JP2011203377A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve a shift of an optical axis between an output part of an optical signal processing module and a photoelectric conversion part with a simple structure and at low cost.SOLUTION: The relative displacement direction of a plurality of photoelectric conversion modules to the optical signal processing module due to thermal expansion of the optical signal processing module (PLC), the plurality of photoelectric conversion modules, and a mount substrate is derived beforehand. The derived displacement direction is made to conform to each optical axis direction from the output end of the optical signal processing module to a photodetector.

Description

  The present invention relates to an optical module, and relates to an optical module applicable to an optical receiver.

  In recent years, with the widespread use of optical fiber transmission, optical communication of various communication systems such as CDMA, OFDM, and QPSK has been developed (Non-Patent Documents 1, 2, and 3). In order to increase the communication capacity, various optical communication devices are being developed toward the realization of an ultrahigh-speed optical transmission system of 100 Gbit / sec or more. In particular, coherent reception methods such as DP-QPSK (Dual Polarization Quadrature Phase-Shift Keying) have attracted attention because of their superior optical noise tolerance and superior chromatic dispersion distortion compensation capability through electrical signal processing after photoelectric conversion. Consideration for application to is increasing.

  FIG. 1 shows a conventional configuration of an optical receiver used for a coherent reception system. The optical receiver is configured by connecting a local oscillation light generator 40, an optical module 100, and a demodulation LSI 200. The optical module 100 includes a PLC (Planar Lightwave Circuit) 110 that performs signal processing on signal light and local oscillation light input from the input ports S1 and S2, and a photodiode that photoelectrically converts the optical signal from the PLC 110 ( PD) array module 130, transimpedance amplifier (TIA) 140 that converts and amplifies the converted electrical signal from current to voltage, and an RF wiring section (not shown) that outputs the voltage signal to the outside. . The PLC 110 includes polarization splitters 111a and 111b that separate signal light and local oscillation light into different output ports according to their polarization states, and optical 90-degree hybrid circuits 112a and 112b that combine the signal light and local oscillation light. And. Output light from the optical 90-degree hybrid circuits 112a and 112b is coupled to the PD array module 130 via an optical wiring. The demodulation LSI 200 includes an AD converter and a digital arithmetic circuit (DSP: Digital Signal Processor). The input electric signal is converted into a digital signal by the AD converter and then digitally processed by the digital arithmetic circuit. .

Hossam M.H.Shalaby, ‘‘ Chip-Level Detection in Optical Code Division Multiple Access ’’, JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol.16, No.6, June 1998 ,, p1077 Yan Tang, et al, ‘‘ Optimum Design for RF-to-Optical Up-Converter in Coherent Optical OFDM Systems ’’, IEEE PHOTONICS TECHNOLOGY LETTERS, Vol.19, No.7, APRIL 1,2007, p483 Jeremie Renaudier, et al, `` Linear Fiber Impairments Mitigation of 40-Gbit / s Polarization-Multiplexed QPSK by Digital Processing in a Coherent Receiver '', JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol.26, No.1, January 1,2008, p36

  In such an optical receiver, conventionally, the optical connection between the PLC 110 and the PD array module 130 is either directly connected as shown in FIG. 2 or via a lens as shown in FIGS. Often connected separately.

  In FIG. 2, the PD array 130 is directly attached to the PLC 110 so that the output port of each waveguide 113 of the PLC 110 faces the light receiving surface of each PD 132 constituting the PD array module 130 in which the PD element is accommodated in a small package. It is configured.

  3 and 4, the PLC 110 and the PD array module 130 are spaced apart from each other. In FIG. 3A, one lens L <b> 1 is disposed between them. In FIG. Two lenses L2 and L3 are arranged, and in FIG. 4, microlens arrays 121 and 122 are arranged between them.

  However, when performing OE conversion at high speed, it is difficult to separate the PD array module 130 and the TIA 140 in order to prevent deterioration of the high frequency characteristics, and it is necessary to dispose them in close proximity. In addition, the photoelectric conversion unit 150 in which the PD array module 130 and the TIA 140 are close to each other is accompanied by heat generation by the TIA 140 and heat generation by multi-channeling. Therefore, it is necessary to ensure sufficient heat dissipation. In addition, since the PLC 110 that processes an optical signal is easily affected by heat, it is preferable to separate the PD array module 130 and the TIA 140 from the photoelectric conversion unit 150 in the vicinity. Therefore, when the photoelectric conversion unit 150 in which the PD array module 130 and the TIA 140 are close to each other is adopted, the size of the OE conversion unit increases, and it is necessary to fix it to a heat sink such as a package housing for heat dissipation. The configuration in which the PLC 110 and the photoelectric conversion unit 150 are directly connected as in 2 cannot be adopted.

  FIG. 5 shows a configuration in which the photoelectric conversion unit 150 in which the PD array module 130 and the TIA 140 are integrated and the PLC 110 are separately arranged. The photoelectric conversion unit 150 is separately arranged in two modules 150a and 150b. In FIG. 5, microlens arrays 121 and 122 are disposed between the PLC 110 and the photoelectric conversion units 150a and 150b. In FIG. 5, the photoelectric conversion unit 150 that generates a large amount of heat needs to be fixed to a housing having high thermal conductivity in order to promote heat dissipation. Further, in order to configure the optical module 100 described above, in order to maintain an optical positional relationship, the photoelectric conversion unit 150 and the PLC 110 are common on the same housing 160 as shown in FIG. It is necessary to fix to the holding member.

  However, since a member having high thermal conductivity is generally a member having a high thermal expansion coefficient, when a member having high thermal conductivity is adopted as the casing 160 on which the photoelectric conversion unit 150 and the PLC 110 are mounted, a relatively low heat The PLC 110 using a material having an expansion coefficient is greatly different in thermal expansion coefficient, and the optical axis shift between the output unit of the PLC 110 and the PD array module 130 becomes a problem at the time of temperature fluctuation.

  In order to deal with such a problem, it is conceivable to use a material having a small thermal expansion coefficient for the housing 160 so that the optical axis shift is not generated as much as possible. However, a material having a small coefficient of thermal expansion is not suitable for heat dissipation because of its low thermal conductivity. In order to avoid this, it is conceivable to separately configure a portion that requires heat dissipation and a portion having a small coefficient of thermal expansion, but the housing structure is complicated and expensive.

Further, as shown in FIG. 5, when the photoelectric conversion unit 150 is divided into two modules, the photoelectric conversion units 150a and 150b are arranged at the center position in the y direction (direction perpendicular to the optical axis) of the housing 160. It is impossible to fix. On the other hand, since the PLC 110 is composed of one module, the PLC 110 can be arranged and fixed at the center position in the y direction (direction perpendicular to the optical axis) of the housing 160. In such an arrangement, when a material having a high thermal conductivity and a high thermal expansion coefficient is used as the housing 160, the position of the PLC 110 hardly changes due to the thermal expansion and contraction of the housing 160. The parts 150a and 150b are greatly displaced as indicated by the arrow k. A symbol with a dash (') indicates a position after displacement.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a simple configuration without requiring a complicated and expensive material or structure as a common holding member for mounting a PLC and a photoelectric conversion unit. Accordingly, an object of the present invention is to provide an optical module in which loss variation due to an optical axis shift between an output unit of a PLC and a photoelectric conversion unit does not occur in a wide temperature range.

  In order to solve the above-described problems, the invention described in claim 1 is an optical signal processing module that performs optical signal processing on an input optical signal, separates the optical signal to output to a plurality of optical waveguides, and the optical signal processing. A light receiving array having a plurality of light receiving elements that photoelectrically convert and output each optical signal output from the unit, and a plurality of amplifiers that amplify electrical signals output from each light receiving element of the light receiving array, From a plurality of photoelectric conversion modules mounted on separate carriers, a common mount base on which the optical signal processing module and the plurality of photoelectric conversion modules are separately mounted, and each output port of the optical signal processing unit A lens optical system that optically couples output light to each light receiving element of the plurality of photoelectric conversion modules, and the optical signal processing module, the plurality of photoelectric conversion modules, and the front Relative displacement directions of the plurality of photoelectric conversion modules with respect to the optical signal processing module due to thermal expansion of the mount base are derived in advance, and the derived displacement directions and each light from the output end of the optical signal processing module to the light receiving element An optical module characterized in that the axial direction coincides with the optical module.

  According to a second aspect of the present invention, in the optical module according to the first aspect, the output end portion of the optical waveguide of the optical signal processing module is bent at a predetermined angle corresponding to the displacement direction with respect to the optical waveguide. A bent portion is provided, and the center of the lens of the lens optical system and the center of the light receiving portion of the light receiving element are arranged in the bending direction.

  According to a third aspect of the present invention, in the optical module according to the first aspect, the lens optical system is fixed to the optical signal processing module that emits light emitted from the optical signal processing unit as collimated light. 1 lens array, and a plurality of second lens arrays fixed to the photoelectric conversion modules that receive light from the first lens array and optically couple the light to the light receiving elements of the light receiving array. The direction of the line segment connecting each output end of the optical waveguide of the optical signal processing module and the center of the light receiving surface of each light receiving element of the light receiving array coincides with the displacement direction, and the first and second lines are on the line segment. The first and second lens arrays are decentered so that the lens center point on the main surface of the lens array is located.

  According to a fourth aspect of the present invention, in the optical module according to any one of the first to third aspects, the optical signal processing module is provided at a substantially central position in a direction in which the plurality of light receiving elements are arranged on the mount base. Two photoelectric conversion modules are provided at positions offset from the central position of the mount base.

  The present invention prevents the optical axis deviation between the PLC and the photoelectric conversion unit due to the difference in thermal expansion coefficient without complicating and expensive the structure and material of the housing, and the optical axis deviation at a low temperature and in a wide temperature range. It is possible to provide a high-performance optical module without any problems.

It is a figure which shows the structure of the optical receiver used for a coherent receiving system. It is a figure which shows the connection of the conventional PLC and PD array module. It is a figure which shows the connection of PLC using a lens system, and PD array module. It is a figure which shows the connection of PLC and PD array module using a micro lens array. It is a figure which shows the mode of expansion displacement of PLC arrange | positioned on a housing | casing and two photoelectric conversion parts. It is a figure which shows the structure of the optical receiver used for this invention. It is a figure which shows an example of the circuit structure of PLC. It is the perspective view and sectional drawing which show the structure of the optical receiver module of the 1st Embodiment of this invention. It is a top view which shows the structure of the optical receiver module of the 1st Embodiment of this invention. It is a figure which shows the principal part of the optical receiver module of the 1st Embodiment of this invention. It is a figure which shows notionally how to determine an optical axis angle. It is a figure which shows the mode of expansion displacement of PLC and two photoelectric conversion parts. It is a figure which shows the principal part of the optical receiver module of the 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail. First, the configuration of the optical receiver 5 to which the optical module of the present invention can be applied will be described. FIG. 6 is a diagram schematically showing the configuration of the optical receiver 5 on which the optical module of the present invention is mounted. In the present embodiment, the modulation signal received as the optical receiver 5 is described using a coherent receiver whose polarization multiplexed quadrature phase shift keying (DP-QPSK) is used. The invention is not limited to DP-QPSK coherent receivers. Further, although the description has been made with the configuration in which the output unit of the PLC and the photoelectric conversion unit are opposed to each other, the present invention can be applied even when the PLC is not opposed as long as it is not contrary to the gist of the present invention. Needless to say, the present invention can be widely applied as long as the output unit of the PLC and the photoelectric conversion unit (for example, the PD array module) are separated and optically coupled between them by a lens optical system.

  In FIG. 6, the optical receiver 5 includes a local oscillation light generation device 400, an optical module 500, and a demodulation LSI 600. The optical module 500 includes an input port S1 for inputting signal light and an input port S2 for inputting local light. The signal light input to the input port S1 is an optical signal received by the optical receiver 5 from the outside, and the local light input to the input port S2 is an optical signal generated by the local oscillation light generator 400. . The optical module 500 optically couples the PLC 510 as an optical signal processing module that performs optical signal processing on optical signals input from two input ports, and the optical signals processed by the PLC 510 to the OE converters 535a and 535b. Lens array 520, OE converters 535 a and 535 b for converting an optical signal into an electrical signal, and an RF wiring unit (not shown) for outputting the converted electrical signal to demodulation LSI 600. .

  The PLC 510 separates the input light into X polarization and Y polarization, and outputs the signals in the same deflection state as the polarization splitters (PBS) 511a and 511b that output the separated light to different output ports according to the polarization state. Optical 90 degree hybrid circuits 512a and 512b are provided which hybridize light and local light by 90 degrees and output them as four optical signals. In the illustrated example, the polarization splitter 511a separates signal light into X polarization and Y polarization, and the polarization splitter 511b separates local light into X polarization and Y polarization. Furthermore, the optical 90-degree hybrid circuit 512a hybridizes the X-polarized signal light and the local light by 90 degrees and outputs them to the four ports on the upper side of the optical waveguide 515. The optical 90-degree hybrid circuit 512b is Y-polarized. The signal light and the local light are hybridized 90 degrees and output to the four ports on the lower side of the optical waveguide 515 in the figure. The PBS 511 and the optical 90-degree hybrid circuit 512 of the PLC 510 are configured in the form of a plurality of optical waveguides 515 as shown in FIG. 7, for example. In the PLC 510 shown in FIG. 7, the optical waveguide 515 is developed so that the optical 90-degree hybrid circuit 512 is easily optically coupled by the lens array 520 and the OE converters 535a and 535b divided and arranged in two modules. Have been routed to

  The optical signal output from the PLC 510 is coupled to the OE converters 535a and 535b divided into two modules via the lens array 520 (microlens arrays 513a, 513b, 514a, and 514b). The OE conversion units 535a and 535b convert PD signals from a current into a voltage by PD array modules 530a and 530b having a plurality of photodiodes (PD) as light receiving elements that photoelectrically convert an optical signal from the PLC 510. And transimpedance amplifiers (TIAs) 540a and 540b for amplification. The electrical signals converted by the OE conversion units 535a and 535b are output to the demodulation LSI 600 via the RF wiring unit, converted into digital signals by the AD converter of the demodulation LSI 600, and then digitally output by the DSP of the demodulation LSI 600. It is processed.

  Here, the optical receiving module 500 of the present invention uses the OE converters 535a and 535b divided into two modules operable at high speed, and the PLC 510 is configured to promote heat generation from the OE converters 535a and 535b. The module housing for fixing the OE conversion units 535a and 535b is made of a material having high thermal conductivity (a material having a high thermal expansion coefficient), and as shown in each embodiment described later, the PLC 510 and the OE conversion unit 535a. 535b are arranged separately on the module housing, and the relative displacement direction (displacement direction) of the OE converters 535a and 535b with respect to the PLC 510 due to thermal expansion between the module housing and the PLC 510 and the OE converters 535a and 535b is determined. The PD array module is calculated in advance from the calculated relative displacement direction and the output end of the PLC 510. Le 530a, so that to match the respective optical axis direction to 530b.

(First embodiment)
The optical module of the first embodiment will be described in detail. FIG. 8A is a perspective view of the optical module, and FIG. 8B is an AA cross-sectional view of the optical module. FIG. 9 is a plan view of the optical module.

  As shown in FIG. 9, the optical module 500 of the present embodiment is provided with a bent portion 515 ′ bent at a predetermined angle with respect to the optical waveguide 515 at the exit end portion of the optical waveguide 515 of the PLC 510. The direction of the optical axis of the emitted light is adjusted.

  As shown in FIG. 8, the optical module 500 includes fixtures D1, D2, and D3 made of a plurality of Pyrex glasses that receive optical fibers F1 and F2 through which optical signals propagate and fix them to the input port of the PLC 510. ing. The PLC 510 has a structure in which an optical waveguide is provided on a silica-based glass thin film formed on a silicon substrate. The PLC 510 is fixed to a module housing 570 as a package substrate (mount base) using a silver paste or the like via a PLC silicon substrate 516. Has been. The module housing 570 is made of aluminum (Al) having a high thermal conductivity so as to promote the heat dissipation of the heat generated from the OE converter 535 operating at a high frequency. In general, in order to configure such an optical module, Kovar (Fe—Ni—Co) having a small thermal expansion coefficient is frequently used in order to reduce the displacement of optical components, but the thermal conductivity is relatively small. Therefore, it is not suitable for an application having a heat of about several W as in this embodiment. In such a case, CuW (copper tungsten), which is a few materials having a high thermal conductivity and a relatively small coefficient of thermal expansion, is used. However, an optical module that handles high-speed signals as in this embodiment still receives light from a PD. Since the diameter is small, the optical axis deviation tolerance is extremely small, and it is difficult to eliminate the optical axis deviation within a desired operating temperature range. In addition, such materials are relatively expensive and difficult to process. On the other hand, in the present embodiment, by applying the configuration of the present invention that does not cause an optical axis shift even when a material having a large thermal expansion coefficient is used, the thermal conductivity is high and inexpensive aluminum. Such materials can be used. On the optical signal output side of the PLC 510, microlens arrays 513a and 513b each having a lens at a position corresponding to the light output port are fixed. The microlens arrays 513a and 513b are directly attached to the end face of the PLC using a UV curing adhesive or the like. In FIG. 8, Pyrex glass D4 is attached in advance on the PLC as a fixing auxiliary member for the microlens array, and the bonding area of the microlens array is increased, thereby realizing highly reliable attachment.

  The OE converters 535a and 535b that receive the optical signal from the PLC 510 are fixed to the module housing 570 by using silver paste or the like via the subcarrier 536 so as to be separated from the PLC 510. The OE converters 535a and 535b include a PD array module 530, a TIA 540, a high-frequency chip 541 such as a chip capacitor and a chip resistor, and a RF carrier on a subcarrier 536 made of CuW or the like having a high thermal conductivity. A high-frequency wiring circuit 550 as a wiring portion is attached using a silver paste. The PD array module 530 is configured such that the PD 531 is fixed with silver paste or the like inside the enclosure 533 and the light receiving surface of the PD 531 is covered with sapphire glass 532 and sealed. A microlens array 514 is attached to the sapphire glass 532 of the PD array module 530 using a UV curable adhesive or the like. An aspherical lens is used as the microlens, and the microlens arrays 513 and 514 form a so-called collimating optical system. In addition, for example, a GRIN lens can be used as the microlens array.

  A plurality of electrode pads 534 electrically connected to the internal PD 531 are provided on the side surface of the PD array module 530, and the electrode pads 534 are bonded to the TIA 540 with wires W1. Further, the TIA 540 is bonded to the high frequency wiring circuit 550 by a wire W2, and an FPC 560 as an external output terminal is connected to the output side of the high frequency wiring circuit 550.

  Here, as shown in FIGS. 8 and 9, the high-frequency wiring circuit 550 is routed so that the wiring pattern 551 from the output end of the TIA 540 to the input end of the FPC 560 is expanded (expanded). This is to correspond to the FPC 560 in which the inter-terminal pitch is matched with the inter-terminal pitch used in the demodulation LSI 600 as an external device. Further, in order to improve the high-frequency characteristics in the high-frequency wiring circuit 550, the output of the TIA 540 of the OE conversion unit 535 and the input terminal of the FPC 560 are made as short as possible without diverting each wiring 551 in the high-frequency wiring circuit 550 as much as possible. The PD array module 530 and the TIA 540 of the OE conversion unit 535 are arranged so as to be separated from each other so that they can be connected with the wiring length. For this reason, in this embodiment, the OE conversion unit 535 is separated into two modules 535a and 535b including the high-frequency wiring circuit 550 portion in addition to the PD array module 530 and the TIA 540. Although not shown, the PLC 510 is also provided with a development portion that is routed so that the optical waveguide 515 is developed, thereby reducing the wiring pattern path length in the high-frequency wiring circuits 550a and 550b. It can be shortened. For these reasons, the OE conversion unit 535 is divided into two modules 535a and 535b.

  Next, main parts of the present embodiment will be described with reference to FIGS. 9 and 10. FIG. 10 is a diagram for explaining the positional relationship among the optical waveguide 515 of the PLC 510, the microlens arrays 513a and 514a, and the PD array module 530.

  As shown in FIGS. 9 and 10, the optical module 500 of this embodiment is provided with a bent portion 515 ′ bent at a predetermined angle α with respect to the optical waveguide 515 at the exit end portion of the optical waveguide 515 of the PLC 510. . Further, the position of the microlens array 513a is adjusted so that the optical axis of the light emitted from the optical waveguide 515 ′ enters and passes through the center of the lens main surface of each lens m1 of the microlens array 513a fixed to the PLC 510. To do. That is, as shown in FIG. 10, the direction of the light beam passing through the lens center on the lens main surface is the same on the lens entrance side and the lens exit side. Therefore, the alignment of the microlens arrays 513a and 513b is adjusted so that the principal ray emitted from the bent portion 515 'passes through the lens center point on the lens principal surface. The light emission direction from the PLC 510 is adjusted by the alignment of the bent portion 515 'and the microlens array 513a.

  Further, as shown in FIG. 9, the OE converters 535a and 535b are arranged on the optical axis of the light emitted from the PLC 510 on the lens main surface of each lens m2 of the microlens array 514a and the light receiving surface center of the PD 531. The subcarriers 536a and 536b on which the OE converters 535a and 535b are mounted are positioned on the module housing 570 so that the OE converters 535a and 535b are mounted.

  Next, how to determine the angle α of the bent portion 515 ′ of the optical waveguide 515 of the PLC 510, the arrangement position of the microlens array 513, the arrangement position of the microlens array 514, and the arrangement position of the PD 531 will be described first. This will be described with reference to FIG.

  Since the microlens has a short focal point and the PLC emission end and the microlens array 513a are arranged close to each other, the positional deviation of the microlens array 513a with respect to the PLC 510 at the time of temperature fluctuation can be ignored. Further, the positional deviation of the PD 531 and the microlens array 514a with respect to the subcarrier 536 can be ignored for the same reason.

  Here, when considering thermal expansion and contraction, the thermal expansion coefficient kp of the PLC module 510 is an effective thermal expansion coefficient of the PLC 510 made of a silicon substrate and a silica-based glass thin film formed on the surface thereof. The PLC module 510M includes a configuration including the PLC 510 and a submount material that is not used in the present embodiment but is provided in a fixed positional relationship with the PLC. The thermal expansion coefficients koe of the OE conversion modules 535a and 535b are effective thermal expansion coefficients of the OE conversion modules 535a and 535b including the respective components including the subcarriers 536a and 536b. The coefficient of thermal expansion kb of the module casing 570 refers to the coefficient of thermal expansion of the module casing 570 as a mount material to which the PLC module 510 and the OE conversion modules 535a and 535b are fixed. When the common mounting material has a composite material and structure, the effective thermal expansion coefficient as a whole may be considered. Usually, kb> koe> kp, and kb is one digit larger than kp. koe and kp are not limited to koe> kp, and may satisfy koe ≦ kp.

  In FIG. 11, due to the thermal expansion and contraction of the PLC module 510M, the OE conversion modules 535aM, 535bM, and the module housing 570, the relative position between the emission end of the microlens array 513a and the emission end of the microlens array 514a is the first relative. In the case of displacement from the position (x0, y0) to the second relative position (x0 ′, y0 ′), the ray angle α may be determined so that y0 / x0 = y0 ′ / x0 ′. (X0, y0) is the relative position at a temperature T1 in a steady state before thermal expansion, and (x0 ', y0') is the relative position at a temperature T2 after thermal expansion. For example, relative positions at a large number of temperatures due to thermal expansion and contraction within an assumed temperature range are obtained by simulation or experiment, and the direction of a typical optical axis angle α is determined using the plurality of relative positions.

  Next, a more specific method for determining the ray angle α will be described with reference to FIG. It is assumed that the point A is an effective fixing point of the PLC module 510M with respect to the module housing 570 and the point B is an effective fixing point of the OE conversion module 535aM with respect to the module housing 570. When the back surface of the PLC is uniformly bonded and fixed to the module housing, the stress in the surface direction of the bonding surface caused by the thermal expansion of the PLC and the module housing is balanced at the central portion of the PLC, and this is a temperature fluctuation. Even in some cases, there is no misalignment between the module housing and the PLC. Accordingly, it is considered that the point A is substantially at the center position in the y direction of the module housing 570, and the point A is not displaced by the thermal expansion of the module housing 570. Similarly, point B is a point where no positional deviation occurs effectively between the OE conversion module and the module housing. Since the point B is offset in the y direction from the center position of the module housing 570 in the y direction, the point B is considered to be displaced due to thermal expansion of the module housing 570. Let x be the distance in the x direction between points A and B, and let y be the distance in the y direction. Further, a is the distance in the x direction from the lens main surface of the microlens array 513a to the point A, and b is the point A from the lens center of one lens (in this case, the outermost side) of the microlens array 513a. Is the interval in the y direction. Further, c is the distance in the x direction from the lens main surface of the microlens array 514a to the point B, and d is one lens of the microlens array 514a (a lens corresponding to a lens that defines the dimension b). In this case, the distance in the y direction from the lens center on the outermost side to the point B.

  The aforementioned y0 / x0 = y0 '/ x0' is expressed as follows when the module mounting structure of FIG. 9 is considered.

(y-b + d) / (xac) = (y'-b '+ d') / (x'-a'-c ') (1)
Therefore, considering the influence of the thermal expansion coefficient, x and y change mainly due to the thermal expansion and contraction of the module housing 570, a and b change mainly due to the thermal expansion and contraction of the PLC module 510M, and c , D changes mainly due to the thermal expansion and contraction of the OE conversion module 535aM.
(y-b + d) / (xac) =
((y-b + d) + (y * kb-b * kp + d * koe) * dT) / ((xac) + (x * kb-a * kp-c * koe) * dT) (2)
It is. Therefore, transform (2)
(x * kb-a * kp-c * koe) / (xac) = (y * kb-b * kp + d * koe) / (y-b + d) (3)
Is established. dT is a temperature difference.

  Therefore, once the thermal expansion coefficients kp, koe, kb are determined, the values of the parameters (a, b, c, d, x, y) may be determined so as to satisfy the above equation (3). Since c, d, and y are restricted by the structure of the OE conversion module and the optical system that can be realized, b, x, and a have a large degree of freedom. Further, if the values of the parameters (a, b, c, d, x, y) are determined, the optical axis angle α is also determined.

  As one specific example, the length of the PLC module 510M in the x direction is 18 mm, the length of the OE conversion module 535aM in the x direction is 9 mm, and the lens thickness of the microlens arrays 513a, 513b, 514a, and 514b is 1 mm. The lens-to-lens distance between the microlens array 513a (513b) and the microlens array 514a (514b) is 2.5 mm, c = 6 mm, y = 5 mm, d = 0 mm, and kp = 3 × 10 ^ −6 (10 (Minus the sixth power), koe = 7 × 10 ^ -6, and kb = 23 × 10 ^ -6, a can be 10 mm, b = 4.277 mm, and x = 18.5 mm. In this embodiment, two sets of four ports having a pitch of 250 μm are arranged separately. However, since the distance between the four ports is small, the actual emitted light position b on the PLC side is b = 4. It may be arranged at a position of ± 0.125 mm and ± 0.375 mm around 277. The OE conversion module side can also be arranged with 4 ports at 0.125 mm and ± 0.375 mm with d = 0 mm as the center.

  According to this configuration, even if an inexpensive aluminum casing is used as the module casing 570, for example, as shown in FIG. 12, the OE conversion modules 535aM and 535bM are displaced along the optical axis set obliquely. Therefore, the optical axis shift does not occur. Incidentally, when the optical axis is not tilted as in the conventional apparatus of the scale, an optical axis shift of about 10 μm occurs at a temperature difference of 100 degrees. Since the PD light receiving diameter is about 15 μm, a significant loss occurs.

  According to this embodiment, the relative displacement direction of the OE conversion modules 535aM and 535bM with respect to the PLC module 510M due to the thermal expansion and contraction of the PLC module 510M, the OE conversion modules 535aM and 535bM, and the module housing 570 is derived in advance, The derived displacement direction and the angle α of the bent portion 515 ′ provided at the exit end portion of the optical waveguide 515 of the PLC 510 are substantially matched, and the center of the lens of the microlens array 513, 514 is located on the bent direction of the bent portion 515 ′. Since the center of the light receiving surface of the PD 531 is arranged, the PLC due to the difference in thermal expansion coefficient between the PLC module 510M, the OE conversion modules 535aM and 535bM, and the module casing 570 is obtained without making the structure and materials of the casing complicated and expensive. Module 510M and OE change Module 535AM, to prevent the optical axis misalignment between the 535BM, can provide a high-performance optical module without light axis deviation in a wide temperature range at a low cost.

(Second Embodiment)
Next, a second embodiment will be described. FIG. 13 is a diagram for explaining the arrangement relationship of the configuration of the main part of the optical module according to the second embodiment. In the optical module of this embodiment, the bent portion 515 ′ is not provided at the exit end portion of the optical waveguide 515 of the PLC 510, and the lens is eccentric and attached to the PLC module 510M so that the thermal expansion direction matches the optical axis. Yes. The OE conversion modules 535aM and 535bM are fixed to the module housing 570 so that the center of the light receiving surface of the PD 531 is positioned on the optical axis.

  In FIG. 13, the bent portion 515 ′ is not provided at the exit end portion of the optical waveguide 515 of the PLC 510. In this embodiment, the angle of the line segment J1 connecting the emission end 515k of the optical waveguide 515 and the center of the light receiving surface of the PD 531 matches the optical axis angle α derived as described above, and the line The lens center point E1 on the lens principal surface of the microlens array 513a on the PLC 510 side and the lens center point E2 on the lens principal surface of the microlens array 514a on the OE converter 535a side are positioned on the minute J1. The microlens arrays 513a and 514a are decentered. Rays passing through E1 and E2 are paraxial rays, not principal rays.

  Due to the eccentricity of the microlens arrays 513a and 514a, the principal ray J2 having the maximum intensity distribution emitted from the optical waveguide 515 is deflected by the microlens arrays 513a and 514a and is incident on the center of the light receiving surface of the PD531. The

  According to this embodiment, the adjustment range is smaller than that of the first embodiment, but the optical axis angle can be easily adjusted.

DESCRIPTION OF SYMBOLS 5 Optical receiver 500 Optical receiver module 511 Polarization splitter 512 90 degree hybrid circuit 513, 514 Micro lens array 515 Optical waveguide 515 'Bending part 516 Silicon substrate 520 Lens array 530 PD array module 535 OE conversion part 536 Subcarrier 550 High frequency wiring Circuit 570 Module housing 600 Demodulation LSI
M mirror

Claims (4)

An optical signal processing module that performs optical signal processing on the input optical signal, separates it and outputs it to a plurality of optical waveguides;
A light receiving array having a plurality of light receiving elements that photoelectrically convert and output each optical signal output from the optical signal processing unit; and a plurality of amplifiers that amplify the electrical signals output from each light receiving element of the light receiving array. A plurality of photoelectric conversion modules each mounted on a separate carrier;
A common mount base on which the optical signal processing module and the plurality of photoelectric conversion modules are mounted separately;
A lens optical system for optically coupling light output from each output port of the optical signal processing unit to each light receiving element of the plurality of photoelectric conversion modules;
With
Relative displacement directions of the plurality of photoelectric conversion modules with respect to the optical signal processing module due to thermal expansion of the optical signal processing module, the plurality of photoelectric conversion modules, and the mount base are derived in advance, and the derived displacement direction and the optical signal An optical module characterized in that the optical axis directions from the output end of the processing module to the light receiving element coincide with each other.   A bent portion that is bent at a predetermined angle corresponding to the displacement direction with respect to the optical waveguide is provided at an output end portion of the optical waveguide of the optical signal processing module, and the lens center of the lens optical system is provided on the bending direction. The optical module according to claim 1, wherein a center of a light receiving portion of the light receiving element is disposed. The lens optical system is
A first lens array fixed to the optical signal processing module that emits the output light of the optical signal processing unit as collimated light;
A plurality of second lens arrays fixed to the respective photoelectric conversion modules for receiving light from the first lens array and optically coupling the light to the respective light receiving elements of the light receiving array;
Have
The direction of the line segment connecting each output end of the optical waveguide of the optical signal processing module and the center of the light receiving surface of each light receiving element of the light receiving array coincides with the displacement direction, and the first and second lens arrays are on the line segment. 2. The optical module according to claim 1, wherein the first and second lens arrays are decentered so that a lens center point on the main surface is located. The optical signal processing module is provided at a substantially central position in a direction in which the plurality of light receiving elements are arranged on the mount base,
4. The optical module according to claim 1, wherein the two photoelectric conversion modules are provided at a position offset from the central position of the mount base.

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