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Lasers with cavities consisting of retroreflecting elements can give the potential for large-dynamic-range alignment-free operation, which makes the important applications in adaptive wireless laser power transfer/communication possible. In such an emerging approach based on resonant laser beam in the cavity, the laser is delivered to the photovoltaic cell for charging application (or photodiode for communication application) at the receiver automatically, without the necessity of positioning and aiming the receiver in conventional laser wireless power transfer techniques. The laser capable of operating alignment-free efficiently across large-dynamic-range is essential for the application. In this work, the requirements for the dynamic range of alignment-free operation are summarized. An alignment-free laser with a cavity consisting of cat-eye retroreflectors is designed, and a large alignment-free dynamic range as never before is experimentally demonstrated. Telescope system in the laser cavity is adopted to suppress the beam expansion to enhance the working distance between the laser transmitter and the receiver. Coupled cavity scheme is used to reduce the laser intensity between the transmitter and the receiver for laser safety. By calculating the stability zone of the laser cavity, it is found that the stability zone of the receiver cat-eye distance is quite narrow. Hence, the laser operation is very sensitive to the defocusing of the cat eye defocusing. Moreover, the cat eye defocusing induced by optical aberrations of spherical aberration and field curvature can be rather serious, when the long working distance results in a large beam size and the angle of incidence is large, hence limiting the effective working distance and the field of view of the alignment-free laser significantly. In the experiment, the improved optical designs with the aberrations compensation are adopted for large-dynamic-range alignment-free operation. The end-pumped Nd:GdVO4 laser at 1063 nm can deliver over 5-W output within a working distance range of 1–5 m, and a receiver field of view of ±30°, without cavity realignment. The transmitter field of view reaching 4.6° (full width at half maximum) at a working distance of 5 m is also realized, with a corresponding receiver transverse movement range of 40 cm. Our work clarifies the optimizing criteria of the large-dynamic-range alignment-free laser based on cat-eye retroreflectors.
1. Introduction
Laser is the most representative directed energy carrier, and it has long been the pursuit of researchers to achieve efficient, high-speed wireless energy and information transmission based on laser. [1,2].In recent years, resonant laser adaptive wireless energy transfer/communication technology based on debug-free laser has emerged. In the conventional laser wireless energy transmission/communication technology shown in Fig. 1(a), the light beam is projected to the receiving end through the tracking and aiming system. In this method, the output mirror of the laser resonant cavity and the photocell/detector at the energy/information receiving end are arranged together, so that the laser oscillates in the resonant cavity and is automatically projected to the receiving end through the output mirror, which does not require a complex and expensive tracking and aiming system, such as Shown in Fig. 1(b).On the other hand, because the transmission optical path between the laser transmitting end and the receiving end is located in the laser resonant cavity, the object intruding into the transmission optical path will block the laser oscillation and will not be irradiated by the laser, so the technology has natural safety. [2,3].In theory, the laser resonator is composed of optical elements with retroreflective characteristics such as pyramids, spherical lenses or cat-eye retroreflector (CER), and the laser has the ability to work without debugging, that is, the laser can work efficiently when the distance and relative orientation between the transmitter and the receiver change within a certain range, thus making adaptive resonant laser wireless energy transfer/communication possible.
Figure 1. Schematic of the (a) conventional laser power transfer based on acquisition, tracking, and pointing (ATP) system and (b) adaptive resonant beam wireless laser power transfer/communication.The technology has attracted wide attention since it was brought to the public's attention by Wi-Charge, an Israeli company. [3,4] followed by Liu et al. [2,5] The application prospect of this method is discussed and prospected.Debug-free laser with large dynamic range is the key to realize resonant laser adaptive wireless energy transfer/communication, where the dynamic range includes three aspects: working distance, transmitting end field of view and receiving end field of view, such as Fig. 2: The working distance is the distance between the laser transmitting end including the total reflection mirror and the gain medium and the laser receiving end (output end). d; field of view (FoV) α refers to the tolerance of the included angle between the optical axis of the receiving end and the oscillation light path when the pitch deflection direction of the receiving end itself changes and its optical axis is not aligned with the transmitting end; the field of view of the transmitting end β represents the tolerance of the optical axis deviation of the receiving end relative to the transmitting end.The laser can work normally only when the transmitting end and the receiving end are in the field of view of each other and the distance between them is within the effective working distance.
Figure 2. Working distance, receiver FoV and transmitter FoV of the alignment-free laser.In terms of the concrete realization of a large-scale adjustment-free laser, Lim et al. In 2019, [6] reported a tuning-free laser based on semiconductor optical amplifier (SOA) gain and pyramid retroreflector, which achieved milliwatt laser output at a working distance of 1 m, and achieved a lateral displacement range of about 40 mm at the receiver end (about 2.3 ° launch end field of view).Wang et al., Shanghai Institute of Optics and Fine Mechanics, 2021 [7] reported a flake-based Nd: YVO The tuning-free laser with 4 gain medium and cat's eye retroreflector achieves a receiver field of view of ± 13 ° at a working distance of 150 mm, a receiver lateral displacement range of about ± 20 mm, and a maximum output power of more than 10 W.Zhang et al., Changchun Institute of Optics and Fine Mechanics, 2022 An optically pumped external cavity VECSEL laser for energy transfer applications is reported in [8]. The output power is 86.3 mW at 15 W pump power at a working distance of 2 m, and the lateral displacement tolerance of the receiver is less than 10 mm.The same year, Javed et al. [9] reported a tuning-free laser based on fiber gain and ball lens retroreflector, which can provide 400 mW laser output power at a working distance of up to 30 m. The ball lens theoretically has an unrestricted field of view at the receiving end, but the fiber coupling structure in this scheme largely limits the field of view at the transmitting end. Even if dispersion is further introduced by elements such as gratings, the receiving end can only be allowed to be off-axis in one direction, and a two-dimensional field of vision at the transmitting end cannot be achieved.Liu et al [5] adopts similar The experimental work was carried out with the Fig. 1(b) optical path structure at a pump power of 37.3 W at 2.A laser output of about 5 W can be generated at a working distance of 6 m, and the off-axis of the receiver is ± 18 cm (the field of view of the transmitter is ± 5.1 °) when the laser power is reduced to near 0. The field of view of the receiver is not described.In addition to universities and research institutes, Huawei, etc. [10] Representatives of industry have also reported on related research work.
In order to realize the large range of adjustment-free operation of the laser, the resonant cavity of the laser is composed of a cat-eye retroreflector. After analysis, it is considered that the cat-eye defocusing caused by spherical aberration and field curvature is the main factor limiting the working distance and the dynamic range of the field of view of the laser.By optimizing the laser resonator design and compensating for aberrations, a wide range of adjustment-free operation of the laser is experimentally realized: without any re-collimation adjustment of the resonator, the end-pumped 1063 nm Nd: GdVO 4 laser pump power 16.6 W, the laser output power is more than 5 W and the fluctuation is less than 10% in the working distance of 1 — 5 m and the field of view of ± 30 ° at the receiving end, and the laser output power is more than 50% of its maximum in the field of view of 4.6 ° at the working distance of 5 m.In addition, the compound cavity structure is used to reduce the laser power density on the transmission light path between the transmitter and the receiver, which optimizes the laser safety. The related experimental results and the design optimization principles of the cat-eye cavity tuning-free laser are summarized and discussed.
2. Design of laser resonator
The schematic diagram of the optical path of the large range adjustment-free laser is given in Fig. 3. The pump light coupled out by the fiber is collimated and focused by the lenses L0 and L1 and then enters the laser crystal. The crystal used in the experiment is doped with 0.5 percent a cut Nd: GdVO The size of the crystal is 4 mm × 4 mm × 8 mm, the laser wavelength is 1063 nm, the pump wavelength is 808 nm, and the radius of the pump spot at the laser crystal is about 500 μm.The plane laser total reflection mirror M1 and the lens L1 form a cat's eye at the transmitting end, and the laser output mirror M3 and the lens L4 form a cat's eye at the receiving end.Considering the requirement of laser working distance and the inherent divergence characteristic of Gaussian beam, two lenses L2 and L3 are inserted into the cavity, and the distance between them is equal to the sum of their focal lengths to form a telescope system, which can expand and collimate the beam and compress the divergence angle.Each lens in the cavity is coated with a 1063 nm laser anti-reflection film. The devices from L0 to L3 constitute the laser emitting end, and the cat's eye composed of L4 and M3 constitutes the laser receiving end.In addition, a plane partial reflection mirror M2 is inserted into the cavity at the overlapping focus of the lenses L2 and L3 to form a composite cavity structure, which plays a role in reducing the laser power density on the transmission light path and improving the laser safety [4,11,12].In the experiment, the reflectivity of M2 and M3 for 1063 nm laser is 40%, and the equivalent coupling output transmittance of the whole composite cavity is about 18%. Nd: GdVO The stimulated emission cross section of the 4 crystal is relatively common for Nd: YVO The 4 crystal is small enough to guarantee the maximum pump power used 16.The cavity section does not oscillate alone at 6 W. The distance between the devices is indicated by the symbol d 1— d 7 means.
Figure 3. Schematic of the alignment-free laser: (a) The receiver and the transmitter are on the optical axes of each other; (b) the receiving end deviates from the optical axis of the transmitting end, and the orientation has an angle with the oscillating optical path.For the parameter design of the compound resonator, first of all, the whole laser resonator M1-M3 should be a stable resonator to form laser oscillation.Considering the requirement of mode coupling between the M1-M2 internal cavity part and the M2-M3 external cavity part, the internal cavity part M1-M2 should be a critical cavity, in which the light incident parallel to the optical axis at any height is allowed to oscillate, while the external cavity part M2-M3 is a stable cavity, so the mode and resonator stability of the laser are completely determined by the external cavity part.M2 is located at the overlapping focus of L2 and L3, and forms two cat's eyes with them respectively.Only the light beam incident through the cat's eye pupil can obtain a more ideal retroreflection effect with the minimum loss; therefore, when the receiving end has a certain offset relative to the optical axis of the transmitting end, Δ, the laser between the transmitting end and the receiving end The optical path shown in Fig. 3(b) oscillates, and the angle between the oscillating optical path and the optical axis of the transmitter θ 1 is determined by the pupil position of the two, and the allowed θ The maximum value of 1 is the field of view of the transmitter. α.The orientation of the receiving end itself may also cause a certain angle between its optical axis and the oscillating optical path. θ 2, allowed θ The maximum value of 2 is the receiving end field of view. β.Ideally, the field of view of the transmitter and receiver is determined by the aperture of the device, but in practice, the aberration of the optical element becomes a more important limiting factor due to the stability of the resonator.
The ABCD matrix is used to calculate the stable region of the resonator. For the application scenario of adaptive laser wireless energy transfer, on the one hand, the working distance d 6 is a variable with a wide range of changes. On the other hand, considering the requirement of long working distance for laser collimation, the distance between lens L3 and M2 mirror d 5 should be exactly equal to the focal length of L3, and other parameters at the transmitting end should also be fixed, so the cat-eye spacing at the receiving end needs to be considered. d 7 and working distance d 6 Effect on Cavity Stability.Fig. 4 gives the working distance d 6 changes in the range of 1 — 5 m d 7, the thermal lens of each lens and laser crystal in the calculation is approximately treated as a thin lens, and the theoretical calculation of Nd: GdVO The maximum pump power used in the experiment for the 4 crystal is 16.Thermal lens focal length at 6 W f t is 500 mm [13], relevant parameters such as 表1.The same parameters of lenses L1 and L2 are selected to simplify the system design. In order to optimize the working distance, the focal length of L3 is about twice that of L2. The beam with a radius of about 500 μm on the left side of L2 is expanded to a radius of about 1 mm. Compared with the case without an intracavity telescope system to expand and collimate the beam, the spot radius at the receiving end at a working distance of 5 m is increased from about 3.4 mm compression to about 2 mm. From As can be seen in Fig. 4, with the working distance d Increase of 6, cat-eye spacing at receiving end d The stability zone of 7 is severely narrowed.When the focal length of the lens L4 f 4 = 50 mm, d The stability zone of 7 ranges from d 50 — 52 at 6 = 1 m.94 mm narrow to d 50 — 50.52 mm at 6 = 5 m.If a shorter focal length lens L4 is used, d The stability zone of 7 is also narrower: e.g. f 4 = 25 mm, d 6 = 5 m d The stable zone of 7 is 25-25.13 mm, its width is only f One quarter of the same working distance at 4 = 50 mm.Therefore, it can be predicted that when the working distance of the laser is long, d A small deviation of 7 from its optimized value will seriously affect the output power of the laser, and even cause the laser to fail to oscillate.From another point of view, only the focused cat's eye can make the divergence angle of the reflected light consistent with that of the incident light; if the divergence angle of the two is not consistent, it is equivalent to that part of the energy in the light beam after being reflected by the cat's eye is not in the original pattern, that is, the pattern cannot be completely self-reproduced and suffers a certain loss.The longer the working distance of the laser, the greater the deviation between the reflected light and the incident light caused by the change of the divergence angle, so the smaller the tolerance of the cat's eye defocus. d The narrower the stability zone of 7.
Figure 4. Stability zones of receiver CER distance d7 as a function of working distance d6.Table 1. Parameters used in the experiment and calculation.Lenses Focal length/mm Distances Length/mm L0 10 d1 23.8 L1 24.6 d2 23 L2 24.6 d3 23.8 L3 48.3 d4 23 L4 25, 50 (51.8) d5 49.1 ft 500 d6 1000—5000 | Show Table
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3. The effect of aberration
Ideally, the adjust-free range of the laser is limited only by the aperture of the optical components.When the beam reaches the receiving end after a long working distance, it will diverge into a larger size, so the receiving end lens is required to have a sufficient aperture; at the same time, the aperture of each cat-eye lens and mirror determines the theoretical upper limit of the field of view.However, in practice, aberrations such as spherical aberration and field curvature will seriously limit the tuning-free range of the laser.
Spherical aberration is an inherent aberration of spherical optical elements. Under the action of spherical aberration, the actual focus of rays at different incident heights deviates from the paraxial image point to varying degrees, such as Shown in Fig. 5(a).However, the cat's eye can only achieve a good retroreflection effect on the focused light, so part of the energy in the beam oscillating in the cavity under the action of spherical aberration must be defocused, which can not be retroreflected and form self-reproduction, affecting the cavity mode and generating loss. [11,14-16].When the working distance is 5 m, the spot radius of the fundamental mode at the receiving end will reach 2 mm. [11], the larger the beam aperture, the more severe the corresponding spherical aberration.Fig. 5(b) gives the theoretically calculated focal length The spherical aberration of a K9 plano-convex lens with f = 25 mm, that is, the offset of the actual focus position of the beam edge with different radii from the theoretical focus of the lens. It can be seen that when the beam radius is 2 mm, the defocus caused by spherical aberration reaches 0.70 mm, which is significantly greater than the cat-eye spacing at the receiving end at a working distance of 5 m d 7 = 0.13 mm. According to the definition of the stable region of the resonant cavity, when the stability condition is not met, the light will escape from the resonant cavity after a limited number of round trips in the cavity, resulting in loss.Therefore, in order to expand the working distance of the laser, it is necessary to effectively control the spherical aberration.
Figure 5. CER defocusing induced by the spherical aberration of a K9 plano-convex spherical lens with f = 25 mm.Such as As shown in Fig. 3(b), when the oscillating laser light path determined by the pupils of the transmitting end and the receiving end has an angle with the optical axes of the transmitting end and the receiving end, the beam is incident on the cat-eye retroreflector at a certain angle; the actual focal plane of the incident beam at different angles is neither a plane nor a curved surface with a radius of curvature (RoC) equal to the focal length of the lens, that is, there is field curvature, as shown in As shown in Fig. 6(a).The field curvature also inevitably leads to the defocus of the cat's eye. [12,17], Fig. 6(b) gives the deviation of the actual focus of the beam from the mirror surface at the theoretical focus of the lens caused by the field curvature in the conventional "telecentric cat's eye" with a flat mirror.When the lens used is When the K9 plano-convex lens with f = 25 mm is used, the defocus of the cat's eye caused by the field curvature reaches 0.13 mm, as Fig. 6(b), at a working distance of 5 m d The stable zone width of 7 is equal, and the defocus increases faster with the incident angle. Therefore, although the ideal case is 25.The field of view of the cat's eye determined by the lens aperture of 4 mm is more than ± 26 °, but the defocus of the cat's eye caused by the field curvature in actual operation will seriously limit the field of view of the laser, especially when the stable zone is very narrow due to the long working distance. In order to realize the large-scale operation of the laser without adjustment, the compensation of the field curvature should also be considered.
Figure 6. CER defocusing induced by the field curvature of a K9 plano-convex lens with f = 25 mm.4. Experimental Results and Discussion
According to The optical path structure of Fig. 3 was experimentally studied, and the incident laser crystal Nd: GdVO The pump power at 808 nm of 4 is 16.6 W. Firstly, the working distance characteristics of the laser are studied by placing the transmitter and the receiver on each other's optical axis.With the laser working distance d With the increase of 6, the spot size at the receiving end increases, the influence of spherical aberration gradually increases, and the stable region of the resonator narrows, resulting in the gradual reduction of laser output power.Focal length of spherical lens at receiving end f 4 = 25 mm, when the spherical aberration at the transmitter is compensated [18], with working distance d 6 is elongated from 1 m to 5 m, and the laser output power is reduced from 5.95 W to 1.16 W, as Blue diamond curve in Fig. 7. When f 4 = 51.At 8 mm, the spherical aberration is relieved to a certain extent. d The stable region of 7 is relatively wide, and the laser output power varies with the working distance. d The downward trend of 6 slows down (black square), and the output power at 1 m and 5 m working distance is 6.28 W and 4.54 W, it is verified that the cat's eye defocusing caused by spherical aberration is the main factor limiting the working distance of the laser.On this basis, select With an aspheric lens of f = 25 mm as the receiving end lens L4, the working distance characteristics of the laser are further improved (red circle), and the output power is 6.45 W and 5.84 W at 1 m and 5 m working distances, respectively.It should be noted that the above output power is at different working distances d Respectively optimize the cat-eye spacing at the receiving end under 6 d Maximum output power obtained by 7.In the process of increasing the working distance, in order to obtain the maximum output power, d 7 is slightly reduced, d During the increase of 6 from 1 m to 5 m, d The variation of 7 and its location d The range of the stable zone at 6 = 5 m is similar.Considering that the whole receiving end should be a solidified whole in practical application, the aspheric lens L4 is used. d Optimize and fix the cat-eye spacing at the receiving end when 6 = 5 m d After 7, working distance d The laser output power of 6 can be kept at 5.More than 75 W (gray dots), and the fluctuation is less than 10%, which realizes a wide range of adjustment-free work in terms of laser working distance.
Figure 7. The experimental working distance behavior of the laser using receiver lenses with different SA.In terms of the field of view at the receiving end, when the working distance of the laser is short, tens of centimeters, the conventional cat's eye design can achieve a larger field of view at the receiving end limited only by the aperture of the device, compared with Wang et al. [7]'s report is similar.However, as the working distance increases, the cat-eye spacing at the receiving end d The stable zone of 7 becomes narrower, and the limitation of the field of view of the receiving end caused by the cat-eye defocus caused by the field curvature becomes more serious.Such as Fig. 8, output mirror RoC = at working distance 5 m f 4 = 51.The receiving field of view of the 8 mm cat-eye (when the output power is reduced to half of its maximum value) is less than ± 3 ° (red dot), while the field of view of the "telecentric cat-eye" with a flat output mirror is smaller (black square), less than ± 2 °, which is also consistent with the theoretical calculation result that the defocus caused by the field curvature is more serious than that caused by the former, verifying that the defocus caused by the field curvature is the main factor limiting the field of view.On this basis, the flat field aspheric lens, the mirror curvature radius matching the lens image plane (blue diamond) and the multi-lens improved cat's eye (green five-star) are designed to compensate the cat's eye defocus caused by the field curvature. [12,19], a maximum receiver field of view of ± 30 ° was experimentally achieved at a long working distance of 5 m, within which 16.The laser output power at 6 W pump power is always kept above 5 W without any re-collimation adjustment of the resonator.Thanks to the good mode volume matching between the pump light and the oscillating light and the effective control of the aberration, the laser output maintains good beam quality during the movement and rotation of the receiver. M 2 at 1.3 — 1.7, the output power does not fluctuate significantly during the dynamic process of the receiver movement.In terms of the field of view at the transmitter, an aspheric lens is designed and processed to compensate the field curvature, which also greatly improves the field of view at the transmitter. If the output power is reduced to half of its maximum value, the allowable lateral displacement range of the receiver at a working distance of 5 m is 40 cm, corresponding to a field of view of 4.6 °, which is about 3 times of the 1. 8 ° field of view before field curvature compensation, but there is still a certain gap with the design level, and the beam quality also deteriorates significantly with the gradual increase of off-axis. [18].It can be inferred that this is related to the aberration of the thermal lens of the laser crystal, and the aberration of the thermal lens is subsequently measured and compensated by designing an aspheric lens to further optimize the field of view of the transmitter.In addition, the off-axis of the oscillating laser path in the crystal leads to a decrease in the overlapping efficiency with the pump light, which also limits the field of view of the emitter to a certain extent; the use of a larger pump spot and a shorter laser crystal can help alleviate this problem, for example, [ 5, A better field of view at the transmitting end is achieved based on a thin laser crystal in [7].
Figure 8. The experimental receiver FoVs with and without FC of the receiver CER compensated.表2 Summarize typical experimental results for a large range of tuning-free lasers.By analyzing the structural characteristics of the resonator and optical aberrations, it is determined that the cat-eye defocusing caused by aberrations and the narrowing of the stable region of the resonator at long working distances are the main factors limiting the tuning-free working range of the laser. By optimizing the optical design to compensate for the aberrations, the tuning-free and high-efficiency operation of the laser is experimentally realized in a large range, which provides a light source support for safe and convenient resonant laser adaptive wireless energy transfer/communication applications.The conversion efficiency of low-cost silicon photovoltaic cells is about 20%, and the efficiency of InGaAs photovoltaic cells can exceed 40% in the 1.06 μm band. [20], which can generate 1-2 W of electrical output power, can support the power supply needs of most low-power Internet of Things devices.If thin slice crystals or semiconductor laser gain media with higher power handling capabilities are used, the output power level of the laser can be further improved to support more practical applications.
Table 2. Typical experimental results of alignment-free lasers for adaptive resonant beam charging/communication applicationsYear Retro-reflector Laser gainmedium Output power/W Optical efficiency/% Working distance/m Receiver FoV/(°) Transmitter FoV/(°) 2019[6] Corner cube SOA 0.0017 — 1 — 6.6°(only one dimension) 2021[7] CER Nd:YVO4 disk >10 — 0.15 ±13°@ 0.15 m ±8.3°@0.15 m(0 output) 2022[8] Ball lens EDFA 0.4 — 30 Unlimited — 2022[5] CER Nd:YVO4 disk >10 ~15 <3 — ±5.1°@2 m(0 output) 2022[9] CER Optically pumped VECSEL 0.863 0.57 2 — 1.37°@0.5 m0.47°@2 m 2021[10] CER — 0.012 — 2 — — Our work CER Bulk Nd:GdVO4 >5 >30 >5 ±30°@5 m 4.6°@5 m(half maximum) | Show TableDownLoad:
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5. Conclusion
In order to meet the needs of adaptive laser wireless energy transfer/communication and other fields for a large range of tuning-free laser, the optimization requirements of the tuning-free working dynamic range of the laser are discussed, and a tuning-free laser based on a cat-eye retroreflector is designed and implemented.By introducing the telescope system and the composite cavity structure, the laser divergence angle on the transmission path is compressed and the laser safety is improved, respectively.Based on the cavity model theory, the stable region of the resonator is analyzed, and it is found that the narrowing of the stable region of the resonator and the cat-eye defocus caused by aberrations are the main factors limiting the adjustment-free dynamic range of the laser at long working distance.Aberration compensation by optimized optical design, end-pumped Nd: GdVO 4 laser pump power 16.At 6 W, the laser can maintain an output power of more than 5 W in the range of 1 — 5 m working distance and ± 30 ° field of view of the receiver. At 5 m working distance, the field of view of the half-power transmitter is 4. 6 °, and the corresponding lateral displacement range of the receiver is 40 cm.In this work, the design requirements and key optimization methods of the cat-eye cavity tuning-free laser are clarified, and the tuning-free operation of the laser in a wide range is realized experimentally, which provides theoretical and experimental support for the practical application requirements and the development of the tuning-free laser.
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图 1 基于跟瞄的激光无线传能(a)和谐振激光自适应无线传能(b)示意图
Figure 1. Schematic of the (a) conventional laser power transfer based on acquisition, tracking, and pointing (ATP) system and (b) adaptive resonant beam wireless laser power transfer/communication.
图 2 免调试激光器的工作距离、接收端视场和发射端视场
Figure 2. Working distance, receiver FoV and transmitter FoV of the alignment-free laser.
图 3 免调试激光器光路示意图 (a)接收端位于发射端光轴上且朝向发射端; (b)接收端相对发射端光轴存在偏离, 且朝向与振荡光路存在夹角
Figure 3. Schematic of the alignment-free laser: (a) The receiver and the transmitter are on the optical axes of each other; (b) the receiving end deviates from the optical axis of the transmitting end, and the orientation has an angle with the oscillating optical path.
图 4 不同工作距离d6下接收端猫眼间距d7的稳区
Figure 4. Stability zones of receiver CER distance d7 as a function of working distance d6.
图 5 使用f = 25 mm的K9平凸球面透镜时球差导致的猫眼逆反射器离焦
Figure 5. CER defocusing induced by the spherical aberration of a K9 plano-convex spherical lens with f = 25 mm.
图 6 使用f = 25 mm的K9平凸透镜时场曲导致的猫眼逆反射器离焦
Figure 6. CER defocusing induced by the field curvature of a K9 plano-convex lens with f = 25 mm.
图 7 不同接收端透镜球差条件下激光器的工作距离特性实验结果
Figure 7. The experimental working distance behavior of the laser using receiver lenses with different SA.
图 8 不同接收端透镜场曲条件下的接收端视场特性实验结果
Figure 8. The experimental receiver FoVs with and without FC of the receiver CER compensated.
表 1 计算和实验中所用参数
Table 1. Parameters used in the experiment and calculation.
Lenses Focal length/mm Distances Length/mm L0 10 d1 23.8 L1 24.6 d2 23 L2 24.6 d3 23.8 L3 48.3 d4 23 L4 25, 50 (51.8) d5 49.1 ft 500 d6 1000—5000 
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表 2 面向谐振激光自适应无线传能/通信应用的免调试激光器典型实验结果
Table 2. Typical experimental results of alignment-free lasers for adaptive resonant beam charging/communication applications
Year Retro-reflector Laser gainmedium Output power/W Optical efficiency/% Working distance/m Receiver FoV/(°) Transmitter FoV/(°) 2019[6] Corner cube SOA 0.0017 — 1 — 6.6°(only one dimension) 2021[7] CER Nd:YVO4 disk >10 — 0.15 ±13°@ 0.15 m ±8.3°@0.15 m(0 output) 2022[8] Ball lens EDFA 0.4 — 30 Unlimited — 2022[5] CER Nd:YVO4 disk >10 ~15 <3 — ±5.1°@2 m(0 output) 2022[9] CER Optically pumped VECSEL 0.863 0.57 2 — 1.37°@0.5 m0.47°@2 m 2021[10] CER — 0.012 — 2 — — Our work CER Bulk Nd:GdVO4 >5 >30 >5 ±30°@5 m 4.6°@5 m(half maximum)
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