Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.     

Photothermal examination of an adhesive layer

An adhesive layer, by which a piezoceramic foil is attached to an aluminum membrane for telephone application, is examined in a nondestructive way by thermal waves. The basic principles of the method are outlined, and its detecting power is demonstrated by evaluation of a well-defined delamination.     

Silver-coated hollow-glass waveguide for applications at 800 nm

A 250-microm-bore size and 50-cm-length hollow-glass waveguide (HGW) coated with a thin film of silver has been used to transport laser pulses at 800 nm from a Ti:sapphire oscillator. The silver film is deposited by a liquid-phase process. The measured transmission of this silver-coated HGW is 95%, which is considerably higher than the transmission of HGWs with no coating, as reported by other groups. The image of the output beam taken at different distances from the fiber output shows that a single HE11 mode couples to free-space modes from the exit of the fiber. Considerable spectral broadening can be obtained with high-intensity femtosecond pulse when this waveguide is filled with argon. This HGW can be used for such applications as beam transport and optical-pulse compression.     

Analysis of a InGaAs/InP single photon detector at 1550 nm

A new type of single-photon detector is introduced and its related properties characterized. The single-photon detector operating in the Geiger mode uses a new type of cooling system to moderate temperature, which can make the temperature drop to ?65?°C. Besides, the single-photon detector adopts a hold-off time modulation feedback control circuit to decrease the afterpulsing effects and the gate pulse is coupled to the avalanche diode through capacitance. In addition, a suitable delay and comparator with latch function circuit are used to detect avalanche signals. Experimental conditions are that the clock frequency is 10 MHz, refrigeration temperature is ?65?°C, and the width of control pulse is 5 ns. The experimental results indicate that quantum efficiency is about 20.42% and the dark count rate is about 5 × 10^?6 ns^?1 with signal-to-noise ratio 27 dB at the optimum operation point of this detector. The designed single-photon detector achieves a tradeoff between lower dark count rates and high quantum efficiency.     

Absorptance behavior of optical coatings for high-average-power laser applications

A modified photothermal deformation technique is used to measure the absorptance behaviors of optical multilayered dielectric coatings for a high-power laser system. The surface thermal-lensing modification uses an enlarged probe beam to facilitate alignment of the laser beam and data acquisition. The coatings, both reflective and transmissive types, are made by a physical vapor-deposition process. Coating absorptances are observed to depend on the laser's exposure time and power density. Time-dependent absorptance defect models are proposed. Also, micrometer-sized sites of high absorptance and an area with physical damage can be found during the spatial scans. It is proposed that absorptance values reported for coatings in high-repetition-rate or cw-laser systems include time- and power-dependent behaviors in addition to other relevant irradiation parameters.     

Deep-etched high-density fused-silica transmission gratings with high efficiency at a wavelength of 1550 nm

We describe the design, fabrication, and excellent performance of an optimized deep-etched high-density fused-silica transmission grating for use in dense wavelength division multiplexing (DWDM) systems. The fabricated optimized transmission grating exhibits an efficiency of 87.1% at a wavelength of 1550 nm. Inductively coupled plasma-etching technology was used to fabricate the grating. The deep-etched high-density fused-silica transmission grating is suitable for use in a DWDM system because of its high efficiency, low polarization-dependent loss, parallel demultiplexing, and stable optical performance. The fabricated deep-etched high-density fused-silica transmission gratings should play an important role in DWDM systems.     

TiO2掺杂Ge-Sn-Se微晶玻璃的结构与光学特性研究

通过热熔融法将作为成核剂的TiO₂引入Ge-Sn-Se三元体系的硫系玻璃中, 并对玻璃样品进行不同时间的热处理。实验结果表明, 热处理能够使TiO₂掺杂Ge-Sn-Se玻璃析出SnSe₂六方晶体与GeSe₂单斜晶体, 并且随着热处理时间的延长, 透明样品的短波吸收边发生了红移, 光学带隙减小, Urbach能量增加, 说明玻璃中缺陷组织的数量在增加。通过Z扫描方法获得了各个样品在通信波长1550 nm下的三阶非线性参数, 研究了热处理时间对TiO₂掺杂Ge-Sn-Se玻璃光学非线性性能的影响。结果表明: 玻璃内部在热处理后析出的纳米级晶体具有很强的局域场效应, 能够极大地增加玻璃的三阶非线性, 样品的非线性折射率n₂最高达到5.75×10^-16 m²/W, 热处理3 h的样品同时具有较高非线性折射率和较高品质因子, 是一种性能优良的非线性光学材料。     

20 W CW 589 nm sodium beacon excitation source for adaptive optical telescope applications

Operation of a doubly resonant sum-frequency generation (SFG) ring containing a lithium triborate (LBO) crystal has been demonstrated. It is pumped by 1.064 and 1.319 μm Nd:YAG injection-locked ring lasers and produces a 20 W, diffraction-limited, single-frequency, continuous wave, 589 nm beam. Nearly 60% conversion of pump laser power is obtained. Such a device produced a guidestar in the mesospheric sodium layer that can provide improved sky coverage for adaptive optical telescope applications. “First light” on the sky for the laser source was 21 November 2002 at the Starfire Optical Range, Kirtland AFB, New Mexico.     

The optical properties of liquid cerium at 632.8 nm

The normal, spectral emissivity, ε_λ(T), and optical constants, n and k, of liquid cerium were measured at 632.8 nm over a temperature range of 1700–2130 K using rotating analyzer ellipsometry. The cerium was electromagnetically levitated to prevent contamination of the liquid metal by contact with a container and purified by vaporization of volatile oxides at high temperature. The emissivity at 0.9 μm and 1900 K was determined from the brightness temperature. The solubility of oxygen in liquid cerium at 1786 K was estimated and the effect of oxygen on the optical properties was demonstrated. Using available thermodynamic data and assumptions of ideal solution behavior, the volatilization of oxygen and nitrogen impurities is discussed. At 1786 K, the solubility of oxygen in liquid cerium is between 3 and 7 atom percent.     

Design of an optical interconnect for photonic backplane applications

A compact alignment-tolerant interconnect has been developed for use within a prototype modulator-based free-space photonic backplane. The interconnect design encompasses several unique features. Microlens arrays are used, and several beams share each microlens by clustering the optical input-output in a small field about the optical axis of each lens. For simplifying the layout, the optical input and output of each smart-pixel array are clustered separately, thereby allowing a Fourier plane patterned-mirror array to be used in the beam-combination optics. This allows a suitable balance between high interconnection densities and reasonable optical relay distances between adjacent boards to be achieved. The primary advantages of this scheme are the simplicity of the optical design and its alignability, making it ideally suited for high-density interconnection applications.     

Nonlinearity of high-power optical fiber power meters at 1480 nm

We describe a calibration system that measures the nonlinearity of optical fiber power meters (OFPMs) at a maximum power of 0.6 W and a minimum power of 0.2 mW at 1480 nm. The system is based on the triplet superposition method. This system measures the nonlinearity of OFPMs by using correction factors at different powers; the system is an important tool for characterizing OFPMs at high powers in the S band. The measurement uncertainties, typically better than 0.2%, k = 2, associated with the high-power nonlinearity system are also described.     

Design of an integrated optical magic T for astronomy applications

A new integrated optical component is introduced that performs the function of the well-known microwave magic T, i.e., that produces the sum and the difference of the two input optical signals. Two structures are proposed and tested theoretically for this purpose. The first is based on the symmetric Y junction, and the second is based on interference phenomena in a multimode waveguide. The theoretical design is tested with a beam-propagation method simulation, and good performance is obtained. The effects of the geometrical design parameters on the structures' performance (bandwidth, cross talk, and losses) are also investigated.     

“Chameleon-like” optical behavior of lanthanide-doped fluoride nanoplates for multilevel anti-counterfeiting applications

Lanthanide-based luminescent anti-counterfeiting materials are widely used in various kinds of products. However, the emission color of traditional lanthanide-based luminescent materials usually remains nearly unaltered upon different excitation lights, which may only work for single-level anti-counterfeiting. Herein, the NaYbF₄:2%Er@NaYF₄ core/shell nanoplates (NPs) with “chameleon-like” optical behavior are developed. These NPs display single-band red or green downshifting (DS) emission upon excitation at 377 or 490 nm, respectively. Upon 980 nm excitation, the color of upconversion (UC) emission can be finely tuned from green to yellow, and to red with increasing the excitation power density from 0.1 to 4.0 W/cm². The proposed materials readily integrate the advantages of excitation wavelength-dependent DS single-band emissions and sensitive excitation power-dependent UC multicolor emissions in one and the same material, which has never been reported before. Particularly, the proposed NPs exhibit excellent performance as security labels on trademark tag and security ink on painting, thus revealing the great potential of these lanthanide-doped fluoride NPs in multilevel anti-counterfeiting applications.

     

Ultrafast nonlinear optical properties of TiO2 nanoclusters at 850 nm

We discuss nanoclusters of titanium dioxide, bulk CdTe and CS₂ as characteristic materials to illustrate two main ideas; firstly, it is possible to argue about the origin of the nonlinearity even with a high repetition laser, provided that you have as large a peak power (50 kW) as the one found in femtosecond lasers. Secondly, the search for dimensional confinement to enhance nonlinear optical properties has experienced some difficulties with conflicting results. We show that electronic nonlinear behavior increases from TiO₂, CS₂ to CdTe and the nonlinear thermal effect increases from CS₂, CdTe to TiO₂.     

Light-scattering measurements of optical thin-film components at 157 and 193 nm

An instrument for total backscattering and forward-scattering measurements of optical coating components at 157 and 193 nm is described. The system is operated in both vacuum and nitrogen purge gas. An excimer laser as well as a deuterium lamp can be used as a radiation source. Suppression of the background signal level to 1 part in 10(6) permits measurements even of low-scatter samples such as superpolished substrates and antireflection coatings. Results of investigations of antireflective and highly reflective multilayers and CaF2 substrates reveal scattering from surface and interface roughness as well as from the volume of the substrate material. First steps to extend the instrument for angle-resolved scatter, transmittance, and reflectance measurements are described.     

Simple iodine reference at 1064 nm for absolute laser frequency determination in space applications

Using an iodine cell with fixed gas pressure, we built a simple frequency reference at 1064 nm with 10 MHz absolute accuracy and used it to demonstrate deterministic phase locking between two single-frequency lasers. The reference was designed to be as simple as possible, and it does not use a cooler or frequency modulator. This system should be useful, especially for space interferometric missions such as the Laser Interferometer Space Antenna.     

Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm

Use of photonic crystal fibers (PCFs) in the field of sensing is relatively new. We propose the application of a PCF for pressure sensing. The fiber analyzed is a polarization-maintaining PCF that has negligible sensitivity to temperature, making it an ideal candidate for pressure sensing in harsh environments. On the basis of theoretical and experimental analysis, PCF is proposed to be applied as a temperature-compensated pressure sensor. Detailed theoretical analysis and the experiment carried out are described to show the concept of the sensor.     

Stabilization of an optical microscope to 0.1 nm in three dimensions

Mechanical drift is a long-standing problem in optical microscopy that occurs in all three dimensions. This drift increasingly limits the resolution of advanced surface-coupled, single-molecule experiments. We overcame this drift and achieved atomic-scale stabilization (0.1 nm) of an optical microscope in 3D. This was accomplished by measuring the position of a fiducial mark coupled to the microscope cover slip using back-focal-plane (BFP) detection and correcting for the drift using a piezoelectric stage. Several significant factors contributed to this experimental realization, including (i) dramatically reducing the low frequency noise in BFP detection, (ii) increasing the sensitivity of BFP detection to vertical motion, and (iii) fabricating a regular array of nanometer-sized fiducial marks that were firmly coupled to the cover slip. With these improvements, we achieved short-term (1 s) stabilities of 0.11, 0.10, and 0.09 nm (rms) and long-term (100 s) stabilities of 0.17, 0.12, and 0.35 nm (rms) in x, y, and z, respectively, as measured by an independent detection laser.     

Robust determination of optical path difference: fringe tracking at the infrared optical telescope array interferometer

We describe the fringe-packet tracking system used to equalize the optical path lengths at the Infrared Optical Telescope Array interferometer. The measurement of closure phases requires obtaining fringes on three baselines simultaneously. This is accomplished by use of an algorithm based on double Fourier interferometry for obtaining the wavelength-dependent phase of the fringes and a group-delay tracking algorithm for determining the position of the fringe packet. A comparison of data acquired with and without the fringe-packet tracker shows a factor of approximately 3 reduction of the error in the closure-phase measurement. The fringe-packet tracker has been able so far to track fringes with signal-to-noise ratios as low as 1.8 for stars as faint as mH = 7.0.