JP2021043469A - Optical coupling method - Google Patents

Abstract

To increase choices in adjusting a positional relationship in order to obtain desired optical coupling strength.SOLUTION: An optical coupling method includes; a step of acquiring first optical coupling strength by placing a first installation surface of a first lens to face a lens mounting surface; a step of acquiring second optical coupling strength by placing a second installation surface of the first lens to face the lens mounting surface; a step of selecting either the first installation surface or the second installation surface on the basis of the first optical coupling strength and the second optical coupling strength; and a step of fixing a base to the selected installation surface.SELECTED DRAWING: Figure 19

Description

The present invention relates to a photocoupling method.

Patent Document 1 discloses a technique relating to a coherent optical receiver. In an optical receiver such as an optical receiving device for coherent communication, an optical signal in which polarization and phase are multiplexed is input via a polarization holding fiber, and a polarization beam splitter (PBS) is used to respond to polarization. It is split. The demultiplexed optical signal is separated according to the phase by, for example, a 90-degree optical hybrid element. The separated optical signal is converted into an electric signal by the light receiving element.

Japanese Unexamined Patent Publication No. 5-158096

FIG. 23 schematically shows the configuration of this coherent optical receiver. The coherent optical receiver 300 shown in FIG. 23 includes a polarization beam splitter 302, a beam splitter 304, a monitor light receiving element 306, two multimode interferers (optical 90 degree hybrid) 311 and 312, and eight (4 sets). The signal light receiving element 334 of the above, four amplifiers 335, and eight (four sets) of coupling capacitors 336 are provided.

In the coherent light receiving device 300, a signal light No having two polarization components having different polarization directions and a local light emitting Lo are input. A part of the signal light No. is branched by the beam splitter 308 and input to the monitor light receiving element 306. The monitor light receiving element 306 detects the average light intensity of the signal light No. The rest of the signal light No reaches the polarization beam splitter 302 via the variable attenuator 310, and is split into one polarization component N1 and the other polarization component N2 by the polarization beam splitter 302. One polarization component N1 is input to one multimode interferer 311 and the other polarization component N2 is input to the other multimode interferer 312.

The local emission Lo is branched by the beam splitter 304. One of the branched station emission L1s is input to one multimode interferer 311 and the other station emission L2 is input to the other multimode interferer 312. The multi-mode interferer 311 outputs two pairs of interference light indicating the XI signal component and the XQ signal component, respectively, by interfering the local emission L1 with the polarization component N1. The multi-mode interferer 312 outputs two pairs of interference light indicating a YI signal component and a YQ signal component, respectively, by interfering the local emission L2 with the polarization component N2. These interference lights are converted into current signals by each signal light light receiving element 334. The current signal output from each signal light receiving element 334 is converted into a differential voltage signal by the amplifier 335, and then output to the outside via the coupling capacitor 336.

In this way, the coherent receiver has a plurality of optical components that are optically coupled to each other, such as a lens and a multimode interferer. When assembling a coherent receiver, the relative positional relationship between the optical components is adjusted in order to obtain a desired optical coupling strength between the optical components. In adjusting the positional relationship, the more adjustment options are available, the easier it is to obtain the desired photobonding intensity.

An object of the present invention is to provide a photocoupling method capable of obtaining a desired photocoupling strength by increasing the options for adjusting the positional relationship.

One embodiment of the present invention is an optical coupling method in which a lens is arranged between a light providing portion and a target portion to photocouple the light provided by the light providing portion to the target portion. It has a lens portion and a support portion, and the support portion is arranged in a positional relationship facing or perpendicular to the first installation surface and the first installation surface that can be installed with respect to the main surface of the first substrate on which the lens is installed. The first distance from the first installation surface to the optical axis of the lens unit, including the second installation surface, is different from the second distance from the second installation surface to the optical axis of the lens unit, and the first installation surface is the first. A process of obtaining the first light coupling strength between the light providing portion and the target portion after mounting the lens so as to face the main surface of the substrate, and a lens having the second installation surface facing the main surface of the first substrate. The first installation surface and the second installation surface are based on the step of obtaining the second light coupling strength between the light providing portion and the target portion and the first light coupling strength and the second light coupling strength. A step of selecting any of the above and a step of fixing the first substrate to the selected installation surface are included.

According to the present invention, there is provided a photocoupling method capable of obtaining a desired photocoupling strength by increasing the options for adjusting the positional relationship.

FIG. 1 is a plan view schematically showing a coherent receiver manufactured by the optical coupling method according to the embodiment. FIG. 2 is a perspective view showing the inside of the coherent receiver shown in FIG. FIG. 3 is a diagram showing one step of the optical coupling method according to the embodiment. 4 (a) and 4 (b) are diagrams schematically showing one step of the optical coupling method according to the embodiment. FIG. 5 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 6 is a diagram showing one step of the optical coupling method according to the embodiment. 7 (a) and 7 (b) are diagrams schematically showing one step of the optical coupling method according to the embodiment. FIG. 8 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 9 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 10 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 11 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 12 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 13 is a diagram showing the relationship between the applied bias voltage of the optical attenuator and the amount of attenuation. FIG. 14 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 15 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 16 is a diagram showing one step of the optical coupling method according to the embodiment. FIG. 17A is a side view of the first lens, and FIG. 17B is a front view of the first lens. FIG. 18A is a front view of the mounting form of the first lens facing the first installation surface as a base, and FIG. 18B is a front view of the first lens facing the second mounting surface as a base. FIG. 18 (c) is a front view of the mounting form, FIG. 18 (c) is a front view of the mounting form of the first lens facing the third mounting surface as a base, and FIG. 18 (d) is a front view of the fourth mounting surface. It is a front view of the mounting form of the first lens facing the base. FIG. 19 is a diagram showing a main step of the optical coupling method according to the embodiment. FIG. 20 is a front view of a configuration in which the first lens and the polarization-dependent optical branching element according to the embodiment are mounted on the base. 21 (a), (b), (c) and (d) are diagrams showing the relationship of the coupling tolerance of each lens in the two lens groups. 22 (a) and 22 (b) are views of a front view of a configuration in which the lens and the polarization-dependent optical branching element according to the comparative example are mounted on the base. FIG. 23 is a diagram schematically showing the configuration of the coherent optical receiver shown in Patent Document 1.

[Explanation of Embodiments of the Invention]
First, the contents of the embodiments of the present invention will be listed and described.

One embodiment of the present invention is an optical coupling method in which a lens is arranged between a light providing portion and a target portion to photocouple the light provided by the light providing portion to the target portion. It has a lens portion and a support portion, and the support portion is arranged in a positional relationship facing or perpendicular to the first installation surface and the first installation surface that can be installed with respect to the main surface of the first substrate on which the lens is installed. The first distance from the first installation surface to the optical axis of the lens unit, including the second installation surface, is different from the second distance from the second installation surface to the optical axis of the lens unit, and the first installation surface is the first. A process of obtaining the first light coupling strength between the light providing portion and the target portion after mounting the lens so as to face the main surface of the substrate, and a lens having the second installation surface facing the main surface of the first substrate. The first installation surface and the second installation surface are based on the step of obtaining the second light coupling strength between the light providing portion and the target portion and the first light coupling strength and the second light coupling strength. A step of selecting any of the above and a step of fixing the first substrate to the selected installation surface are included.

According to the optical coupling method having the above steps, when the lens is attached to the main surface of the first substrate, the first optical coupling strength when the first installation surface is made to face the main surface and the second installation surface are mainly used. The second photobonding strength when face-to-face is obtained. Since the first distance from the first installation surface to the optical axis of the lens portion is different from the second distance from the second installation surface to the optical axis of the lens portion, the first optical coupling strength and the second optical coupling strength Can differ from each other. Therefore, since the options for adjusting the positional relationship are increased, the desired photobonding intensity can be obtained.

Further, the step of selecting either the first installation surface or the second installation surface may be a step of selecting which of the first photobonding strength and the second photobonding strength has the larger photobonding strength. According to this method, the lens is fixed to the first substrate so that the light coupling strength is maximized. Therefore, the photobonding strength can be improved.

Further, a plurality of lenses are provided, and for the plurality of lenses, a step of obtaining the first light coupling strength and a step of obtaining the second light coupling strength are carried out, and in the plurality of lenses, either the first mounting surface or the second mounting surface is performed. In the step of selecting the lens, the installation surface may be selected in relation to the smallest difference in the optical coupling strength of the lens. According to this method, the variation in the photobonding strength can be suppressed.

The target unit is a multi-mode interference unit that obtains a signal by interfering the local light emission with the signal light, and the lens is a signal incident on the optical path of the local light emission incident on the multi-mode interference unit or on the multi-mode interference unit. It may be installed on the light path of light. According to this method, the local emission and the signal light can be photocoupled to the multimode interfering unit with a desired photocoupling strength.

[Details of Embodiments of the present invention]
Specific examples of the optical coupling method according to the embodiment of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. In the following description, the same elements will be designated by the same reference numerals in the description of the drawings, and duplicate description will be omitted.

FIG. 1 is a plan view schematically showing a coherent receiver manufactured by the optical coupling method according to the embodiment. FIG. 2 is a perspective view showing the inside of the coherent receiver 1 shown in FIG. As shown in FIGS. 1 and 2, the coherent receiver 1 causes local light emission (Local Beam: Lo light) and signal light (Signal Beam: Sigma light) to interfere with each other, and information contained in the phase-modulated Sigma light. It is a device that demodulates. The demodulated information is converted into an electric signal and output to the outside of the coherent receiver. The coherent receiver 1 includes an optical system for each of Lo light and Sigma light, and two multi-mode interferators (target unit, multi-mode interferometer: Multi-Mode Interference: MMI 40, 50). Then, it has a housing 2 on which these optical systems and MMIs 40 and 50 are mounted. The optical system and the MMIs 40 and 50 are mounted on the bottom surface 2E (see FIG. 6) of the housing 2 via the carrier 3 (second substrate) and the base 4 (first substrate). Further, wiring boards 46 and 56 on which a circuit for processing demodulated information is mounted are mounted on the carrier 3. The carrier 3 is made of a metal such as copper tungsten (CuW), while the base 4 is made of an insulating material such as _{alumina (Al 2} O _{3) and aluminum nitride (Al N).} The two MMIs 40 and 50 are semiconductor MMIs, for example made of InP. The MMIs 40 and 50 have optical input units 41 and 51 and optical input units 42 and 52, respectively. The Lo light input to the optical input units 41 and 52 and the Sigma light input to the optical input units 42 and 52 interfere with each other to demodulate the phase information. The two MMIs 40 and 50 may be provided independently or may be integrated as one. When the two MMIs 40 and 50 are provided independently, the external dimensions of each of the MMIs 40 and 50 can be reduced. Therefore, when the MMIs 40 and 50 are tilted and installed on the carrier 3, the length per side is shortened, so that the deviation in the height direction can be reduced. Further, when the two MMIs 40 and 50 are integrally integrated, the MMI can be installed in one step.

The housing 2 has a front wall 2A. In the following description, the front wall 2A side is referred to as the front side, and the opposite side is referred to as the rear side. However, these front / rear are for illustration purposes only and do not limit the scope of the present invention. A Lo light port 5 (light providing portion) and a Sigma light port 6 (light providing portion) are fixed to the front wall 2A by, for example, laser welding. _{Lo light L 0} is provided to the port 5 via the polarization holding fiber 35, _{and sig light N 0} is provided to the port 6 via the single mode fiber 36. _{Ports 5 and 6 each have a collimating lens, and Lo light L 0} and Sigma light N ₀ emitted from the polarization-holding fiber 35 and the single-mode fiber 36 (diverge when emitted from the respective fibers). Light) is changed to collimated light and guided into the housing 2.

The Lo optical optical system guides the Lo light provided from the Lo light port 5 to the Lo light input units 41 and 51 of the MMI 40 and 50. Specifically, the Lo optical optical system includes a polarizer 11, a beam splitter (BS12), a reflector 13, two lens groups 14 and 15, a skew adjusting element 16, and an optical attenuator. Includes a vessel (optical ATT71). The skew adjusting element 16 and the optical ATT 71 may be omitted if not necessary.

The lens group 14 is arranged on the optical path between the BS 12 and the MMI 40, and one Lo light L ₁ branched by the BS 12 is focused on the light input unit 41 of the Lo light of the MMI 40. The lens group 15 is arranged on the optical path between the reflector 13 and the MMI 50, and the other Lo light L2 branched by the BS 12 and reflected by the reflector 13 is focused on the Lo light input unit 51 of the MMI 50. .. The lens groups 14 and 15 have a first lens 14b and 15b arranged relatively close to the MMI 40 and 50, and a second lens 14a and 15a arranged relatively separated from the MMI 40 and 50, respectively. In this way, by combining the first lenses 14b and 15b and the second lenses 14a and 15a into a lens, the Lo light L ₁ and L ₂ with respect to the small Lo light input units 41 and 51 of the MMI 40 and 50 can be obtained. The photobonding strength can be increased.

The sig optical system includes a polarization beam splitter (PBS21), which is a polarization-dependent optical splitting element, a reflector 22, two lens groups 23 and 24, a half-wave plate 25, a skew adjusting element 26, and light. Includes an attenuator (optical ATT81). The skew adjusting element 26 and the optical ATT81 may be omitted if not necessary.

Next, a method of manufacturing the coherent receiver 1 will be described.

As shown in FIG. 3, first, outside the housing 2, the base 4 is mounted on the carrier 3 and fixed to each other. The carrier 3 is a rectangular plate-shaped member made of, for example, copper tungsten (CuW). The base 4 is a rectangular plate-shaped member made of, for example, alumina (Al ₂ O _3). For fixing the base 4 and the carrier 3, for example, AuSn eutectic solder can be used. A groove for partitioning the mounting area of the base 4 and the mounting areas of the MMIs 40 and 50 is formed in advance on the carrier 3. By visually aligning the rear end of the base 4 with the front edge, the relative position of the carrier 3 and the base 4 in the front-rear direction of the housing 2 is determined. Instead of this, alignment may be performed so that the front edge of the carrier 3 and the front edge of the base 4 are matched.

When the carrier 3 is arranged in the housing 2 in a later step, since the width of the carrier 3 substantially matches the distance between the inner walls of the housing 2, a pair of carriers formed on the side surface of the carrier 3. It is good to grasp the constriction. Then, for the alignment of the housing 2 of the base 4 in the left-right direction, a pair of constrictions formed on the carrier 3 may be used. That is, since the distance between the central portions of the carrier 3 is narrowed due to the constriction, it is preferable to match the positions of both ends of the narrow portion with the positions of both ends of the base 4.

Next, the MMI 40 is mounted on an MMI carrier (not shown) and fixed (die-bonded) to each other. Similarly, the MMI 50 is mounted on another MMI carrier (not shown) and fixed to each other. The MMI carrier is a rectangular parallelepiped member, and is made of, for example, a ceramic such as _{aluminum nitride (AlN) or alumina (Al 2} O _3). For fixing the MMI 40, 50 and the MMI carrier, for example, a gold-tin (AuSn) -based AuSn eutectic solder is used. For this fixing, a technique similar to a known method of mounting a normal semiconductor device on an insulating substrate can be used. After that, the two MMI carriers equipped with the MMIs 40 and 50 are fixed to the region on the carrier 3 located on the rear end side of the base 4. A groove is formed in advance on the carrier 3 so as to surround the fixed region of the MMI carrier, and the MMI carrier is arranged by visual alignment with reference to the groove.

A groove is formed on the MMI carrier to separate the front side and the rear side of the MMI carrier. The front side of the MMI carrier corresponds to the optical waveguide portions 44, 54 (see FIG. 1) incorporated in the MMI 40, 50. The rear side of the MMI carrier corresponds to the photodiode portion (built-in photodiodes 45, 55: see FIG. 1) incorporated in the MMIs 40 and 50. The back electrode of the MMIs 40 and 50 is also separated into a front side and a rear side, and as a result, the leakage current of the built-in photodiodes 45 and 55 is reduced.

A plurality of die capacitors (parallel plate capacitors) are mounted on the two wiring boards 46 and 56 in parallel with the fixation of the MMI carrier and the MMI 40 and 50 described above. The wiring boards 46 and 56 are made of, for example, aluminum nitride (AlN). For mounting the plurality of die capacitors, for example, AuSn pellets can be used, or a known soldering step may be adopted. After that, one of the two wiring boards 46 and 56 on which a plurality of die capacitors are mounted is fixed to the carrier 3 by surrounding the MMI 40, and the other wiring board 56 is arranged so as to surround the MMI 50 and is attached to the carrier 3. Fix it. The wiring boards 46 and 56 are mounted on the carrier 3, for example, by eutectic solder such as AuSn, and then the carrier 3 is mounted in the housing 2.

Subsequently, the carrier 3 is mounted on the bottom surface 2E of the housing 2 (step S1: see FIG. 19). At this time, for example, the front end of the carrier 3 is abutted against the inner surface of the front wall forming the front wall 2A of the housing 2, the carrier 3 and the housing 2 are aligned, and then the carrier 3 is placed on the side wall by a predetermined size. It is preferable to dispose the carrier 3 on the bottom surface 2E of the housing 2 in that state. Here, the inner surface of each side wall of the housing 2 is configured in two stages, the upper stage is made of metal, and the lower stage is a ceramic feedthrough 61 for insulating a plurality of terminals from each other. The inner dimension of the lower row (distance between walls) is almost the same as the width of the carrier 3, but the inner dimension of the upper row is wider than the width of the carrier 3. Therefore, the carrier 3 can be abutted against the inner surface of the upper side wall, whereby the alignment between the housing 2 and the carrier 3 (and each component already mounted on the carrier 3) can be within ± 0.5 °. It is possible to realize with. The carrier 3 is fixed to the bottom surface 2E by using, for example, solder.

Further, in this step, the VOA carrier 30 is mounted on the bottom surface 2E of the housing 2 together with the carrier 3. At this time, for example, the front end of the VOA carrier 30 is abutted against the inner surface of the side wall forming the front wall 2A of the housing 2, the VOA carrier 30 and the housing 2 are aligned, and then the VOA carrier 30 is provided by a predetermined size. The VOA carrier 30 may be placed on the bottom surface 2E of the housing 2 in a state separated from the side wall. As a result, the front end of the carrier 3 and the rear end of the VOA carrier 30 are parallel to each other. The VOA carrier 30 is fixed to the bottom surface 2E by using, for example, solder.

After fixing the carrier 3 to the bottom surface 2E, the integrated circuits 43 and 53 are mounted on the wiring boards 46 and 56. The integrated circuits 43 and 53 are mounted by a known mounting method using a conductive resin such as silver paste. After mounting the integrated circuits 43 and 53, the temperature of the entire housing 2 is raised (to 180 ° C.) to vaporize the solvent contained in the conductive resin. After that, the electrode pads on the upper surfaces of the integrated circuits 43 and 53 and the terminals 65 on the rear side of the housing 2 are electrically connected by wiring. By this wiring, the test light is input to the active centering of each optical component in the next step and thereafter, that is, the MMI 40, 50, and the output signal of the photodiode (45, 55: not shown) built in the MMI 40, 50. It is possible to arrange each optical component at the position where the intensity is maximized.

Subsequently, each optical component is mounted in the housing 2. First, Lo light for optical alignment is generated. As shown in FIG. 4A, a standard reflector 104 having a light reflecting surface 104a and a bottom surface 104b perpendicular to each other is prepared. The light reflecting surface 104a simulates the front wall 2A of the housing 2, and the bottom surface 104b simulates the bottom surface of the housing 2. The standard reflector 104 is composed of, for example, a rectangular parallelepiped glass block. Then, the standard reflector 104 is installed on the stage 103 fixed on the support base 105 of the centering device. At this time, the bottom surface 104b and the stage 103 are brought into close contact with each other.

Align the optical axis direction of the autocollimator 125 with the optical axis direction of the standard reflector 104. Specifically, the visible laser light L is output from the autocollimator 125, and the visible laser light L is applied to the light reflecting surface 104a. Then, the light intensity of the visible laser light L reflected by the light reflecting surface 104a is detected on the autocollimator 125 side. When the visible laser light L before reflection and the visible laser light L after reflection overlap each other, the detected light intensity becomes maximum. Utilizing this fact, the optical axis direction of the autocollimator 125 is aligned with the normal direction of the light reflecting surface 104a, that is, the optical axis direction of the standard reflector 104. After that, the standard reflector 104 is removed from the stage 103 and replaced with a housing 2 equipped with MMI 40, 50, wiring boards 46, 56, and VOA carrier 30 (FIG. 4 (b)). At this time, the bottom surface of the housing 2 is brought into close contact with the stage 103. Since the optical axis of the autocollimator 125 passes above the housing 2, the visible laser light L passes above the housing 2 and is not introduced into the housing 2.

Subsequently, as shown in FIG. 5, the monitor photodiode 33 is mounted on the VOA carrier 30. Further, the PBS 21, the skew adjusting elements 16 and 26, the half-wave plate 25, the polarizer 11, and the BS 12 are mounted at predetermined mounting positions in the housing 2, respectively. These optical components are optical components that do not perform alignment work, and are fixed after adjusting only the direction of the light incident surface. Specifically, in this step, the angle of the optical component (angle of the light incident surface) is adjusted by using the optical axis of the autocollimator 125 whose adjustment has already been completed. One side surface of these optical components is used as a reflecting surface for the visible laser light L of the autocollimeter 125, and the visible laser light L before reflection and the visible laser light L after reflection are superposed on each other, and the angle (light) of these optical components (light) Axial direction) is adjusted. This work is performed on the optical axis of the autocollimator 125, that is, in the space above the housing 2. Then, while maintaining the orientation (or rotating by a predetermined angle as necessary), these optical components are moved onto the adhesive resin provided at each mounting position, and the adhesive resin is cured to fix them. To do.

Regarding the PBS 21, the skew adjusting elements 16 and 26, and the polarizer 11, since the light incident surface faces the front wall 2A side when mounted on the housing 2, the normal direction of the light incident surface and the autocollimator 125 It is advisable to adjust the direction of the optical axis by matching it with the optical axis and mount it while maintaining that direction. Further, with respect to the half-wave plate 25 and the monitor photodiode 33, since the light incident surface faces sideways when mounted on the housing 2, the normal direction of the light incident surface and the optical axis of the autocollimeter 125 are set. After matching them and adjusting their optical axis directions, they are mounted after rotating 90 ° around the normal of the bottom surface 2E. The monitor photodiode 33 is further electrically connected to the predetermined terminal by wire bonding with the predetermined terminal. Regarding the BS12, the light incident surface faces sideways when mounted on the housing 2, but the light emitting surface faces rearward, so that the normal direction of the light emitting surface or the surface opposite to the light emitting surface. After adjusting the optical axis direction by matching the optical axis of the autocollimator 125 with the optical axis, it is preferable to mount the autocollimator 125 in the housing 2 while maintaining the orientation.

Subsequently, a Sigma light lens 27 that requires alignment because the optical coupling tolerance for MMI 40, 50 is smaller than that of each of the above-mentioned optical components; reflectors 13, 22; ; And each lens group 14, 15, 23, 24; are mounted in the housing 2. As a preparation for this, the simulated connectors 123a and 123b are arranged on the front wall 2A of the housing 2. The simulated connectors 123a and 123b simulate the Sigma light port 6 and the Lo light port 5, respectively, and the simulated connectors 123a and 123b emit test light used for centering the other optical component. Hereinafter, the details of the process of preparing the test light will be described.

FIG. 6 is a perspective view showing a part of the manipulator 100 for holding the simulated connector 123a (see FIG. 8). The manipulator 100 can freely set a position and an angle (specifically, a position in the direction of three axes orthogonal to each other (positions in the directions of the X, Y, Z axes, and an angle around two axes perpendicular to the optical axis direction of the simulated connector 123a)). It has a changeable arm 101 and a head 102 provided at the tip of the arm 101. The simulated connector 123a is held on the head 102 and is arranged at a position where the Sigma optical port 6 is to be attached. The simulated connector 123b is also held by another manipulator 100 in the same manner as the simulated connector 123a, and is arranged at the planned mounting position of the Lo optical port 5.

FIG. 7A is a block diagram showing a configuration for generating test light. As shown in FIG. 7A, in this configuration, the bias voltage output by the bias power supply 111 is applied to the light source 112 (light providing unit, for example, a semiconductor laser) to generate test light (CW light). This test light is introduced into the polarization control element 113, and the polarization plane thereof is controlled. As a result, the test light has a polarization component that simulates the two polarization components of the Sigma light. After that, the test light reaches the connector 116 via the optical coupler 114. The connector 116 is selectively connected to either one of the connectors 117 and 118. A simulated connector 123a is optically coupled to the connector 117, and a power meter 119 is optically coupled to the other connector 118. A power meter 115 is connected to the optical coupler 114. Although FIG. 7A shows a system including two power meters 115 and 119, one power meter may be used in combination with the respective power meters 115 and 119. Further, the same configuration as described above is prepared for the simulated connector 123b.

First, the connector 116 and the connector 118 are connected. Then, the intensity of the test light output from the light source 112 is detected by the power meter 119, and the intensity of the test light, that is, the intensity of the incident light with respect to the housing 2 is set to a predetermined value by adjusting the bias voltage. Next, the housing 2 is removed from the stage 103 again and replaced with a standard reflector 104. Then, the connector 116 and the connector 117 are connected, and the simulated connectors 123a and 123b are made to face the light reflecting surface 104a of the standard reflector 104. When the test light is output from the light source 112 in this state, the test light is emitted from the simulated connectors 123a and 123b, then reflected by the light reflecting surface 104a, and is incident on the simulated connectors 123a and 123b again. The intensity of this test light is detected in the power meter 115 via the optical coupler 114. By adjusting the optical axis directions of the simulated connectors 123a and 123b to maximize the optical detection intensity thereof, the optical axis direction of the simulated connector 123a (or the simulated connector 123b) is aligned with the optical axis direction of the standard reflector 104. After that, as shown in FIG. 7B, the standard reflector 104 is removed from the stage 103 and replaced with the housing 2.

Subsequently, the polarization plane of the test light incident on the housing 2 from the simulated connector 123a is adjusted. Therefore, a test jig having PBS and two monitor photodiodes is arranged inside the housing 2 at the rear stage of the simulated connector 123a (for example, the mounting position of the VOA 31). This test jig is assumed to have a configuration in which a monitor photodiode is attached to each of the two light emitting ends of PBS, for example. Alternatively, this test jig may be one in which each of the two light emitting ends of PBS and the monitor photodiode are photocoupled to each other and both are mounted on a common substrate. Then, the test light is provided in the housing 2 via the simulated connector 123a, the intensities of the two polarization components branched by the polarization beam splitter are detected in each monitor photodiode, and the intensities of the two polarization components are substantially equal to each other. If possible, the polarization control element 113 adjusts the polarization plane of the test light. In this step, instead of the housing 2, a simulation module on which a polarizing beam splitter and two monitor photodiodes are mounted may be prepared, and this may be mounted on the stage 103 to adjust the polarization plane.

In the above-mentioned polarization adjustment, the output signals of the two monitor photodiodes included in the test jig may be taken out via any terminal 65 of the housing 2. Further, when the test jig is provided with terminals for extracting the output signals of the two monitor photodiodes, the polarization of the test light is adjusted as described above before the housing 2 is arranged on the stage 103. You may.

In this step, the simulated connectors 123a and 123b are further aligned. First, the intensity of the test light incident on the housing 2 from the simulated connector 123a is detected by the photodiode built in the MMI 40. Then, the simulated connector 123a is moved on the front wall 2A of the housing 2 in the direction in which the intensity of the detected test light increases, and the simulated connector 123a is centered in a plane perpendicular to the optical axis. Similarly, the intensity of the test light incident on the housing 2 from the simulated connector 123b is detected by the photodiode built in the other MMI 50, and the simulated connector 123b is moved in the direction in which the intensity of the detected light increases. As a result, the alignment is performed in the plane perpendicular to the optical axis of the simulated connector 123b. The field diameter of the test light is as large as about 300 μm, while the optical input ends of the MMIs 40 and 50 are small, for example, a width of several μm and a thickness of 1 μm or less. Therefore, although the intensity of the test light input to the MMIs 40 and 50 is weak, it is possible to obtain a detection signal sufficient to determine the optical axis of the test light.

The positions of the simulated connectors 123a and 123b in the optical axis direction can be determined by bringing the end faces of the simulated connectors 123a and 123b into contact with the front wall 2A of the housing 2.

Subsequently, each optical component that requires alignment is arranged on the optical path between the simulated connector 123a or the simulated connector 123b and the MMI 40, 50, and is detected by the photodiode (or monitor photodiode 33) built in the MMI 40, 50. The intensity of the test light to be tested is referred to, and the alignment of these optical components is performed. Further, these optical components are fixed in the housing 2. The order of centering and fixing of these optical components is not limited to the following description, and may be performed in any order.

In this step, as shown in FIG. 7B, the VOA bias power supply 120 and the voltage monitors 121 and 122 are connected to the housing 2. The VOA bias power supply 120 applies a bias voltage to the VOA 31 when the VOA 31 described later is installed on the VOA carrier 30. The voltage monitors 121 and 122 monitor the voltage signals from the wiring boards 46 and 56, respectively.

First, the BS 32 (see FIGS. 1 and 2) is centered and fixed. That is, the angle (optical axis direction) of the BS 32 is adjusted by using the visible laser light L of the autocollimator 125 passing through the space above the housing 2 with the front surface of the BS 32 as the reflecting surface. Then, while maintaining the orientation of the BS 32, the BS 32 is moved onto the VOA carrier 30. Then, the BS 12 is moved along the optical axis of the Sigma light on the VOA carrier 30 to determine the mounting position of the BS 12 that maximizes the optical coupling strength of the monitor photodiode 33. Then, the BS 12 is VOA using the adhesive resin. It is fixed to the carrier 30.

Next, as shown in FIG. 8, the reflectors 13 and 22 are centered and fixed. First, the front surface of these reflectors 13 and 22 is used as a reflecting surface, and the angle (optical axis direction) of the reflectors 13 and 22 is used by using the visible laser light of the autocollimator 125 passing through the space above the housing 2. To adjust. Then, while maintaining the angles of the reflectors 13 and 22, the test light reflected by the reflectors 13 and 22 is detected by the built-in photodiodes of the MMIs 40 and 50. Then, the reflectors 13 and 22 are slightly moved in the direction perpendicular to the optical axis of the two simulated connectors 123a and 123b to determine the position where the detection intensity of the built-in photodiode is maximized. It should be noted that when the reflectors 13 and 22 are centered, the angle determined by the visible laser light emitted by the autocollimator 125 is maintained in the subsequent centering work. Since the mounting angles of the MMIs 40 and 50 with respect to the housing 2 and the optical axes of the ports 5 and 6 have already been determined, changing the mounting angles of the reflectors 13 and 22 that convert the optical axes by 90 ° is not possible. This is because it upsets the alignment state that has already been carried out.

Subsequently, the four lens groups 14, 15, 23, and 24 are aligned and fixed. As shown in FIG. 9, the first lenses 14b, 15b, 23b, 24b (that is, lenses closer to MMI 40, 50) are aligned and fixed (step S2: see FIG. 19). Subsequently, as shown in FIG. 10, the second lenses 14a, 15a, 23a, and 24a are centered and fixed (step S3: see FIG. 19). The method of aligning the first lenses 14b, 15b, 23b, and 24b will be described in detail later. Further, since the alignment and fixing of the second lenses 14a, 15a, 23a and 24a are the same as the alignment and fixing method of the first lenses 14b, 15b, 23b and 24b, detailed description thereof will be omitted.

Subsequently, as shown in FIG. 11, the Sigma light lens 27 is centered and fixed. A lens is built in the Sigma light port 6, and the focal point of the built-in lens and the focal point of the lens 27 are matched to determine the optical axis direction of the lens 27. Then, by arranging the VOA 31 at the position of the beam waist formed between the built-in lens and the lens 27, the Sigma light can be passed through the shutter having a limited area of the VOA 31, and the extinction ratio of the VOA 31 is increased. be able to. For the above reasons, it is preferable to use another simulated connector 123B containing a lens having the same focal length as the lens built in the Sigma light port 6 instead of the simulated connector 123b for the alignment of the lens 27. .. Therefore, in this step, the simulated connector 123b is replaced with the simulated connector 123B.

Specifically, the standard reflector 104 is re-installed on the stage 103 instead of the housing 2, and the connector 116 (see FIG. 7A) is replaced from the simulated connector 123b to the simulated connector 123B. Then, the simulated connector 123B is arranged at the planned mounting position of the Sigma light port 6 using the manipulator 100 (see FIG. 6), and faces the light reflecting surface 104a of the standard reflector 104. In this state, the test light is output from the simulated connector 123B, the optical axis position of the simulated connector 123B is adjusted to maximize the light intensity detected by the power meter 115, and the simulated connector 123B of the simulated connector 123B is oriented in the optical axis direction of the standard reflector 104. Align the optical axis direction. Next, the polarization plane of the test light incident on the housing 2 from the simulated connector 123B is adjusted by using the test jig described above. That is, the test light is provided in the housing 2 via the simulated connector 123B, the intensities of the two polarization components branched by the PBS of the test jig are detected in each monitor photodiode, and these intensities become substantially equal to each other. The polarization plane of the test light provided by the polarization control element 113 is adjusted. Further, the intensity of the test light incident on the housing 2 from the simulated connector 123B is detected by the photodiode 55 built in the MMI 50, and the simulated connector 123B is moved in the direction in which the optical coupling intensity increases, thereby performing the simulated connector. Aligning is performed in a plane perpendicular to the optical axis of 123B. The position of the simulated connector 123B in the optical axis direction can be determined by bringing the end surface of the simulated connector 123B into contact with the front wall 2A of the housing 2.

Next, the lens 27 is moved to the mounting position, the test light provided by the simulated connector 123B is incident on the lens 27, and the intensity of the passed test light is detected by the photodiode 55 built in the MMI 50. Then, the position of the lens 27 is slightly changed to determine the position (front-back direction, left-right direction, and up-down direction) at which the optical coupling strength of the built-in photodiode 55 is maximized. After the determination, the lens 27 is fixed using an adhesive resin.

Subsequently, as shown in FIG. 12, the VOA 31 is mounted on the VOA carrier 30. In this step, the VOA 31 is gripped by the manipulator 100A, and the VOA 31 is arranged on the optical path of the test light. The manipulator 100A includes two arms 101A that can freely change the position and angle (specifically, the position in the three-axis direction orthogonal to each other and the angle around the two axes perpendicular to the optical axis direction of the VOA 31). It has a head 102A provided at the tip of these arms 101A. The VOA 31 is sandwiched and held by the head 102A. At this time, one head 102A is in electrical contact with one electrode of VOA31. Further, the other head 102A is in electrical contact with the other electrode of the VOA 31. Then, a bias voltage is applied to the VOA 31 from the VOA bias power supply 120 (see FIG. 7A) via the arms 101A and 102A. An ultraviolet curable resin is previously applied on the VOA carrier 30 to a predetermined thickness (for example, 100 μm or more), and the VOA 31 is held in a state where the VOA 31 is separated from the surface of the VOA carrier 30 by a predetermined distance (for example, 100 μm). Then, the bias provided by the VOA bias power supply 120 is repeatedly applied to the VOA 31 between 0V and 5V (for example, a cycle of about 1 second). At the same time, the VOA31 is moved in a direction parallel to the bottom surface 2E of the housing 2 and perpendicular to the optical axis, and the intensities of the two polarization components of the test light after attenuation by the VOA31 are detected by the built-in photodiodes of the MMIs 40 and 50. ..

After that, the VOA 31 is fixed at a position where the difference in the degree of attenuation of the polarized light component after attenuation is within the permissible range. At this time, the output difference of the built-in photodiodes of the MMIs 40 and 50 may be regarded as the difference in the attenuation of the polarization component of the test light. The VOA 31 is mounted at an angle (for example, 7 °) with respect to the optical axis connecting the lens and the lens 27 in the simulated connector 123B. This is because the reflected light is not returned to the port 6 of the sig light.

FIG. 13 is a graph showing an example of the attenuation characteristic of the VOA 31 with respect to the applied bias voltage. Graphs G11 and G22 show the degree of attenuation of each polarization component (graph G11: X polarization, graph G12: Y polarization). Further, the graph G13 shows the difference in the degree of attenuation of the polarization component. When the applied bias voltage is 0V, the VOA 31 is in the fully open state. As shown in FIG. 13, the degree of attenuation increases as the bias voltage increases, but the degree of attenuation of each polarization component is slightly different even if the bias voltage is the same. The difference in the degree of attenuation tends to increase as the bias voltage increases. In the present embodiment, two deviations are obtained by aligning the VOA 31 in three directions: the optical axis direction, orthogonal to the optical axis, parallel to the bottom surface 2E, and orthogonal to the optical axis, and perpendicular to the bottom surface 2E. Keep the difference in the degree of attenuation of the wave component within the permissible range. In one example, when the bias voltage is 4.5V, the degree of attenuation of each polarization component is 12 dB or more, and the VOA31 is centered, and the difference between the degree of attenuation of the two polarization components is the difference between the degree of attenuation of the two polarization components, and the bias voltage is 0V to 5V. It can be contained within ± 0.5 dB in the range.

Subsequently, as shown in FIG. 14, two optical ATTs 71 and 81 are mounted in the respective mounting areas 70 and 80. Specifically, according to the steps so far, in the coherent receiver 1, after the Lo light is branched at _{BS21, the branched Lo light L 1} and L ₂ are divided into the photodiode 45, which is built in the MMI 40, 50. It is in a state where the photobonding intensity with respect to MMI 40 and 50 can be known by 55. For Lo light L ₀ , the two Lo light L ₁ and L ₂ branched by BS12 are photocoupled to MMI 40 and 50 via different optical paths R1 and R2, respectively. For example, it is assumed that the light transmittance of the optical components mounted on the optical paths R1 and R2 is set to 1: 1 depending on the alignment state with respect to the MMI. Even in this case, the photobonding intensities for MMIs 40 and 50 are different. When this difference is large, the accuracy of extracting the phase information contained in the Sigma light by the MMIs 40 and 50 is lowered.

Similarly, for Sigma light, after branching at PBS21, it reaches MMI40,50 via different optical paths R3 and R4. It is difficult to set the polarization-dependent branching ratio of PBS21 to exactly 1: 1, and the optical components intervening in the respective optical paths R3 and R4 are not equivalent, and the optical coupling strength to MMI40 and 50 is also the optical path R3 and R4. Cannot be uniform. In the coherent receiver 1, in order to compensate for the difference in optical coupling strength between Lo light and Sigma light with respect to MMI 40 and 50, Lo light L1 is on the optical path R3 between the skew adjusting element 16 and BS12 on the optical path R1 and Sigma light N1 is on the optical path R3. It is characterized in that optical ATTs 71 and 81 (optical attenuators) are interposed between the skew adjusting element 26 and PBS 21, respectively. As a specific mounting procedure, similarly to BS12 and PBS21, the angles of the optical ATTs 71 and 81 are determined by the visible laser light LD from the autocollimator 125 above the housing 2. Then, while maintaining the angle, the light ATTs 71 and 81 are fixed by placing them on the predetermined mounting areas 70 and 80, respectively, and curing the fixing resin.

Subsequently, as shown in FIG. 15, the lid 2C that closes the housing 2 is attached by a seam seal, and the inside of the housing 2 is airtightly sealed. Then, as shown in FIG. 16, the simulated connectors 123a and 123b are replaced with the original Sigma light port 6 and Lo light port 5, and the Sigma light port 6 and Lo light port 5 are centered and fixed. .. Specifically, simulated Sigma light is introduced from the Sigma light port 6, and the intensity of the Sigma light is detected by the built-in photodiode of the MMI 40. Then, with reference to the detected intensity of the Sigma light, the position of the port 6 of the Sigma light is changed to determine the position where the optical coupling intensity of the built-in photodiode is maximized. Similarly, Lo light is actually introduced into the Lo light port 5, and the intensity of the Lo light is detected by the built-in photodiodes 45 and 55 of the MMI 40 and 50. The position of the port 5 of the Lo light is changed with reference to the detected intensity of the Lo light, and the position where the optical coupling intensity of the built-in photodiodes 45 and 55 is maximized is determined. After the determination, the Sigma light port 6 and the Lo light port 5 are fixed to the housing 2. YAG welding can be adopted for fixing.

Next, the configuration of the first lenses 14b, 15b, 23b, 24b and the method of centering and fixing will be described in detail. The first lenses 14b, 15b, 23b, and 24b have the same configuration as each other, and the method of centering and fixing is also performed according to the same procedure. Therefore, the configuration of the first lens 14b and the method of aligning the first lens 14b will be described in detail, and detailed description of the first lenses 15b, 23b, and 24b will be omitted.

FIG. 17A is a side view of the first lens 14b. FIG. 17B is a front view of the first lens 14b. As shown in FIGS. 17A and 17B, the first lens 14b has a support portion 91 and a lens portion 92, and the support portion 91 and the lens portion 92 are integrally molded. .. The first lens 14b is made of a resin material or a glass material that is transparent to sig light and Lo light.

The support portion 91 is a rectangular flat plate-shaped member that holds the position of the lens portion 92 with respect to the base 4. The support portion 91 includes a pair of light passing surfaces 93a and 93b on which the lens portion 92 is provided, and a first installation surface 94a, a second installation surface 94b, a third installation surface 94c and a fourth that connect the light passing surfaces 93a and 93b. It has an installation surface 94d. That is, the first to fourth installation surfaces 94a to 94d are side surfaces of the support portion 91. The first to fourth installation surfaces 94a to 94d are surfaces facing the base 4 when the first lens 14b is installed on the base 4.

The lens unit 92 of the first lens 14b forms a condensing spot P in the light input unit 41 of the MMI 40. The lens unit 92 has a first lens unit 92a and a second lens unit 92b. The first lens portion 92a is provided on one light passing surface 93a of the support portion 91, and the second lens portion 92b is provided on the other light passing surface 93b of the support portion 91. In the lens unit 92 of the present embodiment, the first optical axis A1a of the first lens unit 92a and the second optical axis A1b of the second lens unit 92b are parallel to each other and arranged on the same virtual line. .. Therefore, the first lens 14b has one optical axis A1 including the first optical axis A1a and the second optical axis A1b. The first optical axis A1a and the second optical axis A1b may have the other optical axis tilted with respect to one optical axis. Further, although the first optical axis A1a and the second optical axis A1b are parallel to each other, they may be displaced in a direction orthogonal to the direction of the optical axis A1.

The lens portion 92 is provided at a position deviated from the physical center (center of gravity) of the support portion 91. Therefore, the distances D1 to D4 from the first to fourth installation surfaces 94a to 94d to the optical axis A1 are different from each other. Specifically, the optical axis A1 is separated from the first installation surface 94a by a distance D1. The optical axis A1 is separated from the second installation surface 94b by a distance D2. The optical axis A1 is separated from the third installation surface 94c by a distance D3. The optical axis A1 is separated from the fourth installation surface 94d by a distance D4. The distances D1 to D4 are different from each other. Of the distances D1 to D4, two distances (for example, distances D3 and D4) may have the same magnitude. Further, of the distances D1 to D4, three distances (for example, distances D2, D3, D4) may have the same magnitude. The amount of deviation between the distances D1 to D4 is larger than the allowable dimension in the design of the first lens 14b. That is, the deviation amount means a deviation larger than the deviation due to the manufacturing error that may occur during the manufacturing of the first lens 14b.

FIG. 18A shows a case where the first lens 14b is installed on the base 4 so that the first installation surface 94a faces the lens arrangement surface 4a (main surface) of the base 4. As shown in FIG. 18A, when the first installation surface 94a is used as the standard installation surface, the optical axis A1 of the first lens 14b is located at the standard height H1 with reference to the base 4. This standard height H1 is due to the distance D1 (see FIG. 17B). Specifically, the standard height H1 is the same as the distance D1, or is the total length of the adhesive portions 96 provided between the base 4 and the first installation surface 94a at the distance D1. .. FIG. 18B shows a case where the first lens 14b is installed on the base 4 so that the second installation surface 94b faces the lens arrangement surface 4a of the base 4. As shown in FIG. 18B, when the first lens portion 92a is installed on the base 4 so that the second installation surface 94b faces the base 4, the optical axis A1 of the first lens 14b is the base. It is located at height H2 with reference to 4. Therefore, the optical axis A1 is located above the standard height H1 by a height ΔH2. FIG. 18C shows a case where the base 4 is installed with the first lens 14b so that the third installation surface 94c faces the lens arrangement surface 4a of the base 4. As shown in FIG. 18C, when the first lens portion 92a is mounted on the base 4 so that the third mounting surface 94c faces the base 4, the optical axis A1 of the first lens 14b is the base. It is located at height H3 with reference to 4. Therefore, the optical axis A1 is located below the standard height H1 by a height ΔH3. FIG. 18D shows a case where the first lens 14b is installed on the base 4 so that the fourth installation surface 94d faces the lens arrangement surface 4a on the base 4. As shown in FIG. 18D, when the first lens portion 92a is installed on the base 4 so that the fourth installation surface 94d faces the base 4, the optical axis A1 of the first lens 14b is the base. It is located at a height of H4 with reference to 4. Therefore, the optical axis A1 is located below the standard height H1 by a height ΔH4.

Next, a method of aligning and fixing the first lens 14b (step S2: see FIG. 19) will be described in detail.

First, the first photobonding strength is obtained (step S2a: see FIG. 19). More specifically, as shown in FIG. 18A, the first lens 14b is placed on the base 4 so that the first installation surface 94a faces the lens arrangement surface 4a. The test light from the simulated connectors 123a and 123b (see FIG. 8) is incident, passes through the first lens 14b, and the test light input to the MMI 40 is detected by the built-in photodiode 45 of the MMI 40. Then, the position and angle of the first lens 14b are slightly changed to determine the position and angle at which the optical coupling strength of the built-in photodiode 45 is maximized. Then, the maximum first photobonding strength is obtained.

Subsequently, the second photobonding strength is obtained (step S2b: see FIG. 19). More specifically, as shown in FIG. 18B, the first lens 14b is placed on the base 4 so that the second mounting surface 94b faces the lens arranging surface 4a. Then, the second photobonding strength is obtained by the above-mentioned procedure (step S2b: see FIG. 19). Subsequently, the third photobonding strength is obtained (step S2c: see FIG. 19). As shown in FIG. 18 (c), the first lens 14b is arranged to obtain the third photobonding strength (step S2c: see FIG. 19). Then, the fourth photobonding strength is obtained (step S2d: see FIG. 19). As shown in FIG. 18D, the first lens 14b is arranged to obtain the fourth photobonding intensity. Subsequently, the actual installation surface is selected by comparing the first to fourth photobonding intensities with each other (step S2e). One of the first to fourth installation surfaces 94a to 94d is selected as the installation surface having the highest photobonding strength. This installation surface is an actual installation surface that faces the base 4 when the first lens 14b is actually fixed to the base 4.

Subsequently, the first lens 14b is fixed to the base 4 (step S2f: see FIG. 19). More specifically, the ultraviolet curable resin is applied to the installation region (lens arrangement surface 4a) of the first lens 14b on the base 4. Subsequently, in the first lens 14b, the actual installation surface selected in the step S2e faces the base 4. Further, the mounting position and mounting angle of the first lens 14b are adjusted so that the horizontal position and angle are finely adjusted to maximize the light coupling strength, as in the case of obtaining the light coupling strength. Then, by irradiating with ultraviolet rays, the ultraviolet curable resin is cured, and the first lens 14b is fixed to the base 4.

The same process is performed for the first lenses 15b, 23b, and 24b, and the first lenses are fixed to the base 4. In the above example, the installation surface having the highest optical coupling strength was selected for each of the first lenses 14b, 15b, 23b, and 24b, but the installation surface may be selected based on another criterion. The installation surface may be selected based on the correlation of each of the first lenses 14b, 15b, 23b, and 24b. For example, after detecting the light intensity on each installation surface in each of the first lenses 14b, 15b, 23b, 24b, the difference in the light coupling intensity in each of the first lenses 14b, 15b, 23b, 24b becomes the smallest. A method of selecting the installation surface as the installation surface of each of the first lenses 14b, 15b, 23b, and 24b is also useful.

Here, the problem will be described while showing a coherent receiver according to a comparative example. 22 (a) and 22 (a) are views of the MMI 210, 220 and the lens 230 constituting the coherent receiver 200 according to the comparative example, viewed from the front. The MMI 210 and 220 have the same configuration as the MMI 40 and 50. The four lenses 230 all have the same configuration. The lens 230 has the same distance from the four side surfaces to the optical axis. Therefore, the height from the base 201 to the optical axis is constant regardless of which side surface is used as the installation surface. The height from the outer shape of the lens 230 or the outer shape of the support portion that supports the lens 230 to the center of the optical axis of the lens 230 is designed to match the height of the optical axis of an optical device such as the MMI 210 or 220.

FIG. 22A shows a configuration in which each of the MMI 210, 220 and the lens 230 is manufactured according to the designed dimensional values and is attached to the base 4 according to the designed dimensional values. When manufactured and assembled according to the design values, the lens 230 forms a condensing spot Q for each of the two light input units 211 of the MMI 210 and the two light input units 222 of the MMI 220. To do. Therefore, the respective lenses 230 and the MMIs 210 and 220 are photocoupled so that the photocoupling strength is maximized.

However, in reality, each of the MMI 210, 220 and the lens 230 has manufacturing variations in the outer shape. Further, when the MMI 210, 220 and the lens 230 are installed on the base 201, variations in assembly occur. As shown in FIG. 22B, when the MMI 210, 220 is installed on the base 201, the MMI 210, 220 may be tilted with respect to the base 201. In this case, the distance from the base 201 to the optical input units 211 and 221 differs for each optical waveguide. Specifically, the lens 230 forms a condensing spot Q for each of the two light input units 211 of the MMI 210 and the two light input units 222 of the MMI 220. However, some of the light-collecting spots Q are displaced from the optical input units 211 and 221. Therefore, the photobonding strength is lowered.

In the configuration of the comparative example, the position of the lens 230 on the base 201 in the X-axis direction can be set to a desired position. Therefore, the deviation along the X-axis direction can be eliminated. On the other hand, the lens 230 has limited room for adjustment in the Y-axis direction. For example, when the condensing spot Q is displaced below the light input unit 221 (see reference numeral K1 in FIG. 22B), it can be adjusted to some extent by the ultraviolet curable resin. However, its adjustable range is small. Moreover, when the condensing spot Q is displaced above the light input unit 211 (see reference numeral K2 in FIG. 22B), it is impossible to shift the position of the condensing spot Q downward. , Virtually impossible to adjust.

FIG. 20 is a front view of a configuration in which the first lenses 14b, 15b, 23b, 24b and MMI 40, 50 according to the embodiment are mounted on the base 4. As shown in FIG. 20, even when the MMIs 40 and 50 are tilted and fixed with respect to the base 4, when the first lenses 14b, 15b, 23b, and 24b are attached to the base 4, the actual installation surface is set. It can be selected from the first to fourth installation surfaces 94a to 94d. Since the distances D1 to D4 from the first to fourth installation surfaces 94a to 94d to the lens unit 92 are different, the base can be selected by selecting the actual arrangement surface from the first to fourth installation surfaces 94a to 94d. The height from 4 to the optical axis A1, that is, the position of the focusing spot P can be selected. Therefore, it is possible to select the installation configuration of the first lenses 14b, 15b, 23b, 24b having higher photocoupling strength.

For example, the first lens 14b is installed on the base 4 so that the third installation surface 94c faces the lens arrangement surface 4a, so that the light focusing spot P overlaps with the light input unit 41 arranged at the lowest position. I can let you. For example, by installing the first lens 24b on the base 4 so that the fourth installation surface 94d faces the lens arrangement surface 4a, the focusing spot P can be overlapped with the light input unit 42. Similarly, by installing the first lens 15b on the base 4 so that the first installation surface 94a faces the lens arrangement surface 4a, the condensing spot P can be overlapped with the light input unit 51. By installing the first lens 23b on the base 4 so that the second installation surface 94b faces the lens arrangement surface 4a, the focusing spot P can be overlapped with the light input unit 52.

Further, in the above optical coupling method, in the base 4, the second lenses 14a, 15a, 23a, respectively, are used between the PBS 21 and the first lenses 23b and 24b, and between the BS12 and the first lenses 14b and 15b, respectively. It further includes a step S4 for installing the 24a. The reason why the lens groups 14, 15, 23, 24 have the second lenses 14a, 15a, 23a, 24a in addition to the first lenses 14b, 15b, 23b, 24b will be described below.

In FIG. 21, when two lenses are arranged side by side in the optical axis direction, the deviation of the lens position from the design position and a minute coupling target (in this embodiment, the optical input units 41, 42 of the MMI 40, 50) are shown. , 51, 52) is a graph showing an example of the relationship with the change in binding efficiency. 21 (a) and 21 (c) show the displacement of the lens on the coupling target side (lens arranged relatively close to the coupling target) ((a) is the displacement in the direction orthogonal to the optical axis. (C) shows the change in the coupling efficiency due to the deviation in the optical axis direction). Further, in FIGS. 21 (b) and 21 (d), the misalignment of the lens (lens arranged relatively separated from the coupling target) on the opposite side of the coupling target ((b) is orthogonal to the optical axis). The change in the coupling efficiency due to the deviation in the direction of movement and (d) the deviation in the optical axis direction is shown. In addition, in FIG. 21B and FIG. 21D, it is assumed that the lens on the coupling target side is arranged in advance at the design position.

First, the deviation in the direction (X, Y) orthogonal to the optical axis is examined. As shown in FIG. 21 (a), in the lens on the coupling target side, the coupling efficiency deteriorates even if the misalignment is only a few μm, and the coupling efficiency deteriorates by as much as 30% due to the misalignment of about 1 μm. On the other hand, as shown in FIG. 21 (c), in the lens on the opposite side of the coupling target, the coupling efficiency hardly deteriorates if the position is displaced by several μm, and the deterioration of the coupling efficiency is several tens. A displacement of μm is required. Further, when the deviation in the optical axis direction is examined, as shown in FIG. 21 (b), the coupling efficiency of the lens on the coupling target side deteriorates even if the displacement is several tens of μm, but FIG. 21 (d) shows. As shown in the above, the coupling efficiency of the lens on the opposite side of the coupling target hardly deteriorates if the lens is displaced by several tens of μm.

Each lens of the lens group 14, 15, 23, 24 is fixed to the base 4 with a resin such as an ultraviolet curable resin. Since the resin shrinks by several μm when solidified, the position of the lens may shift by several μm as the resin solidifies. Then, as described above, the coupling efficiency of the lens on the coupling target side deteriorates even if the lens is displaced by several μm.

On the other hand, in the lens on the opposite side of the coupling target, the coupling efficiency hardly deteriorates if the position is displaced by several μm, so that a significantly larger likelihood can be secured as compared with the lens on the coupling target side. In particular, since a misalignment of several tens of μm is allowed in the optical axis direction, the alignment accuracy in the optical axis direction can be substantially ignored. Therefore, after aligning and fixing the lens on the coupling target side (first lens 14b, 15b, 23b, 24b in the present embodiment), the lens on the opposite side to the coupling target (second lens 14a in the present embodiment). , 15a, 23a, 24a) can be sufficiently compensated for the deterioration of the coupling efficiency that occurs in the lens on the coupling target side.

In the above method, after aligning and fixing the four first lenses 14b, 15b, 23b, 24b closer to the MMI 40, 50, the other four second lenses 14a, 15a, 23a, 24a are adjusted. The core and fixing are performed. On the other hand, for example, when a set of light source 112 and connector 116 (see FIG. 7B) are commonly used for two simulated connectors 123a and 123b, the test light from one simulated connector is used. After aligning and fixing each lens by using the test light, the alignment and fixing of each lens may be performed by using the test light from the other simulated connector. For example, first, the first lenses 14b and 15b are centered and fixed, the first lenses 23b and 24b are centered and fixed, and then the second lenses 14a and 15a are centered and fixed. The lenses 23a and 24a may be aligned and fixed. Thereby, the number of times of reconnection of the light source 112 and the like can be reduced.

Further, in the above method, the lenses arranged close to the MMIs 40 and 50 are fixed at the position where the coupling efficiency is maximized, but the target is located at a position away from the coupling target (offset) by a predetermined distance from the position. The lens may be fixed, and the lens arranged at a relative distance from the MMIs 40 and 50 may be fixed at the position where the coupling efficiency is maximized. The position where the coupling efficiency is maximized only by the lenses arranged in close proximity and the position of the lenses arranged in close proximity when the coupling efficiency is maximized by the combination of the two lenses are different. In the latter case, compared with the former. This is because it is far from the binding target.

The present invention has been described in detail above based on the embodiment. However, the present invention is not limited to the above embodiment. The present invention can be modified in various ways without departing from the gist thereof.

1 ... Coherent receiver, 2 ... Housing, 2C ... Lid, 3 ... Carrier (second substrate), 4 ... Base (first substrate), 4a ... Lens arrangement surface, 5, 6 ... Port (light supply unit), 12 ... BS (optical demultiplexing element), 16, 26 ... skew adjusting element, 13, 22 ... reflector, 14, 15, 23, 24 ... lens group, 14b, 15b, 23b, 24b ... first lens, 14a, 15a , 23a, 24a ... 2nd lens, 30 ... VOA carrier, 21 ... PBS (polarization-dependent optical branching element), 27 ... lens, 31 ... VOA, 33 ... monitor photodiode, 43, 53 ... integrated circuit, 40, 50 ... MMI (multimode interference part, target part), 41,42,51,52 ... optical input part, 44,54 ... optical waveguide part, 45,55 ... built-in photodiode, 46,56 ... wiring board, 61 ... feed Through, 71, 81 ... Optical ATT (optical attenuator), 70, 80 ... Mounting area, 91 ... Support, 92 ... Lens, 92a ... First lens, 92b ... Second lens, 94a ... First installation Surface, 94b ... 2nd installation surface, 94c ... 3rd installation surface, 94d ... 4th installation surface, 96 ... Adhesive part, A1a ... 1st optical axis, A1b ... 2nd optical axis, A1 ... Optical axis, P ... Collection Light spot, L ... visible laser light, L0, L1, L2 ... Lo light (local emission), R1, R2, R3, R4 ... optical path, N1 ... Sigma light (signal light).

Claims (4)

A light coupling method in which the light provided by the light providing unit is photocoupled to the target unit by arranging a lens between the light providing unit and the target unit.
The lens has a lens portion and a support portion, and the support portion faces or faces a first installation surface that can be installed with respect to a main surface of a first substrate on which the lens is installed and the first installation surface. Including the second installation surface arranged at right angles
The first distance from the first installation surface to the optical axis of the lens portion is different from the second distance from the second installation surface to the optical axis of the lens portion.
A step of obtaining a first light coupling strength between the light providing portion and the target portion after mounting the lens with the first installation surface facing the main surface of the first substrate.
A step of obtaining a second light coupling strength between the light providing portion and the target portion after mounting the lens with the second mounting surface facing the main surface of the first substrate.
A step of selecting either the first installation surface or the second installation surface based on the first photobonding strength and the second photobonding strength.
A photocoupling method comprising the step of fixing the first substrate to the selected installation surface. The step of selecting either the first installation surface or the second installation surface is a step of selecting whichever of the first photobonding strength and the second photobonding strength has the larger photobonding strength. Item 1. The optical coupling method according to item 1. With multiple lenses
For the plurality of the lenses, the step of obtaining the first photobonding strength and the step of obtaining the second photobonding strength are carried out.
Claim 1 in the step of selecting either the first installation surface or the second installation surface of the plurality of lenses, the installation surface is selected in relation to the smallest difference in the optical coupling strength of the lenses. The optical coupling method described. The target unit is a multi-mode interference unit that obtains a signal by interfering between local light emission and signal light.
The optical coupling method according to claim 1, wherein the lens is installed on the optical path of the station emission incident on the multimode interference section or on the optical path of the signal light incident on the multimode interference section.

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