Photonic Integrated Circuits Research Papers (original) (raw)

An electrically pumped light source on silicon is a key element needed for photonic integrated circuits on silicon. Here we report an electrically pumped AlGaInAs-silicon evanescent laser architecture where the laser cavity is defined solely by the silicon waveguide and needs no critical alignment to the III-V active material during fabrication via wafer bonding. This laser runs continuous-wave (c.w.) with a threshold of 65 mA, a maximum output power of 1.8 mW with a differential quantum efficiency of 12.7 % and a maximum operating temperature of 40 °C. This approach allows for 100's of lasers to be fabricated in one bonding step, making it suitable for high volume, low-cost, integration. By varying the silicon waveguide dimensions and the composition of the III-V layer, this architecture can be extended to fabricate other active devices on silicon such as optical amplifiers, modulators and photo-detectors.

The design, fabrication, characterization, and modeling of basic building blocks of plasmonic circuitry based on dielectric-loaded surface polariton waveguides, such as bends, splitters, and Mach-Zehnder interferometers are presented. The plasmonic components are realized by depositing subwavelength dielectric ridges on a smooth gold film using mass-production-compatible UV-photolithography. The near-field characterization at telecommunication wavelengths shows the strong mode confinement and low radiation and bend losses. The performance of the devices is found in good agreement with results obtained by full vectorial three-dimensional finite element simulations.

A new hybrid plasmonic waveguide is introduced and characterized in the paper. By coupling the photonic modes of a Si waveguide with the higher-order plasmonic modes of a silver nanowire, we demonstrate that the resultant hybrid modes possess small mode areas and long propagation distances, as well as high excitation efficiency (~90%) from the conventional dielectric modes. Such hybrid waveguides may find applications in the high-dense photonic integrations.

High-speed, tunable integrated silicon photonic delay lines are demonstrated by cascading complementary apodized silicon grating waveguides. The cascaded grating waveguides, with inward and outward super-Gaussian apodization profiles, compensate each other's dispersion and allow high-speed operation. Characterization of the compact delay lines shows that they have low loss, offer true time delays of 82 ps and a tuning range of 32 ps, and can potentially operate at bit rates as high as 107 Gb∕s.

- by saeed khan
- •
- Quantum Physics, Photonic Integrated Circuits, Optoelectronics, Optical physics

Recent remarkable advances in nanoscale siliconphotonic integrated circuitry specifically compatible with CMOS fabrication have generated new opportunities for leveraging the unique capabilities of optical technologies in the on-chip communications infrastructure. Based on these nano-photonic building blocks, we consider a photonic network-on-chip architecture designed to exploit the enormous transmission bandwidths, low latencies, and low power dissipation enabled by data exchange in the optical domain. The novel architectural approach employs a broadband photonic circuit-switched network driven in a distributed fashion by an electronic overlay control network which is also used for independent exchange of short messages. We address the critical network design issues for insertion in chip multiprocessors (CMP) applications, including topology, routing algorithms, path-setup and teardown procedures, and deadlock avoidance. Simulations show that this class of photonic networks-on-chip offers a significant leap in the performance for CMP intrachip communication systems delivering low-latencies and ultra-high throughputs per core while consuming minimal power.

- by Raha Tudu
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- Photonic Integrated Circuits, Routing algorithm, Deadlock Avoidance, Silicon Photonics

Microwave photonics (MWP) is an emerging field in which radio frequency (RF) signals are generated, distributed, processed and analyzed using the strength of photonic techniques. It is a technology that enables various functionalities which are not feasible to achieve only in the microwave domain. A particular aspect that recently gains significant interests is the use of photonic integrated circuit (PIC) technology in the MWP field for enhanced functionalities and robustness as well as the reduction of size, weight, cost and power consumption. This article reviews the recent advances in this emerging field which is dubbed as integrated microwave photonics. Key integrated MWP technologies are reviewed and the prospective of the field is discussed.

- by photon 2013
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- Quantum Physics, Signal Processing, Photonic Integrated Circuits, Silicon Photonics

Similar to the area of microelectronics, InP-based photonic integrated circuits (PICs) in the optical domain as a counterpart is also seeing a clear exponential development. This rapid progress can be defined by a number of active/passive components monolithically integrated on a single chip. Given the probability of achieving low-cost, compact, robust and energy-efficient complex photonic systems, there have been significant achievements made in realizing relatively complex InP-PICs in recent years. The performance of these complex PICs is reaching a stage that can enable a whole new class of applications beyond telecom and datacom. A great deal of effort from both academia and industry has made the significant advances of this technology possible. This development has resulted in a positive and profound impact in many areas including sensing, medical diagnostics, metrology, and consumer photonics. This review paper will mainly discuss the recent, in particular since 2012, progress and findings obtained out of current academic and industry research activities for InP-PICs. Major emphasis will be given to the high-performance and complex PICs that have been reported by the scientific community in this time period. A prospect for further development of this photonic integration in InP-platforms is also briefly described.

Optical resonators have micrometer size dimensions and come mostly in two flavors, namely circular and racetrack shaped microrings (MR), and microdisks (MD), although microsphere (MS) and photonic crystal microring (PCMR) resonators are also expected to gain prominence. Highly advanced fabrication techniques in recent years resulted in the reduction of propagation losses and in a remarkable increase of resonator Q factor and finesse. Newly developed microresonators are therefore ideally suited for applications in highly selective communication filters, delay lines, distributed and localized sensing, industrial measurements, microlaser mirrors and high-resolution spectroscopy. Since the optical signal recirculates and spends a relatively long time trapped in a high Q cavity, microresonators enhance light-light and light-particle interactions and are for this reason most promising to exploit nonlinear effects.

- by Otto Schwelb
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- Photonic Integrated Circuits, Photonic Crystals, Composites, Spectroscopy

We investigate the ''teleportation'' of a quantum state using three-particle entanglement to either one of two receivers in such a way that, generally, either one of the two, but only one, can fully reconstruct the quantum state conditioned on the measurement outcome of the other. We furthermore delineate the similarities between this process and a quantum nondemolition measurement. ͓S1050-2947͑98͒08812-X͔

We present the state of the art for commercial design and simulation software in the 'front end' of photonic circuit design. One recent advance is to extend the flexibility of the software by using more than one numerical technique on the same optical circuit. There are a number of popular and proven techniques for analysis of photonic devices. Examples of these techniques include the Beam Propagation Method (BPM), the Coupled Mode Theory (CMT), and the Finite Difference Time Domain (FDTD) method. For larger photonic circuits, it may not be practical to analyze the whole circuit by any one of these methods alone, but often some smaller part of the circuit lends itself to at least one of these standard techniques. Later the whole problem can be analyzed on a unified platform. This kind of approach can enable analysis for cases that would otherwise be cumbersome, or even impossible. We demonstrate solutions for more complex structures ranging from the sub-component layout, through the entire device characterization, to the mask layout and its editing. We also present recent advances in the above well established techniques. This includes the analysis of nano-particles, metals, and non-linear materials by FDTD, photonic crystal design and analysis, and improved models for high concentration Er/Yb co-doped glass waveguide amplifiers.

- by Marcio Freitas
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- Photonic Integrated Circuits, Photonic Crystals, Modeling, Nanoparticles

The described work is study and design of Multimode Interference based Thermo-Optic switch using Silicon on Insulator (SOI) technology. The main focus of this work is to analysis of thermo-optical switches. First, the physical principle of Thermo-Optics effect is briefly introduced. A comparative analysis of commonly used technology for fabrication of Thermo-Optic switches along with the materials is done.

- by Amit Pisal and +1
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- Optics, Photonic Integrated Circuits, Silicon Photonics, Optoelectronics and Photonics

We report a low-temperature process for covalent bonding of thermal SiO2 to plasma-enhanced chemical vapor deposited (PECVD) SiO2 for Si-compound semiconductor integration. A record-thin interfacial oxide layer of 60 nm demonstrates sufficient capability for gas byproduct diffusion and absorption, leading to a high surface energy of 2.65 J/m2 after a 2-h 300°C anneal. O2 plasma treatment and surface chemistry optimization in dilute hydrofluoric (HF) solution and NH4OH vapor efficiently suppress the small-size interfacial void density down to 2 voids/cm2, dramatically increasing the wafer-bonded device yield. Bonding-induced strain, as determined by x-ray diffraction measurements, is negligible. The demonstration of a 50 mm InP epitaxial layer transferred to a silicon-on-insulator (SOI) substrate shows the promise of the method for wafer-scale applications.

- by Di Liang
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- Photonic Integrated Circuits, Electronic Materials, Surface Chemistry, Optimization

Quantum information science has shown that harnessing quantum mechanical effects can dramatically improve performance for certain tasks in communication, computation and measurement. Already a number of photonic quantum circuits have been realized for quantum metrology, lithography and quantum logic gates. However, these demonstrations have relied on large-scale (bulk) optical elements bolted to large optical tables, thereby making them inherently unscalable and confining them to the research laboratory. This paper reports on the implementation of quantum optic integrated circuits, which not only dramatically reduces the footprint of quantum circuits, but allows unprecedented stability and control of the optical path length; this reveals the possibility for realizing previously unfeasible large scale quantum circuits. Results from femtosecond laser directly-written quantum circuits are also discussed. A large range of chip-scale "photonic building blocks" have been realized using this so-called direct-write technique and they include multimode optical interconnects, directional couplers and interferometers. The directly written quantum circuits exhibited high 2 and 3-photon Hong-Ou-Mandel (HOM) interference visibilities of 95.8% plusmn 0.5 and 84% plusmn 3% respectively.

- by Pruet Kalasuwan
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- Quantum Computing, Information Science, Quantum Optics, Quantum Information

In this paper, we review our work on efficient, broadband and polarization independent interfaces between a silicon-oninsulator photonic IC and a single-mode optical fiber based on grating structures. The high alignment tolerance and the fact that the optical fiber interface is out-of-plane provide opportunities for easy packaging and wafer-scale testing of the photonic IC. Next to fiber-chip interfaces we will discuss the use of silicon grating structures in III-V on silicon optoelectronic components such as integrated photodetectors and microlasers.

- by Muneeb Muneeb
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- Photonic Integrated Circuits, Packaging, Optoelectronics, Photodetectors

This paper presents the design of an index guided photonic crystal fiber which promises to yield very large birefringence (∼ 2.22 × 10 −2 ). Important optical properties, such as birefringence, single modeness, optical confinement, fiber dispersion, walk-off, etc., have been studied employing numerical simulation through finite difference time domain scheme. The fiber also promises a very small walk-off near optical communication wavelength.

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of 80 dBc/Hz at an offset of as low as 200 Hz. Hall, and S. T. Cundiff, " Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis, " Science 288(5466), 635–639 (2000). 2. J. Castillega, D. Livingston, A. Sanders, and D. Shiner, " Precise measurement of the J = 1 to J = 2 fine structure interval in the 2(3)P state of helium, " Phys.

- by Shamsul Arafin
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- Photonic Integrated Circuits, Phase Locked Loop, Tunable Diode Laser

We study the resonant transmission of light in a coupled-resonator optical waveguide interacting with two nearly identical side cavities. We reveal and describe a novel effect of the coupled-resonator-induced reflection (CRIR) characterized by a very high and easily tunable quality factor of the reflection line, for the case of the inter-site coupling between the cavities and the waveguide. This effect differs sharply from the coupled-resonator-induced transparency (CRIT) -- an all-optical analogue of the electromagnetically-induced transparency -- which has recently been studied theoretically and observed experimentally for the structures based on micro-ring resonators and photonic crystal cavities. Both CRIR and CRIT effects have the same physical origin which can be attributed to the Fano-Feshbach resonances in the systems exhibiting more than one resonance. We discuss the applicability of the novel CRIR effect to the control of the slow-light propagation and low-threshold all-optical switching.

Two-dimensional (2-D) compact photonic crystal reflectors on suspended InP membranes were studied under normal incidence. We report the first experimental demonstration of 2-D broadband reflectors (experimental stopband superior to 200 nm, theoretical stopband of 350 nm). They are based on the coupling of free space waves with two slow Bloch modes of the crystal. Moreover, they present a very strong sensitivity of the polarization dependence, when modifying their geometry. A compact (50 50 m 2 ) demonstrator was realized and characterized, behaving either as a broadband reflector or as a broadband transmitter, depending on the polarization of the incident wave. Experimental results are in good agreement with numerical simulations.

- by Haroldo Hattori
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- Photonic Integrated Circuits, Photonic Crystals, Membranes, Photonics

In this paper, temperature variations are detected thanks to an enhanced nano-optical pyroelectric sensor. Sensing is obtained with the pyroelectric effect of lithium niobate (LN) in which, a suitable airmembrane photonic crystal cavity has been fabricated. The wavelength position of the cavity mode is tuned 11.5 nm for a temperature variation of only 32 °C. These results agree quite well with 3D-FDTD simulations that predict tunability of 12.5 nm for 32 °C. This photonic crystal temperature sensor shows a sensitivity of 0.359 nm/°C for an active length of only ~5.2 μm.

- by Gwenn Ulliac
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- Photonic Integrated Circuits, Thermography, Nanotechnology, Systems Integration

The development of an innovative detector technology for photon-counting in X-ray imaging is reported. This new generation of detectors, based on pixellated cadmium telluride (CdTe) and cadmium zinc telluride (CZT) detector arrays electrically connected to application specific integrated circuits (ASICs) for readout, will produce fast and highly efficient photon-counting and energydispersive X-ray imaging. There are a number of applications that can greatly benefit from these novel imagers including mammography, planar radiography, and computed tomography (CT). Systems based on this new detector technology can provide compositional analysis of tissue through spectroscopic X-ray imaging, significantly improve overall image quality, and may significantly reduce X-ray dose to the patient. A very high X-ray flux is utilized in many of these applications. For example, CT scanners can produce ~100 Mphotons/mm 2 /s in the unattenuated beam. High flux is required in order to collect sufficient photon statistics in the measurement of the transmitted flux (attenuated beam) during the very short time frame of a CT scan. This high count rate combined with a need for high detection efficiency requires the development of detector structures that can provide a response signal much faster than the transit time of carriers over the whole detector thickness. We have developed CdTe and CZT detector array structures which are 3 mm thick with 16×16 pixels and a 1 mm pixel pitch. These structures, in the two different implementations presented here, utilize either a small pixel effect or a drift phenomenon. An energy resolution of 4.75% at 122 keV has been obtained with a 30 ns peaking time using discrete electronics and a 57 Co source. An output rate of 6×10 6 counts per second per individual pixel has been obtained with our ASIC readout electronics and a clinical CT X-ray tube. Additionally, the first clinical CT images, taken with several of our prototype photon-counting and energy-dispersive detector modules, are shown.

- by Jan Wessel and +1
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- Bioinformatics, Biomedical Engineering, Computed Tomography, Photonic Integrated Circuits

The broad development of the micro-and nano-technologies in the past few years increased the need of techniques capable of fabricating sub-micron structures with arbitrary surface profiles. Out of the several fabrication approaches (HEBS lithography, laser writing, etc.) the electron beam writing stands out as the one capable of the highest resolution, superior alignment accuracy and very small surface roughness. These characteristics make the technique greatly applicable in the fields of photonics and micro-opto-electro-mechanical-systems (MOEMS). Here we describe the specificity of fabricating 3D diffractive micro-and nano-optical elements using Leica EBPG 5000+ electron beam system. Parameters like speed of writing, dose accumulation, pattern writing specifics, etc. affect greatly the electronbeam resist properties and the desired 3D profile. We present data that can be used to better understand the different dependencies and therefore achieve better profile and surface roughness management. The results can be useful in future developments in the areas of integrated photonic circuits and MOEMS.

The optical phase locked loop (OPLL) photonic integrated circuit (PIC) is a key element for the emerging linear coherent RF-photonic links. One of the main challenges for the OPLL-PIC is the nonlinearity of the Indium Phosphide (InP)based phase modulator. In this paper, we report the experimental results from a multi-quantum well phase modulator fabricated on an InP substrate that is specially designed for the OPLL-PIC. The phase modulator shows low optical loss and good linearity performance. In particular, at a reverse bias voltage of 5.6 V, its phase IP3 and insertion loss per unit length are ~2.8π/mm and 1.2 dB/mm, respectively.

- by John Bowers
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- Photonic Integrated Circuits, High Dynamic Range, Radio Frequency, Quantum Wells

The large-scale photonic integration of microring resonators in three dimensions made possible by recent developments in vertical coupling and wafer bonding technology is shown to be sensitive to lateral mask misalignment for the ring and bus waveguides introduced during the fabrication process. For a typical 20-µm radius, vertically coupled microring calculations reveal a linear relationship between deviation in the coupling coefficient and lateral misalignment. A coupling coefficient reduction of 50% is predicted for a lateral misalignment of 0.3 µm, which is typical for an alignment accuracy limited by the current state-of-theart mask alignment process. The use of a wide multimode bus waveguide is proposed to ameliorate this alignment sensitivity. The mode-expanded bus waveguide, together with its physically wider structure, reduces the dependence of modal overlap and coupling length on precise alignment, resulting in significantly relaxed fabrication tolerance. Deviation of coupling coefficient decreases by an order of magnitude for the new ring coupler geometry, where a sole reduction of 5% is obtained for the same amount of misalignment. The implications of the proposed structure are subsequently investigated for microring laser performance. The differential slope efficiency is shown to be at least five times less sensitive to lateral misalignment for the proposed structure within a small misalignment regime. This readily adaptable coupler geometry based on existing vertical coupling architectures is transferable to any fabrication scheme with multiple waveguide layers coupled vertically, and is of particular importance to microring resonators with small radii.

Waveguiding of surface plasmon polaritons by dielectric-loaded metal structures is studied in detail by combining numerical simulations and leakage radiation microscopy. These types of waveguides are first numerically investigated using the effective index model and the differential method. We analyzed systematically the influence of the ridge width and thickness of the waveguide on the properties of the surface plasmon guided modes. In particular we investigated the confinement factor of the modes and their associated propagation lengths. These two parameters can be optimized by adjusting the thickness of the dielectric layer. Waveguides loaded with thick and thin dielectric ridges are then optically characterized by leakage radiation microscopy. The mode propagation distance is measured by direct-space imaging and the propagation constants are evaluated by Fourier imaging and analysis. Good agreements are found between theoretical and experimental data.

- by Laurent Markey
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- Engineering, Photonic Integrated Circuits, Applied Physics, Numerical Method

We demonstrate a monolithically integrated optical heterodyne receiver consisting of an input fiber waveguide, a single frequency distributed Bragg reflector (DBR) laser, a multimode interferometer-based 3-dB coupler, and a pair of semiconductor optical amplifier (SOA)/p-i-n modules using a single epitaxial growth based on asymmetric twin-waveguide (ATG) technology. The input signal was coupled into a fiber waveguide and mixed with the DBR local oscillator laser through the 3-dB coupler, and then coupled into the SOA/p-i-n modules for detection. Using this monolithically integrated optical receiver with a wide-band rectifier narrow-band amplifier receiver, a 3-GHz frequency modulated coherent analog optical link is demonstrated.

- by Fengnian Xia
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- Photonic Integrated Circuits, Epitaxial Growth, Optical Waveguides, Frequency

The paper proposes a low-cost scanning read-out IC architecture for large arrays of infra-red photon sensors operating at cryogenic temperatures. The low-power and compact 50×100 μm2 active pixel sensor area is achieved by the use of novel CMOS basic building blocks for single-capacitor integration and correlated double sampling, embedded pixel-test, pixel charge-multiplexing, video multiplexing and offset calibration. As a result, a low-cost 500×12 and 60 ns/pixel system-on-chip realization, capable of capturing high-resolution and real-time infra-red images, such as 640×500 @ 100 fps or 2560×500 @ 25 fps, is presented for a standard 0.35 μm CMOS technology.

- by César Mendez
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- Cryogenics, Photonic Integrated Circuits, Sensor Arrays, System on Chip

We put forward a new method to control the spectra of photon pairs generated in parametric downconversion that allows their spectral properties to be tuned from correlation to anticorrelation, including uncorrelation. The method employs tilted pulses and can be implemented in materials and frequency bands for which conventional methods do not hold.

- by Martin Hendrych
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- Quantum Physics, Quantum Optics, Photonic Integrated Circuits, Quantum Mechanics

This paper describes recent progress towards the development of an innovative light weight, high-speed, and selfpowered wireless fiber optic sensor (WiFOS™) structural health monitor system suitable for the onboard and in-flight unattended detection, localization, and classification of load, fatigue, and structural damage in advanced composite materials commonly used in avionics and aerospace systems. The WiFOS™ system is based on ROI’s advancements on monolithic photonic integrated circuit microchip technology, integrated with smart power management, on-board data processing, wireless data transmission optoelectronics, and self-power using energy harvesting tools such as solar, vibration, thermoelectric, and magneto-electric. The self-powered, wireless WiFOS™ system offers a versatile and powerful SHM tool to enhance the reliability and safety of avionics platforms, jet fighters, helicopters, commercial aircraft that use lightweight composite material structures, by providing comprehensive information about the structural integrity of the structure from a large number of locations. Immediate SHM applications are found in rotorcraft and aircraft, ships, submarines, and in next generation weapon systems, and in commercial oil and petrochemical, aerospace industries, civil structures, power utilities, portable medical devices, and biotechnology, homeland security and a wide spectrum of other applications.

- by edgar mendoza
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- Engineering, Aerospace Engineering, Physics, Photonic Integrated Circuits

We present the design of a 4-port photonic crystal-based optical circulator employing ring resonator cross connect filters, suitable for photonic integrated circuits schemes. This unique design allows the operation in both clockwise as well as counterclockwise directions and shows a calculated normalized transmission of over 80%. Since the spectra ranges cover the whole third communication window, any wavelength in these ranges can be circulated through the proposed photonic crystal-based optical circulator even different wavelengths at the same time. Published by Elsevier GmbH.

- by Moab Rajan Philip
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- Photonic Integrated Circuits, Photonic Crystals

We report a waveguide photodetector utilizing a hybrid waveguide structure consisting of AlGaInAs quantum wells bonded to a silicon waveguide. The light in the hybrid waveguide is absorbed by the AlGaInAs quantum wells under reverse bias. The photodetector has a fiber coupled responsivity of 0.31 A/W with an internal quantum efficiency of 90 % over the 1.5 μm wavelength range. This photodetector structure can be integrated with silicon evanescent lasers for power monitors or integrated with silicon evanescent amplifiers for preamplified receivers.

- by John Bowers
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- Photonic Integrated Circuits, Photodetectors, Optical physics, Quantum Well

A resonant tunnelling diode has been monolithically integrated with an optical communications laser [the resonant tunnelling diode (RTD-LD)] to form a simple optoelectronic integrated circuit (OEIC) that is a novel bistable device suitable for an optical communications system. The RTD-LD was based on a ridge-waveguide laser structure and was fabricated from an InAlGaAs-InP epi-wafer grown by molecular beam epitaxy; it emitted at around 1500 nm. Voltage controlled optical-electrical switching and bistability were observed during the characterisation of the RTD-LDuseful features for a fibre-optic communications laser.

—We use the direct temporal domain approach to design spectrally periodic optical filters for pulse repetition rate multiplication (PRRM) with envelope shaping. In particular, we demonstrate a tunable lattice-form Mach–Zehnder interferometer using Silica-based planar lightwave circuit (PLC) for arbitrary 4-bit binary amplitude code generation at 40 GHz and to increase the repetition rate of a 10 GHz input pulse train to 20 GHz or 40 GHz. In addition to PRRM and envelope shaping, the device also has the capability of arbitrary phase coding. Index Terms—Arbitrary binary code generation, Mach-Zehnder interferometers, optical arbitrary waveform generation, planar lightwave circuits, pulse repetition rate multiplication.

- by Payman Samadi
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- Photonic Integrated Circuits, Silica, Radio Frequency

A new way to make high speed modulators using Si waveguides is demonstrated. The hybrid silicon evanescent electroabsorption modulator with offset AlGaInAs quantum wells has an extinction ratio over 10dB and modulation bandwidth of 10GHz. The modulator has a clean open eye at 10Gb/s with sub-volt drive. A high-speed silicon optical modulator based on a metal-oxide semiconductor capacitor," Nature 427, 615-618 (2004).

- by John Bowers
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- Photonic Integrated Circuits, Telecommunications, Electronics, Silicon

We propose coupled-mode analysis of a two-dimensional photonic crystal add-drop filter based on ring resonators, which can be applicable to photonic integrated circuits. Mechanism of this proposed add-drop filter is analogous to that of ring resonators resonance, which involves interaction of waveguides and resonators. Simulation results of this filter obtained from the finite-difference time-domain method are consistent with those from the coupled-mode theory. Total transmission up to 99% is verified by both methods.

- by Mehrdad Djavid
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- Applied Mathematics, Photonic Integrated Circuits, Photonic Crystals, Photonics

We characterize bending losses of curved plasmonic nanowire waveguides for radii of curvature ranging from 1 to 12 µm and widths down to 40 nm. We use near-field measurements to separate bending losses from propagation losses. The attenuation due to bending loss is found to be as low as 0.1 µm −1 for a curved waveguide with a width of 70 nm and a radius of curvature of 2 µm. Experimental results are supported by Finite Difference Time Domain simulations. An analytical model developed for dielectric waveguides is used to predict the trend of rising bending losses with decreasing radius of curvature in plasmonic nanowires.

- by Marko Spasenovic
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- Optics, Photonic Integrated Circuits, Plasmonics, Nanowires

The spectrum of resonance frequencies in so called stand-alone resonators, built with coupled ring or disk resonators is analytically and numerically investigated. These composite resonators which constitute the core of numerous photonic circuits used in channel dropping filters, dispersion compensators, laser mirrors, etc., determine the width of their passband and their free spectral range (FSR). The spectral characteristics of the resonances are determined by the dimensions of the resonators and the strength of coupling between them. Novel relationships between these parameters are described that ensure invariance of the splitting ratios and as a consequence maintain the passband characteristics of the associated devices. Waveguide attenuation is found to have no effect on the spectral characteristics of the composite resonators.

- by Otto Schwelb
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- Photonic Integrated Circuits, Composites, Resonators, Dispersion

We demonstrate compact waveguide splitter networks in siliconon-insulator (SOI) rib waveguides using trench-based splitters (TBSs) and bends (TBBs). Rather than a 90° geometry, we use 105° TBSs to facilitate reliable fabrication of high aspect ratio trenches suitable for 50/50 splitting when filled with SU8. Three dimensional (3D) finite difference time domain (FDTD) simulation is used for splitter and bend design. Measured TBB and TBS optical efficiencies are 84% and 68%, respectively. Compact 105° 1 × 4, 1 × 8, and 1 × 32 trench-based splitter networks (TBSNs) are demonstrated. The measured total optical loss of the 1 × 32 TBSN is 9.15 dB. Its size is only 700 μ m × 1600 μ m for an output waveguide spacing of 50 μ m.

A III-V thin-film single-quantum-well edge-emitting laser is patterned on both sides of the epitaxial layer and bonded to silicon. Injected threshold current densities of 420 A / cm 2 for gain-guided lasers with bottom p-stripes and top n-stripes and 244 A / cm 2 for index-guided bottom p-ridge and top n-stripe lasers are measured with a lasing wavelength of ϳ995 nm. These threshold current densities, among the lowest for thinfilm edge-emitting lasers on silicon reported to date (to our knowledge), enable the implementation of integrated applications such as power-efficient portable chip-scale photonic sensing systems.

- by Sabarni Palit
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- Quantum Physics, Photonic Integrated Circuits, Photonics, Thin Films

For the compact integration of photonic circuits, wavelengthscale structures with a high index contrast are a key requirement. We developed a fabrication process for these nanophotonic structures in Silicon-on-insulator using CMOS processing techniques based on deep UV lithography. We have fabricated both photonic wires and photonic crystal waveguides and show that, with the same fabrication technique, photonic wires have much less propagation loss than photonic crystal waveguides. Measurements show losses of 0.24dB/mm for photonic wires, and 7.5dB/mm for photonic crystal waveguides. To tackle the coupling to fiber, we studied and fabricated vertical fiber couplers with coupling efficiencies of over 21%. In addition, we demonstrate integrated compact spot-size converters with a mode-to-mode coupling efficiency of over 70%.

- by S. Beckx
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- Photonic Integrated Circuits, Silicon on Insulator, Optical physics, High Index Contrast

The authors report, for the first time, a direct comparison between a directional coupler and a multimode interference-based device, in relation to their performance characteristics such as crosstalk, polarization dependence and the effect of fabrication tolerances. The coupling efficiency for a nonidentical coupler, produced inadvertently due to problems with fabrication tolerances, is also demonstrated. The vector finite element (FE) and the least squares boundary residual (LSBR) methods are employed as the numerical tools used in this simulation study.

- by Associate Professor Azizur Rahman
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- Optics, Medical Imaging, Fiber Optics, Finite Element Methods

Some new dielectric waveguide structures suitable for milfimeter-wave and optical integrated circuits are presented. A method of analyzing wave propagation in these guides is developed by assuming simple field distribution and approximating the various regions of the guides in terms of effective dielectric constants. The mathematical formulation utifized results in simple eigenvrdue equations from which the dispersion characteristics of the waveguides are readily obtained. Experimental results are described and the agreement between theory and experiment is shown to be quite good.

Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 m and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 m wavelength. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 m gap layer exhibit a coupling length of 62 m and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed.

- by John Bowers
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- Optics, Medical Imaging, Fiber Optics, Photonic Integrated Circuits