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Recently, electro-optic integrated photonic elements have attracted considerable interest owing to their widespread application in optical communication and signal processing. The strong electro-optical properties and the complementary metal–oxide semiconductor (CMOS) technology compatibility of silicon–organic hybrid structures makes them promising photonic platforms. This study investigated a novel implementation of a high-speed electrically tuned bandpass optical filter using finite-difference time-domain and eigenmode expansion numerical methods. The proposed device was based on a Fabry–Perot cavity and was realized via an electro-optic organic molecular glass filled slot waveguide with Bragg gratings. Furthermore, the calculation considered the plasma dispersion effect, free-carrier absorption in the silicon component of the slot waveguide for different applied voltages, and doping profiles corresponding to ion implantation. It is shown that the spatial distribution of charge carrier density formed by the surface states accumulation/depletion layers has a significant effect on the optical properties of the slot waveguide. Lithographic distortions in the geometry of the proposed structures during fabrication were also considered. Therefore, this paper presents an optical filter designed for fabrication using CMOS-compatible processes on silicon-on-insulator wafers. The filter produced a 3 nm tunable range for a 10 V bias voltage swing, a 0.3 nm full width at half maximum (FWHM) passband with a center at 1550 nm at zero bias voltage, and a 12.5 nm free spectral range with a 27 dB extinction ratio. The proposed device outperforms many narrow passband analogs in terms of sensitivity (tunability: 0.3 nm/V) and can be applied extensively in the fields of optical communications and photonic spectral signal processing. [ABSTRACT FROM AUTHOR]

Photonic Integrated Circuits (PICs) on indium phosphide have matured significantly over the past couple of decades and have found use in many system applications. Some PIC efforts on other group III-V substrates have also been initiated. In numerous cases, the usefulness of these PICs is because of the reduction in size, weight, and power they provide, but in many cases also because of the higher performance made possible by the improved relative phase stability among optical paths as well as the reduction of inter-element coupling losses. In this paper, as part of this special issue in tribute to Prof. Daniel Dapkus, we focus on monolithic PICs that provide a system function, especially those that incorporate and build on widely-tunable laser technology as a key element. Some of the early widely-tunable laser work is reviewed, and a selection of past system-on-a-chip developments is presented as background. Then, more recent system-on-a-chip advances performed by the author’s groups are reviewed in more detail. Key advances are highlighted. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the design, fabrication, and performance estimation of an integrated Bragg grating (IBG) filter having stressed Si3N4 periodic layer over silicon waveguide. The influence of stress-optic effect on the optical performance of the proposed IBG filter is experimentally verified. The proposed IBG filter is fabricated with the different number of grating periods and therefore offers different spectral properties. The proposed filters are designed for a set of target specifications; such as center wavelength, bandwidth, and extinction ratio. The optical performances including temperature sensitivity of the filters are numerically estimated in the absence and presence of stress and are compared with fabricated filter characteristics. The study reveals that the filter, which is designed using numerical simulation considering stress effect, shows the similar optical performance to the fabricated IBG filter. It is also found that the increase of the number of grating periods increases the extinction ratio with narrowing of spectral bandwidth. The IBG filter experimentally demonstrates maximum temperature sensitivity and extinction ratio of 90 pm/°C and 26 dB respectively. The proposed IBG filter offers compact footprint and improved characteristics in comparison to the previously reported filters and finds its potential application in sensing and optical communication. Therefore, the presented work highlights the potency of stress-optic effect in enhancing the capabilities of photonic devices. [ABSTRACT FROM AUTHOR]

Supercontinuum generation has been extensively studied in optical waveguides pumped with femtosecond pulses, while there are few reports using picosecond pump pulses with a small spectral power variation. In this paper, we numerically demonstrate the supercontinuum generation in a dispersion-engineered silicon nitride waveguide pumped with 10-ps pulses at 1550 nm wavelength. A supercontinuum from 656 to 3867 nm (2.5 octaves) is enabled by uniquely tailored dispersion. The spectrum has a power variation of < 15 dB and shows a very flat pedestal varying by < 5 dB. The spectra generated from different dispersion profiles are compared and analyzed, which verifies the unique role of dispersion tailoring in flattened supercontinuum generation. To the best of our knowledge, it is the first study on such broad and flat supercontinuum generation on a chip using picosecond pump pulses, which would be highly desirable for many applications. [ABSTRACT FROM AUTHOR]

Integrated photonics has been pursued on a large variety of materials and platforms over more than half a century. In recent decades, silicon has emerged as the preferred optical and substrate material. However, since many optical functionalities cannot be, inherently or conveniently, implemented on silicon-based devices, heterogeneous integration of other materials has been an inevitable constituent of silicon photonics from its inception. This paper reviews recent progress in the heterogeneous integration of dielectrics and compound semiconductors as the core optical material for ultracompact nonlinear integrated photonics, preferably on silicon substrates. Occasionally, important devices on native substrates of the core nonlinear material are also reviewed. The focus is on ultracompact photonic devices and circuits formed on submicron films of lithium niobate (LiNbO3), and the aluminium-gallium-arsenide (AlGaAs) and aluminium-gallium-nitride (AlGaN) families for second-order nonlinear processes, such as second-harmonic generation, and techniques to address phase-matching in them. Integration of second- and third-order nonlinear devices on the same chip appears to be a future trend, thus the related preliminary results are reviewed. A broader introduction to heterogeneously integrated photonics, shortcomings of conventional silicon photonics for application in nonlinear optics, as well as an overview of modeling second-order nonlinear integrated-waveguide devices are also provided for completeness. [ABSTRACT FROM AUTHOR]

Higher-order digital modulation formats are demonstrated by electrically inducing free-carrier concentration changes in thin films of transparent conducting oxides, integrated into well-established silicon-photonic waveguiding architectures. The proposed near-infrared modulators employ as physical platforms the silicon-rib and silicon-slot waveguides, exploiting the highly dispersive and carrier-dependent epsilon-near-zero behavior of transparent conducting oxides to modulate the optical carrier. Advancing the existing studies on conventional amplitude modulation, phase-shift keying formats are investigated in this paper, using a rigorous and physically consistent modeling framework that seamlessly combines solid-state physics with Maxwell wave theory through carrier-dependent material models. The designed in-line modulators achieve $V_\pi L$ products in the order of 0.1 Vmm, two orders of magnitude lower than their respective all-silicon or lithium niobate counterparts, accompanied by an insertion loss of about $3~\mathrm {dB/\pi }$. Switching speeds in the order of 50 GHz are feasible along with a potential for sub-pJ/symbol energy consumption, meeting the demands for on-chip optical modulation. [ABSTRACT FROM AUTHOR]

Manipulating radio frequency (RF) signals in integrated photonic devices has recently emerged as a new paradigm for wireless communications, enabling high-frequency signal processing and broadband frequency agility in miniaturized photonic platforms. These advances are crucial for space and airborne applications which are weight and size sensitive. Recent progress in on-chip stimulated Brillouin scattering (SBS) using high gain has shown great potentials for RF photonic signal processing, owing to its inherent advantages of high resolution, high reconfigurability, and flexible programmability. On-chip SBS serves as a versatile and high-performance toolbox to process and manipulate the amplitude and phase of RF signals in the optical domain. In this paper, we provide a brief overview of recent advances achieved using SBS in planar waveguides, with a focus on applications requiring phase control of RF signals, including phase shifters, delay lines, and separate carrier tuning. We introduce a power-efficient scheme based on the concept of phase amplification to improve Brillouin-based phase processing capability. [ABSTRACT FROM AUTHOR]

This paper reports the experimental and theoretical assessments of the optical characteristics of recently introduced vertically coupled microdisk resonators made by the selective oxidation of AlGaAs multilayer structures. Experimental measurements show that the Q-factors are in the 103–104 range for diameters ranging from 75 to $300~\mu \text{m}$. To establish the origins of this limited performance, a coupled-mode-theory-based model of the single-access-waveguide-coupled resonator system was developed. It includes features which are specific to oxide-based vertically coupled resonators, namely, losses toward the slab waveguide lying under the resonator and a coupling region with an asymmetric and multilayer structure. Setting this simulation tool required the proposal and validation of a general criterion to select an appropriate set of decomposition permittivity profiles to be able to accurately model the characteristics of these more complex couplers using the coupled-mode-theory approach. This theoretical development is generic and can be now deployed to simulate any device which includes multiwaveguide couplers with arbitrary piece-wise-constant profile of the dielectric permittivity. Exploiting this particular development and experimental measurements of the disk sidewall roughness and of the coupling lengths, the calculated and experimental Q-factors are found to be in good agreement and allow establishing that the current performance is limited by the scattering losses and the slab leakage losses for small- and large-diameter devices, respectively. [ABSTRACT FROM AUTHOR]

The space domain of lightwaves has attracted increasing interest in optical communications. Lightwaves having helical phase front and carrying orbital angular momentum (OAM) have seen potential applications both in free-space and fiber-based optical communications. The widely deployed conventional ITU-T G.652 fiber is single mode fiber at 1550 nm, which, however, might support high-order modes as well as OAM modes at short wavelength. In this paper, we present detailed theoretical analyses on the mode properties of circularly polarized OAM modes in conventional G.652 fiber at three RGB wavelengths (red at 632.8 nm, green at 532 nm, and blue at 476.5 nm). The G.652 fiber has a 4.6- \mu \textm core radius, a 62.5- \mu \textm cladding radius, and 0.277% refractive index difference between the core and the cladding. We first study all the cylindrical vector modes (fiber eigenmodes) and synthesize the circular OAM modes by proper linear combination of degenerate fiber eigenmodes supported in the G.652 fiber at three RGB wavelengths. We then calculate the effective mode area and nonlinearity and discuss the tolerance to fiber ellipticity and bending ( \textn{\text {eff}} differences, $2\pi $ walk-off length, 10-ps walk-off length, loss, and OAM crosstalks) for red, green, and blue OAM modes. Additionally, we investigate the OAM modes properties at another three wavelengths of conventional semiconductor lasers, i.e., 780, 650, and 405 nm. Moreover, we also estimate the fiber attenuation, propagation loss, and communication bandwidth/capacity. The obtained results may stimulate wide interesting OAM related applications using conventional G.652 fiber, especially for hundreds of meters or km-scale short reach/distance applications. [ABSTRACT FROM AUTHOR]

Acousto-optic interaction in optomechanical crystals allows unidirectional control of elastic waves over optical waves. However, as a result of this nonlinear interaction, infinitely many optical modes are born. This paper presents an exact formulation of a coupled mode theory for interaction between elastic and photonic Bloch waves moving along an optomechanical waveguide. In general, an optical wavefront is strongly diffracted by an elastic wave in frequency and wave vector, and thus infinite modes with different frequencies and wave vectors appear. We discuss resonance and mode conversion conditions and present a rigorous method to derive coupling rates and mode profiles. We also find a conservation law which rules over total optical power from interacting individual modes. We present application examples to the theory to optomechanical waveguides and cavities, as well as non-reciprocal transmission of light and optomechanical switches. [ABSTRACT FROM PUBLISHER]

In this paper, terahertz (THz) generation in nonlinear plasmonic waveguides is proposed and thoroughly investigated. The proposed plasmonic waveguide is composed of metal–insulator–metal nanostructure filled with lithium niobate. The THz generation is conducted by means of difference-frequency generation of surface plasmon-polariton (SPP) modes. The SPP modes are designed to be tightly confined inside the plasmonic waveguide, while the generated THz waves diffract rapidly to propagate outside the plasmonic waveguide. It then follows that the THz absorption is minimized. It is shown that viable THz generation can be achieved, despite the SPP losses, by properly choosing the SPP wavelengths and the waveguide dimension. Our numerical evaluations show viable THz generation over the entire frequency band from 1 to 10 THz. The proposed structure introduces a new modality of having the SPP modes totally confined inside a nanoscale waveguide, while most of the generated THz waves are (and thus interacting) with the surrounding medium of the waveguide. These properties promise potential applications in nanocommunication systems and body-centric nanonetworks. [ABSTRACT FROM AUTHOR]

We report the observation of narrow tilted lobes in the far-field emission pattern of leaky oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The VCSEL cavity is surrounded by two selectively oxidized aperture layers, which are intentionally designed to produce a high lateral leakage of the high-order transverse modes of the vertical cavity. The device operates in the fundamental transverse mode at oxide aperture diameters below 5~\mu \textm and currents up to 4 and 5 mA. At higher currents or larger aperture diameters, an additional high-order transverse optical mode evolves. This mode is revealed by the appearance of a shorter wavelength emission line in the electroluminescence spectra of the device, resulting in multi-mode lasing and in the related changes in the near- and far-field patterns. In the far-field pattern, the evolution of the high-order mode is revealed by the evolution of the two overlapping emission lobes at moderate (~5°) tilt angles with respect to the normal to the surface and by the appearance of a multi-spot or a ring pattern in the CCD camera images. Most importantly, the appearance of this high-order transverse mode is accompanied by an observation of much narrower lobes in the far-field pattern observed at significantly larger tilt angles (~35°). The tilt angle and the narrow angular width of these emission lobes in the far-field spectrum are in agreement with those calculated in the 3-D cold cavity modeling of the optical modes of the device. These narrow tilted lobes revealed in this paper are the fingerprints of the leakage effect in specially designed oxide-confined VCSELs with their intensity being proportional to the optical power leaving the aperture region in the direction parallel to the surface and propagating into the oxidized region. The effect can be applied for engineering of single-mode VCSELs, coherently-coupled 2-D VCSEL arrays, laterally integrated VCSEL-photodetector chips, and VCSELs integrated to slow light waveguides, for coupled optical gates for optical computers and other types of photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Integrated microwave photonics is an emerging field in which photonic integrated technologies are employed to realize on-chip integration of microwave photonic systems with the aim to enrich the functionalities and enhance the system performance. Silicon photonics, as one of the various photonic integrated technology platforms, has attracted worldwide attention to achieve microwave photonic system integration for its compatibility with the current CMOS technology and its potential of seamless integration with electronics. In this paper, an overview about our recent work on silicon-based integrated microwave photonics is presented with an emphasis on silicon-based on-chip photonic arbitrary microwave waveform generation and microwave signals processing. [ABSTRACT FROM AUTHOR]

This paper reviews progress in the field of heterogeneously integrated photodiodes with a focus on InP-based high-speed high-power modified uni-traveling carrier photodiodes on silicon-on-insulator waveguides. Discrete, balanced, and photodiode arrays are described. [ABSTRACT FROM PUBLISHER]

In this paper, we have generated an effect of electromagnetic-induced transparency (EIT)-like transmission in a pair of resonators coupled to a metal–insulator–metal waveguide. Resonators are separated by the metallic nanoslit. By controlling single parameter (i.e., the width of the metallic slit), the device is made to exhibit EIT-like transmission. EIT is the result of destructive interference between two resonating modes, which leads to an asymmetrical-shaped resonance called Fano resonance. EIT is generally accompanied with sharp dispersion that reduces the velocity of light near the resonance. The slow-light characteristics of the device are also investigated. An ultra large value of group index ( ng=117.06 ) and a large value of normalized delay bandwidth product (NDBP = 0.88) is obtained over an ultra large bandwidth ( $\Delta f=1.39$ THz). Furthermore, it is theoretically predicted that asymmetry parameter ( $q$ ) of Fano resonance experiences a sign reversal when resonances are swept each other in the tuning process. This reversible Fano resonance and slow-light nature of proposed device open up the avenues for designing on-chip optical buffers, switches, modulators, and so on. [ABSTRACT FROM PUBLISHER]

Wide-stripe design for high-power laser diodes (LDs) permits multilateral-mode optical field distribution and the formation of an unstable filament pattern within the active waveguide. This is a serious drawback leading to a decrease in the emitted beam quality. The filaments cause spatial and time fluctuations in the LDs near- and far-field (FF) characteristics due to their random nature. The multimode optical field induces a widening of the FF pattern (known as FF blooming effects) as the drive current increases due to an increasing number of lateral modes. In this paper, the gain shaping in the LDs active region by ion implantation is proposed as a way to induce beam stability improvement. The optical resonator of the presented LDs consists of a series of interlaced narrow high- and low-gain stripes. The low-gain stripes are pumped only by spreading the current from neighboring stripes. The calculations show that under such conditions, one of the higher lateral modes can be excited at laser threshold due to the best spatial fit to the stripe’s periodicity. This should restrict the FF blooming effect. The predictions are confirmed by measurements of the LDs based on the multistripe design. A reduction of the optical field intensity fluctuations has also been observed. [ABSTRACT FROM AUTHOR]

In this paper, we examine for the first time how to design arbitrary shape modal fields within complex refractive index circular waveguides. In order to achieve this flexibility in field shape, we use complex refractive index profile waveguides, where we determine the required refractive index profile on both real and imaginary refractive index. We develop a technique for calculating directly and accurately the refractive index profiles of cylindrical waveguides from knowledge of the desired modal electric field. The method we use to solve this inverse problem is via modeling the waveguide transversely as a transmission line. We demonstrate this algorithm with a number of example reconstructions of different arbitrary modal electric fields. The refractive index profiles generated supporting the required modal electric fields are complex. We reconstruct complex refractive index profiles which support unusual electric field distributions. We expect this technique to be useful in designing special fibers for mode matching between dissimilar waveguides, in designing sensing optical fibers, in mode division multiplexing, in gain flattening optical fiber amplifiers, and also for high power optical fibers. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the novel behavior of induced focusing in nonlinear metamaterials (MMs) through designing probe-pump configuration, where the coupled waves may simultaneously experience negative refractive index or positive refractive index, or one experiences positive refractive index and another experiences negative refractive index both analytically and numerically. It is shown that cross-phase modulation (XPM) in MM not only brings some new features to the behavior of induced focusing, but also makes it possible in the ordinary positive-index materials (OMs), where it is otherwise impossible. First, we reveal that weak probe beam can be focused by strong pump beam even when their centers are completely overlapping each other. Moreover, it is found that the separated distance between coupled waves has an optimal value, which results in the strongest focusing of probe beam. Finally, another most notable property is that a spatial induced focusing is found to occur for different combinations of the signs of refractive index decided by the probe and pump beams, respectively, implying that a spatial XPM in MMs can be used as a more powerful tool for controlling the inducing focusing, when compared with the corresponding case in OMs. Our findings demonstrate that MMs can provide us unique opportunities unattainable in OMs to manipulate the all-optical control of optical focusing behavior through the new physical mechanism of XPM. [ABSTRACT FROM AUTHOR]

In this paper, we designed the offset frequency locking and active frequency stabilization system for the continuous-wave (CW) and electro-optical Q-switched RF-excited waveguide CO2 lasers to provide an ideal light source for coherent radar. The CW laser is used as a local laser, and the pulsed laser is used as a main laser, which can produce Q-switched and cavity-dumped laser synchronously. A closed-loop laser frequency control system was used to stabilize the Q-switched laser at the gain curve center frequency and to lock the two lasers at a selected heterodyne frequency. The system includes two parts: 1) pulsed laser frequency stabilization and 2) offset frequency locking. The frequency stabilization part can keep the Q-switched laser oscillating at the peak of the gain curve by measuring the pulse build-up time continuously and controlling the cavity length. The offset frequency locking circuits keep the heterodyne frequency around the selected frequency by measuring the frequency of the beat signals and controlling the CW laser cavity length. In the experiment, the long-term frequency shift of the pulse laser was measured to be less than ±16 MHz and the offset frequency fluctuation was less than ±2 MHz when the frequency control system was in a closed-loop operation. [ABSTRACT FROM AUTHOR]

In this paper, the gain, phase, and refractive index dynamics of photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) are investigated for the first time. For this purpose, we establish a comprehensive nonlinear state space model with 1088 state variables to simulate the carrier dynamics of the inhomogeneously broadened InAs/GaAs QD active region embedded in a flat-band slow-light photonic crystal waveguide. The gain and phase recovery responses are monitored during the amplification of an ultrashort pump pulse. Simulation results show that changes in refractive index in the PC-QDSOA active region are much stronger than the index changes in the conventional QDSOAs. In addition, the gain and phase recovery time in PC-QDSOAs are similar to those in the conventional QDSOAs based on ridge waveguide structures. Also, we found that the injected current and the consumed power in PC-QDSOAs can be two orders of magnitude less than those values in the conventional QDSOAs. [ABSTRACT FROM AUTHOR]

A novel asymmetric channel plasmon polaritons (CPPs) is proposed and analyzed. In this paper, the dispersion characteristics of asymmetric two and three-trenched CPPs structures are studied in detail. The suggested asymmetric structures have advantages in terms of propagation length and figure of merit over the symmetric CPP waveguides. In addition, a comparative study of various CPP metals including gold and silver is also presented. It is found that the propagation length and figure of merit of the silver-based structures are better than those of gold-based structures. In addition, the effect of bending on the asymmetric CPP waveguides is investigated. The simulation results are obtained by full-vectorial finite difference method with irregular meshing capabilities and perfectly matched layer boundary conditions. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, the photorefractive effect in plasmonic waveguides is theoretically modeled and investigated in detail. A metal- LiNbO3-metal nanostructure is considered, with the LiNbO3 being doped with donor and acceptor impurities. The interaction between symmetric and antisymmetric interfering SPP modes is studied. It is shown that a strong symmetric mode can be coupled to a week antisymmetric mode by the mean of photorefractive effect. When the modal losses are taken into account, it was found that losses can limit the interaction length. However, by choosing the proper waveguide length, doping concentration, and amplitude inputs, the photorefractive coupling process is shown yet to be viable despite losses. The coupling effect can be conducted either as an amplification or mode conversion process, promising novel future application. For instant, several known photorefractive applications in microphotonics can be borrowed and implemented in the plasmonic field. [ABSTRACT FROM AUTHOR]

The light-transmission resonant behavior of complex-shaped patterns can be difficult to estimate intuitively due to many possible resonant contours. In this paper, we propose a simple method to predict the effective resonant paths of onefold or twofold mirror-symmetry patterns, which exploits the antiphase property of certain field component along the resonant path and the symmetry requirement associated with the incident-wave polarization state. In addition, the resonant wavelengths for aperture-type patterns can further be estimated by a simple modified cutoff wavelength equation for a rectangular waveguide. Such prediction is validated by the simulated results of the finite-difference time domain method. In addition, we discuss how the separation distance between slit elements in the aperture affects the resonant wavelength, showing how the coupling between adjacent slits would play a role in the variation of the spectra. By studying the properties of such factors and how they interact in detail, we could manipulate the spectra with an additional degree of freedom, which could be important to structures with multielements in one unit cell. [ABSTRACT FROM PUBLISHER]

In this paper, we numerically investigate the formation and propagation characteristics of waveguides written by luminescence-induced spatial solitons (LISSs). Such waveguides, realized in erbium-doped lithium niobate crystals by photorefractive and Pockels effects, are analyzed in the transient regime by using a spatiotemporal numerical code for the photorefractive nonlinearity as well as for the erbium emission and light propagation within the induced waveguide. These calculations highlight a great LISS feasibility. Optical characterization of the waveguides indicates light propagation losses lower than 0.05 dB/cm at 1550 nm, pointing out high potentialities of LISS waveguides for active and passive electrooptic devices. [ABSTRACT FROM AUTHOR]

In this paper, we review our work on III–V/SOI photonic integrated circuits for short-wave infrared applications. We focus on the integration of short-wave infrared photodetectors on a silicon photonics platform and on the generation of a short-wave infrared supercontinuum using the \chi^(3) nonlinearity in silicon photonic wires. In addition, the performance of a silicon optical parametric amplifier is reviewed, as a first step towards constructing an integrated tunable short-wave infrared parametric oscillator. [ABSTRACT FROM PUBLISHER]

We introduce a novel concept of discretely tunable semiconductor lasers with on-chip filtered optical feedback. The integrated device is based on a semiconductor ring laser that can sustain two counter-propagating modes. By means of a directional coupler, part of the light emitted by the laser is coupled out to a feedback section integrated on the same chip. The feedback section contains two arrayed waveguide gratings and a set of semiconductor optical amplifiers to provide filtering of particular longitudinal modes sustained by the ring cavity. By controlling the current injected into the semiconductor optical amplifiers, single mode operation in both directions is achieved. In this paper, the design, characterization, and modeling of the device is presented. [ABSTRACT FROM PUBLISHER]

Silicon waveguides integrated with doped dielectric gain media may allow the design of planar light sources with electronic control. In this paper, the effects of design geometries and nonlinear losses on the gain in crystalline silicon waveguides with erbium-doped regions are investigated. We show that by using multitrench geometries, the power confinement can be increased and higher gain-to-nonlinear-loss ratio achieved. Net gain can be improved as much as 0.38 dB/cm in multitrench waveguides compared to single-trench waveguides. [ABSTRACT FROM PUBLISHER]

We study the influence of ion implantation conditions on the performance of depletion-type silicon optical modulators by a combined simulation of the process flow, the electrical characteristic, and the beam propagation. Through calculations using different implantation positions, energies, and tilt angles, this paper reveals that a gap between specific implantation windows is able to alleviate the modulation efficiency degradation due to the lateral straggling of implanted ions, while a tilt angle reduces the optical loss without harming the modulation efficiency. After an optimization of the implantation condition, the extinction ratio of the Mach-Zehnder modulator can be improved by 4.6 dB, while its optical loss falls from 3 to 2.47 dB. Finally, a simplified doping pattern that eliminates two implantation steps is discussed. [ABSTRACT FROM PUBLISHER]

Integrated nonlinear optical devices for the generation of twin photon beams are expected to be a key element for the development of quantum information techniques. This paper presents a quantum theory analysis of counterpropagating twin photon generation (CPTPG) by spontaneous parametric downconversion. Full descriptions of the quantum states of the twin photon beams having unique features are obtained in the Heisenberg and Schrödinger pictures. Mathematical expressions useful for device design and quantitative prediction of the performances, such as efficiency, wavelength spectrum and bandwidth, and photon correlation time, are deduced. Numerical data are given for specific quasi-phase-matched LiNbO\bf 3 waveguide CPTPG devices. [ABSTRACT FROM PUBLISHER]

In this paper, a 3-D model based on the Green's function for analyzing wave propagation in 2-D guided-wave photonic crystals (PhCs) is proposed. The model allows analysis all the physical effects occurring when a source field propagates in a multilayered structure with a periodic arrangement of scatterers, by taking into account both physical and geometrical parameters. Numerical results for PhC waveguides are compared with those obtained using the well-known finite-difference time-domain algorithm and the 3-D multiple-scattering technique already proposed in the literature, showing a very good agreement and some remarkable advantages, in terms of faster determination of electromagnetic field distributions and band diagrams and capability to analyze both in-plane and out-of-plane scattering losses. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the modal behavior and the spatial coherence properties of a gain-guided laser array emitting an optical output power of more than 50 W in quasi-continuous-wave operation at a wavelength of 1070 nm and above. The lateral near- and far-field intensity profiles and the Wigner distribution function were measured from low to high output power. The array modes were calculated by solving the waveguide equation taking into account the power-dependent temperature distribution and were also experimentally determined by a modal decomposition of the cross spectral density. The analysis revealed that, at a low power, a single array mode lases, whereas at high power, multiple single stripe modes dominate the lasing due to the thermally induced index rise under the stripes. [ABSTRACT FROM PUBLISHER]

In this paper, we use the Wigner function in order to determine the photon number statistics of a heralded single-photon source constructed from a photon-pair source using four-wave mixing in optical fibers. Having this result, we discuss the performance of a quantum key distribution system when this kind of single-photon source is employed. [ABSTRACT FROM AUTHOR]

In general, an accurate evaluation of the bending loss of an optical fiber with an arbitrary refractive index profile is a cumbersome task, especially for holey fibers (HFs). In this paper, various approaches are applied and compared for the bending loss evaluations of single-polarization elliptical-hole core circular-hole HFs (EC-CHFs), which are circular-hole HFs having a core with an elliptical-hole lattice structure. Our simulation results showthat when bending loss formulas for weakly guiding circular fibers are applied to a HF by regarding it as an approximate circular fiber having an equivalent step-index (SI) profile, the definition of the core region is the most crucial issue. Moreover, we also show that the results obtained by the approximate approach based on the bending loss formulas for the equivalent SI circular fiber are in good agreement with direct approaches with numerical simulations for the real EC-CHF structure, if the equivalent core radius is suitably defined for the real cross section. [ABSTRACT FROM AUTHOR]

Metal wires for global communication on integrated circuits have become problematic as device integration densities scale with rapid advancements in CMOS technology. They may not be able to deliver the growing bandwidth requirements of future microprocessors. Optical interconnect technologies may provide a solution to meet this challenge and extend Moore's law. In this paper, a novel guided-wave optical interconnect fabric aiming to replace the slow global metal interconnections is proposed and analyzed. The reflection-mode multiple-quantum-well-modulator-based optical interconnection approach is projected to achieve high coupling efficiency and be compatible with standard CMOS processes. The key notion is a prismatic coupling structure that is embedded in the optical waveguide and therefore has a very small footprint in the circuit. Ray-trace and finite-difference time-domain simulation results predict high coupling efficiency of this structure. [ABSTRACT FROM AUTHOR]

Controlling thermal stress is a promising way to reduce the temperature instability of arrayed waveguide gratings (AWGs). A simple method to apply thermal stress is to attach stress plates on the arrayed waveguides. In this paper, a general analytical method to study the temperature sensitivity of the central wavelength in modified AWGs with stress plates is developed. The complete analysis shows that the temperature sensitivity can be controlled effectively by tuning the material parameters and the thickness of the stress plates. To obtain athermal AWGs, a stress plate with large positive thermal expansion coefficient and small Young's modulus should be attached on the bottom of the arrayed waveguides. The material with large negative thermal expansion coefficient suggests another potential scheme. [ABSTRACT FROM AUTHOR]

We present an evanescent coupling method between a semiconductor antiresonant reflecting optical waveguide and a side-polished fiber and apply it to the design and fabrication of several hybrid fiber-semiconductor devices. Unique properties and advantages of these devices over conventional fiber-coupled modules are discussed in detail. Previous realizations of this coupling method have all been one-dimensional, as no lateral confinement mechanism was used. In this paper, we have successfully achieved great improvements in efficiency of coupling by implementing lateral confinement as well. In particular, we demonstrate the first side-coupled fiber semiconductor laser based on this technology, coupling more than 3 mW of power at 850 nm directly into a 5/125 μm single-mode fiber. [ABSTRACT FROM AUTHOR]

In this paper, the propagation of optical pulses in photonic crystal waveguides (PCWs) near the edge of the guided band is numerically investigated. In the linear regime, it is shown that group velocity dispersion can significantly limit the maximum bit rate of the optical signal. On the other hand, better performance is obtained using soliton waves. Both bright and dark solitons can significantly increase the maximum bit rate that can be achieved in the nanosecond delay regime. The influence of higher order dispersion and optical loss is numerically investigated. The results indicate that near the band edge soliton propagation in PCWs can be stable, provided that the optical losses are kept low. This could open a path towards implementing compact nonlinear elements and delay lines in integrated form. [ABSTRACT FROM AUTHOR]

Yb3+-doped silicate fibers are commonly employed in optical systems utilizing fiber lasers and amplifiers. Deployment of such materials and systems in space-based and other adverse radiation environments requires knowledge of their response to fluxes of ionizing radiation. This paper reports the results of gamma radiation exposures on a suite of passive, modern, highly Yb3+-doped aluminosilicate fibers. Of interest are the effects of total dose and dose rate as well as the development of radiation-induced absorption across a broad spectral window (1.0-1.7 μm). Results indicate that these fibers exhibit reasonable radiation resistance to gamma exposures typical of a five-year low-Earth-orbit environment. Maximum transmittance losses of less than 10 % in the 1.0-1.7-μm spectral region for total gamma exposures of 2-5 krad (Si) were observed. In addition, it was found that the dependence of transmittance on radiation dose generally followed a power law that was dependent on dose rate. [ABSTRACT FROM AUTHOR]

This paper presents an improved curvature loss formula for optical waveguides, which is shown to accurately predict the bend loss of both single-mode and multimode fibers. The formula expands upon a previous formula derived by Marcuse, greatly improving its accuracy for the case of multimode fiber. Also presented are the results of bent fiber simulations using the beam propagation method (BPM), and experimental measurements of bend loss. Agreement among simulation, formula and measurement support the validity of both theoretical methods. BPM simulations showed that the lowest order modes of the bent fiber were reduced to their linearly polarized constituents prior to the onset of significant bend loss. This implies that certain LP mode orientations should propagate with much lower loss than previously expected, and should impact the mode stripping ability of bent large mode area fibers, as employed in fiber lasers and amplifiers. [ABSTRACT FROM AUTHOR]

Buried-type benzocyclobutene (BCB) optical waveguides fabricated by UV pulsed-laser illumination are proposed and comprehensively characterized in this paper. The fabrication process is greatly simplified as compared to conventional dry-etched ridge-type BCB waveguides. The measured propagation loss at 1548 nm is as low as 0.6 dB/cm due to the buried waveguide structure. And the produced refractive index change is dependent upon the number of laser shots such that single-mode waveguides with different mode sizes can be tailored for efficient coupling. Furthermore, rigorous analyses of surface damage threshold, rms roughness, and chemical characteristics under different illumination conditions are presented to illustrate the design considerations and the chemical mechanism of the UV-induced BCB waveguides. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically and experimentally study the generation of very high-repetition-rate pulse sources based on multiple four-wave mixing in optical fibers. More precisely, we described the generation of nearly transform-limited pulses at repetition rates of 20, 40, 80, 160, 320, 640 GHz, and 1 THz with a wavelength tunability close to 20 nm around 1555 nm. In particular, frequency resolved optical gating analyses show that 170-fs transform-limited pulses have been generated at 1 THz. [ABSTRACT FROM AUTHOR]

An improved optical self-heterodyne method utilizing a distributed Bragg reflector (DBR) tunable laser and an optical fiber ring interferometer is presented in this paper. The interference efficiency can be increased by 7 dB compared with the scheme using the conventional Mach-Zehnder interferometer. The unsteady process that the beating frequency experiences in each tuning period is investigated. According to the measurement results, the wavelength and optical power of the tunable laser will be steady when the square-wave frequency is lower than 300 kHz. It has been shown that when a square-wave voltage is applied to the phase section of the tunable laser, the laser linewidths vary in a wide range, and are much larger than that under dc voltage tuning. The errors caused by the variations in the linewidth of the beat signal and optical power can be eliminated using the proposed calibration procedures, and the measurement accuracy can, therefore, be significantly improved. Experiments show that the frequency responses obtained using our method agree well with the data provided by the manufacturer, and the improved optical self-heterodyne method is as accurate as the intensity noise technique. [ABSTRACT FROM AUTHOR]

The theoretical investigation of waveguides having nonuniform cross-sections is an attractive and challenging problem which deserves serious interest. In this paper, we present a novel analysis of laminated multilayered three-dimensional wavegulde, based on two modes: 1) a new coupled transmission line approach that considers the sloping of the layers along the longitudinal direction and 2) a transmission line matrix integral equation (TLMLE) modeling that complete and extends the investigation of the field propagation. In method 1), we neglect radiation modes and their EM coupling. All physical effects instead are accounted for by the full-wave TLMLE method. By using TLMIE, we validate the EM analysis and calculate TE/TM losses, arising from radiation modes. [ABSTRACT FROM AUTHOR]