We report a substantial link budget improvement by biasing a DFB laser high above threshold. We demonstrate directly modulated 10 Gb/s transmission at 1550 nm over 80 km of standard single mode fiber. Our numerical simulations agree well with experimental results.

We have systematically studied modulation characteristics of an InGaAsP multiple quantum well laser diode in the temperature range between 300 K to 10 K. We show that the modulation bandwidth increases dramatically at lower temperature which can be attributed to dramatic increase of differential gain. Modulation characteristics at temperatures below 100 K show an additional low frequency roll off that cannot be accounted for by device parasitics. We discuss the origin of this effect in the context of the device carrier transport effects.

The transport of carriers along the confinement region, the carrier capture into, and the carrier escape out of the quantum wells (QWs) are limiting processes affecting the high-frequency properties of QW lasers. The influence of these processes on the laser performance depends mainly on the ratio of the effective carrier transport/capture time and the effective escape time. We present experimental results about the escape times for GaAs/AlGaAs and InGaAs/GaAs high-speed QW lasers with varied geometrical dimensions (cavity width and length), number of QWs, In-concentrations, and p-doping levels in the active region, as extracted from electrical impedance measurements in the sub-threshold regime. In addition to the expected increase of the escape time with increasing QW barrier height, we observe an important increase in the escape time for lasers with p-doping. The escape time dependences on the carrier concentration and on the temperature are determined and discussed.

Mode-locked semiconductor lasers have drawn considerable attention as compact, reliable, and relatively inexpensive sources of short optical pulses. Advances in the design of such lasers have resulted in vast improvements in pulsewidth and noise performance, at a very wide range of repetition rates. An attractive application for these lasers would be to serve as alternatives for large benchtop laser systems such as dye lasers and solid-state lasers. However, mode- locked semiconductor lasers have not yet approached the performance of such systems in terms of output power. Different techniques for overcoming the problem of low output power from mode-locked semiconductor lasers are discussed. Flared and arrayed lasers have been used successfully to increase the pulse saturation energy limit by increasing the gain cross section. Further improvements have been achieved by use of the MOPA configuration, which utilizes a flared semiconductor amplifier stage to amplify pulses to energies of 120 pJ and peak powers of nearly 30 W.

We report on monolithically integrated active/passive coupled cavity mode locked lasers for 1.55 micrometer realized by selective area growth technology of InGaAs(P) quantum wells. Mode locked FP or DBR lasers are fabricated with an integrated cavity comprising up to three different band gaps. The devices emit short light pulses at around 10 GHz repetition rate with pulse width down to 8.7 ps. A time-bandwidth product of 0.5 is achieved for mode locked DBR lasers. Active/passive integrated mode locked laser is used for generation of optical 10 GHz clock signal from optical 10 Gb/s PRBS RZ data stream injected into the laser cavity.

Experimental results from directly modulated semiconductor lasers at 30 Gbit/s are presented. Critical problems for 30 Gbit/s electronic TDM systems are discussed as well as advances in component technology for 30 Gbit/s transmission systems.

We review data on the high temperature operation of a high speed data link operating at 1 micrometer wavelength. The single mode fiber packaged transmitter consists of an 'uncooled' high speed laser diode packaged with a commercial laser driver chip and operates at data rates up to 1.2 Gbit/s. The single mode fiber packaged receiver consists of a high speed photodiode packaged with a combination of a commercial transimpedance amplifier and a limiting amplifier. The link operates with high stability and very low error rates without an optical isolator. The maximum data rate and the minimum link sensitivity are currently limited by the electronic component design.

Prior to the full maturation of electro-absorption modulated laser technology, directly modulated 1.55 micrometer distributed feedback lasers will continue to play a central role in long haul, high bit rate, optical communications systems. Maintaining a competitive advantage, however, requires that these devices be optimized for long fiber length transmission, high power, and low cost. In this talk we discuss the design elements needed to accomplish this. Focus is placed on factors leading to reduction of the linewidth enhancement factor, (alpha) . In particular, the role played by complex gratings is examined. We demonstrate typical cw (alpha) values of 1.65 can be achieved in a robust and manufacturable device. This device is shown to readily serve 2.5 Gb/s applications with span lengths of 200 km (approximately 3600 ps/nm).

The role of push-pull design in electronics is well known. In this paper this role is examined in connection with split contact DFB lasers. Two or three contacts combined with push-pull modulation permit the energy to be moved laterally back and forth in the laser without changing, while modulating the output. Links between changes in the stored energy and the dynamic chirp are examined showing that changes in the symmetry of the push-pull current drive allow one to tailor the chirp so as to minimize dispersion for a given structure and fiber. Push-pull operation changes the fundamental resonances that limit speed of modulation in the laser and in particular the classic photon-electron resonance is replaced with a structural dependent resonance. For a given gain in the laser it appears that push-pull operation offers higher modulation bit rates as well as the potential for controlled chirp. The intrinsic equivalent circuit for push-pull operation of a DFB is shown to have three poles and the design compromises for operation at 50 and 100 Gb/s are discussed briefly.

Using a well-characterized measurement system having 22 GHz bandwidth, we show that the relative intensity noise (RIN) of a commercial InGaAsP laser (multi-longitudinal mode) operating at 77 K is significantly reduced below room temperature values over a broad frequency range. For laser operation with equal drive currents at both temperatures, a RIN reduction of as high as approximately equal to 24 dB/Hz is observed in the frequency region of relaxation oscillations, while for operation with equal power outputs the maximum reduction observed is approximately equal to 14 dB/Hz.

The effect of nonradiative Auger and Shockley-Hall-Read recombinations and nonlinear gain on an InGaAsP/InP (A.=1.3 μm) and AlGaAs/GaAs laser transient process and threshold parameters has been studied on the basis of numerical solving the rate equations of an injection laser. N onradiative recombination increases the delay time of an output switching on and decreases the damping rate of output relaxation oscillations significantly. Keywords: injection lasers, transient processes, output dynamics, Auger recombination, Shocley-Hall-Read recombination, threshold parameters

The emerging growth of wavelength division multiplexing for future long haul and local access networks has spurred interest in many novel components. Tunable and selectable wavelength sources are desired with high spectral stability, high modulation bandwidth and low chirp for long haul applications. Here we present two laser array designs for high speed application as low chirp NRZ transmitters and soliton pulse generators.

High-power semiconductor sources capable of high-speed modulation are very desirable for free-space digital telecommunications such as satellite optical communication links. Moreover, a diffraction limited beam quality is necessary for most applications. We describe advances in the development of high-power, diffraction-limited semiconductor lasers based on the master oscillator/power amplifier (MOPA) architecture and capable of high-speed modulation. Devices containing monolithically integrated electro-absorption or phase modulators demonstrate 5 GHz small signal modulation bandwidth at 1 W output power.

A monolithically integrated opto-electronic device is proposed as a fast wavelength-switching light source. This tunable duplex integrated light source comprises two wavelength-tunable distributed Bragg reflector (DBR) laser diodes (LDs), two MQW-electro-absorption optical switches, a Y-shaped waveguide coupler, a MQW-electro-absorption modulator, and two thermal drift compensators (TDCs). The wavelength-switching time of the optical switches was estimated to be 60 ps including a 50-ps rise time for the electrical-pulse generator. The wavelength of a 10-Gbit/s NRZ-modulated optical signal can be switched without bit loss. The function of the TDCs is to keep the device-chip temperature constant. Thermal-transient- induced wavelength drift with a millisecond-order time constant, which has been reported for DBR-LDs, and thermal crosstalk between the tuning regions of the integrated LDs, which causes wavelength fluctuation, are effectively suppressed by thermal-drift-compensation operation using the TDCs.

This paper describes the essential elements for creating a practical wide bandwidth directly modulated laser source. This includes considerations of the intrinsic limitations of the laser structure, due to the resonant frequency and damping of the laser output, together with carrier transport issues to allow carriers in the device active region to be efficiently modulated at high speeds. the use of a P-doped compressively strained multiple-quantum well active region to provide high intrinsic speed and remove transport limitations is described, together with record setting results of 25 GHz modulation bandwidth for a 1.55 micrometer Fabry-Perot laser and 26 GHz bandwidth for a 1.55 micrometer DFB laser. The challenges of providing high bandwidth electrical connections to the laser on a suitable submount, together with fiber attachment and microwave packaging, are discussed. Results of fully packaged 1.55 micrometer DFB lasers with 25 Ghz modulation bandwidth are shown. Digital modulation of the packaged 1.55 micrometer DFB including impedance matching is described, and the transient wavelength chirp is presented. This low chirp is reduced further using an optical filter, to provide a 10 GBit/s source with chirp similar to that of an external electroabsorption modulator.

Results from modulation measurements of 40 high-speed multi quantum well (MQW) lasers ((lambda) equals 1.55 micrometer) of various designs are presented. By fitting the careful calibrated measurements, both magnitude and phase, to an analytical transfer function we were able to determine if a certain laser was limited by thermal effects, parasitic-like effects, or nonlinear gain effects. We found that most of the devices in the study were limited by thermal effects and/or contact parasitics. The parasitics were found to be determined by the width of the high-doped contact layer and cladding layers below the metallic contact. It was also found that a high doping of the separate confinement heterostructure (SCH) layers decreases the damping of the relaxation peak since it facilitates the carrier transport. Improved contact design and high doped SCH-layers resulted in modulation bandwidths of around 24 GHz.

We describe short-cavity In_0.35Ga_0.65As/GaAs multiple quantum well (MQW) lasers with undoped and p-doped active regions. The epilayer structure consists of four 5.7 nm QWs separated by 20.1 nm barriers in a GaAs core. The cladding layers consist of Al_0.8Ga_0.2As. In the case of p-doped devices a 4.5 nm carbon (C)-doped region (2.5 multiplied by 10¹⁹ cm^-3) was inserted above each QW, separated by a 3.1 nm GaAs spacer, resulting in a modulation-doped core region. Using a CAIBE process, short-cavity ridge-waveguide lasers are fabricated in a triple-mesa geometry suitable for on-wafer probing. The best device (6 multiplied by 130 micrometers squared) with an undoped active region attained a damping-limited direct modulation bandwidth exceeding 40 GHz at a cw bias current of 160 mA. In contrast, the p-doped devices, demonstrating a maximum bandwidth of 37 GHz, are still limited by power dissipation. (alpha) -factors as low as 1.4 and 1.5 for undoped and p-doped devices, respectively, are extracted from measurements of the sub- threshold gain spectra. In addition, we demonstrate eye diagrams at 25 Gbit/s (limited by the pulse pattern generator) for these laser diodes. A complete characterization of dc and rf properties of these lasers is presented.

The small-signal response of a (lambda) /4-shifted multiple-quantum well (MQW) distributed feedback (DFB) laser is investigated. The gain spectrum shows two major peaks located at the lowest heavy-hole and light-hole transitions. Therefore, the MQW DFB laser is treated as a three-level system. In the low-power range the heavy-hole transition dominates, while in the high-power range there is a mixing of the heavy-hole and the light-hole transitions. It is shown that the dynamic response of the MQW DFB laser is significantly affected by the contribution due to the light-hole transition. Its dependence on the number of quantum wells and on the coupling coefficient of the grating ((kappa) ) is also discussed.

Commercial telecommunication systems are now being offered at the OC-192/STM-64 (10 Gb/s) data rates. Research results show that even higher time domain multiplexed rates are feasible. With these increasing data rates, measurement technology is being challenged to keep up the pace. This presentation discusses several new measurement techniques and technologies that will enable measurement and verification of these state of the art systems.

A numerical program was developed to simulate the performance of fiber optic transmission systems and its accuracy was verified by comparisons between the calculated results and experiment data. Using this program, soliton transmission and dispersion compensation schemes at 40 Gbit/s were compared. It was shown that by using dispersion compensation, linear transmissions over 3000 km with non-return to zero (NRZ) and over 4000 km with return to zero (RZ) data forms are possible. Without special soliton transmission control techniques, single channel soliton transmission has no advantage over dispersion compensation transmission.

We propose a novel scheme for interconnection of multiple high-speed (2.5/10 Gb/s) ATM streams through an optical WDM network, with a total network capacity of up to 8 Tb/s. The proposed architecture is based on placing the optical WDM portion of the network in a physically small area, i.e., one central office, or in a single rack. This helps to avoid technological obstacles such as power budget, dispersion, and synchronization limitations, and optical output buffering. The interconnection is an ATM packet switched network, and provides optical contention resolution. We show that the implementation of such a network is possible using currently available optoelectronic technology. Simulation results are presented, indicating network throughput of up to 100%.

A high resolution distance meter has been made using optical wave-guide modulators. The modulation frequencies for the optical modulators are around 3.5 GHz, while the modulation frequencies of optical intensity are around 7 GHz because the modulation bias voltages are set to peak points of the electro-optic characteristic. The distance meter was evaluated in the NRLM tunnel. The measurement resolution is 15 micrometers of a standard deviation for a distance range of 0.5 m to 5 m after a correction of a cyclic error.

Optical fiber storage loops storing packets of high-speed optical return-to-zero data have been demonstrated. Storage times greater than 30 minutes have been achieved. A basic storage loop design, demonstrated at 20 Gb/s, resembles an active-passive harmonically mode-locked fiber laser. A new modulation technique, rational-harmonic modulation, has been used in a similar storage loop design to achieve 50 Gb/s storage, using a modulator with only a 13 GHz 3 dB bandwidth. A 10.6 Gb/s all-optical storage loop has also been demonstrated, in which the electro-optic modulator has been replaced with a semiconductor diode amplifier which is driven by an optical clock.