Servo controller is a fundamental component of the optical storage system. Processing the signal error between optical pick-up head (OPU) present position observed by the photo detector and the next position instruction, the controller generates a control signal which drives the motors in OPU. A new servo controller based on the sliding-mode variable structure control theory is researched. By means of building a physical model of the objective, the servo controller develops the state-space functions. A corresponding sliding-mode switching surface and the reaching law are also designed, and the inner-loop controller and outer-loop controller are finally designed. Compared with the classic controller based on phase correction theory, the simulation results show smaller overshoot and set time of the step response, which proves better response and robustness of the controller by increasing limited resource consumption.

A photoelectronic trigger module with low time jitter and fast rise time is presented which is used to reduce the influence of electrical interference on trigger signal in the high-power laser system. It is made up of a transmitter and a receiver which are connected with each other by an optical fiber. Since the trigger signal is transmitted from the transmitter to the receiver in the form of light, it will not be affected by electrical interference during its transmission. This photoelectronic trigger module is able to provide an electrical pulse with amplitude of 4 V whose rise time is 4.8 ns. The peak-to-peak value of additional time jitter of trigger signal resulting from this trigger module is 317 ps which meets the requirements of high-power laser systems.

In dioptric media, due to the refraction of probe light in the sample and the mismatch of the optical distance with the actual distance, a major impediment to the use of optical coherence tomography (OCT) is its image distortions. This paper describes ray trace method of geometrical optics algorithm for numerical correction of the unavoidable image distortions in the raw image obtained by fiber based spectral domain OCT system, and theoretically deduces the mapping from the raw image of dioptric media to its actual structure. Experimentally, this method is adopted to correct the image of the glass tube and the anterior segment of human eye. The reconstructed image of the glass tube is coincident with the actual structure, and the measured physiological parameters of the human eye, such as cornea thickness, anterior chamber depth and width, pupil width, curvature radius of front and rear surface of cornea, and curvature radius of front surface of lens, are within the reference ranges given by the model one. The method enables OCT system to be applied to dioptric media containing multiple refraction interfaces, including the imaging of complicated optical system consisting of battery of lenses.

The seedlings of wheat (Jinmai No.8) are exposed to He-Ne laser irradiation (5 mW/mm2) and enhanced UV-B radiation [10.08 kJ/(m2·d)], the polyacrylamide gel electrophoresis (PAGE) is used to analyze the patterns of peroxidase (POD), catalase (CAT), esterase (EST), adenosine triphosphatase (ATPase), and malate dehydrogenase (MDH). The results have shown that two new bands of POD zymogram appeare under enhanced UV-B radiation, but the activities of the total POD isoenzymes decrease. However, there is no difference among isoenzyme bands of CAT, EST, ATPase, and MDH, but the activity of the isoenzymes decreases obviously. Our study find that the gene expression and activities of plant are weakened by UV-B radiation, but the ability of plant stress resistance is enhanced by He-Ne laser irradiation.

Dynamic and quantiative observing on the biological samples is important for life and biological sciences research. A digital holographic microscopy for long-term quantitative phase-contrast imaging of living cells is proposed. At the condition that biological cells for microscopic observation are usually in semi-enclosed environment actually, the optical configuration of digital holographic microscopy is designed and optimized by using free-space-fiber hybrid optical structure. Considering the additional phase aberration induced by liquid culture medium in long-term observation, the system aberrations are numerically corrected at the hologram plan and image plan, in order to obtain high quality phase contrast images. The living samples of MC3T3-E1 and MLO-Y4 cells are investigated by long-term microscopic observation, and the experimental results are given to confirm the proposed method.

Based on the optical system using a monochrome charge coupled device (CCD) to record digital color hologram and diffraction’s numerical calculation theory, the common algorithms for digital color holographic wavefront reconstruction is reviewed comprehensively, and an important improvement on an algorithm applied only to static physical detection is made. The improvement not only eliminates the frequency spectrum aliasing effect to the reconstructed wavefield, but also lets the algorithm appropriate for dynamic physical detection of real-time digital holography. Finally, the research work is promoted in the optical system, which using a color CCD to record digital color hologram, and gives an example of reconstructed object color image under illumination of three color lights.

In order to realize the high power CO2 laser welding of 6061-T6 aluminum alloy sheet under high travel speed, filler wire ER4043 and ER5356 are selected for welding. In the experiments, welding hot cracking sensitivity is analyzed by use of fishbone samples, and optical microscope, scanning electron microscope, micro-hardness test and mechanical property test are applied to analyze the microstructure and properties of the joints. Results indicate that compared with filling wire ER5356, the hot crack sensibility of the joint welded with wire ER4043 is lower, and a maximal welding speed of 6 m/min can be reached. The weld contains columnar grains, equiaxes grains, and some dendrites grains. The weld has a micro-hardness of joint with ER4043 of 60~80 HV, a tensile strength of 240~262 MPa and a good bending property.

Nd:YAG pulse laser is used to weld 0.1 mm+0.8 mm+0.1 mm double-sided ultra-thin stainless steel clad plate with high chromium-nickel alloy powders as filling materials. The microstructure, tensile strength, micro hardness of welded joints, and corrosion resistance of welding surface are studied. The results show that it has good welding appearance, little deformation, non-defect, and the connecting among weld metal, stainless steel layer and the base are fine; weld center is small equiaxed of the grain orientation without regularity, and other regional is columnar crystal, barely seeing the heat affected zone (HAZ), and weld microstructure is austenite+a little ferritic+a little martensite; tensile strength of welded joint has reached 92% of the base metal, and elongatiion is 25% of base metal; the micro hardness of weld zone has been significantly improved than the base metal; electrochemical corrosion of the weld surface is similar to the composite layer of the base metal.

Experimental results for the stimulated Brillouin scattering (SBS) in the single-frequency, single-mode, linearly polarized ytterbium-doped fiber amplifier are reported. The fiber amplifier configuration comprises of two-stage master oscillator power amplifier with co-propagating signal and pump light. The evolution of SBS spectra is investigated in the experiments. Multiorder Stokes and anti-Stokes scattering can be observed in the forward and backward directions of the fiber amplifier, which generate through cascaded SBS and four-wave mixing process.

An all-fiber pulsed laser with narrow line width is introduced. The fiber laser consists of a pulsed fiber laser seed and a narrow line width abstraction device. The all-fiber pulsed laser seed is based on a semiconductor saturable absorber mirror (SESAM) with a 3-nm line width. Including an isolator, a coupler and a fiber Bragg grating the narrow line width abstraction device extracts narrow line width optical pulses from seed laser′s optical pulses and produces optical pulses with a 0.1-nm line width. The all-fiber, easy using, simple configuration, pulsed fiber laser can not only output narrow line width optical pulses, but also output the wide line width optical pulses from the pulsed fiber laser seed simultaneously, which greatly broadens the applications of the pulsed fiber lasers.

Cavity dumping is an effective technique for generating Q-switched laser pulses of relatively large energy and extremely short time duration, and the width of Q-switched pulses is primarily a function of the oscillator cavity length. The solid state lateral semi-insulating GaAs photoconductive semiconductor switch (PCSS) has the unique ability to handle high power at very fast response time with very little timing jitter. A novel and effective technique of cavity dumping laser for generating short Q-switched laser pulses with a GaAs PCSS is presented. In a flashlamp pumped Nd:YAG laser with 20 cm long stable resonator, 1.7 ns short laser pulses have been obtained, and the pulse to pulse duration instability is less than 7% and energy instability is less than 3%.

With the help of gain guiding effect, the quality of the beam which emitted from master oscillator power amplifier (MOPA) laser system can be improved without any compensations. Considering thermal effect, gain guiding effect and gain saturation effect comprehensively, a novel model for laser amplifier in MOPA system is developed and numerically caculated. The simulation result approximately agrees with the recently reported experimental counterpart. Moreover, the simulation result reveals that fill factor and pump power are two key aspects influencing the final beam quality of the MOPA system. Besides, the thermal effect and gain guiding effect are the underlying reasons. This analysis is meaningful for improving beam quality of laser emitted from amplifier.

The energy level diagram and absorption spectrum of TmYAP crystal are analyzed, and TmYAP laser dual-end-pumped by laser diode is presented. The wavelength of laser is 1996 nm, the output power of 2 μm continuous wave laser is 40.7 W, the corresponding optical-to-optical efficiency is up to 30.4%, and the slope efficiency is 41.1%. While the acoustic-optical (AO) Q-switch is working at the repetition rate of 10 kHz, the average power is 34.6 W, the single pulse width is 92.08 ns, the corresponding optical-to-optical efficiency is 25.9%, and the slope efficiency is 32.9%. The divergence angles are 11.6 mrad (horizontal) and 12.2 mrad (vertical), respectively.

A pair of metal heat sinks with half-round groove is always used to hold the crystal rod and dissipate heat in solid-state lasers working with round-rod material. The nonuniformly distributing of assembling pressure on the contact surfaces of the crystal rod and heat sinks makes the thermal contact conductance change along the circumference direction, and causes distribution of temperature inside the crystal rod non-axisymmetric. Two methods of using three or four heat sinks to hold the crystal rod are presented. The relationship between thermal contact conductance and assembly pressure is discussed using the truncated-Gaussian model and the plastic-deformation model. Distributions of the temperature inside the crystal are obtained by the finite element method based on the contact heat-dissipating model. The results show that the pressure and the thermal contact conductance on the side-face of the crystal change obviously along the circumference direction when using a pair of metal heat sinks, which reach maximum in the bottoms of the sink grooves and minimum in the joining directions of the surfaces of heat sinks. And the end-face temperature of the crystal changes largely along the circumference direction. In the method of using three heat sinks, the uniformity of pressure, thermal contact conductance and temperature distribution inside the crystal are greatly improved, and central value of the end-face temperature is reduced. When using four heat sinks, the result is the best and the central end-face temperature is the lowest.

This paper theoretically studies the spectral characteristics of the third harmonic generated (THG) in air by focusing a two-color-field laser, which is synthesized by a femtosecond laser pulse (ω0) and its second harmonic (2ω0). It is found that the third harmonic intensity varies as a function of the temporal delay between the fundamental and the second harmonic wave, showing a pronounced periodic modulation. This observation is explained by the interference taking place between two third harmonic sources. One is induced by the direct third harmonic generation of the fundamental wave, while the other is given rise by the four-wave mixing (FWM) of the fundamental and the second harmonic waves. In addition, the third harmonic spectra are investigated when the chirp and the self-phase modulation (SPM) of the fundamental pulse and the second harmonic are taken into account. Our results can provide some key informations for the coherent control of the third harmonic generation induced by two-color-field femtosecond laser in air.

The operating principle of digital micromirror device (DMD) is introduced. When the titled angle of a pixel mirror is set at +12\O or -12\O, it means that the optical transmissivity of this pixel is 0 or 1. With the help of the design method in binary panels, error diffusion method is used to spatially shape the 1053 nm laser pulse, which also realizes an initiative way of spatial modulation for laser pulse. Filling factor (FF) and field modulation (FM) are both factors which decide the quality of the near field laser beam and they directly affect energy availability factor of the high power laser system. In this experiment, FF increases from 33% to 65% and FM decreases from 52% to 28% after being shaped, and the size of the shaped beam is the same as we expected. At the end, the energy availability factor and mirror stability of this DMD are tested.

Laser ignition characteristics of composite modified double-base (CMDB) propellant containing hexanitrohexaazaisowurtzitane (CL-20) are researched by CO2 laser beam at different laser power densities. The effects of Al powder content and burning-rate catalysts on ignition characteristics of CL-20-CMDB propellants are discussed. The results show that the laser ignition delay time of CL-20-CMDB propellants without catalyst decreases with the increase of power density, the change of delay time becomes small at high power density and the ignition process of the propellants has hardly any variety when the heat flux is in the range of 25.5~127.0 W/cm2. The delay time and the ignition process of the propellants containing catalysts have a close dependence on the laser flux. The ignition appears in the gas phase near the propellant surface and the ignition delay time becomes longer at high power density. The content of Al powder has strong effect on the ignition delay time at the lower power density, but the action becomes weak with the laser flux increasing.

A high speed random bit generator is proposed with chaotic semiconductor laser used as the entropy source. Analogue-to-digital conversion is realized by high frequency electronic devices such as amplifier, comparator, and trigger. One bit sequence is generated and exclusive OR (XOR) operated with other different bit sequences, and data processing in computer is needless. The generator outputs a 500 Mb/s random bit sequence. The obtained sequence passed the statistic test of national institute of standards and technology (NIST, SP800-22). It has the advantages of tunable speed and compact size, which make it easy to become a production.

The effect of transverse stimulated Raman scattering (TSRS) in large-aperture KDP frequency-conversion crystals in high-power solid laser drivers operating at long pulse duration and higher energy fluence is studied. The relationship between maximum of the intensity and fluence of Stokes field produced during Raman scattering, and pulse widths of pump laser as well as crystal edge reflectivity have been presented. The result shows that the maximum intensity of scattered light always increases exponentially, regardless of pump laser duration and crystal edge reflectivity. The expression of the growth coefficient G has been presented. The maximum fluence of Stokes can be as high as 10 J/cm2 approaching the damage threshold of KDP crystals, once the growth coefficient G exceeds 25, where the risk evaluation rule of TSRS in large-aperture, high fluence KDP crystal is defined.

Based on the theory of broadband pulsed laser amplification in the homogeneously broadening medium, a numerical model for the temporal pulse shape propagating through the regenerative amplification is established by means of the short-time Fourier transform. Numerical simulation results show that decreasing the detuning between laser wavelength and the center wavelength of gain medium can decrease the FM-AM effect effectively. Increasing the energy of the seed laser pulse can also decrease the FM-AM effect and thus improve the laser beam quality.

Based on the definition of Wigner distribution function and Fresnel diffraction integral, the analytical expressions of Wigner distribution function of Lorentz beam on the waist plane, and on a plane in free space as well as on the exit reference plane of an ABCD system are derived. As their typical applications, the analytical expressions of the second-order moments of Lorentz beam are derived. The transformation rules of beam width and divergence angle of Lorentz beam are simulated and compared with those of the corresponding Gaussian beam. It is shown that Lorentz beam is a more appropriate model than Gaussian beam for diode laser beams.

The fluorescent dye Rhodamine-6G (Rh6G) and Rhodamine-B (RhB) doped DNA-CTMA thin films are prepared by spin-coating technology. The quality and optical spectra properties of Rh6G/RhB/DNA-CTMA thin films are characterized by the measurements of surface morphology, UV/vis/infrared absorption spectra and fluorescence spectra. The amplified spontaneous emission (ASE) of dye-doped DNA-CTMA thin films with different dye contents was researched experimentally by pumping of NdYAG pulse laser at wavelength of 532 nm, and is explained theoretically. The experimental results show that the narrowing phenomenon of emission spectra of Rh6G/RhB/DNA-CTMA thin films is very clear and strong. Compared with single dye doped DNA-CTMA thin films, the co-doped Rh6G/RhB/DNA-CTMA thin film is a potential candidate as an organic polymer laser material because it exhibits more wider tuning range of the ASE spectrum.

The films of polymethyl methacrylate (PMMA) doped three different azo compounds are prepared by using spin coating method. Their thicknesses, indices of refractive and UV-Vis spectra are measured. The second harmonic generation (SHG) densities are detected by real-time corona poling method. For the azobenzene molecules with different substituents, the stronger the ability of pushing (pulling) electron is, the bigger the value of SHG is. The effective frequency-doubling coefficients of the three systems are 0.748, 0.794, and 4.420 pm/V respectively. The results show that because the ability of pushing (pulling) electron is different, the first-order hyperpolarizability is different, which determines whether the molecule is poled easily or not.

To decrease the thermal stress and raise the bonding strength between substrate and bioceramic coating during laser cladding, a rare earth active bioceramic gradient coating is designed. The rare earth active gradient bioceramic coating with HA and β-TCP on TC4 allloy is prepared by using wide-band laser cladding technique. The microstructure, bioactivity and corrosion resistance of bioceramic coating are analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), simulated body fluid (SBF), and electrochemical analyzer. The experimental results show that the bioactive rare earth gradient coating which has excellent chemical metallurgy bonding at the interface consists of substrate, alloying layer and bioceramic coating. Nd2O3 plays an important role in synthesizing HA and β-TCP during wide-band laser cladding. When the mass fraction of Nd2O3 is up to 0.6%, the amount of HA+β-TCP catalyzed during wide-band laser cladding becomes the largest. When the mass fraction of Nd2O3 is 0.4%～0.6%, the corrosion resistance of bioceramic coating is the best one, and the amount of HA deposited on coating becomes the biggest, showing the best bioactivity.

A method using white-light Michelson interferometer and polarization interferometry system for measuring the retardation of wave plates (including the order of retardation) is presented. The linear polarized white-light passes through the test wave plate which introduces retardation between the o-beam and e-beam, and then they are divided by a beam splitter and reflected by two plane mirrors of the Michelson interferometer respectively. Finally three white-light interference packets are formed. For a multiple-order wave plate, the interference packets will be separated absolutely, and according to the optical path between the center packet and one of the side packets, the retardation of multiple-order wave plates can be obtained. The retardation of a lower-order wave plate and the stress of a optical glass can be calculated by using the phase variation after inserting it behind the multiple-order wave plate. The retardations of a multiple-order and zero-order wave plate are measured in experiments, whose results coincide with the ones obtained by spectroscopic method.

A real-time measurement method for retardation of eighth waveplate (EWP) independent of fast axis is presented. The collimated beam passes through the circular polarizer (CP) and the EWP to form a measuring beam. The beam is split to four diffractive beams by a two-dimensional orthogonal grating (2DOG). They are detected by a photodetector array (PA) after passing through a polarizer array (AA). The four light intensity signals can be used to achieve real-time measurement of retardation of EWP. The result is not affected by the fluctuation of the intensity of the laser. In experiments, an EWP whose nominal value of retardation is 45° with accuracy of λ/300 is measured. The mean and standard deviation of measurement results for retardation in different directions of the fast axis are 45.1° and 0.4°. They coincide with the nominal value and accuracy of the retardation, respectively. The usefulness of this method is verified.

A new method based on extended Nijboer-Zernike (ENZ) theory is proposed for testing the wavefront diffracted by a pinhole in the point diffraction interferometer (PDI). The principle of PDI is described and the phase retrieval algorithm based on ENZ is put forward. The way in expansion of the pupil function with Zernike polynomial is analysed. In the simulation experiment, deviation in the image part of the Zernike coefficients obtained from the retrieval result is less than 3×10-5, when singal-to-noise (SNR) is 55 dB with a 10-bit analog-to-digital conversion. The effect of noise and the analog-digital conversion is only involved, the result in this simulation experiment just proves that testing the wavefront diffracted by a pinhole with this method is possible.

A spectral domain optical coherence tomography(OCT) imaging system used to detect the subsurface morphologies of jades is described. It is mainly composed of Michelson interferometer and spectrograph with superluminescent diode light source of 830 nm central wavelength, the depth resolution is 10 μm , lateral resolution is 15 μm, penetration depth is 2 mm. The experimental results validate that the OCT technology can be applied in the quantificational detection of the jades′ morphologies, making use of digital image analysis technology, the precise location and size of disfigurements can be calculated, simultaneously the quantificational method to evaluate the jades′ quality is put forward. In addition, by means of comparing OCT with scanning electro microscope (SEM) detection, it demonstrates that OCT can become a new technological approach to detect subsurface morphologies of jades.

In order to solve problems in linewidth measurement for narrow linewidth laser, a method is put forward based on the phase noise of unbalanced fiber-optic interferometer. The relationship between the phase noise of an unbalanced fiber-optic interferometer with a short optical path difference (OPD) and the laser frequency jitter is analyzed, and the optical power spectrum and linewidth are obtained. The linewidth of a distributed feedback laser is tested using an interferometer with 10 m OPD. The result shows that the power spectrum is an approximate Lorentzian lineshape with 5.4 kHz linewidth, which is close to the theoretical value of the laser. The linewidth of a fiber ring laser (FRL) is tested and the result is 0.75 kHz, which is more accurate than the result of less than 1.5 kHz of the similar FRL obtained using homodyne method.

Tunable diode laser absorption spectroscopy (TDLAS)-based sensor is applied to measurement of path-integrated static temperature, H2O concentration and local velocity for incoming flow hot-firing test of air-breathing rocket engine. The measurements are achieved using time division multiplexing (TDM) system with scanned-wavelength method, which contains 1392 nm and 1395 nm distribute feedback (DFB) diode lasers. The absorption spectra of gases near 7185.597 cm-1 and 7168.437 cm-1 are obtained by modulating the two lasers alternately. The value of temperature is deduced from the ratio of two-line measured absorbances, and the water vapor concentration is deduced from the measured absorbance of one transition and the measured temperature, moreover, gas velocity is deduced from the measured Doppler-shift absorption of the two beams, which make an angle of 70\O. Therefore, the in-situ and non-intrusive measurements of parameters are applied for gas in rocket engine.

Based on the wavelength characteristic of mismatch fiber coupler, the effects of the distance d and the mismatch Δβ between the two cores, the coupling length z on its spectrum characteristics are analyzed theoretically. It is proposed that the fiber coupler can be a comb-filter when Δβ and d are very small. Δβ mainly effects the extinction ratio, d and z mainly effect the interval of the resonant peaks respectively when the two cores are matched. An all-fiber comb-filter based on twin-corn fiber coupler is experimentally fabricated by splicing a section of single mode twin-core fiber (TCF) with core center-to-center distance of 12 μm between two single mode fibers (SMFs), and the filter′s extinction ratio and insertion loss are 25 dB and 3.1 dB respectively. The interval of the resonant peaks can be changed by using TCF of different lengths, and the peak wavelength and extinction ratio are modulated by ultraviolet light of 248 nm.

In order to improve the multiplexing capacity of fiber sensing system, several sensors with overlapped spectra are always connected in series. However, crosstalk effects introduced by serial connections will lead to measurement errors, which means that crosstalk effects between sensors should be well researched. The Monte-Carlo method is introduced to analyze the system composed of several serial sensors with overlapped spectra. This method can take crosstalk effects like spectrum shadowing and arbitrary-order multiple reflections into account and calculate the reflectivity spectrum of the system. In order to verify the reliability of the Monte-Carlo method, reflectivity spectra of a system composed of two serial sensors are calculated by the analytic solution and the Monte-Carlo method, respectively. As the number of light beams set to be 5×106, the calculate error level is about 10-3. The comparison indicates that the two methods have a good agreement, approving the accuracy of the Monte-Carlo method. The reflectivity spectrum of a system composed of more than two serial sensors which have no analytic solution is also analyzed by the Monte-Carlo method.

In the design process of a novel photonic crystal 1×2 power splitter, the coupling of three parallel photonic crystal waveguides can be considered as a multimode interference system in the two-dimensional square photonic crystal. The positions of output waveguides are decided by the positions of periodic twofold image which are formed by the self-imaging effect of multimode interference.The transmission characteristics of the splitter are investigated by using the finite-difference time-domain method. The reflective losses obviously decrease by shifting a dielectric rod in the junction between the multimode waveguide and single-mode output waveguide, and microcavity is constitued, which varies and matches the mode field of the coupling zone. The results show that the transmittance of this splitter can be as high as 99.04% for λ=1.55 μm when the shifted dielectric rod is in the position of 1.85a from the junction between the multimode waveguide and single-mode output waveguide.

It has been known that tunable optical filter technology is one of the most critical techniques for wavelength-division multiplex (WDM), and the tunable optical fiber filter technique is extremely important for the development of all-optical networks and fiber-optic sensors. A new tunable band-rejection optical filter based on large core-diameter multimode optical fiber is projected. The filter is realized by a single-multi-single (SMS) mode fiber optical structure, which is composed of a multimode fiber with the cladding/core diameter of 125/105 μm and standard single mode fiber, with the end interface not welding together. Based on the multimode interference principle, the structure implementes the filtering by use of the structure sensitive to the stress. A broadband source which is amplified spontaneous emission (ASE) and an optical spectrum analyzer are used to monitor the transmission spectrum. Experimental and simulation results are given to prove the feasibility of the improved SMS structure.

Acquisition pointing tracking (APT) is the precondition for communications in atmospheric laser communication system. CCD and quadrant detector (QD) which used in APT are deeply studied for their characteristics, and five kinds of turbulence effects such as beam wander, intensity fluctuations, dispersed spot, angle of arrival fluctuation and beam spreading for tracking precision and their mathematical models are discussed. Then, simulation results of turbulence effects under various conditions are analyzed. Both theoretical analysis and experimental results show that tracking error of shape center capturing algorithms is less than that of centroid localization algorithm which combines five kinds of turbulence effects.

Single point and scan exposure experiments on ultraviolet laser inscribed type I fiber Bragg grating by focused infrared femtosecond laser are reported. The effect of femtosecond laser pulses on the grating transmission spectrum is studied especially when the pulse energy density is far lower than the fiber damage threshold. Experimental results show that the grating spectrum during irradiation shows a red shift, and the spectral structure is no longer a single transmission peak but more irregular transmission peaks. However, after stopping exposure, the resonant wavelength shows blue shift phenomemon and the transmissivity increases, which tend to be saturated with the time increasing. The grating exposure region is considered to be in a non-uniform temperature field, and the laser-induced refractive index change overlaps the original grating refractive index modulation distribution. The spectrum change during exposure and after a certain time ′s exposure is theoretically simulated and the simulation results fit well with the experimental ones.

A cladding-mode resonant specialty fiber sensor system is presented by using an intensity detection method. As a new type of fiber-optic sensor technology, the cladding-mode resonant fiber is sensitive to the measurands of the refractive index and bending. Based on the filtering transmission spectrum and narrow band distributed feedback laser, the variation of measurands can be transformed to intensity changes. In the proposed sensor system, a reference arm is added to reduce the affect of laser power fluctuation. The factors that affect the resolution are analyzed. This intensity-based all fiber demodulation technique has the advantages of low cost, simple configuration and requiring no mechanical adjustment. According to the experimental results of the refractive index sensor, a resolution of 0.0005 R.I.U. (refractive index unit) is achieved.

The switching characteristics of nonlinear optical fiber-loop mirror (NOLM) for continuous wave are different under different pumping conditions. When the pump peak power is greater than the switching threshold power, it is found that the transmitted waveform of single-pumped NOLM has the feature of inverting pump pulse peak and one transmitted pulse is generated respectively at the corresponding rising and falling edges of the original pump pulse. The double-pumped NOLM has the function of comparing pulse peak power of two input pump pulses which have the same parameters except for the power and wavelength, and output pulse power is determined by the deviation of the peak power of two pump pulses. Based on two above characteristics of NOLM, a scheme is designed for all-optically separating the pulses from the same input signal with two-level power. Numerical simulations are executed by using photonics simulation software. The results show that two-level power signal is separated successfully, and output signals are loaded to different wavelengths respectively. No pedestal is observed at the separated output higher-level power pulses. So the scheme also has the ability to eliminate pulse pedestal.

An effective linking and coupling method for single core single mode fiber (SMF) and capillary optical fiber is proposed. Two types of capillary optical fiber which have different structures are investigated. By splicing and tapering at the fusion point of single mode fiber and capillary optical fiber, an effective bi-tapered fiber coupling technique is implemented. The coupling mechanism and the transmission properties are studied and compared. The theoretical prediction is confirmed by the experimental results. The coupling approach is simple and efficiency.

There is signal-signal beating interference (SSBI) when the orthogonal frequency division multiplexing (OFDM) signal is detected by PIN after transmiting over the fiber in 60 GHz OFDM radio-over-fiber (RoF) system. The interleaved configuration of training sequence of OFDM signal is proposed to decrease the influence of the SSBI. The experimental results show that after the 2.5 Gb/s interleaved OFDM signal transmitting over 20 km single mode fiber in 58 GHz millimeter-wave system, the power penalty of the interleaved OFDM signal is only 0.5 dB at the bit error rate (BER) of 10-3 without dispersion compensation. In comparison, the power penalty of the continued OFDM signal under the same conditions is 2 dB. It is demonstrated that the fiber transmission performance of the interleaved OFDM signal is better than the continued OFDM signal in robust tolerance against SSBI.

A new demodulation method is proposed for time division multiplexing system of fiber-optic hydrophone using a 3×3 coupler. In such a scheme, the fiber-optic hydrophone is made by a 2×2 coupler and 3×3 coupler is used as path-matched differential interferometer. The signal is demodulated by linear combination of the three outputs and digital inverse arctangent approach. Parameters used in demodulation are estimated by singular-value decomposition and ellipse fitting. There is no carrier in this demodulation scheme. In addition, fiber-optic hydrophone can form a nearly zero path difference interferometer which is good for reducing system phase noise. The demodulation method is very simple and feasible for a general asymmetric 3×3 coupler. Correspondingly, it is easy to get a large dynamic range for the demodulated signal. A time division multiplexing experiment system with two sensors is set up. At 1 kHz noise floor, dynamic range, and cross talk are less than 31 μrad/Hz, more than 125 dB, less than 64 dB, respectively.

The unified coupled-mode theory for long-period-grating-coupler is obtained by deriving directly from Maxwell’s equation when all the modulation effects of refractive-index, gain and loss are considered. Then, the characteristics of power coupling and signal filtering between the straight-arm and cross-arm of complex-modulated long-period-grating-coupler are investigated thoroughly. The results demonstrate that monodirectional nonreciprocal power coupling is shown when gain/loss is equal with refractive-index modulation. In addition, the complex-modulated long-period-grating-coupler shows different add/drop filtering characteristics if the multiplexed signals are injected from different fibers or directions. For the gain modulation, the phase-matched signal is coupled into the cross-arm and is amplified simultaneously. But for the loss modulation, the signals in straight-arm and cross-arm remain their respective original input power, and can not be filtered according to their wavelengths any more.

The influences of signal to noise ratio (SNR) on the ranging property of laser radar with constant threshold to noise ratio (TNR) are studied comprehensively by experiments. The results indicate that when SNR is much higher than TNR, the distribution of laser radar′s ranging data obeys the Gaussian distribution. And with the decrease of the SNR, the distribution gradually deviates from the Gaussian distribution, and its rising edge becomes steeper and the falling edge becomes more slowly. While the SNR is approaching the TNR, the distribution returns to the Gaussian distribution, but the missing rate increases rapidly. Based on the experiments, the half of the confidence interval with confidence probability of 68.2% is also introduced to evaluate the range accuracy of laser radar. The corresponding method for calculating the range accuracy is presented and used to evaluate the range accuracy of laser radar under different SNRs.

Anti-jamming performance of a chaotic lidar is investigated experimentally and numerically. Using our chaotic correlation range-finder prototype, the anti-jamming capabilities of the chaotic lidar to different undesired signals are studied. Experimental and numerical simulation results indicate that the chaotic lidar, which takes no anti-jamming measure, possesses natural anti-jamming ability and larger noise tolerance to the disturbance from the chaotic laser, continuous-wave modulation laser and pulse laser signals. The feasibility of improving the anti-jamming performance of the chaotic lidar by using an average algorithm is analyzed.