As lightwave transmission systems for comprehensive networks have deployed, optical components have been required to increase their performance functionality, to be more compact in size, to be lower cost, and to be highly reliable. Many activities for developing key optical components have been continued and we are now beginning to see cost effective solutions on 10Gb/s components and practical 40Gb/s components which are all key enablers for building such broadband lightwave systems. In this paper, we will address the state-of-the art of technologies for 10Gb/s and 40Gb/s optical components.

This paper discusses an intensity modulator for current 40G applications with a bandwidth exceeding 35GHz and a drive voltage of less than 5Vp-p (2.5V differential) at 1GHz. This device has also achieved an S11 of less than -13dB up to 35GHz, -10dB for 35-50GHz. We will discuss with some results for wider bandwidth.

We propose a newly designed X-cut lithium niobate (LiNbO3) optical modulator. It has a two-step back-slot structure to satisfy the velocity matching condition without the buffer layer of silicon dioxide (Si02). Accordingly, this modulator can achieve low drive voltage and low optical insertion loss. In addition, dc-drift phenomena due to the buffer layer can be suppressed This structure is fabricated with micro-machining technology using excimer laser ablation. The optical 3-dBe bandwidth of fabricated modulator reaches 30GHz and the drive voltage is less than 3V at 1kHz. From the measurement of optical eye diagram at 43.5-Gb/s, the RF-extinction-ratio resulted in 12dB with the drive voltage of 4.lVp-p. This modulator has the sufficient capability for 40-Gb/s optical transmission systems.

The operation of a semiconductor colliding pulse mode locked (CPM) laser has been analyzed using the time domain approach. In this approach the re-circulating transmission of a pulse through the various elements of the optical cavity such as the gain medium, the waveguide, and, the saturable absorber is carried out with the condition that the pulse must remain unchanged after one round trip. The pulse width of a CPM laser as a function of gain section current, saturable absorber current, and, modulation frequency has been measured. The laser is ~ 8.5 mm long and operates at a pulse repetition rate of ~ 10 GHz. The measurements and modeling results agree well. Both measured and calculated minimum pulse width is ~ 1 ps.

In this paper we will describe some of the latest developments in the area of optical sources for DWDM systems, including tunable lasers and multiwavelength sources. We will start by introducing the basic technologies used for DWDM sources. After that we will give an overview of the source options, and discuss tuning methods and wavelength control issues. The source options under discussion will include monolithic tunable lasers, hybrid structures and external cavity lasers, tunable VCSELs and wavelength selectable laser arrays. This will include both well established solutions and a number of new laser structures. Numerous specific examples will be shown, and the characteristics and performance of the various devices will be discussed. The key performance parameters, such as tuning range, power and switching speed will be related to the expected areas of application. These areas include sparing, fixed wavelength transmitter replacement, and use in wavelength switched networks.

The PIN/Preamp receiver modules suitable for 40 Gb/s optical communication systems are presented. The waveguide PIN photodiodes with a polarization insensitive spot size converter and a GaAs pHEMT traveling wave amplifiers (TWA), which have a typical transimpedance of 150 ohms and a linear operating output voltage more than 700 mVpp, have been assembled in hermetic sealed compact packages. The receiver modules have the responsivity greater than 0.72 A/W, the polarization dependent loss less than 0.2 dB in the wavelength range from 1510 nm to 1620 nm, 45 GHz bandwidth, and the input equivalent noise current density less than 15 pA/sqrtHz. The wide eye opening has been confirmed at the average optical input power of -12 dBm in both 40 Gb/s RZ and NRZ data format. The sensitivity less than -11 dBm has been achieved at BER = 1 x 10^-9 in 40 Gb/s PRBS 2^7-1 NRZ signal. These results indicate that this receiver module can be used not only in long haul application but also in the very short haul application.

Two types of waveguide photodiodes (WG-PD) - an evanescently coupled photodiode (EC-WG-PD) and a separated-absorption-and-multiplication avalanche photodiode (SAM-WG-APD) - have been developed for use in 40-Gbps receivers. The EC-PD is much more robust than a conventional WG-PD under high optical input operation because of its distributed absorbed optical power density along the light propagation in the waveguide. The EC-WG-PD simultaneously exhibited a high external responsivity of 0.96 A/W, a wide bandwidth of >40 GHz, and as high as 10-mA photocurrent operation. On the other hand, the SAM-WG-APD has a wide bandwidth of 30-35 GHz and a gain-bandwidth product of 140-180 GHz as a result of its small waveguide mesa structure and a thin multiplication layer. Record highest receiver sensitivities of -28.8 dBm at 10 Gbps and -19.6 dBm at 40 Gbps have been achieved for the first time.

In general, stress can create about the same change in the mdcx of refraction of an optical modulator as can a thermaloptic approach, but with a faster response, a smaller, simpler configuration and with less power needed to operate. Also, S-O's creates a greater change in the index than do other fields that are commonly used for modulation, such as with Electro-Optic's. The Stress—Optic technique is also durable. A 2 x 2 switch has been in operation at SeaLite Engineering since 1991; it has 1O'S cycles at 1 KHz. To implement this technology SeaLite Engineering is developing a Stress-Optic guided wave switch and technique as an add-on to a photonic integrated circuit substrate. Stress-Optic beam switching within a photomc integrated circuit can be fabricated in a nearly automated process where the S-O films are applied during the assembly of the planar waveguides. The S-O technique is fast (kHz to MHz, depending upon the circuit dimensions), low power (10's ofmicrowatts per cycle) and rugged (< lO"8cycles to date).

A two-mode interference photonic switch with high carrier injection has been designed and fabricated based on free-carrier plasma dispersion effect. It consists of an input Y-branch single-mode ridge waveguide, a two-mode waveguide coupling section, and an output Y-branch single-mode ridge waveguide. The boron doped silicon-germanium material was grown by molecular beam epitaxy and the devices were fabricated by using standard silicon technology. The ridge waveguides were formed by reactive ion etching technique and the input and output facets of the waveguides were ground and polished by a mechanical method. The switch was characterized by using a 1310 nm InGaAsP/InP hetero-structure laser diode. Its insertion loss and On-state crosstalk were measured to be 2.74 and -15.5 dB, respectively, at a total switching current of 110 mA. The switching time is 180 ns and the fastest switching time is up to 30 ns.

An optical interface is expected to solve the problems the electrical counterpart has. However, the conventional optical interface system using optical transceiver modules separately located from LSI packages on a printed circuit board (PCB), electrical interfaces among optical transceivers and LSI packages would limit interconnection speed. In addition, the electrical interface consumes a lot of power to drive the I/O buffers and signal lines on the PCB. To solve these problems, we have proposed a packaging technology to which OIP (Optical-interconnection as Intellectual Property) concept is applied. We developed a 3.125-Gbit/s/port crosspoint switch with 16 optical I/O ports on a 35x35-mm BGA package. It incorporates four small optical I/O modules called PETIT (Photonic/Electronic Tied InTerface).The PETIT consists of a 4-channel VCSEL array, a 4-channel pin-PD array, and a GaAs trans-impedance amplifier on an 8x8-mm ceramic substrate, and a newly developed optical connector interface is attached on the substrate. The sensitivity is 11.9 dBm under 12.5-Gbit/s full-duplex operation of the PETIT.

The current fiber optical communication system has evolved into a complicated multi-wavelength system with the deployment of Wavelength Division Multiplexing (WDM) networks. Many innovative technologies are desired to materialize its vast capacities and promises. MEMS technology has recently emerged as a competitive candidate to solve many technical challenges encountered in current WDM networks. Its applications have spanned from large scale optical switch fabrics such as optical cross-connects, optical add/drop multiplexers, to a large variety of active and passive optical components for transmission networks, such as tunable lasers and filters, dispersion compensation devices, amplifier gain equalizers, polarization controllers, and many others. In this paper we will discuss the current development status, promises and challenges, and the future prospects of MEMS technologies for optical communication, with a primary focus on MEMS-based optical cross-connects.

A new technology invented at JPL of active wavelength filtering on electro-optical switching of internal-reflection states have been proposed for use in DWDM, as add/drop multiplexers.

Equalization of power divergence over the wavelength spectrum is very important in optical WDM networks for optimizing the link performance and maximizing the transmission distance of the link, thereby reducing the cost/bit/km of transmission. In addition to extending the reach of long-haul networks, the ability to from a remote terminal to dynamically equalize the power level changes due to long-term aging of fibers and components, reduces system maintenance costs of today's point-to-point links. As the network evolves to include optical cross-connects and re-configurable optical add-drop nodes for agile and dynamic provisioning, the dynamic gain equalization function allows the ability to compensate the gain variation of the optical amplifiers resulting from varying input power levels. In this presentation we will talk about the DGEF based on silica-on-silicon technology. The device is based on cascading an arrayed waveguide grating (AWG) based de-multiplexer which separates the wavelengths into different bands, an array of Mach-Zhender interferometer (MZI) based attenuators, and an AWG-based multiplexer which recombines all the wavelength bands in to one fiber, all of which are monolithically integrated on one die. The dynamic tuning of the attenuation is achieved by varying the phase of one of the arms of the MZI using the thermo-optic effect. We will present the theory of the DGEF, talk about the control algorithm that is used to obtain the control parameters, and discuss the limitations of the device.

This paper describes a high performance dynamic gain equalizer (DGE) based on a diffractive MEMS structure, called the Grating Light ValveTM (GLVTM) device. The precise attenuation of the GLV-based DGE provides very low spectral ripple after equalization. Additionally, the GLV-based DGE has fine spectral resolution and high dynamic range. This paper will discuss applications of a DGE in optical networks, and experimental results showing performance characteristics of the GLV-based DGE are presented.

This paper reviews NTT Photonics Laboratories' recent progress on advanced photonic devices based on dielectric waveguide technologies such as silica-based planar lightwave circuits, LiNbO3 waveguides, and optical fiber.

In this work we have demonstrated that a single pulse generator, which cascaded two LiNbO3 modulators serially, may be used to demultiplex or drop a 10 Gb/s channel from a 40 Gb/s transmission system. The parts in the experiment are all commercially available, and this technique is scalable to higher speed transmission system.

This paper describes some of our recent results on semiconductor optical amplifier (SOA)-based monolithic functional devices for WDM networks. A WDM channel selector, which can select an arbitrary channel from WDM channels, will be discussed first. A monolithically integrated 64-channel selector on IriP substrate is demonstrated using a novel configuration that allows it to handle a large number of WDM channels. It is composed of two AWGs, SOA gates, and a multimode-interference coupler. The two key concepts are the use of the cyclic function of an AWG and two-step selection. Based on this configuration, the 64-channel WDM channel selector is realized with only 16 optical gates. Zero insertion loss was achieved for almost all channels in the fabricated device. Small sensitivity penalties with a typical value of 1.3 dB and fast channel switching of less than 1 .5 ns were obtained using the fabricated device. An all-optical wavelength converter will be then discussed. We have proposed a Sagnac interferometer integrated with parallel-amplifier structure (SIPAS) for filter-free all-optical wavelength conversion. A Mach-Zehnder interferometer with a SOA in each arm is monolithically integrated with a Sagnac interferometer. Wavelength conversion experiment was performed for lO-Gbitls RZ signal. Clear eye opening and low power penalty of 0.9 dB were achieved using the fabricated SIPAS.

All optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

Recent progress in dry etching technology of GaInAsP/InP compounds enabled realizations of fine vertical groove structures with a high aspect ratio. Since this technology enables the formation of etched mirrors in a wafer batch process, it leads to a low-cost production of not only simple Fabry-Perot lasers but also high performance and functional lasers for optical communications by integrating functional elements such as gratings for wavelength selection and high-reflectivity/low-reflectivity facets, while improvements in the size controllability with precision are still required. In order to keep an initial mask width condition during reactive-ion-etching (RIE) with methane/hydrogen mixture gas, we developed a sequential etching process of the RIE followed by oxygen ashing for relatively short period (for the etching depth of around 240 nm) and repeated the process for required etching depth. The tilt angle of the etched facet was controlled to be less than 1 degree from the normal to the wafer, and the aspect ratio of a narrow groove (140 nm) as high as 17 was obtained. By using this technique we could realize high-reflectivity distributed Bragg reflector (DBR) consisting of semiconductor/polymer pillars and DBR lasers with low threshold current (less than 10 mA for the stripe width of 5 micronmeter) and high differential quantum efficiency of 50 % from the front facet, while the emission spectrum showed a multi-mode operation due to poor wavelength selectivity. A preliminary aging test was carried out at room temperature CW condition, and no degradation was observed after 5,000 hours. With aiming at high performance single-wavelength lasers, we realized a novel distributed feedback (DFB) laser consisting of the first-order corrugations on the sidewalls of the stripe mesa, named ?gVertical Grating (VG),?h as well as a distributed reflector (DR) laser consisting of the VG-DFB structure and above mentioned DBR on the rear side. A stable single-mode operation with a sub-mode suppression ratio of 36dB, thre

Tunable/selectable-wavelength light sources are now beginning to play important roles in dense wavelength-division multiplexing (DWDM) optical transmission systems. Among the many types of the light sources, we have been developing distributed-feedback (DFB) laser-diode (LD)-array-based 'wavelength-selectable' light sources (WSLs), because of their stable and reliable wavelength properties. This paper reviews our recent progress with WSLs devices and WSL modules for wide-band DWDM applications. We start by describing eight DFB-array WSLs, each of which has a tunable wavelength range (Dl) of 15 nm. We took full advantage of an advanced form of selective metal-organic-vapor-phase epitaxy, which we call microarray selective epitaxy (MASE), in fabricating WSLs of six types on two wafers to fully cover the S-, C-, and L-bands. These WSLs demonstrated high fiber output power of up to around 10 mW and had stable single-mode properties. We also describe a 94-channel (50-GHz spacing) WSL module with an integrated multi-wavelength-locker. A wide-band WSL with a Dl of 40 nm for the L-band, was installed with a compact wavelength locker in a standard-sized 22-pin butterfly package. The WSL module showed a stable locking performance of within a 1-GHz range over time and against variations in temperature.

Wavelength tunable pulses with ~ 200 fs pulse width were generated by using a two stage pulse compression mechanism of gain-switched DFB laser pulses which were originally ~ 10 ps long. The pulse compression mechanism utilizes fiber nonlinearities and it involves propagation through specific lengths of various types of fiber and a nonlinear loop mirror. Simulation of the entire compression scheme by solving the nonlinear Schrodinger equation shows good agreement with the experiment results.

The requirements for 14XX nm pumps with wavelength range from 1400 to 1520 nm are not only higher output power but also lower degree of polarization (DOP) for preventing the problem due to the polarization-dependent-gain in Raman amplifier. It is expected that co-propagating Raman pumping could improve system performances in comparison with using only counter pumping. To apply this scheme, the pump lasers should have enough low relative intensity noise (RIN) characteristics. In this paper, we will describe two novel concepts in 14XXnm pumps for Raman amplifiers from above requirements. One is a low DOP-laser-module with ultra high optical output, achieving just one beam output with two-orthogonal polarization already scrambled from a SMF pigtail on a single package. The scrambled optical outputs is as high as over 1W and has DOP as low as 5% over the range of operating current. The other is an ultra low noise and wavelength stabilized laser with integrated partial grating in the laser cavity, that is, eliminating an external fiber-Bragg-grating. The laser showed low noise characteristics less than -150dB/Hz of RIN and the stabilized multi-longitudinal-mode oscillation. We also investigated the advantage of this laser in reduction or suppression of the stimulated-Brillouin-scattering induced by pump.

We present model calculations of gain at 1550 nm for Er-Yb double clad amplifiers as a function of pump power, signal input power, fiber length and temperature. The calculated gain is ~ 20 dB for 6W pump for 20 mW input signal at 25 C. More than 10 W of amplified power can be obtained using 8m long fiber with ~ 25 W of pump power. The gain decreases with increasing input signal. We show that a high power Er-Yb co-doped double-clad fiber amplifier also exhibits high gain for Yb transition near 1060 nm. This is not unexpected since the input pump causes population inversion in Yb also.

This article describes Raman fiber lasers and their application as pumps to a Raman amplified optical communication system. Single wavelength, multiwavelength and dual-order devices are described. The advantages of Raman fiber lasers compared to semiconductor diodes are also discussed.

Recent development on Raman amplifiers for WDM communication is reviewed. The design and demonstration of Raman amplifiers are summarized with concentration on Raman gain equalization by using multi-wavelength pumping scheme. Polarization dependence of Raman gain is measured against the degree of polarization of pump source. In order to realize stable and low degree of polarization, it is investigated how to design a passive depolarizer for pump laser diodes. Finally, a grating-integrated pump laser diode is developed in order to reduce relative intensity noise, which can cause severe degradation of amplifier characteristics.

PMD compensation is one of the requirements for deployment of 40 Gbit/s systems. In this paper, we discuss several important considerations in the design of PMD compensators. Issues regarding PMD-induced distortion detection, feedback and control algorithms in the presence of local minima, cost/performance tradeoffs, and interaction between PMD and other degrading effects (such as chromatic dispersion, PDL, and fiber nonlinearities) are among the topics that will be presented.

The variational method is a useful tool that can be used for design and optimization of dispersion-managed communication systems. Using this powerful tool, we evaluate the characteristics of a carrier signal for certain system parameters and describe several features of a dispersion-managed soliton.

NTT Electronics Corporation (NEL) provides active and passive photonic devices for WDM fiber optics networks and is contributing to the development and enhancement of optical communication systems. Active devices include uncooled DFBs that can be directly modulated at 10Gb/s up to 85C, 10 Gb/s EA-DFBs with EA driver, 10Gb/s photodiode module with pre-amplifier and limiting amplifier. Passive devices are PLC (Planar Lightwave Circuit)-based deices such as AWGs (Arrayed Waveguide Gratings) for wavelength MUX and DEMUX, for example, ultra-low loss AWGs with insertion loss of as low as 2 dB and optical matrix switches. The performance of these devices are discussed.

The problem of chromatic dispersion is well known and has long been a limiting effect in optical networks. The traditional solution for dealing with chromatic dispersion - dispersion compensating fiber - has a variety of drawbacks that limit its effectiveness in some 10 Gbps applications and in many 40 Gbps applications. Several new classes of tunable dispersion compensators have recently been developed to address these limitations. We will first review the causes and manifestations of chromatic dispersion and discuss the impact of residual chromatic dispersion, including its dependencies on transmission distance, bit rate, and data bandwidth. Then we will discuss the factors that create the need for tunability and examine how tunable dispersion compensators address these needs. Finally, we will review the technology behind currently available solutions for tunable chromatic dispersion compensation, including nonlinearly chirped fiber Bragg gratings, and contrast their advantages and disadvantages relative to the traditional solution of dispersion compensating fiber.

The impact of cascaded spectral Slicers on network performance is investigated in this paper. For a dispersive spectral Slicer, its dispersion is inversely proportional to the square of its channel spacing. When many narrow-band spectral Slicers are cascaded together, the total dispersion can cause significant penalty on system performance. We demonstrated the deleterious effects on system performance caused by the dispersion of cascaded spectral Slicers. To solve this problem, we applied a signal processing technique to design theoretically dispersion-free spectral Slicers. The design principle and simulation results of dispersion-free spectral Slicers are presented. Based on this signal processing technique, six dispersion-free 50-GHz Slicers were made and cascaded together. The total group delay ripples across spectrum within ±12GHz around center frequencies are less than ±0.8ps, which are much less than the group delay variation of ±14ps within the same bandwidth for dispersive Slicers. The power penalty of cascade dispersion-free Slicers is investigated by deploying them in a 16-channel OC-192 WDM (wavelength-multiplexing division) link. The measurement result shows no noticeable power penalty.

Although tunable fiber Bragg gratings are flexible and promising solutions for dispersion compensation, but we still have the problems of variable optical communication path characteristics, environmental fluctuations and the variety of applications, that require re-design and fabrication of fiber Bragg gratings for each case. An alternative novel technique of dispersion compensation based on adaptive fiber Bragg gratings scheme would overcome these problems. In this paper three different real time adaptive dispersion compensation schemes, are introduced; scheme based on pulse shape detection, scheme based on crosscorrelation detection and scheme based on pattern recognition.

Thin-film (TF) based dispersion compensators are of necessity some form of allpass filter. Whether these allpass filters are cast in the form of a coupled or a cascaded cavity structure, they can provide compact, low-loss, and highly stable dispersion compensation thereby having the potential of becoming important future components in both optical time-division multiplexing (OTDM) and wavelength division multiplexing (WDM) systems. In this paper, the salient points in the development of these devices are discussed up to the present state of the technology. Particular emphasis is placed on TF coupled cavity allpass (CCAP) filters as devices that provide only third-order dispersion compensation (TODC), having a group delay response that is purely quadratic. These CCAP filters are shown to have evolved over a number of important steps, from a hybrid two-cavity device, to a completely TF two-cavity single-surface filter, and finally to a dual-surface multi-reflection four-cavity device. The adjustable hybrid coupled cavity allpass filter provides TODC between 2.0 and 15.5 ps3 over a bandwidth between 3.6 and 1.2 nm respectively with a center wavelength tunable over an 8 nm range and the four-cavity multi-reflection completely TF device offers TODC between 0.37 ps3 and 3.2 ps3 over a 10 nm bandwidth with a center wavelength tunable over a 10 nm range. Important issues, such as the need to increase the TODC figure of merit, which is directly proportional to the number of cavities and the number of surface reflections, of these devices without incurring large loss penalties are discussed in the context of some of the important technological challenges that need to be addressed and solved before TF dispersion compensators can be effectively employed in optical systems as well as successfully compete with other existing dispersion-compensation technologies.

We report a strategy of industrialization of photonic-crystal based optical devices: We first review requirements for passive photonic crystal components. Although they have remarkable properties, they have at the same time severe difficulties such as difficulty of practical coupling to/from optical fibers and a relatively large propagation loss. This paper present an approach of meeting the requirements using heterostructured photonic crystals fabricated by autocloning. A low-loss, simple structured waveguide and sophisticated functional blocks (such as a resonator) can be integrated by a simple process. We first prepare a substrate patterned and corrugated by electron beam lithography and dry etching. Ta2O5/SiO2 mutilayers are repeatedly deposited on the substrate, and no other process is needed to complete the chip. After dicing and polishing, the waveguide can be butt-jointed with an optical fiber and the loss is estimated as 1.3 dB/mm. A resonator with Q = 270 is also demonstrated. Future outlooks of the technology are also discussed.

We demonstrate how dramatic increases in the induced phase shifts caused by small changes in the index of refraction can be achieved by using very slow group velocities of light, which are readily achievable in photonic crystal systems. Combined with the fact that small group velocity greatly decreases the power requirements needed to operate a device, enhanced phase sensitivity may be used to decrease the size and power requirements of many devices, including switches, routers, all-optical logical gates, wavelength converters, etc. We demonstrate how these advantages can be used to design switches smaller than 20*200 square microns in size, using readily available materials, and at modest levels of power. With this approach, one could have "4O such devices on a surface 2*2 square cm, making it an important step towards large-scale all-optical integration.

We report on the fabrication and optical characterization of photonic superlattices formed of colloidal photonic crystals. The superlattice periodicity induces the formation of minibands due to folding of the photonic band structure. This represents the first instance in which mid-gap states have been incorporated into a colloidal photonic crystal via a specifically engineered structural modification.

Light propagation characteristics of line defect optical waveguides in a photonic crystal slab are explained by the photonic band calculation and experimentally demonstrated at 1.5 micron wavelengths by using the SOI substrate. A high efficiency sharp bend, which is a key for high density photonic ICs, is numerically demonstrated by the FDTD method. The essential low propagation loss against the imperfection of the structure is discussed from the perturbation theory. On the other hand, light transmission characteristics of finite size uniform photonic crystals without defects are theoretically investigated for various applications. The superprism filter is analyzed from dispersion surfaces. The wavelength resolution parameter is defined, which includes the angular dispersion and the beam divergence of light, and the performance of the filter is esti-mated for the optimum design. As another application of the superprism effect, a light deflection device having angled out-put interfaces against the input interface is proposed and numerically demonstrated. The nonlinear response in a photonic crystal made of a Kerr medium is also calculated by the FDTD method. The enhancement of the nonlinearity observed at certain band edges are explained by the photonic band property. To improve the transmission efficiency of these devices, some modified input and output interfaces are proposed and their effects are numerically demonstrated.

Optically thin dielectric slabs, in which a fully etched through two-dimensional patterning is applied, can be used to form high-Q optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength. A cavity design strategy based upon simple group theoretical techniques is presented in which emphasis is placed upon a momentum space description of the resonant modes. It is shown that photonic crystal laser cavities can be designed with a particular wavelength, polarization, and radiation pattern using these methods.

We have experimentally demonstrated single-mode light-wave transmission and tunable waveguiding characteristics in photonic crystal (PC) waveguides constructed on a silicon-on-insulator (SOI) substrate as is most likely to be used for the a large scale integration of photonic circuits. Although off-plane diffractive leakage has been a serious problem in SOI-PC waveguides, we have overcome this problem in our narrow line-defect and phase-shifted-hole line-defect waveguide structures. These devices were developed through intensive theoretical studies on PC line-defect waveguieds. We have also demonstrated low-loss mode profile converter that will enable efficient connection between conventional silica-based waveguides and PC line-defect waveguides. The converter features an inversely-tapered silicon wire waveguide with an ultra-thin tip constructed on an SOI substrate. In our experiments, this converter proved capable of coupling loss as low as 0.5dB per conversion. These SOI-based devices represent an important step towards practical large-scale integrated photonic crystal circuits.

Photonic crystals are well known for their potentials for confining and guiding light in very small structures. Photonic crystals can also exhibit strong dispersion properties. These properties may offer many exciting opportunities for optical communication applications. In this paper, we discuss some of the basic principles for designing photonic crystal structures for optical communication applications, using examples for applications in polarization mode compensations, and add/drop filtering in wavelength division multiplexing.

Two optical functional devices based on 2D photonic crystal are investigated. First of all, add-drop filtering devices based on single defects in 2D photonic crystal slabs are characterized. After describing basic characteristics of channel-drop function, we show the improvement of device characteristics through defect engineering. We also demonstrate the channel-add function of the device. Next, we describe a 2D large-area surface-emitting laser exhibiting single-longitudinal and single-lateral mode oscillation with narrow divergence angle based on the 2D coupling effect of lightwave in 2D photonic crystals. A method of controlling the polarization mode by changing the shape of the unit cell is also presented. These results indicate that 2D photonic crystals are useful for the realization of novel optical functional devices.

Micro-lightwave circuit technologies based on photonic crystal slabs were studied to realize integrated photonic node circuits for use in photonic networks. First, a unique optical multi-exposure technique, which is suitable for drawing large-area, two-dimensional, photonic crystal lattice patterns, is introduced here. The relationship between the resolved pattern size and the light-beam wavelength used for exposure is also discussed. Next, a high-density optical interconnection technique with photonic crystal line-defect waveguides and Si channel waveguides is introduced. A low-loss connection structure for both waveguides and their low bending loss characteristics are also discussed. Furthermore, slab-type, photonic crystal-based optical devices, such as channel-drop filters and optical switches, for constructing the photonic node circuits were proposed and their characteristics investigated by FDTD simulations. A high wavelength resolution for the filters and extremely small switching power for the optical switches were predicted. Before fabricating the optical switches, directional couplers based on photonic-crystal slabs were fabricated and the basic properties of complementary power splitting to two output ports were demonstrated. These results strongly support the possibility of realizing integrated photonic node circuits with photonic crystals.

We present a systematic study of coupled defects in photonic crystals (PCs) and explore their applications in constructing optical components and devices for ultrafast all-optical signal processing. First, we find that very deep band gaps can be generated in the impurity bands of coupled cavity waveguides (CCWs) by a small periodic modulation of defect modes. This phenomenon implies a high-efficiency all-optical switching mechanism. The switching mechanism can be easily extended from one-dimensional (1D) to two-dimensional and three-dimensional PC structures by utilizing the coupling of defect pairs which are generally present in PCs. Second, we suggest that CCWs with quasiflat and narrow impurity bands can be employed as efficient delay lines for ultrashort pulses. Criteria for designing such kind of CCWs have been derived from the analysis of defect coupling and the investigation of pulse transmission through various CCWs. It is found that the availability of quasiflat impurity bands depends not only on the intrinsic properties of the constituting defects but also on the detailed configuration of CCWs. In experiments, optical delay lines based on 1D monorail CCWs have been successfully fabricated and characterized. Finally, we have proposed a new mechanism for constructing waveguide intersections with broad bandwidth and low cross-talk.

Recent progress on holey fibers is reviewed aiming at their application to optical communications. A holey fiber has an array ofair holes surrounding the silica core region. Light is confined to the core by the refractive index difference between the core and the cladding ofthe array of air holes. Holey fibers have special characteristics compared with conventional single mode fibers. One is that the zero dispersion wavelength is shifted to less than 1300 nm and therefore, high-speed transmission at the short wavelength region is possible. Another characteristic is that strong birefringence can be established by designing the size or arrangement of the air holes and is expected to realize a polarization maintaining fiber with high birefringence on the order of 1 x iO. This talk will describe the technology needed to design and fabricate holey fibers. Recent experimental results of a holey fiber with zero dispersion wavelength of 8 1 0 nm and a polarization-maintaining lowloss (1.3 dB/km) holey fiber are shown. The possibility oftheir application to optical communications is discussed.

The PCF with triangular lattice structure has the C, symmetry, the fundamental guided mode belongs to the C group, the third order guided mode belongs to the D31 group, we can simplify the computation by selecting the proper expend functions according to the symmetry ofthe modes. We have calculated the dispersion ofthe PCF with triangular structure and find the proper structure parameter with which the dispersion of fundamental mode at 1 .55jim can be zero. We also calculated the magnetic distribution of the third order guided mode of honeycomb-based PCF and proved that the interstitial holes in the PCF has no effect on the mode distribution.

In recent years several new classes of fibers have emerged based on the same basic technology platform-air/silica microstructures. While all of these fibers act as waveguides, each exhibit different optical properties leading to different applications. Out of these, photonic band-gap fibers are touted as the next generation long-haul transmission fiber. Since light propagates in air or vacuum, these fibers promise lower loss, lower nonlinearity and lower material dispersion. Low chromatic dispersion will undoubtedly be a crucial property of photonic band-gap fibers in long-haul applications. We will present experimental data that shows chromatic dispersion can be as low as tens of ps/nm/km at the transmission-spectrum center.

We will review the recent progress of high-speed photonic devices for next generation optical networks. We will concentrate on optical devices for 10Gb/s SONET/SDH and 10Gb/s Ethernet transponders as examples. Other phonic devices needed for next generation 1P over dynamically reconfigurable WDM networks to enable low-latency and highly efficient network connections will also be discussed here

This paper reviews some of the key enabling technologies for present and future optoelectronic integrated circuits. This review concentrates mainly on technology for lasers, waveguides, modulators, and fast photodetectors as the basis for next generation communication systems. Emphasis is placed on integration of components and mass production of a generic intelligent transceiver.

VCSEL devices for 850nm and 1300nm emission wavelength are presented, suitable for operation in single-channel interconnects as well as parallel optical links. Necessary properties for applications such as 10 Gigabit Ethernet and actual limits for the use of VCSELs are discussed in some detail. Recent progress is demonstrated in developing devices with production-friendly diameters larger than 5µm for 10Gbit/s operation. Also devices with a temperature insensitive monolithically integrated monitordiode are presented and discussed. In order to reach the emission wavelength of 1300nm with a GaAs-based monolithic VCSEL-structure, we use GaInNxAs1-x quantum-wells with a small nitrogen concentration x between one and two percent. We have two different growth approaches, such as solid source MBE with a rf-plasma source to produce reactive nitrogen from nitrogen gas N2 and MOCVD with unsymmetrical di-methylhydrazine as a precursor for nitrogen. The long-wavelength devices comprise intracavity contacts in order to reduce absorption losses due to doped layers. Bitrates up to 10Gbit/s per channel can be achieved within both wavelength regimes.

We have developed opto-electronic conversion module termed " active interposer" and polymeric waveguide film lamination technologies for optical interconnects between LSI chips. The fabricated active interposers are composed of VCSELs, MSM-PDs , submount and composed of Si circuits stacked via through-hole electrodes enabling high-performances. Also, waveguide film lamination technologies developed are capable of cost reductions. We present processing and test results of the fabricated optoelectronic devices suitable for 3D stacking as well as the high-speed transmission characteristics of the active interposers assembled on the PCB where polymeric waveguide film is lammated.

The present paper describes an emerging field, "Si microphotonics", and its application to on-chip interconnection beyond semiconductor roadmap. Current Si-LSIs have been facing three fundamental limits associated with metal interconnection; i.e., slow clock speed, multilayer interconnection for high density interconnects, and high power consumption. These limits are induced by "slow" signal messengers, electrons. There is no solution beyond the Cu and low k technology but optical interconnection. To implement optical clock distribution on a chip, one challenge is sharp bending of waveguides. High-index contrast optics has shown their significant potentials. Right angle bends have been proto-typed whose area is less than 1 tm2. Ge directly grown on Si wafers shows an excellent characteristics as photodetectors for 1.3 and 1 .55 tm. A high-density interconnection needs wavelength division multiplexing (WDM). Ultrasmall multiplexer/demultiplexer (DEMUX/DEMUX) has been achieved on a chip based on micro-ring resonators (1O tm). Minimization ofpower consumption is of importance when light sources are implemented on a chip. Microcavity resonators based on photonic crystal concepts should be a unique solution.

The application area of optical communication is expanding from trunk lines to subscriber loops, and local area networks (LAN). Optical components and their packaging technology also vary based on different application area. This paper describes the trends of key optical components and their packaging/module technologies for WDM application. The state-of-the art of technologies for 10Gb/s and 40Gb/s application are also included. Finally, future, module technologies will also be addressed.

Hybrid integration of optical and electrical components (opt-electronic hybrid integration) leads to great progress in low cost and high volume optical packaging. We have developed various types of opt-electronic hybrid integration Tx/Rx module. Recently, demand for transmission speed is increasing up to 10 Gbps in Metro, LAN networks. A new packaging technique is now requested to realize lower cost and high speed. This paper presents the advance of the opt-electronic hybrid integration technology. A new packaging platform is proposed after revealing the present opt-electronic hybrid integration Tx/Rx module, and the prototype 10G-Ether modules are introduced as a trial

With the development of all-optic network, the hotspot of the research is moving from the backbone network to the metropolitan network, and then to the access network. Much attention has been paid on reducing the cost in these networks. One approach is to adopt Ethernet passive optical network (EPON) architectures in an access network. In this paper a solution of EPON of Broadcasting/WDMA architecture is presented, which is based on several low-cost DWDM devices developed newly by authors, including the precise-wavelength DWDM-LD, DWDM demultipler with interleaver, DWDM receiver array, and dual-window broad-band coupler.

Passive alignment between the light source and coupling lenses may be one of the crucial and yet challenging technical fields to produce low-cost optical modules for telecom and datacom applications. In our presentation, we report the current status of our integration technologies of both surface and edge emitting type lasers with coupling lenses. We propose surfacemountable silicon microlens whose diameter is identical to a conventional optical fiber. The microlens can be passively aligned in the silicon v-groove to realize beam coupling between an edge emitting laser diode and an optical fiber. Coupling efficiency of -3.2dB between distributed feed-back laser diode and a single-mode fiber was experimentally confirmed. Precise rod shape is fabricated by D-RIE technology. We also report monolithic integration of the silicon substrate and a surface-emitting light source accomplished by direct bonding technology. The corresponding collimating lens is fabricated on the back-surface of the same silicon substrate. Passive alignment between the light source and the corresponding lenses are ensured by using a double-view mask aligner with sub-micron accuracy.

This presentation introduces a novel model for analyzing the optical interface performance degradation due to scratches on optical fiber endface. The model indicates that the contribution to the return loss of a scratch is determined by its size, location and its relative reflectivity, which is defined as the ratio of the average reflectivity of the scratch to the base reflectivity of the defectless endface. Based on this new model, the effects on return loss are analyzed for scratches of various numbers, different sizes, with different relative reflectivities, and at different locations. This quantified analysis provides a solid base to establish the specifications of inspection criteria of optical interface. With the new model, the relative reflectivity of a scratch was tested, and estimations of the return loss of scratched connectors were performed, which were in good agreement with measurement results.

The master equation of the actively mode-locked fiber laser is theoretically derived from the time domain for both of the harmonic and rational harmonic AM mode-locked cases when the RF modulating signal is not exactly tuned to the cavity length. It is shown that the existence of the introcavity dispersion will affect the pulse train properties as a function of the normalized detuning. The properties of the pulse train that depend on detuning are the carrier wavelength, the pulse width, the relative phase lag and the frequency chirp.

The most important feature of Raman gain spectrum is that the gain peak wavelength only depends on the pump wavelength (fixed shift about 100nm). Using the gain values of these gain peak wavelengths we can determine how to adjust power and intervals of pumps until the optimal result is made. In this paper, using the peak wavelength gain optimal method and a comprehensive model the Raman gain spectra of multi-pumped FRAs under the various conditions were investigated. The results show that controlling the pump sources power and wavelength intervals can optimize the bandwidth and flatness of gain spectrum. The optimal configuring method for the multi-pump sources of distributed FRAs is simple and effective.

For recently proposed 2-D lightwave circuits (LWCs) the architectural implications of introducing several wavelengths are discussed. Three types of 3-D architectures are considered (1) reconfigurable router (2) straight-forward extension of the 2-D LWCs of any geometry N 3 to 3-D by introducing several wavelengths at every waveguide (WG) and (3) mapping a generated network topology (which starts with the 2-D LWC) onto the 3-D LWC in (2). The architectures in (2) require the generation of the total number of permutations at every switch for non-blocking networks whereas the architectures in (3) allow (amongst others) for some switches the reduction of the number of permutations. The computation of the total number of permutations requires (i) a photonic feedback (FB) controller matrix at several wavelengths which provide rn! x k! permutations and additionally (ii) several frequency conversions (FCs) which complete the total number (m x k)! permutations where k is the size of switches and rn is the number of wavelengths.

This paper has reported the research of a scalable wavelength division multiplexing (WDM) optical routing system applied to the interconnection between CPU and MEM of distributed parallel computer. This system is built on DWDM and the optical switch array, which can connect CPUs and MEMs in a multigigabit WDM fiber, and so take advantage of high throughput, low-latency, error-free parallel transmission. And the paper has analyzed the performances degradation arising from super-speed and multi-wavelength, and put forward practical improvement measures. Furthermore the paper has designed a dual-window DWDM experimental system, and tested the data exchange between CPU and MEM. The purpose of this paper lies in exploring an optical WDM interconnection routing system which can not only be super-capacity, and reduce the complexity in implementation technologies, and also optimize the internal structures, or even external communication mechanisms of parallel computer.

Several tunable optical splitter techniques and some of their applications, including some prospective schemes, are discussed in this paper. It is explained by specific examples that all the variable transmission/reflection film technology, variable fiber couple length technology, acousto-optic/electro-optic deflection technology, and Mach-Zehnder interference technology are the capable technologies to realize tunable optical splitter, and tunable splitter technology to be applied to optical transmission networks, other devices and optical measurements.

In this paper, the process of fabricating coarse wavelength division multiplexing (CWDM) passive components using Fused Biconic Taper (FBT) technology is introduced. The performances and specifications of CWDM passive components are measured and reported. And we compare the performances and cost of this kind of CWDM module with the performances and cost of CWDM module based on thin-film-filter technology and dense wavelength division multiplexing (DWDM) module.

A new type flat-field arrayed waveguide grating (AWG) has been designed. The focal points of all wavelengths of operation distribute on a straight line. With parallel output waveguides, it¡¯s convenient to connect with fiber-array directly. Flat-field AWG could function as a spectrometer when the output waveguides are thrown off. The work based on the developed aberration theory of AWG. In this theory, the restrains imposing on the conventional Rowland-type AWG have been removed. Various restrains will generate new type structures. In the flat-field AWG design, the restrains come from the concurrent imaging theory. Three aberration-free points restrain three dominant geometry parameters of AWG, geometry of star couplers, phased array ports distribution, and length increment between adjacent paths. A 16-channel flat-field AWG is designed. As stigmatic points introduced, the aberration of the device is much lower than that of the conventional Rowland-type AWG.

A new method of distributed fiber Bragg grating sensors with a linear CCD array demultiplexing technique for the simultaneous measurement of pressure and temperature is described. The optical source is a dual-wavelength light-emitting diode (LED). The sensing probe incorporates five pairs of double-wavelength fiber Bragg gratings along a single fiber for measuring axial pressure and temperature simultaneously in oil and gas pipelines. A linear CCD array based spectrometer is used for tracing the wavelength shift of the Bragg grating sensors. The tests were carried out in oil and gas pipelines, pressure resolution is 0. 1 Psi, and temperature resolution is 0. 1 °C .The measurement range of pressure and temperature is 0—1 OOMPa and -20—1 80 C respectively.

We describe in this paper the architecture of a multiphase sinewave generator based on Direct Digital Synthesis techniques. This generator is used as the electric command of a 2?2 switch with an acousto-optic cell architecture using planar phased array piezoelectric transducers. This generator is able to adjust precisely the frequency and the phase of the RF signal on each transducer, and so to improve the switch performance.

Acousto-optic devices play an important role in the field of optical information and communication. For a few years, we have worked upon acousto-optic deflection in the Bragg regime, at 1.55 µm wavelength, by controlling the RF signal applied to the piezoelectric transducer. Recently, still using the acousto-optic interaction, we have taken an interest in the 2×2 switching function. In this paper, we present an acousto-optic switch architecture based on phased array transducers. In the same crystal, we superimpose two diffraction gratings created by two RF signals. Generating a phase shift on an RF signal applied between successive elementary transducers allows us to tilt one grating so as to interconnect inputs to outputs. In order to predict and to study some physical phenomena generated in this switch architecture, we present some characterizations made upon a mono-transducer cell. We point out the optical cross talk between output paths (influence of the intermodulation products due to the superimposition of two RF signals on the same transducer) and the electrical cross talk influence on optical diffraction efficiency.