Design and analysis of a control system for an optical delay-line circuit used as reconfigurable gain equalizer

The design and analysis of a control system for a coherent two-port lattice-form optical delay-line circuit used as reconfigurable gain equalizer is presented. The design of the control system, which is based on a real device model and a least-square optimization method, is described in detail. Analysis on a five-stage device for the 32 possible solutions of phase parameters showed that, for some filter characteristics, the variations in power dissipation can vary up to a factor of 2. Furthermore, the solution selection has influence on the optimization result and number of iterations needed. A sensitivity analysis of the phase parameters showed that the allowable error in the phase parameters should not exceed a standard deviation of /spl pi//500 in order to achieve a total maximal absolute accuracy error not greater than approximately 0.6 dB. A five-stage device has been fabricated using planar lightwave circuit technology that uses the thermooptic effect. Excellent agreement between simulations and measurements has been achieved

THE NATURE OF TURBULENT KINETIC ENERGY IN A DEEP AND NARROW VALLEY UNDER CONVECTIVE (?) CONDITIONS

This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions. The Riviera Valley in southern Switzerland has been chosen for a detailed case study, in which the evaluation of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350 m) large-eddy simulations using the model ARPS. The simulations verify what has already been observed on the basis of measurement data: TKE profiles scale surprisingly well if the convective velocity scale w٭ is obtained from the sun-exposed eastern slope rather than from the surface directly underneath the profiles considered. ARPS is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production mechanism. Therefore, the surface heat fluxes (and thus w٭) on the eastern slope do not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction of thermally-driven crossvalley and along-valley flow. Excellent correlations between w2٭ and the up-valley wind speed solidify this hypothesis

Passive harmonic modelocking in monolithic compound-cavity laser diodes

Passive harmonic modelocking operation of novel compound-cavity laser diodes is demonstrated. The modelocking rates can be readily scaled up into the terahertz domain and enable applications in terahertz imaging, medicine, ultrafast optical links, and atmospheric sensing

The application of the selective intermixing in selected area (SISA) technique to the fabrication of photonic devices in GaAs/AlGaAs structures

We demonstrate the fabrication of multiple wavelength lasers, and multi-channel wavelength division multiplexers using the one-step 'selective intermixing in selected area' quantum well intermixing technique in GaAs/AlGaAs structures. This technique is based on impurity-free vacancy diffusion and enables one to control the degree of intermixing across a wafer. Lasers with the bandgaps tuned to five different positions have been fabricated on a single chip. These lasers showed only small variations in transparency current, internal quantum efficiency and internal propagation loss, which indicates that the quality of the material remains good after being intel mixed. Four-channel wavelength demultiplexers or waveguide photodetectors have also been fabricated. Photocurrent and spontaneous emission spectra from individual diodes showed the shift of the absorption edge by different degrees due to the selective degree of quantum well intermixing. The results obtained also demonstrate the use of this technique in the fabrication of broad wavelength emission superluminescent diodes

Terahertz Frequency Mode-Locking of Monolithic Compound-Cavity Laser Diodes Incorporating Photonic-Bandgap Reflectors

Semiconductor lasers are modelocked at a harmonic of the round-trip frequency with pulse repetition rates up to 2.1 THz. The devices incorporate a monolithic compound cavity with a photonic-bandgap reflector. Possible applications include local oscillators and optical clocks

Modulation of the second-order nonlinear tensor components in multiple-quantum-well structures

In this paper, we present experimental results which demonstrate that quantum-well intermixing techniques can be used to modulate the magnitude of the second-order nonlinear coefficient /spl chi//sup (2)/. Impurity-free vacancy disordering with SiO/sub 2/ and Ga/sub 2/O/sub 3/ caps was used to modulate the position of the band edge and hence, the magnitude of /spl chi//sub eff//sup (2)/. Using a coupled quantum-well structure we were able to demonstrate modulation of the d/sub 33/ tensor components associated with the asymmetric structure and of the d/sub 14/ component associated with the bulk crystal structure

Terahertz-Frequency Mode-Locking of Monolithic Compound-Cavity Laser Diodes

We present harmonic modelocked operation of a novel design of monolithic compound-cavity semiconductor laser. Modelocking is achieved at a harmonic of the fundamental round-trip frequency with pulse repetition rates from 131 GHz to 2.1 THz

Control of the second- and third-order nonlinearities in GaAs-AlGaAs multiple quantum wells

We report the use of impurity-free vacancy disordering techniques to control the nonlinear optical properties of GaAs–AlGaAs multiple quantum wells. These processes result in a shift in the position of the absorption edge to higher energy and have been used to modify the second- and third-order nonlinear coefficients. Working at photon energies just below the half bandgap we have observed a reduction of ∼ 50% in the value of nonlinear refractive coefficient n2 for a bandgap shift of around 40 nm. This change arises due to the combined effects of increasing the bandgap and increasing the detuning. The process can also result in a modulation in the magnitude of the second-order susceptibility χ(2) coefficient and provides a potential mechanism for realizing quasi-phase-matched structures

Quantum-well intermixing for the control of second-order nonlinear effects in AlGaAs multiple-quantum-well waveguides

We present experimental evidence to demonstrate the feasibility of a promising new quasi-phase-matching technique in AlGaAs multiple-quantum-well waveguides. Non-phase-matched second-harmonic-generation measurements indicate that, for sub-half-bandgap excitation near 1.5  µm, quantum-well intermixing by impurity-free vacancy disordering results in a reduction of the nonlinear susceptibility