JP3003688B2 - Multi-channel optical switch and driving method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a waveguide type optical switch which switches an optical path by using an optical waveguide provided on a substrate, and more particularly to an optical switch which is incident on one optical waveguide. The present invention relates to a multi-channel optical switch having a function of switching light to a plurality of optical waveguides and outputting the light or arbitrarily selecting incident light from the plurality of optical waveguides and guiding the light to one optical waveguide. 2. Description of the Related Art The practical use of optical communication systems and optical information processing systems is rapidly progressing, and in these systems, an increase in the amount of information and an increase in system functions are required. [0003] There is an increasing need for an optical switch that enables switching functions of an optical transmission line network, connection and switching between terminals on an optical data bus, and switching between a backup light source and a fiber for improving system reliability. ing. At present, an optical switch using mechanical movement by an electromagnet or the like has been put to practical use, but sufficient characteristics cannot be obtained with respect to high speed, multipoint switching, and reliability. Development of a waveguide-type optical switch that satisfies all of the above conditions and that uses an optical waveguide installed on a substrate as an optical switch with high efficiency, small size, and adaptability to a single-mode fiber system is underway. ing. Particularly, a waveguide type optical switch has a feature that a plurality of optical switch elements can be integrated on one substrate, so that a multi-channel optical switch can be obtained relatively easily. [0004] Optical signals sent from a plurality of terminals are switched in time series and multiplexed on one optical fiber transmission line to be transmitted. Conversely, a plurality of optical signals sent from one fiber are time-division-multiplexed into a plurality of terminals. Or (1 × N) (N
Is an integer of 2 or more) or N × 1 multi-channel switches are required. Since an N × N matrix switch can be formed by arbitrarily combining 1 × N multi-channel optical switches, 1 × N matrix switches must be first used to expand the optical communication and information processing system functions described above. It is important to realize a multi-channel optical switch. Waveguide type optical switches include directional coupling type, total reflection type, branch interference type, balanced bridge type, Y-branch type, etc. Crosstalk which is a particularly important parameter in optical switches is relatively easy. Optical switches of directional coupling type and total reflection type are those which can be made lower, have a simple structure and are easy to be multi-channel. In a directional coupling type optical switch, two optical waveguides having a width of several μm to several tens of μm are brought close to each other at an interval of several μm, and a voltage is applied to a control electrode provided in the vicinity of the optical waveguide by forming an optical directional coupler. By doing so, the degree of coupling between the two optical waveguides is controlled. On the other hand, the total reflection type optical switch crosses two optical waveguides at an angle of several degrees, and a control electrode is provided at the intersection to control the light reflectance at the intersection. In the total reflection type optical switch, in order to obtain low crosstalk, it is necessary to increase the crossing angle. However, in this case, the applied voltage is disadvantageously increased. Since it is usually difficult to obtain a high-voltage high-speed drive circuit, a total reflection type switch is not suitable for high-speed switching. On the other hand, the directional coupling type optical switch operates at low voltage,
Moreover, it is easier to obtain low crosstalk than other optical switches. [0006] A conventional method using a directional coupling type optical switch is described below.
FIG. 4 (plan view) shows a typical example of the configuration of a × N multi-channel optical switch. In FIG. 4, an input optical waveguide 2 and an output optical waveguide 3 are formed on a dielectric substrate such as lithium niobate or a semiconductor substrate 1 such as GaAs by impurity diffusion or crystal growth.
4, 5 and 6 are formed, and three directionally coupled optical switches 10, 11, and 12 are inserted between the input and output optical waveguides to constitute a 1 × 4 multi-channel optical switch as a whole. That is, in the configuration of FIG.
It has a function as a × 2 optical switch, which is connected in two stages to constitute a 1 × 4 optical switch. In such a conventional configuration, by connecting N-1 1 × 2 optical switches, that is, directional coupling type optical switches in multiple stages, a 1 × N multi-channel optical switch is provided. Switches can be configured. Here, in the configuration of FIG. 4, the directional coupling type optical switches 10, 11, and 12 change both the state of the coupling degree of 0 and the state of the coupling degree of 100% to the voltage applied to the control electrodes 20, 21, 22. Must be selectable by Usually, in order to achieve the above object, the control electrodes 20, 21, 22 are divided into two in the light transmission direction as shown in FIG. 4, and each electrode is driven so as to induce electric fields in opposite directions in the substrate. You. FIG. 5 shows the voltage applied to the electrodes and one of the directional coupling type optical switches.
5 is an example showing a relationship between output light levels from two output ports when light is input from one input port. That is, when light enters from the input optical waveguide 2 in FIG. 4, the light level output to the optical waveguide 7 is changed by the curve 30 in FIG.
The light level output to the optical waveguide 8 is shown by a curve 31. In FIG. 5, when the voltage is V1, the coupling amount is 10
When the voltage is 0% V2, the coupling degree becomes zero. Therefore, in the conventional multi-channel optical switch, as described above, V1
, V2, and these voltages usually differ little by little depending on the elements of the optical switch, so that a complicated driving circuit is required. The crosstalk of the directional coupling type optical switch deteriorates due to imperfections of the optical waveguides and electrodes and asymmetry between the two optical waveguides.
In both the% coupling state and the zero coupling state, it is necessary to have a low crosstalk characteristic of -20 dB or less required in a normal system, so that the required manufacturing accuracy is high (asymmetry is ±
0.1 μm or less), and the production yield was a low value (about a fraction). 10 in the conventional configuration and drive system
It is possible in design to obtain either 0% coupling or 0 coupling at 0 volts, but obtaining low crosstalk of -20 dB or less at 0 volts requires very high precision fabrication. In practice it is quite difficult. Further, in order to drive the multi-channel optical switch at high speed, a lower voltage value is required. An object of the present invention is to enable switching between 0 volts and 1 voltage value, to easily obtain low crosstalk, and to operate at a voltage lower than that of a conventional 1 ×.
An object of the present invention is to provide an N-channel optical switch and a driving method thereof. According to the present invention, there are provided n (n is 4)
Optical waveguide of the above (integer) , almost coupled at 0 volt
Not a multichannel optical switch by each optical waveguide via an optical directional coupler equipped with a structure attached to the other optical waveguide for coupling one voltage value, the input optical waveguide 1 th light
I-th when the waveguide (i = 2,3, ..., n ) and wherein the optical waveguide is bonded to through to (i-1) th optical waveguide said optical directional coupler Multi-channel
An optical switch . Further, n (n is an integer of 4 or more) with an optical waveguide of each optical waveguide via <br/> light directional coupler for coupling at one voltage value not substantially bind with 0 volt multichannel optical switch der provided with the structure attached to the other optical waveguide
Therefore, when the input optical waveguide is the first optical waveguide, i
The optical waveguide of the (th) (i = 2, 3,..., N) is the optical direction
A method for driving a multi-channel optical switch coupled to an (i-1) th optical waveguide via a coupler, comprising :
Connected to the output optical waveguide to be output and close to the output port
Of the voltage applied to the control electrode of the optical directional coupler is set to 0, the other
A voltage applied to a control electrode of an optical directional coupler connected to the optical waveguide is set to V (V ≠ 0). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a plan view of a 1 × 4 multi-channel optical switch according to an embodiment of the present invention. One input optical waveguide 32 and four output optical waveguides 33, 34, 35 and 36 are provided on the dielectric or semiconductor device 1, and the input optical waveguide 32 and the four output optical waveguides 33, 34 and 35 are provided. , 36
The light directional couplers 40, 41, 42, and 43 are configured so as to sequentially approach each other in the light transmission direction, and control electrodes 44, 45, 46, and 47 are provided on the light directional couplers, respectively. ing. In this embodiment, a lithium niobate crystal is used as an example of the substrate 1 and the optical waveguides 32 and 3 are used.
3, 34, 35 and 36 were formed by thermally diffusing titanium.
Further, the width of the optical waveguide is several μm to several tens μm, the interval between two optical waveguides constituting the optical directional coupler is about several μm, and the length of the optical directional coupler is several mm to tens of mm. FIG. 2 is a diagram for explaining the operation of the multi-channel optical switch according to the present 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.
When 0 is incident, a curve 48 represents the light level output after being coupled to the optical waveguide 33, and a curve 49 represents the output light level remaining on the optical waveguide 32 without being coupled. In this embodiment, the coupling amount is designed to be 0 when the voltage is V1, and to be 80 to 100% when the voltage is 0. In this embodiment, the voltage of only the control electrode of the optical directional coupler formed between the input and output optical waveguides to be connected is 0, and the voltage V1 'is applied to the other control electrodes. For example, the voltage of the control electrode 46 is set to 0. Assuming that the voltage applied to the other control electrodes is v1 ', the incident light 5 on the input optical waveguide 32
80 to 100% of 0 is coupled to the output optical waveguide 35, and all the remaining light amount passes through the optical waveguide 32 to become outgoing light 51 and is not coupled to other output optical waveguides. Normally, the state where the coupling amount is 0 is not affected by the asymmetry of the optical waveguide, and low crosstalk is easily obtained as compared with the state where the coupling amount is 100%. , 34,
The leakage light to 35 is very small. Similarly, very small crosstalk can be obtained when switching to any of the output optical waveguides. In addition, when the applied voltage is 0, 100%
Is difficult to obtain as described above,
Since a binding amount of about 0 to 97% can be obtained quite easily,
The light amount of the outgoing light 51 that causes a loss in the multi-channel optical switch according to the present embodiment can be reduced to several percent or less. Also, considering a light directional coupler having the same shape, the value of V1 'in this embodiment is much lower than V2 in FIG. FIG. 3 is a plan view of a 1 × 4 multi-channel optical switch according to another embodiment of the present invention. In FIG. 3, reference numeral 1 denotes a dielectric or semiconductor substrate similar to the embodiment of FIG. 1, and an input optical waveguide 52, an output optical waveguide 53,
54, 55, and 56 are provided, and optical directional couplers 60, 61, 62, and 63 are provided so that incident light is sequentially coupled to the input optical waveguide 42 with the output optical waveguides. The control electrode and applied voltage characteristics of the optical directional coupler of this embodiment are the same as those shown in FIGS. 4 and 5, and the coupling amount is 100% at the voltage V1. However, in this embodiment, the voltage of the control electrode of the optical directional coupler at the end of the output optical waveguide to be coupled is 0, and the applied voltage of the other control electrodes is V1. When the voltage is 0, the coupling amount is 0.
It is designed to be ２０20%. In this embodiment as well as in the embodiment of FIG. 1, leakage to the output optical waveguide when output to any one output optical waveguide is very small. Compared with the conventional example shown in FIG. 4, the voltage V2 is unnecessary, so that a low voltage operation is possible. As described above, according to the present invention, switching between 0 volt and 1 voltage is possible, so that the driving circuit is simpler than the conventional one and low crosstalk characteristics can be easily achieved. And a multi-channel optical switch operating at a lower voltage than before can be obtained. Since the multi-channel optical switch of the present invention is reversible, it can be used as an N × 1 optical switch. Further, the substrate material, the optical waveguide, and the shape of the optical switch are not limited to those in the above embodiment. For example, a compound semiconductor such as lithium tantalate or InP can be used, and a rib-shaped optical waveguide, a buried optical waveguide, or the like can be used as an optical waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing an embodiment of a multi-channel optical switch according to the present invention. FIG. 2 is a diagram for explaining a method of driving a multi-channel optical switch. FIG. 3 is a plan view showing another embodiment of the present invention. FIG. 4 is a plan view for explaining a conventional multi-channel optical switch. FIG. 5 is a diagram for explaining a driving method of the multi-channel optical switch. DESCRIPTION OF SYMBOLS 1 Substrate 2 Input optical waveguide 3 Output optical waveguide 4 Output optical waveguide 5 Output optical waveguide 6 Output optical waveguide 32 Input optical waveguide 33 Output optical waveguide 34 Output optical waveguide 35 Output optical waveguide 36 Output optical waveguide 52 Input optical waveguide Waveguide 53 Output optical waveguide 54 Output optical waveguide 55 Output optical waveguide 56 Output optical waveguide

Claims (1)

(57) [Claims] n (n is an integer of 4 or more) with an optical waveguide of 0 Bo
A multichannel optical switch the optical waveguide via an optical directional coupler is provided with a structure that is bonded to another optical waveguide for coupling with one voltage value not substantially bind with belt, input optical wave
When the waveguide is the first optical waveguide, the i-th optical waveguide (i = 2,
A multi-channel optical switch wherein the optical waveguides of 3,..., N) are coupled to the (i−1) th optical waveguide via the optical directional coupler . 2. n (n is an integer of 4 or more) with an optical waveguide of 0 Bo
A multichannel optical switch the optical waveguide via an optical directional coupler is provided with a structure that is bonded to another optical waveguide for coupling with one voltage value not substantially bind with belt, input optical wave
When the waveguide is the first optical waveguide, the i-th optical waveguide (i = 2,
3,..., N) is a method for driving a multi-channel optical switch in which the optical waveguides are coupled to the (i-1) th optical waveguide via the optical directional coupler, wherein the output optical waveguide to be connected is
The voltage applied to the control electrode of the optical directional coupler near the output port is set to 0, and the voltage applied to the control electrode of the optical directional coupler connected to another optical waveguide. To V
A method of driving a multi-channel optical switch, wherein (V ≠ 0).