This PDF file contains the editorial “Year in Review” for OE Vol. 55 Issue 02

This letter reports a pixel architecture that implements a light-to-resistance encoder exploiting the properties of a memristor. A light-to-frequency (L2F) converter is adopted to drive a memristor with pulses, thus changing its resistance according with the light intensity. In a conventional L2F implementation, a binary counter is needed to store the number of pulses generated within the exposure time (T_i). In the proposed circuit, the binary counter has been replaced with an analog counterpart, made of a single memristor. This turns into a smaller pixel pitch, compared with an all-CMOS solution and analog nonvolatile characteristics. The proposed circuit has been simulated in a 3.3 V, 0.35  μm CMOS process, while the memristor behavior relies on the HP model.

Two consecutive frames of a lateral navigation camera video sequence can be considered as an appropriate approximation to epipolar stereo. To overcome edge-aware inaccuracy caused by occlusion, we propose a model that matches the current frame to the next and to the previous ones. The positive disparity of matching to the previous frame has its symmetric negative disparity to the next frame. The proposed algorithm performs probabilistic choice for each matched pixel between the positive disparity and its symmetric disparity cost. A disparity map obtained by optimization over the cost volume composed of the proposed probabilistic choice is more accurate than the traditional left-to-right and right-to-left disparity maps cross-check. Also, our algorithm needs two times less computational operations per pixel than the cross-check technique. The effectiveness of our approach is demonstrated on synthetic data and real video sequences, with ground-truth value.

Future space exploration missions require precise information about the lander pose during the descent and landing steps. An effective algorithm that utilizes crater detection and matching is presented to determine the lander pose with respect to the planetary surface. First, the projections of the crater circular rims in the descent image are detected and fitted into ellipses based on the geometric distance and coplanar circles constraint. Second, the detected craters are metrically rectified through a two-dimensional homography and matched with the crater database by similarity transformation. Finally, the lander pose is calculated by a norm-based optimization method. The algorithm is tested by synthetic and real trials. The experimental results show that our presented algorithm can determine the lander pose accurately and robustly.

Motion blur (MB) presents a significant challenge for obtaining high-contrast image data from biological cells with a polarization diffraction imaging flow cytometry (p-DIFC) method. A new p-DIFC experimental system has been developed to evaluate the MB and its effect on image analysis using a time-delay-integration (TDI) CCD camera. Diffraction images of MCF-7 and K562 cells have been acquired with different speed-mismatch ratios and compared to characterize MB quantitatively. Frequency analysis of the diffraction images shows that the degree of MB can be quantified by bandwidth variations of the diffraction images along the motion direction. The analytical results were confirmed by the p-DIFC image data acquired at different speed-mismatch ratios and used to validate a method of numerical simulation of MB on blur-free diffraction images, which provides a useful tool to examine the blurring effect on diffraction images acquired from the same cell. These results provide insights on the dependence of diffraction image on MB and allow significant improvement on rapid biological cell assay with the p-DIFC method.

We propose an automated calibration method with a closed-form solution for three-dimensional (3-D) integral imaging with randomly distributed sensors of unknown positions in 3-D space. In the method presented, a robust feature-detection algorithm is applied to the elemental image set, and the matching features are used to derive the relations between the corresponding sensors. Once all the sensor positions are determined, the 3-D objects are reconstructed with a ray backprojection reconstruction scheme. The 3-D objects can also be reconstructed from multiple perspectives in this method. To the best of our knowledge, this is the first report on 3-D integral imaging using automated sensor position estimation with a closed-form solution. This approach can provide 3-D object reconstruction without any known sensor positions in a 3-D space.

A bionic optical imaging system with an aspheric solid–liquid mixed variable-focus lens was designed and fabricated. The entire system mainly consisted of a doublet lens, a solid–liquid mixed variable-focus lens, a connecting part, and a CCD imaging device. To mimic the structure of the crystalline lens, the solid–liquid mixed variable-focus lens consisted of a polydimethylsiloxane (PDMS) lens, a polymethyl methacrylate lens, and the liquid of ethyl silicone oil. By pumping liquid in or out of the cavity using a microinjector, the curvatures of the front and rear surfaces of the PDMS lens were varied, resulting in a change of focal length. The overall structure of the system was presented, as well as a detailed description of the solid–liquid mixed variable-focus lens, material, and fabrication process. Under different injection volumes, the deformation of the PDMS lens was measured and simulated, pictures were captured, and the optical performance was analyzed in simulations and experiments. The focal length of the system ranged from 25.05 to 14.61 mm, and the variation of the diopter was 28.5D, which was larger than that of the human eye.

Remote sensing of chemical vapor plumes is a difficult but important task for many military and civilian applications. Hyperspectral sensors operating in the long-wave infrared regime have well-demonstrated detection capabilities. However, the identification of a plume’s chemical constituents, based on a chemical library, is a multiple hypothesis testing problem which standard detection metrics do not fully describe. We propose using an additional performance metric for identification based on the so-called Dice index. Our approach partitions and weights a confusion matrix to develop both the standard detection metrics and identification metric. Using the proposed metrics, we demonstrate that the intuitive system design of a detector bank followed by an identifier is indeed justified when incorporating performance information beyond the standard detection metrics.

An encrypting three-dimensional (3-D) information system based on integral imaging (II) and multiple chaotic maps is proposed. In the encrypting process, the elemental image array (EIA) which represents spatial and angular information of the real 3-D scene is picked up by a microlens array. Subsequently, R, G, and B color components decomposed by the EIA are encrypted using multiple chaotic maps. Finally, these three encrypted components are interwoven to obtain the cipher information. The decryption process implements the reverse operation of the encryption process for retrieving the high-quality 3-D images. Since the encrypted EIA has the data redundancy property due to II, and all parameters of the pickup part are the secret keys of the encrypting system, the system sensitivity on the changes of the plaintext and secret keys can be significantly improved. Moreover, the algorithm based on multiple chaotic maps can effectively enhance the security. A preliminary experiment is carried out, and the experimental results verify the effectiveness, robustness, and security of the proposed system.

Compressive sensing (CS) is a signal processing technique that enables a signal that has a sparse representation in a known basis to be reconstructed using measurements obtained below the Nyquist rate. Single detector image reconstruction applications using CS have been shown to give promising results. In this study, we investigate the application of CS theory to single detector infrared (IR) rosette scanning systems which suffer from low performance compared to costly focal plane array (FPA) detectors. The single detector pseudoimaging rosette scanning system scans the scene with a specific pattern and performs processing to estimate the target location without forming an image. In this context, this generation of scanning systems may be improved by utilizing the samples obtained by the rosette scanning pattern in conjunction with the CS framework. For this purpose, we consider surface-to-air engagement scenarios using IR images containing aerial targets and flares. The IR images have been reconstructed from samples obtained with the rosette scanning pattern and other baseline sampling strategies. It has been shown that the proposed scheme exhibits good reconstruction performance and a large size FPA imaging performance can be achieved using a single IR detector with a rosette scanning pattern.

Michelson interferometer is one of the most popular optical interferometric systems used in optical metrology. Typically, Michelson interferometers are used to measure object displacement with wavefront shapes to one half of the laser wavelength. As testing components and device sizes reduce to micro and nano size, a sensitivity of half the wavelength of light cannot be used to measure several hundred picometer displacement. Multiple-reflection interferometers have been proposed and are used to increase the sensitivity in a Michelson interferometer; however, when altering the number of reflections, the system alignment becomes cumbersome. We describe some of the problems associated with the current multiple-reflection interferometer and introduce a setup for matching path lengths to increase the resolution and allow for the reduction of the stringent requirement on the coherence length of the lasers used. Theoretically, we show that more than 1000 reflections can be achieved. Experimental results of up to 100 reflections are presented in this paper.

Due to their manufacturing process, plastic injection molded lenses do not achieve a constant density throughout their volume. This change of density introduces tensions in the material, inducing local birefringence, which in turn is translated into a variation of the ordinary and extraordinary refractive indices that can be expressed as a retardation phase plane using the Jones matrix notation. The detection and measurement of the value of the retardation of the phase plane are therefore very useful ways to evaluate the quality of plastic lenses. We introduce a polariscopic device to obtain two-dimensional maps of the tension distribution in the bulk of a lens, based on detection of the local birefringence. In addition to a description of the device and the mathematical approach used, a set of initial measurements is presented that confirms the validity of the developed system for the testing of the uniformity of plastic lenses.

Ring polishing is a primary method to polish large aperture planar optics that is widely used in the fabrication of high-power solid-state laser equipment. The relative motion track with the ring polishing is always rotationally symmetrical and the amount of material removal is related to the radius. The height errors are identical when the points are in the same radius, which can largely reduce the coverage area when the subaperture stitching method is used to measure the figure error of the surface. A new sparse lattice for planar optics polished by ring polishing is introduced. The cumulative error is proven small enough for sparse subaperture stitching by the reference of the simulated data. A planar optical element with 200  mm×200  mm aperture was chosen to test the feasibility of our proposed method. The results indicate that sparse stitching is suitable for measuring a large planar surface polished by ring polishing. The results of two chain lattice are closer to the fully covered lattice than a one chain lattice. However, more measuring time could be saved by the one chain lattice method. So, the usage of different lattices could be adapted for different periods of large aperture planar optical manufacturing.

A color-encoded fringe reflection technique is presented for dynamic specular surface measurement. Only one color-encoded fringe pattern is required in this method. In comparison with the reported dynamic specular surface measuring method (the composite fringe pattern method), the proposed color-encoded fringe technique has higher phase accuracy. The color intensity crosstalk problem between the three channels is discussed. As a result, this problem will seldom affect the phase accuracy of the proposed method. This turns out to be the main reason why the presented method can achieve a higher measuring accuracy than the existing dynamic measurement method. In addition, the proposed color-encoded fringe technique is proven to be more suitable than the existing method for the complex tested surface. The vibrating measuring experiment of a wafer proves the ability of the proposed method to achieve dynamic measurement.

Stereo vision-based triangulation systems are commonly used to reconstruct the three-dimensional surface shape of objects. In order to increase accuracy, they typically contain a projector which projects a sequence of patterns onto the object’s surface. However, in spite of a considerable demand to measure dynamic processes, such systems are often limited to static objects. In order to enhance their speed, apart from fast cameras and projection systems, it is useful to use pattern sequences as short as possible. In this contribution, we experimentally compare two different illumination approaches, aperiodic sinusoidal fringes and phase-shifted sinusoidal fringes, with regard to the achievable point cloud completeness and accuracy depending on the pattern parameters and sequence length.

The statistical properties of speckle relevant to short- to medium-range (tactical) active tracking involving polychromatic illumination are investigated. A numerical model is developed to allow rapid simulation of speckled images including the speckle contrast reduction effects of illuminator bandwidth, surface slope, and roughness, and the polarization properties of both the source and the reflection. Regarding surface slope (relative orientation of the surface normal and illumination/observation directions), Huntley’s theory for speckle contrast, which employs geometrical approximations to decrease computation time, is modified to increase accuracy by incorporation of a geometrical correction factor and better treatment of roughness and polarization. The resulting model shows excellent agreement with more exact theory over a wide range. An experiment is conducted to validate both the numerical model developed here and existing theory. A diode laser source with coherence length of 259±7  μm is reflected off of a silver-coated diffuse surface. Speckle data are gathered for 16 surface slope angles corresponding to speckle contrast between about 0.55 and 1. Taking the measured data as truth, both equations show error mean and standard deviation of less than 3%. Thus, the theory is validated over the range of this experiment.

An investigation of the effects of the optical properties of surface-mount-device (SMD) light-emitting diode (LED) (side-view and top-view LEDs) packaging (PKG) components on the light extraction efficiency ηPKG using ray-tracing simulations is presented. In particular, it is found that the optical properties of the PKG resin and the lead-frame (L/F) silver-plating significantly affect ηPKG. Thus, the effects of the surface reflection methods of these components are investigated in order to optimize the optical design of the LED PKG. It is shown that there exists peak extraction efficiency for each PKG, and the cavity angle formed by the cavity wall is important to the optical design. In addition, the effect of phosphor present in the mold resin is examined using a Mie scattering simulation. Finally, an SMD LED PKG optical design method is proposed on the basis of the simulation results.

We present a technique for optimizing advanced optical imaging methods for nanoscale structures, such as those encountered in the inspection of cutting-edge semiconductor devices. The optimization flow is divided to two parts: simulating light-structure interaction using the finite-difference time-domain (FDTD) method and simulating the optical imaging system by means of its optical transfer function. As a case study, FDTD is used to simulate 10-nm silicon line-space and static random-access memory patterns, with irregular structural protrusions and silicon-oxide particles as defects of interest. An ultraviolet scanning-spot optical microscope is used to detect these defects, and the optimization flow is used to find the optimal imaging mode for detection.

This work provides a design and optimization method for total internal reflection (TIR) lenses based on slope-error tolerance analysis. This work focuses on how the slope error impacts the central luminous intensity (CLI) of a TIR lens. The concentration standard index (CSI) is introduced as a metric for analyzing the CLI, both locally and globally. A unique design method for improved manufacturing tolerance is introduced, and a way of optimizing the TIR lens design in order to achieve a better slope-error tolerance is presented by evaluating the CSI. Using the design method, a TIR lens is fabricated and this theoretical approach is then demonstrated by a comparison between the tested contours of the TIR surfaces.

All-optical logic gates are designed to extend the existing design to a higher number of bits, to use the same gate in multifunctions, and to add new gate designs. This type of gate is based on semiconductor optical amplifier (SOA) nonlinearities, since the SOA can provide a strong change of the refractive index together with high gain. The SOA is used with a Mach–Zehnder interferometer (MZI) forming an SOA-MZI structure which is used to perform the logic gates XOR, NOR, OR, and XNOR. Two binary input data signals are used with different number of bits (4, 6, 8, and 16 bit) at 10 Gbps. This work includes the study of the effect of the number of bits on the received power, minimum bit error rate, and maximum Q-factor.

We report on the polarization behavior of painted samples doped with a silicone light diffusion agent and illuminated by linearly polarized laser light centered at 532 and 650 nm. Reflection spectra of the painted samples with dopant concentration of 0 and 12.2 wt.% were examined. The degree of depolarization increases from 0.35 to 0.8 under laser illumination at 650 nm and from 0.5 to 0.94 under laser illumination at 532 nm with an increasing concentration of light diffusion agent. The polarization behavior of painted samples was described, taking into account contribution of both surface scattering and volume scattering.

We propose one-shot Fourier-spectroscopic tomography as a method of ultraminiature spectroscopic imaging. The apparatus used in this technique consists solely of a glass slab with a portion of its surface polished at a certain inclination angle—a device we term a relative-inclination phase shifter—simply mounted on an infinite-distance-corrected optical imaging system. For this reason, the system may be ultraminiaturized to sizes on the order of a few tens of millimeters. Moreover, because our technique uses a near-common-path wavefront-division phase-shift interferometer and has absolutely no need for a mechanical drive unit, it is highly robust against mechanical vibrations. In addition, because the proposed technique uses Fourier-transform spectroscopy, it offers highly efficient light utilization and an outstanding signal-to-noise ratio compared to devices that incorporate distributed or hyperspectral acousto-optical tunable filters. The interferogram, which is a pattern formed by interference of waves at all wavelengths, reflects the spatial variation in the intensity of the interference depending on the magnitude of the phase shift. We first discuss the design of the phase shifter and the results of tests to validate the principles underlying one-shot Fourier-spectroscopic tomography. We then report the results of one-dimensional spectroscopic imaging using this technique.

A miniature laser ablation probe relying on an optical fiber to deliver light requires a high coupling efficiency objective with sufficient magnification in order to provide adequate power and field for surgery. A diffraction-limited optical design is presented that utilizes high refractive index zinc sulfide to meet specifications while reducing the miniature objective down to two lenses. The design has a hypercentric conjugate plane on the fiber side and is telecentric on the tissue end. Two versions of the objective were built on a diamond lathe—a traditional cylindrical design and a custom-tapered mount. Both received an antireflective coating. The objectives performed as designed in terms of observable resolution and field of view as measured by imaging a 1951 USAF resolution target. The slanted edge technique was used to find Strehl ratios of 0.75 and 0.78, respectively, indicating nearly diffraction-limited performance. Finally, preliminary ablation experiments indicated threshold fluence of gold film was comparable to similar reported probes.

A coupled system with varying parameters is proposed to improve the security of optoelectronic delayed feedback system. This system is coupled by two parameter-varied optoelectronic delayed feedback systems with chaotic modulation. Dynamics performance results show that this system has a higher complexity compared to the original one. Furthermore, this system can conceal the time delay effectively against the autocorrelation function and delayed mutual information method and can increase the dimension space of secure parameters to resist brute-force attack by introducing the digital chaotic systems.

We numerically analyze the square pulse emission from a passively mode-locked figure-of-eight microstructured optical fiber laser. Numerical simulations demonstrate that the high nonlinearity of the microstructured fiber plays a key role in the output pulse duration. A dual-stage erbium-doped fiber amplifier has been used in the cavity. The first amplifier, localized in the nonlinear amplifying loop mirror, allows control of the pulse width, while the second amplifier in the unidirectional ring allows variation of the amplitude without affecting the pulse width. Our results give some physical insight to the square pulse formation and the generation of high-energy pulses. Our numerical model provides a general approach to control the properties of a square pulse, and hence could be of great importance for the design of practical high-energy fiber laser systems.

We propose a physically enhanced secure scheme for direct detection–orthogonal frequency division multiplexing–passive optical network (DD-OFDM-PON) and long reach coherent detection–orthogonal frequency division multiplexing–passive optical network (LRCO-OFDM-PON), by employing noise-based encryption and channel/phase estimation. The noise data generated by chaos mapping are used to substitute training sequences in preamble to realize channel estimation and frame synchronization, and also to be embedded on variable number of key-selected randomly spaced pilot subcarriers to implement phase estimation. Consequently, the information used for signal recovery is totally hidden as unpredictable noise information in OFDM frames to mask useful information and to prevent illegal users from correctly realizing OFDM demodulation, and thereby enhancing resistance to attackers. The levels of illegal-decryption complexity and implementation complexity are theoretically discussed. Through extensive simulations, the performances of the proposed channel/phase estimation and the security introduced by encrypted pilot carriers have been investigated in both DD-OFDM and LRCO-OFDM systems. In addition, in the proposed secure DD-OFDM/LRCO-OFDM PON models, both legal and illegal receiving scenarios have been considered. These results show that, by utilizing the proposed scheme, the resistance to attackers can be significantly enhanced in DD-OFDM-PON and LRCO-OFDM-PON systems without performance degradations.

Spatial filtering is an important technique for reducing sky background noise in a satellite quantum key distribution downlink receiver. Atmospheric turbulence limits the extent to which spatial filtering can reduce sky noise without introducing signal losses. Using atmospheric propagation and compensation simulations, the potential benefit of adaptive optics (AO) to secure key generation (SKG) is quantified. Simulations are performed assuming optical propagation from a low-Earth-orbit satellite to a terrestrial receiver that includes AO. Higher-order AO correction is modeled assuming a Shack–Hartmann wavefront sensor and a continuous-face-sheet deformable mirror. The effects of atmospheric turbulence, tracking, and higher-order AO on the photon capture efficiency are simulated using statistical representations of turbulence and a time-domain wave-optics hardware emulator. SKG rates are calculated for a decoy-state protocol as a function of the receiver field of view for various strengths of turbulence, sky radiances, and pointing angles. The results show that at fields of view smaller than those discussed by others, AO technologies can enhance SKG rates in daylight and enable SKG where it would otherwise be prohibited as a consequence of background optical noise and signal loss due to propagation and turbulence effects.

This paper presents the results of our experiments on a comparative study of cesium and potassium diode pumped alkali lasers (DPALs) aimed to determine which of these two lasers has more potential to scale to high powers. For both lasers, we have chosen a “low-pressure DPAL approach,” which uses buffer gas pressure of about 1 atm for spin-orbit mixing of the excited states of alkali atoms to provide population inversion in the gain medium. The goal of this study was to determine power-limiting effects, which affect the performance of these DPALs, and find out how these limiting effects can be mitigated. We studied the performance of both lasers in CW and pulsed modes using both static and flowing gain medium and pump with different pulse duration. We observed output power degradation in time from the initial value to the level corresponding to the CW mode of operation. As a result of this study, some essential positive and negative features of both DPALs were revealed, which should be taken into account for power-scaling experiments.

We report a two-axis fiber inclinometer fabricated using an ultraweak terahertz-range fiber Bragg grating. Three sensing grating structures were inscribed along a single-mode optical fiber using a femtosecond laser, bound together into a sensing array using thermoformed plastic, and fixed to a two-axis rotational stage. Inclination tests were performed in which the fiber was deflected from 0 to 1.7 deg. These tests were repeated at eight azimuthal angles in increments of 45 deg (from 0 to 315 deg). The standard deviation of the largest inclination angle error was 0.048 deg and the stability of the inclination angle was 0.030 deg.

A low-cost packaging method utilizing a fully passive optical alignment and surface-mounting method is demonstrated for pluggable compact and slim multichannel optical interconnection modules using a VCSEL/PIN-PD chip array. The modules are based on a nonplanar bent right-angle electrical signal path on a silicon platform and direct-butt-optical coupling without a bulky and expensive microlens array. The measured optical direct-butt-coupling efficiencies of each channel without any bulky optics are as high as 33% and 95% for the transmitter and receiver, respectively. Excellent lateral optical alignment tolerance of larger than 60  μm for both the transmitter and receiver module significantly reduces the manufacturing and material costs as well as the packaging time. The clear eye diagrams, extinction ratios higher than 8 dB at 10.3 Gbps for the transmitter module, and receiver sensitivity of better than −13.1  dBm at 10.3 Gbps and a bit error rate of 10⁻¹² for all channels are demonstrated. Considering that the optical output power of the transmitter is greater than 0 dBm, the module has a sufficient power margin of about 13 dB for 10.3 Gbps operations for all channels.

We propose an energy-efficient orthogonal frequency division multiplexing-based passive optical network (OFDM-PON) using adaptive sleep-mode control and dynamic bandwidth allocation. In this scheme, a bidirectional-centralized algorithm named the receiver and transmitter accurate sleep control and dynamic bandwidth allocation (RTASC-DBA), which has an overall bandwidth scheduling policy, is employed to enhance the energy efficiency of the OFDM-PON. The RTASC-DBA algorithm is used in an optical line terminal (OLT) to control the sleep mode of an optical network unit (ONU) sleep and guarantee the quality of service of different services of the OFDM-PON. The obtained results show that, by using the proposed scheme, the average power consumption of the ONU is reduced by ∼40% when the normalized ONU load is less than 80%, compared with the average power consumption without using the proposed scheme.

Agile beam steering has been previously reported to be one of the unique properties of a liquid crystal optical phased array. We propose a stochastic scanning method using the property of agile beam steering to shorten acquisition time in building a free-space laser communication link. As a specific example, Gaussian stochastic scan enables higher acquisition probability and shorter acquisition time. In addition, there are two factors to influence the results: standard deviation of stochastic scanning angle and the width of the laser beam. Theoretical analysis is presented that the stochastic scanning method is a unique method to speed up the acquisition process in free-space laser communication.

We propose to use a semiconductor optical amplifier as the nonlinear medium to realize data exchange of two differential quadrature phase-shift keying (DQPSK) signals based on the nondegenerate four-wave mixing (FWM) process. This scheme exploits the parametric depletion effect of the FWM process, when proper pump power and wavelength result in almost negligible noise of the original signal for the converted signal after data exchange. Optical data exchange of two DQPSK signals at 10 Gbps is achieved with a power penalty of less than 4 dB at the bit-error rate of 10⁻⁹.

We reported the modeling result of selectively magnetic fluid infiltrated dual-core photonic crystal fiber based magnetic field sensor. Inside the cross-section of the designed photonic crystal fiber, the two fiber cores filled with magnetic fluid (Fe₃O₄) form two independent waveguides with mode coupling. The mode coupling under different magnetic field strengths is investigated theoretically. The sensitivity of the sensor as a function of the structural parameters of the photonic crystal fiber is calculated. The result shows that the proposed sensing device with 1 cm photonic crystal fiber length has a large sensitivity of 305.8  pm/Oe.

AlGaInN ridge waveguide laser diodes are fabricated to achieve single-mode operation with optical powers up to 100 mW at ∼420  nm for visible free-space, underwater, and plastic optical fiber communication. We report high-frequency operation of AlGaInN laser diodes with data transmission up to 2.5 GHz for free-space and underwater communication and up to 1.38 GHz through 10 m of plastic optical fiber.

A scheduling scheme for a large-scale optical switch is presented and its performance is evaluated. The optical switch is built on an arrayed waveguide grating router (AWGR) and space switching enabled tunable wavelength converter (SS-TWC) and in a Clos switch structure. The SS-TWC has more than one output and in the switch structure enables a multiple fold expansion of the switch port count while using the same dimension AWGR. The switch reconfiguration is triggered by an event, e.g., packet arriving or input port transmitter available for its waiting packets, and the scheduling scheme operates asynchronously. Simulation results demonstrate that the traffic scheduling scheme enables the delivery of high-transmission bandwidth and low packet delay performance, and verify the nonblocking property of the switch.

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach–Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50  dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability.

A microwave photonic link (MPL) with spurious-free dynamic range (SFDR) improvement utilizing the nonlinearity of a distributed feedback (DFB) laser is proposed and demonstrated. First, the relationship between the bias current and nonlinearity of a semiconductor DFB laser is experimentally studied. On this basis, the proposed linear optimization of MPL is realized by the combination of the external intensity Mach–Zehnder modulator (MZM) modulation MPL and the direct modulation MPL with the nonlinear operation of the DFB laser. In the external modulation MPL, the MZM is biased at the linear point to achieve the radio frequency (RF) signal transmission. In the direct modulation MPL, the third-order intermodulation (IMD3) components are generated for enhancing the SFDR of the external modulation MPL. When the center frequency of the input RF signal is 5 GHz and the two-tone signal interval is 10 kHz, the experimental results show that IMD3 of the system is effectively suppressed by 29.3 dB and the SFDR is increased by 7.7 dB.

We propose a microwave photonics system for radio frequency self-interference cancellation using optical techniques. With a simple structure, this system employs two low-cost directly modulated lasers and a balanced photodetector to subtract the strong self-interference signal from a corrupted received signal. For commonly used wireless applications, 40-dB cancellation within 900-MHz band and 33-dB cancellation within 2.4-GHz band are experimentally obtained, both over 400-MHz bandwidth. Moreover, for ultra-wideband cancellation, this system achieves more than 27-dB cancellation over 6-GHz bandwidth. The experimental results show good recovery of the weak signal of interest buried by strong self-interference after the cancellation.

We propose and demonstrate a flexible and filter-free method to generate ultrawideband monocycle and doublet pulses utilizing cross-gain modulation in a semiconductor optical amplifier. The counter-propagation scheme and UWB-over-fiber technology is implemented by exploiting dispersion-induced pulse broadening effect in a single-mode fiber. Owing to the counter-propagation scheme, the pump and probe light can be the same wavelength, which could provide the system better dispersion performance.

To improve the performance of channel estimation (CE), a method of joint frame synchronization and data-aided CE using less training overhead is proposed. A 100-Gb/s polarization-division multiplexing coherent transmission system with quaternary phase-shift keying based on the proposed method is demonstrated by simulation. The simulation results show that the proposed method could achieve accurate timing offset and CE in the presence of strong amplified spontaneous emission noise.

Inductively coupled plasma (ICP) etching has distinct advantages over reactive ion etching in that the etching rates are considerably higher, the uniformity is much better, and the sidewalls of the etched material are highly anisotropic due to the higher plasma density and lower operating pressure. Therefore, ICP etching is a promising process for pattern transfer required during microelectronic and optoelectronic fabrication. Resonator–quantum well infrared photodetectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE). To fabricate R-QWIP focal plane arrays (FPAs), two optimized ICP etching processes are developed. Using these etching techniques, we have fabricated R-QWIP FPAs of several different formats and pixel sizes with the required dimensions and completely removed the substrates of the FPAs. Their QE spectra were tested to be 30 to 40%. The operability and spectral nonuniformity of the FPA is ∼99.5 and 3%, respectively.

A simple laboratory method is presented for producing optical fibers with tips polished at various angles. Angled optical fiber tips are used in applications such as optical sensing and remote laser surgery, where they can be used to control the angle of light leaving the fiber or direct it to the side. This allows for greater control and allows areas to be reached that otherwise could not. Optical fibers were produced with tip angles of 45 deg using a Perspex mounting block with an aluminum base plate. The dispersion of light leaving the tip was tested using a blue (470 nm) LED. The angle imposed an angular shift on the light diffracting out of the tip of approximately 30 deg. Additionally, some light reflected from the tip surface to diffract at 90 deg through the side of the fiber. These observations are consistent with theory and those seen by other studies, validating the method. The method was simple to perform and does not require advanced manufacturing tools. The method is suitable for producing small quantities of angle-tipped optical fibers for research applications.

A single-polarization single-mode (SPSM) photonic crystal fiber (PCF) coupler is designed and investigated by using full-vector finite-element method with the anisotropic perfectly matched layer. We numerically analyze the SPSM coupling properties with respect to the structure parameters and confinement loss characteristics. The results reveal that the coupling length between dual cores is as small as millimeter order of magnitude due to the wide silica bridge of energy transfer, and the SPSM coupling region can be tailored to cover the communication windows of 1.3 or 1.55  μm with optimized design parameters. Moreover, the confinement loss of x polarization is 3 orders of magnitude larger than that of y polarization in single polarization range. The proposed SPSM PCF coupler may find application in polarization-sensitive systems.

The theoretical model of K9 glass irradiated by a 248-nm KrF excimer laser was established, and a numerical simulation was performed to calculate temperature and thermal stress fields in the K9 glass sample using the finite element method. The laser-induced damage thresholds were defined and calculated, and the effect of repetition frequency and the number of pulses on the damage threshold were also studied. Furthermore, the experiment research was carried out to confirm the numerical simulation. The damage threshold and damage morphology were analyzed by means of a metallurgical microscope and scanning electron microscopy. The simulation and experimental results indicated that the damage mechanism of K9 glass irradiated by a KrF excimer laser was melting damage and stress damage, and the stress damage first appeared inside the K9 glass sample. The tensile stress damage threshold, the compressive stress damage threshold, and the melting damage threshold were 0.64, 0.76, and 1.05  J/cm², respectively. The damage threshold decreased with increasing repetition frequency and number of laser pulses. The experimental results indicated that the damage threshold of K9 glass was 2.8  J/cm².

The duty cycle effect on the light extraction efficiency of light-emitting diodes having different periodically corrugated enhancement structures placed opposite to the emission surface was studied. The experimental results were compared with numerical simulation results. The numerical simulation was performed using a rigorous-coupled-wave-analysis method. In the case of common structures such as a patterned-sapphire structure, we found that, in general, extraction efficiency increased drastically when duty cycle was increased from zero, and then it varied relatively slowly as the duty cycle was increased further; after that, the extraction efficiency dropped drastically as the duty cycle approached 100%. However, for a structure that was composed of autocloned-photonic crystals super-imposing on the periodical corrugation, the efficiency increased monotonically with the duty cycle and reached 83.4% (corresponding to 589% enhancement efficiency) when the duty cycle approached 100%. A method for the fabrication of such high-efficiency structures was proposed.

We experimentally investigate the multifold intensity enhancement and spectral narrowing of photoluminescence (PL) from amorphous silicon quantum dots (a-Si QDs) embedded in a silicon-rich SiO_x film of the Ag/SiO_x:a-Si QDs/Au plasmonic nanocavity, through the resonance coupling between the localized surface plasmon (LSP) mode and the Fabry-Pérot (FP) cavity mode, by tuning a one-dimensional (1-D) Ag grating on the top. The LSP resonance can be precisely tuned by adjusting the Ag line widths of the 1-D Ag grating. It is found that the LSP mode strongly couples with the FP cavity mode, resulting in a narrower emission line width and a larger PL enhancement. An optimized Ag grating structure is found to exhibit a narrow emission line width of 15 nm and 2.77-fold enhancement in the PL peak intensity, as compared to an SiO_x:a-SiQDs/Au structure without 1-D Ag grating, due to the strong resonance coupling between the two modes.

We report on the fabrication of waveguides in fused silica using 4.5-MeV nitrogen ion implantation with a fluence of 5.0×10¹⁴  ions/cm². The prism-coupling method was employed to measure the effective refractive indices of guiding modes at the wavelengths of 632.8 and 1539 nm. The effective refractive indices of the first few modes were higher than that of the substrate. The refractive index profiles at 632.8 and 1539 nm were reconstructed by the reflectivity calculation method. Positive index changes were induced in the waveguide layers. The end-face coupling method was used to measure the near-field light intensity distributions at the wavelength of 632.8 nm and the finite-difference beam propagation method was applied to simulate the guided mode profile at the wavelength of 1539 nm. The waveguide structures emerge as candidates for integrated photonic devices.

We experimentally demonstrated a retarder with a wide field-of-view as well as a negative dispersion (ND) of birefringence. We stacked reactive mesogen, which has a positive birefringence, and polymethylmethacrylate, which has a negative birefringence. The out-of-plane retardation (R_th) of the stacked film was 6 nm. This value is about a tenth of that of a general retarder and demonstrates a small change in the retardation (Re) at an oblique viewing angle. The stacked film showed an ND of the birefringence, where Re(450  nm)/Re(550  nm)=0.818 and Re(650  nm)/Re(550  nm)=1.110. The dispersion properties were close to the ideal dispersion of an achromatic retarder and showed a small Re-dependence on the wavelength of light.

Design of a metamaterial based on an S-shaped resonator surrounded by a ground frame and excited by using a feeding transmission line on microstrip technology is presented. Since the resonator, ground frame, and its excitation mechanism are all realized on a microstrip, its characterization can be carried out using common laboratory equipment without needing any waveguide components or plane-wave-illumination techniques. The structure presented here may be realized on any microstrip and does not require special materials. The resonator and ground frame are both on the same side of the microstrip, thus the proposed topology may also be populated with active and passive microwave components, and hybrid active, passive, or reconfigurable microwave circuits may be realized. In metamaterial designs that require plane wave illumination, usually many numbers of periodic unit cells are needed; however, in our design, only one cell is capable of achieving metamaterial properties. The constitutive parameters of the metamaterial are retrieved and compared to demonstrate the agreement between simulations and measurements. The proposed topology is also demonstrated in a sensor application, where simulated and measured results agree well. Thus, it can be realized using standard microwave technology and used for numerous applications where metamaterial properties are needed.

We used bright and dark nanocavities coupled to a metal-insulator-metal waveguide to realize a plasmonic analogue of electromagnetically induced transparency (EIT) in integrated plasmonics. The bright nanocavity is directly coupled to the waveguide, while the dark nanocavity is achieved with the help of evanescent coupling. The numerical simulation shows a typical EIT-like line in the transmission spectrum. Using the model of EIT effect in a three-level atomic system, this phenomenon is well explained. Adding the number of dark nanocavities, we get multiple transparent peaks in the transmission spectrum of plasmon-induced transparency (PIT) effect, and we can realize control of the PIT effect by changing the geometric parameters of the plasmonic structure.

The physical mechanism in efficiency droop of GaN-based light-emitting diodes (LEDs) was investigated using a modified rate equation model considering inhomogeneous carrier distribution and was compared with the measured result. On this basis, the efficiency droop effect on the performance of a code division multiple access (CDMA) visible-light communication (VLC) system using GaN-based LEDs was also analyzed. The results reveal that the obvious transmitted signal error under the effect of LED efficiency droop leads to performance deterioration of multiuser CDMA VLC systems. Also, the performance of CDMA VLC systems is reduced with the user number increase due to LED efficiency droop. The bit error rate of a CDMA VLC system was further calculated for different branch signal levels and bias currents. It is demonstrated that the efficiency droop effect on the performance of CDMA VLC systems can be alleviated by adjusting the branch signal level and the bias current.