JP2017125926A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical receiver capable of suppressing deviation of a phase.SOLUTION: An optical receiver relating to one embodiment recovers information included in signal light L1 by allowing local light L22, L23 to interfere with phase-modulated signal light L12, L13. The optical receiver includes: two MMI elements 32a, 32b for inducing interference between the signal light L12, L13 and the local light L22, L23; and an optical circuit for optically coupling the two MMI elements 32a, 32b with the signal light L12, L13 and the local light L22, 23, respectively. In the optical circuit, the optical axis of the signal light L11 is translated toward the local light L2, and the signal light L12, L13 and the local light L22, L23 propagate in parallel to each other while maintaining a phase relation and enter the two MMI elements 32a, 32b, respectively.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical receiver.

  Patent Document 1 discloses a technique related to a coherent optical receiver. FIG. 6 schematically shows the configuration of this coherent optical receiver. In the coherent optical receiver 100 shown in FIG. 6, an optical waveguide substrate 101, optical 90-degree hybrid circuits 111 and 112, a plurality of signal light receiving elements 134 and 135, and a signal light level monitoring light receiving element 104 are provided in a 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 light receiving element 104 for signal light level monitoring is on either side of the third end face 101c and the fourth end face 101d sandwiched between the first end face 101a and the second end face 101b of the optical waveguide substrate 101. In addition, the second end face 101b is closer to the first end face 101a than the second end face 101b. The light receiving element 104 for signal light level monitoring receives part of the signal light L1 branched by the light branching element 131 on the optical waveguide 106. The remaining signal light L1 is further branched by the optical branching element 132, one of which is input to the optical 90-degree hybrid circuit 111, and the other is input to the optical 90-degree hybrid circuit 112. The local light L2 is branched by the optical branching element 133, one of which is input to the optical 90-degree hybrid circuit 111, and the other local light L2 is input to the optical 90-degree hybrid circuit 112. Interference light output from the optical 90-degree hybrid circuits 111 and 112 is detected by a plurality of light receiving elements 134 and 135 for signal light.

  FIG. 4 shows a connection relationship of an optical receiver different from that described above. In the optical receiver shown in FIG. 4, a polarization beam splitter (PBS) 26, skew adjusting elements 27 a and 27 b, lens systems 28, 31, 36 and 38, and a half-wave plate (λ / 2 plate) 29 , Total reflection mirrors 30a and 30b, a polarizer 33, a beam splitter (BS) 34, and multi-mode interference elements (MMI) 32a and 32b.

  The PBS 26 branches one polarization component L12 and the other polarization component L13 of the signal light L1. One polarization component L12 that travels straight through the PBS 26 passes through the skew adjustment element 27a. The skew adjustment element 27a compensates for a phase difference between one polarization component L12 that transmits the PBS 26 and the other polarization component L13 that the PBS 26 reflects. Thereafter, one polarization component L12 is collected by the lens system 28 and reaches the MMI element 32a. The other polarization component L13 reflected by the PBS 26 is reflected by 90 ° again by the total reflection mirror 30a, and then passes through the λ / 2 plate 29. The λ / 2 plate 29 rotates the polarization direction of the other polarization component L13 by 90 °. Therefore, the polarization direction of the other polarization component L13 that has passed through the λ / 2 plate 29 coincides with the polarization direction of the one polarization component L12 that travels straight through the PBS. Thereafter, the other polarization component L13 is condensed by the lens system 31 and reaches the MMI element 32b.

  The BS 34 branches the local light L2 that has passed through the polarizer 33. The local light L23 transmitted through the BS 34 passes through the skew adjustment element 27b. The skew adjustment element 27b compensates for the phase difference between the local light transmitted through the BS 34 and the other local light L22 reflected by the BS 34. Thereafter, the local light L23 is collected by the lens system 36 and reaches the MMI element 32b. The other local light L22 reflected by the BS 34 is reflected by 90 ° again by the mirror 30b, and then condensed by the lens system 38 and reaches the MMI element 32a.

Japanese Patent Laying-Open No. 2015-084500

  In the optical receiver shown in FIG. 4, the duality between the two signal lights L12 and L13 reaching the two MMI elements 32a and 32b and the two local lights L22 and L23 is not ensured. For example, when considering the signal light L12 and the local light L22 input to the MMI element 32a, the signal light L12 travels straight from the signal light input port and reaches the MMI element 32a, but the local light L22 is transmitted from the BS 34 and the total reflection mirror 30b. The optical path travels longer than the signal light L12 by the distance between the two. Therefore, the phase of the latter (local light) is slightly delayed between the signal light L12 and the local light L22 input to the MMI element 32a. On the other hand, the local light L23 travels straight from the local light input port and reaches the MMI element 32b. However, the signal light L13 travels an optical path length longer than the local light L23 by the distance between the BS 26 and the total reflection mirror 30a. Therefore, the former phase is slightly delayed between the signal light L13 and the local light L23 input to the MMI element 32b.

  FIGS. 5A and 5B are diagrams for conceptually explaining such a phase shift. FIGS. 5A and 5B show the progress of signal light (FIG. 5A) and local light (FIG. 5B) when entering the MMI element. When it is assumed that the distance between the PBS 26 and the total reflection mirror 30a shown in FIG. 4 or the distance between the BS 34 and the total reflection mirror 30b corresponds to the time ΔT, the signal light at the time P1 is obtained in one MMI element. And local light emission at time P2 (= P1 + ΔT) is caused to interfere. In the other MMI element, the signal light at time P2 and the local light at time P1 are caused to interfere with each other.

  It is an object of the present invention to provide an optical receiver that eliminates a phase duality shift.

  An optical receiver according to an aspect of the present invention is an optical receiver that recovers information contained in signal light by causing the local light to interfere with the phase-modulated signal light. Two multi-mode interference elements that interfere with each other, and an optical circuit that optically couples signal light and local light to each of the two multi-mode interference elements, and in this optical circuit, one optical axis of signal light and local light Are translated to the other side, and the signal light and the local light enter each of the two multimode interference elements while being translated and maintaining the phase relationship.

  In one embodiment of the present invention, a phase shift can be suppressed.

FIG. 1 is a perspective view showing a configuration of an optical receiver according to an embodiment of the present invention. FIG. 2 is a plan view showing the configuration of the optical receiver. FIG. 3 schematically shows the connection relationship of each optical component inside the optical receiver. FIG. 4 schematically shows a connection relationship of optical components included in a conventional optical receiver. FIGS. 5A and 5B are diagrams for conceptually explaining the phase shift. FIG. 6 schematically shows the configuration of a coherent optical receiver described in the prior art document.

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

  FIG. 1 is a perspective view showing a configuration of an optical receiver 1A according to an embodiment of the present invention. FIG. 2 is a plan view showing the configuration of the optical receiver 1A. FIG. 3 schematically shows the connection relationship of each optical component inside the optical receiver 1A. The optical receiver 1A recovers information contained in the signal light L1 by causing the 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. . In this embodiment, it is assumed that the signal light L1 is modulated by a so-called DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) method including two polarization components.

  As shown in FIGS. 1 and 2, the optical receiver 1 </ b> A of the present embodiment includes a substantially rectangular parallelepiped housing (housing) 2 and a signal fixed to one end face 2 b of the housing 2 and arranged side by side. An optical input port 11 and a local light input port 13 are provided. The signal light input port 11 is connected to a single mode fiber (SMF), and receives the signal light L1 from the outside of the optical receiver 1A via the SMF. The local light input port 13 is connected to a polarization maintaining fiber (PMF), and receives the local light L2 from the outside of the optical receiver 1A via the PMF. The signal light L1 and the local light L2 are input into the housing 2 through the signal light input port 11 and the local light input port 13, respectively.

  In the signal light input port 11, a cylindrical sleeve that receives a ferrule attached to the tip of the SMF and a lens holder that houses a collimating lens are integrated, and the lens holder is joined to one end surface 2 b of the housing 2. Yes. The signal light L1 propagated in the SMF is converted into collimated light by the collimating lens and enters the housing 2. In the local light input port 13, a cylindrical sleeve that receives a ferrule attached to the tip of the PMF and a lens holder that houses a collimating lens are integrated, and the lens holder is joined to one end surface 2 b of the housing 2. . The local light L2 that has propagated through the PMF is converted into collimated light by the collimating lens and then enters the housing 2.

  The signal light input port 11 and the local light input port 13 are each composed of a combination of a plurality of cylindrical parts. Among the plurality of cylindrical parts, the part having the largest outer diameter (typically a lens holder). Has flat surfaces 11a and 13a at locations facing each other. As a result, the distance between the optical axis of the signal light input port 11 and the optical axis of the local light input port 13 is reduced. The cylindrical part has an outer diameter of, for example, 5.5 mm, and when the flat surfaces 11a and 13a are not provided, the optical axis interval between the ports 11 and 13 is 11 mm. However, by forming the flat surfaces 11a and 13a, it is possible to set the optical axis interval of these ports 11 and 13 to 10 mm or less. In this embodiment, the distance between the optical axes of these ports 11 and 13 is set to 3.4 mm.

  The housing 2 is made of, for example, Kovar. Among the four side surfaces of the housing 2, a plurality of terminals 3 are provided on the other side surfaces except the one end surface (front end surface) 2 b. The plurality of terminals 3 are drawn out from the lowermost layer of multi-layered ceramic layers constituting each side surface. The plurality of terminals 3 include a terminal for taking out an electric signal generated from the signal light L1 to the outside of the optical receiver 1A, a terminal for supplying a bias to an electronic circuit inside the housing 2, a ground terminal, and the like. Flange 4 for fixing the housing 2 to a circuit board or the like extends from the four corners of the bottom surface of the housing 2.

  In addition to the above configuration, the optical receiver 1A of the present embodiment includes multi-mode interference elements (MMI) 32a and 32b that cause the signal light L1 and the local light L2 to interfere with each other. The MMI elements 32a and 32b can be, for example, optical 90 ° hybrid elements. The MMI elements 32 a and 32 b are arranged in the housing 2 so as to face the two input ports 11 and 13.

  In addition, the optical receiver 1A is a polarization beam splitter (PBS) as an optical component for optically coupling the signal light input terminals of the two MMI elements 32a and 32b and the signal light input port 11. ) 26, a skew adjustment element 27, a lens system 28, a half-wave plate (λ / 2 plate) 29, a total reflection mirror 30, and a lens system 31. Further, on the optical path between the PBS 26 and the signal light input port 11, a total reflection mirror 21, a beam splitter (BS) 22 as an optical branching element, and a variable optical attenuator (VOA) 23 are arranged. ing.

  Total reflection mirror 21 and BS 22 are mounted on carrier 20 a provided on the bottom surface of 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 the carrier 20d provided on the base 20c independently of the carriers 20a and 20b. The carriers 20a, 20b, and 20d are made of alumina, for example. The bottom plate of the housing 2 is made of, for example, CuW.

  The total reflection mirror 21 is a light reflecting element disposed on the optical axis of the signal light input port 11. The total reflection mirror 21 reflects all of the signal light L1 from the signal light input port 11 toward the BS 22. The optical axis of the signal light L1 before reflection and the optical axis of the signal light L1 after reflection are substantially perpendicular, for example.

  The BS 22 can be constituted by, for example, a light transmissive member having a front 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 one embodiment. The signal light L1 enters the front surface of the BS 22, and is branched into two by a dielectric multilayer filter. One of the branched signal lights (monitoring signal light L10) passes through the dielectric multilayer filter and is emitted from the back surface of the BS22. At this time, the optical axis direction of the monitor signal light L10 is substantially perpendicular to the optical axis direction of the signal light input port 11, for example.

  The optical receiver 1A further includes a power monitoring photodiode (monitoring PD) 24 as a light detection element. The monitor PD 24 is mounted on the carrier 20a. The monitor PD 24 is arranged on the optical axis of one signal light that passes through the BS 22. The monitor PD 24 receives the monitor signal light L10 that has passed through the BS 22. The monitor PD 24 outputs a detection signal corresponding to the intensity of the received monitor signal light L10.

  The VOA 23 is disposed on the optical axis of the other signal light L11 reflected by the BS 22, and attenuates the intensity of the signal light L11 as necessary. The attenuation amount is set based on the detection signal output from the monitoring PD 24 described above. A control signal for setting the attenuation of the VOA 23 is input from the outside of the optical receiver 1A via the terminal 3. For example, when an over-input state is detected by the monitoring PD 24, the intensity of the signal light L11 directed to the MMI elements 32a and 32b is reduced by increasing the attenuation amount of the VOA 23.

  The carrier 20d has a wiring pattern 41a for transmitting a detection signal output from the monitoring PD 24. The wiring pattern 41a is connected to the terminal 3 through a bonding wire. Further, the carrier 20d has a wiring pattern 41b for transmitting a control signal for setting the attenuation amount of the VOA 23. The wiring pattern 41b and the electrode of the VOA 23 are connected to each other through a bonding wire 41c.

  The PBS 26 has a light incident surface on which the signal light L11 is incident, and is formed by one polarization component of the signal light L11 (for example, the X polarization component, the optical axis of the signal light L11, and the normal of the incident surface of the PBS 26). Component that is included in a plane parallel to the main surface of the carrier L12 and the other polarization component (eg, Y polarization component, perpendicular to the plane formed by the optical axis and normal line) Component L13 (which is a component perpendicular to the main surface of the carrier). The X polarization component L12 passes through the PBS. The Y polarization component L13 is reflected by the PBS 26 and goes straight in a direction orthogonal to the traveling direction of the X polarization component L12. The optical axis direction of the X polarization component L12 and the optical axis direction of the Y polarization component L13 are, for example, substantially perpendicular. In one example, the Y polarization component L13 moves away from the local light L2. In this case, the traveling direction of the Y polarization component L13 differs from the traveling direction of the signal light L1 reflected by the total reflection mirror 21 by 180 °.

  The skew adjusting element 27 and the lens system 28 are disposed 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 X polarization component L12 that has traveled straight through the PBS 26 passes through the skew adjustment element 27. The skew adjustment element 27 is, for example, a block material made of Si, and by equivalently increasing the optical path length of the X polarization component L12, the Y polarization with respect to the X polarization component L12 caused by each optical path length difference. The phase delay of the component L13 is compensated. Thereafter, the X polarization component L12 is collected by the lens system 28 and reaches 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 disposed on the optical path between the PBS 26 and the signal light input end of the MMI element 32b. The Y polarization component L13 reflected by the PBS 26 is changed in its traveling direction by 90 ° again by the total reflection mirror 30, so that its optical axis coincides with the optical axis of the signal light input end of the MMI element 32b. Thereafter, the Y polarization component 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 Y polarization component L13 by 90 °. Therefore, the polarization direction of the Y polarization component L13 that has passed through the λ / 2 plate 29 coincides with the polarization direction of the X polarization component L12 that travels straight through the PBS. Thereafter, the Y polarization component L13 is collected by the lens system 31 and reaches the 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 Y polarization component L13. For example, the λ / 2 plate 29 may be disposed between the PBS 26 and the total reflection mirror 30.

  The optical receiver 1A further includes polarizers 33 and BS34, and lens systems 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. In the present embodiment, the skew adjusting element 27 and the total reflection mirror 30 disposed between the signal light input terminals of the MMI elements 32a and 32b and the signal light input port 11 are respectively connected to the local light emission input terminals of the MMI elements 32a and 32b. And the local light input port 13 are integrated with an optical component for optical coupling. That is, the skew adjusting element 27 and the total reflection mirror 30 have two optical axes for signal light and local light, respectively.

  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 maintained in the PMF is shifted when the housing 2 is assembled, only the polarization component having the polarization direction of 0 ° or 90 ° can be extracted as the local light L2. In the case where the light source of the local light L2 is a semiconductor LD, the polarization of a component parallel to the active layer is usually elliptical polarized light that is dominant. However, in order to obtain the oscillation stability, material reliability, desired output wavelength, etc. of the semiconductor LD, strain due to lattice mismatch may be introduced into the active layer. Laser light output from such a semiconductor LD may be elliptically polarized light having a relatively short minor axis length. Even in such a case, the polarizer 33 converts the local light L2 from elliptically polarized light to linearly polarized light.

  The BS 34 has a light incident surface that is optically coupled to the local light input port 13 via the polarizer 33, and branches the local light L2 that has passed through the polarizer 33 into two local lights L22 and L23. At this time, the branching ratio is 50%. One local light L22 passes through the BS 34 and travels straight. The other local light L23 is reflected by the BS 34 and travels straight in a direction orthogonal to the traveling direction of the local light L22. The optical axis direction of the local light L22 and the optical axis direction of the local light L23 form a substantially right angle. In one example, the local light L23 travels in the same direction as the Y polarization component L13.

  The skew adjusting element 27 and the lens system 38 are disposed on the optical path between the BS 34 and the local light input end of the MMI element 32a (that is, on the optical axis of the local light input end of the MMI element 32a). The local light L22 that has traveled straight through the BS 34 passes through the skew adjustment element 27. The skew adjusting element 27 compensates for the phase delay of the local light L23 with respect to the local light L22 due to the difference in optical path length by equivalently increasing the optical path length of the local light L22. Thereafter, the local light L22 is collected by the lens system 38 and reaches the MMI element 32a. The lens system 38 includes two condenser lenses 38a and 38b arranged in the optical axis direction.

  The total reflection mirror 30 and the lens system 36 are disposed on the optical path between the BS 34 and the local light input end of the MMI element 32b. The traveling direction of the local light L23 reflected by the BS 34 is changed by 90 degrees again by the total reflection mirror 30, so that the optical axis thereof coincides with the optical axis of the local light input end of the MMI element 32b. Thereafter, the local light L23 is collected by the lens system 36 and reaches 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 into the housing 2 are distributed to the two MMI elements 32a and 32b. The MMI elements 32a and 32b are, for example, photodiode (PD) integrated types using a semiconductor substrate made of indium phosphide (InP), and signal lights L12 and L13 and local light sources L22 and L23 optically coupled to the input ends of the MMI elements 32a and 32b, respectively. Are extracted from the signal light L1 from the signal component having the same phase as that of the local light L2, and from the signal light L2 by 90 °. The photocurrent generated by the PD integrated in the MMI elements 32 a and 32 b is converted into a voltage signal by the amplifiers 39 a and 39 b provided in the housing 2, and is output from one of the 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 U-shaped wiring board 20e that collectively surrounds the two MMI elements 32a and 32b.

  Next, effects produced by the optical receiver 1A of the present embodiment will be described. In the optical receiver 1A of the present embodiment, the optical axis of the signal light L1 is translated to the local light emission L2 side by two mirrors (total reflection mirror 21 and BS22) between the signal light input port 11 and the PBS 26. Is done. As a result, the distance between the optical axis of the signal light L11 and the optical axis of the local light L2 is made closer (preferably matched) to the distance corresponding to the distance between the signal light input end and the local light input end of the MMI element 32a. Can do. The signal light L12 after polarization separation and the local light L22 after branching enter the MMI element 32a while being translated and maintaining the phase relationship. Further, the signal light L13 after polarization separation and the local light L23 after branching also enter the MMI element 32b while being translated and maintaining the phase relationship.

  In the coherent optical receiver of the present embodiment, the information contained in the signal light is reproduced by causing the signal light and the local light to interfere with each other in the MMI. This reproduction is performed by a signal processing system (DSP: Digital Signal Processor) connected to the latter stage of the MMI (more specifically, the latter stage of the PD that converts an optical signal into an electrical signal). At that time, processing for improving the information reproduction accuracy by compensating for the phase difference between the two MMIs in the DSP is performed. However, when the phase of the signal light input to each MMI and the phase of the local light are shifted from each other, this shift is a cause of reducing the reproduction accuracy of the DSP. On the other hand, in the optical receiver 1A of the present embodiment, the duality of the phase between the signal light (polarization components L12 and L13) input to the MMI elements 32a and 32b and the local light L22 and L23 is ensured. Thus, it is possible to suppress a decrease in reproduction accuracy in the DSP.

  In the conventional optical receiver shown in FIG. 4, in order to compensate for the time lag due to the optical path difference between the signal light L12 and the signal light L13 and the time lag due to the optical path difference between the local light L22 and the local light L23, Skew adjustment elements 27a and 27b are provided. However, the skew adjustment elements 27a and 27b are intended for adjustment between the signal light L12 and the signal light L13 and adjustment between the local light L22 and the local light L23, respectively. It is not intended for adjustment. The skew adjustment elements 27a and 27b are, for example, Si block materials, which are cut out in a block shape after AR coating is applied to the front and back surfaces of a Si wafer having a thickness of about 1 mm. Accordingly, the optical length varies due to variations in the thickness of the Si wafer. When the skew adjustment elements 27a and 27b are provided independently as described above, the difference (variation) in element characteristics affects the interference action in the MMI element.

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

  In the conventional optical receiver shown in FIG. 4, the signal light input port and the signal light input terminal of the MMI element 32a are arranged on the same optical axis, and the local light input port and the local light input terminal of the MMI element 32b are arranged. Must be arranged on the same optical axis. Accordingly, the distance between the signal light input port and the local light input port is uniquely determined by the distance between the signal light input terminal and the local light input terminal in the MMI elements 32a and 32b and the distance between the MMI element 32a and the MMI element 32b. End up. Further, since the interval between the signal light input end and the local light input end of the MMI element is determined by the maximum curvature of the optical waveguide within the MMI, it is difficult to reduce this interval.

  On the other hand, 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, the interval between the signal light input port 11 and the local light input port 13 can be arbitrarily set by adjusting the interval between these mirrors. Thereby, 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). Instead of translating the optical axis of the signal light L1 to the local light L2 side, the optical axis of the local light L2 can be translated to the signal light L1 side.

  DESCRIPTION OF SYMBOLS 1A ... Optical receiver, 2 ... Housing, 3 ... Terminal, 4 ... Flange, 11 ... Signal light input port, 13 ... Local light input port, 21 ... Total reflection mirror, 22, 34 ... Beam splitter (BS), 23 ... Variable optical attenuator (VOA), 24 ... PD for monitoring, 26 ... Polarization separation element (PBS), 27, 27a, 27b ... Skew adjustment element, 28, 31, 36, 38 ... Lens system, 29 ... λ / 2 Plate, 30, 30a, 30b ... Total reflection mirror, 32a, 32b ... MMI element, 33 ... Polarizer, 39a, 39b ... Amplifier, L10 ... Monitoring signal light, L1, L11 ... Signal light, L12, L13 ... Polarization Component, L2, L22, L23 ... Local light emission.

Claims (6)

An optical receiver that recovers information contained in the signal light by causing the local light to interfere with the phase-modulated signal light,
Two multi-mode interference elements that interfere the signal light and the local light;
An optical circuit for optically coupling the signal light and the local light to each of the two multimode interference elements;
In the optical circuit, one optical axis of the signal light and the local light is translated to the other side, and the signal light and the local light are translated to maintain the phase relationship while the two multimode interferences are performed. Incident on each of the elements,
Optical receiver. A polarization separation element for branching a part of the polarization component of the signal light and the remaining polarization component, a beam splitter for branching the local light into two local lights,
An optical receiver according to claim 1. A skew adjustment element that compensates for a delay caused by a difference in optical path length on an optical path of a part of the polarization component of the signal light and an optical path of the local light that translates with a part of the polarization component of the signal light Is placed,
The optical receiver according to claim 2. The skew adjustment element is common to some polarization components of the signal light and the local light.
The optical receiver according to claim 3. A half-wave plate is disposed on the optical path of the remaining polarization component of the signal light.
The optical receiver as described in any one of Claims 2-4. A signal light input port for inputting the signal light from the outside, and a local light input port for inputting the local light from the outside,
Light input from one of the signal light input port and the local light input port is translated by being reflected by two mirrors.
The optical receiver as described in any one of Claims 1-5.

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