A phase programmable laser

Abstract

The application discloses a laser with arbitrary programmable phase, wherein pump light is transmitted into a laser gain crystal through a focusing objective lens and an input concave mirror, and the laser gain crystal is excited to generate laser; when transmitting along an anticlockwise direction, the laser is reflected by a reflecting concave mirror after being emitted from the laser gain crystal, and is irradiated onto a first spatial light modulator to be spatially phase modulated, and then is transmitted onto a second spatial light modulator through a first lens and a second lens; the second spatial light modulator is loaded with a phase conjugate to the first spatial light modulator; after being restored by the second spatial light modulator, the laser is restored into a fundamental mode Gaussian light beam, and is transmitted onto the input concave mirror, reflected, and reaches the laser gain crystal again to be amplified. Laser in a clockwise direction is transmitted and amplified in the cavity, and the two lasers take the same route and only differ in the opposite direction. The application can realize highly coherent, programmable phase, arbitrary controllable spatial phase laser output.

Description

Technical Field

[0001] This invention relates to the fields of optical field manipulation and lasers, and in particular to a laser whose phase can be arbitrarily programmed. Background Technology

[0002] Lasers possess excellent coherence due to their relatively stable phase, and phase modulation is of great value for laser applications. Lasers exhibit unique and outstanding properties such as high brightness, high collimation, and high coherence. Therefore, since the first ruby ​​laser was invented in the 1960s, its development has been rapid and its applications extremely widespread, playing an irreplaceable role in scientific research, medicine, industry, and the military.

[0003] However, current lasers often only output a limited number of resonant cavity eigenmodes, such as the fundamental Gaussian beam or the Laguerre Gaussian mode. These modes are intrinsic to the laser cavity, and therefore, due to the limitations of the laser cavity structure, the spatial output modes of the laser are often not adjustable and are extremely limited in number. To achieve phase adjustment of the optical field, post-processing outside the laser cavity is usually employed.

[0004] Therefore, there is an urgent need for a technology that can achieve highly coherent, phase-programmable, and arbitrarily controllable spatial phase laser output, filling the gap in this field and breaking through the limitation that lasers can only output lasers in specific spatial modes. Summary of the Invention

[0005] The purpose of this invention is to provide a laser with arbitrarily programmable phase, which can achieve highly coherent, phase-programmable, and arbitrarily controllable spatial phase laser output.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A phase-programmable laser includes: a pump source, a focusing objective, an input concave mirror, a laser gain crystal, a reflecting concave mirror, a first spatial light modulator, a first lens, a second lens, and a second spatial light modulator.

[0008] The pump light emitted from the pump source is focused and reduced by the focusing objective lens, then transmitted through the input concave mirror into the laser gain crystal. Within the laser gain crystal, the population inversion occurs, generating laser light in a Gaussian mode. The laser light propagates in both clockwise and counterclockwise directions. When propagating counterclockwise, the laser light exits the laser gain crystal, is reflected by the reflecting concave mirror, and illuminates the first spatial light modulator. After spatial phase modulation by the first spatial light modulator, it is imaged onto the second spatial light modulator by a 4-f system composed of the first and second lenses. The second spatial light modulator is loaded with a phase conjugate to the first spatial light modulator. After being restored by the second spatial light modulator, the laser light is reduced to a fundamental Gaussian beam and transmitted to the input concave mirror. After reflection by the input concave mirror, it reaches the laser gain crystal again for further amplification. Simultaneously, the clockwise laser light propagates and amplifies within the laser cavity. The clockwise and counterclockwise laser light follow the same path but have opposite circumferential directions.

[0009] Optionally, the pump source is a semiconductor laser.

[0010] Optionally, the wavelength of the pump source is 879 nm.

[0011] Optionally, it also includes: a half-wave plate and a polarizing beam splitter;

[0012] The half-wave plate and the polarizing beam splitter are disposed in the optical path between the second lens and the second spatial light modulator;

[0013] The laser transmitted from the second lens is rotated in polarization direction by the half-wave plate, and then split by the polarizing beam splitter, which is used as the output of the laser and transmitted to the second spatial light modulator. The polarizing beam splitter splits the laser that has been phase modulated by the first spatial light modulator into two beams. One beam is output outside the cavity, and the other beam continues to be transmitted to the second spatial light modulator and is restored to a fundamental mode Gaussian light field.

[0014] Optionally, it also includes: a spectrophotometer;

[0015] The beam splitter is disposed in the optical path between the first spatial light modulator and the second spatial light modulator;

[0016] The beam splitter reflects laser light from both sides, resulting in two laser outputs in opposite directions.

[0017] Optionally, the two laser beams output from the beam splitter carry the phase loaded on the first spatial light modulator and the second spatial light modulator, respectively.

[0018] Optionally, the phase-programmable laser is a laser that outputs an arbitrary phase structure. When an arbitrary phase is loaded onto the first spatial light modulator and the second spatial light modulator, an arbitrarily programmable phase structure laser is generated.

[0019] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0020] The present invention provides a phase-programmable laser, which realizes a programmable digital laser by using a first spatial light modulator and a second spatial light modulator. This makes the output laser no longer limited by the eigenmode of the laser resonator, and can flexibly output lasers with arbitrary spatial phase structures according to needs. Moreover, the adjustment is very simple and fast. By switching different phase diagrams on the spatial light modulator through computer control, the phase structure of the output laser can be flexibly changed. Since the spatial light modulator has a refresh rate of about 100Hz, the present invention can switch the output of lasers with 100 different phase spatial structures per second, which has extremely high flexibility and convenience, and truly realizes a phase-programmable digital laser. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a phase-programmable laser according to Embodiment 1 of the present invention.

[0023] Figure 2 A schematic diagram of the measurement results of a vortex laser carrying a single topological charge vortex phase;

[0024] Figure 3 A schematic diagram illustrating the process of creating a relatively flat laser containing multiple orbital angular momentum (vortex components);

[0025] Figure 4 A schematic diagram of the measurement results of an orbital angular momentum comb laser carrying multiple topological charge vortices simultaneously;

[0026] Figure 5 This is a schematic diagram of a phase-programmable laser according to Embodiment 2 of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The purpose of this invention is to provide a laser with arbitrarily programmable phase, which can achieve highly coherent, phase-programmable, and arbitrarily controllable spatial phase laser output.

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] The present invention provides a phase-programmable laser, comprising: a pump source 101, a focusing objective lens 102, an input concave mirror 103, a laser gain crystal 104, a reflecting concave mirror 105, a first spatial light modulator 106, a first lens 107, a second lens 108, and a second spatial light modulator 111.

[0031] The pump light emitted by the pump source 101 is focused and reduced by the focusing objective lens 102, and then transmitted through the input concave mirror 103 into the laser gain crystal 104. Within the laser gain crystal 104, the population inversion occurs, generating a 1064nm wavelength laser. The laser is in Gaussian mode and propagates in both clockwise and counterclockwise directions. When propagating counterclockwise, the laser light exits the laser gain crystal 104, is reflected by the reflecting concave mirror 105, and illuminates the first spatial light modulator 106. After spatial phase modulation by the first spatial light modulator 106, the laser beam is imaged onto the second spatial light modulator 111 by a 4-f system composed of the first lens 107 and the second lens 108. The second spatial light modulator 111 is loaded with a phase conjugate to the first spatial light modulator 106. After being restored by the second spatial light modulator 111, the laser is reduced to a fundamental Gaussian beam and transmitted to the input concave mirror 103. After being reflected by the input concave mirror 103, the laser beam reaches the laser gain crystal 104 again for re-amplification.

[0032] The laser position in a portion of the cavity is phase-modulated by a spatial light modulator to have an arbitrarily controllable spatial phase distribution, while the remaining portion (especially at the laser crystal) is a fundamental Gaussian beam or other types of cavity intrinsic mode laser.

[0033] like Figure 1 and Figure 5As shown, the laser cavity has an "8"-shaped structure. The laser cavity structure utilizes spatial light modulators. Specifically, two spatial light modulators (a first spatial light modulator 106 and a second spatial light modulator 111) are used within the laser resonant cavity. These spatial light modulators can flexibly load various phase diagrams, thereby spatially controlling the phase of the laser beam irradiated onto their surfaces. The laser beam reflected / transmitted from the spatial light modulators (depending on whether a reflective or transmissive spatial light modulator is used) carries the loaded phase. After imaging by a 4-f imaging system composed of two lenses (a first lens 107 and a second lens 108), the two spatial light modulators are positioned as image planes of each other. A phase conjugate complementary to that of the first spatial light modulator 106 is loaded onto the surface of the second spatial light modulator 111. By adjusting the centers of the two spatial light modulators, the spatial phase carried by the oscillating laser beam after passing through the first spatial light modulator is canceled out and restored to the fundamental Gaussian beam after being modulated by the second spatial light modulator, and continues to propagate until it is amplified again by the laser gain crystal 104. By placing a half-wave plate 109 and a polarizing beam splitter 110 in the cavity circuit between two spatial light modulators, where the spatial structure phase has not yet been restored, adjustable laser output can be achieved. The output laser carries the spatial phase loaded by the spatial light modulators. Since the spatial light modulators are electrically programmable components, they can flexibly load any spatial structure phase as needed. Therefore, the digital laser of this invention can flexibly output lasers with arbitrary spatial phase structures, breaking through the limitations of laser output spatial modes and completely realizing a controllable arbitrary phase laser. Furthermore, because the laser cavity structure of this invention ensures that the laser can oscillate in both clockwise and counterclockwise directions, if the polarizing beam splitter 110 and the half-wave plate 109 are replaced with a beam splitter 112, both clockwise and counterclockwise laser paths can be output, and these two laser paths are coherent.

[0034] The pump source 101 is a semiconductor laser with a wavelength of around 879 nm.

[0035] The pump source 101 has a wavelength of 879 nm, which matches well with the resonant pump absorption peak of the Nd:YVO4 laser crystal at 879 nm, thus improving the absorption rate of the pump light. The laser gain crystal 104 used is a YVO4 / Nd:YVO4 / YVO4 double-end bonded crystal with a length of 10 mm. An anti-reflection coating is deposited on the crystal end face near a wavelength of 1064 nm. The input concave mirror 103 is coated to achieve high transmittance near a wavelength of 879 nm and high reflectivity near a wavelength of 1064 nm. The reflecting concave mirror 105, the first spatial light modulator 106, and the second spatial light modulator 111 are coated to achieve high reflectivity at a wavelength of 1064 nm.

[0036] like Figure 1As shown, the phase-programmable laser in Embodiment 1 provided by the present invention further includes: a half-wave plate 109 and a polarizing beam splitter 110.

[0037] The half-wave plate 109 and the polarizing beam splitter 110 are disposed in the optical path between the second lens 108 and the second spatial light modulator 111.

[0038] When the horizontally polarized laser transmitted from the second lens 108 is rotated in polarization direction by the half-wave plate 109, and then split by the polarizing beam splitter 110, it is output as a laser and transmitted to the second spatial light modulator 111.

[0039] After the polarization direction is rotated by the half-wave plate 109, the laser is still linearly polarized light, but the polarization direction is no longer horizontal. After being split by the polarizing beam splitter 110, the vertical polarization component of the laser radiation is reflected at 45° by the beam splitting surface of the polarizing beam splitter 110 and output as the output port of the laser. The remaining horizontal polarization component is transmitted through the polarizing beam splitter 110 and continues to be transmitted to the second spatial light modulator 111, canceling the phase loaded by the first spatial light modulator 106 carried by the light field.

[0040] The structure of Example 1 can output laser light of arbitrary phase. By changing the phase diagram loaded on spatial light modulators 106 and 111, this digital laser can output laser light of arbitrary phase. As an example, it outputs two major categories of distinctive lasers: a. vortex lasers carrying a single topological charge vortex phase (…). Figure 2 b. Orbital angular momentum comb laser carrying multiple topological charge vortices simultaneously ( Figure 4 ).

[0041] like Figure 2 As shown, by switching the topological charge of the vortex phase loaded on the spatial light modulator, the topological charge of the output vortex beam of the laser is changed, thus achieving flexible control of the vortex laser output with different topological charges. The lasers are switched to vortex lasers with topological charges m = 8, 16, 32, 48, 64, and 128, respectively. The image plane position is recorded using a CCD. Figure 2 First row) and focal plane position ( Figure 2 The spot (second row). Furthermore, the topological charge of the output vortex laser is measured by using a third spatial light modulator outside the laser cavity for phase restoration. After restoration, it is coupled into a single-mode fiber to achieve vortex spectrum measurement. The spot after phase restoration by the third spatial light modulator is shown in the image. Figure 2 As shown in the third row, the results of the vortex spectrum measurement are as follows: Figure 2As shown in the bottom four rows. Experimental results show that the arbitrary phase digital laser of this invention can flexibly output vortex lasers with different topological charges, and the topological charge spectrum (i.e., orbital angular momentum spectrum) of the vortex is very pure.

[0042] like Figure 3 As shown, by designing a special phase structure, it is possible to achieve a relatively flat laser containing multiple orbital angular momentum components (vortex components). Since the intensity of each orbital angular momentum component is the same, resembling the teeth of a comb, it is called an orbital angular momentum comb. For example... Figure 3 As shown in part D, if we want to generate N topological loads in sequence as follows: The orbital angular momentum comb (where n = 1, 2, ... N) is then as follows: Figure 3 Part A shows that the phase diagram is uniformly divided into 2N sectors, and every two opposite sectors have the same phase structure, that is, there are a total of N pairs of sectors. The phase distribution of each sector is as follows: in By numerically calculating the initial phase of each sector, a relatively flat initial phase solution of the spectrum can be obtained. Then, by loading this phase, a relatively flat orbital angular momentum spectrum of the laser can be obtained.

[0043] like Figure 4 As shown, the output is a relatively flat orbital angular momentum comb laser containing multiple orbital angular momentum (vortex components). By changing the phase loaded on the spatial light modulator, orbital angular momentum spectra in 8D, 16D, 32D, 48D, and 64D were achieved. Figure 4 The first column is the phase diagram loaded by the spatial light modulator. Figure 4 The second column shows the spot pattern of the output laser recorded at the image plane position of the spatial light modulator. Figure 4 The third and fourth columns show the focal spot images after laser focusing, obtained from experimental and theoretical calculations, respectively. Figure 4 The fifth column shows the laser image after conjugate phase reconstruction, and the sixth column shows the orbital angular momentum spectrum of the output laser obtained by orbital angular momentum projection measurement using an extracavity spatial light modulator and single-mode fiber. Experimental results show that the digital laser of this invention can flexibly output orbital angular momentum comb lasers of different dimensions according to requirements. This orbital angular momentum comb laser has potential applications in high-dimensional communication and coding.

[0044] like Figure 5 As shown, the phase-programmable laser in Embodiment 2 of the present invention further includes a beam splitter 112.

[0045] The beam splitter 112 is disposed in the optical path between the second lens 108 and the second spatial light modulator 111.

[0046] The beam splitter 112 reflects laser light on both sides to output two laser beams in opposite directions.

[0047] In the above embodiment 2, the half-wave plate 109 and polarizing beam splitter 110 in embodiment 1 are replaced with a beam splitter 112 with a fixed transmittance and reflectance ratio.

[0048] The two laser beams output by the beam splitter 112 carry the phases loaded on the first spatial light modulator 106 and the second spatial light modulator 111, respectively.

[0049] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0050] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A laser with arbitrarily programmable phase, characterized in that, include: Pump source, focusing objective, input concave mirror, laser gain crystal, reflecting concave mirror, first spatial light modulator, first lens, second lens, and second spatial light modulator; The pump light emitted by the pump source is focused and reduced by the focusing objective lens, then transmitted through the input concave mirror into the laser gain crystal. Within the laser gain crystal, the population inversion occurs, generating laser light in Gaussian mode. The laser light propagates in both clockwise and counterclockwise directions. When propagating counterclockwise, the laser light exits the laser gain crystal, is reflected by the reflecting concave mirror, and illuminates the first spatial light modulator. After spatial phase modulation by the first spatial light modulator, it is imaged onto the second spatial light modulator by a 4-f system composed of the first and second lenses. The second spatial light modulator is loaded with a phase conjugate to that of the first spatial light modulator. After being restored by the second spatial light modulator, the laser is reduced to a fundamental Gaussian beam and transmitted to the input concave mirror. After being reflected by the input concave mirror, it reaches the laser gain crystal again for further amplification. At the same time, the clockwise laser beam is transmitted and amplified within the laser cavity. The clockwise and counterclockwise lasers follow the same path, but their directions of rotation are opposite.

2. A phase-programmable laser according to claim 1, characterized in that, The pump source is a semiconductor laser.

3. A phase-programmable laser according to claim 1, characterized in that, The wavelength of the pump source is 879 nm.

4. A phase-programmable laser according to claim 1, characterized in that, Also includes: Half-wave plate and polarizing beam splitter; The half-wave plate and the polarizing beam splitter are disposed in the optical path between the second lens and the second spatial light modulator; The laser transmitted from the second lens is rotated in polarization direction by the half-wave plate, and then split by the polarizing beam splitter, which is used as the output of the laser and transmitted to the second spatial light modulator. The polarizing beam splitter splits the laser that has been phase modulated by the first spatial light modulator into two beams. One beam is output outside the cavity, and the other beam continues to be transmitted to the second spatial light modulator and is restored to a fundamental mode Gaussian light field.

5. A phase-programmable laser according to claim 1, characterized in that, Also includes: Spectrophotometer; The beam splitter is disposed in the optical path between the first spatial light modulator and the second spatial light modulator; The beam splitter reflects laser light from both sides, resulting in two laser outputs in opposite directions.

6. A phase-programmable laser according to claim 5, characterized in that, The two laser beams output from the beam splitter respectively carry the phase loaded on the first spatial light modulator and the second spatial light modulator.

7. A phase-programmable laser according to claim 1, characterized in that, The laser with arbitrarily programmable phase outputs a laser with an arbitrary phase structure. When an arbitrary phase is applied to the first spatial light modulator and the second spatial light modulator, a laser with an arbitrarily programmable phase structure is generated.

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