JPH03292777A - Optical integrated circuit - Google Patents

Abstract

PURPOSE:To realize a two-way light communication optical integrated circuit at a low cost by a method wherein a distributed feedback type semiconductor laser composed of a first conductivity type optical waveguide layer, an active layer, and a clad layer is formed on a primary diffraction grating, a photodetector composed of a first conductivity type layer, a light absorbing layer, and a second conductivity type layer is provided onto a secondary diffraction grating, and they are electrically isolated from each other. CONSTITUTION:An n-type optical waveguide layer 13 (InGaAsP), an active layer 14 (InGaAsP), a P-type clad layer 15 (InP), and a P-type contact layer 15 (InGaAs) are successively and selectively grown on a primary diffraction grating 11 to constitute a distributed feedback semiconductor laser. Then, an N-type clad layer 19 (InP), a non-doped light absorbing layer 20 (InGaAs), and a P-type contact layer (InGaAs) are successively, selectively grown on a secondary diffraction grating 12 to form a photodetector. Furthermore, a region between the distributed feedback type semiconductor laser and the photodetector is etched so deep as to reach an N-type semiconductor substrate 10, and an iron doped InP 23, an iron doped InGaAsP layer 24 and an iron doped lnP layer 23 are selectively grown on the etched part concerned through a vapor growth method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical integrated circuit used for optical communication, and particularly to a semiconductor integrated circuit for bidirectional optical communication.

[Conventional technology]

Optical communication systems range from trunk optical communication systems characterized by long distance and large capacity to short/medium distance and medium capacity subscriber networks,
It is also beginning to penetrate into LANs. In subscriber optical communication systems, the first requirement is to reduce costs, and therefore it is required to realize a two-way communication system with a single optical fiber.

The main methods that can be considered as a two-way optical communication system are explained in the second section.
In the bidirectional transmission system using two optical fibers (Fig. 2 (a)) shown in Figures (a) to (d), the cost of the optical fiber is high, and a directional coupler is used to transmit the same wavelength in both directions. The transmission method (FIG. 2(C)) has the disadvantage that reflection of light deteriorates the characteristics. In addition, the ping-pong transmission method (Fig. 2 (d)
〉) has the disadvantage that the electric circuit becomes complicated. Therefore, the wavelength division multiplexing (WDM) bidirectional transmission system (FIG. 2(b)) is promising as a bidirectional optical communication system.

[Problem to be solved by the invention]

The terminal configuration of the conventional WDM two-way optical communication system is
As shown in the figure. In this case, basically a wavelength filter (distributor)
31, a semiconductor laser 32, and a photodetector 33 are required.

Currently, wavelength filters are very expensive components, and
The optical axes of the three parts had to be adjusted very precisely, requiring a huge amount of man-hours to assemble. Furthermore, it has been difficult to reduce the size of the wavelength filter, making it difficult to miniaturize the overall system.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a small-sized bidirectional optical communication device at low cost.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides a semiconductor optical integrated circuit. A first optical integrated circuit according to the present invention includes a semiconductor optical integrated circuit in which a first-order diffraction grating and a second-order diffraction grating are periodically formed. A distributed feedback semiconductor laser comprising a first conductivity type optical waveguide layer, an active layer, and a second conductivity type cladding layer is formed on a first conductivity type semiconductor substrate on a first order diffraction grating, and
A photodetector consisting of a first conductivity type layer, a light absorption layer, and a second conductivity type layer is formed on the next diffraction grating, and a distributed feedback semiconductor laser is formed on the first order diffraction grating, and a photodetector is formed on the second order diffraction grating. The photodetector is electrically isolated. Further, in the optical integrated circuit of the present invention, the first conductivity type semiconductor substrate near the second-order diffraction grating of the optical integrated circuit described above is etched flat to the vicinity of the diffraction grating, and is thinned by etching. The semiconductor device is characterized in that an electrode is also formed on the back surface of the first conductivity type semiconductor substrate.

[Effect]

Next, the operation of the present invention will be explained with reference to FIG. 2
When light that matches the diffraction grating enters the next diffraction grating parallel to the diffraction grating, the light is not only reflected in the direction of incidence, but also radiates perpendicularly to the second-order diffraction grating. . On the other hand, light that does not match the second-order diffraction grating is not reflected but is transmitted after being slightly reduced in water. Although the diffraction efficiency of light emitted perpendicularly to the diffraction grating varies depending on the shape of the diffraction grating, the composition of the optical waveguide layer, etc., it is known that a diffraction efficiency of about 10% can be obtained.

Now, the pitch of the second-order diffraction grating 41 is set to a light wave with a wavelength of 1°3 μm, and the pitch of the first-order diffraction grating 42 is set to a wavelength of 1.5 μm.
When set to match the light waves in the band, a part 46 of the 13 μm band light incident on the secondary diffraction grating is emitted perpendicularly to the diffraction grating, is photoelectrically converted in the light absorption layer 43, and is converted into photocurrent. Detected. In addition, 1, which is incident on the second-order diffraction grating,
Most of the light in the 3 μm band 47 is reflected, so it does not reach the four active layers of the distributed feedback semiconductor laser, and therefore,
There is no negative effect on the oscillation of the semiconductor laser.Furthermore, in a structure in which a good reflecting mirror is present near the secondary diffraction grating 41 by etching and electrode formation, the diffraction efficiency of the emitted light in the direction perpendicular to the diffraction grating is improved. This increases the sensitivity of the photodetector.

On the other hand, the first-order diffraction grating 42 on the side of the distributed feedback semiconductor laser
is matched to light waves in the 1.5 μm band, so 1.5 μm
An m-band light wave 48 is emitted.

The 1.5 μm band light that reaches the 13 μm band secondary diffraction grating is not diffracted by the 13 μm band secondary diffraction grating, but is mostly transmitted. Furthermore, since the photocurrent on the light receiving side and the modulation current of the distributed feedback semiconductor laser are separated by the semi-insulating layer 44, the photocurrent can be detected satisfactorily.

As described above, by using the optical integrated circuit for WDM two-way optical communication according to the present invention, it is possible to realize a small-sized WDM two-way optical communication system at low cost.

〔Example〕 Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1(a) is a sectional view showing an embodiment of the optical integrated circuit of the present invention. On a sulfur (S)-doped N-type (100) indium phosphide (InP) substrate 10, a 1.55 μm band diffraction grating 11 (pitch 2420) was formed with a length of 300 μm and 1
．． A 3 μm band secondary diffraction grating 12 (pitch 4060) with a length of 100 μm is drawn on a photoresist by electron beam exposure, and the substrate is chemically etched to form diffraction gratings 11 and 12 on the surface of the semiconductor substrate. Next, 1.55 μm
On the band diffraction grating 12, an N-type optical waveguide layer 13 (composition: InGaAsP (=1.3
μm), thickness 0.2 μm) - active layer 14 (composition: I
nGaAsP (λ, = 1.55 μm), thickness 0.1
5 μm>, P-type cladding layer 15 (composition: InP, thickness:
2. czm), P-type contact layer 16 (composition: I
nGaAs, thickness 10.2 μm) was sequentially grown by vapor phase growth method (
A distributed feedback semiconductor laser is formed by selective growth using the VPE method. Next, on the 1.3 μm band second-order diffraction grating 12,
N-type optical waveguide layer 17 (composition: I
nGaAsP (λ, = 1.2 μm), thickness 0.2
μm), N-type optical waveguide layer 18 (composition: InGaAsP (
λ, = 1.3 μm), thickness 0.15 μm), N-type cladding layer 19 (composition: InP, thickness 1 μm), non-doped light absorption layer 20 (composition: InGaAs, thickness 0.5 μm),
P-type contact layer 21 (composition: InGaAs, thickness 10
．． 2 μm) is sequentially selectively vapor-phase grown using VPE to form a photodetector. Furthermore, after etching the area between the distributed feedback semiconductor laser and the photodetector to a depth of 50 μm down to the N-type semiconductor substrate, the area was etched with iron (Fe).
) Doped InP23 (thickness 0.5 μm), iron-doped In
GaAsP layer 24 (thickness 0.15 μm), iron doped I
An nP layer 23 (thickness: 2.2 μm) is selectively grown in vapor phase using VPH. Furthermore, in order to realize a single mode of light, a mesa stripe with a width of about 1.5 μm is formed by chemical etching in the <011> direction, and the etched portion is buried and grown with iron-doped InP. After the buried growth, the N-type InP substrate is polished to a thickness of approximately 150 μm. Finally, as shown in the figure, the P side electrode 26 and the N side electrode 27
, a non-reflective coating M28 is formed to form an optical integrated circuit.

When realizing the optical integrated circuit shown in FIG. 1(b),
The N-type semiconductor substrate in the region 25 below the secondary diffraction grating 12 is etched by chemical etching until it has a thickness of about 10 μm. What is the process of optical integrated circuits? & later P side 26
and tf on N side 27! form and finish.

In the above embodiment, a semi-insulating semiconductor was used for electrically separating the distributed feedback semiconductor laser and the photodetector, but other methods such as a trench isolation (air isolation) structure, a pn junction isolation structure, etc. may also be used. Also, instead of burying a semi-insulating semiconductor in the trench, an insulator (SiC2, Si3N4, etc.) may be buried.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a small-sized optical integrated circuit for bidirectional optical communication at low cost.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are cross-sectional views showing the structure of an embodiment of the optical circuit according to the present invention. Figure 2 (a) to (d)
1 is a schematic diagram showing a transmission method of a two-way optical communication system. (a> is a diagram showing a bidirectional transmission system using two optical fibers, (b) is a diagram showing a wavelength multiplexing bidirectional transmission system,
(c) is a diagram showing the same wavelength bidirectional transmission method using a directional coupler, and (d) is a diagram showing the Bing Bong transmission method. FIG. 3 is a schematic diagram for explaining an example of the configuration of a terminal in a conventional wavelength multiplexing bidirectional optical communication system. FIG. 4 is a schematic diagram for explaining the operating principle of the optical integrated circuit according to the present invention. 10... Semiconductor substrate, 11... First-order diffraction grating, 12
...second-order diffraction grating, 13...optical waveguide layer, 14...
- Active layer, 15... Cladding layer, 16... Contact layer, 17... Optical waveguide layer, 18... Optical waveguide layer, 19
... Cladding layer, 20 ... Light absorption layer, 21 ... Contact layer, 23 ... Semi-insulating semiconductor layer, 24 ...
Semi-insulating optical waveguide layer, 25... Semiconductor substrate etching region, 26... Electrode, 27... Electrode, 28... Anti-reflection coating film, 31... Wavelength filter, 32...
- Semiconductor laser, 33... Photodetector, 41... Second order diffraction grating, 42... First order diffraction grating, 43... Light absorption layer, 44... Semi-insulating semiconductor layer, 46... Diffracted light by the second-order diffraction grating, 47... Diffracted light by the second-order diffraction grating, 48... Light emitted from the semiconductor laser, 4
9...Active layer.

Claims (1)

[Scope of Claims] 1. A first conductivity type semiconductor substrate in which a first-order diffraction grating and a second-order diffraction grating are connected in a direction in which the irregularities of the respective diffraction gratings are arranged in parallel with each other in a periodic manner. A distributed feedback semiconductor laser is formed by laminating at least a first conductivity type optical waveguide layer, an active layer, and a second conductivity type cladding layer on the first-order diffraction grating, and the second-order diffraction grating is formed on the surface. A photodetector is formed by laminating at least a first conductivity type layer, a light absorption layer, and a second conductivity type layer thereon, and the distributed feedback semiconductor laser and the photodetector are electrically separated. An optical integrated circuit featuring: 2. In the optical integrated circuit according to claim 1, the thickness of the first conductive type semiconductor substrate in the region where the second-order diffraction grating is formed is 1.
The electrode is thinner than the thickness of the first conductivity type semiconductor substrate in the region where the next diffraction grating is formed, and an electrode is also formed on the back surface of the first conductivity type semiconductor substrate in the thinner region. Optical integrated circuit.