The increasing demand on the capacity of the communication system is pushing the industry into more advanced development stage, especially true for SONET/SDH TDM 10Gb/s systems. In addition to the long haul network, there is a big interest in short distance, low cost system suitable for local ring architecture around Metropolitan area. In this talk, we investigate directly modulated 10Gb/s DFB laser based transmitters. Both 1.3 micrometer and 1.55 micrometer DFB lasers are evaluated, including uncooled lasers. Since most of the installed fiber in the U.S. is conventional, non-dispersion shifted fiber, we also focus on chirp induced dispersion penalty using the 1.55 micrometer laser. Their performance is compared with some externally modulated transmitters, and experiments are conducted for transmitting over non-dispersion shifted fiber.

Two dimensional finite element analysis of the carrier transport in a 1.55 micrometer floating grating (FG) high power DFB to be used in conjunction with an external modulator as a high bit rate source, has shown that carrier accumulation and crowding for the etch-through grating layers resulted in current being diverted from narrow bandgap sections into the wider band gap sections of the grating. This augments undesirable heating and thermal degradation in laser L-I. To decrease this effect, three changes to the device parameters have been examined. Heavy doping and the use of wider bandgap FG region have been shown to reduce the thermal effects. Thinning the FG layer has little effect. A transfer matrix method (TMM) thermal model has been used to evaluate the performance of the improved structure. The results compared well with measured data and the analysis shows that efficiencies of 0.38 mW/mA and maximum power 100 mW for AR-cleaved are obtainable with the improved FG design.

The explosive growth in internet, multimedia and wireless traffic in recent years is rapidly exhausting capacity in public networks worldwide, forcing network service providers to aggressively install new lines and upgrade old ones. Fortunately, technological breakthroughs in the areas of erbium-doped fiber amplifiers (EDFA's), passive wavelength demultiplexers and low chirp sources have made all-optical dense wavelength-division multiplexed (WDM) systems a cost- effective way to utilize the vast bandwidth already available in the embedded fiber plant. WDM systems offer additional operational advantages, including high ultimate capacity, bit-rate transparency, flexible growth strategies, and the potential to use all-optical wavelength routing in future broadband network architectures. Commercial WDM systems operating at the OC-48 (2.5 Gbit/s) line rate are now available, and OC-192 (10 Gbit/s) terminal equipment which is under development will further enhance the capacity of these systems. One of the keys to viable WDM systems is the availability of inexpensive low-chirp optical transmitters. By taking advantage of photonic integrated circuit technology, it is possible to produce monolithically integrated DFB laser/EA modulators (EML's) with low chirp, low drive voltage and high extinction ratio, in a single compact package. In this talk we discuss the operating characteristics of these devices and their relationship to WDM system performance.

Very-low-driving-voltage (less than 1 Vpp) electroabsorption modulators operating at 40-Gbit/s NRZ large-signal modulation have been fabricated using strained InGaAlAs/InAlAs multiple quantum wells (MQWs). The optimum structure has been discussed with strain magnitude in the wells as a parameter, based on a figure of merit that is defined as the ratio of 3 dB bandwidth to the driving voltage. Blue chirp operation for low insertion loss with prebias has been demonstrated in addition to polarization insensitivity.

We review recent progress at Nortel Technology on the monolithic integration of a truncated-well 1 .55 im gain-coupled DFB with a Mach-Zehnder (MZ) modulator. Integrated MZ designs for both positive and negative chirp are described and analyzed. Link tests at 10 Gbit/s over 80 km ofnon-dispersion-shifted fiber (NDSF) show a negative dispersion penalty of 1 .1 dB, and steep BER curves with no evidence of flooring. The receiver sensitivity is found to be independent of pattern length, and independent ofthe laser operating wavelength, indicating negligible thermal, optical, and electrical crosstalk. Keywords: Integration, Mach-Zehnder, Gain-Coupling

High density wavelength division multiplexing (WDM), where the channels are 100 GHz to 200 GHz separated, is one of the approaches for increasing the fiber optic network capacity to meet the demand of transmitting the ever increased volume of multimedia information. To avoid crosstalk between adjacent channels, the precision of wavelength as well as the wavelength stability of the light sources need to be obtained and maintained throughout the system's service lifetime. Many techniques have been studied in recent years to improve the wavelength stability of semiconductor lasers for the applications in dense WDM systems. In this paper, approaches in achieving wavelength stability by wavelength referencing and locking are discussed. Concerns on depending on wavelength stability of the free running DFB lasers at the stage of mass deployment of multiple wavelength dense WDM systems also are presented.

Formed in January 1995, WEST is a DARPA-supported consortium investigating technologies for implementing add-drop and cross-connect switches operating at 10 Gbit/s. Using wavelength division multiplexing (WDM), each fiber supports 40 Gbit/s (4 by 10 Gbit/s) aggregate bandwidth for SONET/SDH operation. Consortium members include Rockwell Corporation, Ortel Corporation, UCSB, UCSD, UCLA, and Caltech/JPL.

WDM semiconductor sources with precise and stable wavelength registration are needed to fulfill the requirements of future high-speed, all-optical fiber networks. The source should meet the tight requirements on wavelength accuracy and stability over lifetime, high-speed operation, and low cost of future WSM systems. New fiber-grating based devices offer an attractive solution for such sources at a potentially lower cost than conventional DFBs.

Recent progress in the stabilization and ultrahigh- repetition-rate operation of mode-locked semiconductor diode lasers is described. Special attention is given to a new method for stabilizing the mode-locked LD at frequencies over several tens of gigahertz by optical pulse injection, and to methods for generating subterahertz and terahertz rate optical pulses and optical beats.

A tunable millimeter wave source is demonstrated using the frequency multiplication properties of a Mach-Zehnder modulator based analog fiber optic link. Extremely low phase noise millimeter wave output signals (minus 86 dBc/Hz at 1 kHz from a 40.96 GHz carrier) have been obtained using harmonic carrier generation by electrically overdriving the Mach-Zehnder modulator. This technique can be useful for high quality signal synthesis to 100 GHz, well beyond the modulation bandwidth of present optical modulators.

We review the properties of a new class of microwave oscillators called opto-electronic oscillators (OEO). We present theoretical and experimental results of a multi-loop technique for single mode selection. We then describe a new development called coupled OEO (COEO) in which the electrical oscillation is directly coupled with the optical oscillation, producing an OEO that generates stable optical pulses and single mode microwave oscillation simultaneously. Finally we discuss various applications of OEO.

A continuously tunable millimeter-wave optical transmitter is demonstrated by using a monolithic mode-locked semiconductor laser and an electro-optic modulator. By photomixing a microwave subcarrier with the selected harmonics of the mode-locked frequency, millimeter-wave subcarrier frequency transmission up to 300 GHz is achievable. Experimentally, subcarrier frequency continuously tunable from DC to 43 GHz is measured.

The generation of short optical pulses with a repetition rate up to 45 GHz has been realized by using a new method based on cw-light injection from one DFB into another cw operated DFB-laser with a proper frequency detuning. Extremely high extinction ratios of the pulsations could be controlled by two parameters: detuning and injection ratio. An optimized construction of the DBF-laser with respect to single-mode output power has been utilized. Two laser structures with ternary compressively strained In₇₀Ga₃₀As/In₅₃Al₂₃Ga₂₄As/InP and quaternary strain compensated In₇₁Al₉Ga₂₀As/In₃₄Al₂₁Ga₄₅As/InP multiquantum wells (MQW), respectively, provided very high speed in combination with high (greater than 20 mW) output power, low threshold current (less than 8 mA) and low temperature sensitivity (T_o equals 90 K). Comparison of characteristics showed the advantages of lasers with strain compensated MQWs.

As the requirement of transmitted power and the fiber span increase, the transmission fiber is no longer a completely transparent medium with respect to the system performances. The systems are affected by the presence of dispersion and non-linear fiber optics including SBS, SRS and SPM in the case of single transmission channel. In cases of WDM systems, FWM, XPM, and SRS will also participate in degrading the system. We discuss these effects manifested in the system parameters such as CSO, CTB and CNR. We also discuss options and demonstrations of numerous countermeasures rendering better system performance with drastically reduced degradation.

The properties of 1550 nm source lasers are examined in the context of 1550 nm supertrunk video transmission systems. Several key operating parameters such as output power, amplitude noise, and phase noise are investigated. A representative transmission link is simulated to show the system performance benefits of high-power 1550-nm source lasers.

We discuss our efforts in evaluating, planar, batch- fabricable, vertical-cavity surface-emitting lasers (VCSELs) for use in high-speed optical data communication interconnects. For this manuscript, we focus on the flexibility of the established proton-implanted AlGaAs-based (emitting near 850 nm) technology platform. These designs have more than adequately met performance and producibility stipulations. Demonstrated reliability is in excess of 10⁷ hours MTTF (at room T), and three-decibel modulation bandwidths of 15 GHz. We have also demonstrated a novel technique implementing a minor modification of the established platform to engineer low-threshold, high-speed, single-mode VCSELs. Said VCSEls are demonstrated in optical data links with bit error rates (BERS) less than 10^-12 under bias-free operation. Data link issues such as compliance with engineering standards are discussed.

The OPTOBUS^TM family of products provides for high performance parallel interconnection utilizing optical links in a 10-bit wide bi-directional configuration. The link is architected to be 'transparent' in that it is totally asynchronous and dc coupled so that it can be treated as a perfect cable with extremely low skew and no losses. An optical link consists of two identical transceiver modules and a pair of connectorized 62.5 micrometer multi mode fiber ribbon cables. The OPTOBUS^TM I link provides bi- directional functionality at 4 Gbps (400 Mbps per channel), while the OPTOBUS^TM II link will offer the same capability at 8 Gbps (800 Mbps per channel). The transparent structure of the OPTOBUS^TM links allow for an arbitrary data stream regardless of its structure. Both the OPTOBUS^TM I and OPTOBUS^TM II transceiver modules are packaged as partially populated 14 by 14 pin grid arrays (PGA) with optical receptacles on one side of the module. The modules themselves are composed of several elements; including passives, integrated circuits optoelectronic devices and optical interface units (OIUs) (which consist of polymer waveguides and a specially designed lead frame). The initial offering of the modules electrical interface utilizes differential CML. The CML line driver sinks 5 mA of current into one of two pins. When terminated with 50 ohm pull-up resistors tied to a voltage between VCC and VCC-2, the result is a differential swing of plus or minus 250 mV, capable of driving standard PECL I/Os. Future offerings of the OPTOBUS^TM links will incorporate LVDS and PECL interfaces as well as CML. The integrated circuits are silicon based. For OPTOBUS^TM I links, a 1.5 micrometer drawn emitter NPN bipolar process is used for the receiver and an enhanced 0.8 micrometer CMOS process for the laser driver. For OPTOBUS^TM II links, a 0.8 micrometer drawn emitter NPN bipolar process is used for the receiver and the driver IC utilizes 0.8 micrometer BiCMOS technology. The OPTOBUS^TM architecture uses AlGaAs vertical cavity surface emitting lasers (VCSELs) at 850 nm in conjunction with unique opto-electronic packaging concepts. Most laser based transmitter subsystems are incapable of carrying an arbitrary NRZ data stream at high data rates. The receiver subsystem utilizes a conventional GaAs PIN photo-detector. In parallel interconnect systems. The design must take into account the simultaneous switching noise from the neighboring systems. If not well controlled, the high density of the multiple interconnects can limit the sensitivity and therefore the performance of the system. The packaging approach of the VCSEL and PIN arrays allow for high bandwidths and provide the coupling mechanisms necessary to interface to the 62.5 micrometer multi mode fiber. To allow for extremely high electrical signals the OPTOBUS^TM package utilizes a multilayer tape automated bonded (TAB) lead frame. The lead frame contains separate signal and ground layers. The ground layer successfully provides for a pseudo-coaxial environment (low inductance and effective signal coupling to the ground plane).

Multifiber optic interconnects are attractive for high- throughput computer systems and asynchronous transfer mode (ATM) switching systems. We have developed a high- performance 10-fiber interconnect with each fiber operating at a high speed of 1 Gb/s. The modules have a receptacle for mechanically transferred push-on (MTP) multifiber push pull connector. The hermetic package is surface mount type and solder reflowable. The transmitter (Tx) is dc-coupled and the receiver (Rx) is ac-coupled with a cutoff of 7 kHz. The electrical interface is differential current mode logic (CML) or emitter coupled logic (ECL), and the optical interface is a 12-fiber connector. Single-mode glass fibers (9.5 micrometer) or multimode glass graded-index fibers (62.5 micrometer) were used. Tx contains a laser-driver IC, while Rx contains pre-amplifier and postamplifier, and comparator circuits. All the ICs are minus 5.2 V bipolar GaAs, and Tx plus RX consumes 4 W. The power in a fiber is about 100 (mu) W. The back-to-back skew is less than 80 ps. For a non-return-to-zero (NRZ) 2²³-1 pseudo-random bit stream, the error rate was less than 10 ^-12 with all the channels transmitting different signals simultaneously and a 100-m small-skew (1.2 ps/m) fiber ribbon. The link worked up to an atmosphere temperature of 80 degrees Celsius.

We present a 10 channel parallel fiber optic link consisting of a transmitter based on an edge emitting laser diode array operating at 980 nm and a complementary receiver based on an InGaAs pin photodetector array. We demonstrate link performance up to data rates of 1 Gbit/s with measurement time limited bit errors rates lower than 10^-11 over 100 m of multi-mode fiber ribbon cable.

This paper reviews recent advances made at our laboratories in device, circuit-design, and module-design technologies for future very-high-speed lightwave communications. ICs and modules developed using 0.1 micrometer gate-length InAlAs/InGaAs HEMTs demonstrate promising performance suited to 40-Gb/s applications.

Optical networks and their requirement for ever-increasing data rates provide a continuing challenge for electronic circuits. Here we review a number of circuits, implemented in heterojunction bipolar transistors (HBTs), and technologies that have been developed for 40 Gbit/s optical interconnection. These approaches include, multielement arrays for freespace, or guided transmission, wavelength division multiplexing (WDM) of several channels onto different wavelengths, and circuits that attempt to realized 40 Gbit/sec modulation rates directly by time division multiplexing (TDM). The circuit design challenges presented by these various approaches to 40 Gbit transmission are covered as well.

Recent progress in LiNbO₃ based high-speed external optical modulators is reviewed. Techniques to achieve broadband performance, such as, microwave-optical velocity matching, and elimination of coupling to dielectric substrate modes are addressed. The performance of different devices are compared by employing a frequency dependent half-wave switching voltage.

Semiconductor lasers have been the necessities of information infrastructure such as optical fiber communication and information storage. During the recent ten years, great progress has been made in China in the construction of her information infrastructure. As a basic component, semiconductor laser has also attracted much attention in academic research as well as development for industry. In China, there are several bases working on semiconductor lasers, such as State Key Laboratory on integrated optoelectronics, Institute of Semiconductors of Chinese Academy of Sciences, and Wuhan Telecommunication Devices Co., Ltd (WTD). In the State Key Laboratory on Integrated Optoelectronics, 1.3 micrometer and 1.55 micrometer InGaAsP/InP gain-coupled DFB, photonic integrated circuit (PIC), vertical cavity surface emitting lasers are being studied. Commercial class 670 nm visible lasers, 808 nm high power lasers for pumping sources, 1.3 micrometer and 1.55 micrometer InGaAsP/InP strained multiple quantum well (MQW) Fabry-Perot (FP) lasers for communications and 1.3 micrometer and 1.55 micrometer InGaAsP/InP DFB lasers have been developed in Institute of Semiconductors and WTD, respectively. Here, research and development activities on commercial class 670 nm visible laser diodes, 808 nm high power pumping lasers, 1.55 micrometer InGaAsP/InP gain- coupled DFB laser with an improved injection-carrier induced grating, high performance 1.3 micrometer and 1.55 micrometer InGaAsP/InP FP and DFB lasers for communication will be concentrated.