This paper is a survey of recent achievements at the College of Optics and Photonics/CREOL at the University of
Central Florida in the use of newly developed diffractive optical elements which are volume Bragg gratings recorded in
a photo-thermo-refractive (PTR) glass. Three levels of semiconductor laser design are proposed to achieve high-power
low-divergence output. The first level is coherent coupling of emitters by means of PTR Bragg gratings which provide
excitation of only one common mode in a multichannel resonator. This type of phase locking automatically leads to a
narrow spectral width of emission usually not exceeding a few tens of picometers. The second level is a change of the
mechanism of transverse mode selection from spatial selection by apertures to angular selection by PTR Bragg gratings.
This approach allows increasing of the aperture size without increasing the length and selecting of arbitrary mode but not
necessarily a fundamental one. The third level is spectral beam combining by PTR Bragg gratings which re-direct
radiation from several high-power fiber lasers to co-propagate in the same direction with diffraction limited divergence.
This approach allows simplification of the thermal management because only passive devices with low absorption (a
PTR volume Bragg gratings) are placed in the path of high power laser beam.
Five-channel spectral beam combining (SBC) using volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR)
glass with 0.5 nm spectral separation between channels and combined power >750 W has been recently reported. We
report on improvements in this technique with the use of thermal control of VBGs that allows precise high-power
alignment required for dense SBC with 0.25 nm spectral separation of channels. Experimental results of passive coherent
beam combining (CBC) of fiber lasers using multiplexed VBGs are presented and analyzed. Methods for achieving
100 kW class systems using novel hybrid architectures that combine both coherent and spectral beam combining are
We introduce a novel technique of coherently locking fiber lasers using volume Bragg gratings (VBGs) recorded in
photo-thermo-refractive (PTR) glass as a passive multiplexer between channels. A two-channel coherently-locked Ybdoped
fiber laser system with a narrow linewidth (~2.5 pm) and linear polarization (PER >20 dB) is demonstrated at a
level of ~ 4 W (limited by pump). Scaling of this technique to coherently lock multiple (>2) fiber laser channels is
Optical Coherence Microscopy (OCM) is an emerging technology capable of depth sectioning of biological tissue at the micrometer scale. In this paper, we propose a developing technology we call Gabor Domain
Optical Coherence Microscopy (GD-OCM), whose innovation is two folds: (1) A high lateral resolution optical design of a dynamic-focusing optical probe with no moving parts, which provides an invariant resolution of currently 3 μm across a 2mm full-field of view and 2mm imaging depth by design; (2) An acquisition scheme (using the probe) that is capable of performing automatic data fusion to render an in-focus high resolution image throughout the depth of sample at in vivo speeds.
In this paper, we present the design of a 0.2 NA microscope objective operating across a 120nm broadband spectral
range that requires only two doublets and an embedded liquid lens to achieve 3 μm invariant lateral resolution throughout
a large 8 cubic millimeter imaging sample. Achieving invariant lateral resolution comes with some sacrifice in imaging
speed, yet in the approach proposed, high speed in vivo imaging is maintained up to a resolution of 3 μm for a 2x2 mm
sample size. Thus, in anticipation to ultimately aim for a resolution of 0.5 to 1 μm, we are investigating the possibility to
further gain in resolution using super-resolution methods so both hardware solutions and image processing methods
together can provide the best trade-off in overall resolution and speed of imaging. As a starting point to investigate
super-resolution methods, we evaluate in this paper three well-known super-resolution algorithms used to reconstruct a
high resolution image from down-sampled low resolution images of an African frog tadpole acquired en face using our
OCM set-up. To establish ground truth necessary for assessment of the methods, low resolution images were simulated
from a high resolution OCM image. The specification and design performance of the custom designed microscope will
be presented as well as our first results of super-resolution imaging. The performance of each algorithm was analyzed
and all performances compared using two different metrics. Early results indicate that super-resolution may play a
significant role in the optimization of high invariant resolution OCM systems.