CN115236883A - Chip filter based on liquid crystal - Google Patents
Chip filter based on liquid crystal Download PDFInfo
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- CN115236883A CN115236883A CN202110428785.2A CN202110428785A CN115236883A CN 115236883 A CN115236883 A CN 115236883A CN 202110428785 A CN202110428785 A CN 202110428785A CN 115236883 A CN115236883 A CN 115236883A
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
- G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
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Abstract
The invention discloses a chip filter based on liquid crystal, which comprises: the chip substrate layer is a liquid crystal layer distributed with liquid crystal molecules; the core layer is led to the chip, sets up in chip substrate layer surface, and the core layer is led to the chip for the liquid crystal layer that distributes there is the liquid crystal molecule, and the core layer is led to the chip includes: the double-straight waveguide part is used for realizing the input of a white light or multispectral light source and the output of light with any wavelength; and the driving electrode is used for driving the arrangement change of liquid crystal molecules in the chip substrate layer, the double-straight waveguide part and the resonant cavity part and changing the refractive index of the corresponding part. The tunable filter realizes tunable filtering function by adopting modulation of liquid crystal, can cover near ultraviolet to near infrared wave bands and main communication wave bands under low-voltage driving, and has small volume and easy integration.
Description
Technical Field
The invention relates to a filter, in particular to a chip filter based on liquid crystal.
Background
Based on the recent technical needs, a narrow-band filter with excellent performance is urgently needed. Such a narrow band filter should have: small insertion loss, high sharpness, wide free spectrum range and other advantages. The filter has extremely wide application prospect in the fields of DWDM systems, all-optical switching systems and other optical communication, and also has wide application potential in multispectral imaging, high-precision spectral analysis and various sensing systems.
Because the tunable optical filter is limited by bandwidth, high cost and the like, the tunable optical filter is not put into use on a large scale, the diffraction grating is widely adopted in the optical channel performance monitoring module as the optical filter, and a plurality of detectors are needed for a plurality of diffraction wavelengths, however, for a system with a large number of channels, the number of the detectors can be greatly reduced by replacing the diffraction grating with the tunable optical filter, so that the volume of the optical channel performance monitoring module is reduced; in addition, the fixed filter has a shielding property to the out-of-band interference, and the tunable optical filter can find the out-of-band interference in the wavelength tuning process so as to make timely correction.
High-performance tunable optical filters are a topic of interest in recent years, and technologies such as dielectric films, F-P cavities, micro-ring resonant cavities, photonic crystals, fiber gratings and the like are available, but each of the tunable modes has some technical problems:
the existing visible light filter has the following problems:
for the F-P cavity filter, the fineness and the free spectral range of various F-P cavity tunable optical filters are difficult to meet the requirements of an optical channel performance monitoring module on frequency selection and tuning range.
For a dielectric film TFF filter, the dielectric film TFF filter needs to improve the isolation of a device by cascading a plurality of F-P cavities, and the stability of output optical power is influenced.
For the fiber grating type filter, when the fiber grating type filter is applied to multi-channel wave division, a large amount of FBGs are needed by adopting a cascade structure; there is an excess loss with the reflective portion of the circulator.
For the photonic crystal filter, the photonic crystal filter has a common limitation in that the photonic crystal filter can be adjusted by using an external magnetic field, an electric field and heat energy: with the increase of the energy, the wavelength of the transmission peak does not linearly move, so that tuning is not good in controllability, the transmission peak is not narrow enough, the tuning range is not wide enough, the filter structure is more complex, and actual preparation is quite difficult.
The research of the micro-ring resonant cavity filter is developing to multi-ring cascade, and the problem of accurate control of inter-ring resonance tuning and coupling coefficients needs to be solved. The photonic crystal filter has common limitations in that the tunable photonic crystal filter is realized by using an external magnetic field, an electric field and heat energy: with the increase of the energy, the wavelength of the transmission peak does not linearly move, so that tuning is not good in controllability, the transmission peak is not narrow enough, the tuning range is not wide enough, the filter structure is more complex, and actual preparation is quite difficult. Optical devices with tunable optical filters as their core are also widely used in filters, sensors and optical imaging systems, and in addition to high performance, the size of tunable optical filters is also required to be continuously miniaturized. Among various schemes, the micro-ring resonator filter is getting more and more attention and researched by technicians, and has more and more important roles in the fields of sensing detection, fast and slow light, code pattern conversion, wavelength conversion, optical fiber bearing radio waves, filters and the like.
Disclosure of Invention
In order to solve the technical problem, the invention provides a chip filter based on liquid crystal.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a liquid crystal based on-chip filter comprising:
the chip substrate layer is a liquid crystal layer distributed with liquid crystal molecules;
the core layer is led to the chip, sets up in chip substrate layer surface, and the core layer is led to the chip for the liquid crystal layer that has the liquid crystal molecule, and the core layer is led to the chip includes: the double-straight waveguide part is used for realizing the input of a white light or multispectral light source and the output of light with any wavelength:
and the driving electrode is used for driving the arrangement change of liquid crystal molecules in the chip substrate layer, the double-straight waveguide part and the resonant cavity part and changing the refractive index of the corresponding part.
The chip filter based on the liquid crystal realizes tunable filtering function by adopting the modulation of the liquid crystal, the main working wave band can cover near ultraviolet to near infrared wave bands and main communication wave bands under the drive of low voltage, and the chip filter has small volume and is easy to integrate.
On the basis of the technical scheme, the following improvements can be made:
preferably, the dual straight waveguide portion has a symmetrical structure.
The preferred scheme is adopted, so that the preparation is easy.
Preferably, the resonant cavity part comprises: at least two resonant micro-rings cascaded with each other.
By adopting the preferable scheme, the filtering effect is good.
Preferably, the radius of the resonance micro-ring is more than 4 um;
the diameter of the double straight waveguide part is more than 2 um;
the whole structure of the chip filter is more than 20 um.
By adopting the preferable scheme, the output wavelength covers the light with the wave band of 380nm to 780nm, and the output light with the visible light wave band can be tunable.
Preferably, the resonant micro-ring is a symmetrical structure.
The preparation is easy by adopting the preferable scheme.
Preferably, the cavity part comprises:
a first resonant micro-ring, the first resonant micro-ring being transmission coupled with the input straight waveguide in the dual straight waveguide section:
and the second resonance micro-ring is cascaded with the first resonance micro-ring and is in transmission coupling with the output straight waveguide in the double straight waveguide part.
By adopting the preferable scheme, the structure is simple, and the filtering effect is good.
Preferably, the radius of the first resonant micro-ring is greater than the radius of the second resonant micro-ring.
By adopting the optimized method, the filtering effect is good.
Preferably, the refractive index of the liquid crystal of the chip substrate layer and the chip core guiding layer ranges from 1.55 to 1.70.
By adopting the preferable scheme, the orientation of the liquid crystal molecules in the whole chip forms patterned arrangement by a photo-orientation technology, the refractive indexes of the chip core guide layer and the chip substrate layer are changed along with the change of the orientation mode of the liquid crystal molecules by utilizing the birefringence property and the voltage drive of the liquid crystal, and the refractive index change interval is 1.55-1.7.
Preferably, an included angle between 0 and pi is formed between the liquid crystal molecules in the chip guide core layer and the liquid crystal molecules in the chip substrate layer, and the liquid crystal refractive index of the chip guide core layer is larger than that of the chip substrate layer.
By adopting the preferable scheme, the total reflection propagation of the light in the waveguide medium is realized.
Preferably, the driving electrode includes: and the driving units are used for respectively driving the arrangement change of the liquid crystal molecules in the chip substrate layer, the double-straight waveguide part and the resonant cavity part.
By adopting the preferable scheme, the driving electrode adopts a plurality of independent control modules, and the control accuracy and the control system stability are ensured.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Fig. 1 is a schematic structural diagram of a chip filter according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a micro-ring according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a resonance mode provided by an embodiment of the present invention.
Fig. 4 is a second schematic structural diagram of a chip filter according to an embodiment of the invention.
Fig. 5 shows the arrangement of liquid crystal molecules and the patterned electrode of the first resonant micro-ring portion according to an embodiment of the present invention.
Fig. 6 shows the liquid crystal molecular arrangement and the patterned electrode of the first straight waveguide portion according to the embodiment of the present invention.
Fig. 7 is an experimental diagram of the wavelength of the output wave according to an embodiment of the present invention.
Fig. 8 is an experimental diagram of output wave wavelengths according to a second embodiment of the present invention.
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, and 3-driving electrode.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
The use of the ordinal adjectives "first", "second", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.
Also, the expression "comprising" an element is an "open" expression that merely means that there is a corresponding part and should not be interpreted as excluding additional parts.
In order to achieve the object of the present invention, in some embodiments of a liquid crystal-based on-chip filter, as shown in fig. 1, the on-chip filter comprises:
the chip substrate layer is a liquid crystal layer distributed with liquid crystal molecules;
the core layer is led to the chip, sets up in chip substrate layer surface, and the core layer is led to the chip for the liquid crystal layer that has the liquid crystal molecule, and the core layer is led to the chip includes: the double-straight waveguide part 1 and the resonant cavity part 2 are in transmission coupling with the double-straight waveguide part 1, and the double-straight waveguide part 1 is used for realizing the input of a white light or multispectral light source and the output of light with any wavelength:
and the driving electrode 3 is used for driving the arrangement change of liquid crystal molecules in the chip substrate layer, the double-straight waveguide part 1 and the resonant cavity part 2 and changing the refractive index of the corresponding part.
Wherein the double straight waveguide portion 1 includes: a first straight waveguide portion 11 provided at an input end of the resonator portion 2 and a second straight waveguide portion 12 provided at a downstream end of the resonator portion 2.
Liquid crystal is used as an optical transmission and modulation medium in the photonic chip, the functions of the double-straight waveguide part 1 and the resonant cavity part 2 are realized by arranging the molecular direction of the liquid crystal micro-region, the refractive index of the waveguide medium is adjustable by utilizing the electro-optic modulation effect of the liquid crystal, and the wavelength tunable of the filter is realized
The input light source is: white light or multi-spectral light sources, which include the near infrared band to the near ultraviolet band, the input light may be a mixed light source, but only light of a specific band can be coupled into the structure of the cavity portion 2. Input light is coupled into a core guide layer formed by liquid crystal molecules in a transmission coupling mode, 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.
The output end of the dual straight waveguide part 1 can be provided with a detection element such as a spectrometer, and the detection range can include a near infrared band to a near ultraviolet band.
The chip filter based on the liquid crystal realizes tunable filtering function by adopting the modulation of the liquid crystal, the main working wave band can cover near ultraviolet to near infrared wave bands and main communication wave bands under the drive of low voltage, and the chip filter has small volume and is easy to integrate.
In order to further optimize the implementation effect of the present invention, in other embodiments, the rest features are the same, except that the dual-straight waveguide portion 1 has a symmetrical structure.
The preferred scheme is adopted, so that the preparation is easy.
In order to further optimize the effect of the present invention, in other embodiments, the remaining features are the same, except that the resonator portion 2 includes: at least two resonant micro-rings cascaded to each other.
By adopting the preferable scheme, the filtering effect is good.
Further, the radius of the resonance micro-ring is more than 4 um;
the diameter of the double straight waveguide part 1 is more than 2 um;
the whole structure of the chip filter is more than 20 um.
By adopting the preferable scheme, the output wavelength covers the light with the wave band of 380nm to 780nm, and the output light with the visible light wave band can be tunable.
Because the resonant frequency of resonance micro-ring is decided by the effective refractive index of resonant cavity, radius, resonance wavelength progression, and the change range of effective refractive index is limited, the change range of the radius of resonant cavity and resonance wavelength progression is great, so in order to realize that the output light of visible light wave band is tunable, the radius of resonance micro-ring needs to reach more than 4um, the diameter of the double straight waveguide part 1 needs to reach more than 2um, the overall structure of the filter needs to reach more than 20um, the output end wavelength covers 380nm to 780nm wave band.
And after the radius of the resonant micro-ring resonant cavity is determined, the effective refractive index of the resonant micro-ring resonant cavity is adjusted by voltage driving, and at the moment, the order of the resonant wavelength changes, so that the modulation of the resonant wavelength is realized. The precision of the optical orientation technology of the liquid crystal molecules can reach 0.1um, so the structural precision of the filter can also reach 0.1um. 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, so that the distance between the resonant micro-ring and the straight waveguide and the distance between different resonant micro-rings can reach more than 0.1um.
Further, the resonance micro-ring is of a symmetrical structure.
The preparation is easy by adopting the preferable scheme.
In order to further optimize the effect of the present invention, in other embodiments, the remaining features are the same, except that the resonator portion 2 includes:
a first resonant microring 21, the first resonant microring 21 being in transmission coupling with the input straight waveguide in the dual straight waveguide section 1;
and a second resonant micro-ring 22, the second resonant micro-ring 22 being cascaded with the first resonant micro-ring 21 and being in transmission coupling with the output straight waveguide in the dual straight waveguide section 1.
By adopting the preferable scheme, the structure is simple, and the filtering effect is good.
Further, the radius of the first resonant micro-ring 21 is larger than the radius of the second resonant micro-ring 22.
By adopting the optimized method, the filtering effect is good.
The plane structure of the cavity portion 2 includes, but is not limited to, the cascade connection mode in the above embodiments, and the cascade connection mode includes multiple integration modes such as series integration, parallel integration, multi-stage integration, and array integration. Different cascading modes may have the advantages of expanding the free spectral range, reducing crosstalk, having a flat pass band, high stability, small dispersion and the like, but may also have the problems of loss caused by center wavelength mismatch, high processing precision requirement, stability reduction caused by temperature polarization and the like. Different cascading modes comprise respective advantages and disadvantages, a series integration mode is adopted in the embodiment, performance indexes in all aspects are excellent, but preparation difficulty is high, and different cascading modes can be completed through the same liquid crystal photo-orientation technology in different application scenes.
Filtering incident light by using a micro-ring structure of a double-straight waveguide, so that the chip filter outputs tunable light; the driving electrode 3 is used for modulating the waveguide medium, so that the effective refractive index of the resonant cavity part 2 is changed, and monochromatic light with any wavelength is output.
The double-straight waveguide part 1 is formed by arranging liquid crystal molecules with certain included angles in the arrangement direction to form a stepped waveguide structure, and the refractive index of liquid crystal of the core layer of the chip is larger than that of liquid crystal of the substrate layer, so that the total reflection propagation of light in a waveguide medium is realized.
The resonant cavity part 2 is formed by arranging liquid crystal molecules with certain included angles in the arrangement direction to form a stepped waveguide resonant cavity.
Light is coupled into the first resonant micro-ring 21 resonant cavity from the first straight waveguide portion 11 at the input end of the resonant cavity portion 2 and is oscillated and propagated in the resonant cavity, and the first resonant micro-ring 21 resonant cavity and the second resonant micro-ring 22 resonant cavity are resonated, so that the wave propagated in the first resonant micro-ring 21 resonant cavity is coupled into the second resonant micro-ring 22 resonant cavity and is oscillated and propagated in the resonant cavity. The wave in the resonant cavity of the second resonant micro-ring 22 is finally coupled into the second straight waveguide part 12 at the lower end, and is output from the lower end, and monochromatic light with a set wavelength is output through structural design and parameter matching.
Free Spectral Range (FSR), refers to the spectral range between two resonant wavelengths. The definition of FSR is:
wherein
Is the length of the resonant cavity, and λ m is the resonant wavelength of the resonant cavity
R is the radius of the resonant cavity, m is the resonance frequency, n eff Is the effective refractive index of the resonant cavity.
The total FSR of two different radius micro-ring filters can be expressed as: m is a unit of 1 FSR 1 ＝m 2 FSR 2 ＝FSR total . Resonant wave lambda exists in the resonant cavity of the first resonant micro-ring 21 1 After the resonant cavity of the first resonant micro-ring 21 and the resonant cavity of the second resonant micro-ring 22 are resonated, a resonant wave lambda exists in the resonant cavity of the second resonant micro-ring 22 2 The condition of resonance is
At this time, the resonant wave λ in the resonant cavity of the second resonant micro-ring 22 2 And finally coupled into the second straight waveguide portion 12 at the drop end, and output from the drop end. When R is 1 、R 2 When determined，n 1 、n 2 To output modulated λ 'upon change' 1 、λ′ 2 Then m 'of match needs to be found' 1 、m′ 2 I.e. the frequency selection process.
In order to further optimize the implementation effect of the invention, in other embodiments, the rest of the characteristic technologies are the same, except that the refractive index of the liquid crystal of the chip substrate layer and the chip guide core layer is in a range of 1.55-1.70.
By adopting the preferable scheme, the orientation of the liquid crystal molecules in the whole chip forms patterned arrangement by a photo-orientation technology, the refractive indexes of the chip core guide layer and the chip substrate layer are changed along with the change of the orientation mode of the liquid crystal molecules by utilizing the birefringence property and the voltage drive of the liquid crystal, and the refractive index change interval is 1.55-1.7.
In order to further optimize the implementation effect of the invention, in other embodiments, the other characteristic techniques are the same, except that an included angle between the liquid crystal molecules in the chip guide core layer and the liquid crystal molecules in the chip substrate layer is between 0 and pi, and the liquid crystal refractive index of the chip guide core layer is greater than that of the chip substrate layer.
By adopting the preferable scheme, the total reflection propagation of the light in the waveguide medium is realized.
In order to further optimize the effect of the present invention, in other embodiments, the remaining features are the same, except that the driving electrode 3 includes: and the driving units are used 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.
By adopting the preferable scheme, the driving electrode 3 adopts a plurality of independent control modules, and the control accuracy and the control system stability are ensured.
The drive electrode 3 adopts a patterned electrode, and realizes the change of the refractive index of the waveguide medium by modulating liquid crystal molecules, thereby realizing the modulation of the output wavelength. Further, the driving electrode 3 material may be, but is not limited to, ITO glass. The electrode patterning mode can be realized by carrying out patterning orientation on the ITO glass, so that the electrode patterns correspond to the liquid crystal arrangement patterns, and the electrode patterning and the liquid crystal patterning alignment can be realized by an area exposure mode.
The driving electrode 3 can be modulated in various ways, such as voltage modulation, temperature modulation, magnetic field modulation, optical field modulation or coexistence of various modulation ways.
Two driving modes are briefly described below:
the other is electric field drive of electrodes, liquid crystal molecules are driven to rotate by applying voltage by utilizing the electro-optic effect of liquid crystal, the effective refractive index of the resonant cavity part 2 is changed and the resonant wavelength is changed by changing the arrangement directions of the liquid crystal molecules in the chip guide core layer resonant cavity part 2 and the chip substrate layer, and the filter has a switch by changing the arrangement direction of the liquid crystal molecules in the chip guide core layer double-straight waveguide part 1.
One is to mix a photosensitive material (such as an azo material), under the modulation of an optical field, the photosensitive material brings the rotation of liquid crystal molecules of the chip conducting layer and the chip substrate layer, and when the optical field is driven, the focusing and the wavelength of driving light are controlled to correspond to the photosensitive material.
The driving unit for driving the first straight waveguide portion 11 can control whether incident light can propagate in the first straight waveguide portion 11, an aperture angle of the incident light, and a transmission coupling coefficient between the resonant micro-rings, while the driving unit for driving the second straight waveguide portion 12 can control the intensity of the output light and the transmission coupling coefficient between the resonant micro-rings, and the driving unit for driving each resonant micro-ring of the resonant cavity portion 2 can control an effective refractive index of each micro-ring resonant cavity, so that a resonant condition of the resonant cavity is changed, and further a resonant wavelength and a filtering range are changed.
The various embodiments above may be implemented in cross-parallel.
For a better understanding of the foregoing, a description of the principles follows.
The transmission-type structure resonant cavity is formed by coupling two straight waveguides and a micro-ring, and a coupling structure model is shown in figure 2. The transmission resonant cavity has two output ends, namely a through end and a drop end. Let the input laser be E 1 In the coupling region haveA part of the light energy is directly output through the straight waveguide, i.e. the straight end of the resonant cavity, denoted as E 2 (ii) a The other part of the light energy is coupled into the resonant cavity and is recorded as E 4 The part of light is transmitted around the ring in the cavity, and when the part of light energy passes through the coupling region each time, a part of light energy is coupled to the straight waveguide and is output through a downstream port of the resonant cavity, which is marked as E 5 (ii) a And the other part of the light continues to transmit around the ring, denoted as E 3 Eventually forming a closed loop of light.
In the steady state, the light passing through the two coupling regions will reach a dynamic equilibrium state. Expressed by the resonance formula of the resonant cavity, the resonant frequency is as follows:
as shown in fig. 3, the resonant modes circulate in the resonators and may interact in the coupled whispering gallery mode cavity. In the case of strong interactions, one cavity can be seen as the spectral fidelity value of the resonance wavelength of the other cavity. Thus, when the resonance conditions of the two isolated cavities are met, some resonance modes are enhanced while others are attenuated, a phenomenon known as the vernier effect. The conditional formula for resonance is:
on the basis of the above embodiments, two specific embodiments are mentioned.
The first embodiment is as follows:
electro-optical modulation driving of liquid crystal with a double-ring structure is adopted to realize various functions of the microcavity filter, and the adopted cascade mode is shown in figure 4. The effective refractive index range of the liquid crystal of the chip core guide layer and the chip substrate layer can reach 1.55-1.70, and the change of the effective refractive index can reach about 0.2.
As shown in fig. 5 and 6, the three waveguide structures of the first resonant microring 2131, the second resonant microring 2232 and the double straight waveguide portion 1 are all symmetrical structures, the liquid crystal arrangement modes of all portions are all vertically arranged to achieve the purpose of maximum modulation amount, and the bottom of the integrated chip has patterned electrodes to achieve voltage modulation of liquid crystal molecules.
The incident of natural light is adopted, the refractive index of a medium of the double-straight waveguide part 1 is 1.7, the refractive index of an external medium is 1.55, a three-layer waveguide structure is formed, and the incident light is incident from an incident end and is propagated by total reflection.
The first straight waveguide part 11 has a medium refractive index n 2 The refractive index of its external medium is n 1 ；
The refractive index of the external medium of the first resonant micro-ring 21 is n 3 N 'as its internal refractive index' 3 Effective refractive index of n 4 ；
The refractive index of the medium outside the second resonant micro-ring 22 is n 5 And its internal matrix refractive index is n' 5 Effective refractive index of n 6 ；
The second straight waveguide portion 12 has a medium refractive index n 8 The refractive index of its external medium is n 7 。
The radius of the first resonance micro-ring 21 is 10um, and the initial effective refractive index is n 4 =1.600, and the spacing between the first optical straight waveguide portion is 100nm. From the resonant formula of the resonant cavity
It can be seen that the resonant wave coupled into the first resonant micro-ring 21 has a wavelength of 502nm and a modulus of 200.
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. Relation of resonance
It can be seen that the radius of the second resonant micro-ring 22 is 5um, the initial refractive index effective refractive index is 1.600, and the spacing between the first resonant micro-rings 21 is 100nm.
Also from the formula of resonance of the resonant cavity
It can be seen that the resonant wave coupled into the second resonant microring 22 has a wavelength of 502nm and a modulus of 100.
The distance between the second resonant micro-ring 22 and the second straight waveguide portion 12 at the downstream end is 100nm, the resonant wave is coupled into the second straight waveguide portion 12 and is transmitted by total reflection, and a monochromatic wave of 502nm is output from the second straight waveguide portion 12, so as to realize a filtering function, as shown in fig. 7.
The liquid crystal can be electro-optically modulated by the patterned electrode, so that the effective refractive indexes of the dual-straight waveguide part 1 and the resonant cavity part 2 are changed, the wavelength of resonant waves can be obviously changed, and the dynamic modulation function is realized.
In the second embodiment, the effective refractive index of the first resonant microring 21 is changed to 1.700, the wavelength of the resonant wave is changed to 628nm, and the modulus is changed to 170, while the effective refractive index of the second resonant microring 22 is changed to 1.700, the wavelength of the resonant wave is changed to 628nm, and the modulus is changed to 85, and the monochromatic light wavelength at the output end is also changed to 628nm, so that the frequency conversion function of the filter is completed, as shown in fig. 8. The refractive indexes of the first resonant micro-ring 21 and the second resonant micro-ring 22 can be different according to the difference of the applied voltages of the two, so as to realize the modulation of other wavelengths.
The invention relates to a tunable filter based on liquid crystal, wherein the spectrum of the filter comprises a near infrared band to a near ultraviolet band, but the output light is monochromatic light, the half width of the spectrum is 500GHz, and the wavelength range of the output light is 380nm to 780nm. The invention can realize the dynamic modulation output function of laser tunable broadband wavelength, the main working waveband can cover the near ultraviolet to near infrared waveband and the optical communication waveband under the drive of low voltage, and the invention has small volume and easy integration.
Compared with the similar micro-ring filter, the micro-ring filter has the following differences.
Compared with a frequency-selecting filter of a micro-ring resonant cavity based on KDP crystals, the KDP crystals adopt electro-optic modulation, are not as diverse as liquid crystal materials, can realize various modulation modes such as an electric field, an optical field, a magnetic field, temperature and the like, and can be further used under more complicated conditions; KDP crystal is larger in size, and the liquid crystal disclosed by the invention is of a planar structure and is easier to integrate.
Compared with a first-order or high-order annular filter based on SOI, the refractive index of the SOI structure cannot be tuned, and only can be used for filtering and trapping of specific wavelength; the structure is large, the manufacturing process is complex, an ultraviolet photoetching technology is needed, and when the micro-ring is manufactured, the quality of the resonant cavity is reduced due to the defects of the photoetching technology. The invention has simple structure and simple process.
In summary, the invention discloses a liquid crystal-based chip filter, which has the following beneficial effects:
the invention belongs to a chip integrated filter, has simple structure, high integration degree and small volume and can realize multistage cascade.
Secondly, the arrangement change of the liquid crystal can realize the functions of wave guide and microcavity filtering, the integration of the functions can be realized by utilizing the photo-orientation technology, and the liquid crystal can be driven by lower voltage.
Thirdly, the free spectral range is large, the use requirements of various wave bands can be met, the full coverage of ultraviolet to near infrared wave bands and communication wave bands is realized, the filtered light is monochromatic light, the half width of the spectrum is 500GHz, and the spectral modulation range is 380nm to 780nm.
The above-mentioned embodiments are only for illustrating the technical idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention, and all equivalent changes or modifications made according to the spirit of the present invention should be covered in the protection scope of the present invention.
Claims (10)
1. A liquid crystal-based on-chip filter, comprising:
the chip substrate layer is a liquid crystal layer distributed with liquid crystal molecules;
the chip leads the sandwich layer, set up in chip substrate layer surface, the sandwich layer is for distributing the liquid crystal layer of liquid crystal molecule for the chip, the sandwich layer is led to the chip includes: the double-straight waveguide part is used for realizing the input of a white light or multispectral light source and the output of light with any wavelength;
and the driving electrode is used for driving the arrangement change of the liquid crystal molecules in the chip substrate layer, the double-straight waveguide part and the resonant cavity part to change the refractive index of the corresponding part.
2. The on-chip filter of claim 1, wherein the dual straight waveguide section is a symmetric structure.
3. The on-chip filter of claim 1, wherein the cavity section comprises: at least two resonant micro-rings cascaded to each other.
4. The on-chip filter of claim 3,
the radius of the resonance micro-ring is more than 4 um;
the diameter of the double straight waveguide part is more than 2 um;
the whole structure of the chip filter is more than 20 um.
5. The on-chip filter of claim 3, wherein the resonant micro-ring is a symmetric structure.
6. The on-chip filter of claim 3, wherein the cavity section comprises:
a first resonant microring in transmission coupling with an input straight waveguide in the dual straight waveguide section;
a second resonant microring cascaded with the first resonant microring and in transmission coupling with an output straight waveguide in the dual straight waveguide section.
7. The on-chip filter of claim 6, wherein the radius of the first resonant micro-ring is greater than the radius of the second resonant micro-ring.
8. The on-chip filter according to any one of claims 1-7, wherein the refractive index of the liquid crystal of the chip substrate layer and the chip guide core layer is in the range of 1.55-1.70.
9. The on-chip filter according to any one of claims 1 to 7, wherein an angle between liquid crystal molecules in the chip conducting core layer and liquid crystal molecules in the chip substrate layer is from 0 to pi, and a liquid crystal refractive index of the chip conducting core layer is greater than a liquid crystal refractive index of the chip substrate layer.
10. The on-chip filter according to any one of claims 1-7, wherein the driving electrode comprises: and the driving units are used for respectively driving the liquid crystal molecule arrangement change in the chip substrate layer, the double-straight waveguide part and the resonant cavity part.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110428785.2A CN115236883A (en) | 2021-04-22 | 2021-04-22 | Chip filter based on liquid crystal |
| PCT/CN2021/098064 WO2022222235A1 (en) | 2021-04-22 | 2021-06-03 | Liquid crystal-based chip filter |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110428785.2A CN115236883A (en) | 2021-04-22 | 2021-04-22 | Chip filter based on liquid crystal |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5361320A (en) * | 1993-02-19 | 1994-11-01 | University Of Colorado Foundation | Liquid crystal fiber waveguide |
| US20070071394A1 (en) * | 2003-12-24 | 2007-03-29 | Faccio Daniele F A | Low loss microring resonator device |
| KR20060121438A (en) * | 2005-05-24 | 2006-11-29 | 엘지전자 주식회사 | Micro ring optical resonator and fabricating method thereof |
| US7783144B2 (en) * | 2006-04-24 | 2010-08-24 | The Hong Kong University Of Science And Technology | Electrically tunable microresonators using photoaligned liquid crystals |
| CN101840029B (en) * | 2010-04-28 | 2012-07-11 | 中国科学院半导体研究所 | Integrated reconfigurable optical add-drop multiplexer |
| CN102841407B (en) * | 2012-09-20 | 2014-06-04 | 电子科技大学 | Waveguide type polarizing beam splitter |
| CN103760699B (en) * | 2014-02-19 | 2016-08-17 | 华中科技大学 | Micro annular resonant cavity type adjustable light wave-filter based on liquid crystal narrow slit wave-guide |
| CN107991738B (en) * | 2017-12-08 | 2019-11-22 | 华中科技大学 | A kind of silicon substrate multifunctional reconfigurable optical filter |
| CN214411755U (en) * | 2021-04-22 | 2021-10-15 | 苏州大学 | Tunable laser based on liquid crystal |
| CN214409494U (en) * | 2021-04-22 | 2021-10-15 | 苏州大学 | Chip filter based on liquid crystal |
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