2021 Vol. 50, No. 1
2021, 50(1): 20211001.
doi: 10.3788/IRLA20211001
Optical transmission and regulation is an important basis for the development of photonic integrated devices. As a new optical functional material, photonic crystals have great potential in optical manipulation. Inspired by the concept of topological phase in condensed matter physics, the introduction of topological phase in photonic crystal energy band system research breaks through the traditional light field regulation ideas based on the superposition principle of real space light field and the inverse space solid energy band dispersion theory, and provides a novel light field regulation mechanism, rich transport and light control properties, such as high dimensional light field regulation. In this paper, the research achievements of the research group in recent years were reviewed from two aspects: non-Hermitian photon system and topological photonics system. Firstly, the background of optical topology research and optical non-hermitic research was reviewed. Then, the research progress in the fields of high-order photonic topological insulators, high-order quantum spin hall effect, topological field local area of photonic crystals and topological optical transmission in non-Hermitical systems were introduced. In the end, the development trend of the research results in related fields such as optical quantum computing and optical communication was summarized and prospected.
2021, 50(1): 20211002.
doi: 10.3788/IRLA20211002
The thin layer of infrared detection material guarantees the uniformity of the materials and reduces the signal noise in infrared detection. The absorption of infrared detector is limited by the thin layer of infrared detection material attributing to small volume. According to the characteristics of different infrared detection materials, artificial microstructure can effectively improve the performance of infrared detector. The strategies of enhancing the absorption of thin-layer infrared detection materials were introduced. The strategies were based on metal back plate, metal grating and asymmetric Fabry-Perot cavity. They could have an excellent performance in their own adaptive scenarios. Meanwhile, the mechanism of adjusting the absorption peak height and width by artificial microstructure was also elaborated briefly. The application of artificial microstructure in several infrared detectors was demonstrated. Finally, an artificial microstructure HgCdTe infrared detector was designed, which could achieve broadband absorption in 3.5-5.5 μm atmospheric window. The absorption peak reached 91.8% and the relative peak width was 41.8%. In most of frequency in the atmospheric window, the absorption enhancement is higher than 6. The development of artificial microstructure opens up the design idea of traditional infrared devices, and provides theoretical basis and guidance for new infrared devices.
2021, 50(1): 20211003.
doi: 10.3788/IRLA20211003
Metalenses are two-dimensional metasurfaces composed of sub-wavelength scatters with planar configuration and light focusing function. They can manipulate the amplitude, phase, dispersion and polarization of the light field at sub-wavelength spatial resolution, and develop rapidly in recent years. The subwavelength resonant nanostructure suppresses the high-order diffraction, and the incident light can be perfectly modulated to the predesigned diffraction order, thus ensuring the high efficiency of the metadevice for manipulating the photons. Besides, the design flexibility and specific electromagnetic response of the meta-unit enable metasurfaces to achieve customized control of the multiple dimensions of the light field. In contrast to the traditional refraction lens relying on the phase accumulation effect, the broadband achromatic metalens resolves the complex and bulky limitations of the traditional optical system caused by cascading multiple lenses to correct the chromatic aberration by independently and simultaneously manipulating the phase and phase dispersion of the optical field. It provides a promising way for the miniaturization of on-chip integrated photonics. Focusing on the progress of metalens, this review discussed the basic principles of metasurface on engineering the amplitude, phase and polarization state of the light firstly. Then the development of metalens in recent years was focused on, including the realization of single-wavelength metalens and the development of multi-functional broadband achromatic metalenses through manipulating the multiple parameters (polarization, phase and phase dispersion). Finally, the potential challenges and application prospects for further developing the metalenses were discussed.
2021, 50(1): 20211004.
doi: 10.3788/IRLA20211004
High-precision comparison of time-frequency is an important technology to achieve high-precision time-space consistency and time-frequency stability of the whole society information system, and provides a unified time guarantee for key areas of national economic development. Owing to its high detection efficiency, low noise, low timing jitter, and easy integration, silicon single photon detector is the key core chip in the high-precision satellite-to-ground time comparison system. The interrelationship between photon detection efficiency, dark count rate and timing jitter of the silicon single photon detector was analyzed in this paper. Based on the in-depth review of the research of the silicon single photon detector, the relationship between photon detection efficiency and timing jitter was effectively overcome. A silicon single photon detector with a photosensitive diameter of 200 μm, photon detection efficiency of 50% at room temperature, and the timing jitter of 46 ps was developed. Its application in the satellite-to-ground time comparison was briefly introduced finally.
2021, 50(1): 20211005.
doi: 10.3788/IRLA20211005
Metalens, the specific type of lens designed with the surfaces mading of two dimensional array at the subwavelength scale, has shown great flexibilities to control the light field, including the arbitrary modulation abilities of amplitude, phase and polarization at the subwavelength scale. Moreover, the metalens possesses the unique advantages of low loss, integratable and conformable design and ultrathin, therefore attracts immense attentions in recent years. However, in most cases, the metalens designed for a specific wavelength may penetrate through the large chromatic aberration, which limits their usefulness in multi-wavelength or broadband applications. On the other hand, the metalens has renewed new degrees of freedom due to its two-dimensional planar structure, which has the potential in the elimination of chromatic aberration. Some different typical achromatic metalens designs and their achromatic modulation mechanism were reviewed, the existing achromatic metalens were classified from the types of modulated light bands, such as the achromatic matelens for discrete and continuous wavelength respectively, and the latter can be classified as transmissive and reflective from the working mode. Finally, the application of metalenses array in imaging and their prospect of broadband achromatic devices of large depth of field were introduced.
2021, 50(1): 20211006.
doi: 10.3788/IRLA20211006
The long wavelength infrared polarimetric detector can greatly improve the recognition ability of thermal imaging. Owing to the physical limitation of the diffraction limit, the polarization extinction ratio of the current micro-grid polarizer-type long wavelength infrared polarimetric detectors can basically only be as high as about 10∶1. In this paper, a metal/dielectric/metal plasmonic microcavity structure has been fabricated, with the infrared detection active layer of the quantum wells being embedded inside the microcavity. Due to the near-field coupling between the upper grating and bottom reflector metals, a lateral Fabry-Perot resonance was established in the double-metal region, forming the plasmonic microcavity. Benefited from the mode selection characteristics of the microcavity and its resonant coupling with the quantum well intersubband transition, the normal incident light, which cannot be directly absorbed by the intersubband transition of the quantum wells, was coupled into the plasmonic microcavity, transforming its propagation direction into lateral and being absorbed by the quantum wells. The mechanism was confirmed by finite element simulation and the microcavity key parameters such as the grating width and the thicknesses were designed and optimized. Such a structure was applied to the detecting pixels sized at 27 × 27 μm, which was suitable for focal plane arrays. Resulting from the capture and confinement of the incident photons, the detectivity of the detecting pixels could be promoted by about one order of magnitude comparing to the un-structured 45o edge facet coupled detector fabricated from the same epitaxy wafer. The polarization extinction ratio greater than 100∶1 at about 13.5 μm of detecting peak wavelength in the long wavelength infrared waveband was achieved, while the peak intensity dependence on the polarizer azimuth angle fitted Malus law very well. Such a work provides a novel physical foundation and technical route for the development of high extinction ratio long wavelength infrared polarimetric imaging focal planes.
2021, 50(1): 20211007.
doi: 10.3788/IRLA20211007
Recently, the anomalous carrier transport in the quantum wells with the PN junction structures has been found experimentally, and the corresponding physical mechanism and the carrier transport model have been proposed. It is observed that the open circuit voltage or short-circuit current can be measured in the resonant excitation mode. Comparing the photoluminescence (PL) spectra of the two kinds of external circuits, it is found that the PL intensity decreased significantly under the short circuit condition. This suggests that the photogenerated carriers under the short circuit condition are not confined in the quantum well, but escaping from the junction region. However, this phenomenon of photocarriers escaping from the quantum wells is not found in the NN-type quantum well structure. Therefore, the effect of thermal excitation or tunneling is excluded to drive the carrier escaping from the quantum well. Based on this, the corresponding physical mechanism and carrier transport model are proposed. It is concluded that photogenerated carriers can escape from the quantum well directly under the built-in electric field of PN junction, and the radiative recombination luminescence occurs after the carrier escape process.
2021, 50(1): 20211008.
doi: 10.3788/IRLA20211008
In order to meet the needs of accurately detecting and recognizing many kinds of high-value targets (such as stealth), the continuous development of detection technology, and realizing high probability true or false target recognition and high precision target detection, location and tracking in complex battlefield environment, it is of great significance to research stealth and weak feature target detection and anti-jamming detection in complex battlefield environment, the high integration of polarization focal plane infrared detector technology is one of the important direction. Focusing on the development of an integrated MW 256×256 HgCdTe polarization focal plane infrared detector, the research progress from the integration of polarization detectors to design and preparation of polarization structures were introduced, as well as the performance testing of polarization detector. A subwavelength metal grating array was designed and fabricated, the polarization detector was integrated by flip chip, and the infrared polarization performance was tested and evaluated on MW256×256 HgCdTe focal plane device.
2021, 50(1): 20211013.
doi: 10.3788/IRLA20211013
Uncooled infrared detectors are widely used in the infrared field due to their low cost, small size, and low power consumption because they do not need the cooling device and can work at room temperature. In military application field, the uncooled detector has gradually entered the application domain of previous refrigerated detector, and has been widely used in some low-cost weapon systems, even replaced the original uncooled detectors in some application fields. In the civil field, it has shown its advantages in price and ease of use, and has aroused widespread interest and attention in civil in-vehicle night vision, security monitoring and other application field. The working theory of several typical uncooled infrared detectors such as Bolometer, pyroelectric, thermopile, etc. were introduced, and the status of the main products that have been commercialized at home and abroad was enumerated, the development of pixel pitch, array specifications, performance and packaging of mainstream bolometer devices was focused, which were currently the most widely used. In addition to the bolometer, pyroelectric, SOI diode and other products that had been commercialized, some new uncooled detection technologies or new detectors were introduced in detail: such as the application of metasurfaces in enhancing absorption in certain wavebands, the research progress of new materials bolometer, new bi-material uncooled devices, graphene, quantum dots, nanowires and other photoelectric detection technologies. Finally, the future development trend of uncooled infrared detectors were predicted in the end of the review.
2021, 50(1): 20211009.
doi: 10.3788/IRLA20211009
Quantum well infrared photodetectors (QWIPs) has been considered as another excellent candidate in long-wavelength and very-long-wavelength infrared detection. It shows more distinctive advantages than the traditional HgCdTe technology in long-wave infrared detection, multi-color detection and focal plane technology area. Keep research on QWIPs will greatly promote the development of our country's infrared detector technology. The outstanding advantages of QWIPs are its good maturity of III–V compound growth and processing techniques. However, due to the low quantum efficiency and the forbiddance of directly normal incident radiation absorption for n-type QW, it is necessary to design and prepare various gratings or microcavity structures for optical coupling and local electromagnetic field enhancement for different detection wavelengths. How to more effectively improve the optical coupling efficiency of QWIPs, reduce dark current, and increase the operating temperature of the device are still the hotspots of current research. The new type of QWIPs with local electromagnetic field enhancement in the past 5 years was emphatically introduced and summarizesd, focusing on the optical coupling, dark current and working temperature. Finally, the development of QWIPs with local electromagnetic field enhancement were given for future work.
Metal-2D material-metal photodetectors is the most common type of 2D material photodetectors. Due to the simple structure and the ease of integration with other systems, metal-2D material-metal photodetectors have received the widest range of attentions and research interest. The self-driven mode of this type of photodetectors has very low dark current, and then it is regarded as a promising new route for high performance infrared detection. However, there are two bottleneck problems for self-driven metal-2D material-metal photodetectors: (1) photoresponse cancellation caused by antisymmetric 2D material-contact junctions, (2) low responsivity due to limited light absorption of 2D materials. The recent progress on the study of metal-2D material-metal photodetectors with asymmetrically integrated plasmonic nanostructures was introduced, where asymmetrical light coupling was utilized to break the anti-symmetry between the photocurrents at the two contact-2D material junctions for self-driven net photoresponse, and the induced strong local field was utilized to enhance the absorptance and the responsivity of the 2D material. In the hybrid device of graphene and plasmonic nanocavities, the contrast between photoresponses at the two contacts is more than 100 times, which breaks through the problem of photoresponse cancellation caused by symmetric optical coupling. Due to the superior capability to couple the incident light into a localized mode, the plasmonic nanocavity can enhance the responsivity of graphene over one order of magnitude higher than a subwavelength metal grating.
2021, 50(1): 20211012.
doi: 10.3788/IRLA20211012
Terahertz radiation refers to electromagnetic waves with a wavelength range of 30 μm-1 mm, characterized by strong penetration, high safety, strong specificity and good orientation. Therefore, terahertz technology has broad application prospects in the fields of astronomical observation, safety monitoring, substance identification and biomedicine. Blocking-impurity-band detector has the advantages of high sensitivity, large array size and wide detection spectrum, which is an excellent choice for terahertz radiation detection. At present, the blocking-impurity-band detector is mainly based on three material systems, namely Si, Ge and GaAs. Si, Ge and GaAs-based blocking-impurity-band detectors can be used for ultra-wide band detection from 3 μm to 500 μm. Superstructure is an artificial composite structure composed of subwavelength structural units. By introducing superstructure into the photoelectric detector, the electromagnetic field energy will be strongly localized at the interface between the metal and the detector through plasmon resonance and dipole resonance modes. So, the combination of superstructure and blocking-impurity-band detector can effectively regulate the detection peak, reduce the full width at half maximum (FWHM) of detection peak and enhance the spectral resolution ability. So it is expected to be widely used in multiband fusion detection of 3-500 μm. At the same time, the combination of the two technologies can further improve the response rate of the device, reduce the size of the device and reduce the process difficulty. This paper briefly described the working mechanism of the blocking-impurity-band detector. And the research history and status of blocking-impurity-band detector at home and abroad are also introduced. Finally, the superstructure/blocking-impurity-band detector was described in detail in terms of band regulation, spectral resolution and absorption enhance. Combining with the bottleneck problem of this technology, the future research prospect was proposed in the aspects such as high purity material growth and the mechanism of local effect of light field.
2021, 50(1): 20211014.
doi: 10.3788/IRLA20211014
As one of the core devices in the field of aeronautic and astronautics, deep space exploration, environmental monitoring, there is significant scientific research and practical application value for photodetector. In recent years, surface plasmon has become one of the research hotspots in the field of enhanced photodetection, due to the properties of breaking through the optical diffraction limit and realizing nanometer focusing. Hence, surface plasmon is a novel technical method for improving the performance of photodetectors. In this article, the research progress based on the photodetector with enhancement effect was reviewed, the enhancement effect can attribute to the surface plasmon nanostructure. Firstly, various kinds of physical properties of surface plasmon nanostructures were introduced, mainly included localized surface plasmon structure and surface plasmon polaritons structure with propagating nature, as well as the heterostructure that consisted of surface plasmon metal and semiconductor materials. Then, the research progress of photodetector enhanced by surface plasmon nanostructures was introduced focusing on the aspects of performance of photodetector, detection mechanism and fabrication process method. Finally, the photodetector enhanced by surface plasmon nanostructures and the related challenges in the future were both summarized and prospected.
2021, 50(1): 20211015.
doi: 10.3788/IRLA20211015
Terahertz technology has broad application prospects in non-destructive testing, biomedicine, industrial inspection, environmental monitoring, local area communications and national defense security. The terahertz detector in the terahertz system is its core component. Its performance determines the application market of the terahertz system and is one of the important research directions to promote the further development of terahertz technology. However, the low photon energy in the terahertz band makes it challenging to achieve high-speed and sensitive terahertz detection. With the advancement of nanotechnology and new material preparation technology, the high mobility and wide response band of low-dimensional materials provide new opportunities for terahertz detectors. Low-dimensional materials terahertz detectors have received extensive attention and their main advantages is high sensitivity, wide frequency band and low noise, and has made significant research progress in recent years. Although terahertz detectors have achieved breakthrough development, there are still some problems with various terahertz detectors. In this context, starting from the classification of terahertz detectors, the physical mechanism and latest research progress of bolometers, pyroelectric detectors, plasmon resonance detectors and hot carrier control detectors were briefly introduced. And look forward to the future development direction of low-dimensional material terahertz detectors.
2021, 50(1): 20211010.
doi: 10.3788/IRLA20211010
In recent years, infrared photodetectors have attracted increasing interest due to their promising applications in both military and civil areas. To further realize room-temperature, wide-spectrum, high-sensitivity, fast-response and low-power consumption infrared photodetectors, low-dimension semiconductors are considered as potential channel materials and have been studied widely. Among them, nanowires have special electrical and photoelectrical characteristics, showing enormous advantages in the applications of infrared photodetectors such as small size, low power consumption, high light absorption efficiency, abundant surface states, outstanding ability to separate and collect photoelectrons, good compatibility with Si complementary metal-oxide-semiconductor (CMOS) technology and so on. At present, nanowires infrared photodetectors are going through continuous progress and breakthrough. In this review, recent advances in semiconductor nanowires infrared photodetectors were outlined in details. At the beginning, the basic characteristics, material choice and preparation methods of nanowires were introduced. Subsequently, many nanowires including binary and ternary compound semiconductors for the use of infrared detection were presented and their current detectable levels were illustrated precisely. Many methods of further improving their detecting performances were also classified and summarized, including constructing heterostructures, applying external field and integrating with other functional devices. On the basis of the above-mentioned advances, a comparison of advantages and disadvantages among different nanowires infrared detectors was given. In the end, the future development trend was indicated based on the challenges in this area and preliminary suggestions for the technical development route were presented.
2021, 50(1): 20211017.
doi: 10.3788/IRLA20211017
Infrared detection plays an important role in cutting-edge fields such as biomedicine, smart cities, and space exploration. In recent years, a new type of nanoscale semiconductor represented by two-dimensional materials is one of the candidates for a new generation of infrared photodetection technology. This is due to the fact that some index of two-dimensional materials device have exceeded the theoretical limits of traditional thin-film devices, such as detection sensitivity, ultralow dark current, high working temperature, etc. Two dimensional materials can easily be controlled by local field. In this review, the mechanism of three local fields to achieve high performance at room temperature were introduced in the first part, including ferroelectric local field, the interlayer built-in electric field, and the in-plane built-in electric field. Secondly, we introduced the photoelectric enhancement methods of unilateral depletion heterojunction and surface plasmon structure to solve the problem of low quantum efficiency and low light absorption caused by atomic thin effect of two-dimensional materials. Finally, we showed some applications of two-dimensional materials in infrared photodetection field. The exploration reveals the potential and prospect of the novel two-dimensional semiconductor in the field of infrared photodetection, which provides some new methods and ideas for the new generation infrared detector technology.
2021, 50(1): 20211016.
doi: 10.3788/IRLA20211016
Ultra-sensitive single-photon detection is a key technology for the development of optical quantum information and quantum manipulation. It is of important scientific significance and application value to realize high-efficiency, high-sensitivity, low-power and low-cost single-photon photodetectors. There is still a large gap between visible single-photon detector based on silicon and infrared ones in terms of the cost and performance. Exploring the technology of infrared single-photon detection with novel materials and mechanism has become the urgent needs in the field of photodetection. In recent years, low-dimensional materials have offered a new possibility for realizing high-gain, room-temperature and broad-band photodetectors due to their unique physical and chemical properties. The research on the low-dimensional materials based photodetectors with good performance has also become a hot topic in the field of infrared photodetection. In this review, the basic principles of traditional avalanche infrared photodetectors were introduced firstly. On this basis, the latest development of avalanche devices based on novel low-dimensional materials was summarized. Then the new gain amplification mechanism of the photodetector based on photogating effect was discussed and the structure as well as the performance of the devices were reviewed. Finally, the future developing directions and challenges of the infrared single-photon detection technology were prospected.
2021, 50(1): 20211020.
doi: 10.3788/IRLA20211020
Quantum well infrared photodetector (QWIP) is a new device utilizing the intersubband transition in conduction band or valance band, which has a very high free degree of device design. Due to the large conduction band-offset, the ultrafast electron relax time, the ultra-wide infrared transparency and the high energy LO-phonon, the GaN/Al(Ga)N multi-quantum wells (MQWs) has become a potential candidate for the infrared detector since the GaAs based MQWs. In this paper, the research progresses of intersubband transition absorption (ISBT) and corresponding photoresponse of GaN based MQWs were systematically reviewed. First, the operation principle and the selection rule of the quantum well infrared photodetector was explained. Then, the main research work was introduced including the ISBT absorption of polar, nonpolar and nanowire GaN based MQWs, from the near infrared to far infrared, even the THz range. Finally, the progress of GaN based QWIP and quantum cascade detectors (QCD) was reviewed including the photofresponse and the frequency response of the device. A conclusion and perspective was presented for the future research in GaN based QWIP and QCDs.
2021, 50(1): 20211018.
doi: 10.3788/IRLA20211018
Since the era of graphene, two-dimensional layered materials (2DLMs) with distinctive physical, chemical and optoelectronic properties have attracted extensive attention from researchers worldwide. Benefiting from the diversity of material composition and the layer number dependence of their bandgap, the spectral response ranges of 2DLMs can cover an extremely wide band from ultraviolet to infrared radiation. Moreover, because of the lifting of the restriction on lattice matching, 2DLMs can be stacked with other dimensional materials, such as bulk materials, nanowires, and quantum dots, through van der Waals (vdWs) forces, creating unique and exclusive devices from integrated structures. This article reviewed the research progress of several typical 2DLMs heterojunction photodetectors with great potential application in the field of photodetection, focusing on the breakthrough results achieved in performance improvements such as device gain, junction rectification ratio, response time and detection wavelength coverage for devices based on tungsten diselenide (WSe2), arsenic phosphorus (AsP), niobium trisulfide (NbS3) and palladium diselenide (PbSe2), through innovations in heterostructure building and exploitation of 2D processing cutting-edge technology. Meanwhile, we had also briefly analyzed the current challenges confronted by these device researches, and tentatively forecasted its future development trend.
2021, 50(1): 20211019.
doi: 10.3788/IRLA20211019
As Ⅳ-Ⅵ compound, tin telluride belongs to direct band gap semiconductor materials. Under the condition of room temperature and atmospheric pressure, tin telluride has a stable face-centered cubic crystal structure. Being a topological crystal insulator, tin telluride has a highly symmetrical crystal structure. Due to its helical multiple surface states and strong topological protection characteristics, tin telluride can be used to fabricate new electronic devices without energy consumption. Moreover, on account of its excellent properties such as band-gap free topological surface state and narrow band gap posture, it has great potential in the field of preparing new photodetectors with wide spectral response from ultraviolet, visible light to infrared. In addition, because of its high mobility at room temperature, tin telluride is expected to be used for high performance photoelectric detection with ultra-fast response speed. In this review, the preparation methods, crystal structures and properties of tin telluride materials were summarized from the point of view that they were suitable for photodetectors. And the research progress of tin telluride in infrared photoelectric detection in recent years was summarized. Then the development potential of tin telluride in the field of photodetectors was prospected, and several aspects that need to be further studied as photodetectors were also put forward.
2021, 50(1): 20211021.
doi: 10.3788/IRLA20211021
In recent years, transition metal telluride (TMTs) has attracted extensive attention and research in the scientific field due to its unique crystal structure and excellent physical and chemical properties. In this paper, CoTe2 quantum dots (QDs) was prepared by ultrasonic method, the morphology and structure of the prepared CoTe2 QDs were characterized by TEM, AFM, EDS, XPS, XRD and FTIR. The optical properties of the prepared CoTe2 QDs were investigated by Spectrophotometer (UV-Vis), Photoluminescence (PL) and Photoluminescence Excitation (PLE). CoTe2 QDs shows good dispersion, uniform particle size and spherical morphology. The average diameter and height of the grains are about 3.1 nm and 2.9 nm respectively. CoTe2 QDs shows the obvious absorption in the infrared band, and the absorption value decreases with the increase of dilution concentration. When the wavelength of excitation light and emission light increases in turn, the PL and PLE peaks have a red shift, and they have an obvious Stokes shift effect. It shows that the photoluminescence of CoTe2 QDs is wavelength dependent. CoTe2 QDs has the photoluminescence characteristic of multicolor, different excitation light wavelength can emit different colors of light. The fluorescence quantum yield of QDs is 62.6%. The excellent optical characteristics of CoTe2 QDs, especially its absorption and luminescence characteristics in the infrared band, shows that it has important potential application value in infrared detection, laser protective coating, fluorescence imaging, multicolor luminescence and nano-photonic devices, and is expected to become a new type of infrared detection material.
2021, 50(1): 20200103.
doi: 10.3788/IRLA20200103
A Φ1550 mm aperture space mirror’s surface figure RMS was required to be superior to 1/50λ (λ=632.8 nm) under the zero-gravity orbit environment. In order to simulate the state of weightlessness and reduce the influence of gravity in the mirror’s surface figure test with horizontal optic axis, the mirror was actively supported by multiple forces to unload the gravity and the forces’ parameters were optimized. Firstly, the principle to determine the value, the number of support points and the initial axial position of each unload force was proposed based on dividing the mirror into blocks. Secondly, with the optimization goal of the mirror’s surface figure RMS be superior to 0.002λ under the function of gravity along with all unload forces, a structural FEM model was established. Taking the positions of all unload forces along the optic axis as optimal variables, influences on target were analyzed and quick optimization points were concluded to simplify the optimization. Finally, the mirror’s surface figure RMS when unloaded was found minimal of 0.00145λ. Putting the parameters of the optimization result into use of the surface figure test of the mirror with horizontal optic axis, it turned out that when the mirror revolved around the optic axis 0°, 120° and 240°, the surface figure RMS were 0.0157λ, 0.0161λ and 0.0159λ respectively and the figures were consistent, which proved that the gravity impact was eliminated effectively. The optimization method for gravity unload is flexible and efficient which guarantee the large-aperture mirror’s high-precision machining and space mission.
2021, 50(1): 20200117.
doi: 10.3788/IRLA20200117
Aiming at the problems of optical imaging for low altitude, low speed and small target recognition ability and low signal-to-noise ratio, a low altitude and high resolution lidar optical system was designed. The MEMS mirror was used by the scanning device of the transmitting optical system, and the beam expanding system was designed to ensure the beam quality of the laser emitted at different scanning angles. The digital mirror device combine with objective lens, polarizing device were used for receiving optical system, the background noise was greatly lower than laser receiving system using single-point detector and could realize laser echo receiving and visible light imaging at the same time. The structure parameters of the optical system were given, an optical system was designed using optical design software. The optical system has a spatial resolution of 0.5 mrad/pixel and an array scale of 200×200. The simulation results show that design method is feasible. The detection distance can reach 1000 m, and the background noise can be reduced by about 22162 times compared to the single-point detector receiving system.ystem.
2021, 50(1): 20200119.
doi: 10.3788/IRLA20200119
The traditional plant lighting design only evaluates the uniformity of a single reference surface, and it is difficult to meet the light intensity and light quality requirements of different stages of plant growth. Aiming at this problem, first, a space lighting uniformity evaluation system was proposed, and based on this system, a three-dimensional lighting system with a composite light source module was proposed, in order to construct a plant lighting space with uniform lighting. Further, the Taguchi method was used to optimize the experimental process, and the optimal structural parameters were obtained on the basis of ANOVA analysis. Finally, the lamp beads shape analysis and the lighting effect test during the plant growth process were performed on the obtained optimal solution. The experimental results show that the optimal structure can provide a uniform illumination space with horizontal reference plane illumination uniformity of 87.22%, color mixing uniformity of 90.11%; vertical reference plane illumination uniformity of 93.02%, and color mixing uniformity of 91.43%. The plant light source system can meet the requirement of a uniform space lighting environment during plant growth.
2021, 50(1): 20200143.
doi: 10.3788/IRLA20200143
GF-7 stereo mapping satellite launched on November 3, 2019 was equipped with two high-resolution remote sensing cameras “Front camera” and “Back camera”. By the two cameras, the same scene on the ground can be observed from different angles for forming a 3D mapping image. During the development of the stereo mapping camera in the lab, the horizontality of the linear array, field confocal, high-accuracy measurement for elements of interior orientation and distortion should be guaranteed. In order to meet the requirements of the above technical indicators of GF-7 bi-linear array cameras, computer-aided rapid fast adjustment for focal plane and high-precision test for elements of interior orientation and distortion was presented. These methods used in the GF-7 bi-linear array camera improve the efficiency of adjustment and test and guarantee the accuracy of the test results. Finally, confocal plane of each camera is better than ±0.04 mm, horizontality of each linear array is better than ±1′, the accuracy of distortion is better than 2.3 μm. It can provide reference for other large scale mapping camera.
2021, 50(1): 20200104.
doi: 10.3788/IRLA20200104
Motion estimation is an effective way to rectify the distortion of linear array images of moving target in linear measurement system. However, the non-cooperation and motion complexity of instability space targets make it difficult to precisely estimate their motion parameters. In order to improve the estimation accuracy, a feature-driven high-precision motion estimation for instability space targets was presented. Firstly, a self-constrained motion model of instability space targets by means of the spherical coordinate was established, which transformed the motion estimation into an unconstrained nonlinear optimization problem in high dimensional space. Then, according to the existence and uniqueness of global solutions, an effective way was devised to judge the validity of obtained solutions via comparing the similarity of two solutions calculated via two solving processes under different selections of frame number, which evidently improved the effectiveness and robustness of our method. Finally, the solving efficiency among different non-linear solution methods in the view of our problem was numerically analyzed and an efficient solution scheme in terms of the accuracy of initial values was presented to improve the efficiency of our method. Experimental results illustrate that only needing a maximum of 15 frames of linear array images the estimation accuracy of motion parameters all reach (<10−5) and thus achieve the high performance of rectification for distorted linear array images in our research background.
2021, 50(1): 20200081.
doi: 10.3788/IRLA20200081
A super-resolution reconstruction method was proposed to solve the edge blurring and texture copying in the depth map from the super-resolution process when using guided filter. The proposed method was based on the guide filter and high-resolution grey image’s edge feature-constrained. Firstly, up-sampling the low resolution depth image by interpolation and the edge region of the depth image was extracted by multi-scale edge detection. Subsequently, the depth map and high-resolution grey image’s edge were extracted. Then, the public edge region was extracted according to the similarity between gray image and depth map. Finally, the high-resolution depth map was constructed through the position of gray image edge pixels in the public edge region constrainting the feneration of guide filter coefficients. By means of the validation of Middlebury data set and the combination with four super-resolution reconstrcution algorithms based on the filter, the proposed method can better protect the edge feature of depth map reconstruted by super-resolution, attain the high-resolution depth, and has high calculation efficiency. The results can provide theoretical basis for target recognition and scene reconstruction of low resolution lidar.
2021, 50(1): 20200105.
doi: 10.3788/IRLA20200105
An anti-occlusion real time target tracking algorithm employing spatio-temporal context was proposed to solve the problems of tracking instability or even failure, which were caused by illumination variation, background clutters, target deformation or occlusion. Firstly, in the framework of spatio-temporal context model, the adaptive dimensionality reduced color features were adopted to describe the target to promote the distinguish ability in complex scene. Secondly, the peak and the peak-to-sidelobe ratio of confidence map response were combined to evaluate the target tracking status. Then, occlusion was discriminated by the correlation coefficient between target templates. Finally, when the target tracking status fluctuated, the update speed of target model was reduced, and the target coordinates were corrected by the Kalman filter. When the target was occluded seriously, the target coordinates was predicted according to the Kalman filter, and the target model was stopped to update for recapturing and tracking the target again after occlusion released. 36 color sequences with multiple challenging attributes were selected to evaluate the performance of the proposed algorithm, and it was compared with other excellent target tracking algorithms. The experimental results demonstrated that this algorithm has strong anti-occlusion ability, and improved the robustness of target tracking effectively under the influence of disturbance factors such as illumination variation, background clutters and target deformation. Meanwhile, it met the real time requirement of target tracking.
2021, 50(1): 20200098.
doi: 10.3788/IRLA20200098
High brightness laser sources with different wavelengths play an important role in the fields such as defense, industrial, and life sciences etc. However, due to the intrinsic spectral and thermophysical properties of current available laser gain materials, it is difficult to take into account the wavelength and output power of the traditional inversion lasers, which even leads to the decrease of beam brightness. To overcome this problem, beam cleanup by using nonlinear optical technology has been carried out in recent years, which is directly transferring the low beam quality generated from inversion lasers into the high through the effects such as stimulated Raman or Brillouin scattering. Among them, with excellent properties such as high Raman gain coefficient, high thermal conductivity and wide spectral transmission range, diamond exhibits excellent beam brightness enhancement characteristics while realizing high efficiency Raman conversion, which provides a new technical path to generate high power and high brightness laser beam. Here, the development of brightness enhancement based on first-order and cascaded Raman conversion of diamond was reviewed, and its future applications were discussed.
2021, 50(1): 20200082.
doi: 10.3788/IRLA20200082
A compact non-chain pulse deuterium fluoride (DF) laser renewing the working gas by axial-flow has been established. The characteristics of miniaturized axial flow non-chain pulse DF laser were studied experimentally. When the ratio of working gas SF6∶D2 = 10∶1 and total pressure=8 kP, the output energy of DF laser was about 800 mJ and full width at half maximum was about 120 ns at single pulse mode, which was similar to transverse flow DF laser. When working at repetition rate of 20 Hz, a maximum output power of 13.1 W was reached in this laser, whose amplitude difference of laser pulses was less than 5%. Then, the possibility of high repetition rate operation of axial flow DF laser was prospected. An axial flow non-chain pulse DF laser was proposed in this paper, which provides a new technology approach for the miniaturization and engineering application of the mid-infrared laser.
2021, 50(1): 20200084.
doi: 10.3788/IRLA20200084
Gold nanocages (GNCs) were successfully prepared by seed-mediated method and its nonlinear saturated absorption characteristic at 1123 nm was verified for the first time. As a comparison, a MoS2 saturated absorber was prepared. Based on GNCs and MoS2 as saturable absorber (SA), respectively, passively Q-switched Nd: YAG lasers at 1 123 nm were demonstrated.When Q-switched laser with MoS2 as SA, Q-switched pulse with the shortest pulse duration of 412 ns and maximum pulse repetition rate of 233 kHz was achieved under the pump power of 6.81 W with the maximum average output power of 208 mW. When Q-switched laser with GNCs as SA, Q-switched pulse with the shortest pulse duration of 253 ns and maximum pulse repetition rate of 326 kHz was achieved under the pump power of 6.04 W with the maximum average output power of 221 mW. Compared with the experimental results of MoS2 Q-switched laser, the gold nanocage Q-switched laser has higher output power and efficiency, narrower pulse width and higher repetition rate. These results indicate a great potential of the GNCs film as SA in the near-infrared region.
2021, 50(1): 20200120.
doi: 10.3788/IRLA20200120
The existing multispectral imaging technologies usually utilize optical spectroscopy and multiple detectors to capture spectral images. These techniques suffer from complexity, a large amount of data and low efficiency. Addressing these deficiencies, in this paper, a spectral encoded computational ghost imaging technology based on orthogonal modulation model was proposed. The orthogonal spectral encoded matrices fused with Hadamard patterns were used to produce the illumination patterns that modulate the broadband light source. A single-pixel detector was utilized to collect the back-reflected signal from the imaging objects. The evolutionary compressive technology was applied to recover the mixed spectral image. The subsampled spectral channel images were obtained from the mixed spectral image by means of the orthogonality of the spectral encoded matrices. Then the group sparse compressed sensing algorithm was applied to reconstruct the full-sampling spectral channel images, which finally fused the multispectral image of the imaging object. The efficiency of the proposed method was verified by a numerical simulation and an experiment. The proposed technology simplifies the multispectral imaging configuration and greatly reduces the amount of data. The orthogonal spectral encoded strategy can extend to more spectral channels and also can be applied to polarization imaging, information encryption, and other many fields.
2021, 50(1): 20200136.
doi: 10.3788/IRLA20200136
The pollution of heavy metals in the soil has seriously affected agriculture and food safety. Therefore, efficient and accurate detection of heavy metal pollution is a problem that needs to be solved urgently. When using laser induced breakdown spectroscopy (LIBS) to quantitatively analyze the Ni element in the soil, it was found that the characteristic peak of the Ni element with a wavelength of 373.68 nm in the soil would be affected by the spectral line of the Al element at 373.39 nm. Therefore, the spectra of pure aluminum-based soil and tableted soil were compared and measured. A method of using pure aluminum as the substrate and subtracting the spectral line of the Al element in the soil background to eliminate the interference of the Al element in the soil background to the Ni element was proposed. This method was called the background subtraction method. The experiment determined that the optimal delay time for both soil samples was 1.0 μs, and the lens-to-sample distance (LTSD) was 97 mm and 96 mm, respectively. The internal standard method was used to quantitatively analyze Ni in the two soil samples. The calibration curve fitting effect of the Ni element in the pure aluminum-based soil samples was good, the correlation coefficient R2 was 0.997, and the maximum standard deviation (RSD) was 4.34%. The relative error of the Ni element in the soil sample after the base background subtraction method was reduced to 4%. The experimental results show that: when using LIBS technology to measure the content of heavy metal elements in the soil, under the condition that the characteristic line of the element is limited, in order to avoid the interference of the line and improve the detection accuracy, the background subtraction method can effectively eliminate the line between the elements Interference.
2021, 50(1): 20200137.
doi: 10.3788/IRLA20200137
Laser-induced breakdown spectroscopy (LIBS) is a material composition detection technology that has emerged in recent years with the development of laser technology and spectral detection technology. This technology has many advantages such as fast, non-destructive, simple operation, and no sample pretreatment , but the traditional LIBS has the shortcomings of weak spectral intensity and low SNR, which directly affects the accuracy of quantitative analysis.To enhance the laser-induced breakdown spectrum intensity and improve the SNR, some different cavities were designed (height of 1 mm, diameters of 2, 3, 4 , 5, 6 mm; Diameter of 5 mm, heights of 1, 2, 3, 4, 5, 6 mm), the Au-NPs (Au nanoparticles) (diameter of 10, 20, 30 nm) was combined with the cavity to confine the plasma spectrum of the sample. Experiments show that the optimal cavity diameter is 5 mm and the height is 4 mm, the optimal Au-NPs size is 20 nm. Compared with the traditional LIBS, under the optimal cavity, Au-NPs and the combined action of the optimal cavity with Au-NPs, the enhancement factors are 20.6, 7.3, and 31.3, respectively. The cavity can increase the plasma electron temperature and Au-NPs have almost no effect on the electron temperature. Both the Au-NPs and cavity can improve the SNR. Under the combined action of the optimal cavity and the optical Au-NPs, the SNR is the highest.
2021, 50(1): 20200028.
doi: 10.3788/IRLA20200028
The effect of transverse mode instability has gradually become the primary problem that causes laser beam quality degradation and limits power scaling of high-power fiber lasers. This paper conducts a series of study on the transverse mode instability (TMI) in large mode area (LMA) fiber based on a co-pumped all-fiberized narrow linewidth high power amplification platform. According to the calculation results of the coupled mode equations, the nonlinear coupling strength between the LP01 and LP11 modes of the LMA fiber 25/400 μm is the largest, which directly induces the TMI. In order to suppress the generation and amplification of the LP11 mode at the main amplifier, the fiber coiling method was used as an operational mode filtering technique to achieve mode control. The threshold of TMI increased from 1000 W to 1600 W while reducing the bending radius of the main amplifier gain fiber from 6 cm to 5 cm, and the other output performance of the fiber laser was hardly affected. This provides a powerful experimental reference for us to build an actual narrow linewidth, high power, all-fiberized laser system.
