Keyan Dong

Tunable ultra-narrow linewidth microwave generation from a double-loop Brillouin fiber laser

A simple photonic approach to generate an ultra-narrow linewidth microwave signal is proposed and experimentally demonstrated. In this scheme, a multi-wavelength Brillouin fiber laser (BFL) with a double-loop and un-pumped polarization maintaining erbium doped fiber (PM-EDF) is used. The double-loop configuration includes a 50 m long single-mode fiber (SMF) and a 10 m long SMF as Brillouin gain. The threshold and linewidth of the microwave source can be improved by using a double loop, while a 4 m long un-pumped PM-EDF is used to suppress unwanted side-modes. A dual-wavelength optical signal is heterodyned at the high-speed photo detector to produce a microwave signal by adjusting the polarization controller and the wavelength of the Brillouin pump. As a result, a tunable microwave signal from 10.605 to 10.887 GHz can be obtained. The linewidth of the microwave signal is about 14.4 kHz, and the side-mode suppression ratio is about 30 dB.

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.

L-band double Brillouin frequency spaced tunable multiwavelength Brillouin fiber laser

A tunable multi-wavelength Brillouin fiber laser with double Brillouin frequency spacing based on a four-port circulator is experimentally demonstrated. The fiber laser configuration formed by four-port circulator isolates the odd-order Brillouin stokes signal to circulate within the cavity only. In addition, it also allows propagation of the incoming Brillouin pump and even-order Stokes signals from four-port circulator to output coupler .A L-band erbiumdoped fiber (EDF) with 1480nm pump is used to amplify Stokes signals and to get more output channels. At the Brillouin pump power of 8dBm and the 1480 nm pump power of 200mw, 5 output channels with double Brillouin frequency spacing and tuning range of 20 nm from 1568nm to 1588nm are achieved.

Analysis and discussion about the antenna networking structure of three concentric spheres

In order to break through the laser communication technology of one point to multipoint, which is the difficult problems for laser communication. The networking solutions of the antenna structure of three concentric spheres are proposed. Being with the advantages of simple structure, small size and light weight, the antenna structure of three concentric spheres can be applied to short-distance space laser communication. The feasibility of the system can be realized from two aspects, the analysis of link and the analysis of the precision index. On this basis, the whole optical system can be determined by the corresponding optical system design. Under the condition of permitting of link energy, the optical system of antenna structure of three concentric spheres with mobile field azimuth angle of 120°and the pitching angle of 20°is completed. The parameters can meet the requirements in the subsystem of the communication receiving optical path, the communication transmitting optical path and the communication tracking optical system. The results indicate that the antenna structure of three concentric spheres can be applied to the laser communication networking under the short-distance space.

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.

40nm tunable multi-wavelength fiber laser

A Brillouin-Erbium multi-wavelength tunable fiber laser at C-band is demostrated. A 10 km long singlemode fiber(SMF), a 6 m long Erbium-doped fiber, two couplers, a wavelength division multiplexer, a isolator, an optical circulator, a 980nm pump laser and a narrow linewidth tunable laser are included in the structure. A segment of 10 km-long single-mode fiber (SMF) between the two ports of a 1×2 coupler is used as Brillouin gain. Ebiumdoped fiber amplifier（EDFA） consists of a segment of 6m er-doped fiber pumped by 980nm laser dioder . A narrow linewidth tunable laser from 1527 to 1607 nm as Brillouin bump, At the Brillouin pump power of 8mW and the 980 nm pump power of 400 mw, 16 output channels with 0.08 nm spacing and tuning range of 40 nm from 1527 nm to 1567 nm are achieved. We realize the tunable output of wavelength by adjusting the 980 nm pump power and the Brillouin pump wavelength. Stability of the multiwavelength fiber laser is also observed.

Research on UV scattering communication

Ultraviolet (UV) scattering communication is a broadcast communication mode of information transmission by particles in the atmosphere scattering effect on the blind band ultraviolet light, there are many advantages such as unaffected by electromagnetic radiation, good confidentiality, non-line-of sight communication. This type communication mainly used in a short distance, secure communication, which was superior to no line communication in aspect of anti-jamming and secrecy. Firstly the military requirement of UV scattering communication is analyzed in this paper, The development trend is introduced, then the composition and working principle of ultraviolet scattering communication system are also discussed, The key influential factors of UV communication system path transmission loss effects on parameters such as receiver, transmitter and received beam divergence angle, pitch angle and the communication distance were analyzed. Attenuation was quantitatively simulated under different atmospheres, communication patterns and structure parameters. The results show that: transmission distance increases with increasing beam divergence angle and decreasing field angle. And the received view angle of influence on the communication distance is far greater than the emission beam divergence angle; transmission distance increases with increasing beam divergence angle and decreasing field and field angle effects on communication distance is greater than beam divergence angle.

Research on simulation system with the wide range and high-precision laser energy characteristics

The Hardware-in-the-loop(HWIL) simulation test is one of the important parts for the development and performance testing of semi-active laser-guided weapons. In order to obtain accurate results, the confidence level of the target environment should be provided for a high-seeker during the HWIL simulation test of semi-active laser-guided weapons, and one of the important simulation parameters is the laser energy characteristic. In this paper, based on the semi-active laser-guided weapon guidance principles, an important parameter of simulation of confidence which affects energy characteristics in performance test of HWIL simulation was analyzed. According to the principle of receiving the same energy by using HWIL simulation and in practical application, HWIL energy characteristics simulation systems with the crystal absorption structure was designed. And on this basis, the problems of optimal design of the optical system were also analyzed. The measured results show that the dynamic attenuation range of the system energy is greater than 50dB, the dynamic attenuation stability is less than 5%, and the maximum energy changing rate driven by the servo motor is greater than 20dB/s.