2011 Vol. 32, No. 6
Incorporating with ideal magnification element, the universal model for four kinds of liquid optical compensation were analyzed and derived. The mathematical models of reflection and transmission in liquid for optical compensation were acquired. The ray passed through the liquid surface twice due to the mirror in the liquid, which contributed to the designed optical configuration matching with the plane plate or Schimitt prism of ideal magnification. The horizontal and gradient directional accuracy achieved 0.01.The liquid compensation matching table was given, which can be used for other liquid compensation comfigurations. Finally,the compensation error of the designed configuration was analyzed and verified by experiments, the horizontal compensation curve, yawing compensation curve and image rotation compensation curve were given.
With the developments of electronics, laser and signal processing, electro-optical systems for underwater targets detection is becoming an extensively investigated subject. The technical scheme, status, typical systems for underwater target detection with electro-optical technology were summarized，especially for range-gated imaging, laser line scanning and streak tube imaging technologies. The recent developments and trends in underwater targets detection were introduced. It is proved that the electro-optical detection technology has great potential in underwater target detection.
Gimbal is one of the key elements of the electro-optic radar stabilized platform. The 3D model of the gimbal in electo-optic radar stabilized platform was built by Pro-E, and the finite element model was built by Ansys after the simplification of the 3D model. The dynamic characteristics of the gimbal were analyzed through finite element theory and Ansys. Different mesh generations of model were compared. The 8-order modal natural frequencies and vibration modes of the gimbals with different materials were obtained, and the harmonic response was analyzed. Results show that the gimbal doesn-t resonate at 0~50Hz, 2 000Hz~8 000Hz， which meets the design requirments.
Reliability of stabilized electro-optical sight system is important for the helicopter airborne weapon system. The concepts of military electro-optical system are presented, as well as the function and components of the helicopter airborne stabilized sight system. The reliability diagram and mathematical models of shipboard helicopter stabilized sight system are given. The factors influencing the systematical reliability and the failure modes are researched. The reliabilities of stabilized sight system structure, optics and electrics are discussed. A prediction method of reliability for stabilized sight system by computer simulation is proposed. Failure of a shipboard helicopter stabilized sight system occurred for two times during the 96 hours reliability test, which met the reliability requirement that the mean time between failures (MTBF) should be less than 32 hours. Prediction and analysis on the reliability of stabilized sight turret combined with corresponding provisions can improve the design quality and shorten the development cycle.
A miniaturization design of optical system was accomplished based on the technical specifications of optical correlators. Both the Fourier-transform lens and the collimating and beam expanding system adopted the telephoto structure, which could maintain the long focal length and decrease the optical tube length. The optical path was folded with right-angle reflection prism to make the system layout more compact. The structure of the optical system was optimized with ZEMAX. The total length of the miniature optical correlator was less than 150 mm, and the system width was less than 90 mm. This improved optical system utilized double optical path processing structure, and achieved real-time recognition. The experimental results demonstrate that the recognition system has a good correlative performance, as well as the features of low noise, high detection precision.
The field angle of f-theta lens used in laser marking system is generally less than 60. By adopting a telescope structure and using a method of visual magnification, a super wide lens with the field angle of 90was obtained in the optical system. The method is simple, reliable, and easy to achieve. Based on the analysis of primary aberrations, the parameters of initial structure were determined, and the ftheta lens with a large working area of 285 mm in diameter was obtained by optimizing the initial structure with ZEMAX. The linear distortion error of the lens is less than 1%, the energy concentration rate is 80% in the circle with a radius of 698 m and the focusing performance is diffraction-limited.
The technology of beam splitting for 532nm light is widely used in optoelectronic areas such as laser interferomertry for measuring velocities. This paper designed a beam splitter system, through which the 532nm input beam was splitted into identical beams (1 splitted into 2, 1 splitted into 3 and 1 splitted into 4). This system collimated the beam from the incident fiber by using an aspheric lens, and splitted the collimated beam into multiple beams by one or several beam splitter plates. Then, all the beams were coupled in the receiving fiber through lenses which were the same as the collimating lenses.The design of the aspheric lens, structure of beam splitter, assembly and test results were given, and the factors influencing the splitting efficiency were analyzed. Results show that the beam splitter system achieves a high output efficiency of about 77%, which means the additional loss is about 1dB.
The birefringent filter on space solar telescope is sensitive to the change of temperature，however, the precise temperature control of the traditional birefringent filter is difficult to achieve. An active compensation method which added a liquid crystal variable retarder (LCVR) in each single-stage of birefringent filter and introduced an additional retarder to compensate the delay caused by temperature fluctuation was put forward. This allowed the wavelength of the birefringent filter transmission peak to remain stable. The Lyot filter was studied, and the theoretical calculations and simulation proved the feasibility of this method. By applying the method to the spatial birefringent filter, the good performance of the filter could be remained without any temperature control system at the temperature provided by the satellite manufacturer, and the accurate temperature control of spatial birefringent filter was achieved. Since the traditional two-stage temperature control device was abandoned, the volume and weight of the filter were effectively reduced which met the requirements of space payload.
A customized microscope objective for near ultraviolet (UV)-visible spectrum was designed, which was used to observe the image of nuclear fusion irradiated by laser. The operation wavelength was 300 nm~500 nm, the magnification was 10 and the numerical aperture(NA) was 0.3. The transmissionmode structure was established in the microscope objective, by theoretical calculation with PW method and optimization with CODE-V, the apochromatism was achieved. Thus, the problems such as difficult aberration correction and low efficiency of optical system, resulted from the few kinds of UV optical materials and low refractive index, could be solved.
The reversibility of the diffraction optical path of grating and double-grating imaging systems was studied with Fresnel diffraction theory. Firstly, the complex amplitude distribution of the diffraction of single grating was analyzed. According to the phase relation of the complex amplitude distribution, the reversibility of optical path was studied. Then the reversibility of the double-grating diffraction imaging effect was analyzed by using the conclusion for the single optical diffraction grating. It-s found that the diffraction optical path of single grating and double-grating imaging systems has partial reversibility. Based on the partial reversibility of diffraction optical path, the nature of double-grating imaging effect was explained, the spectral combination characteristic was considered to be the reverse effect of the spectral dispersion characteristic, and the image processing was realized.
Numerical simulation experiments on optical field distribution of one-dimensional metallic gratings with dielectric substances and sub-wavelength slits which are different in structure and parameter under transverse electric (TE) polarization excitation were carried out by using the method of finite-difference time domain. Physical mechanism was analyzed based on the theory of charge distribution on metal surface and the surface wave theory. The analysis showed that cylindrical surface waves were generated in metal slits and such kind of surface waves could break the diffraction limit to cause extraordinary transmission. The dynamic response of the dielectric cladding thickness to the transmission peak position and the dynamic relationship between the transmissivity and the wavelength when varying the thickness of metallic thin film were found by analyzing the surface charge distribution and excitation mechanism of Ag, thus the cylindrical surface wave was confirmed as one of the important factors that may cause extraordinary transmission. The theoretical analysis is consistent with the si-mulation results, which provides a good theoretical basis for an further study on the mechanism of extraordinary transmission and the selection of structural parameters under TE polarization excitation.
A new photoelectric trigger based on rotary mirror was designed. The rotary mirror was composed of a motor and a reflection mirror driven by the motor. The fan-shaped light curtain was formed when the rotary mirror was irradiated by laser. When the light curtain passed throught the object, the photoelectric receiver received the laser reflected twice by the reflecting mirror and produced the trigger signal simultaneously. Then the trigger signal was sampled and digitalized by the collection module. Finally, the signal was transmitted to the controlled device to realize trigger.
A wide-angle digital mini-projection lens applied to 0.5digital light processing(DLP) projectors was designed with ZEMAX. The structure is composed of 8 lenses. It is characterized by simlicity,compactness,low cost and easy processing.The effective focal lenth of the lens is 8.25 mm, F number is 2.2, field of view (FOV) is 80.5, the maximum diameter is less than 24 mm,the optical total track is 40mm and the back working distance is 24mm. Its modulated transfer function (MTF) in all fields is higher than 0.45 at 66 lp/mm. The absolute value of the full FOV distortion is less than 0.7%. The lateral chromatic aberration is less than 0.5 pixel .The image quality of the lens is very good.
To provide a power supply for a test instrument operating at high temperature environment, a scheme of using a photodiode as the switch of the power supply was developed, which had the advantages of short response time, high sensitivity and so on. The photodiode received the infrared ray emitted by the high-temperature emitter, the power was switched on after optical-electric conversion, and the desired results were achieved. This paper introduced the concept of the optically controlled switch and its implementation. The simplicity and feasibility of the design was verified by experiment results, and it is suitable for some operations not accessible by human being.
To study the characteristics of side-coupled photonic crystal filter, the coupled mode theory (CMT) and the transfer matrix method (TMM) were used to analyze the dependence of the filter-s reflection spectrum on the period of resonator, the value Q, and the number of cavities. The simulation result showed that the reflection spectrum was symmetrical when the phase shift was n/2, the bandwidth of reflection spectrum peak decreased as Q increased, and the bandwidth of reflection spectrum peak increased and the side lobe occurred at the same time as N increased. To overcome the increasing side lobe due to the increase of bandwidth, the chirp and cascade technology similar to one-dimensional photonic crystal filter was used to achieve sidelobe suppression. This work can be used for the design of the photonic crystal filter.
To highlight the moving targets in fusion images, an imaging fusion algorithm based on target recognition is presented. Firstly, moving targets are detected from dynamic infrared images. At the same time, infrared and low-light-level (LLL) images are fused with the contrast pyramid method. Finally, the profile images of moving targets extracted from infrared image sequences are fused into the fusion image sequences. The experimental results show that the fused images obtained by the algorithm provides rich information similar to conventional fusion methods and enhances target signatures.
Up-conversion board fitted on the lens could enhance the efficiency of CCD acquisition for low-frequency narrow-pulse laser spot because it is capable of changing infrared light into visible light. The up-conversion board made by traditional craft causes internal diffuse reflection and partial saturation effect which leads to the distortion of laser spot shape and intensity distribution. We put forward a new craft called lattice up-conversion board technique, and designed an experiment to compare the photographs acquired by the two crafts. The experimental results show that the lattice up-conversion board has better acquisition on low-frequency narrow- pulse laser spot. In order to evaluate the photographs of the laser spot acquired by lattice up-conversion board, a corresponding model is established.
Random sample consensus (RANSAC) algorithm is one of the most widely used approaches in the field of computer multi-view vision. To improve the efficiency of initial matching with high noise, a new filter algorithm is proposed based on near point consistency. The new method improves the inliers ratio of initial matching set and reduces the iteration times when using RANSAC to find parameters. The experiment on wide-based pictures demonstrates that the new algorithm achieves a significant increase in speed and almost the same result compared with the classical RANSAC algorithm.
In no reference peak signal to noise ratio (PSNR) image quality assessment based on noisy images, in order to get optimal threshold parameters, it is proposed that taking experiment values as a sample, a ［2 7 2］ back-propagation (BP) neural network model is established with the mean square error (MSE) threshold1 of image block and the noise detection threshold2 as the input factors, and the Person and Spearman correlation coefficients as the output factors. The model realizes the prediction of relevant parameters by its generalization capability and offers a theoretical foundation for parameters selection. Experiments indicate that the model is reliable. The prediction results show little difference from the experimental data. The trained BP neural network can precisely predict the relevant parameters. After optimizing, threshold1=101 and threshold2=4 are selected, Pearson Correlation Coefficient and Spearman Rank Order Correlation Coefficient reaches -0.895 0 and -0.913 6 respectively. The assessment result improves a lot, and much time is saved.
Hologram stitching technology was used in phase-shifting interferometry to improve the quality of reconstructed image. By using the principle of correlation, the sub-interferograms captured by CCD were stitched into an integrated hologram. And the stitched hologram was reconstructed by standard four-step phase shifting interferometry algorithm to restore the object light. For the sake of comparison, the same reconstruction operation was conducted on the original sub-interferograms without stitching. Computer simulation experiments verified that the image quality could be improved obviously by this stitching technology. In addition, holograms were processed by zero padding and stitching, and the results showed that the zero padding could only improve the detail displaying ability, while the stitching technology improving both the resolution of reconstructed image and field of view.
Monochromator is a spectroscopic instrument, which decomposes a polychromatic light into monochromatic light with different wavelengths using spectral dispersive element. This paper presents a new calibration method for three-grating monochromator. For the monochromator adopting sinusoidal scanning, its accuracy depends on the number of calibration points. This paper uses sine curve fitting method according to the design of three-grating scanning monochromator. Since grating equation is in compliance with the law of sine, a small number of calibration points could meet the requirements of fitting accuracy. Appropriate parameters to be determined are selected, which significantly reduces the computational complexity in the process of fitting. The analysis results of simulation software show that the wavelength fitting error is less than 0.5 nm.
Due to different situations on the ground and in agravic space, special support structure is demanded to unload mirror gravity when testing large-aperture space mirrors on the ground. Meanwhile, deformation induced by clamping forces must be strictly controlled to meet the requirements of high-precision figure testing. This paper presents test experiments performed on a space aspheric mirror made of SiC with 750 mm aperture. Testing results are compared with the finite element analysis results to investigate the influence of the support structure on mirror surface figure. To analyze the causes of incapability of high-precision surface figure testing, the methods of strip suspension and central supporting are discussed. An improved method of backboard supporting is proposed, it reduces the supporting deformation and the repeatability of surface figure at different angles reaches nanometer level. It is proved to be able to achieve higher precision testing, which is a fundamental solution for improving machining quality and efficiency.
In order to meet the requirements for high-precision test of optical components and systems, the paper researched the assorted alignment method based on the design of a new type of portable interferometer. This new type of interferometer with a theoretical precision of /10(PV, =630 nm) is developed from the improved Tyman-Green interference optical structure, it has several advantages such as off-axis reference mirror, small size, low cost and high accuracy. According to the structure of the portable Tyman-Green interferometer, the alignment method for the overall system with two vertical optical axes as the reference was studied. The interferometer was aligned by using this method. Then the measurement experiment and comparison experiment were carried out. The experiment which focuses on testing the standard spherical mirror with the peak value (PV) of /10 shows that the interferometer has a measurement precision of 0.09 (PV, =630 nm); and the comparison experiment shows that when measuring a regular standard spherical mirror in the same testing environment, the precision of the interferometer is 0.053 (root mean square, =630 nm), while the one of Zygo interferometer is 0.051 (RMS, =632.8 nm). The results indicate that the measurement accuracy of potable Tyman-Green interferometer aligned by the new alignment method is almost equal to the one of Zygo interferometer and closed to the theoretical limit, the new alignment method satisfies the demands of the portable Tyman-Green interferometer.
The standard white field instrument traceable to the national spectral radiometric, photometric and colorimetric primary standard was set up forcharacterizing the photometric and colorimetric parameters of displays. The instrument was calibrated and its spectrum, stability and photometric-colorimetric parameters were given. Using the instrument to study the viewing angle of prevail liquid crystal displays, the influence of the variation of the light-emitting surface during the measurement process was considered, which was usually ignored. The results indicate a difference of more than 8% for the absolute-luminance-based viewing-angle threshold method, which should be considered and avoided in the measurement.
In order to measure high reflectance and high transmittance of optic components and coat films, a precise measurement facility was set up which was based on single reflection measurement using laser power-stabilized technique, double optical path measurement technique and precise detection technique. High reflectance and high transmittance were measured at 632.8 nm and 1 064 nm wavelengths on the facility. Experiment result and uncertainty analysis showed that the measurement uncertainty of high reflectance and high transmittance was less than 0.008% at 632.8 nm and was less than 0.015% at 1 064 nm.
Position deviation measurement between projectile explosion and target is important for accuracy test of naval gun system. By recording the arrival time and output amplitude of acoustic-optic signal during firecracker explosion, the concept of detecting the explosion signal of small equivalent gun powder based on acoustic-optic method was verified. The arrival time difference of acoustic wave and light wave was 14-7 ms at an explosion distance of 5 m. The receiving distance of the sensor was 8 m~20 m at different angles. The arrival time of the explosion acoustic-optic signal and the receiving distance of the sensor were tested. The results validated the feasibility of making the measurement using acoustic-optic signal. Combined with the distance error data between projectile and target, the statistical analysis of the deviation data could be done.
Aiming at the problems of initial phase estimate, transmission factor and convergence judgment, a phase retrieval experiment based on iterative method was done by using a cylindrical lens as the testing object. The experiment results showed that inputting an appropriate initial estimate phase was important to accelerate the convergence rate of algorithm, avoid the local convergence and insure the validity of results. In order to eliminate the error caused by the instability of laser and the uniformity of detector, transmission factor which was calculated by performing the operation of division between the two measured planes- intensities was used in the spectrum propagation formula.
This paper proposed the concept of the remained divergence angle of Scotchlite retroreflector, and designed the testing system. The laser beam was transmitted to the Scotchlite retroreflector, the reflected laser beam was imaged on the sulfuric acid paper（equivalent to receiving screen）, and the image data of the laser spots at different distances were captured by using a camera. In order to calculate the remained divergence angle, a program for corresponding image data was written. Experiment results showed that the remained divergence angle of Scotchlite retroreflector used in the test was 0.447 8.
TiAlON-based materials applied in solar energy were studied by spectroscopic ellipsometry. Different dispersion formulae such as Cauchy, Lorentz and Tauc-Lorentz models were applied to fit the experimental data of insulation TiAlON film and its optical constants were obtained. The application of the different dispersion models and film structures were compared in various spectral ranges. It is demonstrated that the Tauc-Lorentz model is more suitable for fitting ultraviolet to near-infrared spectroscopy. The results suggest that spectroscopic ellipsometry is a reliable method for characterizing the TiAlONbased material system, and can be used for further study on the optical properties of multi-layer film stacks.
Fluid dynamics simulation of fluid jet polishing material removal mechanism was studied base on the Fluent software, and the pressure, velocity and wall shear stress of the flow were analyzed. It indicates that the material removal rate is dependent on the distribution of surface shear stress, and the removal function presents W type. The influence of the entrance velocity, operation distance and abrasive concentration on the polishing result was analyzed by using orthogonal test, the result shows that the material removal rate increases with the increase of the incident velocity and abrasive concentration, it decreases as the operation distance increases, and the operation distance has a significant impact on the removal rate. This work can be used for choosing process parameters in process investigation.
To meet the requirements of infrared dual-band imaging system performance testing and evaluation applications, an off-axis three-mirror system operating at 3m ~ 5m and 8m ~ 12m band was designed for infrared dual-band scene simulator. The aberration characteristics of off-axis three-mirror system with aperture departing far from the primary mirror were analyzed based on the coaxial three-mirror imaging theory, the design methods of the optical structure and aberration balance of the off-axis three-mirror with large eye relief and large relative aperture were discussed. The focal length of the system is 255 mm with F# 3, the field of view is 6 4.5 , the eye relief is 750 mm, the image quality of the system approaches the diffraction limit with MTF0.65 for long-wave infrared band and MTF 0.4 for mid-wave infrared band at 10lp/mm spatial frequency. The system is characterized by large field of view, large eye relief, high resolution and compact structure.
Since traditional non-uniformity correction algorithm has slow convergence and inaccurate prediction, a multi-scale optical flow motion estimation based algorithm is developed. Random image noise between frames is filtered by time-domain low-pass filter, and the next frame is estimated by using the multiscale optical flow, then the non-uniformity correction is carried out. This algorithm is demonstrated in the thermal imager developed by us. Compared with the traditional non-uniformity correction algorithm, the convergence rate of this algorithm decreases form 60 frames to 25 frames; the precision of prediction is improved by 100%, and the corrected image variance is decreased from 76.539 to 32.482.
According to the design of three-in-one composite achromatic wave plate, an infrared composite achromatic /4 wave plate made of quartz was designed, which could be used in optical communication wave band. We further analyzed and tested the wave plate phase delay and composite angle which were the important factors influencing the achromatism scope, and put forward an optimum design scheme. Theoretical analysis and experimental result show that by adjusting the wave plate phase delay or composite angle, the maximum delay deviation for 1/4 composite achromatic wave plate achieves 5% in the wavelength range of 900 nm~1 800 nm with the central wavelength of 1 400 nm,which meets the achromatic requirements; in the optical communication wave band of 1 200 nm~1 600 nm, the maximum delay deviation achieves only 3.2%.
Aiming at the athermal design requirements of infrared imaging systems for defense application such as simple structure, small size and light weight, this paper proposed an infrared optical system (8 m~12 m) with passive optical athermalization design. The parameters of the optical system was F=1，f=60 mm and 2=11.4.The analysis of results showed that the modulation transfer function (MTF) approached to the diffraction limit, the MTF was up to 0.7 in the central field of view(FOV) and better than 0.6 in the marginal FOV at the spatial frequency of 20 lp/mm in the temperature range of -40℃to +60℃. The results meet the athermalization requirements of the system.
To locate the enemy laser source in omni-directional laser warning based on diffuse reflection detection based on geometrical optics principles and machine vision concepts, this paper introduced 8 unknown parameters including R, , , d, , , , to describe the spatial position relationships among enemy laser source, the laser spot radiated on one flat plane and our omni-directional laser warning fisheye lens in typical battlefield environment, deduced the analytic expression of the laser spot contour on image surface, and acquired the 8 parameters from the spot coordinates data on image surface. Thus the spatial position relationships were obtained, the enemy laser source was located, and laser warning was achieved. The experiment result verified the feasibility of the omni-directional laser warning devices.
To improve dynamic range in imaging laser detection system (ILDS), a method using image processing to extend the system dynamic range is proposed based on the existing hardware of wide-angle telecentric fisheye lens and complementary metal oxide semiconductor (CMOS) camera device. Frame subtraction technique is often used in ILDS to recognize and locate the laser spot by filtering out background interference and noise. The paper proposes that different methods should be used to expand the dynamic range corresponding to the received laser energy. When the laser energy is low, the laser signal that may be submerged in noise can not be accurately interpreted and precisely located. The technique of fuzzy weighted averaging filtering is used to remove noise and enhance detection sensitivity of the system, namely extension of the detection lower limit. When the incident laser is strong, the imaging surface may be interfered by stray light due to the reflection produced by the fisheye optical system. Spot matching pattern recognition method is presented to remove stray light and enhance the recognition upper limit. The experimental results show that these methods improve the system-s dynamic range from 70 dB to 89 dB.
Based on the pulsed Gaussian laser as light source and one-dimensional ZnO materials with 500 nm ~ 1000 nm diameter and 10 m length as target, the finite element analysis software ANSYS was used to establish the thermodynamic simulation model of laser cutting ZnO nanowires. The birth-death element technology was adopted to process the unit which temperature was above the melting point. The temperature distribution field and the cutting morphology were obtained, as the laser working parameters and ZnO nanowire diameters changed. The influence of the nanowire diameter and the focusing spot displacement relative to the nanowires on laser cutting was discussed. The results show that the larger the nanowire diameter is, the smaller the tolerance of the laser defocus amount is; when the defocus amount is zero or the negative defocus is small, a better cutting morphology is obtained.
Scattering characteristics of several common objects in battlefield were studied. Massive data of six types of object samples were obtained by experiments, and two bidirectional reflectance distribution function (BRDF) models were established by using the data. The unknown parameters in BRDF models were gained by genetic algorithm. The SSE and R-square indices were introduced to evaluate the adaptability of models. Results show that the five parameters semi-empirical model has better adaptability, which is fitted for the experiment data of the six-type plane samples.
Damage precursors produced during grinding and polishing processes are the widely admitted damage initiators. Two models are built to examine the correlation between precursors and laser damage initiation. In the nano-absorber model, temperature field is simulated to describe the evolution of temperature at the hottest point within the pulse time. In the fracture model, electron density is calculated when the fracture surface is excited by laser shot. The results show that laser damage initiation and growth are strongly correlated with precursors.
To improve the radiation immunity of the charge coupled device (CCD) in satellite optical communication system, the ionization damage and displacement damage effects imposed on CCD in space radiation environment were analyzed. Through theoretical analysis and numerical calculation, the influences of radiation source, buried channel and bias on the charge transfer efficiency (CTE) of CCD were researched. The results show that the space radiation mainly affects the performance of CCD with the bulk dark current density and CTE. The CCD used in satellite optical communication system should be selected as the P channel CCD and set as under unbiased state when the communication system is not working.
High data-rate space laser communication system is capable of providing gigabit data throughput between space-based platforms and is used in aerospace information networks as high speed network link between neighbouring nodes. Tracking and pointing problem due to high-speed movement of space nodes and collaboration problem with network payload are two major challenges. Based on the analysis of system components of high data-rate space laser communication system, this paper proposed a two communication payloads architecture which used the high-rate space laser communication system as the primary communication payload of network nodes in aerospace information networks, designed the collaborative work mechanism between the high data-rate space laser communication system and the network payload, as well as the communication protocol model in aerospace information networks. According to this protocol model, we developed the hardware and software prototypes and carried out some tests. The test result shows that the proposed collaborative work mechanism and protocol model are applicable to aerospace information networks.
A compact 12-channel parallel optical transceiver with data rate up to 6.25 Gb/s per channel for very short reach (VSR) interconnection based on system-inpackage (SiP) techno-logy was implemented and tested. An 850nm vertical cavity surface emitting laser (VCSEL) array with a laser driver die was used as the light source of the transmitter, and a photodiode (PD) array with a trans-impedance amplifier/limiting amplifier (TIA/LA) die was adopted as the detector of the receiver. Passive alignment was used to reduce cost. The electrical design for high frequency and high density package is critical, due to the issues related to power inte-grity (PI) and signal integrity (SI). To meet the needs for small size package, passive embedded substrate was used to suppress the simultaneous switching noise (SSN) and improve PI. To improve the impedance discontinuity, based on electromagnetic and transmission line theories, SI design was made to reduce the crosstalk and maximize the channel bandwidth. The back-to-back eye diagram measurement results showed that the bit rate of each channel reached 6.25 Gbps.
In order to achieve pressure measurement by single fiber Bragg grating (FBG), a novel FBG high-pressure sensor was designed, which was insensitive to temperature. The pre-ssure and temperature responses of the sensor were researched. First, the configuration and package of the sensor were presented. Then the temperature-insensitive principle was analyzed theoretically. The relationship between the central wavelength of FBG and the pressure was deduced, and the analytical expression of pressure sensitivity is given. Finally, the temperature response and pressure response of the sensor were analyzed by experiment. Experimental results show that the temperature compensation is achieved within the temperature range of 21℃ to 260.8℃, the average wavelength shift is 0.75pm/℃, and the pressure response sensitivity of -0.054 8 nm/MPa is obtained in 0~44 MPa, which is 18.27 times higher than that of the bare FBG. The pressure response of FBG sensor has good linearity and repeatability, the experimental results agree with the theoretical one, which indicates that the sensor can achieve precise measurement of pressure by single FBG.
In order to reduce the speckle interference in the multimode fiber emission fields, we investigated whether the coupling of different diffraction grades derived from Bragg acoustooptic diffractive effect to multimode fiber could reduce the speckle field contrast. Through the analysis on the speckle field contrast subsequent to the changing of the sound field frequency, we demonstrated that the anisotropic crystal TeO2 could regulate the contrast of speckle field and improve Gaussian distribution. It is probable that Bragg diffractive effect could reduce the speckle field interference.
To overcome the shortcomings of traditional communication systems which were easily disturbed and weakly encrypted，a laser communication system which could transfer audio and data simultaneously was designed. The audio was compressed to 4 800 bit/s data rate without distortion by using the advanced multi-band excitation (AMBE) algorithm, then the coding data stream of audio and data drove the laser to emit. Audio and data were recovered after electro-optical conversion and decoding at the receiver. The communication experiment with the distance of 2.5km proves that the system features long distance, clear audio and stable data, it can be applied in air-to-air, air-to-ground, ground-to-air and ground -to-ground communications.