This past month has been somewhat of a dilemma for me. I am both teaching a course and taking a course, so I am seeing the learning process from both sides (as a teacher and as a student). I am not being graded on the material I am learning, but I am giving grades in my class, so the students are a little worried. It reminds me of the old joke: Tommy: Teacher, I don't deserve this grade. Teacher: Tommy, I agree with you, but zero is the lowest score I can give.

A bidirectional optical subassembly comprised of a 2.5 Gbps distributed feedback (DFB) laser diode (LD) directly modulated laser transmitter and a 10 Gbps positive intrinsic negative photodiode receiver was developed for an optical network unit of a 10 Gbps passive optical network. Here, a low-cost mini-dual-in-line package was modified to contain whole components of a transmitter and receiver in a single space while satisfying the requirements of 10 Gbps micro-device package standards. The transmitter was fabricated to achieve high optical output power by placing a micro aspheric lens very close to the DFB LD and reducing the thermal resistance between an LD chip and heat sink to bring down the DFB LD chip temperature. As a result, the transmitter output power was 3.5 dB higher than a conventional transistor outline can BOSA due to a high optical coupling efficiency of more than 70% and a low thermal resistance for heat dissipation. The receiver sensitivity was - 21 dBm at a bit error rate of 10^-3 and the sensitivity penalty of the receiver due to signal crosstalk was less than 0.3 dB.

In this letter, we predict that radiative surface phonon polariton (RSPhP) modes, in a multilayer structure consisting of thin-film silicon carbide (SiC) bounded by silicon (Si) and diamond (Di), can be used to achieve negative refraction of mid-infrared light at approximately 11 μm. Dispersion relations, calculated for the Si/SiC/Di structure, show that the RSPhP mode exhibits negative dispersion and couples with incident light. Poynting vector calculations show how the energy flux may be refracted, negatively, in the SiC layer.

Laser damage of optical materials, first reported in 1964, continues to limit the output energy and power of pulsed and continuous-wave laser systems. In spite of some 48 years of research in this area, interest from the international laser community to laser damage issues remains at a very high level and does not show any sign of decreasing. Moreover, it grows with the development of novel laser systems, for example, ultrafast and short-wavelength lasers that involve new damage effects and specific mechanisms not studied before. This interest is evident from the high level of attendance and presentations at the annual SPIE Laser Damage Symposium (aka, Boulder Damage Symposium) that has been held in Boulder, Colorado, since 1969.

Optical properties and laser damage characteristics of thin-film aluminized Kapton® were investigated. Spectral absorptance of virgin and irradiated samples was measured from the Kapton side of multilayered insulation over 0.2 to 15 µm wavelengths at both room temperature and 150°C. The laser-damage parameters of penetration time and maximum temperature were then measured in a vacuum environment at laser wavelengths of 1.07 and 10.6 µm. Differences in damage behavior at these two wavelengths were observed due to differences in starting absorption properties at these wavelengths. During laser irradiation, the Kapton thin film was observed with a calibrated FLIR® thermal imager in the 8 to 9.2 µm band to determine its temperature evolution. Spectral radiance throughout the mid- and long-wave infrared was also observed with a Fourier transform spectrometer, allowing temperature-dependent spectral emittance to be determined. Kapton emittance increased after the material heated past approximately 500°C, and continued to increase as it cooled posttest. This evolving temperature-dependent spectral emittance successfully predicts the increasing absorptance that led to shortened penetration times and increased heating rates for the 1.07 µm laser. For tests with constant absorptance and no material breakdown, a simplified one-dimensional thermal conduction and radiation model successfully predicts the temporally evolving temperature.

All dielectric high-reflectance (HR) mirror coatings consisting of AlF₃/LaF₃/oxide layers were deposited on deep-ultraviolet-grade fused silica and CaF₂. A novel technique was employed to measure the absorption of these mirrors during irradiation by a 193-nm ArF excimer laser source. The method involves the application of a photothermal measurement technique. The setup uses a Shack-Hartmann wavefront sensor to measure wavefront deformation caused by the heating of the coating by the ArF beam. Laser calorimetric measurements of absorption were used to calibrate the wavefront sensor. The new test setup was used to investigate HR mirror coatings both before and after exposure to high average power ArF laser beams. HR mirror samples were irradiated by a 193-nm kilohertz laser source for either 500 million or 18.6 billion pulses. The differences between wavefront distortion measured inside the beam footprint compared to measured outside the beam footprint can be explained by compaction of the coating in the area heated by the ArF laser. Interesting wavefront-distortion results from testing mirrors with either fused silica or CaF₂ substrates can be explained by considering the figure of merit of these materials for excimer-laser mirror substrates.

High-reflectance mirrors, fabricated by use of fluoride coating materials, were irradiated for extended periods by a 193-nm kilohertz repetitive laser source. This irradiation promoted a spectral shift in the reflectance band towards shorter wavelengths. In efforts to determine the mechanism for the observed spectral shifts, various models were investigated by employing such techniques as spectrophotometry, surface profile interferometry, coating design simulation, and x-ray diffraction. The result of the investigation indicates that layers near the top surface of the coating structure underwent densification, which resulted in the observed spectral shift.

Numerous studies have investigated the prerequisite role of photoionization in ultrafast laser-induced damage (LID) of bulk dielectrics. This study examines the role of spectral width and instantaneous laser frequency in LID using a frequency dependent multiphoton ionization (MPI) model and numerical simulation of initially 800 nm laser pulses propagating through fused silica. Assuming a band gap of 9 eV, MPI by an 800 nm field is a six-photon process, but when the instantaneous wavelength is greater than 827 nm an additional photon is required for photoionization, reducing the probability of the event by many orders of magnitude. Simulation results suggest that this frequency dependence can significantly impact the onset of LID and ultrashort pulse filamentation in solids.

Multipulse laser-induced damage is an important topic for many applications of nonlinear crystals. We studied multipulse damage in X-cut KTiOPO₄. Using a 6-ns Nd:YAG laser with a weakly focused beam, a fatigue phenomenon was observed. We addressed whether this phenomenon necessarily implies material modifications. Two possible models were tested, both of them predicting increasing damage probability with increasing pulse number while all material properties are kept constant. The first model, pulse energy fluctuations and depointing, increases the probed volume during multiple pulse experiments. The probability to cause damage thus increases with increasing pulse number; however, this effect is too small to explain the observed fatigue. The second model assumes a constant single-shot damage probability p₁, so a multipulse experiment can be described by statistically independent resampling of the material. Very good agreement was found between the 2000-on-1 volume damage data and this statistical multipulse model. Additionally, the spot size dependency of the damage probability is well described by a precursor presence model. Supposing that laser damage precursors are transient, the presented data explain the experimental results without supposing material modifications.

Third harmonic (TH) microscopy with circularly polarized illumination directly reveals material anisotropy owing to suppression of background optical signals from isotropic media. Because optical thin films and their substrates are expected to be highly isotropic, TH microscopy presents a path to study induced and intrinsic anisotropy in films, providing both insight into laser-induced material modification that precedes damage and feedback about the deposition process. Because nanoscale defects and material strain influence the damage behavior of films, we examined TH sensitivity to similar sources of contrast. We demonstrate imaging of individual 10 nm colloidal gold nanoparticles and 100 mN nanoindentations in fused silica both with signal-to-noise ratio (SNR) ≥ 100∶1. We present TH images (SNR ≥ 210∶1) of sites exposed to femtosecond laser pulses below damage in 100 nm HfO₂ films that are barely visible (SNR ≤ 2.3∶1) with Nomarski and polarization imaging, traditional microscopic techniques known to display contrast for material anisotropy. At our detection limit (320 mW, 50 fs, 790 nm, ≈ 10⁶ photomultiplier tube gain), we examined root mean square in the TH image of nascent films that correlated to the film's macrostrain. TH microscopy presents a relatively simple all-optical method to monitor nanoscale anisotropy in thin films during exposure to high-intensity radiation and during deposition.

Theoretical modeling of photo-induced electron-hole plasma and bandgap dynamics in GaAs at high femtosecond laser intensities ( ∼ TW/cm²) employing a quantum kinetic formalism based on a generalized Boltzmann-type equation, predicts for the first time against expectations, the saturation of plasma densities despite the strong direct bandgap narrowing. Though the transient electronic bandgap renormalization provides a significant positive feedback for all relevant single-photon and impact ionization mechanisms, which is clearly observable at moderate (sub-TW/cm²) laser intensities, the counterintuitive plasma density saturation at higher laser intensities and high plasma densities ( ∼ 1022  cm−3) is dictated by much stronger negative feedback, originating from a highly-nonlinear transient enhancement of the corresponding Auger recombination coefficient for the shrinking bandgap. These theoretical predictions are in semi-quantitative agreement with the results of our time-resolved reflectivity infrared (IR)-pump experiments, which support this newly predicted process of self-limiting ionization dynamics in strongly photo-excited semiconductors, such as GaAs, with induced bandgap shrinkage.

Laser-induced plasma can expedite the deposition of incident laser energy and the laser-induced damage in optical glass is considerably affected by the magnitude and distribution of the plasma shock wave. The spatial distribution of energy deposition and expansion pressure of the laser plasma shock wave is analyzed based on the moving breakdown model. Furthermore, damage morphologies are discussed in light of the spatial distribution of pressure and glass properties. It was found that with the increase of laser pulse energy, the shock wave expands rapidly in the direction opposite to the incident laser, resulting in that the damage morphologies transform from sphere to spindle gradually. The laser energy deposits mostly in a narrow plasma channel. The diffusion of the plasma with high temperature and pressure leads to the shock wave; the intensity of which decreases sharply with the axial distance from the centerline. As a consequence, the glass near the centerline fractures and melts, and the refractive index also changes near the end of cracks.

The energy of a laser beam irradiating a surface is primarily absorbed by electrons within the solid. In actual transparent materials, absorption is low. High-intensity lasers may, however, be absorbed by initially bounded electrons through nonlinear processes. The increase of free-electron density leads eventually to dielectric breakdown, and the material becomes highly absorbing. We present theoretical studies on the dynamics of electrons in dielectrics under irradiation with a visible high-intensity laser pulse. We consider microscopic processes determining absorption, redistribution of the energy among electrons, and transfer of energy to the crystal lattice. We review different aspects of electronic excitation, studied with time-resolved models as the Boltzmann kinetic approach and the time and spatial resolved multiple rate equation. Furthermore, we investigate criteria for damage thresholds. Two concepts are compared, namely a critical free-electron density and the melting threshold of the lattice. We show that in dielectrics both criteria are fulfilled simultaneously. Optical parameters depend on the density of free electrons in the conduction band of the solid, so the free-electron density directly leads to an increased energy absorption causing material modification. We present results on the spatial dependence of dielectric breakdown.

We present the results of theoretical studies of the laser-induced damage in transparent solids containing absorbing inclusions. The investigation is based on the inclusion-initiated thermal explosion model. Key aspects of the model are considered: thermal instability initiated by the inclusions; a mechanism of photoionization of a surrounding layer of a host material by a thermal ultraviolet-radiation of laser-heated inclusions; the thermal instability kinetics, and an associated pulse-width dependence of the laser-induced damage threshold. Also, statistical features of the damage, caused by random spatial distribution of the inclusions in the materials, and a final stage of the damage process-a mechanical stress-produced crack formation-are analyzed. A comparison of the theoretical results, related to the pulse-width dependence of the damage threshold, with experimental data for some typical optical materials in a wide pulse-width range is presented.

The laser-induced deflection (LID) technique, a photo-thermal deflection setup with transversal pump-probe-beam arrangement, is applied for sensitive and absolute absorption measurements of optical materials and coatings. Different LID concepts for bulk and transparent coating absorption measurements, respectively, are explained, focusing on providing accurate absorption data with only one measurement and one sample. Furthermore, a new sandwich concept is introduced that allows transferring the LID technique to very small sample geometries and to significantly increase the sensitivity for materials with weak photo-thermal responses. For each of the different concepts, a representative application example is given. Particular emphasis is placed on the importance of the calibration procedure for providing absolute absorption data. The validity of an electrical calibration procedure for the LID setup is proven using specially engineered surface absorbing samples. The electrical calibration procedure is then applied to evaluate two other approaches that use either doped samples or highly absorptive reference samples.

We applied a Monte Carlo simulation for studies of single-shot laser-induced breakdown in pure transparent dielectrics for the case when the photon energy is close to or exceeds mean electron energy. Avalanche ionization rate dependence on intensity was obtained by solving both the kinetic Fokker-Planck type equation and the quantum kinetic equation. Threshold scaling with pulse width was obtained in the range from 3 ps to 30 ns for several values of laser frequency and initial lattice temperature. Lattice heating influence (during the laser pulse action) on avalanche ionization rate was studied.

Based on the standing-wave theory, a modified method is proposed to separate interface and volume absorption in HfO₂ single layers. HfO₂ single layers with multiple half-wave optical thickness were prepared; in such case, the electric field at air-film and film-substrate interface is equal, and total absorption from both interfaces can be easily expressed by the product of electric field intensity and a simplified total interface absorption coefficient. Ultralow-absorptive substrates were used to eliminate the contribution of substrate absorption. When HfO₂ single layer was irradiated from the coated and uncoated side in the photothermal measurement, two equations were obtained and utilized to separate the interface and volume absorption. The validity of our method was further confirmed using another thickness changing approach. By contrast, irradiation direction changing method is better because only one sample is required.

We demonstrate the formation of self-organized nanogratings on a titanium surface under the irradiation of a single-beam femtosecond laser. Self-formed, periodic nanogratings are printed on a titanium surface by varying the average pulse energy, pulse width, and number of laser pulses in each spot. The direction of the nanogratings is perpendicular to the direction of the laser polarization. The nanograting period shows obvious dependence on the average pulse energy, pulse width, and number of laser pulses. The period of the self-organized nanogratings shows an increasing trend with the increase of laser energy and pulse width, and a decreasing trend with an increase of number of applied laser pulses. We qualitatively explain the formation mechanism of the self-organized nanogratings and their dependence on various laser parameters.

Damage of a metal spherical nanoparticle by femtosecond laser pulses is analyzed by splitting the overall process into two steps. The fast step includes electron photoemission from a nanoparticle. It takes place during direct action of a laser pulse and its rate is evaluated as a function of laser and particle parameters by two approaches. Obtained results suggest the formation of significant positive charge of the nanoparticles due to the photoemission. The next step includes ion emission that removes the excessive positive charge and modifies particle structure. It is delayed with respect to the photo-emission and is analyzed by a simple analytical model and modified molecular dynamics. Obtained energy distribution suggests generation of fast ions capable of penetrating into surrounding material and generating defects next to the nanoparticle. The modeling is extended to the case of a nanoparticle on a solid surface to understand the basic mechanism of surface laser damage initiated by nano-contamination. Simulations predict embedding the emitted ions into substrate within a spot with size significantly exceeding the original particle size. We discuss the relation of those effects to the problem of bulk and surface laser-induced damage of optical materials by single and multiple ultrashort laser pulses.

Previous studies have identified two significant precursors of laser damage on fused silica surfaces at fluences <35  J/cm2: photoactive impurities from polishing and surface fractures. We evaluate isothermal heating as a means of remediating the defect structure associated with surface fractures. Vickers indentations are applied to silica surfaces at loads between 0.5 and 10 N, creating fracture networks. The indentations are characterized before and following thermal annealing under various time and temperature conditions using confocal time-resolved photo-luminescence (CTP) imaging, and R/1 damage testing with 3-ns, 355-nm laser pulses. Improvements in the damage thresholds with reductions in CTP intensity are observed at temperatures well below the glass transition temperature (Tg). The damage threshold on 0.5-N indentations improves from <8 to >35  J/cm2 after annealing at approximately 750°C. Larger fracture networks require longer or higher temperature treatment to achieve similar results. At an annealing temperature >1100°C, optical microscopy indicates morphological changes in some of the fractures surrounding the indentations, although remnants of the original fractures are still observed. We demonstrate the potential of using isothermal annealing to improve the laser damage resistance of silica optics, and provide a means of further understanding the physics of optical damage and mitigation.

Optical instruments and laser systems are often fluence-limited by multilayer thin films deposited on the optical surfaces. When comparing publications within the laser damage literature, there can be confusing and conflicting laser damage results. This is due to differences in testing protocols between research groups studying very different applications. In this series of competitions, samples from multiple vendors are compared under identical testing parameters and a single testing service. Unlike a typical study where a hypothesis is tested within a well-controlled experiment with isolated variables, this competition isolates the laser damage testing variables so that trends can be observed between different deposition processes, coating materials, cleaning techniques, and multiple coating suppliers. This series of damage competitions has also been designed to observe general trends of damage morphologies and mechanisms over a wide range of coating types (high reflector and antireflector), wavelengths (193 to 1064 nm), and pulse lengths (180 fs to 13 ns). For each of the competitions, a double blind test assured sample and submitter anonymity so only a summary of the deposition process, coating materials, layer count and spectral results are presented. In summary, laser resistance was strongly affected by substrate cleaning, coating deposition method, and coating material selection whereas layer count and spectral properties had minimal impact.

We present a direct comparison of two techniques for the determination of laser damage threshold. The two techniques are compared for their accuracy and repeatability and analyzed to understand the intrinsic biases of each test. We show that the damage frequency method underestimates the true value and has poor repeatability and the binary search method over-estimates the threshold, but is the more repeatable method.

The integration of fiber grating demodulation system is a research emphasis in the study of demodulation systems. On-chip arrayed waveguide grating (AWG) demodulation integration makes integration possible in a demodulation system. A 1×8 silicon nanowire AWG for on-chip AWG demodulation integration microsystem is proposed and designed. The center wavelength is 1550.918 nm, the waveguide width is 350 nm, the waveguide thickness is 220 nm, and the effective area is 267×259  μm². The single-mode waveguide cross-section structure is designed according to the refractive index of the silicon-on-insulator material. The mask layout territory of the 1×8 AWG is designed and optimized using the beam propagation method. A cone-shaped mold spots converter is proposed in the design process. Furthermore, the wavelength-division-multiplexing-phasar simulation system is established to simulate the stable output optical propagation characteristics of the designed AWG. The simulation result shows that the insert loss of the AWG is 10.658 dB, and the crosstalk is 3.037 dB, which is lower under the same waveguide, thickness, and size. This condition makes the AWG design the best choice for a fiber Bragg grating demodulation microsystem.

We developed a real-time optical monitoring system consisting of a monochrome complementary metal-oxide semiconductor (CMOS) camera and two light-emitting diodes (LEDs) with a constant temperature incubator for the rapid detection of microbial growth on solid media. As a target organism, we used Alicyclobacillus acidocaldarius, which is an acidophilic thermophilic endospore-forming bacterium able to survive in pasteurization processes and grow in acidic drink products such as apple juice. This bacterium was cultured on agar medium with a redox dye applied to improve detection sensitivity. On the basis of spectroscopic properties of the colony, medium, and LEDs, an optimal combination of two LED illuminations was selected to maximize the contrast between the colony and medium areas. We measured A. acidocaldarius and Escherichia coli at two different dilution levels using these two LEDs. From the results of time-course changes in the number of detected pixels in the detection images, a similar growth rate was estimated amongst the same species of microbes, regardless of the dilution level. This system has the ability to detect a colony of approximately 26 μm in diameter in a detection image, and it can be interpreted that the size corresponds to less than 20 μm diameter in visual inspection.

We investigated the layer dynamics of a conventional surface-stabilized ferroelectric liquid crystal (SSFLC) using a full-optical snapshot Mueller matrix polarimeter (SMMP) based on wavelength polarization coding. Time-resolved polarimetric measurements were performed with different SSFLC samples, and a strong correlation between the polarimetric parameters and the SSFLC under electric field at different exposure times was found. It has been shown that the SMMP polarimeter is able to determine the evolution of the trajectory of the liquid crystal director between the two addressed states, the reversible motion of the smectic layer while switching, as well as the irreversible transition from chevron to bookshelf texture.

The performance of a long-wave infrared type-II InAs/GaSb superlattice photodetector with a 50% cut-off wavelength of approximately 8.7 μm is presented. The ability to lower dark current densities over traditional P-type-Intrinsic-N-type diodes is offered by way of hetero-structure engineering of a pBiBn structure utilizing superlattice p-type (p) and n-type (n) contacts, an intrinsic (i) superlattice active (absorber) region, and unipolar superlattice electron and hole blocking (B) layers. The spectral response of this pBiBn detector structure was determined using a Fourier transform infrared spectrometer, and the quantum efficiency was determined using a 6250 nm narrow band filter and a 500 K blackbody source. A diode structure designed, grown, and fabricated in this study yielded a dark current density of 1.05×10^-5 A/cm² at a reverse bias of - 50 mV and a specific detectivity value of greater than 10¹¹ Jones at 77 K. Theoretical fittings of the diode dark currents at 77 K were used in this study to help isolate the contributing current components observed in the empirical dark current data. A variable temperature study (80 to 300 K) of the dark current is presented for a diode demonstrating diffusion-limited dark current down to 77 K.

There is an increasing request for zero expansion glass ceramic ZERODUR® substrates being capable of enduring higher operational static loads or accelerations. The integrity of structures such as optical or mechanical elements for satellites surviving rocket launches, filigree lightweight mirrors, wobbling mirrors, and reticle and wafer stages in microlithography must be guaranteed with low failure probability. Their design requires statistically relevant strength data. The traditional approach using the statistical two-parameter Weibull distribution suffered from two problems. The data sets were too small to obtain distribution parameters with sufficient accuracy and also too small to decide on the validity of the model. This holds especially for the low failure probability levels that are required for reliable applications. Extrapolation to 0.1% failure probability and below led to design strengths so low that higher load applications seemed to be not feasible. New data have been collected with numbers per set large enough to enable tests on the applicability of the three-parameter Weibull distribution. This distribution revealed to provide much better fitting of the data. Moreover it delivers a lower threshold value, which means a minimum value for breakage stress, allowing of removing statistical uncertainty by introducing a deterministic method to calculate design strength. Considerations taken from the theory of fracture mechanics as have been proven to be reliable with proof test qualifications of delicate structures made from brittle materials enable including fatigue due to stress corrosion in a straight forward way. With the formulae derived, either lifetime can be calculated from given stress or allowable stress from minimum required lifetime. The data, distributions, and design strength calculations for several practically relevant surface conditions of ZERODUR® are given.

Laser transmission welding (LTW) of thermoplastics is a direct bonding technique already used in different industrial applications sectors such as automobiles, microfluidics, electronics, and biomedicine. LTW evolves localized heating at the interface of two pieces of plastic to be joined. One of the plastic pieces needs to be optically transparent to the laser radiation whereas the other part has to be absorbent, being that the radiation produced by high power diode lasers is a good alternative for this process. As consequence, a tailored laser system has been designed and developed to obtain high quality weld seams with weld widths between 0.7 and 1.4 mm. The developed laser system consists of two diode laser bars (50 W per bar) coupled into an optical fiber using a nonimaging solution: equalization of the beam parameter product (BPP) in the slow and fast axes by a pair of step-mirrors. The power scaling was carried out by means of a multiplexing polarization technique. The analysis of energy balance and beam quality was performed considering ray tracing simulation (ZEMAX®) and experimental validation. The welding experiments were conducted on acrylonitrile/butadiene/styrene (ABS), a thermoplastic frequently used in automotive, electronics and aircraft applications, doped with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs). Quality of the weld seams on ABS was analyzed in terms of the process parameters (welding speed, laser power and clamping pressure) by visual and optical microscope inspections. Mechanical properties of weld seams were analyzed by mechanical shear tests. High quality weld seams were produced in ABS, revealing the potential of the laser developed in this work for a wide range of plastic welding applications.

We present a new fusion structure of finite impulse response (FIR) filter and adaptive Kalman filter to suppress the angle random walk (ARW) of the fiber optic gyroscopes (FOGs). In our proposed fusion filter, a low-pass FIR filter first decomposes the discrete-time rotation rate into an approximation part and a detailed part. The detailed part is then put into an adaptive Kalman filter, which generates an increment part to compensate the high-frequency components of the rotation rate suppressed by the FIR filter. Different from the existing adaptive mechanism that modifies the covariance matrix of the error in the predicted estimate to cover model error, our proposal adaptively modifies the state equation of the Kalman filter to give a more accurate model. Therefore, it has the ability to distinguish the high-frequency components of the rotate rate from the high-frequency ARW noise. The new fusion structure integrates the advantages of these two filters. Experiments showed that with this new proposal, the ARW of a specific FOG had been reduced from 0.03741 deg/√h to 0.00976 deg/√h when the tap order M reached 1000, and the tracking error in dynamic cases was smaller than the digital resolution of the FOG.

An 82-km sensing range Brillouin optical time-domain analysis distributed fiber sensor without systematic measurement error is proposed and first experimentally validated, in which the probe wave with two sidebands generates a dual gain-loss Brillouin interaction, giving rise to the remarkable suppressed pump depletion in long sensing range and a relatively narrow Brillouin gain spectrum. Both theoretical analysis and experimental results demonstrate that this technique is capable of accurate long-distance sensing. To the best of our knowledge, it is the simplest technique and does not require extra time for long-distance sensing (>50 km).

In the assembly of fiber optic gyroscope (FOG), the summation of the fiber tail length of waveguide and fiber ring in two directions cannot be exactly equal (i.e., fiber tail length of FOG in two directions is asymmetry). We analyze and calculate the vibration error of FOG due to this fiber tail length asymmetry based on elastic-optic effect. Inertial navigation simulation is performed to show attitude and positioning errors caused by this vibration error, which clearly shows the importance of reducing fiber-tail length asymmetry in high-accuracy applications.

In a high speed and packet-switched quantum computer network, a packet routing delay often leads to traffic jams, becoming a severe bottleneck for speeding up the transmission rate. Based on the delayed commutation circuit proposed in Phys. Rev. Lett. 97, 110502 (2006), we present an improved scheme for accelerating network transmission. For two more realistic scenarios, we utilize the characteristic of a quantum state to simultaneously implement a data switch and transmission that makes it possible to reduce the packet delay and route a qubit packet even before its address is determined. This circuit is further extended to the quantum network for the transmission of the unknown quantum information. The analysis demonstrates that quantum communication technology can considerably reduce the processing delay time and build faster and more efficient packet-switched networks.

Bearings-only tracking has been the focus of distinct research interest in the last few decades. To attack target maneuvering and measuring nonlinearity, most of the existing methods adopt an interactive multiple model (IMM) with a bank of nonlinear filtering recursions, such as an extended Kalman filter, an unscented Kalman filter (UKF), or a particle filter. However, these nine-state coupled-tracking methods usually suffer from low tracking accuracy due to inseparable model probability and high computational burden because of the calculating inverse of 9 x 9 matrices. This present work focuses on target tracking by two platforms's bearings-only measurements in an axial decoupled way. First, the passive ranging formula is derived with the conversion error proven to be Gaussian noises. Then to reduce the computational burden and maintain high tracking accuracy, the diagonal least upper bound for the covariance matrix of conversion error is given. This makes the decoupled tracking algorithm applicable. To attack the target maneuvering, the present decoupled IMM that uses a bank of passive-ranging-based Kalman filters is adopted along each axis separately. Finally, the decoupled tracking algorithm is compared with conventional coupled IMM in Cartesian coordinates by criterions such as tracking accuracy, model probability, and computational burden.

Infrared communication in the near ground free space has both military and civilian potential. To meet the requirements of infrared communication based on a micro-electro-mechanical system Planck infrared source/radiator, we propose a modulation method with large code information content, strong confidentiality, and a high recognition rate. With the characteristics of mid-infrared light, a long-range and anti-EMI wireless communication system is available. The information code is loaded on the carrier signal generated by the infrared source with specific frequency. Taking a 3×3 array system for an instance in our work, the design principle and implementation procedure of encoding and modulation is discussed. The total information content of the optical dynamic code is 1.5 kbytes. The communication system could transmit data in the bound rate of 900  bit/s with a photoelectric code recognition rate of 96.4% and an effective information content of 190 bytes.

A remarkable feature of compressive sensing is that the sensing is completely nonadaptive, but that does not mean that no effort whatsoever should be made to understand the signal acquired. With consideration of the differences and the similarities of the images, the proposed sensing matrix consists of two subsensing matrices: a fixed presensing matrix and a self-adaptive sensing matrix. The identical presensing vectors aim to estimate the compressibility of the image blocks and ensure the minimal measurements for reconstruction. The number of adaptive sensing vectors is flexible and depends on the compressibility estimated. More sensing vectors are assigned to incompressible image blocks than to compressible blocks. For a certain image block, the corresponding adaptive sensing matrix is constructed as a structured sensing matrix by combining the deterministic sensing matrix and the random sensing matrix. The former assigns the sensing vectors to the location where the information most likely lies and acquires the common structure contained in the image blocks, and the latter senses the difference and the individual structure the images possessed as an essential and unique characteristic. The proposed self-adaptive structured block sensing frame provides superior performance compared with many state-of-the-art compressive sensing reconstruction algorithms.

The authors propose a method to obtain a high dynamic range (HDR) image from multiple images with different exposure. Unlike conventional methods that use multiple images with different shutter speeds, the proposed method takes multiple images with identical and short shutter speeds but with different apertures. Consequently, the input low dynamic range image is less affected by scene change, while it has undesirable defocus blur due to different depth of field. In order to mitigate defocus blur of input images with larger apertures, we estimate the defocus map of each input image and use it as the spatially variant point spread function to deblur the image. Then, we extract the weight maps of input images, which are used to combine them to synthesize an HDR image. Our experimental results show that the proposed algorithm produces high-quality HDR images using a small number (typically three) of input images.

Finding defects with automatic visual inspection techniques is an essential task in various industrial fields. Despite considerable studies to achieve this task successfully, most previous methods are still vulnerable to ambiguities from diverse shapes and sizes of defects. We introduce a simple yet powerful method to segment defects on various texture surfaces in an unsupervised manner. Specifically, our method is based on the multiscale scheme of the phase spectrum of Fourier transform. The proposed method can even handle one-dimensional long defect patterns (e.g., streaks by scratch), which have been known to be hard to process in previous methods. In contrast to traditional inspection methods limited to locating particular sorts of defects, our approach has the advantage that it can be applied to segmenting arbitrary defects, because of the nonlinear diffusion involved in the multiscale scheme. Extensive experiments demonstrate that the proposed method provides much better results for defect segmentation than several competitive methods presented in the literature.

Natural feature-based approaches are still challenging for mobile applications (e.g., mobile augmented reality), because they are feasible only in limited environments such as highly textured and planar scenes/objects, and they need powerful mobile hardware for fast and reliable tracking. In many cases where conventional approaches are not effective, three-dimensional (3-D) knowledge of target scenes would be beneficial. We present a well-established framework for real-time visual tracking of less textured 3-D objects on mobile platforms. Our framework is based on model-based tracking that efficiently exploits partially known 3-D scene knowledge such as object models and a background’s distinctive geometric or photometric knowledge. Moreover, we elaborate on implementation in order to make it suitable for real-time vision processing on mobile hardware. The performance of the framework is tested and evaluated on recent commercially available smartphones, and its feasibility is shown by real-time demonstrations.

The range of the accuracy of scalar diffraction theory and effective medium theory for binary rectangular groove phase grating is evaluated by the comparison of diffraction efficiencies predicted from scalar theory and effective medium theory, respectively, to exact vector results calculated by Fourier modal method. The effect of element parameters (depth, period, index of refraction, angle of incidence, and fill factor) on the accuracy of scalar treatment and effective medium theory is quantitatively determined. Generally, it is found that the scalar method is valid when the normalized period is more than fourfold wavelength of incident light at normal incidence. The error of transmittances between vector method and scalar method increases as the incident angle and refractive index increase. Furthermore, when the higher diffraction orders other than zero-th order are not to propagate, the effective medium theory is accurate to evaluate the transmittance of grating at normal incidence. The error of transmittances between effective medium method and rigorous vector theory increases as the incident angle and refractive index increase. Also, the error of diffraction efficiencies between the simple methods and the vector method on the polarization state of incident light is clearly demonstrated.

It is demonstrated that a probability loophole exists for Einstein local hidden variables to violate the Clauser, Horne, Shimony, and Holt contrast.

We used patterned radial polarizers to easily generate and detect radially polarized beams. We then showed how to spatially manipulate the two-dimensional polarization mapping provided by a radial polarizer using different waveplate systems to obtain new two-dimensional polarization states. One system is particularly useful, since it converts the radial polarized beam into the azimuthally polarized beam. The transformed beams were analyzed using linear, circular, and radial polarizers. The Jones matrix formalism was applied for the theoretical analysis.

In this paper, we propose a method for the numerical simulation of optical double random phase encoding (DRPE). This method is based on a discrete model of the DRPE system that retains the properties of its optical counterpart and takes into account the capacity of DRPE to spread a signal’s energy in both the space and the spatial frequency domains. Discrete versions of two narrowband lossless diffusers are created to simulate their analogue optical counterparts and their bandwidths control how much the energy of the input signal is spread in both the space and spatial frequency domains as it passes through the system. The limiting case, when complete aliasing (maximum overlap) takes place, is also discussed in relation to our method. In this case, we show our method reduces to a purely numerical encryption procedure which can, nonetheless, be decrypted perfectly. Simulation results are presented to demonstrate the feasibility of the proposed technique.