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.
The basic design considerations for a spectrally-stable DBR semiconductor laser specifically designed for pulsing in the
nanosecond regime is presented, along with test results from devices fabricated according to these design parameters.
Results show excellent mode selection and spectral stability over an extremely large range of conditions, including
temperature ranges of 15-60°C and peak drive current ranges from threshold to 880 mA. These lasers exhibit peak
output powers of greater than 500 mW for DBR semiconductor lasers at 976 nm and 1064 nm while remaining spectrally
stable. Chirp data shows the chirp can be effectively tuned from approximately 1 GHz to greater than 20 GHz by
varying the pulse width and peak drive current.
We report on novel architectures of the hybrid master oscillator power amplifier (MOPA) assemblies incorporating
vertically stacked surface-emitting laser diodes. Optical coupling between the MO and the PA is provided by nonresonant
grating couplers integrated on both of the devices. The MOPA consists of a MO chip with dual grating reflector
for single wavelength operation and a flared PA chip with two grating outcouplers. Optical peak power over 100W and
spectral bandwidth of 0.2nm were achieved from the single MOPA while the MO operated in the gain-switching regime
and the PA operated as a traveling wave amplifier. New designs of coherent MOPA arrays are proposed based on a
phase locked MO bar and a single transverse mode PA bar. This MOPA assembly requires an optical cross-coupling
between the bars provided by tilted gratings which have been developed and experimentally evaluated.
A dual grating reflector is a scheme for wavelength stabilization of laser diodes. The fabrication of a dual grating reflector involves the fabrication of a grating coupler on the p-side of a laser diode and a feedback grating on the n-side of the same device. The basic theory of the dual grating reflector is presented, along with the methods used to determine the required tolerances for near optimum performance. The fabrication processes used to obtain the required tolerances needed for a dual grating reflector are presented.
Optical coherence tomography (OCT) is an interferometric technique using the low coherence property of light to axially image at high resolution in biological tissue samples. Transverse imaging is obtained with two-dimensional scanning and transverse resolution is limited by the size of the scanning beam at the imaging point. The most common metrics used for determining the axial resolution of an OCT system are the full-width-at-half-maximum (FWHM), the absolute square integral (ASI), and the root-mean-square (RMS) width of the axial PSF of the system, where the PSF of an OCT system is defined as the envelope of the interference fringes when the sample has been replaced by a simple mirror. Such metrics do not take into account the types of biological tissue samples being imaged. In this paper we define resolution in terms of the instrument and the biological
sample combined by defining a resolution task and computing the associated detectability index and area under the receiver operating characteristic curve (AUC). The detectability index was computed using the Hotelling observer or best linear observer. Results of simulations demonstrate that resolution is best quantified as a
probability of resolving two layers, and the impact on resolution of variations in the index of refraction between the layers is clearly demonstrated.