JPH04199030A - light switch - Google Patents

Abstract

PURPOSE:To enable the normal switching operation of a light transmission path performed by the existence of applied voltage to a first electrode in the connected region of two light waveguide paths by forming a second electrode around the input part of either one of two light waveguide paths. CONSTITUTION:In the connected region X of two light waveguide paths 2, 3, a second electrode 18 is formed around the input part of either light waveguide path, the light waveguide path 2, for instance. When high frequency voltage is applied to the second electrode 18, a light signal passing this part is changed in phase so as to have equivalent wavelength change. Accordingly, even if light signals of the same wavelength are inputted into two light waveguide paths 2, 3, both light signals do not interfere strongly with each other in the connected region X of the light waveguide paths 2, 3. The switching of a light transmission path performed by the existence of applied voltage to a first electrode 17 can be performed normally.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an optical switch having a structure in which two optical waveguides are coupled, and the purpose of this invention is to accurately operate when light of the same wavelength is input. In the coupling region of the waveguides, an electrode for changing the refractive index is attached to one of the waveguides, and a phase conversion element or a wavelength conversion element is provided on the input side of one of the waveguides. do.

[Industrial application field]

The present invention relates to an optical switch, and more particularly to an optical switch having a structure in which parts of two optical waveguides are coupled.

In recent years, long-distance, large-capacity optical communication systems have rapidly developed, and their usefulness has increased. In the signal processing section of this communication system, a method was used in which an optical signal was first converted into an electrical signal, and then converted back into an optical signal after being electrically processed.

However, in order to take advantage of the broadband nature of light and to reduce the number of components in a signal processing section, there has been a desire to develop a signal processing technology that can process optical signals in their optical state. One of the elements constituting such a new optical signal processing system is an optical switch.

[Conventional technology]

Optical switches have been proposed as devices for switching optical transmission lines in optical communication systems.

For example, as shown in FIG. 5(a), this device has an n-I
An n-InP layer 51 and an n-InGaA layer are formed on the nP substrate 50.
52 sP layers, an n-InP layer 53, and a p-1nP layer 54 are stacked, and the uppermost p-1nP layer 54 and the upper layer of the n-1nP layer 53 below are patterned to form two convex portions. However, the n-InGaAsP layer 52 under the convex portion is configured to serve as an optical waveguide 55,56.

Further, as shown in FIG. 5(b), the two convex portions approach near the center of the optical switch, so that the first optical waveguide 55 and the second optical waveguide 56 are optically coupled. ing. Then, the optical signal inputted from the first optical waveguide 55,
enters the second optical waveguide 56 in the coupling region and is output to its output port P4, and the optical signal L2 input from the second optical waveguide 56 is output from the first optical waveguide 55.
The structure is such that it comes out from 3.

In addition, the ρ-1nP layer 5 of the first optical waveguide 55 in the coupling region
Electrodes 57 and 58 are formed on the upper surface of 4 and the lower surface of the n-1nP substrate 50, and by applying a voltage between these and changing the refractive index of the first optical waveguide 55, the first optical waveguide 55 is It is configured to emit the optical signal L2 input from the waveguide 55 from its output port P, and output the optical signal L2 input from the second optical waveguide 56 from its output port P4.

Therefore, the output ports of the incident optical signals L+ and Lz can be freely switched depending on whether or not a voltage is applied.

By the way, in the optical switch described above, not only the optical waveguide 55 (56) on one side but also the optical waveguides 55.5 on both sides
It can also be used to input light into 6. That is, when there are two optical signals L, L, when no voltage is applied to the electrodes 57 and 58, the optical signals are emitted from the respective diagonal output ports, and when a voltage is applied, the optical signals are emitted from the same output port. The optical signal is made to travel along the optical waveguides 55 and 56 and is output.

In this way, the optical path of two lights can be switched simultaneously by applying a voltage.

[Problem to be Solved by the Invention] However, depending on the configuration of the optical communication system, optical signals of the same wavelength may be connected to the first input port P, the second input port P,
, P, and thereby the optical waveguide 55
．． The interference between the two optical signals L+ and Lz in the coupling region 56 may become strong.

As a result, when no voltage is applied between the electrodes 57 and 58, the optical signal L1 entering the first input port P is transmitted not only to the second output port P4 but also from the first output port P. This results in a problem that the optical switch may malfunction.

The present invention has been made in view of such problems, and an object of the present invention is to provide an optical switch that can operate accurately when light of the same wavelength is input.

[Means for Solving the Problems] The above-mentioned problem is solved by the problem that, as illustrated in FIG. a first electrode 17 for changing the refractive index;
and one of the optical waveguides I11,
This problem is solved by a directional coupler type optical switch characterized in that a second electrode 18 for applying a voltage for phase conversion is formed near the input section on top of the switch.

Alternatively, as illustrated in FIG. 3.4, an electrode 27 for changing the refractive index is provided on one of the optical waveguides 5 in the coupling region X of the first and second optical waveguides 5.6, This is achieved by a directional coupler type optical switch characterized in that a wavelength conversion element 7 is provided on one input side of the optical waveguide 5.

(Function) According to the first aspect of the present invention, the second electrode 18 is formed near the input portion of one of the optical waveguides 2 in the coupling region of the two optical waveguides 2.3.

In this case, if a high frequency voltage is applied to the second electrode for one day,
The optical signal passing through here changes its phase and becomes equivalent to the wavelength (
frequency) will be subject to change.

Therefore, even if optical signals of the same wavelength are input to the two optical waveguides 2.3, the two optical signals will no longer interfere strongly in the coupling region X of the optical waveguides 2.3, and the voltage applied to the first electrode 17 will be reduced. Switching of the optical transmission line based on the presence/absence is performed normally.

Further, according to the second invention, the wavelength conversion element 7 is provided on the input side of one of the two optical waveguides 5.6.
is formed.

As the wavelength conversion element 7, for example, a DBR mirror or a DFB
There is a bistable semiconductor laser that has a mirror. According to this, it is possible to change the wavelength of an optical signal between input and output, and even if light of the same wavelength enters two optical waveguides 5.6, in the coupling region There will be no interference and it will work normally.

[Example] The details of the present invention will be explained below based on the drawings.

(a) Description of the first embodiment of the present invention Fig. 1 is a plan view of an apparatus showing the first embodiment of the present invention. FIG. 2 is a cross-sectional view of the device shown in FIG. 1 taken along line AA, line B-B, and line C-C.

Reference numeral 1 in the figure is an optical switch that switches the optical transmission path.
It has two optical waveguides 2.3, and the optical waveguides 2.3
are arranged close together in the central binding region,
It is configured such that light entering one optical waveguide 2 (3) when no voltage is applied to the optical switch l is output from the output port P0LIT□ (PollTl) of the other optical waveguide 3 (2). There is.

The optical switch 1 described above is mounted on an n-1nP substrate 10.
-InP layer 11, n-InGaAsP layer 12, n-1n
It has a layer structure in which a P layer 13 and a p-1nP layer 14 are formed,
Further, two convex portions 15.16 are formed in the upper layer portion of the upper n-4nP layer 14 together with the p-1nP layer 13 thereon, and these convex portions 15.1
6, the optical waveguide 2.3 is constructed.

In addition, a first p-electrode 17 is formed on the coupling region X approaching the second optical waveguide 3 in the p-1nP layer 13 on the first optical waveguide 2, and the input port Pi-+
A second P electrode 18 is formed on the nearby p-1nP layer 13.

Further, an n-electrode 19 is formed on the lower surface of the n-1nP substrate 10, and this electrode 19 is connected to a ground line.

Next, the operation of the above embodiment will be explained.

In the embodiments described above, the first and second optical waveguides 2.
When inputting optical signals L1 and L2 of the same wavelength to each input port P, , , , P, , 1□ of 3, a high frequency voltage of about 1 to 10 GHz is applied to the second p-type electrode ]8. Then, the refractive index of the first optical waveguide 2 underneath changes,
The phase of the optical signal L1 propagating through the n-InGaAsP layer 12 changes, equivalently undergoing a wavelength (frequency) change.

Then, the wavelength of the first optical signal L2 that has proceeded to the coupling region X of the first optical waveguide 2 is different from the wavelength of the second optical signal L2 that has entered the second optical waveguide 3. In addition, the interference effect between the two lights weakens in the coupling region X.

As a result, the first optical signal is transmitted to the output port P of the second optical waveguide 3. output from ut□, and also the second optical signal L2
is the output power of the first optical waveguide Fa2)P. The light will be output from Ull, and the optical transmission path will be switched normally.

On the other hand, when a DC voltage is applied to the first p-electrode 17 formed in the coupling region X of the first optical waveguide 2, the refractive index of the optical waveguide 2 changes, and the coupling state of light in the coupling region X changes. Because the light signal changes.

is the output port P of the first optical waveguide 2. , 1, and the optical signal L2 exits from the output port PauL2. In this case as well, since the high frequency voltage is applied to the second PT electrode 18, almost no light interference occurs and the light transmission path is switched normally.

Although the second P electrode 18 described above was provided near the input port Pin+ of the first optical waveguide 2, it is also provided near the input port P, fi2 of the second optical waveguide 3, so that the light passing therethrough is The phase may be shifted.

(b) Description of the second embodiment of the present invention In the embodiment described above, an n-electrode 18 is provided on the p-1nP layer 14 in the region near the input port of the first optical waveguide 2, and a high-frequency voltage is applied to the n-electrode 18. The phase of the optical signal is applied to modulate the phase of the optical signal, and the wavelength is changed equivalently. However, it is also possible to change the wavelength of the light by forming a semiconductor wavelength conversion element in the same region. , the details of which will be explained below.

The third part is a plan view showing the second embodiment of the present invention, and FIG. 4 is a sectional view taken along the line D--D in FIG. 3 and a partially enlarged sectional view taken along the line E-E. In addition, the sectional view taken along the line A-A in FIG.
The cross-sectional view taken along line -B is omitted since it has the same structure as that in FIG.

This optical switch 4 has n-rnP as in the first embodiment.
On the substrate 20, a first n-InGaAsP layer 22 with a thickness of 1.3 μml and an n-InP layer 2L, 22nP2O5- on the n-
While laminating the 1nP layer 24, the p-1nP layer 24 and the n-InPnP2O5 layer below it are simultaneously patterned to form two convex portions 25.26.
The n-InGaAsP layer 23 below the optical switch 6 is configured to serve as an optical waveguide 5.6 of the optical switch 4.

Further, the two convex portions 25 and 26 are formed so as to approach each other in the coupling region X near the center of the optical switch 4, as shown in FIG. 5
The light input from is applied to the second optical waveguide 6 in the coupling region
The structure is such that the light P2 that travels and is input from the No. 20 optical waveguide 6 exits from the output port POuLl of the first optical waveguide 5.

Furthermore, p-1 of the first optical waveguide 5 in the coupling region
A first n-electrode 27 is formed on the upper surface of the nP layer 24.
-Nl poles 27 are formed on the lower surface of the 1nP substrate 20, and an optical waveguide is formed under the p-type electrode 27 by applying a voltage between the first n-electrode 27 and the n-electrode 29. 5 has a large refractive index.

By the way, the input ports P, n of the first optical waveguide 5.

The structure of the nearby optical switch 4 is as follows.

That is, the first n-InGaAsP layer 22 and the upper layer 22
--A second n-InGaAsP layer 3 having a composition of 1.55zzm is provided between the TnP layers 23 along the first optical waveguide 5.
0 is formed at a predetermined length from the input end. In addition, at the interface between the first n-rnGaAsP layer 22 and the lower 22--1nP layer 2I near the end of the second n''-InGaAsP layer 30 near the coupling region X, there is a diffraction layer with high wavelength selectivity. A grating 31 is formed along the first optical waveguide 5 to a predetermined length.
The surface of the 4nP layer 21 is formed by interference exposure method.

Further, on the p-InP layer 24, 200--In
A second n-electrode 28 facing the GaAsP layer 30 is formed, and a gap 32 that crosses the first optical waveguide 5 is formed at the p-electrode 2. The second n-InGaAsP layer 30 is configured to serve as a saturable absorber.

As a result, the input port P in of the first optical waveguide 5
A wavelength converting element 7 made of a DBR type bistable semiconductor laser having tandem electrodes is formed at 1, and its oscillation wavelength is formed to be different from the wavelength of the input optical signal.

Note that the wavelength conversion element 7 may be provided on the input side of the second waveguide 6.

Next, the operation of the above-described device will be explained.

First, a DC voltage is applied to the second n-electrode 28 of the wavelength conversion element 7 to flow an injection current slightly smaller than the oscillation threshold current to lower the absorption coefficient of the saturable absorber.

In this state, the first and second optical waveguides 5.6 have the same wavelength λ,
When the optical signal of , is input, in the wavelength conversion element 7,
The optical signal brings the saturable absorber of the second n-4nGaAsP layer 30 into a saturated state, and the wavelength conversion element 7 starts oscillating.

This allows the optical signal to have a different wavelength λ. is output from the wavelength conversion element 7, and its oscillation wavelength is λ. is λ. −λl/
It becomes E. However, λ is the flag wavelength of the diffraction grating 31, and l is the diffraction order.

Therefore, the optical signal of wavelength λ, 7 input to the first optical waveguide 5 is converted to a wavelength of 7° by the wavelength conversion element 7,
This will proceed to the bonding region X.

As a result, as in the first embodiment, even if optical signals of the same wavelength are input to the two waveguides 5.6 of the optical switch 4, the wavelengths are controlled to be different in the coupling region X.
The interference between the two optical signals is weakened, and malfunctions of the optical switch/chip 4 are eliminated.

Note that in the above two embodiments, a single optical switch 1.
Although the case of 4 is shown, it is also possible to apply them to optical switches connected in a matrix.

〔Effect of the invention〕

As described above, according to the first invention, since the second electrode is formed near the input part of one of the optical waveguides in the coupling region of the two optical waveguides, the high-frequency voltage is applied to the second electrode. When applied, the optical signal passing through this path changes its phase and undergoes an equivalent change in wavelength (frequency), so even if optical signals of the same wavelength are input to two optical waveguides, the coupling between the optical waveguides will change. In this region, both optical signals no longer strongly interfere with each other, and the optical transmission path can be normally switched depending on the presence or absence of the voltage applied to the first electrode.

Further, according to the second invention, since the wavelength conversion element is formed on the input side of one of the two optical waveguides, the wavelength of the optical signal can be changed between the input and output.
Even if light of the same wavelength enters two optical waveguides, no interference occurs in the coupling region, allowing normal operation.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a device according to a first embodiment of the present invention, FIG. 2 is a sectional view showing a device according to a first embodiment of the present invention, and FIG. 3 is a plan view showing a device according to a second embodiment of the present invention. 4 is a sectional view showing a second embodiment of the device of the present invention, and FIG. 5 is a sectional view and a plan view showing an example of a conventional device. (Explanation of symbols) 1.4... Optical switch, 2.3.5.6... Waveguide, 7... Wavelength conversion element, 10.20-n-1nP substrate, 11.21-n- InP layer, 12.22- n-4nGaAsP layer, 13.23 ・
= n-InP layer, 14.24 ・= P -1nP layer, 15.16.25.26... Convex portion, 17.18.27.28... P electrode, 19.29...
-n electrode, 30-n--1nGaAsP layer, 31...diffraction grating, 32...gap. Applicant Fujitsu Co., Ltd.

Claims (2)

[Claims] (1) Coupling region of first and second optical waveguides (2, 3) (
A first electrode (17) for changing the refractive index is provided on either one of the optical waveguides (2) in A directional coupler type optical switch characterized in that a second electrode (18) for applying a conversion voltage is formed. (2) Coupling region of the first and second optical waveguides (5, 6) (
In X), an electrode (27) for changing the refractive index is provided on one of the optical waveguides (5), and a wavelength conversion element (7) is provided on the input side of one of the optical waveguides (5). A directional coupler type optical switch characterized by: