The error caused by aerosol is simulated when ozone is detected with three wavelength dual difference absorption lidar (D-DIAL) and two werelength difference absorption lidar (DIAL). The effects of the aerosol parameters on ozone detection are analyzed, including wavelength exponent and aerosol content. The impact of the factor C, which is introduced by the elimination to the scattering and extinction errors, on the detection results is discussed by using the three wavelength dual differential method. It shows that C optimal values make the error close to zero, and the optimal value of C is simulated. Different wavelengths are used respectively to simulate the error in multi wavelength difference absorption lidar on ozone detection. In the troposphere, the wavelengths of 266 nm and 308 nm (in DIAL), and 266, 289, 308 nm(in D-DIAL) are used, and in the stratosphere, the wavelengths of 308 nm and 351 nm, and 308, 339, 351 nm are used. The simulated results show that when aerosol scattering ratio R is 2, the error of D-DIAL method is less than 1%, and the error of DIAL method is 10%~45%. In the same aerosol content, the error of stratospheric ozone is significantly less than the error of tropospheric ozone. When the aerosol content is high, the error of D-DIAL detecting tropospheric ozone can reach 6%, and in the stratosphere the maximum error is only 3.5%.

The influence of sky background radiation on bit error rate (BER) under on-off keying (OOK) modulation is studied, and the simulation method of sky background radiation received by the communication terminal is introduced. Simulation results show that when the communication BER is constant, the upper threshold of sky background radiation is related to the received signal optical power and the electrical noise of avalanche photodiode (APD). Direct solar radiation is the major background radiation received by atmospheric laser communication system, and atmospheric scattering,relative to the direct solar radiation, is very weak. When the solar zenith angle is small, the optic axis of the communication terminal can be adopted to avoid certain sun radiation angle, and it is ensured that the BER of the communication system is less than 10-9.

In order to obtain the detailed distribution information of background radial brightness, the measuring method of ground-based whole sky background radiance spectra is developed based on the fiber optical spectrometer and two-dimensional turntable. It can realize the fixed point observation and scanning all the sky. Structure of system, scheme of data detection, principle and method of calibration are introduced in detail. After one scanning, 649 samples of radiance can be obtained. Spectral resolution of each sample is 0.5 nm. Measuring position of each sample is used as pixel and each wavelength radiance of the position is used as gray level. The distribution of whole sky background radiation spectrum band is obtained. The proposed method provides more detailed information for further scientific research.

Beam spreading near the sea surface environment is measured in the experiment by dynamically-tested atmospheric beam system. Comparative analyses are then conducted between the experimental data and the theoretical value of both the marine power spectrum and the traditional Kolmogorov power spectrum. Results show that the measured ampltude fluctuation of beam spreading is lager than those of the marine power spectrum and Kolmogorov power spectrum, and the theoritical value of beam spreading for marine power spectrum is small when the measured inner scale is used to calculate. The beam spreading model for the marine power spectrum is closer to the experimental data than that for the Kolmogorov power spectrum with the increase of the refractive index structure constant of atmosphere. The difference between the theoretical value of the marine power spectrum and the experimental data is about 0.1~1.5 cm at 1 km link distance and 0.1~1.8 km at 2 km link distance. Both the relative errors are within 0.1% ~11.4%.

The commonly used CCD in Raman spectroscopy is sensitive to temperature, and cooling can effectively reduce its dark current noise. A cooling system is designed, and the finite element analysis software ANSYS is used to simulate the heat conduction of the heat sink and the heat exchange of gas flow in the vacuum chamber. The temperature change with the cooling time is measured at different vacuum degrees and with different buffer gas including Ar, Ne, N2 and air. The experimental results show that better cooling effect can be realized when N2 is used as buffer gas, and higher vacuum degree does not guarantee better cooling effect, which is consistent with the thermal simulation result. The measured dark current noise of CCD at different temperatures shows that CCD temperature has strong impact on its dark current noise, cooling can reduce the noise effectively, and the noise varies with temperature exponentially.

A structure of crystalline silicon thin film solar cells are proposed, which can absorb broadband spectrum. The antireflection (AR) coating is triangular diffraction grating and the back reflection layer is composed of air column photonic crystal (PC) of triangular lattice on the background of crystalline silicon. The influences of the diffraction grating and PC on the enhancement of the optical absorption in the cell are simulated using the rigorous coupled wave analysis and plane wave theory method. The results show that for the incident angles of 0°～60°, the AR coating has low reflection within the wavelength range of 380～1100 nm and the back reflection layer has high reflection within the wavelength range of 800～1100 nm. For the c-Si thin film solar cell with an active layer thickness of 20 μm, under the TM polarization state of the incident wave and when the white light is at a vertical incidence, the light absorption rate is increased by 18% from the triangular diffraction grating and by 6% from the two-dimensional PC. For the crystalline silicon thin film solar cells with AR coating and the back reflection layer, when the incident angle is less than 60°, the average absorption rate is 87.6% in the wavelength range of 380～850 nm and 49% in the wavelength range of 850～1000 nm.

The self-healing property of non-diffracting two-dimensional Airy beams with different parts blocked is investigated via numerical simulation. The simulation shows that the Airy beams that are partially blocked can be self-reconstructed after propagating for a certain distance. The self-healing property under the Gaussian noise perturbation is also investigated. The result shows that self-healing of the Airy beams can be realized after the beam propagates for a certain distance when the signal-to-noise ratio is appropriate. The self-healing property of Airy beams is robust, and the property can be applied in many fields such as optical tweezer system, atom trapping and manipulating, and wireless optical communications.

Air hole in photonic crystal fiber(PCF) cladding is filled with magnetic fluid(MF). Tuning and sensing of PCF optical properties can be realized by using the refractive index tunable property of MF. The effects of filling MF on the mode and loss characteristics of PCF are analyzed with full vector finite element method. The influences of structural parameters on loss sensitivity of the circular hole PCF filled with MF are analyzed. The loss sensitivity characteristics of circular hole and elliptical hole PCFs filled with MF are compared, and the temperature and magnetic field characteristics of elliptical PCF filled with MF are investigated. Simulation results show that fiber mode effective refractive index, mode area and loss of PCF are increased by filling MF. The loss sensitivity caused by the change of MF refractive index in elliptical hole PCF is about 4 times of that of circular hole PCF. The temperature and magnetic sensitivities of elliptical air hole PCF filled with MF are -0.279 dB/℃ and 0.06 dB/Oe (1 Oe1000/4π A/m), respectively. It provides reference for the design of novel high sensitivity fiber.

An all-fiber optical fiber amplifier with the maximum power output of 106.7 W is established based on a home-made distributed side-coupled cladding-pumped (DSCCP) Yb-doped fiber. The output characteristics of the three pumping schemes (i.e., forward, backward and bidirectional pumping schemes) are also investigated. It shows that the DSCCP fiber is applicable to the fiber laser systems with bidirectional pumping scheme. By comparing the performances of the three pumping schemes, it is found that the slope efficiency of the bidirectional pumping scheme is lower than those of the forward and backward pumping schemes.

A MEMS (micro-electro-mechanical system) magnetic torsion micro-mirror fiber current sensor with composite structure is proposed. The sensor part is composed of a magnetic torsion mirror and a dual-fiber collimator. The structure of MEMS magnetic torsion micro-mirror and the principle of current sensor are introduced. Analysis based on the current sensor model shows that by choosing suitable distance between the collimator and the micro-mirror, signal distortion can be avoided. When the peak-to-peak value of normalized intensity is taken as the output signal of alternating current measurement, the measurement sensitivity changes with the measured value of electric current. When the measured current approaches 0, the sensitivity also approaches 0. Thus, one linear correction processing method for normalized intensity signal is proposed. With this method, a good linear response curve is obtained, and the current measurement sensitivity is not distorted by the current change. Finally, the correctness of theoretical analysis and simulation results are testified by experiments, from which the linear response sensitivity of normalized intensity reaches around 0.034/A.

Stimulated Brillouin scattering (SBS) effect is the main factor limiting the maximum output power of the continuous single frequency fiber laser. In order to suppress SBS effect in the gain fiber, a method is proposed which can broaden Brillouin gain spectrum, reduce Brillouin gain coefficient of the gain fiber, and thus improve the output power of the fiber laser by changing the doping concentration of the gain fiber. Based on the rate equation, thermal conduction and Brillouin gain spectrum calculation models, the thermal distribution of the gain fiber, the output power of laser and Brillouin gain spectrum are simulated under the conditions of constant and gradient doping when the maximum temperatures of the gain fibers are basically the same. Results show that, compared with the conventional constant doping fibers, the designed gradient doping gain fiber can broaden Brillouin gain spectrum by 1.2 times, reduce Brillouin gain coefficient by 41% and increase the SBS threshold power by 1.7 times, which suppresses the optical SBS effect effectively. The fusion point temperature of the gain fiber is reduced, and the stability of the fiber laser is improved.

In order to detect the geometric contour errors of small parts using machine vision inspection technology, a high definition double telecentric optical lens is designed. The optical parameters are setup according to the requirements of detection. The structure analysis method for overall structural design is applied to construct the initial optical structure. The optical software Zemax is used to optimize the initial optical structure. The aspherical design is introduced to this lens, which can not only simplify the structure, but also effectively balance the system aberration and greatly improve the image quality. This structure realizes design requirements of low distortion (maximum distortion is less than one pixel), high resolution[modulation transfer function (MTF) at Nyquist frequency of 90.91 lp/mm is greater than 0.7, MTF at full field of 400 lp/mm reaches 0.15] and double telecentric system.

The two-dimensional distribution of gas concentration field under different distributions of light path is simulated using the computer simulation technology, and the connection between the distribution of light path and the reconstruction accuracy is researched. Reconstruction accuracy in different distributions of light path is compared by calculating the normalized mean absolute distance criterion, and the light path distribution of better reconstruction accuracy is got. The results show that improving the utilization rate of laser path can enhance the reconstruction accuracy in the case of less light path. And the validity of results are verified by calculating the reconstruction accuracy of the optimized light path distribution.

Due to the limitation of diffraction limit, the conventional optical microcopes are unable to obtain resolution of nanometer scale. In order to break through the diffraction limit, a new method of microscopic imaging based on random pulse coding and time-sharing multiplexing is presented. It can code and decode the indistinct image the of point spread function efficiently, and reconstruct the original image. The mathematical principle of the proposed method is expounded, and the simulation analysis in the different sparseness of coding and different image frames is carried on. The results show that the super-resolution image of the tested sample is obtained using the sparse coding and about 1000 frames image. The proposed method can break through the diffraction limit, and it is effective and suitable for the study of living cells.

The machining precisions of phase mask directly affect the performance of a stellar coronagraph imaging system. The error formula of six-level phase mask is derived. The influences on the extinction and the achromatic performance are analyzed when small errors of phase mask are induced. The numerical simulation results show that the errors of phase horizontal hight of phase mask and tilt angle variation can reduce the extinction performance for the monochromic light of specific wavelength. However, in comparison, the coronagraph extinction performance is more sensitive to the tilt angle errors. With in the scope of the broadband, considering the achromatism ability, the level height error can only affect its central wavelength, whilethe small errors of tilt angle can greatly degrade its achromatic performance.

A thickness measurement device based on low-coherent fiber-optic interferometry is proposed to solve coupling loss in thickness measurement system by using zoom lenses. According to optical fiber coupling condition and beam energy distribution，the light beam coupling efficiency influenced by the transverse size of the light beam and the curvature radius of surface is analyzed. Enhancing effect of coupling efficiency is theoretically analyzed when zoom lenses are applied to thickness measurement device. The experimental results show that the signal intensity is obviously improved via the introduction of zoom lenses and the relative measurement error of device is less than 0.05%.

The highlighted light band with a dark stripe under the collector tubes is the main optical characteristic of parabolic trough solar collectors. Based on research on the formation mechanism of light band, it is derived theoretically that the arc length of light band is related to three parameters, viz. the opening width and the focal length of parabolic trough concentrator and the diameter of collector tube. In addition, the influence of the three parameters on the arc length is different from each other. At the same time, the arc length of the dark stripe in the light band is related to the three parameters as well. After optimization, it is considered that the ratio of the focal length of paraboloid and the diameter of collector tube should be far away from 12.5.

Global rainbow technique (GRT) is an effective method for the simultaneous measurement of the size distribution and refractive index of the spray droplets. However, there are some shortcomings in the existing algorithm. An improved reversion algorithm of GRT is proposed based on the least square method and optimization process. The features are extracted from the intensity distribution of the captured global rainbow to estimate the initial value of the size distribution and refractive index of the droplets, so as to build the linear equations. The linear equations are solved by the least square method to get the particle size distribution, and global rainbow is reconstituted according to the results. The refractive index and size distribution of the droplets are optimized according to the angular deviation between the reconstructed and captured rainbows. Both numerical simulations and experiments are carried out to evaluate the feasibility of the improved algorithm. The results show that the error of the inversion result of refractive index is of the order of magnitude 10-4, and the error of the mean diameter is better than 3 μm, and the reverse grain diameter is in accordance with the true value.

The properties of model field and evanescent field are theoretically studied and simulated using finite element method, which have a certain extent effect on the sensitivity of the fiber evanescent field sensors based on eccentric core optical fiber. The distributed sensing length of the fiber evanescent field sensors is also calculated based on the Rayleigh scattering theory. The results show that in order to obtain high sensitivity in evanescent field sensing, the eccentric distance is designed to be about 8~10 μm and the refractive index of fiber coating should be low as soon as possible. The sensing length of the fiber evanescent field sensors is estimated to be 16~160 m.

The influence of curvature radius of the cavity mirrors on the performance of high power single frequency laser is investigated. When the cavity length is kept constant, both the pump power at the optimal operation point and the maximum output power decrease with the increase of curvature radius of the cavity mirrors beside the gain medium. However, if the cavity length is shorten to a certain extent, the pump power at the optimal operation point and the maximun output power can be recovered. The experimental results are consistent with the theoretical expectation.

Based on single dual drive Mach-Zehnder modulator (DDMZM), a scheme of generating wide and flat tunable optical frequency comb (OFC) is proposed. This scheme has the advantages of simple structure easy to implement, and low cost. A theoretical analysis on the principles of the scheme is conducted and simulation research is carried out with the software Optisystem 7.0. The results show that, as for the generated OFC, although the comb-line number is not big, the flatness is better, and both of its center frequency and line spacing can be tuned independently. The center frequency of the tunable light source determines that of OFC. The comb-line spacing of OFC is obtained by the generated microwave radio-frequency signal based on optical heterodyne method as driving signal of DDMZM, which is up to 150 GHz, and the effective band width is 600 GHz.

The evolution processe of laser induced plasma shielding shock wave is studied. The temporal and spatial evolution processes of the plasma and shock wave are investigated, when nanosecond laser focused on the surface of the aluminum target through the glass, using optical shadow imaging diagnostic techniques. The collision time of the shock waves increases with the distance between the glass and the aluminum target. Experimental results demonstrate that the shock waves do not interact with each other but interact with the plasma in the collision, and the shock wave front distortion or even broken will exist, the shock wave is shielded by the plasma. And the physics mechanism of plasma shielding shock wave is analyzed.

A picosecond laser with a high repetition rate of MHz is used to ablate stainless steel 304 and the surface after ablation is observed and measured by laser scanning confocal microscope (LSCM) and scanning electron microscope (SEM). The results show that the ablation rate is jointly determined by the single pulse peak fluence and the repetition rate. The ablation rate increases as the ratio of pulse peak fluence to ablation threshold increases. Better ablation quality of surfaces can be achieved under the conditions of lower peak fluence and higher repetition rate. With the increment of scanning speed, the ablation depth decreases logarithmically, and the roughness degree of ablation surface decreases first and then stabilizes. When the scanning speed is between 1.0 m/s and 1.7 m/s, the ablation rate shows no obvious change. The use of cross scanning path is beneficial for improving the surface quality after ablation.

The influences of optoelectronic feedback on the polarization bistability in a 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) resulting from continuously varying the bias currents along different paths are investigated experimentally. The results show that, typeⅠpolarization switching (PS) can be generated in a free-running 1550 nm-VCSEL through gradually increasing the bias current, while typeⅡPS emerges during the process of gradually decreasing the bias current. The bias currents of typeⅠPS and typeⅡPS point possess different value, i. e. polarization bistability (PB) appears in the free-running 1550 nm-VCSEL. After introducing positive optoelectronic feedback, the bias currents of typeⅠPS and typeⅡPS points are accordingly varied for different feedback strengths, and the width of the bistability loop shows a gradually decreasing trend with the increase of the feedback strength. After introducing negative optoelectronic feedback, the variations of the currents of typeⅠPS and typeⅡPS points are more complex with the increase of feedback strength, and the width of the bistability loop shows a generally decreasing trend with obvious fluctuation.

Ultrasonic signal can cause the SU-8 material thickness change. Based on this, a uniform thin layer thickness of the SU-8 film is plated on the cover glass, the smooth reflecting surface is coated with a layer of uniform metal silver, and then a photoacoustic sensors is made. And a set of real-time, dynamic photoacoustic imaging system is proposed based on the sensor. In this system, the photoacoustic signal of absorbent sample causes the SU-8 material thickness change on the photoacoustic detector. When the laser through the reflector of detector, the changes of thickness will modulate the phase of reflected light. The phase shift is demodulated using the optical phase contrast filter method, and the thickness variation of SU-8 is obtained. The corresponding light distribution of photoacoustic signal of samples is acquired, and the dynamic real time photoacoustic images are obtained. The generating (ultrasonic effect), modulation and demodulation (production of the sensor) of photoacoustic signals are discussed. The response characteristics of photoacoustic signals are studied experimentally by SU-8 photoacoustic detector, and the results indicate that SU-8 can detect photoacoustic signals.

Optically induced photonic lattices are periodic optical structures that can control the beam propagation, which has potential applications in all-optical exchange and optical switch etc. An optimized alternative implicit differential wave propagation method is adopted to numerically simulate the nonlinear Schrdinger equation. The propagation characteristics of a vortex beam in optically induced self-focusing square-like lattices, the influence of the lattices on the beam propagation, and the conditions under which vortex solitons are formed are studied. The results show that the vortices will decay into the fundamental solitons due to self-focusing when there is no lattice. When the lattice exists, the stable propagation of the discrete vortex solitons is related to the applied electric field, the lattice depth and the input light intensity. Off-site single-charged first-order vortices can form discrete vortex solitons that propagate stably under appropriate conditions.

A monolayer closely-packed polystyrene (PS) nanosphere is prepared as mask on p-GaN substrate in the experiment. The structures of GaN nano-pillar arrays with periodic different duty ratios are prepared by changing the diameter of nanosphere mask. The experiment results show that the photoluminescence efficiency of LED of nano-pillar arrays prepared on p-GaN substrate can be raised to 3.8 times of the reference sample after normalizing power of the laser. The three-dimensional finite difference time-domain simulation shows that photoluminescence efficiency is enhanced because the periodic nano structure breaks total reflection of GaN surface, and critical angle of light output of LED structure is enlarged. In addition, we can optimize the size of nano-pillar in the same period to improve photoluminescence efficiency of LED further by changeable nanosphere mask lithography. It can be explained by effective refractive index theory and film transmittance. The theoretical and calculated results are in agreement with the experimental results.

In order to solve the problem of the roundabout crossing illumination, a design method of lens with circular spots is proposed based on the theory of etendue conservation in non-imaging optics. Through the designed single lens and lens arrays, the circular spot can be obtained by simulation of TracePro software. The simulation of single lens shows that the illumination uniformity of the target surface is reduced with light source size increasing, but the efficiency keeps unchanged. The illumination uniformity of the target surface is about 86.5% and the efficiency is about 90.3% when the size of light emitting diode（LED） source is 5 mm×5 mm. For the three kinds of lens arrays, the illumination uniformities are more than 91% and efficiencies are more than 90% by setting the appropriate initial parameters. This design is in comformity with the design standards of road illumination.

Rapid measurement of phytoplankton photosynthetic parameters is important for bloom and red tide prediction as well as water ecological research. In order to solve the problem of high data sampling rate caused by narrow pulse light source when the fast repetition rate (FRR) method is applied, a phytoplankton photosynthetic parameter measurement system based on variable pulse induced fluorescence is designed. The designed system utilizes a single pulse to realize the single turnover excitation mode, and employs pulse integration to implement weak light pulse signal detection in the relaxation mode. The data sampling rate can be reduced from higher than 10 MS/s to 1 MS/s. The functional absorption cross section of photosystem II (PSII), maximum quantum yield of photochemistry in PSII, and QA- (reduced primary electron acceptor) reoxidation time constant, can be measured rapidly. The relative standard deviation of the three parameters is less than 3%.

Based on the plane wave expansion method, the band structure of a square lattice two dimensional (2D) photonic crystal (PC) with rectangular dielectric rods in the air background is studied. When the length and relative permittivity of the rectangular rods are set as 0.3633a and 11.56, respectively, a triply degenerate state is found at the center of the Brillion zone in the band structure. The triply degenerate state consists of two linear bands that generate Dirac cones and an additional flat band intersecting at the Dirac point. This 2D PC can be related to a zero index material with effective permittivity and permeability equal to zero simultaneously. The finite element method is used to simulate the transmission characteristics of electromagnetic waves in photonic crystals. The simulation results show that the phase of the electromagnetic waves at the Dirac point frequency does not change, and their transmission characteristics are the same as those in zero refractive index material. With a concave lens made of such kind of PC, a sub-wavelength focusing with 0.63 λ half-peak width of focus and a 4.12 λ focal length is realized.

Quantum key distribution, with single photon as information carrier, can theoretically provide an absolutely secure way for secret communication through the one time pad scheme of the classical security system. Through a comprehensive analysis with the Lagrange multiplier, the distribution of quantum bit error rate in the way of using only one operator in active phase compensation attack model is obtained. Based on this, the attack model measured by multiple operators is theoretically simulated. The result shows that when different operators are chosen to launch the attack, the relationship between the additional bit error rate and the bit ratio (the ratio of bit 0 and bit 1 in the final quantum key) varies, and the additional quantum bit error rate introduced by hacking is also different when the bit ratio is close to 1. This result has certain reference value to the practical security problems based on the classical mutual process.

The multimode-fiber modal interferometric sensor has been the research focus in the fiber optic sensor field in virtue of its simple structure, low cost, lightweight, high sensitivity, excellent degree of integration, and resistance to electromagnetic interference. It is widely applied to safety monitoring in large-sized architectures for measurement of such physical parameters as stress, temperature, vibration, and displacement. Early fiber optic modal interferometric sensors are mainly based on the reflective Michelson interferometer and the Mach-Zehnder interferometer. The single-mode fiber and the multimode fiber are used as the sensing fiber. Mode coupling is achieved by the fusion splicing of different fibers. Modal interferometric sensor can be used to measure refractive index, concentration and magnetic field etc. by etching the sensing fiber and coating the fiber with corresponding sensitive material. The fabrication of fiber optical modal interferometric sensor mainly depends on fiber fusion methods and fiber types, as well as the optimization of fiber physical parameters. The progress in the multimode-fiber modal interferometric sensor at home and abroad is reviewed, and the merits and drawbacks are analyzed.

The long-time running of a high power Yb-doped fiber laser will cause photodarkening, which reduces the output power of laser. Thus, the research on photodarkening in Yb-doped fiber is of great significance to the development of Yb-doped fiber laser. The latest progress of photodarkening in Yb-doped fiber is detailedly introduced in three aspects including mechanism, impact and suppression method, which provides reference for the further study of the photodarkening.

The resolution of the conventional optical microscope is limited to about half of the incident wavelength because of diffraction limit. Although the super-resolution imaging is realized in many microscopes, their widespread applications are limited due to their complicated design, limited applicable samples and stringent requirement on imaging conditions. Recent researches show that the resolving ability of conventional optical microscopes can be improved significantly when the transparent dielectric microspheres with diameters from several to decades of microns are added on the sample surface, and thus super-resolution imaging with white light illumination is realized. The microspheres can keep their resolving ability when coupled with other types of microscopes. The microsphere nanoscope offers a simple direct way to realize real-time super-resolution imaging for nano-structures and biological samples. We review the research progress in the microsphere nanoscope at home and abroad with our own achievements combined.

Black silicon is widely used in making solar cells and infrared detectors due to its excellent optical absorption property. The detectors made by black silicon have the advantages of high spectral responsivity, wide range and flat spectral response. The research progress of black silicon infrared detectors at home and aboard is introduced, and the involved fabrication methods of black silicon are introduced including femtosecond laser irradiation, picosecond laser irradiation, wet etching, and ion implantation combined with excimer nanosecond laser irradiation. The problems in making black silicon infrared detectors are discussed, including the tremendous decrease of absorption efficiency, during annealing and the difficulty in making electrode on black silicon surface as well as the inferior characteristic of carrier transverse transporting. At the same time, the current solutions of these problems are summarized. The existing problems are analyzed, and the trends and prospect in the developing application of black silicon infrared detectors are also predicted.

As a special kind of fiber Bragg gratings, tilted fiber Bragg gratings (TFBG) have some good features, which are of great application value in optical filtering, fiber sensors, optical fiber communication, etc. In this paper, the mode coupling mechanism of TFBG is briefly introduced. Then a general review on the theories, fabrications and applications of TFBG is presented. The TFBG is a potential technique to suppress stimulated Raman scattering in high power fiber laser systems based on its filtering characteristics.