JPS5990981A - Manufacture of optical integrated circuit - Google Patents

Abstract

PURPOSE:To manufacture the optical integrated circuit, which is manufactured easily, in which a coupling at high efficiency of both a passive waveguide and an active waveguide is enabled and which does not interfere in the operation of a device on the passive waveguide and the active waveguide, by removing upper sections at the stepped difference of a semiconductor substrate in each waveguide and an intermediate layer and forming end surfaces mutually corresponding to the active waveguide and the passive waveguide in approximately parallel. CONSTITUTION:A stepped difference 11 is formed previously on the InP substrate 1 through etching. When forming the stepped difference, various stepped-difference shapes can be selected by selecting etching liquids and substrate orientations, but the stepped difference close to verticality is preferable. An InP buffer layer 2, the InGaAsP active waveguide layer 3, the InP intermediate layer 4, the InGaAsP passive waveguide layer 5 and an InP clad layer 6 are grown continuously on the substrate to which the stepped difference is formed. The depth of the stepped difference and the thickness of the intermediate layer 4 are controlled previously so that the positions of the active waveguide layer 3 and the passive waveguide layer 5 coincide on both sides of the stepped difference at that time. The stepped difference section of the substrate is removed, and the end surfaces of the active waveguide and the passive waveguide are formed. Accordingly, beams 12 generated or amplified by the active waveguide 3 couple with the passive waveguide 5 while interposing a minute clearance removed through etching.

Description

Detailed Description of the Invention The present invention integrates a semiconductor laser, an active waveguide such as a waveguide optical amplifier active layer, and a low-loss passive waveguide for propagating light generated or amplified therein on a semiconductor substrate. The present invention relates to a method of manufacturing an optical integrated circuit integrated with a semiconductor device.

An optical communication system that uses a semiconductor laser (LD) as a light source is
It has already entered the stage of practical use due to improved performance and reliability of the devices that constitute it. This optical communication system is
It is expected that system configurations will become more sophisticated in the future, and as a result, the introduction of various new optical devices and their interconnection,
Further improvements in the performance of optical devices themselves are required. In order to manufacture a complex and commercially viable small system that connects devices with many individual functions with low connection loss and low production costs, optical integrated circuits that integrate each function on one substrate, Among them, in addition to active and receiving optical devices such as light sources, photoreceivers, and modulators, transistors and I”
A monolithic optical Ir2 circuit that can also integrate electrical devices such as ET is essential. In order to realize a monolithic optical integrated circuit, active waveguides for LDs, amplifiers, etc., and low-loss passive waveguides for guiding the light generated or amplified there to parts with other functions on the same substrate are required. It is important to combine efficiently. However, in a normal LD, a reflector is formed by cleavage or the like at both ends of the active layer, and the laser beam is extracted from there to the outside.
It is difficult to extract laser light to a passive waveguide on the same substrate. In order to eliminate this drawback, the following method has been considered as a method for coupling a movable waveguide and a passive waveguide.

1) DBR coupling 2) Taper coupling 3) Directional coupling 1) DBR (Distribution) on the active waveguide
However, since the active waveguide and the passive waveguide are constructed from the same medium die i, there is a drawback that the loss in the passive waveguide is large. Furthermore, the formation of I)BR having a period of minute A11lj also requires a technically advanced one. In 2), an active waveguide and a passive waveguide are formed in contact with each other in the layer direction, and a tapered structure is introduced into one or both waveguides in the light propagation direction to achieve coupling. It is difficult to control and obtain high coupling efficiency. 3) is ITG (integrated T
This is known as a winGuide (Integrated Dual Waveguide) structure, in which an active waveguide and a passive waveguide are directionally coupled in the layer direction via an extremely thin intermediate layer.

This structure requires the two waveguides to be completely phase-locked, which makes it difficult to control during production and does not provide sufficient coupling efficiency. Although the conventionally considered methods have problems particularly in terms of coupling efficiency, the following methods have also been considered to solve this problem. FIG. 1 is a diagram for explaining a conventionally known method of coupling an active waveguide and a passive waveguide. One function of manufacturing this structure will be explained using the drawings. In this case, InGaAs is used as the material.
An example in which a P/I nP phase material is used will be explained.

The fabrication of this structure will be explained. First, an active waveguide layer 3 (Q+) InP intermediate layer 4 made of InGaAsP is formed on an InP substrate 1 with an InP buffer layer 2 interposed therebetween. After that, the InP intermediate layer 4 and the active waveguide layer 3 are selectively mesa-etched, and crystal growth is performed again on them to form a passive waveguide layer 5 made of a second InGaA sP (Qx) having a low optical absorption loss composition. By forming the second cladding layer 6 of InP, the structure shown in FIG. 1 is formed. This structure has the advantage that the active waveguide and the passive waveguide are directly coupled, and very highly efficient coupling can be expected. However, this structure requires two crystal growths and is time consuming. Furthermore, in order to manufacture an LD, a resonator is formed that includes an active waveguide and a passive waveguide, so when integrating a device such as an external modulator in the passive waveguide part, a DBR etc. There is also the problem that unless the LD is introduced and separated, the operating state of the LD will be affected by the operation of the modulator, and the advantages of the external resonator will not be utilized. In order to improve this point, a structure has also been considered in which the connection portion between the active waveguide layer 3 and the passive waveguide layer 5 is removed by etching to form substantially parallel end faces that are close to and opposite to each other. According to this structure, the active waveguide and the passive waveguide face each other in close proximity and are completely separated, resulting in high coupling efficiency and the operation of the device formed on the passive waveguide. The operation of j7LD is not affected. However, in this case as well, the manufacturing process requires two crystal growths and is labor-intensive.

The present invention was made in consideration of the above-mentioned problems.
The purpose of the present invention is to provide a method for manufacturing an optical concentrating RA circuit that is easy to manufacture, allows highly efficient coupling of a passive waveguide and a viscous waveguide, and does not interfere with the operation of devices on the passive waveguide and the active waveguide. shall be.

A method for manufacturing an optical integrated circuit according to the present invention includes forming an active waveguide and a passive waveguide on a semiconductor substrate having a step extending in a direction perpendicular to the propagation direction of light. Light of! 1M+ are formed continuously through the intermediate layer so that they match, and the portions of the respective waveguides and the intermediate layer above the step of the semiconductor substrate are removed, and the active waveguides and passive waveguides are mutually formed. It is characterized by forming substantially parallel end faces.

The following is an example of the present invention.
cExplain.

FIG. 2 is a diagram for explaining a method of manufacturing an optical integrated circuit using unexploded IJIJK. The manufacturing method will be explained using FIG. 2, taking InGaA sP/InP type materials as an example. First, (1) a step 11 is formed in advance on the substrate 1 by etching (FIG. 2(a)). When forming a step, various step shapes can be selected by selecting the etching solution and the orientation of the substrate, but in this case, it is desirable to form a nearly vertical step. InP is placed on the substrate on which this step is formed.
Buffer layer 2, InGaAsP active waveguide layer 3, In
A P intermediate layer 4, an InGaAsP passive waveguide layer 5, and a -cladding layer 6 are successively grown (FIG. 2(b)). At this time, the depth of the step and the thickness of the intermediate layer 4 are controlled in advance so that the positions of the active waveguide layer 3 and the passive waveguide layer 5 coincide on both sides of the step. After that, the step part of the board is removed by etching,
Form the end faces of the active waveguide and passive waveguide (see Figure 2 (
C)).

The extremely small gap thus removed is coupled to the passive waveguide 5 through the gap. Due to recent advances in microfabrication technology, groove widths of several μm or less can be obtained by etching, so that the coupling efficiency can be sufficiently increased. In addition, since a reflecting mirror is formed in the active waveguide by etching, the active waveguide is
When used as a waveguide, it is completely separated from the passive waveguide, and the fiLD is controlled by the operation of the device formed on the passive waveguide.
operation is not affected. Furthermore, the influence of reflection from the end face of the passive waveguide can be reduced by a non-reflection coating. Therefore, with this structure, it is possible to combine the active waveguide and the passive waveguide with high efficiency, and to eliminate interference between the operation of the active waveguide and the device integrated on the passive waveguide, resulting in a high degree of integration. becomes possible. Furthermore, since this structure can be produced in one growth, the production time is reduced to 1J.
It has the advantage of being smaller.

Although crystal growth can be achieved by the most common film phase growth method, vapor phase growth, molecular beam epitaxial methods, etc. are advantageous because they tend to preserve the shape of the lower step. In addition, although wet etching can be used for the etching used to separate the active and passive waveguides at the end, it is better to use dry etching methods such as reactive ion etching and ion beam etching to control the processing. This is a disadvantage in terms of performance and miniaturization. For convenience of explanation, the explanation has been given using InGaAsP/InP type materials as an example, but it goes without saying that the present invention is applicable to other semiconductor materials. Similarly, for convenience of explanation, only a planar waveguide structure has been described, but various methods employed for transverse mode control of an LD can be applied to create a three-dimensional waveguide.

As described in detail above, according to the present invention, it is easy to manufacture, the coupling efficiency between the active waveguide and the passive waveguide is improved, and the operation interference between the active waveguide and the device on the passive waveguide is improved. Thus, a method for manufacturing an optical integrated circuit is obtained.

[Brief explanation of drawings]

Figure 1 shows an example of a conventionally known optical integrated circuit, and Figure 2 (
al, lb), (c) are diagrams showing a method of manufacturing an embodiment of an optical integrated circuit according to the present invention. In the figure, 1 is a semiconductor substrate, 2, 3, 4, 5.6 are semiconductor layers, 11 is a step, and 12 is a light. 11th work year Uchihara Figure 1 1- and-

Claims (1)

[Claims] On a semiconductor substrate with a step extending perpendicular to the light propagation direction, an active waveguide and a passive waveguide are placed between the active waveguide and the passive waveguide on both sides of the step so that the optical axes of the active waveguide and the passive waveguide coincide. The active waveguide and the passive waveguide are formed in a continuous manner through layers, and the portions of the waveguides and the intermediate layer above the step of the semiconductor substrate are removed to form end faces facing the active waveguide and the passive waveguide substantially parallel to each other. 1. A method of manufacturing an optical integrated circuit, characterized by forming an optical integrated circuit.