InGaAs/InGaAsP MQW optical amplifier integrated withgrating-assisted vertical-coupler noise filter

A photonic integrated circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier and a grating-assisted vertical-coupler filter as a noise filter have been demonstrated. A fiber-to-amplifier/filter gain of ~0.5 dB and a 3-dB filter bandwidth (FWHM) of ~70 Å at 1.56 μm filter center wavelength have been achieved. This photonic circuit is potentially suitable as a building-block for preamplifier lightwave receivers or high-gain, high-power optical amplifiers which are essential for optical communication systems and lightwave networks     

Generalized digital Butterworth filter design

This correspondence introduces a new class of infinite impulse response (IIR) digital filters that unifies the classical digital Butterworth filter and the well-known maximally flat FIR filter. New closed-form expressions are provided, and a straightforward design technique is described. The new IIR digital filters have more zeros than poles (away from the origin), and their (monotonic) square magnitude frequency responses are maximally flat at ω=0 and at ω=π. Another result of the correspondence is that for a specified cutoff frequency and a specified number of zeros, there is only one valid way in which to split the zeros between z=-1 and the passband. This technique also permits continuous variation of the cutoff frequency. IIR filters having more zeros than poles are of interest because often, to obtain a good tradeoff between performance and implementation complexity, just a few poles are best     

Factoring very-high-degree polynomials

In this article, we discuss the current status of polynomial factoring (root finding) algorithms with some historical and mathematical background including size limits, convergence, accuracy and speed. The methods of root approximation versus root refinement are also examined. We then focus on two improved general purpose computational techniques, and in particular the factorization algorithm by Lindsey-Fox (L-F), which makes use of the fast Fourier transform to factor polynomials with random coefficients of degrees as high as 1 million. Computer simulations give insight that result in significant improvements in traditional approaches to an ancient problem.     

Characterization of erbium-doped fibers and application to modeling 980-nm and 1480-nm pumped amplifiers

Erbium-doped fibers are characterized using loss and gain coefficients, and one amplifier saturation parameter. With a large-signal amplifier model that resolves the amplified spontaneous emission spectrum, these easily measured parameters allow the fiber performance in 980-nm or 1480-nm pumped optical amplifiers to be assessed rapidly. In tests at 980-nm pump wavelength, good agreement between the theoretical and experimentally measured gains was obtained with amplifiers having either germano-silicate or germano-alumino-silicate core fibers.<>     

A transimpedance APD optical receiver operating at 10 Gb/s

The authors report an optical receiver which uses a separate-absorption-and-multiplication avalanche photodiode (SAM-APD) to achieve high sensitivity at a bit rate of 10 Gb/s. A transimpedance front end incorporating HEMT devices is used for high bandwidth and low noise. The sensitivity (bit-error rate of 10^-9) is -28.7 dBm for a return-to-zero signal, and -27.0 dBm for a nonreturn-to-zero signal     

Dependence of chirping on cavity separation in two-section coupled-cavity lasers

The dynamic linewidth of a C3 laser is measured as the gap width between the two cavities is varied. With the modulation applied only to one cavity, the chirping is largest for the gap which maximises spurious mode suppression. With the modulation split optimally between the two cavities, the chirp is smallest for this same gap.     

Millimetre-waveguide-mounted InGaAs photodetectors

We describe the design and characteristics of InGaAs PIN photodetectors mounted in microwave waveguides for use in transmission of millimetre-wave modulation signals on optical carriers. For an experimental device operating to 60 GHz (5 mm wavelength), we show the wavelength dependence of responsivity, the spatial uniformity of response and the bias dependence of modulation bandwidth.     

4.5 Gbit/s modelocked extended-cavity laser with a monolithically integrated electroabsorption modulator

An electroabsorption modulator has been monolithically integrated with an extended-cavity laser, which incorporates a Bragg reflector. Actively modelocked at the fundamental cavity resonance frequency of 4.5 GHz, the laser provides a train of 6.3 ps pulses with a centre wavelength of 1544 nm onto which data is encoded by the modulator. This 4.5 Gbit/s single-chip transmitter is suitable for systems employing short optical pulses.<>     

Measurement of very-high-speed photodetectors with picosecond InGaAsP film lasers

The impulse responses of very-high-speed photodiodes are determined using 5?15 ps pulses from optically pumped ultrashort-cavity film lasers operating between wavelengths of 1.15 ?m and 1.54 ?m. The measured response time (FWHM) for a back-illuminated InGaAs/InP punch-through PIN photodiode is 30 Ps.     

Parameter Identification of Signals Composed of Delayed Exponentials

This paper develops an approach to the problem of parameter identification from a signal which is a finite sum of possibly delayed exponentials. The coefficients and exponents, as well as the time delays, are found using a noniterative algorithm based on a matrix formulation of discrete-time convolution. Two methods of application are discussed and an example is included.