JPS6237905B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical integrated circuit and a method for manufacturing the same.

In recent years, optical integrated circuits that integrate semiconductor lasers, photodetectors, optical modulators, etc., have been studied as terminal devices for optical communications. The same applies to optical integrated circuits that integrate wavelength multiplexed light sources on the same substrate.

The most important thing in optical integrated circuits is the coupling of semiconductor lasers and photodetectors with optical waveguides, and especially in the case of active devices such as semiconductor lasers, a method that couples the propagation modes directly with high efficiency is absolutely necessary. I'm getting old. Effective coupling methods for optical integrated circuits include a method using a double waveguide and a method using a taper coupling. FIG. 1 simply illustrates the structure of both. Double waveguide method (first
In Figure a), by matching the propagation constants of the two waveguides 1 and 2, waveguide 1 and waveguide 2 are coupled, and an efficiency close to 100% can be obtained. but,
In this method, it is difficult to match the propagation constants of the two waveguides, and as the degree of integration of optical integrated circuits increases, it becomes difficult to efficiently couple all the elements. Method using taper connection (Fig. 1b)
This is a method in which the propagation mode is converted by gradually increasing or decreasing the thickness of the waveguide, and the light propagating inside is guided into another waveguide. This method has the advantage that the two waveguides 1' and 2' can be considered to be integrated into one waveguide, making the design easy. However, it is difficult to form a tapered portion using the tapered bonding method, and it can be said that it is almost impossible to form a large number of tapered portions using the conventional method.

Conventionally, the taper portion has been formed using a method as shown in FIG. 2 during liquid phase crystal growth. 3 is a slide boat movable part, 4 is a slide boat solution reservoir, and 5 is a crystal growth wafer. In this method, a growth inhibiting rod 6 is installed in a boat hole, and the difference in wetting of the growth solution 7 around the growth inhibiting rod 6 is utilized. This method has drawbacks such as the number and position of the taper portions being formed and lack of reproducibility, and thus cannot be applied to optical integrated circuits. The present invention proposes to form a taper portion by a method completely different from the method described above, and to apply it to optical integrated circuits.

FIG. 3 is a diagram showing the principle of forming a tapered portion by the method of the present invention. Epitaxial analysis of the case where a mesa stripe is provided in the <110> or <110> direction on the (100) plane of a - group compound semiconductor single crystal substrate (e.g. GaAs, InP) 8, 8', 8'' and its width is changed. Changes in shape of crystal growth layers 9, 9', 9'' are shown. "a" indicates the case where the mesa stripe width is wide, "c" indicates the case where the mesa stripe width is narrow, and "b" indicates the case where the width is in between. It can be seen that in case a, a crystal growth layer is formed on the mesa stripe, whereas in case c, nothing is formed on the mesa stripe. Furthermore, in case b, a thinner crystal growth layer is formed on the mesa stripe than in case a. However, the conditions in this case are that an InP substrate is used and mesa etching of approximately 2 μm is performed, and the width of the mesa stripe is ~30 μm for a, ~10 μm for b, ~3 μm for c,
The crystal growth thickness of the flat part shall be approximately 0.5 μm.
This means that by controlling the width of the mesa stripe, the thickness of the crystal growth layer formed on the mesa stripe can be controlled. That is, a waveguide having a thickness that correlates with the mesa stripe width is formed. The present invention utilizes this property, and a tapered growth layer can be obtained by the following method.

As shown in FIG. 4, when crystal growth is performed using a mesa stripe in which the mesa etching width is continuously changed, a tapered crystal growth layer 12 as shown in FIG. 5 can be formed. I can do it. However, the fourth
The mesa stripe section 11 shown in the figure has a maximum width of 30 mm.
The minimum width is 3 μm, the mesa depth is approximately 2 μm, and the crystal growth thickness in the flat portion shown in FIG. 5 is approximately 0.5 μm. By the way, it should be noted here that the relationship between the width of the mesa stripe and the growth thickness is not necessarily linear but an anti-logarithmic relationship, so in order to form a linear tapered layer, , it is necessary to make a certain amount of compensation for the change in mesa stripe width.

The tapered layer obtained in this way has good reproducibility and can be formed in multiple numbers at any position on the substrate, so it can be applied not only to optical integrated circuits but also to distributed feedback (DFB) lasers by applying diffraction gratings. Application to distributed reflection (DBR) lasers becomes possible.

Furthermore, in the case of multilayer crystal growth, the method according to the present invention allows the first grown crystal layer to be completely buried by the later grown crystal layer, and even narrow mesa stripes can be thickened. Since it can be embedded by growing crystals, the following structures can be manufactured.

FIG. 6 shows that the output waveguide layer is mesa-etched 13 and a tapered active layer 14 is grown thereon.
By growing the cladding layer 15 further upward, the tapered active layer and output waveguide layer are all buried. At this time, it is of course possible to grow other crystal layers before and after the growth of the tapered active layer.

Figure 7 shows the device manufactured as shown in Figure 6.
This is applied as a DBR laser. In the figure, 10 is a crystal growth wafer, 13 is a mesa stripe optical waveguide, and 16 is a substrate side cladding layer. As explained above, the present invention allows tapered coupling type devices to be freely manufactured on the same substrate, and by combining active devices with various structures, optical integrated circuits can be realized. can.
FIG. 8 shows an example of an optical output monitor type wavelength controlled laser that combines a DBR laser and a light receiving element. By integrating such optical waveguide arrays, it is possible to create wavelength multiplexed light sources, optical control circuits, and the like.

The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

Figure 1a shows the principle of a double waveguide coupler, Figure 1b shows the principle of a tapered coupler, Figure 2 shows the conventional liquid phase growth method for growing a tapered crystal layer, and Figure 3 shows the principle of a dual waveguide coupler. Figures a to c are views showing how crystals grow on mesa stripes according to the present invention, and Figures a to d are top and rear views showing examples of mesa stripes for growing tapered crystal layers. , a front view, a side view, Figures 5a and 5b are a top view and a center cross-sectional view showing an example of crystal growth in Figure 4, respectively, Figures 6a to d are mesa stripes formed by optical waveguides and their embedding. The top view, front view, rear view, central cross-sectional view, and FIG.
Cross-sectional view showing an example of a DBR laser, Figure 8 a, b
1 is a top view and a sectional view showing an example of a combination of a DBR laser and a light receiving element according to the present invention. 8, 8', 8'', 10...crystal growth wafer,
9, 9', 9'', 12...Crystal growth layer, 11, 13
...Mesa stripe section, 14... Active layer, 15...
...Embedded cladding layer, 16...Substrate side cladding layer.

Claims (1)

[Claims] In an optical integrated circuit made of a 1- group compound semiconductor, a tapered waveguide in which the thickness of a part of the layer constituting the optical waveguide layer gradually changes in the direction of light propagation is formed by liquid phase growth. A tapered waveguide with a varying thickness that correlates with the mesa stripe width is formed on the mesa stripe region provided on the substrate by using a substrate with a mesa stripe region whose width gradually changes. A method for manufacturing an optical integrated circuit, characterized by: 2. The method for manufacturing an optical integrated circuit according to claim 1, wherein one or more crystal growth layers are provided in advance on the 2- group compound semiconductor crystal substrate. 3. The method of manufacturing an optical integrated circuit according to claim 1, wherein InP is used as the group compound semiconductor substrate. 4. The method of manufacturing an optical integrated circuit according to claim 1, wherein GaAs is used as the group compound semiconductor substrate.