal material, the transparent electrode being coupled to a drive circuit of the tunable Fabry-Perot filter.

Moreover, the high-reflectivity multilayer dielectric film on the second optically transparent material of the second liquid crystal cell is disposed outside the second optically transparent material, and the inner side of the second optically transparent material is sequentially disposed from the inside to the outside. An optical antireflection film and a transparent electrode, wherein an outer side of the first optically transparent material of the second liquid crystal cell is an optically polished surface, and an inner side of the first optically transparent material is provided with an optical antireflection film and a transparent electrode from the inside to the outside. And a film of a non-conductive material covering a portion other than the clear aperture and a channel connected to the edge of the sheet of optically transparent material about 1 mm wide for providing an outlet for the excess liquid crystal material, and The inside of the second optically transparent material of the two liquid crystal cells constitutes a cavity for providing a liquid crystal material, and the transparent electrode is connected to a driving circuit of the tunable Fabry-Perot filter.

Moreover, a high-reflectivity multilayer dielectric film on the second optically transparent material of the second liquid crystal cell is disposed inside the second optically transparent material, and a transparent electrode is disposed on the inner side of the high-reflectivity multilayer dielectric film. An optical antireflection film is disposed on an outer side of the second optically transparent material, wherein an outer side of the first optically transparent material of the second liquid crystal cell is an optically polished surface, and an inner side of the first optically transparent material is optically disposed from the inside to the outside. An antireflection film, a transparent electrode, and a film of a non-conductive material covering a portion other than the clear aperture and a channel connected to the edge of the sheet of optically transparent material about 1 mm wide for providing excess liquid crystal material An outlet, and a side of the second piece of optically transparent material of the second liquid crystal cell, forms a cavity for providing a liquid crystal material, the transparent electrode being coupled to a drive circuit of the tunable Fabry-Perot filter.

Moreover, the second optically transparent material of the first liquid crystal cell and the first optically transparent material of the second liquid crystal cell are mounted by: bonding together using an optically transparent index matching glue, and making the first reflection The mirror and the second mirror remain parallel to form a Fabry-Perot cavity.

Further, the liquid crystal material is a nematic liquid crystal having a thickness of several micrometers to ten micrometers.

Moreover, the drive circuit of the tunable Fabry-Perot filter is a frequency from one kilohertz to several kilohertz The square wave pulse circuit has a pulse voltage amplitude adjustable from 0 volts to 5 volts.

Moreover, the free spectral range of the tunable Fabry-Perot filter is greater than the half width of the filter bandwidth of the tunable acousto-optic filter.

Moreover, the tunable acousto-optic filter is a narrow-band, non-coaxial birefringence type acousto-optic filter, and the first-order diffraction splits the incident light into two polarization states that are perpendicular to each other and form a certain angle of linear polarization. Light.

Moreover, the tunable acousto-optic filter is driven by a driving circuit of a tunable acousto-optic filter, the driving circuit of the tunable acousto-optic filter is connected to a laser control circuit, and the driving circuit of the tunable acousto-optic filter It is a frequency and power adjustable RF signal generator with frequencies from a few megahertz to hundreds of megahertz.

Moreover, the laser control circuit is coupled to the broadband laser gain medium by a pumping circuit.

The advantages and positive effects of the invention are:

1. The present invention places two nematic liquid crystal materials having mutually perpendicular optical axes in a cavity of a Fabry-Perot etalon and utilizes an electrically controlled birefringence effect of the liquid crystal and an optical phase modulation of the incident light. The continuous, fast and precise tuning of the frequency of the light transmitted through the Fabry-Perot filter over a wide spectral range is achieved regardless of the polarization state of the incident light. Since the thickness of the liquid crystal material is very thin, a wideband tunable Fabry-Perot filter having a small size and a large free spectral range can be fabricated. The multimode optical wave output by the tunable Fabry-Perot filter is filtered by a tunable acousto-optic filter to achieve high-precision, fast, and stable filtering over a large spectral range. Since the present invention employs two laser resonator sub-cavities, the two linearly polarized lights which are separated from each other by the spatially separated polarization states generated by the tunable acousto-optic filter can form laser oscillations, and therefore, the present invention can realize non- Polarized light output.

2. The design of the invention is reasonable, and realizes continuous, rapid and precise tuning of the output light of the laser in a wide spectral range, with no mechanical moving parts, electronic tuning, fast tuning speed, stable and reliable performance, small size and easy Features such as installation and production for reliable operation in demanding small size and extreme operating environments, and are widely used in lasers, optical testing, fiber optic communications, biological, medical devices and fiber optic sensor networks.

DRAWINGS

Figure 1 is a schematic view of a conventional Fabry-Perot etalon;

2 is a schematic structural view of a first liquid crystal cell;

3 is a schematic structural view of a second liquid crystal cell;

4 is a schematic structural view of a tunable Brie-Perot filter;

Figure 5 is a graph showing the phase of light transmitted through the liquid crystal material as a function of an applied electric field;

Figure 6 is a schematic diagram of the transmission spectrum of a conventional Fabry-Perot etalon;

7 is a schematic diagram of a transmission spectrum of a tunable Brill-Perot filter;

Figure 8 is a schematic diagram of a tunable acousto-optic filter; Figure 9 is a schematic view showing the structure of the present invention;

Figure 10 is a schematic diagram of the output spectrum of the tunable acousto-optic filter;

Figure 11 is a schematic diagram of the synthesized output spectrum of a tunable Fabry-Perot filter and a tunable acousto-optic filter; Figure 12 is a schematic diagram of the output spectrum of the present invention.

Specific real Ife^

The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

A schematic of a conventional Fabry-Perot light etalon 100 is shown in FIG. The material of the Fabry-Perot etalon 100 is generally optical glass such as fused silica or BK7 in the near-infrared and visible-light bands, assuming that the material has a refractive index n and both light-passing surfaces 2 and 4 are plated high. The reflective film has a reflectance R and a thickness h. When the light is incident at an incident angle close to zero, the etalon can only be transmitted through 2nh=mA, where m is the order of transmitted light. The free spectral range of the optical etalon 100 FSR1 can be expressed as: Δλ = λ 2 / (2nh), or expressed in frequency: Δv = c / (2nh), where c is the speed of light. The peak frequency of transmitted light can be expressed as: v = mc / (2nh), where m is the interference order, and the frequency broadband of the transmitted light can be expressed as: Δν (FWHM) = c(lR) / (2nhRl/2), where c is the speed of light.

As can be seen from the above two equations, the free spectral range FSR1 of the optical etalon 100 is inversely proportional to the thickness h. Assuming that the material has a refractive index of n = 1.5, it is necessary to achieve FSRl = 100 GHz and a thickness of h - 1 mm. The free spectral range FSR1 is larger, the smaller its thickness. After the material and thickness of the etalon are determined, the bandwidth of the transmitted light is mainly related to the reflectance R. The higher the reflectance, the smaller the bandwidth or the finesse. The Fabry-Perot optical etalon's transmission spectrum is characterized by a very narrow bandwidth for each transmission spectrum, a uniform frequency spacing of the transmission spectrum and a very wide optical frequency response bandwidth, typically covering more than The optical spectrum band of 100 nm, the output light spectrum of the optical etalon 100 is shown in Fig. 6.

Since a liquid crystal material generally used as a photovoltaic device has a high electrical resistivity, it can be considered as an ideal dielectric material. The liquid crystal has anisotropic dielectric properties and uniaxial symmetry due to the ordered orientation of the molecules and the stretched morphology. Like a uniaxial crystal, the direction of the optical axis coincides with the alignment of the molecules. When the liquid crystal molecules act under the external electric field, an electric dipole is formed. Under the action of the moment formed by the electric dipole, the orientation of the liquid crystal molecules is turned to the direction of the electric field, and the direction of the optical axis of the liquid crystal can be changed by changing the strength of the electric field. Therefore, an optical phase modulator, a tunable filter or other optoelectronic devices such as an optical switch and a light intensity modulator can be fabricated using this characteristic of the liquid crystal. The thickness of the liquid crystal film layer generally used as a photovoltaic device is from several micrometers to ten micrometers. The present invention is designed by utilizing the fact that liquid crystals change the refractive index of linearly polarized light under the action of an electric field.

The polarization-independent tunable Fabry-Perot filter involved in the present invention includes two liquid crystal cells whose optical axis directions are perpendicular to each other.

As shown in FIG. 2, the first liquid crystal cell 200 includes two structures. The first structure includes a first piece of optically transparent material 8. The liquid crystal material 14 and the second optically transparent material 22, the high-reflectivity multilayer dielectric film 6 is disposed on the outer surface of the first optically transparent material 8, and the optical anti-reflection film 10 and the transparent electrode film are disposed on the inner side from the inside to the outside. The outer surface 24 of the second optically transparent material 22 is an optically polished surface, and the optical antireflection film 20, the transparent electrode film layer 18 and the non-conductive material film 16, and the thickness of the non-conductive material film 16 are respectively disposed from the inside to the outside. Between a few micrometers and a dozen micrometers, covering a portion other than the clear aperture and a channel having a width of about 1 mm leading to the edge of the optically transparent material 22 for removing excess liquid crystal material, the non-conductive material film 16 and The first optically transparent material 8 constitutes a cavity for arranging the liquid crystal material 14. The liquid crystal material 14 is a nematic liquid crystal having a thickness of about several micrometers and a few micrometers. The second structure of the liquid crystal cell 200 is different from the first structure in that an optical anti-reflection film 6 is disposed on the outer surface of the first optically transparent material 8, and a high-reflectivity multilayer dielectric is disposed on the inner side from the inside to the outside. The film 10 and the transparent electrode film layer 12 are otherwise disposed in the same manner as the first structure of the liquid crystal cell 200, and the purpose thereof is to change the thickness of the Fabry-Perot cavity.

As shown in Fig. 3, the second liquid crystal cell 300 includes two structures. The first structure comprises a first sheet of optically transparent material 28, a liquid crystal material 36, and a second sheet of optically transparent material 42, the outer surface 26 of the second sheet of optically transparent material 42 being provided with a high reflectivity multilayer dielectric film 44, the inside from the inside out The optical anti-reflection film 40 and the transparent electrode film layer 32 are respectively disposed. The outer surface 26 of the first optically transparent material 28 is an optically polished surface, and the optical antireflection film 30, the transparent electrode film layer 32 and the non-conductive layer are respectively disposed from the inside to the outside. The material film 34, the non-conductive material film 34 has a thickness of several micrometers to ten micrometers, covers other portions except the light-passing aperture, and a channel having a width of about 1 mm to the edge of the optically transparent material 28 for eliminating excess The liquid crystal material, the non-conductive material film 34 and the second sheet of optically transparent material 42 form a cavity for providing the liquid crystal material 36. Generally, the portions other than the liquid crystal chambers of the two materials constituting the liquid crystal chamber are bonded together by an epoxy resin or an ultraviolet gel, and the liquid crystal material 36 is a nematic liquid crystal having a thickness of about several micrometers. The road is a dozen microns. The second structure of the liquid crystal cell 300 is different from the first structure in that an optical anti-reflection film 44 is disposed on the outer surface of the second optically transparent material 42, and a high-reflectivity multilayer dielectric film 40 is disposed on the inner side from the inside to the outside. And the transparent electrode film layer 38, the other arrangement is the same as the first structure of the liquid crystal cell 300, the purpose of which is to change the thickness of the Fabry-Perot cavity.

Figure 4 shows a schematic diagram of a polarization-independent tunable Brie-Perot filter. The tunable Fabri

The Perot filter 400 includes a first liquid crystal cell 200, a second liquid crystal cell 300, and a tunable Fabry-Perot filtered drive circuit 52. The outer side of the second piece of optically transparent material of the liquid crystal cell 200 and the outer side of the first piece of optically transparent material of the liquid crystal cell 300 are bonded together by the optically transparent index matching glue 50 and the first optically transparent material and liquid crystal of the liquid crystal cell 200 are made. The faces of the second optically transparent material of the cartridge 300 provided with the high reflectivity dielectric film remain parallel to form a harmonic Fabry-Perot cavity. The driving circuit 52 is connected to the transparent electrodes of the liquid crystal cell 200 and the liquid crystal cell 300, and the driving signal generated by the driving circuit 52 forms a driving electric field between the two transparent electrode film layers; the Fabry-Perot is changed by the electric field. (Fabry-Perot) The effective refractive index n of the liquid crystal in the cavity to adjust the optical frequency v and the free spectral range (FSR) of the transmitted light of the Fabry-Perot filter. A typical driving electric field is a square wave signal having a voltage of several volts and a frequency of 1 kHz to several kilohertz.

Since the thickness of the liquid crystal is small (several micrometers to ten micrometers), tunable Fabry-Perot can be made in the intrinsic free spectral range (ie, the free spectral range of the tunable filter without an applied electric field) filter. Since the optical axes of the liquid crystals in the first liquid crystal cell 200 and the second liquid crystal cell 300 are perpendicular to each other, the filter 400 is independent of the polarization state of the incident light.

In FIG. 4, the light beam 48 incident on the filter 400 is a collimated beam, assuming that the refractive index of the optically transparent material is n, on the first optically transparent material of the first liquid crystal cell 200 and on the second liquid crystal cell 300. The reflectivity of the highly reflective dielectric film on the second optically transparent material is R, and the length of the Fabry-Perot cavity is D. Only the light satisfying 2nD+r=mA can pass through the etalon, where m is the transmission. The order of light. The free spectral range FSR2 and transmitted light frequency of the filter 400 are: Δλ = λ 2 / (2nD + r), respectively, or expressed by frequency: Av = c / (2nD + r), where c is the speed of light, and Γ represents the liquid crystal The optical path produced by the incident light is changed by the refraction under the action of an applied electric field. The peak frequency of transmitted light can be expressed as: v = mc / (2nD + "), where m is the interference order, and the frequency broadband of the transmitted light can be expressed as: Δν ( FWHM ) = c(lR) / ((2nD + DRl / 2), where c is the speed of light. The combination of two different structures of the first liquid crystal cell 200 and the second liquid crystal cell 300 can increase or decrease the length D of the Fabry-Perot cavity, thereby adjusting the filter 400 free spectral range FSR2.

Figure 5 is a graph showing the relationship between the phase change of a 1525 nm light wave with a wavelength of about 10 μm nematic liquid crystal driven by a 2 kHz square wave voltage. A maximum optical phase delay of about 2π can be achieved. Through experiments and analysis, the tunable Fabry-Perot filter 400 can obtain a tuning range of about 1.5 times the transmitted optical frequency of FSR2 for collimated light near zero incidence, and a band of free spectral range Δν and transmitted light. The change in broadband is much smaller. A schematic diagram of the spectrum of the transmitted light 54 of the tunable Fabry-Perot filter is shown in FIG.

It can be seen that the tunable Fabry-Perot filter 400 can achieve a large range of transmission light peak frequency tuning under the action of an applied electric field without substantially changing the bandwidth and free spectral range of the transmitted light. This feature is important for many applications in tunable Fabry-Perot filter 400, such as lasers and spectrum instruments.

Figure 8 shows a schematic of a tunable acousto-optic filter. The medium generally used for the acousto-optic filter 500 is anisotropic and has birefringence characteristics. One of the substances, cerium oxide (Te02), is widely used in such applications due to its high optical uniformity, low light absorption and high optical power capability in shear mode. Other substances such as lithium niobate (LiNb03), gallium phosphide (GaP) and lead molybdate (PbMo04) are also frequently used in various acousto-optic devices. There are many factors that influence the selection of specific substances. Only a few types are listed below, such as: the type of acousto-optic device, the availability of high-quality crystals, and the type and demand of applications, such as diffraction efficiency power loss, dispersion of incident and diffracted light. Degree and The size of the overall device, etc.

The tunable acousto-optic filter 500 is a non-collinear and non-paraxial acousto-optic filter having birefringence characteristics. An acousto-optic crystal 57 and a transducer 58 comprising cerium oxide are used to directly drive the transducer 58 from a drive circuit 60 of the tunable acousto-optic filter to produce an acoustic wave field 59 in the crystal 57 to form a diffraction grating. A collimated beam 56 enters the crystal 57 and forms a Bragg angle with the acoustic field 59. After being diffracted by the tunable acousto-optic filter, the first-order diffracted light is split into two linearly polarized lights, S-light 62 and neon 64, and zero. The order diffracted beam 66. The angle between the two linearly polarized lights 62 and 64 and the zero order diffracted beam is equal to the Bragg angle ΘΒ. The cutting of the acousto-optic crystal 57 causes the incident surface 55 and the exit surface 61 to be perpendicular or nearly perpendicular to the incident light. In order to reduce the loss of light, both the incident surface 55 and the exit surface 61 are plated with an optical antireflection coating. The filter spectrum of the tunable acousto-optic filter 500 is characterized by continuous tunability of the optical frequency over a wide frequency range, as shown in Figure 10. The bandwidth of the filtered spectrum Δ V , half width (FWHM) Δ V 1/2, resolution and diffraction efficiency are dependent on the size of the acousto-optic crystal, the structure of the transducer, and the RF drive power. To achieve narrowband filtering spectra and high diffraction filtering efficiency, it is necessary to increase the size of transducers and acousto-optic crystals.

Fig. 9 shows the structure of the present invention, and the technical solution of the present invention will be described below with reference to Fig. 9. A tunable laser of unpolarized light output includes a first mirror 72, a broadband laser gain medium 76, a tunable Fabry-Perot filter 400, a tunable acousto-optic filter 500, a second mirror 84, and a A three mirror 86 and a drive control system. The drive control system includes a laser pumping circuit 74, a drive circuit 52 of the tunable Fabry-Perot filter 400, a drive circuit 60 of the tunable acousto-optic filter 500, and a laser control circuit 88. The beam emitted by the broadband laser gain medium 76 first passes through the filter 400, and after the output beam 78 passes through the tunable acousto-optic filter 500, the output beam is divided into zero-order diffracted light 81, and the first-order diffracted light is split into two polarization states. The vertical linearly polarized light S polarized light 80 and the erbium polarized light 82, the second mirror 84 and the third mirror 86 are disposed at an angle and a position such that the S polarized light 80 and the Ρ polarized light 82 are reflected back along the original optical path, respectively. Tunable acousto-optic filter 500, and in a first laser resonator sub-chamber consisting of a first mirror 72 and a second mirror 84, respectively, and a second laser consisting of a first mirror 72 and a third mirror 86 Laser oscillation is formed in the resonator cavity, and the laser pump circuit 74 controls and adjusts the laser pump circuit 74, the drive circuit 52 of the tunable Fabry-Perot filter 400, and the drive circuit 60 of the tunable acousto-optic filter 500. Tuning and control of laser output power and wavelength. The collimated beam 76 is incident into the tunable Fabry-Perot filter 400. The spectrum of the transmitted light 78 is shown in Figure 7. The tunable range of the peak frequency of the transmitted light is about 1.5 times the FSR2, in the tunable range. The free spectral range of the tunable Fabry-Perot filter 400 remains substantially unchanged within the spectral range of about 100 nanometers. After the transmitted light 78 passes through the tunable acousto-optic filter 500, the first-order diffracted light is split into two beams 80 and 82 whose polarization states are perpendicular to each other. When the transmission bandwidth ΔV of the tunable acousto-optic filter 500 is less than 2 times, The intrinsic free spectral range FSR2 of the tuned Fabry-Perot filter 400, the transmitted light 80 and 82 are a single mode beam, the spectral characteristics of which are shown in Figure 12 and the tunable Fabry-Perot filter. The spectral characteristics of a transmission mode of 400 are the same. Such as Considering the spectral degree Δ ν of the transmitted light of the tunable Fabry-Perot filter 400 (refer to FIG. 11 ), to achieve a single mode output or a high transmitted light side touch suppression ratio, the acousto-optic filter 500 is tuned. The transmission bandwidth Δ ν also needs to be narrower. It is to be noted that the definition of the spectral width Δ V of the transmitted light of the tunable Fabry-Perot filter 400 and the tunable acousto-optic filter 500 is based on the noise or edge suppression ratio of the laser output spectrum in practical applications. Need to be determined.

Depending on the type of laser gain medium and the requirements on the output, the first mirror 72, the second mirror 84, and the third mirror 86 may employ a total reflection mirror or a partial reflection mirror, such as leakage light from a partial reflection mirror. Different types of mirrors, such as plane mirrors, convex mirrors or concave mirrors, can be used to monitor different types of laser resonators, such as stable chambers, metastable chambers or unstable chambers. . In addition, in order to make the tunable Fabry-Perot filter 400 and the tunable acousto-optic filter 500 in the best working condition, the input beam is required to be a collimated beam, and therefore, if the broadband laser gain medium 76 emits a dispersion A type of beam, such as a semiconductor laser gain medium, can collimate the beam with an intracavity collimating lens.

Since the present invention utilizes the filtering function of the tunable Fabry-Perot filter 400 and the diffraction filtering function of the tunable acousto-optic filter 500, different response characteristics are obtained for beams of different optical frequencies, and therefore, accurate The laser output power and frequency require calibration of the system. The laser control circuit 88 includes a control circuit centered on a digital signal processor and embedded software. The data analysis software and the data type interface are used to control, tune, and receive external control signals and external output signals.

It is to be understood that the foregoing description is not intended to Many modifications and variations of the present invention are possible in the light of the above description. The specific implementation chosen is merely to better explain the principles of the invention and the application in practice. This description enables those skilled in the art to make better use of the present invention, designing different specific implementations and making corresponding changes as needed.

Claims

claims

1. A tunable laser with non-polarized light output, characterized by: including a first reflector, a broadband laser gain medium, a tunable Fabry-Perot filter, a tunable acousto-optic filter, and a second reflector. , the third reflector and the laser control circuit; the first reflector and the second reflector constitute the first laser resonator subcavity, the first reflector and the third reflector constitute the second laser resonator subcavity; the broadband laser gain medium emits After the broadband beam is filtered by a tunable Fabry-Perot filter, and then filtered by a tunable acousto-optic filter, its first-order diffracted beam is divided into two beams of polarized light whose polarization states are perpendicular to each other, and its S-state polarized beam is divided into two beams. The mirror reflects and forms laser oscillation in the first laser resonator cavity, and its P-state polarized beam is reflected by the third mirror and forms laser oscillation in the second laser resonator cavity. Zero-order diffraction of the tunable acousto-optic filter The beam serves as the output beam of the laser; the laser control circuit is connected to the broadband laser gain medium, the tunable Fabry-Perot filter and the tunable acousto-optic filter to realize the tunable output control function of the laser.

2. A tunable laser with non-polarized light output according to claim 1, characterized in that: the first reflector, the second reflector and the third reflector are one of the following three types of reflectors: Plane mirror, concave mirror and convex mirror.

3. A tunable laser with non-polarized light output according to claim 1, characterized in that: the tunable Fabry-Perot filter includes a first liquid crystal cell and a second liquid crystal cell installed in sequence. A driving circuit for a liquid crystal cell and a tunable Fabry-Perot filter. Both liquid crystal cells include a first piece of optically transparent material, a liquid crystal material and a second piece of optically transparent material installed together in sequence. The first piece of liquid crystal cell Two pieces of optically transparent material are installed together with the first piece of optically transparent material of the second liquid crystal cell. A high-reflectivity multilayer dielectric film is arranged on the first piece of optically transparent material of the first liquid crystal cell to form a first reflecting mirror. A high reflectivity multilayer dielectric film is arranged on the second piece of optically transparent material of the two liquid crystal cells to form a second reflecting mirror. The optical axes of the liquid crystal materials in the two liquid crystal cells are perpendicular to each other and are arranged between the first reflecting mirror and the second reflecting mirror. In the Fabry-Perot cavity composed of mirrors, the driving circuit of the tunable Fabry-Perot filter is connected to the two liquid crystal cells and realizes the tuning function of the filter by controlling the effective refractive index of the liquid crystal material. The driving circuit of the tunable Fabry-Perot filter is connected with the laser control circuit.

4. A tunable laser with non-polarized light output according to claim 3, characterized in that: the high reflectivity multilayer dielectric film on the first piece of optically transparent material of the first liquid crystal cell is disposed on the first The outside of the piece of optically transparent material, the inside of the first optically transparent material is provided with an optical anti-reflection film and a transparent electrode in order from the inside to the outside; the outside of the second optically transparent material of the first liquid crystal cell is an optically polished surface, The inner side of the two optically transparent materials is provided with an optical anti-reflection film, a transparent electrode and a non-conductive material film in sequence from the inside to the outside. The non-conductive material film covers the part except the clear aperture and is connected to the second piece with a width of about 1 mm. The channel at the edge of the optically transparent material sheet is used to provide an outlet for the excess liquid crystal material, and forms a cavity with the inside of the first piece of optically transparent material for disposing the liquid crystal material. The transparent electrode is connected with the tunable Fabry-Perot Luo filter drive circuit connected.

5. A tunable laser with non-polarized light output according to claim 3, characterized in that: the first A high-reflectivity multilayer dielectric film on a first piece of optically transparent material of a liquid crystal cell is arranged inside the first piece of optically transparent material, and a transparent electrode is arranged inside the first piece of optically transparent material. An optical anti-reflection film is provided on the outside of the material; the outside of the second optically transparent material of the first liquid crystal cell is an optically polished surface, and the inside of the second optically transparent material is provided with an optical anti-reflection film, a transparent electrode and A film of non-conductive material covering the portion except the clear aperture and a channel approximately 1 mm wide connected to the edge of the second sheet of optically transparent material to provide an outlet for excess liquid crystal material and with The inside of the first piece of optically transparent material forms a cavity for disposing the liquid crystal material, and the transparent electrode is connected to the driving circuit of the tunable Fabry-Perot filter.

6. A tunable laser with non-polarized light output according to claim 3, characterized in that: the high reflectivity multilayer dielectric film on the second optically transparent material of the second liquid crystal cell is disposed on the second The outside of the first piece of optically transparent material, the inside of the second optically transparent material is provided with an optical anti-reflection film and a transparent electrode in order from the inside to the outside, the outside of the first piece of optically transparent material of the second liquid crystal cell is an optically polished surface, The inside of the first piece of optically transparent material is provided with an optical anti-reflection film, a transparent electrode and a non-conductive material film in order from the inside to the outside. The non-conductive material film covers the part except the clear aperture and an approximately 1 mm wide connection to the The channel at the edge of the optically transparent material sheet is used to provide an outlet for excess liquid crystal material, and forms a cavity with the inside of the second piece of optically transparent material in the second liquid crystal cell for disposing the liquid crystal material. The transparent electrode is connected to the tunable Fabry-Perot filter driver circuit.

7. A tunable laser with non-polarized light output according to claim 3, characterized in that: the high reflectivity multilayer dielectric film on the second optically transparent material of the second liquid crystal cell is disposed on the second Inside the piece of optically transparent material, a transparent electrode is arranged inside the high-reflectivity multilayer dielectric film, and an optical anti-reflection film is arranged outside the second optically transparent material. The first piece of optically transparent material of the second liquid crystal cell The outside is an optically polished surface, and the inside of the first piece of optically transparent material is provided with an optical anti-reflection film, a transparent electrode and a non-conductive material film from the inside to the outside. The non-conductive material film covers the part except the clear aperture and an approximately a 1 mm wide channel connected to the edge of the sheet of optically transparent material for providing an outlet for excess liquid crystal material, and forming a cavity with the inside of the second sheet of optically transparent material of the second liquid crystal cell for disposing the liquid crystal material, The transparent electrode is connected to the drive circuit of the tunable Fabry-Perot filter.

8. A tunable laser with non-polarized light output according to claim 3, characterized in that: the second piece of optically transparent material of the first liquid crystal cell and the first piece of optically transparent material of the second liquid crystal cell The installation method is: use optically transparent refractive index matching glue to bond them together, and keep the first reflector and the second reflector parallel to form a Fabry-Perot cavity.

9. A tunable laser with non-polarized light output according to claim 3, characterized in that: the liquid crystal material adopts nematic liquid crystal, and the thickness of the liquid crystal material is from several microns to more than ten microns. .

10. A tunable laser with non-polarized light output according to claim 3, characterized in that: the driving circuit of the tunable Fabry-Perot filter is a frequency ranging from one thousand hertz to Square wave pulse electricity of several kilohertz circuit, the pulse voltage amplitude is adjustable from 0 volts to 5 volts.

11. A tunable laser with non-polarized light output according to claim 1, characterized in that: the free spectral range of the tunable Fabry-Perot filter is greater than that of the tunable acousto-optic filter. The half-width of the filter bandwidth.

12. A tunable laser with non-polarized light output according to claim 1, characterized in that: the tunable acousto-optic filter is a narrow-band, non-coaxial birefringent acousto-optic filter, one of which First-order diffraction divides the incident light into two linearly polarized lights whose polarization states are perpendicular to each other and form a certain angle.

13. A tunable laser with non-polarized light output according to claim 1 or 12, characterized in that: the tunable acousto-optic filter is driven by a driving circuit of the tunable acousto-optic filter, and the tunable acousto-optic filter The drive circuit of the optical filter is connected to the laser control circuit; the drive circuit of the tunable acousto-optic filter is a frequency and power adjustable radio frequency signal generator with a frequency from several megahertz to hundreds of megahertz.

14. The tunable laser with non-polarized light output according to claim 1, characterized in that: the laser control circuit is connected to the broadband laser gain medium through a pump circuit.