2018 Vol. 47, No. 1
column
- Invited paper-Beam combining of fibre laser
- Infrared technology and application
- Laser technology and application
- Laser radar technology
- Laser technology
- Photoelectric measurement
- Optical communication and optical sensing
- Advanced optical materials
- Spectrum detection and analysis
- Information acquisition and identification
2018, 47(1): 103001.
doi: 10.3788/IRLA201847.0103001
Coherent beam combining (CBC) of ultra-short pulsed lasers is a promising way to overcome the power and pulse width limitations from a single fiber. In this paper, the principles and technologies of coherent combining of ultra-short pulsed lasers in spatial, time and spectral domains were described. The current status of ultra-short laser CBC systems and their key technologies were reviewed, several future perspectives were pointed out. This paper can be a reference for future development of CBC of ultra-short pulsed lasers.
A spectral beam combination(SBC) system with dual Multi-Layer Dielectric(MLD) grating dispersion compensation configuration, which can combine multiple fiber lasers into a common aperture beam with high beam quality and relax the linewidth requirement of the individual fiber laser, has become gradually one of the most important technique route of fiber laser beam combining. The basic principle and the key technologies of the SBC system with dual-MLD-grating configuration were introduced and analyzed briefly. The recent progress of the main key technologies about high power beam combinable narrow linewidth fiber laser, high power high efficiency short wavelength narrow linewidth fiber laser, large dispersion high efficiency MLD grating and high integration dense beam combining were reviewed. The recent progress on the key technologies of SBC with dual-MLD-configuration in Institute of Applied Electronics, China Academy of Engineering Physics, were also presented. The potential of the SBC with dual-MLD-configuration was prospected.
2018, 47(1): 103003.
doi: 10.3788/IRLA201847.0103003
Laser phased array technique on coherent combining of multiple beams faces challenges when applied in propagation through the long-range atmosphere. Aberrations in such transmission systems include turbulence-induced dynamic aberrations located at the path from the fiber laser array to the target, besides the inherent phase errors like phase noises and tip/tilt errors. Effective bandwidth for eliminating such aberrations is limited by the optical transmission delay and the increment of the array scale. Existing techniques, e.g., target-in-the-loop and delayed stochastic parallel gradient descent, are difficult to deal with the fast-changing turbulence-induced tip/tilt aberrations. But correcting these aberrations is critical for obtaining combined laser beams on the target with the best beam quality. In this paper, research progress of multi-aperture laser transceiving control for beam combining applications in IOE, CAS was This method provided efficient ways to achieve tip/tilt control for the beam coupling from space to fiber and the outgoing laser beams in the beam combining applications. Correction of the aberrations outside the fiber laser array based on active multi-aperture wavefront sensing of the fiber laser array was proposed. These novel techniques presented here would promote the application of laser phased array technique in atmospheric propagation.
2018, 47(1): 103004.
doi: 10.3788/IRLA201847.0103004
The new development of using divided-pulse amplification system in controlling the fiber nonlinearity, enhancing the pulse energy and breaking through the damage threshold of gain material was reviewed, including the basic types of pulse divider and optical arrangement of amplifiers. The latest advances in high repetition rate, high power Er-doped fiber divided-pulse amplifier was introduced. Based on the double-pass configuration and multi-stage pulse divider, nonlinear amplification and pulse compression were achieved simultaneously, resulting in frequency-doubled output pulses with an average power of hundreds of milliwatts and pulse width less than one hundred femtosecond at 780 nm. This divided-pulse Er-doped amplification method has proven a valuable tool to develop compact, user-friendly and environment stable femtosecond source, which provides an alternative to Ti:sapphire laser in applications to the generation of Terahertz radiation, biological imaging and optical nonlinearity.
2018, 47(1): 103005.
doi: 10.3788/IRLA201746.0103005
All-fiber signal combiner is one of the key components to break through the power scaling limitation of a single fiber laser by combing several high power fibers into a single fiber to realize the higher output power. The basic structures and the research progress of the all-fiber combiner at home and abroad were sumarized. The technical program and features were discussed in detail, existing problem and future research direction were put forward.
2018, 47(1): 103006.
doi: 10.3788/IRLA201847.0103006
The progress of liquid crystal optics phased array devices in high power laser applications was reviewed in this paper. Based on the realization principle of the device, the reason of the device in the high power application was illustrated. Based on the multi-layer structure of the device, the working condition and limitation of the high power laser were introduced, including the transparent conductive layer, alignment layer and liquid crystal. Meanwhile, the latest research progress of these typical functional layers was carried out. At the same time, the relationship between laser threshold and the operating mode or the heat dissipation structure was also analyzed in detail. The related research progress was also reviewed.
2018, 47(1): 103007.
doi: 10.3788/IRLA201746.0103007
As a critical technique for increasing the brightness of narrow-linewidth fiber lasers, coherent polarization beam combining can achieve common aperture joining of multiple lasers, while maintaining higher beam quality and linear polarization state. A polarization control system of combined lasers was investigated based on the linear phase locking technique. A physical model for optical homodyne polarization detection and a mathematical equation for linear phase-locking loop were established and analyzed in detail. The polarization phase of combined lasers was checked by employing high-precision optical homodyne method and then fed back to phase lock lasers in real time. A linear polarization laser was output with the power of 279 mW. After phase locking, the polarization extinction ratio of combined lasers attained 19.3 dB and the control bandwidth was 39.6 kHz. The residual phase noise is 710-4 rad/Hz(1 Hz) and 310-4 rad/Hz. When the power was increased to 1 W, the polarization extinction ratio was -15 dB, which was restricted by power-induced phase noise and spatial mismatch of beam spots.
2018, 47(1): 103008.
doi: 10.3788/IRLA201746.0103008
Spectral beam combining is an effective way to break through the power limitation of a monolithic fiber laser and achieve high brightness fiber laser output.A spectral beam combining scheme was presented that the single element was structured by external-cavity fiber oscillator.This scheme had more compact structure and was able to contain more elements,compared with the current MOPA structure element.A theoretical analysis was conducted about the relationship between the wavelength and position of each element,and a numerical simulation was carried out about the influence of aberrations in the transform lens on cavity loss and combining effects.An experimental system was built,and the experimental results agree well with the theoretical analysis.This work has important guiding significance for the building of next generation spectral beam combining system.
2018, 47(1): 103009.
doi: 10.3788/IRLA201847.0103009
The sticking point of spatial light-single-mode fiber is to find the best position in the transverse plane of fiber precisely. Based on optical fiber migration's influence on the spatial light-single-mode fiber coupling efficiency, an auto-coupling system was proposed, which mainly consisted of two-dimensional piezoceramics, driver, controller, photoelectric detector which was a closed loop control system and coupling lens. The automatic alignment coupling of the spatial light-fiber was realized by combining with simulated annealing algorithm. The coupling efficiency for free-space laser coupling into the fibers and simulated annealing algorithm were analyzed theoretically. Analysis results of experiment show that the method can make the system search the best position automatically based on the power of the light which is coupled into the single-mode fiber. The optimal coupling efficiency is about 51.4%, which can be obtained in short times by the system and it is improved by 6.5% compared with no automatic alignment before. The scheme is practical and it is of great significance for the study of the automatic coupling of spatial light-single-mode fiber.
2018, 47(1): 103010.
doi: 10.3788/IRLA201847.0103010
Maintaining excellent beam quality is very important for the construction of the experimental spectral beam combining(SBC) system. The influence of pointing deviation on the beam characteristic was studied in SBC of fiber laser array theoretically. The incident light field of the laser array with the pointing deviation was corrected, and the variation rule of the combined beam quality with uniformly distributed random perturbations was discussed by the beam propagation model and the statistical analysis. The simulation result shows that the pointing deviation has a significant effect on the output characteristics of the SBC system. When the maximum deflection angle of the laser array is only 0.05, the beam quality of SBC system will increase to(6.491.73). In order to achieve the brightness scaling of combined beam and gradually expand the scale of laser array, the combined beam quality tends to stabilize. As a reference for the array scale(30 fiber lasers) with the changes of relative stability, the variation tendency of the M2 factor and maximum pointing deflection angle is fitted for building the experimental system of SBC.
2018, 47(1): 103011.
doi: 10.3788/IRLA201847.0103011
Beam combining of high energy fibre lasers is the research hotspot especially for the directed energy application in recent years, which can overcome the output power lever limits of one single-mode fibre laser, and establish the theoretical foundation for the application of laser weapons with high power and perfect beam quality. Research status of fibre laser incoherent combining and coherent combining were presented. In the section of incoherent combining, the combining principle and combining level of beam overlap and spectral beam combining were introduced. In the section of coherent combining, the key combining apparatus of transmission-type and reflection-type equivalent large aperture laser array output and optical element of single aperture output were analyzed in detail. The advantages and disadvantages and range of application of high power fibre laser beam coherent combining and incoherent combining were compared briefly.
2018, 47(1): 104001.
doi: 10.3788/IRLA201847.0104001
In the field of space remote sensing, the long wave detector with wavelength of 10 m or more is mainly based on HgCdTe photoconductive(PC) detector, which plays an important role in IR imaging. Nonuniformity is one of the outstanding problems in the long wave PC detector. A new type of long wave PC detector read-out integrated circuit(ROIC) in digital-analog mixed mode with nonuniformity correction was designed. The circuit could not only effectively solve nonuniformity of the linear long wave PC detector in resistance, but also increase the dynamic range of the output signal of the ROIC with almost no increase in power consumption. Simulation results show that the nonuniformity is greatly improved through the correction ROIC, which makes the nonuniformity reduce to less than 0.5%, and it can work at room temperature and low temperature. The correction circuit could not only solve the key problems in current project, but also have guiding significance for circuit future design of high performance large array IR detector.
Identification of flow rate and temperature in a heat supply pipeline based on surface temperature measurement is still at the initial stage in the field of infrared nondestructive testing, which is the key theory for the development of infrared nondestructive testing. In order to solve the problem that the flow rate identification result was less accurate than the temperature identification result and the accuracy of the identification method based on least square fitting was limited, a heat transfer model of the fully developed region of the pipeline had been built based on Gnielinski correlation equation, and the identification problem had been solved by Levenberg-Marquardt(L-M) algorithm based on surface temperature measurement. Through theoretical derivation and numerical examples, it has been found that the parameter relative identification error is inversely proportional to the absolute value of the product of the sensitivity maximum and the true value of the parameter, and the variance between the measurement temperature distribution with measurement error and the temperature distribution based on least square fitting is not equal to the product of the standard deviation of the measurement error and the number of measurement points. The identification method based on equal variance fitting of surface temperature measurement was proposed. Numerical experiments have proved that the method can accurately identify the flow rate and temperature in the pipeline with measurement error.
2018, 47(1): 104003.
doi: 10.3788/IRLA201847.0104003
Infrared optical system self-thermal radiation was evaluated, calculated and measured. Firstly, it introduced and compared the two kinds of the thermal radiation way of evaluation, effective emissivity and equivalent blackbody radiation temperature; Secondly, the way based on experiment of calculation for equivalent blackbody radiation temperature of self-thermal radiation was introduced in detail; Finally, the coaxial reflection infrared optical system thermal radiation was measured by using self-thermal radiation test platform and error analysis was carried out. The result show that self-thermal radiant exitance is proportional to the square of effectively F number of optical system and the linear coefficient for the output gray of self-thermal radiation between the integral time, is inversely proportional to transmittance. It shows that the equivalent blackbody radiation temperature for self-thermal radiation of coaxial reflection infrared optical system is 217.3 K. Error for radiation form background simulation board is 8.5%, the relative uncertainty of linear coefficient for the output gray of self-thermal radiation between integral time is 0.2%. It shows that infrared detector has a good stability under 5×10-4 Pa.
2018, 47(1): 104004.
Infrared (IR) system with imaging fiber bundle has important academic value and broad application prospects in the field of IR detection. The method of combining numerical simulation and experimental analysis was adopted to study the problem of image quality optimization of this system. Based on the system working principle and characteristics, a mathematic model of its modulation transfer function (MTF) had been established. The main influence factors of the image quality had been analysed. The numberical simulation analysis results showed that to ensure its image quality, the MTF of fore objective lens and relay lens should be larger than 0.8 at the system Nyquist frequency, the misadjustment between fiber images and pixels should be less than 0.5 pixel size. To analyze the influence of the imaging fiber bundle defects, system principle-demonstrating experiment had been accomplished. After comparing the push-broom image results with two different formats fiber bundle, a set of technical methods to improve the system image quality had been deduced. Such as, using appropriate relay lens, time delay integral (TDI) mode push-broom with several tiers fibers, coating on the entrance and exit bundle ends, exact uniformity correction processing, et al. All the results above provide necessary technical reserves for the development of such novel system.
2018, 47(1): 106003.
doi: 10.3788/IRLA201847.0106003
By introducing the electron density model of the two-temperature equation, the Drude model and the theory of =/2, it was found that the high frequency ripple period had the characteristics of wavelength dependence. It was analyzed that the high frequency period ripple was close to /4-/6 in a certain range and was proportional to the incident laser fluence when the radiated light flux was close to the damage threshold. Besides, the electric field distribution on silicon surface irradiated by femtosecond laser was numerically simulated by FDTD method. The ripples formed by initial laser pulse on the silicon surface make most laser energy deposit on the edge of the groove, finally causing the generation of high-frequency periodic structure. What's more, through analyzing the initial groove depth and the optical properties (dielectric constant) of the excited silicon surface, the conditions for forming high-frequency periodic ripples were obtained. With the increase of dielectric constant which can be also expressed by the laser flunece, the surface morphology become more obvious. This study is of great significance for understanding the formation of high spatial frequency periodic structure of silicon surface caused by femtosecond laser and its application in the field of silicon materials processing.
2018, 47(1): 106005.
doi: 10.3788/IRLA201847.0106005
Coupling efficiency between the sodium laser and sodium atoms in the mesosphere is one of the most important parameters for the sodium laser guide star system. A photometry system of the sodium beacon had been built on the 1.8-meter telescope at Lijiang Observatory, Yunnan Province, to measure the brightness of the beacon and coupling efficiency of the laser. The system consisted several parts:sodium laser, beam transfer optics and laser launch telescope, receiver telescope, atmospheric coherence length measuring instrument, and ground-based sodium lidar. Measurements of the sodium beacon on different output power, polarization status and central wavelength, excited by the 20 W class quasi-continuous wave sodium laser of Technical Institute of Physics and Chemistry, Chinese Academy of Sciences had been carried out Since 2011. The apparent full width with half maximum of the beacon spot could be as small as 3', or 1.3 meter at 90 km altitude. Detail of calculating the returned photons had been presented. Taking into account the transmission through astronomical V-band filter and quantum efficiency of the CCD camera, the corrected brightness of the sodium beacon produced by 19 Watts of circular polarized light was equivalent to a 7.4-V-magnitude natural star, or 9.55106 photonss-1m-2 on the top of the atmosphere.
2018, 47(1): 126002.
doi: 10.3788/IRLA201847.0126002
The quality of vehicle records was seriously influenced along with the bumping and shaking driving, and the jittering videos would impact observer reading and interpreting the information. In order to improve the quality of the records, a real-time image stabilization method for vehicle cloud platforms had been proposed. Firstly, the nonlinear filter was adopted to build scale space for the purpose of highlighting edge information; Secondly, a feature detection combined fast image brightness test and gradient calculation was put forward for more quality features, furthermore, increasing the self-salience and differences between descriptors brought discriminative power; Finally, similar features was availably distinguished by location verification for accurate estimation of global motion vector. The time experimental results shown that the proposed approach fulfile the task of real-time, and the average frame rate is over 60 even when the resolution is 720 P. In effective capability experiments, the repeatability of new method is more than 65%, which indicates the enhancement of detection power. Furthermore, the ITF of 6 group tested increase 46.8%, 30.8%, 28.44%, 28.1%, 33.9% and 53.4% after dejitter design, which illustrates that the method significantly improves the effectiveness and precision of the vehicle image stabilization algorithm.
2018, 47(1): 106001.
doi: 10.3788/IRLA201847.0106001
In order to investigate the transient response characteristics of photovoltaic detectors irradiated by short-pulse laser, the response waveforms of a HgCdTe photodiode to laser pulses with 16 ns duration and different laser intensities were measured. The photodiode worked with room temperature and zero bias, and the laser wavelength was in the response spectrum of the photodiode. In the detector's linearly logarithmic response zone, the signal waveform broadened gradually with the incident laser energy density from 7.2 nJ/cm2 to 75 J/cm2. The full width at half maximum of signal waveform rose to 235 ns from 55 ns, at the same time the bottom width rose to 380 ns from 170 ns. The pulse response broadening of the detector implied degradation of its transient response characteristics. The mechanism of the response degradation was explained via analysis on the diffusion process of photocarriers in the quasineutral region and on the changes of junction electric field and junction capacitance under high-injection condition.
Combined with particle swarm optimization (PSO) algorithm, the parameter of photodiode was extracted from I-V characteristics curve based on the equivalent circuit which was obtained before and after irradiation on Si photodiode. Then the experimental law of equivalent parameter before and after being damaged was acquired. When the photodiode was damaged, the reverse saturation current was decreased and the series resistance was increased, and the shunt resistance was decreased. The damage mechanism was given qualitatively based on semiconductor physics theory. The decrease of the reverse saturation current was on account of decrease in doping concentration. The increase of series resistance was due to the decrease in doping concentration and carrier lifetime. The decrease of the shunt resistance was caused by the defects in the surface and internal of semiconductor.
In order to acquire medical implants with excellent performance, research needs to be conducted on the performance of selective laser manufacturing parts after heat treatment. Tensile testing machine and impact testing machine were adopted to carry out tensile and impact experiments respectively to the manufacturing parts. Metalloscope and SEM were used to observe the surface topography and study its fracture mechanism. The results show that the untreated manufacturing parts built by SLM have high strength of extension. SLM manufacturing CoCrMo alloy has higher ductility under cold condition in 1 200℃ annealing furnace. The hardness decreases with the temperature increase of heat treatment. There is a U-shaped relationship between the impact energy and heat treatment temperature. With the increase of heat treatment temperature, crystal grain of SLM manufacturing parts become bigger gradually and the internal stress reduces. The fracture mechanism under the condition of 1 200℃ annealing is ductile fracture, which provides the basis for the application of SLM CoCrMo alloy in the medical implants.
2018, 47(1): 106006.
Many parts with closed cavity structure are widely used in many fields. This kind of structure has large incline angle, the molten pool will collapse and even the forming is unable to continue, when the way of horizontal slices is adopted. Especially, there is interference between parts deposited and the laser beam by the method of variable angle normal direction slices without adjacent layers. Based on hollow laser beam inside powder feeding technology, the closed hemisphere shell parts was researched. The closed hemisphere shell parts were divided into two parts including normal direction slices area and oblique orientation slices area. Normal direction slices method was used to eliminate staircase effect when depositing normal direction area and the oblique orientation dislocation slices method was adopted to avoid interference between parts deposited and the laser beam. The offset model of oblique orientation oblique orientation was established and the feasibility was verified by inclined wall depositing experiment. The cladding forming of the closed hemisphere shell was finished. Results show that the surface of the formed parts is smooth, the size error is within 5%, the thickness is stable around 2.7 mm, the microstructure of two forming area is compact, the distribution of hardness and tensile strength are stable.
2018, 47(1): 105001.
doi: 10.3788/IRLA201847.0105001
A stable multiwavelength erbium-doped fiber laser was proposed and experimentally demonstrated by using a compounded fiber filter, which was composed of a Mach-Zehnder interferometer(MZI) and a birefringence fiber filter-Lyot filter. The MZI was fabricated by using the fiber fusion splicer to splice a section of SMF to form two cascaded spherical structures. The Lyot filter was incorporating a segment of polarization maintaining fiber(PMF) and two polarization controllers(PCs), which provided nonlinear polarization rotation(NPR) and birefringent filter effect to suppress the mode competition and generate multiwavelength. Using cascaded spherical-shape structures MZI and the Lyot filter as mode restricting elements respectively, the transmission spectrum of cascaded spherical-shape structures MZI was modulated by the Lyot filter, which determined the period of the compounded structure. In the experiments, 9-wavelength operation with a side-mode suppression ratio (SMSR) of~40 dB was achieved, and the space of wavelength was 0.68 nm defined by the Lyot filter. When the stability of proposed structure was observed for 2 hours every 10 minutes, the fluctuation of the central wavelength's output power was less than 0.67 dB. Furthermore, when the two spherical-shape structures MZI was fixed on a furnace and the temperature varied from 30℃ to 110℃, the spectrum of output wavelength can be tuned within the range of 6.69 nm.
2018, 47(1): 105002.
doi: 10.3788/IRLA201847.0105002
In order to make full use of the advantages of single emitter semiconductor diode laser and obtain a light beam of more wavelengths, higher power, higher optical power density, a fiber coupled diode laser module was designed, which consisted of 32 single emitter semiconductor diode lasers using incoherent multiplexing by ZEMAX. The wavelengths of semiconductor diode laser were 975 nm and 915 nm, the power was 15 W. After the simulation of fast axis collimation, slow axis collimation, spatial multiplexing, polarization multiplexing, wavelength multiplexing, focusing and fiber coupling, this module can produce 467.46 W from a standard optical fiber with core diameter of 200 m and numerical aperture(NA) of 0.22. The coupling efficiency before-after fiber was above 98.47%, the total coupling efficiency was above 97.39%. The optical power density was above 12.86 MW/(cm2sr), module can be used as pump laser and high power device. The corresponding packaging structure was designed by Solidworks and its thermal performance was simulated by ANSYS. The final result demonstrates that this module plays a great heat dissipation performance and is of high feasibility.
2018, 47(1): 105003.
doi: 10.3788/IRLA201847.0105003
The eye-safe kilohertz repetition rate solid-state laser was developed by using the OPO of unstable resonator. Using pulse LD side-pumping Nd:YAG laser crystal and electro-optical Q-switched techniques, the laser achieved high beam quality of 1.064 m fundamental frequency light. The Ⅱ type noncritical phase-matching KTP crystal was adopted in optical parametric oscillation. In order to get high beam quality, the OPO cavity made use of plane-convex unstable resonator structure. The laser system could operate stably at the wavelength of kilohertz repetition rate 1.57 m. When the pumping current of LD was 125 A and the electro-optical Q-switched repetition rate was 1 kHz, the maximum average output power of 1.57 m laser was 4.67 W and the pulse width of the output laser was 4.3 ns, the power instability of 1.57 m was 3%. The laser pumping threshold was about 45 A.
2018, 47(1): 117001.
doi: 10.3788/IRLA201847.0117001
For the sake of retrieving soil moisture by the polarized information, a polarized reflection model of soil surface was established, and an experimental study of soil moisture and reflected light's polarized information was carried out in the visible wavebands. Firstly, the polarized reflection model of soil surface was established based on the geometrical optics theory and the measured data. Secondly, the soil samples of different moisture contents were made, the experimental platform was set up, the soil samples polarized information were obtained by a polarized imaging detection system with high precision in a variety of incident and observation conditions, the model was verified by analyzing the experimental data. Finally, a quantitative relationship among the micro-surface slope variance, the diffuse reflection coefficient, the equivalent refractive index and the soil moisture was established in the model and the soil moisture was retrieved according to the quantitative relationship. The research results show that:on 476 nm, the polarized information of a soil sample with a moisture content of 26% is measured by a polarized imaging detection system in the indoor environment, the soil moisture is calculated as 24.73% according to the proposed retrieval method in an error of 4.88%. Therefore, it is proved that the proposed method of retrieving soil moisture by the polarized information is correct and feasible.
2018, 47(1): 117002.
Two research goals had been accomplished in this paper. One was to realize the calibration of strapdown inertial navigation devices in higher precision on the test equipment with lower accuracy outside. The other was to implement the synchronization of the inertial measurement frame in the process of calibration, and to improve its dynamic navigation accuracy. Accordingly, through deeply analysis of the space relative position between the two inertial measurement frames, the orthogonalization of inertial measuring frame was realized, and its misalignment model was established. Thereby, the paper designed the systemic calibration filter, which was based on the crossing angle and the misalignment angle, and raised the systemic calibration scheme, in this paper formulated the disturbance resistance measures of systemic calibration and a test was carried out. The test results showed that this calibration method can systematically calibrate all parameters of a strapdown navigation system and improve its dynamic navigation accuracy more than three times.
2018, 47(1): 117003.
doi: 10.3788/IRLA201847.0117003
Based on the double light-path experiment device measuring for diffraction efficiency of diffractive optical elements(DOEs), a correcting formula of diffraction efficiency was introduced to ensure the measurement accuracy of diffraction efficiency when light of secondary order diffraction was received by the detector after passing through the pinhole aperture. The diffraction efficiency of the designed hybrid refractive-diffractive optical system was measured at three laser wavelengths over the visible waveband for the incident angle upon microstructure surface was 12. The measurement results were simulated and analyzed. Due to some manufacturing errors and blocking effect, the measured diffraction efficiency was smaller than the theoretical. Based on the fitted curve of measurement results, the deviation of the polychromatic integral diffraction efficiency from the theoretical value was 12.84% over the 473-632.8 nm waveband.
2018, 47(1): 117004.
doi: 10.3788/IRLA201847.0117004
In order to solve the online calibration problem of the angle measuring system in practical application, an online self-calibration system of circular grating angle sensor was designed. Based on the principle of round closure and Fourier series, the relationship between the measured value and the error of single reading head was established, and the single reading head self-calibration was realized. The self-calibration system consisted of a reading head, a glass circle grating, a single-axis turntable and a multi-channel acquisition control system. The experimental result shows that the accuracy of the single reading head of the self-calibration system is 5.90, which is close to the accuracy of the harmonic compensation method with external reference standard, the measuring repeatability is less than 0.76. Self-calibrated measurement system could realize the online calibration of circular grating angle measuring system, which meets the requirement of precision and reliability in precision measurement field.
2018, 47(1): 117005.
doi: 10.3788/IRLA201847.0117005
A digital Moir phase-shifting interferometry with partial compensation lens was expounded to test the figure error of aspheric surfaces with high accuracy measurement. The real interferometer and the ideal interferometer model were established to obtain the real and ideal wavefront at the image plane of the interferometer. Then the image wavefront in the real interferometer related to the surface figure error of the aspheric surface under test was obtained by using the digital Moir phase-shifting technique. The error analysis of this measuring system was presented, and the reverse optimization procedure was applied to eliminate retrace error for the large figure error and reconstruct the test aspheric surface large figure error. Experimental results show that, compared to the profilometer, for the small figure error, the accuracy of the aspheric surface figure error measurement with the one-half method can achieve less than /20, both PV error and RMS error. For the large figure error, the reverse optimization method need to be used to obtain the accuracy of aspheric surface errors measurement of less than /5, both PV error and RMS error. Partial compensating digital Moir phase shifting interferometry for the test aspheric surface error based on reverse optimization procedure can effectively correct the retrace error, and reconstruct the large figure error of aspheric surfaces with high-accuracy.
2018, 47(1): 117006.
doi: 10.3788/IRLA201847.0117006
In order to solve the problem for the non-contact and high precision nondestructive testing of steel-plumbum bonding structures used for radiation inhibition in nuclear industry, the laser ultrasonic testing method was studied. The model of the steel-plumbum bonding structure was established. The propagation of laser ultrasonic and the wave reflection and attenuation induced by the debonding defect were analyzed. The narrowband laser ultrasonic signals were measured at the good bonding and debonding region, and the variation of the amplitude of the interface reflected signal induced by the debonding defect was observed. For the characterization of the debonding defects, the relation of the reflection coefficient with the wave frequency and measuring position was analyzed. The detection and imaging of the specimen with simulated debonding defects were realized by the laser ultrasonic C-scan method. The research results show that the imaging testing of debonding defects in the two-layer steel-plumbum bonding structure can be realized using the laser ultrasonic method, it has application prospect in the nuclear industry for the testing of radiation protection structures.
2018, 47(1): 122001.
doi: 10.3788/IRLA201847.0122001
A theoretical model was established to describe the influence of the angle of arrival (AOA) fluctuations on the bit error rate (BER) performance of ground-to-satellite laser communication under the Kolmogorov turbulence. A closed form expression of BER of ground-to-satellite laser communication system was then derived based on this model. Then, considering the combined effect of scintillation, beam wander and AOA fluctuations, the probability density function of the received intensity and closed form expressions of BER for an uplink were derived. Coherent detection of circle polarization shift keying modulation was employed, which was suitable for ground-to-satellite laser communication. For an uplink, the BER performance was analyzed and compared to the conditions without taking AOA fluctuations into account under the weak, medium and strong turbulence. Variations in BER as a function of AOA fluctuations were also analyzed. Finally, the influence of intensity scintillation, beam wander and AOA fluctuations on system performance was analyzed based on laser transmission power restrictions. The results show that in addition to the intensity scintillation and beam wander, AOA fluctuations is also a non-negligible factor in the study of communication performance.
2018, 47(1): 122002.
doi: 10.3788/IRLA201847.0122002
In order to develop a miniature fiber-optic temperature sensor with simple structure, low cost and mass production, the principle of optical coating interference-based temperature sensor was analyzed. The coating formula of temperature sensing probe was designed by TFCalc formula designing software using ZrO2 and Al2O3 materials. The thin film was deposited on the tip of multimode fiber by using electron-beam evaporation in Nanguang ZZS1100-8/G box type vacuum coating machine. The measurement system of coating interference-based temperature sensor was interrogated. The experimental result shows that the wavelength shift of the fiber-optic temperature sensor is linear in the range of 200-600℃, and the correlation coefficient was calculated to be 99.7%, the sensitivity of temperature is 8.3710-6/℃. The temperature sensor based on Fabry-Perot interference is suitable for mass production with stable performance, accurate point measurement, narrow installation position or higher application requirements for integrated sensor.
2018, 47(1): 121001.
doi: 10.3788/IRLA201847.0121001
The optical shutter glasses were fabricated for selecting suitable nonlinear optical materials with large nonlinear refractive index,ultrafast nonlinear response,and small absorption by adding heavy metal ionization to the tellurite glasses.The optical Kerr signals were investigated using the femtosecond optical Kerr shutter technology.It was shown that the Kerr signal of the glass was symmetrical,the full width at half maximum (FWHM) of the optical gating time for both materials were measured to be about 225 fs,the third order nonlinear susceptibility is~0.810-20 m2/V2,and the optical transmission achieves 70%-80%.This result indicates that glasses studied in this work are very good candidates for the development of Kerr optical shutter applications in the femto and picosecond regimes.
2018, 47(1): 121002.
doi: 10.3788/IRLA201847.0121002
The coupling mechanism of bright and dark modes in metamaterials have got enormous attention after the vivid mimicking of electromagnetically induced transparency(EIT) with plasmonic metamaterials. The research progress based on the coupling effects of bright and dark modes over the past few years was reviewed, including the EIT by planar metamaterials, the EIT effect with stereo metamaterials, electromagnetically induced absorption(EIA) from vertically coupling of bright and dark modes and asymmetric excitation of surface wave. The inner mode-coupling mechanism in each unit cell which consisted of the metamaterial determined the far-field and near-field responses. These different coupling mechanisms had important promising value in the designing of functional devices, like optical switch, slow-light devices, sensitive optical sensor and on-chip optical system.
2018, 47(1): 123001.
doi: 10.3788/IRLA201847.0123001
In order to solve the problem of complex and time-consumption of reference signal zero crossings in the traditional Brault sampling method, a method based on Fourier interpolation technique was proposed to find the zero-crossing. Compared with other interpolation methods, the results showed that this method could ensure the accuracy of zero-crossing information and simplify the complexity of data processing. The linear fitting coefficient of zero-crossing information obtained was greater than 0.999. In the range of 2 100-2 200 cm-1, when the error of reference laser signal was small, the instrumental SNR obtained by the Fourier interpolation method was 1.03 times that obtained by the cubic spline interpolation method, and the result obtained by the linear interpolation method was consistent with Fourier interpolation method. When the error of reference laser signal was relatively large, the instrumental SNR obtained by the Fourier interpolation method was 1.05 times of the SNR obtained by the linear interpolation method.
2018, 47(1): 123002.
doi: 10.3788/IRLA201847.0123002
The accuracy of polarized detection for field-portable spectropolarimeter directly influences the precision of polarization spectrum of ground object, and thus affects the interpretation accuracy of the polarized characteristic of targets. A polarization measurement group unit was designed for grating spectrometer. Then the two kinds of grating spectrometers were transformed into spectropolarimeters. Based on variable polarization light source, the performances of the two spectropolarimeters were verified. The polarization sensitivity of the two spectropolarimeters was analyzed at first. The different degree of polarization spectra output from variable polarization light source was measured using the two spectropolarimeters. The results show that both of them have polarization sensitivity and the degree of polarization of output light measured by the two spectropolarimeters are consistent with the theoretical output of the variable polarization light source. The error between theoretical output and measured results are within 2% when the wavelength range is from 460 nm to 920 nm. It verifies that the feasibility of two spectropolarimeter polarization measurement group unit which could meet the experiment requirements.
2018, 47(1): 126001.
doi: 10.3788/IRLA201847.0126001
During the complex flight process of UAV, the affections such as atmospheric disturbances, optical equipment imaging and other factors, result in low resolution of the acquainted infrared images. In addition, the resolution of each frame infrared image may be different, and extraction of a salient map using the traditional fixed-level decomposition of the pyramid model will be different in the same area, which causes extraction of interested region of UAV difficult, and cannot use visual technology to achieve UAV target positioning and autonomous navigation. In this paper, an improved the interested regional extraction for infrared image and SR reconstruction algorithm based on Itti model was proposed. Firstly, the multi-feature was introduced to construct hierarchical model of the pyramid dynamic of the infrared image sequence. Secondly, the dynamic extraction of the interested region for multi-frame infrared images of different resolution was used to overcome the shortcomings of the traditional Itti algorithm. Finally, the new infrared image reconstruction algorithm based on Fletcher-Reeves majorization-minimization was proposed for spatial SR reconstruction of the interested region to improve the spatial resolution of the interested regional target. Experimental results prove the validity and accuracy of the proposed algorithm.
2018, 47(1): 126003.
doi: 10.3788/IRLA201847.0126003
The object detection method of multi-view Single Shot multibox Detector(SSD) based on deep learning was proposed. Firstly, the model and the working principle of classical SSD were expounded. According to the concept of convolution receptive field and the mapping relationship between the feature map and the original image, the sizes of covolution receptive field in different levels and the scales of the default boxes mapped to the original image were analyzed to find the reason why the classical SSD was not good at small object detection. Based on this, the multi-view SSD model was put forward, and the model architecture and its working principle were deeply expounded. Then, through the test in a dataset of 106 images for small object detection, the detection performance of multi-view SSD and classical SSD were evaluated and compared in object retrieval ability and object detection precision. Experimental results show that with the confidence threshold of 0.4, the multi-view SSD is 0.729 in Average F-measure(AF) and 0.644 in mean Average Precision(mAP), and has respectively raised 0.169 and 0.131 compared to the classical SSD in the two evaluation indexes, thus verifying the effectiveness of the proposed method.
