JP4956004B2 - Optical isolator - Google Patents

Description

  The present invention relates to an optical isolator used as an optical passive component mainly in the field of optical communication and fiber laser to prevent return light.

  In recent years, in an optical communication system, an optical amplifier that is an apparatus that directly amplifies an optical signal without converting the optical signal into an electric signal, or several tens of optical signals having slightly different wavelengths are combined into one optical fiber. Optical multiplex communication technology for simultaneous transmission has been put into practical use, and a system with higher capacity and lower attenuation rate is being realized.

  In such an optical communication system, when an optical semiconductor laser is used as a light source for an optical signal transmission system such as optical measurement, a part of light emitted from the semiconductor laser is reflected at each connection portion of the transmission line or the optical component for electric transmission. When the feedback is made to the semiconductor laser, the oscillation characteristics of the semiconductor laser become unstable and noise increases. In order to prevent the return light from returning, an optical isolator is generally used.

  Patent Document 1 discloses a conventional optical isolator. As shown in FIG. 5, the basic configuration of this optical isolator is a FR (Faraday Rotator) 43 having a Faraday effect, a pair of first polarizer 45 and second polarizer 47, and Faraday rotation. It comprises a magnet 49 for applying a magnetic field to the child 43, and the optical axes of the FR 43, the first polarizer 45 and the second polarizer 47 are adjusted.

  In FIG. 5, incident light propagating in the direction of the arrow a passes through the first polarizer 45 and then enters the Faraday rotator 43 as linearly polarized light. While propagating through the Faraday rotator 43, the light enters the second polarizer 47 with its incident surface rotated by 45 degrees normally by the magnetic field strength of the magnet 49. Here, since the inclination of the second polarizer 47 is set in advance equal to the polarization plane inclination (45 degrees) of the incident light, the second polarizer 47 transmits the incident light.

On the other hand, incident light (return light) propagating in the reverse direction as indicated by an arrow b in FIG. 5 passes through the second polarizer 47 and the Faraday rotator 43, and thus enters the polarization plane of the first polarizer 45. On the other hand, linearly polarized light having a plane of polarization inclined by 90 degrees is incident on the first polarizer 45, so that the incident light in the opposite direction does not pass through the first polarizer 45. Therefore, the return of return light can be prevented by using this optical isolator.
Japanese Patent Laid-Open No. 5-71327

  By the way, when a high-power semiconductor laser or fiber laser is used and a conventional optical isolator is used, the amount of return light increases, so the influence of return light in the optical isolator cannot be ignored. The return light is scattered, and as a result, the temperature inside the module rises, causing deterioration of module characteristics such as a decrease in isolation, module failure, and return light is collected near the incident side fiber. It has a problem of damaging the adhesive and the member that are fixing.

  Similarly, in the forward direction, leakage light is generated due to a deviation of the polarization plane and the transmission axis of the polarizer caused by the setting error of the optical axis of the birefringent crystal used and the wavelength characteristics of the Faraday rotation. The rise in temperature caused module deterioration and failure factors when using a high-power semiconductor laser as well as return light.

  Therefore, in the present invention, a mechanism for receiving the return light and the leakage light in the forward direction is provided, where the light is converted into heat and further dissipated, whereby the optical isolator module itself is damaged by the return light and the temperature rises. For example, an optical isolator that exhibits stable characteristics even when used under high output, such as a fiber laser of a 1080 nm band, is proposed.

A first aspect of the optical isolator according to the present invention includes an incident collimator, a nonreciprocal part and an output collimator that are sequentially arranged on the optical axis of the incident collimator, a housing in which the nonreciprocal part is accommodated, and the output A non-reciprocal portion, a first polarizer made of a birefringent crystal, a Faraday rotator, and a first birefringent crystal. The light incident from the incident collimator is configured to propagate in the order of the first polarizer, the Faraday rotator, and the second polarizer, and the return light is It propagates through an offset path different from the outgoing light defined by the reciprocal part and enters the first heat conversion processing unit, and the first heat exchange processing unit is connected to the casing via a heat insulating structure. it characterized in that it is fixed It is an isolator.

A second aspect of the optical isolator according to the present invention includes an incident collimator, a nonreciprocal part and an output collimator that are sequentially arranged on an optical axis of the incident collimator, a housing that accommodates the nonreciprocal part, A second thermal conversion processing unit that thermally converts leaked light leaking from the reciprocal part, and the non-reciprocal part includes a first polarizer, a Faraday rotator, and a second polarizer, The light incident from the incident collimator is configured to propagate in the order of the first polarizer, the Faraday rotator, and the second polarizer, and the leaked light is incident upon the second polarizer. A part of the linearly polarized light component whose angle of incidence on the optical axis is shifted, and propagates through an offset path different from the light coupled to the output collimator and enters the second thermal conversion processing unit, The second heat exchange processing unit has a heat insulating structure in the housing. An optical isolator you characterized in that it is fixed to.

According to a third aspect of the optical isolator of the present invention, the optical isolator includes a second thermal conversion processing unit that thermally converts leaked light leaking from the non-reciprocal part, and the leaked light is incident on the second polarizer. A part of the linearly polarized light component whose incident angle with respect to the optical axis is deviated, propagates through an offset path different from the light coupled to the output collimator, and enters the second thermal conversion processing unit; second heat exchange unit, it is optical isolator you characterized being secured through a heat insulating structure to the housing.
In the first to third aspects, the return light or the leaked light is incident on the first or second heat conversion processing unit via a space.
Furthermore, in the first to third aspects, the incident light is an optical isolator characterized by being a laser beam in a 1080 nm band.

  According to a fourth aspect of the optical isolator of the present invention, the first thermal conversion processing unit and / or the second thermal conversion processing unit is arranged perpendicular to the optical axis direction. It is.

  A fifth aspect of the optical isolator of the present invention is an optical isolator characterized in that the first thermal conversion processing unit and / or the second thermal conversion processing unit includes a lens.

  According to a sixth aspect of the optical isolator of the present invention, the return light is guided to the first thermal conversion processing unit by the optical path conversion mechanism.

  A seventh aspect of the optical isolator according to the present invention is an optical isolator characterized in that leakage light is guided to the second thermal conversion processing unit by an optical path conversion mechanism.

  According to an eighth aspect of the optical isolator of the present invention, the optical path changing mechanism is a prism.

  The optical isolator according to the present invention is provided with a mechanism for receiving the return light and the leakage light in the forward direction, so that the light is converted into heat and further dissipated so that the direct light caused by the return light of the module itself can be directly obtained. It became possible to prevent damage and temperature rise. Therefore, an optical isolator exhibiting stable characteristics can be realized even when a high-power semiconductor laser or fiber laser is used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4.

(First embodiment)
FIG. 1 is a plan view of an optical isolator according to the present invention. The optical isolator 1 includes an incident collimator 3, a nonreciprocal part 5, and an output collimator 7 on the optical axis inside a housing 2. In addition, a first heat conversion processing unit 9 and a second heat conversion processing unit 11 are externally attached to the optical isolator 1 perpendicular to the optical axis direction.

  The incident collimator 3 includes an optical fiber 13 a through which incident light propagates and a lens 15 a that suppresses the spread of incident light output from the optical fiber 13 a, and the incident light is output to the nonreciprocal part 5. The optical fiber 13a and the lens 15a are preferably made of a material that can withstand a high-power laser.

  The non-reciprocal unit 5 includes a first polarizer 17 that polarizes incident light output from the incident collimator 3, an FR 19 that rotates a plane of polarization by the Faraday effect, and a crystal rotator that compensates the temperature characteristic or wavelength characteristic of the FR 19. 21 and a second polarizer 23 that polarizes incident light transmitted through the quartz crystal rotator 21. For the polarizers 17 and 23, birefringent crystals having a small absorption coefficient with respect to the wavelength to be used are used in order to realize low loss and optical isolation regardless of the polarization state of incident light and to raise the laser damage threshold. .

As the birefringent crystal, rutile (TiO ₂ ), calcite (CaCO ₃ ; calcite), YVO ₄ crystal, LN crystal (LiNbO ₃ ; lithium niobate) and the like having a large refractive index and excellent extinction ratio characteristics are mainly used. It is done. In the example shown here, the birefringent crystal has a function of offsetting the optical path of the return light horizontally with the propagation direction of the light. However, as is well known as a configuration of the optical isolator, A configuration using a parallel plate type in combination is also conceivable. Various configurations are conceivable depending on the application, such as the use of a polarizing prism such as a Glan-Thompson prism. When a wedge-shaped birefringent crystal is used, return light and leakage light take an optical path inclined at an angle from the light propagation direction. A magnet 49 for applying a magnetic field to the FR 19 is provided around the FR 19.

  The FR 19 and the quartz crystal rotator 21 have a structure sandwiched between the first polarizer 17 and the second polarizer 23. The crystal rotator is arranged for the purpose of compensating for the temperature characteristics and wavelength characteristics of the FR 19, and may be arranged behind the FR 19 or may be arranged in front of it depending on the design. In addition to the quartz rotator, the same effect can be obtained by using or combining a retardation plate of a birefringent crystal such as quartz or LN. These designs are optimized by the characteristics of the FR 19 used. When the wavelength characteristic and temperature characteristic of the FR 19 are allowed in use, the compensation element is not necessary. The output collimator 7 includes a lens 15b that condenses the emitted light output from the nonreciprocal part 5 on the end face of the output side fiber, and an optical fiber 13b through which the emitted light propagates.

  The first heat conversion processing unit 9 is disposed between the incident collimator 3 and the nonreciprocal part 5 perpendicular to the optical axis direction. And the light (return light) which returns to the direction of the incident collimator 3 from the output collimator 7 is absorbed, converted into heat, and radiated to the outside. In the present embodiment, the first thermal conversion processing unit 9 is arranged perpendicular to the optical axis direction, but is not limited to being arranged perpendicularly.

  The second heat conversion processing unit 11 is disposed between the emission collimator 7 and the nonreciprocal part 5 perpendicular to the optical axis direction. Then, when propagating from the second polarizer 23 to the output collimator 7, the incident light (leakage light) partially leaked is absorbed and converted into heat and radiated to the outside. In the present embodiment, the second heat conversion processing unit 9 is arranged perpendicular to the optical axis direction, but is not limited to being arranged perpendicularly.

  Therefore, the direction of the return light and leakage light is changed from the optical axis direction to the vertical direction by the optical path changing mechanism 25 such as a prism disposed between the incident collimator 3 or the outgoing collimator 7 and the nonreciprocal part 5. And it can guide to each heat conversion processing part.

  Next, the operation of the optical isolator 1 of the present invention will be described with reference to the drawings. FIG. 2 is a plan view schematically showing thermal conversion of return light. As shown in FIG. 2, the return light returning from the output collimator 7 to the incident collimator 3 passes through the second polarizer 23, the crystal rotator 21, FR 19, and the first polarizer 17. However, in the first polarizer, the return light does not return to the incident collimator 3, but is guided to the first heat conversion processing unit 9 by the optical path conversion mechanism 25, and the return light is converted into heat and air-cooled. When the return light processing unit and / or the module main body is mounted on the heat sink via a material having good heat transfer, the heat radiation efficiency can be further increased and the temperature rise of the module can be prevented.

  FIG. 3 is a plan view schematically showing thermal conversion of leakage light. As shown in FIG. 3, a high-power laser beam of about 30 kW enters the incident collimator 3. Incident light output from the incident collimator 3 enters the first polarizer 17 formed inside the nonreciprocal part 5. In the first polarizer 17, the incident light incident from the incident collimator 3 becomes linearly polarized light and enters the FR 19.

  The incident light that has entered the FR 19 has its angle rotated by the Faraday effect, passes through the crystal rotator 21, and then enters the second polarizer 23. In the second polarizer 23, the linearly polarized light that is emitted from the crystal rotator 21 and rotated by the FR 19 is transmitted toward the output collimator 7, and the accuracy and wavelength characteristics of the optical element and the placement accuracy of the polarizer are transmitted. For example, a part of the linearly polarized light component whose incident angle with respect to the optical axis of the second polarizer 23 deviates from the design leaks to the outside of the second polarizer 23, and the direction is changed by the optical path changing mechanism 25. Heat conversion is performed by the two heat conversion processing units 11 and air-cooled.

By these two heat conversion processing units 9 and 11 described above, the temperature rise in the module is suppressed, and the failure of the optical isolator can be prevented. This makes it possible to realize an optical isolator that exhibits stable characteristics even when used at high output.

  Next, the above-described heat conversion processing unit will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the structure similar to each part of the optical isolator shown by FIG. 1, and the description is abbreviate | omitted.

  FIG. 4 is a plan view of the heat conversion processing unit. As shown in FIG. 4, the heat conversion processing unit 9 includes a light receiving unit 27 that receives return light or leakage light, and a joint unit 29 that joins the light receiving unit 27 and the heat insulating material 33. Furthermore, the light receiving unit 27 is formed with a ball lens 31 that diffuses return light and the like. The arrows shown in FIG. 4 indicate that the return light or the like is multiply reflected.

  Here, the material of the light receiving portion 27 is preferably a material having a high melting point and high temperature resistance and a high thermal conductivity, such as a metal such as aluminum or ceramics. Further, in order to prevent heat from being transmitted from the heat conversion processing unit to the module side, it is preferable to have a heat insulating structure in which a heat insulating material 33 such as a resin is interposed between the module and the heat conversion processing unit. As a material (heat insulating material) for the joint portion, a heat insulating resin having high temperature resistance and high heat insulating properties such as Delrin (registered trademark), PPS (polyphenylene sulfide), thermoplastic polyimide, etc. and having small outgas is desirable. Thereby, heat inflow into the housing can be suppressed.

  The thermal conversion processing unit may be separated from the module body, or may be incident on the thermal conversion processing unit after receiving the return light with a collimator or the like and propagating it through the optical waveguide. When it is difficult to separate the return light and the incident light, such as when using a wedge-shaped birefringent crystal, for example, the incident side collimator has three core fibers, and a single mode fiber (SMF) If a mode fiber (MMF) is arranged for receiving the return light, it is not necessary to separate the light by a prism, etc., and by separating the heat conversion processing part, the temperature rise of the optical isolator itself can be prevented and the size can be reduced. It is also possible.

  In the heat conversion processing unit 9, the reflected light or leaked light that flows in through the ball lens 31 is reflected multiple times and is absorbed. The received light is converted into heat and air-cooled. It is desirable to adopt a structure having an optical trap function so that light is efficiently converted into heat and incident light is not leaked into the module. In addition to the structure of the present embodiment, a conical light receiving portion may be provided. Increasing the absorption coefficient of the light receiving unit 27 is also effective in preventing return light from leaking to the outside as in the structure. In order to increase the absorption coefficient of metal, there are a surface treatment method such as a radiant treatment, a plating treatment such as NiP electroless plating, and a black alumite. In addition, by diffusing light through the ball lens 31, heat absorption by the light receiving unit 27 is performed as a whole, and air cooling can be performed earlier. A Peltier element or the like may be used for air cooling.

  Furthermore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Even in high-power modules other than optical isolators, when the amount of extra reflected light in the module is large, such as filter modules and WDM (Wavelength Division Multiplexing) modules, the reflected light is received. A similar effect can be obtained by converting to heat.

  The optical isolator according to the present invention provides a mechanism for receiving the return light and the leakage light in the forward direction, so that the light is converted into heat and further radiated to prevent the temperature rise of the module itself. It becomes possible and has high industrial applicability.

FIG. 1 is a plan view of an optical isolator according to the present invention. FIG. 2 is a plan view schematically showing thermal conversion of return light. FIG. 3 is a plan view schematically showing thermal conversion of leakage light. FIG. 4 is a plan view showing a heat conversion processing unit. FIG. 5 is a perspective view showing a conventional optical isolator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 41 Optical isolator 2 Case 3 Incident collimator 5 Non-reciprocal part 7 Outgoing collimator 9 1st thermal conversion process part 11 2nd thermal conversion process part 13 Optical fiber 15 Lens 17, 45 1st polarizer 19, 43 Faraday rotator 20, 49 Magnet 21 Quartz optical rotator 23 Second polarizer 25 Optical path conversion mechanism 27 Light receiving part 29 Connection part 31 Ball lens 33 Heat insulating material

Claims (10)

An incident collimator;
A non-reciprocal portion and an output collimator arranged in order on the optical axis of the incident collimator;
A housing that accommodates the non-reciprocal portion;
A first heat conversion processing unit that converts the return light returning from the output collimator into heat;
With
The nonreciprocal portion includes a first polarizer made of a birefringent crystal, a Faraday rotator, and a second polarizer made of a birefringent crystal, and light incident from an incident collimator The return light is propagated in the order of a polarizer, a Faraday rotator, and a second polarizer, and the return light propagates through an offset path different from the outgoing light defined by the non-reciprocal part to be the first. Is incident on the thermal conversion processing section of
It said first heat exchange unit shall be the feature that it is fixed via a heat insulating structure to the housing, the optical isolator. An incident collimator;
A non-reciprocal portion and an output collimator arranged in order on the optical axis of the incident collimator;
A housing that accommodates the non-reciprocal portion;
A second thermal conversion processing unit that thermally converts leaked light leaking from the non-reciprocal part;
With
The non-reciprocal portion includes a first polarizer, a Faraday rotator, and a second polarizer, and light incident from an incident collimator receives the first polarizer, the Faraday rotator, and the second polarizer. Is configured to propagate in the order of polarizers,
The leakage light is a part of a linearly polarized light component whose incident angle with respect to the optical axis is shifted when entering the second polarizer, and has a different path from the light coupled to the output collimator. Propagates and enters the second thermal conversion processing unit,
It said second heat exchange unit, you characterized in that it is fixed via a heat insulating structure to the housing, the optical isolator. A second heat conversion processing unit that thermally converts leaked light leaking from the non-reciprocal part;
The leakage light is a part of a linearly polarized light component whose incident angle with respect to the optical axis is shifted when entering the second polarizer, and has a different path from the light coupled to the output collimator. Propagates and enters the second thermal conversion processing unit,
It said second heat exchange unit, you characterized in that it is fixed via a heat insulating structure to the housing, the optical isolator of claim 1. 4. The optical isolator according to claim 1, wherein the return light or the leakage light is incident on the first or second thermal conversion processing unit via a space. 5. The optical isolator according to any one of claims 1 to 4, wherein the incident light is a laser beam in a 1080 nm band. The said 1st heat conversion process part and / or a said 2nd heat conversion process part are arrange | positioned perpendicularly | vertically with respect to an optical axis direction, The any one of Claim 1 to 5 characterized by the above-mentioned. The optical isolator described. The light according to any one of claims 1 to 6, wherein the first heat conversion processing unit and / or the second heat conversion processing unit includes a lens. Isolator. The optical isolator according to any one of claims 1, 3, 4, 5, 6, and 7, wherein the return light is guided to the first thermal conversion processing unit by an optical path conversion mechanism. . 8. The optical isolator according to claim 2, wherein the leaked light is guided to the second thermal conversion processing unit by an optical path conversion mechanism. 9. . The optical isolator according to claim 8 or 9, wherein the optical path changing mechanism is a prism.

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