Showing papers in "Journal of Lightwave Technology in 2006"

Photonic-Crystal Fibers

Abstract: The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed

A tutorial on microwave photonic filters

Abstract: Microwave photonic filters are photonic subsystems designed with the aim of carrying equivalent tasks to those of an ordinary microwave filter within a radio frequency (RF) system or link, bringing supplementary advantages inherent to photonics such as low loss, high bandwidth, immunity to electromagnetic interference (EMI), tunability, and reconfigurability. There is an increasing interest in this subject since, on one hand, emerging broadband wireless access networks and standards spanning from universal mobile telecommunications system (UMTS) to fixed access picocellular networks and including wireless local area network (WLAN), World Interoperability for Microwave Access, Inc. (WIMAX), local multipoint distribution service (LMDS), etc., require an increase in capacity by reducing the coverage area. An enabling technology to obtain this objective is based on radio-over-fiber (RoF) systems where signal processing is carried at a central office to where signals are carried from inexpensive remote antenna units (RAUs). On the other hand, microwave photonic filters can find applications in specialized fields such as radar and photonic beamsteering of phased-arrayed antennas, where dynamical reconfiguration is an added value. This paper provides a tutorial introduction of this subject to the reader not working directly in the field but interested in getting an overall introduction of the subject and also to the researcher wishing to get a comprehensive background before working on the subject.

Free-Space Optical Communications

Abstract: With recent successes of laboratory, inatmosphere, and space demonstrations of free-space optical communications, there is no doubt that the technology is ready for operational deployment. While these successes have shown that there are no laws of physics against such systems, their estimated system costs are still much too high for serious considerations. Two types of development can reduce the cost dramatically. The first is via the improvement of physical-link communication efficiency by an order of magnitude using photon-counting receivers for vacuum channels, system complexity, weight, and power for space systems can be greatly reduced. The second is through the use of coherent systems in links where clear-air turbulence impairs communication efficiency, and in multiple access applications where coherent processing can reduce the level of interference, significant reduction in system costs can be realized

Silicon Photonics

Abstract: After dominating the electronics industry for decades, silicon is on the verge of becoming the material of choice for the photonics industry: the traditional stronghold of III-V semiconductors. Stimulated by a series of recent breakthroughs and propelled by increasing investments by governments and the private sector, silicon photonics is now the most active discipline within the field of integrated optics. This paper provides an overview of the state of the art in silicon photonics and outlines challenges that must be overcome before large-scale commercialization can occur. In particular, for realization of integration with CMOS very large scale integration (VLSI), silicon photonics must be compatible with the economics of silicon manufacturing and must operate within thermal constraints of VLSI chips. The impact of silicon photonics will reach beyond optical communication-its traditionally anticipated application. Silicon has excellent linear and nonlinear optical properties in the midwave infrared (IR) spectrum. These properties, along with silicon's excellent thermal conductivity and optical damage threshold, open up the possibility for a new class of mid-IR photonic devices

Microwave Photonics

Abstract: The low-loss wide bandwidth capability of opto-electronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. This paper reviews the development status of microwave photonic devices, describes their systems applications, and suggests some likely areas for future development

Optical Packet and Burst Switching Technologies for the Future Photonic Internet

Abstract: This paper reviews advanced optical burst switching (OBS) and optical packet switching (OPS) technologies and discusses their roles in the future photonic Internet. Discussions include optoelectronic and optical systems technologies as well as systems integration into viable network elements (OBS and OPS routers). Optical label switching (OLS) offers a unified multiple-service platform with effective and agile utilization of the available optical bandwidth in support of voice, data, and multimedia services on the Internet Protocol. In particular, OLS routers with wavelength routing switching fabrics and parallel optical labeling allow forwarding of asynchronously arriving variable-length packets, bursts, and circuits. By exploiting contention resolution in wavelength, time, and space domains, the OLS routers can achieve high throughput without resorting to a store-and-forward method associated with large buffer requirements. Testbed demonstrations employing OLS edge routers show high-performance networking in support of multimedia and data communications applications over the photonic Internet with optical packets and bursts switched directly at the optical layer

Advanced Modulation Formats for High-Capacity Optical Transport Networks

Abstract: Advanced optical modulation formats have become a key ingredient to the design of modern wavelength-division-multiplexed (WDM) optically routed networks. In this paper, we review the generation and detection of multigigabit/second intensity- and phase-modulated formats and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Fiber to the Home Using a PON Infrastructure

Abstract: Traffic patterns in access networks have evolved from voice- and text-oriented services to video- and image-based services. This change will require new access networks that support high-speed (> 100 Mb/s), symmetric, and guaranteed bandwidths for future video services with high-definition TV quality. To satisfy the required bandwidth over a 20-km transmission distance, single-mode optical fiber is currently the only practical choice. To minimize the cost of implementing an FTTP solution, a passive optical network (PON) that uses a point-to-multipoint architecture is generally considered to be the best approach. There are several multiple-access techniques to share a single PON architecture, and the authors addressed several of these approaches such as time-division multiple access, wavelength-division multiple access, subcarrier multiple access, and code-division multiple access. Among these multiple techniques, they focus on time-division multiplexing (TDM)-PON and wavelength-division multiplexing (WDM)-PON, which will be the most promising candidates for practical future systems. A TDM-PON shares a single-transmission channel with multiple subscribers in time domain. Then, there exists tight coupling between subscribers. A WDM-PON provides point-to-point optical connectivity using a dedicated pair of wavelengths per user. While a TDM-PON appears to be a satisfactory solution for current bandwidth demands, the combination of future data-rate projections and traffic patterns coupled with recent advances in WDM technology may result in WDM-PON becoming the preferred solution for a future proof fiber-based access network

Coherent detection of optical quadrature phase-shift keying signals with carrier phase estimation

Abstract: This paper describes a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals. At the receiver, a phase-diversity homodyne detection scheme is employed without locking the phase of the local oscillator (LO). To handle the carrier phase drift, the carrier phase is estimated with digital signal processing (DSP) on the homodyne-detected signal. Such a scheme presents the following major advantages over the conventional optical differential detection. First, its bit error rate (BER) performance is better than that of differential detection. This higher sensitivity can extend the reach of unrepeated transmission systems and reduce crosstalk between multiwavelength channels. Second, the optoelectronic conversion process is linear, so that the whole optical signal information can be postprocessed in the electrical domain. Third, this scheme is applicable to multilevel modulation formats such as M-array PSK and quadrature amplitude modulation (QAM). The performance of the receiver is evaluated through various simulations and experiments. As a result, an unrepeated transmission over 210 km with a 20-Gb/s optical QPSK signal is achieved. Moreover, in wavelength-division multiplexing (WDM) environment, coherent detection allows the filtering of a desired wavelength channel to reside entirely in the electrical domain, taking advantage of the sharp cutoff characteristics of electrical filters. The experiments show the feasibility to transmit polarization-multiplexed 40-Gb/s QPSK signals over 200 km with channel spacing of 16 GHz, leading to a spectral efficiency as high as 2.5 b/s/Hz.

Recent Advances of VCSEL Photonics

Abstract: A vertical-cavity surface emitting laser (VCSEL) was invented 30 years ago. A lot of unique features can be expected, such as low-power consumption, wafer-level testing, small packaging capability, and so on. The market of VCSELs has been growing up rapidly in recent years, and they are now key devices in local area networks using multimode optical fibers. Also, long wavelength VCSELs are currently attracting much interest for use in single-mode fiber metropolitan area and wide area network applications. In addition, a VCSEL-based disruptive technology enables various consumer applications such as a laser mouse and laser printers. In this paper, the recent advance of VCSEL photonics will be reviewed, which include the wavelength extension of single-mode VCSELs and their wavelength integration/control. Also, this paper explores the potential and challenges for new functions of VCSELs toward optical signal processing

Optical MEMS for Lightwave Communication

Abstract: The intensive investment in optical microelectromechanical systems (MEMS) in the last decade has led to many successful components that satisfy the requirements of lightwave communication networks. In this paper, we review the current state of the art of MEMS devices and subsystems for lightwave communication applications. Depending on the design, these components can either be broadband (wavelength independent) or wavelength selective. Broadband devices include optical switches, crossconnects, optical attenuators, and data modulators, while wavelength-selective components encompass wavelength add/drop multiplexers, wavelength-selective switches and crossconnects, spectral equalizers, dispersion compensators, spectrometers, and tunable lasers. Integration of MEMS and planar lightwave circuits, microresonators, and photonic crystals could lead to further reduction in size and cost

Optical frequency combs from semiconductor lasers and applications in ultrawideband signal processing and communications

Abstract: Modelocked semiconductor lasers are used to generate a set of phase-locked optical frequencies on a periodic grid. The periodic and phase coherent nature of the optical frequency combs makes it possible for the realization of high-performance optical and RF arbitrary-waveform synthesis. In addition, the resulting optical frequency components can be used for communication applications relying on direct detection, dense wavelength division multiplexing (WDM), coherent-detection WDM, optical time-division multiplexing, and optical code division multiple access. This paper highlights the recent results in the use of optical frequency combs generated from semiconductors for ultrawideband signal processing and communication applications.

Capacity Demand and Technology Challenges for Lightwave Systems in the Next Two Decades

Abstract: Ten to 20 years from now, optical networks will have to carry vastly increased amounts of Internet traffic. Today's knowledge (2006) already points to ultimate technology limits in the physical layer, foretelling the end of the so-called "Optical Moore's Law." Such an observation is discordant with the generic and optimistic view of a "virtually infinite" optical bandwidth combined with unlimited Internet-traffic growth. In order to meet long-term needs and challenges, therefore, basic research in wideband optical components and subsystems must be urgently revived today

Photonic microwave tunable single-bandpass filter based on a Mach-Zehnder interferometer

Abstract: The authors present the theoretical analysis and experimental demonstration of a novel single-bandpass tunable microwave filter. The filter is based on a broadband optical source and a fiber Mach-Zehnder interferometer and shows a high Q factor over a tuning range of 5-17 GHz. A generalized analysis considering that the optical signal propagates along optical delay lines with a dispersion slope different from zero is presented.

Design and optimization of microring resonators in biochemical sensing applications

Abstract: Microring resonators can be exploited for biochemical sensing applications. To gain a better understanding of the design and optimization of microring sensors, the authors analytically derive the detection limit and the sensitivity. Other important parameters, including the ON-OFF contrast ratio and the signal-to-noise ratio (SNR), are also considered. In this paper, the combination of two sensing mechanisms and two sensing schemes are analyzed. These calculations provide a guideline for determining the microring geometry to satisfy the desired sensing requirements. In addition, the results can provide insights on how to enhance the sensitivity and lower the detection limit

All-optical signal processing using /spl chi//sup (2)/ nonlinearities in guided-wave devices

Abstract: The authors present a review of all-optical signal-processing technologies based on /spl chi//sup (2)/ nonlinear interactions in guided-wave devices and their applications for telecommunication. In this study, the main focus is on three-wave interactions in annealed proton-exchanged periodically poled lithium niobate waveguides due to their suitable properties with respect to nonlinear mixing efficiency, propagation loss, and ease of fabrication. These devices allow the implementation of advanced all-optical signal-processing functions for next-generation networks with signal bandwidths beyond 1 THz. In this paper, integrated structures that will allow for improvements of current signal-processing functions as well as the implementation of novel device concepts are also presented.

OCDMA over WDM PON-solution path to gigabit-symmetric FTTH

Abstract: It will be revealed that a myth of deploying low bit-rate uplink fiber-to-the-home (FTTH) services while providing a high bit-rate downlink is wrong. Therefore, for the future broadband FTTH services, the focus should be on the capability to provide gigabit- or even multigigabits-per-second both in up- and downlinks, namely gigabit symmetric systems. Optical code-division multiple access (OCDMA) now deserves a revisit as a powerful alternative to time-division multiple access and wavelength-division multiple (WDM) access in FTTH systems. In this paper, the authors will first highlight the OCDMA systems. The system architecture and its operation principle, code design, optical en/decoding, using a long superstructured fiber Bragg grating (SSFBG) en/decoder, and its system performance will be described. Next, an OCDMA over WDM passive optical network (PON) as a solution for the gigabit-symmetric FTTH systems will be proposed. The system architecture and the WDM interchannel crosstalk will be studied. It will be shown that by taking advantage of reflection spectrum notches of the SSFBG en/decoder, the WDM interchannel crosstalk can be suppressed and can enable OCDMA over WDM PON to simultaneously provide multigigabit-per-second up- and downlinks to a large number of users.

Hybrid DWDM-TDM long-reach PON for next-generation optical access

Abstract: A novel long-reach passive optical network (PON) architecture based on hybrid dense wavelength-division multiplexing (DWDM) and time-division multiplexing (TDM) is presented as a possible candidate for the next generation of optical access networks. The approach combines access and backhaul functions in a single optical network infrastructure that links end customers directly to core networks without the need for intermediate electronic conversions. A centralized optical carrier distribution and wavelength-independent remote modulation scheme is employed to avoid the potential inventory and deployment costs associated with the use of wavelength-specific lasers in the customer transmitter (TX). The customer TX is based on an electroabsorption modulator (EAM) monolithically integrated with two semiconductor optical amplifiers (SOAs), providing sufficient net gain and bandwidth to support large splitting factors and upstream bit rates up to 10 Gb/s. The experimental results reported show that the network, with a total reach of 100 km and an upstream bit rate of 10 Gb/s, can potentially support 17 TDM PONs operating at different wavelengths each with up to 256 customers, giving an aggregate number of 4352 customers in total.

All-optical multiple logic gates with XOR, NOR, OR, and NAND functions using parallel SOA-MZI structures: theory and experiment

Abstract: The authors have proposed, simulated, and experimentally demonstrated all-optical multiple logic gates using two parallel semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) structures that enable simultaneous operations of various logic functions of XOR, NOR, OR, and NAND. The proposed scheme, which is optimized by adjusting the optical gain and phase differences in SOA-MZI structures with creative and systematic method, has great merits to achieve the reshaped output pulses with high extinction ratio and enable the high-speed operation at over 10 Gb/s through performance enhancement of SOAs. Its validity is confirmed through simulation and experiments at 2.5 and 10 Gb/s, respectively

Tunable lasers in optical networks

Abstract: Tunable lasers have been the subject of considerable interest ever since the start of the wavelength division multiplexing (WDM) revolution. In this paper, we bring together views on tunable lasers from different types of companies in the value chain, from operators to laser manufacturers. The purpose of the paper is to give an overview of the state of the art in both deployment and development, as well as to try to predict trends over the coming years.

The microfiber loop resonator: theory, experiment, and application

Abstract: This paper describes the theory of a microfiber loop resonator (MLR) and experimentally demonstrates a high quality factor MLR in free space. The MLR is fabricated from the /spl sim/1-/spl mu/m diameter waist of a biconical fiber taper using the CO/sub 2/ laser indirect heating technique. The high coupling efficiency of an MLR is achieved through an adiabatically slow variation of the microfiber diameter in the coupling region. An MLR-loaded Q-factor of 120 000 and an intrinsic Q-factor of 630 000 were demonstrated. As an application, the performance of an MLR as an ultrafast direct contact temperature sensor is also demonstrated. The MLR heating/cooling relaxation time was measured to be /spl sim/3 /spl mu/s, in good agreement with the developed theory.

Error-free all-optical wavelength conversion at 160 gb/s using a semiconductor optical amplifier and an optical bandpass filter

Abstract: Error-free and pattern-independent wavelength conversion at 160 Gb/s is demonstrated. The wavelength converter utilizes a semiconductor optical amplifier (SOA) with a recovery time greater than 90 ps and an optical bandpass filter (OBF) placed at the amplifier output. This paper shows that an OBF with a central wavelength that is blue shifted compared to the central wavelength of the converted signal shortens the recovery time of the wavelength converter to 3 ps. The wavelength converter is constructed by using commercially available fiber-pigtailed components. It has a simple configuration and allows photonic integration.

The Role of Optics and Electronics in High-Capacity Routers

Abstract: This paper examines the role of optical and electronic technologies in future high-capacity routers. In particular, optical and electronic technologies for use in the key router functions of buffering and switching are compared. The comparison is based on aggressive but plausible estimates of buffer and switch performance projected out to around 2020. The analysis of buffer technologies uses a new model of power dissipation in optical-delay-line buffers using optical fiber and planar waveguides, including slow-light waveguides. Using this model together with models of storage capacity in ideal and nonideal slow-light delay lines, the power dissipation and scaling characteristics of optical and electronic buffers are compared. The author concludes that planar integrated optical buffers occupy larger chip area than electronic buffers, dissipate more power than electronic buffers, and are limited in capacity to, at most, a few IP packets. Optical fiber-based buffers have lower power dissipation but are bulky. The author also concludes that electronic buffering will remain the technology of choice in future high-capacity routers. The power dissipation of high-capacity optical and electronic cross connects for a number of cross connect architectures is compared. The author shows that optical and electronic cross connects dissipate similar power and require a similar chip area. Optical technologies show a potential for inclusion in high-capacity routers, especially as the basis for arrayed-waveguide-grating-based cross connects and as components in E/O/E interconnects. A major challenge in large cross connects, both optical and electronic, will be to efficiently manage the very large number of interconnects between chips and boards. The general conclusion is that electronic technologies are likely to remain as integral components in the signal transmission path of future high-capacity routers. There does not appear to be a compelling case for replacing electronic routers with optically transparent optical packet switches

Future Optical Networks

Abstract: This paper presents views on the future of optical networking. A historical look at the emergence of optical networking is first taken, followed by a discussion on the drivers pushing for a new and pervasive network, which is based on photonics and can satisfy the needs of a broadening base of residential, business, and scientific users. Regional plans and targets for optical networking are reviewed to understand which current approaches are judged important. Today, two thrusts are driving separate optical network infrastructure models, namely 1) the need by nations to provide a ubiquitous network infrastructure to support all the future services and telecommunication needs of residential and business users and 2) increasing demands by the scientific community for networks to support their requirements with respect to large-scale data transport and processing. This paper discusses these network models together with the key enabling technologies currently being considered for future implementation, including optical circuit, burst and packet switching, and optical code-division multiplexing. Critical subsystem functionalities are also reviewed. The discussion considers how these separate models might eventually merge to form a global optical network infrastructure

Passive integrated optics elements based on long-range surface plasmon polaritons

Abstract: Waveguides and passive integrated optics elements constructed from thin metal films of finite width embedded in a homogeneous background dielectric and propagating long-range surface plasmon polaritons (LRSPPs) have been characterized experimentally at free-space optical wavelengths near 1550 nm. Straight and curved waveguides, s-bends, four-port couplers, y-junctions, and Mach-Zehnder interferometers have been carefully characterized. Additionally, rigorous models based on modal decomposition have been proposed for all of these elements and validated via comparisons with the measurements. Excellent qualitative and quantitative agreement between theory and experiment is observed for all structures over all measurement wavelengths. It is hoped that this work will help further establish this new integrated optics technology, taking it beyond demonstrators.

Evolution toward the next-generation core optical network

Abstract: With high-bandwidth and on-demand applications continuing to emerge, next-generation core optical networks will require significant improvements in capacity, configurability, and resiliency. These advancements need to be achieved with architectures and technologies that are scalable with respect to network cost, size, and power requirements. To investigate the limitations of extending today's solutions to meet these goals, a North American backbone network with a tenfold growth in traffic is modeled. The results of this paper illuminate at least three areas that will potentially require innovative solutions, namely 1) transmission modulation formats, 2) switching granularity, and 3) edge traffic grooming. In addition to probing issues related to increased capacity, configurability is also examined, mainly in the context of switching architectures. Advanced network protection is discussed as well, at a high level. A central theme is how to harness the trend of optics scaling better than electronics. Throughout this paper, potential advancements in architecture and technology are enumerated to serve as a foundation for the research needed to attain the goals of next-generation core networks

Optical properties of deep lamellar Gratings: A coupled Bloch-mode insight

Abstract: A coupled-Bloch-mode model for explaining various optical properties of strongly modulated subwavelength lamellar gratings is proposed. The model evidences the key role played by propagative Bloch modes, which bounce inside the grating and couple at the grating interfaces. Many optical properties of these gratings, such as their broadband reflectance, their polarization effect, and the presence of sharp anomalies, are understood as resulting from vertical resonances of the coupled-resonator modes. The approach provides a new insight on the physical mechanisms or optical behaviors observed, which is different from the classical study of the poles and zeros of the scattering operator.

Characterization of a full encoder/decoder in the AWG configuration for code-based photonic routers-part I: modeling and design

Abstract: A detailed description of the design guidelines for a full encoder/decoder that is able to generate/process a set of optical codes simultaneously is reported. The device has an array-waveguide-grating configuration, but the corresponding design rules are different from those of a multiplexer/demultiplexer. In an accurate model, based on diffraction theory, the slab diffraction effect and the loss nonuniformity are analyzed. Furthermore, the performance of the phase-shift-keyed codes simultaneously generated by the device and the corresponding packet-loss probability are also investigated.

Over-1000-channel ultradense WDM transmission with supercontinuum multicarrier source

Abstract: In this paper, ultradense wavelength-division multiplexing (WDM) transmission technologies are discussed, and a field demonstration of over-1000-channel ultradense WDM transmission is reported. The generation of an ultradense WDM signal using a supercontinuum multicarrier source that generates more than 1000 carriers and uniform precise channel spacing of 6.25 GHz is presented. The influence of four-wave-mixing generated in the transmission fiber and the requirements placed on the WDM multiplexer and demultiplexer is described. An over-1000-channel ultradense WDM transmission experiment is reported. A 1046 /spl times/ 2.67-Gbit/s 6.25-GHz-spaced ultradense WDM signal is successfully transmitted over 126 km of field-installed fibers in the test bed of JGN II.

Optical amplification and lasing by stimulated Raman scattering in silicon waveguides

Abstract: Achieving light amplification and lasing in silicon is one of most challenging goals in silicon-based optoelectronics. As a nonlinear optical effect, stimulated Raman scattering (SRS) provides a means to generate optical gain in silicon. Recent results of a nonlinear optics approach to optical amplification and lasing in silicon at the Photonics Technology Laboratory of Intel Corporation are reviewed. This paper starts with the description of the underlying physics related to the Raman scattering in silicon and experimental results of SRS in silicon waveguides. Then, it is shown that nonlinear optical absorption associated with the two-photon absorption (TPA)-induced free carrier absorption (FCA) is a dominant loss mechanism limiting optical gain in a silicon waveguide in addition to the linear optical scattering loss due to the waveguide sidewall roughness. The design and fabrication of a low-loss silicon waveguide containing a p-i-n diode to reduce the nonlinear optical loss are described. It is demonstrated that the free carrier density inside the waveguide can be reduced significantly with a reverse bias of the p-i-n diode. As a result, net optical gain in a silicon waveguide is achieved. The design, fabrication, and characterization of a Raman silicon laser are also described. Both pulsed and continuous-wave (CW) lasing in silicon are achieved using SRS