CN104865770A - Method for achieving one-dimensional deflection and beam divergence angle scaling of laser beam based on optical phased array - Google Patents

Abstract

The invention provides a method for achieving one-dimensional deflection and beam divergence angle scaling of a laser beam based on an optical phased array. According to the method, a phase surface having a linear component and a non-linear component at the same time is modulated for the laser beam through a liquid crystal optical phased array, the linear component is determined according to the deflection angle of the laser beam, and the nonlinear component is determined according to the beam divergence angle of the laser beam. Deflection of the laser beam and scaling of the beam divergence angle are achieved at the same time through one liquid crystal optical phased array, the complexity and the power consumption of a system are lowered, the flexibility of the system is improved, and operation is easy and convenient.

Description

Method for realizing one-dimensional deflection and beam divergence angle scaling of laser beam based on optical phased array

Technical Field

The invention belongs to the technical field of optical phased array laser radars, and particularly relates to a beam control technology of an optical phased array laser radar.

Background

The optical phased array laser radar has the advantages of high stability, high resolution, synchronous multi-beam shaping capability, dynamic focusing/defocusing capability, high cost performance and the like, and can be widely applied to the fields of distance measurement, three-dimensional imaging, target capturing and tracking and the like. The optical phased array laser radar modulates the phase of a laser beam through the optical phased array to realize programmable random inertia-free beam scanning of the laser beam in the field range of the laser beam. The liquid crystal optical phased array has the advantages of high phase modulation precision, wide birefringence range, wide waveband, low driving voltage, high damage threshold value, low cost, mature process and the like, and is widely applied to the optical phased array laser radar. Generally, the field of view of the liquid crystal optical phased array is not less than 100mrad (which is the corresponding radian value when the field of view is ± 3 °), and the beam divergence angle of the laser beam is typically a few tenths of a milliradian. In spatial optical communication, the beam spread angle of the laser beam is even only a few micro radians. When the laser radar scans the whole field range once with the small divergence angle laser beam, a long time is consumed, which is not beneficial to the laser radar to quickly detect the target entering the field range, and the working efficiency of the laser radar is reduced.

In order to improve the beam scanning efficiency of the laser radar, the laser radar can firstly scan the whole field range by the wide beam divergence angle laser beam, and then accurately position the target by the small beam divergence angle laser beam after finding the target. In general, the beam spread angle of a laser source is fixed, which requires the capability of the lidar to adaptively scale the beam spread angle of the laser beam. The laser source in the laser radar is usually a fundamental mode gaussian beam, and our research results are disclosed in proc.spie 8557, Optical Design and Testing V,85570I, and the method of optimizing the controlling the laser beam divergence angle based on the liquid crystal Optical phased array indicates that the purpose of adaptively scaling the gaussian beam divergence angle can be achieved by modulating a nonlinear phase plane for the gaussian beam by the liquid crystal Optical phased array, but the gaussian beam is not deflected at this time.

In order to deflect the Gaussian beam to any angle within the field range of the laser radar, a linear phase plane needs to be applied to the Gaussian beam by using a liquid crystal optical phased array, and two liquid crystal optical phased arrays are needed for realizing one-dimensional deflection and beam divergence angle scaling of the laser beam simultaneously.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for simultaneously realizing one-dimensional deflection and beam divergence angle scaling of a laser beam by using a single liquid crystal optical phased array.

The invention adopts the technical scheme that the method for realizing the one-dimensional deflection and the beam divergence angle scaling of the laser beam based on the optical phased array comprises the following steps:

1) parameter configuration step: the laser radar comprises a one-dimensional liquid crystal optical phase control array LCOPA and a laser source which emits light beams as fundamental mode Gaussian light beams; the LCOPA is provided with N phase control units, the distance between adjacent phase control units is d, and the serial numbers N from left to right of the phase control units are-N/2 +1, …, -1,0,1, … and N/2; the wavelength of the laser source is lambda and the beam waist radius is omega₀；

2) Calculating a linear phase plane for realizing one-dimensional deflection: when the incident beam is to be deflected to an angle θ, the LCOPA is applied to the linear phase plane of the laser beamComprises the following steps:

delta phi is the phase difference between adjacent phase control units in the LCOPA, the delta phi is-2 pi dsin (theta)/lambda, and theta is any angle in the range of the field of the LCOPA;

3) the nonlinear phase plane calculation step for realizing beam spread angle scaling comprises the following steps: when the incident beam is to be scaled to the beam divergence angle theta_widWhile LCOPA is applied to the non-linear phase plane of the laser beamComprises the following steps:

wherein,k is wave number, k is 2 pi/lambda; f is the angle theta with the beam divergence_widA corresponding phase control parameter of the LCOPA;

4) phase synthesis: the phase modulation amount of each phase control unit in the LCOPA is obtained by combining the linear phase plane and the nonlinear phase planeComprises the following steps:

5) a voltage code generation step: by looking upCurve, the phase modulation amount can be obtainedCorresponding voltage code <math> <mrow> <mi>v</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>,</mo> <mi>n</mi> <mo>=</mo> <mo>-</mo> <mfrac> <mi>N</mi> <mn>2</mn> </mfrac> <mo>+</mo> <mn>1</mn> <mo>,</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>,</mo> <mo>-</mo> <mn>1,0,1</mn> <mo>,</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>,</mo> <mfrac> <mi>N</mi> <mn>2</mn> </mfrac> <mo>;</mo> </mrow> </math>

6) A phase modulation step: loading each voltage code v (n) on each phase control unit in the LCOPA correspondingly through a controller to modulate the phase of incident laser, and controlling the laser beam to deflect to an angle theta and scale to a beam divergence angle theta_wid。

The invention provides a laser beam deflection and beam divergence angle scaling method based on a monolithic liquid crystal optical phased array.

The invention has the advantages that the deflection and beam divergence angle scaling of the laser beam can be realized simultaneously through one liquid crystal optical phased array, the complexity and the power consumption of the system are reduced, the flexibility of the system is increased, and the operation is simple and convenient.

Drawings

FIG. 1 is a flow chart of an embodiment.

FIG. 2 is a model of a typical one-dimensional liquid crystal optical phased array.

FIG. 3 is a model of the spatial propagation of a fundamental mode Gaussian beam.

FIG. 4 shows the distance θ between the beam waist of incident Gaussian beam and the LC phased array at 1m_wid-f-curve.

FIG. 5 shows an optical phase-control array of liquid crystalsCurve line.

Fig. 6 shows a linear phase plane applied to the gaussian beam by the liquid crystal optical phased array when the gaussian beam is deflected 1 ° to the right.

Fig. 7 shows a nonlinear phase plane applied to a gaussian beam by a liquid crystal optical phased array when the beam divergence angle of the gaussian beam is enlarged by 2 times.

Fig. 8 is a composite phase plane to be applied to the gaussian beam by the liquid crystal optical phased array when the beam divergence angle of the gaussian beam is enlarged by 2 times and deflected to the right by 1 °.

Fig. 9 shows the found voltage codes corresponding to the resulting phase planes, (a) the voltage codes of all the phase control elements of the LCOPA, and (b) a partial enlargement of (a) giving the voltage codes of the phase control elements numbered from-100 to 100.

Fig. 10 is a far field spot of a gaussian beam without any phase modulation.

Fig. 11 shows the far field spot of a gaussian beam after the resultant phase plane modulation is applied.

Detailed Description

A flow chart of a preferred method according to the invention is shown in fig. 1, comprising the following steps:

step 1: and (5) parameter configuration. The model of the one-dimensional transmissive liquid crystal optical phased array used in the present invention is shown in fig. 2, and comprises N phased units, the numbers of the phased units from left to right are-N/2 +1, …, -1,0,1, …, and N/2, and the distance from the center to the center of the adjacent phased units is d. The laser beam emitted by the laser source is a fundamental mode gaussian beam, and the spatial propagation model of the laser beam is shown in fig. 3. The beam waist radius of the fundamental mode Gaussian beam is omega₀The included angle between the asymptotes of a pair of hyperbolas is the beam divergence angle thereof. In addition, the wavelength of the Gaussian beam is lambda, and the distance between the beam waist and the liquid crystal optical phased array is z₀。

Step 2: a deflection angle for emitting laser light is set. The deflection angle of the laser beam after passing through the liquid crystal optical phased array is set as theta, wherein theta can take a positive value or a negative value, the positive sign only indicates the deflection direction of the light beam and is irrelevant to the actual size of the deflection angle, the positive sign indicates that the light beam deflects towards the right, and the negative sign indicates that the light beam deflects towards the left.

And step 3: the phase difference between adjacent phase control elements in the LCOPA is calculated. The phase difference can be given by Δ φ ═ 2 π dsin (θ)/λ.

And 4, step 4: a linear phase plane is designed. The linear phase plane controls the deflection direction of the laser beam, and the required linear phase plane is that for deflecting the laser beam to an angle theta

And 5: the beam divergence angle of the emitted laser light is set. The beam divergence angle of the emitted laser beam can be arbitrarily set within the range of scaling the beam divergence angle of the laser beam by the LCOPA, and the beam divergence angle θ of the laser beam can be multiplied or reduced_wid。

Step 6: phase control parameters of the LCOPA are determined. Phase control parameter f of LCOPA and beam divergence angle theta of emergent laser beam_widHas the relation ofTo increase the computation speed of the control system, the theta is generated in advance_wid-f data tables stored in a data memory of the control system. From the above formula, f and θ_widWith the parameter z in step 1₀Of close relationship, in lidar or other apparatus, z₀The value of (b) is generally fixed. When z is₀When 1m is equal to f and theta_widThe relationship of (2) is shown in FIG. 4. As can be seen from FIG. 4, most of θ_widBoth correspond to two f-values, one of which is optional. Here, it is necessary to say that z is₀Taking negative values indicates that the LCOPA is in front of the laser source.

And 7: designing a nonlinear phase plane. According to the determined phase control parameter f of LCOPA, the nonlinear phase plane can be formed byIt is given.

And 8: two phase planes are combined. In order to achieve the purpose of realizing laser beam deflection and beam divergence angle scaling based on a monolithic liquid crystal optical phased array, a phase plane is required to be designed to simultaneously have the linear phase plane component and the nonlinear phase plane component, and the synthesized phase plane is as follows:

and step 9: a voltage code loaded onto the LCOPA is generated. The voltage phase shift static characteristic curve of LCOPA is shown in FIG. 5, each phase modulation amountA corresponding voltage code v (n) can be found. As can be seen from the static characteristic curve in fig. 5, the maximum phase modulation amount of the LCOPA reaches about 3.6 π rad. In fact, the maximum phase modulation of LCOPA only needs 2 π rad, so that the search and the matching are performedIn principle, any phase modulation interval with interval length of 2 pi can be selected to search the corresponding voltage code v (n) when the voltage code corresponds to the voltage code. However, the phase modulation effect of the LCOPA is slightly different in consideration of different sections, and can be adjusted through experiments to select a more appropriate section.

Step 10: the phase of the incident laser light is modulated. Coding the string of voltages generated in step 9Loading the phase control unit onto the corresponding phase control unit in LCOPA via the controller, and providing the synthetic phase plane designed for modulation of the incident laser light to deflect the emergent laser light to an angle theta and have a beam divergence angle theta_wid。

It should be noted that, by changing the beam divergence angle and the deflection angle of the laser beam as required and repeating the above steps, the laser beam can be scanned within the field of view of the LCOPA by adaptively changing the beam divergence angle.

Examples

Step 1: the LCOPA comprises 1920 phase control elements, and the distance from the center to the center of adjacent phase control elements is 5 multiplied by 10^-6And m is selected. The wavelength of the laser beam is 1.064X 10^-6m, beam waist radius of 0.675 × 10^-3m, the distance between the beam waist and the LCOPA is 1 m.

Step 2: the deflection angle θ takes 1 °, i.e., the outgoing laser light is deflected 1 ° to the right.

And step 3: the phase difference between adjacent phased units is-0.5153 rad.

And 4, step 4: the linear phase plane component isWhere n-959, …, -1,0,1, …,960, see fig. 6. It should be noted here that, as is clear from the static characteristic curve shown in fig. 5, since the phase modulation amount of the LCOPA is actually a positive value, the entire linear phase plane is shifted upward so that the linear phase component of each phase control element is equal to or greater than zero while the relative phase between the phase control elements is kept unchanged.

And 5: here we set the divergence angle of the laser beam to be enlarged by a factor of 2, the divergence angle of the incident laser beam can be made from 2 λ/(π ω)₀) To make an estimate. The beam divergence angle of the incident laser light is 1 × 10 according to the laser wavelength and beam waist radius given in the previous step^-3rad, so that the beam spread of the outgoing laser beam is 2X 10^-3rad。

Step 6: the phase control parameter f and the beam spread angle theta for the LCOPA given in fig. 4_widWe find that f can be-1.36 or 0.69, where we take f-0.69.

And 7: the nonlinear phase plane component isWhere n-959, …, -1,0,1, …,960, see fig. 7. The same processing method as that in step 4 is adopted, and the nonlinear phase components of the phase control units are all larger than or equal to zero.

And 8: the resultant phase plane isThe value of n is the same as the previous steps, and the resultant phase plane is shown in fig. 8. Similarly, the same processing method as that in step 4 is also employed here, so that the phase modulation amount of each phase control unit is not less than zero.

And step 9: it should be noted that, as can be seen from fig. 8, the maximum phase modulation amount is close to 1000rad, and in order to facilitate the search of the voltage code, we will perform a remainder operation on the designed synthetic phase plane with respect to 2 pi during the search process, so that the phase modulation amount of each phase control unit is [0,2 pi ]]Within the range. Based on the static characteristic curve of LCOPA shown in FIG. 5, we select the phase modulation interval [15.5,21.78 ]]To find and synthesize the phase planeThe corresponding voltage code v (n) is shown in fig. 9. Fig. 9 (b) is a partially enlarged view of (a), showing the details of the search result.

Step 10: and loading the searched voltage code v (n) to a phase control unit of the LCOPA, carrying out phase modulation on the Gaussian beam, and observing a far-field light spot of the emergent beam. Here we give the simulation results with MATLAB software, FIG. 10 is the far-field light spot of the Gaussian beam without any phase modulation, according to the simulation data, the transverse and longitudinal beam divergence angles of the light spot are all 1 × 10^-3And (7) rad. The far field spot of the outgoing beam after modulating the upper composite phase plane for the gaussian beam is shown in fig. 11. Comparing fig. 11 and 10, we can observe that the transverse divergence angle of the exit beam is significantly broadened, the longitudinal divergence angle is substantially unchanged, and the exit beam is deflected approximately 1 ° in the transverse direction and is not deflected in the longitudinal direction. From the simulation data, the transverse divergence angle of the emergent beam was 2 × 10^-3rad, longitudinal beam divergence angle of 1X 10^-3rad, the transverse divergence angle of the visible emergent beam is amplified by two times, and the longitudinal divergence angle is unchanged; the deflection angle of the outgoing beam in the transverse direction is 1 deg., and the deflection angle in the longitudinal direction is 0 deg.. By combining the two points, the method can achieve the purpose of simultaneously realizing laser beam deflection and beam divergence angle scaling based on a single LCOPA.

Claims (1)

1. The method for realizing the one-dimensional deflection and beam divergence angle scaling of the laser beam based on the optical phased array is characterized by comprising the following steps of:

1) parameter configuration step: the laser radar comprises a one-dimensional liquid crystal optical phase control array LCOPA and a laser source which emits light beams as fundamental mode Gaussian light beams; the LCOPA is provided with N phase control units, the distance between adjacent phase control units is d, and the serial numbers N from left to right of the phase control units are-N/2 +1, …, -1,0,1, … and N/2; the wavelength of the laser source is lambda;

2) linear phase plane calculation step for one-dimensional deflection: the LCOPA applies a linear phase plane to the laser beam when the incident beam is to be deflected to an angle thetaComprises the following steps:

delta phi is the phase difference between adjacent phase control units in the LCOPA, the delta phi is-2 pi dsin (theta)/lambda, and theta is any angle in the field range of the LCOPA;

3) the nonlinear phase plane calculation step for realizing beam spread angle scaling comprises the following steps: when the incident beam is to be scaled to the beam divergence angle theta_widWhile LCOPA is applied to the non-linear phase plane of the laser beamComprises the following steps:

wherein,k is wave number, k is 2 pi/lambda; f is the angle theta with the beam divergence_widA corresponding phase control parameter of the LCOPA;

4) phase synthesis: the phase modulation amount of each phase control unit in the LCOPA is obtained by combining the linear phase plane and the nonlinear phase planeComprises the following steps:

5) a voltage code generation step: by looking upCurve, the phase modulation amount can be obtainedThe corresponding voltage codes v (n), $n=-\frac{N}{2}+1,...,-\mathrm{1,0,1},...,\frac{N}{2};$

6) a phase modulation step: loading each voltage code v (n) on each phase control unit in the LCOPA correspondingly through a controller to modulate the phase of incident laser, and controlling the laser beam to deflect to an angle theta and scale to a beam divergence angle theta_wid。