JPH0473606A - Semiconductor polarizing beam splitter - Google Patents

Abstract

PURPOSE:To attain low loss by constituting a Y-branch optical waveguide with an optical guide layer provided with superstructure and a clad layer whose refractive index is lower than that of the optical layer, and making the superstructure into mixed crystal and dissipating it at a part of a Y-branch part. CONSTITUTION:The Y-branch optical guide formed on a semiconductor substrate 10 consisting of InP is composed of the optical guide layer 12 consisting of InGaAs(P)/InP super lattice and first and second clad layers 11, 13 consisting of InP, and the superstructure of the optical guide layer 12 is made into the mixed crystal and dissipated at a part of the Y-branch part. Thereby, total reflection for waveguide light of TE mode can be attained, and transmission for the waveguide light of TM mode, and remarkable change in the refractive index of the waveguide light of TE and TM modes before and after the making into the mixed crystalization can be obtained, and miniaturization that a Y- branch angle can be set at around 4 deg. and element length is less than 100mum can be attained, and low loss can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a waveguide type polarizing beam splitter that is a component of a semiconductor optical integrated circuit.

(Prior Art) Polarizing beam splitters that separate a light beam incident at an arbitrary polarization angle into TE and TM mode light beams are important in the field of coherent optical communication, which makes advanced use of optical frequency and phase information. In particular, it has become an essential device for polarization diharstic reception systems. Among these, semiconductor waveguide type polarizing beam splitters have the characteristic of being able to be monolithically integrated with semiconductor elements such as semiconductor lasers, photodetectors, optical switches, and 3dB couplers, and will be used to build future optical communication network systems. It is expected to be a basic element for semiconductor optical integrated circuits. As an example of the conventional technology, there is a report by Ehrman et al. (European Conference on Optical Communications (ECOC'89), ThB20-1
．． (1989). The conventional example has a structure in which metal is loaded on one side of two rib-type optical waveguides (so-called directional coupler type) placed close enough to cause optical coupling, and the value of the effective refractive index of the leading waveguide is This takes advantage of the difference between guided light in TE mode and TM mode. The value of effective refractive index is T
If the E mode and TM mode are different, the optical coupling length of the directional coupler will be different between the TE mode and the TM mode, and by selecting the element length, the guided light of the TE and TM modes can be separated.

In the conventional example, the element length is from 900.4 m to 1100/im.
An extinction ratio of about 15 dB is obtained for both TE mode and TM mode guided light in the range of .

(Problems to be Solved by the Invention) In the conventional polarizing beam splitter described above, in principle, the guided light in the TM mode is absorbed by the metal loaded on the waveguide, causing optical loss, and the width of the waveguide is 0.
It requires processing accuracy of 1□m or less, and has problems such as difficulty in manufacturing elements with good reproducibility.

The purpose of the present invention is to solve these problems, to be easy to manufacture, and to
An object of the present invention is to provide a semiconductor waveguide type polarization beam splitter with low loss.

(Means for Solving the Problems) In order to solve the above-mentioned problems, a semiconductor polarizing beam splitter of the present invention is provided in which a Y branch optical waveguide on a semiconductor substrate is refracted by an optical guide layer having a superlattice structure and the optical guide layer. It is characterized in that the superlattice structure of the light guide layer becomes a mixed crystal in a part of the Y branch and disappears.

(Function) A guiding waveguide having a superlattice structure represented by InGaAs/InP or GaAs/AlGaAs has TE and TM
Different refractive index values (each n
TE, 11T8), and when it becomes a mixed crystal, the refractive index changes and takes the same value (set as no) for guided light in the TE and TM modes. These openings include nT8〉no
> nTM relationship exists. Therefore, in the present invention in which a part of the Y branch of the superlattice structure waveguide is mixed crystal as shown in FIG. 1, the TE mode guided light is totally reflected, and the TM mode guided light is totally reflected. can be passed through. T.E.
and the refractive index change before and after mixed crystallization for guided light in TM mode (respectively “TE = IITE −nO1△rlTM
= “O”TM) are both approximately 4X10
Most importantly, the Y-branch angle is about 4 degrees, and the element length is 100 □m or less, which allows for miniaturization and low loss. Furthermore, in the structure of the present invention, a processing accuracy of about 0.5 pm is sufficient for the waveguide width, and it is easier to manufacture and has better reproducibility of characteristics than the conventional example, which required a processing accuracy of 0.1 μm. It has the characteristics of

Therefore, it is possible to realize a semiconductor waveguide type polarizing beam splitter that is easy to manufacture and has low loss.

(Example) Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1(a) is a plan view of a semiconductor waveguide type polarizing beam splitter showing the main part of an embodiment of the present invention, and FIG. 1(b) is a cross-sectional view taken along line A-B in FIG. 1(a). .

In this embodiment, a Y-branch leading waveguide formed on a semiconductor substrate 10 made of InP has an optical guide layer 12 made of an InGaAs(P)/InP superlattice and a first waveguide made of InP. It is composed of second cladding layers 11 and 13, and the superlattice structure of the optical guide layer 12 becomes a mixed crystal in a part of the Y branch and disappears.

Next, the manufacturing method of this example will be explained. n-I
On a semiconductor substrate 10 made of nP, a first cladding layer 11 made of non-doped InP (thickness 1 μm) and a non-doped InGaAs(P) (thickness 28 μm) lattice-matched to InP are formed by vapor phase growth or molecular beam growth. An optical guide layer 12 consisting of a 100-period superlattice of undoped InP (thickness: 46 mm) and non-doped InP (thickness: 46 mm) is grown. Next, plasma CVD
A SiNx film is selectively formed using the method of oxidation and photo-roughing, and heat treatment is performed at 800°C to make the superlattice structure under the SiNx film into a mixed crystal and disappear (so-called cap annealing mixed crystal formation method). forming a chemical region 14. Next, after removing SiNx, a second cladding layer 13 (thickness: 1 pm) made of non-doped InP is grown by vapor phase growth, molecular beam growth, or the like. Furthermore, the waveguide width was reduced to 3 using dry etching technology using chlorine gas.
A Y-branch optical waveguide 15 with an etching depth of 0.8 m and a branching angle of 4° is formed. Here, the first and third optical waveguides were arranged to be straight lines. In this case, the mixed crystal region 14
is the Y branch optical waveguide 15 plane shown in FIG. 1(a).
It needs to be at the branch point. The angle between the mixed crystal region and the first optical waveguide was set to 2°, which is half the branching angle. Finally, the semiconductor substrate 1o is polished to a thickness of 11004z, and cleaved to form a light entrance surface and a light exit surface.
A semiconductor waveguide type polarizing beam splitter is completed.

Next, the operation of the semiconductor waveguide type polarizing beam splitter of this embodiment will be explained. Rikatsu I mentioned in the section on action.
An optical waveguide with a superlattice structure represented by nGaAs/InP exhibits different refractive index values (nTE, nTM, etc.) for guided light in TE and TM modes, and when mixed crystal, it exhibits different refractive index values for guided light in TE and TM modes. It takes almost the same value (set to no) for the guided light. Between these, nTE>no
＞nTM exists, the TE mode component of the light 1 incident on the first leading waveguide 4 is totally reflected at the Y branch, and the second
On the other hand, the TM mode component is transmitted through the mixed crystal region 14 and guided to the third leading waveguide 6. T.E.
and refractive index changes before and after mixed crystallization for guided light in TM mode (ΔnTE=nTF, -no, ΔnTM=no, respectively)
-nTM) are both large, approximately 4×10 −3 , and the Y branch angle is approximately 4°, and the element length is 100 μm or less, allowing for miniaturization and a waveguide loss of 0.1 dB. Furthermore, in the structure of the present invention, the processing accuracy of the waveguide width is 0.5 μm.
It is enough. Therefore, it is possible to realize a semiconductor waveguide type polarizing beam splitter that is easy to manufacture and has low loss.

Incidentally, in the above embodiments, size examples are also shown, but since the appearance of crystal growth, mixed crystal formation, and etching vary greatly depending on the growth method and conditions, it goes without saying that appropriate dimensions should be adopted. stomach. Although InGaAs(P)/InP has been described as the material for the semiconductor waveguide type polarizing beam splitter, it is not limited to this.
InGaAs/InAlAs system, GaAs/GaAlA
S-based materials may also be used, and the method of mixed crystallization of the superlattice is as follows:
Although the gap annealing mixed crystallization method is used, a method of impurity diffusion such as Zn, Cd, etc., or an ion implantation method of Si, H, etc. may also be used. The shape of the figure 7, the branching angle, and the mixed crystal region of the Y-branch waveguide can be freely modified as necessary. In the mixed crystal region, only one mode may be reflected, the other mode may be transmitted, and each mode may be guided.

(Effects of the Invention) As explained in detail above, according to the present invention, a semiconductor waveguide type polarizing beam splitter that is easy to manufacture and has low loss can be obtained, and it can be used for future semiconductor optical integrated circuits used in coherent optical communication systems and the like. It is the dog that contributes to the realization.

[Brief explanation of drawings]

FIG. 1(a) is a plan view of a semiconductor waveguide type polarizing beam splitter showing the main part of an embodiment of the present invention, and FIG. 1(a) is a sectional view taken along the line AB in FIG. 1(a). In the figure, 1...Incoming light, 2...Outgoing light 1 (TE mode), 3
... Outgoing light 2 (TM mode), 4... First leading wave path, 5... Second leading wave path, 6th river third leading wave path, 1
0... InP semiconductor substrate, 11... Second cladding layer made of InP, 12-I
a light guide layer made of nGaAs(P)/InP superlattice;
13... Second cladding layer made of InP, 14...
-Mixed crystal region, 15... Leading waveguide.

Claims (1)

[Claims] A Y-branch optical waveguide on a semiconductor substrate is composed of an optical guide layer having a superlattice structure and a cladding layer having a lower refractive index than the optical guide layer, and the superlattice structure of the optical guide layer is a part of the Y-branch. A semiconductor polarizing beam splitter characterized in that it becomes a mixed crystal and disappears.