Optical receiver and optical block

An optical receiver includes: an optical stub which includes an optical fiber; an optical demultiplexer; a plurality of photo detectors; a TIA; an optical block including a first concavity, a second concavity, a first reflective plane, a second reflective plane, and a third reflective plane, the first concavity being configured to hold the optical stub, the second concavity being configured to accommodate the optical demultiplexer, the first reflective plane and the second reflective plane being configured to sequentially reflect a multiplex optical signal so that the multiplex optical signal emitted from an end surface of the optical stub is folded back toward the optical stub and is sequentially incident to the optical demultiplexer, and the third reflective plane being configured to reflect the plurality of single-wavelength optical signals emitted from the optical demultiplexer toward the plurality of photo detectors; and a circuit board.

TECHNICAL FIELD

An aspect of the present disclosure relates to an optical receiver and an optical block.

BACKGROUND

Japanese Unexamined Patent Publication No. 2017-32731 describes an optical receiver that wavelength-divides an input light including a plurality of signal lights having different wavelengths and reproduces an electrical signal from each signal light. Such an optical receiver includes an optical component, a photo detector, a signal amplifying IC (Transimpedance Amplifier (TIA)), and the like.

Here, in a transmission device, a large number of optical transceivers including an optical transmitter and an optical receiver are provided in parallel. If the optical receiver can be miniaturized, the number of transceivers arranged in parallel can be increased and the transmission device as a whole can perform large-capacity, high-speed, wide-band communication.

SUMMARY

An optical receiver according to an aspect of the present disclosure is an optical receiver configured to receive a multiplex optical signal including a plurality of single-wavelength optical signals having peak wavelengths different from each other, the optical receiver including: a circuit board having a first side; a plurality of photo detectors mounted on the first side and configured to convert the plurality of the single-wavelength optical signals to a plurality of electrical signals, each photo detector being configured to receive one of the optical signals in a relation of one to one; an amplifier mounted on the first side and configured to amplify the plurality of the electrical signals; an optical stub including an optical fiber configured to transmit the multiplex optical signal toward an inside of the optical receiver; an optical demultiplexer configured to demultiplex the multiplex optical signal to the single-wavelength optical signals; and an optical block having a first concavity, a second concavity, a first reflective plane, a second reflective plane, and a third reflective plane, the optical block being mounted on the first side, the first concavity being configured to hold the optical stub, the second concavity being configured to accommodate the optical demultiplexer, the first reflective plane being configured to reflect the multiplex optical signal from the optical stub toward the second reflective plane, the second reflective plane being configured to reflect the multiplex optical signal from the first reflective plane toward the optical demultiplexer, and the third reflective plane being configured to reflect the single-wavelength optical signals from the optical demultiplexer toward the photo detectors, in which the optical block is fastened to the first side and covers the plurality of the photo detectors and the amplifier.

DETAILED DESCRIPTION

Detail of Embodiment

A detailed example of an optical receiver according to an embodiment of the present disclosure will be described below with reference to the drawings. Additionally, the present disclosure is not limited to these examples, is defined by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope. In the following description, the same reference numerals are given to the same components in the description of the drawings and redundant description will be omitted.

FIGS. 1 to 4are views schematically illustrating an optical receiver1according to this embodiment. The optical receiver1according to this embodiment receives a multiplex optical signal (wavelength-division multiplexing beam) in which a plurality of (single-wavelength optical signals (single-wavelength beams) having different peak wavelengths (or center wavelengths) are multiplexed. Hereafter, wavelength-division multiplexing is abbreviated as WDM. The optical receiver1is a WDM optical receiving module that optically demultiplexes the multiplex optical signal into the single-wavelength optical signals and regenerates the signal included in each single-wavelength optical signal. Each regenerated signal may be, for example, a Non Return to Zero (NRZ) signal having a binary signal level in amplitude or may be a Pulse Amplitude Modulation (PAM)4signal having a quaternary signal level in amplitude.

As illustrated inFIGS. 1 to 4, the optical receiver1includes an optical stub10, an optical block20, an optical demultiplexer30, a plurality of photo detectors40, a Transimpedance Amplifier (TIA)50, a circuit board60(seeFIG. 4), and a connector portion70.

The optical stub10includes an optical fiber90which is embedded therein so as to transmit a multiplex optical signal to the optical block20. The optical stub10is accommodated in the connector portion70and is optically connected to another stub (not illustrated) in the connector portion70. Another stub includes another optical fiber. The optical stub10and another stub may make physical contact (PC) between the optical fiber90and another optical fiber. That is, the optical stub10forms an optical connection in such a manner that an end surface of the embedded optical fiber90contacts (physically contacts) an end surface of the optical fiber90of another stub. The multiplex optical signal which is transmitted by the optical fiber90is emitted from an end surface10xof the optical stub10to a collimating lens26(to be described later) of the optical block20.

The optical block20is a lens component (a resin member) which is integrally molded. For example, the optical block is made from resin. As illustrated inFIG. 4, the optical block20includes a first concavity21, a second concavity22, a first reflective plane23, a second reflective plane24, a third reflective plane25, a collimating lens26, transmissive planes27and28, and a positioning portion29(seeFIG. 1).

The optical block20holds the optical stub10in the first concavity21. That is, the optical stub10is fitted into the first concavity21so as to be positioned to the optical block20. The optical stub10may be press-fit into, for example, the first concavity. The optical block20accommodates the optical demultiplexer30in the second concavity22. Additionally, the optical demultiplexer30may be fitted into the second concavity22when being accommodated in the second concavity22. For example, the optical demultiplexer30may be fitted into the second concavity22in such a manner that its outer shape is held by a protrusion or the like provided in the second concavity22. Here, the fitting means, for example, that the optical demultiplexer30is accommodated in the second concavity without rattling. Thus, the optical demultiplexer30is fitted into the second concavity22so as to be positioned to the optical block20. More specifically, the optical demultiplexer30is precisely positioned to the second reflective plane24by the second concavity. The multiplex optical signal emitted from the end surface10xof the optical stub10toward the collimating lens26is referred to as WDM beam. The WDM beam emitted from the end surface10xof the optical stub10is a diverging beam, which is converted to a collimate beam by the collimating lens26. The WDM beam converted to the collimate beam travels from the collimating lens26toward the first reflective plane23in the optical block20. Additionally, in the following description, a description can be made such that the direction of the WDM beam traveling from the collimating lens26to the first reflective plane23is the Z direction, the direction intersecting the Z direction and intersecting the light receiving plane of the photo detectors40is the Y direction, and the direction intersecting the Z direction and the Y direction is the X direction. Further, more specifically, the Z direction can be described such that the direction from the collimating lens26to the first reflective plane23is the +Z direction (incoming direction) and the opposite direction is the −Z direction. Further, more specifically, the Y direction can be described such that the direction toward the light receiving plane of the photo detectors40(for example, the downward direction inFIG. 4) is the −Y direction and the opposite direction is the +Y direction. Further, a description can be made such that the plane parallel to the X direction and the Y direction is the XY plane, the plane parallel to the Y direction and the Z direction is the YZ plane, and the plane parallel to the Z direction and the X direction is the ZX plane. The optical block20includes a main body20bhaving a rectangular parallelepiped outer shape and a protrusion20aextending from the main body20bin the −Z direction. The protrusion20ahas a cylindrical outer shape in which a line parallel to the Z axis is a center axis. The first concavity21is provided inside the protrusion20a. The optical stub10has a cylindrical outer shape in which a line parallel to the Z axis is a center axis. The first concavity21is a cylindrical hole in which the line parallel to the Z axis is a center axis and, for example, the optical stub10is fitted into the first concavity21so that its center axis matches the center axis of the first concavity21. Due to such fitting, the first concavity21is positioned with respect to the X direction and the Y direction. The main body20bof the optical block20has, for example, a rectangular parallelepiped outer shape which is elongated in the longitudinal direction (the Z direction). For example, the second concavity22is provided in the plane facing toward the +Y direction. The second concavity opens toward the +Y direction. The optical demultiplexer30has a rectangular parallelepiped outer shape and its outer shape includes an input plane which receives a WDM beam and an output plane which outputs a plurality of single-wavelength beams demultiplexed from the WDM beam. The input plane and the output plane are located on the opposite sides thereof in the outer shape of the optical demultiplexer. For example, the optical demultiplexer30is fitted into the second concavity22so that the input plane faces toward the +Z direction and the output plane faces toward the −Z direction.

The collimating lens26converts a diverging beam emitted from the end surface10xof the optical stub10to a collimate beam. That is, the WDM beam passing through the collimating lens26travels in the +Z direction toward the first reflective plane23after being converted to the collimate beam.

The first reflective plane23is formed so that the WDM beam traveling from the −Z direction toward the +Z direction is reflected toward the +Y direction. The first reflective plane23is located in the +Z direction with respect to the end surface10xof the optical stub10. For example, the first reflective plane23is located between the collimating lens26and an end portion20cof the optical block20. The first reflective plane23is formed as a boundary plane between the resin member and a first reflective concavity while the optical block is provided with the concavity (the first reflective concavity). For example, when the optical block20is placed in air, the first reflective concavity is filled with air. The WDM beam is reflected due to a difference between the refractive index of the resin member and the refractive index of the air. The WDM beam which is reflected by the first reflective plane23travels toward the second reflective plane24. The second reflective plane24is located in the +Y direction with respect to the first reflective plane23. The optical block20is fixed onto the first side of the circuit board60to be described later. The first reflective plane23reflects the WDM beam traveling in a direction parallel to the first side toward a direction opposite to the first side. The direction of the WDM beam traveling from the end surface10xto the first reflective plane23may be referred to as incoming direction. The WDM beam reflected by the first reflective plane23approaches the second reflective plane24in the direction opposite to the first side with going far from the first side. The first reflective plane23is located between the second reflective plane and the first side in the normal direction of the first side. Additionally, the reflection direction of the first reflective plane23is not limited to exactly a right angle (90°) to the first side (the +Y direction). The first reflective plane23may be somewhat inclined from the +Y direction to the Z direction, for example by several degrees. More specifically, the angle of the reflection direction from the first side in the YZ plane can be set to a value from 70° to 110°, namely within 90°±20°. Accordingly, the angle between the incoming direction and the direction of the WDM beam reflected by the first reflective plane23is adjustable in a range of 90°±20.

The second reflective plane24is formed so that the WDM beam reflected by the first reflective plane23is reflected toward the −Z direction. The optical block20is fixed onto the first side of the circuit board60to be described later. The second reflective plane24reflects the WDM beam traveling from the first reflective plane23in a direction opposite to the first side toward a direction parallel to the first side. At this time, the WDM beam reflected by the second reflective plane24travels in the opposite direction of the Z direction (namely the −Z direction) with respect to the WDM beam incident to the first reflective plane23. In this way, the first reflective plane23and the second reflective plane24sequentially reflect the WDM beam so that the WDM beam traveling in the incoming direction is folded back toward the optical stub10(that is, the direction of the WDM beam directed in the +Z direction is changed by 180° in the YZ plane so as to be directed in the −Z direction). The second reflective plane24is formed as a boundary plane between the resin member and the second reflective concavity while the optical block is provided with the concavity (the second reflective concavity). For example, when the optical block20is disposed in air, the second reflective concavity is filled with the air. The WDM beam is reflected due to a difference between the refractive index of the resin member and the refractive index of the air. More specifically, when the angle between the reflection direction of the first reflective plane23and the incoming direction is set to a value A23, an angle between the reflection direction of the second reflective plane24and the incident direction to the second reflective plane24may be set to a value A24so that an equation A23+A24=180□ is satisfied. The WDM beam reflected by the second reflective plane24passes through the transmissive plane27and reaches the optical demultiplexer30provided in the second concavity22. Additionally, the transmissive plane27is one plane that forms the second concavity22in the main body20band is a boundary plane between the second concavity22and the main body20bof the optical block20. Then, four single-wavelength beams for respective wavelengths obtained by the demultiplexing (wavelength-dividing) in the optical demultiplexer30pass through the transmissive plane28, are incident to the optical block20again, and reach the third reflective plane25. The four single-wavelength beams are also collimate beams. The transmissive plane28is one plane that forms the second concavity22in the main body20band is a boundary plane between the second concavity22and the main body20bof the optical block20.

The third reflective plane25is formed so that four (a plurality of) single-wavelength beams emitted from the optical demultiplexer30are reflected toward the plurality of photo detectors40(seeFIG. 1). The third reflective plane25is located between the end surface10xof the optical stub10and the optical demultiplexer30, for example, in the Z direction. The third reflective plane25is formed as a boundary plane between the resin member and the third reflective concavity while the optical block is provided with the concavity (the third reflective concavity). For example, when the optical block20is disposed in air, the third reflective concavity is filled with the air. The single-wavelength beams are reflected due to a difference between the refractive index of the resin member and the refractive index of the air. Additionally, the third reflective plane25performs a reflection, for example, so that one single-wavelength beam is incident to one of four photo detectors40and four single-wavelength beams correspond to four photo detectors40in a relation of one to one. The third reflective plane25reflects the plurality of single-wavelength beams so that the incident angle of the single-wavelength beam with respect to the light receiving plane of the photo detector40is not perpendicular. That is, the third reflective plane25reflects each single-wavelength beam toward a direction slightly inclined in the Z direction (for example, the +Z direction) instead of the perfect −Y direction (the direction perfectly perpendicular to the light receiving plane of the photo detector40). When the single-wavelength beam enters the photo detector40, the incident angle different from the perpendicular direction prevents some portion of the single-wavelength beam reflected by the light receiving plane from returning straight to the third reflective plane25. Each single-wavelength beam reflected by the third reflective plane25is condensed on the light receiving plane (the surface) of the photo detectors40by an exit lens20c(seeFIG. 4). The exit lens20cincludes a lens which focuses a single-wavelength beam on the light receiving plane of a photo detector. Here, the light receiving plane of the photo detectors40is, for example, a plane parallel to the XZ plane. Alternatively, the light receiving plane of the photo detectors40is a plane which is parallel to a mounting plane61x(a first side) of the circuit board60on which the photo detectors40are mounted.

The positioning portion29is provided in, as illustrated inFIG. 1, a portion facing the circuit board60(seeFIG. 4) in the optical block20. For example, the positioning portion29is a cylindrical portion extending toward the circuit board60. For example, the positioning portion29is provided on a plane facing toward the −Y direction of the main body20bof the optical block20and is a cylindrical protrusion extending in the −Y direction. The optical block20is provided with a plurality of (for example, two) positioning portions29. The positioning portion29is formed so as to be insertable into an insertion hole (not illustrated) formed in the circuit board60. The positioning portion29is inserted into the insertion hole of the circuit board60. The plurality of positioning portions29are provided with a plurality of insertion holes. The plurality of positioning portions29are provided so as to correspond to the plurality of insertion holes in a relation of one to one so that each positioning portion29is inserted into each of the plurality of insertion holes. Accordingly, the optical block20is positioned with respect to the circuit board60. For example, the plurality of insertion holes are provided in the mounting plane61x(the first side) of the circuit board60and the plurality of positioning portions29are provided on the plane of the main body20bof the optical block20facing the mounting plane61x. For example, the position of the optical block20with respect to the mounting plane61xis fixed by inserting one positioning portion29into one insertion hole and the direction of the optical block20on the mounting plane61xis determined by inserting the other positioning portion29into the other insertion hole. Additionally, the aligning and positioning may be performed by forming the insertion hole of the circuit board60to be slightly larger than the positioning portion29. Further, the positioning may be performed more finely by press-inserting the positioning portion29into the insertion hole of the circuit board60. In this way, if the positioning portion29can be inserted into the insertion hole, the outer shape of the positioning portion may be, for example, a rectangular prism. In that case, the shape of the insertion hole may be a rectangular shape similar to the rectangular shape in the cross-section of the positioning portion29perpendicular to the Y direction.

The optical demultiplexer30is configured to demultiplex a WDM beam to a plurality of single-wavelength beams. The optical demultiplexer30is provided in the second concavity22and divides the WDM beam reflected by the second reflective plane24into single-wavelength beams on the basis of the wavelength. In order to sequentially guide the incident WDM beam to respective wavelength filters30b(seeFIG. 5), the optical demultiplexer30includes, as illustrated inFIG. 3, a plane (an input plane) to which the WDM beam is incident and a plane (an output plane) which outputs the single single-wavelength beams. The input plane and the output plane are inclined with respect to the direction (the +X direction) intersecting the direction (the −Z direction) to which the WDM beam is incident. For example, when the optical block20is viewed in plan view from the +Y direction, the optical demultiplexer30has a parallelogram shape.

FIG. 5is an explanatory diagram of the optical demultiplexer30included in the optical receiver1. As illustrated inFIG. 5, the optical demultiplexer30has a configuration in which a single reflective member30ais integrated with the plurality of wavelength filters30bhaving different wavelength transmission bands by a transparent optical member30c. The wavelength filter30bis configured as, for example, a dielectric multilayer film (filter group). Specifically, when single-wavelength beams having a plurality of different peak wavelengths (λ0, λ1, λ2, and λ3) are incident to the optical demultiplexer30, the WDM beam is first incident to the wavelength filter30bdisposed at the first position so that only the single-wavelength beam of the wavelength λ3is transmitted and the WDM beam (λ0, λ1, and λ2) of the other wavelengths are reflected. Additionally, inFIG. 5, for convenience of description, the optical paths of the plurality of single-wavelength beams are depicted as lines, respectively, but in fact, one WDM beam includes a plurality of single-wavelength beams having different peak wavelengths. The reflected WDM beam (λ0, λ1, and λ2) are reflected by the reflective member30aand are incident to the second wavelength filter30bso that only the beam of the wavelength λ2is transmitted and the WDM beam (λ0and λ1) of the other wavelengths are reflected. Hereinafter, the WDM beam input to the input plane by repeating the transmission and the reflection in the same way is demultiplexed into a plurality of single-wavelength beams having different peak wavelengths and the single-wavelength beams are output from the output plane. In this way, the optical demultiplexer30optically demultiplexes the WDM beam into a plurality of single-wavelength beams. When the WDM beam is a collimate beam, each single-wavelength beam keeps to be a collimate beam. The input plane is inclined at a significant angle with respect to the X direction and the output plane is inclined at the same significant angle as the input plane with respect to the X direction.

The plurality of photo detectors40are elements that respectively receive a plurality of single-wavelength beams demultiplexed by the optical demultiplexer30and reflected by the third reflective plane25. In this embodiment, the optical receiver1includes four photo detectors40which are provided so as to respectively correspond to four demultiplexed single-wavelength beams (seeFIG. 3). That is, four photo detectors respectively receive four single-wavelength beams. The plurality of photo detectors40convert the plurality of received single-wavelength beams into a plurality of electrical signals (current signals) and output the electrical signals. The plurality of photo detectors40are mounted on the mounting plane61x(the first side) of a Flexible printed circuits (FPC)61of the circuit board60. As illustrated inFIG. 4, the light receiving planes of the plurality of photo detectors40are disposed between the end surface10xof the optical stub10and the optical demultiplexer30in the Z direction.

The TIA50is an amplifier which converts the electrical signals (current signals) output from the plurality of photo detectors40into voltage signals and amplifies the voltage signals. The TIA50is mounted on the mounting plane61x(the first side) of the FPC61of the circuit board60and is disposed so as to be adjacent to the plurality of photo detectors40in the +Z direction. The electrical signal (the voltage signal) output from the TIA50is output to the outside via the FPC61.

The circuit board60includes, as illustrated inFIG. 4, the FPC61and a reinforcing substrate62. The reinforcing substrate62is a substrate that reinforces the thin FPC61so as to have a planar shape and is provided so as to mount the FPC61. The FPC61is a flexible printed substrate. The FPC61includes the mounting plane61x(the first side). The mounting plane61xmounts, for example, the plurality of photo detectors40and the TIA50thereon. For example, other ICs or circuit components may be mounted on the mounting plane61x. In the circuit board60, the optical block20is disposed on the mounting plane61xof the FPC61so as to cover the plurality of photo detectors40and the TIA50. The optical block20may be fixed onto the mounting plane61x. The FPC61and the reinforcing substrate62are provided with the above-described insertion hole. When the plurality of positioning portions29of the optical block20are fitted into the plurality of insertion holes of the circuit board60, a plurality of single-wavelength beams reflected by the third reflective plane25of the optical block20can be respectively incident to the light receiving planes of the plurality of photo detectors40mounted on the mounting plane61x. Accordingly, he fitting of the positioning portions29to the insertion holes allows the optical coupling between the optical block20and the photo detector40mounted on the mounting plane61xto be easily obtained.

Next, the effects of the optical receiver1according to this embodiment will be described.

First, an optical receiver100according to a comparative example will be described with reference toFIG. 6. As illustrated inFIG. 6, the optical receiver100according to the comparative example includes an optical stub117, an optical demultiplexer126, a photo detector129, and a TIA132similarly to the optical receiver1according to this embodiment. Here, in the optical receiver100according to the comparative example, a WDM beam emitted from the end surface of the optical stub117is incident to the optical demultiplexer126and a plurality of single-wavelength beams demultiplexed by the optical demultiplexer126are reflected toward the photo detector129by the reflective member127. The plurality of single-wavelength beams reflected by the reflective member127are received by the photo detector129and an electrical signal output from the plurality of photo detectors129are amplified by the TIA132. In such an optical receiver100, the optical demultiplexer126, the photo detector129, and the TIA132are sequentially arranged in the emission direction (the +Z direction) of the WDM beam emitted from the end surface of the optical stub117. In such a configuration, since the position of the photo detector129is located at a position equal to or deeper than the entire length of the optical demultiplexer126(the deep position in the emission direction) and the TIA132is disposed at the rear stage (the deeper position) of the photo detector129, the entire length of the optical receiver100(the length of the outer shape of the +Z direction) becomes larger than the sum of at least the entire length of the optical demultiplexer126(the length of the outer shape of the +Z direction) and the entire length of the TIA132(the length of the outer shape of the +Z direction).

In contrast, as illustrated inFIG. 4, the optical receiver1according to this embodiment is an optical receiver that receives a multiplex optical signal in which a plurality of single-wavelength optical signals having different peak wavelengths are multiplexed. The optical receiver1includes the optical stub10, the optical demultiplexer30, the photo detector40, the TIA50, the optical block20, and the circuit board60. The optical stub10includes the optical fiber90which is embedded therein so as to transmit a multiplex optical signal. The optical demultiplexer30demultiplexes (wavelength-divides) a WDM beam into a plurality of single-wavelength beams. The plurality of photo detectors40respectively receive the plurality of single-wavelength beams demultiplexed by the optical demultiplexer30. The TIA50amplifies a plurality of electrical signals output from the plurality of photo detectors40. The optical block20includes the first concavity21, the second concavity22, the first reflective plane23, the second reflective plane24, and the third reflective plane25. The first concavity21is formed in the cylindrical protrusion20aextending in the −Z direction from a side facing the −Z direction of the optical block20and holds the optical stub10. The second concavity22is provided so as to be located in the +Y direction with respect to the signal light traveling from the optical stub10toward the first reflective plane23. The second concavity22is provided in the optical block20so as to open in the +Y direction and accommodates the optical demultiplexer30. The first reflective plane23and the second reflective plane24sequentially reflect the WDM beam so that the WDM beam emitted from the end surface10xof the optical stub10and traveling in the +Z direction is folded back by 180° in the YZ plane of the direction of the optical stub10(the −Z direction) and is incident to the optical demultiplexer30. That is, the WDM beam which is incident to the first reflective plane23is reflected in the +Y direction and the WDM beam which is reflected by the first reflective plane23and is incident to the second reflective plane24is reflected in the −Z direction. The optical path of the WDM beam folded back by the first reflective plane23and the second reflective plane24is located in the +Y direction in relation to the optical path of the WDM beam which is incident to the first reflective plane23before being folded back. The third reflective plane25reflects the plurality of single-wavelength beams emitted from the optical demultiplexer30toward the plurality of photo detectors40. At this time, the plurality of single-wavelength beams are reflected so that one single-wavelength beam is incident to one photo detector40. The circuit board60includes the mounting plane61x, the plurality of photo detectors40and the TIA50are mounted on the mounting plane61x, and the optical block20is disposed on the mounting plane61xso as to cover the plurality of photo detectors40and the TIA50.

In such an optical receiver1, the WDM beam emitted from the end surface10xof the optical stub10is folded back by 180° toward the optical stub10by the first reflective plane23and the second reflective plane24and is incident to the optical demultiplexer30. At this time, WDM beam which is incident to the first reflective plane23is reflected in the +Y direction and the WDM beam which is reflected by the first reflective plane23and is incident to the second reflective plane24is reflected in the −Z direction. Then, in the optical receiver1, the plurality of single-wavelength beams emitted from the optical demultiplexer30are reflected toward the plurality of photo detectors40by the third reflective plane25. At this time, the reflection is performed so that one single-wavelength beam is incident to one photo detector40and the plurality of single-wavelength beam correspond to the plurality of photo detectors40in a relation of one to one. According to such a configuration, since the WDM beam travels in the +Z direction in relation to the position of the optical demultiplexer30, is folded back toward the optical stub10, and is incident to the optical demultiplexer30, the photo detector40can be disposed, for example, on the side of the end surface10xof the optical stub10in relation to the optical demultiplexer30. As described above, the entire length of the optical receiver can be made smaller than the configuration in which the optical demultiplexer, the photo detector, and the amplifier are arranged sequentially (in one direction) (the configuration of the optical receiver100according to the comparative example illustrated inFIG. 6). Specifically, for example, in the optical receiver100according to the comparative example, the entire length (from the end surface117xof the optical stub117to an end portion120xof a package) needs to be about 20 mm. However, in the optical receiver1according to this embodiment, since the TIA50can be disposed below the optical demultiplexer30, the entire length of the optical receiver1(from the end surface10xof the optical stub10to an end portion20cof a package) becomes about 15 mm without depending on the entire length of the TIA50. That is, the optical receiver1according to this embodiment is miniaturized to be about 5 mm in the Z direction compared to the optical receiver100according to the comparative example as an example. As described above, according to the configuration of this embodiment, the optical receiver1suitable for miniaturization can be provided. Accordingly, when a large number of optical receivers1are arranged in the transmission device, higher density mounting becomes possible and the communication band per mounting area can be widened. Further, even when the optical receiver1is combined with an optical transmitter and an electronic circuit to form an optical transceiver module (optical transceiver), the size of the optical transceiver can be reduced as compared with the conventional one. Accordingly, since a large number of optical transceivers can be arranged in the transmission device, a larger number of optical transceivers can be mounted and the communication band per mounting area can be widened.

In the above-described optical receiver1, the light receiving plane of the photo detector40may be disposed between the end surface10xof the optical stub10and the optical demultiplexer30in the emission direction of the multiplex optical signal emitted from the end surface10xof the optical stub10. According to such a configuration, the photo detector40is reliably disposed on the side of the end surface10xof the optical stub10in relation to the optical demultiplexer30and hence the entire length of the optical receiver1can be further reduced.

In the above-described optical receiver1, the third reflective plane25may reflect the plurality of single-wavelength beams so that the incident angle of the plurality of single-wavelength beams with respect to the light receiving plane of the photo detector40does not become perpendicular. When the plurality of single-wavelength beams are incident to the light receiving plane of the photo detector40in the perpendicular direction, there is concern that the reflected light of the light receiving plane may be returned straight to the third reflective plane25(as a return light). Regarding this point, the generation of the return light described above can be prevented by reflecting the plurality of single-wavelength beams so that the incident angle with respect to the light receiving plane does not become perpendicular.

In the above-described optical receiver1, the optical block20may include the positioning portion29(seeFIG. 1) which extends toward the circuit board60and the positioning portion29may be formed so as to be insertable into an insertion hole (not illustrated) formed in the circuit board60. According to such a configuration, when the positioning portion29is inserted into the insertion hole, the optical block20can be easily and reliably positioned to the circuit board60.