Chung-En Zah

High-performance uncooled 1.3-/spl mu/m Al/sub x/Ga/sub y/In/sub 1-x-y/As/InP strained-layer quantum-well lasers for subscriber loop applications

Design considerations for fabricating highly efficient uncooled semiconductor lasers are discussed. The parameters investigated include the temperature characteristics of threshold current, quantum efficiency, and modulation speed. To prevent carrier overflow under high-temperature operation, the electron confinement energy is increased by using the Al/sub x/Ga/sub y/In/sub 1-x-y/As/InP material system instead of the conventional Ga/sub x/In/sub 1-x/As/sub y/P/sub 1-y//InP material system. To reduce the transparency current and the carrier-density-dependent loss due to the intervalence-band absorption, strained-layer quantum wells are chosen as the active layer. Experimentally, 1.3-/spl mu/m compressive-strained five-quantum-well lasers and tensile-strained three-quantum-well lasers were fabricated using a 3-/spl mu/m wide ridge-waveguide laser structure. For both types of lasers, the intrinsic material parameters are found to be similar in magnitude and in temperature dependence if they are normalized to each well. Specifically, the compressive-strained five-quantum-well lasers show excellent extrinsic temperature characteristics, such as small drop of 0.3 dB in differential quantum efficiency when the heat sink temperature changes from 25 to 100/spl deg/C, and a large small-signal modulation bandwidth of 8.6 GHz at 85/spl deg/C. The maximum 3 dB modulation bandwidth was measured to be 19.6 GHz for compressive-strained lasers and 17 GHz for tensile-strained-lasers by an optical modulation technique. The strong carrier confinement also results in a small k-factor (0.25 ns) which indicates the potential for high-speed modulation up to 35 GHz. In spite of the aluminum-containing active layer, no catastrophic optical damage was observed at room temperature up to 218 mW for compressive-strained five-quantum-well lasers and 103 mW for tensile-strained three-quantum-well lasers. For operating the compressive-strained five-quantum-well lasers at 85/spl deg/C with more than 5 mW output power, a mean-time-to-failure (MTTF) of 9.4 years is projected from a preliminary life test. These lasers are highly attractive for uncooled, potentially low-cost applications in the subscriber loop. >

Observation of highly nondegenerate four-wave mixing in 1.5 mu m traveling-wave semiconductor optical amplifiers and estimation of nonlinear gain coefficient

Nondegenerate four-wave mixing is measured in the 1.5 mu m traveling-wave semiconductor optical amplifier medium as a function of the pump-probe detuning frequency ranging from a few GHz to 400 GHz. It is found that two different sources are responsible for the four-wave mixing: the carrier density modulation and the nonlinear gain effect. The latter is clearly observed when the detuning frequency increases above 100 GHz. The nonlinear gain coefficient epsilon , which induces a gain grating through the pump-probe beating, is estimated to be 1.75*10/sup -23/ m/sup 3/. The change in the real refractive index associated with the nonlinear gain effect, which generates an index grating, is negligibly small. The relaxation time involved in the nonlinear gain effect is found to be less than 0.3 ps. These results support the role of the spectral hole burning rather than the carrier heating in the nonlinear gain effect. >

500-nm Optical Gain Anisotropy of Semipolar (1122) InGaN Quantum Wells

We studied the effect of carrier population on light emission polarization of green InGaN quantum wells (QWs) on the semipolar (1122) plane. The 3 nm thick QWs emitting light at about 540 nm at low pumping power have electrical field (E) component E∥[1123] stronger than that E∥[1100]. However, we found that increasing the pumping power changed the sign of the polarization ratio. Using the varied stripe length (VSL) method, we measured the optical gain for light propagating ∥[1123] direction to be ~2 times that of light propagating ∥[1100] direction. We explain this behavior by inhomogeneous QW state filling.

Low-threshold 1.5 mu m compressive-strained multiple- and single-quantum-well lasers

Design considerations for low-threshold 1.5- mu m lasers using compressive-strained quantum wells are discussed. Parameters include transparency current density, maximum modal gain, bandgap wavelength, and carrier confinement. The optical confinement for a thin quantum well in the separate-confinement heterostructure (SCH) and the step graded-index separate-confinement heterostructure (GRINSCH) are analyzed and compared. 1.5- mu m compressive-strained multiple- and single-quantum-well lasers have been fabricated and characterized. As a result of the compressive strain, the threshold current density is loss limited instead of transparency limited. By the use of the step graded-index separate-confinement heterostructure to reduce the waveguide loss, a low threshold current density of 319 A/cm/sup 2/ was measured on compressive-strained single-quantum-well broad-area lasers with a 27 mu oxide stripe width. >

Multiwavelength DFB laser arrays with integrated combiner and optical amplifier for WDM optical networks

In this paper, we describe the design, fabrication and performance of multiwavelength DFB laser arrays with integrated combiner and optical amplifier built for wavelength-division-multiplexed (WDM) optical networks. The goal is to reduce the per-wavelength transmitter cost in both initial procurement and subsequent operation. Using photonic integration, we have addressed and resolved several important issues related to laser arrays such as wavelength accuracy, output power, high-speed modulation and optical packaging. State of the art results have been obtained. By the use of wavelength redundancy and proximity effect, wavelength deviations of /spl plusmn/0.2 nm or less from the designated eight-wavelength comb have been achieved with high yield. Simultaneous operation of ten wavelengths has also been demonstrated. In spite of the inherent splitting loss of 13 dB, high-output powers of about -13 and 0.5 dBm per wavelength have been measured, under simultaneous operation, into a single-mode fiber (SMF) without and with on-chip optical amplification, respectively. The DFB laser has a 3-dB bandwidth of 9 GHz. A 2.5-Gb/s (OC-48) error-free transmission through 120 km conventional SMF has been demonstrated under single channel operation. The electrical crosstalk from neighboring channels cause negligible degradation to the eye diagram and the bit-error-rate (BER) curve at a bit rate of 2.5 Gb/s. The optical crosstalk due to four-wave mixing and cross-gain modulation (XGM) of the semiconductor optical amplifier (SOA) is also characterized. The impact of this integrated laser array on WDM optical networks is assessed in the conclusion.

A study on the reliability of indium solder die bonding of high power semiconductor lasers

High power semiconductor lasers have found increased applications. Indium solder is one of the most widely used solders in high power laser die bonding. Indium solder has some advantages in laser die bonding. It also has some concerns, however, especially in terms of reliability. In this paper, the reliability of indium solder die bonding of high power broad area semiconductor lasers was studied. It was found that indium solder bonded lasers have much shorter lifetime than AuSn solder bonded devices. Catastrophic degradation was observed in indium solder bonded lasers. Nondestructive optical and acoustic microscopy was conducted during the lifetime testing to monitor the failure process and destructive failure analysis was performed after the lasers failed. It was found that the sudden failure was caused by electromigration of indium solder at the high testing current of up to 7A. It was shown that voids were created and gradually enlarged by indium solder electromigration, which caused local heating near...

Gallium Indium Nitride-Based Green Lasers

In this review article, we describe group-III nitride laser diodes that emit light in the green spectral range, using epitaxial structures grown on gallium nitride (GaN) substrates with c- and semipolar-plane orientations. We address the motivation for these lasers, the challenges faced in creating them, and the progress made in this field to date. Different structural design choices are described, taking into account specific material properties and crystal growth requirements for these orientations. We review various properties of the materials involved, including optical gain, optical confinement, internal optical losses and carrier injection. We also discuss mechanical strain during the growth of active and passive regions, and the way in which it limits the structural design. Various aspects of laser chip fabrication are discussed, including self-aligned ridge waveguides and facet formation. Finally, we outline the status of green laser reliability and challenges in this area.

High-temperature continuous-wave operation of low power consumption single-mode distributed-feedback quantum-cascade lasers at λ∼5.2 μm

Continuous-wave operation of a distributed-feedback quantum-cascade laser in a packaged module is demonstrated up to a heat sink temperature of 80 °C with an output power of greater than 10 mW and a power consumption of less than 3.8 W. Single longitudinal mode emission near 5.24 μm is observed over a temperature range from 10 to 80 °C with a side mode suppression ratio greater than 20 dB limited by the instrumentation. A single spatial mode is determined with far-field pattern measurement. The above performance is achieved using a buried heterostructure and a small cavity of 7.6 μm×1.5 mm.

Thermal management strategies for high power semiconductor pump lasers

Semiconductor pump lasers are an important component in Erbium-doped fiber amplifiers and Raman amplifiers. Thermal management has become one of the major obstacles of pump laser development. Understanding of the thermal behavior of high power laser packages is crucial to the thermal design and optimization of pump lasers. In this paper, we report on the thermal characteristics of a high power pump laser and discuss the issues associated with heat dissipation. The thermal management of high power pump laser modules mainly consists of three aspects. One is the thermal resistance reduction which reduces bulk temperature rise in the laser diode chip. The second is facet temperature control and the third is the thermoelectric cooler (TEC) coefficient of performance improvement. In this paper, the approaches to reduce thermal resistance and facet temperature at the chip level and package level will be reviewed and the thermal design and optimization of the package assembly to improve the TEC coefficient of performance will be discussed.

Multiple-reflection-induced intensity noise studies in a lightwave system for multichannel AM-VSB television signal distribution

In a lightwave system used for transmission and distribution of multichannel AM-VSB (amplitude-modulated vestigial side-band) television signals, the dependence of multiple-reflection-induced intensity noise on laser diode linewidth, fiber jumper length, modulation index, and the number of connectors is studied. The noise is investigated for systems both with and without optical amplifiers. The requirements on the reflectance of fiber connectors/splices, the maximum number of connectors, and the usable optical amplifier gain are discussed.<<ETX>>