Analog Optical Links presents the basis for the design of analog links. Following an introductory chapter, there is a chapter devoted to the development of the small signal models for common electro-optical components used in both direct and external modulation. However this is not a device book, so the theory of their operation is discussed only insofar as it is helpful in understanding the small signal models that result. These device models are then combined to form a complete link. With these analytical tools in place, a chapter is devoted to examining in detail each of the four primary link parameters; gain, bandwidth, noise figure and dynamic range. Of particular interest is the inter-relation between device and link parameters. A final chapter explores some of the trade offs among the primary link parameters.

Analog Optical Links: Theory and Practice

The two-dimensional (2-D) quantum-well (QW) laser diode simulator Minilase-II is presented in detail. This simulator contains a complete treatment of carrier dynamics including bulk transport, quantum carrier capture, spectral hole burning, and quantum carrier heating. The models used in the simulator and their connectivity are first presented. Then the simulator is used to demonstrate the effects of various nonlinear processes occurring in QW lasers. Finally, modulation responses produced by Minilase-II are compared directly with experimental data, showing good quantitative agreement.

Simulation of carrier transport and nonlinearities in quantum-well laser diodes

By using strong optical injection locking, we report resonance frequency enhancement in excess of 100 GHz in semiconductor lasers. We demonstrate this enhancement in both distributed feedback (DFB) lasers and vertical-cavity surface-emitting lasers (VCSELs), showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for resonance frequency enhancement. We have also identified the key factors that cause low-frequency roll-off in injection-locked lasers. By increasing the slave laser's DC current bias, we have achieved a record intrinsic 3-dB bandwidth of 80 GHz in VCSELs.

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Strong optical injection-locked semiconductor lasers demonstrating > 100-GHz resonance frequencies and 80-GHz intrinsic bandwidths.

In this paper, the basic principle of operation, design issues, limitations, recent developments and emerging research trends on wide-bandwidth lasers and modulators for radio-frequency photonic applications are reviewed. The topics covered are wide-bandwidth lasers, lumped and traveling-wave electroabsorption modulators, traveling-wave LiNbO/sub 3/, GaAs, and polymer modulators.

Wide-bandwidth lasers and modulators for RF photonics

A large number of novel devices have been recently demonstrated using wafer fusion to integrate materials with different lattice constants. In many cases, devices created using this technique have shown dramatic improvements over those which maintain a single lattice constant. We present device results and characterizations of the fused interface between several groups of materials.

Wafer fusion: materials issues and device results

We demonstrate record direct modulation bandwidths from MBE-grown In/sub 035/Ga/sub 065/As-GaAs multiple-quantum-well lasers with undoped active regions and with the upper and lower cladding layers grown at different growth temperatures Short-cavity ridge waveguide lasers achieve CW direct modulation bandwidths up to 40 GHz for 6/spl times/130 /spl mu/m/sup 2/ devices at a bias current of 155 mA, which is the damping limit for this structure We further demonstrate large-signal digital modulation up to 20 Gb/s (limited by the measurement setup) and linewidth enhancement factors of 14 at the lasing wavelength at threshold of /spl sim/11 /spl mu/m for these devices

Damping-limited modulation bandwidths up to 40 GHz in undoped short-cavity In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers

We present results from In/sub 0.35/Ca/sub 0.65/As-GaAs 4 QW lasers whose Al/sub 0.8/Ga/sub 0.2/As binary short-period superlattice (SPSL) cladding layers were grown at either 700/spl deg/C or 620/spl deg/C. The threshold current densities (J/sub th/) are /spl sim/3 times smaller for the lasers whose AlGaAs cladding layers were grown at 620/spl deg/C. At the same time, the internal differential quantum efficiency (/spl eta//sub i/) increases from 60% to 70%. We attribute the lower J/sub th/ and increased /spl eta//sub i/ to a significant decrease in the concentration of point defects in the MQW active region, consistent with the observed improvement of the diode ideality factor. Temperature-dependent photoluminescence (PL) results suggest that these nonradiative recombination centers are related to point defects recently observed with Raman scattering. Ridge lasers grown with low-temperature SPSL Al/sub x/Ga/sub 1-x/As have achieved 3-dB modulation bandwidths of 24 GHz at record low bias currents of only 25 mA. >

Improved performance from pseudomorphic In y Ga/sub 1-y/As-GaAs MQW lasers with low growth temperature Al x Ga/sub 1-x/As short-period superlattice cladding

Short-haul fiber-optic communication systems require high-speed semiconductor lasers that can operate uncooled over a wide temperature range. In this letter, we describe high-speed short-cavity InGaAs-GaAs multiple-quantum-well lasers operating at 1.1-/spl mu/m wavelength. The Fabry-Perot lasers were fabricated in a triple-mesa geometry suitable for on-wafer probing. With 3/spl times/200 /spl mu/m/sup 2/ ridge-waveguide lasers, which showed the best compromise between high-temperature and high-speed performance, a 3-dB modulation bandwidth of 14.5 GHz at 130/spl deg/C was achieved. Uncooled 20-Gb/s operation of these lasers is presented over a wide-temperature range from 25/spl deg/C to 130/spl deg/C without automatic power control.

Uncooled high-temperature (130/spl deg/C) operation of InGaAs-GaAs multiple quantum-well lasers at 20 Gb/s

We have recently reported short-cavity In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers with modulation bandwidths up to 33 GHz using beryllium (Be) as p-dopant in the active region. At the growth temperatures used for this structure, however, a modulation-type p-doping in the core can not be realized due to the redistribution of Be during the growth process. In this work, we present InGaAs/GaAs MQW lasers with a similar epilayer structure, but with the Be-doping in the core replaced by carbon (C), resulting in a modulation-doped core region. Short-cavity lasers fabricated using this epilayer structure demonstrate record CW direct modulation bandwidths up to 37 GHz in 6x130 /spl mu/m/sup 2/ devices at room temperature.

37 GHz direct modulation bandwidth in short-cavity InGaAs/GaAs MQW lasers with C-doped active regions

We have fabricated dry-etched mirrors in high-speed InGaAs/GaAs/AlGaAs pseudomorphic multiple quantum well ridge-waveguide lasers at 60°C and in InGaAs/InP bulk lasers at 5°C using enhanced chemically assisted ion-beam etching (CAIBE) technique. The technique allows the etching of laser structures with good surface morphology and excellent anisotropy without cold traps in the etching system. Characteristics of the dry-etched facet lasers match those of cleaved devices. The low sample temperatures for etching allowed the use of standard photoresists as etch masks.

W. Benz

Papers

Damping-limited modulation bandwidths up to 40 GHz in undoped short-cavity In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers

Improved performance from pseudomorphic In y Ga/sub 1-y/As-GaAs MQW lasers with low growth temperature Al x Ga/sub 1-x/As short-period superlattice cladding

Uncooled high-temperature (130/spl deg/C) operation of InGaAs-GaAs multiple quantum-well lasers at 20 Gb/s

37 GHz direct modulation bandwidth in short-cavity InGaAs/GaAs MQW lasers with C-doped active regions

Fabrication of dry-etched mirrors in GaAs-based and InP-based lasers using chemically assisted ion-beam etching at low temperatures