Near-field scanning optical microscopy (NSOM) can provide direct information about the electric fields inside optoelectronic devices with subwavelength resolution. This letter describes direct, wavelength-resolved measurements of the amplitude and phase of the standing waves within a fiber Bragg grating, using a heterodyne interference variant of NSOM that works at telecommunications wavelengths. The amplitudes of forward- and backward-going components of the standing wave can be measured separately, and the position shift of the standing wave antinodes as the wavelength varies across the stop band is imaged directly.
Summary form only given. In recent years, the use of focused femtosecond laser pulses to direct-write three-dimensional arrays of waveguides, couplers and other devices within the bulk of glass has become increasingly prevalent. The study of the physical damage created by such lasers has also begun to be investigated with properties such as anomalous anisotropic light scattering, and uniaxial birefringence being observed in irradiated samples. At present, the microscopic processes underlying such anisotropies remain unclear. We have identified an additional property present in fused silica which is apparent after being irradiated by an amplified Ti:sapphire femtosecond laser system-strong reflection from the damaged region occurs only along the direction of polarization of the writing laser.
We have investigated the evanescent field associated with an optical fiber Bragg grating using the subwavelength imaging properties of scanning near-field optical microscopy. Imaging of either the field distribution within the grating, or the periodic refractive index changes along the grating can be performed by tuning the launched light on or off the grating resonance. These measurements reveal nonuniformity in the resonant standing-wave pattern that occur due to phase errors in the refractive index profile of the grating under study.
This paper deals with the design of impulse noise resistant receivers for providing telephony-over-cable (ToC) services over hybrid fiber coax (HFC) networks. We first discuss the overall scenario of ToC services and the impulse noise problems faced by such systems in HFC networks. We then briefly describe the time-frequency characteristics of impulse interference and derive the probability of error for binary and quadrature PSK signalling schemes for impulse noise afflicted channels. In light of the constraints imposed by the ToC problem, the performance of the proposed solution strategies which make use of non-linear processing and channel coding, is evaluated in detail along with simulation results.
Abstract— We present a process for active‐matrix flat‐panel‐display manufacture based on solution processing and printing of polymer thin‐film transistors. In this process, transistors are fabricated using soluble semiconducting, conducting, and dielectric polymer materials. Accurate definition of the transistor channel and other circuit components are achieved by direct ink‐jet printing combined with surface‐energy patterning. We have used this process to create 4800‐pixel 50‐dpi active‐matrix backplanes. These backplanes were combined with polymer‐dispersed liquid crystal to create the first ink‐jet‐printed active‐matrix displays. Our process is, in principle, environmentally friendly, low temperature, compatible with flexible substrates, cost effective, and advantageous for short‐run length and large display sizes. As well as polymer‐dispersed liquid crystal, this technology is applicable to conventional liquid‐crystal and electrophoretic display effects.
Correlation between anisotropic reflection and birefringence in glass irradiated with femtosecond pulses is observed. Direct evidence of self-induced nanogratings and form birefringence is obtained.
The use of lasers to directly pattern optoelectronic devices primarily utilizes direct irradiation by UV light. We present here an alternative route using multi-photon absorption within a spherical focus in 3D space, thus allowing complex embedded structures to be directly written. In wide-bandgap materials such as chalcogenide, fluoride and silica glasses, our observations suggest free electrons are produced within the focus of a high-power infrared ultrashort pulse. The anisotropic interaction of this plasma with the incident pulse produces micron-sized DBR gratings of a 150nm pitch. An amplified Ti:S laser with 250kHz repetition rate, 150fs pulse duration, and wavelength tuned from 800-850nml is used to write embedded diffraction gratings and arrays of dots. The laser beam is focussed with a 50x objective into transparent polished samples, with pulse energies ranging from 0.1-1.1pJ (Fig.la). During the writing process broadband sub-bandgap UV light is emitted from a micron-sized spot at the sample focus. The written structures are permanent, typically with large refractive index changes on the order of Delta.n = +0.01 depending on the material.
The Laser-Induced Forward Transfer (LIFT) technique [1] exists as a simple method for the direct-writing of a wide range of materials with sub-micron to 100s of microns feature sizes. A thin film of the material to be deposited (the donor) is coated onto one face of a transparent carrier substrate and transferred to another substrate (the receiver) placed some microns away by irradiating the carrier-donor interface through the carrier with a CW or pulsed laser. The process is inherently thermal in nature, with melting and ablation of the donor required to provide the necessary thrust for transferring material. Hence, the technique is not readily applied to the deposition of thermo-sensitive materials
We compare the performances of low intensity (~18 nJ/pulse) femtosecond 244 nm grating writing with that of CW (20 mW) 244 nm grating writing for fixed fluencies. We find no evidence of any improvement using pulsed light with duration commensurate with phonon-assisted relaxation away from the excited state.
Summary form only given. We have developed a novel technique, which enables us to write such structures within the bulk of an optical fiber through its cleaved face, enabling control over light subsequently exiting the fiber. We show the experimental set-up where an amplified Ti:sapphire 150 fs pulsed laser with a repetition rate of 250 kHz is used to irradiate the samples at 850 nm, via a 50X objective.
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