Random lasing in a dye-doped polymer thin film waveguide deposited on a Si surface microstructured by femtosecond laser ablation

Random laser action with ~8 nm of bandwidth from a special waveguide structure is reported. The waveguide structure is composed of a layer of rhodamine 6G-doped PMMA film and a silicon substrate with a microstructured surface induced by a femtosecond laser. The silicon substrate featured two-dimensional island-like microstructures with average sizes ranging from 0.8 μm to 3 μm and average heights at about 0.7 μm. A red-shift of laser peak positions and decrease of threshold were observed with decreasing size of silicon surface microstructures. The spectra at different probe directions were also measured, and the results reveal that the waveguide laser action is strongly confined within ±10° from the direction of the edge. The lasing modes emitted from the edge of the waveguide are found to be mainly transverse electric-polarized. Our experiments demonstrate a promising method to achieve waveguide random lasers.     

Parabolic mirror optics for collimation of a crescent blue laser beam radiated from channel waveguide Čerenkov second-harmonic generation

Parabolic mirror optics to collimate the crescent-shaped blue laser beam that radiates from ?erenkov second-harmonic generation (SHG) in a channel waveguide configuration is proposed. Mirror collimation optics has a large tolerance to the variations of SHG element parameters, such as the laser source wavelength, as well as to mirror displacement. The anisotropy of a nonlinear crystal in which the waveguide is fabricated has been taken into account. The optimum mirror alignment to obtain a collimated blue laser beam is evaluated in terms of Marechal's criterion. The minimum wave-front aberration with beam intensity weighted is 0.054 λSH. The convergence of the collimated beam is less than 1.6 mrad, and, by using an objective lens, the collimated beam can be focused to a diameter of less than 1 μm, which is 1.27 times the diffraction-limited focusing point.     

玻璃基掩埋式光波导堆栈的制作与表征

在硅酸盐光学玻璃基片上制作了光波导堆栈, 这种光波导堆栈通过Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散技术顺次制作了两层掩埋式光波导. 对光波导堆栈的横截面显微结构进行了观察, 并对堆栈中两层波导的损耗特性进行了测试. 所获得的光波导堆栈中的上、下两层波导芯部分别位于玻璃表面以下14和35 μm处; 上层光波导芯部尺寸约为12 μm×7 μm; 下层光波导芯部尺寸约为9 μm×8 μm. 通光测试显示两层波导在1.55 μm工作波长下均为单模光波导, 且两者之间没有相互耦合. 损耗测试分析结果显示: 堆栈中两层光波导的传输损耗均约为0.12 dB/cm,与单模光纤之间的耦合损耗分别为0.78和0.73 dB. 分析表明, 这种光波导堆栈在玻璃基集成光芯片的高密度集成方面具有很好的应用前景.     

Non-linear optical wavelength conversion in Ti:LiNbO3 waveguides

Phase matching temperatures for second harmonic generation were measured for fundamental wavelengths from 1.06 to 1.24 μm in a planar waveguide and compared with bulk crystal values. Furthermore, both second harmonic generation and sum frequency generation were achieved in a channel waveguide, the latter by mixing the Nd-YAG laser wavelength at 1.064 μm with Raman-shifted light from the same light source. A conversion efficiency for second harmonic generation in a channel waveguide of 4.2% at a fundamental power of 120 mW was obtained. Some material-related aspects on waveguides for this type of application are also discussed.     

新型静电驱动双向平动MEMS变形镜(英文)

设计了一种新型静电驱动双向平动的MEMS变形镜,其结构包括3部分:中央下电极,4个静电驱动杠杆结构以及反射镜面(上电极).该变形镜有两种驱动模式:向下驱动模式和向上驱动模式.在向上驱动时,4个杠杆结构实现了位移的放大;向下驱动时,利用了非线性弹性系数法扩展了镜面的平动范围.采用表面硅工艺完成了变形镜的加工.通过白光干涉仪对变形镜的测试表明:在向上驱动模式下,变形镜在驱动电压为31 V时位移达到1.1μm;在向下驱动模式下,变形镜在6 V的驱动电压下位移达到1.1μm.变形镜的总行程为2.2μm,达到了同样工艺下传统变形镜的3倍左右.     

Hollow-waveguide delivery systems for high-power, industrial CO(2) lasers

Hollow-sapphire and metal-dielectric-coated hollow-glass waveguides have been used to deliver CO(2) laser power for industrial laser applications. The transmission, bending loss, and output-beam properties of these waveguides are described. The bore sizes of the hollow-sapphire waveguides were 1070 and 790 μm, and the hollow-glass waveguide had a bore of 700 μm. The waveguides ranged in length from 1.1 to 1.5 m. The sapphire waveguides were bent to 90°, and the hollow-glass waveguides were bent into a full 360° loop. We delivered a maximum of 1.8 kW through the 1070-μm-bore sapphire waveguide and 1.0 kW through the hollow-glass waveguide. All the hollow waveguides incorporated a water jacket to prevent overheating.     

Optical properties of dual-core hollow waveguides

A new type of hollow glass waveguide has been fabricated that transmits radiation from visible to infrared wavelengths with low loss. The broadband transmission is achieved with a structure consisting of two distinct core regions; a silica annulus for transmission of wavelengths from 0.3 to 2.0 μm and a hollow core for transmission from 2.0 to 12.0 μm. Losses in the silica core at 633 nm are 0.3 dB/m. Losses in the 575-μm bore hollow core at 10.6 μm are 0.6 dB/m. Bending loss is negligible for radiation transmitted in the solid silica core, whereas the hollow guide loss exhibits a 1/R dependence. The dual-core waveguide can transmit broadband radiation, is rugged and flexible, and therefore, is a good candidate for medical or sensor applications.     

Split-spectrum intensity-based optical fiber sensors for measurement of microdisplacement, strain, and pressure

A self-referencing technique compensating for fiber losses and source fluctuations in reflective air-gap intensity-based optical fiber sensors is described. A dielectric multilayer short-wave-pass filter is fabricated onto or attached to the output end face of the lead-in-lead-out multimode fiber. The incoming broadband light from a white light or a light-emitting diode is partially reflected at the filter. The transmitted light through the filter projects onto a mirror. The light returning from the reflecting mirror is recoupled into the lead-in-lead-out fiber. These two reflections from the filter and the reflecting mirror are spectrally separated at the detector end. The power ratio of these two reflections is insensitive to source fluctuations and fiber-bending loss. However, because the second optical signal depends on the air-gap separation between the end face of the lead-in-lead-out fiber and the reflecting mirror, the ratio provides the information on the air-gap length. A resolution of 0.13 μm has been obtained over a microdisplacement measurement range of 0-254 μm. The sensor is shown to be insensitive to both fiber-bending losses and variations in source power. Based on this approach, a fiber-strain sensor was fabricated with a multilayer interference filter directly fabricated on the end face of the fiber. A resolution of 13.4 microstrain was obtained over a measurement range of 0-20,000 microstrain with a gauge length of 10 mm. The split-spectrum method is also incorporated into a diaphragm displacement-based pressure sensor with a demonstrated resolution of 450 Pa over a measurement range of 0-0.8 MPa.     

Focusing characteristics of a planar solid-immersion mirror

The focusing characteristics of a planar waveguide solid-immersion mirror with parabolic design have been investigated. The solid-immersion mirror is integrated into an optical waveguide, and light focusing is achieved with a parabolic mirror parallel to the waveguide plane and waveguide mode confinement normal to the waveguide plane. Optical-quality tantala silica planar waveguides can be obtained by evaporation. The parabolic sidewall reflects over 50% of the incident waveguide mode and generates a diffraction-limited focus. The measured spot size for the solid-immersion mirror described here is less than one third of the wavelength. Polarization analysis shows that the electric field near the focal region has components parallel and normal to the polarization state of the incident beam. The planar solid-immersion mirror is essentially free of chromatic aberration, and the alignment of the illumination beam is within a fraction of degrees.     

Design and analysis of a highly efficient coupler between a micro/nano optical fiber and an SOI waveguide

A compact coupling structure is proposed for highly efficient coupling between a micro/nano fiber and a silicon-on-insulator waveguide. The proposed structure is characterized by high coupling efficiency, wavelength insensitivity, large misalignment tolerance, and easy fabrication. Theoretical analysis and numerical simulation results show that coupling efficiency of >90% can be achieved with a taper length of ～4.5 μm.     

Grain structure of ion-plated coatings

The structures of ion-plated copper coatings were studied and were related to plating parameters. It is shown that the structures vary from tapered or nodular growth structures with weak porous boundaries to dense fine-grained (1 μm) structures. If the discharge is intensified using a triode-supported system, dense structures with very fine grains (0.1 μm) are obtained.     

Efficient Raman conversion through backward stimulated Brillouin scattering

We report a new scheme for efficient Raman conversion in high-pressure CH(4) gas. Through the use of backward stimulated Brillouin scattering as a resonator mirror for the pump wave at a wavelength of 1.06 μm, Raman laser generation at the eye-safe wavelength of 1.54 μm has been obtained from a passively Q-switched Nd:YAG laser. At a pressure of 600 psi, we obtained Raman conversion efficiencies of up to 48%.     

Poling-induced birefringence phase matching for 1.5-μm-band wavelength conversion in a polymeric rib waveguide

A birefringence phase-matching (BPM) scheme for second harmonic generation, difference frequency generation (DFG), and their cascading is developed in a polymer rib waveguide. Poling-induced birefringence (n_TM–n_TE) of PMMA:DANS side-chain polymer films showed quadratic increase upon applied DC poling fields, and was controlled for satisfying the BPM. The three conversion processes using the nonlinear coefficient of the d₁₅ were simultaneously phase matched at the poling field around 150 V/μm when the fundamental guiding modes of a pump (DFG: 0.775 μm, cascading: 1.55 μm) and a signal (∼1.55 μm) waves were used. In addition, a numerical simulation of the DFG including the waveguide losses showed high conversion efficiencies around 0 dB on the conditions: the pump power of 100 mW, the waveguide length around 2 cm, and the waveguide losses of 2 dB/cm, demonstrating that the poling-induced BPM is an effective phase-matching method in the wavelength conversion processes.     

用于Triplexer Monitor的波长不敏感耦合器

为了提高Triplexer Monitor的光信号采样性能和集成度,提出一种基于非对称锥形波导结构的波长不敏感耦合器.该耦合器采用SiO2-on-Si掩埋型光波导结构,位于中心部位的锥形波导构成耦合区,与之衔接的S型弯曲波导实现信号光的输入和输出.采用传输矩阵法分析了光监测端口输出的归一化的耦合光功率,分析时将耦合区的中心部位作为非对称矩形波导而外侧作为对称矩形波导.利用光束有限差分传播法(FDBPM)和MATLAB数值仿真得出:当耦合区中心非对称矩形波导宽度分别为5.50μrn和3.35 μm时,对于1 300 nm到1 600 nm的输入光波长范围,可实现光监测端口4％～8％的归一化耦合光功率.特别的,在1310nm、1490 nm和1550 nm输入光波条件下,耦合器在输出端的分光比分别为:92∶8、96∶4和93∶7,同时TE模和TM模的分光比变化保持在5％以内.所设计的波长不敏感耦合器具有体积小、可靠性高等优点,适合与PLC型的Triplexer实现单片集成.     

Tunable high-power narrow-spectrum external-cavity diode laser at 675 nm as a pump source for UV generation

High-power narrow-spectrum diode laser systems based on tapered gain media in an external cavity are demonstrated at 675 nm. Two 2 mm long amplifiers are used, one with a 500 μm long ridge-waveguide section (device A), the other with a 750 μm long ridge-waveguide section (device B). Laser system A based on device A is tunable from 663 to 684 nm with output power higher than 0.55 W in the tuning range; as high as 1.25 W output power is obtained at 675.34 nm. The emission spectral bandwidth is less than 0.05 nm throughout the tuning range, and the beam quality factor M(2) is 2.07 at an output power of 1.0 W. Laser system B based on device B is tunable from 666 to 685 nm. As high as 1.05 W output power is obtained around 675.67 nm. The emission spectral bandwidth is less than 0.07 nm throughout the tuning range, and the beam quality factor M(2) is 1.13 at an output power of 0.93 W. Laser system B is used as a pump source for the generation of 337.6 nm UV light by single-pass frequency doubling in a bismuth triborate (BIBO) crystal. An output power of 109 μW UV light, corresponding to a conversion efficiency of 0.026% W(-1), is attained.     

Fabrication of large-core, high-Δ optical waveguides in polymers

The realization of polymer optical waveguides that have a large core size and high refractive-index difference (LCHD) Δ transmission characteristics is presented. A fabrication procedure for the waveguide based on vertical dip coating and reactive ion etching has been studied. To achieve the lower propagation loss, this procedure includes two original techniques, i.e., the lamination of thick polymer films and sidewall flattening. With these techniques, Δ of 5.4% and a 80 μm × 83 μm core polymer waveguide with 1.4-dB/cm propagation loss were achieved at 680 nm. The LCHD polymer waveguides are useful for practical power-transmission devices.     

Baseband integrated acousto-optic frequency shifter/modulator module for fiber optic at 1.3 mum

A baseband integrated acoustooptic (AO) frequency shifter/modulator module that consists of a pair of titanium-indiffused proton-exchanged (TIPE) waveguide lenses and a pair of cascaded guided-wave AO Bragg cells has been realized in a Y-cut LiNbO(3) waveguide substrate 0.1 cmx1.0 cmx2.0 cm in size. A device module operating at the optical wavelength of 1.3 mum has provided a -3-dB tunable bandwidth of 120 MHz at baseband. The frequency-shifted or -modulated light propagates in a fixed direction, irrespective of the magnitude of frequency shift or modulation, and is focused into a spot (FWHM) of 6.2-mum size on the output edge of the waveguide. Accordingly, this optical frequency shifter/module can be directly interfaced with single-mode optical fibers to facilitate applications in fiber optic systems.     

Linear control of the spectral characteristics of wavelength-selective components with a high-index tapered thin-film planar waveguide and a single-mode half-coupler

A simple system of linearly tunable fiber-film wavelength-dependent components is demonstrated that includes a linearly tapered high-index thin-film planar waveguide (PWG) evanescently coupled by a single-mode-fiber half-coupler. We present experimental and theoretical results for the linear tuning of spectral responses such as coupled power, resonance position (lambda(0)), and fiber output-light polarization through position shifting of the linearly tapered PWG, in the direction of the propagating light in the fiber, over the half-coupler block. We achieved almost linear control of the spectral response by changing the temperature of mixture-of-oils and overlay-doped poly(methyl methacrylate) PWG's when the refractive index of the system decreases with temperature. The variation in thickness of the tapered film is along the direction of the interaction length of the system. Linear tapered PWG's that comprised a mixture of oils, BK7 glass, and overlay-doped PMMA with high refractive indices were fabricated that could operate the device at lower and higher modes. We investigated the dependence of tuning lambda(0) on the PWG mode. Tuning by shifting of a linear tapered PWG over a fiber half-block is mode dependent, whereas tuning by changing the refractive index of a uniform PWG is mode independent. Wavelength shift Dlambda(0) is found to decrease with an increase in the resonant PWG mode number m for linearly tapered PWG's. A fiber-to-asymmetric linear tapered-PWG coupler, which maintains the taper slope to within a specific limit, can function as a linearly tunable polarizer for the light in the fiber.     

Design and fabrication of tapered microfiber waveguide with good optical and mechanical performance

In this paper, the inherent dependence of optical and mechanical characteristics of tapered microfiber waveguide on its contour profile is studied. Both theoretical analysis and experimental investigation are given. In theory, the optimal profile parameters of the tapered microfiber are proposed to improve the microfiber performance, where it is better to make the tapered microfiber keep two longer than 5-mm-long transition regions which have a decaying exponential profile. And the uniform waist diameter of the tapered microfiber should be more than 600?nm and less than 1?μm. In this case, the microfiber indicates several favorable advantages, such as low loss, strong evanescent field and relatively shorter transition region. In experiment, according to the profile parameters we proposed, we successfully fabricated a tapered microfiber with a low loss of 0.05?dB in air and 0.8?dB on a MgF₂ substrate at the wavelength of 1550?nm, and it has low surface roughness.     

Fabrication and characterization of a third-order nonlinear organic-polymer composite glass waveguide: a self-phase modulator

Composite organic-polymer glass optical waveguides in which coupling to the nonlinear organic-polymer layers was achieved by excitement of the underlying ion-exchanged glass waveguide and coupling of the light to the organic-polymer layer were fabricated and measured. A picosecond pulsed color center laser (λ = 1.5 μm) was used to measure the third-order optical susceptibility χ((3))(-w; w, -w, w) in an organic-dye-polymer composite glass waveguide with a Mach-Zehnder interferometer. For a squaryliumdye-doped poly(methyl methacrylate)-styrene-acrylonitrile matrix polymer layer, a composite χ((3)) of roughly 90, in units of (χLiNbO)(3)((3)), was measured.