Quantitative analysis of bending efficiency in photonic-crystal waveguide bends at lambda = 1.55 mum wavelengths

Based on a photonic-crystal slab structure, a 60 degrees photonic-crystal waveguide bend is successfully fabricated. Its bending efficiency within the photonic bandgap is measured, and near 100% efficiency is observed at certain frequencies near the valence band edge. The bending radius is ~1mum at a wavelength of lambda~1.55mum . The measured eta spectrum also agrees well with a finite-difference time-domain simulation.     

High transmission through waveguide bends by use of polycrystalline photonic-crystal structures

A hybrid photonic-crystal structure is presented as a candidate for enhancing transmission through sharp photonic-crystal waveguide bends built on a perforated dielectric slab. This structure, which we refer to as a polycrystalline structure, combines two photonic-crystal lattices. Polycrystalline photonic-crystal structures offer the ability to minimize reflections as well as mismatches that a propagating wave might encounter while undergoing a sharp corner or a discontinuity between different waveguide sections. The availability of polycrystalline structures in photonic crystals opens a broad range of possibilities for the development of optical devices. Numerical experiments are performed with two- and three-dimensional finite-difference time domain methods.     

带有环形谐振器的1×2光子晶体功率分配器传输性能

 利用正方格2维光子晶体设计了带有环形谐振器的1×2光子晶体功率分配器结构,该结构具有1个输入端口和2个输出端口。采用时域有限差分法研究了该功率分配器对电磁波的传输性能,结果表明：其结构在第三通信窗口(1 550 nm波长)实现了电磁波的高效传输,同时具有优良的电磁波通频带功率二等均分性,以及电磁波传输转向设计灵活、损耗低、结构紧凑等优点。     

Low-reflection photonic-crystal taper for efficient coupling between guide sections of arbitrary widths

We design and fabricate a new taper structure for adiabatic mode transformation in two-dimensional photonic-crystal waveguides patterned into a GaInAsP confining layer. The taper efficiency is validated by measurement of a reduction of the reflection between an access ridge and a photonic-crystal guide with one missing row from 6% to less than 1%. This taper is then incorporated into a 60 degrees bend; simulations demonstrate a 90% transmission between multimode ports.     

Determination of the possibility of controlling the optical properties of dielectric photonic-crystal fibers with semiconductor inclusions

We have shown that the characteristics of propagation of optical radiation in a photonic-crystal fiber that contains semiconductor elements can be controlled by external radiation that acts on the structure. We have studied a photonic-crystal fiber that is formed by air holes in a dielectric that contains a semiconductor (GaAs) tube in the central region (core region) filled inside with the same dielectric. We have shown that the power of the radiation that is necessary to control the transmission characteristics at a wavelength λ = 1550 nm is determined by the construction of the device and can be fairly small (10⁹ W/m²).     

High-efficiency coupling structure for a single-line-defect photonic-crystal waveguide

We present the design and fabrication of a planar structure for coupling light from a multimode feed waveguide into a single-line-defect photonic-crystal waveguide. Finite-difference time-domain calculations predict a coupling efficiency of greater than 90%, and preliminary experimental results indicate successful coupling through a single-line-defect photonic-crystal waveguide. Device design, fabrication, and characterization are presented.     

Extraordinary refraction and dispersion in two-dimensional photonic-crystal slabs

Studies of the refraction and dispersion properties of two-dimensional (2D) photonic-crystal (PC) slab waveguides are reported. The photonic band structure is strongly modified in a slab PC, and only a small number of bands satisfy the guiding conditions imposed by the lack of translation symmetry in the direction perpendicular to the slab; however, it was found that a significant number of the guided modes retain the giant refraction and strong dispersion properties discovered previously in pure 2D PCs. A small change in incident angle resulted in a dramatic change in refraction angle. Furthermore, the dispersion surface exhibited a strong dependence on the frequency, resulting in a superprism effect similar to what has been predicted for pure 2D PCs. In the silicon-based slab PC studied, refraction angles as high as nearly 70 degrees were predicted for incident angles of less than 7 degrees , and frequency components differing by 3% were separated by 15 degrees . The demonstration of giant refraction and superprism phenomena in slab waveguide PCs open the possibility of developing new classes of optical devices that can, for example, be used to develop 2D optical integrated circuits for communications and computing.     

RF discharge slab CO laser operating in both fundamental and first-overtone bands

A compact sealed-off cryogenically cooled radio frequency (RF) discharge slab CO laser, operating in both first-overtone (FO) and fundamental band (FB), was launched. Repetitively pulsed and CW modes of RF discharge excitation were studied. Average FB output power was up to 12 W, with laser efficiency 14%. The multiline FB laser spectrum was observed within the wavelength range ∼5.1-5.4 μm. An optical scheme “frequency selective master oscillator - laser amplifier” was applied for getting FB tuning. Single line FB lasing with average power up to several tens of mW was observed on ∼100 FB vibrational-rotational transitions of CO molecule within the spectral range ∼5.0-6.5 μm. Multiline FO lasing was observed on ∼80 spectral lines within the spectral range ∼2.5-4.0 μm, with maximum single line average output power 12 mW. Total output power of the slab FO CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Results of parametric studies of the FB and FO slab CO laser including complicated time behavior for laser pulses on different FO vibrational-rotational transitions are discussed.     

Design of annular photonic crystal slabs

We present the design of realistic annular photonic-crystal (APC) structures of finite thickness aiming to obtain a complete photonic bandgap (PBG). The APC is composed of dielectric rods and circular air holes in a triangular lattice such that each rod is centered within each hole. The optical and geometrical values of the structure are studied, and the interplay between various design parameters is highlighted. The coupled role of the inner-dielectric-rod radius, material types, and slab thickness is investigated. It is shown that the slab thickness is vital to obtain a complete photonic bandgap below the light line, and the specific value of the inner-dielectric-rod radius to sustain the maximum PBG if the hole radius is fixed at proper value is found.     

A Kilowatt Radio-Frequency Excited Diffusively Cooled All-Metal Slab Waveguide CO2 Laser

A new type of rf excited diffusively cooled all-metal slab waveguide CO2 laser is presented, in which the waveguide channel is constructed by two copper side walls and two copper electrodes, and the discharge is confined in the slab waveguide channel in terms of the voltage division structure. From this type of structure, over 1 kW laser power is obtained with an efficieney of more than 13%.     

Self-compression of subgigawatt femtosecond laser pulses in a hollow photonic-crystal fiber

We report experimental evidence of waveguide self-compression for high-power Cr: forsterite-laser femtosecond pulses in a hollow photonic-crystal fiber. Dispersion spreading typical of low-intensity laser pulses is replaced by nonuniform compression for pulses with high power (above 100 MW) with the compression efficiency reaching its maximum around the peak of the laser pulse.     

High power composite Nd:YAG/YAG zigzag dual-slab laser oscillator

We report a high power zigzag slab laser oscillator employing two composite Nd:YAG/YAG slab in the cavity. The CW laser output with the power of 401 W was achieved from the oscillator with the optical-optical efficiency of 32.6%. The beam quality is estimated as M _x ² ≈ 10, M _y ² ∼ 50 in the slab width and thickness direction, respectively.     

Ultrafast and low-power terahertz wave modulator based on organic photonic crystal

We theoretically investigate the modulation efficiency, response time, and pump power of a terahertz-beam intensity modulator by using an organic photonic crystal slab structure with high quality factor “defect” cavity. The basic operation of an ultrafast low-power terahertz wave modulator actuated by the dynamical shifts of the defect mode induced by pump intensity is discussed in detail. The finite-difference time-domain method is used to verify and analyze the characteristics of the terahertz wave modulator. The device exhibited extinction ratio of 47.15 dB and insertion loss of 3.2 dB at frequency of 1.062 THz with ultrafast response times on the order of several picoseconds.     

High-power continuous-wave Nd:GdVO4 slab laser pumped directly into the F3/2 emitting level

95.6 W continuous-wave laser power output in 880 nm LD partially end-pumped Nd:GdVO₄ slab laser with a hybrid resonator is presented. The slope efficiency and optical-to-optical efficiency were 46.5% and nearly 42.6%, respectively. At the output power of 82 W, beam quality M² factors were 1.1 in the unstable direction and 1.36 in the stable direction, respectively.     

基于光子晶体耦合波导的宽带慢光研究

提出了在完整三角晶格光子晶体中引入两线缺陷构成的耦合型波导结构。通过分析谱带形对不同结构参数的依赖关系,在最优化的光子晶体耦合波导中,找到了一种独特的、群速近似为零的谱带。通过对波导宽度的啁啾实现了不同频率光的色散补偿,最终得到了带宽为13.24nm、平均群折射率为28的宽带理想慢光,并进一步采用二维时域有限差分(FDTD)算法进行了验证。数值分析结果表明,高斯脉冲在耦合波导中传输后的相对时域展宽低于10%。     

宽带光子晶体插分滤波器

 通过使用正方格介质柱二维光子晶体设计了带有环形谐振器的一种插分滤波器ADF(add drop filter)结构,该结构具有1个输入端口和2个输出端口,采用时域有限差分法研究了带有1个环形谐振器和2个环形谐振器的ADF结构传输性能。结果表明：该ADF结构在第三通信窗口具有优良的滤波作用,能够根据需要将电磁波信号沿着波导向前后上下4个方向传输,ADF结构还具有可调性开关波长、宽频带、高传输率等特点,在光子晶体集成化、光器件制作等方面具有潜在价值。     

Thin Nd:YAG slab laser pumped by lens duct coupled diode laser stacks

High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100. PACS 42.55.Xi; 42.60.Pk; 42.60.By     

Edge-pumped, folded zig-zag Nd:YAG slab laser

 We report the design and performance of conduction-cooled, edge-pumped, folded zig-zag continuous wave Nd:YAG slab laser. The Nd:YAG slab is pumped with waveguide coupled laser diode bars. The coupling efficiency of waveguide to laser diode radiation is 97%. In a folded zig-zag resonator, a maximum output power of 37 W in multimode operation is achieved for an incident pump power of nearly 180 W on the Nd:YAG slab. This corresponds to an optical-to-optical conversion efficiency of 20% and slope efficiency of 32%. We obtained more than 10 W of output power with the beam quality factors in the width dimension and in the thickness dimension equal to 8.     

Calculated out-of-plane transmission loss for photonic-crystal slab waveguides

A fully three-dimensional finite-difference time domain numerical model is presented for calculating the out-of-plane radiation loss in photonic-crystal slab waveguides. The propagation loss of a single-line defect waveguide in triangular-lattice photonic crystals is calculated for suspended-membrane, oxidized-lower-cladding, and deeply etched structures. The results show that low-loss waveguides are achievable for sufficiently suspended membranes and oxidized-lower-cladding structures.     

Wet-chemical etching of Mn-Zn ferrite by focused Ar+-laser irradiation in H3PO4

Maskless etching of Mn-Zn ferrite in H₃PO₄ aqueous solution by Ar⁺-ion laser irradiation has been investigated to obtain high etching rates and aspect-ratios of etched grooves. The etching processes have been found to be photochemical in the low laser power region and thermochemical in the high laser power region. High etching rates of up to 340 μm/s and an aspect-ratio of 30 for slab structures have been achieved. In the case of high aspect-ratio structure, the etching rate was limited by the low diffusion efficiency of etched products in the etchant. Periodic ripple structures have been observed under specific etching conditions.