阅读说明：本技术 基于铌酸锂微腔的中红外光频梳产生系统及方法 (Mid-infrared optical frequency comb generation system and method based on lithium niobate microcavity ) 是由 王擂然 孙启兵 张文富 曾超 范炜晨 赵卫 于 2019-11-07 设计创作，主要内容包括：本发明属于中红外光频梳产生领域,涉及一种基于铌酸锂微腔的中红外光频梳产生系统及方法。解决了硅基材料微腔光频梳存在的光谱带宽和效率限制等问题,实现宽带宽、转换效率高及超高重频的中红外光频梳,带来一系列全新的军事国防以及民间应用。该中红外光频梳产生系统包括泵浦单元、合束单元、非线性频率变换单元及滤波单元；泵浦单元为两路,用于提供两路泵浦光；合束单元用于将两路泵浦光进行合束；非线性频率变换单元用于接收合束后的泵浦光,并发生非线性四波混频过程,产生中红外波段的宽带光频梳；滤波单元用于滤掉剩余泵浦光,输出中红外光频梳。(The invention belongs to the field of generation of mid-infrared optical frequency combs, and relates to a system and a method for generating a mid-infrared optical frequency comb based on a lithium niobate microcavity. The problems of spectral bandwidth, efficiency limitation and the like of a silicon-based material microcavity optical frequency comb are solved, the mid-infrared optical frequency comb with wide bandwidth, high conversion efficiency and ultrahigh repetition frequency is realized, and a series of brand new military and national defense and civil applications are brought. The mid-infrared optical frequency comb generating system comprises a pumping unit, a beam combining unit, a nonlinear frequency conversion unit and a filtering unit; the pumping units are two paths and are used for providing two paths of pumping light; the beam combining unit is used for combining the two paths of pump light; the nonlinear frequency conversion unit is used for receiving the combined pump light, generating a nonlinear four-wave mixing process and generating a broadband light frequency comb of a middle infrared band; the filtering unit is used for filtering residual pump light and outputting a mid-infrared light frequency comb.)

1. A mid-infrared optical frequency comb generation system based on a lithium niobate microcavity is characterized in that: comprises a pumping unit, a beam combining unit, a nonlinear frequency conversion unit and a filtering unit;

the pumping units are two paths and are used for providing two paths of pumping light;

the beam combining unit is used for combining the two paths of pump light;

the nonlinear frequency conversion unit is used for receiving the combined pump light, generating a nonlinear four-wave mixing process and generating a broadband light frequency comb of a middle infrared band;

the filtering unit is used for filtering residual pump light and outputting a mid-infrared light frequency comb.

2. The lithium niobate microcavity-based mid-infrared optical frequency comb generation system of claim 1, wherein: each path of pump unit comprises a narrow-linewidth tunable continuous laser source (1), a power amplifier (2) and a polarization controller (4);

the narrow-linewidth tunable continuous laser source (1) is used for emitting continuous signal light; the power amplifier (2) is used for amplifying the intensity of the signal light; the polarization controller (4) is used for adjusting the polarization direction of the signal light.

3. The lithium niobate microcavity-based mid-infrared optical frequency comb generation system of claim 2, wherein: each pump unit also comprises an attenuator (3) for adjusting the intensity of the signal light.

4. The lithium niobate microcavity-based mid-infrared optical frequency comb generation system of claim 3, wherein: the beam combining unit is a beam combiner (5).

5. The mid-infrared optical frequency comb generating system based on lithium niobate microcavities of any one of claims 1 to 4, wherein: the nonlinear frequency conversion unit comprises a lithium niobate microcavity (6) and a temperature controller (7) for controlling the temperature of the lithium niobate microcavity (6).

6. The lithium niobate microcavity-based mid-infrared optical frequency comb generation system of claim 4, wherein: the filtering unit is a filter (8).

7. The method for generating the mid-infrared optical frequency comb by the mid-infrared optical frequency comb generating system based on the lithium niobate microcavity, which is characterized by comprising the following steps of:

adjusting two pumping units to emit two signal lights; the intensity and the phase of the two paths of signal light meet the intensity condition and the phase matching condition for generating four-wave mixing;

combining the two paths of signal light through a beam combining unit to serve as pump light of a nonlinear frequency conversion unit;

generating a four-wave mixing effect on the incident pump light signal by using a nonlinear frequency conversion unit to generate a mid-infrared light frequency comb;

and step four, filtering the residual pump light by using a filtering unit, and outputting a mid-infrared light frequency comb.

8. The method for generating the mid-infrared optical frequency comb according to claim 7, wherein the step three is to use the lithium niobate microcavity (6) to generate a four-wave mixing effect on the incident pump optical signal.

9. The method for generating a mid-infrared-frequency comb as claimed in claim 8, wherein the first step is specifically:

step 1.1, adjusting two narrow-linewidth tunable continuous laser sources (1) to output two beams of laser, and taking the two beams of laser as signal light of a pumping unit;

step 1.2, adjusting the intensity of two paths of signal light by using a power amplifier (2) and an attenuator (3) to enable the intensity to meet the intensity condition of four-wave mixing; the polarization directions of the two paths of signal light are respectively adjusted by the two paths of polarization controllers (4) so as to meet the phase matching condition for generating four-wave mixing.

Technical Field

The invention relates to a system and a method for generating a mid-infrared optical frequency comb, in particular to a system and a method for generating a high repetition frequency adjustable broadband mid-infrared optical frequency comb based on a lithium niobate microcavity.

Background

It is well known that mid-infrared band lasers have particular important applications in spectroscopy, remote sensing, medical treatment, communications, etc. Compared with near-infrared band laser, the mid-infrared band laser covers absorption peaks of a plurality of atoms and molecules, and has the advantage of being unique in the field of spectral measurement. Undoubtedly, the measurement of mid-infrared light waves and spectra is not only the key to solve numerous scientific problems, but also the key to drive numerous field developments related to the national civilization.

The key of the wide application of the mid-infrared light waves lies in the generation of ultra-wideband, ultra-fine and multi-wavelength light sources, but the problems of low spectral fineness, narrow bandwidth and the like are often faced. The emergence of optical frequency combs (optical frequency combs for short) brings hopes for solving the problems of ultra-wideband, ultra-fine and multi-wavelength light sources. The invention relates to an optical frequency comb which is an optical frequency scale for determining the interval and frequency of optical frequency comb teeth, which is a work with milestone significance in the 21 st century in the field of laser technology and the field of metering science, and based on the fact, professor Hansch in Germany and professor Hall in America obtain the 2005 Nobel prize in physics.

Through the development of nearly 20 years, a series of significant progress has been made on the mid-ir frequency comb, which is usually generated by a mode-locked laser through a frequency-stabilizing phase-locking method, but is greatly limited in practical application due to the constraints of the size, weight, power consumption (SWaP) and cost of the mode-locked laser.

In recent years, the photon integration technology is rapidly developed, a new technical means is provided for the development of the optical frequency comb technology, wherein the microcavity optical frequency comb makes a major breakthrough, and a new technical revolution of the optical frequency comb technology is caused. The microcavity optical frequency comb is characterized in that continuous laser is injected into a reasonably designed microcavity, and the generation of the ultrahigh repetition frequency integrated optical frequency comb is realized by utilizing the high-efficiency nonlinear optical effect and the smaller size of a resonant cavity in the microcavity, so that the performances of the optical frequency comb system such as volume, power consumption and cost are greatly improved. The conventional microcavity is generally based on a silicon-based material, however, the silicon-based material has the problems of large linear loss, multiphoton absorption and the like in a middle infrared band, so that the performances of the optical frequency comb such as bandwidth, conversion efficiency and the like are greatly limited, and the further development of the middle infrared microcavity optical frequency comb is restricted.

Disclosure of Invention

The invention aims to provide a system and a method for generating a high-repetition-frequency adjustable mid-infrared optical frequency comb based on a lithium niobate microcavity, solves the problems of spectral bandwidth, efficiency limitation and the like of a silicon-based material microcavity optical frequency comb, realizes a mid-infrared optical frequency comb with wide bandwidth, high conversion efficiency and ultrahigh repetition frequency, brings a series of brand-new military and national defense and civil applications, and has great research significance and application value.

The lithium niobate material has low linear loss and nonlinear loss in a middle infrared band, has excellent linear and nonlinear characteristics and strong electro-optic effect, simultaneously has second-order nonlinear effect and third-order nonlinear effect, can meet the functions of low loss, high-efficiency frequency conversion, rapid modulation and the like, and becomes an ideal platform for generating and applying a middle infrared microcavity optical frequency comb.

In order to solve the above problems, based on the above analysis, the technical solution of the present invention is to provide a high repetition frequency adjustable broadband mid-infrared optical frequency comb generating system based on a lithium niobate microcavity, which is characterized in that: comprises a pumping unit, a beam combining unit, a nonlinear frequency conversion unit and a filtering unit;

the pumping units are two paths and are used for providing two paths of pumping light;

the beam combining unit is used for combining the two paths of pump light;

the nonlinear frequency conversion unit is used for receiving the combined pump light and generating a nonlinear four-wave mixing process to generate a broadband light frequency comb of a middle infrared band;

the filtering unit is used for filtering residual pump light and outputting a mid-infrared light frequency comb.

Furthermore, each pump unit comprises a narrow-linewidth tunable continuous laser source, a power amplifier and a polarization controller; the narrow-linewidth tunable continuous laser source is used for emitting continuous signal light, the power amplifier is used for amplifying the intensity of the signal light, and the polarization controller is used for adjusting the polarization direction of the signal light;

further, in order to optimize the intensity of the signal light so that the intensity of the signal light meets the intensity condition under which the four-wave mixing occurs, the pumping unit further includes an attenuator for adjusting the intensity of the signal light.

Further, the beam combining unit is a beam combiner;

further, the nonlinear frequency conversion unit comprises a lithium niobate microcavity for generating a nonlinear four-wave mixing process and a temperature controller for controlling the temperature of the lithium niobate microcavity.

Further, the filtering unit is a filter.

The invention also provides a method for realizing the generation of the mid-infrared optical frequency comb based on the system, which comprises the following steps:

step one, adjusting two paths of signal light emitted by a pumping unit; the intensity and the polarization of the two paths of signal light meet the intensity condition and the phase matching condition for generating four-wave mixing;

combining the two paths of signals through a beam combining unit to serve as pump light of a nonlinear frequency conversion unit;

step three, simultaneously, the nonlinear frequency conversion unit generates a four-wave mixing effect on the signal light incident into the nonlinear frequency conversion unit, so that nonlinear frequency conversion and frequency domain expansion are realized, and a mid-infrared light frequency comb is generated;

and step four, filtering the residual pump light by using a filtering unit and outputting a mid-infrared light frequency comb.

Further, the nonlinear frequency conversion unit is a lithium niobate microcavity.

Further, the first step is specifically as follows:

step 1.1, adjusting two tunable continuous laser sources with narrow line widths to enable the laser wavelength interval emitted by the two laser sources to be integral multiples of the free spectral range of the lithium niobate microcavity, and taking two beams of laser as signal light of a pumping unit;

step 1.2, adjusting the intensity of two paths of signal light by using a power amplifier and an attenuator to enable the intensity to meet the intensity condition of four-wave mixing; the polarization directions of the two paths of signal light are respectively adjusted by the two paths of polarization controllers, so that the phase matching condition of four-wave mixing is met.

The invention has the advantages that:

1. the method for generating the mid-infrared optical frequency comb by adopting the double-pump lithium niobate microcavity breaks through the capacity limitations of bandwidth, repetition frequency, efficiency and the like in the traditional method, and can realize the mid-infrared optical frequency comb with low threshold, wide bandwidth, ultrahigh repetition frequency and adjustable repetition frequency.

2. The invention realizes the mid-infrared optical frequency comb, the spectral bandwidth is more than or equal to 1000nm, the repetition frequency is more than or equal to 200GHz, and the repetition frequency is improved by about 2-3 orders of magnitude compared with the traditional method.

3. The invention realizes the high-repetition-frequency adjustable mid-infrared optical frequency comb, and the repetition frequency is adjustable by controlling the wavelength interval of two paths of pumping light, and the highest repetition frequency is more than or equal to 1 THz.

4. The system has a low threshold value which is less than or equal to 15mW, so that the efficiency of the mid-infrared optical frequency comb system is effectively improved, and the power consumption of the system is reduced.

5. The system has the characteristics of simple structure, convenience, practicability, low SWaP (volume, weight and power consumption), easiness in integration, low cost, wide bandwidth, adjustable repetition frequency, high stability and the like.

Drawings

FIG. 1 is a schematic frame diagram of the present invention;

FIG. 2 is a schematic diagram of the apparatus of the present invention;

FIG. 3a is a graph of mid-infrared optical frequency combing results at a repetition frequency of 203 GHz;

FIG. 3b is a graph showing the result of the middle infrared optical frequency combing at 609GHz repetition frequency;

FIG. 3c is a graph of mid-infrared optical frequency combing results at 1.02THz multiples;

the reference numbers in the figures are: the tunable laser comprises a 1-narrow linewidth tunable continuous laser source, a 2-power amplifier, a 3-attenuator, a 4-polarization controller, a 5-beam combiner, a 6-lithium niobate microcavity, a 7-temperature controller and an 8-filter.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments.

Referring to fig. 1 and fig. 2, the present embodiment provides a mid-infrared optical frequency comb generating system based on a lithium niobate microcavity, including a pumping unit for providing two pumping lights, a beam combining unit for combining the two pumping lights, a nonlinear frequency conversion unit for generating a four-wave mixing process, and a filtering unit for filtering out remaining pumping lights.

As shown in fig. 2, in the present embodiment, the pumping units are two paths, and each path of pumping unit includes a narrow-linewidth tunable continuous laser source 1, a power amplifier 2, an attenuator 3, and a polarization controller 4, which are connected in sequence. The beam combining unit is a beam combiner 5 and is used for combining the two paths of pump light; other forms of beam combining components may be used in other embodiments as long as beam combining can be achieved. The nonlinear frequency conversion unit comprises a lithium niobate microcavity 6 for generating a four-wave mixing effect and a temperature controller 7 for adjusting the temperature of the lithium niobate microcavity 6. The filtering unit is a filter 8 and is used for filtering residual pump light to obtain a mid-infrared light frequency comb; in other embodiments, other forms of filtering components may be used as long as filtering can be achieved.

The mid-infrared frequency comb can be generated by the following process:

1, adjusting two tunable continuous laser sources 1 with narrow line widths to enable the laser wavelength interval emitted by the two laser sources to be integral multiples of the free spectral range of the lithium niobate microcavity 6 microcavity, and taking two beams of laser as signal light of a pumping unit;

2, adjusting the intensity of the two paths of signal light by using a power amplifier 2 and an attenuator 3 to enable the intensity to meet the intensity condition of four-wave mixing (so that the comb spectrum bandwidth of the output light frequency is maximized); the polarization directions of the two paths of signal light are respectively adjusted by the two paths of polarization controllers 4 to meet the phase matching condition for generating four-wave mixing;

and 3, injecting the two paths of adjusted signal light into a high-nonlinearity low-flat-dispersion lithium niobate microcavity 6 after the two paths of adjusted signal light pass through a beam combiner 5, adjusting the temperature of the lithium niobate microcavity 6 by using a temperature controller 7 to enable the temperature to meet the resonance condition of the microcavity (namely the wavelength of the injected light is matched with the resonance wavelength of the microcavity) and the phase matching condition of four-wave mixing, generating a high-efficiency low-threshold four-wave mixing effect, and obtaining medium-infrared optical frequency comb output after the four-wave mixing effect passes through a filter 8.

The working principle of the invention is as follows:

firstly, performing power amplification on narrow-linewidth tunable continuous laser to be used as pump light of a nonlinear frequency conversion unit; the power of the pump light is adjusted by using the attenuator 3 and the power amplifier 2 to meet the intensity condition of four-wave mixing, the polarization direction of the pump light is adjusted by using the polarization controller 4 to meet the phase matching condition of the four-wave mixing, the pump light is injected into the high-nonlinearity low-flat-dispersion lithium niobate microcavity 6 after passing through the beam combiner 5, the temperature of the lithium niobate microcavity 6 is accurately adjusted by using the temperature controller 7 to meet the resonance condition of the microcavity and the phase matching condition of the four-wave mixing, the high-efficiency low-threshold four-wave mixing effect is generated, and the mid-infrared light frequency comb is obtained after being filtered by the filter 8.

Referring to fig. 3a, 3b and 3c, mid-infrared optical frequency combs produce results. The method of the double-pump lithium niobate microcavity can realize the ultra-high repetition frequency and repetition frequency adjustable broadband mid-infrared optical frequency comb, the spectral bandwidth is more than or equal to 1000nm, and the highest repetition frequency is more than or equal to 1 THz. The invention utilizes a double-pumping method to construct a pumping unit, constructs a nonlinear frequency conversion unit based on the high-efficiency low-threshold four-wave mixing effect in the lithium niobate microcavity, and realizes the ultra-high repetition frequency and repetition frequency adjustable broadband mid-infrared optical frequency comb by controlling parameters such as power, polarization, wavelength and the like of pumping light. The size, power consumption and the like of a traditional mid-infrared optical frequency comb system can be reduced by several orders of magnitude, and meanwhile, the repetition frequency can reach hundreds of GHz and even THz, which is far higher than that of an optical frequency comb generated by a traditional mode-locked laser.