R. Nagar

Coupling between barrier and quantum well energy states in a multiple quantum well optical amplifier

We describe the interaction between carriers in three‐dimensional barrier and confinement regions and two‐dimensional quantum well regions of a 1.5 μm multiple quantum well optical amplifier. We present a model and measurements of the spontaneous emission and gain spectra dependence on an external optical pump signal.

Four-wave mixing among short optical pulses in semiconductor optical amplifiers

We describe the dependence of four-wave mixing conversion efficiency among short optical pulses in a semiconductor optical amplifier. We show a strong dependence on pulse shape and pulse overlap, predicted theoretically and confirmed in experiments.<<ETX>>

Temperature dependent loss and overflow effects in quantum well lasers

We report a detailed study of the temperature dependent internal loss in 1550-nm quantum well lasers. Measurements of lasers with different cavity lengths as well as of lasers with modified facet reflectivities are presented. The internal loss is found to be mainly associated with intervalance band absorption and to include contributions from confined as well as unconfined carriers with the latter dominating at elevated temperatures. Measurements are consistent with calculations based on a detailed carrier injection model. Threshold current density dependence on temperature and on cavity length as well as photon density dependent internal losses are also addressed.<<ETX>>

Nonequilibrium effects in quantum well lasers

We present a simple technique of measuring the effect of the finite capture time of carriers in quantum well lasers on the homogeneity of the gain. The effect is measured using an extended cavity laser configuration in which we control the feedback level and compare the two extreme cases of a laser and a nonlasing amplifying gain medium. Broadband measurements of the spontaneous emission at energies near the top of the well and above the barriers show an inhomogeneous gain saturation which depends on the photon density inside the cavity. The results agree with a simple model for carrier injection in quantum well lasers.

Measurements of the barrier‐well injection bottleneck in a multiple quantum well optical amplifier

We describe broadband static pump probe measurements of the barrier‐well injection bottleneck caused by a complicated interaction between three‐ and two‐dimensional carriers in a 1.5‐μm multiple quantum well optical amplifier.

Distributed Bragg reflector active optical filters

The characteristics of active optical filters based on distributed Bragg reflector (DBR) laser diodes are described. The authors present a theoretical model for the small and large signal filter response which can be used to optimize the filter design and operating point. The large signal filter response is dominated by a variety of nonlinear effects, including a wavelength domain bistability. The authors describe a series of experiments in which the predicted filter characteristics are demonstrated. The authors present detailed measurements of the filter transfer function in both transmission and reflection modes under low and high power injection. For the small signal measurements a powerful technique which uses the swept frequency concept is presented. For the large signal regime, measurements of both frequency pulling and wavelength domain bistability are presented. >

Frequency tuning and pulse generation in a fiber laser with an intracavity semiconductor active filter

The authors demonstrate optical frequency tuning by direct electrical means as well as FM and AM mode-locking in an erbium-doped fiber laser with an intracavity distributed Bragg reflector active filter/modulator. They obtained a 6 nm discrete tuning range and pulses of 38 and 78 ps duration in AM and FM mode-locking, respectively.<<ETX>>

Near-field scanning optical microscopy studies of V-grooved quantum wire lasers

Detailed near-field scanning optical microscopy studies of GaAs/AlGaAs V-grooved quantum wire lasers at room temperature were performed. We measured the spectrally resolved near-field intensity distributions, emitted from the complex epitaxially grown optical waveguide in the V groove with a spatial resolution of ∼0.1 μm. Distinct regions emitting at different wavelengths were identified, and a heart shaped modal distribution of less than 0.5 μm in diameter was measured and well matched the calculated light distribution of this structure.

Pure phase-modulation mode locking in semiconductor lasers

Pure phase-modulation mode locking of an extended-cavity semiconductor laser, operating near 1.5 microm, is demonstrated. The mode-locked laser uses a two-section optical amplifier that provides both gain and phase modulation.

Bistability and optical control of a distributed-Bragg-reflector laser.

We demonstrate bistable operation and optical control of a specially designed distributed-Bragg-reflector laser. Optically controlled turn-on and turn-off with 1-pJ pulses at 1.5 μm and 2-pJ pulses at 1.3 μm, respectively, is demonstrated as well as all-optical flip-flop operation.