Shoufeng Tong

Modeling of Fine Tracking Sensor for Free Space Laser Communication Systems

The optical communication networks comprised of ground stations, aircraft, high altitude platforms, and satellites become an attainable goal, however, some challenges need to be overcome. One of challenges involves the difficulty of acquisition, tracking, and pointing (ATP) a concentrated beam of light arriving from another platform across the far reach of space. To meet the pointing accuracy requirement, the basic method of tracking between the terminals of optical communication systems includes the use of a beacon laser and tracking system with a quadrant detector sensor on each terminal. In some future optical communication networks, it is plausible to assume that tracking system and communication receivers will use the same sensor. In this paper, the architecture of the fine tracking assembly of the designing optical communication terminal (OCT) is described, and the fine tracking assembly sensor is modeled based on the correlation coefficient. The simulation and experiment results of the sensor show that the detecting accuracy satisfies the design demand for our developing OCT. Keywords-modeling; quadrant detector; fine tracking sensor; optical communication networks

Athermal design of LWIR hybrid refractive/diffractive optical system

Thermal properties of diffractive optical element and method of design athermal hybrid infrared optical system are introduced. Athermal LWIR hybrid infrared optical system for no cooled staring detector is designed. The system consists of three lenses, the effective focal length is 100mm，the relative aperture is 1:1,the wavelength spectrum is 8~11μm, the field view is 14° and the total optical length is just 140mm. The result shows that the modulation transformation function at 17lp/mm is greater than 0.6 between -40-60°C，which prove that the system can work correctly at a large temperature range.

Modeling and reality analysis of beaconless spatial acquisition for intersatellite laser communication system

Abstract. For an optical satellite link, the error sources that influence the pointing accuracy of the terminals include the attitude estimation error, ephemeris accuracy, and the boresight alignment error. It means an uncertainty cone (UC) exists for the spatial acquisition process. The acquisition process is a continuous adjustment for the visual axis of the two communication terminals, to enable them to detect the light signal from the other end, and finally realize the light closed loop. Beaconless acquisition algorithm and the corresponding acquisition process, modeling for spiral scan pattern and the simulation results of staring-scanning mode are presented. The UC scan range is 5 mrad, through the overlap with a spot divergence angle of 80u2009u2009μrad, the total acquisition time is 98 s.

Influence of optical dome for airborne laser communication beam far-field divergence

When the center of the dome inner and outer concentric spherical surfaces and the gimbal joint of the airborne laser communication antenna are not coincidence, the influence of asymmetry dome to communication beam far-field divergence angle for different transmitting angles is analyzed. The simulations shows that, at a maximum off-axis transmitting angle 54°, a K9 spherical dome with a 200mm diameter and 5mm thickness makes the communication beam far-field divergence angle expands to 5.27~6.46mrad from 126μrad. The divergence angle variation purely introduced by the dome manufacturing precision is very tiny, and can be ignored compared the variation introduced by the dome optical power. A lens with spherical surfaces is used to compensate the far-field divergence angle change, and after the compensation the far-field divergence angle of the beam on the whole range of transmitting angles is reduced to no more than 600μrad.

Design galvanometer position detection unit based on single detector compound axis tracking system

The fine tracking unit of composite axis of acquisition, pointing and tracking(APT) is a key component of space laser communication system. In order to prevent the principal axis in open-loop without proper input of control after started the tracking of auxiliary axis, which led to the target out of field. In a single detector composite shaft structure, we need to provide the accurate position of PZT volume feedback for the principle axis to control. This article has made an galvanometer position detective method of the single detector composite shaft structure. It provided the theory of circuit design and optimization plan. Researchers conducted a multiple sets of experiments. The experimental result shows that the galvanometer 1 per deflection Angle, the detection circuit can retrieve 13 mV voltage change. At the same time, compared with the traditional camera calibration, we put forward a new calibration method which using optical autocollimator that the maximum error control within 1 . Finally, the control formula is given and the error should be within 0.01mrad. So that the calibration precision of the detecting plate is improved.

Link Budget and Simulation of Double-Wavelength Full-Duplex Free-Space Laser Communication Based on Modulating Retro-reflector

Free-space optical communication (FSO) based on modulating retro-reflector (MRR) is beneficial for future wireless communication because of less power and weight. Double-wavelength full-duplex FSO system based on MRR is proposed. The link budget of distance and bit error rate (BER) are calculated for evaluating performance. Based on theoretical analysis, communication distance from 300 to 500 km can be achieved at received power from −30 to –40 dBm, and communication distance is estimated about 350 km when transmitted power is 37 dBm and BER is less than 10−9. A simulation model by Optisystem software is established for further study. The simulation results show that communication distance is estimated about 130 km with the same parameters. The simulation results are worse than theoretical analysis. The reason may be due to the all kinds of device noise and atmospheric effect in simulation model. In conclusion, the proposed system can be used in light-weight full-duplex laser communication in short distance. It may be one of the future development trends of FSO system.

Research on the intelligent control simulation target with IR imaging target for hardware-in-the-loop simulation test

The intelligent control of simulation target with infrared imaging target in the indoor and outdoor environment can effectively and quantitatively evaluated the parameters such as the minimum resolution temperature difference（MRTD）and spatial resolution of airborne forward looking infrared, infrared detection and tracking, infrared alarm, and etc. This paper focused on introducing the working principles of the intelligent control simulation target of Infrared imaging target, studying the thermal radiation characteristics of the infrared target surface material, analyzing the influences of the infrared radiation energy distribution, and developing the intelligent control simulation target with IR imaging target for hardware-in-the-loop simulation test. The intelligent control simulation target which area was 5 ㎡ and concluded 44 infrared targets including two kinds of infrared targets ,0.25ｍ×0.25ｍ, and 0.25m×0.5m, achieved 1℃～10℃ temperature simulation of target and the background, and temperature control precision better than 0.5℃. Field test requirements were achieved by actual test.

Development of the infrared target simulation system

In order to provide a set of field test equipment for the infrared system of modern weapon equipments and other optics instruments, a set of large-scale resistance-type infrared target system was designed. First, the large-scale infrared target was designed in modular construction. It was decomposed into several independent and controllable units. Then the working principle of the system was introduced. Three modes of thermal exchange (conduction, convection and radiation) and the computing methods for each mode were given under thermal equilibrium conditions through modeling and simulating. Periphery electro-circuit and control software were carried out as well. Finally, the performance of the system was tested. Meanwhile novel ways of temperature compensation to improve the uniformity of the surface temperature of the target was introduced. The experimental results show that the infrared target could meet test requirements for infrared imaging weaponry which wavelengths from 8 μm to 14 μm. The temperature control precision can reach 0.5ms. In conclusion, the infrared target system can satisfy requirements of reliability, high precision, as well as strong anti-jamming and stabilization.

Research on the liquid crystal adaptive optics system for human retinal imaging

The blood vessels only in Human eye retinal can be observed directly. Many diseases that are not obvious in their early symptom can be diagnosed through observing the changes of distal micro blood vessel. In order to obtain the high resolution human retinal images,an adaptive optical system for correcting the aberration of the human eye was designed by using the Shack-Hartmann wavefront sensor and the Liquid Crystal Spatial Light Modulator(LCLSM) .For a subject eye with 8m-1 (8D)myopia, the wavefront error is reduced to 0.084 λ PV and 0.12 λRMS after adaptive optics(AO) correction ,which has reached diffraction limit.The results show that the LCLSM based AO system has the ability of correcting the aberration of the human eye efficiently,and making the blurred photoreceptor cell to clearly image on a CCD camera.

Research on power measurement device of jamming bomb based on Infrared Radiation

In order to realize the non-connect measurement on the power and character of jamming bomb, we carried out the research on power measurement device of jamming bomb based on Infrared Radiation. First, the power and infrared radiant band of the jamming bomb was summarized and refined. Then, ensuring the feature and power of jamming bomb was characterized by the magnitude of Infrared Radiation. Afterwards, based on the theory of the above, a power measurement device of Infrared Radiation was simulated and developed. Including the selection of detector and the detector application design, analog signal processing and digital signal processing, using correlation measurement method to detect and calculate the power of device. Finally, the specific method and advantage of the device was introduced. The results of the experiment show that: the response time of the device is less than 3ms; the detection sensitivity is better than 3 x 108cm √HZ / W . The device successfully accomplished the accuracy measurement of Infrared Radiation between 1 to 20um wavelength with higher detection sensitivity and lower response time.