JPH0344989A - Ic type optical semiconductor unit - Google Patents

Abstract

PURPOSE:To obtain a highly stable and reliable IC type optical semiconductor unit for broadcasting reception at low cost by integrating optical components to form a receiver, receiving a beat signal produced by a signal light and station emission, and feeding back a part of the output to a laser control region. CONSTITUTION:This semiconductor unit is designed to comprise a waveguide passage 21 on a filter side and a waveguide passage 24 on a laser side and a light receiving element 25 so that the element 25 may be electrically connected with a control region 28 of a wavelength variable laser 23 by way of a control circuit 27. Under this structure, multi-channel signal light input from the left side of an optical filter 20 is selected by the filter 20 and jointed with the light of the laser 23 at a coupler 22 and its beat signal is detected by the element 25. The output of the element 25 is partially is fed back to a region 28 of the laser 23 by way of an amplification circuits 26 and the control circuit 27. This feedback mechanism enables stable reception constantly under the stable beat signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an integrated optical semiconductor device that is highly safe and low in cost.

(Prior art) Subscriber-based coherent optical communication systems will
It is attracting attention as a system that can distribute large amounts of information to each subscriber in SDN. Various methods have been proposed for this purpose, but after distributing optical signals of more than ten channels to each subscriber using a star coupler, etc.
A method in which the subscriber selects the channel to receive is becoming mainstream.

Conventionally, in such a system, on the subscriber side, for example, 1
A receiving module equipped with optical components such as an optical filter for selecting 6 channels of signal light, a semiconductor laser for local oscillation light, a light-receiving element for signal reception, and a fiber coupler for combining signal light and local oscillation light. A method of receiving the information has been proposed.

(Problem to be Solved by the Invention) However, the above-mentioned method requires many optical components and good optical coupling characteristics between them, resulting in an increase in system cost. . Considering the future expansion of subscriber systems and the installation of receiving devices in each home, reducing system costs is the most important requirement. Furthermore, in future technology, optical components will be incorporated in the form of a module, which will not be sufficient in terms of stability, reliability, etc.

In view of the above, an object of the present invention is to provide an integrated optical semiconductor device that can be mass-produced, is low in cost, and has excellent stability and reliability, and is used as a receiving device in a broadcasting type subscriber coherent system, etc. It is about providing.

(Means for Solving the Problems) An integrated optical semiconductor device of the present invention is an integrated optical semiconductor device in which at least a waveguide optical filter and a wavelength tunable laser are integrated on a semiconductor substrate. a filter side waveguide and a laser open waveguide formed on the side and the output side of the wavelength tunable laser, respectively; an optical coupling unit that couples light guided through the filter side waveguide and the laser (111 waveguide); The light receiving element is provided with a light receiving element into which the light coupled by the optical coupling part is incident, and the light receiving element and the wavelength control region of the wavelength tunable laser are electrically connected via a control circuit.

(Function) In the present invention, as described above, the optical filter, local tunable wavelength laser, coupler, receiver, etc. necessary for reception are all integrated on the same semiconductor substrate. In that case, it may not be possible to obtain a good beat signal just by linking the optical filter and the wavelength tunable laser, so the signal from the light receiving element formed after the optical coupling part, which corresponds to a coupler, is fed back to the wavelength tunable laser. At the same time, the means are provided. This allows the variable wavelength laser to always follow the signal light selected by the optical filter, making it possible to realize a receiver for broadcasting systems with excellent stability and reliability.

(Example) The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a schematic plan view of an integrated optical semiconductor device according to an embodiment of the present invention. The multi-channel signal light is selected by the optical filter 20, passes through the filter@waveguide Fl@21, and is connected to the optical coupling section 22.
The light is combined with the wavelength tunable laser light, and the beat signal thereof is detected by the light receiving element 25. A part of the output of the light receiving element 25 is fed back to the control region 28 of the wavelength tunable laser 23 via the amplifier circuit 26 and the control circuit 27.

This feedback R top makes it possible to always receive a stable beat signal.

The first manufacturing method for obtaining the above-mentioned integrated optical semiconductor device is described below.
It is a sectional view of the AA' and BB' portions in the figure. This will be explained using FIGS. 2 and 3.

First, a diffraction grating 2 including a phase shift region 3 is partially formed on an n-InP substrate 1 . The period of the diffraction grating is approximately 24
00 people. Further, the phase shift region can be formed by an interference exposure method using a normal phase control mask. Note that the diffraction grating 2 is formed only in the region where the optical filter 20 and the wavelength tunable laser 23 are formed.

As described above, on the substrate 1 on which the diffraction grating 2 is partially formed, an I nGaAsP guide layer 4 with an emission wavelength of 1.2 μm, an I
nP etch stop layer 5, In with an emission wavelength of 1.55 μm
The GaAsP active layer 6 and pInP cladding layer 7 are each 0.1 μm thick.

Thicknesses of 0.02 μm, O, 1 μm, and 0.3 μm are sequentially grown.

Thereafter, the active layer 6 is removed except for the active region of the wavelength tunable laser and optical filter shown in FIG. 1, and the portion that will become the light receiving element, and the necessary portions are mesa-etched by chemical etching in the top layer as shown in FIG. The waveguide and other areas are formed into mesa stripes. The width and height of the mesa stripe are both 1.5 μm. At that time, while leaving the insulating film used as a mask, buried growth was performed, and an Fe-doped high-resistance 1nP layer 9, n-
Each InP layer ■0 has a thickness of 1.3 μm.

Grows 0.2 μm.

Subsequently, after removing the insulating film, p-1n was applied over the entire surface.
P buried layer 11, InGaAs with emission wavelength of 1.3 μm
The P contact layer 12 has a thickness of 1 μm and 0.5 μm, respectively.
grow up. Furthermore, independent electrodes in necessary areas 12.13
Then, a separation groove 15 for separating each region and an antireflection film 16 (FIG. 2) are formed on the light incident end face to obtain a desired integrated optical semiconductor device.

Each of the three divided regions of the optical filter 20 has a length of 100 μm.
m, the central part of the wavelength tunable laser 23 is divided into two regions each having a length of 50 μm. Further, the separation groove 15 has a length of 20 μm.

In FIG. 1, the active layer 6 remains only in the shaded area.

The length of the light receiving element 25 is 200 czm, and the length of the optical coupling part is 600 μm. The total length of the integration device is 1.2 mm.

Among the three divided regions of the optical filter 20, while applying an appropriate bias current to the region having a double-opened active layer, current is injected into the central portion to control the effective amount of phase shift there. It is possible to change the resonant frequency conditions of the optical filter. The frequency range can be approximately 150 GHz by optimizing the length of each region and the coupling coefficient of light with the diffraction grating. The oscillation wavelength of the wavelength tunable laser 23 can also be controlled using the same principle.

Further, the optical filter 20 has an active layer 6, and by injecting a current into the active layer 6, it is possible to provide an amplification effect. It is easy to obtain a gain of about 20 dB, and therefore it is possible to receive weak signal light well.

In the above, as shown in FIG. 1, both the optical filter 20 and the wavelength tunable laser 23 include a diffraction grating, a guide layer,
It has an active layer and is divided into three parts in the optical resonance direction, and the active layer is removed only in the divided central region to form a phase region. Further, the central region of the wavelength tunable laser is further divided into two parts, and the output of the control circuit is connected to one of the parts.

After selecting the signal light incident on such a device through the open optical filter 20, it is possible to receive the broadcast signal light of 16 channels satisfactorily by multiplexing and receiving the signal light. l,
When used in a 2 Gb/s high-speed broadcasting system, the receiving sensitivity is approximately -40 dBm on average, which is a sufficiently good receiving sensitivity state. Moreover, since the main optical components are integrated on the same substrate, it is expected to significantly improve stability and reliability compared to conventional configurations.

In the examples, a 1 μm band element using InP as a substrate was described, but the material system used is not limited to this, and other materials such as GaAs may be used without any problem. Of course, this can be obtained by using not only chemical etching but also dry etching and other methods. Further, the waveguide structure is not limited to the buried 'W4 structure.

The optical filter and wavelength tunable laser are divided into three or four parts, with the central area serving as the control area, but the configuration is of course not limited to this, and various configurations that have been reported and proposed are possible. be. Furthermore, although an active type optical filter having an internal active layer is shown, a structure without an active layer may be used without any problem.

(Effects of the Invention) As explained above, the present invention forms a receiver that integrates the main optical components, and signals the beat signal of the signal light and the local light by a light receiving element, and a part of the output is transmitted. Since feedback is provided to the control region of the wavelength tunable laser, which is the local light region, it is possible to construct a broadcast type subscriber optical system, etc., which is excellent in stability and reliability and has low system cost.

[Brief explanation of drawings]

FIG. 1 is a plan view of an integrated optical semiconductor device which is an embodiment of the present invention, and FIGS. 2 and 3 are taken along lines A-A' and B in FIG.
It is a sectional view of the -B' portion. 1... Substrate, 2... Diffraction grating, 3... Phase shift region, 4... Guide layer, 5... Etch stop layer,
6... Active layer, 7... Cladding layer, 8... Mesa stripe, 9... High resistance layer, 10... n-InP layer, 11... Buried layer, 12... Contact layer, 1
3...p electrode, 14...n electrode, 15...separate sake, 16...antireflection film, 20...optical filter, 21
...Filter side waveguide, 22... Optical coupling section, 23.
... Tunable wavelength laser, 24 ... Laser side waveguide, 25
... Light receiving element, 26 ... Amplification circuit, 27 ... Control circuit, 28 ... Control region.

Claims (1)

[Claims] In an integrated optical semiconductor device in which at least a waveguide optical filter and a wavelength tunable laser are integrated on a semiconductor substrate, a filter side waveguide and a laser are respectively formed on the output side of the optical filter and the output side of the wavelength tunable laser. a side waveguide, an optical coupling section that couples light guided through the filter side waveguide and the laser side waveguide, and a light receiving element into which the light coupled by the optical coupling section is incident, An integrated optical semiconductor device, wherein a light receiving element and a wavelength control region of the wavelength tunable laser are electrically connected via a control circuit.