A secure free-space optical (S-FSO) communication system based on data fragmentation multipath transmission (DFMT) scheme is proposed and demonstrated for enhancing the security of FSO communications. By fragmenting the transmitted data and simultaneously distributing data fragments into different atmospheric channels, the S-FSO communication system can protect confidential messages from being eavesdropped effectively. A field experiment of S-FSO communication between two buildings has been successfully undertaken, and the experiment results demonstrate the feasibility of the scheme. The transmission distance is 50m and the maximum throughput is 1 Gb/s. We also established a theoretical model to analysis the security performance of the S-FSO communication system. To the best of our knowledge, this is the first application of DFMT scheme in FSO communication system.

Frequency responses of optoelectronic devices are essential to obtain the precise performance of electrical-to-optical-to-electrical signal conversion or optical signal processing. We reviewed the development of optical or electrical measurement methods proposed for characterizing electrical/optical (E/O) devices, optical/electrical (O/E) devices and optical/optical (O/O) devices in the frequency domain from the perspective of accurate calibration standard. It is found that full calibrated E/O or O/E measurement requires at least an optoelectronic thru standard for the conversion between optical and electrical domains, and an electrical port extension for de-embedding the error or adapter network of microwave source or detector. The indetermination problem still exists in most O/E and E/O device characterization, which appears in different forms for different measurement techniques. Nevertheless, it should be noticed that obtaining an optoelectronic thru standard can be transferred to characterizing a microwave source or detector in the electrical domain, and a precise electrical calibration standard is much easier to be obtained as compared with an optoelectronic calibration standard. Therefore, the calibration standard transfer from optical to electrical domain is a prominent approach to solve the indetermination problem.

Edge couplers are widely utilized in photonic integrated circuits and are vital for ensuring efficient chip-to-fiber coupling. In this paper, we present a high-efficiency and compact polarization-insensitive multi-segment linear silicon nitride edge coupler for coupling to high numerical aperture fibers. By optimizing the thickness of the up cladding and introducing air slots in the transverse direction, we have further modified the limiting effect of the mode field. This innovative edge coupler scheme boasts a compact structure and is compatible with existing mature standard processes, with a total length of only 38 μm. We numerically demonstrate that the proposed edge coupler exhibits a low coupling loss of 0.22 dB/0.31 dB for TE/TM modes at λ = 1550 nm. Furthermore, the proposed coupler displays high wavelength insensitivity within the range of 1400–1850 nm and maintains a coupling loss of less than 0.2 dB with a manufacturing deviation of ±20 nm.

A noise suppression method based on f-x deconvolution and the wavelet transform is proposed for eliminating jump edges in the phase noise of distributed acoustic sensing. Experimental results show that the proposed method has good performance in terms of enhancing the quality of seismic waves. It ensures relatively stable phase sensitivity and improves the signal-to-noise ratio, making the characteristics of seismic wave signals more obvious.