InGaAsP/InP 1.3-µm wavelength surface-emitting LED's for high-speed short-haul optical communication systems

Performance and reliability for InGaAsP/InP 1.3-µm wavelength high-speed surface-emitting DH light emitting diodes (LED's) have been investigated. High-speed and high-radiance performances were obtained by the optimal design of both structural parameters and LED driving circuit. Rise and fall times were both 350 ps and peak optical power coupled to a 50-µm core 0.20 NA graded-index fiber at the 100-mA pulse current was - 15.8 dBm with 6-dB optical ON/OFF ratio. A 2-Gbit/s non-return-to-zero (NRZ) pulse transmission over a 500-m span was carried out, Feasibility of using surface-emitting LED's in a high-speed optical communication system has been confirmed. Accelerated aging tests on high-speed LED's were carried out. The half-power lifetimes have been estimated to be more than 1 × 10⁸h at 50°C ambient temperature.     

1.3-µm BH laser performance at microwave frequencies

We have studied the performance of In1-xGaxAsyP1-yburied heterostructure (BH) 1.3-µm lasers in the microwave range. This study consisted of small-signal, large-signal, and digital pseudo-random word evaluation of these lasers. The small-signal study pointed out the impact of the oxide stripe capacitance on the laser response at microwave frequencies. The large-signal study uncovered basic laser non-linearities that affect the temporal response, spectral broadening, and wavelength chirp. Finally, digital pseudo-random word tests performed at 1.7 Gbit/s indicated that in spite of these inherent laser nonlinearities, the 1.3-µm BH lasers performed well enough to be considered as promising sources for gigabit optical communication systems.     

1.3-µm BH laser performance at microwave frequencies

We have studied the performance of In1-xGaxAsyP1-yburied heterostructure (BH) 1.3-μm lasers in the microwave range. This study consisted of small-signal, large-signal, and digital pseudo-random word evaluation of these lasers. The small-signal study pointed out the impact of the oxide stripe capacitance on the laser response at microwave frequencies. The large-signal study uncovered basic laser non-linearities that affect the temporal response, spectral broadening, and wavelength chirp. Finally, digital pseudo-random word tests performed at 1.7 Gbit/s indicated that in spite of these inherent laser nonlinearities, the 1.3-μm BH lasers performed well enough to be considered as promising sources for gigabit optical communication systems.     

A 1.3-µm microwave fiber-optic link using a direct-modulated laser transmitter

A 1.3-μm 1.1-km-long single-mode fiber-optic link with a 4.1-4.7 GHz frequency response has been developed. This is one of the highest freqUency fiber-optic links reported to date. A 60-dB SNR, ±1.0-dB gain flatness, and 44-dB spur-free dynamic range was observed. The performance of this link is primarily determined by the direct-modulated laser transmitter. This paper discusses the design of that component along with the development and performance of the complete fiber-optic link.     

A 16-µm source for laser isotope enrichment

A potentially efficient, high-energy 16-μm source is proposed based on stimulated rotational Raman scattering in H2or D2using a TEA CO2laser source. The calculated pump energy threshold for rotational Raman scattering on theS(0) 354.33 cm^-1Raman line of H2at 77 K and 1 atm pressure is 3.1 J.     

Transmission characteristics of a single-mode fiber in the 1.3-µm wavelength region

Transmission characteristics of 1.3-μm-band single-mode optical fibers were studied experimentally and theoretically. OH-ion content dependence of optical loss in the 1.3-μm region was investigated on single-mode fibers fabricated by the VAD method. The optical loss was evaluated for OH-ion content by calculating correlation factors between the optical loss and 1.39-μm OH-peak absorption loss. It was clarified that the optical loss calculated by correlation factors agreed approximately with the loss given by Lorentzian absorption in case of 0.0253-μm absorption half width, Next, the relationship between chromatic dispersion and fiber parameters was studied for step-index single-mode fibers. It was found that the zero-dispersion wavelength and the incline at the wavelength was expressed as simple functions of effective cutoff wavelength and relative index difference. Experimentally obtained zero-dispersion wavelengths on single-mode fibers fabricated by the VAD method were found to be in excellent agreement with the calculated values.     

Broadband modulation of 3-µm light by 10-µm light in p-germanium

High-power CO2laser radiation at 1045 cm^-1is shown to enhance the room temperature transmission of p-Ge in a spectral region extending at least from 3000 to 4000 cm^-1. The interaction arises from radiation-induced changes of the hole populations within the three valence bands. Ultrafast nonradiative relaxation is responsible for the very large interaction bandwidth observed and allows the prediction of a minimum switching time of 1 ps.     

Compact 1.3-µm laser transmitter for the SL undersea lightwave system

The mechanical, optical, and electrical design leading to a reliable, high-performance, robust, and compact transmitter are described. Reliability considerations are of paramount importance in the design of undersea systems. Main features of the laser-fiber-monitor package and the light-feedback control strategy are outlined. The functions of the laser drive circuit, consisting of a low-speed feedback IC and a high-speed modulation IC are discussed. Access to multiple test points through an edge board connector permits automated tuning and reliability testing. The transmitter circuit can provide a 200-mA bias current, about double the expected end of life laser bias requirement, and 60-mA modulation current, double the typical value, with < 0.75-ns rise and fall time. The transmitter operates up to 800 Mbit/s, far beyond the TAT-8 bit rate of 295.6 Mbit/s. Transmitter redundancy is planned to meet the extreme reliability requirements for the transatlantic system. Up to four of the compact transmitters can be mounted per regenerator, thus providing as many as three redundant transmitters for improved system reliability.     

Recombination, gain and bandwidth characteristics of 1.3-µm semiconductor laser amplifiers

The influence of the spontaneous recombination mechanism and the temperature- and wavelength-dependent material gain on the performance of 1.3-μm InGaAsP traveling-wave semiconductor laser amplifiers is analyzed. Measurements of signal gain are presented. Frequency detuning and optical bandwidth characteristics are discussed. By considering the trade-off between optical bandwidth and resonant signal gain, guidelines for the requirements to the facet reflectivity are given.     

InGaAsP/InP photodiodes: Microplasma-limited avalanche multiplication at 1-1.3-µm wavelength

Photodiodes for use in the1-1.3-mum wavelength region have been fabricated from double-heterostructure InGaAsP/InP wafers grown by liquid-phase epitaxy (LPE). The measured avalanche multiplication in mesa-configuration devices was limited to values of 10 or less. The results of careful measurement of the photoresponse, quantum efficiency, and reverse-biasI-Vcharacteristics suggest that the gain is limited by microplasma breakdown. The density of microplasmas was estimated to be about 10⁶cm^-2, approximately equal to the etch pit density of the InP substrates used in growth of the epitaxial layers.     

An optically defined 1.3-µm NMOS ring oscillator

n-channel enhancement/depletion (E/D) gate MOS ring-oscillators (RO) based on 1.3- and 2-µm layout design rules have been fabricated using 10:1 reduction projection aligner. A delay/stage of 80 ps and a power-delay product of 3.6 fJ have been obtained for a 401-stage RO consisting of 1.3-µm feature-size devices.     

FM-CW radar range measurement at 10-µm wavelength

The results are reported of some preliminary experiments on FM-CW range measurement using a CO2laser and a nitrogen-cooled PbSnTe detector. In clear conditions diffuse targets at ranges up to 10 km have been detected.     

Optical properties of a 1.3-µm InGaAsP superluminescent diode

The optical properties of a 1.3-µm InGaAsP-InP buried heterostructure (BH) superluminescent diode (SLD) are described. The spectra of this device exhibit a large number of longitudinal modes. The light output at constant current from an SLD has a strong temperature dependence in the superluminescent region (high currents) and week temperature dependence in the spontaneous region (low currents). This severe temperature dependence will limit the systems application of this type of device unless thermoelectric cooling is used. The coupling efficiency (butt-coupling) into a 0.23-NA 50-µm-diameter graded index fiber is 26 percent. A model of the SLD including a temperature dependent nonradiative mechanism (same as in 1.3-µm InGaAsP lasers) suggests that the strong temperature dependence in the superluminescent region is a fundamental property of the device.     

InGaAsP/InP buried crescent laser diode emitting at 1.3 µm wavelength

The fabrication procedure, designing of an active region and a p-n-p-n current blocking structure, characteristics and the aging results of an InGaAsP/InP buried crescent (BC) laser diode are described. The BC laser diodes exhibit high laser performances, such as a low-threshold current, a fundamental transverse mode oscillation with linear light output-current characteristics. CW operation at as high as 100°C is achieved with a junction up configuration as a result of the improvement in the current blocking structure. A stable CW operation at 80°C has been realized with a constant optical output power of 5 mW.     

High-speed optical pulse transmission at 1.29-µm wavelength using low-loss single-mode fibers

Optical-fiber transmission experiments in the 1.3-μm wavelength region are reported. GaInAsP/InP double-heterostructure semiconductor laser emitting at 1.293 μm is modulated directly in nonreturn-to-zero (NRZ) codes at digit rates tanging from 100 Mbit/s to 1.2 Gbit/s. Its output is transmitted through low-loss GeO2-doped single-mode silica fibers in 11-km lengths. Transmitted optical signals are detected by a high-speed Ge avalanche photodiode. Overall loss of the 11-km optical fibers, including 11 splices, is 15.5 dB at 1.3 μm. Average received optical power levels necessary for 10^-9error rate are -39.9 dBm at 100 Mbit/s and -29.1 dBm at 1.2 Gbit/s. In the present system configuration, the repeater spacing is limited by loss rather than dispersion. It seems feasible that a more than 30 km repeater spacing at 100 Mbit/s and a more than 20 km even at 1.2 Gbit/s can be realized with low-loss silica fiber cables, whose loss is less than 1 dB/km. Distinctive features and problems associated with this experimental system and constituent devices are discussed.     

Gigabit single-mode fiber transmission using 1.3-µm edge-emitting LEDs for broad-band subscriber loops

This paper describes gigabit single-mode fiber transmission using 1.3-μm edge-emitting LED's for broad-band subscriber loops, focusing on a method of calculation for maximum transmission distance and 1.2-Gbit/s and 600-Mbit/s transmission experiments. Gigabit single-mode fiber transmission is necessary for subscriber loops, especially in broad-band ISDN and optical CATV systems. Edgeemitting LED's are excellent light sources because of their high power launched into the fiber compared with surface-emitting LED's, and currently lower cost and higher reliability than laser diodes. The maximum transmission distance is carefully estimated by taking into account the wavelength dependence for both chromatic dispersion and loss of the single-mode fiber, and the possibility of gigabit transmission near the dispersion free wavelength 1.3 μm, is confirmed. Encouraged by the above results, we demonstrate 1.2-Gbi,t/s 10-km and 600-Mbit/s 20-km transmission experiments using a newly developed 1.3-μm edge-emitting LED and a new driver circuit with a simple response compensation circuit. These results show the proposed calculation method and the LED response compensation circuit to be powerful tools for the realization of low-cost gigabit single-mode fiber transmission using edge-emitting LED's.     

Analysis of leakage currents in 1.3-µm InGaAsP real-index-guided lasers

We describe leakage current calculation in several real-index-guided laser structures using an electrical equivalent circuit model. The structures analyzed are different types of buried heterostructures in which heterojunctions are used for lateral carrier confinements. The device types are: 1) the etched-mesa buried heterostructure (EMBH); 2) the channeled-substrate buried heterostructure (CSBH); 3) the double-channel planar buried heterostructure (DCPBH); 4) the planar buried heterostructure (PBH); and 5) the buried crescent (BC). Adequate current confinement is necessary in a laser structure for both linearity and low threshold operation. Thus leakage current, i.e., the difference between the injected current and the current through the active region, should be small. We have identified the main leakage paths in these structures and the parameters (the relevant layer thicknesses and doping levels) that determine the magnitude of the leakage current. The effect of nonradiative recombination sites on junction parameters and the consequent increase in leakage current is discussed.     

Criterion for improved linearity of 1.3-µm InGaAsP-InP buried-heterostructure lasers

Nonlinearities in tile light-current characteristics of planar-active buried-heterostructure (BH) lasers are associated with higher order mode transitions, spectral broadening and, in some cases, the onset of TM polarized stimulated emission. Measurements and calculations are presented which show that these nonlinearities appear at higher power in devices with reduced active volume. These results provide a practical guide to the fabrication of "kink-free" 1.3-μm InGaAsP buried-heterostructure lasers for use in high-bit-rate fiber communication systems.