In the field of space optical communication, coherent communication system has the advantages of high sensitivity, compatibility with a variety of modulation formats and strong anti-interference ability compared with intensity modulation direct detection (IM-DD) system. The typical disadvantage of coherent communication system is the complexity of the receiver, which requires carrier recovery. Space optical communication is also developing from point-to-point communication to optical communication network. In this paper, a fast phase locking method based on direct phase control is proposed. After the auxiliary frequency acquisition is completed, the time to recover the carrier is equal to the loop delay. The realization of this method depends on the direct control of the local oscillator carrier phase. Different from the traditional second-order loop method, this method does not need to consider the laser linewidth. This method can greatly save the time of carrier recovery, so it can be used for fast switching of optical network channels and can improve the utilization of optical networks.
This article mainly shows that coherent accumulation of multi-aperture receiver array based on frequency modulation continuous wave (FMCW) coherent lidar has an excellent performance for the weak signal detection of target which is far distance or moving with a high velocity. This method can improve the signal and noise ratio (SNR) and detection range accuracy by multi-aperture receiver array. In addition, the analysis done by simulation shows that phase fluctuation of atmospheric turbulence has a significant influence on the performance of coherent accumulation of multi-aperture receiver array. Stimulation result shows that while μx is equal to - σ2x , the amplitude fluctuation of signal could degrade the quality of coherent accumulation based on multi-aperture receiver array and its existence leads to the worse performance before non-amplitude fluctuation. Phase fluctuation of signal deteriorates the performance of coherent accumulation while its size is big or small.
In an optical phased array (OPA) free space laser communication system, one of the main issues is to control the phase of each beam to acquire fast and stable phase-locking for phase consistency, in which the number of the elements in the array is of vital importance. In this paper, we studied the method on improving the performance of phase-locking about speed and stability of optical phased array with large number of elements. The performance of OPA with different number of emitting elements was analyzed with the simplified stochastic parallel gradient descent (SPGD) algorithm for closed-loop phase-locking. And the algorithm showed a poor performance when the elements of the array were in large amounts. An optimal algorithm, the distributed SPGD (DSPGD) algorithm, was proposed to improve the performance of the array, which revealed fast speed and stability in phase-locking of a large number of emitting elements of optical phased array, suggesting the algorithm is effective.
A coherent laser phase shift range finder based on optical phase modulation and phase shift measurement can measure distance and velocity precisely at the same time. In this paper, methods to improve the sensitivity of the range finder is presented. Matched filter algorithm is used to calculate the range velocity in frequency domain. Experiment is conducted at different signal power. The relationship between RMSE of measured range, as well as measured velocity, and the signal power is shown in the result.
The performance of satellite-to-ground downlink optical communications over Gamma-Gamma distributed atmospheric turbulence are discussed for a direct detection differential phase shift keying system with spatial diversity, which combines the beam coherently before demodulation. Bit-error rate (BER) performances for various numbers of apertures are analyzed and compared for different zenith angle. We also consider the effect of the fiber coupling efficiency and loss ratio of beam coupler to the final BER. The results of numerical simulation shows that the advantage increases with the number of aperture. All the numerical results are verified by Monte-Carlo simulations.
In the field of intersatellite laser communication, there are two high-sensitivity demodulation methods: binary phase-shift keying (BPSK) coherent detection and differential phase-shift keying (DPSK) coherent detection. After taking into account the advantages and disadvantages of BPSK and DPSK, a DPSK heterodyne coherent detection scheme with local oscillation enhancement is proposed. The structure and the principles of this detection system are described, and the theoretical deduction is presented. Moreover, an experimental setup was constructed to test the proposed detection scheme. The offline processing procedure and results are presented. This scheme has potential applications in high-speed intersatellite laser communication.
The method to realize the integration of laser communication and ranging is proposed in this paper. In the transmitter of two places, the ranging codes with uniqueness, good autocorrelation and cross-correlation properties are embed in the communication data and the encoded with the communication data to realize serial communication. And then the encoded data are modulated and send to each other, which can realize high speed two one-way laser communication. At the receiver, we can get the received ranging code after the demodulation, decoding and clock recovery. The received ranging codes and the local ranging codes do the autocorrelation to get a roughly range, while the phase difference between the local clock and the recovery clock to achieve the precision of the distance.
Laser beam's acquisition, pointing and tracking are crucial technologies of free space optical communication. Fine tracking
system is an important component of APT (acquisition, pointing and tracking) system. Traditional fine tracking system
use CCD or quadrant detector as the position detector of signal light. In order to simplify the system and improve accuracy,
we propose a fine tracking system based on fiber nutation which don’t need a position detector and theoretically prove that
the system is feasible. Meanwhile corresponding fine track system was built, experiment on position detection of the fine
tracking system is done.
This paper proposes a new method for variable rate DPSK in the satellite-to-ground laser communication. Compared to
the general method, this method doesn’t need to change the original communication rate, reduces the complexity of the
system. In theory, SNR can improve above 3 dB when rate into half. We construct a simplified experimental apparatus to
verify the effectiveness of the proposed method. The experimental devices and results are presented. Offline processing
results are very similar to theory, is superior to the traditional means. The further study about doppler effect and clock
synchronization is being conducted.
In the field of satellite communication, space laser communication technology is famous for its high communication rate,
good confidentiality, small size, low power consumption and so on. The design of coherent optical communication
detection device based on modified balanced optical phase-locked loop (OPLL) is presented in the paper. It combined by
local oscillator beam, modulator, voltage controlled oscillator, signal beam, optical filter, 180 degree hybrid, balanced
detector, loop filter and signal receiver. Local oscillator beam and voltage controlled oscillator trace the phase variation of
signal beam simultaneously. That taking the advantage of voltage controlled oscillator which responses sensitively and
tunable local oscillator laser source with large tuning range can trace the phase variation of signal beam rapidly and achieve
phase locking. The demand of the phase deviation is very low, and the system is easy to adjust. When the transmitter
transmits the binary phase shift keying (BPSK) signal, the receiver can demodulate the baseband signal quickly, which has
important significance for the free space coherent laser communication.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.