JPH11231176A - Optical reception module, optical transmission-reception module, and manufacture of the optical reception module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical reception module capable of being coupled with a single-mode fiber, reduced in the small number of components without providing a branching and optical demultiplexer, small in size and low in price. SOLUTION: This optical reception module 67 is constituted by installing a 1st optical fiber 62, a semitransmissive type PD (photodetecting element) 64 which transmits part of signal light and absorbs part of it, and a 2nd optical fiber 65 linearly on a mount. An optical transmission and reception module 67 is constituted by connecting a light emitting element to the 2nd optical fiber 65. To use two-wavelength light for transmission and reception, a PD 64 is used which absorbs almost all of received light wavelength and transmits almost all of wavelength of transmit light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiving module or an optical transmitting / receiving module used for two-way optical communication. Optical communication includes ping-pong transmission in which light of one wavelength is alternately used for transmission and reception, and simultaneous bidirectional communication using light of two wavelengths. The present invention can be applied to any of them.

[0002]

2. Description of the Related Art Due to a reduction in transmission loss of an optical fiber and an improvement in characteristics of a semiconductor laser (hereinafter abbreviated as LD) and a semiconductor light receiving element (hereinafter abbreviated as PD), light having a wavelength of 1.3 μm or 1. Communication of signals (telephone, facsimile, television image, and the like) using light in a long wavelength band of 55 μm is becoming active. This is generally called optical communication. In particular, recently, a system for simultaneously exchanging signals in two directions using one optical fiber has been studied. The advantage of this method is that only one fiber is required.

FIG. 1 is a principle diagram of bidirectional communication using one wavelength (λ) in such a system. This is the office,
The optical demultiplexers 2 and 4 are required on the subscriber side. The office side amplifies the telephone or facsimile (FAX) signal into a digital signal or an analog signal, and then amplifies the semiconductor laser LD1.
Drive. The semiconductor laser (LD) sends the signal of the wavelength λ as an intensity signal to the optical fiber 1. The optical signal enters the optical fiber 3 by the optical demultiplexer 2 and propagates through it.
Distributed to subscribers. The optical fiber 3 is laid around subscribers such as homes, offices, factories and the like. The direction in which a signal is sent from the station side to the subscriber side in this way is called a downlink system.

On the subscriber side, the downstream signal is taken out to the optical fiber 5 by the optical demultiplexer 4 and received by the light receiving element PD2. The PD 2 converts the received optical signal into an electric signal, amplifies the signal, performs signal processing, and reproduces the signal as a telephone voice or a FAX signal. On the other hand, the subscriber transmits a telephone or facsimile image signal to the office. A semiconductor laser LD2 emitting light of wavelength λ is modulated by a telephone signal or an image signal,
The signal is transmitted as an optical signal to the station through the optical fiber 6, the optical demultiplexer 4, and the optical fiber 3. The direction in which a signal is sent from the subscriber side to the station side in this way is called an uplink system. The station side extracts this optical signal to the optical fiber 7 by the optical demultiplexer 2, and
Receive by. This is converted into an electric signal and sent to the exchange or signal processing circuit. Here, in a one-wavelength system in which light having the same wavelength is used for both transmission light and reception light, uplink and downlink signal transmission cannot be performed simultaneously. Therefore, in the case of a system using one wavelength, upstream and downstream signals are transmitted alternately at different times. This is called ping-pong transmission.

As described above, using one optical fiber,
To perform two-way communication using light of one wavelength, the station side,
Both of the subscribers need a functional element for separating the optical path. In FIG. 1, the optical demultiplexers 2 and 4 play the role. The optical demultiplexers 2 and 4 can collectively introduce light having the wavelength λ into one optical fiber. Conversely, light having a wavelength λ propagating through one optical fiber can be distributed to two different optical fibers. An optical demultiplexer is indispensable for bidirectional communication using one optical fiber.

Several optical demultiplexers have been proposed. There are a type using two optical fibers, a type using an optical waveguide, and a type using a multilayer mirror. FIG. 2 shows an optical fiber or optical waveguide type. The two light waveguide portions are brought into close proximity and evanescently coupled to enable energy exchange. By appropriately selecting the distance D and the length L of the coupling portion, the demultiplexing of light
A multiplexing function can be provided. In FIG. 2, the light entered into the optical fiber 8 comes out to the optical fiber 11 as P3. However, about half of the light is transferred to the fiber 12 and is not used. Conversely, when the light P4 is input from the fiber 11, the light P4 is divided into approximately half the light amount, and the fibers 8 and 9 are separated.
Go out of.

[0007] Such an optical waveguide type optical demultiplexer can be similarly used for an optical demultiplexer on the station side and an optical demultiplexer on the subscriber side. The optical demultiplexer shown in FIG. 3 is obtained by depositing a dielectric multilayer film on a diagonal surface of an isosceles triangular prism glass block and attaching another equivalent glass block to form a square prism. The dielectric multilayer film serves as an interference filter. When light having an angle of 45 degrees with respect to the bonding surface is incident, about half of the light is reflected and the other half of the light is transmitted. Such a light demultiplexing function is realized by appropriately selecting the thickness and the refractive index of the dielectric film. Several other optical demultiplexers have been proposed.

[0008] As described above, light has a certain intensity ratio (for example, 1:
The element that is divided into different paths in 1) is called an optical demultiplexer or a demultiplexer / demultiplexer. Those using optical fibers or glass blocks are already commercially available. It should be emphasized that the function of each of the above elements is reduced to about half in all cases. This is one wavelength and unavoidable due to the reversibility of light.

FIG. 4 is a schematic diagram showing a configuration example of a conventional optical transmission / reception module on the subscriber side. The end of the optical fiber 16 connected to the office is connected to an outdoor optical fiber 18 by an optical connector 17. This is separated into upstream light and downstream light by an optical fiber type optical splitter 21. As described above, it is possible to provide a function of splitting light 1: 1 according to the length of the proximity distance between the proximity portions 20 of the two optical fibers. The optical demultiplexer 21 uses a semiconductor laser (L
D) Incoming light is input and transmitted to the optical fiber 16, and light from the optical fiber 16 is extracted to the optical fiber 19 side. This light is received by a photodiode (PD).

[0010] The optical fiber 18 is connected to an LD module 25 by an optical connector 22. The LD module is for converting a digital signal from the subscriber into an optical signal and transmitting it to the station. The optical fiber 19 is connected to the PD module 27 by the optical connector 23. This is for converting an optical signal from the station side into an electric signal and receiving it on the subscriber side. There is also an example using an optical demultiplexer called a beam splitter. For example, EP4632
14-B1 and the like.

FIG. 5 is a sectional view of a semiconductor light emitting element module 28 according to a conventional example. A semiconductor laser chip 29 and a photodiode 30 for monitoring the output of the semiconductor laser chip 29 are provided. The semiconductor laser 29 is mounted on the pole 31 of the header 32 via a submount. The photodiode 30 is fixed to the center of the upper surface of the header 32. A plurality of lead pins 33 are provided at the bottom of the header 32.
The semiconductor laser 2 has a cylindrical cap 34 having a window 35.
9. It is welded to the header 32 so as to surround the photodiode 30. Lead pin 33 and chip 2 by wire
The electrodes 9 and 30 are connected. These elements are connected to an external circuit through lead pins.

Above the header is a cylindrical lens holder 36. The lens holder 36 has a condenser lens 37 in the center hole. A conical housing 38 is further welded onto the lens holder 36. Housing 3
At 8 is attached a ferrule 39 and an optical fiber 40 whose tip is fixed by the ferrule. The lens holder 36 and the housing 38 are fixed by aligning the semiconductor laser 29, the lens, the optical fiber, and the like. The lens enhances the light collecting property to increase the coupling efficiency between the laser and the optical fiber. The light emitted from behind the semiconductor laser is monitored by the monitoring photodiode, and the drive current is controlled by the feedback circuit. Thus, the output of the semiconductor laser can be kept constant even if there is a temperature change.

The present invention relates to a novel structure of a module including a light receiving element. Therefore, the light receiving element module according to the conventional example will also be described. FIG. 6 is a sectional view of a light receiving element module 27 according to a conventional example. A PD chip 41 is fixed on a disk-shaped header 42. The header 42 has a plurality of lead pins 43. A lens holder 46 holds the condenser lens 47. A housing 48 is welded to the top of the lens holder 46. Housing 48
A ferrule 49 to which the tip of the optical fiber 50 is fixed is inserted into the optical fiber 50.

The tip of the optical fiber 50 is cut obliquely. Light emitted from the optical fiber 50 is condensed by a lens and enters the light receiving element 41. In order to receive 1.3 μm light or 1.55 μm light as a light receiving element (PD),
PDs using nP as a substrate and InGaAs as a light receiving layer are often used. As described above, since the present invention relates to the structure of the light receiving element, the structure of the conventional light receiving element chip will be described in more detail.

FIG. 7 is a sectional view of a conventional semiconductor light receiving element chip. On the n-InP substrate 52, n-InP
P buffer layer 53, n-InGaAs light receiving layer 54, n-
The InP window layer 55 is epitaxially grown. n-I
The central portion of the nP window layer 55 and the InGaAs light receiving layer 54 is a zinc diffusion region 56. Since the zinc diffusion region becomes p-type, a pn junction is formed between the zinc diffusion region and the n-type region. On this p-type region 56, a ring-shaped p-electrode 57 is formed.
An n-electrode 61 is formed below the n-InP substrate 52. The region surrounded by the p-electrode 57 has an antireflection film 5
8 are coated. The window layer outside the p-electrode 57 and the end of the pn junction are protected by a passivation film 59. Signal light enters from the side of the InP window layer where the antireflection film 58 is located, is absorbed by the InGaAs light absorbing layer (light receiving layer) 54, and is converted into an electric signal.

FIG. 8 is a graph showing the sensitivity characteristics of such a light receiving element. The horizontal axis is wavelength (μm), and the vertical axis is sensitivity (A / W). The sensitivity graph shows the rising part P,
A flat portion Q and a falling portion R are included. In this example, the wavelength range showing high sensitivity ranges from 1.0 μm to 1.6 μm. The high sensitivity range is determined by the materials of the light absorbing layer (light receiving layer) 54 and the window layer 55. Only light between the band gap of the light receiving layer and the band gap of the window layer is sensed. In this case, I
Since nGaAs is the light receiving layer 54, the upper limit is about 1.6 μm.
And the lower limit is 1.0 μm because InP is the window layer 55.
become. A photodiode having such a wide sensitivity characteristic has been used in a conventional light receiving element module for optical communication. The light emitted from the optical fiber spreads in a substantially circular shape. Therefore, a light receiving element having a circular light receiving surface is used.

[0017]

A conventional optical transmitting / receiving module combining an optical demultiplexer, a semiconductor light emitting element and a light receiving element is composed of three main parts as shown in FIG. Having three parts increases the size and price. In addition, there is a problem that it is difficult to use for long-distance communication because light is lost at a coupling part such as a duplexer or an optical fiber. Therefore, there is a problem that it is difficult to spread the optical transmission / reception module to general households.

Several modules for bidirectional communication without using an optical demultiplexer have been proposed. Tokuhei 7-58806
No .: These are arranged in the order of LED and PD in the order of multimode optical fiber + surface emitting LED + light receiving element. Small LEDs are glued directly onto large PDs. L
Although the ED partially blocks the incident light, the light receiving element can detect the part entering from the side. JP-A-57-172
No. 783: Surface-emitting LEDs and PDs are also arranged from the side closer to the multi-mode optical fiber. A small LED is manufactured in a part of the PD. The whole is housed in a package.

Each of them is a multimode optical fiber and has a large diameter. The diameter of the emitted light is as large as about 100 μm. This is N. A. (Numerical aperture), the beam becomes wider with a larger cross-sectional area. In this case, even if a small laser is provided at the center of a wide PD, most of the light reaches the light receiving element through portions other than the laser. Since the beam is wide (200 μm to 300 μm in diameter) and the LED chip is small, a lot of light reaches a place other than the shadow of the LED, and the light enters a light receiving element having a wide light receiving surface. Does not absorb the received light by the LED. This is possible because wide multimode light is propagated through the multimode optical fiber. However, this cannot be used for optical communication using a single mode fiber, which is the object of the present invention. A multi-mode fiber having a large core diameter is easy to optically couple, but cannot transmit much information without being distorted.

The optical fiber used in the optical communication of the present invention is a single mode fiber having a core diameter of 10 μm. Since the optical transmission system using a single mode fiber has a small core diameter, coupling is difficult, and the laser must be positioned and fixed near the core end face of the fiber. Since the laser chip has a thickness of several hundred μm and a width of several hundred μm, if it is placed in front of a single mode fiber, most of the light will be blocked. Even if a photodiode is placed behind it, no light reaches the photodiode. , Cannot be used for subscriber optical communication using single mode fiber.

It is a first object of the present invention to provide a small and inexpensive optical receiving module which can be coupled to a single mode fiber and has a smaller number of components. It is a second object of the present invention to provide an optical receiving module with low light loss. It is a third object of the present invention to provide an optical receiving module that can greatly contribute to practical use of an optical subscriber system. It is a fourth object of the present invention to provide an optical receiving module having a small number of alignment points and capable of reducing the assembly cost. It is a fifth object of the present invention to provide a low-cost optical transmitting / receiving module using the optical receiving module of the present invention.

[0022]

An optical receiving module according to the present invention comprises a first optical fiber, a semi-transmissive light-receiving element that absorbs a part of signal light and transmits a part of the signal light, and a second light. The fiber is provided on a straight line. In the case of using light of one wavelength, the optical transmitting and receiving module of the present invention has a first optical fiber, a semi-transmissive light receiving element, and a second optical fiber provided in a straight line on an appropriate mount. Two optical fibers are connected to a light emitting element that emits light of that wavelength. The light receiving element absorbs a part of the received light transmitted from the outside and converts it into an electric signal, and the transmission light emitted from the light emitting element enters the semi-transmissive light receiving element from the second optical fiber and is received by the light receiving element. The portion is absorbed, and the remainder enters an optical transmission line through an optical fiber and is transmitted outside.

In order to arrange the first and second optical fibers in a straight line on the mount, it is preferable to previously cut a groove in the mount. For example, a groove such as a V groove, a circular groove, or a square groove is linearly provided on the mount. For the mount, for example, a Si substrate, a glass substrate, a ceramic substrate, a metal substrate, or the like can be used. Except for the combination with an optical fiber, there are many common features with the prior application of the inventor of the present invention, Japanese Patent Application No. 8-104405, entitled “Optical Transmitting / Receiving Module”.

A light receiving module according to the present invention is such that a light receiving element and an optical fiber through which signal light partially passes are arranged in a straight line on an appropriate mount. The optical fiber-partially transmitted light-receiving element-the optical fiber or the light emitting element is arranged in a straight line. There is no branch for spatially separating light. The salient features of the present invention are that there are no branches and no optical demultiplexers. The reception light and the transmission light are not spatially separated by the branch. The reception light and the transmission light propagate on the same straight line. Since the light travels on the same straight line, there is no need to separate transmitted and received light, and no branching is required.

The present invention has a novel feature in the light receiving element (photodiode). It uses a partially transmissive and partially absorbing photodiode. Since it is partially transmissive, a light emitting element can be provided immediately after that through an optical fiber. It is a feature of the present invention that the light receiving element is partially transmissive and the incident side optical fiber, the light receiving element, and the outgoing side optical fiber are connected in series. The light receiving element has a very unique property of partial absorption and partial transmission. The ratio of absorption: transmission may be any number as long as it is finite. This can be freely determined according to the purpose of the module and the capabilities of the light emitting element and the light receiving element. However, for the sake of simplicity, the embodiments of the present invention will be described hereinafter with half absorption and half transmission. The light receiving element is also simply referred to as a transflective type.

Photodiodes are classified into a front illuminated type (as shown in FIG. 7) and a back illuminated type (incident from the substrate side). In any of the conventional photodiodes, the side opposite to the incident side is shielded by an electrode so that light does not leak. In a conventional light receiving element, it can be said that all light is absorbed by the light receiving element. Instead, the light receiving element used in the present invention uses a transmission type (semi-transmission type) light receiving element. The transflective light receiving element itself is new. The present invention is not limited to a novel light receiving element, and a light emitting element can be provided behind such a light receiving element to form an optical transceiver module. This is a very novel device in which a light receiving element, an optical fiber, and a light emitting element are linearly arranged.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Why conventional optical transceiver modules are large and expensive? The present inventor has thought variously about the cause. Conventional optical transmission / reception modules always use expensive optical demultiplexers. Why do we need an optical demultiplexer? I thought about it. In order to realize two-way communication with one optical fiber, light must be divided into going and returning. Outgoing light exits the light emitting element and return light is detected by the light receiving element, but the light emitting element and the light receiving element must be in different optical paths. Therefore, in the conventional optical transmitting and receiving module, the optical demultiplexer was essential.

In the optical fiber couplers shown in FIGS. 1 and 2 and the multilayer mirror shown in FIG. 3, the light intensity is reduced to half or to a predetermined designed branch ratio. The ratio of the amount of light that enters the optical fiber from the laser and the ratio of the amount that exits the optical fiber and enters the light receiving element is complementary. That is, when the coupling efficiency T of the laser is increased, the light receiving efficiency R of the photodiode is reduced. Since branching is used, T + R = 1 even in the best case due to its geometric constraints. There is such a thumb rule even if there is no loss. For example, T = 0.5, R = 0.
5 This was an unavoidable difficulty as long as the system used one wavelength.

Here, for the sake of simplicity, the case where the branching ratio is 1: 1 will be described. Why use an optical fiber demultiplexer or a mirror demultiplexer? This is because it is necessary to clearly distinguish the light paths of the light emitting element and the light receiving element. FIG.
If the optical demultiplexer shown in FIG. 3 is used, the optical path is clearly divided into two. Since the transmitted light and the received light have different directions of flow, it seems natural that the optical path must be bisected.

There is an error in common sense. Don't be preoccupied with prejudice. Is it really necessary to bother the optical path to the point of using a branch? It may be necessary if transmitting and receiving at the same time. However, here, it is limited to ping-pong transmission. In the case of ping-pong transmission, transmission and reception times are different. Transmission and reception are not simultaneous. It is sufficient that the laser emits light during transmission and that only the photodiode operates during reception.

The inventor has noticed that branching the optical path is not essential for ping-pong transmission. Even if a photodiode and a laser diode are placed in series on a single optical path, the laser light should reach the optical fiber if the photodiode transmits some light. That is, if a transflective light receiving element is used, the light receiving element, semiconductor laser, optical fiber, and the like can be arranged on a straight line. The present invention has been made based on such an idea. That is, the present invention provides an optical transmission line (optical fiber),
A transflective light receiving element, an optical fiber, and a light emitting element are arranged in series on one optical path. The difference from the conventional module lies in the non-branching linear type and the light-receiving element semi-transmission type.

FIG. 9 shows the principle of the present invention. A first optical fiber 62, a photodiode 64, and a second optical fiber 65 are arranged in series on the same optical path. At the other end of the second optical fiber 65, a laser 70 is installed. As described above, the photodiode 64 includes a light receiving layer (absorption layer).
This is a semi-transmissive photodiode that is thin and allows half of incident light to escape. A relay optical fiber 65 is provided behind the photodiode 64, and a semiconductor laser 70 is provided behind the optical fiber 65.
There is. The optical fiber may bend, but substantially
A photodiode, an optical fiber, and a laser are arranged in series in the optical fiber path. There is no distinction between the optical paths of the received light and the transmitted light, and there is no branch for separating the transmitted light and the received light. The transmission light from the semiconductor laser 70 can enter without loss by connecting the fibers. The use of the transflective photodiode 64 eliminates the need for an optical demultiplexer. It is significant that an expensive optical demultiplexer can be omitted. FIG. 9 is a conceptual diagram as a matter of course, and other specific measures are taken to make an actual module.

The basic idea of the present invention utilizes the basic physical phenomenon that light travels straight ahead. Furthermore, a photodiode absorbs all light,
This overturns the conventional idea that it is better to obtain a sensitivity close to 0%. Rather, the present invention uses an entirely new photodiode that absorbs only half of the incident light and converts it photoelectrically, while transmitting the other half. This has enabled an unbranched straight optical path module. In the conventional bidirectional module, the optical path of the light-receiving element and the light-emitting element has been captured by a firm prejudice that the optical path must be different, so an optical demultiplexer that forcibly bends the optical path has been used. In the present invention, the light receiving element and the light emitting element are arranged in a straight optical path, and there is no branch. There is no branch, so no optical demultiplexer is required.

According to the present invention, since the transflective photodiodes are arranged on the axis extension of the optical fiber, the following effects are obtained. One is that an optical coupler (optical demultiplexer) is not required. Another is that the entire module can be reduced in size because all the components can be accommodated in one package. Furthermore, since the number of parts is small, the module is inexpensive. In order to spread optical communication widely, it is most important that equipment be inexpensive. The present invention meets such a need.

Further, as shown in FIG. 9, an optical transmitting / receiving module for ping-pong transmission can be easily configured by combining with a standard semiconductor laser currently manufactured. Further, since the receiving section and the transmitting section are separated by the optical fiber, the receiving section and the transmitting section can be freely arranged on the board.

[0036]

Embodiment 1 (FIG. 9: Basic Configuration) In the embodiment of FIG. 9, an optical fiber 62, a semi-transmissive photodiode 64, and an optical fiber 65 are arranged on a mount 66 in series. The PD 64 and the optical fibers 62 and 65 are mounted on the mount 66.
Is fixed and the relative position is determined. A semiconductor laser 70 may be provided at the end of the second optical fiber 65. Here, the optical fiber 67 for guiding the light of the semiconductor laser 70 is
At the connection point 71. The photodiode 64 is of a semi-transmissive type, in which a thin active layer (also referred to as a light absorbing layer and a light receiving layer) and other epitaxially grown layers are provided on an InP substrate. Therefore, only about half of the light is absorbed and the remaining light is transmitted as it is. Assuming that the light absorption coefficient of the active layer is α, the light traveling by x is exp (−αx)
Therefore, if the thickness is determined to a value of 0.5, half absorption and half transmission are obtained. 0.5 =
Since exp (−0.7), x where x = 0.7 / α gives a thickness that realizes half absorption and half transmission.

For example, when the light absorption layer is made of InGaAs (λ
g = 1.67 μm) is α = 1 μm ⁻¹ , so if its thickness is d = 0.7 μm, it can absorb exactly half light and transmit half light. For example, if the light absorption layer is InG
In the case of aAsP (λg = 1.4 μm), α = 0.7 μm
^Since it is ^-1 , if the thickness d is 1 μm, it means half absorption and half transmission. However, it is not strictly half-transmitting and half-absorbing. Sometimes it is better to increase the transmission ratio by the power of the laser,
In some cases, it is better to increase the absorption ratio. The received light travels right through the first optical fiber 62 and enters the semi-transmissive PD 64 where it is sensed. The other half of the received light is transmitted and further proceeds to enter the laser 70.

However, this is ping-pong transmission, and at the time of reception, since the laser is at rest, there is no problem with the laser due to transmitted light. At the time of transmission, transmission light is emitted from the laser 70 and travels to the left along the optical fibers 67 and 65. This is P
This is half absorbed by D64, but is not perceived because it is not during reception. Half of the transmitted light travels through the optical fiber 62 to the office side. Since the transmission and reception times are different in ping-pong transmission, the laser light may be half absorbed by the PD.

[Embodiment 2 (FIG. 10: Built-in Amplifier)] In the embodiment of FIG. 10, an amplifier (for example, a Si IC) 72 for amplifying a photocurrent signal of a light receiving element is provided on the same mount 66. The amplifier and the electrode of the light receiving element are connected by a short wire on the same mount. Therefore, a stray capacitance is small, and a high-sensitivity receiver which is hard to receive noise can be manufactured. Such a module incorporating an amplifier in the same module is called PIN-AMP. If an amplifier is provided close to the light receiving element, it will be amplified by this and the impedance will drop,
After that, noise does not enter even if the wiring becomes slightly longer. This increases the degree of freedom in arrangement of other components of the receiving circuit. The manner of connection between the amplifier 72, the light receiving element 64, and the power supply varies depending on the purpose. FIG. 10B shows a general circuit example. In this case, the cathode of the _PD 64 is connected to the power supply V _PD , and the anode is connected to the input of the amplifier. A weak photocurrent can be amplified by the amplifier.

Example 3 (FIG. 11: V-groove cut) FIG.
In the embodiments of FIGS. 1A and 1B, a Si substrate 74 having a V groove 73 cut is used as a mount. FIG. 11A is a plan view, and FIG. 11B is a side view. V groove 7 in a straight line
3, the semi-transmissive PD 64, the first optical fiber 62, and the second optical fiber 65 are fixed to this. Since the two optical fibers are fixed in the V-groove, the optical axes of the optical fibers are easily aligned. The V groove serves as a guide for the optical fiber.

[Embodiment 4 (FIG. 12: V-groove is cut and filled with resin)] The embodiment of FIG. 12 also uses a Si substrate 74 as a mount. The same applies to the point that the V groove 73 is cut to serve as a guide. Further, the space between the optical fibers 62 and 65 and the PD 64 is filled with a translucent (transparent to the wavelength λ) resin 75. The refractive index is almost the same as that of the optical fiber core. It is possible to reduce the reflection of light at the end faces of the optical fibers and the PD, and to prevent the end faces of the optical fibers 62 and 65 and the PD 64 from being damaged due to collision. Of course, this resin 75 can be used for fixing the fiber.

Fifth Embodiment (FIG. 13: Self-Alignment Type) A single mode fiber has a core system of only about 10 μm, and it is difficult to align the axes. In order to facilitate the alignment, it is effective to assemble a method in which one optical fiber is fixed to a substrate in advance, an intermediate portion is cut off, and a PD is inserted and fixed there. This will be described with reference to FIG. FIG. 13 (a)
As shown in FIG.
Cut. The optical fiber 76 is fixed there with an embedding resin or the like. Since the optical fiber is fixed in the linear groove 73, the optical fiber is also fixed in a straight line. Next, a hollow is made flat in the center of the Si substrate 74 in a direction orthogonal to the optical fiber. FIG. 13B shows this. The depth of the groove is greater than the depth of the V-groove. Flat PD insertion groove 7 orthogonal to V groove on substrate
7 can be done. By cutting the PD insertion groove 77, the optical fiber 76 is simultaneously cut right and left. The left is the first optical fiber 62, and the right is the second optical fiber 65.

The semi-transmissive PD 6 is inserted into the flat PD insertion groove 77.
Insert 4 and fix. This is the state shown in FIG. Since one optical fiber 76 was originally cut to the left and right, the direction of the axis coincides from the beginning. Transmitted light from the laser 70 enters the optical fiber 62 from the optical fiber 65 through the PD 64. This method has less deviation of the optical axis between the optical fibers 62 and 65 than the method of fixing the PD and fixing the optical fibers 62 and 65 in the V groove as shown in FIG. Therefore, there is an advantage that the transmission light has lower loss.

Embodiment 6 (Structure of transflective PD: planar type: FIG. 14) The present invention uses a transflective PD. The transflective PD is the first one proposed by the present inventors. In the present invention, the structure of a semi-transmissive PD is described because the PD is not a target but a transflective PD is an essential requirement. Unlike normal PD, it transmits some light. Although the distribution ratio is arbitrary, for example, about half of the light is absorbed and detected, and about half of the light is transmitted. Therefore, neither the front surface nor the back surface of the PD is blocked by the electrode. It is characterized in that the light receiving layer is extremely thin. The conventional PD has a light-receiving layer thickness of 4 μm to 6 μm regardless of whether it is an InGaAs light-receiving layer or an InGaAsP light-receiving layer. However, the PD of the present invention has a thickness of about 0.7 μm in the case of an InGaAs light receiving layer. The thickness of the InGaAsP light receiving layer is about 1.0 μm.

FIG. 14 shows a semi-transmissive P used in the present invention.
D will be described. FIG. 14A is a sectional view, and FIG. 14B is a plan view. InGa with sensitivity between 1.0 μm and 1.6 μm
It is an example of AsPD. On the n-InP substrate 90, n-
An InP buffer layer 91, an n-InGaAs light receiving layer 92,
The n-InP window layer 93 is epitaxially grown in this order. The substrate was 300 μm thick sulfur S-doped n-In.
P wafer. The carrier concentration is n = 5 × 10 ¹⁸ cm
It is ^-3 . The thickness of the n-InP buffer layer 91 is 2.5 μm.
m. The InGaAs light receiving layer 92 has a thickness of only 0.7 μm. The carrier concentration of the InGaAs layer is n = 1 × 1
0 ¹⁵ cm ^-3 . The thickness of the InP window layer is 1.5 μm, and the carrier concentration is n = 2 to 3 × 10 ¹⁵ cm ⁻³ .
Epitaxial growth is performed by chloride vapor phase epitaxy (C-VPE) using a chloride or an organic metal MO-CVD method.

At the center of the upper surface, a circular p-type region 94 is formed.
It is formed by a zinc selective diffusion method using an iNx film as a mask. The central part of the window layer 93 and a part of the central part of the light receiving layer 92 become p-type. A pn junction is formed at the boundary between the n-type part and the p-type part. The upper portion of the InGaAs light-receiving layer 92 is p-type, and the lower portion is n-type, and a pn junction exists therein. On the upper surface of the p-type region 94, a p-electrode 95 on the ring is provided. For example, Au
This is a p-electrode of a Zn alloy. The inside of the ring p-electrode 95 is a region where light is to enter. Here, an anti-reflection film 96 is formed. The outside of the ring p electrode 95 is covered with a passivation film 97. The passivation film 97 covers and protects the edge of the pn junction with the window layer 97.

The n-InP substrate 90 is originally 300 μm
The back surface is polished to a thickness of 100 μm. This is to make the distance between the optical fibers 62 and 65 as short as possible to reduce the coupling loss. From the limit of the polishing technique and the limit of the subsequent handling technique, about 50 μm is the limit of the thinning. On the back surface of the thinned InP substrate,
The ring-shaped n-electrode 98 is formed not on the entire surface but only on the outer portion. For example, an AuGeNi alloy electrode. The portion surrounded by the ring n-electrode 98 is
9 covered. This is λ / 4 (λ =
1.3 μm). In this light receiving element, both the p-electrode 95 and the n-electrode 98 are electrodes whose central portions are open. Approximately 5 of the incident light entering from the top (surface)
0% exits through the lower opening.

In the transflective PD used in the present invention,
About half of the incident light from the front exits the back. There are two conditions for this to happen. One is that both the p-electrode and the n-electrode are open at the center and are, for example, ring-shaped. Another reason is that the thickness of the light receiving layer is set to a thickness that absorbs half of the light. Semiconductors and insulators have a band gap. Light having a wavelength longer than the wavelength corresponding to the band gap is transmitted, but light having a wavelength shorter than the band gap wavelength is absorbed. InP has a wide band gap and transmits light of 1.0 to 1.6 μm. The light-receiving layer has the narrowest band gap among the epitaxial layers. Therefore, absorption is determined by the thickness of the light receiving layer.

Assuming that the absorption coefficient is α, the intensity of transmitted light traveling x from the surface is reduced to exp (−αx). FIG. 15 is a graph showing the relationship between InGaAs thickness and transmittance.
The horizontal axis is the thickness, and the vertical axis is the transmittance (%). Light transmittance T
= Exp (-αx). exp (−αx) = 0.5
The transmitted light intensity is halved at a depth x. If the thickness of the light receiving layer is determined as x, the light receiving layer absorbs half of the light. exp (−0.7) = 0.5. d = 0.7
The thickness d corresponding to / α realizes half transmission and half absorption. I
In the case of nGaAs, α = 1 μm ⁻¹ , so that when the thickness of the light receiving layer is 0.7 μm, a half-permeation and half absorption are obtained. Since InGaAsP has α = 0.7 μm ⁻¹ , half transmittance and half absorption can be obtained when d = 1.0 μm.

[Embodiment (Structure of transflective PD; mesa type: FIG. 16)] The present invention can be applied to a mesa type light receiving element as well as the present invention. FIG. 16 shows a mesa-type transflective PD. FIG. 16A is a sectional view, and FIG. 16B is a plan view. n-type In
On a P substrate 100, an n-type InP buffer layer 101, n
-Type InGaAs light-receiving layer 102, p ⁺ -type InP window layer 103
Are epitaxially grown. A p ⁺ -type InP window layer is grown from the beginning rather than by Zn diffusion. p ⁺
Carrier concentration of the p-type InP window layer is p = 1-5 × 10 ¹⁸ cm
It is ^-3 . The thickness of the n-type InGaAs light receiving layer 102 is equal to 0.1.
7 μm.

Window layer 103, light receiving layer 102, buffer layer 1
The area around 01 is removed by etching. It is called mesa because it has a trapezoidal shape. The exposed slope is covered with a passivation film 106 of SiNx. The InP substrate has a thickness of 300 μm at the beginning.
The thickness is reduced to 00 μm. A ring-shaped p-electrode 104 is mounted on the p ⁺ -type window layer 103. The central part is covered with the antireflection film 105. A ring-shaped n-electrode 109 is attached to the back surface of the InP substrate. The central part is similarly covered with an anti-reflection film 110. Again, the transmittance for 1.3 μm light was 50%.

[Embodiment (Fixing Planar Type PD to PD Carrier: FIG. 17)] FIG. 17 shows an embodiment using the above-mentioned planar type semi-transmissive PD.

(1) The PD carrier 121 is used. It is made of alumina and has raised left base 122 and right base 123
With. The center of the PD carrier 121 has a recess 124. In other words, the left and right bases 122 and 123 are partially connected, but the upper half of the center is an opening (300 μm × 300 mm).
μm) 124. An electrode pattern 127 is printed on the left front end face 125 and the left base 122. An electrode pattern 128 is formed on the right front end face 126 and the right base 123. Transflective PD chip 1 with a light receiving diameter of 200 μm
20 is the front end face 125 of the alumina PD carrier 121,
126 is bonded by SnPb solder.
The bottom electrode is directly joined to the left electrode pattern 127. On the right front end surface 126, there is an isolated metallized pattern (not shown in FIG. 17) different from the electrode pattern 128 so that the bottom electrode of the PD can be soldered. The p electrode of the PD is connected to the right electrode pattern 128 by an Au wire 129 having a diameter of 20 μm.

(2) On the other hand, a square Si substrate 130 of 15 mm × 20 mm × 1 mm is prepared. Square Si substrate 130
V-groove 13 for fixing the fiber with a dicing saw
1, 133 are cut in a straight line. Core diameter 10 in V groove
Single mode fibers (SMF) 135 and 136 having a diameter of 125 μm and a cladding diameter of 125 μm are fixed with an adhesive. Next, the PD carrier groove 13 is perpendicular to the V groove.
2 is formed by etching. PD carrier groove 13
2 is 1 mm long × 3 mm wide × 0.5 mm deep. This separates the V-groove into two parts 133 and 131 at the front and rear. The optical fiber also splits into two parts 135,136. However, the axes of the optical fibers are coincident.

The PD to which the transflective PD 120 was fixed earlier
The carrier 121 is fitted into the PD carrier groove 132 and fixed with an adhesive. The end faces of the optical fibers 135 and 136 face each other before and after the light receiving surface of the PD.
Thereafter, a translucent (transparent) resin, for example, a silicon-based adhesive is filled between the fiber (SMF) and the front and back surfaces of the PD. This is to prevent the reflection of light at the end face of the optical fiber or the PD by eliminating the air gap. Although only the PD may be mounted on the Si substrate, an amplifier (AMP) may be mounted in addition to the PD 120. In that case, the photocurrent of the PD can be immediately amplified. One optical fiber is connected to an external optical fiber, and the other optical fiber is connected to a semiconductor laser. As a whole, it becomes an optical transceiver module. The only part is the optical receiving module.

(3) The above step (2) can be replaced by another step. First, a V-shaped groove 131 is formed linearly on a Si substrate 130. Then, in the center,
The D carrier groove 132 is formed by etching so as to be orthogonal to the V groove 131. In the PD carrier groove 132,
The PD carrier 121 to which the D120 is attached is fitted and fixed. Next, from the left and right of the PD carrier 121, the V groove 1
33, 131 are single mode fibers 135, 136.
Press lightly. Further, the PD 120 and the optical fiber 1
A translucent resin such as a silicon-based resin is filled between the end faces 35 and 136. Further, the two optical fibers 135 and 136 are fixed to the V-shaped grooves 133 and 131 with an epoxy resin. Also in this case, the PD may be used alone, or the AMP may be set to S
You may make it mount on an i substrate. In the following embodiment, a device manufactured by the method (3) will be described.

(4) The electrode patterns 127 and 128 of the PD carrier 121 and the electrode patterns (not shown) on the substrate 130 were connected by gold wires. Next, the Si substrate 130
Was stored in a package 140. The lead pins 141, 142, 143, 144, etc. which are exposed to the outside and the Si substrate 1
The 30 electrode patterns were connected with Au wires. The package was covered with a metal cap. Thus, a state as shown in FIGS. 18A and 18B having optical fibers on both sides is obtained. The optical receiving module 150 of the present invention is located at the middle.
Optical fibers (SMF) 153 and 154 extend on both sides. Each is 50 cm long. FC connectors (optical connectors) 151 and 152 are attached to both sides. In the case of FIG. 18A, the equivalent optical connectors 151, 1
In the case of FIG. 18B, the LD module 155 is connected to one of them. The PD module 150 and the LD module 155 are combined to form an optical transceiver module.

(5) First, only the PD is transferred to the PD module 15
The data when mounted on 0 will be described. 1.3 of laser LD
μm light from the optical connector 151 on the left side of FIG.
The light is incident on the PD of the D module 150. 5V for PD
The reverse bias is applied. The sensitivity was 0.45 A / W. The best sensitivity for a conventional PD that absorbs 100% light is 0.95 A / W. The PD of the present invention is about half as sensitive. Since the absorption was set to be half, it is as theoretical. The absorption loss due to the optical connector is slightly included, so that it is slightly smaller than half. Further, 1.3 μm light was made incident from the right optical connector 152 and the transmittance was obtained by measuring the intensity of light emitted from the left optical connector 151. As a result, the transmittance is 4
It turned out to be 5%. From the above measurement, it can be seen that the light receiving module 150 divides the incident light into approximately 1: 1 and absorbs half and transmits half.

(6) Next, the AMP is used for the PD module 15.
Experiments were carried out on those housed in 0. AMP is Si-I
C. The power supply voltage is 3.3V. A pulse light of 1.3 μm is transmitted from the LD module 155 on the right side, and a pulse signal light of 1.3 μm is also transmitted from the left side to 50 Mbp.
An experiment of ping-pong transmission at a speed of s was performed. As a result, FIG.
It has been found that the same transmission characteristics as those of the optical transmission / reception module according to the conventional example using the optical fiber type coupler as shown in FIG.

FIG. 19A shows the configuration of a conventional optical transceiver module. FIG. 19B shows an optical transceiver module of the present invention. Since it is ping-pong transmission, only light of one wavelength is used. For example, 1.3 μm can be used for transmission and reception. Comparing the two, (B) is significantly simplified. The excellence and usefulness of the present invention will become apparent.

In the optical transmitting and receiving module of the present invention, the flow of light stays within one fiber. Therefore, no optical coupler is required. Conversely, if the flexibility of optical fiber is used, PD
Modules and LD modules can be arranged freely. Although the received signal is very weak and the drive signal for the transmitted signal is large current, noise is likely to enter from the transmitting side to the receiving side. However, since the present invention separates the PD module and the LD module, there is no fear of noise contamination. Absent. It is also cut off thermally. A ping-pong transmission type optical transmission / reception module can be configured in combination with the light receiving element module of the present invention without obtaining a new coupler or manufacturing a module integrated with the coupler, as long as there is an LD module.

Another advantage is that only a receiving unit can be newly added without changing the conventional transmitting module or transmitting supply. As described above, the present invention can provide an inexpensive and convenient receiving module or transmitting / receiving module that has never been seen before.

Embodiment (Simultaneous Bidirectional Optical Transmit / Receive Module; PD in FIG. 20) Although the above description is an improvement relating to ping-pong transmission, the present invention can also be applied to a simultaneous bidirectional optical transmit / receive module. Light of two different wavelengths is used separately for transmission and reception. In this case, the meaning of “semi-transmissive” of the semi-transmissive PD is different from before. Until now, one wavelength of light was used for both transmission and reception, and the half-absorbing and half-transmitting light was of the semi-transmissive type. Here, completely absorbing the reception light λ ₁ and transmitting all the transmission light is called a semi-transmission type.

Here, a semi-transmissive PD having a thickness of 3 μm
４4 μm InGaAsP-based (λg = 1.4 μm) is used. Since the light receiving layer has λg of 1.4 μm, 1.
It absorbs 3 μm and not 1.55 μm at all. FIG.
FIG. 0 shows the structure of such a photodiode 164.
An InGaAsP light-receiving layer (1.4 μm) 172 is used, and both the p-electrode 174 and the n-electrode 177 are ring-shaped electrodes. Since the thickness of the InGaAsP light receiving layer is 3 μm to 4 μm, 1.3 μm is almost completely absorbed. FIG. 21 shows the light transmittance of such a PD. 1.3 μm does not pass,
1.55 μm is transmitted. Therefore, this can be said to be a 1.3 μm band selection PD. FIG. 22 is a graph showing the light receiving sensitivity characteristics of the 1.3 μm band selection PD.

Such a light receiving element is shown in FIGS.
When used as a PD in FIGS. 1, 12 and 13 (c), an optical transceiver module for simultaneous two-way communication can be obtained. The semiconductor laser emits 1.55 μm as transmission light. This passes through the PD as it is and is transmitted to the station through an optical fiber. The light from the station is 1.3 μm light. This enters the 1.3 μm band selection PD from the optical fiber, but does not reach the semiconductor laser because it is all absorbed.
Since two types of wavelengths, 1.3 μm and 1.55 μm, are used for reception and transmission, simultaneous two-way communication is possible.

FIG. 23 shows an embodiment using a wavelength selection PD. FIG. 23A shows a conventional wavelength multiplexing optical transmission / reception module combining an LD / PD with a wavelength selective coupler in which optical fibers are fused. FIG. 23 (B) shows an embodiment of the present invention.
1. PD module with 3 μm absorption and 1.55 μm transmission;
This is an embodiment in which a 55 μm LD module is combined. In both modules, the characteristics of simultaneous two-way communication were evaluated at a transmission rate of 155 Mbps, but there was no difference between the two.

[0067]

(1) In the present invention, since the optical fiber, the PD and the optical fiber are arranged in a straight line, a coupler or a wavelength demultiplexer is not required. An optical receiving module that can be coupled to a single mode fiber and has a smaller number of components can be provided. (2) Since a wavelength demultiplexer is not required and the structure is simple, a small-sized and low-priced optical receiving module can be provided. (3) Since the optical fiber is fixed to the substrate by cutting the V groove,
The number of alignment points is small and the assembly cost can be reduced. (4) Since this is an improvement of the receiving module, an optical transmitting and receiving module can be easily obtained by connecting an LD module after an optical fiber. (5) The present invention can be applied not only to ping-pong transmission using one wavelength but also to simultaneous two-way optical communication using two wavelengths. Also in that case, the wavelength demultiplexer is unnecessary and the structure is simple.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of optical two-way communication using one wavelength.

FIG. 2 is a schematic configuration diagram of an optical demultiplexer using an optical waveguide.

FIG. 3 is a schematic configuration diagram of an optical demultiplexer using a dielectric multilayer film.

FIG. 4 is a diagram illustrating a configuration example of an optical transceiver module on the subscriber side in conventional optical two-way communication.

FIG. 5 is a cross-sectional view of an LD module according to a conventional example.

FIG. 6 is a cross-sectional view of a PD module according to a conventional example.

FIG. 7 is a sectional view of a PD chip according to a conventional example.

FIG. 8 is a sensitivity characteristic graph of a conventional photodiode.

FIG. 9 is a configuration diagram of an optical transceiver module of the present invention.

FIG. 10 is a configuration diagram of an optical transmission / reception module of the present invention including an amplifier. (A) is a block diagram of the whole optical transceiver module, (b) is an electric circuit diagram.

FIG. 11 is a configuration diagram of an optical receiving module according to an embodiment of the present invention. (A) is a plan view and (b) is an end view.

FIG. 12 is a configuration diagram of an optical receiving module according to another embodiment of the present invention in which a transparent resin is filled between an optical fiber and a PD.

FIG. 13 is a view for explaining a procedure for manufacturing the optical receiving module according to the embodiment of the present invention. (A) shows a substrate in which a V groove is cut. (B) shows a P perpendicular to the V groove on the substrate.
D shows the cut groove. (C) shows P in the PD insertion groove.
D is fixed.

14A and 14B are a cross-sectional view and a plan view of a planar transflective PD used in the present invention. (A) is a sectional view, and (b) is a plan view.

FIG. 15 is a graph showing the relationship between the thickness of an InGaAs light receiving layer and transmittance in an InGaAs PD.

FIG. 16 is a cross-sectional view and a plan view of a mesa-type transflective PD used in the present invention. (A) is a sectional view, and (b) is a plan view.

FIG. 17 is a perspective view showing steps such as processing of a Si substrate and mounting of a PD for manufacturing the optical receiver module of the present invention. (A) shows processing of a Si substrate. (B) is a perspective view showing a state where the PD is attached to the carrier. (C) is a diagram showing a state where an optical fiber is fixed in a V groove. (D) is a diagram showing a state where the PD carrier is attached to the PD carrier groove.

FIG. 18 is a perspective view showing an embodiment of the optical transceiver module of the present invention in which an optical connector, a laser module, and the like are connected to both sides of an optical receiver module incorporating a semi-transmissive PD.

FIG. 19 is a comparative configuration diagram of an optical transceiver module according to a conventional example and the present invention. (A) is a conventional optical transceiver module,
(B) shows the optical transceiver module of the present invention.

FIG. 20 is a sectional view of a PD used in a 1.3 μm selection PD module for performing simultaneous bidirectional communication.

FIG. 21 is a graph showing light transmission characteristics of the epitaxial layer of the 1.3 μm selection PD of FIG. 20;

FIG. 22 is a graph showing sensitivity characteristics of a 1.3 μm selection PD.

FIG. 23 is a comparative configuration diagram of a conventional example and an optical transceiver module of the present invention for simultaneous bidirectional optical communication. (A) shows a conventional optical transceiver module, and (B) shows the optical transceiver module of the present invention.

[Explanation of symbols]

 62 first optical fiber 64 PD 65 second optical fiber 66 mount 67 receiving module 70 laser 71 connection point 72 amplifier 73 V groove 74 Si substrate 75 resin 76 optical fiber 77 PD insertion groove 90 InP substrate 91 InP buffer layer 92 InGaAs light receiving layer 93 InP window layer 94 p-type region 95 p-electrode 96 anti-reflection film 97 passivation film 98 n-electrode 99 anti-reflection film 100 n-type InP substrate 101 n-type InP buffer layer 102 n-type InGaAs light-receiving layer 103 p-type InP window layer 104 p Electrode 105 anti-reflection film 106 passivation film 109 n-electrode 110 anti-reflection film 120 transflective PD 121 PD carrier 122 left base 123 right base 124 recess 125 front end surface 126 front end surface 127 electrode pattern 128 electrode pattern Down 129 Wire 130 Si substrate 131 V groove 132 PD carrier grooves 133 V groove

Claims (10)

[Claims] 1. A mount, a first optical fiber linearly provided on the mount, and a part of the incident light, which is used for optical communication utilizing light of the same wavelength for both transmission and reception. An optical receiving module, comprising: a semi-transmissive light-receiving element that transmits the remainder; and a second optical fiber. 2. A light receiving element having an InGaAs light receiving layer and
2. The optical receiving module according to claim 1, wherein the thickness of the nGaAs (λg = 1.67 μm) light receiving layer is about 0.7 μm. 3. The light-receiving element has an InGaAsP light-receiving layer, and the thickness of InGaAsP (λg = 1.4 μm) is about 1 μm.
The optical receiving module according to claim 1, wherein: 4. A mount, a first optical fiber linearly provided on the mount, used for optical communication utilizing a wavelength of λ ₁ for transmission and a wavelength of λ ₂ for reception, and a wavelength of the received light. An optical receiving module, comprising: a semi-transmissive light-receiving element that absorbs λ ₂ and transmits a wavelength λ ₁ of transmission light; and a second optical fiber. 5. The optical receiving module according to claim 1, wherein an amplifier is arranged at a position close to the light receiving element. 6. The optical receiving module according to claim 1, wherein the mount is a Si substrate having a V groove, and the optical fiber is fixed to the V groove of the Si substrate. 7. The optical receiving module according to claim 1, wherein a translucent resin is filled between the optical fiber and the light receiving element. 8. A mount for use in optical communication utilizing light of the same wavelength for both transmission and reception, a first optical fiber provided linearly on the mount and receiving an optical signal from the outside, A light receiving element that absorbs a part of the incident light and transmits the rest, a second optical fiber, and a semiconductor laser connected to the second optical fiber and emitting light at substantially the same wavelength as the received light. Optical transceiver module. 9. A V-shaped groove is cut in a straight line in a mount, an optical fiber is buried in the V-shaped groove, and then the PD is orthogonal to the V-shaped groove.
A method of manufacturing an optical receiving module, comprising cutting a groove for use and inserting a semi-transmissive PD that absorbs a part of incident light and transmits the remaining light into the groove. 10. A V-shaped groove is cut in a straight line in a mount, and
Cut the PD groove so as to be perpendicular to the groove, embed and fix two optical fibers in the V groove, and insert and fix a semi-transmissive PD that absorbs part of the incident light and transmits the rest into the PD groove. A method for manufacturing an optical receiving module, comprising: