Two AlGaAs/GaAs broadened waveguide laser structures, one asymmetric, one nearly symmetric, were designed for high power at about 780 nm. The design concept is based on low losses and higher gain for the fundamental mode with higher losses and lower gain for higher-order modes. To achieve these results, the positions of the quantum wells, thicknesses of the cladding layers, doping profiles, and the compositions of all the layers are carefully chosen. The structures are designed to have a loss of about 0.5/cm for the TE0 mode and more than 5 /cm for higher order modes for both structures. The asymmetric structure has a lower threshold current density (~750 A/cm2) and a higher slope (about 0.9 W/A) of the light-current curve compared to the symmetric structure. Increased L-I slope for the asymmetric structure results mainly from increased hole injection efficiency because the quantum wells are close to the p-side. Ridge-guide lasers fabricated with the asymmetric structure produced greater than 350 mW at 25°C. The beam divergence of the asymmetric structure was 6° × 14°.
The emergence of spectrally multimode smart missiles requires hardware-in-the-loop (HWIL) facilities to simulate
multiple spectral signatures simultaneously. While traditional diode-pumped solid-state (DPSS) sources provide a great
basic testing source for smart missiles, they typically are bulky and provide substantially more power peak power than
what is required for laboratory simulation, have fixed pulse widths, and require some external means to attenuate the
output power. HWIL facilities require systems capable of high speed variability of the angular divergence and optical
intensity over several orders of magnitude, which is not typically provided by basic DPSS systems. In order to meet the
needs of HWIL facilities, we present a low-cost semi-active laser (SAL) simulator source using laser diode sources that
emits laser light at the critical wavelengths of 1064 nm and 1550 nm, along with light in the visible for alignment, from a
single fiber aperture. Fiber delivery of the multi-spectral output can provide several advantages depending on the testing
setup. The SAL simulator source presented is capable of providing attenuation of greater than 70 dB with a response
time of a few milliseconds and provides a means to change the angular divergence over an entire dynamic range of 0.02-
6º in less than 400 ms. Further, the SAL simulator is pulse width and pulse repetition rate agile making it capable of
producing both current and any future coding format necessary.
Spectral and output power data of distributed Bragg reflector lasers emitting in the technologically important wavelength
range from 780 nm to 1083 nm are presented. These devices are fabricated in a single molecular beam epitaxy growth
step, and the gratings are defined by holographic interferometry. Spectral dependencies on the grating and gain section
lengths are systematically investigated. Experimental data for the side-mode suppression ratio, mode spacing, and
thermal wavelength shift are given for devices emitting in the near infrared wavelength range between 780 nm and 1083
The chief properties and possible applications of periodic waveguides and their leaky modes are presented in this paper. After summarizing the basic physics of the guided-mode resonance, computed leaky-mode field patterns are provided to illustrate their structure and the high local focal field enhancement obtainable. An example fabricated bandstop filter is found to exhibit 90% efficiency, 1 nm linewidth, and low sidebands. Computed spectra for a single-layer bandpass filter operating at 1.55 μm wavelength yield low sidebands, extending 100 nm, and an angular aperture of ~1.7°. Resonant vertical-cavity surface-emitting lasers (VCSEL) are presented in which multilayer Bragg-stack mirrors are replaced with leaky-mode resonance layers. The use of guided-mode resonance mirrors provides optical power flow across and laterally along the laser active region. The round-trip gain is thereby increased resulting in high laser efficiency and relaxed mirror reflectivity constraints. As the GMR mirror achieves high reflectivity at resonance, the laser wavelength is locked at the resonance wavelength principally defined by the period. Example resonant VCSEL embodiments are shown along with their computed characteristics. Resonant biosensors are addressed last. The high parametric sensitivity of the guided-mode resonance effect, a potential limitation in filter applications, can be exploited for sensors as illustrated by several examples.
Photoexcited intrinsic silicon 'pixels' are applied as coupling elements between microstrip lines. Under proper illumination, the free-carrier concentration of the silicon increases sufficiently to pass a microwave signal across the pixels. Illumination is accomplished through the use of multimode fiber coupling between high-power laser diodes and multimode prismatic-waveguide output couplers. The prismatic couplers are fabricated on the endfaces of thick glass slab waveguides to direct the light onto the silicon pixel. This configuration delivers up to approximately 75% of the total laser diode light to the prism-waveguide couplers and these couplers, in turn, deliver up to approximately 70% of the input light to the silicon pixels. The prismatic waveguide couplers provide illumination uniformity within approximately ± 15% over the length of a 1mm X 5mm pixel. As a simple in-line coupler between microstrip lines, the fully illuminated pixel allowed an increase in transmitted signal of > 5dB over most of the range from 0.5GHz to 15GHz with > 10dB obtained over intermediate ranges. A silicon pixel tunable transmission line termination exhibits impedance matching at increasing wavelengths by successive illumination of multiple pixels, effectively increasing the length of the termination. This is illustrated by shifts in the resonant frequencies of the device reflection characteristics.
High-efficiency resonance coupling effects in zero-order diffractive multilayer structures have applications in fields such as optical filtering and laser technology. These resonance effects arise on phase matching of an incident laser beam to a leaky waveguide mode. Then, in theory, complete energy exchange between the input wave and a reflected wave can take place within narrow ranges in wavelength, angle of incidence, index of refraction, or layer thickness. This paper addresses theoretical modeling, experimental realization, and applications of this so-called guided-mode resonance (GMR) effect. In particular, the achievable GMR-filter efficiencies, spectral linewidths, sideband levels, and polarization characteristics are treated with a plane-wave model and a Gaussian-beam model. Resonance bandpass filters operating in reflection and transmission are shown to exhibit high efficiencies and extended low sidebands. Genetic algorithms are applied to solve inverse resonance-filter design problems. Applications including GMR laser mirrors, electro-optic modulators, and resonant Brewster filters are presented. Experimental results are shown to agree well with theoretical calculations.
To obtain uniform illumination of photonic reconfigurable antennas, a waveguide grating with a nonuniform grating profile may be used. Theoretical studies using approximate models indicate that the grating profile should have a hyperbolic spatial variation along the length of the coupler. This yields a spatially varying diffraction efficiency that compensates for the loss of light as it is diffracted out of the waveguide. Utilizing a holographic interferometer with a computer controlled shutter in one arm, gratings with appropriate spatial profile variation have been recorded in photoresist and transferred to produce photopolymer waveguide gratings. These planar couplers are integrated with optical fiber bundles for input light delivery. The grating periods are chosen to produce orthogonally propagating output waves. A dielectric mirror arrangement is used to reflect the parasitic diffracted order back onto the antenna element. The best devices obtained to date exhibit output uniformity of plus or minus 6% over a coupler length of 20 mm with total efficiency exceeding 50%.