Free-space optical communication brings large-capacity communication with excellent confidentiality, though fatal obstacles are set by atmospheric turbulence that causes phase shifting in laser links. Therefore, we derived a novel, to the best of our knowledge, iterative wavefront correction algorithm based on a complete second-order deformable mirror (DM) Shack-Hartmann wavefront sensor model as a solution to it. For correcting static wavefront aberration, the proposed algorithm possesses a converging speed faster than the traditional one. In terms of correcting dynamic atmospheric turbulence, it can achieve convergence within two iterations with a residual wavefront root mean square value of less than 1/8 wavelength. The input wavefront under 1.5 wavelength can be corrected on our testbed due to the deformability of the micromachined membrane DM. The research result offers a solution for atmospheric turbulence in the adaptive optics field and may contribute to the development of free-space optical communication.

The traditional space telemetry, tracking, command and communication system works in the radio frequency band. With the improvement on measurement accuracy and communication capacity in space missions, the traditional means have a certain bottleneck in dealing with the development of future space missions. The inherent lightweight, high parallel, high capacity and fine processing capabilities of Optics and microwave photonics show the potential to solve the above problems. This paper summarizes the innovative work of the Southwest China Institute of Electronic Technology in the application of laser measurement and communication integration, microwave photonic RF front-end technology in space telemetry, tracking, command and communication system. The experimental platform is established for verification, the accuracy of ranging and velocity measurement reaches millimeter level at 10Gbps single channel transmission rate with 1E-9 bit error rate under a simulation satellite-ground link. The microwave photonic RF front-end can be compatible with S to Ka band, with a sampling rate of 20Gsps and a signal bandwidth of 5GHz. It is expected to be applied to next generation of space telemetry, tracking, command and communication system or navigation and relay system.

The space-based integrated information network is composed of space-based backbone network, space-based access network and ground-based node network. It is interconnected with the ground Internet and mobile communication network to build a “ global coverage, on-demand access, on-demand service, safe and reliable ” space-based integrated information network system. As an important part of the system, the space-ground laser communication equipment is faced with many problems, such as the integration of multiple modulation systems and the location of different places. In this paper, the related problems are analyzed and verified by experiments. The results show that the system works at 1550nm wavelength, adopts coherent communication system and IM/DD communication system, coherent communication system supports BPSK, QPSK and DPSK modulation format, IM/DD communication system adopts OOK modulation format, the communication rate reaches 5Gbps under the condition of 1E-9 bit error rate.

In challenging environments such as forests, valleys and higher latitude areas, there are usually fewer than four visible satellites. For cases with only two visible satellites, we propose a dual-satellite alternate switching ranging integrated navigation algorithm based on the broadband low earth orbit (LEO) constellation, which integrates communication and navigation (ICN) technology. It is different from the traditional dual-satellite integrated navigation algorithm: the difference is that it can complete precise real-time navigation and positioning without an altimeter and continuous observation. First, we give the principle of our algorithm. Second, with the help of an unscented Kalman filter (UKF), we give the observation equation and state equation of our algorithm, and establish the mathematical model of multipath/non-line of sight (NLOS) and noise interference. Finally, based on the SpaceX constellation, for various scenarios, we analyze the performance of our algorithm through simulation. The results show that: our algorithm can effectively suppress the divergence of the inertial navigation system (INS), in the face of different multipath/NLOS interference and various noise environments it still keeps good robustness, and also has great advantages in various indicators compared with the traditional dual-satellite positioning algorithms and some existing 3-satellite advanced positioning algorithms. These results show that our algorithm can meet the real-time location service requirements in harsh and challenging environments, and provides a new navigation and positioning method when there are only two visible satellites.

To solve the problem of location service interruption that is easily caused by incomplete visual satellite environments such as occlusion, urban blocks and mountains, we propose an altimeter + inertial navigation system (INS) + giant low earth orbit (LEO) dual-satellite (LEO2) switching integrated navigation algorithm based on a similar ellipsoid model and unscented Kalman filter (UKF). In addition to effectively improving the INS error, for the INS + LEO dual-satellite switching algorithm without altimeter assistance, our algorithm can also significantly suppress the problem of excessive navigation and positioning error caused by this algorithm in a long switching time, it does not require frequent switching of LEO satellites, and can ensure navigation and positioning functions without affecting LEO satellite communication services. In addition, the vertical dilution of precision (VDOP) value can be improved through the clock error elimination scheme, so, the vertical accuracy can be improved to a certain extent. For different altimeter deviations, we provide simulation experiments under different altimeter deviations; it can be found that after deducting the fixed height deviation, the algorithm can also achieve good accuracy. Compared with other typical algorithms, our proposed algorithm has higher accuracy, lower cost and stronger real-time performance, and is suitable for navigation and positioning scenarios in harsh environments.

In this Letter, based on two advanced tunable ultra-flat optical frequency comb generators (T-FOCGs), a coherent channelized receiver with high channelized efficiency and reconfigurability is proposed. In the T-FOCG, the number of 1 dB comb lines increases with the gain, but the optical power of these 1 dB comb lines has almost the constant variance. In the proposed scheme, one optical carrier can support four sub-channels. Meanwhile, the number and bandwidth of sub-channels, as well as the bandwidth and center frequency of an original broadband signal, are all tunable. In this Letter, we verify the feasibility of the coherent channelized receiver by channelizing a 4 GHz signal with a 20 GHz center frequency into four 1 GHz sub-channels, and the reconfigurability is demonstrated by channelizing a 10 GHz signal with frequencies from 18 to 28 GHz into five 2 GHz sub-channels. Moreover, the error-vector magnitude curves of the directly received and the channelized quadrature amplitude modulation (QAM) signal at different amounts of beat noise are compared.

Due to the limitation of analog-to-digital/digital-to-analog converters, photonics-assisted channelized receivers are thought to be a promising approach to receiving wideband microwave signals. Herein, based on the spectrum analysis and the coherent channelization, we develop a photonics-assisted channelized receiver for multi-band microwave signals. In the proposed channelized receiver, the instantaneous spectral analysis is introduced to determine the frequencies and bandwidth of a dynamic wideband signal. The dynamic wideband signal is then received by a multi-band coherent channelizer. By exploiting transparency of the optoelectronic devices, we equivalently build a multi-band coherent channelizer that can work for dynamic microwave signals, where a few optoelectronic devices are required. Compared with the existing coherent channelizers, the operative bandwidth of the proposed multi-band coherent channelizer is much larger (up to 28 GHz). The proposed photonics-assisted channelized receiver doesn’t need tunable optical comb generators and radio frequency sources, and it also doesn’t require knowing the spectrum information in advance. Moreover, the designed example of the proposed photonics-assisted channelized receiver for a 4 GHz original signal in 2–30 GHz microwave bands is given and discussed. The spectrum information of the dynamic original signals is obtained by monitoring the optical power in each sub-channel. We verify the feasibility of the multi-band coherent channelizer by channelizing two 4 GHz linearly-chirped signals with center frequencies of 4 and 28 GHz into four 1 GHz sub-channels, respectively.

The space TT&C system is the only means for humans to conduct life cycle tracking, telemetry, command and communication for spacecraft. Multi-function, high-precision, real-time TT&C system has always been the goal pursued by researchers in TT&C technology. These features are based on high-speed and high-precision manipulation of microwave signals, but are limited by ‘electronic bottlenecks’. The generation, control and processing of wideband signals is extremely complex and impossible to accomplish in traditional electronics. Photonic technology's inherently large bandwidth, low transmission loss, and anti-electromagnetic interference make it a key enabling technology for breaking the TT&C system bandwidth and high-precision measurement bottleneck and "illuminating the future of TT&C system." Meanwhile, the optical subsystem is light in weight, small in size, and integrable. Therefore, the introduction of photonic technology may change the system of the existing TT&C system. This paper summarizes the main research progress of optical technology in TT&C system at home and abroad, discusses the key technologies of laser and microwave photon technology in TT&C system, and forecasts its development trend.

The Integrated Laser Communication/Ranging System, which uses a coded signal as the ranging information carrier, is of great importance to the next large-capacity inter-satellite information network. In this paper, a system design with a high-sensitivity feedback-homodyne detection scheme and an asynchronous ranging algorithm is demonstrated with real-time field-programmable gate array-implementation (FPGA). The parallel fast Fourier transformation (FFT) estimation is applied to improve the speed and the range of the wavelength drift tracking, which can handle a dynamic wavelength drift up to 2.4 pm/s (300 MHz/s). Meanwhile, for clock sources with subtle dynamic frequency offset and sufficient stability, the proposed fractional symbol ranging method is proven to achieve millimeter-level measurement accuracy. The designed system is shown to perform well in terms of both laser linewidth tolerance and noise resistance.

The Integrated Laser Communication/Ranging System, which uses coded signal as the ranging information carrier, is of great importance to the next large-capacity inter-satellite information network. In this paper, the parallel FFT estimation is applied to improve the speed and range of tracking wavelength drift caused by both the trajectory estimation error and laser instability, it can handle dynamic wavelength drift up to 2.4 pm/s (300 MHz/s). Meanwhile, for clock sources with subtle dynamic frequency offset and sufficient stability, the proposed fractional symbol ranging method based on the timing offset compensation in the receiver is proven to achieve millimeter-level measurement accuracy. The Integrated Laser Communication/Ranging Link with high-sensitivity feedback-homodyne detection and fractional symbol ranging is demonstrated with real-time FPGA implementation and is shown to perform well in terms of both laser linewidth tolerance and noise resistance.

A novel double-efficiency photonic channelization scheme with optical carrier power suppression (OCS) is proposed for the first time, to the best of our knowledge. In this scheme, a tunable optical frequency comb generator is used to efficiently generate radio-frequency (RF) carriers, and a Fabry-Perot filter (FPF) is introduced to split a broadband signal into multiple narrowband signals. With the well-designed frequency of RF carriers, the wavelength spacing of optical carriers, and the free spectrum range of the FPF, double-channelized efficiency can be obtained. A proof-of-concept system is demonstrated to verify the feasibility of this double-efficiency channelization scheme, in which a 5 GHz baseband signal is channelized into five 1 GHz sub-channels, and about 35 dB OCS is obtained. Moreover, the performance of the double-efficiency channelization scheme is analyzed based on a 5 Gbit/s baseband signal with an on-off keying (OOK) format in which the influence of the 3rd order term interference is discussed.

Based on analysis on the present research status of the lunar and deep space Tracking,Telemetry and Command (TT&C) systems at home and abroad,four major difficulties and challenges for building a TT&C system are studied.Then urgent needs for antenna arraying technology,laser TT&C technology,Ka and millimeterwave band hypothermia receiver,superconducting nanowire single photon detectors,deep space optical tracking system,narrow linewidth laser source generating technology,optical communication modulation technology and highpower low-noise amplifier were summed up.A latest cutting-edge technology for deep space TT&C system,namely Integrated Radio and Optical Communications (IROC) system was described.Finally,with the current situation,recommendations for future developments of lunar and deep space TT&C systems have been put forward.The research results provide references for the development of the lunar and deep space TT&C systems.

The circuit structure and noise characteristics of a high-speed spatial coherent balanced de-tector were analyzed ,and the dependence of key technical parameters on the circuit structure of the balanced detector was clarified .Two kinds of high-speed spatial balanced photoelectric detectors were designed by using resistance sampling and double TIA (Transimpedance Amplifier) synthesis ,and their performance parameters were verified by experiments .The experiments indicate that both kinds of high-speed coherent detectors can be used for high-speed coherent detection ,while the detection sensitivity and anti-noise performance from the double TIA voltage synthesis balanced detector are better than those from the resistance sampling type detector .When the communication rate is 5Gbps and the bit error rate is 10-8 ,the optimal detection sensitivity of resistance sampling type balanced de-tector is -33 .51 dBm ,and that of the double TIA synthesis balanced detector is -43 .4 dBm ,higher nearly 8dB than that of the Discovery's 5Gbps balanced detector .The research on the structure of high-speed spatial coherent photodetector provides a theoretical basis for the establishment of a high-sensitivity and high-speed spatial coherent optical communication system .

This paper analyzes the present research status of the lunar-earth and deep space telemetry, track and command (TT&C) system, four major difficulties and challenges to establish the TT&C system are studied. Then urgent needs for antenna arraying technology, laser TT&C technology, Ka and millimeter-wave band hypothermia receiver, superconducting nanowire single photon detectors, deep space optical tracking system, narrow linewidth laser source generating technology, optical communication modulation technology and high-power low-noise amplifier were summed up. A latest cutting-edge technology for deep space TT&C system, namely the iROC (integrated radio and optical communications, iROC) system was described. Finally, with the current situation, the recommendations of future developments of the lunar-earth, deep space TT&C system have been put forward. The research results can supply references for the development of the lunar-earth, deep space TT&C system.

In this paper, to improve the reliability of a two-axis fast steering mirror system with minimum hardware consumption, a fault diagnosis method based on Kalman filter was developed. The dynamics model of the two-axis FSM was established firstly, and then the state-space form of the FSM was adopted. A bank of Kalman filters for fault detection was designed based on the state-space form. The effects of the sensor faults on the innovation sequence were investigated, and a decision approach called weighted sum-squared residual (WSSR) was adopted to isolate the sensor faults. Sensor faults could be detected and isolated when the decision statistics changed. Experimental studies on a prototype system show that the faulty sensor can be isolated timely and accurately. Meanwhile, the mathematical model of FSM system was used to design fault diagnosis scheme in the proposed method, thus the consumption of the hardware and space is decreased.