D.L. Coblentz

Mode-locked hybrid soliton pulse source with extremely wide operating frequency range

The authors report a mode-locked pulse source with extremely wide operating frequency range and very stable operation, through the use of a long, linearly chirped Bragg reflector as the output coupler integrated in a fiber external cavity. A 1.55 mu m strained MQW laser diode is used, with one facet high reflectivity (HR) coated for improved cavity Q, and the other antireflection (AR) coated to allow coupling to the external cavity and suppress Fabry-Perot modes. Near-transform-limited pulses are obtained over a frequency range of 700 MHz around a system operating frequency of 2.488 GHz, with pulsewidths of 50 ps, as required for a practical soliton transmission system.<<ETX>>

Frequency response subtraction for simple measurement of intrinsic laser dynamic properties

The authors describe a new technique for extracting the intrinsic laser-diode dynamic properties accurately. This simple technique eliminates the need for accurate microwave calibration of the test equipment and problems of microwave reflections, nonideal frequency response of laser mount, and detector. The effect of the parasitic components of the laser diode are also eliminated from the results so that measurements of important dynamic properties of the laser can be found up to high frequencies (10-20 GHz) on standard laser diodes. The techinque being used to measure variations of resonance peak and damping factor at different bias levels for a standard bulk active region 1.3 mu m laser diode is shown.<<ETX>>

High temperature characteristics of InGaAsP/InP laser structures

We investigate the high temperature performance of conventional separate confinement and lattice matched and compressively strained multi‐quantum‐well InGaAsP lasers emitting at 1.3 μm. Low threshold buried heterostructure lasers operate reproducibly at temperatures as high as 130 °C. The rate of threshold change with temperature is described by T0∼45°–55° for both conventional and quantum well lasers. The rate of change is not influenced by any modifications in the active layer structure. In contrast, excellent correlation is observed between the active layer structure, parametrized as the threshold gain, and the peak cw operating temperature.

32 Gb/s optical soliton data transmission over 90 km

The authors demonstrate error-free optical soliton transmission at 32 Gb/s over 90 km of dispersion-shifted fiber. Fiber loss was compensated for by using diode laser pumped Er/sup 3+/-doped fiber amplifiers located every 30 km and a 4 Gb/s data pattern was passively multiplexed to 32 Gb/s. Approximately 16-ps-wide, near transform-limited pulses were launched into the system and the output pulsewidth was about 14 ps. At the receiver, four-wave mixing was employed to perform all optical demultiplexing of the data down to the base data rate. At a 10/sup -9/ (2/sup 15/-1 word length) bit-error rate, the penalties from the demultiplexing and the 90-km soliton transmission were approximately 1.6 and 0.5 dB, respectively.<<ETX>>

Strained multiple quantum well lasers emitting at 1.3 μm grown by low‐pressure metalorganic vapor phase epitaxy

Low‐threshold and high‐output power of the first InGaAsP/InP graded index strained multiple quantum well lasers emitting near 1.3 μm wavelength is reported. A continuous wave threshold current of 10 mA and a quantum efficiency of 60% with maximum output power of 100 mW/facet is observed in uncoated lasers having compressively strained InGaAsP quantum wells. With high reflectivity on both facets, a reduced threshold current as low as 3.5 mA is observed. Highest output power of 250 mW was observed in lasers with antireflection‐high reflection coating configuration operating at 10 °C. The improved performance of the lasers is attributed to both the reduced internal absorption loss (6 cm−1) and the suppressed nonradiative recombination in the structure.

Temperature dependence of long wavelength semiconductor lasers

We compare the temperature dependent characteristics of multiple quantum well semiconductor laser diodes and light emitting diodes operating at a wavelength, λ=1.3 μm. No model in which Auger recombination is the dominant temperature sensitive parameter can explain our experimental observations. We suggest that net gain is the appropriate temperature dependent variable which determines laser diode performance at elevated temperatures.

Strained quaternary quantum well lasers for high temperature operation

We describe compressively strained separate confinement heterostructure 1.3 μm quantum well lasers optimized for high temperature operation. The active layer consists of ten GaInAsP wells, each 40–80 A thick, grown under compressive lattice mismatch strain of Δa/a≤0.75%. Within the constraints of the well composition and thickness imposed on the active region, strain is necessary for efficient laser operation. Best results are obtained for Δa/a∼0.2%–0.3% with the laser threshold as low as 5 mA and slope efficiency of 42 mW/mA. In the temperature range of 25–85 °C a slope efficiency change as small as 30% was achieved. Power output of at least 20 mW can be maintained up to 100 °C at a current drive below 150 mA.

On the temperature sensitivity of semiconductor lasers

The temperature dependence of below‐threshold emission from multiple quantum well semiconductor lasers is well characterized by a power law, in excellent agreement with Landau–Ginzburg theory of second‐order phase transitions. We thereby show that it is the temperature dependence of net gain and not that of nonradiative recombination which primarily determines temperature sensitivity of threshold in long‐wavelength injection lasers.

Effect of barrier recombination on the high temperature performance of quaternary multiquantum well lasers

We use spectrally resolved measurements of spontaneous emission to investigate the temperature characteristics of strained and lattice matched InGaAsP multiquantum well lasers. Carrier overflow into the barriers and separate confinement layers and the resulting recombination are demonstrated to be an important factor limiting high temperature performances in these devices. The barrier recombination does not saturate above threshold, instead it increases with the drive current. This effect is further enhanced with increased temperature. We show that the reduction in the barrier recombination correlates quantitatively with increased high temperature slope efficiency.

High-speed InGaAsP/InP multiple-quantum-well laser

The authors describe practical high-speed InGaAsP/InP lasers based on compressively strained quantum wells. Buried heterostructure lasers with threshold currents of 10 mA and slope efficiencies of 0.23 mW/mA are used. A modulation bandwidth of 20 GHz is obtained at a low drive current of 90 mA. A K factor of 0.25 ns is obtained and the intrinsic bandwidth of these lasers is estimated at 35 GHz.<<ETX>>