THEORY OF NONLOCAL ASYMMETRIC ELASTIC SOLIDS

In this paper, a nonlinear theory of nonlocal asymmetric, elastic solids is developed on the basis of basic theories of nonlocal continuum field theory and nonlinear continuum mechanics. It perfects and expands the nonlocal elastic field theory developed by Eringen and others. The linear theory of nonlocal asymmetric elasticity developed in [1] expands to the finite deformation. We show that there is the nonlocal body moment in the nonlocal elastic solids. The nonlocal body moment causes the stress asymmetric and itself is caused by the covalent bond formed by the reaction between atoms. The theory developed in this paper is applied to explain reasonably that curves of dispersion relation of one-dimensional plane longitudinal waves are not similar with those of transverse waves.

Observation of wedge waves and their mode transformation by laser ultrasonic technique

Wedge waves （WWs） in wedges, including their dispersion characteristics and mode transformation, are investigated using the laser ultrasound technique. Pulsed laser excitation and optical deflection beam method for detection are used to record WWs. Numerous WWs are detected by scanning the excitation laser along the wedge tip. Dispersions of WWs are obtained by using the two-dimensional （2D） Fourier transformation method, and different WW orders are revealed on the wedges. Mode transformation is determined by fixing the distance between the excitation and detection position, as well as by scanning the samples along the normal direction of the wedge tip.

Analysis of dispersion compensation for position-dependence in externally modulated CATV lightwave systems by using chirped fiber grating

The dispersion compensation characteristics of the chirped fiber grating （CFG） for different dispersion compensation positions are analyzed in externally modulated cable television （CATV） lightwave system and the analytic expression of the composite second order （CSO） distortion is derived. The analyses give a reasonable explanation for the position-dependent effect of CFG dispersion compensator, which was found in practical systems. Moreover, the theoretical result is also verified by an experiment. It is believed that the theory will be helpful in designing optical CATV fiber links with nodes at proper positions both for intensity amplification and dispersion compensation.

Effects of group-velocity mismatch and cubic-quintic nonlinearity on cross-phase modulation instability in optical fibers

The synthetic effects of group-velocity mismatch and cubic-quintic nonlinearity on cross-phase modulation induced modulation instability in loss single-mode optical fibers have been numerically investigated. The results show that the quintic nonlinearity plays a role similar to the case of neglecting the group-velocity mismatch in modifying the modulation instability, namely, the positive and negative quintic nonlinearities can still enhance and weaken the modulation instability, respectively. The group-velocity mismatch can considerably change the gain spectrum of modulation instability in terms of its shape, peak value, and position. In the normal dispersion regime, with the increase of the group-velocity mismatch parameter, the gain spectrum widens and then narrows, shifts to higher frequencies, and the peak value gets higher before approaching a saturable value. In the abnormal dispersion regime, two separated spectra may occur when the group-velocity mismatch is taken into account. With the increase of the group-velocity mismatch parameter, the peak value of the gain spectrum gets higher and shorter before tending to a saturable value for the first and second spectral regimes, respectively.

Modulation instability of broad optical beams in nonlinear media with general nonlinearity

The modulation instability of quasi-plane-wave optical beams is investigated in the frame of generalized SchrSdinger equation with the nonlinear term of a general form. General expressions are derived for the dispersion relation, the critical transverse spatial frequency, as well as the instability growth rate. The analysis generalizes the known results reported previously. A detailed discussion on the modulation instability in biased centrosymmetric photorefractive media is also given.

High power pulse amplification of ytterbium-doped double-clad fiber amplifier

By solving a set of time-dependent equations, the characteristics of the ytterbium-doped double-clad fiber amplifier are presented. Besides the steady state in the fiber of the upper-state population, pump power and amplified spontaneous emission without the input signal, the dynamic characteristics of the high power Gaussian pulse amplification like the evolution of pulse waveform distortion, upper-state population distribution and stored energy and pulse energy of the amplifier under the forward and backward pump, are simulated. The relations between the output pulse energy of the amplifier and the different input pulse peak power or pump power are also discussed. The models and results can provide important guide for the design and optimization of the high power pulse amplification.

Rotation, scaling, and translation invariant local watermarking technique with Krawtchouk moments

A rotation, scaling, and translation invariant local watermarking is proposed with one or two Krawtchouk moment（s） of the original to estimate the geometric distortion parameters including rotation angle, scaling factor, and translation parameter. Krawtchouk moments can be used as private key of watermark extractor. Watermark is inserted into perceptually significant Krawtchouk moments of original, and watermark based on Krawtchouk moments is local. Independent component analysis （ICA） is utilized to extract watermark blindly. Experimental results show that this method has a good robustness against distortions preformed by watermark benchmark - Stirmark.

Image recognition of laser radar using linear SVM correlation filter

Through deducing the relationship between support vector machine （SVM） and correlation principle, the optimal hyperplane is proved as a correlation filter when the kernel function is the linear kernel. So a new correlation filter, named linear SVM correlation filter （LSCF）, is proposed. The filter has not only shift-invariance, but also SVM properties. The real images of laser radar are used as experiment data, and LSCF is used to solve the in-plane rotation invariance. The results show that the filter can recognize the different rotated objects, and the correlation output is stable. The filter is insensitive to the noise and gray change, and has good discrimination ability. In the same design way, LSCF is also suitable to solve other problems of correlation distortion.

Four-wave mixing based 10-Gb/s tunable wavelength conversion in dispersion-flattened microstructure fibers

All-optical wavelength conversion of 10-Gb/s signal based on four-wave mixing is experimentally demonstrated in a 30-m-long dispersion-flattened microstructure fiber with small positive dispersion. For an average pump power of 26 dBm, the conversion efficiency was around -19.5 dB with the fluctuation less than ±1.4 dB, covering a conversion bandwidth of 20 nm. The eye diagram of the converted signal shows good eye opening.

Pulse dynamics controlled by saturable absorber in a dispersion-managed normal dispersion Tm-doped mode-locked fiber laser

Based on the coupled Ginzburg-Landu equation, we numerically investigate the pulse dynamics in a dispersion-managed normal dispersion Tin-doped mode-locked fiber laser. The influences of the rood-ulation depth and saturation power of saturable absorber on the pulse dynamics are presented. The simulation results show that these parameters are crucial to achieve high pulse energy and high pulse peak power pulsed laser near 2-μm wavelength.

Group velocity dispersion and polarization mode dispersion compensation by high-birefringence linearly chirped fiber Bragg grating

A high-birefringence linearly chirped fiber Bragg grating (FBG) is written into a polarization-maintaining photosensitive fiber by ultraviolet (UV) beam through a linearly chirped phase mask.Its performance as group velocity dispersion (GVD) and polarization mode dispersion (PMD) compensator is demonstrated in short pulse fiber optical transmission systems.

312 MHz, compact all-normal-dispersion Yb:fiber ring laser with an integrated WDM-ISO

A compact and stable all-normal-dispersion mode-locked ring fiber laser with the repetition rate of 312 MHz is obtained with a wavelength-division multiplexing isolator. The compressed pulse is nearly transform-limited and the pulse width is 118 fs. It exhibits an optical efficiency of 50% and the maximum output power is about 205 mW with a 410 mW pump.

Picosecond soliton transmission using concatenated gain-distributed nonlinear amplifying fiber loop mirrors

Stable picosecond soliton transmission is demonstrated numerically by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors （NALMs）. We show that, as compared with previous soliton transmission schemes that use conventional NALMs or nonlinear optical loop mirror （NOLM） and amplifier combinations, the present scheme permits significant increase of loop-mirror （amplifier） spacing. The broad switching window of the present device and the high quality pulses switched from it provide a reasonable stability range for soliton transmission. Soliton-soliton interactions can be reduced efficiently by using lowly dispersive fibers.

Experimental verification of combinational-deformable-mirror for phase correction

In adaptive optics （AO） system, the phase compensation capability is limited greatly by the actuator number of the deformable mirror （DM）. The actuator number of DM is mainly restricted by the manufacture techniques. The spatial correction capability of AO system can be improved by two or more combinational- DMs （CDMs） with conjugation relationship. The CDM AO system for wavefront correction is built, which consists of two 32-element DMs. The experimental results are in agreement with the numerical simulation results. It is indicated that the CDM AO system provides better correction performance than the single 32-element DM AO system.

New spectroscopic method for the determination of optical rotatory dispersion

A new spectroscopic methodology is proposed to measure optical rotatory dispersion （ORD） of optically active media. ORD is obtained from a three-step phase shifting algorithm using transmission spectra taken at three independent probing angles. Optical rotation angles of four sugar solutions are investigated. The results obtained by using the new method show excellent agreement with the reference data, indicating the new method can be used as a reliable way for studying ORD of optically active media.

Weighted nonlinear phase shift with group velocity dispersion to assess the nonlinear penalty in C+L band long-haul fiber optical amplified transmission link

To assess the penalty due to nonlinear effect in C＋L band long-haul optical amplified transmission link, a new parameter of modified nonlinear phase shift （ФD） is proposed, which is the accumulated nonlinear phase shift weighted by a normalized group velocity dispersion （GVD）. Based on the numerical simulation result of broadband long-haul hybrid Raman/erbium-doped fiber amplified transmission line, it is validated that CD is more reasonable and suitable than the previous proposed nonlinear phase shift （ФNL） for broadband applications.

Influence on photonic crystal fiber dispersion of the size of air holes in different rings within the cladding

The influence on photonic crystal fiber dispersion of the size of air holes in different rings within the cladding is investigated using a semivectorial finite difference method. Numerical results reveal that the photonic crystal fiber dispersion is more sensitive to the variation of the air hole size in the first and second rings, indicating that design of photonic crystal fibers with desirable dispersion properties requires more precise control of the parameters of the air holes in the vicinity of the fiber core.

Study on the 4×10 Gb/s,400 km dispersion compensation by chirped optical fiber grating

In this paper, the dispersion compensation for 4×10 Gb/s. 400 km G.652 fiber by chirped optical fiber Bragg grating (FBG) is introduced. For the first time, we have measured and compensated the polarization mode dispersion (PMD) of FBG. which in each channel is less than 1.1 ps. When the bit error rate (BER) is 10-and the bit error is zero, the transmission power penalty of each channel is less than 2 dB, and the best result is negative which means that the receiver sensitivity is increased after transmission.

Performance evaluation for 160-Gb/s optical phase conjugation systems considering dispersion mapping and third-order dispersion

The impact of third-order dispersion （TOD） is investigated by numerical simulations in 160-Gb/s singlechannel systems incorporated with dispersion mapping and optical phase conjugation （OPC）. System performances using retrun-to-zero （RZ） or carrier-suppressed RZ （CSRZ） modulation format are evaluated on the optimized dispersion map. The results indicate that even though TOD has been fully compensated, the intra-channel nonlinearity induced by local TOD would degrade the system performance in nonlinear regime. The scheme with an optimized dispersion map provides a much higher performance and offers a larger tolerance on a variation of pre-compensation. CSRZ modulation format is more robust due to its tradeoff between tolerances on intra-channel nonlinearity and dispersion.

Quartz optical filter for wavelength selection of frequency-doubled laser based on optical rotatory dispersion effect

Based on the optical rotatory dispersion effect, an optical filter for selecting the second harmonic of a frequency-doubled laser is constructed from quartz in combination with polarizers. The operating principle is analyzed by matrix formulation, and the result indicates that the second harmonic of a frequency-doubled laser will be obtained when the rotation angle has a difference of （2n ＋ 1）π/2 （n = 0, 1, 2, 3, ... ） between the two polarizations of the second-harmonic laser and the fundamental laser. The spectrum of the output laser is taken by the AQ-6315A spectrometer, and the experimental results are in good agreement with the theoretical results.