We propose a coupled modes analysis of second-harmonic generation in microdisk resonators. We demonstrate that whispering gallery modes can be used to obtain a combination of modal and geometrical quasi-phase-matching (without domain inversion) to obtain efficient conversion in isotropic and nonferroelectric materials such as III-V semiconductor compounds. Finally we use an analytical model to describe the coupling between a bus waveguide and the nonlinear microdisk to achieve an optimization scheme for practical configuration.

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Whispering-gallery-mode analysis of phase-matched doubly resonant second-harmonic generation

This paper overviews the properties and possible applications of long wavelength vertical-cavity semiconductor optical amplifiers (VCSOAs). A VCSOA operating in the 1.3-/spl mu/m wavelength region is presented. The device was fabricated using wafer bonding; it was optically pumped and operated in reflection mode. The reflectivity of the VCSOA top mirror was varied in the characterization of the device. Results are presented for 13 and 12 top mirror periods. By reducing the top mirror reflectivity, the amplifier gain, optical bandwidth, and saturation output power were simultaneously improved. For the case of 12 top mirror periods, rye demonstrate 13-dB fiber-to-fiber gain, 0.6 nm (100 GHz) optical bandwidth, a saturation output power of -3.5 dBm and a noise figure of 8.3 dB. The switching properties of the VCSOA are also briefly investigated. By modulating the pump laser, we have obtained a 46-dB extinction ratio in the output power, with the maximum output power corresponding to 7-dB fiber-to-fiber gain. All results are for continuous wave operation at room temperature.

Long wavelength vertical-cavity semiconductor optical amplifiers

We demonstrate second-harmonic generation in a doubly resonant semiconductor microcavity. The monolithic cavity consists of an AlGaAs active medium sandwiched between two AlGaAs/AlAs dual-wavelength mirrors. The mirrors do not have any apparent periodicity because, unlike single- or dual-wavelength Bragg reflectors, they are engineered with dispersion taken into account. Quasi-phase matching is obtained by addition of the appropriate phases at reflection so as to compensate for the dephasing between the fundamental and the second-harmonic fields.

Second-harmonic generation in a doubly resonant semiconductor microcavity.

We present the signal gain, wavelength tuning characteristics, saturation properties, and noise figure (NF) of MEMS-based widely tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) for various optical cavity designs, and we compare the theoretical results to data generated from a number of experimental devices. Using general Fabry-Pe/spl acute/rot relationships, it is possible to model both the wavelength tuning characteristics and the peak signal gain of tunable vertical-cavity amplifiers, while a rate-equation analysis is used to describe the saturation output power and NF as a function of the VCSOA resonant wavelength. Additionally, the basic design principles for an integrated electrostatic actuator are outlined. It is found that MEMS-tunable VCSOAs follow many of the same design trends as fixed-wavelength devices. However, with tunable devices, the effects of varying mirror reflectance and varying single-pass gain associated with the MEMS-based tuning mechanism lead to changing amplifier properties over the wavelength span of the device.

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MEMS-tunable vertical-cavity SOAs

We present experimental measurements of bistable characteristics for the case of a 1.55-/spl mu/m symmetric Fabry-Perot laser amplifier with a particularly rich variety of behavior for reflected signals. Three main forms of hysteresis loops are observed on reflection. The hysteresis loop changes from anticlockwise to clockwise hysteresis in the optical output-input characteristic when the drive current or initial phase detuning is changed. A "butterfly" hysteresis loop is observed experimentally at an optical input power as low as 300 /spl mu/W for a drive current equal to 94% of the lasing threshold. The dependence of the reflective optical bistability on drive current, initial phase detuning, and injected optical pewter has been investigated for the first time in an uncoated 1.55-/spl mu/m amplifier. Measurements of the device voltage shifts on switching reveal hysteresis loops which match those in the corresponding optical powers and which indicate the amount of gain saturation and nonlinear refraction responsible for bistability. An analytical model is used to describe the observed reflective bistability and to give insight into the detailed physical mechanisms responsible.

Measurements and modeling of reflective bistability in 1.55-/spl mu/m laser diode amplifiers

Optical amplification by stimulated emission is achieved in a vertical microcavity. A fast response of 20 ps and a gain of 2.5 dB point to an optical switch with a modulation width > 10 GHz, capable of handling 2 THz signals.

Vertical microcavity optical amplifying switch

A numerical method for the optimisation of dual-wavelength Bragg mirrors is presented. It takes into account the dispersion of the refractive index, and can be applied to generate two highly separated stopbands. The method is tested in a configuration useful for doubly-resonant second harmonic generation (stopbands at λ and 2λ), a situation for which simple analytical methods fail.

Optimisation of dual-wavelength Bragg mirrors

A simple technique for characterising nonlinear gratings for quasi-phase-matched structures is presented. The method is based on an analysis of the spectral characteristics of the second-harmonic beam generated in a pulsed regime. The potential of the technique is experimentally demonstrated using periodically poled D-shaped silica fibres, a promising second order nonlinear material.

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J.A. Levenson

Papers

Vertical microcavity optical amplifying switch

Optimisation of dual-wavelength Bragg mirrors

Spectral characterisation of χ(2) grating