JPH04155309A - Matrix optical switch - Google Patents

Abstract

PURPOSE:To reduce the element capacity of a optical gate switch body to make its very high speedy switching possible by providing an optical branching circuit to branch an optical signal given through an optical wave guide path, a means for applying an electric field to a optical wave guide path for semiconductor, and an optical confluent circuit on a high resistance semiconductor substrate. CONSTITUTION:Optical signals 14a, 14b inputted into optical branching circuits 11a, 11b are severally bisected, and led to each optical gate switch. When the reverse bias voltage of a photo-absorbing layer 3 is zero, the switch turns into a ON-state to pass light fed to the each optical gate switch for feeding it out. When the reverse bias voltage is applied to the photo-absorbing layer 3, light is absorbed on account of electric field absorbing effect to turn the switch into a OFF-state. In this case, a quenching ratio depends on applied wavelength, the wavelength composition of the photo-absorbing layer and the length of the photo-absorbing layer. Optional switching between incident rays 14a, 14b and out-going rays 15a, 15b can therefore be carried out on the ON, OFF-states of the switch. In addition to that, the incidental capacity of an element can be sharply reduced by using a high resistance semiconductor substrate, and since the modulation frequency zone of the optical gate switch is above 50GHz, very high speed switching becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a matrix optical switch used in ultra-high speed optical switching systems and the like.

(Prior Art) With the recent development and practical use of optical communication systems, systems that provide new functions and services not available in the past are being considered. An example of a device required in such a system is a matrix optical switch that arbitrarily and quickly switches connections between a large number of optical transmission lines.

A branch gate matrix optical switch consisting of an optical branch circuit, an optical gate switch, and an optical convergence circuit is superior in matrix configuration because it can handle wideband signals, has a broadcast mode function, and can easily expand the matrix scale.

As this type of optical switch, 4X prototyped by Himeno et al.
An example of a four-matrix optical switch is described in 1985 IEICE Proceedings 57-3, p. 1-345. This uses silica-based optical waveguides as optical branching circuits and optical combining circuits, and InGaAsP LD as optical gate switches.
It is constructed using optical gates.

(Problem to be solved by the invention) In the conventional example, since an LD optical gate is used as an optical gate, the switching speed of light is slow, and it is difficult to apply it to a future optical switching system that uses both space division and time division. was there.

The purpose of the present invention is to reduce the element capacitance of a single optical gate switch and achieve ultra-high-speed switching by fabricating an optical gate switch and an optical convergence circuit using an optical branch circuit and the electric field absorption effect of semiconductors on a high-resistance semiconductor substrate. The object of the present invention is to provide a branch gate type matrix optical switch that enables the following.

(Means for Solving the Problem) The matrix optical switch of the present invention transmits an optical signal input from one input optical waveguide onto a high resistance semiconductor substrate m (≧
2) n 1×m optical branching circuits to form a book of optical branches, a semiconductor optical waveguide having a PIN structure in a positional relationship to be optically coupled to each branch destination of the optical branching circuit, and the PI
means for applying an electric field to a semiconductor optical waveguide having an N structure;
m nX1 optical merging circuits in a positional relationship to be optically coupled to the semiconductor optical waveguide having the PIN structure connected to one of the m branch destinations of each of the n optical branching circuits; It is characterized by being prepared.

(Function) The present invention includes n 1×m optical branch circuits, an optical gate switch using the electric field absorption effect of a semiconductor that is optically coupled to each branch destination, and an optical gate switch that uses the electric field absorption effect of a semiconductor that is optically coupled to each branch destination. n of pieces
We are exploring a configuration in which an X1 optical merging circuit is integrated on a high-resistance semiconductor substrate. The basic operation is that after the light that enters from one input terminal is branched into m lights, the light is output to the output port via the nXl light combining circuit only when the optical gate switch in the subsequent stage is in the ON state. Therefore, any switching state of the matrix optical switch is possible depending on the ON/OFF state of the optical gate switch.

The optical gate switch used here has an element length of 200 μm.
It is small in size and has excellent characteristics such as an extinction ratio of 15 dB or more at a voltage of about 3 V. Therefore, a matrix optical switch that operates at a sufficiently low voltage can be obtained. Furthermore, in terms of configuration, even if the number of optical branches is increased, the number of stages of optical gate switches that pass between one input and output does not increase, so it is very easy to expand the number of branches. Furthermore, the speed of an electro-absorption type optical switch is determined by the capacitance of the element, and the use of a high-resistance semiconductor substrate can significantly reduce the parasitic capacitance of the element, making it possible to obtain a bandwidth of 40 GHz or more, as reported by the Institute of Electronics, Information and Communication Engineers in 1990. It is stated in the Spring National Conference Proceedings, page 4-294.

Therefore, the matrix optical switch according to the present invention has a configuration in which an optical branching circuit, an optical gate switch using an electric field absorption effect, and an optical combining circuit are integrated on a high-resistance semiconductor substrate.
The switching speed of an optical gate switch is extremely fast, and it not only switches spatially divided light at high speed, but also spatially switches ultra-high-speed time-divided optical signals. Optical exchange using both space division and time division. Application to systems is also possible.

(Example) FIG. 1 is a perspective view showing an example of the matrix optical switch according to the present invention, and FIG. FIG. Here, a 2×2 case is shown, and Y-branch optical waveguides are used as the optical branching circuit and the optical combining circuit, respectively. We will explain a structure in which an InGaAsP/InP system is used as the material system, and an optical waveguide with a double hetero DH structure in which the waveguide layer wavelength composition is different in the optical branching/combining circuit section and the optical gate switch section. The material, composition, and structure are not limited to these, but include InAlAs, InAlAs, and Ga.
As/AlGaAs-based materials, MQW structures, etc. may also be used.

First, the manufacturing method of the embodiment of the present invention will be briefly explained using FIG. An n+-InP cladding layer 2 with a thickness of 0.5 □m and non-doped 1-InGa is formed on a high-resistance substrate 1.
AsP (band gap wavelength 1.45 μm) light absorption layer 3
with a thickness of 0.3 pm, and p+-InP cladding layer 4 with a thickness of 0.8 pm. Gm, MOVPE method is used to sequentially grow a layered structure that will become an optical gate switch. Next, light branching,
The part where the confluence circuit will be formed is removed by photolithography and etching until the high resistance InP substrate 1 is exposed on the surface, and non-doped 1-I is applied only to the etched part.
The nP cladding layer 5 has a thickness of 0.5.4 m and is made of 1-InGa.
AsP (bandgap wavelength 1.1.um) guide layer 6
0.3 μm, 1-InP land layer 7 0.8 μm
1 is selectively grown using the MOVPE method. As a result, a layered structure as shown in the cross-sectional view taken along line BB' is formed. 1-I of the part where the optical branching circuit and optical combining circuit are formed
nGaAsP guide layer 6 and 1- which becomes an optical gate switch
Good optical coupling is achieved between the InGaAsP light absorption layer 3 and the light absorption surface 3.

Next, a SiO2 mask pattern is formed by a normal photolithography method in order to form an optical branching circuit, a converging circuit, and an optical gate switch. The width of the stripe at this time is 1.
It is 5 μm. Using this SiO2 mask, n-InP
The cladding layer 2 and the 1-InP cladding layer 5 are etched until they are exposed on the surface, first forming an optical waveguide pattern with a high mesa structure, and then using a resist mask, the p-side electrode is etched on one side of the waveguide of the optical gate switch. Further etching the n''-InP cladding layer 2 only in the portion to be formed,
Expose the high resistance InP substrate l. After peeling off the resist mask, the entire structure is buried with a high-resistance InP buried layer 8 using any SiO□ mask as a mask for selective growth. At this point, the optical branching circuits 11a, llb and the optical combining circuits 12a, 12b are completed, and an optical waveguide with a buried structure is formed.

In order to take out the n-side electrode of the optical gate switch, the opposite side of the waveguide from where the p-side electrode will be formed is etched to 100. Drill a hole of about zmX 100μm, and
InP cladding layer 2 is exposed on the surface. As shown in the final cross-sectional view taken along line A-A' in FIG. The p-side electrode 9 of the optical gate switch is formed on the right side of the waveguide, and the n-side electrode 10 is formed on the opposite side of the p-side electrode 9 where the n''-InP cladding layer 2 is exposed. is completed.The substrate is polished to a thickness of approximately 100 μm, the element length of the optical gate switch portion is 200 gm, and the area of the pad portion of the p-side electrode is 80 μm x 80 μm.Each optical gate switch The interval between the two is 250 pm, the branching angle of the Y branch in the optical branching and merging circuit section is 5 degrees, and the element size as a matrix optical switch is as small as 8 mm x 1 mm.

Next, the operation of this matrix optical switch will be explained using FIG. 1.

The wavelength of the incident light is 1.55 pm. Optical branch circuit 11a
.

The optical signals 14a and 14b incident on the optical signal 11b are each divided into two parts and guided to each optical gate switch. Y of optical branch circuit
The branch angle of the branch is very small, 5 degrees, and the wavelength composition of the guide layer 6 in the optical branch circuit section is 1. Since it is ll1m,
There is almost no excess loss or absorption loss at the branch. When the reverse bias voltage of the light absorption layer 3 of the switch is O, the light incident on each optical gate switch is in the ON state, so the light passes through the optical gate switch as it is and is outputted via the optical synthesis circuit. When a reverse bias voltage is applied to the light absorption layer 3, light is absorbed by the electric field absorption effect and the optical gate switch is turned off. At this time, the extinction ratio (ON-O
The FF ratio) is determined by the wavelength used, the wavelength composition of the light absorption layer, and the length of the absorption layer, but in the case of this example, an extinction ratio of 15 dB was obtained at a voltage of 3 V, which is sufficient for an optical gate switch. ing. O of these optical gate switches
N, depending on the OFF state, the incident light 14a, 14b and the outgoing light 15a.

15b can be arbitrarily switched. For example, turn the optical gate switch 13a-OFF, 13b-ON, 1
By setting 3c - ON and 13d - OFF, the incident light 14a is output as the output light 15b, and the incident light 14b is output as the output light 15a.

Next, we will discuss switching speed. As mentioned in the section on operation, the switching speed or modulation band of a switch using a field effect is approximately determined by the capacitance C of the element and is expressed by Af=1/(=rCR). In the present invention, a high-resistance semiconductor substrate is used, and the entire area under the p-side electrode pad is a high-resistance semiconductor layer, so that the parasitic capacitance of the element can be almost ignored, resulting in a structure in which the element capacitance is extremely small. In the case of the example, the capacitance of the entire element is 0.12 pF)
Since the modulation frequency band of the optical gate switch is 50 GHz or more, ultra-high-speed switching is possible. Therefore, since the matrix optical switch according to the present invention has an optical gate switch that operates at ultra-high speed, it can operate at several tens of Gb/s.
It is possible to apply this method to future optical switching systems that use both space division and time division, which require extremely high-speed switching of optical signals.

In this article, we have described a 2×2 matrix optical switch using a Y branch as an optical branching and optical combining circuit, but it is also fully possible to expand to 4×4.8×8 with a similar configuration. In this case, if a Y-branch is used in the optical branching or optical law circuit section, the entire element will become longer; however, if an optical branching or optical convergence circuit that vertically folds the light using a 90-degree mirror or the like is used, these elements can be completed within a few mm. realizable.

(Effects of the Invention) As described in detail above, according to the present invention, by using a 1×m optical branching circuit, an optical waveguide, and an nX1 optical combining circuit, a matrix optical switch capable of ultra-high-speed switching can be obtained. This will greatly contribute to the realization of ultra-high-speed optical switching systems of tens of Gb/s or more in the future.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of a matrix optical switch of the present invention, and FIG. 2 is a partial sectional view thereof. In the figure, 1 is a high-resistance InP substrate, 2 is an n''-InP substrate
cladding layer, 3 is 1-InGaAsP light absorption layer, 4 is p
"-InP cladding layer, 5 is 1-InP cladding layer, 6 is 1-InGaAsP guide layer, 7 is 1-In
P cladding layer, 8 is a high-resistance InP buried layer, 9 is a p-side electrode, 10 is an n-side electrode, lla, Ilb are optical branching circuits, 12a, 12b are optical combining circuits, 13a, 13b,
13c, 13d are optical gate switches, 14a, 1
4b is incident light, and 15a and 15b are outgoing lights.

Claims (1)

[Claims] On a high-resistance semiconductor substrate, there are n 1×m beams that split an optical signal input from one input optical waveguide into m (≧2) beams.
an optical branching circuit, a semiconductor optical waveguide having a PIN structure in a positional relationship to be optically coupled to each branch destination of the optical branching circuit, and means for applying an electric field to the semiconductor optical waveguide having the PIN structure; m n x 1 optical converging circuits in a positional relationship to be optically coupled to the semiconductor optical waveguide having the PIN structure connected to each of the m branch destinations of the n optical branch circuits; A matrix optical switch characterized by comprising: