This PDF file contains the front matter associated with SPIE Proceedings Volume 9288, including the Title Page, Copyright information, Table of Contents, Authors, Introduction, and Conference Committee listing.

Thermal lensing in diode pumped solid state lasers can seriously affect laser performance and cause beam distortions resulting in degradation of beam quality. Estimating thermal lens is important in designing stable laser cavities with minimum laser mode size fluctuations and high output power. The common techniques used to estimate the thermal lens under lasing condition deploy a probe beam or a wave front sensor. Both these techniques need precise alignment and the laser beam quality factor has to be measured separately for thermal lens calculations. It is well-known that beam quality varies considerably at different pump intensities. We demonstrate a simple technique based on ABCD law for Gaussian beams that is capable of estimating the thermal lens accurately by taking into account the fluctuation of beam quality factor at various pump intensities. The technique is experimentally tested using a diode-pumped Yb:KYW laser at different pump intensities.

Vanadium pentoxide V₂O₅ thin films were grown on glass substrates by the LAMBD deposition system with different laser energies. The structure, composition and optical properties of the films have been investigated with atomic force microscopy, x-ray photoemission spectroscopy, ellipsometry and the transmittance analysis. Upon the increase of laser energy, the results showed that the changes in the optical constants are consistent with the thickness changes of the film. The refractive index increases and the absorption coefficient increases when the laser energy increases. The AFM analysis showed a change of the roughness and structure of the deposited films at different laser energies. The prepared films deposited by LAMBD showed interesting properties with correct V₂O₅ phase without need of annealing after deposition.

An analytical cross-phase modulation (XPM) model is developed for coherent fiber-optic transmission systems. The XPM fields are calculated using a first-order perturbation theory. Statistical analysis is then applied to calculate the XPM variance. The analytical XPM model is applicable to dispersion-managed fiber-optic systems with arbitrary pulse shapes. For non-Gaussian pulses, a summation of time-shifted Gaussian pulses is used to fit the target pulse shape, which makes it possible to analytically derive the XPM variance. The analytical XPM model is validated by extensive numerical simulations.

Nonlinear Schrödinger equation (NLSE) is solved using different split-step Fourier methods (SSFM). The uniform step size distribution is traditionally utilized and the efficiency of the scheme can be improved by using the adaptive step sizes. One scheme of using the adaptive step size is the local error method, which updates the step size based on the local error of the current step. In this paper, a novel scheme which combines the minimum area mismatch (MAM) and the local error method is proposed. The MAM method can be used to find the optimal step size distribution based on minimizing the area mismatch between the ideal effective nonlinear coefficient curve and its stepwise approximation. The local error is a criterion to choose the total number of steps per span. The simulation results show that the proposed scheme outperforms the schemes using uniform step size and adaptive step size.

In this paper, we experimentally study DC-PM-BPSK, PM-QPSK, and PM-16QAM at 35 Gbaud for undersea transmission in a WDM environment with frequency spacing ranging from 50 GHz (DWDM) to 33 GHz (Super-Nyquist). The experimental study focuses on noise, linear cross-talk, and nonlinear tolerance in two undersea applications: (1) Legacy dispersion-managed submarine cables up to 5,000 km in length and (2) New uncompensated submarine cables up to 12,500 km in length. We experimentally demonstrate that a reduction in frequency spacing below the symbol rate can be achieved, and quantify the performance penalties. We also show a comparison of performance and reach between legacy dispersion-managed applications, and new uncompensated applications, as the frequency spacing is reduced below the symbol rate. It is shown that the constellation and line system dispersion map have a significant impact on the tolerance to linear and nonlinear interference generated by narrow frequency spacing.

We numerically investigate and compare the performance of modulation format independent carrier phase esti- mation (CPE) (or universal CPE (U-CPE)) and decision directed CPE (DD-CPE) along with digital backward propagation (DBP) to compensate fiber non-linearity, for polarization multiplexed (PM) 4 and 16-ary quadrature amplitude modulation (QAM) coherent systems. We analyze the impact of each of the CPE methods in reducing the complexity of DBP, in terms of required DBP steps, as well as the influence of the laser line width effects on their performance. By optimizing the step size, the U-CPE method, in spite of its low complexity, exhibits a similar performance as the DD-CPE method in non-linearity mitigation. However, at high signal launch powers, and in the presence of laser phase noise, the performance of DD-CPE method is significantly impaired owing to increased erroneous pre-decisions, whereas, the U-CPE method is still capable of mitigating both non-linearity and phase noise, equivalently good as the ideal DD-CPE case. Moreover, also without DBP for non-linear compensation, U-CPE method outperforms the DD-CPE method allowing high signal launch powers and with greater tolerance towards phase noise.

Optical fiber is considered the most competitive wired transmission support thanks to its low attenuation, wide optical bandwidth, long reach, and low cost. However, optics do not yet perform higher functionalities such as switching. In fact, all-optical switches face a contention issue, due to the lack of practical optical buffers. Thus, the switching function is still performed electronically, which requires energetically costly optical-to-electronic conversions. The energy consumption is a critical issue within the growing data traffic. Thus, a proposition of hybrid switch architecture supplementing optical switch with an electronic buffer. In this paper, we propose to investigate the performance of hybrid switch that supports different priority classes where the priority is defined in terms of Packet Loss Ratio (PLR). We show that the hybrid switch is a good trade off since it allows significant performance improvements towards a buffer-less all optical switch in terms of PLR and sustainable load, for relatively few electronic ports of the buffer, which would reduce energy consumption compared to an electronic switch.

The fiber withdrawal of Group 4 (mated-thermal cycle) was observed up to 100 nm as in previous work¹. We predict that this withdrawal is mainly caused by the impact of hot temperature (at 75ºC) based on GR-326² thermal cycle test profile repeated 21 cycles over 7 days; and thus, it was studies here for the purpose of reducing test time. All connectors were separated into four groups: 1) unmated-stored at room temperature, 2) mated-stored at room temperature, 3) unmated-stored at hot temperature, and 4) mated-stored at hot temperature. The hot temperature test was performed on Groups 3 and 4 for 1 hour, while Groups 1 and 2 was left at room temperature. The sample size of each group is 28 LC/UPC connectors. Radius of curvature, fiber height and apex offset were measured before and after that 1 hour. The fiber withdrawal up to 100 nm is found in Group 4 (mated-hot temperature), but no changes are observed in Groups 1-3. These results confirm the impact of hot temperature on fiber height, same as the thermal cycle test in previous work¹. Afterward, Group 1-4 were unmated at room temperature for 1 day, 1 week, and 1 month. No significant change in fiber height is found. On the contrary, when Group 1-4 were re-tested as being mated at hot temperature for 1 hour, the fiber withdrawal up to 100 nm is now found in Group 1-3. However, the additional withdrawal up to 50 nm is still observed in Group 4.

We present a novel LMS equalizer (FDE) for compensating polarization-mode dispersion (PMD) in polarization-multiplexed coherent fiber-optic systems based on the least mean squares (LMS) method with unstructured channel estimation (USE). It is a low-complexity algorithm compared to the traditional time-domain decision-directed LMS (DD-LMS) algorithm. Also, it converges faster and shows better bit error rate (BER) performance as compared to the frequency-domain block training-directed LMS (BTD-LMS) method.

In this paper, we propose to demonstrate a long haul and high speed network based on a 2 band Orthogonal Frequency Division Multiplexing (OFDM) signal and a Carrier Suppression (CS) Non Return to Zero (NRZ) Differential QPSK non-coherent modulation format. We considered 112 Gbit/s per channel bit rate and multiplexed 32 channels following the 100 GHz WDM ITU grid. We demonstrate a transmission over more than 3000 km with a BER bellow 10^-3.

Investigation of optical back propagation performances under some practical impairments such as non-ideal optical phase conjugation and non-ideal amplifier noise is presented. The results can also be used to determine the optimum operating system parameters under non-ideal conditions.

The response of metal clad nano-lasers to direct current modulation has been analysed in both the small signal and large signal regimes. Calculations have been performed using rate equations which include the Purcell cavity-enhanced spontaneous emission factor, F, and the spontaneous emission coupling factor β. Calculations of both the small signal and large signal direct modulation response of nano-lasers indicate opportunities to achieve modulation bandwidth up to 60 GHz with peak responses at resonant frequencies of order 40 GHz and 30 GHz respectively.

Ga(As)Sb quantum dots (QDs) are grown on GaAs substrate in the Stranski-Krastanov mode. The molecular beam epitaxial (MBE) growth is monitored by reflectance anisotropy spectroscopy (RAS). For certain photon energies of the light used for RAS, the RAS signal values for GaAs layers, GaSb layers, and Ga(As)Sb QD surface morphologies can clearly be distinguished. The finding verifies that RAS is a valuable tool to identify growth of these QDs.

Optical waveguides have been a subject of an intensive theoretical research, resulting in applications in several fields, and stimulated research in integrated optics. Homogeneous dielectric waveguides and their properties are covered in detail in many articles and textbooks. However, in waveguides loaded with arbitrary inhomogeneous dielectrics, analytical solutions are possible only for a limited number of permittivity profiles in simple geometries. The analysis of longitudinally inhomogeneous waveguides has been already proposed, but the main drawback of this approach is that it requires cumbersome and time-consuming integration. We therefore suggest to take this a step further by applying our new original analytical approach that does not require integration. The aim of this work is to establish a different method that is generally applicable to any vectorial time-dependent, anisotropic, non-linear, inhomogeneous, dissipative and dispersive media to analyze the field distribution of inhomogeneous 1-D and 2-D waveguides with symmetric and asymmetric permittivity profiles. Our initial consideration of slab problems with arbitrary profiles by means of analytical method shows a great deal of potential for use in applications in fields such as physics, and engineering.

The edge-emitting distributed Bragg reflector (DBR) laser with a metal nano-strip grating is proposed. It achieves a high reflectivity with a much shorter grating length of 200μm due to the high refractive index contrast of the metal and the semiconductor. Moreover, the modal coupling (κL) of the grating can be tuned in a wide range by simply changing the design parameters of the metal nano-structure. In this work, the metal grating is investigated by the coupled-wave theory (CWT) and the complex mode matching method (CMMM). Results from these two methods are compared and the effects of changing the grating parameters, such as the spacing of the grating and the core region, the thickness of nano-strips and the duty cycle, are discussed regarding the peak reflectivity and the full-width half-maximum (FWHM) of the reflection spectrum. Further simulation of the laser output with the multi-mode rate equation model demonstrates the single-mode operation for a broad range of the metal grating’s design parameters, thus the design freedom is provided. For various applications of the DBR laser, the requirements such as a shorter cavity length, a lower threshold current, or a very high SMSR can be satisfied by properly setting the design parameters.

The high-cost of fabrication of nanohole arrays for extraordinary optical transmission, surface-plasmon-resonance-based sensors, inhibits their widespread commercial adoption. Production typically involves the application of small-area patterning techniques, such as focused-ion-beam milling, and electron-beam lithography onto high-cost gold-coated substrates. Moving to lower-cost manufacturing is a critical step for applications such as the detection of environmental oil-leaks, or water quality assurance. In these applications, the sensitivity requirements are relatively low, and a bio-compatible inert surface, such as gold, is unnecessary. We report on the optical response of aluminum-coated nano-bucket arrays fabricated on flexible polyethylene terephthalate substrates. The arrays are fabricated using an economical roll-to-roll UV-casting process from large sheets of nickel templates generated from master quartz stamps. The nano-featured surface is subsequently coated with 50 nm of thermally-evaporated aluminum. The roll-to-roll production process has a 97% yield over a 600 m roll producing nano-buckets with 240 nm diameters, 300 nm deep, with a 70° taper. When exposed to a series of refractive index standards (glucose solutions), changes in the locations of the resonance transmission peaks result in optical sensitivities as high as 390 ± 20 nm/RIU. The peak transmission is approximately 5% of illumination, well within the sensitivity requirements of most common low-cost detectors.

This paper investigates the use of fiber Bragg grating (FBG) accelerometers for wide band vibration monitoring in a wound rotor induction generator. The sensor performance is assessed in a series of experiments on a laboratory test rig comprising a 30kW induction machine operating under steady state and variable speed regimes. Vibration measurements are investigated in the frequency domain for generator fault specific electromagnetically induced vibration components. The fiber optic sensor effectiveness in detection of wide band spectral effects (<1kHz) in the vibration signal is compared with that of a commercial piezoelectric based solution. The potential and limitations of the prototype wide band FBG accelerometer are evaluated for use in vibration monitoring applications.

We have studied thin films of Ge₂₅As₃₀S₄₅ glass evaporated by electron-beam technique. We have analyzed the transmission spectra of thin films of the same nominal composition, obtained under identical conditions, but with four different thicknesses varying from 1 to 7 micrometers. All fabricated films were annealed for 1h at 300^oC (below the glass transition temperature of this glass). As a result, we observed a thickness dependent blue-shift of about 100 nm of their transmission edge. We have calculated the optical band gap of those annealed thin films and we have observed that the slope of absorption edge becomes less abrupt and the band gap decreases when their thickness increases. Furthermore, this band gap decrease is accompanied with a broadening of the tails and localized states, which indicates an increase of the degree of disorder in the vitreous network. This could be explained by the higher density of defects and dangling bonds in the thinner films since the amount of deposited material is smaller. This implies therefore an increase of both the degree of disorder and the concentration of defects, and consequently the decrease of the optical gap.

We describe the photo induced formation of gradient index (GRIN) lenses in thin films of chalcogenide glass (ChG) of Ge₂₅As₃₀S₄₅ composition. We examine the changes of thickness of these samples by DekTak profilometry, as well as the optical performance and wave front distortions of the obtained lenses by using a Shack Hartmann sensor. The GRIN formation is related to the photo induced shift of the band gap towards shorter wavelengths (so-called photo-bleaching effect). The corresponding photo-induced birefringence of this material is in the origin of anisotropic GRIN lenses formed [1].

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

We report the analyses of the photo induced anisotropy generated by a mesogenic azobenzene dye complex that is doped in isotropic and anisotropic matrices. By using time resolved polarized spectroscopy and photo induced dichroism studies, we show that this specific dye composition undergoes photo isomerization process, but has very limited angular mobility in all tested matrices.

Nonlinear photonic chips have succeeded in generating and processing signals all-optically with performance far superior to that possible electronically - particularly with respect to speed. Although silicon-on-insulator has been the leading platform for nonlinear optics, its high two-photon absorption at telecommunications wavelengths poses a fundamental limitation. This paper reviews some of the recent achievements in CMOS-compatible platforms for nonlinear optics, focusing on amorphous silicon and Hydex glass, highlighting their potential future impact as well as the challenges to achieving practical solutions for many key applications. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement.

The thorough characterization of skin samples is a critical step in investigating dermatological diseases. The combination of depth-sensitive anatomical imaging with molecular imaging has the potential to provide vast information about the skin. In this proof-of-concept work we present high-resolution mosaic images of skin biopsies using Optical Coherence Tomography (OCT) manually co-registered with standard microscopy, bi-dimensional Raman spectral mapping and fluorescence imaging. A human breast skin sample, embedded in paraffin, was imaged with a swept-source OCT system at 1310 nm. Individual OCT volumes were acquired in fully automated fashion in order to obtain a large field-of-view at high resolution (~10μm). Based on anatomical features, the other three modalities were manually co-registered to the projected OCT volume, using an affine transformation. A drawback is the manual co-registration, which may limit the utility of this method. However, the results indicate that multiple imaging modalities provide complementary information about the sample. This pilot study suggests that multi-modal microscopy may be a valuable tool in the characterization of skin biopsies.

Periventricular leukomalacia (PVL) is a condition that may cause significant neurodevelopmental handicap in premature newborns. It is characterized by white matter injury, associated with inflammation. This work aimed to assess the impact of inflammation on cerebral oxygen saturation (sO₂) using depth-sensitive photoacoustic tomography (PAT). The aspects of PVL were reproduced in a rodent model by injection of lipopolysaccharide (LPS) into the corpus callosum. The results of this exploratory work reveal lower sO₂ values in LPS group, as compared to sham controls; showing decreased values in the corpus callosum and in the left cortex, ipsilateral to the injection site. Interhemispherical connectivity was not affected by LPS injection, as shown by functional connectivity analysis. This study supports the use of PAT as a non-invasive tool to assess oxygenation values in vivo in the newborn brain.

Multi-modal imaging combining fluorescent molecular tomography (FMT) with MRI could provide information in these two modalities as well as optimize the recovery of functional information with MR-guidance. Here, we present a MRI-guided FMT system. An optical probe was designed consisting of a fiber plate on the top and bottom sides of the animal bed, respectively. In experiment, animal was installed between the two plates. Mounting fibers on each plate, transmission measuring could be conducted from both sides of the animal. Moreover, an accurate fluorescence reconstruction was achieved with MRI-derived anatomical guidance. The sensitivity of the FMT system was evaluated with a phantom showing that with long fibers, it was sufficient to detect 10nM Cy5.5 solution with ~28.5 dB in the phantom. The system was eventually used to image MMP activity involved in atherosclerosis with two ATX mice and two control mice. The reconstruction results were in agreement with ex vivo measurement.

Measuring heart rate traditionally requires special equipment and physical contact with the subject. Reliable non-contact and low-cost measurements are highly desirable for convenient and comfortable physiological self-assessment. Previous work has shown that consumer-grade cameras can provide useful signals for remote heart rate measurements. In this paper a simple and robust method of measuring the heart rate using low-cost webcam is proposed. Blood volume pulse is extracted by proper Region of Interest (ROI) and color channel selection from image sequences of human faces without complex computation. Heart rate is subsequently quantified by spectrum analysis. The method is successfully applied under natural lighting conditions. Results of experiments show that it takes less time, is much simpler, and has similar accuracy to the previously published and widely used method of Independent Component Analysis (ICA). Benefitting from non-contact, convenience, and low-costs, it provides great promise for popularization of home healthcare and can further be applied to biomedical research.

Fiber Bragg grating sensors have been developed beyond a laboratory curiosity to become a mainstream sensing technology because of their small size, passive nature, immunity to electromagnetic interference, and capability to simultaneously measure multiple physical parameters such as temperature, strain and pressure. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This presentation will give a review of some of the more recent developments of femtosecond laser induced fiber Bragg gratings.

Large-area silicon-on-insulator (SOI) ring resonators, to be used as optical gyroscopes, have been designed and fabricated using an e-beam process. To characterize the devices, an automated turntable stage with an embedded high resolution gyroscope has been built. Its large payload capacity allows for safe rotation of a temperature-controlled opto-mechanical setup. A field programmable gate array interface has been implemented for mechanical actuation and signal acquisition. Various rotation schemes have been implemented to characterize the apparatus and devices. The turntable exhibits a bandwidth of 0.54 Hz, and minimum and maximum repeatable angular rates of 27 and 74.3 degrees per second (dps), with a maximum associated angular rate noise level of 2 dps.

Although recently Minimal Invasive Robotic Surgery (MIRS) has been more addressed because of its wide range of benefits, however there are still some limitations in this regard. In order to address the shortcomings of MIRS systems, various types of tactile sensors with different sensing principles have been presented in the last few years. In the present paper a MEMS-based optical sensor, which has been recently proposed by researchers, is investigated using numerical simulation. By this type of sensors real time quantification of both dynamic and statics contact forces between the tissue and surgical instrument would be possible. The presented sensor has one moving part and works based on the intensity modulation principle of optical fibers. It is electrically-passive, MRI-compatible and it is possible to be fabricated using available standard micro fabrication techniques. The behavior of the sensor has been simulated using COMSOL MULTIPHYSICS 3.5 software. Stress analysis is conducted on the sensor to assess the deflection of the moving part of the sensor due to applied force. The optical simulation is then conducted to estimate the power loss due to the moving part deflection. Using FEM modeling, the relation between force and deflection is derived which is necessary for the calibration of the sensor.

The suitability and use of long-range surface plasmon-polaritons for leukemic biomarker detection is discussed. A novel optical biosensor comprised of gold straight waveguides embedded in CYTOP with an etched microfluidic channel was tested for detecting leukemia in patient serum. Gold surface functionalization involved the interaction of protein G (PG) with antibodies by first adsorbing PG on bare gold and then antibodies (Immunoglobulin G, IgG). Differentiation between healthy and leukemia patients was based on the difference in ratios of Ig kappa (Igκ) and Ig lambda (Igλ) light chains in both serums. The ratio for a normal patient is ~1.4 - 2, whereas for a leukemia patient this ratio is altered. As a receptor (primary antibodies), goat anti-human anti-IgGκ and anti-IgGλ were used to functionalize the surface. Diluted normal and leukemia patient serums were tested over the aforementioned surfaces. The ratios of mass surface densities of IgGκ:IgGλ for normal serum (NS) and patient serum (PS) were found to be 1.55 and 1.92 respectively.

The perception of blur in humans is intrinsic to our visual system, and dioptric power can improve clarity in many cases. This was evaluated experimentally to establish the best correction with dioptric power shifts. We used Near Infrared Spectroscopy (NIRS) to measure Oxy-, Deoxy- and Total-hemoglobin concentration changes in the brain while viewing images and reading a Snellen chart. Participants were tested with their usual correction (no diopter power shift (0 D)), with a 0.25 diopter power shift (0.25 D), and with a 0.5 diopter power shift (0.5 D). The concept of Approximate Entropy (AE) was applied to quantify the regularity of these hemoglobin time series of finite length. AE computations are based on the likelihood that similar templates in a time series remain similar on the next incremental comparison, so that time series with large AE have high irregular fluctuation. We found that the dioptric power shift eliciting the highest AE indicates the clearest visual condition for subjects. This technique may impact the current way in which ophthalmic lenses are prescribed.

Optical microspheres can support whispering gallery modes whose resonance wavelengths are sensitive to the external medium. By coating the microsphere with a fluorescent quantum dot (QD) layer, the structure can perform as a fluorescence sensor for local refractometric changes. In these proceedings, we focus on the methods for fabricating and measuring a QD-coated silica microsphere. By constructing a system that uses a square capillary into which a single microsphere is inserted, a simple refractometric sensor can be demonstrated. The WGM resonance shifts were measured in sensorgram format as small amounts of solvent were pumped into the capillary. This method enables the sphere to act as a single passive microfluidic sensor for refractive index changes in the analyte. We finally discuss the main experimental problems that currently plague the application of these QD-coated fluorescent structures for sensing applications.

Metallic nanostructures possess many advantages for utilization in various applications including sensing applications. However, achieving an easy to fabricate platform with high sensitivity performance is considered the main challenge in designing such nanostructures. Two factors should be considered when designing a wavelength based nanostructured sensor; the field distribution around the nanostructures, and the full width at half maximum (FWHM) of the sensor spectral response. In this paper, we study suspended nanodisc structures as a candidate for enhancing the electric field distribution in-plane and out of plane axes of the nanodiscs, and hence enhancing the probe depth of the nanosensor. Another advantage of the suspended nanodisc structure is that it offers a 100% surface coverage. The Finite Difference Time Domain (FDTD) method is used for the study of optical properties of the structure. The resonance location depends on the dimensions of the nanodiscs as well as the polymer base. Higher order modes can also be supported by nanodiscs with larger dimensions. The local electric field is enhanced as it is distributed in both perpendicular and horizontal planes with respect to the plane of gold nanodiscs without altering the FWHM relative to the regular nanodisc structure. This is considered as an advantage in sensing applications. Another advantage of this structure is that it can be readily fabricated by nanoimprint lithography and gold deposition.

This work presents optimization analysis of the sensitivity to variations of the external refractive index (RI) of long-period fiber grating (LPFG) coated with a nano-overlay of diamond-like carbon (DLC) material. Through numerical simulations, we have shown that both the dual-resonance and mode transition phenomena can be simultaneously exploited to substantially increase the sensitivity to variations of the external RI. The tuning of the DLC layer thickness to displace the dual-resonance band into a more suitable region of the spectrum is also reported. To perform this analysis, we implemented a novel pseudo-heuristic simulation model based on a 4-layer step-index fiber layer model and coupled mode theory. The dispersion dependence on the DLC overlay thickness was modeled from experimental data. LPFG parameters were fitted to an experimental transmission spectrum. The simulation model and the obtain results provides guidance for the fabrication of the device.

An analytic model of the scattering response of a highly Yb³⁺/Er³⁺-codoped phosphate glass microring resonator matrix is considered to obtain the transfer functions of an M x N cross-grid microring resonator structure. Then a detailed model is used to calculate the pump and signal propagation, including a microscopic statistical formalism to describe the high-concentration induced energy-transfer mechanisms and passive and active features are combined to realistically simulate the performance as a wavelength-selective amplifier or laser. This analysis allows the optimization of these structures for telecom or sensing applications.

Vernier racetrack resonators offer advantages over single racetrack resonators such as extending the free spectral range (FSR).^1-3 Here, we have presented a theoretical sensitivity analysis on quadruple Vernier racetrack resonators based on varying, one at a time, various fabrication dependent parameters. These parameters include the waveguide widths, heights, and propagation losses. We have shown that it should be possible to design a device that meets typical commercial specifications while being tolerant to changes in these parameters.

Radiation coupling plays a key role in the bending waveguide structure with very small bending radius. Insights of radiation coupling and energy transfer by way of high order bending modes have been discussed. Modes in bending waveguide structures with small bending radii are investigated.

Spoof plasmons are bound electromagnetic waves (EM) at frequencies outside the plasmonic range mimicking (“spoofing”) surface plasmons (SPs), which propagate on periodically corrugated metal surfaces. In recent years, electromagnetic waves propagating at an interface between a metal and dielectric have been of significant interest. Although most plasmonic research so far has focused on the near-infrared and optical ranges of the electromagnetic spectrum (where noble metals support highly confined surface waves), there exists an increasing interest in transferring SPs-based photonics to lower frequencies. However, in these spectral ranges, noble metals behave like perfect electric conductors, whose surface charges are able to screen any external EM excitation with extreme efficiency, preventing the formation of a tightly bound SP. It has been shown that the binding of EM fields to a metal surface can be increased by its corrugation. A surface of a metal perforated with a one-dimensional periodic array of rectangular grooves has already been considered. The question that remains open is the calculation of the effective permittivities for arbitrary grooves. The number of works describing the calculation of the effective dielectric constants for the grooved surfaces is limited. Here we have obtained an analytical dispersion relation of spoof plasmons on an arbitrary perforated surface of a real metal. We have derived analytical expressions for calculation of the permittivities of arbitrary grooves. Based on those results we have determined the minimum spot size for a triangular groove structure.

We propose and study a box-shaped waveguide based on Si3N4 which confines the light in a sub-wavelength region. The mode characteristics of the proposed structure have been investigated thoroughly.

Passive optical network (PON) is considered as the most appealing access network architecture in terms of cost-effectiveness, bandwidth management flexibility, scalability and durability. And to further reduce the cost per subscriber, a Fabry-Perot (FP) laser diode is preferred as the transmitter at the optical network units (ONUs) because of its lower cost compared to distributed feedback (DFB) laser diode. However, the mode partition noise (MPN) associated with the multi-longitudinal-mode FP laser diode becomes the limiting factor in the network. This paper studies the MPN characteristics of the FP laser diode using the time-domain simulation of noise-driven multi-mode laser rate equation. The probability density functions are calculated for each longitudinal mode. The paper focuses on the investigation of the k-factor, which is a simple yet important measure of the noise power, but is usually taken as a fitted or assumed value in the penalty calculations. In this paper, the sources of the k-factor are studied with simulation, including the intrinsic source of the laser Langevin noise, and the extrinsic source of the bit pattern. The photon waveforms are shown under four simulation conditions for regular or random bit pattern, and with or without Langevin noise. The k-factors contributed by those sources are studied with a variety of bias current and modulation current. Simulation results are illustrated in figures, and show that the contribution of Langevin noise to the k-factor is larger than that of the random bit pattern, and is more dominant at lower bias current or higher modulation current.

We report recent progress made in our laboratory on travelling wave Mach-Zehnder Interferometer based Silicon Photonics modulators with segmented transmission lines, as well as on resonant ring modulators and add-drop multiplexers with peaking enhanced bandwidth extended beyond the photon lifetime limit. In our segmented transmission lines, microstructuring of the electrodes results in radio-frequency modes significantly deviating from the transverse electromagnetic (TEM) condition and allows for additional design freedom to jointly achieve phase matching, impedance matching and minimizing resistive losses. This technique was found to be particularly useful to achieve the aforementioned objectives in simple back-end processes with one or two metallization layers. Peaking results from intrinsic time dynamics in ring resonator based modulators and add-drop multiplexers and allows extending the bandwidth of the devices beyond the limit predicted from the photon lifetime. Simple closed form expressions allow incorporating peaking into system level modeling.

We developed a highly parallel simulator of Optical Coherence Tomography (OCT) of objects with arbitrary spatial distributions. This Monte Carlo method based simulator models the object as a tetrahedron-based mesh, and implements an advanced importance sampling scheme. This new method makes OCT simulations more practical, since the corresponding serial Central Processing Unit (CPU) based implementation requires approximately 360 hours to simulate OCT imaging of a single B-scan. We implemented this new simulator on Graphics Processing Units (GPUs) using the Compute Unified Device Architecture (CUDA) platform and programming model by NVIDIA. We demonstrated that our new simulator requires one order of magnitude less time, compared to its serial implementation, to simulate the same OCT images. Our new parallel OCT simulator could be an important and practical tool to study different OCT phenomena and to design novel OCT systems with superior imaging performance.

Metallic nanostructures can be designed to operate effectively as a coupling structure for incident beams to surface plasmon polaritons (SPPs). On a semiconductor, metal nanostructures can act simultaneously as a device electrode while ensuring strong optical field overlap with the active region. Additionally, SPP fields can be confined to sub-wavelength dimensions and significantly enhanced relative to the exciting field. These features are very attractive for nano-scale optoelectronic devices such as photodetectors as the excitation of SPPs alters conventional trade-offs between responsivity and speed respectively. This is due to the facts that sub-wavelength confinement enables the active region to be shrunk to nano-scale dimensions yet good optoelectronic performance can be maintained due to the SPP field enhancement. In this paper we discuss recent progress on surface plasmon enhanced photodetectors.

The effect of the substrate to the absorption spectra of silver nanoparticles of sphere-like shapes is investigated. Silver nanoparticles of broken spherical symmetry are placed on substrates of different dielectric functions at various contact angles (α). The absorption efficiency of the supported nanoparticles is calculated by using the Discrete Dipole Approximation (DDA) method. Increasing the value of α and, hence the contact area of the supported nanoparticles, results in an inhomogeneous distribution of the polarization charges over the nanoparticle-substrate system. This leads to the excitation of plasmonic bands of different characters (dipolar and quadrupole modes). The admixture of both dipolar and quadrupole modes is found to be more pronounced when a nanoparticle with highest contact area (α = 90o, hemispherical shape) is considered. The band position of the Longitudinal Mode (LM) is red-shifted with α, while the resonance wavelength of the Transverse Mode (TM) is blue-shifted.