A finite moreover impulse response (FIR) microwave photonic filter with a rejection up to 60dBimplemented by slicing light after a superstructured FBG and dispersive medium was achieved [37]. Microwave photonic filters with negative coefficients have also been developed [38�C41]. With the development of microwave photonics technology, the applications of this technology have started to attract research attention and the application of microwave photonic technology in communication and sensing systems has been exploited [42�C44].In this review, we will provide a comprehensive overview of the applications of advance photonic technology, including fiber lasers and microwave photonics for sensing systems, and the newest and most promising Inhibitors,Modulators,Libraries techniques for sensing applications.
The remainder of this review article will be divided into three parts: in the first Inhibitors,Modulators,Libraries part, the fiber laser technology and its applications in sensing systems will be reviewed; in the second part, the microwave photonic technology and its applications in sensing systems will be reviewed; finally Inhibitors,Modulators,Libraries come the conclusions.2.?Fiber Lasers and Their Sensing Applications2.1. Inhibitors,Modulators,Libraries Fiber Lasers Sensing ApplicationsFiber lasers are being widely used in sensor systems, in which they act as the optical light source or the sensor element. When the fiber laser is used as the sensor, it can usually achieve high signal-to-noise ratio (SNR), high sensitivity, long distance sensing and multi-parameter sensing. In 1993, Ball et al. reported the operation of an active, single-frequency, polarimetric, Bragg-grating fiber-laser strain sensor [45].
The short Bragg-grating fiber-laser has two orthogonal polarization modes which yielded a single beat frequency after optical mixing and the beat frequency provided the sensing information with a rate of ?4.1 MHz/mstrain for linear strain and �C0.37 MHz/(deg/cm) for torsional strain. Hadeler et al. reported the application of a dual polarization distributed feedback (DFB) fiber Brefeldin_A laser which was used as a strain and temperature sensor [46]. By measurement of the absolute wavelength of one polarization as well as the polarization beat frequency, strain and temperature were determined simultaneously. The demonstrated sensor has an accuracy of ��3 �̦� and ��0.04 ��C. Guan et al. demonstrated a novel fiber-optic hydrophone that uses a dual polarization DBR fiber laser as the sensing element, whose experimental scheme is shown in Figure 1 [47].Figure 1.The diagram of the dual polarization DBR fiber laser based fiber sensor.The operation principle of the sensor is based on the modulation of the birefringence of the fiber Imatinib solubility laser by high-frequency ultrasound.