The project team of University of California at Merced (UC-Merced), Gas Technology Institute (GTI) and MicroLink
Devices Inc. (MicroLink) are developing a hybrid solar system using a nonimaging compound parabolic concentrator
(CPC) that maximizes the exergy by delivering direct electricity and on-demand heat. The hybrid solar system
technology uses secondary optics in a solar receiver to achieve high efficiency at high temperature, collects heat in
particles and uses reflective liftoff cooled double junction (2J) InGaP/GaAs solar cells with backside infrared (IR)
reflectors on the secondary optical element to raise exergy efficiency. The nonimaging optics provides additional
concentration towards the high temperature thermal stream and enables it to operate efficiently at 650 °C while the solar
cell is maintained at 40 °C to operate as efficiently as possible.
Nanopores are a new class of low dimensional semiconductor nanostructures which have been recently proposed for use
in lasers and other photonic applications. This paper provides an overview of patterned nanopore lattices with an
emphasis on their electronic and optical properties. The ability to control nanopore properties by geometry and material
composition are demonstrated. Two methods for controlled nanopore fabrication are presented and compared. Spectral
characteristics of nanopore lasers are presented. Finite element numerical simulations are also performed to determine
the band structure and emission properties of nanopores.
Compact, efficient visible lasers are important for heads up displays, pointing and illumination, undersea
communications, and less than lethal threat detection. We report on high power red, green, and blue lasers with output
powers above 3 watts and efficiencies greater than 20%, 15%, and 5% respectively.
InP based diode lasers are required to realize the next generation of eyesafe applications, including direct rangefinding
and HEL weapons systems. We report on the progress of high power eyesafe single spatial and longitudinal mode
1550nm MOPA devices, where we have achieved peak powers in excess of 10W with 50ns pulse widths. A conceptual
model based on our recent MOPA results show the path towards scaling to high powers based on spatial beam
combination with operating conditions suitable for direct rangefinding applications. We also report on the progress
towards high power 14xx and 15xx nm pump lasers for eyesafe HEL systems.
High power semiconductor lasers with wavelengths in the eye-safer region have application to a variety of defense,
medical and industrial applications. We report on the reliability of high power multimode and single mode InGaAsP/InP
diode lasers with wavelengths in the range 1320 to 1550 nm in a variety of configurations, including single-chip,
conduction-cooled arrays, arrays incorporating internal diffraction gratings, master-oscillator power amplifiers, and
fiber-coupled modules of the above. In all cases we show very low rates of degradation in optical power and the absence
of sudden failure from catastrophic optical damage or from laser-package interactions.
The development of on-chip grating stabilized semiconductor lasers for diode pumped solid state lasers is discussed. The
diode lasers, specifically at wavelengths of 808nm, 976nm, and 1532nm are stabilized via internal gratings to yield a
typical center wavelength tolerance of ± 1nm, FWHM of < 1-2nm, and a temperature tuning coefficient of < 0.09 nm/°C.
We also report on the CW and QCW operation of conduction cooled bars, stacks, and fiber coupled modules.
Simulations show that on-chip stabilized pump sources yield performance improvements over standard pumping
schemes. A comparison in laser performance is shown for typical DPSS configuration.
Narrow-linewidth (<100 kHz) 850 nm distributed Bragg reflector (DBR) three-section tunable laser diodes are reported. An asymmetric cladding ridge-waveguide structure was used for transverse and lateral mode control. Single longitudinal mode performance was achieved via first-order DBR surface-etched gratings fabricated using inductively-coupled plasma reactive ion etching (ICP-RIE). Epitaxial material with spontaneous emission peak values at 835 nm and 850 nm were used for device fabrication. Stable single-mode powers of up to 30-mW were achieved at 100 mA with spectral side-mode suppression ratio (SMSR) values in excess of 35 dB. Laser tuning by DBR current injection in excess of 7 nm was measured. Narrow spectral linewidths were observed on both sets of devices, with linewidths below 40 kHz for devices with the 835 nm spontaneous emission peak. This is due to the reduced spontaneous emission contribution to the device linewidth. These results demonstrate that extremely narrow linewidths can be achieved using onestep epitaxial growth in an unstrained material system with surface etched first-order gratings on asymmetric cladding ridge-waveguide lasers.
Photonic crystal microcavity devices containing InGaAs active layers grown on GaAs substrates have demonstrated poor performance largely because of rapid, non-radiative recombination at the air-InGaAs interface formed during the fabrication of the photonic crystal slab. We have used selective area epitaxial regrowth of the quantum well active layer to localize it to the defect of the photonic crystal structure. The fabrication process is described and the potential application to resonant photonic crystal devices is discussed.
Novel waveguide structures are presented that facilitate high power, single lateral mode output in narrow stripe semiconductor lasers. Flared tapered waveguide lasers, fabricated by a metal-organic chemical vapor deposition (MOCVD) selective area epitaxy (SAE), are shown to attain output powers of 650mW with stable single lateral mode beam properties. Novel integrated mode filters, which induce mode selective lateral radiation loss via curvature, or frustration of the index guide, are shown to increase the threshold for the 1st order mode to prevent it from attaining threshold. The addition these unique mode filters, which do not increase the fabrication complexity, extends the range of single lateral mode operation in narrow stripe devices.