D.A. Ackerman

Efficient coupling of a semiconductor laser to an optical fiber by means of a tapered waveguide on silicon

A Si3N4 core waveguide, matched to a laser mode, is adiabatically tapered into a SiO2:P core waveguide, matched to a fiber mode. When used to couple the light from a semiconductor laser into an optical fiber, a loss of 3.1 dB is obtained, compared to a loss of 4.5 dB obtained with a lensed fiber.

Analysis of gain in determining T/sub 0/ in 1.3 /spl mu/m semiconductor lasers

Rapid decrease of differential gain has been determined to dominate the temperature dependence of threshold current in 1.3-/spl mu/m multiquantum well and bulk active lasers giving rise to low values of T/sub 0/. Extensive experimental characterization of each type of device is described. Results are presented for the dependence of gain on chemical potential and carrier density as a function of temperature. The data indicate the important role of the temperature-insensitive, carrier density dependent chemical potential in determining differential gain. Modeling of the temperature dependence of threshold carrier density in MQW and bulk active lasers based on a detailed band theory calculation is described. The calculated value of T/sub 0/ depends on the structure of the active layer, e.g., multiquantum well versus bulk. However, the calculated values are substantially higher than measured. >

Performance characteristics of a 1.5 mu m single-frequency semiconductor laser with an external waveguide Braff reflector

Single-frequency operation of 1.5- mu m semiconductor lasers was obtained by combining a regular Fabry-Perot laser to an external waveguide Bragg reflector. The laser is characterized by very pure single-frequency operation, 10-MHz linewidth, and greatly-reduced frequency chirp under direct modulation. The laser has been tested in 1.7-Gb/s transmission experiments over 82.5 km of fiber. >

Impedance‐corrected carrier lifetime measurements in semiconductor lasers

Differential carrier lifetime as a function of subthreshold bias current in 1.3 m bulk active lasers is obtained by measurement of small‐signal modulation of amplified spontaneous emission together with careful characterization of frequency‐ and current‐dependent device impedance. The strong influence of rapidly varying device impedance upon these measurements is illustrated. In contrast to other studies, neither saturation of differential lifetime at low currents nor linear dependence of spontaneous emission on carrier density is observed. Recombination parameters, fit from current versus carrier density, along with consistent fits of spontaneous emission versus carrier density, are presented.

Analysis of T0 in 1.3 μm multi‐quantum‐well and bulk active lasers

Temperature dependence of threshold in 1.3 μm semiconductor lasers is analyzed in terms of contributions due to gain, internal efficiency, internal loss, and nonradiative recombination. Rapid decrease of differential gain and roughly proportional increase in transparency carrier density are determined to dominate temperature dependence of threshold current. Auger recombination is found to play a secondary role in reducing T0 by compounding the effects of rapidly increasing threshold carrier density.

Gain characteristics of 1.55-μm high-speed multiple-quantum-well lasers

We describe the important characteristics of high-speed p-doped compressively strained MQW lasers obtained from comprehensive below-threshold DC measurements. Results of gain and differential gain versus wavelength and carrier density are verified by above-threshold resonance measurements. Measurement-derived design curves of gain, differential gain, and linewidth enhancement factor allow device optimization for high speed and low chirp.<<ETX>>

Second- and third-order harmonic distortion in DFB lasers

The second- and third-order harmonic distortion in distributed feedback (DFB) lasers is simulated using a time domain large signal dynamic model. The effects of the longitudinal spatial hole burning, nonlinear gain, spontaneous emission, and current leakage are included in the model. Composite second-order (CSO) and composite triple beat (CTB) are calculated for an 80 channel 60-540 MHz system with 3% modulation depth in each channel. The simulation results are compared with the experimental harmonic distortion measurements. >

Wavelength, modal and power stabilization of tunable electro-absorption modulated, distributed Bragg reflector lasers

Optical sources for dense wavelength division multiplexed (DWDM) systems must produce constant wavelength and power output over a system lifetime despite aging-induced changes that affect both wavelength and power. Tunable sources, such as distributed Bragg reflector (DBR) lasers, require additional modal stabilization to prevent aging-induced failure due to mode hopping. We demonstrate a practical scheme for simultaneously stabilizing the wavelength, mode and power of a tunable DBR laser which was then observed to operate stabilized and error-free within a transmitter at 2.5Gb/s over 680km ofnon-dispersion shifted fiber. Feedback is proven robust against sudden and large perturbations. A five-section electro-absorption modulated (EA) DBR laser serves as an electrically tunable source coupled to three closed feedback loops, which independently provide robust modal, wavelength and power stabilization.

Characterizing residual reflections within semiconductor lasers, integrated sources, and coupling optics

We describe a method for analyzing reflections within or near semiconductor lasers and more complicated integrated sources. Through Fourier transformation of an optical spectrum from the wavevector to the length domain, reflections are analyzed for strength, round-trip path length, and current or voltage dependence. Identification of reflections from within semiconductor lasers, integrated electro-absorption modulated lasers, and from coupling optics is presented. Spatial resolution in InP of /spl sim/5 /spl mu/m with over two orders of magnitude in dynamic range is demonstrated. Inverse transformation of a spatially resolved feature in a transformed reflection spectrum provides an optical spectrum due to that individual feature of sufficient resolution to study wavelength dependence, for example, of coatings and gratings.

High-speed, low chirp, directly modulated 1.55-/spl mu/m DFB laser sources for 10 Gbit/s local distribution

Summary form only given. In this paper we describe 1.55-/spl mu/m DFB lasers for communications applications using p-doped compressively strained multiple quantum well (MQW) active regions to provide devices with extremely high modulation bandwidths and low wavelength chirp.