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

We review state-of-the-art intensity-modulation direct-detection (IMDD) analog optical links, focusing on advances since 1990. We contrast direct and external modulation with respect to gain, noise figure, and dynamic-range performance.

Direct-detection analog optical links

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

Modulation bandwidths of 24 GHz (I/sub bias/=25 mA) and 33 GHz (I/sub bias/=65 mA) are demonstrated for 3/spl times/100 /spl mu/m/sup 2/ In/sub 0.35/Ga/sub 0.65/As/GaAs multiple quantum well ridge-waveguide lasers with undoped and p-doped active regions, respectively. These performance enhancements have been achieved both by lowering the growth temperature of the high-Al-mole-fraction cladding layers and by utilizing short-cavity devices, fabricated with dry-etched facets using chemically-assisted ion-beam etching. Both the undoped and p-doped lasers also demonstrate modulation current efficiency factors exceeding 5 GHz/mA/sup 1/2/, the best reported results for any semiconductor laser. >

Low-bias-current direct modulation up to 33 GHz in InGaAs/GaAs/AlGaAs pseudomorphic MQW ridge-waveguide lasers

The impurity-free interdiffusion technique has been utilized to modify the operating wavelength of high-speed In/sub 0.3G/a/sub 0.65/As-GaAs multiple quantum well lasers. Modulation bandwidths of up to 26 GHz (I/sub bias/=50 mA) and modulation current efficiency factors of 5 GHz/mA/sup 1/2/ are demonstrated for 3/spl times/100 /spl mu/m/sup 2/ ridge waveguide lasers following wavelength shifts of 32 nm (34 meV). These results demonstrate the feasibility of fabricating monolithic multiple wavelength laser arrays in which each element is capable of low-bias-current direct modulation at bandwidths exceeding 20 GHz. >

Wavelength tuning of high-speed InGaAs-GaAs-AlGaAs pseudomorphic MQW lasers via impurity-free interdiffusion

We have developed a two‐component chemically‐assisted ion‐beam etching (CAIBE) technique for dry‐etching of high‐speed multiple quantum well (MQW) laser mirrors. This two‐component process relaxes several constraints in the dry‐etching of Al containing opto‐electronic device structures with Cl2 alone. The strained 3×100 μm2 In0.35Ga0.65As/GaAs undoped and p‐doped 4‐QW ridge waveguide lasers containing GaAs/AlAs binary short‐period superlattice cladding layers with cavities fabricated by this CAIBE technique demonstrate record direct modulation bandwidths of 24 GHz (Ibias=25 mA) and 33 GHz (Ibias=65 mA), respectively.

Characteristics of a two‐component chemically‐assisted ion‐beam etching technique for dry‐etching of high‐speed multiple quantum well laser mirrors

We have investigated the compatibility of Cl2/BCl3/IBr3 etch gas mixtures with a cryo‐pumped ultrahigh vacuum chemically assisted ion‐beam etching system. The machine was designed for the fabrication of ultrahigh‐quality laser facets in monolithically integrated GaAs‐ and InP‐based optoelectronic integrated circuits. The chemical composition of etch byproducts deposited in the vacuum chambers and the pumping system has been examined in particular detail. After 70 h of process time, samples of such deposits were scraped from the chamber walls and the various stages of the cryo‐pump and roughing pump; these samples were analyzed using energy‐dispersive x‐ray measurements. Automated overnight regeneration of the cryopump, the use of integrated external bakeout heaters, and the implementation of a cryo‐pumped load‐lock chamber allow the deposition of reactive Cl‐containing residues to be confined to surfaces and components which can be cleaned or replaced during routinely scheduled yearly maintenance.

Chemical analysis of a Cl2/BCl3/IBr3 chemically assisted ion‐beam etching process for GaAs and InP laser‐mirror fabrication under cryo‐pumped ultrahigh vacuum conditions

R.E. Sah

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

Low-bias-current direct modulation up to 33 GHz in InGaAs/GaAs/AlGaAs pseudomorphic MQW ridge-waveguide lasers

Wavelength tuning of high-speed InGaAs-GaAs-AlGaAs pseudomorphic MQW lasers via impurity-free interdiffusion

Characteristics of a two‐component chemically‐assisted ion‐beam etching technique for dry‐etching of high‐speed multiple quantum well laser mirrors

Chemical analysis of a Cl2/BCl3/IBr3 chemically assisted ion‐beam etching process for GaAs and InP laser‐mirror fabrication under cryo‐pumped ultrahigh vacuum conditions