49 results about "Thermo-optic coefficient" patented technology

The invention discloses acousto-optic chalcogenide glass with a high laser damage threshold, the chemical composition formula of the acousto-optic chalcogenide glass is GexSySez, x, y and z respectively represent the mole fractions of Ge, S and Se, x = 10-30, y = 5-40, z = 40-70, x + y + z = 100, and the microscopic network structure of the acousto-optic chalcogenide glass contains a [GeSe4] tetrahedron, a [GeSSe3] tetrahedron, a [GeS2Se2] tetrahedron, a [GeS3Se] tetrahedron, a [GeS4] tetrahedron and a Se ring. The acousto-optic chalcogenide glass provided by the invention has a relatively high laser damage threshold Fth (9.72-15.58 J / cm < 2 > at1550 / 20ns / 5kHz), a relatively low thermo-optic coefficient dn / dT and good acousto-optic characteristics and mechanical properties, is high in near-infrared band transmittance, and has a relatively high laser damage threshold while ensuring a high acousto-optic quality factor. The material can be used as a material basis for developing high-performance and high-stability infrared acousto-optic modulation devices.

A temperature measurement device (1) comprises: a light emission unit (10) that generates coherent, continuous measurement-light; a light detection unit (30) that detects reflected light or transmitted light of the continuous measurement-light which is projected onto a sample (50) to be measured; and an analysis unit (42) that calculates a temperature distribution of the sample (50) to be measured on the basis of the intensity of the reflected light or the transmitted light detected by the light detection unit (30). The analysis unit (42) calculates the optical thickness of the sample (50) to be measured from a temporal change in the intensity of the reflected light or the transmitted light and, by using a refractive index distribution model representing the relationship between the optical thickness and a refractive index distribution in the thickness direction of the sample (50) to be measured at the time of a temperature change, calculates the refractive index distribution from the optical thickness, and calculates the temperature distribution of the sample (50) to be measured by converting the refractive index distribution into the temperature distribution on the basis of the thermo-optical coefficient of the sample (50) to be measured.

The application discloses a modulation-insensitive dual-mode waveguide optical switch and a preparation method thereof, and belongs to the technical field of planar optical waveguide devices. The switch is composed of a silicon wafer substrate, a polymer lower cladding layer, a polymer optical waveguide core layer and a polymer upper cladding layer from bottom to top, the polymer optical waveguide core layer is covered in the polymer upper cladding layer, and the refractive index of the polymer optical waveguide core layer is higher than that of the polymer upper cladding layer and the polymer lower cladding layer. The application utilizes the advantages of simple asymmetric directional coupling structure and asymmetric Y branch structure and the large thermal-optical coefficient of organic polymer materials, and realizes the modulation-insensitive switch of two signal optical modes through mode conversion by using the asymmetric Y branch when the heating electrode is modulated. The preparation process of the application is simple, only needs spin coating, photoetching and wet etching, effectively reduces the production cost, improves the production efficiency of the device, is favorable for large-scale batch production, and enables the mode signal optical switch to be applied to actual use.

A rare-earth doped optical fiber (active optical fiber) is presented that exhibits a thermal coefficient of optical refraction (dn / dT) of the core region that is reduced relative to the thermal coefficient of optical refraction (dn / dT) of the surrounding cladding. The reduction of the dn / dT of the core region has been found to reduce the impact of transverse mode instability (TMI) in the presence of high levels of pump power (or other conditions that can also increase the thermal load present in the core region). Specifically, it has been found that reducing the dn / dT of the core region relative to the dn / dT of the cladding by at least 10% is sufficient to extend the temperature range in which the active optical fiber is maintained in single mode operation. The reduction of the dn / dT can be provided by modifying the dopants introduced into the core region, where, for example, it is known to introduce boron into ytterbium doped optical fibers to reduce the dn / dT of the core region.

The invention relates to chalcogenide glass with a low thermo-optical coefficient as well as a preparation method and application of the chalcogenide glass. The chalcogenide glass with the low thermo-optical coefficient is prepared from the following components in percentage by weight: 78 to 84 percent of Se; 12%-20% of Ge; and 4%-8% of As. Through specific component design, the thermo-optical coefficient is reduced, and the influence of temperature on the optical system is reduced, so that the wavefront distortion control precision of the optical system in an extreme temperature environment is ensured.

The present invention relates to the field of optical waveguide manufacturing technology, specifically disclosing an optical waveguide, a manufacturing method thereof, and an optical waveguide spot adapter. The optical waveguide is manufactured using silicon oxycarbide with a refractive index ranging from 1.457 to 2.7 (inclusive), exhibiting low transmission loss and a good thermo-optical coefficient. The optical waveguide is suitable for optical waveguide devices of various sizes and can be used for optoelectronic monolithic and hybrid integration. Furthermore, the optical waveguide can achieve single-mode transmission even with a large refractive index difference between the core and cladding, resulting in lower loss compared to standard single-mode fiber coupling. Furthermore, the provided optical waveguide manufacturing method utilizes a low process temperature during the manufacturing process, eliminating the need for high-temperature annealing and being compatible with IC manufacturing processes.

This invention discloses an ultra-low residual amplitude modulation waveguide-optical phase modulator, comprising a first electrode layer and a second electrode layer parallel to each other. An α-phase waveguide channel and a substrate layer are disposed between the first and second electrode layers. The optical axes of the α-phase waveguide channel and the substrate layer are both perpendicular to the plane of the first electrode layer. The difference between the thermo-optical coefficient of the α-phase waveguide channel and the thermo-optical coefficient of the substrate layer is less than a preset thermo-optical coefficient difference threshold. Part of the side of the α-phase waveguide channel is covered by the substrate layer. The electric field between the first and second electrode layers uniformly covers the entire α-phase waveguide channel and the substrate layer. The two ends of the α-phase waveguide channel serve as the input and output ends of the light beam, respectively. This invention, by changing the electric field application method and thermo-optical coefficient matching, fundamentally maintains the consistency of the interference phase, thereby significantly reducing the sensitivity of RAM signals to voltage and ambient temperature fluctuations.

The utility model discloses a polydimethylsiloxane sensitization optical fiber temperature and strain simultaneous measurement sensor. The sensor comprises an incident optical fiber, an optical fiber coupler, an optical fiber patch cord, a transmission optical fiber, a sensing cavity, a reference cavity and an emergent optical fiber, an optical signal enters the optical fiber coupler through the incident optical fiber and is divided into two beams of equal-intensity light in the coupler, the two beams of light are respectively input into the transmission optical fiber through the optical fiber patch cord and then enter the sensing cavity and the reference cavity which are coated with the polydimethylsiloxane, and the light is reflected by the cavities to form interference; the interference light is transmitted back to the optical fiber coupler through respective transmission optical fibers, so that a vernier spectrum is formed; the emergent optical fiber transmits an optical signal containing temperature strain information to a spectrograph, trough drift is analyzed through a dual-wavelength matrix demodulation method, and simultaneous measurement is achieved. According to the utility model, the vernier effect, the structural advantages of the Fabry-Perot interferometer and the advantage of high thermo-optic coefficient of polydimethylsiloxane are combined, and the vernier interferometer has the advantages of low cost, high sensitivity, high stability and the like.

Provided in the present invention is a thermo-optic phase shifter array, including at least one first waveguide and at least one second waveguide, where the first waveguide extends in a first direction, the second waveguide extends in a second direction, the first waveguides and the second waveguides are alternately arranged in a third direction, the first waveguide includes a first waveguide section, the second waveguide includes a second waveguide section, the first waveguide sections and the second waveguide sections are alternately arranged in the third direction, the first waveguide section is integrated with a heater, and a thermo-optic coefficient of the second waveguide section is smaller than that of the first waveguide sections. The thermo-optic phase shifter array provided by the present invention has lower thermal crosstalk, and has a compact structure, facilitating high-density integration. The present invention further provides an interferometer array and an optical phased array.

The invention provides a chiral coupling ytterbium-doped optical fiber and a high-power optical fiber laser, and relates to the technical field of optical fibers. The ytterbium-doped optical fiber sequentially comprises a central fiber core, a plurality of spiral side cores, an inner cladding and an outer cladding from inside to outside, wherein the spiral side cores are spirally wound on the central fiber core along the axial direction of the central fiber core; wherein the basic mode refractive index of at least one spiral side core in the multiple spiral side cores is different from the refractive index of the central fiber core in a preset high-order mode, and the thermo-optical coefficient of the spiral side core with the refractive index different from the refractive index of the central fiber core in the preset high-order mode is larger than that of the central fiber core. The chiral coupling ytterbium-doped optical fiber provided by the invention can effectively remove a high-order mode in the central fiber core.

The invention relates to the field of integrated optics, and particularly provides an array waveguide grating, and the array waveguide grating comprises a first array waveguide which comprises a group of first transmission waveguides which are arranged at intervals, and each first transmission waveguide comprises a first sub-waveguide and a second sub-waveguide which are arranged at intervals in a signal transmission direction; the second array waveguide comprises a group of second transmission waveguides which are arranged at intervals, the first transmission waveguides and the second transmission waveguides are arranged in a one-to-one correspondence manner, and the thermo-optical coefficient of the second transmission waveguides is greater than that of the first transmission waveguides; the phase shifter array comprises a plurality of phase shifters, and the phase shifters and the second transmission waveguides are arranged in a one-to-one correspondence mode; optical signals are coupled and transmitted to the corresponding second transmission waveguides through the first sub-waveguides, phase modulation is carried out on the optical signals through the phase shifters, and the optical signals subjected to phase modulation are coupled and transmitted to the corresponding second sub-waveguides. The scheme can effectively reduce the insertion loss of the transmission waveguide and effectively improve the modulation efficiency.

The invention discloses CsSnCl3 nanocrystal doped chalcogenide glass and acousto-optic application of the CsSnCl3 nanocrystal doped chalcogenide glass, the molar composition formula of the chalcogenide glass is 97 (0.8 GeS2-0.2 Sb2S3)-3 CsSnCl3, and CsSnCl3 nanocrystals separated out in situ through heat treatment are dispersed in the chalcogenide glass. The chalcogenide glass has the advantages as follows: the chalcogenide glass has excellent thermal mechanical properties and high robustness, the comprehensive characteristics are outstanding, the Vickers hardness, the elastic modulus, the thermo-optical coefficient, the laser damage threshold and other parameters of the chalcogenide glass are remarkably improved compared with those of current mainstream acousto-optic chalcogenide glass, and a guarantee is provided for stable operation of a device in a high-temperature and high-power environment; the CsSnCl3 nanocrystals are packaged by using the stable glass matrix, so that the problems that the Sn-based perovskite material is easy to oxidize in the environment and poor in stability are fundamentally solved; the material has good infrared acousto-optic comprehensive characteristics and an ultra-wide infrared transmission range, can be used as an acousto-optic medium to be applied to acousto-optic devices, and has a wide application prospect in the acousto-optic field.

The invention relates to the technical field of optical communication, and provides a Mach-Zehnder electro-optical modulator, a preparation method thereof and optical communication equipment. The Mach-Zehnder electro-optical modulator comprises a lithium niobate waveguide layer which is used for responding to a direct current bias electric signal so as to adjust a preset optical parameter of an input optical signal; the negative thermo-optical coefficient functional layer is positioned on the surface of the lithium niobate waveguide layer; wherein the lithium niobate waveguide layer and the negative thermo-optical coefficient functional layer form a combined layer, and the equivalent thermo-optical coefficient of the combined layer is smaller than a preset thermo-optical coefficient; and the transmission electrode is positioned on the surface, deviating from the lithium niobate waveguide layer, of the negative thermo-optical coefficient functional layer and is used for introducing a direct-current bias electric signal. According to the Mach-Zehnder electro-optical modulator, the defect that heat dissipation needs to be increased through a temperature control chip or manufacturing of a heat sink in the prior art is overcome, the state of the electro-optical modulator can be kept near the optimal direct-current bias point only by controlling parameters of the negative thermo-optical coefficient functional layer, and the purpose of restraining the heat effect of the electro-optical modulator is achieved.

The invention discloses a Na5Tb9F32 magneto-optical crystal and a preparation method and application thereof, the chemical formula of the Na5Tb9F32 magneto-optical crystal is Na5Tb9F32, the crystal is of a cubic structure, the space group structure is Fm-3m, and birefringence does not exist; the order of magnitude of the thermo-optical coefficient of the material reaches 10 <-6 > K <-1 >, and the Vierdet constant is 33-34 Rad.m <-1 >. T <-1 > at 1064nm; the uniform melt crystallization characteristic is realized. The Na5Tb9F32 magneto-optical crystal is of a cubic structure, and birefringence does not exist; the thermo-optical coefficient is small, and the system is suitable for a high-power and high-stability optical system; the crystals have consistent melt crystallization characteristics, and large-size crystals are easy to grow. The Na5Tb9F32 magneto-optical crystal can be prepared by adopting a well-known crystal growth method, is a novel magneto-optical material with great potential, and is very suitable for being used as a crystal element of a high-power and high-stability magneto-optical device.

The invention provides an optical switch and a silicon optical chip, the optical switch comprises a first waveguide and a second waveguide, and the first waveguide and the second waveguide are arranged in parallel; the second waveguide comprises a main body and a first slot arranged in the main body; the first waveguide is made of a first material, the main body is made of the first material, and the first gap is filled with a second material; the thermo-optical coefficient of the first material is greater than that of the second material; the optical switch is sequentially provided with an input port area, an input coupling area, a non-coupling phase modulation area, an output coupling area and an output port area in the light propagation direction, and the input port area, the input coupling area, the non-coupling phase modulation area, the output coupling area and the output port area are all arranged on the first waveguide and the second waveguide. The width of the first waveguide in the uncoupled phase modulation area is 450 nanometers, and the width of the second waveguide in the uncoupled phase modulation area is 600 nanometers. The cost is reduced while the optical switch is realized.

An optical sensor system is adapted for a sensing method using fiber segment interferometry. A sensing element with a thermo-optic coefficient larger than the thermo-optic coefficient of an optical fiber is arranged at a distal end of the fiber.

The invention relates to a micro-ring filter based on a polymer cladding. The micro-ring filter comprises an upper cladding, a micro-ring filter and a lower cladding, the upper cladding layer is a PDMS (Polydimethylsiloxane) polymer; the lower cladding is made of silicon dioxide; the micro-ring filter comprises an input grating coupler connected with an input light source, and the input light source sequentially passes through the input grating coupler, an input conical waveguide, a straight-through waveguide and a straight-through end output conical waveguide and is finally output from a straight-through end output grating coupler; and the straight waveguide is matched with an annular waveguide. Through the complementary design of the negative thermo-optical coefficient of the PDMS upper cladding and the positive thermo-optical coefficient of the silicon core layer, the self-shielding of the micro-ring resonant wavelength to the external temperature change is realized.

A thermo-optic coefficient measurement system can include a housing structure (101) configured to retain at least a first plate sample (103a), a second plate sample (103b), and a third plate sample (103c) in a stacked, alternating stagger arrangement such that a gap (105) exists between the first plate sample (103a) and the third plate sample (103c) that is the thickness of the second plate sample (103b). The system also includes a first optical device (107) connected to the housing (102) to output a first laser (107a) configured to be transmitted through the first plate sample (103a) and the third plate sample (103c) without the second plate (103b) in between. The first optical device (107) is configured to receive a first return signal. The system also includes a second optical device (109) connected to the housing (101) to output a second laser (109a) configured to be transmitted through the second plate sample (103b) only, the second optical device (109) is configured to receive a second return signal. The system includes an optical interrogator module (111) configured to be connected to the first optical device (107) to output the first laser (107a) thereto and to receive the first return signal therefrom. The optical interrogator module is configured to be connected to the second optical device (109) to output the second laser (109b) thereto and to receive the second return signal therefrom. The optical interrogator module (111) is configured to determine a thermo-optical coefficient of the second plate sample (103b) as a function of the first return signal and the second return signal at a plurality of temperatures.

A mode-selectable modulated four-mode waveguide optical switch and its manufacturing method belong to the technical field of planar optical waveguide devices. It consists of a silicon wafer substrate, a polymer lower cladding, a strip-shaped polymer optical waveguide core layer, a polymer upper cladding, and a heating electrode. The optical switch of the present invention utilizes the advantages of an asymmetric Y-branch structure and a simple MMI optical waveguide structure, as well as the large thermo-optic coefficient of organic polymer materials, to achieve switching of four optical modes by heating the MMI structure; by heating different heating electrodes, switching functions can be realized for two of the four modes, or for all four modes simultaneously; in addition, the use of polymer materials makes the device manufacturing process simpler, only requiring conventional processes such as spin coating, photolithography, and wet etching, effectively reducing production costs, improving the production efficiency of the device, and facilitating large-scale mass production, enabling this mode optical switch to be applied in practice.

The invention discloses a groove-type micro-ring resonant cavity sensor, and relates to the field of optical waveguide sensors, the sensor comprises a coupling area integrated with an S-shaped bent waveguide and a groove-type micro-ring resonant cavity formed by a groove-type waveguide formed by waveguide ridges, and the groove and the cavity of the groove-type micro-ring resonant cavity are filled with an aqueous solution with a negative thermo-optical coefficient as an upper cladding. According to the invention, the optical coupling efficiency is optimized through the design of the S-shaped bent waveguide, and the energy of an optical field is highly converged in the groove, so that the interaction efficiency of light and a to-be-detected substance is improved, and the sensing sensitivity of the sensor is improved; meanwhile, the negative thermo-optic effect of the aqueous solution is utilized to accurately compensate the positive thermo-optic effect of silicon and silicon dioxide, so that the effect that the change rate of the effective refractive index to the temperature tends to zero is achieved, the sensing sensitivity of the sensor is further improved, and the problem that in a traditional scheme, sensing sensitivity improvement and temperature drift suppression contradict with each other is effectively solved.

The invention relates to the technical field of optical waveguide manufacturing, and particularly discloses an optical waveguide, a manufacturing method thereof and an optical waveguide spot size adapter, for the optical waveguide, silicon oxycarbide with the refractive index range of 1.457-2.7 (including 1.457 and 2.7) is used as a material for manufacturing the optical waveguide, the optical waveguide has the characteristics of low transmission loss and good thermo-optical coefficient, and is suitable for optical waveguide devices with different sizes, and the optical waveguide spot size adapter is suitable for optical waveguide devices with different sizes. The optical waveguide can be used for photoelectric monolithic integration and hybrid integration, meanwhile, the optical waveguide can still achieve single-mode transmission under the condition that the refractive index difference of the core cladding is large, compared with standard single-mode optical fiber coupling, loss is low, and the provided optical waveguide manufacturing method is low in process temperature in the manufacturing process, does not need high-temperature annealing and is compatible with the IC manufacturing process.

To provide a method for solving a problem of a conventional sensing method, and an optical sensor system 100.SOLUTION: According to the present invention, an optical sensor system (100) adapted for a sensing method using fiber segment interferometry is provided, wherein at the distal end of the fiber (73) a sensing element (1. I) is arranged having a thermo-optic coefficient larger than the thermo-optic coefficient of the optical fiber (73. I).SELECTED DRAWING: Figure 4

The invention relates to an optical sensor system (100), a sensing method suitable for interferometry using a fiber segment, in which a sensing element 1. I having a thermo-optical coefficient greater than that of the fiber 73. I is arranged at the distal end of the fiber 73.

The present invention provides a thermo-optic phase shifter array including at least one first waveguide and at least one second waveguide, wherein the first waveguide extends along a first direction, the second waveguide extends along a second direction, the first waveguide and the second waveguide are alternately arranged in a third direction, the first waveguide includes a first waveguide segment, the second waveguide includes a second waveguide segment, the first waveguide segment and the second waveguide segment are alternately arranged in the third direction, a heater is integrated in the first waveguide segment, and the thermo-optic coefficient of the second waveguide segment is smaller than that of the first waveguide segment. The thermo-optic phase shifter array according to the present invention has relatively low thermal crosstalk and has a compact structure, which is advantageous for high-density integration. The present invention further provides an interferometer array and an optical phased array.

The waveguide electro-optic phase modulator comprises a first electrode layer and a second electrode layer which are parallel to each other, and an alpha-phase waveguide channel and a substrate layer are arranged between the first electrode layer and the second electrode layer. The optical axis of the alpha-phase waveguide channel and the optical axis of the substrate layer are both perpendicular to the plane where the first electrode layer is located, and the difference value between the thermo-optical coefficient of the alpha-phase waveguide channel and the thermo-optical coefficient of the substrate layer is smaller than a preset thermo-optical coefficient difference threshold value; part of the side face of the alpha-phase waveguide channel is covered by the substrate layer, an electric field between the first electrode layer and the second electrode layer evenly covers the whole alpha-phase waveguide channel and the substrate layer, and the two ends of the alpha-phase waveguide channel serve as the input end and the output end of light beams respectively. According to the invention, by changing the electric field application mode and thermo-optical coefficient matching, the consistency of interference phases is fundamentally maintained, so that the sensitivity of RAM signals to voltage and environment temperature fluctuations is remarkably reduced.

The invention discloses a Na5Tb9F32 magneto-optical crystal and a preparation method and application thereof, the chemical formula of the Na5Tb9F32 magneto-optical crystal is Na5Tb9F32, the crystal is of a cubic structure, the space group structure is Fm-3m, and birefringence does not exist; the order of magnitude of the thermo-optical coefficient of the material reaches 10 <-6 > K <-1 >, and the Vierdet constant is 33-34 Rad.m <-1 >. T <-1 > at 1064nm; the uniform melt crystallization characteristic is realized. The Na5Tb9F32 magneto-optical crystal is of a cubic structure, and birefringence does not exist; the thermo-optical coefficient is small, and the system is suitable for a high-power and high-stability optical system; the crystals have consistent melt crystallization characteristics, and large-size crystals are easy to grow. The Na5Tb9F32 magneto-optical crystal can be prepared by adopting a well-known crystal growth method, is a novel magneto-optical material with great potential, and is very suitable for being used as a crystal element of a high-power and high-stability magneto-optical device.

The present application relates to the technical field of resins, and in particular to an optical resin, a preparation method therefor, and use thereof. The optical resin is a polyamide-imide resin containing at least two of repeating units represented by formula I, formula II, and formula III, wherein R1, R2, R3, R4, and R5 are each independently selected from one of aryl and substituted aryl. According to the optical resin of the present application, by means of introducing the repeating units represented by formula I, formula II, and formula III and an amide bond, the interaction of hydrogen bonds between molecules is used to make the optical resin polymer have a relatively low thermo-optic coefficient. In addition, by means of the reasonable proportioning and combined action of different repeating unit chain segments, the optical resin has good optical properties, good optical transmittance at 1550 nm, and melt processing performance, which can meet injection molding processing requirements.

This invention discloses a multimodal integrated optical microcavity, belonging to the field of integrated photonic device technology. The multimodal integrated optical microcavity includes a first microcavity structure and a second microcavity structure coupled in a vertical direction. The first and second microcavity structures are made of different materials, and by adjusting the waveguide thickness and width, the two microcavities have approximately the same free spectral range within a preset operating wavelength band. Because the two materials have different thermo-optic coefficients, differential resonant frequency shifts can be naturally generated during thermal tuning of the bilayer microcavity. Combined with the vernier coupling effect between the microcavities, a Moore acceleration effect is formed, thereby achieving a wide range of adjustment of the microcavity's dispersion characteristics. By controlling the thermal excitation conditions, switching between normal dispersion and anomalous dispersion can be achieved, enabling a single device to support multiple optical operating modes. This invention has a simple structure, stable control, and strong process compatibility, making it suitable for reconfigurable integrated photonic systems.

The invention relates to the field of photon integrated circuits, in particular to a temperature sensor based on an enhanced vernier effect and an optical chip, and aims to improve the structure of the temperature sensor and improve the detection sensitivity. In order to achieve the purpose, the temperature sensor comprises two Mach-Zehnder interference structures which are connected in parallel, and upper cladding layers of a sensing arm and a reference arm are made of two upper cladding layer materials with opposite thermo-optical coefficients. Through the design of the sensing arm and the reference arm which are connected in parallel, an enough separation space is formed between the two arms, different upper cladding materials can be conveniently covered, and the process difficulty is reduced; two upper cladding materials with opposite thermo-optical coefficients are adopted as the upper cladding of the sensing arm and the upper cladding of the reference arm respectively, the wavelength drift amount of the envelope of the output combined spectrum along with the temperature change can be greatly improved, and therefore the sensitivity of the temperature sensor is improved.

A spatial light modulator having a layer of thermo-optical medium, where the thermo-optical medium is at least partially transparent for at least one spectral component of visible or near infrared light and having the thermal conductivity between 0.01 and 30 W K−1 m−1 at the temperature of 20° C. and the layer having a thickness up to 100 μm is disclosed. At least one heating microsource in thermal contact with the layer of the thermo-optical medium, where each heating microsource has at least one dimension smaller than 10 μm, and at least one substrate in thermal contact with the thermo-optical medium, the substrate having a thermo-optic coefficient at least 10 times smaller than a thermo-optic coefficient of the thermo-optical medium and a thermal conductivity of at least 1 W K−1 m−1 while the thermal conductivity of the substrate is higher than the thermal conductivity of the thermo-optical medium.