JPH0486622A - Optical demultiplexer - Google Patents

Abstract

PURPOSE:To facilitate very high-speed operation by providing an optical branching circuit, a semiconductor optical waveguide which has a PIN structure having the positional relation to be optically coupled to the respective branching points of this optical branching circuit and an impressing means. CONSTITUTION:This optical demultiplexer has the optical branching circuit 11 which branches the light signal entering from one optical waveguide for incidence to n-pieces of light rays, the semiconductor optical waveguide which has the PIN structure having the positional relation to be optically coupled to the respective branching points of this optical branching circuit 11, and the means for impressing an electric field to the semiconductor optical waveguide having the PIN structure. The optical demultiplexer is constituted by integrating the optical branching circuit 11 and optical gate switches 22 to 25 for which an electric field absorbing effect is used on a high-resistance semiconductor substrate. The switching speed of the gate switches 22 to 25 is extremely first in this way and the very-high speed processing of time series light signals is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical demultiplexer used in ultra-high speed optical communication systems, optical switching systems, etc.

[Conventional technology]

With the recent development of optical communication systems and optical switching systems,
It is desired to realize an optical demultiplexer that can process ultra-high-speed optical pulse trains or time-division optical signals at low speed. Such optical demultiplexers are required not only to operate at extremely high speeds but also to operate at low voltages, and to be easily miniaturized and integrated.

As an example of an optical demultiplexer, the 1× prototype produced by Haga et al.
A four-speed optical switch/demultiplexer is described in the IEE Journal of Lightweight Technology, 1985, Volume 3, Page 116. This uses a lithium niobate substrate and integrates three IX2 switches consisting of a Y branch, an asymmetrical X branch, and an optical waveguide that provides phase modulation between them to form an IX4 switch. 4 Gb
/s input optical signal is output from each of the four optical waveguides as an IGb/s optical signal. The total length of the device is as large as approximately 4C)n, and the operating voltage is 6.6 to 13.3V.

[Problem to be solved by the invention]

In the conventional example, the operating principle of the 1×2 switch, which is the basic element, is the change in refractive index due to the electro-optic effect of lithium niobate, which requires a fairly long element length and also requires a relatively high operating voltage. There was a problem.

Therefore, with this element size, it is difficult to expand to 1 x 8.1 x 16, etc., and application in ultra-high speed regions such as 20 Gb/s and 40 Gb/s requires the use of complex structures such as traveling wave electrodes. It is difficult to realize.

The purpose of the present invention is to integrate an optical gate switch and an optical branch circuit using the electric field absorption effect of a semiconductor, thereby facilitating miniaturization and integration, and reducing the voltage. The objective is to provide an optical demultiplexer that reduces the element capacitance of a single optical gate switch and achieves ultrahigh-speed operation by manufacturing the optical gate switch.

[Means to solve the problem]

The optical demultiplexer of the present invention includes, on a high-resistance semiconductor substrate, an optical branching circuit that branches an optical signal input from one input optical waveguide into n beams, and a branching destination of each of the optical branching circuits. It is characterized by comprising a semiconductor optical waveguide having a PIN structure in a positional relationship for optical coupling, and means for applying an electric field to the semiconductor optical waveguide having the PIN structure.

[Effect]

The present invention employs a configuration in which an IXn optical branch circuit and a PIN optical waveguide optically coupled to each branch destination, that is, an optical gate switch using the electric field absorption effect of a semiconductor, are integrated. The basic operation is that light is output only to the output port when the optical gate switch is turned on.
Operation as an optical demultiplexer can be realized by sequentially turning on the optical gate switches in synchronization with the optical pulse train or the bit rate of the optical signal. The optical gate switch used here is small with an element length of 200 μm.
It has excellent characteristics with an extinction ratio of 15 dB or more at a voltage of about 3 V. Therefore, an optical demultiplexer that operates at a sufficiently low voltage can be obtained. Furthermore, due to the structure, even if the number of optical branches is increased, optical gate switches are not connected in series.
It is also easy to expand the number of branches. Furthermore, the overall element length is approximately determined by the length of the optical branch circuit, and by optimizing this, sufficient miniaturization can be achieved. The speed of an electroabsorption type optical switch is determined by the capacitance of the device, and by using a high-resistance semiconductor substrate, the parasitic capacitance of the device can be significantly reduced, and it is possible to achieve speeds up to 40G.
It is stated in the Proceedings of the 1990 Spring National Conference of the Institute of Electronics, Information and Communication Engineers, page 4-294 that a band of Hz or higher can be obtained.

Therefore, since the optical demultiplexer according to the present invention has a structure in which an optical branch circuit and an optical gate switch using an electric field absorption effect are integrated on a high-resistance semiconductor substrate, the switching speed of the gate switch is extremely fast, and the switching speed of the gate switch is extremely high. It becomes possible to process time-series optical signals.

〔Example〕

FIGS. 1(a), (b), and (c) are perspective views showing an embodiment of an optical demultiplexer according to the present invention, and A in the perspective view.
It is a sectional view between -A' and BB'. Here 1×4
In this case, a two-stage Y branch was used as the optical branch circuit. As a material system, InGaAs
A P/I nP system is used, and a double heterostructure (D
The case where an optical waveguide with an H-tube structure is used will be explained, but the composition and structure of the material 1 are not limited to this, and the I
nGaAs/I nA IAs system.

GaAs/AlGaAs materials, as well as multiple quantum wells (
MQW) structure etc. may also be used.

First, a manufacturing method of an embodiment of the present invention will be briefly explained using FIG. n”-InP on high resistance InP substrate 1
The cladding layer 2 has a thickness of 0.5 μm and is made of i-InGaAsP (
The bandgap wavelength is 1.45 μm) and the light absorption layer 3 is set to 0.
3. czm, p”-InP cladding layer 4 with a thickness of 0.8 μm,
The parts that will become optical gate switches are sequentially grown using the MOVPE method. The parts where the zero-order optical branch circuit will be formed are removed by etching until the high-resistance InP substrate 1 is exposed on the surface.
The 1-InP cladding layer 5 is O, '5Bm, 1-InGaAsP (bandgap wavelength 1.1 μm), the guide layer 6 is 0.3 μm, 1-InP only in the etched part.
The cladding layer 7 is selectively grown to a thickness of 0.8 μm by MOVPE. This results in a cross-sectional view between B-B' (Figure 1 (
As shown in C)), the 1-InGaAsP light absorption layer 3
and i-InGaAsP guide layer 6 are optically coupled in the layer direction. In order to form an optical branch circuit and an optical gate switch, a Si*2 mass pattern is formed by a normal photolithography method. The width of the stripe at this time is 1
．． It is 5 μm. Using this SiO□ mask, n”-I
The nP cladding layer 2 and the i''-InP cladding layer 5 are etched until they are exposed on the surface to form an optical waveguide pattern with a high mesa structure, and then a p-side electrode is formed on one side of the waveguide of the optical gate switch using a resist mask. Further etching is performed only on the portion where the resist mask is formed to expose the high resistance InP substrate 1. After peeling off the resist mask, which Si
Using the 02 mask as it is as a mask for selective growth, the entire structure is buried with a high-resistance InP buried layer 8. At this point, the optical branch circuit 11 is 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, a hole of about 100 .mu.m x 100 .mu.m is made by etching on the opposite side of the waveguide where the p-side electrode will be formed, and the n"-InP cladding layer 2 is exposed on the surface. Finally, as shown in the A-A' cross-sectional view, high-resistance InP is directly applied on the waveguide of the optical gate switch and on the high-resistance InP substrate 1.
A p-side electrode 9 is formed on the side where the buried layer 8 is located, and an n-side electrode 10 is formed on the side opposite to the p-type electrode 9 where the n+-InP cladding layer 2 is exposed, thereby completing the device. The substrate was polished to a thickness of approximately 100 μm, the element length of the optical gate switch portion was 200 μm, and the area of the pad portion of the p-side electrode was 80 μm×80 μm. The distance between each optical gate switch is 250 μm, the branching angle of the Y branch in the optical branch circuit is 5 degrees, and the element size as an optical multiplexer is 9
It is as small as dragon Xl+u, which is less than one-fourth of the conventional example.

Next, the operation of the optical demultiplexer of this embodiment will be explained using FIGS. 1, 2, and 3. first first
The basic characteristics will be described using diagrams.

The wavelength of the incident light is 1.55 μm. The light incident on the 11 optical branch circuits passes through two Y-branches, is divided into four parts, and is guided to each optical gate switch. The branching angle of the Y branch is very small, 5 degrees, and the wavelength composition of the guide layer 6 in the optical branching circuit section is 1.1 μm, so there is almost no branching loss or absorption loss here. When the reverse bias voltage of the optical gate switch is O, the optical gate switch is in the ON state, and the light incident on the optical absorption layer 3 of the optical gate switch passes through as it is and is output. is applied, the light is absorbed by the electric field absorption effect and the optical gate switch turns OF.
It becomes F state. The extinction ratio (ON-OFF ratio) at this time 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, the extinction ratio is 15d at a voltage of 3
B was obtained, and sufficient characteristics as an optical gate switch were obtained.

Next, as mentioned in the zero effect section that describes switching speed, the switching speed or modulation band △f of a switch using field effect is approximately determined by the capacitance C of the element, and is expressed as △f=1/(πCR). be done. In the present invention, a high-resistance semiconductor substrate is used, and since the entire area under the pad of the p-side electrode is a high-resistance semiconductor layer, 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 device is 0.12 pF. Therefore, the modulation frequency band of the optical gate switch used in the present invention is 50 GHz or more, and ultra-high speed switching is possible.

Next, the operation of the optical demultiplexer will be explained using FIGS. 2 and 3. Here, a case is shown in which a 40 Gb/s optical pulse train of incident light is divided into four and converted into four 10 Gb/s optical pulse trains.

The incident optical pulse train passes through the optical branching circuit 21 and is divided into four parts, each of which reaches the optical gate switch 22, 23, 24, 25 at the same time. Fig. 3 shows the temporal relationship between the incident optical pulse train and the reverse bias voltages V1 to V4 applied to each optical gate switch, and shows the relationship between the incident light pulse train and the reverse bias voltages V1 to V4 applied to each optical gate switch.
In other words, the time for setting the reverse bias voltage to 0 is set to 25 ps, which is the time equivalent to one bit, and an electrical signal is applied to each optical gate switch with a delay of 2 Sps compared to the previous stage. As a result, as shown in Figure 2, 40 Gb/
Each of the s optical pulse trains is converted into 10 Gb/84 optical outputs and output. As explained earlier, this optical gate switch is capable of ultra-high-speed operation, so it
It is easy to extract an optical signal of approximately b/s.

In addition, this optical demultiplexer can process time-division optical communication signals (10 Gb in this case) depending on how the reverse bias voltage is applied.
/s is divided into four to become 40 Gb/s) and can also be used as an optical exchanger that can spatially distribute 10 Gb/s optical signals.

Here, Y branches are connected in cascade as an optical branch circuit, 1×
Although the optical demultiplexer of IX8. It is clear that expansion to lX16 is also easy. In this case, the optical branching circuit becomes long, but if you use an optical branching circuit that folds the light vertically using a 90 degree mirror, etc.
The element can be realized within a few dragons.

〔Effect of the invention〕

As described in detail above, according to the present invention, an optical demultiplexer capable of ultra-high-speed operation can be obtained, which will greatly contribute to the realization of future ultra-high-speed optical communication systems and optical switching systems.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1(a), (b), and (c) are a perspective view and a sectional view of each part showing an embodiment of the optical demultiplexer of the present invention,
FIGS. 2 and 3 are diagrams for explaining the operation of the optical demultiplexer of the present invention. In the figure, 1... high resistance InP substrate, 2... n
"-InP cladding layer, 3...i-I n G
aA sP light absorption layer, 4...p"-InP cladding layer 25...1-InP cladding layer, 6-.i-I n
GaAsP guide layer, 7...1-InP cladding layer,
8... High resistance InP buried layer, 9... P-side electrode,
10...n-side electrode, 11.21...optical branch circuit, 2
2.23°24.25... Optical gate switch. Figure 1

Claims (1)

[Claims] On a high-resistance semiconductor substrate, there is an optical branching circuit that branches an optical signal input from one input optical waveguide into n beams, and a positional relationship that optically couples each branch destination of the optical branching circuit. An optical demultiplexer comprising: a semiconductor optical waveguide having a certain PIN structure; and means for applying an electric field to the semiconductor optical waveguide having the PIN structure.