Application Research on Space Laser Communication in Bistatic Radar System

There exist three synchronizing problems in the bistatic radar system that some signals of the radar receiver must be synchronized with those of the radar transmitter. Several methods realizing data transmission, which are used to complete the synchronization existing in the bistatic radar system, are described. Then a new idea is brought forward that employs space laser communication in the bistatic radar system to realize its data transmission. The theoretic analysis of the idea's usability and its merits are discussed in details. Finally the latest development of space laser communication is introduced, and the utility of the idea is pointed out further.

Study on Satellite-to-ground Laser Communications with Existence of Atmosphere

The laser beam used to establish a communication channel between satellite and ground segments has a small divergence angle and a tiny spot on the Earth's surface,which may lead to the fail of the system.So it's important to study the deflection of laser beam by the Earth's atmosphere and find a way to calibrate this error.Both theoretical analysis and real data processing method are used to obtain the mathematical model for divergence angle of laser communication beam and its correction function.Then the model has been applied to the data,which was used to describe the atmosphere state by traditional ground segments to obtain the critical elevation angle.According to the results of calculation,our conclusion will be that the correction should be done when the critical elevation happens.

Acquisition,Pointing and Tracking System for Shipborne Space Laser Communication without Prior Information

A space laser communication acquisition,pointing and tracking(APT)system based on the beacon laser is designed without prior information.And then,a new target scanning method and a pointing and tracking algorithm are proposed.The target scanning mode is the round-trip triangular wave scanning,and it means that scanning track of the PAN-TILT platform follows the triangular wave repeatedly.For the pointing and tracking algorithm,the beacon laser is used as the auxiliary aiming light source.The position of the beacon laser in the viewfield of the complementary metal oxide semiconductor(CMOS)camera is calculated by the centroid algorithm.In order to realize the target tracking,the joint control method of the angle control and the angular velocity control is used.The simulation and experimental results show that the APT system can achieve full coverage scanning in the scanning area and capture the target in one scanning cycle successfully.After capturing the PAN-TILT platform,the pointing and tracking algorithm can track the PAN-TILT platform quickly and accurately,and the tracking accuracy is up to 0.22 mrad.

All-optical suppression on the impact of Sun outage in laser satellite communication systems by using a nonlinear semiconductor optical amplifier

We introduce an all-optical approach,optical parametric amplification(OPA)processor to suppress the impact of Sun outage in laser satellite communication systems,which is implemented by only one nonlinear semiconductor optical amplifier driven by both electrical and optical pumps.The optimized OPA processor,with a current of 539 mA and a pump-to-signal ratio of 16 dB,could significantly improve the signal quality by 3.5 dB in experiments for the elevation angle of Sun radiation of 0 rad.The signal quality improvement is observed in the whole range of the elevation angle,confirming the effectiveness of the proposed OPA processor in the field of Sun radiation mitigation.

Advanced Space Laser Communication Technology on CubeSats

The free space optical communication plays an important role in space-terrestrial integrated network due to its advantages including great improvement of data rate performance,low cost,security enhancement when compared with conventional radio frequency(RF) technology.Meanwhile,CubeSats become popular in low earth orbit(LEO) network because of the low cost,fast response and the possibility of constituting constellations and formations to execute missions that a single large satellite cannot do.However,it is a difficult task to build an optical communication link between the CubeSats.In this paper,the cuttingedge laser technology progress on the CubeSats is reviewed.The characters of laser link on the CubeSat and the key techniques in the laser communication terminal(LCT) design are demonstrated.

20.231 Gbit/s tricolor red/green/blue laser diode based bidirectional signal remodulation visible-light communication system

We propose and experimentally demonstrate a recorded 1-m bidirectional 20.231-Gbit/s tricolor R/G/B laser diode(LD) based visible-light communication(VLC) system supporting signal remodulation. In the signal remodulation system, an LD source is not needed at the client side. The client reuses the downstream signal sent from the central office(CO) and remodulates it to produce the upstream signal. As the LD sources are located at the CO, the laser wavelength and temperature managements at the cost-sensitive client side are not needed.This is the first demonstration, to our knowledge, of a >20 Gbit∕s data rate tricolor R/G/B VLC signal transmission supporting upstream remodulation.

Faraday laser at Rb 1529 nm transition for optical communication systems

We experimentally demonstrate a Faraday laser at Rb 1529 nm transition by using a performance-improved Rb electrodeless-discharge-lamp-based excited-state Faraday anomalous dispersion optical filter as the frequency- selective element. Neither the electrical locking scheme nor the additional frequency-stabilized pump laser are used. The frequency of the external-cavity diode laser is stabilized to the Rb 1529 nm transition, and the Allan deviation of the Faraday laser is measured by converting the optical intensity into frequency. The Faraday laser can be used as a frequency standard in the telecom C band for further research on metrology, microwave photonics, and optical communication systems.

空间激光通信捕获与跟踪技术

The divergence angle of laser beam used in space laser communication is usually no more than 100μrad.Using laser beam with small divergence angle to achieve acquisition and tracking for space laser link has always been a difficult problem.In addition,the random nature of the atmosphere will affect the satellite-ground laser link,which increases the difficulty of the acquisition and stable tracking for the laser link.Thus,taking into account the above challenges for satellite-ground laser communication,an acquisition and tracking scheme of using both beacon beam and signal beam was designed for the Laser Communication Terminal(LCT)of Shijian 20 satellite.In-orbit test results indicated that under the condition of moderate atmospheric turbulence(atmospheric coherence length r0≈3 cm),the process of acquisition and tracking for the satellite-ground laser link can be completed within 1 s after the initial pointing between the LCT and Optical Ground Station(OGS)is performed,and the tracking error was less than 1μrad(3σ).In addition,the laser link can be re-established quickly once being interrupted by unsteady atmospheric turbulence,and can be maintained for a long time under moderate twurbulence conditions,which lays a foundation for future application of satellite-ground laser communication.

Direct phase control method for binary phase-shift keying space coherent laser communication

An optical phase locking method based on direct phase control is proposed.The core of this method is to synchronize the carrier by directly changing the phase of the local beam.The corresponding experimental device and the supporting algorithm were configured to verify the feasibility of this method.Phase locking can be completed without cycle skipping,and the acquisition time is 530 ns.Without an optical preamplifier,a sensitivity of-34.4 d Bm is obtained,and the bit error rate is 10^(-9) for 2.5 Gbit/s binary phase-shift keying modulation.The measured standard deviation of the phase error is 5.2805°.

Off-axis two-mirror laser communication antenna designed using differential equations

In satellite laser communication technology, which is built between planets and between a planet and the Earth, the optical antenna is the key point. Thus, research on optical system design is important. The off-axis reflective system has no obscuration and hence possesses a high efficiency for energy transfer. This study proposes a novel method for designing a free-form off-axis reflective imaging system. This study also introduces differential equations that depend on Fermat＇s principle and sine condition. Finally, a free-form off-axis two-mirror optical system was designed by using the differential equation method. This system includes one intermediate image plane, in which the field of view （FOV） is -5° to -4° in the y-axis and -1° to 0° in the x-axis. The modulation transfer function was greater than 0.7 at 50 lp/mm, and the efficiency of energy transmission was high. The free-form off-axis two-mirror optical system involves a wide range of application prospects in the optical antenna used in the satellite laser communication systems. Moreover, the design method that used differ- ential equations was proven simple and effective.

Wide angle space laser communication receiver based on asymmetric array structure

In this paper, an asymmetric array structure of space laser communication receiver is proposed. This structure can greatly reduce alignment requirement, and lighten the signal strength jitter caused by atmospheric turbulence. A prototype of the proposed structure is fabricated and a 2.5 Mbit/s on-off keying(OOK) modulated demonstration link over 40 m free space is built. This asymmetric array structure can effectively collect optical signal while rotating in a window angle of ±17°, and the bit error ratio(BER) keeps zero.

Self-seeded quantum-dash laser based 5 m-128 Gb/s indoor free-space optical communication: erratum

On page 100604-3 in our work [1], the caption for Fig. 2 should be ＂at the 98% output of the 2：98 coupler＂ （not ＂at the 2% output of the 2：98 CP＂）.