Latch-type optical switch

Abstract

The purpose of the present invention is to provide a latching type optical switch to which energy is required to be supplied to an optical waveguide only at the time of switching of the switch, and which has a high degree of flexibility in the control of switching of the switch and the selection of material. For this purpose, in the present disclosure, this latching type optical switch is configured to comprise: a waveguide substrate 1 having an input optical waveguide 13 to which an optical signal Pi is inputted, a plurality of branch waveguides 14a, 14b which are connected to the input waveguide 13, and an output waveguide Pout which collects and outputs light P1, P2 outputted from the plurality of branch waveguides 14a, 14b; and a heating unit 11 which heats a branch waveguide 14b that is one of the plurality of branch waveguides 14a, 14b. The latching type optical switch is configured such that the refractive index of at least part of a region to be heated 12 that is a region of the branch waveguide 14b heated by the heating unit 11 changes to a first refractive index upon receiving light irradiation, and changes from the first refractive index to a second refractive index by heating by the heating unit 11.

Description

Technical Field

[0001] The present disclosure relates to a latch-type optical switch.

Background Art

[0002] In recent years, with the increase in the capacity of optical communication represented by 5G (the fifth-generation mobile communication system), the construction of a network with low latency, high reliability, and simultaneous connection of a large number of devices has been progressing. In the future, it is expected that communication traffic will continue to increase further due to the spread of ultra-high-definition video, IoT (Internet of Things), big data, artificial intelligence (AI) technology, etc. In order to cope with such a situation where the communication capacity increases, it is required to realize a further increase in the capacity of the backbone optical communication network. In order to meet such requirements, research and development of dense wavelength division multiplexing (DWDM) devices and phase-sensitive amplification have been progressing. Here, the dense wavelength division multiplexing device enables further high-speed transmission in the multiplexing of optical wavelengths in optical communication. Also, phase-sensitive amplification enables amplification with a principle that the signal-to-noise ratio does not decrease by utilizing the non-linear optical effect.

[0003] In addition, with the development of optical communication, the backbone optical communication network has come to have very complex branches, and since the number of switching of the transmission path in the optical communication device has increased significantly, a large number of optical switches are required. The switching method of the optical switch includes a method of switching the optical path by electrically or optically changing the refractive index of the optical path, and a method of mechanically switching the optical path (fiber). As such an optical switch, for example, those described in Patent Document 1 and Patent Document 2 are known.

[0004] Patent Document 1 describes an optical switch that automatically moves an optical fiber to the home position in the event of an abnormality where no input signal is input. The optical switch of Patent Document 1 includes an optical fiber with a movable block connected to its tip, a permanent magnet, and a coil. By changing the state of the magnetic flux of the permanent magnet by flowing or not flowing a current through the coil, the movable block is configured to be held in the home position or the make position. Further, the optical switch described in Patent Document 2 includes two light sources that emit short-wavelength control light and long-wavelength control light. By irradiating the short-wavelength control light or the long-wavelength control light to change the refractive index of the photochromic material, the output of the signal light input from the input signal optical waveguide is switched between the first output signal optical waveguide and the second output signal optical waveguide.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] Incidentally, in a communication network for long-distance communication between cities using a large number of optical switches, from the viewpoint of energy conservation, it is preferable to use a latch-type optical switch that consumes power only when the switch is switched. However, when the above optical switch holds the movable block in the make position, that is, while a normal electrical signal is obtained, a current that controls the magnetic flux of the permanent magnet flows. For this reason, the optical switch described in Patent Document 1 is a non-latch-type optical switch that consumes power even during operation. Further, since the optical switch described in Patent Document 2 switches between two isomerized states of a photochromic material, it is necessary to control the refractive indices n1 and n2 of the photochromic material with high precision, that is, to control the irradiation states of short-wavelength control light and long-wavelength control light with high precision. Patent Document 2 describes that there is a condition of na < n2 < nb < n1 among the refractive index na of the input signal optical waveguide, the refractive index nb of the second output optical waveguide, and the refractive indices n1 and n2 of the photochromic material. For this reason, the optical switch of Patent Document 2 has a relatively low degree of freedom in the selection of optical waveguides and light sources, and high precision is required for the control of the control light irradiation state.

[0007] The present disclosure has been made in view of the above points, and relates to a latch-type optical switch that only needs to supply energy to the optical waveguide only when the switch is switched, and moreover has a high degree of freedom in the control of switch switching and the selection of materials.

[0008] In order to achieve the above object, a latch-type optical switch according to one embodiment of the present invention includes an input waveguide to which an optical signal is input, a first branch waveguide and a second branch waveguide connected to the input waveguide, a confluence section that aggregates the light output from the first branch waveguide and the light output from the second branch waveguide, and an output waveguide that outputs the optical signal aggregated at the confluence section. A waveguide substrate having a heating section that heats a part of the first branch waveguide, and at least a part of the heated region, which is a region of the first branch waveguide heated by the heating section, has a refractive index that changes to a first refractive index when irradiated with light, and changes from the first refractive index to a second refractive index by heating by the heating section. by doing soBy controlling the phase difference between the phase of the optical signal passing through the first branching optical waveguide and the phase of the optical signal passing through the second branching optical waveguide to maintain the amplitude of the output signal from the merging section at 0, it is turned off. or adjust the amplitude of the output signal from the confluence section to a non-zero magnitude to turn it on Do.

[0009] According to the above form, it is only necessary to supply energy to the optical waveguide only when the switch is switched, and moreover, a latch-type optical switch with a high degree of freedom in controlling the switch switching and selecting materials can be provided.

Brief Description of the Drawings

[0010]

Figure 1

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, a latch-type optical switch according to an embodiment of the present invention will be described. This embodiment is intended to explain the technical idea, configuration, function, relationship between each part, operation and effect, etc. of the optical switch, and there may be differences in design and specifications from the implemented latch-type optical switch. In addition, the drawings used in the description of this embodiment prioritize the ease of understanding of the description and do not necessarily accurately represent the dimensions, shapes, sizes, aspect ratios, etc. of the illustrated configurations.

[0012] FIG. 1 is a diagram for explaining an optical switch which is a latch-type optical switch according to the present embodiment, and is a top view of the optical switch 10. Note that the "top surface" in the present embodiment refers to the surface of the optical transmission substrate on which the optical waveguide is formed, regardless of whether the optical waveguide is formed on or inside the substrate. The optical switch shown in FIG. 1 is an optical signal P in has an input waveguide 13 to which an input is made, at least two branched waveguides 14a and 14b connected to the input waveguide 13, and an output waveguide 15 that aggregates and outputs optical signals P1 and P2 output from the at least two branched waveguides 14a and 14b. The waveguide substrate 1 includes the above. In FIG. 1, a branching portion 161 of the input waveguide 13 and a merging portion 162 of the branched waveguides 14a and 14b are shown. According to such an optical switch 10, the signal light P input from the input waveguide 13 in is branched into signal light P1 passing through the branched waveguide 14a and signal light P2 passing through the branched waveguide 14b, and reunites at the merging portion 162 and is output as signal light P from the output waveguide 15 out .

[0013] Further, as shown in FIG. 1, the optical switch 10 includes a heating unit 11 that heats a part (here, the branched waveguide 14b) of the plurality of branched waveguides 14a and 14b. The heating unit 11 of the present embodiment is configured as an electrode that locally heats the branched waveguide 14b. The material of the electrode is not particularly limited, but Au (gold) or Pt (platinum) is preferable. The region of the branched waveguide 14b heated by the heating unit 11 is shown as a heated region 12. Note that the heated region in the present embodiment refers to a range in which the crystal structure changes due to the heating of the heating unit 11. However, it does not define the degree of change in the crystal structure. At least a part of the heated region 12 has its refractive index changed to a first refractive index by light irradiation, and is changed from the first refractive index to a second refractive index by heating by the heating unit 11. Note that in the present embodiment, the refractive index of the heated region before becoming the first refractive index is also referred to as the "refractive index before change".

[0014] The optical switch 10 configured as described above can control the phase difference between the signal light P1 and the signal light P2 at the merging section 162 by appropriately setting the refractive index before the change of the branching waveguide 14a and the first refractive index of the branching waveguide 14b. Then, by making the phase difference between the signal light P1 and the signal light P2 as represented by the following formula (1), the amplitude of the signal light P out output from the output waveguide 15 can be made zero, and the optical switch 10 can be turned off (n in formula (1) is an integer). π(2n + 1) Formula (1)

[0015] Also, in this embodiment, by controlling the phase difference between the signal light P1 and the signal light P2 at the merging section 162, the amplitude of the signal light P out output from the output waveguide 15 is adjusted, and in the on state of the optical switch, the magnitude of the signal light P out can be adjusted. Hereinafter, such an optical switch 10 will be described in more detail.

[0016] (Waveguide substrate) The material of the waveguide substrate 1 may be a linear optical material or a non - linear optical material. As the linear optical material, there is no particular limitation regarding crystallinity, and for example, it may be a glass substrate such as a quartz substrate or an amorphous substrate. The non - linear optical material may be any material having a non - linear optical effect, and the optical effect may be a second - order non - linear optical effect or a non - linear optical effect of the third order or higher. Examples include lithium niobate (LiNbO3), lithium tantalate (LiTaO3), beta - barium borate (BBO), potassium titanyl phosphate (KTP), etc. The non - linear optical material may have a periodically poled inversion structure for increasing the non - linear optical effect. When using a non - linear optical material having a periodically poled inversion structure, it is necessary to appropriately find the process conditions below the Curie temperature (about 1130 °C in the case of a lithium niobate crystal) at which the periodic poling inversion is not lost in the process of waveguide formation.

[0017] In addition, the input waveguide 13, the branching waveguides 14a and 14b, and the output waveguide 15 may have any waveguide structure through which light can propagate. For example, they may be any of a slab-type optical waveguide, a ridge-type optical waveguide, or an embedded optical waveguide.

[0018] (Light irradiation) FIG. 2 is a diagram for explaining the irradiation of light to the heated region 12 and shows the laser irradiation system 33. FIG. 3 is a diagram for explaining the relationship between the heating portion 11 and the heated region 12 in the branching waveguide 14b shown in FIG. 2. As shown in FIG. 2, the irradiation of light to the heated region 12 is performed by setting the optical switch 10 on the stage 31. The laser light P emitted from a laser light source (not shown) L is irradiated to the heated region 12 formed on the waveguide substrate 1 through the condenser lens 32. In the present embodiment, a femtosecond laser is used as the laser irradiated to the heated region 12. Then, by focusing the laser light on the surface or inside of the waveguide substrate 1 from the outside of the optical switch 10 and irradiating it, the crystal in the range corresponding to the heated region 12 in the branching waveguide 14b is amorphized. The refractive index of the heated region 12 changes to a refractive index corresponding to the amorphized state.

[0019] The femtosecond laser light P L is irradiated to the heated region 12, for example, under the conditions that the central wavelength is 1030 nm, the pulse width is from 300 fs to 10 ps, and the pulse energy is from 200 nJ to 600 nJ. The laser light P L is circularly polarized in consideration of the anisotropy of the material. Such laser light P L is irradiated to the surface of the waveguide substrate 1 through the condenser lens 32 with NA 0.4. Note that such irradiation conditions are only an example, and the laser light P LThe irradiation conditions may be any conditions under which a damage region (amorphized region) due to weak point defects occurs in the optical crystal or the state of the damage region in the amorphous substrate changes. The inventors obtained information regarding the amorphization of the material from end-face observation by a transmission optical microscope image and measurement of Raman scattering spectra by Raman spectroscopy, and optimized the irradiation conditions under which a desired structural change occurs from the end-face observation image by the optical microscope and the Raman scattering spectrum. Further, the inventors made the stage 31 that fixes the optical switch 10 a highly accurate movable three-axis stage, and determined the region to be amorphized by relatively moving the focal position by moving the position of the optical switch 10. Laser beam P L The heated region 12 irradiated with the laser beam P changes from the crystalline state to the amorphous state, and its refractive index changes to the first refractive index.

[0020] (Heating section) In this embodiment, the waveguide substrate 1 is a crystal substrate such as lithium niobate, for example. Therefore, the heating section 11 of this embodiment changes the first refractive index of the heated region 12 to the second refractive index by heating the heated region 12 to crystallize it. The second refractive index of this embodiment is assumed to be equal to the refractive index before the change. Heating by the heating section 11 is a process of changing the structure using a process of heat-treating a sample called annealing. Although there is no particular determination of the annealing temperature, for example, when using a material capable of forming a polarization inversion structure such as a lithium niobate substrate, it is necessary to perform annealing at a temperature lower than the temperature at which the polarization inversion structure does not burn out. The temperature at which the polarization inversion structure does not burn out is 1130°C or lower, which is the Curie temperature of the lithium niobate crystal.

[0021] More specifically, when using a lithium niobate crystal for the waveguide substrate 1, the annealing temperature is about room temperature to 300 °C, and the annealing time is about 0 to 3 hours. However, the annealing conditions of this embodiment are not limited to such examples, and any conditions under which the amorphous lithium niobate crystal recrystallizes may be used. Further, annealing may be performed in a specific gas such as in air, an oxygen atmosphere, or a nitrogen atmosphere. Also, as shown in FIGS. 2 and 3, when using an electrode for the heating unit 11, in order to prevent the laser light during laser irradiation from being blocked by the electrode and reducing the melting efficiency of the heated region 12, the electrode may be formed on the lower surface of the waveguide substrate 1 or below the branch waveguide 14b. Further, in order to prevent the laser light from being blocked by the electrode, the first embodiment may use laser light in a region where the wavelength penetrates the metal. Furthermore, as shown in FIG. 2, the first embodiment may provide a heater 35 on the lower surface of the waveguide substrate 1 to heat the entire waveguide substrate 1, or the heating unit 11 and the heater 35 may be used in combination to adjust the cooling time and the like. In this way, it is possible to heat the entire waveguide substrate 1 including the amorphous region and recrystallize the amorphous region.

[0022] As described above, the heated region 12 of the branch waveguide 14b of this embodiment is rapidly melted by receiving laser light irradiation and cooled to room temperature within a short time after the laser irradiation stops. For this reason, the heated region 12 becomes an amorphous state in which molecules are randomly arranged after cooling. On the other hand, the heating of the heated region by the heating unit 11 provides less energy to the heated region 12 per unit time compared to laser irradiation, and the heated region 12 melts slowly over a longer time than during laser light irradiation and then cools to room temperature over a longer time than during laser irradiation. The heated region 12 that has been slowly cooled over a long time becomes a crystalline state in which atoms are regularly arranged. The inventors of the present invention focused on such points and used different melting methods for the heated region 12, namely laser irradiation and annealing, to change the state of the heated region 12, change the refractive index, and utilize it for switching.

[0023] Figs. 4(a), 4(b), and 4(c) are schematic diagrams for explaining the relationship between the change in refractive index and switching on the above-described branched waveguide 14b. Fig. 4(a) shows a state where the laser beam P L is irradiating the preset heating region 12, and Fig. 4(b) shows a state where the refractive index of the heating region 12 has changed upon receiving the irradiation of the laser beam P L . Fig. 4(c) shows a state where the heating region 12 is heated and recrystallized, and the refractive index of the heating region 12 has returned to the refractive index before the change. As described above, in this embodiment, the first refractive index of the heating region 12 is determined such that the wavelengths of the light passing through the branched waveguides 14a and 14b are shifted by π(2n + 1) in the output waveguide 15. Therefore, from the start of irradiation of the laser beam P L shown in Fig. 4(a), the optical switch 10 is on for a certain period of time, the optical switch 10 shown in Fig. 4(b) is off, and the optical switch 10 shown in Fig. 4(c) is again in the on state.

[0024] That is, the optical switch 10 of this embodiment has a structure that switches between on and off by controlling the optical phase difference between the two arms of the Mach-Zehnder interferometer from the outside. The external control causes a refractive index change in the heating region 12 of the branched waveguide 14b, thereby causing an optical phase difference between the two arms. As a method for changing the refractive index of one arm portion of the Mach-Zehnder interferometer, a refractive index change using the amorphization of a crystal and a refractive index increase using the recrystallization of the amorphized portion are used. When turning off the optical switch 10, the refractive index can be changed by changing the crystal structure of one arm portion of the Mach-Zehnder interferometer, and the optical phase difference between the two arms can be shifted by π(2n + 1). Since the crystal structure does not change at room temperature, the off state is maintained without applying power.

[0025] In addition, in order to turn on the optical switch 10 in the off state, heat is applied to the amorphized heated region 12, that is, annealing is performed to crystallize it, and the refractive index can be restored to the original state. Similar to the switching to the off state, since the crystal structure does not change at room temperature, the on state of the optical switch 10 is maintained without applying power. Thus, the optical switch 10 of the present embodiment functions as a latch-type optical switch having a self-holding function.

[0026] In addition, as described above, the present embodiment is not limited to the configuration in which the branching portion of the optical switch 10 is a Y-branch of a Mach-Zehnder interferometer. FIGS. 5(a) and 5(b) are diagrams for exemplifying variations of the branching portion of the optical switch 10. FIG. 5(a) shows a Y-branch constituted by the input waveguide 13 and the branching waveguides 14a and 14b of the optical switch 10 described above. On the other hand, FIG. 5(b) shows a branching path of an MMI (Multi-Mode Interference) element. The branching path of the MMI element shown in FIG. 5(b) has a 1×2 branching path constituted by an input waveguide 53, a multi-mode waveguide 55, and branching waveguides 54a and 54b. The MMI element has an advantage that the required processing accuracy is lower than that of a Mach-Zehnder interferometer, and the yield when constructing an optical switch can be increased.

[0027] As described above, the present embodiment can provide a latch-type optical switch that maintains the on state and the off state without receiving energy supply once it is turned on or off. In addition, in the present embodiment, the refractive index of the branching waveguide is changed by light irradiation and heating to switch on and off. Therefore, in the present embodiment, the optical waveguide can be amorphized or crystallized to change the refractive index. In such a present embodiment, the optical waveguide may be crystallized or amorphized, and switching can be performed regardless of the amorphized state. For example, the degree of freedom in selecting the light irradiation conditions, the light source wavelength, and the material of the waveguide substrate can be increased rather than changing the crystal state by light irradiation with different wavelengths.

Explanation of Reference Numerals

[0028] 1 Waveguide Substrate 10 Optical Switch 11 Heating Section 12 Heated Region 13, 53 Input Waveguide 14a, 14b, 54a, 54b Branch Waveguide The wavelengths of the lights passing through 15 respectively are the output waveguide 31 Stage 32 Condensing Lens 33 Laser Irradiation System 35 Heater 55 Multi-Mode Waveguide 161 Branch Section 162 Confluence Section

Claims

1. An input waveguide into which an optical signal is input, a first branching waveguide and a second branching waveguide connected to the input waveguide, light output from the first branching waveguide, and light output from the second branching waveguide. A waveguide substrate having a merging section for aggregating the light and an output waveguide for outputting the optical signal aggregated by the merging section; A heating section for heating a part of the first branching waveguide; At least a part of the heated region, which is the region of the first branching waveguide heated by the heating section, has its refractive index changed to a first refractive index upon receiving light irradiation, and is changed from the first refractive index to a second refractive index by heating by the heating section, thereby controlling the phase difference between the optical signal passing through the first branching waveguide and the optical signal passing through the second branching waveguide, and turning off by maintaining the amplitude of the output signal from the merging section at 0, or turning on by adjusting the amplitude of the output signal from the merging section to a non-zero magnitude; A latching optical switch.

2. The latching optical switch according to claim 1, wherein at least a part of the heated region changes its crystal structure upon receiving light irradiation and crystallizes upon heating by the heating section.

3. The latching optical switch according to claim 2, wherein at least a part of the heated region changes its crystal structure upon irradiation with light from a femtosecond laser.

4. The latching optical switch according to claim 1 or 2, wherein the heating section locally heats the first branching waveguide or heats the entire waveguide substrate.

5. The latching optical switch according to any one of claims 1 to 4, wherein the input waveguide, the first branching waveguide, the second branching waveguide, the merging section, and the output waveguide constitute a Mach-Zehnder interferometer.

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