I graduated high school when I was 16 and it was not because I was all that bright. I had moved from Savannah, Georgia, to Memphis, Tennessee, which corresponded to states that required 24 and 18 high school credits to graduate, respectively. I moved at the end of my sophomore year, so I skipped 11th grade completely. So, there I was, 16 and out of school. I hated school at the time, and my father would not let me move to Hollywood to become an actor, so I lied about my age and became an orderly in a local hospital. There I met a registered nurse, we fell in love, and I was convinced I needed to get married. The wedding was scheduled for the month after I turned 18 years of age. My father was against it, and he told me I didn’t know what I was doing and to just wait some period of time. The marriage lasted only a few short years and I realized my father was right. No 18 year old young man listens much, especially to his father. I quickly tired of orderly work and went to school.

Free space optical links get adversely affected by atmospheric turbulence besides aerosol-based scattering and attenuation, causing signal degradation at the receiving terminal. The gamma–gamma probability density function has been extensively utilized for modeling the received signal strength under all turbulence regimes. An estimator with an underlying gamma–gamma turbulence model is being proposed. For the estimation of optical signal intensity, a minimum mean square error criterion has been used to develop the proposed estimator. It is assumed that the receiver is operating under shot noise–limited conditions, and the received signal is detected using a PIN photodiode.

The design of a biwavelength transceiver (TRx) module for parallel simultaneous bidirectional optical interconnects is described. The TRx module has been implemented using two different wavelengths, 850 and 1060 nm, to send and receive signals simultaneously through a common optical interface while optimizing cost and performance. Filtering mirrors are formed in the optical fibers which are embedded on a V-grooved silicon substrate for reflecting and filtering optical signals from/to vertical-cavity surface-emitting laser (VCSEL)/photodiode (PD). The VCSEL and PD are flip-chip bonded on individual silicon optical benches, which are attached on the silicon substrate for optical signal coupling from the VCSEL to fiber and from fiber to the PD. A high-speed and low-loss ceramic printed circuit board, which has a compact size of 0.033 cc, has been designed to carry transmitter and receiver chips for easy packaging of the TRx module. Applied for quad small form-factor pluggable applications at 40-Gbps operation, the four-channel biwavelength TRx module showed clear eye diagrams with a bit error rate (BER) of 10−¹² at input powers of −5 and −5.8  dBm for 1060 and 850 nm operation modes, respectively.

We present a method to solve a distance issue. In digital holography, the reconstruction distance is different from the original one because of the difference of the pixel size between an imaging device and a display device. In general, the distance is larger because the pixel size of the display is larger than that of the imaging device. This makes it hard to recognize perception of the stereoscopic effect when holographic reconstructed images are used for the stereopsis system. Typically, a numerical propagation method and a spherical phase addition are used to shorten the distance. However, each method is not shortened enough. To clear the criterion, the limitation of each method is verified. By combining two methods, the reconstruction distance is shortened from 4440 to 547 mm. In addition, it is successfully shown that the proposed combining method is useful for the stereopsis by visual perception evaluation.

An innovative single-camera two-dimensional digital image correlation (DIC) technique based on camera self-calibration is developed for use in the field where specialized fixed setups are not practical. The technique only requires attaching a planar calibration cover to the specimen surface and capturing images of the specimen from different orientations before and after deformation. A camera calibration procedure allows the camera to be freely repositioned without fixed mounts or known configurations, after which displacements are calculated with DIC. Computer simulated, random speckle images are used to test the proposed technique and good results are reported. Compared with the classical techniques which require precise fixed setups, the proposed technique is easier to use and more flexible, advancing the DIC beyond the laboratory into the real world.

Existing light field-based lighting follows the representation on plane, such as the commonly used light slab. A novel light field representation on scene surface is proposed. The illumination is captured by a panorama camera on translation stage with a nonuniform sampling and calibration strategy. Sampled light rays are reprojected on the reconstructed scene to generate the scene surface light field representations for both direct light source and indirect light. This representation is more consistent with the actual emission and reflection of light transport than the existing ones. An accurate light source estimation and a practical indirect light resampling approach are presented based on the representation. The rendering results illustrate the realistic lighting effect, especially in spatially varying illumination.

This paper presents a three-dimensional (3-D) reconstruction method of outdoor scenes from an image sequence captured by a moving handheld video camera. The proposed method works in a coarse-to-fine manner and can be divided into three steps: First, an initial 3-D shape is reconstructed according to the image correspondences obtained by optic flow tracking. Second, an initial depth map is generated according to the initial 3-D shape. Finally, a global energy function for refining the initial depth is used to acquire better results. Experimental results are demonstrated for a variety of complex scenes.

An uncooled infrared (IR) focal plane array (FPA) with 23.5 μm pixel pitch has been successfully demonstrated and has found wide commercial applications in the areas of thermography, security cameras, and other applications. One of the key issues for uncooled IRFPA technology is to shrink the pixel pitch because the size of the pixel pitch determines the overall size of the FPA, which, in turn, determines the cost of the IR camera products. This paper proposes an innovative pixel structure with a diaphragm and beams placed in different levels to realize an uncooled IRFPA with smaller pixel pitch (≦17  μm ). The upper level consists of a diaphragm with VO_x bolometer and IR absorber layers, while the lower level consists of the two beams, which are designed to be placed on the adjacent pixels. The test devices of this pixel design with 12, 15, and 17 μm pitch have been fabricated on the Si read-out integrated circuit (ROIC) of quarter video graphics array (QVGA) (320×240 ) with 23.5 μm pitch. Their performances are nearly equal to those of the IRFPA with 23.5 μm pitch. For example, a noise equivalent temperature difference of 12 μm pixel is 63.1 mK for F/1 optics with the thermal time constant of 14.5 ms. Then, the proposed structure is shown to be effective for the existing IRFPA with 23.5 μm pitch because of the improvements in IR sensitivity. Furthermore, the advanced pixel structure that has the beams composed of two levels are demonstrated to be realizable.

We present a new device, the diffractive optics calibrator, for measuring duty cycle and etching depth for computer-generated holograms (CGHs). The system scans the CGH with a collimated laser beam and collects the far-field diffraction pattern with a CCD array. The relative intensities of the various orders of diffraction are used to fit the phase shift from etching and the duty cycle of the binary pattern. The system is capable of measuring variations that cause 1-nm peak-to-valley (PV) phase errors in the wavefront created by the CGH. The measurements will be used primarily for quality control CGHs, but the data can also be used to provide a lookup table for corrections that allow calibration of the lithography errors. Such calibrations may be necessary for us to achieve our goal of measuring freeform aspheric surfaces with 1-nm RMS accuracy.

Eliminating the sign ambiguity is one of the important steps in phase extraction from a single interferogram. We propose a new method based on energy minimization to remove the sign ambiguity when retrieving a phase. Markov random field (MRF) is used to build up the pairwise relationship of a sign map. The method is thus a compromise between “global” and “local” methods. To alleviate the disturbance of noise, we employ additionally a neighborhood-direction-averaging and an adaptive filter instead of using optical flow. The gradient orientation is properly smoothed for MRF observation. Various techniques for minimizing MRF energy are compared and simulation results demonstrate the effectiveness of our method.

We have proposed a method to determine the focal length of microlens array (MLA) based on the measurement of transverse displacement of image spot in the focal plane for a change of angle of incidence of plane wavefront. An existing interferometer test setup, meant for the surface figure measurement of MLA substrate, along with a charge-coupled device (CCD) is used for this purpose. The interferometer generates as well as measures the angle of incidence of plane wavefront at the MLA, and the transverse displacement of the image spot is determined from images recorded with the CCD. We have also discussed the theory of estimation of the focal length of MLA with spherical wavefront. Error analysis is carried out for both methods and is compared. The proposed plane wavefront method is experimentally demonstrated with an off-the-shelf MLA, and the measured focal length is within 1% of catalogue value.

A stroboscopic scanning white light interferometer (SSWLI) can characterize both static features and motion in micro(nano)electromechanical system devices. SSWLI measurement results should be linked to the meter definition to be comparable and unambiguous. This traceability is achieved by careful error characterization and calibration of the interferometer. The main challenge in vertical scale calibration is to have a reference device with reproducible out-of-plane movement. A piezo-scanned flexure guided stage with capacitive sensor feedback was attached to a mirror and an Invar steel holder with a reference plane—forming a transfer standard that was calibrated by laser interferometry with 2.3 nm uncertainty. The moving mirror vertical position was then measured with the SSWLI, relative to the reference plane, between successive mirror position steppings. A light-emitting diode pulsed at 100 Hz with 0.5% duty cycle synchronized to the CCD camera and a halogen light source were used. Inside the scanned 14 μm range, the measured SSWLI scale amplification coefficient error was 0.12% with 4.5 nm repeatability of the steps. For SWLI measurements using a halogen lamp, the corresponding results were 0.05% and 6.7 nm. The presented methodology should permit accurate traceable calibration of the vertical scale of any SWLI.

This work presents the fabrication of a contiguous f/#=f/15 Fresnel microlens array (MLA) by employing a low-cost home-built maskless exposure lithographic system based on a digital light projector technology by using Texas Instruments’ digital micromirror device chip. A continuous diffractive phase relief structure was generated on a photoresist-coated silicon wafer, replicated in polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. The whole exposure time takes 10.8 min to expose a 2.4×2.4  mm MLA, with a resolution of 2.5 μm. This exposure time is relatively short, enabling high throughput or fast prototyping. Optical characterization was carried out using a He-Ne laser source (λ=633  nm ), by evaluating the maximum intensity of each spot generated at the MLA focal plane, Imax, as well as its sharpness by measuring their full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot average values were FWHM _AVG =20±8%  μm and Imax _AVG =0.71±7%  a.u. , respectively. The quality of replication was evaluated by profile characterization of the resulting mold and replica based on step height measurement along 180 μm. The maximum obtained difference was 32 nm, corresponding to 2.5% of the total mold height or λ/20 . AFM measurements were also carried out to quantify the roughness quality between mold and replica. The resulting RMS roughness was 4.73 nm (λ/130 ) and 6.66 nm (λ/95 ) for mold and replica, respectively. A comparison between theoretical and measured intensity profiles at the MLA focal plane was also carried out. A good correspondence between the results was found. Such an MLA can be applied as a Shack–Hartmann wavefront sensor in optical interconnects and to enhance the efficiency of detector arrays.

Choosing an adequate initial design for optimization plays an important role in obtaining high-quality extreme ultraviolet (EUV) lithographic objectives. A grouping design method with real ray tracing model is developed to acquire initial configurations of high numerical aperture (NA) objective for EUV lithography. In this method, the objective system is first divided into three mirror groups. The initial parameters of each mirror group are then determined by real ray calculation under design constraints. Finally, the three mirror groups are connected directly into a feasible initial system. Due to real ray calculation, the discrepancy of the ray path induced by paraxial approximation and the exhaustive search of variables is avoided in a high-NA objective design. In addition, the incidence angles on reflective mirrors can be controlled in the design of each group, which makes the initial configuration suited to further optimization and compatible multilayer design. An NA 0.33 six-mirror EUV lithographic objective is designed as an example to implement this method.

We investigate the intrachannel cross-phase modulation (IXPM)-induced phase shift in optical return-to-zero pulse propagating in a periodically dispersion-managed long-haul optical fiber transmission line. Necessary dynamical equations for various pulse parameters have been derived using variational analysis to estimate the phase shift. These equations are solved by the Runge–Kutta method. The analytical result is verified by numerical simulation based on split-step Fourier method. We therefore explore the effects of various parameters, such as transmission distance, input power, duty cycle, dispersion map strength, and residual dispersion, on phase shift for a 40  Gb/s single-channel transmission system. We also check the impact of variation of bit rate on phase shift. We find that IXPM-induced phase shift can be mitigated by proper adjustment of dispersion management and different pulse parameters like duty cycle, dispersion map strength, and peak power.

We have demonstrated the dissipative solitons generated in an ytterbium-doped fiber laser cavity using graphene oxide as the saturable absorber. The lasing light, centered at 1077.2 nm, has a 3 dB spectral bandwidth of ∼1.12  nm . Under different launched pump powers and appropriate polarization orientations, harmonic mode-locked of second- and third-order pulse trains have been achieved; the corresponding 3-dB bandwidth and pulse duration have been detected.

For an annular beam incidence, the power scintillation index in a weakly turbulent atmosphere is derived at the receiver plane, which has a Gaussian aperture. Employing this derivation, the receiver-aperture averaging factor is evaluated. Annular beams are found more advantageous than the Gaussian beams when compared on receiver-aperture averaging basis. The analyses indicate that the effect of the aperture averaging increases as the propagation length increases. Increase in the structure constant and the secondary beam source size is observed to strengthen the effect of the aperture averaging when the primary beam source size is fixed.

The operation frequency band and the output signal-to-noise ratio of the optical fiber accelerometer are decided by the natural frequency and phase sensitivity of the accelerometer, respectively. Until now, existing theoretical models have been incapable of analyzing the performance of the accelerometer coated with the rigid package. In this paper, an improved model is presented to explain the interreaction between the rigid package and the mass spring assembly inside. The natural frequency and phase sensitivity are affected by both the package mass and the damping of the surrounding medium. With the increase of the package mass, the natural frequency becomes lower and the phase sensitivity becomes higher. The damping of the surrounding medium induces the additional mass added on the package, which increases with the density of the medium. Further, the performance of the three-component vector accelerometer is analyzed by using the improved model. Experiments on the unpackaged and packaged accelerometers in different surrounding mediums indicate that our method is efficient. The improved model is also useful for the traditional piezoelectric accelerometer.

The relative phase and frequency stabilization setups for diode lasers are discussed. The construction and performance of an optical phase lock loop based on integrated phase-locked loop chips are shown along with practical tips facilitating its preparation. The interference pattern between two electronically locked lasers is shown as a proof of the system stability. The fringes contrast is a quantitative indicator of the mean-square phase error. Finally, an example of a very simple frequency offset lock realized with an all-in-one radio chip is also provided.

The work presented here describes the development and characterization of intensity fiber optic sensor integrated in a specifically designed piece of garment to measure elbow flexion. The sensing head is based on macrobending incorporated in the garment, and the increase of curvature number was studied in order to investigate which scheme provided a good result in terms of sensitivity and repeatability. Results showed the configuration that assured a higher sensitivity (0.644  dBm/deg ) and better repeatability was the one with four loops. Ultimately, this sensor can be used for rehabilitation purposes to monitor human joint angles, namely, elbow flexion on stroke survivors while performing the reach functional task, which is the most common upper-limb human gesture.

We demonstrated a photonic approach to generate a phase-continuous frequency-linear-chirped millimeter-wave (mm-wave) signal with high linearity based on continuous-wave phase modulated optical frequency comb and cascaded interleavers. Through linearly sweeping the frequency of the radio frequency (RF) driving signal, high-order frequency-linear-chirped optical comb lines are generated and then extracted by the cascaded interleavers. By beating the filtered high-order comb lines, center frequency and chirp range multiplied linear-chirp microwave signals are generated. Frequency doubled and quadrupled linear-chirp mm-wave signals of range 48.6 to 52.6 GHz and 97.2 to 105.2 GHz at chirp rates of 133.33 and 266.67  GHz/s are demonstrated with the ±1 st and ±2 nd optical comb lines, respectively, while the RF driving signal is of chirp range 24.3 to 26.3 GHz and chirp time 30 ms.

An all-fiber high modulation speed pseudorandom-coded laser based on master oscillator power amplifier configuration is proposed. We use a high modulation rate distributed feedback laser diode as the seed laser to generate the original pseudorandom pulse train. The modulation rate is 1  Gb/s, which corresponds to a minimum pulse interval of 1 ns. A 1 kHz repetition frequency of 10-order M-sequence pseudorandom pulse train is chosen to balance on-line data processing speed and laser ranging resolution. Then, the pseudorandom pulse train is amplified by two-stage amplifiers to boost the output power. All components used in the amplifiers are built in single mode (SM) fiber, so the final output laser is SM with excellent beam quality. Finally, the peak power of pseudorandom code laser is amplified to 23.6 W from 1.5 mW without wave distortion, corresponding to a gain of 42 dB. The ranging experiment of using the optical fiber delay method indoors shows the transmitter of combining modulated laser diode and multistage fiber amplifiers as a promising solution for developing laser for pseudorandom-coded laser ranging.

In the work, we have presented the technique based on the graphics processing unit accelerated finite-difference time-domain (FDTD) method for characterization of a single-mode photonic crystal fiber (PCF) with an arbitrary refractive index profile. In contrast to other numerical methods, the FDTD allows studying the mode propagation along the fiber. Particularly, we have focused attention on the method details that allowed us to reduce dramatically the computation time. It has been demonstrated that the accuracy of dispersion obtained by the FDTD method is comparable to the one provided by the finite elements method while possessing lower computation time. The method has been used to determine the fundamental mode cut-off of all-normal dispersion PCF and to find fiber losses beyond this wavelength.

We have demonstrated the possibility of quality light absorption in plasmonic nanostructured metal-semiconductor-metal (MSM) photodetectors with different groove shapes and analyzed the device performance by varying the physical parameters. The simulations revealed the quality light absorption for various nanogratings. The MSM photodetectors (MSM-PDs) utilizing nanostructure fabrication enable future high-speed devices to achieve high-responsivity bandwidth product. Finite difference time-domain method is used to evaluate the quality light absorption by plasmonics one dimensional nanostructures with the illumination of transverse magnetic light, since the surface plasmon polariton excitation is polarization sensitive. In our modeling, various nanograting profiles incorporated on the conventional MSM-PDs perform in different ways to improve the light absorption capacity in the subwavelength aperture region of the device. Therefore, the grooves’ shape and size are the effective parameters to enhance the light concentration below the diffraction limit. The simulation results demonstrated the light absorption enhancement of ∼33.6 times for newly introduced nonlinearly tapered (or trapezoidal) ellipse wall nanogratings with the aid of plasmonic nanogratings effects.

A bandpass microwave photonic filter based on an integrated optical signal processor is proposed and demonstrated by numerical simulation. The optical signal processor consisting of double-bus-coupled and series-cascaded silicon microrings (MRs) is used to produce two bandpass responses to process optical carrier signal and sideband signal separately. Because of the tunability of MRs, variable −3  dB bandwidth and tunable operating frequency are achieved. The −3  dB bandwidth and operating frequency can be tuned from 1.5 to 12 GHz and from 15 to 34 GHz, respectively. The loss impact, tuning method, and fabrication error tolerance are also discussed.

A model is proposed to realize light collimation by surface modes that propagate on a corrugated surface around the output of a photonic crystal (PhC). The dispersion relation of the surface corrugation is given for a number of surface terminations. Self-collimation effect simulation can be obtained compared to the structure without surface corrugation. Precision collimation is shown at the chosen frequency, which matches with the self-collimation frequency in the PhCs.

A wavelength selective wideband uncooled infrared (IR) sensor that detects middle-wavelength and long-wavelength IR (MWIR and LWIR) regions has been developed using a two-dimensional plasmonic absorber (2-D PLA). The 2-D PLA has a Au-based 2-D periodic dimple-array structure, where photons can be manipulated using a spoof surface plasmon. Numerical investigations demonstrate that the absorption wavelength can be designed according to the surface period of dimples over a wide wavelength range (MWIR and LWIR regions). A microelectromechanical system-based uncooled IR sensor with a 2-D PLA was fabricated using complementary metal oxide semiconductor and micromachining techniques. Measurement of the spectral responsivity shows that the selective enhancement of responsivity is achieved over both MWIR and LWIR regions, where the wavelength of the responsivity peak coincides with the dimple period of the 2-D PLA. The results provide direct evidence that a wideband wavelength selective IR sensor can be realized simply by design of the 2-D PLA surface structure without the need for vertical control in terms of gap or thickness. A pixel array where each pixel has a different detection wavelength could be developed for multicolor IR imaging.