Email alert
RSS2023 Vol. 35, No. 4
Display Method:
2023,
35: 1-2.
2023,
35: 041001.
doi: 10.11884/HPLPB202335.220305
Abstract:
The optical phased array technology has the advantages of fast response speed, compact structure, and flexibility in control, thus it has been widely used in many scientific and technological fields. Over the past 50 years, many excellent research results have emerged. To give an overview of the optical phased arrays, the article first briefly reviews the history of the optical phased arrays, and introduces the basic principles. From the perspective of different applications including beam projecting and receiving, combined with the author’s thinking, the current status of the developments in high-quality laser source, laser coherent combining, laser steering, atmospheric distortion correction, and synthetic aperture imaging are introduced in detail. Finally, the bottleneck and the future development trends of the optical phased arrays are given.
The optical phased array technology has the advantages of fast response speed, compact structure, and flexibility in control, thus it has been widely used in many scientific and technological fields. Over the past 50 years, many excellent research results have emerged. To give an overview of the optical phased arrays, the article first briefly reviews the history of the optical phased arrays, and introduces the basic principles. From the perspective of different applications including beam projecting and receiving, combined with the author’s thinking, the current status of the developments in high-quality laser source, laser coherent combining, laser steering, atmospheric distortion correction, and synthetic aperture imaging are introduced in detail. Finally, the bottleneck and the future development trends of the optical phased arrays are given.
2023,
35: 041002.
doi: 10.11884/HPLPB202335.220282
Abstract:
This article summarizes the research progress of common aperture coherent beam combining based on diffraction optical elements domestically and abroad, starting from the basic principles of diffraction optical elements, and focusing on the two application fields of continuous waves and pulsed waves. Domestically, the Shanghai Institute of Optics and Fine Mechanics has achieved the synthesis of both continuous and pulsed light. Continuous light output of 206 W was achieved with a beam quality of 1.38 and a beam combining efficiency of 29.6%; pulsed light output of a nanosecond-level pulse coherent combining beam with a peak power of 1.02 kW and a repetition frequency of 2.2 MHz was achieved, beam combining efficiency is 61%. Abroad, 4.9 kW coherent beam combining output has been achieved in continuous light, with a beam coupling efficiency of 82%; in the case of pulsed light, a femtosecond-level pulsed coherent beam combining beam with an average power of 150 mW and a repetition frequency of 100 MHz has been achieved, with a beam coupling efficiency of 83.4%. Finally, the future development of laser coherent beam combining technology based on diffraction optical elements is discussed, and it is believed that in the near future, diffraction optical element-based coherent beam combining technology will continue to develop, gradually break through technical bottlenecks, and lay a solid foundation for more application fields.
This article summarizes the research progress of common aperture coherent beam combining based on diffraction optical elements domestically and abroad, starting from the basic principles of diffraction optical elements, and focusing on the two application fields of continuous waves and pulsed waves. Domestically, the Shanghai Institute of Optics and Fine Mechanics has achieved the synthesis of both continuous and pulsed light. Continuous light output of 206 W was achieved with a beam quality of 1.38 and a beam combining efficiency of 29.6%; pulsed light output of a nanosecond-level pulse coherent combining beam with a peak power of 1.02 kW and a repetition frequency of 2.2 MHz was achieved, beam combining efficiency is 61%. Abroad, 4.9 kW coherent beam combining output has been achieved in continuous light, with a beam coupling efficiency of 82%; in the case of pulsed light, a femtosecond-level pulsed coherent beam combining beam with an average power of 150 mW and a repetition frequency of 100 MHz has been achieved, with a beam coupling efficiency of 83.4%. Finally, the future development of laser coherent beam combining technology based on diffraction optical elements is discussed, and it is believed that in the near future, diffraction optical element-based coherent beam combining technology will continue to develop, gradually break through technical bottlenecks, and lay a solid foundation for more application fields.
2023,
35: 041003.
doi: 10.11884/HPLPB202335.220323
Abstract:
This paper introduces the state-of-the-art coherent beam combination of phased fiber laser array (PFLA), and summarizes the latest research progress in this area at the Institute of Optics and Electronics, Chinese Academy of Sciences, including optimization of coherent combining capability of PFLA based on amplitude modulation, transceiving coherent combining of PFLA, coherent combining of PFLA using target-in-the-loop, co-phasing combining of receiving beamlets of PFLA under atmospheric turbulence, the method of coherent combining based on multi-aperture wavefront detection, as well as the large-angle high-precision continuous addressing scanning of beams using adaptive fiber-optics collimator and microlens array scanner. The above research will promote the evolution of PFLA technology towards more units, higher power, longer distance etc., and facilitate its combinations and developments with laser atmospheric transmission, space laser communication, adaptive optics and other related theories and applications.
This paper introduces the state-of-the-art coherent beam combination of phased fiber laser array (PFLA), and summarizes the latest research progress in this area at the Institute of Optics and Electronics, Chinese Academy of Sciences, including optimization of coherent combining capability of PFLA based on amplitude modulation, transceiving coherent combining of PFLA, coherent combining of PFLA using target-in-the-loop, co-phasing combining of receiving beamlets of PFLA under atmospheric turbulence, the method of coherent combining based on multi-aperture wavefront detection, as well as the large-angle high-precision continuous addressing scanning of beams using adaptive fiber-optics collimator and microlens array scanner. The above research will promote the evolution of PFLA technology towards more units, higher power, longer distance etc., and facilitate its combinations and developments with laser atmospheric transmission, space laser communication, adaptive optics and other related theories and applications.
2023,
35: 041004.
doi: 10.11884/HPLPB202335.220259
Abstract:
The all-fiber laser array with active phase control uses an all-fiber network to realize internal detection and control of piston phases, which is one of the important development directions of large-scale fiber laser coherent beam combining. It has the advantages of compact structure, no external feedback optical elements and easy expansion. The phase detection based on an all-fiber structure is employed in this paper. The principles of the active phase control method of an all-fiber laser array and the phase-locking process by fiber couplers are introduced. Then, the key techniques are summarized, and the proof-of-concept experiments are carried out based on optimum algorithms. The issue of π phase ambiguity is discussed and the numerical simulation result is given by double wavelength detection. At last, the research status is introduced, and the prospects are presented from the perspectives of expansion, power enhancement and applications.
The all-fiber laser array with active phase control uses an all-fiber network to realize internal detection and control of piston phases, which is one of the important development directions of large-scale fiber laser coherent beam combining. It has the advantages of compact structure, no external feedback optical elements and easy expansion. The phase detection based on an all-fiber structure is employed in this paper. The principles of the active phase control method of an all-fiber laser array and the phase-locking process by fiber couplers are introduced. Then, the key techniques are summarized, and the proof-of-concept experiments are carried out based on optimum algorithms. The issue of π phase ambiguity is discussed and the numerical simulation result is given by double wavelength detection. At last, the research status is introduced, and the prospects are presented from the perspectives of expansion, power enhancement and applications.
2023,
35: 041005.
doi: 10.11884/HPLPB202335.220316
Abstract:
The output power of high-power single fiber laser is limited by various physical effects, and it is difficult to achieve a breakthrough in the short term. Coherent beam combination (CBC) of fiber lasers is an effective technical solution to break the power limit of single fiber laser and achieve higher output power. This paper introduces the status quo of CBC research, which mostly uses free-space structure. It is analyzed that the CBC scheme of spatial structure requires complex optical adjustment, and suffers the problem of long-term drifting. The all-fiber coherent beam combination based on all-fiber combining device can enhance the stability and practicability of the combining laser source, and the recent development of CBC in all-fiber format is reviewed in detail. The combining schemes and research status based on fiber coupler, photon lantern, coherent signal combining device and all-fiber device of self-imaging effect are introduced respectively. The main limiting factors and development bottlenecks of different fiber devices are discussed, and the future development prospects are analyzed.
The output power of high-power single fiber laser is limited by various physical effects, and it is difficult to achieve a breakthrough in the short term. Coherent beam combination (CBC) of fiber lasers is an effective technical solution to break the power limit of single fiber laser and achieve higher output power. This paper introduces the status quo of CBC research, which mostly uses free-space structure. It is analyzed that the CBC scheme of spatial structure requires complex optical adjustment, and suffers the problem of long-term drifting. The all-fiber coherent beam combination based on all-fiber combining device can enhance the stability and practicability of the combining laser source, and the recent development of CBC in all-fiber format is reviewed in detail. The combining schemes and research status based on fiber coupler, photon lantern, coherent signal combining device and all-fiber device of self-imaging effect are introduced respectively. The main limiting factors and development bottlenecks of different fiber devices are discussed, and the future development prospects are analyzed.
2023,
35: 041006.
doi: 10.11884/HPLPB202335.220359
Abstract:
The development history of nonlinear optics laser beam combining technology is reviewed. The basic principles and beam combining ideas based on optical phase conjugation and nonlinear amplification process are expounded. The landmark achievements of laser beam combining methods involving the overlapping coupling, the seed injection and the Brillouin four-wave mixing enhanced phase locking are sorted out. The advantages and bottlenecks of plasma cross beam energy transfer, diamond Raman amplification and liquid Brillouin amplification laser beam combining technologies are summarized. Facing the requirements for realizing high peak power, high average power and high repetition rate laser output, based on the advantages of simple system structure, high power load and high heat dissipation efficiency of the Brillouin amplification laser beam combining technology, we proposed a feasible scheme of the combining laser output with pulse energy of 100 J, pulse width of 10 ns, and repetition rate of 10 Hz.
The development history of nonlinear optics laser beam combining technology is reviewed. The basic principles and beam combining ideas based on optical phase conjugation and nonlinear amplification process are expounded. The landmark achievements of laser beam combining methods involving the overlapping coupling, the seed injection and the Brillouin four-wave mixing enhanced phase locking are sorted out. The advantages and bottlenecks of plasma cross beam energy transfer, diamond Raman amplification and liquid Brillouin amplification laser beam combining technologies are summarized. Facing the requirements for realizing high peak power, high average power and high repetition rate laser output, based on the advantages of simple system structure, high power load and high heat dissipation efficiency of the Brillouin amplification laser beam combining technology, we proposed a feasible scheme of the combining laser output with pulse energy of 100 J, pulse width of 10 ns, and repetition rate of 10 Hz.
2023,
35: 041007.
doi: 10.11884/HPLPB202335.220411
Abstract:
We provide a review of the theoretical research progress on the influence of atmospheric turbulence and thermal blooming on the characteristics and beam quality of laser array beams propagating in the atmosphere. The analytical and numerical simulation methods to study the propagation of laser array beams in the atmosphere are introduced. The influence of the atmospheric turbulence on the intensity, angular spread, directionality, curvature radius and turbulence distance of laser array beams is reviewed, and the influence of the atmospheric thermal blooming on the intensity, propagation efficiency, beam centroid, time scale of thermal blooming and focal shift of laser array beams is also reviewed. It is shown that the influence of atmospheric turbulence and thermal blooming on the beam quality of laser array beams is closely related with the beam combination methods, beam parameters and atmospheric parameters.
We provide a review of the theoretical research progress on the influence of atmospheric turbulence and thermal blooming on the characteristics and beam quality of laser array beams propagating in the atmosphere. The analytical and numerical simulation methods to study the propagation of laser array beams in the atmosphere are introduced. The influence of the atmospheric turbulence on the intensity, angular spread, directionality, curvature radius and turbulence distance of laser array beams is reviewed, and the influence of the atmospheric thermal blooming on the intensity, propagation efficiency, beam centroid, time scale of thermal blooming and focal shift of laser array beams is also reviewed. It is shown that the influence of atmospheric turbulence and thermal blooming on the beam quality of laser array beams is closely related with the beam combination methods, beam parameters and atmospheric parameters.
2023,
35: 041008.
doi: 10.11884/HPLPB202335.220258
Abstract:
This paper introduces our recent research on the coherently combined fiber laser based on spatial structure internal phase locking including the principle of spatial structure internal phase locking, and the experiment of 7-channel fiber laser array carried out to experimentally verify the feasibility of this technique. The detailed results indicate that when the phase noises in the laser channels are locked, the external phase differences an be compensated together, and the laser array can be locked with a same phase wavefront. In addition, the researches on the CBC of target in the loop (TIL) technique and constructing the light fields are introduced as well. In the experiment, the control bandwidth of the CBC system of TIL could be improved effectively, and the orbital angular momentum beams could be generated in the far field, the topological charge could be changed from −1 to +1.
This paper introduces our recent research on the coherently combined fiber laser based on spatial structure internal phase locking including the principle of spatial structure internal phase locking, and the experiment of 7-channel fiber laser array carried out to experimentally verify the feasibility of this technique. The detailed results indicate that when the phase noises in the laser channels are locked, the external phase differences an be compensated together, and the laser array can be locked with a same phase wavefront. In addition, the researches on the CBC of target in the loop (TIL) technique and constructing the light fields are introduced as well. In the experiment, the control bandwidth of the CBC system of TIL could be improved effectively, and the orbital angular momentum beams could be generated in the far field, the topological charge could be changed from −1 to +1.
2023,
35: 041009.
doi: 10.11884/HPLPB202335.220285
Abstract:
The principle of the multi-frequency dithering algorithm is analyzed. The 2-11 channel coherent combining system is simulated as a mathematical model based on the principle of wave optics. The dynamic noise model is introduced, and the root-mean-square (RMS) phase error of the totally combined beam is taken as the evaluation function. The effects of noise frequency and amplitude on the phase locking effect of coherent combining system with different arrays are analyzed. When the noise frequency or amplitude is very large, the algorithm can no longer compensate the phase noise, the phase locking will fail. It is proved that there is an optimal interval between the gain coefficient and the modulation amplitude and only within this interval can phase locking be completed quickly. By introducing the concept of effective bandwidth control, the phase-locking performance of the multi-frequency algorithm has been evaluated intuitively. The research shows that the effective control bandwidth is directly proportional to the sampling frequency and the first-way modulation frequency, and inversely proportional to the noise amplitude, and the effective control bandwidth decreases with the increase of array size.
The principle of the multi-frequency dithering algorithm is analyzed. The 2-11 channel coherent combining system is simulated as a mathematical model based on the principle of wave optics. The dynamic noise model is introduced, and the root-mean-square (RMS) phase error of the totally combined beam is taken as the evaluation function. The effects of noise frequency and amplitude on the phase locking effect of coherent combining system with different arrays are analyzed. When the noise frequency or amplitude is very large, the algorithm can no longer compensate the phase noise, the phase locking will fail. It is proved that there is an optimal interval between the gain coefficient and the modulation amplitude and only within this interval can phase locking be completed quickly. By introducing the concept of effective bandwidth control, the phase-locking performance of the multi-frequency algorithm has been evaluated intuitively. The research shows that the effective control bandwidth is directly proportional to the sampling frequency and the first-way modulation frequency, and inversely proportional to the noise amplitude, and the effective control bandwidth decreases with the increase of array size.
2023,
35: 041010.
doi: 10.11884/HPLPB202335.220312
Abstract:
Aiming at the problem of tilt control in coherent beam combining of laser array, a tilt control method, of which the evaluation function is based on second order moment of combined laser beam, is proposed. The performances of the tilt control method are investigated theoretically and experimentally. In the theoretical study, adopting the second order moment of the combined beam as the evaluation function, the tilt control process of 7 laser beam is simulated based on stochastic parallel gradient descent algorithm. In the experiments, a coherent beam combining system of 7-channel fiber array is built and an adaptive fiber collimator is used as the tilt-control device. Adopting the stochastic parallel gradient descent algorithm, the closed-loop operation of tilt control is achieved with the second order moment of the combined spot as the evaluation function. The theoretical and experimental results show that the tilt control method based on the second order moment of laser beam has great potential on coherent beam combination.
Aiming at the problem of tilt control in coherent beam combining of laser array, a tilt control method, of which the evaluation function is based on second order moment of combined laser beam, is proposed. The performances of the tilt control method are investigated theoretically and experimentally. In the theoretical study, adopting the second order moment of the combined beam as the evaluation function, the tilt control process of 7 laser beam is simulated based on stochastic parallel gradient descent algorithm. In the experiments, a coherent beam combining system of 7-channel fiber array is built and an adaptive fiber collimator is used as the tilt-control device. Adopting the stochastic parallel gradient descent algorithm, the closed-loop operation of tilt control is achieved with the second order moment of the combined spot as the evaluation function. The theoretical and experimental results show that the tilt control method based on the second order moment of laser beam has great potential on coherent beam combination.
2023,
35: 041011.
doi: 10.11884/HPLPB202335.220317
Abstract:
A polarization and sequence incoherent combining technology of pulsed laser beam is introduced. A 100 W level microsecond-pulse all-solid-state sodium beacon laser is performed, via combining two independent 50 W level 589 nm lasers at 500 Hz to be one beam by a polarized coupler. Through a pulsed laser synchronizing and delay controller, the two pulsed laser beams are added successfully at time sequence, and the corresponding repetition rate is up to 1 kHz. The beam quality factor M2 of the combined laser is about 1.41, maintaining at almost equal level with one of two laser beams, and the beam pointing stability is measured to be about 40 μrad, which can well meet the requirements at the time of laser guide star testing. Compared with the coherent beam combining, the approach of polarization and sequence incoherent combining has high efficiency, simple combination, and no specific restriction on phase and frequency spectrum, providing a new way for pulsed laser power scaling. Based on a self-proposed precise polarized splitting technology, four beams of (25 W/beam) μs-pulsed yellow laser are projected up to the sodium layer through one launching telescope at Lijiang Observatory, and successfully generate four sodium guidestars, which could promote the development of multi-conjugate adaptive optics systems on large-aperture ground-based telescopes.
A polarization and sequence incoherent combining technology of pulsed laser beam is introduced. A 100 W level microsecond-pulse all-solid-state sodium beacon laser is performed, via combining two independent 50 W level 589 nm lasers at 500 Hz to be one beam by a polarized coupler. Through a pulsed laser synchronizing and delay controller, the two pulsed laser beams are added successfully at time sequence, and the corresponding repetition rate is up to 1 kHz. The beam quality factor M2 of the combined laser is about 1.41, maintaining at almost equal level with one of two laser beams, and the beam pointing stability is measured to be about 40 μrad, which can well meet the requirements at the time of laser guide star testing. Compared with the coherent beam combining, the approach of polarization and sequence incoherent combining has high efficiency, simple combination, and no specific restriction on phase and frequency spectrum, providing a new way for pulsed laser power scaling. Based on a self-proposed precise polarized splitting technology, four beams of (25 W/beam) μs-pulsed yellow laser are projected up to the sodium layer through one launching telescope at Lijiang Observatory, and successfully generate four sodium guidestars, which could promote the development of multi-conjugate adaptive optics systems on large-aperture ground-based telescopes.
2023,
35: 041012.
doi: 10.11884/HPLPB202335.220203
Abstract:
As a beam control device, optically addressed liquid crystal light valve is easy to produce thermal effect due to absorption under the action of high-power density laser, resulting in damage to photoconductive materials, conductive films and liquid crystals. At the same time, thermal effect will also affect the uniformity of the device, reduce the extinction performance of the device. These factors limit the application of the device in laser processing, high power density laser shaping and other fields. To solve the application limitation of optically addressed liquid crystal light valve in the field of high power density beam control, an optically addressed liquid crystal light valve for high power density laser system is developed. The on/off ratio of the light valve is not less than 140∶1. It can work normally in the continuous laser system higher than 2300 W/cm2. At the same time, the light valve can work normally in the femtosecond pulse laser system with high repetition frequency gigawatt power density. Under the action of the maximum power density laser of the system, the light valve has no obvious temperature change. The maximum average power density of the pulse system exceeds 300 W/cm2.
As a beam control device, optically addressed liquid crystal light valve is easy to produce thermal effect due to absorption under the action of high-power density laser, resulting in damage to photoconductive materials, conductive films and liquid crystals. At the same time, thermal effect will also affect the uniformity of the device, reduce the extinction performance of the device. These factors limit the application of the device in laser processing, high power density laser shaping and other fields. To solve the application limitation of optically addressed liquid crystal light valve in the field of high power density beam control, an optically addressed liquid crystal light valve for high power density laser system is developed. The on/off ratio of the light valve is not less than 140∶1. It can work normally in the continuous laser system higher than 2300 W/cm2. At the same time, the light valve can work normally in the femtosecond pulse laser system with high repetition frequency gigawatt power density. Under the action of the maximum power density laser of the system, the light valve has no obvious temperature change. The maximum average power density of the pulse system exceeds 300 W/cm2.
