CN111525379B - Broadband topology load tunable Laguerre Gaussian optical parameter oscillator - Google Patents
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
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Abstract
本发明公开了一种宽带拓扑荷可调谐的拉盖尔高斯光参量振荡器，包括纳秒脉冲激光器、光束整形装置、镀膜腔镜、周期极化铌酸锂晶体、温控装置、偏振元件和矢量涡旋波片。镀膜腔镜包括镀膜前腔镜和镀膜后腔镜，二者形成谐振腔。本发明使矢量涡旋波片和镀膜前腔镜的相对位置满足凹面镜1：1成像关系，从而形成由实心光束向空心拉盖尔高斯光束平滑过渡的自再现腔模，提高了腔模和泵浦光的耦合效率，降低了腔内损耗，最终实现了高效率、高纯度、波长和拓扑荷可调谐的拉盖尔高斯光束输出。
The invention discloses a wideband topological charge tunable Laguerre Gaussian optical parametric oscillator, comprising a nanosecond pulse laser, a beam shaping device, a coated cavity mirror, a periodically polarized lithium niobate crystal, a temperature control device, a polarizing element and a Vector vortex waveplate. The coated cavity mirror includes a pre-coated cavity mirror and a post-coated cavity mirror, which form a resonant cavity. The invention makes the relative position of the vector vortex wave plate and the coating front cavity mirror satisfy the 1:1 imaging relationship of the concave mirror, thereby forming a self-reproducing cavity mode with a smooth transition from a solid beam to a hollow Laguerre Gaussian beam, improving the cavity mode and The coupling efficiency of the pump light reduces the intra-cavity loss, and finally realizes the Laguerre-Gaussian beam output with high efficiency, high purity, and tunable wavelength and topological charge.
Description
Technical Field
The invention relates to an optical parametric oscillator, in particular to an optical parametric oscillator for outputting broadband and topology load tunable Laguerre Gaussian beams.
Background
Laguerre Gaussian (LG) modes are a set of intrinsic solutions of paraxial approximation wave equations in a cylindrical coordinate system, and different Laguerre Gaussian modes are marked by an angular index l and a radial index p and are used for solving the problem that the Laguerre Gaussian modes are not matched with the angular index l
And (4) showing. When l, p is 0, the laguerre gaussian beam is degraded to a fundamental mode gaussian beam; when l is not equal to 0, each photon in the Laguerre Gaussian beam carries orbital angular momentum with the magnitude of
The azimuthal exponent l is also known as the topological charge number. The Laguerre Gaussian beam carrying the orbital angular momentum has wide application in the fields of optical control, optical precision measurement, optical communication, super-resolution imaging, quantum information processing and the like. High-purity Laguerre Gaussian beam can effectively improve optical precision measurementThe signal to noise ratio of the optical chip is improved, the resolution of super-resolution imaging is improved, and the coupling efficiency of the optical chip with orbital angular momentum is improved. Therefore, for general purposes in the field, a high-quality Laguerre Gaussian beam light source with integrated functions is necessary.
The optical parametric oscillator relies on a quasi-phase matching mechanism to convert a frequency omega by a parametric down-conversion process1The pumping light photon is converted into the frequency omega2Signal light photon of and frequency omega3Of idler photons of, wherein ω1＝ω2+ω3And the wavelength of the output signal light and the idler frequency light can be adjusted by changing the phase matching condition, so that the method is widely applied to the generation of broadband light sources. The optical parametric oscillation system is combined with the generation of the Laguerre Gaussian beam, so that the broadband Laguerre Gaussian beam light source can be obtained.
Currently, the generation techniques for broadband laguerre gaussian beams can be divided into two categories: one type is to output a broadband fundamental mode Gaussian beam by using a common optical parametric oscillator, and then convert the Gaussian beam into a Laguerre Gaussian beam by using a mode conversion device outside a resonant cavity, wherein the mode conversion device generally comprises a vector vortex wave plate, a fork-shaped grating, a spiral phase plate, a spatial light modulator and the like. Such methods typically produce laguerre gaussian beams with low modal purity and inadequate system integration. In the second method, a laguerre gaussian beam can be directly output by a resonant cavity, the mode purity of the output beam is improved by using the mode selection effect of the resonant cavity, for example, a beam carrying orbital angular momentum is used as a pumping light [ Controlled switching of orbital angular momentum in an optical parametric oscillator ], because the orbital angular momentum is conserved in the conversion process under a parameter, the generated parametric light carries the orbital angular momentum, the laguerre gaussian mode can be directly output by the interaction with the resonant cavity, but the optical power density of the annular pumping beam carrying the orbital angular momentum is low, so that the frequency conversion efficiency is not high; in addition, a gaussian beam pump is adopted, and a mode conversion device is added into a resonant cavity to realize output of a laguerre gaussian beam, for example [ a laser for outputting a 1064nm tunable laguerre gaussian beam ], but in the scheme, output of a single-wavelength laguerre gaussian beam is only realized, and the loss in the resonant cavity is increased while the output mode purity is improved by using small-hole mode selection, and the efficiency improvement is needed.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems in the prior art, the invention provides the broadband topological load tunable Laguerre Gaussian optical parameter oscillator which is high in efficiency and purity.
The technical scheme is as follows: the broadband topological charge tunable Laguerre Gaussian optical parametric oscillator comprises a nanosecond pulse laser, a light beam shaping device and a coated cavity mirror which are sequentially arranged along a light propagation direction, wherein a periodically polarized lithium niobate crystal, a polarization element and a vector vortex wave plate are sequentially arranged in the coated cavity mirror along the light propagation direction, and a temperature control device is arranged below the periodically polarized lithium niobate crystal, wherein:
the nanosecond pulse laser is used as a pumping light source to provide pumping light beams with specified wavelengths;
the beam shaping device is used for shaping and shrinking the pumping beam and adjusting the beam waist size and position of the pumping beam so as to obtain a pumping Gaussian beam matched with the beam waist size and position of the intrinsic cavity of the resonant cavity;
the coating cavity mirror comprises a coating front cavity mirror and a coating rear cavity mirror which form a resonant cavity;
the periodically polarized lithium niobate crystal is used for interacting with the pumping Gaussian beam, providing parametric gain, amplifying the parametric down-conversion light field and generating signal light;
the temperature control device is used for stabilizing and regulating the temperature of the periodically polarized lithium niobate crystal so as to change the quasi-phase matching condition and control the wavelength of the generated signal light;
the polarization element is used for adjusting the polarization state of the signal light at each position in the resonant cavity, so that the polarization can be reversely converted, and the resonant cavity is ensured to meet the polarization self-reproduction condition;
and the vector vortex wave plate is used for providing a spiral phase and generating Laguerre Gaussian beams with different angular indexes so as to realize tunable topological charge of the output Laguerre Gaussian beam.
Furthermore, the coating cavity mirrors are all plated with multilayer films, the coating front cavity mirror is a concave mirror, and the concave surface of the coating front cavity mirror is plated with a film which is anti-reflection for the pump light and highly reflective for the signal light; the film-coated rear cavity mirror is a concave mirror, and the concave surface of the film-coated rear cavity mirror is plated with a signal light reflection film.
Further, the effective distance between the before-coating cavity mirror and the after-coating cavity mirror is L, and the following conditions are met:
R1and R2Showing the curvature of the pre-coated cavity mirror and the coated back cavity mirror.
Further, the polarization element comprises a broadband Faraday rotator and a broadband quarter wave plate which are sequentially arranged along the light propagation direction.
Furthermore, the vector vortex wave plate is a broadband vector vortex wave plate and is placed at the curvature center of the cavity mirror before film coating.
Furthermore, the effective distance between the vector vortex wave plate and the front cavity mirror is L1An effective distance L from the rear cavity mirror2And satisfies the following relationship: l is1＝R1And L1+L2L, wherein R1The curvature of the film coating front cavity mirror is shown, and L is the effective distance between the film coating front cavity mirror and the film coating rear cavity mirror.
Furthermore, the periodically polarized lithium niobate crystal is arranged at the beam waist of the pumping beam, and the front end face and the rear end face are plated with broadband antireflection films.
Furthermore, the temperature control device comprises a temperature control power supply and a temperature control furnace connected with a temperature control power supply lead, the temperature control furnace is positioned below the crystal, a groove is formed in the surface of the temperature control furnace and used for fixing the periodically polarized lithium niobate crystal, and the temperature control device enables the temperature of the periodically polarized lithium niobate crystal to be kept stable.
Has the advantages that: the invention provides an optical parametric oscillator which can efficiently output Laguerre Gaussian beams with high purity, wavelength and topological charge number:
(1) according to the invention, by designing the optical parametric oscillation system to be combined with the generation of the Laguerre Gaussian beam, the optical parametric oscillation resonant cavity meets the stability condition and the wave front and polarization self-reproduction condition, the Laguerre Gaussian beam can be directly output by the resonant cavity, the wavelength tuning range is wider, and the topological load tuning range is larger. Taking the specific implementation example as an example, the tuning range of the output wavelength reaches 100nm, and the topological load range of the output Laguerre Gaussian beam can reach-4 to 4.
(2) The position relation between the vector vortex wave plate and the front cavity mirror meets the following requirements that 1: 1, the cavity mode smoothly evolves into a hollow Laguerre Gaussian beam from a solid beam in the propagation process under the imaging condition of the concave mirror, no aperture is needed in the resonant cavity for mode selection to improve the purity, lower cavity loss is realized, and higher gain is obtained by matching with the pumping Gaussian beam, so that the optical parametric oscillator has higher output efficiency. The specific implementation example is taken as an example to output Laguerre Gaussian beam, and the efficiency of the Laguerre Gaussian beam in the wavelength range of 1500nm-1600nm can reach more than 15 percent at most.
(3) Due to the arrangement of the imaging relation between the vector vortex wave plate and the concave mirror of the front cavity mirror, the parametric light obtains gain at the front cavity mirror and smoothly evolves into hollow annular distribution and then passes through the vector vortex wave plate, so that the generation of a high-order radial mode is effectively inhibited, and the output of a high-purity Laguerre Gaussian mode is ensured. Taking a specific implementation example as an example, the output Laguerre Gaussian mode is in a topological load tuning range of-4 to 4, and the mode purity can reach more than 97 percent at most.
(4) The Laguerre Gaussian optical parametric oscillator designed by the invention can meet the requirement of high-efficiency output of high-purity Laguerre Gaussian beams in different wavelength ranges by replacing elements with different working wavelengths and pump lasers with corresponding wavelengths.
Drawings
FIG. 1 is a light path diagram of a broadband topology load tunable Laguerre Gaussian optical parametric oscillator provided by the present invention;
FIG. 2 is a simulation diagram of the intensity distribution of the optical field profile during propagation of the cavity mode of the resonant cavity;
FIG. 3(a) shows the output of an optical parametric oscillator within the 1500nm-1600nm working bandwidth
A scatter diagram of conversion efficiency of light beam, and (b) for output of 1550nm
A light intensity profile of the light beam;
FIG. 4(a) shows an optical parametric oscillator output of 1550nm
A weight distribution map of the mode components of the light beam, and (b) adjusting the output wavelengths of the optical parametric oscillator at 1525nm and 1575nm
The modal content weight profile of the beam.
Detailed Description
Fig. 1 is a schematic diagram of an optical path structure of a broadband topology charge tunable laguerre gaussian optical parametric oscillator provided by the invention, wherein the laser is a solid laser, and as shown in fig. 1, the laser comprises a nanosecond pulse laser 1, a beam shaping device 2, a coated cavity mirror 3, a periodically polarized lithium niobate crystal 4, a temperature control device 5, a polarization element 6 and a vector vortex wave plate 7. The nanosecond pulse laser 1, the light beam shaping device 2 and the film coating cavity mirror 3 are sequentially arranged along the light propagation direction, the periodically polarized lithium niobate crystal 4, the polarization element 6 and the vector vortex wave plate 7 are sequentially arranged in the film coating cavity mirror 3 along the light propagation direction, and the temperature control device 5 is arranged below the periodically polarized lithium niobate crystal 4. The nanosecond pulse laser 1 serves as a pump light source to provide a pump beam with a specified wavelength, in this embodiment, a 1064nm pump beam. The beam shaping device 2 is composed of a lens group and is used for adjusting the beam waist and the position of a 1064nm beam to generate a 1064nm Gaussian beam, and the maximum pumping power can reach 5 w. The film coating cavity mirror 3 comprises a film coating front cavity mirror 31 and a film coating back cavity mirror 32 which form a resonant cavity, the film coating front cavity mirror 31 is positioned in front of the periodically polarized lithium niobate crystal 4, the film coating back cavity mirror 32 is positioned at the last of the optical parametric oscillator, the film coating front cavity mirror 31 and the film coating back cavity mirror 32 are both coated with multilayer films, the film coating front cavity mirror 31 is a concave mirror, and the curvature is R1The concave surface is plated with 1064nm anti-reflection layer with 1450-1650 nm widthWith a highly reflective coating, the coated mirror 32 is a concave mirror with a curvature R2The concave surface is plated with a 1450nm-1650nm broadband reflection film. The periodically polarized lithium niobate crystal 4 has the size of 25mm multiplied by 12.3mm multiplied by 1mm, is arranged at the beam waist of a 1064nm pumping Gaussian beam and is used for interacting with the 1064nm pumping Gaussian beam to provide parametric gain and amplify a converted light field under parameters, the pumping light and the parametric light are both vertically polarized, the front end face and the rear end face of the periodically polarized lithium niobate crystal 4 are plated with 1380nm-1800nm broadband antireflection films, and are provided with ten channels with different polarization periods, so that signal light with the wavelength of 1480nm-1650nm can be generated within the temperature range of 25 ℃ to 138 ℃. The temperature control device 5 is used for stabilizing and regulating the temperature of the periodically polarized lithium niobate crystal so as to change the quasi-phase matching condition and control the wavelength of the generated signal light, the temperature control device 5 comprises a temperature control furnace and a temperature control power supply, and a groove is formed in the surface of the temperature control furnace and used for fixing the crystal; the temperature control precision of the temperature control device is 0.1 ℃, the temperature of the periodically polarized lithium niobate crystal can be constant, and the stable output of the optical parametric oscillator is ensured. The polarization element 6 comprises a broadband Faraday rotator 61 and a broadband quarter-wave plate 62 which are sequentially arranged along the propagation direction of light beams, and the polarization element 6 adjusts the polarization state of signal light at each position in the resonant cavity so that the optical field in the resonant cavity meets the condition that the phase distribution and the polarization state are reversible, and simultaneously, the light incident on the vector vortex wave plate 7 is circularly polarized light. The vector vortex wave plate 7 is a broadband vector vortex wave plate, the working wave band is 1500nm-1600nm, and the vector vortex wave plate is used for adding a spiral phase to circularly polarized incident light and respectively generating Laguerre Gaussian beams with angular indexes l being +/-1, +/-2 and +/-4 so as to obtain Laguerre Gaussian beam output with tunable topological charge.
The design of the resonant cavity of the optical parametric oscillator firstly meets the stability condition of the resonant cavity and the reversible condition of polarization. Curvature R of cavity mirror before and after coating1And R2The effective cavity length L of the resonant cavity meets the stability condition of the resonant cavity:
so as to ensure that the resonant cavity can stably start oscillation. In order to make the circularly polarized light incident on the vector vortex wave plate to obtain spiral phase, a quarter wave plate is introduced into the resonant cavity for polarization conversion,meanwhile, in order to meet the polarization reversibility condition of the resonant cavity, a Faraday optical rotator with an optical rotation angle of 45 degrees needs to be introduced and placed between the periodically polarized lithium niobate crystal and the quarter-wave plate, so that the polarization state of a light beam is restored after the light beam makes a round trip in the resonant cavity.
In order to reduce the loss in the resonant cavity and obtain high-purity output of the Laguerre Gaussian beam, a cavity mode of the resonant cavity needs to be designed, and on one hand, the cavity mode is located at the front cavity mirror and is distributed by a solid optical field to be matched with the pumped Gaussian beam to ensure higher conversion efficiency; on the other hand, the cavity mode is positioned at the rear cavity mirror and is in a standard Laguerre Gaussian mode to ensure high-purity output, so that the cavity mode is propagated from the front cavity mirror to the rear cavity mirror, smoothly evolves into a hollow beam from a solid beam and generates a standard Laguerre Gaussian beam after passing through the vector vortex wave plate.
The invention arranges a vector vortex wave plate and a front cavity mirror to form a structure 1: 1 concave mirror imaging, namely: l is1＝R1，L1The effective distance between the vector vortex wave plate and the front cavity mirror is realized, because a plurality of optical elements with the refractive index larger than 1 are arranged between the front cavity mirror and the vector vortex wave plate, the actual distance between the vector vortex wave plate and the front cavity mirror is slightly larger than R1。
According to the resonant cavity configuration of the optical parametric oscillator, the scalar diffraction theory analysis is utilized, the standard Laguerre Gaussian mode starts from the rear cavity mirror, and returns to the starting position after the resonant cavity makes a round trip, so that the amplitude and phase distribution self-reproduction is realized. And (3) simulating by a fox-li iterative algorithm to obtain the light intensity distribution of the cavity mode of the resonant cavity in the transmission process, verifying theoretical analysis, and as shown in figure 2, smoothly evolving the cavity mode light beam from the front cavity mirror to the vector vortex wave plate from the solid light beam to the hollow Laguerre Gaussian light beam, adding a spiral phase through the vector vortex wave plate, generating a standard Laguerre Gaussian light beam and outputting the standard Laguerre Gaussian light beam. The resonant cavity die of the optical parametric oscillator provided by the invention has different optical field distributions at the front cavity mirror and the rear cavity mirror, the optical field evolution process is smooth, and the output of high-purity Laguerre Gaussian beams is ensured; and a small-hole filtering mode is not needed, so that the diffraction loss is effectively reduced, and the cavity mode and the pumping light beam are higher in matching degree, so that higher output efficiency is ensured.
FIG. 3(a) shows the output in the range of 1500nm to 1600nm at a pump power of 4.2w using the optical parametric oscillator of the present example
The conversion efficiency scatter plot of the beam, at 1550nm output,
the light beam conversion efficiency is respectively as high as 15.2%, 15.8% and 15.6%, and the output efficiency can reach more than 10% within the working bandwidth exceeding 80 nm; FIG. 3(b) is a graph showing an output of 1550nm
A light intensity profile of the light beam; experimental results show that the optical parametric oscillator provided by the invention can efficiently output Laguerre Gaussian beams with various topological charges in a broadband working range.
Fig. 4 is a result of testing the mode purity of the output beam of the optical oscillator in this example, a characteristic identification method is adopted for analyzing the mode purity of the output laguerre gaussian beam, a spatial light modulator is used to generate a standard laguerre gaussian mode with different angular and radial indexes, and the cross correlation measurement is performed on the standard laguerre gaussian mode and the beam to be measured, and the measurement result can be expressed as:
when the standard mode is consistent with the measured mode, the optical field distribution with the maximum central light intensity can be obtained, and the composition and the weight of the measured mode can be obtained according to the ratio of the central light intensity of the measurement result. FIG. 4(a) shows the output of an optical parametric oscillator at 1550nm
The weight distribution of the mode component of the light beam can be seen to obtain the output of the optical parametric oscillator
The purity of the beam mode is as high as 97% and 96.6%, when outputting higher order mode
In the case of light beams, the mode purity can still reach 95.2% and 93.7%; FIG. 4(b) shows the outputs of the optical parametric oscillator at 1525nm and 1575nm
The weight distribution map of the mode component of the light beam, and output
The mode purity of the beam was 97.1% and 95.9%, respectively; experimental results show that the optical parametric oscillator provided by the invention can ensure high-purity output of Laguerre Gaussian beams with different topological loads in a broadband working range.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (7)
1. A broadband topology load tunable Laguerre Gaussian optical parametric oscillator is characterized in that: including nanosecond pulse laser, beam shaping device and the coating chamber mirror of placing in proper order along light propagation direction, periodic polarization lithium niobate crystal, polarization component and vector vortex wave plate have been placed in proper order along light propagation direction in the coating chamber mirror, be provided with temperature control device under the periodic polarization lithium niobate crystal, wherein:
the nanosecond pulse laser is used as a pumping light source to provide pumping light beams with specified wavelengths;
the beam shaping device is used for shaping and shrinking the pumping beam and adjusting the beam waist size and position of the pumping beam so as to obtain a pumping Gaussian beam matched with the beam waist size and position of the intrinsic cavity of the resonant cavity;
the coating cavity mirror comprises a coating front cavity mirror and a coating rear cavity mirror which form a resonant cavity;
the periodically polarized lithium niobate crystal is used for interacting with the pumping Gaussian beam, providing parametric gain, amplifying the parametric down-conversion light field and generating signal light;
the temperature control device is used for stabilizing and regulating the temperature of the periodically polarized lithium niobate crystal so as to change the quasi-phase matching condition and control the wavelength of the generated signal light;
the polarization element is used for adjusting the polarization state of the signal light at each position in the resonant cavity, so that the polarization can be reversely converted, and the resonant cavity is ensured to meet the polarization self-reproduction condition;
the vector vortex wave plate is used for providing a spiral phase and generating Laguerre Gaussian beams with different angular indexes so as to realize tunable topological charge of the output Laguerre Gaussian beam, and the effective distance between the vector vortex wave plate and the film-coated front cavity mirror is L1And the effective distance from the rear cavity mirror of the coating film is L2And satisfies the following relationship: l is1=R1、L1+L2= L, wherein R1Is the curvature of the front mirror for film coating, and L is the effective distance between the front mirror and the back mirror for film coating.
2. The broadband topologically tunable laguerre gaussian optical parametric oscillator of claim 1, wherein: the coating cavity mirrors are all plated with multilayer films, the coating front cavity mirror is a concave mirror, and the concave surface is plated with a film which is anti-reflection to pumping light and highly reflective to signal light; the film-coated rear cavity mirror is a concave mirror, and the concave surface of the film-coated rear cavity mirror is plated with a signal light reflection film.
3. The broadband topologically tunable laguerre gaussian optical parametric oscillator of claim 1, wherein: the effective distance between the front film-coating cavity mirror and the rear film-coating cavity mirror is L, and the following conditions are met:
R1and R2Showing the curvature of the pre-coated cavity mirror and the coated back cavity mirror.
4. The broadband topologically tunable laguerre gaussian optical parametric oscillator of claim 1, wherein: the polarization element comprises a broadband Faraday rotator and a broadband quarter-wave plate which are sequentially arranged along the light propagation direction.
5. The broadband topologically tunable laguerre gaussian optical parametric oscillator of claim 1, wherein: the vector vortex wave plate is a broadband vector vortex wave plate.
6. The broadband topologically tunable laguerre gaussian optical parametric oscillator of claim 1, wherein: the periodically polarized lithium niobate crystal is arranged at the beam waist of the pumping beam, and the front end face and the rear end face are plated with broadband antireflection films.
7. The broadband topologically tunable laguerre gaussian optical parametric oscillator of claim 1, wherein: the temperature control device comprises a temperature control power supply and a temperature control furnace connected with a temperature control power supply lead, the temperature control furnace is positioned below the crystal, a groove is formed in the surface of the temperature control furnace and used for fixing the periodically polarized lithium niobate crystal, and the temperature control device enables the temperature of the periodically polarized lithium niobate crystal to be kept stable.
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| CN112764214A (en) * | 2021-02-24 | 2021-05-07 | 重庆两江卫星移动通信有限公司 | Diffraction simulation method for generating hollow light beam |
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