A liquid crystal-based chip filter

Abstract

The present invention discloses a chip-based filter based on liquid crystal. The chip-based filter includes: a chip substrate layer, which is a liquid crystal layer in which liquid crystal molecules are distributed; a chip guiding core layer, which is arranged on the surface of the chip substrate layer and is also a liquid crystal layer in which liquid crystal molecules are distributed. The chip guiding core layer includes: a double straight waveguide part and a resonant cavity part that is transmission-coupled to the double straight waveguide part. The double straight waveguide part is used to realize the input of white light or a multi-spectral light source and the output of light with any wavelength; a driving electrode, which is used to drive the arrangement change of the liquid crystal molecules in the chip substrate layer, the double straight waveguide part, and the resonant cavity part, and change the refractive index of the corresponding parts. The present invention realizes a tunable filtering function by using the modulation of liquid crystal. Under low-voltage driving, the main working band can cover the near-ultraviolet to near-infrared band and the main communication band, and it has a small volume and is easy to integrate.

Description

Technical Field

[0001] The present invention relates to a filter, and more particularly to a chip-based filter based on liquid crystal. Background Art

[0002] Based on the technical needs in recent years, there is an urgent need for a class of narrowband filters with excellent performance. Such narrowband filters should have the advantages of small insertion loss, high sharpness, wide free spectral range, etc. Such filters not only have extremely wide application prospects in optical communication fields such as DWDM systems and all-optical switching systems, but also have the potential for wide application in multi-spectral imaging, high-precision spectral analysis, and various sensing systems.

[0003] Due to the limitations of the bandwidth and high cost of tunable optical filters, they have not been put into large-scale use. Diffraction gratings are widely used as optical filters in optical channel performance monitoring modules. For each diffracted wavelength, several detectors are required. However, for systems with a large number of channels, replacing the diffraction grating with a tunable optical filter can greatly reduce the number of detectors and thus reduce the volume of the optical channel performance monitoring module; in addition, fixed filters have a "shielding" effect on out-of-band interference, and tunable optical filters can detect out-of-band interference during wavelength tuning for timely correction.

[0004] High-performance tunable optical filters have been a topic of concern in recent years. There are already technologies such as dielectric films, F-P cavities, micro-ring resonators, photonic crystals, and fiber gratings. However, these tunable methods still have some problems in technology:

[0005] Existing visible light filters have the following problems:

[0006] For F-P cavity filters, it is difficult for various F-P cavity tunable optical filters to simultaneously meet the requirements of the optical channel performance monitoring module for frequency selection and tuning range in terms of fineness and free spectral region.

[0007] For dielectric film TFF filters, dielectric film TFF filters need to use the cascade of multiple F-P cavities to improve the device isolation, which will affect the stability of the output optical power.

[0008] For fiber grating type filters, when fiber grating type filters are applied to multi-channel demultiplexing, a large number of FBGs are required for the cascade structure; there will be extra losses when using a circulator to reflect part of the light.

[0009] For photonic crystal filters, photonic crystal filters have common limitations in realizing tunability by using external magnetic fields, electric fields, and thermal energy: as these energies increase, the wavelength of the transmission peak does not move linearly, so the tuning is not well controllable, and the transmission peak is not narrow enough, the tuning range is not wide enough, the filter structure is more complex, and the actual preparation is quite difficult.

[0010] The research on microring resonator filters is developing towards multi-ring cascades, and problems such as inter-ring resonance tuning and precise control of coupling coefficients need to be solved. Photonic crystal filters have common limitations in achieving tunability using external magnetic fields, electric fields, and thermal energy: as these energies increase, the wavelength of the transmission peak does not move linearly, so the tuning is not very controllable, the transmission peak is not narrow enough, the tuning range is not wide enough, and the filter structure is more complex, making actual fabrication quite difficult. Tunable optical filters, as core optical devices, are also widely used in filters, sensors, and optical imaging systems. In addition to high performance, the size of tunable optical filters also needs to be continuously miniaturized. Among various solutions, microring resonator filters have received increasing attention and research from technicians and play an increasingly important role in fields such as sensing detection, slow and fast light, code conversion, wavelength conversion, fiber-borne radio waves, filters, etc. Summary of the Invention

[0011] To solve the above technical problems, the present invention proposes a liquid crystal-based chip filter.

[0012] To achieve the above object, the technical solution of the present invention is as follows:

[0013] A liquid crystal-based chip filter includes:

[0014] A chip substrate layer, which is a liquid crystal layer with liquid crystal molecules distributed therein;

[0015] A chip waveguide core layer, disposed on the surface of the chip substrate layer, which is a liquid crystal layer with liquid crystal molecules distributed therein. The chip waveguide core layer includes: a double straight waveguide part and a resonator part that is transmission-coupled to the double straight waveguide part. The double straight waveguide part is used to achieve the input of white light or multi-spectral light sources and the output of light of any wavelength:

[0016] A driving electrode, which is used to drive the arrangement change of liquid crystal molecules in the chip substrate layer, the double straight waveguide part, and the resonator part, and change the refractive index of the corresponding parts.

[0017] The liquid crystal-based chip filter of the present invention realizes a tunable filtering function through the modulation of liquid crystal. Under low-voltage driving, the main working band can cover the near-ultraviolet to near-infrared band and the main communication band, and it has a small volume and is easy to integrate.

[0018] Based on the above technical solution, the following improvements can be made:

[0019] As a preferred solution, the double straight waveguide part is a symmetric structure.

[0020] Adopting the above preferred solution is easy to fabricate.

[0021] As a preferred solution, the resonator part includes: at least two cascaded resonant micro-rings.

[0022] Adopting the above preferred solution, the filtering effect is good.

[0023] As a preferred solution, the radius of the resonant micro-ring is above 4um;

[0024] The diameter of the double straight waveguide part is above 2um;

[0025] The overall structure of the chip-based filter is above 20um.

[0026] Adopting the above preferred solution, the output wavelength covers the light in the 380nm to 780nm band, realizing tunable output light in the visible light band.

[0027] As a preferred solution, the resonant micro-ring is a symmetric structure.

[0028] Adopting the above preferred solution, it is easy to fabricate.

[0029] As a preferred solution, the resonator part includes:

[0030] The first resonant micro-ring, the first resonant micro-ring is transmission-coupled with the input straight waveguide in the double straight waveguide part:

[0031] The second resonant micro-ring, the second resonant micro-ring is cascaded with the first resonant micro-ring and is transmission-coupled with the output straight waveguide in the double straight waveguide part.

[0032] Adopting the above preferred solution, the structure is simple and the filtering effect is good.

[0033] As a preferred solution, the radius of the first resonant micro-ring is greater than the radius of the second resonant micro-ring.

[0034] Adopting the above preferred solution, the filtering effect is good.

[0035] As a preferred solution, the liquid crystal refractive index range of the chip substrate layer and the chip core layer is between 1.55 and 1.70.

[0036] Adopting the above preferred solution, the orientation of liquid crystal molecules throughout the chip is formed into a patterned arrangement by the photo-alignment technique. Utilizing the birefringence property and voltage drive of liquid crystal, the refractive indices of the chip core layer and the chip substrate layer change with the orientation mode of liquid crystal molecules, and the refractive index change range is from 1.55 to 1.7.

[0037] As a preferred solution, there is an included angle between 0 and π between the liquid crystal molecules in the chip core layer and the liquid crystal molecules in the chip substrate layer, and the liquid crystal refractive index of the chip core layer is greater than the liquid crystal refractive index of the chip substrate layer.

[0038] By adopting the above preferred solution, total internal reflection propagation of light in the waveguide medium is achieved.

[0039] As a preferred solution, the driving electrode includes: a plurality of driving units for respectively driving the arrangement change of liquid crystal molecules in the chip substrate layer, the double straight waveguide part, and the resonant cavity part.

[0040] By adopting the above preferred solution, the driving electrode adopts a plurality of independent control modules to ensure the accuracy of control and the stability of the control system. Brief Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0042] Figure 1 It is a schematic structural diagram of a chip-based filter provided by an embodiment of the present invention.

[0043] Figure 2 It is a schematic diagram of a micro-ring principle provided by an embodiment of the present invention.

[0044] Figure 3 It is a schematic diagram of a resonance mode principle provided by an embodiment of the present invention.

[0045] Figure 4 It is a schematic structural diagram of a chip-based filter provided by an embodiment of the present invention.

[0046] Figure 5 It is the arrangement of liquid crystal molecules and the patterned electrode of the first resonant micro-ring part provided by an embodiment of the present invention.

[0047] Figure 6 It is the arrangement of liquid crystal molecules and the patterned electrode of the first straight waveguide part provided by an embodiment of the present invention.

[0048] Figure 7 It is an experimental diagram of the output wave wavelength provided by a specific embodiment one of the present invention.

[0049] Figure 8 It is an experimental diagram of the output wave wavelength provided by a specific embodiment two of the present invention.

[0050] Wherein: 1 - double straight waveguide part, 11 - top first straight waveguide part, 12 - top second straight waveguide part, 2 - resonant cavity part, 21 - first resonant micro-ring, 22 - second resonant micro-ring, 3 - driving electrode. Detailed Embodiments

[0051] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] The use of ordinal numbers such as "first" and "second" to describe ordinary objects only represents different instances of similar objects, and does not intend to imply that the objects so described must have a given order in terms of time, space, sorting, or any other way.

[0054] In addition, the expression of "including" elements is an "open" expression, and this "open" expression only means that there are corresponding components, and should not be interpreted as excluding additional components.

[0055] In order to achieve the purpose of the present invention, in some embodiments of a liquid crystal-based chip filter, as Figure 1 shown, the chip filter includes:

[0056] A chip substrate layer, which is a liquid crystal layer with liquid crystal molecules distributed therein;

[0057] A chip guiding core layer, which is disposed on the surface of the chip substrate layer. The chip guiding core layer is a liquid crystal layer with liquid crystal molecules distributed therein. The chip guiding core layer includes: a double straight waveguide part 1 and a resonant cavity part 2 that is transmittively coupled to the double straight waveguide part 1. The double straight waveguide part 1 is used to realize the input of white light or a multi-spectral light source and the output of light of any wavelength:

[0058] A driving electrode 3, which is used to drive the arrangement change of the liquid crystal molecules in the chip substrate layer, the double straight waveguide part 1, and the resonant cavity part 2, and change the refractive index of the corresponding part.

[0059] Among them, the double straight waveguide part 1 includes: a first straight waveguide part 11 disposed at the input end of the resonant cavity part 2 and a second straight waveguide part 12 disposed at the lower path end of the resonant cavity part 2.

[0060] Using liquid crystal as an optical transmission and modulation medium in a photonic chip, by arranging the molecular orientation of liquid crystal micro-regions, the functions of the double straight waveguide part 1 and the resonant cavity part 2 are realized, and the electro-optic modulation effect of the liquid crystal is utilized to make the refractive index of the waveguide medium adjustable, so that the filter can achieve wavelength tunability.

[0061] The input optical light source is: white light or a multi-spectral light source, which includes the near-infrared band to the near-ultraviolet band. The input light can be a mixed light source, but only light of specific bands can be coupled into the structure of the resonant cavity part 2. The input light is coupled into the waveguide core layer composed of liquid crystal molecules by means of transmission coupling, and the transmission coupling coefficient can be controlled by controlling the distance between the double straight waveguide part 1 and the resonant cavity part 2.

[0062] A detection element such as a spectrometer can be placed at the output end of the double straight waveguide part 1, and the detectable range includes the near-infrared band to the near-ultraviolet band.

[0063] A liquid crystal-based chip filter of the present invention realizes a tunable filtering function by using the modulation of liquid crystal. Under low-voltage driving, the main working band can cover the near-ultraviolet to near-infrared band and the main communication band, and it has a small volume and is easy to integrate.

[0064] In order to further optimize the implementation effect of the present invention, in some other embodiments, the remaining characteristic technologies are the same, except that the double straight waveguide part 1 is a symmetric structure.

[0065] Adopting the above preferred scheme, it is easy to fabricate.

[0066] In order to further optimize the implementation effect of the present invention, in some other embodiments, the remaining characteristic technologies are the same, except that the resonant cavity part 2 includes: at least two cascaded resonant micro-rings.

[0067] Adopting the above preferred scheme, the filtering effect is good.

[0068] Furthermore, the radius of the resonant micro-ring is above 4um;

[0069] The diameter of the double straight waveguide part 1 is above 2um;

[0070] The overall structure of the chip filter is above 20um.

[0071] Adopting the above preferred scheme, the output wavelength covers the light in the 380nm to 780nm band, realizing tunable output light in the visible light band.

[0072] Since the resonant frequency of the resonant micro-ring is determined by the effective refractive index of the resonant cavity, the radius, and the resonant wavelength series, and the change range of the effective refractive index is limited, while the change ranges of the radius of the resonant cavity and the resonant wavelength series are relatively large. Therefore, in order to realize tunable output light in the visible light band, the radius of the resonant micro-ring needs to reach above 4um, the diameter of the double straight waveguide part 1 needs to reach above 2um, the overall structure of the filter needs to reach above 20um, and the output wavelength at the output end covers the 380nm to 780nm band.

[0073] When the radius of the resonant micro-ring resonator is determined, the effective refractive index of the resonant micro-ring resonator is adjusted by voltage driving. At this time, the resonant wavelength series changes, realizing the modulation of the resonant wavelength. The precision of the optical orientation technology of liquid crystal molecules can reach 0.1 μm, so the structural precision of the filter can also reach 0.1 μm. The smaller the distance between the resonant micro-ring and the straight waveguide, and the smaller the distance between different resonant micro-rings, the larger the transmission coupling coefficient. Therefore, the distance between the resonant micro-ring and the straight waveguide, and the distance between different resonant micro-rings can reach more than 0.1 μm.

[0074] Furthermore, the resonant micro-ring has a symmetric structure.

[0075] Adopting the above preferred scheme, it is easy to fabricate.

[0076] In order to further optimize the implementation effect of the present invention, in some other embodiments, the remaining characteristic technologies are the same, and the difference lies in that the resonant cavity part 2 includes:

[0077] A first resonant micro-ring 21, which is transmission-coupled with the input straight waveguide in the double straight waveguide part 1;

[0078] A second resonant micro-ring 22, which is cascaded with the first resonant micro-ring 21 and is transmission-coupled with the output straight waveguide in the double straight waveguide part 1.

[0079] Adopting the above preferred scheme, the structure is simple and the filtering effect is good.

[0080] Furthermore, the radius of the first resonant micro-ring 21 is larger than the radius of the second resonant micro-ring 22.

[0081] Adopting the above preferred method, the filtering effect is good.

[0082] The planar structure of the resonant cavity part 2 includes but is not limited to the cascading methods in the above embodiments. The cascading methods include various integration methods such as series integration, parallel integration, multi-segment integration, and array integration. Different cascading methods may have advantages such as expanding the free spectral range, reducing crosstalk, flat passband, high stability, and small dispersion, but may also have problems such as loss caused by central wavelength mismatch, high processing precision requirements, and reduced stability caused by temperature polarization. Different cascading methods have their own advantages and disadvantages. In this embodiment, the series integration method is adopted, and the performance indicators in all aspects are excellent but the fabrication difficulty is relatively large. In different application scenarios, different cascading methods can be completed by the same liquid crystal optical orientation technology.

[0083] The micro-ring structure using double straight waveguides filters the incident light, enabling the chip-based filter to output tunable light; the driving electrode 3 modulates the waveguide medium, thereby changing the effective refractive index of the resonant cavity part 2 and realizing the output of monochromatic light with any wavelength.

[0084] The dual straight waveguide section 1 is formed by arranging liquid crystal molecules at a certain angle, forming a stepped waveguide structure. The refractive index of the liquid crystal in the chip waveguide core layer is greater than that of the liquid crystal in the substrate layer, thereby realizing the total reflection propagation of light in the waveguide medium.

[0085] The resonator section 2 is formed by arranging liquid crystal molecules at a certain angle, forming a stepped waveguide resonator.

[0086] Light is coupled into the first resonant micro-ring 21 resonator at the input end of the resonator section 2 through the first straight waveguide section 11 and oscillates and propagates in this resonator. The first resonant micro-ring 21 resonator and the second resonant micro-ring 22 resonator form resonance, so that the wave propagating in the first resonant micro-ring 21 resonator is coupled into the second resonant micro-ring 22 resonator and oscillates and propagates in this resonator. The wave in the second resonant micro-ring 22 resonator is finally coupled into the second straight waveguide section 12 at the lower output end and output from the lower output end. Through structural design and parameter matching, monochromatic light output of a set wavelength is realized.

[0087] The free spectral range (FSR) refers to the spectral range between two resonant wavelengths. The definition of FSR is: Where is the resonator length, λm is the resonant wavelength of the resonator R is the radius of the resonator, m is the resonance order, n eff is the effective refractive index of the resonator.

[0088] The total FSR of two micro-ring filters with different radii can be expressed as: m1FSR1 = m2FSR2 = FSR total . There is a resonant wave λ1 in the first resonant micro-ring 21 resonator. After resonance is formed between the first resonant micro-ring 21 resonator and the second resonant micro-ring 22 resonator, there is a resonant wave λ2 in the second resonant micro-ring 22 resonator. The resonance condition is At this time, the resonant wave λ2 in the second resonant micro-ring 22 resonator is finally coupled into the second straight waveguide section 12 at the lower output end and output from the lower output end. When R1 and R2 are determined and n1 and n2 change, to output the modulated λ′1 and λ′2, it is necessary to find the matching m′1 and m′2, which is the frequency selection process.

[0089] In order to further optimize the implementation effect of the present invention, in some other embodiments, the remaining characteristic technologies are the same, and the difference is that the refractive index ranges of the liquid crystal in the chip substrate layer and the chip waveguide core layer are between 1.55 and 1.70.

[0090] With the above preferred solution, the orientation of liquid crystal molecules throughout the chip is formed into a patterned arrangement by the photo-alignment technique. Utilizing the birefringence property of liquid crystals and voltage driving, the refractive indices of the chip core layer and the chip substrate layer change with the orientation mode of the liquid crystal molecules, and the refractive index change range is from 1.55 to 1.7.

[0091] In order to further optimize the implementation effect of the present invention, in some other embodiments, the remaining characteristic technologies are the same, and the difference lies in that there is an included angle between 0 and π between the liquid crystal molecules in the chip core layer and the liquid crystal molecules in the chip substrate layer, and the liquid crystal refractive index of the chip core layer is greater than the liquid crystal refractive index of the chip substrate layer.

[0092] With the above preferred solution, total internal reflection propagation of light in the waveguide medium is achieved.

[0093] In order to further optimize the implementation effect of the present invention, in some other embodiments, the remaining characteristic technologies are the same, and the difference lies in that the driving electrode 3 includes: a plurality of driving units for respectively driving the arrangement change of the liquid crystal molecules in the chip substrate layer, the double straight waveguide part 1, and the resonant cavity part 2.

[0094] With the above preferred solution, the driving electrode 3 adopts a plurality of independent control modules to ensure the accuracy of control and the stability of the control system.

[0095] The driving electrode 3 adopts a patterned electrode. By modulating the liquid crystal molecules, the change of the refractive index of the waveguide medium is realized, and further the modulation of the output wavelength is realized. Further, the material of the driving electrode 3 can be but not limited to ITO glass. The electrode patterning method can be achieved by patterning and orienting the ITO glass so that the electrode pattern corresponds to the liquid crystal arrangement pattern, and the alignment of the electrode patterning and the liquid crystal patterning can be realized by area exposure.

[0096] The driving electrode 3 can be modulated in various ways, such as voltage modulation, temperature modulation, magnetic field modulation, light field modulation, or a combination of multiple modulation methods.

[0097] The following briefly introduces two driving methods:

[0098] One is the electric field driving of the electrode. Utilizing the electro-optical effect of liquid crystals, the liquid crystal molecules are driven to rotate by applying a voltage. The change in the arrangement direction of the liquid crystal molecules in the resonant cavity part 2 of the chip core layer and the chip substrate layer will cause a change in the effective refractive index of the resonant cavity part 2, thereby changing the resonant wavelength. The change in the arrangement direction of the liquid crystal molecules in the double straight waveguide part 1 of the chip core layer will cause the filter to have a switch.

[0099] One is to incorporate photosensitive materials (such as azo materials). Under the modulation of the optical field, the photosensitive materials will cause the rotation of liquid crystal molecules in the chip core layer and the chip substrate layer. When driving with the optical field, it is also necessary to control the focusing, wavelength of the driving light corresponding to the photosensitive materials.

[0100] The driving unit for driving the first straight waveguide portion 11 can control whether the incident light can propagate in the first straight waveguide portion 11, the aperture angle of the incident light, and the transmission coupling coefficient between the incident light and the resonant micro-ring. The driving unit for driving the second straight waveguide portion 12 can control the intensity of the output light wave and the transmission coupling coefficient between the output light wave and the resonant micro-ring. The driving units for driving each resonant micro-ring of the resonant cavity portion 2 can control the effective refractive index of each micro-ring resonator, so that the resonant condition of the resonant cavity changes, thereby changing the resonant wavelength and the filtering range.

[0101] The above-mentioned multiple implementation manners can be realized in a cross-parallel manner.

[0102] To better understand the above content, the following is a description of the principle.

[0103] The transmissive structure resonant cavity is composed of two straight waveguides and a micro-ring coupling. The coupling structure model is as Figure 2 shown. The transmissive resonant cavity has two output ends, namely the through end and the drop end. Let the input laser be E1. In the coupling region, a part of the optical energy is directly output through the straight waveguide, that is, the through end of the resonant cavity, denoted as E2; another part of the optical energy is coupled into the resonant cavity and denoted as E4. This part of the light travels around the ring in the cavity. Each time it passes through the coupling region, a part of the optical energy is coupled to the straight waveguide and output through the down port of the resonant cavity, denoted as E5; while another part of the light continues to travel around the ring, denoted as E3, and finally forms a closed loop of light.

[0104] In the steady state, the light passing through the two coupling regions will reach a dynamic equilibrium state. Expressed by the resonant formula of the resonant cavity, it is:

[0105] As Figure 3 shown, in the coupled whispering gallery mode cavity, the resonant modes circulate in each resonator and can interact with each other. In the case of strong interaction, one cavity can be regarded as the spectral fidelity value of the resonant wavelength of another cavity. Therefore, when the resonant conditions of two isolated cavities are satisfied, some resonant modes will be enhanced while other modes will be weakened. This phenomenon is called the Vernier effect. Expressed by the resonant condition formula, it is:

[0106] Based on the above embodiments, two specific embodiments are given.

[0107] Embodiment 1:

[0108] The electro-optic modulation drive using a double-ring structure liquid crystal is adopted to realize the various functions of the microcavity filter. The cascading method adopted is as Figure 4 shown. The effective refractive index range of the liquid crystal in the chip guiding layer and the chip substrate layer can reach 1.55 to 1.70, and the change in the effective refractive index can reach about 0.2.

[0109] As Figure 5 and 6 shown, the three-layer waveguide structures of the first resonant micro-ring 2131, the second resonant micro-ring 2232, and the double straight waveguide part 1 are all symmetric structures. The liquid crystal arrangement in each part is a vertical arrangement to achieve the purpose of the maximum modulation amount, and there are patterned electrodes at the bottom of the integrated chip to realize voltage modulation of liquid crystal molecules.

[0110] Natural light is incident. The refractive index of the medium in the double straight waveguide part 1 is 1.7, and the refractive index of the external medium is 1.55, forming a three-layer waveguide structure, which is incident from the incident end and propagates by total reflection.

[0111] The refractive index of the medium in the first straight waveguide part 11 is n2, and the refractive index of its external medium is n1;

[0112] The refractive index of the external medium of the first resonant micro-ring 21 is n3, the refractive index of its internal medium is n′3, and the effective refractive index is n4;

[0113] The refractive index of the external medium of the second resonant micro-ring 22 is n5, the refractive index of its internal medium is n′5, and the effective refractive index is n6;

[0114] The refractive index of the medium in the second straight waveguide part 12 is n8, and the refractive index of its external medium is n7.

[0115] The radius of the first resonant micro-ring 21 is 10um, the initial effective refractive index is n4 = 1.600, and the distance from the first optical straight waveguide part is 100nm. From the resonance formula of the resonant cavity it can be obtained that the wavelength of the resonant wave coupled into the first resonant micro-ring 21 is 502nm, and the mode number is 200.

[0116] The resonant wave propagates in the resonant cavity of the first resonant micro-ring 21, resonates with the second resonant micro-ring 22, and is coupled into the second resonant micro-ring 22. From the resonance relation formula it can be obtained that the radius of the second resonant micro-ring 22 is 5um, the initial refractive index effective refractive index is 1.600, and the distance from the first resonant micro-ring 21 is 100nm.

[0117] Similarly, from the resonance formula of the resonant cavity it can be obtained that the wavelength of the resonant wave coupled into the second resonant micro-ring 22 is 502nm, and the mode number is 100.

[0118] The distance between the second resonant micro-ring 22 and the second straight waveguide section 12 at the drop end is 100 nm. The resonant wave is coupled into the second straight waveguide section 12 and undergoes total reflection transmission, and a monochromatic wave of 502 nm is output from the second straight waveguide section 12, realizing the filtering function, as Figure 7 shown.

[0119] Since the liquid crystal can be electro-optically modulated by the patterned electrode, changing the effective refractive indices of the double straight waveguide section 1 and the resonant cavity section 2, and thus can significantly change the wavelength of the resonant wave, realizing the dynamic modulation function.

[0120] In the second embodiment, the effective refractive index of the first resonant micro-ring 21 is changed to 1.700, the wavelength of the resonant wave becomes 628 nm, the mode number becomes 170, while the effective refractive index of the second resonant micro-ring 22 becomes 1.700, the wavelength of the resonant wave of resonance becomes 628 nm, the mode number becomes 85, and the wavelength of the monochromatic light at the output end also becomes 628 nm, completing the frequency conversion function of the filter, as Figure 8 shown. The refractive indices of the first resonant micro-ring 21 and the second resonant micro-ring 22 can also adopt different refractive indices according to the different voltages applied to the two, and thus realize the modulation of other wavelengths.

[0121] A tunable filter based on liquid crystal according to the present invention, the spectrum of the filter includes the near-infrared band to the near-ultraviolet band, but the output light is monochromatic light, the spectral half-width is 500 GHz, and the output light wavelength range is 380 nm to 780 nm. The present invention can realize the function of dynamically modulating and outputting the wide-band wavelength of the laser, and the main working band under low-voltage driving can cover the near-ultraviolet to near-infrared band and the optical communication band, and has a small volume and is easy to integrate.

[0122] The present invention has the following differences compared with the similar micro-ring filters.

[0123] Compared with the frequency selection filter of the micro-ring resonator based on the KDP crystal, the KDP crystal uses electro-optic modulation, but the types of liquid crystal materials are not as diverse as those of the liquid crystal, and various modulation methods such as electric field, light field, magnetic field, and temperature can be realized, and thus can be used in more complex situations; the KDP crystal has a larger volume, while the liquid crystal disclosed in the present invention is a planar structure and is easier to integrate.

[0124] Compared with the first-order or higher-order ring filter based on SOI, the refractive index of the SOI structure cannot be tuned and can only be used for filtering and notch of specific wavelengths; the structure is larger, the manufacturing process is complex, and ultraviolet lithography technology needs to be adopted, and when preparing the micro-ring, the quality of the resonant cavity will be reduced due to the defects of the lithography process. While the structure of the present invention is simple and the process is simple.

[0125] In summary, the present invention discloses a chip-based filter based on liquid crystal, which has the following beneficial effects:

[0126] First, the present invention belongs to a chip-integrated filter, which has a simple structure, a high degree of integration, a small volume, and can achieve multi-stage cascading.

[0127] Second, the change in the arrangement of liquid crystals can achieve the functions of waveguide and microcavity filtering, which can be integrally realized by using the photo-alignment technology and can be driven by a relatively low voltage.

[0128] Third, it has a large free spectral range, can meet the usage requirements of multiple bands, achieve full coverage from the ultraviolet to the near-infrared band and the communication band, the filtered light is monochromatic light, the spectral half-width is 500 GHz, and the spectral modulation range is 380 nm to 780 nm.

[0129] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement it. However, the protection scope of the present invention cannot be limited thereby. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A liquid crystal-based chip filter, characterized in that, Comprising: A chip substrate layer, which is a liquid crystal layer with liquid crystal molecules distributed therein; A chip guiding core layer, disposed on the surface of the chip substrate layer, which is a liquid crystal layer with liquid crystal molecules distributed therein. The chip guiding core layer includes: a double straight waveguide part and a resonant cavity part that is transmission-coupled to the double straight waveguide part. The double straight waveguide part is used to achieve the input of white light or a multi-spectral light source and the output of light of any wavelength; Drive electrodes, used to drive the arrangement change of liquid crystal molecules in the chip substrate layer, the double straight waveguide part, and the resonant cavity part, and change the refractive index of the corresponding parts; The double straight waveguide part is formed by arranging liquid crystal molecules with an arrangement direction at a certain angle, forming a stepped waveguide structure; There is an angle between 0 and π between the liquid crystal molecules in the chip guiding core layer and the liquid crystal molecules in the chip substrate layer, and the liquid crystal refractive index of the chip guiding core layer is greater than the liquid crystal refractive index of the chip substrate layer, realizing total reflection propagation of light in the waveguide medium; The resonant cavity part is formed by arranging liquid crystal molecules with an arrangement direction at a certain angle, forming a stepped waveguide resonant cavity.

2. The chip filter according to claim 1, wherein The double straight waveguide part is a symmetric structure.

3. The chip filter according to claim 1, characterized in that, The resonant cavity part includes: at least two cascaded resonant micro-rings.

4. The chip-based filter according to claim 3, wherein The radius of the resonant micro-ring is above 4 um; The diameter of the double straight waveguide part is above 2 um; The overall structure of the chip-based filter is above 20 um.

5. The chip filter according to claim 3, characterized in that, The resonant micro-ring is a symmetric structure.

6. The chip filter according to claim 3, characterized in that, The resonant cavity part includes: A first resonant micro-ring, which is transmission-coupled to the input straight waveguide in the double straight waveguide part; A second resonant micro-ring, which is cascaded with the first resonant micro-ring and is transmission-coupled to the output straight waveguide in the double straight waveguide part.

7. The chip filter according to claim 6, characterized in that, The radius of the first resonant micro-ring is greater than the radius of the second resonant micro-ring.

8. The chip filter according to any one of claims 1-7, characterized in that, The liquid crystal refractive index range of the chip substrate layer and the chip guiding core layer is between 1.55 and 1.

70.

9. The chip filter according to any one of claims 1-7, characterized in that The drive electrodes include: a plurality of drive units for respectively driving the arrangement change of liquid crystal molecules in the chip substrate layer, the double straight waveguide part, and the resonant cavity part.

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