In this work, the optical characteristics of monolithic passively mode-locked lasers (MLLs) fabricated from 1.24-&mgr;m
InAs dots-in-a-Well (DWELL), 1.25-&mgr;m InGaAs single quantum well (SQW), and 1.55-&mgr;m GaInNAsSb SQW
structures grown using elemental source molecular beam epitaxy (MBE) are reported. 5 GHz optical pulses with sub-picosecond
RMS jitter, high pulse peak power (1W) and narrow pulse width (< 10 ps) were demonstrated in monolithic
two-section InAs DWELL passive MLLs. With the 42% indium InGaAs SQW MLL, a record high-temperature
performance for a monolithic passively mode-locked semiconductor laser is found. Compared with the typical operating
range of the InAs DWELL devices (<60°C), the operation is in excess of 100 °C. The first 1.55-&mgr;m GaInNAsSb SQW
MLL operates at a repetition rate of 5.8 GHz and has a 3-dB bandwidth of 170 kHz in the RF spectrum indicating
respectable jitter.
Lei Zhang, Ling-Shen Cheng, Allen Gray, Hua Huang, Srivatsa Kutty, Hua Li, John Nagyvary, Faisal Nabulsi, Leonard Olona, Edwin Pease, Qi Sun, Chris Wiggins, John Zilko, Zhengzhong Zou, Petros Varangis
Low timing jitter (< 5 ps), high peak power (1 W at the laser facet), narrow pulses (< 10 ps) at a 5 GHz pulse
repetition rate is demonstrated by monolithic passively mode-locked quantum dot lasers. Their low cost, compact
size and DC-biased operation make them ideal for high speed optical interconnects and optical clocking
applications.
For understanding the fundamental processes in QDs and optimizing the design of QD optical devices, it is essential to obtain accurate optical gain and absorption spectra. An improved segmented-contact method is described that subtracts the unguided spontaneous emission that normally introduces error into the calculated gain and absorption. Using the technique a QD gain spectrum is measured to an accuracy of less than 0.2/cm at nominal gain values below 2/cm. This capability also enables precise measurement of waveguide internal loss, unamplified spontaneous emission spectra and Stark shift data.
We measure, for the first time, the gain compression coefficient and above-threshold linewidth enhancement factor (alpha parameter) in quantum dot (QD) distributed feedback lasers (DFB) by time-resolved-chirp (TRC) characterization. The alpha parameter is measured to be 2.6 at threshold and increases to 8 when the output power of the QD DFB is increased to 3 mW. The dependence of the above-threshold alpha parameter on the optical power is found to be stronger than the optical gain compression effect alone can predict. The inhomogeneous gain broadening, gain saturation at the ground states and carrier filling in the excited states in QDs are proposed to explain the results.
In this paper, we overview several of the critical materials growth, design and performance issues for nitride-based UV (less than 400 nm) LEDs. The critical issue of optical efficiency is presented through temperature-dependent photoluminescence studies of various UV active regions. These studies demonstrate enhanced optical efficiencies for active regions with In-containing alloys (InGaN, AlInGaN). We discuss the trade-off between the challenging growth of high Al containing alloys (AlGaN, AlGaInN), and the need for sufficient carrier confinement in UV heterostructures. Carrier leakage for various composition AlGaN barriers is examined through a calculation of the total unconfined carrier density in the quantum well system. We compare the performance of two distinct UV LED structures: GaN/AlGaN quantum well LEDs for (lambda) less than 360 nm emission, and InGaN/AlGaInN quantum well LEDs for 370 nm less than (lambda) less than 390 nm emission.
The recent development of a high-aspect ratio Si etch (HARSE) process has enabled the fabrication of a variety of Si structures where deep trench etching is necessary. The HARSE process relies on the formation of a sidewall etch inhibitor to prevent lateral etching of the Si structures during exposure to an aggressive SF6/Ar plasma etch chemistry. The process yields highly anisotropic profiles with excellent dimensional control for high aspect ratio features. In this study, Si etch rates and etch selectivities to photoresist are reported as a function of chamber pressure, cathode rf-power, ICP source power, and gas flow. Si etch rates greater than 3 micrometer/min with etch selectivities to resist greater than 75:1 were obtained. Lateral dimensional control, etch selectivities to SiO2 and Si3N4, and aspect ratio dependent etching (ARDE) will also be discussed.
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