窄带干涉滤光片抗击不同输出方式激光的损伤特性研究

利用Nd：YAG调Q单脉冲激光和自由脉冲激光对硬膜窄带干涉滤光片进行激光损伤阈值的测试，并且采用表面热透镜技术测量了滤光片的吸收率。实验发现：窄带干涉滤光片的吸收率和激光损伤阈值强烈依赖于辐照激光波长与窄带干涉滤光片通带的相对位置；在调Q单脉冲激光作用下，不同中心波长的滤光片损伤形貌存在明显的差别，而在自由脉冲激光作用下，各滤光片的损伤形貌则趋于相同．均表现为典型的热熔烧蚀破坏。根据实验结果，结合损伤形貌，通过驻波场理论对激光作用下滤光片内电场分布的分析与模拟．探讨了两种激光模式作用下滤光片的损伤特征和损

鉴别用变方位角导模共振滤光片的设计

设计了在0°和90°方位角下都具有低旁带的鉴别用导模共振滤光片。利用严格的耦合波理论，分析了这种器件在不同入射角、不同光栅槽深和覆盖不同厚度SiO2层情况下的衍射特性。得到了满足鉴别要求的导模共振滤光片结构。在30°入射角情况下，对于TE模式偏振光，设计的滤光片在0°和90°方位角下都有形状对称的反射光谱、低的旁带、两个位置分开的共振峰和适当的半宽度。

Design of high-efficiency diffraction gratings based on rigorous coupled-wave analysis for 800nm wavelength

We report on the design of a high diffraction efficiency multi-layer dielectric grating with wide incident angle and broad bandwidth for 800 nm. The optimized grating can achieve > 95% diffraction efficiency in the first order at an incident angle of 5 degrees from Littrow and a wavelength from 770nm to 830 nm, with peak diffraction efficiency of > 99.5% at 800 nm. The electric field distribution of the optimized multi-layer dielectric grating within the gratings ridge is 1.3 times enhancement of the incidence light, which presents potential high laser resistance ability. Because of its high-efficiency, wide incident, broad bandwidth and potential high resistance ability, the multi-layer dielectric grating should have practical application in Ti:sapphire laser systems.

Guided-mode resonant grating filter with an antireflective surface for the multiple channels

In this paper, a new type of guided-mode resonant grating (GMRG) filter with an antireflective surface called the 'moth-eye structure' for the multiple channels is presented by using rigorous coupled-wave analysis (RCWA) and the S-matrix method. Long range, low sidebands and multiple channels are found when the GMRG filters with antireflective surface are illuminated with incident polarization light. It is calculated that the multiple channel phenomenon can be shown when the depth of antireflective surface is increased. Moreover, the wavelengths of the multiple channels can be easily shifted by changing the depth of the homogenous layer which is under the antireflective surface, and the optical properties of GMRG filters such as low sideband reflection and narrow band are not badly spoiled when the depth is changed.

Surface relief resonant Brewster niters with multiple channels

In this paper, a new type of resonant Brewster filters (RBF) with surface relief structure for the multiple channels is first presented by using the rigorous coupled-wave analysis and the S-matrix method. By tuning the depth of homogeneous layer which is under the surface relief structure, the multiple channels phenomenon is obtained. Long range, extremely low sidebands and multiple channels are found when the RBF with surface relief structure is illuminated with Transverse Magnetic incident polarization light near the Brewster angle calculated with the effective media theory of sub wavelength grating. Moreover, the wavelengths of RBF with surface relief structure can be easily shifted by changing the depth of homogeneous layer while its optical properties such as low sideband reflection and narrow band are not spoiled when the depth is changed. Furthermore, the variation of the grating thickness does not effectively change the resonant wavelength of RBF, but have a remarkable effect on its line width, which is very useful for designing such filters with different line widths at desired wavelength.

Compensation of reflectance response deviations of guided-mode resonant filters induced by overetching fabrication

Unless the fabrication error control is well treated, it easily causes overetched fabrication errors, which causes the resonant peak value deviation during the fabrication process of guided-mode resonant filters (GMRFs). Hence, the fabrication error control becomes a key point for improving the performance of GMRF. We find that, within the range of the groove depth from 93 to 105 nm, the relationship between the overetched error and the resonant peak value deviation is nearly linear, which means that we can compensate the reflectance response deviation and reduce the resonant peak value deviation by the method of covering the layer film on the GMRF. Simulation results show that the deviation is compensated perfectly by this way. (C) 2008 Optical Society of America

Surface plasmon resonance transmission filters at 1053 nm based on metallic grating with narrow slit

Metallic gratings with narrow slits can lead to special optical properties such as strongly enhancing the transmission and considerably strengthening the polarized effect. A narrow-band filter suitable for application in optical communication is designed by sandwiching a metallic grating between two identical dielectric films. The maximum transmission can reach 96% after optimizing the parameters of films and grating at a central wavelength of 1053 nm. It is the first time, to our knowledge, that such high transmission has been reported since the discovery of the extraordinarily high transmission through periodic holes or slits; moreover, the extremely polarized effect is also found in P mode of this symmetric grating.

Nonconstant quality of auditory filters in the porpoises, Phocoena phocoena and Neophocaena phocaenoides (Cetacea, Phocoenidae)

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in porpoises Phocoena phocoena and Neophocaena phocaenoides asiaeorientalis. The EFR was evoked by amplitude-modulated probes with a modulation rate of 1000 Hz and carrier frequencies from 22.5 to 140 kHz. Equivalent rectangular quality Q(ERB) of the obtained tuning curves varied from 8.3-8.6 at lower (22.5-32 kHz) probe frequencies to 44.8-47.4 at high (128-140 kHz) frequencies. The QERB dependence on probe frequency could be approximated by regression lines with a slope of 0.83 to 0.86 in log-log scale., which corresponded to almost frequency-proportional quality and almost constant bandwidth of 34 kHz. Thus, the frequency representation in the porpoise auditory system is much closer to a constant-bandwidth rather that to a constant-quality manner. (c) 2006 Acoustical Society of America.

Degenerate four-wave mixing based all-optical wavelength conversion in a semiconductor optical amplifier and highly-nonlinear photonic crystal fiber parametric loop mirror

The idler is separated from the co-propagating pump in a degenerate four-wave mixing (DFWM) with a symmetrical parametric loop mirror (PALM), which is composed of two identical SOAs and a 70 m highly-nonlinear photonic crystal fiber (HN-PCF). The signal and pump are coupled into the symmetrical PALM from different ports, respectively. After the DFWM based wavelength conversion (WC) in the clockwise and anticlockwise, the idler exits from the signal port, while the pump outputs from its input port. Therefore, the pump is effectively suppressed in the idler channel without a high-speed tunable filter. Contrast to a traditional PALM, the DFWM based conversion efficiency is increased greatly, and the functions of the amplification and the WC are integrated in the smart SOA and HN-PCF PALM. (C) 2008 Elsevier B.V. All rights reserved.

Transmission properties through a double quantum dot with a wave packet

The transmiss on time and tunneling probability of an electron through a double quantum dot are studied using the transfer matrix technique. The time-dependent Schrodinger equation is applied for a Gaussian wave packet passing through the double quantum clot. The numerical calculations are carried out for a double quantum clot consisting of GaAs/InAs material. We find that the electron tunneling resonance peaks split when the electron transmits through the double quantum dot. The splitting energy increases as the distance between the two quantum dots decreases. The transmission time can be elicited from the temporal evolution of the Gaussian wave packet in the double quantum dot. The transmission time increases quickly as the thickness of tire barrier increases. The lifetime of the resonance state is calculated tram the temporal evolution of the Gaussian-state at the centers of quantum dots.

A traveling-wave electroabsorption modulator with a large optical cavity and intrastep quantum wells

This paper reports a novel traveling-wave electroabsorption modulator (TWEAM) with a large optical cavity waveguide and an intrastep quantum well structure designed to achieve a high bandwidth, high saturation power and better fiber-matched optical profile, which is good for high coupling efficiency. The optical mode characteristic shows a great improvement in matching the circular mode of the fiber and the saturation power of 21 dBm, and a 3 dB bandwidth of 23 GHz was achieved for the fabricated TWEAM.

Continuous-wave operation of GaN based multi-quantum-well laser diode at room temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5 mu m x 800 mu m ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110mA and 10.5V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12 degrees and 32 degrees, respectively.

Slow wave effect of 2-D photonic crystal coupled cavity array

We designed a two-dimensional coupled photonic crystal resonator array with hexagonal lattice. The calculation by plane-wave-expansion method shows that the dispersion curve of coupled cavity modes in the bandgap are much flattened in all directions in the reciprocal space. We simulated the transmission spectra of transverse electric (TE) wave along the Gamma K direction. Compared with the PC single cavity structure, the transmission ratio of the coupled cavity array increases more than three orders of magnitude, while the group velocity decreases to below 1/10, reaching 0.007c. The slow wave effect has potential application in the field of miniaturized tunable optical delay components and low-threshold photonic crystal lasers.