Since its birth, the nanograting structure in glass induced by a single femtosecond laser has attracted extensive attention and becomes a hot topic in the field of femtosecond laser interaction with matter, which has gained major progress in both basic research and application exploration after more than ten years of development. The research status of femtosecond laser induced self-organized nanogratings in glass is reviewed. As for the major influence parameters, formation mechanism, application exploration, and other aspects of nanogratings, the main progress in recent five years is specifically introduced. In addition, as for this topic, the critical issues at present are commented and the future development is prospected.

Femtosecond laser has been widely used in elaborate processing and micro/nano manufacturing field due to its ultrashort pulse width and extremely high peak intensity. At present, the fabrication of flexible devices by laser direct writing has attracted much attention. The following four research directions based on laser direct writing technology are reviewed: 1) laser direct writing microball lens for wide angle imaging; 2) laser fabrication of Au/reduced graphene oxide micro supercapacitor; 3) preparation of multilayer supercapacitor on polyimide substrate; 4) laser fabrication of capacitive biosensor. Relevant research work of our group is introduced at the same time. This paper provides a reference for the research, application and future direction of the micro/nano device fabrication by laser direct writing.

The research status of dispersion, alignment and assembly of carbon nanotubes (CNTs)/polymer composite material is reviewed. In addition, the assembly and alignment in the arbitrary 3D space of multi-wall CNTs (MWNTs) are realized via the laser direct writing technique based on two-photon polymerization (TPP). The addition of thiol molecules makes the dispersion and doping concentration of CNTs in MWCNTs/polymer composites improved, and the optical and mechanical performances enhanced, and the fabrication of 3D CNTs functional devices realized. The research results indicate that, under the combination of TPP laser direct writing technique and thermal annealing process, the precise control of the orientation and placement of CNTs clusters can be achieved.

Fabrication and application of micro-optical components are attracting broad attention in recent years. Micro-optical components have important applications in the fields of optical fiber communication, information, aerospace, biomedicine, laser technology, and optical computing, because they can achieve function that the ordinary optical components are hard to realize for their small size, light weight, low cost and ease to integrate with micro-electromechanical systems. Femtosecond laser can achieve micro/nano fabrication with ultra-high precision due to their ultrashort pulse width and ultrahigh pick power, which breaks the diffraction limit easily. Femtosecond laser can process almost any materials flexibly with arbitrary complex structures, which enriches the fabrication of micro-optical components. Further, the femtosecond laser processing can be carried out on the existing structure or system, which greatly expands the application of micro-optical components. A brief overview of the advantage and common fabrication methods of micro-optical components is given and the femtosecond laser processing technology briefly is summarized. Then, the experimental and applied research of micro-optical components fabricated with femtosecond laser are reviewed. Finally, some prospects and forecasts about the research of micro-optical components are given.

Laser microfabrication has unique advantages in medical devices, especially for biomedical compatible materials, due to its properties of ultrashort pulses and high precision. Some new investigations are summarized, such as laser micromachining of biomaterial surface microstructure, laser microfabrication of medical devices and stents as well as rapid prototyping of three-dimensional biomaterial scaffold. It points out the disadvantages of current laser microfabrication technologies in biomedical field and proposes suggestions for further development.

Beams with double-helix shaped focal spots are obtained by equally weighted linear superposition of Laguerre-Gauss(LG)beams. Five modes along the line with a slope of 3 in the modal plane are chosen for superposition, which increases the number of spirals in the double-helix focal spot, enhances the chirality, and broadens spectral bandwidth. However, side lobes simultaneously enhance, which results in severe adhesion of two main lobes during the process of two-photon polymerization. One optimization algorithm with the combination of double-Gaussian function and step function under the tight focusing condition is proposed here which can obviously suppress the side lobes and realize a phase-only mask. This phase-only mask is loaded on the spatial light modulator and a double-helix microstructure with both non-adhesion and more spirals is finally fabricated with a single exposure.

We carried out a research on the precision of femtosecond laser induced silver nanowiring and its application in micro-device integration. The precision of the silver nanowires could be controlled by the laser power, exposure duration, surfactant type and their concentrations in the precursor solution. An experiment of interaction between femtosecond laser and Ag precursor solution was conducted. Experimental results show that silver nanowires with high precision (140 nm) could be prepared, which was confirmed by means of scanning electron microscope. Meanwhile, a micro-pattern of silver nanowires and a micro-catalytic-reactor were produced by femtosecond laser direct writing technique. The research may open up a new way to the designable patterning of silver microstructures toward flexible fabrication and integration of silver functional devices.

To address the problems of relative movement control of laser and samples and the focus energy control in the femtosecond laser micro-nanofabrication technologies, a new method, which is based on dynamically loading computer-generated holograms through a liquid crystal-on-silicon spatial light modulator, is proposed to simultaneously control the position and energy of the focal spot. By loading superposed blazed grating holograms, two-dimensional structure fabrication can be achieved by single point scanning without platform movement. Further, by controlling the active zone in the hologram, the incident beam energy can be modulated, and thus the lattice morphology can be controlled. Taking advantages of this method, we have fabricated ring structures successfully, and got the corresponding effect under an optical microscope. This proves that the method is feasible in the field of femtosecond laser micro-nanofabrication.

Yb-doped photonic crystal fiber femtosecond laser amplification system is used as the processing light source, and nanostructures are produced from copper thin films by laser induced forward transfer (LIFT) technique. Metal films composed of different nanostructures can be obtained by controlling the parameters of femtosecond laser source. Nanoclusters are produced under lower power, and their sizes grow bigger with the power increasing. Then nanowire structures appear when the power rises to a certain level. Some physical processes of the interaction between femtosecond laser and materials are analyzed by experiments. On the basis of the mechanisms, experimental results of copper thin films with three different thicknesses of 20, 40, 200 nm are compared under the same experimental conditions. According to the results, optimum parameters are obtained for the generation of nanoclusters and nanowire structures.

We report the fabrication of two-dimensional periodic composite micro- and nano-structures consisting of subwavelength ripples and nanowires on tungsten surface by adjusting femtosecond laser pulse number with either linear or azimuthal polarization in repetitive irradiation. The experiment results show that both the spatial periodicity and ridge width of the subwavelength ripples tend to decrease with the increase of the overlapped pulse number. Femtosecond laser pulses induced metallic nanowires on the sample surface gradually disappear when the overlapped pulse number of femtosecond laser with both polarization states increases. The structured area of the sample surface gradually increases with the increase of overlapped laser pulses number, but the obtained area appears to be saturated when the pulse number reaches up to 150.

The internal defects are induced by irradiating pure silica glass with different hydroxyl concentrations by femtosecond laser pulses. Influences of hydroxyl concentration, laser pulse width and laser power on the type and concentration of defects are systematically investigated. The micro fluorescence spectra, absorption and emission spectra of silica glass show that the tested samples produce three kinds of defects including non-bridging oxygen hole center (NBOHC), non-relaxation oxygen deficient center [ODC(Ⅱ)]and E′ center. ODC(Ⅱ) defect is easier to be induced when the hydroxyl concentration is lower, while NBOHC defect is easier to be induced when the hydroxyl concentration is higher. The obvious red fluorescence (650 nm) under ultraviolet lamp excitation (254 nm) in irradiated glass with high OH content can be observed. It is found that red fluorescence (650 nm) intensity closely depends on the laser pulse width and laser power, to be specific, it increases at first and then decreases with the increase of laser pulse width, and increases at first and then tends to slow with the increase of laser power.

The tiny differences of physical performance and chemical performance among monocrystal silicons with various crystal surfaces have great effect on micronano processing results, and the behavior characteristics of different monocrystal silicon surfaces under femtosecond laser irradiation are studied by the electron backscatter diffraction (EBSD) technology. The results indicate that the amorphous region and the etching region are formed on the (111) surface of monocrystal silicon when the energy densities of femtosecond lasers are under and above the damage threshold. However, the etching region is formed only on the (111) surface of monocrystal silicon irradiated by femtosecond lasers with different energies. The femtosecond laser is widely used in micronano processing. The study of the behavior characteristics of different crystal surfaces irradiated by femtosecond laser is beneficial to fabricating novel micronano devices.

To avoid the defects of conventional methods to manufacture gas film holes for gas turbine blades, femtosecond laser is applied to trepanning supper-alloy with thermal barrier coating, and holes without crack extension, attached debris, and recast layer are obtained. Combined with the material removal mechanism of femtosecond laser drilling, it can be obtained through analysis that the taper of holes is larger under trepanning with same angular speed. In addition, the process of material removal is considered as adiabatic cooling, that is, thers is nearly no heat exchange between processing material and the surrounding material. Therefore, the process of substrate material melting and re-solidifying to form a recast layer does not happen. However, black attachments are found around the hole entrance, and as the cutting times increase, they gradually cover the entire part of the entrance edge. Nanoparticles with elements nickel, zirconium and oxygen are collected during processing, which proves that the removed material leaves the substrate quickly in nanoparticles through the phase explosion mechanism. This explains why no attached debris is found on the pore wall. Compared with low-speed single layer cutting, high-speed multilayer cutting is much more efficient.

Titanium alloy has excellent comprehensive properties, and it is widely used in clinical applications. Studies show that it is helpful to improve the biocompatibility of titanium alloy implant by introducing specific textures to the surface. A pulsed picosecond laser emitting at 1064 nm was used to process titanium alloy (Ti-6Al-4V), and the biocompatibility of laser textures was verified. Orthogonal experiments were designed, and the surface morphology of the samples was analyzed by using scanning electron microscope, scanning probe microscope and confocal microscope. The relationship between surface morphology of titanium alloy and picosecond laser processing parameters was investigated in order to determine the optimal process parameters. Meanwhile, cell culture and actin cytoskeleton staining were conducted. The experiments show that the picosecond laser surface texturing plays a role in promoting and guiding growth of cells.

The rear surface ablation damage phenomenon is investigated in the process of picosecond laser ablation cutting of K9 glass. The ablation qualities on the front and rear surfaces are compared, and the influences of laser fluence, scanning times and scanning speed, etc., on the rear surface damage are studied. Based on the ablation morphology and quality on the rear surface, the laser fluence, scanning speed, and other parameters at the cutting condition of single line and single pass are optimized. The ablation and damage mechanism of rear surfaces is discussed and the potential approach to suppress the rear surface damage is proposed. Experimental results show that, when the laser beam is focused on the front surface and the ablation cutting occurs, the rear surface is seriously ablated and damaged, and the morphology and ablation rule on rear surface are significantly different from those on front surface.

An all-fiber ultrafast laser system was demonstrated by utilizing polarization-maintaining fibers and polarization-maintaining fiber components. The central wavelength of the system was 1064 nm. A passively mode-locked fiber laser, a pulse selector, and subsequent fiber amplifiers realized micro joule pulse energy with tunable repetition rate and alterable pulse number in a single pulse string. In addition, an application of this laser system was carried out on dicing of 110 μm thick sapphire wafer. Experimental results showed that the pulse energy, the pulse number in a single pulse string, and the beam quality significantly affected the ablation performance. Up to 99.58% yield rate was achieved by using 100 kHz repetition rate, 7 pulses in a pulse string, 97% beam circularity, 0.37 W average power, and 600 mm/s dicing speed.

The possibility of using nanosecond pulsed laser ablation of aluminium matrix composite reinforced with SiC ceramic particles under the assistance of high pressure gas is investigated. The results indicate that the ablation depth increases with the increase of pulse energy. It is very difficult to find the isolate SiC particle on the ablated surface due to the occurrence of complicated metallurgical reaction during the ablation process. The Al, Si, C, and O elements within the re-solidified layers have a relatively uniform distribution, and the thickness and surface roughness of the re-solidified layers increase with the increase of pulse energy, which presents a tendency of saturation. The mechanical action of high pressure co-axial gas is the key mechanism of material removal.

The nanosecond-scale laser pulse generation technology with high adjustment precision for laser fusion driver is investigated. By employing a laser diode with central wavelength of 980 nm as reference light and controlling the bias point automatically, an amplitude modulator operating in the pulse mode is implemented. All-fiber laser pulse generation device based on the master oscillator power amplifier structure is established by using high speed electro-optic modulation technology and two-level amplitude modulators simultaneously. The initial precise pulse shaping of input single frequency continuous laser is done by the first amplitude modulator, and the secondary pulse shaping and decreasing noise of temporal shaped pulses are done by the other one. The experimental results show that the device can generate arbitrary shaped pulses with contrast ratio larger than 20001 and pulse duration of 0.1~50.0 ns, which satisfies the requirement of powerful control capability of laser pulse generation device.

A highly-sensitive pharmacokinetic diffuse fluorescence tomographic system is proposed to achieve the indocyanine green (ICG) pharmacokinetic imaging of small animals. The system employs a photon-counting technique based on discrete optical fiber measurement of computed tomography scanning mode in the computer tomography, which effectively improves spatial sampling resolution of the system on the premise of high sensitivity and wide dynamic measurement range. Meanwhile, it adopts serial-parallel mixed measurement mode through switching four photomultiplier tube photon-counting channels by optical switch to obtain a balance between time resolution of measurement and cost-effectiveness of the system. We investigate the principle validity of the system by designing a dynamic phantom that can simulate ICG metabolism in living tissue. In addition, combined with the algorithm of fluorescent agent pharmacokinetic imaging developed by our laboratory, the reconstruction of ICG metabolic velocity is realized. Experimental results show that the proposed system has high sensitivity, spatial resolution and quantitativeness.

Tissue optical clearing technique combined with two-photon microscopy (TPM) can improve the imaging depth of biological samples. However, the refractive index mismatch between objective medium and optical clearing agent will cause spherical aberration which degrades the fluorescence intensity and axial resolution. To solve this problem, we analyzed the effect of SA at the focus, and built a spherical aberration compensation model based on objective characteristics (numerical aperture and immersion media), the imaging depth and the sample refractive index. Then, we corrected the spherical aberration by incorporating a spatial light modulator into the TPM system. The TPM images of fluorescent bead phantom and optical clearing brain tissues show considerable improvement of fluorescence intensity and axial resolution. The proposed correction process is simple and fast since it does not require repeated imaging. More importantly, it is suitable for different objectives and optical clearing agents.

Based on the traditional multi-wavelength iterative algorithm, we introduce the angular spectrum transmission theory and the gradient acceleration function, and present a fast convergent phase restoration iterative algorithm, namely, the multi-wavelength gradient acceleration phase retrieval iterative algorithm. The algorithm uses the light field intensity information detected at a fixed position when the light sources with different wavelengths go through the same light path. Through iterative approximation and by introducing the gradient acceleration function in the iterative process, the convergence speed is improved, and the input phase information is recovered. The simulation model is built, the initial iteration value is selected randomly, the input field for a known phase distribution is recovered, and the result is compared with that of the traditional multi-wavelength iteration algorithm. The relative root mean square value, which represents the phase plane reconstruction accuracy of the algorithm, achieves 10-3 orders of magnitude. Convergence rate is increased by more than two times. In the contrast experiments, multiple sets of light sources with different wavelength number within 635 nm to 785 nm are selected. The results show the method has good fast convergence and high precision phase retrieval ability when the wavelength number is 7 and 8.

Thermal wavefront distortion in the gas cooled Nd:Glass laser amplifier based on edge heating is analyzed theoretically. Temperature distribution and thermal wavefront distortion under different heating temperatures of the Nd:Glass are simulated numerically and verified by an experiment. The results show that the numerical simulation is in good agreement with the experimental results. Thermal wavefront distortion decreases as the heating edge temperature increases when the heat deposition is 0.6 W/cm3, but starts increasing when the edge temperature is higher than 90 ℃. Optimal design of the edge heating structure and heating temperature can suppress the thermal wavefront distortion effectively in the gas cooled Nd:Glass laser amplifier.

An approach for wavelength tuning of Stokes optical pulse with high speed and wide range for coherent anti-Stokes Raman scattering (CARS) excitation source is presented based on the liquid crystal phase retardance. Influences of the photonic crystal fiber (PCF) length and optical pulse peak power on the frequency shift resulting from the soliton self-frequency shift (SSFS) are analyzed through the numerical simulation. Result shows that when an optical pulse with peak power 2.7 kW is launched into a 2 m PCF, the detectable wavenumber is 3509 cm-1. A fast wavelength tuning module is constructed with a liquid crystal variable retarder, and then the experiment setup is established. Experimental results show that the response time of wavelength switching can reach 0.165 ms. Tuning range of the central wavelength of the first order soliton is from 807 nm to 1064 nm when the optical pulse peak power with a range from 0.108 kW to 2.517 kW is launched into a 1.98 m PCF, and the theoretical detectable wavenumber will range from 432 cm-1 to 3422 cm-1.

The thermal effect of sub-THz microchip dual frequency lasers (DFL) based on Nd:YVO4 crystals and its influence on the frequency difference of laser output signals are experimentally studied. In the experiment, the frequency difference tuning of laser signals is realized by tuning the DFL temperature. The experimental results indicate that, within a certain temperature range, the frequency difference of DFL signals linearly increases with the increment of temperature. Based on this point, one can realize the temperature tuning of frequency difference.

A widely tunable distributed feedback (DFB) semiconductor laser with constant power and narrow linewidth is fabricated. The laser chip is based on the asymmetric phase-shifted DFB structure, which can effectively narrow the bandwidth of the output. By precisely controlling the temperature and driving current, the dynamic characteristic of internal carriers and the refractive index of the material can be controlled effectively, so wide-band tuning wavelength and constant output power are obtained. The wavelength tuning range is over 3.5 nm, the laser power is 7.4 mW, the linewidth is about 220 kHz and the side mode suppression radio is 52.7 dB. This laser has wide application prospects for tunable diode laser absorption spectroscopy (TDLAS).

Based on the speckle suppression theory of the superimposed statistically independent speckle image, a mask with N apertures is designed. It is placed in the pupil plane of the imaging lens. Required conditions of producing the statistically independent speckle images are studied theoretically. In the simplified optical system, diffuser and the detection plane of the CCD are placed on the conjugate imaging planes of the lens, respectively. The effects of the center spacing between the adjacent apertures and the single aperture diameter on the formation of statistically independent speckle image are experimentally analyzed. Diameter of the single aperture has an effect on the speckle particle size. Without considering the impact of the experimental apparatus on the measured accuracy, the experimental results agree with the theoretical analysis.

One dual-pumped tunable optical parametric oscillator (OPO) is designed. With a 1.065 μm single-frequency pulsed fiber laser pumping the periodically poled domain MgO-doped lithium niobate (MgO:PPLN) and a reflective volume Bragg grating narrowing the oscillation signal linewidth, the idler signal linewidth is reduced from 38 nm at free oscillation to 0.42 nm, the oscillation threshold is reduced to 6.7 W, and the mid-infrared laser output with a high conversion efficiency is realized. By adjusting the temperature and angle of the volume grating, a 230 GHz tunable output of idler light is realized and the beam quality factors in the horizontal and vertical directions are 1.8 and 1.9 respectively when the output power of idler light is 2.5 W.

The surface flaws and internal knots in a film of high power laser lens are experimentally measured by using a near field micro-image method, and their formation mechanisms are analyzed as well. The evanescent waves radiated by a conic tip at a 100 nm diameter interact with the defects embedded in the films. After the evanescent waves are converted into radiation waves, they are collected by the objective lens and imaged point by point in the far field. Atomic force microscopy (AFM) images and scanning near-field optical microscopy (SNOM) images on the surface of the thin film are obtained synchronously, so as to visually identify the physical mechanisms of the defects formation. The results show that the surface flaw and the internal knot in thin film are accurately identified at the same time in effective interacting areas of evanescent wave. By comparing AFM result with SNOM result, we find that the surface flaw of substrate accumulates the residual stress in the processing of coating, which results in a layered cracking on the surface of film. The crosswise profile scale of single minimum flaw is 165 nm, which is beyond experimental detection precision of traditional far field detection. In addition, the high hot spot in SNOM graph shows that refractive index of knots exist in the thin film is higher than that in substrate.

In order to measure optical element surface defects accurately, a method of optical element surface defect measurement based on the multispectral technique is presented. Incident light sources with different wavelengths are used to illuminate optical element surface uniformly, and defects images are captured by a dark field microscopic imaging system for every wavelength. The multispectral optical element surface defect measurement system is developed. The experiments to detect optical element surface defects and standard test samples are performed under illumination of light with different wavelengths (365, 405, 436, 486, and 550 nm) and white light. The experimental results show that compared with the traditional measurement technology with white light, significant improvement on the measurement performance of optical element surface defects is observed by using the multispectral measurement technique where the wavelength of incident light can be selected according to the material characteristic of tested object. Furthermore, the defect measurement accuracy is improved and many defects which cannot be detected with the traditional method are also obtained.

Spatial light modulator (SLM) is an alternative product as it can change the distribution of amplitude, phase and polarization state under the control of the electric signals. In recent years, SLM is used in aspheric testing in place of the computer generated holography (CGH) plate. However, SLM pixel pitch is around 3.5~20 μm, which is much larger than the CGH plate etching resolution and the phase modulation is discrete, error existing with ideal continuous phase modulation and causing detection accuracy reduction. So it is necessary to consider the influence of SLM pixel pitch on detection accuracy so as to choose SLM with proper pixel pitch. Wave-front reconstructed by SLM and spread to the measured surface process is simulated based on Fresnel diffraction theory and fast Fourier transform algorithm. And the relationship between the reference wave-front precision and SLM pixel pitch is analyzed. Several sets of wave-front are computed and the error distribution is analyzed. The conclusion is that the SLM generation compensation wave-front is related to the maximum frequency presented by SLM pixel pitch, and it is necessary to keep the maximum frequency presented by SLM pixel pitch above the compensation wave-front maximum frequency range.

In the large inversion range, wavelet-regularization inversion method (WRIM) is an effective method to improve the inversion accuracy of dynamic light scattering (DLS) data. However, the inversion accuracy of WRIM is still low for the strong noise and bimodal particles data. Based on WRIM, combined with the advantages of the traditional single scale Tikhonov and Truncated singular value decomposition (TSVD) regularization in DLS inversion, the multi-scale Tikhonov-TSVD-WRIM (TTWRIM) used for the DLS data is proposed. In this method, Tikhonov is applied to the adaptive adjustment of the coarse scale inversion range, and then TSVD is applied to the fine scale inversion, and its inversion result is processed by cubical smoothing algorithm with five-point approximation. Under three kinds of noise levels with 0.001, 0.005 and 0.01, the simulated data are inverted by Tikhonov, TSVD, WRIM and TTWRIM, respectively. The results show that TTWRIM has a high accuracy, strong anti-interference ability and bimodal resolution. Finally, the inversions of the measured particles also verify the conclusions of the simulated data. In the inversion range of ［1 nm, 2000 nm］, the peak value error of TTWRIM for 300 nm unimodal and 100~500 nm bimodal measured particles are 0.18% and 2.81%, respectively.

To improve the location accuracy of two-dimensional stage, a profile online detection method for two-dimensional stage x axis mirror is proposed. Without the y axis mirror, the quadratic differential information of the stage x axis mirror is detected by the three-path laser interferometer. The quadratic integral is conducted for the obtained data to obtain the accurate profile of stage mirror. The influence of zero error on the profile deviation detection for stage mirror is analyzed and a corresponding calibration scheme is proposed. Theoretical analysis and experimental verification are conducted for the proposed method. The results show that the accuracy of detection repeatability is better than 2.6521 nm by the proposed method, the correctness of the profile deviation detection for stage mirror is verified, and the real-time compensation for the profile deviation of the stage x axis mirror is achieved.

A method for single-shot detection of ultrashort terahertz (THz) pulse based on wavelength coding is proposed. This method combines the new crossed and balanced electro-optic sampling technology and the wavelength coding technology, which has the advantages of both of them: it realizes single-shot real-time measurement for ultrafast THz pulse with high modulation depth and high signal-noise ratio. In order to achieve single-shot measurement, linear chirped laser pulses are used as the probe laser to map the temporal modulation of THz wave to the frequency domain, and the information of which is singly-acquired by spectrometers. In the aspect of electro-optic sampling technique, instead of the traditional wavelength coding single-shot measurement method, we use a novel crossed and balanced method. By setting two optical paths with a pair of equal and opposite static bias phases, the symmetrical push-pull modulation is achieved. The detecting linearity and modulation depth near 0° optical bias can be improved effectively, and the dynamical noise is suppressed.

Large field of view airborne down-looking synthetic aperture imaging ladar with sine phase modulation is reported. The high resolution and high quality synthetic aperture imaging is realized at target distance of 3.8 km outdoors. Then the airborne down-looking synthetic aperture imaging ladar is used for flight demonstration. The height of the flight is 3 km. High quality and large field of view is achieved. The field of view is enhanced by over an order of magnitude, which is up to 4.8 mrad.

The nonlinearity introduced by the detector of atmospheric vertical sounder (AVS) is analyzed. The comparison between the ideal interferometric data and the simulated interferometric data with quadratic nonlinearity is conducted, and the influence of quadratic nonlinearity on spectrum is illuminated. The correction to quadratic nonlinearity in the practically acquired interferometric data is performed and the corrected data are adopted to the radiation calibration of AVS. The experimental results indicate that the goodness-of-fit of calibration curves after data correction is approximately increased by 0.3%. The data after correction are more accurate than before in the two-point calibration on stars.

In order to develop both cheap and stable ultra-broadband light sources, the output spectral characteristics of ultra-broadband light source based on Bismuth-Erbium co-doped fiber (BEDF) are investigated. With the 830 nm lasers as pump, the output spectrum covers the whole O-, E-, S-, C-, L-bands and the full width at half maximum (FWHM) reaches 525 nm. With the application of BEDF ultra-broadband light source in wavelength division multiplexing fiber Bragg grating (FBG) sensing system, the strain sensing at O band and C band is realized. Experimental results indicate that the application of BEDF ultra-broadband light sources to large-scale FBG network can greatly increase the multiplexing capacity of the sensing system.