KEYWORDS: Clocks, Laser communications, Signal processing, Power supplies, Reliability, Telecommunications, Oscillators, Voltage controlled current source, Aerospace engineering, Imaging systems
Space laser communication is moving in a wider
bandwidth, greater distances, is more accurate and more narrow laser
communication beam direction, faster bandwidth as well as
communication interface chip high-speed clock more demanding
requirements of the low frequency noise, and good reliability, small
size and low power consumption characteristics. Production of
ADI's ADF4350 integrated voltage-controlled oscillator (VCO)
bandwidth frequency synthesizer just to meet this requirement clock
frequency This paper describes the basic principles and operating
characteristics of the broadband frequency synthesizer. In this paper
we use CPLD to control the ADF4350 and give a control electric
circuit with CPLD structure and based on Verilog program.
Simulation and experimental results show that the lock-in effect is
good, easy to control, and reliable performance. It is able to generate
stable clock, suitable for applications in laser communication.
With the rapid development of modern science and technology in
astronomical imaging, optical communications, optical radar, optical
information processing, high-precision ranging, tracking, guidance, and
remote sensing, light waves propagating in the medium, especially in the
turbulent atmosphere spread more and more important. Atmospheric
turbulence is one of the main factors which have influence on the
performance of a laser communication system. Adaptive optics technology
is an important means to solve the problem of atmospheric turbulence. This
paper states how adaptive optics technique can be used in space laser
communication system to compensate atmospheric turbulence when laser beam
transmission through it. The core content of adaptive optics is correct
laser beam wave-front disturbance in real-time,with it to enhance optical
system imaging quality and the next aim is reach the level of diffraction
limitation. Adaptive optics system consists of wave-front detection,
wave-front control and wave-front correction . The demo platform
including: atmospheric turbulence simulation unit、adaptive correction
unit、signal transmitting and receiving unit. Liquid crystal spatial light
modulator applications in adaptive optics system and the turbulence
simulation system introduced. And used zernike polynomials method to
produce atmospheric turbulence phase screen simulation analysis.
Simulation results show that: in the low spatial frequency components,
the atmospheric turbulence phase screen generated by Zernike polynomial
method consistent with the theoretical values, but in the high spatial
frequency components, the simulation results with large difference
between the theoretical values. In addition, the simulation results also
show that: we can change the distribution of turbulence in the atmospheric turbulence phase screen by increasing the Zernike polynomials of orders
or change the receiving apertures, but to calculate the large calculate
the complex and other shortcomings. If adaptive optics technique can be
applied in space laser communication system and is proved by practice,
must make a space laser communication system performance has greatly
improved.
With the development of optical fiber communications, especially
the maturity of the optical amplifiers and the WDM technology, space optical
communication at 1550 nm becomes a promising solution for future high
speed satellite communication. Receiving technology with optical amplifiers
and coupling space light into single mode fiber are key technologies in space
optical communication at 1550 nm. Free-space-to-fiber coupling technique
investigated in this paper is the first challenge of applying fiber communication
techniques to free space optical communications. We analyzed the factors
that affect the efficiency of free-space-to single-mode-fiber coupling based on
mode-matching theory of electromagnetic fields. On this objective, in this
paper, the theoretical analysis of the effect of atmospheric turbulence on the
space light-single mode fiber coupling efficiency is discussed. On this basis,
the short-distance experiment coupling space light into single mode fiber is
carried out.
1. The main factors affecting the process coupling space light into single
mode fiber are analyzed. This paper introduced the statistical theory of
atmospheric turbulence and gave out the main turbulence parameters and
meteyard based on the theory of the space light-single mode fiber coupling
efficiency under ideal conditions.
2. The influence of atmospheric turbulence on the space light-single mode
fiber coupling efficiency is analyzed and simulated. In the weak turbulence
condition, mathematical model of the mean coupling efficiency and its
fluctuation variance was given. And the fluctuation variance of coupling
efficiency was simulated studied under the atmospheric conditions. The
influences on the average coupling efficiency was theoretically studied, which
were induced by the structure constant of atmospheric refractive index, the
diameter of coupling lens and the single-mode fiber mode field radius.
3. Validating the theoretical model by a experiment under a short link coupling
condition.
The results of this paper lay the theoretical and experimental foundation for
indeed establishing the efficient space light-single mode fiber coupling
systems.
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