A quasi-distributed sensor system based on optical frequency domain reflectometry where the sensing points were identical, low-reflective fiber gratings in a single fiber was investigated. Firstly, the spatial distribution function of fiber gratings was deduced in theory, and the effects of interference among each sensing fiber grating and between the gratings with broadband reflector were investigated. Then the strain sensor system cascaded 215 fibers Bragg gratings (FBGs) in a single fiber had been numerical investigated, the spatial domain addressing and wavelength demodulation of the fiber gratings was implemented according to Fourier transform and inverse Fourier transform. Finally, the internal relations between interaction noise and distribution position of the gratings were simulation analysis. The results show that the interference exists among each sensing fiber grating，but it can be suppressed by buffer fiber. This allows obtaining more realistic values of the performance and design parameters such as the number of FBGs, the reflectivity of the gratings, and the distance between the sensors.
Based on the coupled mode theory, the transfer matrix approach is presented to investigate the fiber grating external
cavity semiconductor lasers (FGECSL). As a result, the P-I curve, the lasing wavelength and the side-mode-suppression-ratio
(SMSR) have been investigated numerically in detail. With the length of the fiber grating increasing, the reflection
spectrum of FGECSL changes obviously, the threshold current and threshold carrier density decreases, the mode
distribution is irregular, and the output spectrum becomes complex. Moreover, the optical bistablility is also observed.
Based on the theoretical model of the synchronization system with incoherent optical feedback, message encoding
and decoding of the chaotic system have been investigated. The results show that message can be hidden efficiently in
the chaotic signal during the transmission with three encryption schemes (i.e., chaos shift keying (CSK), chaos masking
(CMS) and additive chaos modulation (ACM)); the message of 250Mb/s can be decoded in the receiver with CSK and
CMS; when the bit rate increases to 2.5Gb/s, the message can not be decoded with CSK and the quality of message
decoded with CMS becomes bad; and when the bit rate increases to 12.5Gb/s, the message can not be decoded with CSK
and CMS, however the message can be decoded perfectly by adopting ACM.