Ganesh K. Gopalakrishnan

Microwave-optical mixing in LiNbO/sub 3/ modulators

An investigation study of microwave-optical mixing in different configurations of LiNbO/sub 3/ Mach-Zehnder interferometric modulators is presented. In each case, models that describe mixer performance are developed and are shown to be in good agreement with measurements. For antenna remoting applications, a technique to down-convert RF signals is demonstrated by cascading in series a pair of Mach-Zehnder interferometric modulators. In general, it is shown that by virtue of their truly broadband characteristics, interferometric modulators can also by employed as microwave mixers at frequencies up to 40 GHz. >

Performance and modeling of broadband LiNbO/sub 3/ traveling wave optical intensity modulators

The design, fabrication and characterization of a traveling wave Ti:LiNbO/sub 3/ Mach-Zehnder interferometric modulator are discussed. The dependence of the velocity match condition on electrode thickness and wall angle is demonstrated experimentally and with finite element calculations. A set of test electrode structures is fabricated to study electrical losses in the modulator electrode. Loss coefficients are assigned to different sections of the device, and dielectric and radiative losses are shown to play an important role at high frequencies. This information is used in conjunction with finite-element calculations to develop accurate models for both the electrical and optical responses. The frequency dependence of the half-wave voltage is measured and shown to be in good agreement with a model. >

A low-loss downconverting analog fiber-optic link

An analog fiber-optic link for concurrent detection and downconversion of microwave signals is reported. Optical amplification is employed in conjunction with electrical power combining of photodetectors to demonstrate link losses of 19.6 and 22.9 dB at RF carrier frequencies of 9 and 16 GHz, respectively. Analytic expressions validating the experimental observations are also developed. The link may be employed to detect phase sensitive or phase-modulated microwave signals and shows excellent potential for application in sensor systems involving remoting of an antenna element. >

Performance and modeling of resonantly enhanced LiNbO/sub 3/ modulators for low-loss analog fiber-optic links

The performance of resonantly enhanced LiNbO/sub 3/ traveling wave optical modulators is investigated. High-frequency performance of broad band velocity matched LiNbO/sub 3/ modulators with low half-wave voltages is shown to be relatively independent of termination. A resonant enhancement technique involving external line stretching of the length of the nonactive section of the modulator is proposed and demonstrated at low-frequencies. An accurate model is developed to facilitate design of resonantly enhanced optical modulators. >

SBS suppression using a depolarized source for high power fiber applications

A depolarized source for fiber applications is demonstrated using a traveling wave LiNbO/sub 3/ phase modulator. The source suppresses stimulated Brillouin scattering (SBS) in the fiber when operated at high drive frequencies, enabling more power to be delivered to a remote location. The threshold for SBS is examined in detail using optical powers up to 150 mW and drive frequencies up to 4 GHz. A resonant enhancement technique is demonstrated which reduces the drive power requirement for frequencies <2 GHz by up to 7.6 dB.