CN115241729A - Tunable laser based on liquid crystal - Google Patents

Tunable laser based on liquid crystal Download PDF

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CN115241729A
CN115241729A CN202110438791.6A CN202110438791A CN115241729A CN 115241729 A CN115241729 A CN 115241729A CN 202110438791 A CN202110438791 A CN 202110438791A CN 115241729 A CN115241729 A CN 115241729A
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liquid crystal
straight waveguide
light
resonant
core layer
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张新君
黄文彬
吴佳辰
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Suzhou University
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Suzhou University
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Priority to PCT/CN2021/098062 priority patent/WO2022222234A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1686—Liquid crystal active layer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/0813—Configuration of resonator
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials

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  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Liquid Crystal (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

The invention discloses a tunable laser based on liquid crystal, comprising: pump light source and photon chip, photon chip includes: the liquid crystal display panel comprises a liquid crystal substrate layer, a liquid crystal core layer and a driving electrode, wherein the liquid crystal core layer is arranged on the surface of the liquid crystal substrate layer; the liquid crystal conducting core layer is distributed with: the input end of the optical transmission straight waveguide is used for inputting a pumping light source; the output end of the light output straight waveguide is used for outputting light with any wavelength; a resonant cavity, comprising: one or more cascaded resonant micro-cavities, which are respectively coupled with the optical transmission straight waveguide and the optical output straight waveguide in a transmission way; the driving electrode is used for driving liquid crystal molecules in the liquid crystal substrate layer, the light transmission straight waveguide part of the liquid crystal core layer, the light output straight waveguide part and the resonant cavity part to change in arrangement, and the refractive index of the corresponding parts is changed. The invention discloses a tunable laser based on liquid crystal, which has the advantages of simple structure, high integration degree, small volume, realization of multi-stage cascade and high output efficiency.

Description

Tunable laser based on liquid crystal
Technical Field
The invention relates to a laser, in particular to a tunable laser based on liquid crystal.
Background
The optical microcavity of the Whispering-Gallery mode (WGM for short) utilizes the principle of optical total reflection to realize strong limitation on the optical field, so that a mode with a higher quality factor is generated in the resonant cavity, and the optical field is well constrained in the micron order. Therefore, the WGM optical microcavity device is considered to have very wide application prospects in the fields of nonlinear optics, optical communication, optical sensing detection and the like. Optical microcavity lasers are increasingly gaining attention because of their small mode size, low power consumption, high speed, ease of integration, and the like.
The tunable laser is a key component of modern optical fiber communication systems, optical sensing systems and spectral analysis systems, and mainly comprises a pumping source, a resonant cavity, a gain medium and a tunable filter. The structure, material, process and other parameters of the resonant cavity, the gain medium and the tunable filter all affect the tuning effect and the working efficiency of the laser.
The traditional tunable optical microcavity laser has the following problems:
1) The tunable optical microcavity Raman laser adopts acousto-optic modulation, so that the fineness and the free spectral region cannot simultaneously meet the requirements of miniaturization, high efficiency and easy integration.
2) The tunable optical microcavity doped laser needs to be tuned by using a fiber grating or a fiber ring mirror and is greatly influenced by the outside.
Disclosure of Invention
In order to solve the technical problem, the invention provides a tunable laser based on liquid crystal.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a liquid crystal-based tunable laser, comprising: pump light source and photon chip, photon chip includes: the liquid crystal display panel comprises a liquid crystal substrate layer, a liquid crystal core layer and a driving electrode, wherein the liquid crystal core layer is arranged on the surface of the liquid crystal substrate layer;
the liquid crystal guide core layer is a liquid crystal layer doped with a gain medium, and the liquid crystal guide core layer is distributed with:
the input end of the optical transmission straight waveguide is used for inputting a pumping light source;
the output end of the light output straight waveguide is used for outputting light with any wavelength;
a resonant cavity, comprising: one or more mutually cascaded resonant microcavities, the resonant cavities being in transmission coupling with the optical transmission straight waveguide and the optical output straight waveguide, respectively;
the driving electrode is used for driving liquid crystal molecules in the liquid crystal substrate layer, the light transmission straight waveguide part of the liquid crystal core layer, the light output straight waveguide part and the resonant cavity part to be arranged and changed, and the refractive index of the corresponding part is changed.
The invention discloses a tunable laser based on liquid crystal, which belongs to a chip integrated laser, has simple structure, high integration degree and small volume, can realize multi-stage cascade and has high output efficiency.
On the basis of the technical scheme, the following improvements can be made:
preferably, the liquid crystal refractive index variation ranges of the liquid crystal substrate layer and the liquid crystal core layer are both between 1.55 and 1.7.
By adopting the preferable scheme, the tunable wavelength can be effectively realized.
As a preferred scheme, an included angle exists between liquid crystal molecules in the liquid crystal guide core layer and liquid crystal molecules in the liquid crystal substrate layer, and the included angle is 0-pi.
By adopting the preferable scheme, the total reflection propagation of light in the waveguide medium and the gain medium is realized, wherein the waveguide medium is a liquid crystal material, and the gain material is a material with optical gain, such as dye, perovskite material, conjugated polymer and the like.
Preferably, the liquid crystal refractive index of the liquid crystal core guiding layer is larger than that of the liquid crystal substrate layer.
By adopting the preferable scheme, the total reflection propagation of the light in the waveguide medium and the gain medium is realized.
Preferably, the radius of the resonant microcavity is more than 4 um;
the diameter of the light transmission straight waveguide and/or the light output straight waveguide is more than 2 um;
the whole structure of the tunable laser is above 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 liquid crystal core layer is further distributed with:
the input end of the optical transmission straight waveguide is used for inputting a pumping light source;
a filter, comprising: one or more cascaded filtering micro-cavities, the filter is respectively coupled with the light input straight waveguide and the light transmission straight waveguide in a transmission way.
By adopting the preferable scheme, the output efficiency is improved, and the filtering operation is performed on the incident light.
Preferably, the driving electrode includes:
the resonant cavity driving electrode is used for driving the liquid crystal molecules in the resonant cavity part of the liquid crystal conducting core layer to change in arrangement;
the straight waveguide driving electrode is used for driving liquid crystal molecules in the liquid crystal guide layer light transmission straight waveguide part, the light output straight waveguide part and the light input straight waveguide part to be arranged and changed;
and the substrate layer driving electrode is used for driving the liquid crystal molecules in the liquid crystal substrate layer to be arranged and changed.
By adopting the preferable scheme, the driving electrode adopts a plurality of independent control modules, so that the control accuracy and the stability of a control system are ensured.
Preferably, the driving electrode is ITO glass having an electrode pattern corresponding to the distribution of each portion on the liquid crystal core layer.
With the above preferred arrangement, driving can be performed efficiently.
Preferably, the resonant microcavity or the filtering microcavity has one or more of the following structures:
an annular microcavity structure, a triangular microcavity structure, a square microcavity structure, a hexagonal microcavity structure, an elliptical microcavity structure, or a stadium-type microcavity structure.
With the above preferred scheme, resonance or filtering can be achieved.
As a preferred scheme, a plurality of resonant microcavities or filtering microcavities are cascaded in one or more modes of series integration, parallel integration, multi-section integration and array integration.
With the above preferred scheme, a suitable integration mode is selected according to specific situations.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required 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 those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is a schematic structural diagram of a tunable laser 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 in an embodiment of the present invention.
Fig. 4 is a second schematic structural diagram of a tunable laser according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of an arrangement of liquid crystal molecules and a 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 light-transmitting 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-optical transmission straight waveguide, 2-optical output straight waveguide, 3-resonant cavity, 31-first resonance micro-ring, 32-second resonance micro-ring, 4-filter, 41-first filtering micro-ring 42-second filtering micro-ring, 5-optical input straight waveguide, and 6-drive 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.
To achieve the object of the present invention, in some embodiments of a tunable liquid crystal-based laser, as shown in fig. 1, a tunable liquid crystal-based laser includes: pump light source and photonic chip, the photonic chip includes: the liquid crystal display device comprises a liquid crystal substrate layer, a liquid crystal core layer arranged on the surface of the liquid crystal substrate layer and a driving electrode 6;
the liquid crystal conducting core layer is a liquid crystal layer doped with a gain medium, and the liquid crystal conducting core layer is distributed with:
the optical transmission straight waveguide 1, the input end of the optical transmission straight waveguide 1 is used for inputting a pumping light source;
the output end of the light output straight waveguide 2 is used for outputting light with any wavelength;
a resonant cavity 3, comprising: one or more cascaded resonant microcavities, wherein the resonant cavity 3 is respectively coupled with the optical transmission straight waveguide 1 and the optical output straight waveguide 2 in a transmission way;
the driving electrode 6 is used for driving liquid crystal molecules in the liquid crystal substrate layer, the light transmission straight waveguide part of the liquid crystal core layer, the light output straight waveguide 2 part and the resonant cavity 3 part to change arrangement, and changing the refractive index of the corresponding part.
The laser can emit laser light spontaneously through resonance by adding a pumping light source.
The gain material may be a material having an optical gain, such as a dye, a perovskite material, or a conjugated polymer.
The pumping light source is input from the input end of the light transmission straight waveguide 1, the light transmission straight waveguide 1 is in transmission coupling with the resonant cavity 3, the resonant cavity 3 is also in transmission coupling with the light output straight waveguide 2, and the output end of the light output straight waveguide 2 outputs light with any wavelength.
The pump source wavelength may be monochromatic or mixed. The pumping light source comprises a near infrared band to a near ultraviolet band, the input light can be a mixed light source, but only the light with a specific band can be coupled into the resonant microcavity of the resonant cavity 3. Input light is coupled into a liquid crystal guide core 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 straight waveguide and the resonant cavity 3.
The functions of the waveguide and the resonant cavity 3 can be realized by the arrangement change of the liquid crystal, the integrated realization by the photo-alignment technology is realized, and the drive can be realized by lower voltage. Liquid crystal is used as an optical transmission and modulation medium in the photonic chip, functions of waveguide, a resonant cavity 3 and the like are realized by arranging liquid crystal micro-area molecular orientation, the refractive indexes of the waveguide medium and the gain medium are adjustable by utilizing the electro-optic modulation effect of the liquid crystal, and the wavelength of the laser can be tuned.
The resonant cavity 3, the optical transmission straight waveguide 1 and the optical output straight waveguide 2 adopt a transmission coupling mode, and the transmission coupling coefficient is controlled by controlling the distance between the straight waveguide and the resonant cavity 3. The output end of the light output straight waveguide 2 can be placed with a detection element such as a spectrometer, and the detection range comprises a near infrared band to a near ultraviolet band.
The invention discloses a tunable laser based on liquid crystal, which belongs to a chip integrated laser, has the advantages of simple structure, high integration degree, small volume, capability of realizing multistage cascade, high output efficiency and large free spectral range, can meet the use requirements of various wave bands, and realizes full coverage of ultraviolet to near-infrared wave bands.
In order to further optimize the implementation effect of the invention, in other embodiments, the rest of the characteristic techniques are the same, except that the liquid crystal refractive indexes of the liquid crystal substrate layer and the liquid crystal core layer are all varied within a range of 1.55 to 1.7.
By adopting the preferable scheme, the orientation of the liquid crystal molecules on the whole chip forms patterned arrangement by the optical orientation technology, the refractive indexes of the liquid crystal core layer and the liquid crystal 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, the refractive index change interval is 1.55-1.7, and the wavelength tuning can be effectively realized.
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 exists between the liquid crystal molecules in the liquid crystal guide core layer and the liquid crystal molecules in the liquid crystal substrate layer, and the included angle is 0 to pi.
By adopting the preferable scheme, the total reflection propagation of the light in the waveguide medium and the gain medium is realized.
In order to further optimize the implementation effect of the invention, in other embodiments, the rest of the characteristic techniques are the same, except that the refractive index of the liquid crystal in the liquid crystal core layer is greater than that of the liquid crystal in the liquid crystal substrate layer.
By adopting the preferable scheme, the total reflection propagation of the light in the waveguide medium and the gain medium is realized.
In order to further optimize the implementation effect of the invention, in other embodiments, the rest of the characteristic techniques are the same, except that the radius of the resonant microcavity is more than 4 um;
the diameter of the light transmission straight waveguide 1 and/or the light output straight waveguide 2 is more than 2 um;
the whole structure of the tunable laser is above 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 resonant cavity 3 is decided by resonant cavity 3's effective refractive index, radius, resonance wavelength progression, and the change range of effective refractive index is limited, resonant cavity 3's radius and resonance wavelength progression change range are great, so in order to realize that the output light of visible light wave band is tunable, the radius of resonance microcavity need reach more than 4um, the diameter of straight waveguide need reach more than 2um, tunable laser's overall structure need reach more than 20um, just can effectively output wavelength 380nm to 780nm wave band light.
When the radius of the resonant cavity 3 is determined, the effective refractive index of the resonant cavity 3 is adjusted by voltage drive, and at the moment, the resonant wavelength progression changes, so that the modulation of the resonant wavelength is realized, and the dynamic modulation of the broadband wavelength of the laser is realized. The precision of the optical orientation technology of the liquid crystal molecules can reach 0.1um, so the structural precision of the laser can also reach 0.1um. The smaller the distance between the resonant cavity 3 and the straight waveguide and the smaller the distance between different resonant microcavities are, the larger the transmission coupling coefficient is, so that the distance between the resonant cavity 3 and the straight waveguide and the distance between different resonant microcavities can reach more than 0.1um.
In order to further optimize the implementation effect of the present invention, in other embodiments, the rest features are the same, except that:
the input end of the optical transmission straight waveguide 1 is used for inputting a pumping light source;
a filter 4, comprising: one or more mutually cascaded filtering micro-cavities, and a filter 4 is respectively in transmission coupling with the light input straight waveguide 5 and the light transmission straight waveguide 1.
By adopting the preferable scheme, the output efficiency is improved, and the filtering operation is performed on the incident light.
The tunable filter 4 in the existing tunable laser needs to introduce an additional optical device, so that the complexity and the insertion loss of a system are increased.
Further, the driving electrode includes:
the resonant cavity driving electrode is used for driving the liquid crystal molecules in the resonant cavity part of the liquid crystal core layer to change the arrangement;
the straight waveguide driving electrode is used for driving liquid crystal molecule arrangement change in the liquid crystal guide layer light transmission straight waveguide 1 part, the light output straight waveguide 2 part and the light input straight waveguide 5 part;
and the substrate layer driving electrode is used for driving the liquid crystal molecules in the liquid crystal substrate layer to be distributed and changed.
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.
Furthermore, the driving electrode is ITO glass with electrode patterns, and the electrode patterns correspond to the distribution of each part on the liquid crystal conducting core layer.
With the above preferred arrangement, driving can be performed efficiently.
The driving electrode is 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 on the liquid crystal core layer. The electrode patterning and liquid crystal patterning alignment can be realized by an area exposure mode. The driving electrodes can adopt, but are not limited to, the following two driving modes:
one is electric field drive of the electrode, the electro-optic effect of the liquid crystal is utilized to drive liquid crystal molecules to rotate by applying voltage, the arrangement direction of the liquid crystal molecules in the resonant cavity 3 part of the liquid crystal core layer and the liquid crystal substrate layer is changed, so that the effective refractive index of the resonant cavity 3 is changed, and further the resonant wavelength is changed, and the arrangement direction of the liquid crystal molecules in the optical transmission straight waveguide 1 part of the liquid crystal core layer is changed, so that a switch is arranged between the filter 4 and a laser part which does not comprise the filter 4;
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 in the liquid crystal core layer and the liquid crystal 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.
Further, the straight waveguide driving electrode of the optical transmission straight waveguide 1 can control whether incident light can be transmitted in the straight waveguide, the aperture angle of the incident light and the transmission coupling coefficient between the resonant microcavities, the straight waveguide driving electrode of the optical output straight waveguide 2 can control the intensity of the output light and the transmission coupling coefficient between the resonant microcavities, and the resonant cavity driving electrode can control the effective refractive index of each resonant microcavity, so that the resonant condition of the resonant cavity 3 is changed, and the resonant wavelength and the laser output range are further changed.
In order to further optimize the implementation effect of the invention, in other embodiments, the rest of the features are the same, except that the structure of the resonant microcavity or the filtering microcavity is one or more of the following:
the micro-cavity structure comprises complex micro-cavity structures such as an annular micro-cavity structure, a triangular micro-cavity structure, a square micro-cavity structure, a hexagonal micro-cavity structure, an elliptical micro-cavity structure and a stadium type micro-cavity structure.
With the above preferred scheme, resonance or filtering can be achieved.
In order to further optimize the implementation effect of the invention, in other embodiments, the rest features are the same, except that a plurality of resonant micro-cavities or filtering micro-cavities are cascaded through one or more of series integration, parallel integration, multi-segment integration and array integration.
With the above preferred scheme, a suitable integration mode is selected according to specific situations.
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 methods all have advantages and disadvantages.
The various embodiments above may be implemented in cross-parallel.
To better understand the tunable liquid crystal-based laser disclosed in the present invention, an embodiment is described below, in which a micro-ring structure of a dual-straight waveguide is used to modulate a pump source, so that the laser outputs tunable light; the driving electrode is used for modulating the waveguide medium, so that the effective refractive index of the resonant cavity 3 is changed, and monochromatic light with any wavelength is output.
The liquid crystal guide core layer at the double straight waveguide part formed by the light transmission straight waveguide 1 and the light output straight waveguide 2 is formed by arranging liquid crystal molecules with certain included angles in the arrangement direction to form a stepped waveguide structure, and the liquid crystal refractive index of the liquid crystal guide core layer is larger than that of the liquid crystal substrate layer, so that the total reflection propagation of light in the waveguide medium and the gain medium is realized.
The liquid crystal core layer at the resonant cavity 3 part is formed by arranging liquid crystal molecules with certain included angles in the arrangement direction to form a stepped waveguide resonant cavity. The resonant cavity 3 includes: a first resonant micro-ring 31 resonant cavity and a second resonant micro-ring 32 resonant cavity.
The light of the pumping source 2 is coupled into the first resonant micro-ring 31 resonant cavity from the optical transmission straight waveguide 1 and is oscillated and propagated in the resonant cavity. The first resonant micro-ring 31 resonant cavity and the second resonant micro-ring 32 resonant cavity resonate such that a wave propagating in the first resonant micro-ring 31 resonant cavity couples into the first resonant micro-ring 31 resonant cavity and oscillates and propagates in the resonant cavity 3. The wave in the second resonant micro-ring 32 resonant cavity is finally coupled into the light output straight waveguide 2 for output, and monochromatic light output with set wavelength is realized through structural design and parameter matching. In the embodiment, the resonant microcavity adopts a series integration mode, the performance indexes of all aspects are excellent, but the preparation difficulty is high, and different cascade modes can be completed through the same liquid crystal photo-orientation technology in different application scenes.
In order to improve the output efficiency, the filtering operation may be performed on the incident light, that is, the mixed light is input to the pump source 1 and filtered in the filter 4, so that the light before entering the resonant cavity is similar to the monochromatic light, and the utilization rate of the gain medium is increased. The filter 4 includes: a first filtering micro-ring 41 resonator and a second filtering micro-ring 42 resonator.
Free Spectral Range (FSR), refers to the spectral range between two resonant wavelengths.
The definition of FSR is:
Figure BDA0003032771200000101
wherein
Figure BDA0003032771200000102
Is a resonant cavity 3 long, lambda m Is the resonant wavelength of the resonant cavity
Figure BDA0003032771200000111
R is the radius of the resonant cavity, m is the resonance frequency, n eff Is the effective refractive index of the cavity 3.
The total FSR of the two resonant micro-ring resonators with different radii can be expressed as: m is a unit of 1 FSR 1 ＝m 2 FSR 2 ＝FSR total . There is a resonant wave λ in the first resonant micro-ring 31 resonant cavity 1 After the first resonant micro-ring 31 resonant cavity and the second resonant micro-ring 32 resonant cavity form resonance, a resonant wave lambda exists in the second resonant micro-ring 32 resonant cavity 2 The condition of resonance is
Figure BDA0003032771200000112
At this time, the resonant wave lambda in the resonant cavity of the second resonant micro-ring 32 2 And finally, the light is coupled into the light output straight waveguide 2 for output.
When R is 1 、R 2 When determined, n 1 、n 2 To output modulated λ 'upon change' 1 、λ′ 2 Then m 'needs to be found matching' 1 、m′ 2 I.e. the frequency selection process.
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, a part of the light energy is directly output through the straight waveguide, i.e. the straight end of the resonator, denoted as E 2 (ii) a Another 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. Resonant cavityThe expression of formula is:
Figure BDA0003032771200000113
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 a 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 formulation with resonance is:
Figure BDA0003032771200000121
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 laser, and the adopted cascade mode is shown in figure 4. The effective refractive index range of the liquid crystal core layer and the liquid crystal substrate layer can reach 1.55 to 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 micro-ring 31 resonant cavity, the second resonant micro-ring 32 resonant cavity and the double straight waveguides are all symmetrical structures, the liquid crystal arrangement modes are all vertically arranged to achieve the purpose of maximum modulation amount, and the bottom of the integrated chip is provided with a patterned electrode to achieve voltage modulation of liquid crystal molecules.
Natural light is adopted to enter a pumping source 1, and enters an optical transmission straight waveguide 1 after being filtered by a filter 4, the refractive index of a medium of the optical transmission straight waveguide 1 is 1.7, the refractive index of an external medium is 1.55, a three-layer waveguide structure is formed, and the natural light enters from an incident end and is propagated by total reflection.
The refractive index of partial medium of the optical transmission straight waveguide 1 is n 2 The refractive index of its external medium is n 1 ；
The refractive index of the medium outside the first resonant micro-ring 31 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 32 is n 5 N 'as its internal refractive index' 5 Effective refractive index of n 6 ；
The refractive index of partial medium of the light output straight waveguide 2 is n 8 The refractive index of its external medium is n 7 。
The radius of the first resonance micro-ring 31 is 10um, and the initial effective refractive index is n 4 =1.600, and the spacing between the light-transmitting straight waveguide 1 is 100nm. From the resonant formula of the resonant cavity 3
Figure BDA0003032771200000122
It can be seen that the resonant wave coupled into the first resonant micro-ring 31 has a wavelength of 502nm and a modulus of 200.
The resonant wave propagates in the micro-ring resonator 3, resonates with the second resonant micro-ring 32, and is coupled into the second resonant micro-ring 32. Relation of resonance
Figure BDA0003032771200000123
It can be seen that the radius of the second resonant micro-ring 32 is 5um, the initial refractive index effective refractive index is 1.600, and the spacing between the first resonant micro-rings 31 is 100nm.
Also from the formula of resonance of the cavity 3
Figure BDA0003032771200000131
It can be seen that the resonant wave coupled into the second resonant micro-ring 32 has a wavelength of 502nm and a modulus of 100.
The distance between the second resonant micro-ring 32 and the light output straight waveguide 2 is 100nm, the resonant wave is coupled into the light output straight waveguide 2 and is transmitted by total reflection, and a monochromatic wave of 502nm is output from the output end of the light output straight waveguide 2, so that a monochromatic light output function is realized, 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 straight waveguide and the resonant cavity 3 are changed, the wavelength of the resonant wave can be obviously changed, and the dynamic modulation function is realized.
In the second embodiment, the effective refractive index of the first resonant micro-ring 31 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 micro-ring 32 is changed to 1.700, the wavelength of the resonant wave of the resonance is changed to 628nm, and the modulus is changed to 85, and the wavelength of the monochromatic light at the output end is also changed to 628nm, so that the tunable function of the laser is completed, as shown in fig. 8. The refractive indexes of the first resonance micro-ring and the second resonance micro-ring can also adopt different refractive indexes according to the difference of the applied voltages of the first resonance micro-ring and the second resonance micro-ring, and further the modulation of other wavelengths is realized.
The invention relates to a tunable laser based on liquid crystal, wherein the spectrum of the laser 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 function of dynamically modulating and outputting 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.
The above embodiments are merely illustrative of the technical concept and features of the present invention, and the purpose thereof 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 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 scope of the present invention.

Claims (10)

1. A liquid crystal-based tunable laser, comprising: a pump light source and a photonic chip, the photonic chip comprising: the liquid crystal display device comprises a liquid crystal substrate layer, a liquid crystal core layer arranged on the surface of the liquid crystal substrate layer and a driving electrode;
the liquid crystal conducting core layer is a liquid crystal layer doped with a gain medium, and the liquid crystal conducting core layer is distributed with:
the input end of the optical transmission straight waveguide is used for inputting a pumping light source;
the output end of the optical output straight waveguide is used for outputting the light with any wavelength;
a resonant cavity, comprising: one or more mutually cascaded resonant microcavities, said resonant cavities being respectively transmission coupled to said light-transmitting straight waveguide and light-outputting straight waveguide;
the driving electrode is used for driving liquid crystal molecules in the liquid crystal substrate layer, the light transmission straight waveguide part of the liquid crystal core layer, the light output straight waveguide part and the resonant cavity part to change in arrangement, and the refractive index of the corresponding parts is changed.
2. The liquid crystal-based tunable laser of claim 1,
the variation range of the liquid crystal refractive indexes of the liquid crystal substrate layer and the liquid crystal core layer is between 1.55 and 1.7.
3. The liquid crystal-based tunable laser of claim 1,
an included angle exists between liquid crystal molecules in the liquid crystal guide core layer and liquid crystal molecules in the liquid crystal substrate layer, and the included angle is 0-pi.
4. The liquid crystal-based tunable laser of claim 1,
the liquid crystal refractive index of the liquid crystal core guiding layer is larger than that of the liquid crystal substrate layer.
5. The liquid crystal-based tunable laser of claim 1,
the radius of the resonant microcavity is more than 4 um;
the diameter of the light transmission straight waveguide and/or the light output straight waveguide is more than 2 um;
the whole structure of the tunable laser is more than 20 um.
6. The tunable liquid crystal-based laser of any one of claims 1-5, wherein the liquid crystal core layer further has distributed thereon:
the input end of the optical transmission straight waveguide is used for inputting a pumping light source;
a filter, comprising: and the filters are respectively in transmission coupling with the optical input straight waveguide and the optical transmission straight waveguide.
7. The liquid crystal-based tunable laser of claim 6, wherein the drive electrode comprises:
the resonant cavity driving electrode is used for driving the liquid crystal molecules in the resonant cavity part of the liquid crystal core guiding layer to change in arrangement;
the straight waveguide driving electrode is used for driving liquid crystal molecules in the liquid crystal guide core layer light transmission straight waveguide part, the light output straight waveguide part and the light input straight waveguide part to be arranged and changed;
and the substrate layer driving electrode is used for driving the liquid crystal molecules in the liquid crystal substrate layer to change in arrangement.
8. The liquid crystal-based tunable laser of claim 7,
the driving electrode is ITO glass with an electrode pattern, and the electrode pattern corresponds to the distribution of all parts on the liquid crystal conducting core layer.
9. The liquid crystal-based tunable laser of claim 6,
the structure of the resonant microcavity or the filtering microcavity is one or more of the following structures:
an annular microcavity structure, a triangular microcavity structure, a square microcavity structure, a hexagonal microcavity structure, an elliptical microcavity structure, or a stadium-type microcavity structure.
10. The liquid crystal-based tunable laser of claim 6, wherein a plurality of the resonant or filtering microcavities are cascaded by one or more of series integration, parallel integration, multi-segment integration, and array integration.
CN202110438791.6A 2021-04-22 2021-04-22 Tunable laser based on liquid crystal Pending CN115241729A (en)

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CN117091686A (en) * 2023-09-04 2023-11-21 江南大学 Distributed optical fiber vibration sensor based on frequency division multiplexing

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US7783144B2 (en) * 2006-04-24 2010-08-24 The Hong Kong University Of Science And Technology Electrically tunable microresonators using photoaligned liquid crystals
CN104934850B (en) * 2015-07-03 2018-09-11 安徽大学 Tunable Optical Microcavity Raman Laser
CN108683078B (en) * 2018-06-21 2023-06-09 中国科学院福建物质结构研究所 Wavelength tunable semiconductor laser

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* Cited by examiner, † Cited by third party
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CN117091686A (en) * 2023-09-04 2023-11-21 江南大学 Distributed optical fiber vibration sensor based on frequency division multiplexing
CN117091686B (en) * 2023-09-04 2024-04-09 江南大学 Distributed optical fiber vibration sensor based on frequency division multiplexing

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