JPH01219828A - Optical switch - Google Patents

Abstract

PURPOSE:To efficiently switch optical paths by forming a switching part by using a supergrid formed by laminating different kinds of semiconductors alternately, and forming an optical waveguide part other than the switching part by using a semiconductor formed by making the supergrid into mixed crystal. CONSTITUTION:The switching part 4 of the optical waveguide 5 is formed of the supergrid and the remaining optical waveguide part is formed of the semiconductor obtained by making the supergrid where the switching part 4 is formed into the mixed crystal to manufacture the optical switch without any regrowing process. Further, the supergrid is made into the mixed crystal, and consequently an absorption end lambdag before the supergrid is made into the mixed crystal becomes an absorption end lambdag which is shifted to a short- wavelength side after the complete mixed crystallization and when light with nearby wavelength is incident on the absorption end lambdag, the incident light has wavelength lambdain>>lambdag, so that the absorption loss of the mixed crystal decreases. Therefore, the optical switch is switched in this wavelength range to maximize variation in refractive index at the time of the application of an electric field to the switch part and the absorption loss of the optical waveguide part decreases. Consequently, the optical paths are switched efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a total internal reflection type optical switch in which a leading waveguide formed of a semiconductor is arranged in an X-shape.

(Prior art) A total reflection type optical switch using a semiconductor changes the refractive index of an optical switch part formed at the center of the intersection of leading waveguides crossed in an X shape by applying an electric field, and causes total reflection at the optical switch part. The light output direction is switched by causing this to occur.

FIG. 2 is a diagram for explaining the switching operation of this type of optical switch, and in the figure, ■ indicates an optical waveguide section, and ■ indicates a switch section. According to FIG. 2, for example, the pin
When the electric field applied to the optical switch section ■ is off, the light that enters the optical waveguide section ■ and propagates through the optical waveguide section ■ goes straight and exits from the output port PL, and when the electric field applied to the optical switch section ■ is on. Sometimes it is totally reflected and emitted from the output port P2.

In forming such a semiconductor optical waveguide, a so-called superlattice, in which semiconductors of different types are alternately stacked at a rate of approximately 10A, is suitable as an optical switch part because the refractive index when an electric field is applied is large near the absorption edge. If the same material as the switch part is used for the optical waveguide part other than the switch part, the absorption loss will increase (for example, GaAs-
AN To explain the GaAs system, the superlattice of the switch part is GaAs-AΩAs (80A each)1
00 period, the absorption edge due to excitons λex
is located at a position of 8200A, and the refractive index change when an electric field is applied is maximum at this wavelength λex. When using this wavelength range, if the same superlattice is used in the optical waveguide section, the absorption loss there will be about 10@3 cm@-1, which will be very large.

For this reason, in a conventional total reflection optical switch using a superlattice, after cutting out the superlattice forming the switch part into a convex shape,
In the optical waveguide portion, a material located on the short wavelength λgd side compared to the absorption edge λ13X, for example, A N x G a I-xA 5
(x-0,3, λgd-7500 people) was regrown, thereby forming a transparent leading waveguide with little absorption loss for the wavelength used.

(Problem to be Solved by the Invention) However, according to the above-mentioned optical switch, when the switch portion is cut out in a convex shape, the interface is not vertical but tapered, so that a perfect P-N junction is formed. As a result, the application of an electric field to the switch portion becomes insufficient, resulting in a problem in that total reflection is not performed sufficiently.

In addition, when regrowing the optical waveguide after cutting out the switch part into a convex shape, the regrowth part is also formed on the side surface of the convex part.
There is a problem that loss occurs at the connection interface between the optical waveguide part and the switch part, and furthermore, the manufacturing process becomes complicated because the switch part is cut out into a convex shape and then regrown.

In view of the above-mentioned problems, an object of the present invention is to reduce the absorption loss of the optical waveguide section, improve the quality of the connection interface between the switch section and the optical waveguide section, and perform optical path switching operations efficiently. Our purpose is to provide optical switches.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an optical switch having a switch section at the center of the intersection of semiconductor optical waveguides crossed in an X shape, in which different types of semiconductors are alternately laminated. The switch section was formed using a superlattice obtained by mixing the superlattice, and the optical waveguide section other than the switch section was formed using a semiconductor obtained by mixing the superlattice.

(Function) According to the present invention, the switch portion of the leading waveguide is formed of a superlattice, and the other optical waveguide portions are formed of a semiconductor in which the superlattice that formed the switch portion is mixed, so that regrowth is possible. Manufacture can be performed without obtaining any steps.

In addition, by mixing the superlattice, the absorption edge λg before mixing becomes the absorption edge λg° shifted to the short wavelength side after complete mixing, and light with a wavelength close to the absorption edge λg is incident. In this case, the wavelength of the incident light becomes λ1n>λg°, and the absorption loss due to the mixed crystal becomes small.

Therefore, if the switching operation of the optical switch is performed in this wavelength range, the change in the refractive index when an electric field is applied to the switch section is maximized, and the absorption loss in the optical waveguide section is reduced.

(Example) FIG. 1 is a perspective view showing a tip switch according to the present invention, FIG. 3(a) is a sectional view taken along the line A-A in FIG. 1, and FIG. 3(b) 2 is a sectional view taken along the line B-B in FIG. 1. FIG. 1 and 3, 1 is a substrate made of GaAs, 2 is a buffer layer made of n-GaAs laminated on the substrate 1, and 3 is a n-k layer laminated on the buffer layer 2.
l A cladding layer made of GaAs, 4 is a switch part,
Laminated on the cladding layer 3, GaAs (80A),
It consists of a superlattice in which AN As (80 people) are stacked alternately (100 periods), and its absorption edge λg is 8200 people. Reference numeral 5 denotes an optical waveguide section that forms a leading waveguide with the switch section 4, and is made of the same material (GaAs (
80A).

A11) It is made of a semiconductor obtained by mixing As(80A) ) by the method described below, and its absorption edge λg° is 7070. 6 is a switch section 4. A cladding layer made of PA and 17 GaAs laminated on the optical waveguide portion 5, a cap layer 7 made of P-GaAs laminated on the cladding layer 6, and an electrode made of CrAu deposited on the cap layer 7. It is.

Further, the structural parameters of this optical switch are, for example, an element length of 500 μm, an optical waveguide width of 8 μm, a width of the switch section 4 of 2 μm, and a crossing angle of 9 degrees.

FIG. 4 is a diagram showing a grown wafer structure that is the basis of the above-mentioned optical switch. Next, a method of manufacturing the optical switch according to the present invention will be explained.

First, an n-GaAs cladding layer 2 is placed on a GaAs substrate 1.
, n-AΩGaAs cladding layer 3, superlattice layer (GaAs
(80A), AΩAs(80A))4 a,' P-A
The ΩGaAs cladding layer 6 and the l''GaAs capping layer 7 are grown in this order by molecular beam epitaxy.Next,
A SiO3 film is formed on the surface of the P-GaAs cap layer 7 by plasma CVD, and then the portion to which SiO2 is attached is formed into a convex shape by using reactive ion etching, which has excellent smoothness. Furthermore, 5102 on the top of the part to be the switch part is removed to open a window, and the p-GaAs cap layer 7 side coated with 5I02 of this wafer and the GaAs substrate 1 are stacked together in a hydrogen atmosphere. By heat treatment, the superlattice layer 4a is mixed crystallized. Finally, a CrAu electrode is placed on the P-GaAs cap layer 7 side above the superlattice layer 4a (switch part) that has not been mixed crystallized, and n
-AuGeN i electrode (not shown) on the GaAs substrate 1 side
The fabrication is completed by forming by vapor deposition.

FIG. 5 is a diagram showing the optical output characteristics when an electric field is applied to the optical switch according to this example formed by the above method, and the horizontal axis is C.
The voltage applied to the rAu electrode and the old AuGe electrode, and the vertical axis shows the relative optical output. According to FIG. 5, when an electric field is applied to the switch section 4, the optical outputs from the two first output ports PL and P2 switch in magnitude at around 6V, and are reversed at around 10V. I know what you're doing.

In addition to the characteristics shown in FIG. 5, the optical switch according to this embodiment has the following characteristics.

(1) The change in refractive index of the superlattice portion of the switch section 4 when an electric field is applied is maximum in the wavelength region near the absorption edge, and is approximately 1%.

(2) The reflectance at the interface between the switch section 4 and the optical waveguide section 5 is about 0.04%, and the loss due to the interface between the superlattice and the mixed crystal is small.

(3) Absorption edge λg of forward switch section 4 (8200 people)
The difference between the absorption edge λg' (7070 people) of the optical waveguide section 5 is about 100 OA. In addition, since SiO2 was coated on the surface and heat treated to form a mixed crystal, the absorption loss in the wavelength region near the absorption edge of the superlattice where the refractive index change is maximum due to the lack of free carriers, etc. It is small, about 1 dB/cm.

In this embodiment, an optical switch using a GaAs-A, Q GaAs superlattice is used as an example, but it is needless to say that the present invention is not limited to this. Although 5102 coating was used as a method for creating a superlattice mixed crystal, other methods such as diffusion of St or Zn or implantation of Si ions may also be used.

(Effects of the Invention) As explained above, according to the present invention, in an optical switch having a switch section at the center of the intersection of semiconductor guided waveguides crossed in an X shape, a superlattice in which different types of semiconductors are alternately laminated The switch part was formed using the above switch part, and the optical waveguide part other than the switch part was formed from a semiconductor mixed with the superlattice, so the optical switch part was cut out into a convex shape and manufactured without going through a regrowth process. Provides an optical switch that can simplify the manufacturing process, has less absorption loss due to free carriers in the optical waveguide, has less loss at the interface between the optical waveguide and the switch, and can perform efficient switching operations. There are advantages that can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an optical switch according to the present invention, Fig. 2 is an explanatory diagram of the switching operation of the optical switch, Fig. 3 is a sectional view of Fig. 1, and Fig. 3(a) is a line taken along line A-A. 3(b) is a sectional view taken along line B-B in the arrow direction, FIG. 4 is a diagram showing the wafer structure, and FIG. 5 is a diagram showing the optical output characteristics of the optical switch according to the present invention. be. In the figure, 1-n-GaAs substrate, 2- n-GaAs buffer layer, 3... n-AN GaAs cladding layer, 4
... Switch section, 5... Optical waveguide section, 6... P-
AJ7 GaAs, cladding layer, 7...P-GaAs
Cap layer, 8...electrode. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] In an optical switch having a switch section at the center of the intersection of semiconductor optical waveguides crossed in an X shape, the switch section is formed using a superlattice in which different types of semiconductors are alternately laminated; An optical switch characterized in that an optical waveguide section other than the switch section is formed of a semiconductor in which the superlattice is mixed crystal.