Multiwavelength Raman fiber laser with a continuously-tunable spacing

A spacing-tunable multiwavelength Raman fiber laser with an independently-adjustable channel number is proposed and demonstrated. It uses a novel free-spectral-range (FSR)-tunable comb filter based on a superimposed chirped-fiber Bragg grating (CFBG) and a linear cavity formed by a bandwidth-tunable CFBG reflector, a pumped highly-nonlinear fiber for Raman gain, and an optical circulator based loop mirror. Multiwavelength laser operations with spacing tuning from 0.3 to 0.6 nm and channel number adjustment from 2 to 10 have been achieved.

Thermally switchable and discretely tunable comb filter with a linearly chirped fiber Bragg grating

We propose and experimentally demonstrate a novel switchable and discretely tunable comb filter based on a thermally induced linearly chirped fiber Bragg grating. Experimentally we achieved a thermally induced optical bandpass filter that has eight switchable passband peaks with peak separations of 1.6 and 3.2 nm, a very narrow bandwidth (as small as 10 pm) of each peak, a tunable range of 16.5 nm, and a greater than 25 dB rejection ratio. Two spectral peaks separated by only 0.8 nm were also obtained with this comb filter. This filter provides the unique advantages of an all-fiber structure, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, low polarization sensitivity, simple structure, ease of fabrication, and low cost.

Optical functions of (x)GeO2:(1-x)SiO2 films determined by multi-sample and multi-angle spectroscopic ellipsometry

Thin films of (x)GeO2:(1-x)SiO2, 0 </= x </= 0.4, were fabricated via the sol-gel technique. Many applications of optics and photonics can benefit from the knowledge of the optical dispersion relationship of this ubiquitous binary ceramic material. The optical properties of the homogeneous and amorphous silica-based films were derived by spectroscopic ellipsometry (SE) with a multi-sample and multi-angle technique. The physical model used in SE has been rigorously verified. A simple, yet reliable, method is described to produce a dispersion-composition surface for visualizing, and hence, predicting refractive indices of the films. The Sellmeier model was effectively used to describe the optical dispersion properties of the GeO2:SiO2 films for a range of wavelengths from 210 to 1700 nm. Dispersion parameters were determined to evaluate the change in the compositional-dependent dispersion characteristics. In addition, the material dispersion coefficient and zero-dispersion wavelength were found to vary with x.

Thermally tunable narrow-bandpass filter based on a linearly chirped fiber Bragg grating

We propose a new method for the development of a tunable optical bandpass filter (TOBF) based on a linearly chirped fiber Bragg grating (LCFBG). A NiCr wire heater is used to heat the LCFBG at a small point to introduce a narrow passband within the stop band of the LCFBG. The central wavelength of the passband is tuned by scanning the wire heater along the LCFBG. As an example demonstrating the effectiveness of the proposed method, we demonstrate a TOBF with a very small 3-dB bandwidth of approximately 7 pm, a tuning range of 16.4 nm, and a rejection ratio of more than 25 dB. Compared with previously reported tunable-fiber-based bandpass filters, this method provides the advantages of a large tuning range, continuous tunability, a switchable passband, a simple tuning mechanism, low cost, and narrow bandwidth.

Simple reflow technique for fabrication of a microlens array in solgel glass

A simple reflow method for fabrication of refractive microlens arrays in inorganic-organic SiO2-ZrO2 solgel glass is presented. To our knowledge, this is the first report that presents a simple reflow technique for transforming a negatively induced hybrid solgel material into desirable spherical microlenses. It is shown that the microlenses have excellent smooth surfaces and uniform dimensions. The reflow technique is considerably cheaper than use of a high-energy beam-sensitive gray-scale mask and is suitable for mass production.

Amplified double-coupler double-ring optical resonators with negative optical gain

Optical resonators with a double-coupler and double-ring configuration incorporated into optical amplifiers that have negative gain are analyzed. The resonators are presented with a unique signal-flow graph together with z-transform variables for sampled optical signals. Their optical transfer functions are obtained by a graphical technique. The poles and zeroes in the z plane of the transfer functions are examined, which leads to some unique design features of the resonators for optical-filtering applications.

Fiber-optic array algebraic processing architectures

A high-accuracy fiber-optic array processor (FOAP) based on the algorithm of digital multiplication by analog convolution is proposed. The FOAP architecture is a local regularly interconnected processor that utilizes an array of identical all-optical elemental-processing lattice units, namely, an optical splitter, an optical combiner, and a binary programmable fiber-optic transversal filter. Various FOAP matrix multipliers are proposed for nonnegative and twos-complement binary arithmetic matrix-vector, matrix-matrix, triple-matrix, and high-order matrix operations. The overall performances of the FOAP matrix multipliers are compared with the time-integrating and space-integrating architectures and with the digital multipliers. Extension of the digital-multiplication-by-analog-convolution algorithm is also considered.