JP6641931B2 - Optical module assembling method and optical receiver assembling method - Google Patents

Description

  The present invention relates to an optical module assembling method and an optical receiver assembling method.

  Patent Literature 1 discloses a technique relating to a coherent light receiving device. FIG. 15 schematically shows the configuration of the coherent light receiving device. In the coherent optical receiver 100 shown in FIG. 15, the optical waveguide substrate 101, the optical 90-degree hybrid circuits 111 and 112, the plurality of light receiving elements 134 and 135 for signal light, and the light receiving element 104 for monitoring signal light level are provided in the housing 105. Is housed in The signal light L1 and the local light L2 are input from the first end face 101a of the optical waveguide substrate 101 to the optical waveguides 106 and 107 in the optical waveguide substrate 101, respectively.

  The signal light level monitoring light receiving element 104 receives one of the signal lights L1 branched by the light branching element 131 on the optical waveguide 106. The other signal light L <b> 1 is further split by the optical splitter 132, and one of the split signal lights L <b> 1 is input to the 90-degree optical hybrid circuit 111, and the other is input to the 90-degree optical hybrid circuit 112. The local light L2 is branched by the optical branching element 133, one local light L2 is input to the 90-degree optical hybrid circuit 111, and the other local light L2 is input to the 90-degree optical hybrid circuit 112. The light intensity of the interference light output from the light 90-degree hybrid circuits 111 and 112 is detected by a plurality of signal light receiving elements 134 and 135.

JP-A-2005-08500

  In the optical receiving apparatus 100 shown in FIG. 15, optical components such as optical splitters 131, 132, and 133 are provided as an optical system for inputting signal light and local light to the optical 90-degree hybrid circuits 111 and 112. . These optical components have an optical surface that transmits and reflects light input to the optical component, and this optical surface is positioned with respect to an optical axis when signal light and local light are input into the housing 105. It is inclined at a predetermined angle. In order to improve the efficiency of incidence of signal light and local light on the 90-degree light hybrid circuits 111 and 112, it is necessary to precisely adjust the angle of the optical surface with respect to the optical axis of the incident light.

  In general, when an optical surface is provided perpendicular to the optical axis of incident light, an autocollimator is used to reflect the optical axis of light incident on the optical surface from the autocollimator and the optical surface to return to the autocollimator. By matching the optical axis of the light, the angle of the optical surface can be easily adjusted with respect to the optical axis of the incident light. However, when the optical surface is inclined with respect to the optical axis of the incident light, the angle adjustment of the optical surface is not easy.

  The present invention has been made in view of such a problem, and assembles an optical module that can easily adjust the angle of an optical surface even when the optical surface is inclined with respect to a predetermined optical axis. It is an object to provide a method and a method for assembling an optical receiver.

  In order to solve the above-described problem, an optical module assembling method according to an embodiment of the present invention includes an optical input port attached to one end surface of a housing, and an optical axis of the optical input port disposed in the housing. An optical module having an optical component having an optical surface forming an angle other than 0 ° and 90 ° with respect to a pair of surfaces parallel to each other and one of the pair of surfaces. Mounting a jig having a reference surface forming a predetermined angle on the alignment rotation stage while pressing one of the pair of surfaces against a mounting reference surface provided on the alignment rotation stage; and A process in which the reference surface is oriented in a predetermined direction by rotating the stage, a process in which the casing is mounted on the alignment rotary stage while pressing the housing instead of the jig, and a state in which the optical surface is oriented in a predetermined direction And disposing the optical component in the housing.

  An assembling method of an optical receiver according to an embodiment of the present invention is an assembling method of an optical receiver. The optical receiver has a housing, a signal light input port fixed to one end face of the housing, and a signal light input port for inputting signal light including two polarization components orthogonal to each other from outside, and a signal light input port fixed to one end face. A local light input port that has an optical axis parallel to the optical axis of the port and externally inputs local light mainly including one polarization component, and signal light that is disposed in the housing and has one polarization component A first multi-mode interference element that interferes with the local light and recovers information contained in the one polarization component, and a signal light and a local light that are disposed in the housing and have the other polarization component. A second multi-mode interference element that causes interference to recover information contained in the other polarization component, and a predetermined angle other than 0 ° and 90 ° with respect to the optical axes of the signal light input port and the local light input port. A first optical component having an optical surface, and first and second signal light and local light. A light-collecting component that focuses light toward the second multi-mode interference element is disposed in the housing, and optically connects the signal light input port and the local light input port to the first and second multi-mode interference elements. And an optical system for coupling. The assembling method includes a step of disposing the first and second multimode interference elements in a housing, a pair of surfaces parallel to each other, and a reference surface forming a predetermined angle with any one of the pair of surfaces. The jig is mounted on the centering rotary stage while pressing one of the pair of surfaces against the mounting reference surface provided on the centering rotary stage, and the centering rotary stage is rotated to direct the reference surface in a predetermined direction. Mounting the housing on the alignment rotary stage while pressing the housing against the mounting reference surface instead of the jig, and disposing the first optical component in the housing with the optical surface oriented in a predetermined direction; The alignment of the two simulated ports instead of the optical input port and the local light input port is performed by connecting the test light from the two simulated ports to the first and second multi-mode interference elements via the first optical component. Perform the process while referring to the incident intensity and adjust the focusing part. Is performed with reference to the incident intensity of the test light on the first and second multi-mode interference elements. The two simulated ports are replaced with a signal light input port and a local light input port, respectively. Aligning the signal light input port and the local light input port with reference to the incident light intensity of the signal light and the local light to the multimode interference device, and fixing the signal light input port and the local light input port to the housing. And

  According to the method of assembling an optical module and the method of assembling an optical receiver according to the present invention, it is possible to easily adjust the angle of an optical surface even when the optical surface is inclined with respect to a predetermined optical axis.

FIG. 1 is a plan view showing a configuration of an optical receiver (optical module) which is an object of an assembling method according to an embodiment of the present invention. FIG. 2 schematically shows a connection relation of each optical component inside the optical receiver. FIG. 3 shows a process of arranging a carrier, an MMI element mounted on the MMI carrier, and a circuit board on a base. FIG. 4 shows a process of mounting the base on which the carrier, the MMI element, and the circuit board are mounted on the bottom surface of the housing. FIG. 5 shows a process of mounting the monitoring PD on the carrier via the PD carrier. FIG. 6 is a diagram for explaining details of a step of arranging the first optical component. FIG. 7 is a diagram for explaining details of a step of arranging the first optical component. FIG. 8 is a diagram for explaining details of a step of arranging the second optical component. FIG. 9 shows a step of disposing the third optical component in the housing. FIG. 10 shows a step of performing alignment and fixing of the lens system. FIG. 11 shows a step of arranging the VOA on the VOA carrier. FIG. 12 shows a process of replacing the test port with the original signal light input port and local light input port, and performing alignment and fixing of the signal light input port and the local light input port. FIG. 13 schematically illustrates a connection relationship between optical components included in an optical receiver as a comparative example. FIGS. 14A and 14B are diagrams for conceptually explaining the phase shift. FIG. 15 schematically shows a configuration of a coherent optical receiver described in the prior art document.

  Specific examples of an optical module assembling method and an optical receiver assembling method according to an 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 exemplifications, but is indicated by the appended claims, and is intended to include all modifications within the meaning and scope equivalent to the appended claims. In the following description, the same elements will be denoted by the same reference symbols in the description of the drawings, without redundant description.

  FIG. 1 is a plan view showing an optical receiver 1A as an optical module which is an object of an assembling method according to an embodiment of the present invention. FIG. 2 schematically shows a connection relationship between optical components inside the optical receiver 1A. The optical receiver 1A causes local oscillation light (hereinafter, referred to as local light) L2 to interfere with the phase-modulated received signal light (hereinafter, referred to as signal light) L1, and extracts information included in the signal light L1. In the present embodiment, the signal light L1 includes two polarization components orthogonal to each other, and includes phase components orthogonal to each other, that is, information modulated at 0 ° ⇔180 ° and 90 ° と 270 °. This is an optical module for a signal modulated by so-called DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) including information phase-modulated by. Note that the local light L2 mainly includes one polarization component, and is typically linearly polarized light.

  As shown in FIG. 1, the optical receiver 1 </ b> A includes a substantially rectangular parallelepiped housing (housing) 2, and a signal light input port 11 and a local light input port 13 fixed to one end surface 2 b of the housing 2. . The optical axis of the signal light input port 11 and the optical axis of the local light input port 13 are parallel to each other. The signal light input port 11 is connected to a single mode fiber (Single Mode Fiber: SMF), and receives the signal light L1 from outside the optical receiver 1A via the SMF. The local light input port 13 is connected to a polarization maintaining fiber (PMF), and receives a local light L2 from outside the optical receiver 1A via the PMF. The signal light L1 and the local light L2 are input into the housing 2 via the signal light input port 11 and the local light input port 13, respectively. The light source of the local light L2 is, for example, a semiconductor laser diode (Laser Diode: LD).

  The signal light input port 11 is formed by integrating a cylindrical sleeve for receiving a ferrule attached to the tip of the SMF and a lens holder containing a collimator lens, and the lens holder is fixed to one end surface 2 b of the housing 2. ing. The signal light L <b> 1 that has propagated in the SMF is converted into collimated light by the collimating lens and enters the housing 2. The local light input port 13 is formed by integrating a cylindrical sleeve for receiving a ferrule attached to the tip of the PMF and a lens holder containing a collimator lens, and the lens holder is fixed to one end surface 2 b of the housing 2. ing. The local light L2 that has propagated in the PMF is converted into collimated light by the collimating lens and enters the housing 2.

  Each of the input ports 11 and 13 is constituted by a combination of a plurality of columnar components. For the component having the largest outer diameter (typically a lens holder) among the plurality of columnar components, a portion facing each other is used. Are flat surfaces 11a and 13a. Thus, the distance between the optical axis of the signal light input port 11 and the optical axis of the local light input port 13 can be reduced. The outer diameter of the component is, for example, 5.5 mm, and if no flat surface is provided, the optical axis interval between these ports 11, 13 is 11 mm. However, by providing the flat surfaces 11a and 13a, in the present embodiment, the distance between the optical axes of these ports 11 and 13 can be made 10 mm or less. In this embodiment, the distance between the optical axes of these ports 11 and 13 is 3.4 mm.

  The housing 2 is made of Kovar. A plurality of terminals 3 are provided on the other side surface of the four side surfaces of the housing 2 except the one end surface 2b. The plurality of terminals 3 are drawn from the lowermost layer of the multi-layered ceramics constituting each side surface. The plurality of terminals 3 include a terminal for extracting a reception signal extracted from the signal light L1 to the outside of the optical receiver 1A, a terminal for supplying a power supply voltage and a bias to an electronic circuit inside the housing 2, a ground terminal, and the like. It is. From four corners of the bottom surface of the housing 2, flanges 4 for fixing the housing 2 to a circuit board or the like are drawn out.

  The optical receiver 1A has, in addition to the above configuration, a first MMI element 32a and a second MMI element that are multi-mode interference (MMI) elements for causing the signal light L1 and the local light L2 to interfere with each other. An MMI element 32b is provided. The MMI element 32a causes one of the polarization components of the signal light L1 to interfere with the local light L2, and recovers information contained in the one of the polarization components. In addition, the MMI element 32b causes the other polarization component of the signal light L1 to interfere with the local light L2, and recovers information included in the other polarization component. The MMI elements 32a and 32b are, for example, optical 90 ° hybrid elements. The MMI elements 32a and 32b are arranged side by side with respect to the one end face 2b.

  The optical receiver 1A further includes an optical system that optically couples the input ports 11, 13 and the MMI elements 32a, 32b. This optical system includes a polarization splitting element (Polarization Beam Splitter: PBS) 26 and a skew adjusting element for optically coupling the signal light input terminals of the two MMI elements 32 a and 32 b to the signal light input port 11. 27, a lens system (light collecting part) 28, a wave plate (λ / 2 plate) 29, a total reflection mirror 30, and a lens system (light collecting part) 31. Further, this optical system includes a total reflection mirror 21, a beam splitter (BS) 22, and a variable optical attenuator (VOA) 23 disposed on an optical path between the PBS 26 and the signal light input port 11. Including.

  These optical components arranged on the optical path between the signal light input port 11 and the MMI elements 32a and 32b are all housed in the housing 2. Specifically, as shown in FIG. 1, the total reflection mirror 21 and the BS 22 are mounted on a carrier 20a provided on the bottom surface of the housing 2. The VOA 23 is mounted on a carrier 20b provided on the bottom surface of the housing 2 independently of the carrier 20a. Other optical components are mounted on a carrier 20d provided on a base 20c independently of the carriers 20a and 20b. The carriers 20a, 20b and 20d are made of AlN. The base 20c is made of CuW.

  The total reflection mirror 21 is a flat mirror and is arranged on the optical axis of the signal light input port 11. The total reflection mirror 21 has a light reflection surface optically coupled to the signal light input port 11. The total reflection mirror 21 receives the signal light L1 on the light reflecting surface and reflects the entire signal light L1. The optical axis of the signal light L1 before reflection and the optical axis of the signal light L1 after reflection form a substantially right angle. In other words, the optical axis of the reflected signal light L <b> 1 is substantially perpendicular to the optical axis of the signal light input port 11.

  The BS 22 may be configured by a flat light-transmitting member having a front surface (optical surface) and a back surface facing each other, and a dielectric multilayer filter formed on the front surface. The reflectance of the dielectric multilayer filter is, for example, 90% or more at the wavelength of the signal light L1, and is 95% in this example. The signal light L1 enters the front surface of the BS 22 and is split by the dielectric multilayer filter. One of the branched signal lights (monitor light L10) passes through the dielectric multilayer filter and exits from the back surface of BS22. The other signal light L11 is reflected by the dielectric multilayer filter. The optical axis of the incident signal light L1 and the optical axis of the reflected signal light L11 form a substantially right angle. Thus, the optical axis of the reflected signal light L11 is parallel to the optical axis of the signal light input port 11.

  The optical receiver 1A further includes a monitoring photodiode (monitor PD) 24. As shown in FIG. 1, the monitor PD 24 is fixed to a side surface of the PD carrier 24a, and the PD carrier 24a is mounted on the carrier 20a. Further, as shown in FIG. 2, the monitor PD 24 is arranged on the back side of the BS 22. The monitor PD 24 is optically coupled to the back surface of the BS 22 and receives the monitor light L10 transmitted through the BS 22. The monitor PD 24 outputs a detection signal corresponding to the received monitor light L10. The carrier 20a has a wiring pattern for transmitting the detection signal, and the wiring pattern is connected to the terminal 3 via a bonding wire.

  The VOA 23 is arranged on the optical path of the signal light L11 reflected by the BS 22, in other words, on the optical axis of the signal light input end of the MMI element 32a, and attenuates the signal light L11 as necessary. The amount of attenuation is set based on the detection signal output from the monitor PD 24 described above. A control signal for setting the attenuation is input from the outside of the optical receiver 1A via the terminal 3. For example, when the monitor PD 24 detects the excessive input state, the attenuation of the VOA 23 is increased, and the intensity of the signal light L11 traveling to the MMI elements 32a and 32b is reduced.

  The PBS 26 is a plate-shaped member and has a light incident surface (optical surface) optically coupled to the BS 22 via the VOA 23. The PBS 26 splits the signal light L12 having one polarization component (for example, X polarization component) and the signal light L13 having the other polarization component (for example, Y polarization component). The branching ratio at this time is 50%. The signal light L12 passes through the PBS 26. The signal light L13 is reflected by the light incident surface of the PBS 26, and travels straight in a direction intersecting the traveling direction of the signal light L12. The optical axis of the signal light L12 and the optical axis of the signal light L13 make a substantially right angle. The signal light L13 moves away from the local light L2. In this case, the traveling direction of the signal light L13 is opposite to the traveling direction of the signal light L1 reflected by the total reflection mirror 21.

  The skew adjustment element 27 and the lens system 28 are arranged on the optical path between the PBS 26 and the signal light input end of the MMI element 32a (that is, on the optical axis of the signal light input end of the MMI element 32a). The signal light L12 that has traveled straight through the PBS 26 passes through the skew adjustment element 27. The skew adjusting element 27 is, for example, a block material made of Si. The skew adjusting element 27 increases the optical path length between the PBS 26 and the signal light input end of the MMI element 32a equivalently, thereby reducing the optical path length of the signal light L13 with respect to the signal light L12. Compensate for delays due to differences. That is, the signal light L13 has a longer distance from the PBS 26 to the MMI element 32b by the distance from the PBS 26 to the total reflection mirror 30. The skew adjusting element 27 gives a phase delay of the signal light L13 corresponding to the distance to the signal light L12. Thereafter, the signal light L12 is condensed by the lens system 28 on the signal light input end of the MMI element 32a. The lens system 28 includes two condenser lenses 28a and 28b arranged in the optical axis direction.

  Further, the λ / 2 plate 29, the total reflection mirror 30, and the lens system 31 are arranged on the optical path between the PBS 26 and the signal light input end of the MMI element 32b. The signal light L13 having the Y-polarized component reflected (branched) by the PBS 26 is reflected again by the total reflection mirror 30, and its optical axis coincides with the optical axis of the signal light input end of the MMI element 32b. Thereafter, the signal light L13 passes through the λ / 2 plate 29 arranged between the total reflection mirror 30 and the MMI element 32b. The λ / 2 plate 29 rotates the polarization direction of the signal light L13 by 90 °. Therefore, the polarization direction of the signal light L13 that has passed through the λ / 2 plate 29 matches the polarization direction of the other signal light L12 that has traveled straight through the PBS 26. After that, the signal light L13 is condensed by the lens system 31 on the signal light input end of the other MMI element 32b. The lens system 31 includes two condenser lenses 31a and 31b arranged in the optical axis direction. The λ / 2 plate 29 may be disposed anywhere on the optical path of the signal light L13, and may be disposed, for example, between the PBS 26 and the total reflection mirror 30.

  The optical module 1A includes polarizers 33, BS34, lens systems (light collecting components) 36 and 38 as optical components for optically coupling the local light input terminals of the two MMI elements 32a and 32b and the local light input port 13. Further included. These optical components are all housed in the housing 2. In the present embodiment, the skew adjusting element 27 and the total reflection mirror 30, which optically couple the signal light input terminals of the MMI elements 32a and 32b and the signal light input port 11, are used for the two signal lights L11 and L12. The skew adjusting element and the total reflection mirror arranged on the road are integrally formed. That is, the skew adjusting element 27 and the total reflection mirror 30 have two optical axes.

  The polarizer 33 determines the polarization direction of the local light L2 input from the local light input port 13. Thereby, even if the polarization direction of the local light to be maintained by the PMF coupled to the input port 13 is deviated when the housing 2 is assembled, the local light L2 having only a linearly polarized component of 0 ° or 90 ° in the polarization direction. Can be obtained. When the light source of the local light L2 is a semiconductor LD, the polarization of the component parallel to the active layer is generally elliptically polarized light. However, in order to obtain the oscillation stability, material reliability, desired output wavelength, and the like of the semiconductor LD, an active layer having lattice mismatch may be employed. In a laser beam output from an active layer having such a lattice mismatch, the minor axis of elliptically polarized light may be relatively large. Even in such a case, the polarizer 33 converts the local light L2 from elliptically polarized light to linearly polarized light.

  The BS 34 is a plate-shaped member, has a light incident surface (optical surface) optically coupled to the local light input port 13 through the polarizer 33, and transmits the local light L 2 passing through the polarizer 33 to two local light. It branches to the light emission L22, L23 with a branching ratio of 50%. One local light L22 transmits through the BS. The other local light L23 is reflected by the BS 34 and travels straight toward the total reflection mirror 30. The optical axis of the local light L22 and the optical axis of the local light L23 form a substantially right angle. In this embodiment, the local light L23 translates with the signal light L13.

  The skew adjusting element 27 and the lens system 38 are arranged on the optical path between the BS 34 and the local light input terminal of the MMI element 32a (that is, on the optical axis of the local light input terminal of the MMI element 32a). The local light L22 that travels straight through the BS 34 passes through the skew adjusting element 27. The skew adjusting element 27 compensates for the delay due to the difference in the optical path length of the local light L23 with respect to the local light L22 by equivalently increasing the optical path length of the local light L23 from the BS 34 to the local light input end of the MMI element 32a. . That is, the local light L23 has a longer distance from the BS 34 to the MMI element 32b by the distance from the total reflection mirror 30 than the local light L22. The skew adjusting element 27 gives the local light L22 a phase delay corresponding to the distance. Thereafter, the local light L22 is condensed by the lens system 38 on the local light input end of the MMI element 32a. The lens system 38 includes two condenser lenses 38a and 38b arranged in the optical axis direction.

  Further, the total reflection mirror 30 and the lens system 36 are arranged on the optical path between the BS 34 and the local light input terminal of the MMI element 32b. The local light L23 reflected (branched) by the BS 34 is reflected again by the total reflection mirror 30, and its optical axis matches the optical axis of the local light input end of the MMI element 32b. Thereafter, the local light L23 is condensed by the lens system 36 on the local light input end of the MMI element 32b. The lens system 36 includes two condenser lenses 36a and 36b arranged in the optical axis direction.

  As described above, the signal light L1 and the local light L2 input to the optical module 1A are distributed to the two MMI elements 32a and 32b. The MMI elements 32a and 32b are photodiode (PD) integrated interference waveguide elements using a semiconductor substrate made of, for example, indium phosphide (InP), and the signal lights L12 and L13 and the local light L22 and L23 input to the MMI elements 32a and 32b, respectively. Are caused to interfere with each other, thereby extracting a signal component having the same phase as that of the local light L2 of the signal light L1 and a signal component having a phase different from that of the local light L2 by 90 ° for each polarization component. The photocurrents generated by the PDs integrated in the MMI elements 32a and 32b are converted into voltage signals by the amplifiers 39a and 39b (see FIG. 1) mounted in the housing 2 and output from a plurality of terminals 3. . The MMI elements 32a and 32b are mounted on a CuW base. The amplifiers 39a and 39b are mounted on a circuit board 20e surrounding the two MMI elements 32a and 32b.

  Here, a method of assembling the optical receiver 1A of the present embodiment will be described with reference to FIGS. The above-described PBS 26, total reflection mirror 30, and BS 34 form a light incident surface (optical surface) that forms a predetermined angle (eg, 45 °) other than 0 ° and 90 ° with respect to the optical axis of the input ports 11 and 13. Have. In the following description, a component whose light incident surface forms a predetermined angle is referred to as a first optical component. Further, the total reflection mirror 21 and the BS 22 have a light incident surface (optical surface) which forms a supplementary angle (for example, 135 °) of the predetermined angle with respect to the optical axes of the input ports 11 and 13. In the following description, these are referred to as second optical components.

  In the first step, the MMI elements 32a and 32b are arranged in the housing 2. Specifically, first, as shown in FIG. 3, a carrier 20d, MMI elements 32a and 32b mounted on MMI carriers 20f and 20g, respectively, and a circuit board 20e on which electronic components such as capacitors are mounted in advance. Are arranged on the base 20c. The MMI elements 32a and 32b and the MMI carriers 20f and 20g are bonded by, for example, AuSn eutectic solder, and AuSn solder is used for bonding other portions. Then, as shown in FIG. 4, the base 20c on which the carrier 20d, the MMI elements 32a and 32b, and the circuit board 20e are mounted is mounted on the bottom surface of the housing 2. After that, the amplifiers 39a and 39b are mounted on the circuit board 20e using a conductive resin. Further, the carrier 20a is mounted on the bottom surface of the housing 2, and is fixed by an adhesive such as a UV resin.

  In the next step, as shown in FIG. 5, the monitor PD 24 is mounted on the carrier 20a via the PD carrier 24a. At this time, the monitor PD 24 is mounted on the PD carrier 24a outside the housing 2 to assemble the intermediate assembly in advance, and the intermediate assembly is mounted on the carrier 20a. The alignment of the PD carrier 24a is visually performed on the alignment mark formed on the carrier 20a.

  Subsequently, the first optical components (the PBS 26, the total reflection mirror 30, and the BS 34) are arranged on the carrier 20d and fixed with an adhesive. Here, FIGS. 6 and 7 are views for explaining details of the step of arranging the first optical component on the carrier 20d. In this step, a centering jig 60 shown in FIG. 6 is used. The alignment jig 60 has a block shape having a pair of surfaces 61 and 62 parallel to each other and a reference surface 63 that forms a predetermined angle θ with any one of the surfaces 61 and 62 (for example, the surface 61). It is a member of.

  In this step, first, the one end surface 2b of the housing 2 is at a predetermined angle with respect to the reference axis (that is, the optical axis of the input ports 11, 13) (the angle of the optical surface with respect to the optical axis of each of the input ports 11, 13; 45 °). First, the alignment jig 60 described above is mounted on an alignment rotation stage 70. Specifically, one of the surfaces 61 and 62 (the surface 61 in this case) is pressed against the mounting reference surface 71 provided on the alignment rotary stage 70, and the alignment jig 60 is rotated. Mount on top. Thereafter, the centering rotary stage 70 is rotated to direct the reference surface 63 in the reference axis direction (predetermined direction). Specifically, light La whose optical axis coincides with the reference axis is emitted from an autocollimator whose position is absolutely fixed. The light La is reflected by the reference surface 63, and the reflected light Lb is observed by an autocollimator, so that the optical axis of the light La coincides with the optical axis of the light Lb. Adjust the angle of.

  Next, instead of the alignment jig 60, the housing 2 is mounted on the alignment rotary stage 70 while being pressed against the mounting reference surface 71. Then, the first optical components (the PBS 26, the total reflection mirror 30, and the BS 34) are arranged in the housing 2 with their light incident surfaces facing the reference axis direction (see FIG. 5). Specifically, as shown in FIG. 7, a first optical component (a PBS 26 is shown as an example in the figure) is gripped above the housing 2, and the light La of the autocollimator is reflected on the light incident surface. While observing the reflected light Lb with an autocollimator, the angle of the first optical component is adjusted so that the optical axis of the light La matches the optical axis of the light Lb. Then, the first optical component is arranged at a predetermined position in the housing 2 while maintaining the angle. Note that the position of the first optical component on the carrier 20d is determined only by visual observation with respect to the alignment mark formed on the carrier 20d in advance. The above operation is sequentially performed on all of the PBS 26, the total reflection mirror 30, and the BS 34, which are the first optical components.

  FIG. 5 is referred to again. Subsequently, the second optical component (the total reflection mirror 21 and the BS 22) is arranged on the carrier 20a in the housing 2 and fixed with an adhesive. Here, FIG. 8 is a diagram for explaining the details of the step of arranging the second optical component on the carrier 20a. Also in this step, the above-described alignment jig 60 is used.

  In this step, first, the housing 2 already mounted on the centering rotary stage 70 in the previous step is once removed from the centering rotary stage 70. Then, the alignment jig 60 is mounted on the alignment rotation stage 70 again. At this time, the centering jig 60 is turned upside down with respect to the previous step, and the other of the pair of surfaces 61 and 62 (the surface 62 in this case) is pressed against the mounting reference surface 71, and To be mounted on. Thereafter, in the same manner as in the previous step, the angle of the centering rotary stage 70 is adjusted using an autocollimator, and the reference surface 63 is directed in the reference axis direction (predetermined direction).

  Next, instead of the alignment jig 60, the housing 2 is mounted on the alignment rotary stage 70 while being pressed against the mounting reference surface 71. Then, similarly to the above-described first optical component, the second optical component (the total reflection mirror 21 and the BS 22) is arranged on the carrier 20d with their light incident surfaces facing the reference axis direction ( (See FIG. 5). This operation is sequentially performed for the total reflection mirror 21 and the BS 22 as the second optical components.

  Subsequently, as shown in FIG. 9, a third optical component, that is, a skew adjusting element 27 in which a light incident surface (optical surface) forms 0 ° or 90 ° with respect to a reference axis, a λ / 2 plate 29, and polarization. The child 33 is placed on the carrier 20d in the housing 2 and fixed with an adhesive. Specifically, instead of the alignment jig 60 described above, a jig in which two surfaces that are in contact with each other forms a right angle is mounted while pressing one of the surfaces against the mounting reference surface 71 of the alignment rotary stage 70. . Then, using the other surface as a reference surface, the angle of the centering rotary stage 70 is adjusted using an autocollimator, and the reference surface is oriented in the reference axis direction (predetermined direction). Subsequently, the housing 2 is mounted on the alignment rotary stage 70 while pressing the housing 2 against the mounting reference surface 71 in place of the jig, and the third optical component (in the same manner as the first and second optical components described above). The skew adjusting element 27, the λ / 2 plate 29, and the polarizer 33) are arranged in the housing 2 with their light incident surfaces facing the reference axis direction. This operation is sequentially performed for all of the skew adjusting element 27, the λ / 2 plate 29, and the polarizer 33, which are the third optical components.

  Subsequently, as shown in FIG. 10, the alignment and fixing of the lens systems 28, 31, 36, and 38 are performed. As a preparation, two simulation ports are arranged on one end surface 2b of the housing 2. These simulated ports replace the input ports 11 and 13. From these simulated ports, test light (signal light L1, local light L2) used for alignment of the lens systems 28, 31, 36, and 38 is provided. ) Are emitted. Each simulation port has a collimating lens mounted inside, and these test lights are substantially collimated lights.

  Align these simulation ports. First, test light is introduced into the housing 2 from one of the simulation ports, and the test light that has passed through the first to third optical components is detected by a PD built in the MMI element 32a. Then, the simulation port is slid on the one end surface 2b of the housing 2 to search for the position of the simulation port where the test light intensity is maximum. Similarly, test light is introduced into the housing 2 from the other test port via the simulation port, and the test light that has passed through the first to third optical components is detected by the PD built in the MMI element 32b. Then, the simulation port is slid on the one end face 2b to search for a position of the simulation port where the test light intensity detected via the PD becomes maximum. Although the effective areas of the signal light input port and the local light input port of the MMI elements 32a and 32b are very small, about several μm square, since the test light is converted into collimated light, the lens systems 28, 31, 36, and Even if the optical coupling is not through 38, the position of the simulated port that gives the maximum optical coupling can be determined.

  Next, alignment and fixing of the condenser lenses 28a, 31a, 36a, and 38a are performed. These condenser lenses 28a, 31a, 36a, and 38a are arranged on the carrier 20d, test light from each simulation port is made incident, and the test light that has passed through the condenser lenses 28a, 31a, 36a, and 38a is subjected to MMI. It is detected by the built-in PD of the elements 32a and 32b. Then, while slightly changing the positions and angles of the condenser lenses 28a, 31a, 36a, and 38a, each condenser lens 28a, 31a, 36a, 38a (MMI element 32a, The position and angle of the lens disposed relatively close to 32b are determined. After the determination, the condenser lenses 28a, 31a, 36a and 38a are fixed to the carrier 20d using an adhesive resin after offsetting the MMI elements 32a and 32b by a predetermined amount. Subsequently, the focusing and fixing of the condenser lenses 28b, 31b, 36b, and 38b (lenses arranged at a distance from the MMI elements 32a, 32b) are performed. These alignment and fixing methods are the same as the above-described methods of aligning and fixing the condenser lenses 28a, 31a, 36a, and 38a.

  The test light output from the simulation port is split by the PBS 26 and the BS 34 and enters the two MMI elements 32a and 32b. Therefore, when the detection results of the MMI elements 32a and 32b are compared, a difference in magnitude naturally occurs. In the alignment of the lens systems 28, 31, 36, and 38, the alignment of the lens system having the smaller coupling efficiency of the two MMI elements 32a, 32b is performed first in the unaligned state of the lens systems. That is, when the position on the one end face 2b of the simulation port is determined, in the alignment step, the alignment of the lens system is first performed on the MMI element having a small optical coupling efficiency. Then, when the alignment of the other lens system is performed, the coupling efficiency with respect to the MMI element that is subsequently performed is reduced so as to match the coupling efficiency of the lens system that has been previously aligned. The coupling deviation at 32a and 32b can be compensated. This can be performed by offsetting one of the condenser lenses (28b, 31b, 36b, 38b; a lens group mounted relatively apart from the MMI element).

  Subsequently, as shown in FIG. 11, the VOA 23 is arranged on the VOA carrier 20b. At this time, in order to obtain the maximum extinction ratio with respect to the applied voltage, test light was input from the simulated port while passing a control signal from the bias power supply to the VOA 23 through a collet holding the VOA 23, and passed through the VOA 23. The intensity of the test light is detected by a PD built in the MMI element 32a, and the alignment is performed while confirming the extinction ratio. After that, the VOA 23 is fixed with resin, and wire bonding is performed. The temperature at the time of wire bonding is preferably a temperature that does not affect the UV resin already used for fixing each component.

  Subsequently, a lid for closing the housing 2 is attached by a seam seal while replacing the inside of the housing 2 with dry nitrogen. The inner surface of the lid is plated with black to prevent stray light. Then, as shown in FIG. 12, the test ports are replaced with the original input ports 11 and 13, and the input ports 11 and 13 are aligned and fixed. Specifically, a 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 MMI element 32a. Then, the signal light input port 11 is slid on the end face 2b while referring to the intensity of the detected signal light, and the light reception intensity of the built-in PD is the same as that when the lens system is aligned using the simulation port. Position. Similarly, the local light is input to the local light input port 13 and the intensity of the local light is detected by the built-in PD of the MMI element 32b. Then, the local light input port 13 is slid on the end face 2b to determine a position having the same strength as when the lens system is aligned. After the determination, the input ports 11 and 13 are fixed to the housing 2 by, for example, YAG welding. At this time, the rotation angle of the local light input port 13 around the optical axis is set to a predetermined angle and fixed.

  The effects obtained by the method of manufacturing the optical receiver 1A (optical module) according to the present embodiment described above will be described. In this manufacturing method, the first optical component (the PBS 26, the total reflection mirror 30, and the BS 34) and the second optical component (the total reflection mirror 21) are formed by using the alignment jig 60 shown in FIGS. And BS22). Thereby, the angle of the optical component having the light incident surface (optical surface) inclined with respect to each optical axis of the input ports 11 and 13 can be easily adjusted with extremely high accuracy without going through complicated steps. it can.

  Here, a further effect provided by the optical receiver 1A of the present embodiment will be described together with a comparative example. FIG. 13 schematically illustrates a connection relationship between optical components included in an optical receiver 1B as a comparative example. The optical receiver 1B differs from the optical receiver 1A of the present embodiment in that the optical axis of the signal light L1 coincides with the optical axis of the signal light input end of one MMI element 32a. That is, the signal light L12 having one polarization component proceeds linearly and enters the MMI element 32a. In FIG. 13, the monitor PD 24 and the VOA 23 are omitted.

  The configuration of this comparative example will be specifically described. The PBS 26 splits the signal light L1 into a signal light L12 having one polarization component (for example, X polarization component) and a signal light L13 having another polarization component (for example, Y polarization component). The signal light L12 that has traveled straight through the PBS 26 passes through the skew adjustment element 27a. The skew adjusting element 27a compensates for a phase delay corresponding to the distance from the PBS 26 of the other signal light L13 branched by the PBS 26 to the prism mirror (total reflection mirror) 30a. After that, the signal light L12 is focused on the MMI element 32a by the lens system 28.

  The signal light L13 reflected (branched) by the PBS 26 passes through the λ / 2 plate 29 and is reflected again by the total reflection mirror 30a. The λ / 2 plate 29 rotates the polarization direction of the signal light L13 by 90 °. Therefore, the polarization direction of the signal light L13 that has passed through the λ / 2 plate 29 matches the polarization direction of the signal light L12 that has traveled straight through the PBS 26. After that, the signal light L13 is condensed by the lens system 31 on the MMI element 32b.

  The BS 34 splits the local light L2 that has passed through the polarizer 33 into two. The local light L23 that travels straight through the BS 34 passes through the skew adjustment element 27b. The skew adjusting element 27b compensates for a phase delay of the other local light L22 branched by the BS 34, which corresponds to a distance from the BS 34 to the prism mirror (total reflection mirror) 30b. After that, the local light L23 is focused on the MMI element 32b by the lens system 36. The other local light L22 reflected (branched) by the BS 34 is reflected again by the mirror 30b and is condensed by the lens system 38 on the MMI element 32a.

  The problem of the optical receiver 1B according to the comparative example will be described. In the optical receiver 1B, duality between the signal lights L12 and L13 input to the MMI elements 32a and 32b and the local light L22 and L23 is not ensured. Specifically, considering the signal light L12 and the local light L22 input to the MMI element 32a, the signal light L12 goes straight from the signal light input port to reach the MMI element 32a, but the local light L22 is totally reflected by the BS34. The light travels along an optical path longer than the signal light L12 by the distance from the mirror 30b. Therefore, a difference occurs between the phase of the signal light L12 input to the MMI element 32a and the phase of the local light L22. Similarly, the local light L23 travels straight from the local light input port to reach the MMI element 32b, but the signal light L13 travels an optical path longer than the local light L23 by the distance between the PBS 26 and the total reflection mirror 30a. . Therefore, a difference occurs between the phase of the signal light L13 input to the MMI element 32b and the phase of the local light L23.

  FIGS. 14A and 14B are diagrams for conceptually explaining such a phase shift. FIGS. 14A and 14B show the phase relationship between the signal light (FIG. 14A) and the local light (FIG. 14B) incident on the MMI element. Assuming that the phase of the signal light and the phase of the local light are shifted by a time ΔT corresponding to the distance from the PBS 26 to the mirror 30a or the distance from the BS 34 to the mirror 30b, one of the MMI elements will This causes interference with the local light at time P2 (= P1 + ΔT). In the other MMI element, the signal light at time P2 interferes with the local light at time P1.

  In contrast to the above problem of the comparative example, in the optical receiver 1A of the present embodiment, in the optical system of the signal light L1, two mirrors (total reflection mirror 21 and BS22) are used between the signal light input port 11 and the PBS 26. The optical axis of the signal light L1 is translated toward the local light L2. Thereby, the distance between the optical axis of the signal light L1 and the optical axis of the local light L2 is made closer to (preferably the same as) the distance corresponding to the distance between the signal light input end and the local light input end of the MMI element 32a. Can be. Then, the signal light L12 after the polarization separation and the local light L22 after the branching enter the MMI element 32a while translating each other and maintaining the phase relationship between them. The signal light L13 after the polarization separation and the local light L23 after the branching are also translated into each other, and enter the MMI element 32b while maintaining the same phase relation as the signal light L12 and the local light L22. Therefore, according to the optical receiver 1A of the present embodiment, duality of the phase relationship between the signal light and the local light between the X-polarized light component and the Y-polarized light component can be secured.

  In the coherent optical receiver as in this embodiment, information contained in the signal light is extracted by causing the signal light and the local light to interfere with each other by the MMI. This extraction is performed by a signal processing system (DSP: Digital Signal Processor) connected to a subsequent stage of the MMI (more precisely, a subsequent stage of a PD for converting an optical signal into an electric signal). At this time, processing for compensating the phase difference between the two MMIs in the DSP and improving the information extraction accuracy is performed. However, when the duality between the phase of the signal light input to each MMI and the phase of the local light is not ensured as in the comparative example, this may be a factor in lowering the DSP extraction accuracy. On the other hand, according to the optical receiver 1A of the present embodiment, the phase relationship between the signal lights L12 and L13 input to the MMI elements 32a and 32b and the local light L22 and L23 can be made similar. A decrease in extraction accuracy in the DSP can be suppressed.

  In the optical receiver 1B according to the comparative example, a skew adjustment element is used to compensate for a time lag caused by an optical path difference between the signal light L12 and the signal light L13 and a time lag caused by an optical path difference between the local light L22 and the local light L23. 27a and 27b are individually provided. However, the skew adjusting elements 27a and 27b aim at the adjustment between the signal light L12 and the signal light L13 and the adjustment between the local light L22 and the local light L23, respectively. It is not intended to adjust for. The skew adjustment element is, for example, a block material made of Si, and is obtained by applying an AR coating to the front and back surfaces of a Si wafer having a thickness of about 1 mm and then cutting the block into a block shape. Therefore, the optical length of the Si wafer varies due to the variation in the thickness of the Si wafer. In the optical receiver 1B, since the skew adjusting elements 27a and 27b are provided independently of each other, these variations affect the signal extraction accuracy by the DSP. The above-mentioned ΔT can be compensated to some extent by the skew adjusting elements 27a and 27b, but due to the difference in element characteristics between the skew adjusting elements 27a and 27b, ΔT in one MMI element 32a and in the other MMI element 32a There is a possibility that a deviation may occur from ΔT.

  On the other hand, in the optical receiver 1A of the present embodiment, a skew adjusting element 27 common to the signal light L12 and the local light L22 is provided. As a result, it is possible to suppress the difference in characteristics of the skew adjustment elements as described above, and to suppress the influence on the interference action in the MMI element.

  In the optical receiver 1B according to the comparative example, the signal light input port 11 and the signal light input terminal of the MMI element 32a are arranged on the same optical axis, and the local light input port 13 and the local light input terminal of the MMI element 32b are connected to each other. Are arranged on the same optical axis. Accordingly, the distance between the signal light input port 11 and the local light input port 13 is uniquely determined by the distance between the signal light input terminals of the MMI elements 32a and 32b and the local light input terminal and the distance between the MMI elements 32a and 32b. It will be decided. Since the distance between the signal light input terminal and the local light input terminal of the MMI element depends on the maximum curvature of the optical waveguide in the MMI, it is not preferable to reduce the distance. Light loss (bending loss) in the MMI element is increased.

  In contrast, in the optical receiver 1A of the present embodiment, the optical axis of the signal light L1 is translated using two mirrors (total reflection mirror 21, BS22). Therefore, by adjusting the distance between these mirrors, the distance between the signal light input port 11 and the local light input port 13 can be arbitrarily set. Thus, for example, the signal light input port 11 and the local light input port 13 can be integrated, and one optical coupling system (sleeve or the like) can be provided for two optical fibers (SMF, PMF).

  1A, 1B: Optical receiver, 2: Housing, 2b: One end face, 3: Terminal, 4: Flange, 11: Signal light input port, 13: Local light input port, 20a, 20b, 20d: Carrier, 20c: Base , 20e: circuit board, 20f, 20g: MMI carrier, 21: total reflection mirror, 22: beam splitter (BS), 23: variable optical attenuator (VOA), 24: monitor PD, 24a: PD carrier, 26: polarized Wave separation elements (PBS), 27, 27a, 27b: skew adjustment elements, 28, 31, 36, 38: lens system, 29: λ / 2 plate, 30: total reflection mirror, 32a, 32b: MMI element, 33: Polarizer, 34 BS, 39a, 39b amplifier, 60 alignment tool, 61, 62 pair of surfaces, 63 reference surface, 70 alignment rotation stage, 71 mounting reference surface, L1 signal Light, L10 ... monitor light, L11, L12, L13 ... signal light, L2, L22, L23 ... local light.

Claims (5)

An optical input port attached to one end surface of the housing, and an optical component disposed in the housing and having an optical surface forming a predetermined angle other than 0 ° and 90 ° with respect to an optical axis of the optical input port. An assembly method of an optical module comprising:
A jig having a pair of surfaces parallel to each other and a reference surface forming the predetermined angle with one of the pair of surfaces is mounted on one of the pair of surfaces provided on a centering rotary stage. A step of mounting on the alignment rotary stage while pressing against a reference plane,
Rotating the centering rotary stage to orient the reference surface in a predetermined direction;
Replacing the jig with the one end surface of the housing, or mounting the other surface parallel to the one end surface of the housing on the alignment rotation stage while pressing the other surface parallel to the mounting reference surface,
Disposing the optical component in the housing with the optical surface oriented in the predetermined direction.   The method for assembling an optical module according to claim 1, wherein the step of directing the reference surface of the jig in a predetermined direction and the step of directing the optical surface of the optical component in the predetermined direction are performed by an autocollimator.   The optical module assembling method according to claim 1, wherein the predetermined angle is 45 ° or 135 °. An optical receiver assembling method,
The optical receiver,
A housing,
A signal light input port fixed to one end surface of the housing and externally inputting signal light including two polarization components orthogonal to each other,
A local light input port fixed to the one end face, having an optical axis parallel to the optical axis of the signal light input port, and externally inputting local light mainly including one polarization component;
A first multi-mode interference element disposed in the housing and interfering the signal light having one polarization component and the local light to recover information contained in the one polarization component,
A second multi-mode interference element disposed in the housing and interfering the signal light having the other polarization component and the local light to recover information included in the other polarization component,
A first optical component having an optical surface forming a predetermined angle other than 0 ° and 90 ° with respect to the optical axis of the signal light input port and the local light input port, and the signal light and the local light A light-condensing component for converging light toward the first and second multi-mode interference elements, wherein the light-collecting part is disposed in the housing, and the signal light input port, the local light input port and the first and second multi-mode interference An optical system that optically couples the element and
The assembling method is
Disposing the first and second multi-mode interference elements in the housing;
A jig having a pair of surfaces parallel to each other and a reference surface forming the predetermined angle with any one of the pair of surfaces is mounted on a mounting reference provided on one of the pair of surfaces on a centering rotary stage. Mounted on the centering rotary stage while pressing against a surface, rotating the centering rotary stage to direct the reference surface in a predetermined direction, and replacing the jig with the one end surface of the housing, or the housing. The other surface parallel to the one end surface of the body is mounted on the alignment rotating stage while pressing against the mounting reference surface, and the first optical component is placed in a state where the optical surface is oriented in the predetermined direction. Arranging in a housing;
The alignment of the two simulation ports instead of the signal light input port and the local light input port is performed by using the first and second multiplying test light from the two simulation ports via the first optical component. Performing the step with reference to the incident intensity to the mode interference element,
Performing the alignment of the light-collecting component with reference to the incident intensity of the test light on the first and second multi-mode interference elements;
The two simulation ports are replaced with the signal light input port and the local light input port, respectively, and the signal is input to the first and second multimode interference devices while referring to the incident intensity of the signal light and the local light. Aligning the optical input port and the local light input port and fixing the signal light input port and the local light input port to the housing. The optical system further includes a second optical component having an optical surface forming a supplementary angle of the predetermined angle with respect to the optical axis of the signal light input port and the local light input port,
The assembling method includes, after the step of arranging the first and second multi-mode interference elements in the housing and before the step of centering the two simulation ports, performing the other of the pair of surfaces. The jig is mounted on the alignment rotary stage while being pressed against the mounting reference surface, and the alignment surface is rotated in a predetermined direction by rotating the alignment rotary stage, and the housing is replaced with the jig. 2. The method according to claim 1, further comprising a step of mounting the second optical component in the housing with the optical surface facing in the predetermined direction, mounted on the alignment rotary stage while pressing the mounting reference surface. 5. The method for assembling the optical receiver according to 4.

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