Quantum box fabrication tolerance and size limits in semiconductors and their effect on optical gain

Lower and upper limits on size are established for quantum boxes. The lower limit is shown to result from a critical size below which bound electronic states no longer exist. This critical size is different for electrons and holes. The optical gain of arrays of quantum boxes is computed taking into account the inhomogenous broadening of the gain spectrum resulting from fabricational variations in quantum box size and shape. The dependence of maximum possible gain on an rms quantum box roughness amplitude is determined. For high gain operation a medium composed of quantum boxes does not offer significant advantages over a conventional bulk semiconductor unless quantum box fabricational tolerances are tightly controlled. For low gain operation, however, arrays of quantum boxes may offer the unique advantage of optical transparency at zero excitation. This property does not require excellent fabricational control and may make possible ultralow threshold semiconductor lasers and low noise optical amplifiers

Modal Spectroscopy of Optoexcited Vibrations of a Micron-Scale On-Chip Resonator at Greater than 1 GHz Frequency

We analyze experimentally and theoretically >1 GHz optoexcited mechanical vibration in an on-chip micron-scaled sphere. Different eigen-mechanical modes are excited upon demand by the centrifugal radiation pressure of the optical whispering-gallery-mode, enabling an optomechanical modal spectroscopy investigation of many vibrational modes. Spectral analysis of the light emitted from the device enables deduction of its natural vibrational modes in analogy with spectroscopy of a molecule's vibrational levels, and its eccentricity perturbation is shown to induce spectral splitting

Highly nondegenerate four-wave mixing efficiency of an asymmetric coupled quantum well structure

An asymmetric coupled quantum well structure is theoretically investigated as a means of tailoring the conversion efficiency of the four-wave mixing process at terahertz detuning rates. In this structure, a coherent electronic oscillation between the two wells can be excited that introduces a resonance peak in the four-wave mixing frequency response. A calculation based on the density matrix formalism shows that an increase in the power conversion efficiency on the order of 10 dB can be attained at the selected resonance frequency for low temperature operation. Finally, we propose a novel technique for exciting the interwell oscillations that takes advantage of the polarization dependence of the interband optical transitions in alternating strain quantum wells

Observation of Kerr nonlinearity in microcavities at room temperature

We have devised and experimentally verified a method for observation of the optical Kerr effect in microcavities at room temperature. The technique discriminates against the much larger and typically dominant thermal component of nonlinearity by using its relatively slow frequency response. Measurement of the Kerr coefficient or equivalently of the third-order nonlinear susceptibility of the cavity material is demonstrated for a silica microcavity. With this approach, useful information about the characteristic thermal response time in microresonators can also be acquired

Four-wave mixing and generation of terahertz radiation in an alternating-strain coupled quantum-well structure

We propose a scheme for exciting steady-state tunneling oscillations of an electronic wave packet in a semiconductor coupled quantum-well structure with strain of the opposite polarity in the two wells. A detailed study of the four-wave mixing process in this structure is then presented, based on the density matrix formalism. Our results show that a resonance peak is introduced in the four-wave mixing frequency response at the tunneling frequency, leading to a significant enhancement in the wavelength conversion efficiency for low temperature operation. Furthermore, we consider this structure under the same excitation condition as a potential source of coherent radiation in, the terahertz frequency band

Parasitic-free modulation of semiconductor lasers

Active-layer photomixing is a technique for modulating semiconductor lasers with nearly perfect immunity to device parasitics. Measurements of the intrinsic modulation response of a laser diode using this technique at temperatures as low as 4.2 K are discussed. From these measurements, the temperature dependence of important dynamical parameters is determined. In addition, this provides a stringent test of the active-layer photomixing technique since parasitic response is degraded, while the intrinsic response is improved for low-temperature operation. At 4.2 K, the ideal intrinsic response is measured for frequencies as high as 15 GHz despite an estimated parasitic corner frequency of 410 MHz

Fiber-taper coupling to Whispering-Gallery modes of fluidic resonators embedded in a liquid medium

We demonstrate efficient coupling to the optical Whispering-Gallery (WG) modes of a fluidic resonator consisting of a droplet embedded in a liquid medium. Unlike previous experiments the droplet is not levitated in an optical or electrostatic trap and free space coupling is replaced by phase-matched, waveguide coupling using a fiber-taper. We have observed critical coupling to fundamental WG modes of a 600 μm diameter water droplet at 980 nm. The experimental challenges towards making, stabilizing and coupling to the droplet resonators are addressed in this paper

Measurement of the fundamental modulation response of a semiconductor laser to millimeter wave frequencies by active-layer photomixing

The room-temperature modulation response of a GaAs/GaAlAs semiconductor laser (relaxation resonance frequency, vR=6.5 GHz) is measured to 37 GHz using the active-layer photomixing technique. The measured response function agrees with the theoretical ideal, and there is no indication of device parasitic effects. An ultrahigh-finesse Fabry–Perot interferometer is used to detect the optical modulation, which appears as sidebands in the laser field spectrum. With a moderately faster laser diode (i.e., vR~10 GHz), the modulation response should be measurable beyond 100 GHz

Low-temperature measurement of the fundamental frequency response of a semiconductor laser by active-layer photomixing

We use the active-layer photomixing technique to directly modulate the output of a GaAs semiconductor laser operating at temperatures as low as 4.2 K. The technique produces modulation with nearly perfect immunity to device parasitic effects, revealing the laser diode's intrinsic modulation response. At 4.2 K the parasitic corner frequency is estimated to be 410 MHz, yet the response appears ideal out to 15 GHz. We measure the dynamical parameters governing the response function, the relaxation resonance frequency, and the damping rate, and discuss their low-temperature behavior

Cathodoluminescence of oval defects in GaAs/AlxGa1–xAs epilayers using an optical fiber light collection system

A cathodoluminescence system using a novel optical fiber light collection system is employed to study oval defects in GaAs/Alx Ga1–x As epilayers grown by molecular beam epitaxy. Spatially and spectrally resolved data on the luminescence of oval defects are presented. Oval defects are found to contain an enhanced concentration of gallium, which is consistent with current theories regarding the origin of these defects