JPH0659294A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To provide the waveguide type optical switch which is low in crosstalk, is good in production characteristic in terms of the crosstalk and is excellent in yield. CONSTITUTION:A light absorption part IV is disposed between an optical switching part II and a light output part III. This optical switching part II and light output part III are respectively separated by an electrical sepn. groove 9. The light absorption part IV is constituted by providing an output port C side with a p<+>-InGaAs cap layer 2 on a p-InP clad layer 3. Electrodes 10 are formed on this cap layer 2. Electrodes 11 are similarly formed on the p<+>-InGaAs cap layer 2 on the p-InP clad layer 3 on an output port D side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical switch having excellent crosstalk characteristics and good manufacturability.

[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. 8 is a perspective view of a conventional directional coupler type optical switch using MQW, and FIG. 9 is a sectional view taken along the line AA 'of FIG. In the figure, 1 is a p-side electrode, 2 is p ⁺ -InG
aAs cap layer, 3 is p-InP clad layer, 4 is i
-InP clad layer, 5 is i-MQW layer, 6 is n-In
A P substrate, 7 is an n-side electrode, and 9 is an electrical isolation groove. Here, the MQW layer 5 is an InGaAlAs well 9 nm, I
Heavy hole exciton (H
The absorption peak of easy-hole exciton) can be set to 1.44 μm, and switching operation can be performed at a wavelength of 1.55 μm. In FIG. 8, I is an optical input unit, II is an optical switch unit, and III is an optical output unit. To operate this, an electric field may be applied between the p-side electrode 1 and the n-side electrode 7. That is, in this optical switch, an electric field is directly applied to the waveguide, and the light absorption coefficient is slightly shifted to the long wavelength side due to the electro-optic effect caused by the MQW structure. When the absorption coefficient changes, the refractive index changes due to the Kramers-Kronig relationship, and accordingly, the refractive index of the waveguide is changed to perform switching. The material for forming the i-MQW layer 5 may be a bulk material such as i-InGaAsP having a Franz-Keldysh effect other than the material having QCSE.

The main steps in manufacturing this directional coupler type optical switch are as follows.

As shown in FIG. 10, an i-MQW layer 5, an i-InP clad layer 4, and a p-I layer are formed on an n-InP substrate 6.
The nP clad layer 3 and the p ⁺ -InGaAs cap layer 2 are crystal-grown in this order.

After applying a photoresist 8 on the p ⁺ -InGaAs cap layer 2 by spin coating,
A photoresist 8 is formed at a predetermined position as shown in FIG. 11 by the photolithography technique.

A mesa as shown in FIG. 12 is formed by wet etching or dry etching using the photoresist 8 as a mask.

Similarly, as shown in FIG. 8, the photolithography technique is used to electrically separate the optical switch unit II from the optical input unit I and the optical switch unit II from the optical output unit III. While forming the groove 9, p
After the side electrode 1 and the n-side electrode 7 are formed, the p-side electrode 1 and the cap layer 2 on one side are removed.
The optical switch of is completed.

[0009]

In the conventional directional coupler type optical switch having such a structure, the p-InP layer 3 and the i-type InP layer 3 are formed.
The width W of the p-InP layer at the contact surface with the -InP layer 4 and the gap G during the manufacture are large, and the mesas are not symmetrically removed during etching, and the distance between the centers of the two waveguides is large. S may also vary. Unless the two mesas are cut symmetrically, the two optical waveguides have different equivalent refractive indices.
As can be seen from the example in which two pendulums of different weights cannot exchange energy completely, the transfer of light between two optical waveguides forming a directional coupler is incomplete and leakage light or crosstalk occurs. . Further, variations in the width W of the p-InP layer, the gap G, and the distance S between the waveguides lead to variations in the complete coupling length of the guided light (the length at which the guided light is completely transferred), which results in complete coupling as the guided light. Due to the difference between the length and the manufactured coupling length, the crosstalk of the guided light also occurs in this case. Therefore, a manufacturing accuracy of 0.1 μm or less is usually required for a width W and a gap G of about 2 μm, which is difficult to manufacture and the manufacturing yield is significantly reduced.

Above, 2 inputs, 2 outputs (2 × 2 switch)
The 4 × 4 switch will now be described as the next largest switch. FIG. 13 shows a conventional 4 × 4 dilated-Benefit (Dilated-B).
nes) shows a non-blocking switch configuration. Here, the non-block configuration means a configuration in which light input from any port can be output to any port. Note that one square box in FIG. 13 corresponds to a 2 × 2 switch element as a switch unit.

Next, the influence of the leakage of light in the preceding stage, that is, crosstalk, on the interference rate in the succeeding stage will be briefly considered. For example, if the optical power of P ₁ is input to SW _{1 in} the bar state (pass through without switching), the main power is S
Although the light passes through W1 as shown by the solid line, γP ₁ crosstalk occurs (where γ is the crosstalk rate). This γP ₁ crosstalk enters SW3. SW here
It is assumed that light is made incident on 2 to be in a cross state and light is switched to SW3. If the crosstalk rate of SW3 is also γ, then S
The amount of crosstalk γP ₁ leaking from W1 to the signal sent from SW2 and causing interference is γ ² P ₁ .
That is, γ ² crosstalk occurs in this conventional 4 × 4 switch. By the way, the conventional 2 × 2 switch causes γ crosstalk.

A 4x4 switch requires 16 2x2 switches, or 8x8 or even 16x1.
With 6 switches, it is necessary to fabricate a very large number of 2 × 2 switches. In the case of manufacturing such many 2 × 2 switches, it is difficult to manufacture all 2 × 2 switches with low crosstalk, and not only a great amount of labor is required to manufacture them with high accuracy, but also N There is a drawback that the yield of the × N optical switch is significantly deteriorated. The -10 dB crosstalk means that the power of the leaked light is 10% and the power of the non-leaked light is 90%. Therefore, the insertion loss is 2 × 2 switch 1
With only a 0.45 dB increase per stage, crosstalk will determine the yield of NxN optical switches.

Further, in the N × N switch, -40 dB
Alternatively, there is a drawback in that it is difficult to realize ultra-low crosstalk below that.

Therefore, an object of the present invention is to solve these problems and to provide a waveguide type optical switch having low crosstalk, good manufacturability in terms of crosstalk, and excellent yield.

[0015]

In order to achieve such an object, a waveguide type optical switch of the present invention according to claim 1 comprises at least two or more optical waveguides, and the two optical waveguides. Light that switches the optical path of the guided light by at least one of the function of adjusting the phase of the guided light propagating in the optical path and coupling the guided light propagating through the two optical waveguides, or the function of reflecting the guided light. A waveguide type optical switch including a switch section is characterized in that an absorption section for absorbing crosstalk light generated when the optical path is switched is provided.

According to a second aspect of the present invention, there is provided a waveguide type optical switch comprising at least two optical waveguides and an optical switch section for switching optical paths of guided light propagating through the at least two optical waveguides. It is characterized in that the two optical waveguides are provided with a light absorbing portion that absorbs crosstalk light generated when the optical paths are switched.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the waveguide type optical switch according to the description, the light absorbing portion is
It is characterized in that it is provided in at least a part of at least one of the input optical waveguide to the optical switch section and the output optical waveguide from the optical switch section.

The invention according to claim 4 is the invention according to claims 1 to 3.
In the waveguide type optical switch according to any one of items 1 to 3, the energy band gap of the material forming the light absorbing portion changes when an electric field is applied to the light absorbing portion, and the crosstalk It is characterized by absorbing light.

According to a fifth aspect of the present invention, a plurality of optical switch units each including at least two optical waveguides and an optical switch unit for switching optical paths of guided light propagating through the at least two optical waveguides are provided on the same substrate. In a waveguide type optical switch in which the optical switch units are arranged in a matrix and connected by a plurality of optical waveguides, each of the connecting optical waveguides absorbs crosstalk light generated when the optical paths are switched. It is characterized in that a light absorbing section for

According to a sixth aspect of the present invention, in the waveguide type optical switch according to the fifth aspect, the optical switch unit is integrated in a non-block configuration.

[0021]

According to the present invention, not only can an ultra-low crosstalk characteristic be realized by absorbing the generated crosstalk by, for example, applying an electric field, but also the yield of optical switch manufacturing, which is limited by the crosstalk, can be realized. Can be greatly improved.

[0022]

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

(Embodiment 1) FIG. 1 is a perspective view for explaining a first embodiment of the present invention. Among the constituent elements of the 2 × 2 optical switch shown in FIG. 1, those common to the constituent elements of the conventional 2 × 2 optical switch shown in FIG. 7 are designated by the same reference numerals and the description thereof will be omitted. Or simplify. In FIG. 1, I is an optical input unit, II is an optical switch unit, and II.
I is a light output part, and IV is a light absorption part. The light absorption section IV is disposed between the optical switch section II and the light output section III, and the optical switch section II and the light output section III are separated by the electrical separation groove 9. Explaining the configuration of the light absorbing section IV, p− on the output port C side.
The p ⁺ -InGaAs cap layer 2 is provided on the InP clad layer 3, and the electrode 10 is formed on the cap layer 2. Each of these layers 2 and 3, and the electrode 10 is 1
It constitutes one light absorption part IV. Also, output port D
Similarly, on the side, p ⁺ -In on the p-InP clad layer 3
An electrode 11 is formed on the GaAs cap layer 2, and each of these layers 2 and 3 and the electrode 11 constitutes another light absorbing portion IV.

Next, the operation of the 2 × 2 optical switch having the above configuration will be described. For example, when light is incident from the first light input port A and is emitted from the second light output port D (cross state), leak light, that is, crosstalk occurs at the first light output port C. Therefore, as shown in FIG. 2, by applying an electric field to the electrode 10 on the side of the first optical output port C, Q
Due to CSE, the absorption edge of the MQW layer 5 is shifted to the long wavelength side, and crosstalk light is absorbed. Further, when it is desired to emit light to the first light output port C (bar state), a voltage is applied to the electrode 1. The crosstalk light of the second light output port D generated at this time can be absorbed by applying a voltage to the electrode 11 on the second light output port D side.

Thus, by providing an electrode on the output side port of the 2 × 2 optical switch (or the input port of the next stage optical switch) and applying an electric field, the leaked light can be absorbed and the crosstalk component becomes −∞. It is also possible to significantly improve the manufacturing yield when manufacturing the directional coupler. The length of the light absorbing portion IV is 50 μm to 100 μm.
Since about m is sufficient, it has almost no influence on the insertion loss and frequency characteristics of the optical switch when there is no electric field.

(Embodiment 2) FIG. 3 is a plan view for explaining a second embodiment of the present invention, in which the present invention is applied to the conventional 4 × 4 optical switch shown in FIG. Is. That is, the electrodes 10 and 11 as one component of the light absorbing portion are arranged on the routing waveguide (communication waveguide) between the 2 × 2 optical switches as the switch unit. For example, suppose that the optical power of P ₁ is input to SW _{1 in} the bar state (passing through without switching). The main power passes through SW1 as indicated by the solid line, but γP ₁ crosstalk occurs (where γ is the crosstalk rate).
However, the crosstalk light of γP ₁ is absorbed as shown in FIG. 2 by applying the electrode 11 before entering the SW3. As a result, the crosstalk light to the SW3 can be sufficiently reduced to a negligible level. Therefore, even when a large-scale optical switch is manufactured, not only ultra-low crosstalk characteristics can be realized, but even if the crosstalk characteristics of each 2 × 2 switch are bad, yield deterioration due to crosstalk can be completely eliminated. . In other words, the deterioration of crosstalk is left only as an increase in insertion loss, but as described in the section of the prior art, the increase in insertion loss is not so large even if the crosstalk characteristic is bad to some extent.

(Embodiment 3) FIG. 4 is a perspective view of a third embodiment of the present invention. In the figure, I and III are light input / output units, and I
I is an optical switch section, IV is an absorption section for crosstalk light, and V is a 3 dB coupler section using a directional coupler, which constitutes an optical switch of the Mach-Zehnder interference system type. In the optical switch section II, the two ridges are separated from each other so that the two optical waveguides are not coupled to each other.

The operating principle of this optical switch will be briefly described. The guided light entering from the input section I is equally divided into equal powers at the 3 dB coupler section V on the optical input side. Next, after propagating through the two switch sections, they are multiplexed by the 3 dB coupler section V ₂ on the optical output side and emitted from the optical waveguide of the output section III. At this time, the output ports of the output section III can be made different depending on whether the phases of the lights propagating in the switch section II are in phase with each other or when the phases are opposite to each other due to the application of an electric field, and a switching operation is possible. Becomes
Also in this case, as in the first embodiment of the present invention shown in FIG. 1, crosstalk light can be absorbed by applying a voltage to the electrodes 10 and 11.

Here, 2 × as an optical switch unit
The crosstalk of the two switch elements and the crosstalk of the N × N switch as a whole and the absorption of the crosstalk light are N ×
A more detailed consideration will be given to the effect on the crosstalk of the N switch as a whole.

First, consider the 4 × 4 switch. FIG. 5 is a ratio of the signal power of the 4 × 4 switch and the power of the crosstalk light when the crosstalk light absorptance At in the crosstalk light absorber is used as a parameter and the crosstalk of the 2 × 2 switch element is used as a variable. It is a characteristic view which shows (S / N ratio). In FIG. 5, the solid line indicates the conventional type that does not absorb crosstalk light, and the one-dot chain line and the broken line indicate 5 dB and 1 respectively.
This corresponds to the case where light absorption of 0 dB crosstalk is performed. S of 4x4 switch due to absorption of crosstalk light
It can be seen that the / N characteristic (that is, the crosstalk characteristic) can be improved by 2 × AtdB.

FIG. 6 shows the S / N ratio of the N × N switch. However, the absorption factor At of the crosstalk light is set to zero for simplicity. Here, the solid line is N = 4, the dashed line is N = 16,
The broken line corresponds to N = 64. As can be seen from FIG. 6, when the scale N of the switch increases, the crosstalk of the switch as a whole decreases even though the crosstalk of the elements of the 2 × 2 switch is the same. Even in this case, it is considered that not only 4 × 4 but also the conventional difficulty can be obtained by adding the absorptance At (generally, it is easy to realize the absorptance of about 10 dB to 30 dB) in the crosstalk light absorber. It is also possible to realize a switch of the size of 16 × 16, which was previously used, and a size of 64 × 64, which was considered impossible.

FIG. 7 is a graph showing the calculation results of the crosstalk of 2 × 2 switch elements and the increase in loss as an N × N switch, with the switch scale N as a parameter. As can be seen from FIG. 7, if the crosstalk of the 2 × 2 switch is 10% (−10 dB), the loss increase as a 4 × 4 switch is within 2 dB, and the crosstalk of the 2 × 2 switch is 5% (−13 dB). Then, it can be seen that the loss increase of the 16 × 16 switch can be suppressed within 2 dB.

In the above description, the configuration using the optical directional coupler has been described as the configuration of the 2 × 2 optical switch element, but also in the reflection type (generally X-shaped configuration) switch using the refractive index change. Needless to say, the present invention can be applied, and it is possible to absorb crosstalk light which cannot be completely reflected and leaks, by the light absorbing portion. Although the 2 × 2 optical switch element has been described as an example of the optical switch unit, other types such as the 1 × 2 optical switch element can also be used as the optical switch unit in the present invention.

In addition, as the MQW layer, InGaAlAs /
Although the InAlAs structure is used, other MQW materials and structures, or the effect of the bulk material such as the Franz-Keldish effect may be used. When the MQW material is used, the energy band gap of the optical switch unit is 1.44 μm (Heavy-h) as shown in FIG.
ole exciton wavelength), but the energy band gap of the light absorption part may be set to a long wavelength side of about 1.47 μm, or the absorption part may be non-doped regardless of whether it is an MQW material or a bulk material. If the internal electric field strength is set to be high by reducing the thickness of the layer, the applied voltage necessary for absorbing the crosstalk light can be reduced. Since the key point of the present invention is to eliminate the leakage light in the optical switch operation, that is, the crosstalk light, on the emission side of the optical switch (or in the path to the incident port of the optical switch of the next stage), as described above. What if crosstalk light could be eliminated, such as a mechanism that not only absorbs crosstalk light by applying an electric field but also injects carriers and absorbs them by free carriers, or a mechanism that reflects light by changing the refractive index? It goes without saying that a different structure may be provided.

[0035]

As described above, according to the present invention, since the crosstalk light in the optical switch operation can be absorbed by the light absorbing section, it is possible to realize an ultra-low crosstalk characteristic.
Further, according to the present invention, when the two optical waveguides forming the directional coupler are manufactured, variations in width and gap of the optical waveguides, or crosstalk deterioration due to asymmetry of the two optical waveguides or Since crosstalk degradation in reflective optical switches can be completely eliminated,
The directional coupler can be easily manufactured, and the yield of manufacturing the optical switch can be significantly improved.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a wavelength and a light absorption coefficient for explaining the operating principle of the first embodiment of the present invention.

FIG. 3 is a plan view for explaining a second embodiment of the present invention.

FIG. 4 is a perspective view for explaining a third embodiment of the present invention.

FIG. 5 is a diagram for explaining a third embodiment of the present invention, in which the absorptance At of crosstalk light is used as a parameter,
It is a characteristic view which shows the ratio (S / N ratio) of the signal power of 4x4 switch and the power of crosstalk light when the crosstalk of 2x2 switch element was made into the variable.

FIG. 6 is a diagram for explaining the third embodiment of the present invention, and is a characteristic diagram showing the S / N ratio of the N × N switch when the absorptance At of the crosstalk light is zero. .

FIG. 7 is a diagram for explaining the third embodiment of the present invention, in which the switch scale N is used as a parameter and the relationship between the crosstalk of the 2 × 2 switch elements and the loss increase amount as the N × N switch. It is a graph which shows (calculation result).

FIG. 8 is a perspective view showing a configuration of a conventional directional coupler switch.

9 is a cross-sectional view taken along the line AA ′ in FIG.

FIG. 10 is a cross-sectional view illustrating a manufacturing procedure of a conventional directional coupler type optical switch.

FIG. 11 is a cross-sectional view illustrating a manufacturing procedure of a conventional directional coupler type optical switch.

FIG. 12 is a cross-sectional view illustrating a manufacturing procedure of a conventional directional coupler type optical switch.

FIG. 13 is a plan view showing a configuration of a conventional 4 × 4 optical switch.

[Explanation of symbols]

1 p-type electrode 2 p ⁺ -InGaAs cap layer 3 p-InP clad 4 i-InP clad 5 i-MQW layer 6 n-InP substrate 7 n-side electrode 8 photoresist 9 electrical separation groove 10 provided in the light absorbing part Electrode 11 Electrode provided on the light absorption part I Light input part II Optical switch part III Light output part IV Light absorption part V ₁ Light input side 3 dB coupler part V ₂ Light output side 3 dB coupler part A 1st input port B 2nd input Port C 1st output port D 2nd output port

Claims (6)

[Claims] 1. A function comprising at least two or more optical waveguides, adjusting a phase of guided light propagating through the two optical waveguides, and coupling the guided light propagating through the two optical waveguides, Alternatively, in a waveguide type optical switch including an optical switch unit that switches the optical path of the guided light by at least one of the functions of reflecting the guided light, an absorption unit that absorbs crosstalk light generated when the optical path is switched. A waveguide type optical switch characterized by being provided. 2. A waveguide type optical switch comprising at least two optical waveguides and an optical switch section for switching an optical path of guided light propagating through the at least two optical waveguides, wherein the at least two optical waveguides are provided. A waveguide type optical switch, comprising a light absorbing portion for absorbing crosstalk light generated when the optical path is switched. 3. The waveguide type optical switch according to claim 1, wherein the light absorbing section is an optical waveguide for input to the optical switch section or an optical waveguide for output from the optical switch section. A waveguide type optical switch, which is provided in at least a part of at least one of the above. 4. The waveguide type optical switch according to claim 1, wherein the light absorbing portion is made of a material forming the light absorbing portion when an electric field is applied to the light absorbing portion. A waveguide type optical switch, wherein the energy band gap is changed and the crosstalk light is absorbed. 5. A plurality of optical switch units having at least two optical waveguides and an optical switch unit for switching optical paths of guided light propagating through the at least two optical waveguides are arranged in a matrix on the same substrate. In the waveguide type optical switch in which each of the optical switch units is connected by a plurality of optical waveguides, each of the connecting optical waveguides is provided with a light absorbing portion that absorbs crosstalk light generated at the time of switching the optical paths. A waveguide type optical switch characterized by the above. 6. The waveguide type optical switch according to claim 5, wherein the optical switch unit is integrated in a non-block configuration.