Fast frequency tuning of diode-pumped monolithic semi-nonplanar ring lasers was investigated experimentally using a piezoelectric transducer (PZT). A 0.5 mm thick PZT plate was affixed to a monolithic laser crystal with dimensions of 13 mm×14 mm×3 mm. Beat frequency between two monolithic lasers was observed to check the frequency tuning effect. When the modulation frequency was lower than 100 kHz and the frequency tuning amplitude was 5 V, a widened beat signal could be observed, which gave a PZT tuning coefficient over 1 MHz/V. If the modulation frequency was much higher, such as higher than 100 kHz, the beat signal became unstable and shifted obviously. The shape of the beat signal changed too. Thus the PZT response bandwidth was near 100 kHz for a stable laser frequency tuning.

The injection current of the diode laser can be modulated by radio-frequency (RF) signal. The RF signal of 20 MHz is input to the high frequency modulation port of diode laser, and part of it is phase shifted and mixed with the saturated absorption spectral signal then input to the low-pass filter. The resulted similar dispersion signal is used to stabilize the frequency of laser to 6S1/2 (F=4)→6P3/2 (F′=5) transition of cesium atom and the frequency stability is better than 1 MHz in 10 s. The stabilization technology has the characteristics of lower intensity noise and higher frequency capture range.

The hollow lens duct is introduced for the application in the coupling of pump radiation from extended two-dimensional semiconductor laser diode arrays into solid state laser gain media. With the help of numerical analysis of three-dimension ray tracing, a computer simulation program for longitudinal-pump laser diode (LD) coupling system was developed. Based on the result of simulation, a coupling system for large-aperture high-power LD arrays using hollow lens duct was build. Coupling efficiency beyond 90% was reached with perfect pumping-uniformity on the surface of gain material. An experience formula for hollow lens duct design was deduced at the same time, it would be very helpful in designing coupling system of large-scale diode-pumped solid-state lasers (DPSSLs).

A two-dimensional Hartmann wavefront sensor is used to measure the aero-optical effects when the optical beam passes through a low velocity heat turbulent jet. The wavefronts are reconstructed by the results of the measured wavefront gradient, and the wavefront aberration is obviously shown. The correlation function is obtained from angular beam-jitter measurements, and the convection velocity and turbulence scale size of the flowing turbulence jet are calculated. These results show that the Hartmann wavefront sensor is not only used to measure the aero-optical effects in turbulent medium, but also utilized to perform non-intrusive studies of fluid flows.

The theory of photoacoustic spectrum is presented briefly in this paper. The optical fiber phase sensor is used to replaces traditional microphone, and the relationship between light phase and photoacoustic signal is discussed. Multiple-reflection system is used to enhance absorption effectively. The dye laser is used as light source to measure SO2 gas concentration. It shows that the sensitivity of 1.2×10-10 can be obtained. The combination of spectrum technology and optical fiber technology provides higher sensitivity, stronger ability to resist electromagnetic interference, avoiding fire and explosion. The gas probe has small volume, relatively fast response speed. The signal processing circuit has high ability to suppress noise interference. The experiments show that the sensor and its system match the requests of sensitivity, accuracy, and response time in detecting the gas concentration.

A ring-cavity fiber laser based fiber Bragg grating (FBG) sensor system, in which two FBGs are used, is reported in this paper. One of the employed gratings, acted as the end mirror, is sensor element. Another is used as a tunable filter controlled by a piezoelectric stack, which is driven by an electrical sine wave signal. The measured strain applied on the sensor axially can be judged by observing the interval of the output laser between two notches within a driving period in time-domain. Experiment demonstrated that the sensing sensitivity and the resolution of this system are 88.152 με/ms and 1.8 με respectively, within the work range of from -140 με to 720 με. The perturbation of the environmental temperature was proved not to affect the measured results theoretically. It was verified by experiments.

The method of intensity demodulation with matched fiber Bragg gratings (FBG) is introduced. The FBG whose reflection spectrum overlaps with that of sensor FBG is selected to demodulate signals by detecting the changes of the intensity of reflected laser of demodulation FBG. The question that the intensity of reflected laser is a Gauss function of strain, i.e., two-values question caused by this method in strain sensors is studied. And a novel method that demodulation FBGs with well selected Bragg wavelength and bandwidth are in parallel connection is deduced so that the intensity of reflected laser is linear with strain. A theoretical model is set up and formulas are deduced. Finally this method is proved by experiment with two demodulation FBGs to be practicable and the sensor range is 522 με and the sensitivity is 2.6 με.

The article introduces an advanced approach to fiber grating wavelength demodulation based on the principle of polarized-light interference. The polarized-light interferometer is also a kind of unbalanced interferometer which can convert the Bragg wavelength shifts into interferometer phase shifts. Different from the conventional unbalance interferometer, this polarization interferometer is based on the unequal refractive index ne and no rather than the unbalanced paths. In addition, the polarized-light interference is generated in the yttrium vanadate (YVO4) crystal with superior birefringence characteristic rather than in the optical fiber by which the interferometer bias is unavoidable. This article points out that through analyzing the properties of YVO4 crystal, ±0.4℃ temperature accuracy can be reached in temperature measurement by this method.

A long-period fiber grating (LPFG) couples light from the core to the cladding, which is highly sensitive to micro-bends. In this paper a novel pressure sensor based on LPFGs incorporated with a strain diaphragm structure is proposed and demonstrated. It was found that when the pressure changed from 0 to 0.13 MPa, the resonant peak wavelength was red-shifted linearly about 1.8 nm, and the peak amplitude decreased uni-directionally up-to about 13 dB. By the method of detecting the change of the transmission output power at a fixed wavelength inside the rejection band, the value of pressure could be measured. The resolution of this device could reach to 10-4 MPa, which is suitable for real applications.

Resonator fiber optic gyro (R-FOG) is an inertial rotation sensor with high accuracy which is based on the Sagnac effect. The signal detection system has important role in the R-FOG. The detecting precision influences the maximum resolution of the gyro directly. The fiber ring resonator is the core-sensing element in the R-FOG. This paper presents the scheme to detect the resonance point using two-frequency serrodyne modulation, and uses the Lorentzian function to describe the expression of the output power at the exit port of the fiber ring resonator taking the temporal coherence of the laser into account. According to near linear relationship between amplitude of the square waveform and the resonant frequency deviation near the resonant point, frequency feedback time after time is used for frequency tracking for both clockwise (CW) and counterclockwise (CCW) waves. Therefore, complex root finding process can be avoided. Simulation shows that both CW and CCW waves can be locked at the resonance frequency of the resonator quickly by frequency feedback operation.

A novel model for light propagation in elliptical-hole photonic crystal fibers (PCF) is developed with localized orthogonal function method. The dielectric constant of the PCF missing the central air hole is considered as the sum of two different periodic dielectric structures of virtual perfect photonic crystals, and the electric field is decomposed using the localized Hermite-Gaussian functions. From the wave equations and the orthonormality of Hermite- Gaussian functions, the propagation characteristics of the PCF, such as the mode field distribution, the effective area, the birefringence, and the dispersion properties are obtained. The birefringence and group velocity walkoff parameters of elliptical-hole PCF are analyzed with this model. It is shown that the birefringence and group velocity walkoff parameters are typically stronger than that of the conventional fibers for comparable parameters, and exhibit frequency dependence quite unlike conventional birefringence systems. Moreover the unusual combination of strong birefringence with zero group velocity walkoff can be obtained, which may allow the novel nonlinear applications.

In X-ray imaging technology, coded imaging is a process of two steps. The first step is coding process, in which the information of object is collected using coded aperture. The second step is decoded process, in which the coded image is filtered and reconstructed in order to obtain a visible object image with high resolution. There are two kinds of coded aperture, one according to the shape of apertures and the other according to the space position of aperture plane. Wiener filtering is used in the decoded process, because it can obtain better reconstruction results with lower calculated cost. A method of coded imaging using ring-coded aperture and its image restoration technique are presented, the development of coded aperture imaging technologies is described. Difform aperture is adopted in coded and recoded process, compared with each other optimal aperture is chosen. As experiments prove, using this aperture, good imaging result can be gained and restored, because this method combines all of high resolution-capability, large radiation collection efficiency ,and high signal-to-noise ratio.

Multilevel recording, which allows multiple status in each recording pit, is an alternate way to increase the recording density, but need not to directly reduce the spot size by increasing NA (numerical aperture) or reducing λ. The absorption of photochromic material varies with the different optical writing energy, which can be used to realize multilevel data storage. At first, the exposure characteristic of this material as the media of multilevel storage is studied, and the mathematical model of multilevel storage using this material has been achieved. The nonlinear relation between absorption and exposure energy is reflected in the model, which supports to optimize the write strategy of photochromic multilevel data storage. In the results of 4-level and 8-level static multilevel storage experiments, each level of signal amplitude varies obviously without overlap, which proves the possibility of applying this material to multilevel data storage. The capacity of optical disk will be improved by double or treble if this multilevel technology is implemented into practical optical disk storage.

HA (hydroxyapatite) bioceramic gradient coatings are prepared on titanium by laser cladding, the microstructure and phases analysis of laser clad HA bioceramic coating are studied by means of electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The results show that when the laser power is 600 W and the scanning speed is 3.5 mm/s, the compact and good-bonding HA bioceramic gradient coatings can be obtained, and the microstructure is cellular and dendritic crystal which is similar to that of human hard tissue. The coatings consist of the phases of HA, α-Ca2P2O7, Ca3(PO4)2 and so on, and the Ca/P ratio in bottom coating is near to that in HA, but in upper coating it is a little higher. If laser power rises, porous structure is produced which is favor to the embedding and growing of bone tissue, but the Ca/P ratio in HA coatings increases and the biocompatibility decreases. If the scanning speed is faster, the coating will not melt enough, so the microstructure is loose and the coating strength descends.

Theoretical and experimental study is presented on temperature-tuned signal-resonated quasi-phase-matched optical parametric oscillator (OPO) in multi-grating periodically poled lithium niobate (PPLN) pumped by an acousto-optically Q-switched cw-diode-end-pumped Nd∶YVO4 laser. The continuously tunable signal output from 1369.7 nm to 1678.8 nm without wavelength overlap is demonstrated. The formula of calculating the signal wavelength as a function of the grating period and the temperature is given. The formula of calculating the temperature as a function of the signal wavelength and the grating period is also given. Based on those work, the relative temperature tuning ranges for each grating period to realize continuously tunable signal output without wavelength overlap can be calculated directly. So it does not need to solve simultaneous equations of energy and momentum conservation through point-by-point computation. In addition, the uniform deviation of the grating period in the whole periodically poled crystal from the ideal length is usually inevitable, as well as the random variation in the length of the domain. The method of correction computation on grating period is given by using the temperature tuning curve got in the experiment.

In this paper, a combinative technology of harmonic solid-state laser and stimulated Raman scattering (SRS) has been investigated to obtain multi-wavelength laser output with definite power. Multi-order harmonics of a Nd∶YAG laser, second harmonic (SH), thrird harmonic (TH) and fourth harmonic (FH) have been employed to generate multiple Raman lines by pumping the gases of hydrogen, methane, etc. The output Raman lines cover waveband from ultraviolet to near infrared. The characteristics of frequently used Raman gases, methane and hydrogen have been discussed, both have advantages and disadvantages. The mixture gas of these two gases makes up the overlarge frequency shift of hydrogen on the one hand, and restrains the decomposition of methane on the other hand. The rare buffer gases and the mixture gas have also been employed to optimize the Raman output. The table of 24 Raman lines is listed in this paper, including 13 lines of rather strong power. Multi-wavelength Raman lasers integrating the technologies of SRS and harmonic solid-state lasers could be applied in lidar and other application field.

The application of pump cavity in laser diode (LD) side-pumped laser head is introduced. By using ray tracing calculation, the effects of the pump cavity on the absorption efficiency and the intensity distribution of the pump light in the crystal were analyzed. The experiments were carried out respectively under the conditions of with and without pump cavity, with gold-plating pump cavity and with polished gold-plating pump cavity. The result showed that a gold-plating pump cavity greatly improved the output character of the pump head.

A single stable frequency and narrow line width external cavity semiconductor laser used in interference measurement is proposed. It is constructed with a semiconductor laser, collimation system, a blaze grating, and current and temperature control systems. The one facet of the semiconductor laser is covered by high transmission film, and the other is covered by high reflection film. The blaze grating is used as external cavity light feedback element to select the mode of the semiconductor laser. The current control system is used to provide drive current to the semiconductor laser, and the drive current is allowed to be adjusted in certain range. The temperature is controlled with double temperature controls to make the temperature of the external cavity stabilized in order of 10-3℃. Thus a single longitudinal mode, narrow spectral line width and stable frequency external cavity semiconductor laser is realized, and its spectral line width is compressed to be less than 1.4 MHz and the output stability (including power and mode) is remarkably improved.

A single-longitudinal-mode Nd∶YLiF4 (Nd∶YLF) laser pumped by laser diode array, using a novel two-step Q-switching driver for the low-voltage KTiPO4 (KTP) Pockels cell was obtained. The amplitude and lasting time of the driver′s second step pulse is adjustable and the Nd∶YLF rod is end polished. Stable, low time jitter single longitudinal mode output was generated taking the advantages of prelase and etalon. The laser has produced pulse with width of 6.7 ns, energy of 1.156 mJ and a peak power of 0.17 MW. This laser holds the good single longitudinal mode probability of 100% and the stability of pulse energy of 3%. The time jitter between the Q-switching trigger and output pulse is less than 4 ns. The laser is easy to adjust and would have practical use in many fields with its simple peripheral electronic equipment and high reliability.

A kind of birefringent filter based on the combination of the polarization function of the type Ⅰ critical phase-matching doubling frequency crystal LBO (LiB3O5) and the quartz full-wave plate is presented. The stable operation of laser diode (LD) pumped Nd∶YAG (Nd∶Y3Al5O12)/LBO blue laser is obtained. When the pumping power input into Nd∶YAG is 1.2 W, 25 mW 473 nm blue laser with single longitudinal mode is obtained.

Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse (1015～1016 W/cm2) and icosahedral hydrogen atomic clusters H13, H55, H147 and H309 has been studied. The expansion process of the clusters during and after laser irradiation has been examined, showing that the expansion of clusters is isotropic. The expansion scale R(t)/R(0) decreases with the increasing cluster size. This conclusion means that if the cluster size becomes larger, the process of expansion and explosion becomes slower. It is revealed that with an increase in the number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. Because of the symmetrical shell structure of the icosahedron, the distribution of the ionic kinetic energy features some pinnacles. It is also found that the calculated maximal kinetic energy Emax of the produced ions from Coulomb explosion of Hn clusters is roughly proportional to the square of the original cluster size. If laser intensity I increases, the maximal kinetic energy Emax of the produced ions also increases. But after I reaches a certain value Is, the maximal kinetic energy Emax of the produced ions no longer increases, i.e., it will be saturated. The reason is that the atoms in the cluster have been fully ionized, so the increase of laser intensity I doesn′t change the ionized state of the atoms in the cluster. It is concluded that with an increase in the cluster size, the kinetic energies of the produced ions and the laser saturation intensity increase too.

With the linear approximation method, the intensity correlation function C(t) and normalized mean intensity fluctuation C(0) are calculated, which reflects dynamic properties of the laser. The time evolution of C(t) is discussed in a loss-noise model of single mode laser system by pump noise and quantum noise with cross-correlation real and imaginary parts. The influences on the time evolution of C(t) are analyzed from cross-correlation coefficient between the real and imaginary of quantum noise λq, intensities of the pump noise P and quantum noise Q, respectively. The time evolution of C(t) is a monotonous descending process, while the whole C(t) versus t curve falls down with noises intensity reducing and the cross-correlation between real and imaginary parts of the quantum noise weakening, which shows that the great influence of the noises intensity and the cross-correlation between real and imaginary parts of the quantum noise on the time evolution of C(t). When t increases, an extremum or three extrema appears in the C(t) versus λq curve. Finally, the valid range for the linear approximation method is discussed.

Yb∶YAG (Yb∶Y3Al5O12) crystal with Yb3+ doping level up to 50 at.-% has been grown by Czochralski method. The absorption, emission spectra and fluorescence lifetime of Yb∶YAG crystal at room temperature have also been studied. Two absorption bands are centered at 939 nm and 969 nm of Yb3+, respectively, which are suitable for InGaAs diode laser pumping, and the main fluorescence band is located around 1032 nm. The fluorescence lifetime of Yb∶YAG laser crystal is 390 μs. The spectral parameters of low and high doping Yb∶YAG crystals are compared. The results indicate that Yb∶YAG with high doping concentration is a promising laser material for high power laser output.

Sb-doped SnO2/SiO2 nano-composite thin films are prepared by sol-gel method. The surface topograph of the thin films is observed by atomic force microscopy (AFM). The optical properties of the thin films are studied by ultraviolet-visible spectra and p-polarized light reflectance angular spectrum. The results show that the crystalline grain size is about 35 nm, the specific surface area is large, and the duty porosity is high;the optical transmissivity is high, near 95% in visible spectrum range,and the optical band gap is about 3.67 eV. So Sb-doped SnO2/SiO2 nano-composition thin films is ideal candidate for optical gas-sensing. Further more, the gas-sensing test is made to three kinds of gas C3H8, C2H5OH and NH3, the results indicate, the doping of Sb to SnO2 films greatly improves the gas sensitivity to C2H5OH, and the gas sensitivity of Sb∶SnO2/SiO2 nano-composite thin films is higher than that of Sb∶SnO2 thin films.

A new method of auto-measuring the roundness error by means of the linear CCD (charge coupled device) is proposed. The principle and design process of the system to measure the roundness error using the Lloyd mirror, linear CCD image-processing system are described. The measuring results indicate that the accurate, real-time and on-line measuring of the roundness error can be realized.

The expanding of the pulse duration due to the dispersion of the beam splitter adopted in normal single-shot second-order auto-correlator (SSA) was calculated. It is shown that, for ultra-short pulses, this kind of pulse-expanding will introduce imprecision of the result (e.g., for a pulse with the duration of about 3 fs, the expanding of a 100 μm thick beam-splitter of K9 glass is 10%). Based on these results, a kind of total-reflection single-shot auto-correlator is proposed. Via changing the beam splitting method from wave-front splitting to wave-surface splitting, the dispersion of the beam-splitter is avoided. By adopting this kind of SSA, the accuracy of the measurements for ultrashort pulses is improved. The calculated results show that the accuracy is about 3.6 fs.

How to utilize wavelength conversion is the key factor in improving the blocking performance in wavelength-routed all-optical networks. The paper studies the novel conversion wavelength architectures and methods, and proposes a hybrid wavelength conversions, which can reduce the number of wavelength converters and preserve the performance. The paper examined five different wavelength converter utilization schemes and presented the best wavelength converter utilization strategy with simulation. Considering hybrid wavelength conversion and wavelength converter utilization strategy, a scheme of optimal wavelength converter placement in optical networks is presented by genetic algorithm and the simulation results demonstrate that it can hold the network performance and need not increase the number of wavelength.

A 780 nm Rb Faraday atomic dispersive optical filter (FADOF) that operates in the wings of Rb D2 resonance line is experimentally studied with a single photon detector. The measure result shows that the maximum transmission of the 780nm Rb FADOF is 28% and the full width at half maximum is 0.7 GHz. A minimum detectable laser power of 0.16 pW/cm2 is obtained with the signal-to-noise ratio of transmission spectrum of 2. Therefore, the detection sensitivity of Rb FADOF is remarkably increased when a single photon detector is used. If the Rb FADOF is used to replace a interferential optical filter in laser communication, it can lead to a lower bit error ratio and the system that operates with single photon detector is able to work during daytime when optical background is much larger.

A polarization-insensitive multiple-quantum-well optical amplifier for 1.3 μm wavelength employing both four compressively-strained wells (1.0% strain, 6 nm well width) and three tensile-strained wells (-0.95% strain, 11 nm well width) in active region was grown by low pressure metalorganic vapor phase epitaxy (LP-MOVPE). The amplifier was fabricated forming ridge waveguide structure with 7° tilted cavity. The two facets were coated with two layers Ti3O5/Al2O3 anti-reflection (AR) thin films, residual facet reflectivity was found to be less than 3×10-4. The 3-dB bandwidth of the amplified spontaneous emission (ASE) spectra was above 50 nm and the amplitude of the optical power ripple was bellow 0.4 dB. The amplifier exhibited an excellent polarization insensitivity (less than 0.6 dB) over the entire range of wavelength (1.28～1.34 μm). A small signal gain of 30 dB and a saturated output power of more than 10 dBm at bias current of 200 mA and 1305 nm wavelength were obtained. The noise figure of the amplifier was 7.5 dB.

In the practice intersatellite optical communication (IOC), the method of multi-field scanning is needed to capture the goal satellite. And the scanning range is a key parameter of multi-field scanning, so the precise study of it is needed. Based on the constructed theoretical single-field scanning model, the theoretical analysis has been preceded and a theoretical model of multi-raster scanning has been founded too. According to this model, the results of analysis proved that there is an optimization in the selection of scanning range, in order to achieve a shortest acquisition time. And for the convenience in practice, a numerical simulation has been carried on. With the presented simulation results, an experimental formula to choose the optimum scanning range in multi-raster scanning has also been proposed.