JPS58215632A - Multichannel optical switch and its driving method - Google Patents

Abstract

PURPOSE:To perform switching with low crosstalk with 0-1 volt by coupling (n-1) optical waveguides with one optical waveguide mutually different coupling points. CONSTITUTION:One input optical waveguide 32 and four output optical waveguides 33-36 are installed on a dielectric or semiconductor substrate 1 and optical directional couplers 40-43 having mutual close light transmission directions are constituted successively between the optical waveguide 32 and four optical waveguides 33-36; and control electrodes 44-47 are arranged on those optical directional couplers. Then, only the control electrode of an optical directional coupler constituted between inpt and output optical waveguides to be connected mutually is held at 0V, and the other control electrode is applied with a voltage V'. When the amount of coupling is zero, low crosstalk is obtained easily without any influence of the asymmetry of the optical waveguides. Therefore, switching with low crosstalk is carried out between 0 and 1volt.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveguide-type optical switch that switches optical paths using optical waveguides installed on a substrate. The practical application of optical communication systems and optical information processing systems related to multi-channel optical switches that have the function of arbitrarily selecting incident light from multiple optical waveguides and guiding it to one leading waveguide is rapidly progressing. , these systems are required to increase the amount of information and expand system functions.

There is an increasing need for optical switches that enable switching functions in optical transmission networks, connections and switching between terminals in optical data buses, and switching between standby light sources and fibers to improve system reliability.

Currently, optical switches using mechanical movement using electromagnets or the like are in practical use, but they do not have sufficient characteristics in terms of high speed, switching between multiple points, reliability, etc. The development of a waveguide optical switch that satisfies all of the above conditions and is also highly efficient, compact, and adaptable to single-mode fiber systems is underway, consisting of a guiding waveguide installed on a substrate. ing. In particular, a waveguide type optical switch has the advantage that a plurality of optical switch elements can be integrated on one substrate, so a multi-channel optical switch can be obtained relatively easily.

Optical signals sent from multiple terminals can be switched in time series and multiplexed and transmitted over a single optical fiber transmission line, or conversely, multiple optical signals sent from a single fiber can be time-divided and distributed to multiple terminals. IXN (N is an integer greater than or equal to 2)
or NXI multi-channel switches are required. In addition, 1×N multi-channel optical switches can be arbitrarily combined to
Since it is also possible to configure a matrix switch of N, it is important to first realize an IXN multichannel optical switch in order to expand the functions of the optical communication and information processing system described above. Waveguide type optical switches include directional coupling type, total internal reflection type, branching interference type, balanced bridge type, and Y
There are methods such as the branch type, but the directional coupling type and total internal reflection type are relatively easy to reduce crosstalk, which is a particularly important parameter for optical switches, and are easy to configure and can be multi-channeled. A zero-directional coupling type optical switch is an optical switch in which two optical waveguides with a width of several μm to several tens of μm are placed close to each other with an interval of several μm to form an optical directional coupler, which is installed near the optical waveguide. The degree of coupling between the two optical waveguides is controlled by applying a voltage to the control electrode.On the other hand, a total internal reflection optical switch crosses two optical waveguides at an angle of several degrees, and A control electrode is installed at the intersection to control the reflectance of light at the intersection.

In a total internal reflection type optical switch, in order to obtain low crosstalk, it is necessary to increase the above-mentioned crossing angle, but in this case, the applied N
There is a drawback that 1 pressure increases conversely. Generally, it is difficult to obtain a high-voltage, high-speed drive circuit, so total reflection switches are not suitable for high-speed switching. On the other hand, a directional coupling type optical switch operates at a low voltage, and it is easier to obtain low crosstalk than other optical switches.

A typical example of the configuration of a 1×N multi-channel optical switch using a conventional directional coupling type optical switch is shown in FIG. 1 (plan view).

In Figure 1, an electrolyte such as lithium niobate or GaA
An input optical waveguide 2 and an output optical waveguide 3, 4, 5, 6 are formed on a semiconductor substrate 1 such as s by the wave number of impurities, crystal growth, etc., and these three directionally coupled light beams are formed between the leading waveguides. Switches 10, 11 and 12 are inserted and the total is IX4
It constitutes a multi-channel optical switch. That is, the first
In the configuration shown in the figure, one directional coupling type optical switch has a function as an IX2 optical switch, and is connected in two stages to form a 1×4 optical switch.

In such a conventional configuration, by connecting N-1 1.times.2 optical switches, that is, directional coupling type optical switches in multiple stages, it is possible to construct a 1.times.N multilayer optical switch. Here, in the configuration of FIG. 1, the directional coupling type optical switches 10.11 and 12 have control electrodes 20.21, .
It is necessary to be able to select the voltage applied to 22. Usually, to achieve the above purpose, control electrodes 20, 21, 22
As shown in Figure 1, the electrode is divided into 1 and 2 parts in the light transmission direction, and each electrode number is driven to create 8 electric fields in the substrate in opposite directions. This is an example showing the relationship between the voltage applied to the switch and the level of output light from two output ports when light enters from one input port of a directional coupling type optical switch. That is, in FIG. 1, when light enters from the manual optical waveguide 2, the leading waveguide 7
If the light level output to the optical waveguide 8 is between the curves in FIG.
The light level output to is shown by curve 31.

In FIG. 2, when the voltage is 7 times, the coupling amount i ooqA voltage ■ voltage-up coupling degree becomes 0. Therefore, in a conventional multi-channel optical switch, Vn lVs is 2
A complicated driving circuit was required because a large number of voltages were required, and these voltages usually varied slightly depending on the elements of the optical switch.

In addition, crosstalk in a directional coupling type optical switch causes deterioration due to imperfections in the optical waveguides and electrodes and asymmetry between the two optical waveguides, but in the conventional configuration, it is normal in both the tool coupling and 0 coupling states. -20d required in the system of
Since it was necessary to have low crosstalk characteristics of B or less, the required manufacturing precision was high (asymmetry within ±01 μm).
, the production yield was low (about a fraction of a fraction). Even with the conventional configuration and drive method, it is possible in design to obtain either Zoo% coupling or 0 coupling state at 0 volts, but it is extremely expensive to obtain a low crosstalk of -20 dB or less at 0 volts. In reality, it is quite difficult to make one because precision manufacturing is required. In addition, multi-channel optical switches can be installed at high speeds.
In order to drive this, a lower voltage value is required.

The object of the present invention is to provide a 1xllJ multichannel optical switch that can perform switching between 0 volts and 1 voltage value, easily obtain low crosstalk, and can operate at a lower voltage than conventional ones, and a method for driving the same. Our goal is to provide the following.

The multi-channel optical switch of the present invention has one (n-1, 2
, 3, ...), where (n-1) optical waveguides are coupled to one optical waveguide via an optical directional coupler, or The optical waveguide is (n-
1.) The structure is such that the optical waveguides are connected to each other.

Further, the driving method of the present invention is to apply a voltage of 0 volts to the control electrode ζ of the optical directional coupler connected to the leading waveguide to be connected in the multi-channel optical switch, and to In this method, a voltage of V (V+o) volts is applied to the control electrode.

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

FIG. 3 shows a plan view of a 1×4 multi-channel optical switch which is an embodiment of the present invention. pm, body or semiconductor substrate 1
One input optical waveguide 32 and four leading waveguides 33 on top
．． 34, 35, and 36 are installed, and the input optical waveguide 32 and the four output optical waveguides 33, 34, 35, and 36 are sequentially brought close to each other in the light transmission direction to form an optical directional coupler 40.
．． 41, 42, 43 are constructed, and one control electrode 44, 45, 46, 47 is installed on each optical directional coupler. In this embodiment, a lithium niobate crystal is used as an example of the substrate 1, and the optical waveguides 32, 33.
34, 35, and 36 were formed by thermally diffusing titanium. The width of the optical waveguide is several μm to several tens of μm, the distance between the two leading waveguides constituting the optical directional coupler is about several μm, and the length of the optical directional coupler is several μm to several tens of μm. I am panting.

FIG. 4 is a diagram for explaining the operation of the multi-channel optical switch of this embodiment, and shows the relationship between the voltage applied to the control electrode of the optical directional coupler and the output light level. That is, in FIG. 3, when light is input to the input optical waveguide 32, the level of light coupled to the optical waveguide and outputted is a curved line, and the level of outputted light remaining in the leading waveguide 32 without being coupled is a curved line. It is 49.

In this example, when the voltage is v, the amount of coupling is 0,
It is designed so that the amount of coupling is 80 to 100% when the voltage is 0.

In this embodiment, only the control electrode of the optical directional coupler configured between the input and output optical waveguides to be connected has a voltage of 0, and the voltage Vu' is applied to the other control electrodes.

For example, when the voltage of the control electrode 46 is set to 0 and the voltage applied to the other control electrodes is set to V', 80 to 100 beams of light incident on the leading waveguide 32 are coupled to the output optical waveguide A, and the remaining amount of light is All of the light passes through the leading waveguide 32 and becomes the output light 51, which is not coupled to any other leading waveguide 1. Normally, the state where the total amount is 0 is not affected by the asymmetry of the leading wavepath, and the coupling amount Zoo % state ζ Since low crosstalk can be easily obtained compared to this state ζ, in the above example
．． The leakage light to 36 is very small.Similarly to 0, very small crosstalk can be obtained when switching to either leading waveguide. Also, when the applied voltage is O, it is completely 100
As mentioned earlier, it is difficult to obtain a binding amount of %, but
Since a coupler with a ratio of about 90 to 97% can be easily obtained, the amount of output light 51 resulting in a loss in the multi-channel optical switch of this embodiment can be reduced to several Fahrenheit or more. Also, when considering an original directional coupler with the same shape, V% of this example is
The value of ) is much lower than r in FIG.

FIG. 5 is a plan view of a 1×4 multi-channel optical switch which is another embodiment of the present invention. In Figure 5, 1 is the third
It is a dielectric or semiconductor substrate similar to the embodiment shown in the figure, and has a manual optical waveguide 52 and an output optical waveguide fi3.54 on the substrate 1.
55 and 56 are installed, and the input optical waveguide 521 is installed so that the incident light is sequentially coupled to each of the above output optical waveguides (optical directional couplers (!1, 61, fi2, 63 are installed). The control electrode and applied voltage characteristics of the original directional coupler of this example are the same as those shown in Figures 1 and 2, and the coupling amount is 100% at voltage Vu.However, in this example, the coupling amount is 100%. The voltage of the control electrode of the optical directional coupler at the end of the output optical waveguide is 0, and the applied voltage of the other control electrodes is V. When the voltage t is 0, the connection -1 is θ ~ 20 Similar to the embodiment shown in FIG. 3, this embodiment is also designed to have a high output power, and when one output is sent to any one leading waveguide, the leakage to other output optical waveguides is very small.

Compared to the conventional 91i shown in FIG. 1, since the voltage Vt< is not required, low-pressure operation is possible.

As described above, according to the present invention, switching is possible between one voltage value above O volts, so the drive circuit is simpler than the conventional one, and low crosstalk characteristics can be easily obtained. It is possible to obtain a multi-channel optical switch that operates at a lower voltage than the multi-channel optical switch of the present invention.
Since Sochi is reversible, it can also be used as an NXI optical switch. In addition, the substrate monthly rate, optical waveguide, and optical switch shape are limited to those of the above embodiment. : (11
For example, a compound semiconductor such as tantalum lithium or InP can be used, and a rib-shaped leading waveguide or a buried leading waveguide can be used as the optical waveguide.

[Brief explanation of the drawing]

FIG. 1 is a plan view for explaining a conventional multi-channel optical switch, and FIGS. 3 and 5 are plan views showing an embodiment of a multi-channel optical switch according to the present invention. FIGS. 2 and 4 are plan views for explaining a multi-channel optical switch. It is a figure for explaining the driving method of an optical switch. In the figure, l is the substrate, 2.32.52 is the input optical waveguide, 3.4 + 5 I6 e 33.34 + 3
5 + 36 + 53. 54, 55, and 56 are Deba leading waveways. Fang 1 Fig. 2 Fig. 3 Fig. 4 Fig. - Fang S Fig.

Claims (1)

[Claims] i.Equipped with one (n-131...) optical waveguide, each optical waveguide is coupled to one other optical waveguide via an optical directional coupler. An optical switch IC with a structure of
-1) A multi-channel optical switch characterized in that two leading waveguides are coupled together. In an optical switch that includes 21 optical waveguides and has a structure in which each leading waveguide is coupled to another optical waveguide via a directional coupler, the L-th (Lx2, 3, etc.)
, n) are coupled to the (A-t)th optical waveguide. 31 optical waveguides are connected to n1 optical waveguides at different coupling points via each optical directional coupler (01''' 2 + 3 + 4
A multi-channel optical switch to which leading wavepaths of L-2@3
e....... In a multi-channel optical switch in which the leading waveguide n) is coupled to the (↓-1)th optical waveguide via an optical directional coupler, the optical directional coupler connected to the leading waveguide to be connected is Driving a multi-channel optical switch characterized in that the voltage applied to the control electrode is 0, and the voltage applied to the control electrode of an optical directional coupler connected to another leading waveguide is v (Φ0). Method.