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Aiming at low precision of remote sensing image scene classification, a classification method DCNN_FF based on deep convolutional neural network (DCNN) feature fusion (FF) is proposed. This method utilizes the existing pre-trained network models CaffeNet and GoogLeNet, and extracts the features of the classified remote sensing images by fine tuning on the target dataset. After dimension reduction by principle component analysis (PCA), the features extracted from the two network models are combined. Finally, the support vector machine (SVM) is used for classification of the combined features. The experimental results on the commonly used and latest datasets show that, this method can utilize the existing network models and combine with the structural advantages of different models, and its average classification accuracy is higher than that of single network model by more than 1.68%. Thus it improves the accuracy of remote sensing image scene classification.

A 1064 nm, 1 mJ pulsed fiber MOPA module, housed in 16”x14”x2.5” package for application in a lunar and planetary in-situ surface dating instrument is demonstrated. The module is based on a three-stage MOPA with a 60 μm core tapered fiber terminal amplifier. The master oscillator and first two preamplifier stages, which generate 20 μJ pulses, are all contained on a 13”x11”x1” board. Several improvements to the electronic signal control were instrumental to the laser development, including bipolar drive of the phase modulator for SBS suppression, shaping of the seed pulse to compensate pulse steepening, and pulsed operation of the power amplifier pump to reduce spontaneous emission at low pulse repetition frequency. The packaged laser runs at a repetition rate of 10 kHz and generates 10 ns pulses at 1 mJ with a 40 GHz linewidth, an M 2 ~ 1.2 beam quality, and an 18 dB polarization extinction ratio. The modular design enables seven independent lasers to be stacked in a 20”x18”x16.25” enclosure, supporting a path towards a fiber laser based LARIMS for advanced materials characterization and chronological dating in harsh and remote environments.

We demonstrate high power, deep ultraviolet (DUV) conversion to 266 nm through frequency quadrupling of a nanosecond pulse width 1064 nm fiber master oscillator power amplifier (MOPA). The MOPA system uses an Yb-doped double-clad polarization-maintaining large mode area tapered fiber as the final gain stage to generate 0.5-mJ, 10 W, 1.7- ns single mode pulses at a repetition rate of 20 kHz with measured spectral bandwidth of 10.6 GHz (40 pm), and beam qualities of Mx 2=1.07 and My 2=1.03, respectively. Using LBO and BBO crystals for the second-harmonic generation (SHG) and fourth-harmonic generation (FHG), we have achieved 375 μJ (7.5 W) and 92.5 μJ (1.85 W) at wavelengths of 532 nm and 266 nm, respectively. To the best of our knowledge these are the highest narrowband infrared, green and UV pulse energies obtained to date from a fully spliced fiber amplifier. We also demonstrate high efficiency SHG and FHG with walk-off compensated (WOC) crystal pairs and tightly focused pump beam. An SHG efficiency of 75%, FHG efficiency of 47%, and an overall efficiency of 35% from 1064 nm to 266 nm are obtained.

Single-clad and double-clad Yb:YAG crystalline fiber waveguides (CFWs) have been prepared with Adhesive-Free Bonding (AFB®) technology. By using a fiber coupled laser diode as pump source, a single-mode laser with near diffraction limited beam quality M 2 =1.02 has been demonstrated in a double-clad CFW. The laser output power and efficiency are 13.2 W and 34%, respectively. In a single-clad CFW, core pumping was used. The laser output has top-hat beam profile. An output power of 28 W and a slope efficiency of 78% have been achieved respectively. Keywords: Crystalline fiber, waveguide, laser, master oscillator power amplifier, adhesive-free bond 1. INTRODUCTION There is great interest in making rare-earth (RE) doped YAG crystalline fiber lasers due to their higher power scalability compared to glass fibers [1]. However, current fiber growth (or pulling) techniques, such as laser heated pedestal growth (LHPG) [2-4] and micro pulling down [5], have not yet been successful in producing low loss, double-clad, or even single-clad fully crystalline fibers. As an alternative to conventional fiber pulling technologies, Onyx Optics’ well established Adhesive-Free Bond (AFB®) technology circumvents the problems with the fabrication of low-loss crystalline fiber waveguides (CFW) [6-8]. In the present work , we report on the first laser diode (LD) cladding pumped single-mode 1030-nm laser in a double-clad Yb:YAG CF W with a near diffraction-limited beam quality of M

A new solution for building high power, solid state lasers for space flight is to fabricate the whole laser resonator in a single (monolithic) structure or alternatively to build a contiguous diffusion bonded or welded structure. Monolithic lasers provide numerous advantages for space flight solid-state lasers by minimizing misalignment concerns. The closed cavity is immune to contamination. The number of components is minimized thus increasing reliability. Bragg mirrors serve as the high reflector and output coupler thus minimizing optical coatings and coating damage. The Bragg mirrors also provide spectral and spatial mode selection for high fidelity. The monolithic structure allows short cavities resulting in short pulses. Passive saturable absorber Q-switches provide a soft aperture for spatial mode filtering and improved pointing stability. We will review our recent commercial and in-house developments toward fully monolithic solid-state lasers.

Double-clade crystalline fiber waveguide (CFW) has been produced by using adhesive-free bond (AFB®) technology. The waveguide consists of a 1 at.% Yb:YAG core, un-doped YAG inner cladding and ceramic spinel outer cladding. It is a direct analog of the conventional double-clad glass fiber laser in the crystal domain. Signal gain of 45 or 16.5 dB has been measured in a preliminary master oscillator power amplifier (MOPA) experiment. Due to the high laser gain and the weak Fresnel reflection at the uncoated waveguide ends, the CFW even starts self-lasing above a certain pump power. Laser output power of 4 W in the backward propagation direction has been measured for input pump power of 44 W. After considering the same amount of forward propagated laser power, the laser efficiency to the absorbed pump power is estimated to be about 44%. In principle, CFW can have extremely large single mode area for high efficiency and high power laser applications. So far, Single mode area < 6700 μm2 has been demonstrated in Er:YAG CFWs.

Referring to the problem of SAR image registration, an image registration method based on Scale Invariant Feature Transform (SIFT) and Multi-Scale Autoconvolution (MSA) is proposed. Based on the extraction of SIFT descriptors and the MSA affine invariant moments of the region around the keypoints, the feature fusion method based on canonical correlation analysis (CCA) is employed to fuse them together to be a new descriptor. After the control points are rough matched, the distance and gray correlation around the rough matched points are combined to build the similarity matrix and the singular value decomposition (SVD) method is employed to realize precise image registration. Finally, the affine transformation parameters are obtained and the images are registered. Experimental results show that the proposed method outperforms the SIFT method and achieves high accuracy in sub-pixel level.

We demonstrated nearly a quantum defect limited CW operation of a 41-mm-long Er:YAG large area crystalline waveguide laser with a diffraction limited output, which was resonantly pumped by a fiber laser at 1532 nm. Using a Er(0.25%):YAG, 62 μm x 62 μm waveguide, surrounded by a 3 x 5 mm rectangular cladding of undoped YAG, an output power of 9.1 W with slope efficiency of 92.8% has been achieved. The output laser beam had a Gaussian profile with a ~ 2.8 x 10 -2 rad divergence, which is in good agreement with the divergence expected from a waveguide with a low NA value. The waveguide laser operated simultaneously at two wavelengths, 1617 nm and 1645 nm, when the transmission of the laser cavity output coupler was less than 20-25%, and operated only at 1617 nm when the laser output mirror had a higher transmission.

We propose a sub-100 μm double-clad single-crystalline Tm:YAG square core adhesive-free bond (AFB) waveguide structure as a prototype gain medium for an LMA ~2-μm fiber laser with ~790-nm diode laser pumping and present its mode simulation. The structure uses an undoped YAG and ceramic spinel for the inner and outer claddings, respectively. The mode simulation indicates that such double-clad structure can have over 1000-μm2 mode area in a 2% Tm:YAG core which will maintain a single transverse mode laser operation. The structure also has a large numerical aperture (~ 0.22) for the un-doped YAG inner cladding available for pumping.

Adhesive-free bonded (AFB®) un-doped end-capped and segmentally bonded Tm:YLF laser composites have been investigated for high efficiency LD-pumped laser operations. With a fiber coupled 792-nm diode laser as pump source and a single-end pump arrangement, an optical-to-optical laser efficiency of 48.3% (quantum efficiency of 116%) and a slope efficiency of 55% (quantum efficiency of 132%) have been measured at the laser output wavelength of 1.908 μm. A maximum laser output power up to 29 W has been also achieved before the thermal stress fracture limit. The high laser efficiencies and output power can be attributed to the two-for-one cross-relaxation process and the efficient thermal management of the AFB laser composites.

We have demonstrated a novel folded linear resonator for walk-off compensated (WOC) optical parametric oscillation (OPO) in a single ZGP crystal. The OPO uses the doubled ZGP crystal length in a WOC configuration while simplifying requirements on crystal alignment. With a Q-switched Ho:YAG laser as a pump source, a maximum output power of 2 W at a wavelength of 4.72 μm has been measured for a pump power of 11.9 W in a 15-mm long type-I phase-matched ZGP crystal. The measured OPO quantum slope efficiency is above 50%.

A maximum output power of 18.6 W has been measured at a pump power of 23.7 W in a Tm:fiber laser pumped adhesive-free bonded (AFB®) YAG/Ho:YAG/YAG composite. The corresponding optical-to-optical efficiency and slope efficiency are 78.5% and 81.2%, respectively. When the laser is operated in Q-switched mode, the shortest laser pulse width of 11 ns has been measured in our experiment at repetition rate of 5 KHz. The laser has been used as pump source of a mid-infrared ZGP OPO. The wavelength tuning range from 3.06 to 6.6 μm has been achieved in a 15-mm long ZGP crystal. The maximum output power is 1.44 W at pump power of 10 W with repetition rate of 5 KHz.

We report on the fracture toughness as it is related to the fracture strength when different orientations of YAG single crystals are bonded to each other to make a selection of a mechanically desirable waveguide configuration. We have found that the K IC (211//211) conforming twin is greater than K IC (110//110) conforming twin that is about the same as K IC of (111//111) twist 180° and flip 180° twins. All K IC converge to the same value that is comparable if not greater than the non-composite counterparts 1 when the composite samples are fabricated using the standard AFB R (Adhesive- Free Bond) process. A second equally important consideration is the refractive index difference as function of dopant concentration. We have developed a technique to measure the difference of refractive index between Er:YAG and undoped YAG, and between Nd:YAG, and undoped YAG. We have found that the specific refractive index variation for YAG is 4.22 × 10 -4 per 1% Nd dopant concentration, and is 2.08 × 10 -4 per 1% Er dopant concentration.

With adhesive-free bond (AFB) technology, two walk-off compensated (WOC) KTP composites that consist of 16 layers of 2-mm thick single KTP crystals in each have been designed and prepared for 1.064-μm pumped 2-μm OPO's by means of quasi-noncritical phase-matching (QNCPM) and quasi-phase-matching (QPM). Output pulse energies of 49 μJ and 35 μJ have been achieved for QNCPM and OPM OPO's at pump energy of 523 μJ with pulse duration of 15 ns and repetition rate of 1 KHz, respectively. The OPO pump thresholds were measured as low as 254 μJ (44.6 MW/cm 2 ) for the both types of OPO's. The wavelength shifts were measured to be around 11 nm for both the signal and idler beams when KTP temperature was raised from room temperature to 220°C.

We report on the bond strength at the interfaces of Adhesive-Free-Bonded (AFB ® ) single crystal sapphire composite bars as deduced from the fracture toughness. Fracture toughness (K IC ) characterizes the resistance of a bulk brittle material to fractural failure caused by unstable crack propagation. Correlation between the well-defined initial flaw size and the apparent failure strength gives the fracture toughness that is a function of the average bond strength at the fractured interfaces. To ensure that the fracture interface coincides with the AFB ® interface, we make a pre-notch at the AFB ® interface to be the initial surface flaw using a 532 nm wavelength marking laser. The measured failure strength yields the fracture toughness of the AFB ® composites. We have found in this study that the average fracture toughness of AFB composite samples is 2.51 MPa * √m and that of non-composite control samples is 2.39 MPa * √m. The correlating fracture energy is 13.1 J/m 2 and 11.9 J/m 2 , respectively. The apparently greater fracture toughness of composite samples compared to that of non-composite samples conforms with the hypothesis that attributes the origin of the bonding forces at the AFB interfaces to the Lodon-Van der Waals interaction between two solid bodies.

A quasi-noncritical phase-matching (QNCPM) technology has been developed employing adhesive-free bonding (AFB) for high efficiency and high beam quality frequency conversion. A 16-layer KTP composite with total length of 32 mm was fabricated for a low pulse energy pumped 2-μm optical parametric oscillator (OPO). Our calculations indicate that the KTP composite has a 16 times lower walk-off effect and 16 times higher angle acceptance compared with the OPO in the same length single KTP crystal. Even only considering the walk-off correction, the threshold pump pulse energy in such a QNCPM OPO can be expected to be reduced by 256 times. In addition, the AFB technique was demonstrated to have uniform bonding quality and immeasurably small interface loss. Therefore, it can be expected to allow engineering of other critical phase-matched nonlinear optical devices into QNCPM devices.

We have observed that the temperature of the electrons drifting under a relatively-high electric field in an AlN/GaN-based high-electron-mobility transistor is significantly higher than the lattice temperature (i.e. the hot electrons are generated). These hot electrons are produced through the Frohlich interaction between the drifting electrons and long-lived longitudinal-optical phonons. By fitting electric field vs. electron temperature deduced from the measurements of photoluminescence spectra to a theoretical model, we have deduced the longitudinal-optical-phonon emission time for each electron is to be on the order of 100 fs. This value is consistent with the value measured previously from Raman scattering.

We have studied the coupling between the InAs quantum dots and coupled quantum wells strained by the InAs quantum dots (i.e. coupled-quantum-well dots) by measuring photoluminescence spectra. By comparing the photoluminescence spectra of the coupled-quantum-well dots in which either the narrow well or wide well is grown next to the InAs quantum dots, we have evidenced the spatially inhomogeneous strains applied by the InAs quantum dots on the coupled quantum wells. Moreover, we have also investigated the three coupling regimes, i.e. when the dot level is higher than, lower than, and aligned to the lowest quantum-well transition. Based on our measurements, we conclude that the optical properties for the coupled-quantum-well dots have been significantly improved over the quantum dots.

We have systematically designed, fabricated, and tested chalcogenide-glass waveguides. Among all the characterization techniques, we have found that the prism-coupling method is the most effective and accurate for determining all the parameters describing the performance of the slab waveguides. Furthermore, we have also achieved the end-fire coupling in these waveguides to study the characteristics of the transmitted beams. These waveguides can be optimized eventually for the biosensor applications.

We demonstrate that longitudinal-optical (LO) phonons efficiently pump electrons from the quasi-X states to the quasi-Γ states in short-period type-II GaAs/AlAs superlattices. At a very low temperature, the phonon-assisted electron up-transfer can occur if the energy difference between the lowest quasi-Γ states and quasi-X states is equal to or less than the LO phonon energies. As the temperature increases, however, kinetic energies of the electrons can facilitate the electron up-transfer. As a result, we have observed peculiar behaviors on these superlattices. First, photoluminescence intensity for the quasi-direct transition drastically increases as the temperature or pump power increases. Second, the dependence of the integrated photoluminescence intensity on the pump power exhibits a square power law.

We report our recent results on characterization of GaAs/AlAs superlattices exhibiting evidence of a quasi- indirect transition between minibands. These structures have potential applications in semiconductor optical amplifiers with greatly-reduced cross-talk at high bit rates and Q-switched lasers.

Self-assembled InP/InAs/InP quantum wires have been successfully stacked for 10 vertical periods and characterized based on photoluminescence (PL) studies. Compared with single-period quantum wires, unique behaviors appear in the PL spectra and some fundamental effects have been observed. Through the detailed analyses of the PL shapes, linewidths, and polarizations at different pump wavelengths, pump intensities and sample temperatures, it is evidenced that the wire width and subband energy gradually decrease while the average wire thickness increases from the bottom period to the top one, period by period. Meanwhile, the average wire width gradually decreases. In addition, from the bottom to the top period the size fluctuation within each period decreases. Furthermore, above certain temperature or pump intensity all the quantum wires are vertically coupled among one another. Following these results, new growth conditions have been suggested, which can be essential to improving the optical quality of these self-assembled quantum wires.

We have observed first-, second- and third-order quasi- phase-matched second-harmonic generation in the reflection geometry from GaAs/AlAs multilayers. We have measured phase- matching curves and identified all the peaks. The linewidth for the first order is limited only by wave-vector mismatch. We have demonstrated two-order-of-magnitude enhancement solely using quasi-phase-matched multilayers. We have also achieved cavity-enhanced quasi-phase-matched second-order and non-phase-matched second-harmonic generation from GaAs/Al0.8Ga0.2As multilayers. We have determined the element of the second-order susceptibility tensor used for quasi-phase matching. We have measured the conversion efficiencies and discussed possibilities for further enhancements.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We review our recent results on efficient generation of coherent blue/green light based on different configurations and structures. We have used second-harmonic generation with forward or backward configuration in short-period periodically-poled bulk and waveguide KTP to generate blue light. We have used backward second-harmonic generation to characterize periodically-segmented sub-micron KTP waveguides. By cascading second-harmonic generation and subsequent sum-frequency generation, we have generated coherent blue light in KTP and/or Ce:KTP crystals. We have also studied damage threshold of bulk KTP; we hope that we can eventually use it towards efficient generation of CW coherent green light.

In this letter, we report a new electro-optic (EO) polymer film DMACB/PEK-c. After poling of the film the refractive indices nt and nn, viz. the in-film-plane and the normal-to-film plane indices of refraction at 0.63-micrometer and the thickness d were determined using the quasi-waveguide m-line method. The electric field-induced changes in the refractive indices of the film, (delta) nt and (delta) nn, were also independently measured when an electric field was applied normal to the film plane. The EO coefficients of the film, (gamma) 13 and (gamma) 33, are found to be 32.9 pm/V and 82.6 pm/V respectively.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new electro-optic polymer film DMACB-PEK-c has been prepared. The refractive indices of the film at 0.63- micrometer, nt and nn, are determined by the quasi- waveguide m-line method. The results of measurement and calculation are: nt equals 1.6573 plus or minus 0.0017, nn equals 1.6278 plus or minus 0.0019.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The influences of the contradirectional two-wave mixing (CTWM) on the total-internal reflected self-pumped phase conjugator (CAT SPPC) and on the stimulate photorefractive scattering self-pumped phase conjugator (SPS SPPC) are studied. The experimental and the theoretical results both show that the CTWM is an important interaction in the SPPC process, it can obviously change the output characters of the SPPC. Especially in the SPS-SPPC, the CTWM is an indispensable interaction, it changes the structure of the SPPC in the basic.

The contradirectional two-wave mixing (CTWM) is studied and compared with the forward two-wave mixing, the results show that the CTWM offers some unique wave-coupling characters, the energy transfer direction in the process of CTWM is not only decided by the sign of the main light induced carries, but also decided by the relative value of every element in the electro-optical tensor.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A mutually pumped phase conjugator is demonstrated with a novel photorefractive crystal of copper-doped potassium sodium strontium barium niobate, in which the beams travel in a geometric path similar to the outline of a sickle. The maximum reflectivity is up to 168%. Faster response times are measured and are also simulated as a function of incident beam power ratio. Four available input geometries are found. The phase conjugation signals exist wide range of angular and position alignment.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.