JP4794056B2 - Optical device - Google Patents

Description

【００４９】
【発明の効果】
以上のように本発明によれば、直交する２つの偏光を合成・分離する光学素子と前記２つの偏光またはこれらの合成光が通過する１つの光アイソレータとからなる光デバイスを構成したことにより、光アイソレータを２個から１個に削減できるため、部材コストを低減することができるとともに、体積を約３０％小型化する事ができた。
【図面の簡単な説明】
【図１】（ａ）〜（ｄ）は本発明の光デバイスのさまざまな実施形態を示す断面図である。
【図２】（ａ）〜（ｄ）は本発明の光デバイスにおける光アイソレータの機能を説明するための図である。
【図３】（ａ）は本発明の光デバイスにおける光アイソレータの機能を説明するための図であり、（ｂ）は順方向及び逆方向の偏光の挙動を示す図、（ｃ）は他の実施形態を示す断面図である。
【図４】（ａ）〜（ｃ）は本発明の他の実施形態を示す断面図である。
【図５】（ａ）、（ｂ）は本発明の他の実施形態を示す断面図である。
【図６】従来の光デバイスの断面図である。
【図７】（ａ）は従来の偏光依存型光アイソレータの断面図であり、（ｂ）は順方向及び逆方向の偏光の挙動を示す図である。
【符号の説明】
１：ケース
２：光学素子
３：光アイソレータ
４：入射光
５：入射光
６：出射光
７：偏光
８：偏光
１１：偏光子
１２：ファラデー回転子
１３：磁石
２０：吸収型偏光子
２１：吸収型偏光子
２２：吸収型偏光子
２３：１／２波長板
２４：１／２波長板
３１：レンズ
３２：レンズ
３３：入射側光ファイバ
３４：入射側光ファイバ
３５：出射側光ファイバ
３６：レンズ
３７：ファイバグレーティング
３８：波長フィルター
３９：波長フィルター
５１：ＬＤモジュール
５２：ＬＤモジュール
５３：偏波保持ファイバ
５４：偏波保持ファイバ
５５：シングルモードファイバ
５６：光アイソレータ
５７：光アイソレータ
５８：偏光合成膜
５９：偏光結合器
６１：金具
６２：磁石
６３：偏光子
６４：偏光子
６５：ＬＤ
６６：レンズ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical device that combines two polarized lights used for optical communication and has an optical isolator function.
[0002]
[Prior art]
An optical device using an LD module with a polarization fiber and a polarization coupler using a polarization combining film is used in an optical submarine repeater or the like as a light source redundant circuit in an optical transmitter. A configuration example of a conventional optical device using an LD module with a polarization fiber and a polarization coupler is shown in FIG. The polarization coupler 59 has two polarization fibers 53 and 54 and one single mode fiber 55 in the body having a polarization synthesis film 58 in the center, and the polarization synthesis film surface and the light beam have an angle of 45 degrees. It is attached to make. From the polarization fiber 53 facing the single mode fiber 55, linearly polarized light (P-polarized light) having a component perpendicular to the film surface, and from the other polarization fiber 54, linearly polarized light (P-polarized light) having a component horizontal to the film surface ( (S-polarized light) is emitted.
[0003]
Each of the LD modules 51 and 52 is configured by combining a linearly polarized light direction emitted from a laser diode (hereinafter referred to as LD) element and a principal axis direction of the polarization fiber. The polarization combining film 58 transmits all the P-polarized light and reflects all the S-polarized light.
[0004]
In the optical device having such a configuration, noise may occur in the modulated optical signal due to the far-end reflected light from the single mode fiber 55 on the output side of the polarization coupler 59. In addition, fluctuations in the light output may occur. Therefore, in order to prevent reflected light, the polarization coupler 59 is provided with polarization-dependent optical isolators 56 and 57 each including a polarizer, an analyzer, and a Faraday rotator at positions corresponding to the two polarization fibers 53 and 54. Yes.
[0005]
FIG. 7A shows a cross-sectional view of a polarization-dependent optical isolator that prevents reflected return light to a conventional laser light source, and FIG. 7B shows the behavior of polarization in the forward and reverse directions. The forward direction indicates a direction in which light incident on the optical isolator transmits, and the reverse direction indicates a direction in which light incident on the optical isolator does not transmit. As shown in FIG. 7A, the optical isolator includes a Faraday rotator 12 disposed between two polarizers 63 and 64, a magnet 62 for applying a magnetic field to the Faraday rotator 12, and a holding jig 61. Is done.
[0006]
As shown in FIG. 7B, in the forward direction, the light emitted from the LD 65 becomes parallel light by the lens 66 and enters the polarizer 63. After passing through the polarizer 63, it becomes linearly polarized light, and the Faraday rotator 12 rotates the 45 ° polarization plane and passes through the polarizer 64. In the reverse direction, the light that has passed through the polarizer 64 is rotated by 45 ° by the Faraday rotator 12. However, since the light has a polarization direction orthogonal to the transmission polarization direction of the polarizer 63 due to the nonreciprocity of the Faraday rotator 12, the light is attenuated by the polarizer 63 and does not return to the LD 65. Thereby, the light from one direction is allowed to pass, and the function of blocking the passage of light in the opposite direction is achieved.
[0007]
[Problems to be solved by the invention]
However, in the conventional optical device shown in FIG. 6, in order to prevent the reflected return light to the LD modules 51 and 52, the polarization-dependent optical isolators 56, Since the configuration includes 57, two optical isolators 56 and 57 are required, and there are a large number of parts and a high member cost.
[0008]
[Means for Solving the Problems]
In view of the above problems, an optical device of the present invention includes an absorption polarizer, a Faraday rotator, one half-wave plate set to rotate polarized light 22.5 degrees clockwise, and the one The other half-wave plate, which is arranged in parallel with the half-wave plate and set to rotate the polarized light by 22.5 degrees counterclockwise, is arranged after the one-half wave plate. The polarized light that has passed through the one-half wavelength plate is disposed after one absorption-type polarizer and the other half-wave plate in the transmission direction, and has passed through the other half-wave plate. A polarization-dependent optical isolator composed of the other absorption polarizer whose polarization is in the transmission direction, and a birefringent crystal disposed on the rear side of the optical isolator, and two incident light incident on the optical isolator The polarization direction of light is parallel to each other That.
[0011]
Further, the present invention is characterized in that with at least one binding optics of the incident side及beauty exit morphism side.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 shows a cross-sectional view of an optical device according to an embodiment of the present invention. As shown in FIG. 1A, the optical element 2 and the optical isolator 3 in the subsequent stage are housed in the same case 1. Two incident lights 4 and 5 incident from the same direction form linearly polarized light 7 and 8 orthogonal to each other, and these are synthesized by the optical element 2 made of a flat birefringent crystal. The combined incident light passes through an optical isolator 3 that is polarization independent and becomes outgoing light 6. Since the reflected return light from the outgoing light 6 passes through an optical path different from the forward direction by the optical isolator 3, the light does not return to the positions of the incident lights 4 and 5. After the two incident lights 4 and 5 are combined in this way, the polarization-independent optical isolator 3 is disposed, so that one optical isolator can be provided.
[0014]
Calcite, lithium niobate, YVO ₄ , molybdate, rutile, etc. can be used as the plate-like birefringent crystal used in the optical element 2, but when reducing the thickness and reducing the size, normal light and extraordinary light are used. Rutile having a large refractive index difference is desirable.
[0015]
Next, another embodiment of the present invention will be described. FIG. 1B shows a case where two incident lights having parallel linearly polarized light are incident from the same direction. Two incident lights 4 and 5 incident from the same direction form linearly polarized light 7 and 8 parallel to each other, both of which pass through the polarization-dependent optical isolator 3 and become linearly polarized light orthogonal to each other after passing through. The output light 6 is synthesized by the optical element 2 made of a flat birefringent crystal. Since the reflected return light from the emitted light 6 is absorbed by the optical isolator 3, the light does not return to the positions of the incident light 4 and 5. In this way, if the incident lights 4 and 5 from the same direction are linearly polarized light parallel to each other and the optical isolator 3 is arranged in front of the optical element 2, one optical isolator can be provided.
[0016]
Further, another embodiment of the present invention will be described.
[0017]
As shown in FIGS. 1C and 1D, a polarizing beam splitter having a polarization combining / separating film in accordance with the incident direction of incident light can be used as the optical element 2 in addition to the flat birefringent crystal. FIG. 1C shows a case where two incident light beams 4 and 5 forming orthogonal linear polarizations 7 and 8 are incident from the same direction, and FIG. 1D shows two light beams having orthogonal linear polarizations 7 and 8. In this case, the incident light beams 4 and 5 are incident from different directions by 90 degrees.
[0018]
In the above embodiment, the optical isolator 3 and the optical element 2 are described as separate bodies. However, the optical element 2 can be incorporated into the housing of the optical isolator 3 and integrated.
[0019]
The fixing of the case 1 and each component can be carried out even in a form in which each component is housed and fixed in a cylindrical or rectangular case, or a configuration in which each component is mounted and fixed in a box-shaped case. The material of the case 1 is preferably a nonmagnetic or soft magnetic metal, but a resin such as ceramics or plastic can also be used. The case 1 can be fixed to each component by laser welding fixing, solder fixing, low melting point glass fixing, or adhesive fixing.
[0020]
Further, each of the optical elements 2 and the optical isolator 3 can be tilted to prevent reflection, and the internal optical elements of the optical isolator can be tilted.
[0021]
FIG. 2 shows the function of the optical isolator 3 in each of the above embodiments. FIG. 2A shows the embodiment of FIG. 1A in detail. Two incident lights 4 and 5 incident from the same direction form linearly polarized light 7 and 8 orthogonal to each other, and these are synthesized by the optical element 2 made of a flat birefringent crystal. The combined incident light passes through a polarization-independent optical isolator 3 composed of a pair of polarizers 11 that are wedge-shaped birefringent crystals, a Faraday rotator 12, a magnet 13, and a case 14 that houses them. It becomes the light 6.
[0022]
On the other hand, as shown in FIG. 2B, the reflected return light from the emitted light 6 passes through an optical path different from the forward direction by the optical isolator 3, so that the light does not return to the positions of the incident lights 4 and 5. After the two incident lights 4 and 5 are combined in this way, the optical isolator 3 is disposed, so that one optical isolator can be provided.
[0023]
FIG. 2C shows the embodiment of FIG. 1D in detail, and shows a case where a polarizing beam splitter having a polarization combining film is used as the optical element 2.
[0024]
Further, as shown in FIG. 2D, instead of the polarization-independent optical isolator 3 shown in FIGS. 2A and 2B, a pair of polarizers 15 made of a flat birefringent crystal, Faraday rotation Even when the polarization-independent optical isolator 3 including the child 12, the magnet 13, the half-wave plate 17 and the case 14 for housing them is used, one optical isolator performs the same function.
[0025]
The optical isolator 3 can be used even when it is housed in the case 14 or in a form in which each member is mounted and fixed on one substrate.
[0026]
Calcite, lithium niobate, YVO ₄ , molybdate, rutile, etc. can also be used as the birefringent crystals used as the polarizers 11 and 15, but when reducing the thickness and reducing the size, normal light and extraordinary light are used. Rutile having a large refractive index difference is desirable.
[0027]
The Faraday rotator 12 can be implemented by a garnet having a square hysteresis curve and having a self magnetic field in addition to a Bi-substituted garnet and YIG crystal to which Tb, Gd, and Ho are added. In the case of a garnet having a square hysteresis curve and having a self-magnetic field, no magnet is required, which has the effect of reducing the number of parts and the number of assembly steps.
[0028]
The half-wave plate 17 uses a birefringent crystal, but quartz is desirable in consideration of characteristics. The magnet 13 is a member that applies the Faraday rotator to the saturation magnetic field strength, and is preferably a rare earth magnet in view of characteristics.
[0029]
The case 14 is preferably made of a non-magnetic or soft magnetic metal like the case 1, but can also be used with a resin such as ceramics or plastic.
[0030]
Next, FIG. 3 shows the function of the optical isolator in the embodiment of FIG.
[0031]
In FIG. 3A, incident lights 4 and 5 having the same polarization directions 7 and 8 are incident on the optical isolator 3. The optical isolator 3 includes a glass substrate absorption polarizer 20, a Faraday rotator 12, a magnet 13, half-wave plates 23 and 24, absorption polarizers 23 and 24, and an optical isolator 3. It comprises an optical element 2 that synthesizes linearly polarized light 7 and 8 orthogonal to each other after passing.
[0032]
FIG. 3B shows the behavior of the polarization of the incident lights 4 and 5 in the forward direction and the reverse direction when passing through the optical isolator 3. In the forward direction, the incident lights 4 and 5 are the same linearly polarized light and pass through the polarizer 20. In the Faraday rotator 12, the polarization plane rotates 45 degrees clockwise, and half-wave plates 23 and 24 are arranged for each incident optical path in order to make the polarization directions of the incident lights 4 and 5 orthogonal after passing through the optical isolator. To do. With respect to the polarization direction of incident light 4 and 5 after passing through the Faraday rotator, the half-wave plate 23 is set so that the crystal axis is 22.5 degrees clockwise, and the half-wave plate 24 is the crystal axis. Is set to 22.5 degrees counterclockwise. As a result, the polarization directions of the incident lights 4 and 5 after passing through the half-wave plates 23 and 24 are orthogonal to each other, and pass through the absorption polarizers 21 and 22 whose transmission directions are the transmission directions. Thereafter, the incident lights 4 and 5 are synthesized by the optical element 2.
[0033]
In the reverse direction, due to the nonreciprocal effect of the Faraday rotator 12, the polarization direction of the reflected return light after passing through the Faraday rotator 12 coincides with the absorption azimuth direction of the absorption polarizer 20 in both of the two optical paths 4 and 5. It will function as an isolator without returning. Thereby, even when the incident lights 4 and 5 from the same direction are linearly polarized light parallel to each other, one optical isolator can be provided.
[0034]
When the extinction ratio characteristic of the optical element 2 is excellent, the present invention can be implemented even if the absorption polarizers 21 and 22 are omitted as shown in FIG.
[0035]
The same function can be achieved by using a polarizing beam splitter having a polarization synthesizing / separating film in addition to the absorbing polarizer.
[0036]
The optical device of the present invention can include a coupling optical system such as a lens or an optical fiber on the incident side and / or the outgoing side.
[0037]
As shown in FIG. 4A, lenses 31 and 32 are disposed on the incident side of the case 1 to which the optical element 2 and the optical isolator 3 are fixed. Two lenses are arranged on the incident side, but one lens can be implemented. A lens that sets the incident light 4 and 5 to the optical element 2 to be parallel light or convergent light is set. The lenses 31 and 32 can be a spherical lens, an aspherical lens, or a refractive index distribution lens.
[0038]
In addition to the above, the incident side optical fibers 33 and 34 and the emission side optical fiber 35 can be arranged as shown in FIG. Since incident light from the incident side optical fibers 33 and 34 needs to have linearly polarized light orthogonal to each other, a polarization maintaining fiber is desirable. For the exit-side optical fiber 35, a polarization maintaining fiber is required to maintain polarization,
If it is not necessary to maintain, a single mode optical fiber may be used. As a form of transmitting light, an optical waveguide can be connected in addition to an optical fiber.
[0039]
In addition, in order to prevent reflected return light from the end face of the optical fiber, it is necessary to make the end face of the optical fiber oblique, and the oblique angle is desirably in the range of 4 to 10 degrees. Furthermore, as shown in FIG. 4C, a lens 36 for converging light can be arranged on the emission side optical fiber 35.
[0040]
Yet another embodiment is shown in FIG.
[0041]
As shown in FIG. 5A, it is also possible to use a fiber grating 37 that controls the light wavelength on the incident side optical fibers 33 and 34. In the figure, the fiber grating 37 is provided on the outside of the case 1, but the fiber grating 37 can be implemented even if it is housed in the case 1.
Further, as shown in FIG. 5B, wavelength filters 38 and 39 can be arranged to control the wavelengths of the incident light beams 4 and 5.
[0042]
In the above embodiment, only the example in which the two polarized lights are combined and emitted has been described, but conversely, the present invention can be applied to an optical device that receives the combined light and separates and emits the two polarized lights. it can.
[0043]
【Example】
Here, an optical device according to the present invention was prototyped and optical characteristics were evaluated.
[0044]
An optical eye sorter 3 using a rutile flat plate and a wedge-shaped rutile polarizer is bonded and fixed to the case 1, and a coupling optical system of the polarization maintaining fibers 33 and 34, the single mode optical fiber 35 and the lenses 31, 32 and 36 is provided. The optical device of the present invention shown in FIG. 4C fixed in alignment, the polarization separation film 58 and the two optical isolators 56 and 57 shown in the conventional example of FIG. 6, the polarization maintaining fibers 53 and 54, and the lens A polarization coupler 59 having the above coupling optical system was fabricated and the characteristics were compared. In the optical device of the present invention, the rutile plate 2 and the optical isolator 3 were fixed at an angle of 4 degrees in order to prevent internal reflection. The interval between the incident lights was set to 0.5 mm so that the incident lights 4 and 5 did not overlap, and the thickness of the rutile plate was 5 mm in order to synthesize the incident lights 4 and 5.
[0045]
As optical characteristics, insertion loss and reverse loss were measured between the incident light 4 and the outgoing light 6, and between the incident light 5 and the outgoing light 6, respectively.
[0046]
The results are shown in Table 1, and it was confirmed that the embodiment of the present invention has the same level of performance in both the forward loss and the reverse loss as compared with the conventional example, and is at a practical level.
[0047]
In addition, since the embodiment of the present invention has one optical isolator, the volume can be reduced by about 30% compared to the conventional example.
[0048]
[Table 1]

[0049]
【The invention's effect】
As described above, according to the present invention, by configuring an optical device that includes an optical element that combines and separates two orthogonally polarized lights and one optical isolator through which the two polarized lights or combined light passes, Since the number of optical isolators can be reduced from two to one, the member cost can be reduced and the volume can be reduced by about 30%.
[Brief description of the drawings]
1A to 1D are cross-sectional views showing various embodiments of an optical device of the present invention.
FIGS. 2A to 2D are views for explaining the function of an optical isolator in an optical device of the present invention.
3A is a diagram for explaining the function of an optical isolator in the optical device of the present invention, FIG. 3B is a diagram showing the behavior of polarization in the forward direction and the reverse direction, and FIG. It is sectional drawing which shows embodiment.
4A to 4C are cross-sectional views showing other embodiments of the present invention.
5A and 5B are cross-sectional views showing another embodiment of the present invention.
FIG. 6 is a cross-sectional view of a conventional optical device.
7A is a cross-sectional view of a conventional polarization-dependent optical isolator, and FIG. 7B is a diagram showing the behavior of polarized light in the forward and reverse directions.
[Explanation of symbols]
1: Case 2: Optical element 3: Optical isolator 4: Incident light 5: Incident light 6: Emission light 7: Polarized light 8: Polarized light 11: Polarizer 12: Faraday rotator 13: Magnet 20: Absorbing polarizer 21: Absorption Type polarizer 22: absorption type polarizer 23: 1/2 wavelength plate 24: 1/2 wavelength plate 31: lens 32: lens 33: incident side optical fiber 34: incident side optical fiber 35: output side optical fiber 36: lens 37: fiber grating 38: wavelength filter 39: wavelength filter 51: LD module 52: LD module 53: polarization maintaining fiber 54: polarization maintaining fiber 55: single mode fiber 56: optical isolator 57: optical isolator 58: polarization synthesis film 59: Polarizing coupler 61: Metal fitting 62: Magnet 63: Polarizer 64: Polarizer 65: LD
66: Lens

Claims (2)

An absorptive polarizer, a Faraday rotator, one half-wave plate set to rotate the polarization clockwise by 22.5 degrees, and one half-wave plate are arranged in parallel. Is placed behind the other half-wave plate and the other half-wave plate set to rotate 22.5 degrees counterclockwise, and passes through the other half-wave plate. One absorptive polarizer in which the polarized light is in the transmission direction and the other absorptive polarizer in which the polarized light that has passed through the other half-wave plate is disposed in the subsequent stage and in the transmission direction And a birefringent crystal disposed on the rear side of the optical isolator, and the polarization directions of two incident lights incident on the optical isolator are parallel to each other And optical device.   The optical device according to claim 1, further comprising a coupling optical system on at least one of the incident side and the emission side.

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