JP2017034492A - Manufacturing method for coherent light reception module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a coherent light reception module, capable of making the attenuation degree of two polarization components, included in signal light, approach mutually equal magnitude.SOLUTION: The manufacturing method includes: a first step which prepares test light having two polarization components to simulate two polarization components of the signal light, to substantially equalize the strength of the two polarization components of the test light; a second step which disposes a VOA 23 on the optical path of the test light, to vary the attenuation degree of the VOA 23, while monitoring the strength of the two polarization components of the test light after attenuation, and to move the VOA 23; and a third step which fixes the VOA 23 at a position where the difference of the attenuation degree between the two polarization components of the test light after the attenuation falls within a tolerable range.SELECTED DRAWING: Figure 16

Description

  The present invention relates to a method for manufacturing a coherent optical receiver module.

  Patent Documents 1 and 2 disclose an optical receiver in which a variable optical attenuator is provided in front of a light detection element (photodiode). The variable optical attenuator described in Patent Document 1 is an etalon type. In Patent Document 1, the degree of attenuation is changed by changing the angle or temperature of the variable optical attenuator. Patent Document 2 describes that a MEMS element made of silicon can be used as the variable optical attenuator. This MEMS element has a Si plate whose position is shifted by an electric field when a voltage is applied, and the Si plate is coated with an antireflection film. In a non-energized state in which no voltage is applied, the Si plate is perpendicular to the optical axis of the signal light, so that the signal light beam is not modulated and enters almost the center of the light receiving portion of the photodiode. On the other hand, when a voltage is applied to the MEMS element, the Si plate is tilted, and the signal light is refracted when entering the Si plate. The signal light is refracted again when it is emitted from the Si plate, and its traveling direction is parallel to the traveling direction before the incident, but since it travels in a direction inclined with respect to the traveling direction inside the Si plate, The optical path is offset in a direction perpendicular to the traveling direction. For this reason, the incident position of the signal light to the photodiode also moves, and as a result, the amount of light received by the photodiode can be varied.

JP 2009-177449 A JP 2009-244833 A

  In recent years, in the long-distance large-capacity communication of the trunk line system, in order to increase the communication capacity and increase the speed, it is desired to apply the polarization multiplexing method in addition to the conventional DWDM (Dense Wavelength Division Multiplexing). It is rare. For example, the coherent light receiving module receives signal light modulated by DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) method and separates the signal light into two polarization components. Then, a product operation (typically interference) between each polarization component and the locally transmitted light (local light) is performed, and the intensity of the light after the operation (interference light) is detected, thereby being included in each polarization component. Extract information.

  In the above coherent optical receiver module, a variable optical attenuator for attenuating signal light is provided for the purpose of adjusting the intensity of the input signal light and preventing excessive input to the photodiode. Since the signal light includes two polarization components in the coherent light receiving module, it is desirable for the variable optical attenuator to make the attenuation of these polarization components close to each other (more desirably, match).

  An object of the present invention is to provide a method for manufacturing a coherent light receiving module that can bring the attenuation of two polarization components contained in signal light close to each other.

  In order to solve the above-described problem, a method of manufacturing a coherent optical receiver module according to an embodiment of the present invention attenuates input signal light including two polarization components whose polarization directions are orthogonal to each other using a variable optical attenuator. A method for manufacturing a coherent optical receiver module that extracts information by performing a product operation of two polarization components of input signal light after attenuation and local oscillation light, and simulates the two polarization components of input signal light A test light having two polarization components is prepared, a first step in which the intensity of the two polarization components of the test light is approximately equal to each other, and a variable optical attenuator is disposed on the optical path of the test light, and the test after attenuation While monitoring the intensity of the two polarization components of light, the second step of changing the attenuation of the variable optical attenuator and moving the variable optical attenuator, and the attenuation of the two polarization components of the attenuated test light difference At a position within the allowable range and a third step of fixing the variable optical attenuator.

  According to the method for manufacturing a coherent light receiving module according to the present invention, the attenuation degree of two polarization components included in signal light can be made close to each other.

FIG. 1 is a plan view showing a configuration of an optical receiver module according to an embodiment of the present invention. FIG. 2 is a perspective view of the optical receiver module as viewed obliquely from above. FIG. 3 is an enlarged perspective view showing the VOA carrier, the beam splitter, the VOA, and the monitor PD. FIG. 4 is a perspective view showing an appearance of a VOA base on which the VOA is mounted. FIG. 5 is a front view partially showing the configuration of the VOA, and shows a state in which the opening of the VOA is viewed from the optical axis direction. FIG. 6 is a block diagram showing the internal configuration of the optical 90-degree hybrid element. FIG. 7A shows a process of preparing a standard mirror having a light reflecting surface and a bottom surface perpendicular to each other. FIG. 7B shows a process of removing the standard mirror from the alignment table and replacing it with a package on which an optical 90-degree hybrid element, an amplifier and a VOA carrier are mounted. FIG. 8 shows a process of mounting the monitor PD on the VOA carrier. FIG. 9 shows the process of placing the test port on one end face of the package. FIG. 10 is a perspective view showing a part of the manipulator holding the test port. FIG. 11A is a block diagram showing a configuration for preparing test light. FIG. 11B shows a process of removing the standard mirror again from the alignment table and replacing it with a package. FIG. 12 shows a process of aligning and fixing the first mirror and the second mirror. FIG. 13 shows a process of aligning and fixing the condenser lens. FIG. 14 shows a process of aligning and fixing the condenser lens. FIG. 15 shows a process of aligning and fixing the collimating lens. FIG. 16 shows a process of mounting the VOA on the VOA carrier. FIG. 17 is a perspective view showing how the VOA is mounted on the VOA carrier. FIG. 18 is a graph showing an example of the attenuation characteristic of the VOA. FIG. 19 shows a process of attaching a lid for closing the package. FIG. 20 shows a process of aligning and fixing the signal light input port and the local light input port.

  A specific example of a method for manufacturing a coherent optical receiver module according to an embodiment of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included. In the following description, the same reference numerals are given to the same elements in the description of the drawings, and redundant descriptions are omitted.

  FIG. 1 is a plan view showing a configuration of a coherent optical receiver module (hereinafter referred to as an optical receiver module) 1A according to an embodiment of the present invention. FIG. 2 is a perspective view of the optical receiver module 1A as viewed obliquely from the front. The optical receiver module 1 </ b> A of this embodiment includes a substantially rectangular parallelepiped package (housing) 2, a signal light input port 11 and a local light input port 13 fixed to one end surface 2 b of the package 2. Hereinafter, in the description of the internal structure of the package 2, the one end surface 2b side may be referred to as a front side.

  The signal light input port 11 is connected to the single mode fiber 10 and receives received signal light (SiGnal; hereinafter referred to as signal light) from the single mode fiber 10. The signal light is modulated by a so-called DP-QPSK system and includes two polarization components whose polarization directions are orthogonal to each other. The local light input port 13 is connected to the polarization maintaining fiber 12 and receives local oscillation light (Local; hereinafter referred to as local light) from the polarization maintaining fiber 12. These signal light and local light are input into the package 2 via the signal light input port 11 and the local light input port 13, respectively.

  In addition, among the four side surfaces of the package 2, a plurality of terminals 3 are provided on the other side surface except the one end surface 2 b. The plurality of terminals 3 include a terminal for taking out an electrical reception signal generated from the signal light to the outside of the optical reception module 1A, a terminal for supplying a power supply voltage and a bias to an electronic circuit inside the package 2, Includes grounding terminals.

  The signal light input port 11 is formed by integrating a cylindrical sleeve that receives a ferrule attached to the tip of the single mode fiber 10 and a lens holder that houses a condenser lens, and the lens holder is one end surface of the package 2. It is fixed to the package 2 by being joined to 2b. The signal light propagating through the single mode fiber 10 enters the package 2 while being collected by the condenser lens.

  The local light input port 13 is formed by integrating a cylindrical sleeve that receives a ferrule attached to the tip of the polarization maintaining fiber 12 and a lens holder that accommodates a collimating lens. The lens holder is an end surface of the package 2. It is fixed to the package 2 by being joined to 2b. The local light propagating through the polarization maintaining fiber 12 is collimated by the collimating lens and then enters the package 2.

  In addition to the above configuration, the optical receiver module 1A of the present embodiment optically couples the two optical 90-degree hybrid elements 32a and 32b, and the input ports 11 and 13 and the optical 90-degree hybrid elements 32a and 32b. Various optical parts are provided. Specifically, the optical receiving module 1A is a polarization beam splitter (Polarization Beam) as an optical component for optically coupling the signal light input terminals of the two optical 90-degree hybrid elements 32a and 32b and the signal light input port 11. Splitter) 26, skew adjustment element 27, first lens system 28, wavelength plate (λ / 2 plate) 29, first mirror 30, and second lens system 31. Further, a beam splitter 22, a variable optical attenuator (VOA) 23, and a collimator lens 25 are disposed on the optical path between the polarization beam splitter 26 and the signal light input port 11. All of these optical components arranged on the optical path between the signal light input port 11 and the optical 90-degree hybrid elements 32 a and 32 b are accommodated in the package 2.

  The beam splitter 22 separates part of the signal light input from the signal light input port 11. The separated signal light is incident on a power monitoring photodiode (monitoring PD) 24 disposed in the package 2. The monitor PD 24 generates an electrical signal corresponding to the intensity of the signal light. The intensity of the signal light separated in the beam splitter 22 is less than 10% of the signal light intensity before entering the beam splitter 22.

  The VOA 23 attenuates the signal light that has passed through the beam splitter 22 as necessary. The degree of attenuation is controlled by an electrical signal from the outside of the optical reception module 1A. For example, when an over-input state is detected based on the electrical signal from the monitor PD 24 described above, the attenuation of the VOA 23 is increased and the intensity of the signal light directed to the optical 90-degree hybrid elements 32a and 32b is decreased. To do.

  The beam splitter 22, the VOA 23, and the monitor PD 24 are fixed on the VOA carrier 20 mounted on the bottom surface 2a of the package 2. FIG. 3 is an enlarged perspective view showing the VOA carrier 20, the beam splitter 22, the VOA 23, and the monitor PD 24. As shown in FIG. As shown in FIG. 3, the VOA carrier 20 mounts these optical components on two upper and lower surfaces 20a and 20b forming a step. Specifically, the surface 20a is disposed in front of the surface 20b, and the height from the bottom surface of the package is higher than that of the surface 20b. A beam splitter 22 and a monitor PD 24 (more specifically, a submount on which the monitor PD 24 is mounted on the side surface) are mounted on the surface 20a, and the VOA 23 faces the beam splitter 22 on the surface 20b. It is mounted on. Since the outer diameter of the VOA 23 in a cross section perpendicular to the optical axis is larger than that of the beam splitter 22, the beam splitter 22 and the VOA 23 are mounted on each of these surfaces 20 a and 20 b, so that the optical axis of the VOA 23 passes through the beam splitter 22. It can be within the range of possible.

  Further, the VOA 23 of the present embodiment is mounted and fixed on a VOA base (base member) 44. That is, the VOA 23 is mounted on the VOA carrier 20 via the VOA base 44. 4A and 4B are perspective views showing the appearance of the VOA base 44 on which the VOA 23 is mounted. FIG. 4A is a perspective view of the VOA base 44 as viewed obliquely from the front, and FIG. 4B is the VOA base 44. It is the perspective view which looked at from diagonally back. As shown in FIG. 4, the VOA base 44 has a rectangular plate shape and is made of an insulating material such as alumina. The VOA base 44 has a front surface 44a, a back surface 44b, a top surface 44c that connects the front surface 44a and the back surface 44b, a pair of side surfaces 44d, and a bottom surface 44e. The back surface 44b faces the beam splitter 22 shown in FIG. A through hole 44f for allowing the signal light to pass through passes from the front surface 44a to the back surface 44b.

  The VOA 23 is attached to the back surface 44b via an adhesive such as Ag paste. The VOA 23 has a circular opening 23 a through which signal light passes, and the opening 23 a communicates with the through hole 44 f of the VOA base 44. The VOA base 44 has a pair of metal bodies 45 and 46. The metal body 45 has a portion 45a disposed on the front surface 44a, a portion 45b disposed on the back surface 44b, and a portion 45c disposed on the upper surface 44c for connecting these portions 45a and 45b. The upper part of the VOA base 44 is gripped and attached to the VOA base 44. The portion 45a extends along the upper side of the front surface 44a (side between the upper surface 44c), and the length of the portion 45a along the side is longer than ½ of the length of the VOA base 44 in the same direction. . The portion 45b is electrically connected to one of the pair of electrodes of the VOA 23 via a wire 47a.

  The metal body 46 has a portion 46a disposed on the front surface 44a, a portion 46b disposed on the back surface 44b, and a portion 46c disposed on the upper surface 44c for connecting these portions 46a and 46b. The upper part of the VOA base 44 is gripped and attached to the VOA base 44. Among these portions, the portion 46c is disposed so as to be separated from the portion 45c of the metal body 45. In one example, the portion 45c of the metal body 45 is one end of the upper surface 44c, the portion 46c of the metal body 46. Are arranged close to the other end of the upper surface 44c. The portion 46b extends along the upper side of the back surface 44b (side between the upper surface 44c) and is electrically connected to the other of the pair of electrodes of the VOA 23 via the wire 47b.

  FIG. 5 is a front view partially showing the configuration of the VOA 23 and shows a state in which the opening 23a of the VOA 23 is viewed from the optical axis direction. As shown in FIG. 5, the VOA 23 of the present embodiment is a MEMS-type VOA, and has a substantially square plate-like shutter 23b inside an opening 23a. The size of the shutter 23b is, for example, 50 μm on a side. Comb-like electrodes 23c extend from the shutter 23b toward both sides. The comb-like electrode 23c is one of the pair of electrodes described above. The shutter 23b is connected to the main body of the VOA 23 through an elastic member 23d. A comb-like electrode 23e is further provided on the main body, and the comb-like electrode 23e is opposed to the comb-like electrode 23c by alternately positioning the comb teeth. The comb-like electrode 23e is the other of the pair of electrodes described above.

  A bias voltage is applied between the two comb-like electrodes 23c and 23e from the outside of the optical reception module 1A via the wires 47a and 47b and the metal bodies 45 and 46. When a bias voltage is applied between the comb-shaped electrodes 23c and 23e, an attractive force is induced between the comb-shaped electrodes 23c and 23e, and the shutter 23b moves together with the comb-shaped electrodes 23c. In one example, the shutter 23b can be moved by 60 μm by applying a bias voltage of 5V. At this time, the shutter 23b completely overlaps the optical path LA of the signal light existing near the center of the opening 23a. Thereby, the signal light is completely blocked (that is, the attenuation is 100%). Then, the moving distance of the shutter 23b can be adjusted by adjusting the bias voltage, and as a result, the attenuation of the signal light can be adjusted.

  As shown in FIG. 5, the shutter 23b does not cover the entire opening 23a, but covers only a part near the center of the opening 23a. The signal light passes as it is. Therefore, in order to ensure a large attenuation ratio in the VOA 23, it is desirable that the signal light passes through the central portion of the opening 23a with high accuracy. Furthermore, in order to ensure a sufficiently narrow beam diameter with respect to the shutter 23b, the signal light when passing through the opening 23a is focused light, and the position of the convergence point (beam waist) in the optical axis direction. Is preferably coincident with the position of the VOA 23. In the present embodiment, the signal light is focused by the condenser lens of the signal light input port 11, and the VOA 23 is disposed at the convergence point (beam waist).

  Please refer to FIG. 1 and FIG. 2 again. The collimator lens 25 collimates the signal light that has passed through the VOA 23. By making the signal light into collimated light by the collimating lens 25, high coupling efficiency can be secured for the optical path to the signal light input ends of the optical 90-degree hybrid elements 32a and 32b.

  The polarization beam splitter 26 has a light incident surface that is optically coupled to the signal light input port 11 via the beam splitter 22 and the VOA 23, and a part of the polarization component (for example, X polarization component) of the signal light and the remaining polarization component. (For example, Y polarization component) is branched. At this time, the branching ratio is 50%. The skew adjustment element 27 and the first lens system 28 are disposed on the optical path between one light output surface of the polarization beam splitter 26 and the signal light input end of the light 90-degree hybrid element 32b. The signal light traveling straight through the polarization beam splitter 26 passes through the skew adjustment element 27. The skew adjusting element 27 compensates for a delay time between the other signal light branched by the polarization beam splitter 26. Thereafter, the signal light is collected by the first lens system 28 and reaches the light 90-degree hybrid element 32b. Note that the first lens system 28 includes two condenser lenses 28a and 28b arranged in the optical axis direction.

  Further, the λ / 2 plate 29, the first mirror 30, and the second lens system 31 are on the optical path between the other light output surface of the polarization beam splitter 26 and the signal light input end of the light 90-degree hybrid element 32b. Has been placed. The signal light bent (branched) in the polarization beam splitter 26 passes through the λ / 2 plate 29. The λ / 2 plate 29 rotates the polarization direction of the signal light by 90 °. Therefore, the polarization direction of the signal light that has passed through the λ / 2 plate 29 coincides with the polarization direction of the signal light that has traveled straight through the polarization beam splitter 26. Thereafter, the traveling direction of the signal light is bent by 90 ° by the first mirror 30, and then converges by the second lens system 31 and reaches the light 90-degree hybrid element 32 a. Note that the second lens system 31 includes two condenser lenses 31a and 31b arranged in the optical axis direction. Further, the first mirror 30 is constituted by, for example, a cubic mirror (a rectangular parallelepiped or a cubic mirror having a reflecting surface extending in a diagonal direction between a pair of opposed surfaces).

  The optical receiving module 1A includes a beam splitter 34, a skew adjusting element 35, and a third lens as optical components for optically coupling the local light emitting input terminals of the two optical 90-degree hybrid elements 32a and 32b and the local light emitting input port 13. A system 36, a second mirror 37, and a fourth lens system 38 are further provided. Further, a polarizer 33 is disposed on the optical path between the beam splitter 34 and the local light input port 13. All of these optical components arranged on the optical path between the local light input port 13 and the optical 90-degree hybrid elements 32 a and 32 b are accommodated in the package 2.

  The polarizer 33 determines the polarization direction of the local light input from the local light input port 13. Thereby, even if the polarization direction maintained in the polarization maintaining fiber 12 is shifted when the package 2 is assembled, only the polarization component having the polarization direction of 0 ° or 90 ° can be extracted as the local light.

  The beam splitter 34 has a light incident surface that is optically coupled to the local light input port 13 via the polarizer 33, and branches the local light that has passed through the polarizer 33 into two. At this time, the branching ratio is 50%. The skew adjustment element 35 and the third lens system 36 are disposed on the optical path between one light output surface of the beam splitter 34 and the local light emission input terminal of the light 90-degree hybrid element 32a. The local light that travels straight through the beam splitter 34 passes through the skew adjustment element 35. The skew adjustment element 35 compensates for a delay time between the other local light branched by the beam splitter 34. Thereafter, the local light reaches the light 90-degree hybrid element 32 a while being collected by the third lens system 36. Note that the third lens system 36 includes two condenser lenses 36a and 36b arranged in the optical axis direction.

  The second mirror 37 and the fourth lens system 38 are disposed on the optical path between the other light output surface of the beam splitter 34 and the local light input end of the light 90-degree hybrid element 32b. The local light that has been bent (branched) by the beam splitter 34 is bent by 90 ° by the second mirror 37 and then condensed by the fourth lens system 38 and reaches the light 90-degree hybrid element 32b. To do. The fourth lens system 38 is constituted by two condenser lenses 38a and 38b arranged in the optical axis direction. Moreover, the 2nd mirror 37 is comprised by the cubic mirror, for example.

  As described above, the signal light and local light input into the package 2 are distributed to the two light 90-degree hybrid elements 32a and 32b. The optical 90-degree hybrid elements 32a and 32b of this embodiment are photodiode (PD) integrated multimode hybrids using a semiconductor substrate made of, for example, indium phosphide (InP). FIG. 6 is a block diagram showing the internal configuration of the optical 90-degree hybrid elements 32a and 32b. The optical 90-degree hybrid element 32a is formed by integrating a 90-degree hybrid coupler 51a (first 90-degree hybrid coupler) and a PD 52a (first photodiode) in a common package. Similarly, the optical 90-degree hybrid element 32b is formed by integrating a 90-degree hybrid coupler 51b (second 90-degree hybrid coupler) and a PD 52b (second photodiode) in a common package. The 90-degree hybrid couplers 51a and 51b are a combination of a plurality of optical waveguides and optical couplers. The 90-degree hybrid coupler 51a performs these product operations by causing one polarization component La of the signal light and the local light Lo to interfere with each other. The 90-degree hybrid coupler 51b performs these product operations by causing the other polarization component Lb of the signal light to interfere with the local light Lo.

  The optical 90-degree hybrid elements 32a and 32b output four units of optical signals such as IX, QX, IY, and QY. Here, “I” means “In-Phase”, that is, components corresponding to 0 ° component and 180 ° component in phase with the local light Lo in the signal light, and “Q” means “Quadrature”, that is, the signal light. Of these, components corresponding to a 90 ° component and a 270 ° component that differ by 90 ° from the phase of the local light Lo are meant. X and Y mean “X polarized light” and “Y polarized light”, respectively. These optical signals are output as differential optical signals from the 90-degree hybrid couplers 51a and 51b.

  The PDs 52a and 52b are optically coupled to the optical output terminals of the 90-degree hybrid couplers 51a and 51b, respectively, and detect output light (interference light, that is, IX, QX, IY, and QY) after their product operation, A photocurrent corresponding to the intensity is output. Photocurrents generated in the PDs 52 a and 52 b are converted into voltage signals by the amplifiers 39 a and 39 b provided in the package 2, and output from any of the plurality of terminals 3. In this way, information (reception signal) included in the signal light is extracted by the optical 90-degree hybrid elements 32a and 32b.

  A method for manufacturing the optical receiver module 1A of the present embodiment having the above configuration will be described. First, the optical 90-degree hybrid elements 32 a and 32 b shown in FIGS. 1 and 2 are mounted in the package 2, and the VOA carrier 20 is mounted on the bottom surface 2 a of the package 2. At this time, for example, after the front end of the VOA carrier 20 is abutted against the inner surface of the side wall constituting the one end surface 2b of the package 2 and the VOA carrier 20 and the package 2 are aligned, the VOA carrier 20 is attached to the side wall by a predetermined dimension. In this state, the VOA carrier 20 may be disposed on the bottom surface 2a of the package 2. The VOA carrier 20 is fixed to the bottom surface 2a using, for example, solder.

  Next, the amplifiers 39a and 39b are mounted. The amplifiers 39a and 39b are mounted by a known mounting method using a conductive resin such as silver paste. After mounting the amplifiers 39a and 39b, the temperature of the entire package 2 is raised (up to 120 ° C.), thereby evaporating the solvent contained in the conductive resin. Thereafter, wiring for electrically connecting the electrode pads on the upper surfaces of the amplifiers 39a and 39b and the terminal 3 on the rear side of the package 2 is performed. By this wiring, the active alignment of the optical component in the subsequent process, that is, the test light is input to the optical 90-degree hybrid elements 32a and 32b, and the output signal of the PD built in the optical 90-degree hybrid elements 32a and 32b is obtained. Each optical component can be arranged at a position where the intensity is maximum.

  Subsequently, as shown in FIG. 7A, a standard mirror 104 having a light reflecting surface 104a and a bottom surface 104b perpendicular to each other is prepared. The light reflecting surface 104 a simulates one end surface 2 b of the package 2, and the bottom surface 104 b simulates the back surface of the package 2. The standard mirror 104 is configured by a rectangular parallelepiped glass block, for example. Then, this standard mirror 104 is set on an alignment table (stage) 103 fixed on the support table 101. At this time, the bottom surface 104b and the alignment table 103 are brought into contact with each other.

  Subsequently, the optical axis direction of the autocollimator 102 is aligned with the optical axis direction of the standard mirror 104. Specifically, the visible laser beam L1 is output from the autocollimator 102, and the laser beam L1 is applied to the light reflecting surface 104a. Then, the light intensity of the visible laser beam L1 reflected on the light reflecting surface 104a is detected on the autocollimator 102 side. When the visible laser light L1 before reflection and the visible laser light L1 after reflection overlap each other, the detected light intensity becomes maximum. By utilizing this, the optical axis direction of the autocollimator 102 is aligned with the normal direction of the light reflecting surface 104a, that is, the optical axis direction of the standard mirror 104.

  Thereafter, the standard mirror 104 is removed from the alignment table 103 and replaced with the package 2 on which the optical 90-degree hybrid elements 32a and 32b, the amplifiers 39a and 39b, and the VOA carrier 20 are mounted (FIG. 7B). At this time, the bottom surface of the package 2 is brought into contact with the alignment table 103. Since the optical axis of the autocollimator 102 passes through the space above the package 2, the visible laser light L 1 passes above the package 2 and is not introduced into the package 2.

  Subsequently, as shown in FIG. 8, the monitoring PD 24 is mounted on the VOA carrier 20. Further, the polarizing beam splitter 26, the skew adjusting element 27, the λ / 2 plate 29, the polarizer 33, the beam splitter 34, and the skew adjusting element 35 are mounted at predetermined mounting positions in the package 2, respectively. These optical components are optical components that do not require alignment work, and are fixed after being adjusted only in the optical axis direction.

  In this step, the angle (optical axis direction) of the optical component is adjusted using the optical axis of the autocollimator 102 (see FIG. 7A). That is, one side surface of these optical components is used as a reflection surface for the visible laser light L1 of the autocollimator 102, the visible laser light L1 before reflection and the visible laser light L1 after reflection are superimposed on each other, and the angle of these optical components Adjust (optical axis direction). This operation is performed on the optical axis of the autocollimator 102, that is, in the space above the package 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 and fixed. To do.

  With respect to the polarization beam splitter 26, the skew adjustment element 27, the polarizer 33, and the skew adjustment element 35, since the light incident surface faces forward when mounted on the package 2, the normal direction of the light incident surface and the autocollimator It is preferable that the optical axis direction is adjusted by matching the optical axis 102, and the optical axis direction is maintained while the direction is maintained. In addition, with respect to the λ / 2 plate 29 and the monitor PD 24, the light incident surface faces sideways when mounted on the package 2, so that the normal direction of the light incident surface coincides with the optical axis of the autocollimator 102. Then, after adjusting the direction of the optical axis, it may be mounted after being rotated by 90 ° around the normal line of the bottom surface 2a. The monitor PD 24 is further electrically connected to the predetermined terminal 3 by performing wire bonding with the predetermined terminal 3. With respect to the beam splitter 34, the light incident surface faces sideways when mounted on the package 2, but the light exit surface faces rearward, so that the normal direction of the light exit surface or the surface opposite to the light exit surface And the optical axis direction of the autocollimator 102 and the optical axis direction are adjusted, and then mounted while maintaining the direction.

  Subsequently, since the optical coupling tolerance for the optical component different from each of the above-described optical components, that is, the optical 90-degree hybrid elements 32a and 32b is smaller than that of each of the above-described optical components, the first collimating lens 25 requires first alignment. The mirror 30, the first lens system 28, the second lens system 31, the third lens system 36, the second mirror 37, and the fourth lens system 38 are mounted in the package 2. In preparation for this, as shown in FIG. 9, test ports (simulated connectors) 50 a and 50 b are arranged on one end surface 2 b of the package 2. The test ports 50a and 50b simulate the signal light input port 11 and the local light input port 13, respectively. Test light used for alignment of the other optical components is emitted from the test ports 50a and 50b. Hereinafter, details of the process of preparing the test light will be described.

  FIG. 10 is a perspective view showing a part of the manipulator 60 for holding the test port 50a. The manipulator 60 includes an arm 61 that can freely change a position and an angle (specifically, a position in three axial directions orthogonal to each other and an angle around two axes perpendicular to the optical axis direction of the test port 50a), And an arm head 62 provided at the tip of 61. The test port 50 a is mounted on the arm head 62 and is disposed at a position where the signal light input port 11 is to be attached. Note that the test port 50b is also held by another manipulator 60 in the same manner as the test port 50a, and is arranged at the planned mounting position of the local light input port 13.

  FIG. 11A is a block diagram showing a configuration for preparing test light. In this configuration, a bias voltage is applied from the bias power source 111 to the light source 112 (for example, a semiconductor laser) to generate test light. This test light is introduced into the polarization control element 113 and its polarization plane is controlled. Thus, the test light has two polarization components that simulate the two polarization components of the signal light. Thereafter, the test light passes through the optical coupler 114 and reaches the connector 116. One of the connectors 117 and 118 is selectively connected to the connector 116. A test port 50 a is optically coupled to the connector 117, and a power meter 119 is optically coupled to the connector 118. A power meter 115 is connected to the optical coupler 114. One power meter may be used in combination as the power meters 115 and 119. A configuration similar to the above is also prepared for the test port 50b.

  First, the connector 118 is connected to the connector 116. 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 is brought close to a predetermined intensity by adjusting the magnitude of the bias voltage. Next, the package 2 is removed from the alignment table 103 again and replaced with the standard mirror 104. Then, the connector 117 is connected to the connector 116, and the test ports 50a and 50b are opposed to the light reflecting surface 104a of the standard mirror 104. When test light is output from the light source 112 in this state, the test light is emitted from the test ports 50a and 50b, then reflected by the light reflecting surface 104a, and is incident on the test ports 50a and 50b again. The intensity of the test light is detected by the power meter 115 via the optical coupler 114. By adjusting the optical axis direction of the test ports 50a and 50b to maximize the light detection intensity, the optical axis direction of the test port 50a (or 50b) can be aligned with the optical axis direction of the standard mirror 104. Thereafter, as shown in FIG. 11B, the standard mirror 104 is removed again from the alignment table 103 and replaced with the package 2.

  Subsequently, the polarization plane of the test light entering the package 2 from the test port 50a is adjusted (first step). For this purpose, a test jig having a polarizing beam splitter and two monitor PDs is arranged in the rear stage of the test port 50a in the package 2 (for example, the mounting position of the VOA 23). This test jig is formed by attaching a monitoring PD to each of two light emitting ends of a polarizing beam splitter, for example. Alternatively, this test jig may be one in which each of the two light emitting ends of the polarizing beam splitter and the monitor PD are optically coupled to each other and mounted on a common substrate. Then, the test light is provided in the package 2 through the test port 50a, and the intensity of the two polarization components branched by the polarization beam splitter is detected in each monitor PD, and these intensities are made substantially equal to each other, The polarization control element 113 adjusts the polarization plane of the test light. In this step, instead of the package 2, a simulation module on which a polarization beam splitter and two monitor PDs are mounted may be prepared and mounted on the alignment table 103 to adjust the polarization plane. .

  In the polarization adjustment described above, output signals from the two monitor PDs included in the test jig may be taken out from any terminal 3 of the package 2. In addition, when the test jig is provided with terminals for taking out output signals from the two monitor PDs, the polarization adjustment described above may be performed before the package 2 is placed on the alignment table 103. Good.

  In this step, the test ports 50a and 50b are further aligned. First, the intensity of the test light entering the package 2 from the test port 50a is detected by the PD built in the optical 90-degree hybrid element 32a. Then, while referring to the intensity of the detected test light, the test port 50a is moved in the direction in which the intensity increases, thereby performing alignment in a plane perpendicular to the optical axis of the test port 50a. Similarly, the intensity of the test light entering the package 2 from the test port 50b is detected by the PD built in the optical 90-degree hybrid element 32b. Then, while referring to the intensity of the detected test light, the test port 50b is moved in the direction in which the intensity increases, thereby performing alignment in a plane perpendicular to the optical axis of the test port 50b. The mode field diameter of the test light is as large as 300 μm, for example, while the light input ends of the optical 90-degree hybrid elements 32a and 32b 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 optical 90-degree hybrid elements 32a and 32b is weak, it is possible to obtain a detection signal that determines the optical axis of the test light.

  The positions of the test ports 50a and 50b in the optical axis direction can be determined by bringing the end surfaces of the test ports 50a and 50b into contact with the one end surface 2b of the package 2.

  Subsequently, each optical component that requires alignment is placed on the optical path between the test port 50a or 50b and the optical 90-degree hybrid elements 32a and 32b, and the PD (or the built-in optical 90-degree hybrid elements 32a and 32b) (or These optical components are aligned while referring to the intensity of the test light detected in the monitor PD 24). Further, these optical components are fixed in the package 2. In addition, the order of alignment and fixing of these optical components is not restricted to the following description, It can carry out in arbitrary orders.

  In this step, the VOA bias power source 120 and the voltage monitors 121 and 122 are connected to the package 2 as shown in FIG. The VOA bias power supply 120 applies a bias voltage to the VOA 23 when the VOA 23 described later is installed. The voltage monitors 121 and 122 monitor voltage signals from the amplifiers 39a and 39b, respectively.

  First, the beam splitter 22 (see FIGS. 1 and 2) is aligned and fixed. In other words, the angle (optical axis direction) of the beam splitter 22 is adjusted using the visible laser light of the autocollimator 102 passing through the space above the package 2 with the front surface of the beam splitter 22 as a reflection surface. Then, the beam splitter 22 is moved onto the VOA carrier 20 while maintaining the direction of the beam splitter 22. Then, while moving the beam splitter 22 in the front-rear direction on the VOA carrier 20, the mounting position at which the received light intensity at the monitor PD 24 is maximized is determined. After determining the mounting position, the beam splitter 22 is fixed to the VOA carrier 20 using an adhesive resin.

  Next, as shown in FIG. 12, the first mirror 30 and the second mirror 37 are aligned and fixed. First, the angles of the mirrors 30 and 37 (optical axis direction) are adjusted using the visible laser light of the autocollimator 102 passing through the upper space of the package 2 with the front surfaces of these mirrors 30 and 37 as reflection surfaces. . Then, the mirrors 30 and 37 are moved onto the carrier 40 while maintaining the orientation of the mirrors 30 and 37. Test light from the test ports 50a and 50b is made incident on these mirrors 30 and 37, and the test light reflected by the mirrors 30 and 37 is detected by the built-in PD of the light 90-degree hybrid elements 32a and 32b. Then, the angle at which the received light intensity at the built-in PD is maximized is determined while slightly changing the angles of the mirrors 30 and 37. After the angle is determined, the mirrors 30 and 37 are fixed to a predetermined mounting position using an adhesive resin.

  Subsequently, the first lens system 28, the second lens system 31, the third lens system 36, and the fourth lens system 38 are aligned and fixed. First, as shown in FIG. 13, the focusing lenses 28a, 31a, 36a, and 38a (that is, the focusing lenses near the light 90-degree hybrid elements 32a and 32b) are aligned and fixed. These condensing lenses 28a, 31a, 36a, and 38a are arranged at predetermined mounting positions, and test light from each test port 50a, 50b is made incident and passed through the condensing lenses 28a, 31a, 36a, and 38a. Test light is detected by the built-in PD of the optical 90-degree hybrid elements 32a and 32b. Then, while slightly changing the positions and angles of the condenser lenses 28a, 31a, 36a, and 38a, the position and angle at which the received light intensity at the built-in PD is maximized are determined. After determining the position and angle, the condenser lenses 28a, 31a, 36a, and 38a are fixed using an adhesive resin. Subsequently, as shown in FIG. 14, the condenser lenses 28b, 31b, 36b, and 38b are aligned and fixed. These alignment and fixing methods are the same as the alignment and fixation methods of the condenser lenses 28a, 31a, 36a, and 38a described above.

  Subsequently, as shown in FIG. 15, the collimating lens 25 is aligned and fixed. As described above, the condensing lens is mounted on the signal light input port 11 shown in FIGS. 1 and 2, and the collimating lens 25 is made to coincide with the focal point of the converging lens 25. The position in the optical axis direction is determined. By arranging the VOA 23 at the position of the beam waist formed between the condenser lens and the collimating lens 25, the signal light can be passed through the narrow opening of the VOA 23, and the extinction ratio in the VOA 23 is increased. be able to. For this reason, instead of the test port 50a, the collimating lens 25 is centered with another test port 50c on which a condensing lens having the same focal length as that mounted on the signal light input port 11 is mounted. Use it. Accordingly, in this step, the test port 50a is replaced with the test port 50c.

  Specifically, the standard mirror 104 is installed again on the alignment table 103 instead of the package 2, and the connector 116 shown in FIG. 11 is changed from the test port 50a to the test port 50c. Then, the test port 50c is arranged at a position where the signal light input port 11 is to be attached using the manipulator 60 shown in FIG. 10, and is made to face the light reflecting surface 104a of the standard mirror 104. In this state, test light is output from the test port 50 c, the optical axis direction of the test port 50 c is adjusted to maximize the light intensity detected by the power meter 115, and the light of the test port 50 c is aligned with the optical axis direction of the standard mirror 104. Match the axial direction. Next, the polarization plane of the test light entering the package 2 from the test port 50c is adjusted using the test jig described above. That is, the test light is provided in the package 2 via the test port 50c, and the intensity of two polarization components branched by the polarization beam splitter of the test jig is detected by each monitor PD, and these intensities are substantially reduced. The polarization plane of the test light is adjusted by the polarization control element 113. Further, the test port 50c is moved in the direction in which the intensity increases while detecting the intensity of the test light incident from the test port 50c into the package 2 by the PD built in the 90-degree optical hybrid element 32a. Alignment is performed in a plane perpendicular to the optical axis of the port 50c. The position of the test port 50c in the optical axis direction can be determined by bringing the end surface of the test port 50c into contact with the one end surface 2b of the package 2.

  Next, the collimator lens 25 is moved to the mounting position, the test light from the test port 50c is made incident on the collimator lens 25, and the intensity of the test light that has passed is detected by the built-in PD of the light 90-degree hybrid element 32a. Then, while slightly changing the position of the collimating lens 25, the position (front-rear direction, left-right direction, and up-down direction) at which the received light intensity at the built-in PD is maximized is determined. After the determination, the collimating lens 25 is fixed using an adhesive resin.

  Subsequently, as shown in FIG. 16, the VOA 23 is mounted on the VOA carrier 20. In this step, first, the VOA 23 is mounted on the VOA base 44 shown in FIG. 4, and the pair of electrodes of the VOA 23 and the pair of metal bodies 45 and 46 of the VOA base 44 are electrically connected by wires 47a and 47b. To do. Then, the VOA base 44 on which the VOA 23 is mounted is disposed on the optical path of the test light introduced into the package 2 from the test port 50c (second process). At this time, an ultraviolet curable resin is applied on the VOA carrier 20 in a predetermined thickness (for example, 100 μm or more) in advance, and the VOA 23 is held in a state separated from the surface of the VOA carrier 20 by a certain distance (for example, 100 μm). Then, the voltage from the outside of the package 2 is applied between the pair of metal bodies 45 and 46 while repeatedly increasing or decreasing between 0 and 5 V (the period of increase or decrease in one cycle is, for example, 1 second or less). In parallel with this, the VOA 23 is moved in a direction parallel to the bottom surface 2a and perpendicular to the optical axis to change the position little by little. At the same time, the intensities of the two polarization components of the test light attenuated by the VOA 23 are Monitoring is performed using the built-in PD of the optical 90-degree hybrid elements 32a and 32b.

  Here, FIG. 17 is a perspective view showing how the VOA 23 is mounted on the VOA carrier 20. As shown in FIG. 17, in this step, the VOA 23 is placed on the optical path of the test light while the VOA base 44 with the VOA 23 mounted is gripped by the manipulator 70. The manipulator 70 has two arms 71 and 72 that can freely change positions and angles (specifically, positions in three axial directions orthogonal to each other and angles around two axes perpendicular to the optical axis direction of the VOA 23). And a pair of arm heads 73, 74 provided at the tips of these arms 71, 72. The VOA base 44 is sandwiched and held by a pair of arm heads 73 and 74. At this time, one arm head 73 is in contact with one metal body 45 (see FIG. 4) of the VOA base 44 and is electrically connected to the one metal body 45. The other arm head 74 is in contact with the other metal body 46 (see FIG. 4) of the VOA base 44 and is electrically connected to the other metal body 46. When the attenuation of the VOA 23 is changed, the pair of metal bodies 45, the VOA bias power source 120 shown in FIG. 11 (b) is passed through the arms 71 and 72 and the arm heads 73 and 74 of the manipulator 70. A voltage is applied across 46.

  Thereafter, the VOA 23 is fixed at a position where the difference in attenuation between the two polarization components of the test light after attenuation falls within an allowable range (third step). At this time, an output difference from the built-in PD of the optical 90-degree hybrid elements 32a and 32b may be regarded as a difference in attenuation between the two polarization components of the test light. The VOA 23 is mounted with an inclination of a predetermined angle (for example, 7 ° or less) with respect to the optical axis connecting the condenser lens and the collimating lens 25 in the test port 50c. This is to prevent the reflected light from returning to the signal light input port 11.

  FIG. 18 is a graph showing an example of the attenuation characteristic of the VOA 23. Graphs G11 and G12 show the relationship between the voltage applied to the VOA 23 (unit: V) and the degree of attenuation (left vertical axis, unit: dB) of each polarization component (graph G11: X component, graph G12: Y component). Indicates. The graph G13 shows the relationship between the voltage applied to the VOA 23 (unit: V) and the difference in attenuation of each polarization component (right vertical axis, unit: dB). When the applied voltage is 0 V, the shutter 23b (see FIG. 5) of the VOA 23 is fully opened.

  As shown in FIG. 18, in the VOA 23, the higher the applied voltage, the greater the attenuation, but even with the same applied voltage, the attenuation is slightly different for each polarization component. Then, the difference in the degree of attenuation tends to increase as the applied voltage increases. In the present embodiment, by adjusting the position of the VOA 23 in the three orthogonal directions (the optical axis direction, the direction orthogonal to the optical axis and parallel to the bottom surface 2a, and the direction orthogonal to the optical axis and perpendicular to the bottom surface 2a) The difference in the degree of attenuation of the polarization component is within an allowable range. In one example, when the applied voltage is 4.5 V, the attenuation of each polarization component is 12 dB or more, and the position of the VOA 23 is adjusted, and the difference in attenuation between the two polarization components is in the range of 0 V to 5.0 V. Within ± 0.5 dB.

  Subsequently, as shown in FIG. 19, a lid 2c for closing the package 2 is attached by a seam seal, and the inside of the package 2 is hermetically sealed. Then, as shown in FIG. 20, the test port is replaced with the original signal light input port 11 and the local light input port 13, and the signal light input port 11 and the local light input port 13 are aligned and fixed. Specifically, simulated signal light is introduced from the signal light input port 11, and the intensity of the signal light is detected by the built-in PD of the optical 90-degree hybrid element 32a. Then, the position of the signal light input port 11 is slightly changed while referring to the intensity of the detected signal light, and the position where the light reception intensity at the built-in PD is maximized is determined. Similarly, local light is actually introduced into the local light input port 13 and the intensity of the local light is detected by the built-in PD of the light 90-degree hybrid element 32b. Then, the position of the local light input port 13 is slightly changed while referring to the detected local light intensity, and the position where the received light intensity at the built-in PD is maximized is determined. After the determination, the signal light input port 11 and the local light input port 13 are fixed to the package 2.

  The effects obtained by the method for manufacturing the optical receiver module 1A according to the present embodiment described above will be described. The manufacturing method according to the present embodiment prepares test light having two polarization components simulating two polarization components of signal light, and makes the intensity of the two polarization components of the test light substantially equal to each other; A second step of arranging the VOA 23 on the optical path of the test light and changing the attenuation of the VOA 23 and moving the VOA 23 while monitoring the intensities of the two polarization components of the attenuated test light, and the attenuated test light And a third step of fixing the VOA 23 at a position where the difference in attenuation between the two polarization components falls within an allowable range. According to such a method, the attenuation of the two polarization components included in the signal light can be made close to each other.

  Further, as in the present embodiment, in the first step, the test port 50c that simulates the signal light input port 11 of the optical receiver module 1A is arranged at a position where the signal light input port 11 is to be installed, and the test port 50c is interposed. A step of inputting the test light into the optical receiver module 1A and a step of aligning the test port 50c may be included. Thereby, the position accuracy of the optical axis of the test light can be increased, and the position of the VOA 23 can be adjusted more accurately.

  Further, as in this embodiment, in the second step, the intensities of the two polarization components of the test light are monitored using the PDs built in the optical 90-degree hybrid elements 32a and 32b. The output difference from the PD may be regarded as a difference in attenuation between the two polarization components of the test light. As a result, the difference in attenuation between the two polarization components can be easily detected.

  Conventionally, many voltage-driven MEMS VOAs have been employed for coherent optical receiver modules. The opening diameter of the MEMS type VOA is as small as about 70 μm, for example. Therefore, for example, when mounting the VOA immediately before the PD, it is preferable to mount the VOA while aligning the position of the opening of the VOA with the PD visually. However, in the coherent optical receiver module of this embodiment, the VOA 23 is not disposed immediately before the PD, but is disposed between optical components such as the beam splitter 22 and the collimating lens 25. Therefore, in this embodiment, the test light is incident on the VOA 23, and the relative positional relationship between the shutter 23b and the test light is appropriately adjusted while opening and closing the shutter 23b of the VOA 23. However, since the size of the VOA is generally very small, it is difficult to adjust the position of the VOA while directly applying a voltage to the VOA electrode.

  For this problem, in the second embodiment, in the second step, the VOA 23 is mounted on the VOA base 44 having the pair of metal bodies 45 and 46 corresponding to the pair of electrodes of the VOA 23, and the pair of electrodes and the pair of electrodes are mounted. The attenuation of the VOA 23 is changed by electrically connecting the metal bodies 45 and 46 and applying a voltage between the pair of metal bodies 45 and 46. According to such a configuration, the position of the VOA 23 can be easily adjusted by moving the VOA base 44 while applying a voltage to the pair of metal bodies 45 and 46.

  Further, as in the present embodiment, in the second step, while the VOA base 44 with the VOA 23 mounted is gripped by the manipulator 70, the VOA 23 is placed on the optical path of the test light, and a pair of A voltage may be applied between the metal bodies 45 and 46. Thereby, the position of the VOA 23 can be adjusted more easily.

  DESCRIPTION OF SYMBOLS 1A ... Optical receiver module, 2 ... Package, 2a ... Bottom surface, 2b ... One end surface, 2c ... Cover, 3 ... Terminal, 10 ... Single mode fiber, 11 ... Signal light input port, 12 ... Polarization maintaining fiber, 13 ... Station Light emitting input port, 20 ... VOA carrier, 22 ... beam splitter, 23 ... variable optical attenuator (VOA), 23a ... opening, 23b ... shutter, 23c, 23e ... comb electrode, 23d ... elastic member, 25 ... collimator Lens, 26 ... Polarizing beam splitter, 27 ... Skew adjusting element, 28 ... First lens system, 29 ... [lambda] / 2 plate, 30, 37 ... Mirror, 31 ... Second lens system, 32a, 32b ... 90 degree optical hybrid element 33 ... Polarizer, 34 ... Beam splitter, 35 ... Skew adjustment element, 36 ... Third lens system, 38 ... Fourth lens system, 39a, 39b ... Amplifier, 4 ... carrier, 44 ... VOA base, 45, 46 ... metal body, 47a, 47b ... wire, 50a-50c ... test port, 51a, 51b ... 90 degree hybrid coupler, 60, 70 ... manipulator, 61, 71, 72 ... Arm, 62, 73, 74 ... arm head, 101 ... support base, 102 ... autocollimator, 103 ... alignment base, 104 ... standard mirror, 111 ... bias power source, 112 ... light source, 113 ... polarization control element, 114 ... light Coupler 115... Power meter 116 to 118 Connector 119 Power meter 120 VOA bias power supply 121 Voltage monitor

Claims (5)

By attenuating an input signal light including two polarization components whose polarization directions are orthogonal to each other by a variable optical attenuator, and performing a product operation of each of the two polarization components of the input signal light after attenuation and the local oscillation light A method for manufacturing a coherent optical receiver module for extracting information, comprising:
Preparing a test light having two polarization components simulating the two polarization components of the input signal light, and making the intensities of the two polarization components of the test light substantially equal to each other;
The variable optical attenuator is disposed on the optical path of the test light, and while monitoring the intensity of the two polarization components of the test light after attenuation, the attenuation of the variable optical attenuator is changed and the variable light is changed. A second step of moving the attenuator;
A third step of fixing the variable optical attenuator at a position where a difference in attenuation between the two polarization components of the test light after attenuation falls within an allowable range;
A method for manufacturing a coherent optical receiver module. The first step includes
Placing a test port simulating the signal light input port of the coherent light receiving module at a position where the signal light input port is to be installed, and inputting the test light into the coherent light receiving module via the test port; ,
Aligning the test port; and
The manufacturing method of the coherent optical receiver module of Claim 1 containing this. The coherent optical receiver module is
A first 90-degree hybrid coupler that performs a product operation of one of the polarization components and the local oscillation light;
A first photodiode for detecting output light after product operation from the first 90-degree hybrid coupler;
A second 90-degree hybrid coupler that performs a product operation of the other polarization component and the local oscillation light;
A second photodiode for detecting output light after a product operation from the second 90-degree hybrid coupler;
With
In the second step, the intensity of the two polarization components of the test light is monitored using the first and second photodiodes,
3. The coherent light receiving module according to claim 1, wherein, in the third step, an output difference from the first and second photodiodes is regarded as a difference in attenuation between the two polarization components of the test light. 4. Manufacturing method.   In the second step, the variable optical attenuator is mounted on a base member having a pair of metal bodies corresponding to the pair of electrodes of the variable optical attenuator, and the pair of electrodes and the pair of metal bodies are electrically connected. The coherent optical receiver module according to any one of claims 1 to 3, wherein the attenuation of the variable optical attenuator is changed by connecting the optically connected and applying a voltage between the pair of metal bodies. Method.   In the second step, the variable optical attenuator is disposed on the optical path of the test light while holding the base member on which the variable optical attenuator is mounted with a manipulator, and the pair of the pair of optical attenuators is interposed via the manipulator. The manufacturing method of the coherent optical receiver module of Claim 4 which applies a voltage between metal bodies.

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