JPH0667221A - Method for controlling semiconductor optical switch - Google Patents

Abstract

PURPOSE:To provide the control method for the semiconductor optical switch which can be improved in not only crosstalk characteristics, but also insertion loss. CONSTITUTION:When light is made to enter through an input port A and to go out through an output port D, a photocurrent due to crosstalk light is detected from the electrode 10 of the crosstalk light absorption part IV on the side of an output port C where the crosstalk light is outputted and an electric field is applied to an electrode 1 or electrode 12 so as to minimize the photocurrent and maximize a photocurrent detected from an electrode 11 on the side where the main power of the light is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical switch control method capable of controlling a small semiconductor optical switch with low loss.

[0002]

2. Description of the Related Art As an optical device applied to optical modulation or a semiconductor waveguide type optical switch, a multiple quantum well (Multiply well) is used.
le Quantum Well: hereinafter abbreviated as MQW). These materials have a large quantum well confinement effect (Quantum Conf
ined Stark Effect: QCSE
Since it has an electro-optical effect due to (abbreviation), it has the characteristics that it can realize various optical devices such as highly efficient and small optical modulators and waveguide type optical switches. Research on these optical devices Is being promoted.

FIG. 4 is a perspective view of a directional coupler 2 × 2 optical switch using an MQW disclosed in Japanese Patent Application No. 4-215277 by Kono et al. As an example of a conventional waveguide type optical switch. . In the following, the principle of the conventional optical switch control method will be described while describing the structure of the optical switch. I is a light input unit, II is a light switch unit, III is a light output unit, and IV is a light absorption unit. 1 is a p-side electrode, 2 is a p ⁺ -InGaAs cap layer, 3 is a p-InP clad layer, 4 is an i-InP clad layer, 5 is an i-MQW layer,
6 is an n-InP substrate, 7 is an n-side electrode, 8 is an n-InP buffer layer, and 9 is an electrical isolation groove. Where i-MQW
As the layer 5, InGaAlAs well 9 nm, InA
Heavy hole excitons (Hea
The absorption peak of vy-hole exciton) is 1.
It can be set to 44 μm, and switching operation can be performed at a wavelength of 1.55 μm. To make it work, p
An electric field may be applied between the side electrode 1 and the n-side electrode 7. That is, when an electric field is directly applied to the waveguide and the absorption coefficient of light changes due to the electro-optic effect caused by the MQW structure, the refractive index changes from the Kramers-Kronig relationship, and the refractive index of the waveguide changes accordingly. This is a structure for switching. Note that the i-MQW layer 5 is an i-MQ having QCSE.
I-I having the Franz-Keldysh effect in addition to the W layer
A bulk material such as nGaAsP may be used.

In the conventional directional coupler type optical switch having such a structure, for example, when light is input from the optical input port A and emitted from the optical output port D (cross state), the optical output is output. Light leakage, that is, crosstalk, occurs at the port C. As shown in FIG. 5, by applying an electric field to the electrode 10 there, the i-MQW layer 5 is formed for QCSE.
It is possible to absorb the crosstalk light by largely shifting the absorption edge of to the long wavelength side. In addition, the light is output from the optical output port C
When it is desired to output (bar state), a voltage is applied to the electrode 1. The crosstalk light of the optical output port D generated at this time can be absorbed by applying a voltage to the electrode 11. In this way, an electrode is provided on the output side port of the 2 × 2 optical switch (or the input port of the next stage optical switch), and crosstalk light can be eliminated by applying an electric field or injecting a current, and the crosstalk component is suppressed to an extremely small level It is also possible to do so, and there is an advantage that the manufacturing yield when manufacturing the directional coupler is significantly improved.

[0005]

By the way, in such a structure, since the crosstalk light is leakage light, the main power propagating through the optical waveguide on the side opposite to the side where the crosstalk light is generated is lost. Will be there. Since the control system of the conventional optical switch simply eliminates the crosstalk light, low crosstalk can be realized, but improvement in insertion loss due to the crosstalk light cannot be expected. When configuring a large-scale switch, the number of stages of optical switches that pass through increases, so that the loss increase due to this crosstalk light also increases as a whole.

As described above, the conventional optical switch control system has a very good crosstalk characteristic, but has a drawback that the insertion loss due to the crosstalk light cannot be improved.

Therefore, an object of the present invention is to solve this problem and to provide a method of controlling a semiconductor optical switch which can improve not only crosstalk characteristics but also insertion loss.

[0008]

In order to achieve such an object, the invention according to claim 1 provides at least two or more optical waveguides and a phase of guided light propagating through the at least two optical waveguides. In the method of controlling a semiconductor optical switch, comprising: an optical switch unit that switches the optical path of the guided light by a function of adjusting the optical path and coupling the guided light propagating through the two optical waveguides. Crosstalk light is detected by photocurrent,
An adjusting voltage is applied to the optical waveguide or its vicinity so as to minimize the photocurrent of the crosstalk light.

According to a second aspect of the present invention, at least two or more optical waveguides and the guided light that propagates through the two optical waveguides are adjusted while adjusting the phases of the guided light that propagates through the at least two optical waveguides. In a method of controlling a semiconductor optical switch, which comprises an optical switch unit that switches the optical path of the guided light by a function of coupling the guided light, a photocurrent of the main power of the guided light is detected, and a photocurrent of the main power of the guided light is detected. The adjusting voltage is applied to the optical waveguide or its vicinity so as to maximize the voltage.

The invention according to claim 3 is characterized in that the invention according to claim 1 and the invention according to claim 2 are carried out at the same time.

According to a fourth aspect of the present invention, at least two or more optical waveguides and the guided light propagating through the two optical waveguides while adjusting the phase of the guided light propagating through the at least two optical waveguides are provided. In the method of controlling a semiconductor optical switch, comprising: an optical switch unit that switches an optical path of the guided light by a function of coupling the optical path, and a crosstalk light absorbing unit that absorbs crosstalk light generated when the optical path is switched. The photocurrent of the crosstalk light is detected by using the electrode of the light absorption portion, and an adjustment voltage is applied to the electrode of the crosstalk light absorption portion so as to minimize the photocurrent of the crosstalk light. Characterize.

According to a fifth aspect of the present invention, at least two or more optical waveguides and the guided light that propagates through the two optical waveguides are adjusted while adjusting the phases of the guided light that propagates through the at least two optical waveguides. In the method of controlling a semiconductor optical switch, comprising: an optical switch unit that switches an optical path of the guided light by a function of coupling the optical path, and a crosstalk light absorbing unit that absorbs crosstalk light generated when the optical path is switched. The photocurrent of the main power of the guided light is detected by using the electrode of the light absorption portion, and an adjustment voltage is applied to the electrode of the crosstalk light absorption portion so as to maximize the photocurrent of the main power of the guided light. It is characterized by applying.

The invention according to claim 6 is characterized in that the invention according to claim 4 and the invention according to claim 5 are carried out at the same time.

[0014]

According to the present invention, since the adjusting voltage is applied to the optical waveguide, the crosstalk light can be reduced and the insertion loss as the optical switch can be reduced.

[0015]

Embodiments of the present invention will be described in detail below with reference to the drawings.

Here, the principle of the control method of the semiconductor optical switch of the present invention will be described by taking the case where the optical switch constitutes a directional coupling type optical switch as an example.

The principle of the present invention will be described with reference to FIG.
When light is input from the input port A and is output from the output port D (cross state), leak light, that is, crosstalk light is generated at the output port C. The generation of crosstalk light at the output port C means that the power at the output port D is reduced by the amount of crosstalk.

FIG. 1 shows the loss of light emitted from the output port D when the crosstalk of the output port C is used as a variable. As can be seen from FIG. 1, for example, crosstalk is −
When it is as low as 20 dB, the increase of insertion loss is 0.04 dB.
If the crosstalk is as high as -7 dB,
The increase in insertion loss is as large as 0.97 dB. One of the factors causing the crosstalk component is the asymmetry of the two optical waveguides that form the directional coupler. If the two optical waveguides are asymmetrical, the equivalent refractive index of the two optical waveguides is different, so that light transfer between the waveguides is not complete. FIG. 1 also shows the equivalent refractive index Δn _WG due to the asymmetry of these two optical waveguides.

As can be seen from FIG. 1, the difference Δn _{WG in} the equivalent refractive index of the guided light propagating through the two optical waveguides is only 2.
A difference of 6 × 10 ^-4 results in a crosstalk of -8 dB and an insertion loss of 0.75 dB. Therefore, in this case, if a voltage is applied to the optical waveguide so as to eliminate Δn _WG , not only the crosstalk light can be canceled but also the insertion loss can be reduced, and the total insertion loss of the large-scale switch can be significantly reduced. Can be lowered to

FIG. 2 shows the refractive index change Δn as a waveguide when a voltage is applied to the optical axis having a ridge width of 1.6 μm and a length of the refractive index modulation section of 1.2 mm. . When a voltage is applied, as seen from FIG. 5, when a voltage is applied, the insertion loss increases due to the shift of the exciton absorption peak. This increase in insertion loss is shown on the right vertical axis.

From the figure, it can be seen that in order to eliminate the above-mentioned difference in refractive index of 2.6 × 10 ^-4, a voltage of only about 1.6 V should be applied, and the insertion loss at this time can be almost ignored. By applying 1.6V, not only the crosstalk characteristics are significantly improved, but also the insertion loss is 2 × 2.
0.75 dB is reduced for each stage of the optical switch, and a large loss reduction can be achieved in the case of a large-scale optical switch.

A method of controlling the optical switch of the present invention will be described using the optical switch of FIG. When light is input from the input port A and emitted from the output port D in FIG. 3, leak light, that is, crosstalk light is generated at the output port C, and thus the output port C side where the crosstalk light is output. The photocurrent caused by the crosstalk light is detected from the electrode 10 of the crosstalk light absorption section IV of the above, and the photocurrent is detected from the electrode 11 on the side where the main power of light is output so as to minimize the photocurrent. An electric field is applied to the electrode 1 or the electrode 12 so that the photocurrent is maximized, and the adjustment voltage is determined.

When a large-scale optical switch is actually manufactured, it is always necessary to inspect the 2 × 2 optical switch constituting the optical propagation characteristic, element characteristic, and driving voltage. In this inspection step, if the characteristics of each 2 × 2 optical switch are measured by the above-mentioned procedure, the large-scale optical switch with low insertion loss can be obtained by using the optical switch control method of the present invention in the actual operation of the system. The operation can be realized. In the case of a large-scale switch, one 2
After determining the adjustment voltage of the × 2 optical switch, a voltage is applied to the crosstalk light absorbing electrode to completely suppress the crosstalk light. Next, the adjustment voltage is determined for the next 2 × 2 optical switch in the same procedure. Further, the procedure of completely suppressing the crosstalk light at this stage and then determining the adjustment voltage at the next stage may be repeated.

In the directional coupler type optical switch of FIG. 3, the state in which light is output to the port to which light is input is called the bar state. In the case of the bar state, however, the optical waveguide to which light is input is 75% of the path is 25 for the optical waveguide on the other side.
% Light propagates. Therefore, when the coupling length is short, by applying a voltage to the optical waveguide on the side opposite to the optical waveguide into which light is input, the propagation loss due to absorption due to the exciton peak shift can be reduced. As a result, a high voltage can be applied, crosstalk can be reduced, and insertion loss can be suppressed low.

The basic concept of the present invention is to detect a photocurrent with an electrode provided behind the optical switch, determine each 2 × 2 optical switch adjustment voltage so that the photocurrent becomes minimum or maximum, and once adjust the adjustment voltage. Once, is determined, the electrode used to detect the photocurrent is then used for crosstalk suppression. Therefore, it goes without saying that it does not depend on the type or shape of the waveguide in the electrode portion for detecting the photocurrent. Furthermore, in the above description, the adjustment voltage was directly applied to the optical waveguide, but it goes without saying that it may be applied in the vicinity of the optical waveguide.
Not only the directional coupler type optical switch, but also various waveguide structures or various MQWs, as well as the effect of the bulk material such as Franz-Keldish, and the current injection type optical switch can be applied.

[0026]

As described above, according to the present invention, since the crosstalk light component can be reduced by applying the adjusting voltage to the constituent elements of the optical switch, the insertion loss of the optical switch is reduced. it can.

[Brief description of drawings]

FIG. 1 is a characteristic diagram for explaining the principle of the present invention.

FIG. 2 is a characteristic diagram for explaining the principle of the present invention.

FIG. 3 is a perspective view for explaining the principle of the present invention.

FIG. 4 is a perspective view of a conventional directional coupler type 2 × 2 optical switch.

FIG. 5 is a characteristic diagram illustrating the operating principle of a conventional optical switch.

FIG. 6 is a plan view showing a configuration of a conventional 4 × 4 switch.

[Explanation of symbols]

1 p-side electrode 2 p ⁺ -InGaAs cap layer 3 p-InP clad layer 4 i-InP clad layer 5 i-MQW layer 5'i-InGaAsP etch stop layer 6 n-InP substrate 7 n-side electrode 8 n-InP buffer Layer 9 Electrical separation groove 10, 11 Electrode provided in absorption part 12 P-side electrode

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Mitsuaki Yanagibashi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. At least two optical waveguides and a function of adjusting the phase of the guided light propagating through the at least two optical waveguides and combining the guided light propagating through the two optical waveguides. A method for controlling a semiconductor optical switch, comprising: an optical switch unit that switches an optical path of guided light, wherein a crosstalk light generated when the optical path is switched is detected by a photocurrent, and a photocurrent of the crosstalk light is minimized. A method for controlling a semiconductor optical switch, characterized in that an adjusting voltage is applied to the optical waveguide or the vicinity thereof. 2. At least two optical waveguides and the function of adjusting the phase of the guided light propagating through the at least two optical waveguides and coupling the guided light propagating through the two optical waveguides. A method for controlling a semiconductor optical switch, comprising: an optical switch unit for switching the optical path of guided light, wherein a photocurrent of the main power of the guided light is detected and adjusted to maximize the photocurrent of the main power of the guided light. A method for controlling a semiconductor optical switch, characterized in that an application voltage is applied to the optical waveguide or the vicinity thereof. 3. A method for controlling a semiconductor optical switch, wherein the method for controlling a semiconductor optical switch according to claim 1 and the method for controlling a semiconductor optical switch according to claim 2 are performed at the same time. 4. The at least two optical waveguides and the function of adjusting the phase of the guided light propagating through the at least two optical waveguides and coupling the guided light propagating through the two optical waveguides. In a method of controlling a semiconductor optical switch including an optical switch unit for switching an optical path of guided light and a crosstalk light absorbing unit for absorbing crosstalk light generated at the time of switching the optical path, an electrode of the crosstalk light absorbing unit is provided. A semiconductor optical switch characterized by using the photocurrent of the crosstalk light to detect the photocurrent of the crosstalk light, and applying an adjusting voltage to the electrode of the crosstalk light absorbing section so as to minimize the photocurrent of the crosstalk light. Control method. 5. The at least two optical waveguides and the function of adjusting the phases of the guided light propagating through the at least two optical waveguides and coupling the guided light propagating through the two optical waveguides. In a method of controlling a semiconductor optical switch including an optical switch unit for switching an optical path of guided light and a crosstalk light absorbing unit for absorbing crosstalk light generated at the time of switching the optical path, an electrode of the crosstalk light absorbing unit is provided. Detecting the photocurrent of the main power of the guided light using, and applying an adjusting voltage to the electrode of the crosstalk light absorbing section so as to maximize the photocurrent of the main power of the guided light. Method for controlling semiconductor optical switch. 6. A method for controlling a semiconductor optical switch, wherein the method for controlling a semiconductor optical switch according to claim 4 and the method for controlling a semiconductor optical switch according to claim 5 are performed at the same time.