JP2858744B2 - Multi-channel optical switch and driving method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical switch for switching an optical path by using an optical waveguide provided on a substrate, and more particularly to switching an incident light to one optical waveguide to a plurality of optical waveguides and outputting the same. And a multi-channel optical switch having a function of arbitrarily selecting incident light from a plurality of optical waveguides and guiding the same to one optical waveguide. 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. There is an increasing need for an optical switch that enables a switching function of an optical transmission network, connection and switching between terminals in an optical data bus, and switching between a backup light source and a fiber for improving the reliability of the system. 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, switching between multiple points, reliability, and the like. Satisfies all of the above conditions, with higher efficiency,
Development of a waveguide-type optical switch configured using an optical waveguide installed on a substrate as a small-size optical switch having adaptability to a single-mode fiber system has been advanced. 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. Switching optical signals sent from multiple terminals in time series to 1
Multiplexed transmission over two optical fiber transmission lines,
When distributing a plurality of optical signals transmitted from one fiber to a plurality of terminals in a time division manner, a 1 × N (N is an integer of 2 or more) or N × 1 multi-channel switch is 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. The 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, there is a disadvantage that the applied voltage increases. Since it is usually difficult to obtain a high-speed driving circuit with a high voltage, a total reflection type switch is not suitable for high-speed switching. On the other hand, the directional coupling type optical switch operates at a low voltage, and it is easier to obtain low crosstalk than other optical switches. FIG. 1 (plan view) shows a typical example of the configuration of a 1 × N multi-channel optical switch using a conventional directional coupling type optical switch. In FIG. 1, a dielectric such as lithium niobate or GaAs
An input optical waveguide 2 and output optical waveguides 3, 4, 5, and 6 are formed on a semiconductor substrate 1 such as by diffusion of impurities or crystal growth, and three directional coupling type optical switches are provided between the input and output optical waveguides.
10, 11, and 12 are inserted to form a 1 × 4 multi-channel optical switch as a whole. That is, in the configuration of FIG. 1, one directional coupling type optical switch has a function as a 1 × 2 optical switch, which is connected in two stages to constitute a 1 × 4 optical switch. In such a conventional configuration, a 1 × N multi-channel optical switch can be formed by connecting N−1 1 × 2 optical switches, that is, directional coupling type optical switches in multiple stages. Here, in the configuration of FIG. 1, the directional coupling type optical switches 10, 11, and 12 have a coupling degree of 0 and a coupling degree of 10, respectively.
It is necessary that both of the 0% states can be selected by the voltage applied to the control electrodes 20, 21, 22. Usually, in order to achieve the above object, the control electrodes 20, 21, and 22 are divided into two in the light transmission direction as shown in FIG. 1, and each electrode is driven so as to induce electric fields in directions opposite to each other in the substrate. Is done. FIG. 2 is an example showing the relationship between the voltage applied to the electrodes and the output light levels from two output ports when light enters from one input port of the directional coupling type optical switch. That is, when light enters from the input optical waveguide 2 in FIG. 1, the light level output to the optical waveguide 7 is changed by the curve shown in FIG.
At 30, the light level output to the optical waveguide 8 is indicated by the curve 31. The coupling degree 0 when bond content 100% voltage V ₂ when the voltages V ₁ in Figure 2. Therefore, in the conventional multi-channel optical switch, two voltage values of V ₁ and V ₂ are required as described above, and since these voltages usually differ little by little by the elements of the optical switch, a complicated driving circuit is required. Was needed. The crosstalk of the directional coupling type optical switch is deteriorated due to imperfections of the optical waveguides and electrodes and the asymmetry between the two optical waveguides. It was necessary to have a low crosstalk characteristic of -20 dB or less, which is required by the system of the above, so the required manufacturing accuracy was high (asymmetry was within ± 0.1 μm), and the manufacturing yield was low (a fraction of a few Degree). In the conventional configuration and driving method, it is possible in design to obtain one of the states in which the 100% coupling is in the coupling 0 state at 0 volt.
Obtaining low crosstalk of less than -20 dB in volts is quite difficult in practice, as it requires very high precision fabrication. Further, in order to drive the multi-channel optical switch at high speed, a lower voltage value is required. SUMMARY OF THE INVENTION An object of the present invention is to provide a 1 × N multichannel optical switch capable of switching between 0 volts and 1 voltage, easily obtaining low crosstalk, and operable at a lower voltage than conventional ones. It is to provide a driving method. The multi-channel optical switch of the present invention has n (n = 4,
5,...), And each of the optical waveguides is coupled to another optical waveguide via an optical directional coupler. It is characterized in that (n-1) optical waveguides are coupled to one optical waveguide at mutually different coupling points with the same refractive index and size of the waveguide. The driving method of the multi-channel optical switch according to the present invention includes n (n = 4, 5,...) Optical waveguides, and each optical waveguide is coupled to another optical waveguide via the optical directional engaging device. (N-1) optical waveguides are coupled to one optical waveguide at different coupling points from each other at the same refractive index and the same size. The voltage applied to the control electrode of the optical directional coupler connected to the optical waveguide to be connected is set to 0, and the optical switch connected to the other optical waveguide is controlled. The voltage applied to the electrode is set to V (V ≠ 0). Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 3 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 substrate 1, and the input optical waveguide 32 and the four output optical waveguides 3 are provided.
Light directional couplers 40, 41, 42, and 43 are sequentially arranged in the light transmission direction between 3, 34, 35, and 36 to form control electrodes 44, 45, 46 and 47 are installed respectively. 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 are formed by thermally diffusing titanium. The width of the optical waveguide is several μm to several tens μm, and the width of the optical waveguide is 2 μm.
The distance between the optical waveguides is about several μm, and the length of the optical directional coupler is several mm to several tens of mm. FIG. 4 is a diagram for explaining the operation of the multi-channel optical switch of 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, when the light 50 enters the input optical waveguide 32 in FIG. 3, the light level coupled to the optical waveguide 33 and output is represented by a curve 48, and the output light level remaining in the optical waveguide 32 without being coupled is represented by a curve 49. is there. In the present embodiment, the coupling amount is 0 at the voltage V ₁ ,
It is designed so that the coupling amount is 80 to 100% when the voltage is 0. In this embodiment, only the control electrode of the optical directional coupler formed between the input and output optical waveguides to be connected has a voltage of 0, and the other control electrodes are applied with the voltage V ₁ ′. For example, the control electrode 46
Is 0 and the applied voltage of the other control electrodes is V ₁ ′, 80 to 100% of the incident light 50 to the input optical waveguide 32 is coupled to the output optical waveguide 35 and the remaining light quantity is all in the optical waveguide 32. The output light 51 passes through the optical waveguide 51 and is not coupled to another output optical waveguide. 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, 36, the leakage light 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, 10
Although it is difficult to obtain a coupling amount of 0% as described above, a coupling amount of about 90 to 97% can be obtained quite easily, which results in a loss of the multi-channel optical switch of this embodiment. The light amount of the emitted light 51 can be set to several percent or less. Further, when considering a light directional coupler having the same shape, the value of V ₁ ′ in this embodiment is much lower than V ₂ in FIG. FIG. 5 is a plan view of a 1 × 4 multi-channel optical switch according to another embodiment of the present invention. In FIG. 5, reference numeral 1 denotes a dielectric or semiconductor substrate similar to that of the embodiment shown in FIG. 3, and an input optical waveguide 52 and output optical waveguides 53, 54, 55, 56 are provided on the substrate 1; Optical directional couplers 60, 61, and 6 so that incident light is sequentially coupled to each of the output optical waveguides.
2,63 are installed. The control electrode and the applied voltage characteristics of the optical directional coupler according to the present embodiment is a bond of 100% at voltages V ₁ is the same as the example shown in FIGS. 1 and 2. However the voltage of the control electrode of the optical directional coupler output optical waveguide end to be coupled in the present embodiment is 0, the voltage applied to the other control electrode has a V _1. In addition, the coupling amount when the voltage is 0 is designed to be 0 to 20%. Similarly to the embodiment of FIG. 3, in this embodiment, when the light is output to any one output optical waveguide, the leakage to the other output optical waveguide is very small. Voltage V ₂ as compared with the conventional example of FIG. 1 is capable of low voltage operation because it is unnecessary. As described above, according to the present invention, switching between 0 volts and 1 voltage value is possible, so that the driving circuit is simpler than before, and low crosstalk characteristics can be easily obtained and lower voltage than before. , A multi-channel optical switch that operates on 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, lithium tantalate,
A compound semiconductor such as InP or the like can be used, and a rib-shaped optical waveguide, a buried optical waveguide, or the like can be used as the optical waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS 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 the multi-channel optical switch according to the present invention. FIG. 4 is a diagram for explaining a driving method of the multi-channel optical switch. In the figure, 1 is a substrate, 2, 32, 52 are input optical waveguides, 3, 4, 5, and
6, 33, 34, 35, 36, 53, 54, 55, and 56 are output optical waveguides.

Claims (1)

(57) [Claims] An optical switch comprising n (n = 4, 5,...) optical waveguides, wherein each optical waveguide is coupled to another optical waveguide via an optical directional coupler. The refractive index and dimensions of the optical waveguides constituting the sexual coupler are equal,
A multi-channel optical switch, wherein (n-1) optical waveguides are coupled to one optical waveguide at different coupling points. 2. the optical directional coupler includes n (n = 4, 5,...) optical waveguides, and each optical waveguide is coupled to another optical waveguide via an optical directional coupler. Is an optical switch in which (n-1) optical waveguides are coupled to one optical waveguide at different coupling points and have the same refractive index and dimensions. The applied voltage to the control electrode of the connected optical directional coupler is set to 0,
A method for driving a multi-channel optical switch, wherein a voltage applied to a control electrode of an optical directional coupler connected to another optical waveguide is set to V (V ≠ 0).