Nonlinear-optical-loop-mirror-based wavelength conversion is studied in details. A set of two-phase-shifted Bragg gratings are introduced into the coverter, serving as a narrow band-pass filter to remove new frequencies generated by walk-off and to compensate the dispersion. Numerical simulations are performed to validate our method. The results show that the converted pulses after the filter are reshaped and, sometimes, even compressed.

We built a numerical model for evaluating the coupling processes of a mixed structure of a Bragg fiber grating and a long-period grating. From the numerical results, we not only confirmed the wavelength switching phenomena observed in previously reported experiments, but also discovered a new coupling mechanism, which generated the reflection of a signal with its wavelength longer than the Bragg wavelength. The dependencies of the wavelength switching behaviors on various parameters of the mixed grating structure were demonstrated. Such results should be useful for optimizing the design of such a potentially useful fiber component.

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

A novel wideband digitally tunable laser based on fiber Bragg grating external cavities and 1*N optical switch provides 5 ms fast tuning time with output power more than 1 dBm over whole C-band that is only limited by the laser emission bandwidth. Less than 50 pm wavelength drift over -10 to 55 oC temperature range make that the wavelength locker and monitor are not necessary in this tunable laser.

A novel hollow-core tapered coupler has been theoretically designed and fabricated by fiber drawing machine. The coupler's inner wall is coated with a polycrystalline GeO2 film. The coupling loss of hollow-core tapered coupler is about 0.2 dB. Hollow-core tapered coupler reduces the transmission loss of hollow-core optical fiber (HCOF) by 0.5 dB/m, therefore the coupler is suitable for coupling high power CO2 laser in industrial application.

This paper describes the high performance of narrow-beam divergence spot size converter (SSC) integrated separately confined heterostructure (SCH) LD. The upper optical confinement layer (OCL) and the butt-coupled tapered thickness waveguide were regrown simultaneously, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. The threshold current was as low as 5.4 mA, the output power at 55 mA was 10.1 mW, the vertical and horizontal far field divergence angles were as low as 9oand 15o, and the 1-dB misalignment tolerances were 3.6 and 3.4 μm, respectively.

InGaAs/GaAsP strain-compensated multiple quantum wells (SCMQWs) and strained InGaAs/GaAs multiple quantum wells (MQWs) were grown on GaAs substrates by metal organic vapor phase epitaxy (MOVPE). The results of double crystal X-ray diffraction (DCXRD) revealed that strain relief had been partly accommodated by the misfit dislocation formation in the strained MQW material. It led to that the full width half maximums (FWHMs) of superlattice satellite peaks are broader than those of SCMQWstructures, and there was no detectable room temperature photoluminecence (RT-PL) for the strained MQW structures. With the increasing of the P/As ratio, the separation angle between the substrate peak and the zeroth order peak of SCMQW decreased. The FWHMs of both the zeroth order satellite and RT-PL of SCMQW structures also decreased, whereas the intensity of RT-PL increased. This indicated that the quality of epitaxial layers was improved with the increasing of the strain compensation.

With a tabletop hybrid Nd:YAG-Nd:glass laser as pump source, a compact optical parametric chirped pulse amplification (OPCPA) laser system with a peak output power of 16.7 TW and a pulse duration of 120 fs has been demonstrated. Chirped pulses are amplified from 50 pJ to more than 3.1 J with an energy gain of above 6×10^(10) by three LBO optical parametric amplifiers with a pump energy of 12.4 J at 532 nm. After compression, a final output of 2.0-J/120-fs pulse is obtained. To the best of our knowledge, it is the highest peak output power from an OPCPA laser so far. In addition, a practical design of 1-PWlaser system based on the technique of OPCPA is also proposed.

The band-pass characteristic of fiber grating Michelson interferometer is analyzed, which acts as both band-pass filter and Q-switch. An erbium-doped fiber ring laser based on fiber grating Michelson interferometer is implemented for producing single longitudinal mode CW operation with 5 MHz spectral linewidth and up to 6 mW output power. In Q-switched operation, stable fiber laser output pulses with repetition rate of 800 Hz, pulse width of 0.6 μs, average power of 1.8 mW and peak power of 3.4 W are demonstrated. The peak power and average power of the Q-switched pulses are varied with the repetitionrate.

A passively Q-switched operation of a diode-pumped Nd:YVO4 laser is demonstrated, in which a GaAs film is used as the saturable absorber as well as the output coupler. At the pump power of 10 W, a stable fundamental-mode average power output of 2.11 W was obtained with a pulse duration of 140 ns, pulse energy of 76 μJ and pulse repetition rate of 28 kHz. A theoretical analysis that describes the passive Q-switching dynamics of GaAs is presented.

Theoretical studies on laser gain of a multi-stage dye laser amplifier are presented in this paper. The results show that the influences of amplified spontaneous emission (ASE) and nonlinear absorption of excitedstate on the gain are different for different input laser energies and gains. A threshold input intensity exists for a specific system. If the input intensity is higher than the threshold, the nonlinear absorption of excited-state will be the main cause for gain decrease. Otherwise, the ASE is the main cause. A new scheme is proposed to calculate the gain of the amplifier by the comparison of the input intensity with the effective saturation intensity and the choice of the calculation gain method.

The effects of Al2O3, Yb2O3, Er2O3 and OH- on spectral properties of P2O5.Na2O.SrO.Al2O3.Yb2O3.Er2O3 erbium phosphate glass were studied. 5, 8, and 13 mol% Al2O3, 4, 5, 6, 7 and 8 mol% Yb2O3 and 0.05, 0.2, and 0:4 mol% Er2O3 were used. It was found that Al2O3 can improve fluorescent lifetime of Er3+ ions, but the integrated absorption cross section of Er3+ ions decreases with the increase of Al2O3 concentration. Evaluating from energy transfer efficiency of Yb3+ to Er3+ and spectral parameters of Yb3+ and Er3+, we conclude that 6 mol% Yb2O3 and 0:4 mol% Er2O3 are needed for LD pumped microchip laser applications. OH- groups in glass affect greatly fluorescent intensity and lifetime of Er3+, Yb3+:phosphate glass. The OH- absorption coefficient at 3000 cm^(-1) should be less than 1 cm^(-1) for laser applications. Pumped with a 2-W, 974-nm InGaAs laser diode, CW laser centered at 1530 nm with slope efficiency of 10:6 % and maximum output of 43 mW was achieved in our 2-mm-thick Er3+, Yb3+:phosphate glass at room temperature.

The changes of holographic characteristics of photopolymer induced by temperature are studied experimentally. The results show that the exposure sensitivity increases with the increase of temperature. The maximum diffraction efficiency and the final maximum diffraction efficiency increase with the increase of temperature when the temperature is lower than Tg (glass transition temperature), while they decrease with the increase of temperature when the temperature is higher than Tg. The effect of the change of temperature on the saturation refractive index modulation is very weak.

Experimental techniques for measurement of optical penetration depth and refractive index of human tissue are presented, respectively. Optical penetration depth can be obtained from the measurement of the relative fluence-depth distribution inside the target tissue. The depth of normal and carcinomatous human lung tissues irradiated with the wavelengths of 406.7, 632.8 and 674.4 nm in vitro are respectively determined. In addition, a novel simple method based on total internal reflection for measuring the refractive index of biotissue in vivo is developed, and the refractive indices of skin from people of different age, sex and skin color are measured. Their refractive indices are almost same and the average is 1.533.

In this paper, we discuss what causes the superluminal propagation of a pulse through dispersion by solving Maxwell's equations without any approximation. The coherence of the pulse plays an important role for superluminal propagation. When the pulse becomes partially coherent, the propagation changes from superluminal to subluminal. The energy velocity is always less than the vacuum velocity. The shape of the pulse is changed during the propagation.

We present a new mechanism of energy gain of electrons accelerated by a laser pulse. It is shown that when the intensity of an ultrafast intense laser pulse decreases rapidly along the direction of propagation, electrons leaving the pulse experience an action of ponderomotive deceleration at the descending part of a lower-intensity laser field than acceleration at the ascending part of a high-intensity field, thus gain net energy from the pulse and move directly forward. By means of such a mechanism, a megaelectronvolt electron beam with a bunch length shorter than 100 fs could be realized with an ultrafast (<=30 fs), intense (&gt 10^(19) W/cm2) laser pulse.

We demonstrate three-dimensional tomographic imaging using a Fresnel lens with broadband terahertz pulses. Objects at various locations along the beam propagation path are uniquely imaged on the same imaging plane using a Fresnel lens with different frequencies of the imaging beam. This procedure allows the reconstruction of an object’s tomographic contrast image by assembling the frequency-dependent images.

In this work we present experiments by focusing 42 femtosecond laser pulses in air using three different focal length lenses: f=100, 30 and 5 cm. For the longest focal length, only the filament, which is a weak plasma column, is observed. When the shorter focal length lens is used, a high density plasma is generated near the geometrical focus and coexists with a weak plasma channel of the filament. Under the tightest focusing condition, filamentation is prevented and only a strong plasma volume appears at the geometrical focus.

We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laser field with wavelength of 810 nm and intensities ranging from 1.4×10^(14) to 2.6×10^(15) W/cm2 by mass spectroscopy. Abundant fragment ions were observed in addition to the strong parent ion. The effect of frequency chirp was investigated and it was found that the negatively chirped pulses dramatically enhanced the dissociation probability, which might be used to control the dissociation pathways.