LU502041B1 - A generation method of turnkey optical micro-comb in single-soliton state based on thin-film lithium niobate - Google Patents
A generation method of turnkey optical micro-comb in single-soliton state based on thin-film lithium niobate Download PDFInfo
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- 230000003287 optical effect Effects 0.000 title claims abstract description 90
- 239000010409 thin film Substances 0.000 title claims abstract description 49
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 48
- 238000000034 method Methods 0.000 title claims abstract description 28
- 239000000835 fiber Substances 0.000 claims abstract description 54
- 230000000694 effects Effects 0.000 claims abstract description 26
- 230000010287 polarization Effects 0.000 claims abstract description 22
- 238000001228 spectrum Methods 0.000 claims abstract description 16
- 239000012212 insulator Substances 0.000 claims abstract description 5
- 230000008859 change Effects 0.000 claims abstract description 3
- 230000004083 survival effect Effects 0.000 claims abstract description 3
- 230000008878 coupling Effects 0.000 claims description 27
- 238000010168 coupling process Methods 0.000 claims description 27
- 238000005859 coupling reaction Methods 0.000 claims description 27
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 12
- 229910052744 lithium Inorganic materials 0.000 claims description 12
- 239000013307 optical fiber Substances 0.000 claims description 8
- 210000001520 comb Anatomy 0.000 claims description 7
- 230000008569 process Effects 0.000 claims description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- 239000006185 dispersion Substances 0.000 claims description 6
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- 239000010703 silicon Substances 0.000 claims description 4
- 235000012239 silicon dioxide Nutrition 0.000 claims description 3
- 239000000377 silicon dioxide Substances 0.000 claims description 3
- 239000000758 substrate Substances 0.000 claims description 3
- 230000002159 abnormal effect Effects 0.000 claims description 2
- 241000206607 Porphyra umbilicalis Species 0.000 claims 1
- 238000010408 sweeping Methods 0.000 abstract description 4
- 238000005086 pumping Methods 0.000 abstract description 2
- 239000013078 crystal Substances 0.000 abstract 2
- 238000010586 diagram Methods 0.000 description 7
- 230000008901 benefit Effects 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 230000033228 biological regulation Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 230000000739 chaotic effect Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
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- 238000004088 simulation Methods 0.000 description 2
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- 244000126211 Hericium coralloides Species 0.000 description 1
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 230000001709 ictal effect Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- ORUIBWPALBXDOA-UHFFFAOYSA-L magnesium fluoride Chemical compound [F-].[F-].[Mg+2] ORUIBWPALBXDOA-UHFFFAOYSA-L 0.000 description 1
- 229910001635 magnesium fluoride Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
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- 230000009022 nonlinear effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
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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
- G02F1/03—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 ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—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 ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
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- 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
- G02F1/35—Non-linear optics
- G02F1/39—Non-linear optics for parametric generation or amplification of light, infrared or ultraviolet waves
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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
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Abstract
The invention utilizes the photorefractive effect of the lithium niobate crystal to spontaneously start and change the relative detuning amount between the resonant frequency of the microring and the frequency of the pumping laser, and finally locks it in the survival region of the optical micro-comb in single-soliton state. Moreover, the high-speed electro-optic phase modulation characteristics of lithium niobate crystals are used to ensure the deterministic generation of optical micro-comb in single-soliton state. The invention is realized by connecting pump laser with fixed frequency, erbium-doped fiber amplifier, polarization controller, lens fiber, thin-film lithium niobate on insulator chip, optical spectrum analyzer, photodetector and electrical spectrum analyzer. This invention uses low-power, fixed-frequency continuous laser source to generate optical micro-comb in single-soliton state in a self-starting and deterministic manner. The high-cost frequency-sweeping light source, complex start-up operation, feedback control like which are necessary in the traditional method are not needed by this invention.
Description
Description A generation method of turnkey optical micro-comb in singis-soliton state based on thin-film lithium niobate Technical field This invention relates to nonlinear optics, nonlinear frequency conversion, optical frequency comb generation based on microresonator, particularly relates to a generation method of tumkey optical micro-comb in single-solilon state based on thin-film lithium riobate.
Background As a superior coherent broadband laser source and accurate frequency scale, optical frequency comb has altracted the attention of many scientists and research instituiss in recent ten years. Among various mechanisms and methods for generating optical frequency combs, Kerr optical frequency combs based on optical microrasonator have many advantages, such as compact struciure, integration, low pump power, wide spectral bandwidth, etc, so it has become a ressarch hotspot in the field of optical frequency combs in recent years, especially since the existence of dissipative Kerr solitons was confirmed by the Kippenberg reasearch group of the Federal Institute of Technology in Lausanne in 2014, Whan the dissipative Kerr soliton is formed, if means that each comb tooth of the optical frequency comb is phase locked, and the optical frequency comb has excellent coherence at this time. This Kind of frequency comb based on soliton state in rmicroresonsator is also called optical comb in soliton state.
Soliton optical comb has been realized on many material platforms, including silicon nitride, magnesium fluoride, silicon, high refractive index glass, aluminum nitride, lithium niobate, etc, and plays an important role in astronomy, metrology, spectroscopy, optical communication, quantum optics and many other fields.
During the generation of soliton optical comb, the thermo-optic effect of microrssonator, including thermal refractive index effect and thermal expansion effect, will lead to thermal bistability, which makes it difficult to stabilize the pump frequency in the effective red detuning region of microresonator, namely, the soliton stats survival region. Although several methods have been reported fo overcome the thermal instability of microresonator, including pump sweep rate regulation, two-step pump power regulation, thermal compensation with auxiiary laser, etc, these methods usually require complex external control system and accurate parameter adiusiment The soliton opticai comb, which can be produced by directly fuming on the pump laser with one key and without these complicated start-up and feedback control is called turnkey mode, Turnkey soliton optical comb has great research and application value for miniaturized and fully integrated optical comb source.
in addition, in the traditional frequency sweeping process, although the soliton stale optical comb can be obtained, the optical held in the cavity experiences chaotic stale during the frequency sweeping process, and the number of solitons in the soliton comb finally produced is random. However, in practical application, it is more desirable to produce the single achion optical comb, because the single soliton optical comb has a smooth spectral ariveiope and a singe soliton time period. Therefore, it is of great significance 10 deterministically generate single soliton optical comb in practical application.
in recent years, thinfiim lithium niobate (aiso called lithium niobate on insulator) as a multifunctional material platform has attracted wide attention from the industry. Thin-film Hum niobate has the advantages of large transparent window (0.4~5um}, second-order and third-order nonlinear effects, good light field binding, and many other effecis, including slectro-optic effect, thermo-optic effect, photoelastic effect and piezoelectric effect. Based on this platform, researchers have developed many Superior functional devices, including high-speed electro-optic modulator, acousto-optic modulator, rare earih-doped waveguide amplifier, soliton comb source, etc. As one of the unique affects of Bihium niobate, photorefractive effect has also attracted some attention. Because the photorefractive effect is similar to the negative thermo-optic effect, it is possible {0 produce the turnkey soliton optical comb on thin-film lithium niobate. In addition, the phase modulation of the pump can definitely produce a single solifon optical comb, and high-speed phase modulation is one of the advantages of thin-film lithium nichate. Therefore, the combination of the two can realize the deterministic generation of turn-key single soliton optical comb.
Summary in order to solve the problem exist in the prior art, this invention provides a generation method of tumkey optical micre-comb in single-soliton state based on thin-fiim Bthium niobate. The invention utilizes the photorefractive effect to generates the soliton state optical Thicro-comb in a turn-key manner, and by performing phase modulation on the pump, the deterministic generation of the single soliton state optical micro-comb can be realized.
The production method of that invention is realize by pump laser with fixed frequency, erbium-doped fiber amplifier, polarization controller, lensed fiber, thin-film lithium niobate chip, an optical spectrum analyzer, photodetector, electrical spectrum analyzer and single-mode fiber connected with them. The output end of the pump laser is connected with the input end of the erbium-doped fiber amplifier through single-mode fiber; the output end of the srbium-doped fiber amplifier is connected with the input end of the polarization controller through single-mode fiber, the output end of the polarization controller is connected with the input end of the lens fiber through single-mode fiber, The output end of the lens couples the light field to the input end of the coupling input waveguide of the thin-film lithium niobate chip through the end face coupling, On thin-film lithium nichate chip, the output of a coupling Input waveguide is connected with the input of high-speed phase modulator, the output of the high-speed phase modulator is connected with the input of a polarization rotator through a transmission waveguide, the output of the polarization rotator is connected with the input of the coupling output waveguide, and the coupling output waveguide and the micro-nng resonant cavity are close to each other to generate coupling; the light is output from the output end of the coupling output waveguide on the thin-film lithium niobate chip and coupled to the input end of the lens fiber through the end face: the output end of the lens is connected with the input end of the single-mode fiber; the output end of the single-mode optical fiber is divided into Ihres ports through optical fiber coupling, thess three ports are respeclively connected with the input ends of optical spectrum analyzer, photoelectric detector and electrical specirum analyzer.
The thin-film hthium niobate chip is based on an X- cut lithium niobate on insulator platform, and is substrate is lithium niobate or silicon, the buried oxide layer is silicon dioxide, and the covering layer is air There is an inclination angle on the side wall of the waveguide due to processing. When the light field mode is TE fundamental mode and the traveling wave electrode is used for modulation, high-speed phase modulation can be realized. When the light field mode is THM fundamental mode, because the thermal optical coefficient of ordinary refractive index of lithium niobate is almost zero at room temperature, the generation of soliton optical comb can hardly be affected by thermal optical effect The erbium-doped fiber amplifier is used for amplifying the power of the pump laser io make it meet the power threshold for generating soliton optical combs; If the pump laser power is large enough, the erbium-doped fiber amplifier may not be needed.
The polarization controller is used for controling the polarization state of the ight field at the output end of the lens fiber, When the light field is coupled from the output end of the lens fiber to the input end of the coupled input waveguide of the trun-fim lithium niobate chip through the end face, only the TE fundamental mode in the waveguide is excited, however, the TM fundamental mods or the higher order modes of TE and TM is not excited.
The polarization rotator on the thin-film lithium nichate chip is used for rotating the TE fundamental mode from the high-speed phase modulator into the TM fundamental mods; the polarization rotator can be realized by using the gradient waveguid to first convert the TE fundamental mode into the TM first-order mode, next, using the asymmetric directions! coupler to convert the TM first-order mods into the TM fundamental mode. The polarization rotator can also be realized by two connected U-shaped waveguides, The rmicro-ring resonant cavity on the thin-film ithium niobate chip has high quality factor and abnormal dispersion characteristics at the pump wavelength, So as to be used for generating sollten optical combs, The optical field of soliton optical comb is based on the TM fundamental mode of waveguide to ignore the influence of thermo-optic effect. The micro-ming resonator and the coupling-out waveguide meet the critical coupling state, that is, the loss of the light field in the micro-ring resonator is equal to the coupling loss of the rmicro-ring resonator The optical spectrum analyzer is used for detecting and recording the frequency domain results of the generated soiton optical comb, Fhotoeiectric detector is used to detect and record the waveform and energy results of soliton optical comb. Electrical spectrum analyzer is used to detect and record the noise characteristics of soliton optical comp, so as to judge the quality of its coherence.
According to the invention, the generation of the turnkey soliton optical comb can be realized by utilizing the photorefractive effect of thindfiim lithium niobate, which doss not require an expensive and bulky frequency-sweeping laser, instead, it only needs a continuous laser with a fixed frequency, Using ihe high-speed phase modulation characteristic of thin-film lithium niobate, single soliton can be generated deterministically, instead of random number of solitons. Combining the generation of turnkey soliton optical comb based on photorefractive with high-speed phase modulation, the furnkey and deterministic single soliton optical comb can be generated on the fhin-fiim lithium niobate platform.
This invention has beneficial effects as followings: (1) The present invention adopts an X-cut thin-film ithium niobate platform, which has the advantages of large transparent window and large electro-optic coefficient; for the TE fundamental mode, the pump laser can be phase-modulated at high spesd by using the traveling wave slactrode; For the TM fundamental mode, since the thermo-optic coefficient of the ordinary light of lithium niobate is almost zero at room temperature, the generation of the achiton optical microcomb can be hardly affected by the thermo-optic effect; (2) The invention makes use of the photorefractive effect of thin-film lithium niobale to achieve the purpose of generating soliton-state optical micro-comb in tumkey mode, thus avoiding the use of expensive and bulky freguency-ewept laser and complex external control system, and it only nesds à continuous optical pumping laser with fixed frequency: (3) According io the invention, the X- cut thin-film lithium niohbais modulator is used is perform high-speed phase modulation on the pump laser, so that 3 single soliton optical comb can be generated deterministically, instead of the soliton optical comb with random number of solitons, the high-speed phase modulator and micro-ring resonant cavity are integrated on the same fhin-fim lithium niobate chip at the same time, and the tumkey operation is combined with high-speed phase modulation, so that the tumkey and deterministic single sollten optical comb can be generated. Brief Description Of The Figures Fig. 1 is a schematic diagram of a turnkey single soliton optical como generation method based on thin-film lithium niobate.
Fig. Z is a schematic diagram of the structure of a thindiim lithium niobate chip.
Fig, 318 a schematic structure diagram of a high-speed phase modulator on a thin-film thium niobate chip.
Fig. 4 is a schematic cross-sectional view of a waveguide on a thin-film lithium niobals chip.
Fig © is the time domain result of the pump after phase modulation.
Fig. 6 is the frequency domain result of the pump after phase modulation, Fig, 7 is a time-domain evolution diagram of an open-key single soliton optical comb based on thin-film lithium niobate, Fig. 8 18 the final time domain result of an open-key single soliton optical comb based on thin-film lithium niobate.
Fig, 9 is the final frequency domain result of an open-key single soliton optical comb based on thindilm lithium niobate.
Description of the present invention The present invention will be further explained with reference to the attached figures and embodiment of a generation method of tumkey optical micro-Comb in single-soliton state based on thin-film lithium nichate.
As Fig. 1 shown, a generation method of turnkey optical micro-comb in single-soliton state based on thin-film lithium niobate, the outout end of the pump laser (1) with fixed frequency is connected with the input end of the erbium-doped fiber amplifier (3) through the first single-mode fiber (2); the output end of the erbium-doped fiber amplifier (3) is connected with the input end of the polarization controller (5) through a second single-mode fiber (4); the output end of the polarization controller (5) is connected with the input end of the lens fiber (7) through a third single-mode fiber (6); the output end of the first lens fiber (7) couples the light field to the input end of the coupling input waveguides (17) of the thin-film lithium niobate chip (8) through end-face coupling; the light is output from the output end of the coupling output waveguide (21) of the thin-film lithium nichats chip and coupled to the input end of the second lens fiber (8) through the end face, the output end of the second lens fiber (9) is connected with the input end of the fourth single-mode fiber {10} the output end of the fourth single-mode fiber (10) is divided into threes parts through fiber coupling, and ils output ports are connected with the input ports of the fifth single-mode fiber (11), the sixth single-mode fiber (12) and the seventh single-mode fiber (13) respectively, the output end of the fifth single-mode optical fiber (11) is connected with the input end of the optical spectrum analyzer (14) The output end of the sikth single-mode optical fiber (12) is connected with the input end of the photceleciric detector(15) the output end of the seventh single-mode optical fiber (13) is connected with the input end of the electrical spectrum analyzer (16).
Fig, 2 is a schematic diagram of the structure of a thin-film lithium niobate chip. The output of the coupling waveguide 17 is connected with the input of the modulation waveguide 24 in the high-spesd phase modulator 18; the output of the modulation waveguide 24 in the high-speed phase modulator 18 is connected with the input of the polarization rotator 20 through the transmission waveguide 19; The output end of the polarizer 20 is connected with the input end of the coupling output waveguide 21; the coupling waveguide 21 and the micro-ring resonator 22 are close to each other, resulting in COLRHNG.
Fig. 3 is a schematic structure diagram of a high-speed phase modulator on a thin-film ithium niobate chip. The light is transmitted in the modulation waveguide 24, and the first traveling wave electrode 23 and the second traveling wave sisctrode 25 are arranged on both sides of the modulation waveguide 24 for high-speed phase modulation of the light field in the modulation waveguide 24.
Fig. 4 is a schematic cross-sectional view of a waveguide on a thin-film lithium niobate chip, the thin-film lithium niobate chip is based on an X- cut lithium nichate on insulator platform, the substrate (26) is lithium niobate or silicon, the buried oxide layer (27) is silicon dioxide, and the waveguides layer (28) is a lithium niobats thin-film; the covering layer (29) is air, due to the technological process, there is an inclination angle 9 on the side wall of the waveguide, which is usually 60° The simulation adopts the coupled Lugulaic-Lefever equation. The dynamic evolution of soliton comb in micro-ring resonator is described by Luguiato-Lefever equation as follows: = = & + to} À + Fos + iglARA + VE Wherein, À is the slowly changing envelope of the light field in the cavity and normalized by the photon number, and {is the slowly changing time, © is the azimuth angle corresponding to a circle of the light field in the micro-ring resonator; Sw=lwe+bwhPR is the relative detuning, where dus is the initial relative detuning, OWPR=gEEsp is the deturing caused by photorefractive effect, wherein, gi 18 the electro-optical coupling cosfficiant, Esp is the space charge field produced by photorefractive effect K=wa/0 is the ictal loss rais of the micro-ring resonator, where wes the frequency of the pump laser and © is the quality factor considering the intrinsic loss and coupling loss of the micrg-ring, n is the ratio of the loss caused by the coupling of the micro-ring resonator to the total loss when the pump light travels in the micro-ring resonator; g is the normalized Kerr nonlinear coefficient; D2 is the second-order dispersion coefficient, which has a certain transformation relationship with the group velocity dispersion Bz; Pin is the pump laser power; À is the reduced Planck constant. The space charge field Esp produced by photorefractive effect is coupled with Luguiato-Lefever equation, and its dynamics is described by the excitation-relaxation process as follows: dEsp = —TspEsp + NspPave dt
Where [sp is the relaxation rate of the space charge field, Nsp is the light production coefficient, and Pave is the average power of one circle in the micro-ring resonator. Due to the photorefractive effect, the detuning dwPR is related to the space charge field Esp, which in turn is related to the average power Pave in the cavity. Therefore, the relative detuning dwPR will automatically evolve during the evolution of the optical field in the cavity, so the external frequency scanning of the pump laser is unnecessary.
In the simulation calculation, it is assumed that the group velocity dispersion of the micro-ring resonator 22 at the pump wavelength is B>=-40ps2/km, the quality factor is Q=2*106, and the free spectrum range is FSR=100 GHz, which is easy to realize in the actual process. Relatively speaking, the smaller the group velocity dispersion Ba, the better, and the higher the quality factor Q, the better, the power of the pump laser is Pin=0.2 W, and the frequency of the pump laser is 1 GHz higher than the resonant peak frequency of the micro-ring resonator (i.e. the blue-detuned side); In the excitation-relaxation equation of photorefractive effect, the relaxation rate of space charge field is 'sp=125 KHz, the light generation coefficient is nsp=3.91x1010 Hz-V/(m-W), and the electro-optical coupling coefficient is gE=2.55x104 Hz-m/V, which is selected according to the existing experimental results. The phase modulation is sinusoidal response, the modulation frequency is synchronized with the FSR of the microresonator, and the modulation depth is 11/2.
According to the invention, the photorefractive effect of the thin-film lithium niobate chip is utilized to spontaneously change the relative detuning amount between the frequency of the micro-ring resonant cavity and the frequency of the pump laser, so as to achieve the purpose of generating soliton-state optical comb in an open-key mode; By high-speed phase modulation of the pump laser, the single soliton optical comb can be generated deterministically. Combining key-opening operation with high-speed phase modulation can realize turnkey and deterministic single soliton optical comb generation.
Figs. 5 and 6 show the time domain and frequency domain results of the pump laser after phase modulation. As far as the time domain results are concerned, the time domain intensity of phase modulated pump laser has almost no influence. As far as the frequency domain results are concerned, the phase modulation will cause the pump energy to shift to the sidebands on both sides.
Fig. 7 is a time-domain evolution diagram of an open-key single soliton optical comb based on thin-film lithium niobate. After self-starting, the light field in the cavity first passes through chaotic state, and then generates multi-soliton state. Under the action of phase modulation, the generated multi-soliton states converge to the maximum phase point (phase modulation will produce potential well effect), and collide and annihilate in the process of moving. Finally, only one soliton remains stable at the maximum phase, thus realizing the deterministic generation of single soliton states.
Fig. 8 is the final time domain result of an open-key single soliton optical comb based on thin-film lithium niobate. We can clearly see the existence of single soliton in time domain, and the full width at half maximum of the single soliton is about 23 femtoseconds.
Fig. 9 is the final frequency domain result of an open-key single soliton optical comb based on thin-film lithium niobate. It can be clearly seen that the frequency domain envelope is very smooth, which is the characteristic of single soliton optical comb. In addition, due to the phase modulation, the pump energy is transferred to the sidebands on both sides of the pump, which weakens the pump energy and strengthens some sidebands.
The above examples are used to illustrate the present invention, but not to limit it. Any modifications and changes made to the present invention within the scope of protection of the spirit and claims of the present invention will fall within the scope of protection of the present invention.
Claims (8)
1. À generation method of turnkey optical micro-Comb in single-soliton state based on thin-film Hthium nichate is characterized in that the method utilizes the photorefractive effect of thin-film lithium niobate chip to spontaneously start and change the relative detuning between the frequency of micro-ring resonator and the frequency of pump laser, and finally locks the relative detuning in the survival area of soliton optical comb moreover, the high-speed electro-optic phase modulator of thin-film hihium niobhate chips used io ensure the deterministic generation of optical comb in single soliton state; the generating method is realized by pump laser with fixed frequency, erbium-doped fiber amplifier, polarization controller, lens fiber, thindfiim lithium niobate chip, optical spectrum analyzer, photodetector, electrical spectrum analyzer and single-mode fiber connected with them, the output end of the pump laser (1) with fixed frequency is connected with the input end of the erbium-doped fiber amplifier (3) through the first single-mode fiber (2); the output end of the erbium-doped fiber amplifier (3) is connected with the input end of the polarization controller (5) through a second single-mode fiber (4) the output end of the polarization controller (6) is connected with the input end of the lens fiber (7) through a third single-mode fiber (8); the output end of the first lens fiber (7) couples the light field to the input end of the coupling input waveguide (17) of the thin-film lithium niobate chip (8) through end-face coupling; the Hoht is output from the output end of the coupling output waveguide {21} of the thin-film thium niobate chip (8) and coupled to the input end of the second lens fiber (93 through the and face, the output end of the second lens fiber (9) is connected with the input end of the fourth single-mode fiber (10) the output end of the fourth single-mode fiber (10) is divided into three parts through fiber coupling, and its output ports are connected with the input ports of the fifth single-mode fiber (11), the sixth single-mode fiber (12) and the seventh single-mode fiber (13) respectively, the output end of the fifth single-mode optical fiber {11} is connected with the input end of the optical spectrum analyzer (14); the output end of the sixth single-mode optical fiber (12) is connected with the input end of the photoelectric detector{ 15); the output end of the seventh single-mode optical fiber (133 is connected with the input end of the electrical spectrum analyzer (16).
2. À generation method of tumkey optical micre-comb in single-soliton state based on thin-Him lithium niobate, according to claim 1, is characterized in that the thin-film Hthium richate chip Is based on an X- out lithium niobate on insulator platform, the substrate (26) is Hthium niobate or silicon, the buried oxide layer (27) is silicon dioxide, and the waveguide laver (28) is à lithium niobate thin-film; the covering layer (29) is air, due to the technological process, there is an inclination angle 6 on the side wall of the waveguide, which is usually ai".
à A generation method of turmkey optical micro-comb in single-soliton state based on thin-film lithium niobate, according to claim 1 or 2, is characterized in that when the Hght field mode is TE fundamental mode and the traveling wave electrode is used for modulation, thus realizing high-speed phase modulation when the light field mode is TM fundamental mode, the tharmal-optical coefficient of ordinary refractive index of lithium niobate is almost zero at room temperature, so the generation of optical comb is hardly affected by thermal-optical effect
4. À generation method of tumkey optical micro-comb in single-soliton state based on thin-Him ithium niobate, according to claim 3, is characterized in thai the erbium-dopec fiber amplifier (3) is used for amplifying the power of the pump lager (1) 10 make it meet the power threshold for generating soiton state optical combs; if the power of the pump laser {1} is large enough, the erbium-doped fiber amplifier (3) may not be needed,
5. À generation method of turnkey optical micre-comb in single-soliton siate based on thin-Him lithium niobate, according to claim 3, is characterized in that the polarization controller (5) is used for controling the polarization state of the ight field at the output end of the first lens fiber (7); When the light field is coupled from the output end of the first lens fiber (7) to the input end of the coupled input waveguide (17) of the thin-film ithium niobate chip (8) through the end face, only the TE fundamental mode in the waveguide is excited, but the TM fundamental mode or the higher order modes of TE and TM modes are not excited, &.
À generation method of turnkey optical Micro-ComDb in single-soliton state based on thin-film lithium niobate, according to claim 4 or 9, is characterized in that the polarization rotator (20) on the thin-film lithium nichate chip (8) is used for rotating the TE fundamental mode from the high-speed phase modulator (18) into the TM fundamental mode, the reglization of the polarization rotator: firstly, the TE fundamental mode is converted into the TH first-order mode by using the graded waveguide, and then the TM first-order mode is converted into the TM fundamental mode by using the asymmetric directional coupler, the polarization roistor can also be realized by using two connected U-shaped waveguides.
7. À generation method of turnkey optical micre-comb in single-soliton siate based on thin-film lithium niobate, according to claim 8, is characterized in that the micro-ring resonant cavity (22) on the thin-film Bithium niobate chip (5) has high quality factor and abnormal dispersion characteristics at the pump wavelength, so as to be used for generating soliton state optical combs; the optical field of soliton optical comb is based on the TM fundamental mode of waveguide {0 ignore the influence of thermo-optic effect; the mmicro-ring resonator (22) and the coupling-out waveguides (21) are in a critical coupling state, that is, the loss of light field in the micro-ring resonant cavily (22) is equal to the coupling loss of the micro-ring resonant cavity (22).
8. À generation method of tumkey optical micrg-comb in single-soliton state based on thin-Him lithium niobate, according to claim 7, is characterized in that the optical spectrum analyzer (14) is used for detecting and recording the frequency domain results of the generated sollten optical comb; the phoicelectric detector (19) is used for detecting and recording the waveform and energy results of the generated soliton optical comb, the slectrical spectrum analyzer (16) is used to detect and record the noise characteristics of the generated soiiton optical comb, so as fo judge iis coherence.
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