JP2000347231A - Optical gate switch device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in the extinction ration caused by stray light or reflection on the end face and to realize both of decrease in the energy for switching operation and low insertion loss by integrating a multimode interference optical coupler having an oversaturation absorption region and an optical branching and coupling mechanism. SOLUTION: In the device, a 1×2 multimode interference optical coupler 1 equipped with one optical input/output port 2 on one end face and two optical input/output ports 3, 4 on the other end face is used. The device is equipped with a tapered optical waveguide 5 to introduce the signal light into the optical input/output port 2 on one end face, with an oversaturation absorption region 15 in the midway of the optical waveguide, with an optical waveguide 6 to introduce the controlling light into one port 3 of the two input/output ports on the other end face, and with a bend waveguide 7 connected to the other port 4 to output the signal light. The bend waveguide 7 has a bent part to transmit the output light in the direction perpendicular to the incident direction of the signal light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical gate switch element particularly suitable for ultra-high-speed optical communication.

[0002]

2. Description of the Related Art In recent years, when constructing an ultra-large-capacity optical communication system, there is an increasing demand for an all-optical optical transmission technology and an optical signal processing technology which are not limited by the response speed of an electronic circuit. One of the main technologies is an all-optical gate switch that switches an optical signal by light. As an attempt to realize an all-optical optical gate switch, the following method has been conventionally known. The method is that a signal light and control light for switching the signal light are incident on a semiconductor optical waveguide including a saturable absorption region from directions facing each other, and absorption saturation by the control light in the saturable absorption region is used. The signal light subjected to the switching control is extracted from the optical waveguide and separated from the control light using a half mirror or an optical circulator, and is extracted. What is achieved is, for example, "I. Ogura et al.,
“Picosecond all-optical gate using a saturable a
bsorber in Mode-locked laser ”, IEEE Photon. Thchn
ol. Lett., vol.10, No.4, pp.603-605, April 1998 "
Has been reported to.

FIG. 2 shows a configuration of an all-optical optical gate switch using a semiconductor optical waveguide structure including a saturable absorption region as the above-mentioned prior art. In this example, the optical waveguide 20 including the saturable absorption region is a saturable absorption region 21.
Having an electrode divided into two electrodes of
It has a GaAs / InGaSP multiple quantum well structure, and antireflection films 23 are provided on both end faces of the device. In the operation of this element, signal light 26 whose switching is controlled enters from the left side of the optical waveguide, passes through the saturable absorption region 21, is further amplified by the gain region 22, and exits from the right end. On the other hand, the control light 27 for controlling the signal light 26 enters from the right side of the optical waveguide, is amplified in the gain region 22 and enters the saturable absorption region 21. In this case, as a mechanism of the switching operation, the control light 27 in the saturable absorption region 21 is used.
Is used. That is, when the relatively strong control light 27 is not incident on the saturable absorption region, the signal light 26
Suffers a large loss when passing through this area, and is hardly output from the right end. On the other hand, control light 2
7 is incident, the saturable absorption region 21 is
7 causes absorption saturation, the light absorption loss in this portion is reduced, and signal light is output.

A switching operation can be performed by the mechanism described above. In this case, the light output from the right side of the optical waveguide passes on the same straight line as the control light 27. A device for separating light waves is required. According to the conventional example, in this case, the optical circulator 2
5 are used to separate these two light waves. The optical circulator 25 performs traffic control in the light passing direction using the magneto-optical effect. In this example, as shown in FIG.
Although two light input / output ports are provided, light can pass only in the direction shown in the figure, so that the switched signal light 28 and control light 27 can be separated.

[0005]

However, according to the conventional example described above, in an all-optical switch using a semiconductor optical waveguide including a saturable absorption region, an optical circulator is required to separate signal light and control light. Expensive optical parts such as the above are required, the configuration is complicated, and there is a problem of lack of mechanical stability. In addition, since the signal light and the output light are optically propagated on the same line, stray light propagating other than the optical waveguide including the saturable absorption region is mixed with the switching-controlled signal light and output. The extinction ratio of the characteristics may be deteriorated, and further, the extinction ratio may be deteriorated by mixing the control light into the signal output light due to light reflection at the end face of the saturable absorption light gate. In addition, a semiconductor optical waveguide including a saturable absorption region needs to have a narrow waveguide structure as much as possible to efficiently confine light waves and reduce the operating energy of switching. The optical coupling when signal light and control light enter the semiconductor waveguide is deteriorated, and it has been difficult to obtain a high coupling ratio.

The present invention has been made in view of the above circumstances, and has been made in consideration of the problems described above.
By integrating and integrally forming a multi-mode interferometer type optical coupler for combining, the disadvantages of the conventional all-optical switch using a combination of the semiconductor waveguide including the saturable absorber described above and a plurality of optical components are eliminated. , The mechanical stability is good by integration, and the extinction ratio deterioration due to stray light and end face reflection is suppressed,
It is another object of the present invention to provide an optical gate switch element capable of achieving both low switching operation energy and low insertion loss.

[0007]

According to a first aspect of the present invention, there is provided an optical gate switch device comprising at least one optical input / output port on one end face and two optical input / output ports on the other end face. A multi-mode interferometer type optical coupler having an optical input / output port and performing multiplexing / demultiplexing of light by a multi-mode interference effect of light waves, and one optical input / output port on one end face of the multi-mode interferometer type optical coupler And a signal waveguide that has a saturable absorption region in the middle thereof and performs switching of the signal light, and the two optical input / output ports at the other end face of the multimode interferometer type optical coupler. An optical waveguide for inputting control light to one of the two optical input / output ports and an optical waveguide for outputting the signal light to the remaining optical input / output ports of the two optical input / output ports are provided.

According to a second aspect of the present invention, there is provided the optical gate switch element according to the first aspect, wherein the optical waveguide for outputting the signal light takes out the output light in a direction perpendicular to the incident direction of the signal light. It is characterized by having a bent portion. The optical gate switching device according to claim 3 is the device according to claim 2, wherein a width of the optical waveguide portion including the saturable absorption region is smaller than a width of an optical waveguide connected thereto, and The optical waveguide is characterized in that the optical waveguide is connected to the saturable absorption region optical waveguide while the width of the optical waveguide changes in a tapered manner with respect to the width of the connected optical waveguide.

According to a fourth aspect of the present invention, there is provided an optical gate switch element according to the first or third aspect, wherein the optical waveguide including the saturable absorption region and the multi-mode interferometer type optical coupler are integrally formed. It is characterized in that it is monolithically integrated on a single semiconductor substrate. An optical gate switch element according to claim 5, wherein an electrode is formed on the multi-mode interference type optical coupler according to the element according to claim 4, and a forward current is caused to flow to inject a carrier to the semiconductor optical amplifier. And amplifies the incident signal light and control light.

In the above-described configuration, by integrating a multi-mode interference type optical coupler having a saturable absorption region and an optical multiplexing / demultiplexing mechanism, deterioration of the extinction ratio due to stray light or end face reflection is suppressed, and the switching operation energy is reduced. Reduction and low insertion loss can both be achieved.

[0011]

FIG. 1 is a diagram showing a structure of an optical gate switch element according to an embodiment of the present invention. The optical gate switch element of the present invention is a semiconductor substrate 16 made of InP or the like.
It can be made monolithically on top. Since the saturable absorption region 15, the tapered optical waveguide portion 5 including the saturable absorption region, and the multi-mode interferometer type optical coupler portion 1 can be realized by the same layer structure, here, n is placed on the n-InP semiconductor substrate. -InP cladding layer (about 1 μm), non-doped I
An nGaAsP active layer (about 0.3 .mu.m), a p-InP upper cladding layer (about 2 .mu.m), and ap @ + -InGaAsP cap layer (about 0.2 .mu.m) are sequentially laminated. A saturable absorption region 15 having a tapered optical waveguide portion 5 as shown in FIG.
1 × 2 optical input / output ports (one optical input / output port 2 is provided on one end face, and two optical input / output ports 3 and 3 are provided on the other end face)
4), and a multimode interferometer type optical coupler 1 having a branching ratio of 50%, and processed into an input / output optical waveguide including a bent waveguide portion 7 for updating. The length of the saturable absorption region 15 was about 200 μm, the width was 1 μm, and the size of the multi-mode interferometer type optical coupler 1 was 10 μm in width and 140 μm in length.
The radius of curvature of the bent waveguide portion 7 is 100 μm,
The width of these optical waveguides except for the tapered portion was 2 μm.

In order to operate as the saturable absorption region 15, it is necessary to form an electrode in this portion and apply a reverse bias voltage. Therefore, a separation electrode is formed in this portion, and a reverse bias voltage can be applied only to this region. Further, since the multi-mode interferometer type optical coupler 1 is also used as a semiconductor optical amplifier, a separation electrode is also formed at this portion, so that a forward current can be injected. Further, an antireflection film 11 is provided on an end face of the optical waveguide on which signal light and control light are incident and on an end face on which output light is emitted.

Hereinafter, the operation of the optical gate switch shown in FIG. 1 will be described in detail. First, the optical switching operation by saturable absorption will be described. The tapered optical waveguide 5 including the saturable absorption region 15 has a non-linear transmission characteristic depending on the incident light intensity. That is, when light having an intensity lower than the saturation intensity of the saturable absorption enters, the light passing through this region suffers a large loss because the saturable absorption region 15 has a large absorption loss. However, when light with an intensity higher than the saturation intensity of saturable absorption is incident, absorption saturation occurs,
The absorption loss in this region is small, and the loss of light passing through this region is small.

Utilizing such a mechanism in the saturable absorption region 15, only the signal light 8 enters and the control light 9
When light is not incident, the signal light 8 is almost absorbed in this region and is not output because absorption saturation is not caused and absorption loss is large. However, when the control light 9 is simultaneously incident in addition to the signal light 8, , The loss in this region is reduced due to absorption saturation, and the signal light 8 is output. With such an operation, the switching operation can be realized by the tapered optical waveguide 5 including the saturable absorption region 15. The saturable absorption region responds to absorption saturation and its recovery in a very short time, so that a picosecond optical switching operation can be realized.

Next, the signal light 8 whose switching is controlled by the tapered optical waveguide 5 including the saturable absorption region 15,
The function of multiplexing / demultiplexing light waves by the multi-mode interferometer type optical coupler 1 for separating the control light 9 will be described. 1x
The two-port multi-mode interferometer type optical coupler 1 can perform light multiplexing / demultiplexing by the multi-mode interference effect of light waves in the inside. For example, in the case of a multimode interferometer type optical coupler 1 having a 1 × 2 port and a branching ratio of 50% as shown in FIG. 1, light (signal light 8) incident from the optical input / output port 2 on the left end face
Are emitted from the two light input / output ports 3 and 4 on the right end face at an intensity of 50% of the incident light intensity. Conversely, when a light wave enters from one of the two light input / output ports 3 and 4 on the right end face, it is coupled to the light input / output port 2 on the left end face at an intensity of 50% of the incident light intensity. Propagate through the optical waveguide. On the other hand, the remaining 50% of the light wave is not coupled to the left optical input / output port 2 and propagates outside the optical waveguide, so that the light is scattered and disappears in the multi-mode interferometer type optical coupler 1.

This allows, with proper design,
Light incident from one of the two light input / output ports 3 (4) on the right end face is not output from the other light input / output port 4 (3) on the right end face. Therefore, the signal light 8 incident from the optical input / output port 2 on the left end face is distributed and output to the two optical input / output ports 3 and 4 on the right emitting face by 50% each. Further, the control light 9 entering from the light input / output port 3 on the right end face is emitted from the light input / output port 2 on the left end face at half the intensity of the incident light, and the light guide light having the saturable absorption region 15 is provided. The other optical input / output port 4 on the right end face which can enter the waveguide 5
The signal light output 10 and the control light 9 can be separated.

Furthermore, since the saturable absorption region 15 and the multi-mode interferometer type optical coupler 1 can be manufactured on the same semiconductor substrate 16, they can be monolithically integrated and can be integrated. No optical parts are required for coupling of light waves between the optical coupler 1 and the multimode interferometer type optical coupler 1. According to the conventional example, since the switching-controlled signal light and control light are arranged on the same straight line, even if optical components such as an optical circulator for separating light waves are used, the saturable absorption region Since the light (stray light) transmitted through the optical waveguide without passing through the optical waveguide is output as output light, the extinction ratio may be degraded due to the stray light. On the other hand, in the structure of the present invention, in order to separate the stray light and the output light, the bent waveguide 7 is provided so that the port of the output light is not on the same straight line of the incident signal light, It is designed to extract output light. Further, unlike the case of the saturable absorption type optical gate shown in the conventional example, in the monolithically integrated device, since the end face of the optical waveguide portion including the saturable absorption region does not exist, the problem of end face reflection can be eliminated.

In the optical switch, the narrower the width of the optical waveguide including the saturable absorption region, the higher the light intensity inside the waveguide with respect to the incident light of the same power, and the greater the absorption saturation. Switching operation is desirable in terms of reducing optical power. However, when the waveguide width is reduced to 1 μm or less, it becomes difficult to input light from the outside, and the waveguide loss increases. Therefore, it is desirable that the width of the optical waveguide including the saturable absorption region be as narrow as possible and 1 μm or less, and the width of the light incident end face be as wide as about 2 μm. Therefore, in the present invention, the width of the waveguide in the saturable absorption region is narrowed to about 1 μm or less by using the tapered optical waveguide 5, and the incident end face is formed into a tapered and smooth shape to be about 2 μm.

Further, the multimode interferometer type optical coupler 1 used in the present invention can be manufactured as a semiconductor optical waveguide structure having the same PIN junction diauto structure as the saturable absorption region. By forming an electrode on 1 and injecting a carrier by flowing a forward current of 100 mA to 200 mA, a function as a semiconductor optical amplifier can be provided and the light propagation loss of the entire waveguide can be compensated.

As described above, the optical waveguide 5 including the saturable absorption region and the multi-mode interferometer type optical coupler 1 for separating / combining light waves are integrally formed, so that the light to the saturable absorption region is formed. An optical gate switch that solves the coupling problem or does not require an optical circulator can be realized.

[0021]

As described above, the optical gate switch according to the present invention has one optical input / output port on one end face and two optical input / output ports on the opposite end face. A multimode interferometer-type optical coupler having two ports is used, and an optical waveguide for inputting signal light and an optical waveguide for the signal input / output port at one end face of the multimode interferometer-type optical coupler. An optical waveguide for providing control light to one of the two input / output ports on the opposite end face of the multimode interferometer type optical coupler having a saturable absorption region on the way. An optical waveguide for outputting a signal light is provided on the other optical input / output port of the optical waveguide, and the optical waveguide for outputting the signal light further outputs the signal light. Perpendicular to the direction of light incidence It is also intended to be characterized comprises a curved portion for exiting. By integrating such a multimode interference type optical coupler having a saturable absorption region and an optical multiplexing / demultiplexing mechanism, it is possible to suppress the extinction ratio deterioration due to stray light and end face reflection, and to reduce the switching operation energy and reduce the insertion loss. Can be compatible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an embodiment of an optical gate switch according to the present invention.

FIG. 2 is a diagram showing a structure of an optical gate switch exemplified as a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1x2 multimode interferometer type optical coupler (part) 2, 3, 4 ... Optical input / output port 5 ... Tapered optical waveguide (part) 6 ... Optical waveguide (part) through which control light propagates 7 ... Bend guide Wave path (part) 8 ... Signal light 9 ... Control light 10 ... Signal light output 11 ... Anti-reflection film 15 ... Saturable absorption region 16 ... Semiconductor substrate

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroyuki Yokoyama 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation F-term (reference) 2H047 KA04 KA12 RA08 TA05 TA31 2K002 AA02 AB04 BA01 BA02 CA13 DA06 DA11 EA15 HA06 HA30

Claims (5)

[Claims] At least one optical input / output port is provided on one end face, and two optical input / output ports are provided on the other end face,
A multi-mode interferometer-type optical coupler for multiplexing / demultiplexing light by a multi-mode interference effect of light waves, and a signal light is input to one optical input / output port at one end face of the multi-mode interferometer-type optical coupler. A control light to one of two optical input / output ports on the other end face of the multimode interferometer type optical coupler, the optical waveguide having a saturable absorption region in the middle thereof and performing switching of the signal light. An optical gate switch element comprising: an optical waveguide to be incident; and an optical waveguide that outputs the signal light to the remaining optical input / output ports of the two optical input / output ports. 2. The optical gate switch according to claim 1, wherein the optical waveguide for outputting the signal light has a bent portion for extracting the output light in a direction perpendicular to the incident direction of the signal light. element. 3. The optical waveguide portion having the saturable absorption region has a width smaller than a width of an optical waveguide connected thereto.
3. The optical waveguide according to claim 2, wherein said optical waveguide is connected to said saturable absorption region optical waveguide while changing the width of said optical waveguide in a tapered manner with respect to the width of said optical waveguide.
3. The optical gate switch element according to claim 1. 4. An optical waveguide including the saturable absorption region,
4. The optical gate switch device according to claim 1, wherein the multi-mode interferometer type optical coupler is integrally formed and monolithically integrated on a single semiconductor substrate. 5. An electrode is formed on the multi-mode interference type optical coupler, and a forward current is applied to inject carriers to provide a function as a semiconductor optical amplifier, and amplify incident signal light and control light. The optical gate switch element according to claim 4, wherein