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The use of femtosecond laser pulses to impulsively excite thermal and mechanical transients in matter has led, in the last years, to the development of picosecond acoustics. Recently, the pump-probe approach has been applied to nano-engineered materials to optically generate and detect acoustic waves in the gigahertz-terahertz frequency range. In this paper, we review the latest advances on ultrafast generation and detection of thermal gradients and pseudo-surface acoustic waves in 2-D lattices of metallic nanostructures. Comparing the experimental findings to the numeric analysis of the full thermomechanical problem, these materials emerge as model systems to investigate both the mechanical and thermal energy transfer at the nanoscale. The sensitivity of the technique to the nanostructure mass and shape variations, coupled with the phononic crystal properties of the lattices, opens the way to a variety of applications ranging from hypersonic waveguiding to mass sensors with femtosecond time resolution.

The conventional double-modulated terahertz differential time-domain spectroscopy (double-modulated THz-DTDS) of liquids requires linear dithering of the sample to rapidly vary the sample thickness in order to produce the required sample and reference signals. Linear dithering, however, imposes a fundamental limitation as it introduces mechanical noise into the system, thereby contributing to measurement uncertainty. In this paper, we address this limitation for the terahertz spectroscopy of liquids by using a fixed dual-thickness sample mounted on a spinning wheel. The concept of spinning the sample allows rapid switching between two fixed sample thicknesses in order to produce sample and reference signals without the introduction of added mechanical noise. We validate this new technique by measuring the dielectric properties of a number of liquids and confirm the results against the Debye relaxation model.

The phenomenon of fast-light pulse propagation has seen renewed interest in recent years, but its relationship to the speed of information transfer is still being debated. In this paper, we define the speed of information transfer as the propagation speed of a point of constant signal-to-noise ratio (SNR) on the leading edge of a signal pulse. We use standard telecommunication analysis to include the effects of noise so that the bit-error rate (BER) can be calculated as a function of a variable decision time. We introduce the concept of a time-dependent Q-factor so that pulse arrival times can be compared at equivalent BERs. We show that when receiver noise is included in a gain-assisted fast-light system, the measured speed of information transfer can exceed the speed of light for an equivalent pulse travelling through a vacuum.

In this paper, a bismuth-based erbium-doped fiber amplifier (Bi-EDFA) that operates in both the C- and L-band wavelength regions is demonstrated. The system employs two pieces of bismuth-based erbium-doped fiber (Bi-EDF) as the gain medium with a midway broadband fiber Bragg grating (FBG). The FBG functions to prevent the gain saturation at the C-band region, flatten the overall gain spectrum, and reduce the noise figure, particularly for the C-band. At an input signal power of $-$30 dBm and a pump power of 150 mW for both pumps, a flat gain of around 29 dB is obtained with a gain variation of $\pm$3.5 dB within the wavelength region from 1525 to 1615 nm using a backward-pumping scheme. At an input power of 0 dBm, the gain varies from 10 to 13 dB within the wavelength range from 1530 to 1620 nm, while the corresponding noise figure varies from 9.5 to 14 dB over this wavelength range.

The transmission performance of a free-space optical (FSO) link could be severely degraded due to atmospheric turbulence, which causes the temporal and spatial fluctuation of light intensity. Both the space diversity reception technique (SDRT) and advanced modulation formats can successfully mitigate the transmission impairments of the atmospheric turbulence. The purpose of this paper is to study and compare the bit-error-rate (BER) performance of several widely used modulation formats under different atmospheric turbulence scenarios with and without SDRT. The modulation formats studied in this paper include on–off keying (OOK), differential phase-shift keying (DPSK), and differential quadrature phase-shift keying (DQPSK). We derive a series-form formula for evaluating the BER performance of the DPSK format in the Gamma–Gamma distributed channel with SDRT. We use both theoretical analysis and simulation to examine the BER performance of OOK, DPSK, and DQPSK formats with and without SDRT. It is found that, in the strongly turbulent scenario, the OOK and DPSK formats can have as large as 19.5 and 20.3 dB of SDRT gains at the BER of $10^{-3}$, respectively. Using SDRT, the modulation gains of the DPSK format over the OOK format are 3.2 dB in the strongly turbulent scenario and 4.5 dB in the weakly turbulent scenario, respectively. In addition, in the moderately and strongly turbulent scenarios, it is found that the DPSK and DQPSK formats have almost the same BER performance under the same symbol rate.

In this paper, we have investigated the enhancement of the plasmonic light beaming efficiency by near-field resonance in different subwavelength metallic slit-groove beaming structures. We show that by selecting the suitable film thickness and separation distance of beaming gratings, the intensity of the near field can be greatly enhanced by resonance, which leads to the increase of the beaming efficiency in the far field. Moreover, we obtain a nanocavity above the nanoslit by integrating a metal nanostrip with a conventional beaming structure. The resonance of this nanocavity can further enhance the near-field intensity and improve the beaming efficiency.

Photoacoustic tomography (PAT) is a fast-developing biomedical imaging technology suitable for in vivo imaging. PAT in spherical or circular geometry gives good image resolution yet is slow or expensive in signal acquisition and image formation. Reducing the number of detection angles can ameliorate such issues, usually at the expense of image quality. This paper introduces a deconvolution-based algorithm that models the imaging process as a linear and shift-invariant system. As demonstrated by the in vivo experiment, this algorithm not only runs much faster than the back-projection algorithm but also shows stronger robustness in that it provides better image quality when detection angles are sparse. Therefore, this algorithm promises to enable real-time PAT in circular geometry.

In this paper, two different paradigms to realize a scalable all-optical packet switch with label swapping will be reviewed. The two paradigms are based on wavelength routing switch and space routing switch. All the functions required for switching the packets, namely, the label processor, the label rewriter, and the optical switch, are based on all-optical signal processing with no electronic control. This allows for very fast processing time and potential photonic integration of the systems. We report, for both techniques, experimental results showing the routing operation of the 160-Gb/s packets and beyond. We will discuss and compare both techniques in terms of devices and bit-rate scalability, power consumption, power penalty performance, and cascadability as key parameters for the realization of an all-optical packet switch.

Photonic integration technologies, which have been developed since the deployment of optical communications, are essential for increasing the network capacity at a low cost and with efficient power consumption. This paper reviews recent progress on photonic integrated devices for higher bit-rate and long-distance transmission technologies with advanced modulation formats.

Traveling-wave semiconductor cascade lasers (TWSCLs) are a form of series cascade laser (SCL) in which series-connected laser diodes are interconnected with commensurate transmission lines to create a periodically loaded structure. The inclusion of transmission line segments allows broadband impedance matching in addition to preserving the link gain improvements of conventional SCLs. This paper describes the small-signal analysis of TWSCLs using both transmission line theory and Bloch waves. The latter technique is then applied to a study of how transmission line and laser diode parameters affect both the return loss and gain-bandwidth product of TWSCLs.

In this paper, we report a direct comparison between coupled resonator optical waveguides (CROWs) and photonic crystal waveguides (PhCWs), which have both been exploited as tunable delay lines. The two structures were fabricated on the same silicon-on-insulator (SOI) technological platform, with the same fabrication facilities and evaluated under the same signal bit-rate conditions. We compare the frequency- and time-domain response of the two structures; the physical mechanism underlying the tuning of the delay; the main limits induced by loss, dispersion, and structural disorder; and the impact of CROW and PhCW tunable delay lines on the transmission of data stream intensity and phase modulated up to 100 Gb/s. The main result of this study is that, in the considered domain of applications, CROWs and PhCWs behave much more similarly than one would expect. At data rates around 100 Gb/s, CROWs and PhCWs can be placed in competition. Lower data rates, where longer absolute delays are required and propagation loss becomes a critical issue, are the preferred domain of CROWs fabricated with large ring resonators, while at data rates in the terabit range, PhCWs remain the leading technology.

This paper reviews the major accomplishments in the demonstration of plasmabased soft x-ray lasers in 2009. Advances in shaping the plasma density and increasing the pump power have enabled the engineering of table-top laser systems operating at wavelengths as short as 10.9 nm and with stable and significant average power for use in applications.

This paper presents a short review of the development of and the motivation for short-wavelength free-electron lasers. The first observation of coherent X-ray production was reported from the Linac Coherent Light Source in April 2009.

The word “magic” is usually associated with movies, fiction, children stories, etc., but seldom with the natural sciences. Recent advances in metamaterials have changed this notion, in which we can now speak of “almost magical” properties that scientists could only dream about a decade ago. In this paper, we review some of the recent “almost magical” progress in the field of photonic metamaterials.

Femtosecond (fs) lasers have become common tools for microfabrication and nanofabrication, and a large amount of research has been carried out in this field in 2009. This paper reviews the major areas of achievement in 2009 relating to bio-microchips such as the so-called lab-on-a-chip (LOC) and optofluidics.

Photonic integration technologies, which have been developed since the deployment of optical communications, are essential for increasing the network capacity at a low cost and with efficient power consumption. This paper reviews recent progress on photonic integrated devices for higher bit-rate and long-distance transmission technologies with advanced modulation formats.

There is a common belief that coherent optical orthogonal frequency-division multiplexing (CO-OFDM) has inferior nonlinear performance in the fiber optic channel due to its high peak-to-average power ratio (PAPR). In this paper, we show that due to the uniqueness of chromatic dispersion in the optical fiber, properly designed CO-OFDM can, in fact, possess a nonlinearity advantage over a coherent single carrier (SC) for ultrahigh-speed transport at 100 Gb/s and beyond. In particular, we propose a novel approach called multiband DFT-spread OFDM (MB-DFT-S-OFDM), by which the DFT-S-OFDM is applied to each subband of the multiband CO-OFDM to reduce the PAPR within each subband. It is found that eight-band DFT-S-OFDM surpasses the conventional OFDM and the coherent SC by 1.3 and 0.5 dB, respectively, for SSMF107-Gb/s transmission over a 1000-km standard-single-mode-fiber (SSMF).

This paper reports a mathematical model for the evaluation of the bit error rate (BER) performance of burst-mode receivers by taking the effect of random noise and charging/discharging parameters of the receiver into consideration. The distribution of the threshold voltages will be similar to that of the distribution of the values corresponding to logical 1's of the preamble for threshold setting. The threshold setting will also vary when a long string of consecutive 0's arrive in the incoming data that report errors in detection. The average threshold is determined for a particular bit position in the consecutive string of 0's. The expression based on the threshold is also used to determine the BER of the receiver.

This paper focuses on high-speed cabling using polymer optical fibers (POF) in home networking. In particular, we report about the results obtained in the POF-ALL European Project, which is relevant to the Sixth Framework Program, and after two years of the European Project POF-PLUS, which is relevant to the Seventh Framework Program, focusing on their research activities about the use of poly-metyl-metha-acrilate step-index optical fibers for home applications. In particular, for that which concerns POF-ALL, we will describe eight-level pulse amplitude modulation (8-PAM) and orthogonal frequency-division multiplexing (OFDM) approaches for 100-Mb/s transmission over a target distance of 300 m, while for that which concerns POF-PLUS, we will describe a fully digital and a mixed analog-digital solution, both based on intensity modulation direct detection, for transmitting 1 Gb/s over a target distance of 50 m. The ultimate experimental results from the POF-ALL project will be given, while for POF-PLUS, which is still ongoing, we will only show our most recent preliminary results.

This paper reviews recent work on the design, experimental implementation, and application of two fundamental all-optical analog signal processing functionalities, namely, photonic temporal differentiation and photonic temporal integration, using customized grating devices directly written in optical fibers.

Fiber-optic research in signal processing for the first generation of coherent communication systems was dominated by receivers with blind adaptation. Next-generation systems will require a scalable and modular design for higher order modulation formats. Due to the nature of the fiber channel and the required parallelization in high-speed receivers, data-aided and blind algorithms call for a general reassessment when used in coherent optic receivers employing higher order modulation formats. In this paper, blind and data-aided receivers are compared for coherent single-carrier optical systems in terms of complexity, tracking ability, and convergence speed. Methods for equalization are discussed for time-domain- and frequency-domain-based receivers covering the most important algorithms. The general superiority of data-aided frequency-domain equalization is demonstrated.

The efficient use of optical nonlinearities in silicon is crucial for the implementation of silicon-based photonic devises. In this paper, we present an approximate analytical study of nonlinear polarization rotation in silicon-on-insulator (SOI) waveguides; the rotation is predominantly caused by the effects of self-phase modulation and cross-phase modulation, stemming from the anisotropic Kerr nonlinearity. In the first part of the paper, we analyze the transmittance of the Kerr shutter in the continuous-wave regime and address the problem of its optimization. It is essential for the generality of our conclusions that both free-carrier effects and two-photon absorption are properly accounted for in this study. We specifically show that the signal transmittance may be optimized by adjusting the waveguide length, the pump power, and the incident linear polarizations of pump and signal beams. In the second part of the paper, we examine the problem of power equalization with SOI waveguides. We validate the derived analytical solutions by comparing their predictions with the data from numerical simulations and illustrate the solutions by the examples of practical interest. The results of our work may prove useful for the design and optimization of SOI-based Kerr shutters, all-optical switches, and power equalizers.

In this paper, we present a new angular selective filter design that is based on photonic bandgap engineering principles. The operation of the filter is based on the occurrence of angular-dependent photonic stopbands and passbands in a photonic crystal structure. Such a filter allows for the propagation of normally incident light while disallowing the propagation of obliquely incident light waves. When the filter is applied to a solar cell structure that consists of a diffraction grating structure on the back surface, a high-efficiency light trap can be formed. Hence, the light-trapping capacity of the new structure is dependent on the photonic band structure of the light filter rather than on refractive optical properties of the active photovoltaic material. This paper presents a model of such a structure and investigates the possibilities afforded by the new structure.

The choice of polarity of operation in a quantum cascade (QC) laser is made at the beginning of every QC laser design and growth, yet little work has been done to ascertain any performance benefits of one polarity versus the other. In this paper, we compare two QC lasers of the same design, differentiated only by the reversing of the growth order of the heterostructure layers in the laser core, which results in opposite polarities of operation. Analysis is performed through continuous wave (CW) and pulsed threshold current measurements to observe the change in active core temperature with input power. A thermoelectric effect is observed, where the direction of current flow improves thermal transport in negative polarity lasers (electron flow toward the heat sink) over positive polarity (electron flow away from the heat sink), leading to a maximum observed reduction in laser core heating of 10.0 ± 5.5 K for a thermal load of 7.2 kW/cm2 in CW operation.

Radio-on-free space optical (RoFSO) communication systems are rapidly gaining popularity as an efficient and cost-effective means of transferring high data rates and radio frequency (RF) signals with the same capacity as optical fiber. However, the performance of those systems depends strongly on the atmospheric conditions and the nonlinear characteristics of the optical link. In this paper, we introduce an analytical model for the transmission of orthogonal frequency division multiplexing (OFDM)-based signals over freespace optics (FSO) links. Further, we derive a closed-form bit error probability (BEP) and outage probability expressions, taking into account the optical noises, the laser diode nonlinear distortion, and the atmospheric turbulence effect on the FSO channel modeled by the gamma-gamma distribution. This paper reports the most significant parameters that degrade the transmission performance of the OFDM signal over FSO links and indicates the cases that provide the optimal operating conditions for the link. The obtained results can be useful for designing, predicting, and evaluating the RoFSO system's ability to transmit wireless services over turbulent FSO links under actual conditions.

In this paper, we successfully apply multilevel kinoform computer-generated hologram (CGH) patterns, which are recorded on a fine texture paper by a photo printer, into the hologram identification (ID) tag system. The 11-level kinoform CGH images are generated on our tag samples by a modified simulated annealing method at a low quantization error rate of 0.4% compared with the original data and then retrieved by a commercial digital camera and reconstructed in the computer to the original data with about 4% reconstruction error rate. The low reconstruction error is accomplished by suitable pattern recognition and image processing. We also propose a kinoform reconstruction algorithm that can considerably reduce reconstruction errors occurring when the tag is damaged. It is shown that the original image of a fingerprint can be reconstructed at a low error rate of about 12%, although nearly half of the tag data are lost.

In this paper, we propose a nonuniform coded-modulation format based on iterative polar quantization (IPQ) as a scheme to enable achieving channel capacity in ultrahigh-speed optical communication systems. The proposed modulation format is coded with structured low-density parity-check (LDPC) codes optimized for Gaussian channels and, in combination with polarization-multiplexing, can achieve 800 Gb/s per wavelength aggregate rate and beyond utilizing the currently available components operating at 50 GS/s. Using coded IPQ, we show that we can achieve capacity for signal-to-noise ratios (SNRs) of up to 25 dB and increase the total propagation distance over optical transmission systems by 275 km over coded star-quadrature amplitude modulation (QAM).

In this paper, we propose a heterogeneous optical access networking scenario, in which communication links between source and destination nodes are heterogeneous, composed of free-space optical, plastic optical fiber (POF), and indoor infrared (IR) links. To deal with bandwidth limitations of POF and IR links, a power-variable rate-adaptive low-density parity-check (LDPC)-coded orthogonal frequency division multiplexing (OFDM) scheme is used, while to deal with atmospheric turbulence, the spatial diversity is used. The rate-adaptive LDPC codes are designed using a modified progressive edge-growth (MPEG) algorithm. We show that with the proposed heterogeneous communication systems, we can deliver a high-speed optical signal (40 Gb/s and beyond) to an end-user.

Numerical models play an important role in the design of the optical fiber drawing process for tailored mechanical properties and optical transmission characteristics. The rigorous part of a numerical fiber drawing model is the determination of the neck-down profile, which is calculated based on a force balance along the fiber axis, requiring intensive numerical iterations for solution. An alternative approach has been the use of an empirical neck-down profile based on experimental results; however, this approach is restricted to the simulation of the particular drawing conditions used in the experiments. This paper presents an approach to numerical simulations of an optical fiber drawing process where an analytical hyperbolic tangent function is used to describe the neck-down shape in a generalized manner, and the parameters of the function are determined based on a force balance for the drawing conditions. The physical model is based on a 2-D numerical analysis of the flow, heat, and mass transfer phenomena involved in the drawing and cooling processes during the manufacturing of optical glass fibers. The effects of fiber draw speed, maximum furnace temperature, and the furnace length on the neck-down profile are investigated and discussed in terms of the final fiber radius and the draw tension. The approach provides for computationally efficient process simulations without the need to fit the neck-down profile to experimental data.

In this paper, photonic cavities made of point defects in 2-D photonic crystals are modeled by finite-size transmission lines terminated at both ends by appropriate scalar impedances. The proposed model forms a simple transmission line resonator and is demonstrated to be quite beneficial in fast extraction of resonant frequency, quality factor, and mode profile of such photonic cavities. In this manner, an approximate yet quite accurate approach is introduced to characterize the electromagnetic properties of photonic crystal cavities. This method is successfully applied to different structures for both major polarizations and is shown to be as accurate as rigorous numerical methods, viz. the finite-element method.

Simultaneous provision of multiple services using a centralized light source can greatly reduce the complexity and cost of a wavelength-division multiplexing passive optical network (WDM-PON). In this paper, we report two schemes to simultaneously provide an ultra-wideband (UWB) service and a wired service using a centralized light source. In one scheme, a UWB signal and a wired signal are multiplexed and modulated on a single wavelength in the center office for wireless and wired downstream services. In the other scheme, the wavelength from a UWB downstream signal is reused in the optical network unit to provide a wired upstream service. Both schemes are experimentally demonstrated with the data-transmission performance evaluated by measuring the electrical spectra, eye diagrams, and receiver sensitivities. The proposed schemes would greatly reduce the cost while significantly improving the spectrum efficiency of a WDM-PON network incorporating UWB-over-fiber (UWBoF) systems for broadband wireless access, making the WDM-PON network more attractive for practical deployment.

In this paper, we investigate an optical-trap-based method for the detection of structural changes of the red blood cell (RBC) membrane affected by Ca2+ ions. Individual cells are immobilized by the use of optical tweezers and are monitored live, while the concentration of Ca2+ ions in the buffer is changed simultaneously. Ca2+ ions are known to affect the cells' membrane morphology. These changes are attributed to the formation of calcium-induced hydrophobic aggregates of phospholipid molecules in the RBC membrane, resulting in a net change in membrane rigidity. Membrane deformation results in the change of effective radius and the drag coefficient of the cell, both of which affect the Brownian motion of the cell in solution. This motion is indirectly measurable by monitoring the forward scattering light and its dependence on the size and drag coefficient of the cell. We show the relationship between the Ca2+ ion concentration and the optical trap specifications. The results are in agreement with previous biological studies and the phase contrast observations of living RBCs under investigation.

This paper reports fabrication, characterization, and testing of the thermal stability of ZnO-based Schottky ultraviolet photodetectors. The ZnO thin film was grown on a p-type Si 〈100〉 substrate by the sol-gel technique. The surface morphological and the structural properties of the thin film were studied by an atomic force microscope (AFM) and a scanning electron microscope (SEM). For the investigation of the surface chemical bonding, X-ray photoelectron spectroscopy (XPS) measurements were also performed. The I-V characteristics of the Schottky barrier photodetector were studied, and the parameters such as ideality factor, leakage current, and barrier height were extracted from the measured data at room temperature. With applied bias voltages in the range from -3 to 3 V, the contrast ratio, responsivity, detectivity, and quantum efficiency of the photodetectors were measured for an incident optical power of 0.1 mW at 365-nm wavelength. The electrical and optical study revealed that the performance of the device improves with increasing post metal deposition annealing temperature up to 100°C. The device exhibited excellent thermal stability in the annealing temperature range of 100°C to 200°C. For annealing temperatures beyond 200°C, the performance of the device degrades drastically. It was also found that at under 200°C, there is a harmonious correlation between the photoresponse and electrical characteristics of the device. Above this temperature, there is no correlation between the variations of photoresponse and electrical characteristics with increasing annealing temperature. The variation of the electrical and photoresponse properties of the Schottky photodetector subjected to different post-fabrication annealing can be attributed to the combined effects of interfacial reaction and phase transition during the annealing process.

Future optical networks will require the implementation of very high capacity (and therefore spectral efficient) technologies. Multi-carrier systems, such as Orthogonal Frequency Division Multiplexing (OFDM) and Coherent WDM (CoWDM), are promising candidates. In this paper, we present analytical, numerical, and experimental investigations of the impact of the relative phases between optical subcarriers of CoWDM systems, as well as the effect that the number of independently modulated subcarriers can have on the performance. We numerically demonstrate a five-subcarrier and three-subcarrier 10-GBd CoWDM system with direct detected amplitude shift keying (ASK) and differentially/coherently detected (D) phase shift keying (PSK). The simulation results are compared with experimental measurements of a 32-Gbit/s DPSK CoWDM system in two configurations. The first configuration was a practical 3-modulator array where all three subcarriers were independently modulated, the second configuration being a traditional 2-modulator odd/even configuration, where only odd and even subcarriers were independently modulated. Simulation and experimental results both indicate that the independent modulation implementation has a greater dependency on the relative phases between subcarriers, with a stronger penalty for the center subcarrier than the odd/even modulation scheme.

This paper presents a novel camera simulation framework capable of simulating the optical path of a variety of camera systems through the technique of Monte Carlo Path tracing. Path tracer is a ray-tracing technique that uses Markov chains to solve the global illumination problem, i.e., the problem of calculating the distribution of light in an environment, taking into account all forms of scattering, absorption, and interreflection. In global illumination, we deal with the interaction of light that reaches a surface directly from a light source (direct lighting) as well as the interaction of light that reaches a surface as a result of scattering or transmission from or through other objects (indirect lighting). Available pieces of ray-tracer software use very simple models for their camera system like the pinhole camera, the thin-lens camera, and the thick-lens camera. The novelty and strength of our simulation tool is the capability to simulate any arbitrary and complex camera system. Any kind of optical component (like mirrors, prisms, and optical filters) can be placed inside the camera system or on the image sensor, and the tool synthesizes the image taken by that complex camera system, which can be used to optimize the parameters of the system for a specific application. The tool was used to simulate the optical path of a variety of passive depth recovery systems (like stereoscopy, Plenoptic Camera, and Bi-prism camera) that are included in this paper.

In this paper, high-order silicon/air vertical 1-D photonic crystals (PhCs) featuring a deep reflectivity notch (Q of about 3000) within the third telecommunication transmission window are fabricated by electrochemical micromachining of silicon and optically characterized. Although, from scanning electron microscope (SEM) investigations, the microfabricated structures appear to be of high quality in terms of in-plane and out-of-plane uniformity as well as of low surface roughness, optical measurements highlight variability of the spectral position of reflectivity notches, which turns out to be affected by fine variations of structural features induced by fabrication. A nondestructive optical method is used to recover the distribution of typical fabrication features, which is not easily quantifiable with other techniques in these high aspect-ratio vertical structures, from the experimentally detected distribution of the optical features. Optical distribution is obtained by scanning the device with high spatial resolution and recording spectral reflectivity at normal incidence (in the wavelength range 1.0-1.7 μm) on different locations of the 1-D PhC surface (X-Y plane). Distribution of silicon thickness variation on the X-Y plane is then inferred by best fitting the experimental spectral reflectivity data with theoretical spectra that are calculated by taking into account nonidealities of both PhC structure and measuring setup. On-sample fabrication-induced variation of the average silicon thickness, as a function of the X-Y position, is estimated to be limited to ±80 nm (percentage error of ±1%) within a range of ±100 μm from a reference location. As a consequence of such thickness variation, a maximum shift of the reflectivity spectrum of 40 nm occurs as a function of the X-Y position in the range of ±100 μm. Sample-to-sample average silicon thickness variation among nominally equivalent structures is also tested in similar X-Y positions and found to be lower than ±1.5% (absolute variation of ±120 nm), within a range of ±15 μm, with respect to the average value on the investigated samples.

Theoretical investigation on commanding the self-pulsation characteristics of the semiconductor distributed feedback (DFB) laser using electronic feedback is carried out in this paper. This device can be used as the sample-and-hold element for high-speed photonic analog-to-digital converter circuit. A recommendation for experimental realization of this scheme with the short-feedback-delay requirement is proposed. The effect of the feedback loop parameters have been simulated numerically based on the rate equations to manipulate the relaxation oscillation frequency of the laser. The results, which to our knowledge are reported for the first time, clearly demonstrate the effect of the feedback loop parameters on the laser intensity modulation frequency response transfer function. A detailed analysis of the noise effects on the performance of this system is also carried out. The conclusion establishes that the theoretical foundation for optimizing and controlling the DFB laser system pulsing source for the photonic analog-to-digital conversion application by tuning the laser drive current may have the potential to replace mode-locked fiber lasers in many other applications, from radio frequency (RF) photonics to chaos communication.

In this paper, a novel and simple scheme to realize flexible access for gigabit wireline and impulse radio ultrawideband (IR-UWB) wireless services is proposed. The UWB signals are generated by multi-carrier upconverting and reshaping the baseband signals. The proposed system was experimentally demonstrated with the performances of 2.0-Gb/s data in both baseband and UWB formats after 46-km single mode fiber transmission and further 0.5-m wireless for UWB data. The flexibility of the system is confirmed by investigating the system performance at different data rates including 1.0 and 1.6 Gb/s. Optical wavelength independency and data-rate variability of UWB signal generation makes the system attractive for potential wireline and wireless applications in existing wavelength division multiplexing (WDM)-passive optical network (PON) systems.

We present a rigorous electrical and optical analysis of a strained and graded base SiGe Heterojunction Bipolar Transistor (HBT) electrooptic (EO) modulator. In this paper, we propose a 2-D model for a graded base SiGe HBT structure that is capable of operating at a data bit rate of 80 Gbit/s or higher. In this structure, apart from a polysilicon/monosilicon emitter (Width = 0.12 μm) and a strained SiGe graded base (Depth = 40 nm) , a selectively implanted collector (SIC) (Depth = 0.6 μm) is introduced. Furthermore, the terminal characteristics of this new device modeled using MEDICI are closely compared with the SiGe HBT in the IBM production line, suggesting the possibility of fast deployment of the EO modulator using established commercial processing. At a subcollector depth of 0.4 μm and at a base-emitter swing of 0 to 1.1 V, this model predicts a rise time of 5.1 ps and a fall time of 3.6 ps. Optical simulations predict a π phase shift length (Lπ) of 240.8 μm with an extinction ratio of 7.5 dB at a wavelength of 1.55 μm. Additionally, the tradeoff between the switching speed, Lπ and propagation loss with a thinner subcollector is analyzed and reported.

The design and experimental performance of a 40-GHz microwave photonic link scheme developed for broadband analog signal transmission that exhibits an increased input dynamic range compared with conventional microwave photonic links is presented. The scheme achieves an extension in the input power operating range by switching between two photonic links designed to operate at different input power levels, where the optical fiber provides the required delay for the switching operation. Although the extension in the dynamic range is noninstantaneous, the scheme has application in high-sensitivity receiver systems in a pulsed signal environment due to its feedforward gain control mechanism. This paper presents, through a realistic simulation study, the device parameter values required for optimized performance of a wideband (2-40 GHz) link with the noise figure, sensitivity, and dynamic range performance of each link and the composite link. A total "synthetic" dynamic range >;100 dB with a minimum detectable signal of -110 dBm at a 100-kHz noise bandwidth can be achieved for the 2-40-GHz frequency range operation. The simulation results compare well with experimental results obtained with a practical implementation of the dual link architecture. The design and operational details of the switching circuitry required are also presented.

Fluctuations of the optical power incident on a photodiode can be converted into phase fluctuations of the resulting electronic signal due to nonlinear saturation in the semiconductor. This impacts overall timing stability (phase noise) of microwave signals generated from a photodetected optical pulse train. In this paper, we describe and utilize techniques to characterize this conversion of amplitude noise to phase noise for several high-speed (>; 10 GHz) InGaAs p-i-n photodiodes operated at 900 nm. We focus on the impact of this effect on the photonic generation of low phase noise 10-GHz microwave signals and show that a combination of low laser amplitude noise, appropriate photodiode design, and optimum average photocurrent is required to achieve phase noise at or below -100 dBc/Hz at 1 Hz offset for a 10-GHz carrier. In some photodiodes, we find specific photocurrents where the power-to-phase conversion factor is observed to go to zero.

Laser amplifiers seek high power, efficiency, and short pulse durations. Research laboratories in this field have focused their investigations toward new laser materials that can be efficiently diode pumped, sustain high-power pumping, and have broad emission bandwidth to achieve ultrashort pulse amplification. This is why, for more than ten years now, new Yb-doped materials have been intensively investigated. In the actual state of the art, they represent the more promising and successful materials for these kinds of applications. In this paper, we will do a short review of the last and more impacting discoveries and demonstrations in this field over the last few years.

Graphene, which is a single layer of carbon atoms assembled in a honeycomb lattice, has recently attracted significant attention, primarily due to its extraordinary electronic properties. In fact, its photonic properties are not less exciting. Graphene interacts with light strongly from ultraviolet to far infrared, and such interaction is tunable by electric field. Moreover, although graphene itself is gapless, a direct, tunable bandgap can be created by breaking its intrinsic crystallographic symmetry. These unique properties make graphene a promising candidate for various light detection, manipulation, and generation applications in an ultra-wide operational wavelength range. In this paper, we first discuss a few possible photonic applications based on the exceptional photonic properties of graphene, followed by detailed presentation on graphene photodetectors. Finally, two major future directions on graphene nanophotonic research will be covered.

In this paper, we review recent progress toward efficient and versatile devices for terahertz applications. Low-loss transmission lines and waveguides are discussed, as well as potentially high-power photomixing devices based on carbon nanotubes.

Optical fiber communications continued to advance at a rapid pace in 2010. This paper presents a brief overview of the most exciting technological advances of 2010, eking out record capacity out of optical fiber through enhancing spectral efficiency and shrinking power consumption using modern optical fiber communication system designs.

Enabling technologies for optical wireless broadband access networks have been explored and developed with respect to optical components, modules, transmission systems, and networks. In this paper, we review the most significant accomplishments reported during 2010 with emphasis on radio-over-fiber (RoF) technology that is critical for the deployment of optical wireless broadband access networks in the near future.

In this paper, an ultracompact design of a low-loss silicon (Si) polarization rotator based on a silicon-on-insulator platform, which contains an asymmetric strip Si nanowire waveguide core, is presented. A full-vectorial finite element method and the least squares boundary residual method are used to study the effects of the device parameters, the results of which indicate that a very high polarization conversion with a very low polarization crosstalk is possible.

This paper proposes an accurate method that combines a hybrid genetic algorithm (GA) with a geometric compensation technique applied to an analytical Raman amplifier model to obtain the optimal design of multipump distributed Raman amplifiers. The geometric compensation enables partial determination of the GA initial population and works as a refinement in the search of the best possible solutions. We develop a self-contained algorithm that is capable of meeting on-off gain and ripple specifications to broadband Raman amplifiers, without the need for a previous study of the search space. As a result, we determine wavelengths and powers using the minimum number of pump lasers necessary to meet the given specifications. Our method has shown to be robust in the simultaneous analysis of multiple parameters and multiple objective problem. The processing time required to design large bandwidth Raman amplifier is minimized when compared with that obtained by a standard GA.

In this paper, we investigate the possibility of using accurate prediction models for the prediction of protoporphyrin bleaching dynamics to achieve photobleaching-insensitive methods to improve the evaluation of data in an existing clinical fluorescence-guided resection technique. To simulate the scenario, measurements were carried out in vivo on skin of healthy volunteers using a compact fiber-based fluorescence spectroscopy system. We have developed an effective method for the parameterization of sequences of bleaching spectra. We analyze convergence and decay rates with respect to initial conditions and excitation irradiance. We also discuss the consequences and the potential for bleaching-insensitive measurements and their applicability in a few examples from in vivo open brain surgery.

This paper presents a continuously tunable microwave photonic notch filter with a complex coefficient. The complex coefficient is generated using a radio-frequency (RF) phase shifter that consists of a dual-parallel Mach-Zehnder modulator (DPMZM) and a tunable optical bandpass filter (TBPF). By simply controlling the bias voltage of the DPMZM, the frequency response of the filter can be continuously tuned over a full free spectral range (FSR) without changing the shape of the frequency response.