Electro-optic (EO) modulators encode electrical signals onto fiber optic transmissions. High drive voltages limit gain and noise levels. Typical polymeric and lithium niobate modulators operate with halfwave voltages of 5 volts. Sterically modified organic chromophores have been used to reduce the attenuation of electric field poling-induced electro-optic activity caused by strong intermolecular electrostatic interactions. Such modified chromophores, incorporated into polymer hosts, were used to fabricate EO modulators with halfwave voltages of 0.8 volts (at a telecommunications wavelength of 1318 nanometers) and to achieve a halfwave voltage-interaction length product of 2.2 volt-centimeters. Optical push-pull poling and driving were also used to reduce halfwave voltage. This study, together with recent demonstrations of exceptional bandwidths (more than 110 gigahertz) and ease of integration (with very large scale integration semiconductor circuitry and ultra-low-loss passive optical circuitry) demonstrates the potential of polymeric materials for next generation telecommunications, information processing, and radio frequency distribution.

https://science.sciencemag.org/content/sci/288/5463/119.full.pdf

Low (Sub-1-Volt) Halfwave Voltage Polymeric Electro-optic Modulators Achieved by Controlling Chromophore Shape

An overview is given of the direct modulation performance of high-speed semiconductor lasers. The high-speed response characteristics are described using a cascaded two-port model of the laser. This model separates the electrical parasitics from the intrinsic laser and enables these subsections to be considered separately. The presentation concentrates on the small-signal intensity modulation and frequency modulation responses, and the large-signal switching transients and chirping. Device-dependent limitations on high-speed performance are explored and circuit modeling techniques are briefly reviewed.

High-speed modulation of semiconductor lasers

The frequency response of a group of 1.3 μm InGaAsP vapor-phase-regrown buried heterostructure lasers of various cavity lengths is analyzed by fitting the measured response curves. The dependence of resonant frequency f 0 and damping rate \Gamma on bias power is determined. The differential gain coefficient for InGaAsP is determined as 3.5 \times 10^{-16} cm2. The damping rate is found to be proportional to the square of the resonant frequency with a proportionality factor which is independent of device geometry and facet reflectivity. The existence of such a universal relationship between \Gamma and f 0 and the observed magnitude of the damping rate is explained by the interband relaxation model of nonlinear gain.

Frequency response of 1.3&#181;m InGaAsP high speed semiconductor lasers

Microwave subcarrier multiplexing (SCM) is an important approach to the design of lightwave systems for broadband distribution. Recent progress in the design and performance of both analog and digital multichannel SCM systems is reviewed. The application of broadband SCM systems to both passive and optically amplified distribution networks is discussed. The discussion covers the general features of SCM systems; the electrooptic components that have been used in the system experiments described here, including laser intensity noise and noise due to intermodulation products; the carrier-to-noise ratio requirements; some multichannel FM systems experiments; and a 20-channel digital systems experiment; and a hybrid system carrying 60 FM SCM channels plus a 100-Mb/s baseband digital channel. Several approaches to broadband subscriber distribution networks are analyzed. >

Subcarrier multiplexed lightwave systems for broad-band distribution

System concepts for millimeter-wave personal communication systems and the advantages of millimeter-wave band usage are briefly described. Demonstration of broadband millimeter-wave subcarrier transmission concepts over fiber-optic links is performed. Several fiber-optic link architectures, including one using a combination of direct laser modulation and indirect (external) optical modulation, are outlined with respect to signal transmission at millimeter-wave frequencies. Several configurations are experimentally investigated using 70-MHz, 300-MHz, and 26-GHz subcarriers which transmit either FM or QPSK data signals. Additionally, the use of optical MMIC technology, which can result in the design of compact and cost-effective optical receivers, is described with respect to personal communication radio base station equipment. MMIC HEMTs operating as photodetectors are newly characterized in terms of digital and analog signal reception with excellent performance being observed. >

Millimeter-wave fiber optics systems for personal radio communication

RF fiber-optic links have numerous applications to microwave systems. To fully exploit their usefulness, and RF system designer must understand their properties in terms of the performance parameters that are used to describe the terminal properties of other RF components such as loss, signal-to-noise, linearity, and dynamics. This review paper details the performance of direct and external modulation fiber-optic links in terms of those parameters. Specific examples of a 4.1-4.7 GHz direct modulation link and a 2.0-12.0 GHz external modulation link are used.

System characteristics of direct modulated and externally modulated RF fiber-optic links

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.

W. Stephens

Papers

System characteristics of direct modulated and externally modulated RF fiber-optic links

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

W. Stephens

Papers

System characteristics of direct modulated and externally modulated RF fiber-optic links

A 1.3-&#181;m microwave fiber-optic link using a direct-modulated laser transmitter

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