JPS60170992A - Optical integrated circuit - Google Patents

Abstract

PURPOSE:To attain a high industrial productivity by a method wherein a plurality of photo elements provided in a single substrate is intercommunicated in an outer wave path so that laser coupling of the photo elements with the outer wave path may be properly established. CONSTITUTION:A laser-emitting element 14 and laser-receiving element 13 are formed on a semiconductor substrate 1. The element 14 is of a distributed feedback type, with the surface of diffraction lattice 4 provided on the substrate 1 facing an activation layer 3 inside the element 14. The element 13 is again of the distributed feedback type, incorporating a lattice surface 4 provided within a mode selecting feature within. An end face 24 of the element 13 is a crystal cleavage face wherefrom a laser beam is emitted. Between the elements 14, 13, an outer wave path 9 is provided, not furnished with a diffraction lattice face, for the establishment of optical coupling. The beam outputted by the element 14 is led through a wave path 9 to be guided into the element 13 and the yielded power is monitored there. With the circuit being constructed as such, the growth is effected with ease on crystals between the wave paths inside the elements 14, 13 constituting the outer wave path 9, ensuring operation even in the presence of coupling inefficiency. This results in an excellent industrial productivity.

Description

[Detailed Description of the Invention] <Field of the Invention> The present invention is directed to forming a distributed feedback type laser emitting element, a light receiving element, a modulating element, etc. on the same semiconductor substrate, and optically coupling between each element using an external waveguide. The invention relates to optical integrated circuits.

<Prior art and its problems> Conventionally, a laser emitting element, a light receiving element, a modulating element, etc. are grown on a compound semiconductor substrate of In, P, etc. to form an optical integrated circuit, such as the one shown in Fig. 1. Are known.

FIG. 1 is a cross-sectional view along the laser optical axis of an optical integrated circuit in which a distributed reflection type radar emitting device is formed, and is an InP
In the buffer layer 4 (Inp) on the compound semiconductor substrate 1,
Corresponding to the external optical waveguide (region) 9, a diffraction grating surface 4 having a constant pitch and having mode selectivity is uniformly formed by photolithography.

The radar light emitting element 1o is of a distributed reflection type having an external distributed reflector a, and the output of multiple laser beams emitted from this element is monitored by a light receiving element 12 (or 11) so that the power is always constant. ing.

Now, as mentioned above, an optical integrated circuit having a distributed reflection type laser emitting element and coupling with other optical elements is performed through an external optical waveguide in which a diffraction grating having mode selectivity is formed. It had the following problems in terms of industrial productivity.

In other words, since the external waveguide itself has mode selectivity, it is effective in suppressing as much as possible the multi-order modes generated when light passes through the receiving and modulating elements, etc., but the external waveguide itself has mode selectivity. It is difficult to grow crystals between the edges of the diffraction grating plane and the internal waveguides (or active waveguides) between each element, and mismatches such as diffuse reflection occur at the coupling parts, resulting in extremely low light coupling efficiency. It rarely tends to get worse. For this reason, it has been very difficult to manufacture a device that can be put to practical use because it has a large effect on characteristics such as threshold current.

<Object of the Invention> The present invention has been made in view of the problems of the prior art, and its purpose is to improve laser light coupling between an external optical waveguide and an optical element such as a laser emitting element. The object of the present invention is to provide a distributed feedback type optical integrated circuit with good performance and industrial productivity.

<Structure of the Invention> In order to solve the above-mentioned problems, the present invention employs a distributed feedback type optical element epitaxially grown on a semiconductor substrate to form a low-loss optical waveguide having no diffraction grating plane between each element. It is characterized by the fact that

<Example> An example of the present invention and its manufacturing process are shown in FIGS. 2 and 3.

FIG. 2 shows a cross-sectional view along the optical axis of a case where a laser emitting element 14 and, for example, a light receiving element 13 are formed on the semiconductor substrate 1 (laser emitting element with a light receiver).

The laser emitting device is a distributed feedback type device having a diffraction grating surface 4 on a semiconductor substrate 1 corresponding to an active layer 3 inside the device, preferably with respect to the laser optical axis as shown by a broken line 17. One end surface of the crystal is roughened and cut in an oblique direction using a wire saw or the like, or an oblique facet is formed.

Like the light emitting element, the light receiving element is a distributed feedback type element having a diffraction grating surface 4 having mode selectivity therein.

One end surface 24 of the light-receiving element 13 forms a crystal cleavage plane, and a laser beam is emitted from this surface in a direction 23.

For optical coupling between the two elements h1J, there is an external waveguide 9 (not having a diffraction grating surface) whose thickness is controlled to have low loss and equal refractive index to the waveguide layers on both sides.
is formed, and the output light of the laser emitting element is guided through an external waveguide 9 and input to the light receiving element 13, and the output power is monitored.

In addition, in the above explanation! Although d and 13 are used as light receiving elements, they may also be used as modulation elements. It is possible to arbitrarily form a plurality of optical elements with a similar configuration on a semiconductor substrate.

By the way, the length of each element in the laser optical axis direction is 300 to 1000 μm for the laser element and 100 to 1000 μm for the optical waveguide.
μm 1 light receiving element is 200 to 500 μm 1 modulation element is 20
It is 0 to 300 μm.

Next, this manufacturing method will be sequentially explained based on FIG.

(1) A diffraction grating surface 4 with a constant pitch is formed on an n-InP semiconductor substrate 1 by photolithography, and on top of that, an n=InGaAsP optical waveguide layer 19, an InGaAs
P active layer 3, p-InP cladding layer 8, p-InGaA
The sP cap layer 16 is epitaxially grown (
Figure 3(a)).

(2) Externally, the region 9 that will become the 93 wave path is etched down to the substrate surface (FIG. 3(b)).

(3) Epitaxially growing an InGaAsP waveguide layer 15 and an InP outer cladding layer 7 in the outer waveguide region 9; Create an external waveguide (Fig. 3 (Q). Alternatively, do not grow the InP external cladding layer 7 and grow an InGaAsP
On the waveguide layer, a protective film 7 of SiO2, 5t31"14, etc.
may be formed.

(4) An etching-resistant protective film such as SiO2 is formed in a stripe shape in the direction of the radar axis, and the sides of the film are etched away (FIG. 3(d)).

(5) P-InP layers 19, n embedded on both sides
- The InP layer 20 is epitaxially grown to become a current confinement layer, and after lapping, a current injection region is left and a protective film 21 is formed.
is formed, and then metal electrode portions 22 are deposited on both sides.

After annealing, it is made into chips (FIG. 3(e)).

Table 1 shows the λ (oscillation wavelength composition) in each layer.

Table 1 In the above description, an n-type InP substrate is used, but if a p-type substrate is used, a crystal layer of the opposite conductivity type may be grown thereafter. Further, depending on the oscillation wavelength, a GaAs substrate may be used to grow a crystal having a GaAs-based composition.

Further, in the embodiment, an example was shown in which the diffraction grating surface was formed directly on the semiconductor substrate, but the diffraction grating surface may be formed after growing a guffer layer (InP or GaAs substrate) on the substrate.

Next, as coupling types of optical elements, direct coupling type, L -0
・C (Large・0ptical・Cavity)
Integrated Twi
It can be applied to various bond types such as n-Guide) type.

<Effects of the Invention> As is clear from the above description, the present invention forms a plurality of distributed feedback type optical elements on the same uniform bar, and couples each confectionery with an external waveguide that does not have a diffraction grating. Therefore, crystal growth between the external waveguide and the internal optical waveguide is easy, and operation can be achieved even if the coupling efficiency is poor.

For this reason, it has become possible to provide an optical integrated circuit with a very high manufacturing yield and excellent single-channel productivity.

However, when one surface of the light emitting element is formed obliquely to the laser optical axis (preferably formed by roughening it), it is effective to suppress optical axis mode oscillation (Fabry-Perot mode) and to define the laser traveling direction. It can have the desired effect.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view along the laser optical axis of a conventional optical integrated circuit. FIG. 2 is a cross-sectional view along the laser optical axis of the optical integrated circuit according to the present invention. FIG. 3 shows the manufacturing process of the optical integrated circuit according to the present invention, in which (a), (b), and (c) are cross-sectional views taken along the laser optical axis, and (d), ( e) is a cross-sectional view of a plane perpendicular to the laser optical axis. In the figure, 1... Half-body substrate, 3... Active #j, 4...
・Diffraction grating surface, 7... Cladding layer, 9... External waveguide, 13- Light receiving (modulating) element, 14... Laser emitting element, 15... Optical waveguide F'j+ 0 Applicant Fujikura Electric Cable Co., Ltd. Agent Mamoru Takeuchi Figure 1? l

Claims (1)

[Claims] 1. A plurality of distributed feedback optical elements are formed, each having a mode-selective diffraction grating plane formed directly on a semiconductor substrate or on a buffer layer grown on the semiconductor substrate. An optical integrated circuit characterized in that an optical waveguide layer is formed directly on a semiconductor substrate between elements or on a buffer layer grown on the semiconductor substrate.