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Optical isolators play unique roles in photonic circuits. We have developed an optical isolator with silicon waveguides, based on a Mach–Zehnder interferometer. The device characteristics were temperature dependent. We investigated the temperature dependence of the refractive index (dn/dT) and the magneto-optical coefficient ( d\theta _f /dT) of a magneto-optical garnet Ce:YIG, and estimated these as 9.1 \times 10^-5 K−1 and 44^\circ \cdot cm^- 1 \cdot K^- 1 , respectively. We discuss the design of an athermal silicon waveguide optical isolator, in which the temperature dependences of the magneto-optical effect and refractive indices are canceled in the backward direction. The high optical isolation, greater than 20 dB, is demonstrated for temperature in the 20–60 °C range. [ABSTRACT FROM PUBLISHER]

Most on-chip optical isolators utilize nonreciprocal magneto-optic (MO) garnet-materials that require an external bias magnetic field to operate. The magnetic field is applied through incorporation of either a permanent magnet or an active electromagnet. Permanent magnets add significantly to device bulk and electromagnets increase fabrication complexity and power consumption. Hence, it is highly desirable to reduce or eliminate the magnetizing component in these devices. Here, we experimentally demonstrate a first of its kind bias-magnet-free (BMF) on-chip waveguide optical isolator with integrated Polarcor UltraThin polarizers. The BMF isolator device obviates the need for magnetizing components while possessing superior performance, relative to other on-chip isolators, with ≥25 dB of isolation ratio (IR), and ≤3.5 dB of insertion loss (IL) across the entire infrared optical C-band. [ABSTRACT FROM AUTHOR]

In this study, we present optical isolators and circulators fabricated by bonding cerium-substituted yttrium iron garnet (Ce:YIG) on silicon microring resonators. A novel integrated electromagnet is fabricated by depositing a metal micro-strip on the bonded chip. We experimentally prove that it can be efficiently used to control the magnetic field needed to induce the nonreciprocal phase shift effect in the Ce:YIG. The fabricated devices exhibit extremely small footprint (<70 μm) and can be packaged, eliminating the need of a large size permanent magnet. A large optical isolation of 32 dB and 11 dB is measured for the isolator and the circulator, respectively. Moreover, a two microring solution is also investigated to provide larger bandwidth and higher isolation. The proposed approach represents a promising solution for large-scale integration of nonreciprocal components in silicon photonics. [ABSTRACT FROM PUBLISHER]

An efficient and accurate technique for evaluating the characteristics of a polarization converter consisting of a dielectric waveguide with a single asymmetric section is proposed and discussed with the aid of the imaginary-distance beam-propagation method. Detailed consideration regarding the optical-axis rotation angle reveals the necessity and effectiveness of introducing the excitation efficiency of the two hybrid eigenmodes of the asymmetric section. This enables us to assess the incident mode dependence, which cannot be done by the conventional rotation angle. We derive concise formulas regarding the polarization extinction ratio and the insertion loss using the hybrid eigenmodes. It is found that the present formulas provide reasonable results, showing a good agreement with the results obtained from a time-consuming FDTD simulation. [ABSTRACT FROM AUTHOR]

This paper extends our previous work on the microring resonator-type serial-to-parallel conversion scheme aimed for all-optical label processing on the silicon photonic platform. In the previously proposed scheme, the architecture of the delay lines was silicon wires. This resulted in considerable propagation loss, confining multibit operation of serial-to-parallel conversion to a label packet of 2 bits. However, during a practical application, propagation loss at the delay lines has to be improved to support label packets comprising of a greater number of bits. The purpose of this article is twofold. First, we confirm that propagation loss can be lowered to sub-dB/cm values by introducing rib waveguides via simulations and experiment. Second, we demonstrate multibit serial-to-parallel conversion on a 4-bit label “1101” by utilizing a cascaded microring resonator device of which the straight sections of the delay lines are of rib waveguide architecture. In order to focus on free-carrier dispersion effect of silicon during operation, we left out a temporal delay between the pump pulses and probe bits to be extracted. As a result, serial-to-parallel conversion was viable even at peak pump power levels as low as ∼100 mW. We hereby verify that the proposed serial-to-parallel conversion scheme incorporated with rib waveguide delay lines is a realistic solution in realizing a photonics-based solution to all-optical label processing. [ABSTRACT FROM AUTHOR]

Integrating photonics with CMOS electronics in silicon is essential to enable chip-scale, electronic-photonic systems that will revolutionize classical and quantum communication and computing systems. However, the lack of an on-silicon isolator, capable of blocking unwanted back reflections and ensuring the stable operation of the laser, precluded many previous demonstrations from providing single-chip solutions. For most optical systems employing a laser, magneto-optic isolators have been indispensable, but such isolators are incompatible with silicon. To stabilize on-chip lasers, reflections-cancellation circuits were proposed as a way to reduce the reflections going back to the laser. Yet, a stable laser against time-varying back reflections was never demonstrated. Here we demonstrate a stable quantum well-distributed feedback (QWDFB) laser against slowly time-varying reflections using a reflections-cancellation circuit (RCC) on a foundry-produced, silicon-photonic (SiP) chip. The optical spectrum and the relative intensity noise (RIN) of the laser when the RCC was running is comparable to when an isolator was used. By accurately locking the laser in a stable optical feedback regime, the RCC further enhances the QWDFB laser performance by reducing its linewidth by a factor of 100, down to 3 kHz. Both results are enabled using novel techniques in the design, calibration, tuning, and control of the proposed SiP RCC. The optical insertion loss of the RCC is less than 1.5 dB for reflections smaller than −20 dB and can yield isolation ranges of up to 64 dB. Our device paves the way towards the mass production of fully integrated, low-cost electronic-photonic silicon chips without attaching magneto-optic isolators between the laser and the SiP chip. [ABSTRACT FROM AUTHOR]

Optical absorption of a guided light wave in a waveguide by a metal is undesirable in many photonic integrated devices. However, the heating due to the optical absorption enables to realize novel applications such as nonvolatile optical memories and all-optical thermo-optic devices. We report an efficient heating due to the optical absorption of an evanescent field by a metal heating layer deposited on a silicon microring resonator and consequent light-to-heat conversion. We investigate the design of the microring resonator by both theoretical and experimental approaches, which enable an efficient light-to-heat conversion. An enhanced thermo-optic effect by the optical absorption of the heating layer is observed. In addition, a heating efficiency larger than 40 K/mW is expected. [ABSTRACT FROM AUTHOR]

Presents the table of contents for this issue of the publication. [ABSTRACT FROM AUTHOR]

Optical isolators and circulators are fundamental building block in photonic integrated circuits to block undesired reflections and routing light according to a prescribed direction. In silicon photonics, heterogeneous integration of magneto-optic garnet bonded on a pre-patterned silicon layer has been demonstrated to be an effective solution for manufacturing optical isolators and circulators for TM polarized light. However, most integrated semiconductor lasers emit TE polarized light, which indicates the need to find a reliable solution for this polarization. In this paper, we demonstrated broadband optical isolators and circulators for TE polarized light based on heterogeneous bonding on the silicon photonics platform. To achieve this goal, an integrated adiabatic coupler and a broadband polarization rotator are designed and optimized. The nonreciprocal behavior is induced through an energy-efficient integrated electromagnet with a minimum power consumption of 3 mW. Two isolators/circulators are fabricated with small and large free spectral range, respectively. In the former case, an optical isolation ratio as large as 30 dB is measured at 1555 nm with an insertion loss of 18 dB, while for the broadband circulator, an optical isolation larger than 15 dB is guaranteed over more than 14 nm (1.75 THz) for all port combinations with an insertion loss between 14 and 18 dB at 1560 nm. Finally, it has been theoretically shown that the insertion loss can be reduced below 6 dB with design and fabrication improvements. To the best of the authors’ knowledge, the proposed integrated TE optical circulator is the first experimental demonstration of this device in silicon photonics. [ABSTRACT FROM AUTHOR]

We demonstrate a technique to precisely control and stabilize the beat frequency of a photonic microwave signal generator based on beating the optical signals of two lasers on a high-speed photodetector. The approach does not require high-speed electronic circuitry, but allows the control of the generated signal frequency up to hundreds of GHz. The demonstrated technique can readily be integrated on a chip-scale device using heterogeneous silicon platform, opening possibilities for widespread use in signal generation, sensing, instrumentation, and communications. [ABSTRACT FROM PUBLISHER]

We investigate the effect of tunable filtered optical feedback on a commercial DFB laser edge coupled to a silicon photonic planar integrated circuit in which a tunable reflector has been implemented by means of a ring resonator-based add–drop multiplexer. Controlled optical feedback allows for fine-tuning of the laser oscillation frequency. Under certain conditions, it also allows suppression of bifurcation modes triggered by reflections occurring elsewhere on the chip. A semianalytical model describing laser dynamics under combined optical feedback from the input facet of the edge coupler and from the tunable on-chip reflector fits the measurements. Compensation of detrimental effects from reflections induced elsewhere on a transceiver chip may allow moving isolators downstream in future communications systems, facilitating direct hybrid laser integration in silicon photonic chips, provided a suitable feedback signal for a control system can be identified. Moreover, the optical frequency tuning at lower feedback levels can be used to form a rapidly tunable optical oscillator as part of an optical phase-locked loop, circumventing the problem of the thermal to free carrier effect crossover in the FM response of injection current-controlled semiconductor laser diodes. [ABSTRACT FROM PUBLISHER]

We propose a compact silicon-on-insulator polarization splitter-rotator (PSR). The PSR consists of an asymmetric bilevel lateral taper in an adiabatic directional coupler and convert TM0 mode to TE0 mode directly without changing the input TE0 mode. Compared to the previously reported PSR based on TM0 –TE1 polarization rotator connected to a TE1–TE0 spatial mode order convertor in series, the proposed PSR has a one-step mode conversion, and is inherently more compact. Beside, since the conversion is fully adiabatic, it preserves the benefits of large fabrication tolerance and operation bandwidth. The simulation results show that the TM0–TE0 polarization conversion loss is less than 0.5 dB from 1500 to 1700 nm and even less than 0.2 dB over the whole C-band. The TE0 –TE0 insertion loss is less than 0.01 dB from 1450 to 1750 nm. The polarization crosstalk is below –35 dB within 300-nm bandwidth. [ABSTRACT FROM PUBLISHER]

Raman amplification has been commercially utilized in optical transmission systems for more than a decade. The drive toward higher spectral density has increased the interest in Raman to improve system performance. This tutorial reviews the benefits of Raman amplification, defines methods to analyze system performance, and describes the issues involved with system deployment and operation. [ABSTRACT FROM PUBLISHER]

We investigated the core-width dependence of the birefringence of silica-based waveguides with different relative refractive index differences (Δ), namely a 0.75%-Δ GeO2-doped waveguide and a 5%-Δ Ta2O5 -doped waveguide. We revealed that the birefringence of the 0.75%-Δ GeO2-doped waveguide is almost the same as the stress-induced birefringence and that the 5%-Δ Ta2O5 -doped waveguide has a large geometrical birefringence. By utilizing the core-width dependence of the birefringence, we have successfully demonstrated a 0.75%-Δ polarization beam splitter (PBS) with an operating wavelength range of more than 150 nm and a dual-polarization optical hybrid including a compact 5%-Δ PBS with a polarization extinction ratio of more than 20 dB over the C-band. [ABSTRACT FROM AUTHOR]

The 40-year history of research on semiconductor lasers for high-speed long-distance optical fiber communications, so-called dynamic single-mode (DSM) lasers, is reviewed. DSM lasers include phase-shift distributed feedback (DFB) lasers, uniform DFB lasers, wavelength tunable (WT) distributed Bragg reflector lasers, WT distributed reflector lasers, and external reflector lasers. The vertical cavity surface emitting laser is also a type of DSM laser that is applied for rather short-distance communication. Photonic-integrated circuits with monolithic integration of DSM lasers with other devices, as well as photonic crystal lasers, have advanced significantly to support stable operation of photonic subsystems. The DSM laser is currently essential for most long-haul optical communications and transoceanic submarine cables, as well as medium-distance local area networks. Its application to sensing systems is another interesting area. [ABSTRACT FROM PUBLISHER]

A statistical model is proposed for estimating the chromatic dispersion in the passband of a filter using an arrayed waveguide grating (AWG) with random phase errors. The model is derived without assuming the independence of random errors and can be applied to AWGs with frequency-dependent array amplitude coefficients as well as conventional AWGs. The average and variance of the chromatic dispersion in the passband can be calculated by using simple expressions without random computation once the standard deviation and correlation of random phase errors are given. The behavior of the chromatic dispersion in a synchronized-router-based flat-passband filter consisting of a multiple-input AWG and cascaded Mach-Zehnder interferometers (MZIs) was investigated. The standard deviation of the chromatic dispersion monotonically increases with the standard deviation of random phase errors, and has a distinctive dependence on frequency. The average and standard deviation of the chromatic dispersion in the passband obtained by the model are in good agreement with those obtained by random simulation for both a synchronized-router-based flat-passband filter and conventional AWGs. [ABSTRACT FROM PUBLISHER]

The optical diode effect, which is useful for on-chip optical information processing, has been recently demonstrated in cascaded nonlinear silicon microrings. In this paper, a semianalytical model for the diode is described in details, which extends the scope of the coupled-mode theory for linear microresonators to nonlinear regime through perturbation theory. The nonlinear effects addressed include the Kerr effect, two-photon absorption, free-carrier effect, and thermo-optic effect (TOE). Nonlinear effective mode volumes that characterize nonlinearities in the lumped element model are expressed using fields in vector forms. Simulations of the optical diode based on our model show good agreement with the measured spectra, where a forward–backward transmission ratio of \sim 28 dB is observed at an input power of \sim 1 mW. Moreover, TOE is discerned as the dominant nonlinearity in determining the diode functionality with this model. Being capable of dealing with photon–photon, photon–electron, and photon–phonon interactions, the methodology used here can be generalized and applied to model other microresonator-based opto-electronic devices. [ABSTRACT FROM PUBLISHER]

The filtering performance of a synchronized-router-based flat-passband filter with random phase errors is analyzed. For this purpose, an analytical model of a synchronized-router-based flat-passband filter using a multiple-input arrayed waveguide grating (AWG) with phase errors is derived without the assumption of the independence of random errors so that the model can treat general types of phase errors. For average transmittance, we proposed the analytical model for the variance of transmittance for a multiple-input AWG to predict the deviation of the transmittance. By using the proposed analytical model, device performance can be estimated once the spectral information of phase errors is given. The analysis clarifies that the frequency dependence of crosstalk reflects the spatial spectral distribution of phase errors. We also compared the transmittance characteristics of the synchronized-router-based flat-passband filter with conventional Gaussian and flat-type AWGs. We found that the crosstalk in the synchronized-router type has a different behavior from those in the conventional types, i.e., the crosstalk in the synchronized-router type has a periodic behavior according to the function of the input router. The probability distribution of the transmittance of the flat-passband filter is also calculated by random simulation and compared with the result from the analytical model. The agreement between the model and the random simulation confirms that the proposed model is effective for analytically estimating the performance of a synchronized-router-based flat-passband filter with phase errors. [ABSTRACT FROM PUBLISHER]

Asymmetric slot waveguides with a magnetooptic material filling the slot are studied for their nonreciprocal phase shift properties. General properties and performance are first evaluated by a one-dimensional silicon slot waveguide model, to find optimal asymmetric waveguide profiles. The results are verified with a two-dimensional calculation for a realistic optimal waveguide structure. The achieved ratio of the waveguide nonreciprocal phase shift to the specific Faraday rotation of the magnetooptic material is at a level comparable with semiconductor waveguides having a garnet cladding. The geometry may be applied to silicon-based vertical slot waveguides for quasi-TE polarization, which provides integration potential with active components in Si photonic circuits. [ABSTRACT FROM PUBLISHER]

A liquid crystal tunable bidirectional isolator is proposed. A wave plate is employed to realize a wavelength interleaving function. If it works as a full wave plate, the corresponding light only may pass along a specific direction while the opposite way is isolated. However, for wavelengths that the light experiences a half wave plate, the isolator's passing direction is reversed. A liquid crystal cell is utilized to tune the isolator so that both the isolated wavelength and direction could be reconfigured. A 100-GHz channel-interleaved tunable bidirectional isolator is demonstrated with \sim \ 30 dB isolation in both directions. The spectral response at ITU grids are further flattened by using a wave plate stacking technique. [ABSTRACT FROM PUBLISHER]

Presents the table of contents for this issue of the publication. [ABSTRACT FROM PUBLISHER]

A tunable band-selection interleaver filter switch formed on a silicon-on-insulator (SOI) substrate for dense wavelength-division-multiplexing (DWDM) system was fabricated, and its fundamental performances were experimentally demonstrated. The device consists of monolithic integration of a Michelson interferometer (MI) structure with two arm-waveguides with different lengths, appropriately designed for ITU-grid separation, a phase-modulation electrode on one arm and tunable wideband Bragg gratings reflectors. An SOI rib waveguide structure with a medium mode size was adopted for low loss and easy fabrication. A bandwidth of the grating, formed by electron beam (EB) lithography and deep reactive-ion etching (Deep-RIE), was rather large of 4 nm at -10 dB transmission level, from which a large coupling coefficient of the Bragg grating of 105 cm-1 was evaluated. A large tuning range of the Bragg grating of 17 nm was obtained. An extinction ratio of the interleaver filter was about 18 dB, and the interleaving switching was also attained with an applied electric power of 50 mW and a switching speed of about 1 ms. [ABSTRACT FROM PUBLISHER]

By implanting nonreciprocal phase shifts (NPS) into a ring-coupled Mach-Zehnder interferometer (RCMZI) structure, wavelength-selective isolation can be obtained over a wideband range. Different transmission lineshapes and structures of the nonreciprocal RCMZI were examined to meet the requirements of multiwavelength usage. It was demonstrated that a multiwavelength isolation with wideband and high-peak isolation could be achieved with just a reciprocal ring-coupled arm and a nonreciprocal linear arm in a MZI structure. For 5% ring loss per loop, the ring power coupling ratio kappa has a tolerance of 0.06 to keep the 30-dB isolation band wider than 0.3 × FSR. Also, an isolator over C-band was designed to verify the feasibility and discuss the wavelength-dependence issues. [ABSTRACT FROM PUBLISHER]

The monolithic integration of optical isolators with semiconductor lasers has remained an unsolved problem in photonics. Challenges associated with fabrication and incorporation of new materials with conventional III-V semiconductors have resulted in many novel approaches. This paper discusses these different approaches and also presents a summary of our own work on the monolithic integration of optical isolators. [ABSTRACT FROM PUBLISHER]

A polarization-independent magneto-optical waveguide isolator using nonreciprocal phase shift for a TM mode is proposed. The isolator is a Mach-Zehnder interferometer (MZI) that is composed of transverse electric (TE)-transverse magnetic (TM) polarization converters and nonreciprocal phase shifters. The MZI induces a phase difference between the reciprocal TE and nonreciprocal TM modes that are converted to each other by the polarization converter. Since the design uses a nonreciprocal phase shift only for the TM mode, it allows fabrication of an integrated structure. This paper describes the principle of operation and its design. [All rights reserved Elsevier]. [ABSTRACT FROM PUBLISHER]

We demonstrate multi/demultiplexers with a very flat passband and small excess loss using a multi-input arrayed waveguide grating combined with a cascaded Mach-Zehnder interferometer structure. We also analyze the impact of coupling between input waveguides just before the input slab on chromatic dispersion and investigate a waveguide structure for reducing the chromatic dispersion. We fabricated flat-passband multi/ demultiplexers with 100-GHz channel spacing using 2.5%-Delta silica waveguides and experimentally investigated the dependence of their optical characteristics on design parameters to demonstrate the effectiveness of the proposed theoretical model. We obtained a very flat passband response having a 1-dB bandwidth of 0.645-0.658 nm and 20-dB bandwidth of 0.944-0.960 nm with a loss penalty due to the passband-flattening of 0.9-1.0 dB and chromatic dispersion of -22.1-17.5 ps/nm over 0.5 nm in the passband. The measured passband shape and chromatic dispersion generally agreed with the simulation results. [ABSTRACT FROM PUBLISHER]

In this paper, the numerical studies on optical-bistability phenomena in third-, fifth-, and seventh-order nonlinear periodic media are presented. By cross-phase modulation with strong Gaussian pump, the continuous-wave probe transmission that operates in bistability regime can be permanently switched from low to high and vice versa using the property of the unstable state. While there is only one hysteresis in the third-order nonlinear periodic media, double hysteresis are observed in the nonlinear-transmission characteristics of pi phase-shifted periodic media with third-fifth and third-fifth-seventh-order nonlinearities. In the context of double hysteresis, unique-bistability regime is defined where the high state can be reached as input comes from low to high with fast enough rise time such that the output rises above the unstable state during its transient. Finally, all-optical transistor operation is shown as a prominent application of optical bistability based on the unstable-state principle [ABSTRACT FROM PUBLISHER]

The three-dimensional (3-D) beam-propagation method is applied to the analysis of a novel transverse electric/transverse magnetic (TE/TM) wave splitter using a light-guiding metal (Ag) line with an embedded dielectric (SiO2) waveguide. Before analyzing the splitter, a mode converter with a tapered metal is designed to smoothly convert the guided mode of an embedded waveguide into the surface plasmon-polariton (SPP) mode, and vice versa. After demonstrating the effectiveness of a converter consisting of a two-step linear taper, the performance of the splitter is evaluated. To obtain a high coupling efficiency, the wavefront mismatch of the SPP mode is compensated for. In addition, a TE-pass polarizer is added to the TE output waveguide, reducing the undesirable TM wave. In contrast to the long device length of a conventional branch-type splitter (>1000 mum), the present splitter is found to have a noticeably short device length of less than 200 mum, although a loss of about 3 dB is observed for the TM wave. The crosstalk and the extinction ratio are, respectively, evaluated to be less than -15 dB and more than 15 dB for a branching angle of 16plusmn2deg at wavelengths of 1.31 and 1.55 mum [ABSTRACT FROM PUBLISHER]

A novel all-optical header and payload separation technique that can be utilized in unslotted optical-packet-switched networks is proposed. The technique uses two modified terahertz optical asynchronous demultiplexers: One is for packet header extraction with differential modulation scheme, and the other performs a simple xor operation between the packet and its self-derived header to get the separated payload. The main virtue of this system is simple structure and low-power consumption. Through numerical simulations, the operating characteristics of the scheme are illustrated. In addition, the parameters of the system are discussed and designed to optimize the performance of the scheme [ABSTRACT FROM PUBLISHER]

We present a theoretical model of a multi-input arrayed waveguide grating (AWG) based on Fourier optics and apply the model to the design of a flattened passband response. This modeling makes it possible to systematically analyze spectral performance and to clarify the physical mechanisms of the multi-input AWG. The model suggested that the width of an input/output mode-field function and the number of waveguides in the array are important factors to flatten the response. We also developed a model for a novel AWG employing cascaded Mach-Zehnder interferometers connected to the AWG input ports and numerically analyzed its optical performance to achieve low-loss, low-crosstalk, and flat-passband response. We demonstrated the usability of this model through investigations of filter performance. We also compared the filter spectrum given by this model with that given by simulation using the beam propagation method [ABSTRACT FROM PUBLISHER]

In this paper, the authors review some of the recent advances in the theory of photonic crystals, drawing examples from their own work in magnetooptical and dynamic photonic crystals. The combination of theory and simulations shows that these crystal structures exhibit rich optical physics effects and can provide new ways to accomplish sophisticated optical information-processing tasks [ABSTRACT FROM PUBLISHER]

A novel technique to minimize the mode mismatch between the fiber and waveguide modes in integrating optical fiber to polymer waveguides is presented. The mode fields at the facets of the waveguides were tailored, optimizing the waveguide geometry as well as tuning the index of refraction of the lower cladding near the facets, by chemical composition. No additional processes were required after the core was deposited. The modified lower cladding can be integrated efficiently with any other lower-cladding material used in the remaining portion of the waveguide, resulting in hybrid waveguides. A power-coupling loss as low as 0.46 dB at the fiber-waveguide interfaces was demonstrated with the available fiber [ABSTRACT FROM PUBLISHER]

A 40-Gb/s asynchronous self-routing network and node architecture that exploits bit and packet level optical signal processing to perform synchronization, forwarding, and switching in the optical domain is presented. Optical packets are self-routed on a hop-by-hop basis through the network by using stacked optical tags, each representing a specific optical node. Each tag contains necessary control signals for configuring the node-switching matrix and forwarding each packet to the appropriate outgoing link and onto the next hop. In order to investigate the feasibility of their approach physical-layer simulations are performed, modeling each optical subsystem of the node showing acceptable signal quality and end-to-end bit error rates. In the All-optical self-RouTer EMploying bIt and packet-level procesSing (ARTEMIS) control plane, a timed/delayed resource reservation-based signaling scheme is employed combined with a load-balancing feedback-based contention-avoidance mechanism that can guarantee a high performance in terms of blocking probability and end-to-end delay [ABSTRACT FROM PUBLISHER]

A novel optical correlator employing an opto-very-large-scale-integration (VLSI) processor to construct the routing lookup table, in conjunction with an array of fiber Bragg gratings (FBGs) for multiwavelength optical header recognition is demonstrated. The FBG array provides wavelength-dependent time delays, whereas the opto-VLSI processor generates wavelength intensity profiles that match arbitrary bit patterns. The recognition of 4-b optical patterns is experimentally demonstrated at 2.2 Gb/s by showing that the correlator produces an autocorrelation waveform of high peak whenever the input bit pattern matches the wavelength intensity profile. [ABSTRACT FROM PUBLISHER]

The authors have fabricated transverse electric (TE) mode InGaAsP/InP active waveguide optical isolators based on the nonreciprocal loss shift and demonstrated improved TE mode isolation ratio of 14.7 dB/mm with reduced insertion loss at a wavelength of 1550 nm for monolithically integrable optical isolators. The wavelength dependence of the isolation ratio and the propagation loss were also measured. An isolation ratio greater than 10 dB/mm was realized over the entire wavelength range of 1530-1560 nm. These results lead to the monolithic integration of semiconductor waveguide optical isolators with edge-emitting semiconductor lasers and highly functional photonic integrated circuits with many cascaded optical devices. [ABSTRACT FROM PUBLISHER]

In the context of guided optics, the authors derive, analytically and geometrically, a rigorous general criterion to design wavelength-insensitive interferometers with mirror symmetry, which are needed for wavelength multiplexing/demultiplexing. The criterion is applied to a practical case, resulting in an interferometer that works on a band wider than 70 nm. [ABSTRACT FROM PUBLISHER]

This paper described a process that was developed for the active alignment of optical fibers to planar waveguides using a thermal-curing adhesive, in order to improve the performance and reliability of waveguide-based components. The process combines alignment at a temperature selected for adhesive curing with offline postthermal treatment of the aligned device that is suitable for volume manufacturing. A specially designed fiber-array holder and a waveguide-device holder were used to overcome the effects of temperature and stress on the alignment, simplifying the alignment from high temperature to room temperature. By studying the adhesive curing kinetics and the buildup of adhesive bonding strength, the alignment was tuned to balance performance and efficiency. Using this alignment process, fiber-to-waveguide couplings that provide low optical loss, strong bonding, and excellent reliability were achieved. [ABSTRACT FROM PUBLISHER]

In this paper, we demonstrate optical transparency in packet formatting and network traffic offered by all-optical switching devices. Exploiting the bitwise processing capabilities of these "optical transistors," simple optical circuits are designed verifying the independency to packet length, synchronization and packet-to-packet power fluctuations. Devices with these attributes are key elements for achieving network flexibility, fine granularity and efficient bandwidth-on-demand use. To this end, a header/payload separation circuit operating with IP-like packets, a clock and data recovery circuit handling asynchronous packets and a burst-mode receiver for bursty traffic are presented. These network subsystems can find application in future high capacity data-centric photonic packet switched networks. [ABSTRACT FROM PUBLISHER]

This paper investigates the effect of a high-refractive-index layer added onto the clad layer of an optical waveguide. With proper design, the value of the fundamental mode's confinement factor in the added layer can exhibit a resonance. This resonance depends on the added layer's location, thickness, complex index, and wavelength of operation. If loss is incorporated into this added layer, relatively small changes in waveguide properties can result in large changes in loss. This phenomenon is referred to in this paper as the resonant-layer effect (RLE). A number of devices, including isolators, polarizers, and modulators, can be made and/or improved by using the RLE. As examples, this paper describes an integratable isolator giving 240-dB/cm isolation and 13-dB/cm insertion loss, an integratable polarizer with 90-dB/cm rejection and about 0.8-dB/cm insertion loss, and a 300-μm-long modulator requiring electric fields of ±5 V/μm for ∼45% intensity modulation. In general, the resonant layer need not be epitaxial with the waveguide, allowing for integration with a variety of material systems. [ABSTRACT FROM PUBLISHER]

A new analytical formalism to study the effect of discontinuities in a nonreciprocal waveguide has been developed. The analysis is based on 1) the general orthogonality relation obtained from the reciprocity theorem, 2) the modal expansion of the transverse electromagnetic fields within the waveguide, and 3) the continuity of the tangential components of such electromagnetic fields at both sides of the discontinuity. The formalism is presented in a matrix form, which allows the treatment of several discontinuities as a simple summation and product of coupling and propagation matrices. The matrix formalism is developed for magnetooptic waveguides in the three different orientations of the magnetization, and, within this context, two practical applications of magnetooptic isolators are studied. [ABSTRACT FROM PUBLISHER]

Digital optical logic circuits capable of performing bit-wise signal processing are critical building blocks for the realization of future high-speed packet-switched networks. In this paper, we present recent advances in all-optical processing circuits and examine the potential of their integration into a system environment. On this concept, we demonstrate serial all-optical Boolean AND/XOR logic at 20 Gb/s and a novel all-optical packet clock recovery circuit, with low capturing time, suitable for burst-mode traffic. The circuits use the semiconductor-based ultrafast nonlinear interferometer (UNI) as the nonlinear switching element. We also present the integration of these circuits in a more complex unit that performs header and payload separation from short synchronous data packets at 10 Gb/s. Finally, we discuss a method to realize a novel packet scheduling switch architecture, which guarantees lossless communication for specific traffic burstiness constraints, using these logic units. [ABSTRACT FROM PUBLISHER]

We have fabricated GaP-AlGaP tapered waveguide semiconductor Raman amplifiers, and analyzed the effect of tapering in pulse-pumped high-gain operation. The finesse measurement and 80-ps pulse pumped Raman amplification experiment were performed. Although the tapering has caused additional optical loss, the highest gain of 23 dB has been obtained for a tapered waveguide with input facet of 6.0 μm2 and back facet of 2.9 μm2 at averaged input power of 170 mW (peak power 26 W). It is shown that the optical loss of the pump light is more severe than the linear optical loss of the signal light when the gain is higher than 20 dB. [ABSTRACT FROM PUBLISHER]