Gain functionalization of silica microresonators

Erbium-doped solgel films are applied to the surface of silica microspheres to create low-threshold microcavity lasers. This gain functionalization can be applied by use of a number of different dopants, thereby extending the wavelength range of this class of device. Also, by varying the doping concentration and thickness of the applied solgel layer, one can vary the laser dynamics so that both continuous-wave and pulsating modes of operation are possible

Ultralow Loss, High Q, Four Port Resonant Couplers for Quantum Optics and Photonics

We demonstrate a low-loss, optical four port resonant coupler (add-drop geometry), using ultrahigh Q (>108) toroidal microcavities. Different regimes of operation are investigated by variation of coupling between resonator and fiber taper waveguides. As a result, waveguide-to-waveguide power transfer efficiency of 93% (0.3 dB loss) and nonresonant insertion loss of 0.02% (<0.001 dB) for narrow bandwidth (57 MHz) four port couplers are achieved in this work. The combination of low-loss, fiber compatibility, and wafer-scale design would be suitable for a variety of applications ranging from quantum optics to photonic networks

Observation of relaxation resonance effects in the field spectrum of semiconductor lasers

Subsidiary maxima are observed in the field spectra of single mode semiconductor lasers. Measurements of their power dependence show they are linked to the relaxation resonance. We attribute these maxima to combined phase and amplitude fluctuations at the relaxation resonance. A theoretical calculation of the field spectrum using the results of a noise analysis incorporating carrier dynamics agrees very well with observations

Fiber-coupled erbium microlasers on a chip

An erbium-doped, toroid-shaped microlaser fabricated on a silicon chip is described and characterized. Erbium-doped sol-gel films are applied to the surface of a silica toroidal microresonator to create the microcavity lasers. Highly confined whispering gallery modes make possible single-mode and ultralow threshold microlasers

Soft lithographic fabrication of microresonators

Using ultra-high-Q toroid microcavity masters, soft lithography is applied to fabricate polymer microcavity arrays with Q factors in excess of 10^6. This technique produces resonators with material-limited quality factors

Enhanced modulation bandwidth of GaAlAs double heterostructure lasers in high magnetic fields: Dynamic response with quantum wire effects

The modulation bandwidth of GaAlAs double heterostructure (DH) lasers in high magnetic fields is measured. We found that the modulation bandwidth is enhanced by 1.4× with a magnetic field of 20 T. This improvement is believed to result from the increase of the differential gain due to two-dimensional carrier confinement effects in the high magnetic field (quantum wire effects). A comparison of the experimental results with a theoretical analysis indicates that the intraband relaxation time tauin of the measured DH laser in the range of 0.1 to 0.2 ps

Reduction of the spectral linewidth of semiconductor lasers with quantum wire effects—Spectral properties of GaAlAs double heterostructure lasers in high magnetic fields

The spectral linewidth of a GaAlAs double heterostructure laser placed in a high magnetic field is measured at 190 K. It is found that the power-dependent spectral linewidth is reduced by a factor of 0.6 in a magnetic field of 19 T. This reduction is believed to result mainly from the reduction of the linewidth enhancement factor alpha due to a quasi-one-dimensional electronic system formed by the high magnetic field (i.e., by quantum wire effects)

Quantum-well capture and interwell transport in semiconductor active layers

The dynamics of electrons and holes in multiquantum-well semiconductor gain media involves several different transport processes, such as diffusion and drift across the barrier region, as well as capture and escape transitions between the bound and the unbound states of the quantum wells. In addition to their fundamental interest, these processes are important because of their implications for the dynamic properties of multiquantum-well lasers and optical amplifiers. Experimentally, they have been studied with several time-domain optical techniques having (sub)picosecond resolution and, more recently, with frequency-domain techniques based on laser modulation measurements. This article gives a brief review of the work done in this area and then presents in detail a frequency-domain approach, four-wave mixing spectroscopy in semiconductor optical amplifiers, to investigate intrinsic capture and interwell equilibration. This technique allows one to extend the device modulation frequency to several hundreds of gigahertz, thus providing the required time resolution, and can be configured to isolate and directly study the transport process of interest

Scanning probe microscopy of thermally excited mechanical modes of an optical microcavity

The resonant buildup of light within optical microcavities elevates the radiation pressure which mediates coupling of optical modes to the mechanical modes of a microcavity. Above a certain threshold pump power, regenerative mechanical oscillation occurs causing oscillation of certain mechanical eigenmodes. Here, we present a methodology to spatially image the micro-mechanical resonances of a toroid microcavity using a scanning probe technique. The method relies on recording the induced frequency shift of the mechanical eigenmode when in contact with a scanning probe tip. The method is passive in nature and achieves a sensitivity sufficient to spatially resolve the vibrational mode pattern associated with the thermally agitated displacement at room temperature. The recorded mechanical mode patterns are in good qualitative agreement with the theoretical strain fields as obtained by finite element simulations

On the linewidth enhancement factor alpha in semiconductor injection lasers

A simple model for the linewidth enhancement factor alpha and its frequency dependence in semiconductor lasers is presented. Calculations based on this model are in reasonable agreement with experimental results