JPH11218651A - Optical transmission and reception module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical transmission and reception module which consists of a small number of components and is easily manufactured in high yield. SOLUTION: This optical transmission and reception module consists of a filter 66 which is provided obliquely halfway in a light guide part of a 1st substrate 7 and reflects part of light downward and reflects the other light, an LD 62 which is provided at a step part of the 1st substrate 70 opposite an end part of a light guide 54, a 2nd substrate 51 which has a metallized layer 64 on the top surface and a 2nd longitudinal hole 72 at a position corresponding to a 1st longitudinal hole 68 and has the top-surface metallized layer joined with a metallized layer 64 on the reverse surface of the 1st substrate 70, a PD which is fitted onto the bottom surface of the 2nd substrate right below the longitudinal hole of the 2nd substrate 51, and an amplifier which is fixed on the bottom surface of the 2nd substrate and amplifies the photocurrent of the PD. The metallized layer at the border between the 1st substrate 70 and 2nd substrate 51 is at the ground potential and the tip of an optical fiber is fixed in the front V groove of the 1st substrate 70; and part of the light exiting from the optical fiber is reflected downward and made incident on the PD and the part from the LD 62 is partially transmitted through the filter and enters the optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical bidirectional communication for transmitting information between a base station and a subscriber by passing optical signals of two or more different wavelengths through an optical fiber in one direction or two directions. The present invention relates to an optical transceiver module in which a light receiving element and a light emitting element are integrated.

[Description of Optical Bidirectional Communication] In recent years, the transmission loss of an optical fiber has been reduced, and the characteristics of a semiconductor laser (hereinafter abbreviated as LD) and a semiconductor light receiving element (hereinafter abbreviated as PD) have been improved. For this reason, transmission of various information using light has become possible. Since the communication uses light, these technologies are called optical communication. Examples of the form of information to be transmitted include telephone, facsimile, television image signal, and the like.
In particular, communications using long wavelength light such as light having a wavelength of 1.3 μm and light having a wavelength of 1.55 μm have been actively performed.

[0003] Recently, a system has been studied in which a signal can be bidirectionally transmitted using one optical fiber, and the signal can be transmitted and received simultaneously. Since signals are transmitted in both directions, this is called two-way communication. The advantage of this scheme is that only one fiber is required. FIG. 1 is a principle diagram of wavelength multiplexing bidirectional communication using light of different wavelengths among such bidirectional communication. One station and a plurality of subscribers are connected by an optical fiber. Here, only one subscriber is shown. Actually, there are many branch points, and the optical fiber from the station is branched into many optical fibers on the way to reach the subscriber's device.

The station amplifies telephone or TV signals as digital or analog signals, and drives the semiconductor laser LD1 with these signals. This signal enters the optical fiber 1 as a signal of the wavelength λ ₁ . This is guided to the intermediate optical fiber 3 by the splitter 2. Further, the light enters the optical fiber 5 by the branching filter 4 on the subscriber side, and is received by the light receiving element PD2. The light is photoelectrically converted by the light receiving element to become an electric signal P3. The electric signal P3 is amplified and signal-processed by a device on the subscriber side, and is reproduced as telephone sound or television image. The signal going from the base station to the subscriber side is called a downlink signal, and the flow of information in this direction is called a downlink system.

On the other hand, the subscriber converts a telephone or facsimile signal into an optical signal having a wavelength of λ ₂ by a semiconductor laser LD ₂ . The light of λ ₂ is incident on the optical fiber 6,
Is guided to the intermediate optical fiber 3 by the branching filter 2 on the station side.
Through the light receiving element PD1. The device at the office is λ
The optical signal ₂ is photoelectrically converted by the PD 1 into an electric signal. This electric signal is sent to an exchange or a signal processing circuit to undergo appropriate processing. The direction in which a signal is sent to the station in this way is called an uplink system. The signal is called an up signal.

In the above description, λ ₁ is used only for the downlink and λ ₂ is used only for the uplink. However, in practice, light of the same wavelength may be used for downstream and upstream. At times, light of two wavelengths may be propagated both up and down. In such a case, separation of two lights having different wavelengths becomes a very important problem.

[Explanation of optical demultiplexer] As described above, in order to perform two-way communication using two wavelengths of light and one optical fiber, both the station side and the subscriber side are required. A function of identifying the wavelength of light and separating an optical path is required. The duplexers 2 and 4 in FIG. 1 perform the function. The demultiplexer combines light of wavelengths λ ₁ and λ ₂ and introduces it into one optical fiber, or selects only one light from two wavelengths and extracts it to one optical fiber. Has the effect of doing. A duplexer plays an extremely important role in performing wavelength multiplexing bidirectional communication.

There are several types of duplexers currently proposed. This will be described with reference to FIGS. In the example of FIG. 2, the splitter is made of an optical fiber or an optical waveguide. The two light paths 8, 9 are adjacent in part 10, where the exchange of light energy takes place. Depending on the distance D and the distance L between the adjacent portions 10, various types of coupling can be realized.
Here, when light is incident on the optical path 8 at λ ₁ ,
_One light comes out. When light of λ ₂ enters the optical path 12, light of λ ₂ comes out on the optical path 9. This is a waveguide type duplexer.

FIG. 3 shows the use of a multilayer mirror. A dielectric multilayer film is formed on the oblique sides of the glass blocks 13 and 14 having an isosceles triangular column shape. By properly combining the refractive index and thickness of the dielectric, all light of λ ₁ is transmitted,
The light of λ ₂ is all reflected. It has the function of reflecting or transmitting light incident at an angle of 45 °. This duplexer can also be used as the duplexers 2 and 4 in FIG. Such a duplexer is also called a duplexer / combiner. Sometimes called WDM. Those using optical fibers or glass blocks are already commercially available.

[0010]

2. Description of the Related Art An optical transceiver module on the subscriber side will be described with reference to FIG. In FIG. 16, the end of an optical fiber 16 laid from a station to a subscriber is connected to an indoor optical fiber 18 by an optical connector 17.
The optical fiber WDM 21 (demultiplexer) is provided in the ONU module located indoors of the subscriber. The optical fiber 18 and the optical fiber 19 are wavelength-selectively coupled inside the WDM 21. An LD module 25 is connected to the optical fiber 18 by an optical connector 22. The PD module 27 is connected to the optical fiber 19 via the optical connector 23.

The LD 25 and the optical fiber 24 form an upstream system. The 1.3 μm band light transmits the subscriber's signal to the station. The optical fiber 26 and the PD module 27 are a downstream system. Upon receiving a 1.5 μm band signal from the station, the PD module performs photoelectric conversion. The LD 25 as a transmitting device includes a circuit for amplifying and modulating a telephone or facsimile signal, a semiconductor laser for converting an electric signal to an optical signal, and the like. The PD module 27, which is a receiving device, receives the T
It includes a photodiode for photoelectrically converting an optical signal such as a V signal and a telephone, an amplifier circuit, a demodulation circuit, and the like.

The wavelength demultiplexer (WDM module) 21 includes:
It has the function of separating 1.5 μm band light and 1.3 μm band light. In this example, 1.3 μm band light is used as an upstream signal,
1.5 μm band light is used as a downstream signal. The present invention relates to an improvement in an optical transceiver module for performing bidirectional communication using optical signals of two different wavelengths.
The optical transmitting and receiving module includes a light emitting element, a light receiving element, and electric circuits around them. Conventional techniques for these elements will be described.

[Description of Conventional Semiconductor Light-Emitting Element (LD Module)] A conventional semiconductor light-emitting element (LD module) 28 will be described with reference to FIG. This is a module including a semiconductor laser chip (LD) 29 and a photodiode chip 30 for monitoring. The LD chip 29 is fixed to the front surface of the raised portion (pole) 31 of the header 32. This is because parallel light is generated on the surface of the LD chip. The PD chip 30 is fixed to the bottom surface of the header 32 at a position where the rear emission of the LD is incident. An appropriate number of lead pins 33 are provided on the lower surface of the header 32. The element mounting surface of the header 32 is covered with a cap 34.

Light from a semiconductor laser (LD) having a window 35 opened at the center of the cap 34 exits vertically from the chip. A lens 37 is located immediately above the window 35. It is supported by a lens holder -36. Lens holder
Above 36 is a housing 38 on which a ferrule 39 is fixed. Ferrule 3
9 holds the tip of the optical fiber 40. The ends of the ferrule and the optical fiber are polished diagonally. This is to prevent the reflected return light from entering the LD 29.

While monitoring the light of the semiconductor laser (LD) 29 at the other end of the optical fiber 40, the holder 36 is positioned with respect to the header 32, and the housing 38 is further positioned.
Is positioned with respect to the lens holder -36. Each electrode of the semiconductor laser 29 and the photodiode 30 is connected to one of the lead pins 33 by a wire.

Light emitted from the semiconductor laser is converged by a lens and enters the end of the optical fiber. Since the semiconductor laser is modulated by a signal, this light transmits the signal. The output of the semiconductor laser is monitored by a monitoring photodiode 30 on the opposite side. 1.
The oscillation wavelength in the 3 μm to 1.5 μm band is determined by the material of the semiconductor layer.

[Description of Conventional Semiconductor Photodetector Module] A conventional PD module will be described with reference to FIG. The light receiving element chip 41 is die-bonded to the upper surface of the header 42. Lead pins 43 are provided on the lower surface of the header 42. The upper surface of the header 42 is covered by a cap 44. At the center of the cap 44 is an opening 45 for transmitting light. A cylindrical holder 46 is further fixed to the outside of the cap. This is for holding the lens 47.

Above the lens holder 46, a conical housing 48 is fixed. The tip of the optical fiber 50 is fixed by the ferrule 49. Ferrule 49
Is held by the housing. The ferrule and the tip of the optical fiber are obliquely polished.

Also in the case of the light receiving element, the holder-4 is monitored by passing light through an optical fiber and monitoring the output of the PD chip 41.
6, the position of the housing 48, and the position of the ferrule are determined. The wavelength range in which light can be received is determined by the semiconductor layer of the light receiving element. In the case of visible light, a Si PD can be used. In the case of a transmission / reception module using near-infrared light, a Si PD is inappropriate. In order to receive near-infrared light, it is necessary to use a compound semiconductor light receiving element having InP as a substrate (the light receiving layer is made of InGaAs or IGaAs).
nGaAsP).

[0020]

The majority of optical two-way communication subscribers are ordinary households. So there should be a market for only the number of phones now. But ordinary homes are difficult to buy unless they are as cheap as regular metal phone calls. Modules need to be low cost. However, the conventional individual modules (LD modules,
In the case of the combination of the PD module and the WDM module), the price is the sum of the individual module prices, which is expensive. The high cost of such modules has hindered the development of optical subscriber systems. Inexpensive equipment must be prepared so that the general consumers are willing to purchase.

Therefore, several attempts to reduce the number of parts, make the device more compact, and lower the cost have been proposed and published. 6, 7, and 8 show some of the newly proposed modules. Each has new advantages. However, from the viewpoint of the present inventor, they are still insufficient and each has its own drawbacks.

[A. Lateral reflection WDM type (FIG. 6)] Masahiro Ogusu, Tasuko Tomioka, Shigeru Oshima, "Receptacle type bidirectional wavelength multiplexing optical module", 1996 IEICE Electronics Society, C-208, p208
(1996) has proposed a mirror-type WDM element. FIG. 6 shows a module using a mirror-type WDM. A WDM filter 81 is set at the center of a rectangular housing 80 at a diagonal angle of 45 degrees. Housing 80
The LD 83 and the PD 85 are installed on the two side surfaces. WDM
A lens 82 is provided between 81 and the LD 83. W
A lens 84 is provided between the DM 81 and the PD 85.
An optical fiber 86 and a lens 87 are provided on a straight line connecting the LD 83 and the center of the WDM 81. Transmitted light λ ₁ from LD
Is transmitted through the WDM and enters the optical fiber. The signal light λ ₂ from the other from the optical fiber is reflected laterally by the WDM and enters the PD 85. Two different wavelengths are separated because the transmission and reflection performance differs depending on the wavelength. However, this is not much different from that of FIG. It is an extension of the conventional one, such as the form of LD and PD, the arrangement of condenser lenses, and the use of WDM. Cost reduction is also insufficient. Not a big improvement.
It is necessary to further reduce the number of parts.

[B. Y-branch waveguide type] N. Uchida, H. Yama
da, Y. Hibino, Y. Suzuki, T. Kurosaki, N. Ishihara, M.
Nakamura, T.Hashimoto, Y.Akahori, Y.Inoue, K.Moriw
aki, K.Kato, Y.Tohmori, M.Wada, and T.Sugie, "LOW-CO
ST AND HIGH-PERFORMANCE HYBRID WDM MODULE INTEGRAT
ED ON A PLC PLATFORM FOR FIBER-TO-THE-HOME ", 22nd
European Conferenceon Optical Communication- ECOC '
96, OSLO, TuC.3.1, P2.107 (1996)
A DM element has been proposed. FIG. 7 shows a transmission / reception module using a quartz optical waveguide in which WDM is embedded.
Quartz waveguides 89, 90, 91 branched on a substrate 88;
92 and 93 are formed. The Y-branched waveguides 90 and 91 become a unified waveguide 89, and are connected to the other Y-branch waveguides 92 and 93. The WDM filter 102 is installed at the branch point of the Y branch. A PD 99 is provided at the end of the branch waveguide 90 at the tip of the Y branch 89. An LD 98 is provided at the tip of the branch waveguide 91. Electrode patterns 96 and 97 are formed on the substrate surface. P on it
D99 and LD98 are soldered. 1.3 μm exits from the end face 100 of the LD 98 and the WDM filter 10
2 and is emitted as free space light 95 from the waveguide 93. A 1.3 μm signal from the base station passes from the waveguide 93 through the WDM 102 to the waveguide 90 and enters the end face 101 of the PD 99. This is an end-face incident type PD. WD
The M filter reflects 1.55 μm and transmits 1.3 μm.

This simplifies the structure a little without lenses. The signal light also travels 1.3 μm back and forth, and a WDM filter is used simply to return the light (1.55 μm) out. Therefore, it cannot be used for the application (use of two wavelengths λ ₁ and λ ₂ ) considered in the present invention. This method changes the traveling direction of light in the plane of the optical waveguide. Naturally, there is a loss due to the waveguide other than the half loss due to the branch. In addition, a fine optical waveguide must be formed on a substrate, which is extremely difficult to manufacture.

[C. Upward reflection type (Fig. 8)] Tomoaki Uno, Toru Nishikawa, Masahiro Mitsuda, Motoji Higashimon, Yasushi Matsui "Surface Mount Type LD
/ PD integrated module "1997 IEICE Electronics Society Conference, C-3-89, p1
98 (1997); Motoji Higashimon, Tomoaki Uno, Naoki Takenaka, Toru Nishikawa, Hiroaki Asano, Yasushi Matsui, "Receiving Characteristics of PD Modules Using Fiber-Embedded Optical Circuits" 1997 IEICE General Conference, C-3-59, p244 proposes a WDM element that reflects light upward. FIG. 8 shows an optical transmitting / receiving module that reflects received light upward. A vertically long V groove 108 is formed on the Si substrate 105, and the optical fiber 104 is fixed thereon. There is a step 106 at the end of the substrate 105, and the LD 107 is fixed. L
1.3 μm light of D107 enters the optical fiber and is transmitted. There is a cut 110 in which the substrate 105 and the optical fiber are cut at an angle of 45 degrees in common.
1 is inserted and fixed. The PD 109 is attached to the oblique upper part so that the light receiving surface faces downward.

1.55 propagating through the optical fiber 104
The μm light is reflected obliquely upward by the WDM filter 111. This is received by the PD 109. WDM
Through 1.3 μm as in FIGS. 6 and 7.
55 μm is reflected. The WDM is mounted obliquely upward to reflect 1.55 μm to the PD obliquely above. There is no lens, no optical waveguide, and the structure is simple. However, this is a pigtail type where the LD is attached behind the fiber. After all, it is not much different from that of FIG.

In any case, the optical transmission / reception module proposed in recent years has a large material cost, an assembling cost, etc., is large, and its structure is not yet simple. Both are merely extensions of current technology. Many defects have yet to be put to practical use. SUMMARY OF THE INVENTION It is a first object of the present invention to provide a smaller optical transmission / reception module with a smaller number of components, rather than a mere collection and mere connection of existing modules. It is a second object of the present invention to provide an optical transceiver module that can reduce both material costs and assembly costs. More specifically, the present invention provides an optical transceiver module that is more compact than that of FIG. 6, easier to manufacture than that of FIG. 7, and lower in price than FIG.

[0028]

An optical transmitting / receiving module according to the present invention comprises an optical guide for guiding light provided at an intermediate portion, a first vertical hole formed in a part of the optical guide, and an optical fiber provided at one end. A first substrate having a metallization layer on the bottom surface and a step portion for mounting the LD at an end opposite to the V-groove for fixing the tip, and a part of the first substrate that is inclined and provided in the middle of the light guide portion, A filter that reflects downward and reflects some light;
An LD provided on the step of the first substrate so as to face the end of the light guide, and a second vertical hole having a metallized layer on the upper surface and provided at a position corresponding to the first vertical hole, the back surface of the first substrate A second substrate in which an upper metallization layer is joined to the metallization layer, a PD attached to the bottom surface of the second substrate immediately below the vertical hole of the second substrate, and an amplifier fixed to the bottom surface of the second substrate and amplifying the photocurrent of the PD. The metallized layer at the boundary between the first substrate and the second substrate is at the ground potential, the tip of the optical fiber is fixed in a V-groove in front of the first substrate, and part of the light emitted from the optical fiber is filtered. The light is reflected downward and enters the PD, and part of the light from the LD passes through the filter and enters the optical fiber.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION In any of the objects introduced as conventional examples, a part of light is bent laterally or upward.
The present invention has a completely different idea compared to these conventional examples.
Rather than reflecting light sideways or upwards, the present invention reflects light downwards. This is one feature. The present invention, the optical transceiver module, the transmitter and receiver are separated vertically,
Separate modules are created, inspected and non-defective products are selected and combined to form a transmission / reception module. Since they can be manufactured separately, the yield increases. Since the transmitting unit and the receiving unit are vertically separated, it is necessary to reflect light downward. For this purpose, the filter is installed by tilting it downward.

There are two types of filters.
One is a case where only light λ ₁ of a single wavelength is used. In that case, the transmission light is λ ₁ and the reception light is λ ₁ . The transmission timing and the reception timing are different. This is called ping-pong transmission. In this case, the filter partially reflects and partially transmits both the transmission light and the reception light.

Another filter is a filter having wavelength selectivity. Using two types of light, λ ₁ and λ ₂ , λ ₁
And λ ₂ must be completely separated when used for transmission and reception. The filter for that is called a WDM filter. In the present invention, the received light is WDM
The reflected light is reflected downward by the filter, and the transmission light is transmitted through the WDM filter.

Another feature of the present invention resides in that a light guide is provided on a substrate and a WDM filter is inserted at an intermediate point of the light guide. It is a simple linear light guide. Also WDM
Separate light having different wavelengths. One wavelength λ ₁ goes straight, and another wavelength λ ₂ is reflected downward. A PD is provided below the reflected light to receive it.

The present invention creates a light guide, which is straight and easy to manufacture. Although a light guide is made, no WDM coupler or filter is formed by a surface waveguide (PLC) as shown in FIG. The so-called PLC is an optical circuit using a planar waveguide (Planar Lightwave).
Circuit). The main part of the waveguide type shown in FIG. 7 is made of this PLC. The difficulty of the production is as described above. The present invention does not use an optical waveguide. The present invention uses a simple straight light guide. Of course, it is a single mode light guide, but it is a straight line and has no curved portions or branches. Therefore, the light guide of the module of the present invention can be manufactured at high yield and at low cost.

FIG. 10 is a sectional view of a light guide used in the present invention. If the extension direction of the guide is taken on the x-axis, this is a yz sectional view. SiO on a Si substrate (Si bench) 51
_{There are two} buffer layers 52 on which there is a SiO ₂ layer.
At the center of the SiO ₂ layer 51 is a Ge-doped high refractive index SiO ₂ layer 54. A portion of SiO ₂ surrounding the cladding layer 53 has a low refractive index. The core portion 54 has a slightly higher refractive index due to Ge and has an effect of guiding light. This light guide is straight and has no bends or branches.

A method for manufacturing the light guide will be described. A low refractive index SiO ₂ buffer layer 52 is formed on a Si substrate 51 (for example, 15 mm × 20 mm × 1 mm) by a flame deposition method or a sputtering method. Further, a Ge-containing high refractive index SiO ₂ layer having a thickness of, for example, 50 μm is formed on the entire surface. Next, the Ge-containing SiO ₂ layer is removed by photolithography using a mask having a stripe pattern on both sides except for a part of the central part. As a result, the high refractive index portion 54 remains on the buffer layer 52. This has a cross section of, for example, 8 μm × 8 μm. Next, a cladding layer 53 having a low refractive index is formed by a flame deposition method or a sputtering method. The high refractive index portion 54 is surrounded by the cladding layer. The high refractive index portion 54 has a refractive index higher than that of the cladding layer 53 by about 0.3%. This serves as a light guide 54 that strikes the core and guides light. Hereinafter, the linear high refractive index portion 54 is referred to as a light guide 54.

The module according to the present invention comprises an upper structure and a lower structure, and the two are bonded together. FIG. 9 shows the upper structure, and FIG. 11 shows the lower structure. The light guide of FIG. 10 is provided on the superstructure.

The superstructure will be described with reference to FIG. FIG.
(A) is a plan view of the upper structure, and (b) is a central longitudinal sectional view. The above-described linear light guide 54 is formed on the surface of the flat Si first substrate 51 by doping Ge in the longitudinal direction (x-axis direction). A step 55 is provided at one end surface in the x direction, and a V groove 67 is cut in the center in the x direction. The bottom of the V-groove is formed so as to match the light guide 54. The tip of the single mode fiber 56 is positioned in the V groove 67. At that position, the end face of the optical fiber is bonded to the end face of the step. Single mode fiber 56
Consists of a central core 57 and a cladding 58 surrounding it. The core diameter is about 10 μm. V groove 67, step 5
5 has an appropriate shape and size, and the light guide 54 and the core 57 are x
It is made to match the direction. A metallized surface 64 is formed on the entire back surface of the first substrate 51. This is, for example, a gold layer. This is the layer that also becomes the ground plane.

There is a step 59 on the side of the first substrate 51 opposite to the side on which the optical fibers are mounted. The electrode patterns 60 and 61 are formed on the upper surface of the step 59. An LD chip 62 is bonded on one electrode pattern 60.
The LD can be attached to the electrode pattern using, for example, a solder such as AuGe. The electrode on the upper surface of the LD chip 62 is connected to the other electrode pattern 61 by a wire 63. The LD chip 62 is, for example, a 1.3 μm InGaAsP light emitting laser. The size of the chip is, for example, 300 μm × 300 μm × 100 μm.

An oblique groove 65 is formed at an intermediate point of the light guide 54 so as to face obliquely downward. The oblique groove 65 is-with respect to the yz plane.
It is pierced in a direction inclined at 45 degrees to the x direction. Diagonal groove 6
5, a WDM filter 66 is obliquely inserted and fixed. A first vertical hole 68 is formed below the diagonal groove 65 below the diagonal groove 65.
WDM is a dielectric multi-layer film having a thickness of about 30 μm, transmitting 1.3 μm, and reflecting 1.55 μm.

The transmission light S (for example, 1.3 μm) emitted from the rear LD 62 enters the tip of the light guide 54, passes through the WDM filter 66, passes through the light guide 54 in the −x direction, and passes through the core 57 of the optical fiber 56. Incident on. The reception light R (for example, 1.55 μm) propagating through the optical fiber enters the light guide 54 and travels in the + x direction, is reflected by the WDM filter 66 and travels downward through the vertical hole 68. As described later, a light receiving element is provided here and light is received by the light receiving element. That is, the received light is bent by the WDM, neither laterally nor upwardly.

The lower structure will be described with reference to FIG. A metallized layer 71 is uniformly formed on a flat rectangular insulator second substrate 70. This serves as a bonding surface and a ground surface. Metallization with gold etc. The second substrate 70 is, for example, ceramic. A second vertical hole 72 is formed in the center at a position corresponding to the vertical hole 68 described above.
A metallized electrode pattern 74 on the lower surface of the second substrate 70;
79 are formed. The electrode pattern 74 is located around the second vertical hole 72. Here, the back illuminated PD 73 is soldered with the back side up. This PD 73 is, for example, 550 μm
It has dimensions of square × 100 μm thick. The back-illuminated PD is a light-receiving element in which light enters from the n-type substrate side, passes through the buffer layer, and reaches a light-receiving layer near the p-region.

The light receiving wavelength range of the light receiving element is determined by the materials of the light receiving layer and the window layer. For example, 1.55 μm or 1.3 μm
To receive the band, a PD using InGaAs as a light receiving layer is used. In the case of receiving only 1.3 μm, InGa
A PD having AsP as a light receiving layer can be used. In each case, the substrate is an InP crystal. According to FIG.
An example of D will be described. On the n-InP substrate 141, n-
InP buffer layer 142, n-InGaAs light receiving layer 14
3. An epitaxial wafer on which the n-InP window layer 144 is epitaxially grown is used. Then, Zn is diffused to the upper surface using a mask to form p-type regions 145, 146, and 14.
Make 7. The central p-type region 145 serves as a light receiving section. The p-type regions 146 and 147 on the side are provided to prevent signal flow by preventing light from flowing into the electrodes and generating photocurrent even when light enters this portion to form an electron-hole pair.

For Zn diffusion, pn junctions 150, 15
1, 152 occur. The central pn junction contributes to the detection. The pn junctions 151 and 152 at the ends prevent the extra carrier from running. On the central p-type region 145, a p-electrode 149 having a diameter of 60 μm is formed. The p-electrode is not ring-shaped because it does not enter from the surface. There is no opening. It has a small (60 μm) circular shape. p-type region 1
45 itself is also narrow. Therefore, the capacitance of the pn junction is reduced.

On the back surface of the n-InP substrate 141, a ring-shaped n-electrode 153 is formed. Although the area of this is large, it does not matter. The central opening is 200 μmΦ, where light enters. The opening is covered with an antireflection film 154.

Since the light is of the back-illuminated type, light is incident from the n-type substrate side. The n-electrode on the back is ring-shaped. A ring-shaped n-electrode is soldered to the pattern 74. In general, a back-illuminated PD can have a p-electrode formed in a small disk rather than a ring.
Also in this embodiment, there is a disk-shaped (not ring-shaped) p-electrode 76 on the p-type region 75 near the surface. The wire is this p
Since it can be bonded to the electrode, the p-electrode can be made smaller. Since the p-electrode is small, the pn junction can be narrowed and the light receiving area can be narrowed. Therefore, the capacitance of the pn junction can be reduced.
For example, the light receiving diameter can be set to about 50 μm to 100 μm. In that case, the capacitance of the junction is 0.2 pF or more.
0.8 pF. Since the capacitance is small, the PD can respond at high speed. Back-illuminated type P for the present invention
Adoption of D is essential. This enables high-speed optical communication.

An amplifier (amplifier) chip 77 is fixed to the side of the back surface of the substrate 70. The p electrode of the PD 73 and the input of the amplifier 77 are connected by a wire 78. PD7
The photocurrent of No. 3 is amplified by the nearby amplifier 77. The other electrode of the amplifier 77 is connected to the metallized pattern 79. Since the received signal of the PD is very weak and is susceptible to noise, an amplifier 77 is provided in the immediate vicinity so as to amplify before the noise enters. When the signal is amplified, the impedance of the output circuit becomes low and becomes strong against noise. This method is PIN-AMP
Called. As AMP77, S as an amplifier circuit
An i-IC or a GaAs-IC can be used. The chip size is, for example, 1 mm square to 2 mm square.

The second vertical hole 72 of the second substrate 70 is formed at a position where the light of the optical fiber is reflected by the WDM. A metallized portion having the same size as the PD chip is provided on the bottom surface around the vertical hole 72. This is for mounting the PD, but also serves as a mark for positioning the PD. The size of the PD chip is, for example, 550 μm as described above.
Although the size of the corner is large, the light receiving area is 50 μm diameter to 100 μm.
They are small in diameter. Therefore, the first vertical hole 68 and the second vertical hole 72 can have a diameter of, for example, about 200 μm. Since the light receiving diameter of the light receiving element is as wide as 50 μm to 100 μm, positioning is easy.

The upper structure shown in FIG. 9 can be called a transmitting section. Only the transmitting part is manufactured and inspected to select non-defective products. The lower structure is a receiving unit. The receiver is also manufactured independently and inspected to select a good product. Since it is independently manufactured and non-defective products are selected, the yield is higher than in the case of making a united product from the beginning. If the whole is made from the beginning, no matter which part is bad, the whole will be rejected and all parts and work will be wasted. The present invention avoids such waste by combining separately made ones.

The transmitting unit and the receiving unit of the non-defective products that have passed the inspection are combined as shown in FIG. Therefore, a mark is made on the Si bench (first substrate) 51 of the upper structure (transmitting unit) and the ceramic bench (second substrate) 70 of the lower structure (receiving unit). For example, through holes may be formed at four corners of each substrate, and these may be used as marks. The metallized layer 64 on the lower surface of the first substrate 51 is superimposed on the metallized layer 71 on the upper surface of the second substrate 70, and the relative positions of the substrates 51 and 70 are adjusted so that these marks match. At this time, it is preferable to determine the position where high sensitivity can be obtained while making the light enter the optical fiber and observing the output of the PD 73. When the optimum position is determined, the substrates 51 and 70 are combined at that position.

The bonding of the substrates can be performed by thermocompression bonding. The thermocompression bonding also heats the elements (PD, LD, amplifier). If it is desired to combine at a lower temperature, ultrasonic waves may be applied in addition to thermocompression bonding. Since only the metallized surface is locally heated by ultrasonic waves, bonding can be performed at a lower temperature.

FIG. 14 shows a state in which the sheets are stuck together. Metallized layers 64, 71 between the upper and lower structures
Are combined and this becomes the ground plane. The LD 62 through which a relatively large current flows may be a source of noise,
PDs and amplifiers with high impedance are susceptible to noise. However, with this structure, LD and
Since there is a wide ground plane between PD and AMP, noise is cut off. LD and PD + AMP depending on ground plane
Are electrically separated from each other. Ground plane 64, 7
1 prevents crosstalk between the transmitting side and the receiving side.

The module thus attached is further housed in a case. FIG. 15 shows a state where it is mounted on a case. The case is a container made of metal, ceramic, or the like. In that case, since there is an internal space, an inert gas is filled and hermetic sealing is performed. FIG. 15 shows the case of a ceramic case. In the case of a metal case, it is necessary to insulate the lead pin portion. Alternatively, for cost reduction, a resin mold, a plastic package, or the like can be used.

In FIG. 15, a case 119 includes a rectangular lower case 120 having a bottom and a rectangular upper case 121 having a ceiling plate. A side hole 1 on the front of the upper case 121
22 is pierced. The lower case 120 has the first step 12
3 has a second step portion 124 on the rear surface. Lower case 120
A plurality of vertical holes 127 are formed in the second step 124. This is a hole for passing the lead pin 128. Second step 124
(Not shown) corresponding to the patterns 74 and 79 in FIG.

The second substrate (ceramic bench) 71 of the combined module of the present invention is connected to the step 12 of the lower case 120.
3. Place on 124 and fix. The PD 73 and the AMP 77 are located in the internal space of the lower case 120. In this example, a monitor PD 129 is mounted on the step portion 59 in addition to the LD 62 in this example. This is for detecting and monitoring the output of the LD 62. 13 and 14, the monitor PD
However, in this example, the PD 129 is added. Ray
It is well known to add an extra PD to monitor the output. The electrodes of the amplifier 77 and the PD 73 in the receiving section are connected to the electrode patterns 74 and 7 on the bottom surface shown in FIG.
9 is connected to a pattern (not shown) on the step portion 124 and further connected to the lead pin 128.

The tip of the optical fiber is inserted into the lateral hole 122 of the upper case 121 and fixed in the V groove in front of the Si bench (first substrate) 51. The connection between the optical fiber and the case is performed by soldering, resin bonding, or the like. A part of the surface of the optical fiber is metallized and soldered with a hole in the case. Alternatively, it can be fixed with a resin having low moisture permeability.

The end surfaces 125 and 126 of the upper case 121 are
It is joined on the steps 123 and 124 of the lower case 120.
An inert gas is sealed in the sealed case. The lead pin 128 is a terminal for supplying a power supply voltage to the receiving unit (the PD 73 and the amplifier 77) and the transmitting unit (the LD 62 and the PD 129), extracting a reception signal, and supplying a transmission signal. The laser 62 is driven by the transmission signal and λ ₁
(For example, 1.3 μm). This enters the light guide 54. It simply passes through the WDM 66 and enters the core 57 of the optical fiber 56 from the light guide 54. This propagates to the base station.

The received light of λ ₂ (for example, 1.55 μm) sent from the station is transmitted from the optical fiber core 57 to the light guide 54.
And is reflected by the WDM 66. This is vertical hole 68,7
2 and enter the back-illuminated PD 73. The PD 73 converts the received light into a photocurrent. The photocurrent is immediately amplified by the amplifier 77. This is taken out by one of the lead pins 128. In this example, the lead pins are arranged in a line in the rear half of the case. However, the lead pins may be separated in the front half and the rear half. Such a lead pin distribution can be appropriately determined by a combination with an electric circuit.

[0058]

EXAMPLE An optical transceiver module of the present invention having the following parameters was manufactured. And its characteristics were evaluated. The semiconductor laser LD of the transmitting section has an emission wavelength of 1.3 μm.
MQW-LD (quantum well laser). Chip size is 300μm (width) x 300μm (length) x 100
μm (thickness). The threshold current It is 7 mA. Driving with a 155 Mbps signal at a peak current of 50 mA yielded an average fiber output of 1 mW (0 dBm). The monitoring PD is a waveguide type p having a 3 μm-thick InGaAs light receiving layer.
In-PD. The same size as the LD chip (3
00 μm × 300 μm × 100 μm).

The receiving unit is a 1.55 μm light receiving device. The WDM filter has a function of 1.3 at 45 ° incident light.
μm is transmitted and 1.55 μm is reflected. Therefore, only 1.55 μm reaches the receiving unit. The PD of the receiver is I
This is a back-illuminated PD having an nGaAs light-receiving layer. Therefore, both 1.3 μm and 1.55 μm can be sensed,
Since only μm comes here, 1.55 μm is detected. P
The dimension of D is 550 μm (width) × 550 μm (length) × 1
00 μm (thickness). The light receiving diameter is 60 μm. The capacitance was 0.3 pF for a 2 V bias.
Very small capacitance.

The amplifier (AMP) is a GaAs-IC. A transimpedance circuit having a feedback resistance of 1 kΩ was used. The receiving sensitivity was measured using the above devices. 155M
At a signal speed of bps, the error rate was set to 10 ⁻⁹ or less, and the receiving sensitivity was −40 dBm. It can be seen that the sensitivity is extremely high.

[0061]

According to the present invention, the following excellent effects can be obtained. The transmission unit (LD) and the reception unit (PD) can be manufactured completely separately, and inspection and burn-in can be performed separately. The quality of each can be confirmed. In a system in which LD and PD are integrated at once, all parts and all work are wasted even if any part is bad. Since the WDM filter is used, the size becomes compact. WDM filter is a dielectric (optical) on a glass substrate
It is possible to use a laminate of multilayer films or a laminate of an optical (dielectric) multilayer film on a polymer thin film. Since the light is bent down and passes through the pinhole, L
Diffuse light from D hardly enters the PD. That is, crosstalk of the received light and transmitted light hardly occurs. Since a large ground (earth) is provided between the transmission side and the reception side, a large current (for example, 50 to 100 m) is provided.
A) Transmitting side that flows A, and P that handles minute currents of 1 μA or less
The IN-AMP side is electrically isolated. Almost no electric crosstalk occurs. Since the PD is of the back-illuminated type, the capacitance can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of wavelength multiplexed bidirectional optical communication.

FIG. 2 is a schematic configuration diagram of a WDM using an optical waveguide having a Y-branch.

FIG. 3 is a schematic configuration diagram of a WDM using a dielectric multilayer film.

FIG. 4 is a cross-sectional view of an LD module according to a conventional example.

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

FIG. 6 is a cross-sectional view of an optical transceiver module according to a conventional example in which transmission light and reception light are separated by a mirror-type WDM filter.

FIG. 7 is a perspective view of an optical transceiver module according to a conventional example in which unnecessary light is reflected by an optical waveguide having two Y-branches and a WDM filter.

FIG. 8 shows WD obliquely in the middle of a fixed optical fiber.
FIG. 9 is a cross-sectional view of an optical transceiver module according to a conventional example in which an M filter is provided and reflects 1.55 μm to guide it to a PD.

FIG. 9 is a diagram of an upper structure of the optical transceiver module according to the present invention, which includes an upper structure and a lower structure. (A) is a plan view,
(B) is a central sectional view.

FIG. 10 is a longitudinal sectional view of a light guide forming a part of a superstructure of the present invention.

FIG. 11 is a diagram of a lower structure of the optical transceiver module according to the present invention, which includes an upper structure and a lower structure. (A) is a longitudinal sectional view at the center, and (b) is a bottom view.

FIG. 12 is a cross-sectional view illustrating an example of a back-illuminated PD.

FIG. 13 is a cross-sectional view of an upper structure and a lower structure according to the present invention, showing that the upper structure and the lower structure are bonded together to be integrated.

FIG. 14 is a cross-sectional view of the optical transceiver module in a state where the upper structure and the lower structure are attached to each other.

FIG. 15 is a cross-sectional view of a completed optical transceiver module of the present invention showing a state in which an upper structure and a lower structure are attached to each other in a case.

FIG. 16 is a schematic configuration diagram of an optical transceiver module on the subscriber side of a bidirectional optical communication system according to a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 optical fiber 2 splitter 3 optical fiber 4 splitter 5 optical fiber 6 optical fiber 7 optical fiber 8 optical fiber 9 optical fiber 10 proximity coupling part 11 optical fiber 12 optical fiber 13 glass block 14 glass block 15 WDM dielectric mirror Reference Signs List 16 single mode fiber 17 optical connector 18 optical fiber 19 optical fiber 20 proximity coupling section 21 WDM module 22 optical connector 23 optical connector 24 optical fiber 25 LD module 26 optical fiber 27 PD module 28 light emitting element module 29 LD chip 30 PD chip 31 pole 32 Header 33 Pin 34 Cap 35 Window 36 Lens Holder 37 Condensing Lens 38 Housing 39 Ferrule 40 Optical Fiber 41 PD Chip 42 Header 43 Pin 44 Cap 45 window 46 lens holder 47 condenser lens 48 housing 49 ferrule 50 optical fiber 51 Si bench (Si substrate) 52 SiO ₂ buffer layer 53 SiO ₂ clad layer 54 light guide 55 steps 56 single mode fiber 57 core 58 clad 59 steps 60 Electrode pattern 61 Electrode pattern 62 LD 63 Wire 64 Metallization layer 65 Oblique hole 66 WDM filter 67 V groove 68 First vertical hole 69 Fiber end face 70 Substrate 71 Metallization layer 72 Second vertical hole 73 PD 74 Bottom electrode 75 p-type region 76 p electrode 77 amplifier 78 wire 79 electrode 80 housing 81 WDM filter 82 lens 83 LD 84 lens 85 PD 86 optical fiber 87 lens 88 substrate 89 optical waveguide 90 optical waveguide 91 optical waveguide 92 optical waveguide 9 Optical waveguide 94 Free space light 95 Free space light 96 Electrode pattern 97 Electrode pattern 98 LD 99 PD 100 Light emitting point 101 Light receiving point 102 WDM filter 104 Optical fiber 105 Si substrate 106 Step 107 LD chip 108 V groove 109 PD 110 Oblique notch 111 WDM Filter 112 Transmitted light 113 Received light 114 Reflected light 119 Case 120 Lower case 121 Upper case 122 Side hole 123 Front stage 124 Rear stage 125 End surface 126 End surface 127 Vertical hole 128 Lead pin

Claims (10)

[Claims] 1. A light guide provided at an intermediate portion for guiding light, a first vertical hole formed in a part of the light guide, and an end opposite to a V-groove provided at one end for fixing a tip of an optical fiber. L in part
D having a step portion for mounting D and a metallized layer on the bottom surface
A substrate, a filter which is provided in the middle of the light guide portion of the first substrate and which is inclined and reflects part of the light downward and reflects part of the light, and a filter of the first substrate facing the end of the light guide. A second LD having a metallization layer on the upper surface and a second vertical hole provided at a position corresponding to the first vertical hole, wherein the upper metallization layer is joined to the metallization layer on the back surface of the first substrate;
A substrate and a PD attached to the bottom surface of the second substrate immediately below the vertical hole of the second substrate. The metallized layer at the boundary between the first substrate and the second substrate has a ground potential, and light is applied to the V groove in front of the first substrate. The tip of the fiber was fixed, a part of the light emitted from the optical fiber was reflected downward by the filter and entered the PD, and a part of the light from the LD passed through the filter and entered the optical fiber. An optical transmitting and receiving module, comprising: 2. The light guide is a linear optical waveguide,
The filter that is provided obliquely at the intermediate position is a filter that reflects and transmits one wavelength of light at a predetermined ratio.
2. The optical transceiver module according to claim 1, wherein a part of the light having the same wavelength received by D and transmitted from the LD passes through the filter and enters the optical fiber. 3. The light guide is a linear optical waveguide,
The filter which is provided obliquely at the intermediate position is a wavelength-selective filter that reflects a certain wavelength λ ₁ almost 100% and transmits another wavelength λ ₂ radiated from a laser almost 100%. The optical transceiver module according to claim 1, wherein: 4. The optical transmitting / receiving module according to claim 1, wherein the optical guide is formed of a quartz optical waveguide. 5. The filter according to claim 1, wherein the filter is formed by forming an optical multilayer film on a transparent polymer thin film.
The optical transceiver module according to any one of the above. 6. The filter according to claim 1, wherein the filter is formed by forming an optical multilayer film on a translucent glass substrate.
The optical transceiver module according to any one of the above. 7. The optical transmitting / receiving module according to claim 1, wherein the photodiode is made of Si, and the semiconductor laser is made of a GaAlAs-based light emitting element. 8. A photodiode having a light receiving layer of InGaAs or InGaAsP, and a semiconductor laser comprising
7. An nGaAsP-based material.
The optical transceiver module according to any one of the above. 9. The optical transceiver module according to claim 1, wherein the photodiode is a back-illuminated photodiode. 10. The optical transceiver module according to claim 1, wherein an amplifier is arranged near the photodiode.