JP2713598B2 - Light switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical switch that operates at a high speed.

(Prior Art) Conventionally, as this type of optical switch, one having a configuration shown in FIG. 2 is known (literature; M. Ojima et al.,
Optical NOR gate using diode laser sources ", Appl.O
pt., vol. 25. no. 14, pp. 2311-2313, 1986).

In FIG. 2, 1 is a signal light source for emitting a signal light I,
2a, 2b, 2c, and 2d are condensing lenses, 3 is a control light source that emits control light C, 4 is a polarization beam splitter that combines signal light I and control light C, and 5 is a Fabry-Perot etalon. An optical nonlinear medium 53 having a multiple quantum well structure is arranged between the highly reflective films 51 and 52 made of a derivative multilayer film.

FIG. 3 is a diagram showing the characteristics of the light output intensity Pout with respect to the light input intensity Pin of the Fabry-Perot etalon 5 in FIG. 2, wherein the horizontal axis represents the light input intensity Pin and the vertical axis represents the light output intensity Pout. I have.

Next, the operation of the configuration shown in FIG. 2 will be described based on FIG. It is assumed that the initial state of the Fabry-Perot etalon 5 having the high reflection films 51 and 52 is set to a state where the transmittance is low with respect to the wavelength of the input signal light I, that is, a reflection state.

Each of the signal light I emitted from the light source 1 and the control light C emitted from the light source 3 enters the polarization beam splitter 4 via the lenses 2a and 2b, and is combined so that their polarization planes are orthogonal to each other. Is done. The combined light (I + C) is condensed by the lens 2c and input to the Fabry-Perot etalon 5.

At this time, when the intensity of the input light increases (increases the intensity of the control light C), the refractive index of the optical nonlinear medium 53 decreases due to free carriers generated by light absorption, and the input light intensity decreases as shown in FIG. When the intensity reaches the medium level Pc, the Fabry-Perot etalon 5 suddenly transitions from the reflection state to the transmission state. Thereby, the input light passes through the Fabry-Perot etalon 5 and is output through the lens 2d.

On the other hand, when the input light intensity decreases (the intensity of the control light C decreases) from this transmission state, as shown in FIG. 3, the input light intensity becomes Pa in FIG.
Suddenly, the Fabry-Perot etalon 5 transitions from the transmission state to the reflection state at the time when the intensity indicated by. This allows
The input light is reflected and moves backward with respect to the input direction.

As described above, the switching operation of the signal light I based on the control light C is performed by utilizing the function of the Fabry-Perot etalon 5 as a so-called optical bistable element.

As can be seen from the above-described operation, if the control light C is injected into the Fabry-Perot etalon 5 at a light intensity of Pc or more, the light intensity is in a transmission state over Pa or more, and the signal light I is also transmitted. It becomes possible.

In the configuration shown in FIG. 2, the polarization beam splitter 4 is used for multiplexing the signal light I and the control light C in a state where the polarization planes are orthogonal to each other to reduce the insertion loss. To make it wave. Therefore, if an insertion loss of 3 dB is allowed, a similar function can be obtained with a semi-transparent mirror.

(Problems to be Solved by the Invention) However, the conventional optical switch has the following disadvantages.

The signal light reflected by the Fabry-Perot etalon 5 reverses on the same optical path as the input signal light, and adversely affects the signal light source 1.

In order to extract the signal light reflected by the Fabry-Perot etalon 5, an optical circulator or a semi-transparent mirror is required, which increases the number of parts, complicates the configuration, and increases the insertion loss.

The present invention has been made in view of such circumstances,
An object of the present invention is to provide an optical switch which can separate an input port and an output port, does not affect a signal light source, and has a simple configuration and low loss.

(Means for Solving the Problems) In order to achieve the above object, according to claim (1), a change in the refractive index is included in a part of a coupling region of a directional coupler composed of two waveguides that are closely adjacent in parallel. A switching unit that switches between transmission and reflection of light, and a unit that changes a refractive index of the switching unit. The length of the switching unit is set to be sufficiently shorter than the length of the coupling region, and The length of the coupling region of the input waveguide was set to (n + 1/2) times the complete coupling length (however,
n = 0,1,2,3 ...).

Further, in claim (2), the switching unit is formed of a Fabry-Perot etalon or a grating.

(Operation) According to claim (1), the signal light input to one waveguide end propagates through this waveguide and reaches the input side end of the coupling region. As the signal light propagates through one waveguide of the coupling region, a small amount of light is coupled into the other optical waveguide. In this way, the signal light propagates through the coupling region by a distance of (n + 1/2) and reaches the switching unit.

Here, if the switching unit is switched to the reflection state, the signal light is reflected and propagates in the coupling region on the input side in the opposite direction. At the time when the signal light has propagated the distance of (n + 1/2), the signal light is ,
It is 100% coupled to the other waveguide, propagates through the other waveguide, and is output from one end.

On the other hand, when the switching unit is switched to the transmission state, the signal light passes through the switching unit, proceeds further straight through the coupling region, and for example, propagates the distance of (n + 1/2) at the time when the other light is transmitted. 100% coupled to the wave path and output from the other end.

Further, according to claim (2), the switching unit is formed of a Fabry-Perot etalon or a grating, and switching control of transmission and reflection is performed based on input conditions such as control light or electric field, current, heat, and the like.

(Embodiment) FIG. 1 is a view showing a first embodiment of an optical switch according to the present invention. FIG. 1 (a) is a configuration diagram, and FIG.
FIG. 1 (a) is an enlarged cross-sectional view taken along line XX of FIG. 1, and FIG. 1 (c) is an enlarged cross-sectional view taken along line YY of FIG. 1 (a).

In FIG. 1, reference numerals 11, 12, and 13 denote waveguides, and FIG.
And (c), a width of about 5 μm and a thickness of about 0.5 μm
Core consisting of In _0.72 G _0.28 As _0.59 P _0.41 set to m
11a, 12a, 13a, and InP covering these cores 11a, 12a, 13a
Each of the claddings 14 is composed of a cladding 14.

Of these waveguides, two of the waveguides 11 and 12 have cores 11a and 12a formed in parallel and close to each other via a cladding 14 in a part of the light propagation direction, and are used in the optical directional coupler. The connection region 15 is formed. Further, one end of the waveguide 11 has an input port Iin of the signal light I having a wavelength of 1.55 μm, and the other end of the waveguide 11 and both ends of the waveguide 12 have output ports O ₁ , O ₂ , O ₃ of the signal light I. Has been selected.

On the other hand, the waveguide 13 is composed of the waveguides 11, 1 constituting the coupling region 15.
The two cores 11a and 12a are formed so as to be substantially perpendicular to the longitudinal side surfaces at the central portion, and one end thereof is selected as an input port Cin of the control light C having a wavelength of 1.50 μm.

The coupling region 15 has a complete coupling length L set to about 5 mm, and a switching unit 20 is disposed at a substantially central portion thereof as described later. , The input side coupling length l _G1 is set to L / 2. Similarly, the coupling length l _G2 on the right side of the switching unit 20 is set to L / 2.

20 is a switching unit composed of, for example, Fabry-Perot etalon,
Highly reflective films 21, 22 having a reflectivity of 0.82 (extinction ratio of 20 db or more) formed by sputtering a multilayer film of TiO ₂ and SiO ₂
And a well layer 231 having a thickness of 50 A made of In _0.47 Ga _0.53 As and disposed between the high reflection films 21 and 22 as shown in FIG.
An optical nonlinear medium 23a, 23b having a multiple quantum well structure in which about 40 barrier layers 232 each having a thickness of 75 A made of InP are alternately stacked. Note that the optical nonlinear media 23a and 23b
At room temperature, there is an exciton peak formed by electrons and heavy holes at a wavelength of 1.5 μm, and a waveguide 13 for control light injection is formed between them.

The length l _E of the switching unit 20 having such a configuration is set to about 5 μm (the same as the width of the core). In addition, the optical nonlinear medium 23
The optical axis of a is the optical axis of the core 11a of the waveguide 11 and the optical nonlinear medium 23.
The optical axis of b corresponds to the optical axis of the core 12a of the waveguide 12, respectively,
Further, the coupling region 15 is formed such that the outer surface in the length direction of the optical nonlinear medium 23a is joined orthogonally to the end surface of the core 13a of the waveguide 13.
Are arranged substantially at the center in the light propagation direction.

Next, the operation principle of the coupling region 15 will be described.
In the coupling region 15 where the waveguides 11 and 12 are close to each other in parallel, even and odd symmetric modes exist as normal modes orthogonal to each other, and their propagation constants are βe and βo. When light is input from the waveguide 11 at the input end z = 0, this input end z
, Even and odd modes having the same electric field amplitude are excited in phase.
As these modes propagate through the coupling region 15,
A phase difference (βe−βo) z occurs between the two modes, and the phase difference becomes π when the propagation distance is L = π / (βe−βo). At this time, the combined electric field distribution of the even / odd mode is
If the length (coupling length) of the coupling region 15 is L, the light input to the waveguide 11 is transferred to the waveguide 12 without loss. Where L is the complete bond length.

Next, the operation of the configuration shown in FIG. 1 will be described. The initial setting of the Fabry-Perot etalon constituting the switching unit 20 is such that the transmittance of the input signal light I is low with respect to the wavelength of 1.55 μm, and the control light C having the wavelength of 1.50 μm is applied to the optical nonlinear medium.
When injected into 23a and 23b, it is absorbed and the wavelength of signal light 1 is 1.55
It is assumed that the refractive index in μm changes and the state becomes high in transmittance.

The signal light I input from the input port Iin propagates through the input waveguide 111, reaches the incident end z of the coupling region 15, and
Further, the light propagates through the coupling area 15 for a distance of L / 2, and
To enter.

At this time, when the control light C is not injected into the optical nonlinear media 23a and 23b of the switching unit 20 via the waveguide 13, the signal light I is reflected by the switching unit 20 and reciprocates in the coupling region 15. I do. As a result, the signal light I propagates through the coupling region 15 by 2l _G1 = L and is 100% coupled to the output waveguide 121. Signal light I which is coupled to the output waveguide 121, after having propagated through the output waveguide 121, is output from the output port O _1.

On the other hand, when the control light C is injected into the optical nonlinear media 23a and 23b of the switching unit 20 when the input signal light I reaches the switching unit 20, the signal light I passes through the switching unit 20 and is output. Waveguide 11
Propagate 2,122. When the signal light I propagates through the coupling region 15 by L / 2 in this manner, the signal light I propagates by l _G1 + l _G2 = L, whereby the signal light I is 100% coupled to the output waveguide 122. Signal light I which is coupled to the output waveguide 122 after propagating through the output waveguide 122, is output from the output port O _2.

Actually, the propagation distance of the transmitted or reflected signal light I in the coupling region 15 is a maximum, and the length l _E =
Although it deviates from the perfect coupling length L = 5 mm by 5 μm, the first embodiment satisfies the relationship L >> _E, so that it does not actually cause a problem and the above deviation is ignored. it can.

As described above, according to the first embodiment, the input port
The signal light I input from Iin and reflected by the switching unit 20 is
Can be output by different output ports O ₁ and input port Iin without using an optical circulator, etc., no adverse effect on the signal source, yet, which has a simple structure, low loss, yet Because of the waveguide structure, an optical switch with stable operation and high speed operation is realized.

In the first embodiment, the coupling lengths l _G1 and l _G2 on the input side and the output side of the coupling region 15 are set to 1 / the full coupling length L.
Although set to twice, the present invention is not limited to this. By changing the coupling lengths l _G1 and l _G2 so as to satisfy the following conditions, the output waveguide for coupling the signal light I is optional. Can also be selected. That is, if the input side coupling length l _G1 is selected so as to satisfy the relationship l _G1 = (n + ｎ) L (where n = 0, 1, 2, 3,...), The input waveguide 11
The signal light I incident on 1 and reflected by the switching unit 20 can be coupled to the output waveguide 121. On the other hand, switching unit 2
The signal light I that has passed through 0 can be coupled to the output waveguide 112 or 122 according to the coupling length l _G2 . That is, when the input side coupling length l _G1 satisfies the above condition, if the relationship l _G2 = (n + 1/2) L (where n = 0, 1, 2, 3,...) Is satisfied, the output waveguide When the relationship of l _G2 = (n + 3/2) L (where n = 0, 1, 2, 3,...) Is satisfied, the light is coupled to the output waveguide 112.

In the first embodiment, the control light C is injected through the waveguide 13. However, the same effect can be obtained by injecting the control light C in the form of a beam. In addition to controlling the refractive index of the Fabry-Perot etalon, in addition to the light shown here, a method of applying a reverse electric field by providing a pn junction in the etalon, a method of flowing a forward current, or heating and cooling the etalon This is also possible. Also in this case, since the control area is small, high-speed operation is possible.

FIG. 4 is a view showing a second embodiment of the optical switch according to the present invention. FIG. 4 (a) is a configuration diagram, and FIG.
FIG. 2 is an enlarged cross-sectional view taken along a line ZZ in FIG. In FIG. 4B, hatching of the core 11a and the clad 14 is omitted to make the drawing easier to see.

Different points of the the present first embodiment the first embodiment, instead of constituting the switching unit 24 in the Fabry-Perot etalon, the length l _g consisting of optical nonlinear medium and the same medium 50 [mu] m, about the maximum reflectance It is constituted by gratings 24a and 24b of 98%, and the width of the control light waveguide 13 is set to about 50 μm accordingly.

The pitch of the gratings 24a and 24b matches the secondary wavelength of 0.48 μm with a wavelength of 1.55 μm. Therefore, pitch Λ
The thickness t is set to 0.5 μm and the thickness t is set to 0.5 μm. further,
Since the refractive indices of the multiple quantum well structure portions of the gratings 24a and 24b and the cladding 14 are about 3.5 and 3.2, respectively, the reflection coupling coefficient に お け る in the gratings 24a and 24b is about 0.05 μm ⁻¹ or more.

FIG. 5 is a diagram showing the characteristics of the reflectance (R) with respect to the wavelength (λ) of the gratings 24a and 24b. The horizontal axis represents the wavelength λ, and the vertical axis represents the reflectance R. In FIG.
The waveform indicated by A indicates a so-called initial state (reflection state) in which the control light C is not incident, and the waveform indicated by B indicates a state (transmission state) when the control light C is incident.

As can be seen from FIG. 5, the reflection bandwidth Δλ at which the reflectivity is initially zero is 183A. Therefore, when only the signal light I having a wavelength of 1.55 μm is incident on the grating, the gratings 24a and 24b are in a reflection state. Here, when the control light C is incident on the gratings 24a and 24b, the refractive index of the multiple quantum well structure is changed, and the center wavelength λc of the reflectance is changed by △ λ, the gratings 24a and 24b are in the reflection state. To the transparent state.

Thus, also in this second embodiment, like the first embodiment, it is output from the input port Iin signal light I in accordance with the presence or absence of the control light C from the different output ports O ₁ or O ₂ Thus, the same effect as in the first embodiment can be obtained.

In the second embodiment as well, the complete coupling length L of the coupling region 15 is 5 mm, and the relationship with the length of the switching portion 24, that is, the length l _g (= 50 μm) of the gratings 24a and 24b is ,
L >> L _g is satisfied, and the displacement of the grating can be ignored as in the case of the first embodiment.

Also, the refractive index of the gratings 24a and 24b can be controlled by beam light, electric field, current, heat, etc., as in the case of the first embodiment. Also in the case of control using this electric field or the like, since the control area is small,
High-speed operation is possible.

(Effects of the Invention) As described above, according to claim (1) or claim (2), there are the following advantages.

The input port and the output port (plural) of the signal light can be separated.

The signal light reflected by the switching unit does not adversely affect the signal light source.

When extracting the signal light reflected by the switching unit, an optical circulator, a semi-transparent mirror, and the like are not required, and a simple configuration can be realized.

The loss is small in principle.

Since it can be configured as a waveguide type, the control power can be small, and multi-stage connection is possible.

The operation can be stabilized because it can be configured as a waveguide.

Since the control area is a part of the directional coupler and the area is small,
When compared by the same control method, high-speed operation is possible.

[Brief description of the drawings]

FIG. 1A is a configuration diagram showing a first embodiment of an optical switch according to the present invention, FIG. 1B is an enlarged cross-sectional view taken along line XX of FIG. 1A, FIG. 1 (c) is an enlarged cross-sectional view taken along line YY of FIG. 1 (a), FIG. 2 is a configuration diagram of a conventional optical switch, and FIG. FIG. 4 (a) is a configuration diagram showing a second embodiment of the optical switch according to the present invention, and FIG.
FIG. 4B is an enlarged cross-sectional view taken along the line ZZ in FIG. 4A, and FIG. In the figure, 11, 12, 13 ... waveguide, 11a, 12a, 13a ... core, 14
... clad, 15 ... coupling region, 20 ... switching part (Fabry-Perot etalon), 21, 22 ... high reflection film, 23a, 23b ... optical nonlinear medium, 24 ... switching part, 24a, 24b ... Grating.

Continuation of front page (56) References JP-A-64-50016 (JP, A) JP-A-63-234227 (JP, A) JP-A-57-161707 (JP, A) JP-A-63-197130 (JP, A) , A) Applied Optics, Vol. 25 No. 14 p. 2311-p. 2313 (July 15, 1986)

Claims (2)

(57) [Claims] 1. A switching unit for switching transmission / reflection of light by changing a refractive index, in a part of a coupling region of a directional coupler comprising two waveguides arranged in parallel and a refractive index of the switching unit. Means for changing the length of the switching portion is set sufficiently shorter than the length of the coupling region, and the length of the coupling region of the light input side waveguide is set to (n + 1 / 2) An optical switch characterized in that it is set to double (where n = 0, 1, 2, 3 ...). 2. The optical switch according to claim 1, wherein said switching section is made of a Fabry-Perot etalon or a grating.