S. Sriram

Sensitivity enhancements to photonic electric field sensor

This paper describes an electrode-less, all-optical, wideband electric field sensor fabricated in an electro-optic lithium niobate substrate. The sensor component is an integrated optic Mach-Zehnder interferometer. The electric field sensor uses the electro-optic properties of lithium niobate to modulate the phase of the light propagating in each arm of the Mach-Zehnder interferometer. The phase modulated light is then converted to intensity modulation at the output of the interferometer. The unique feature of the sensor device is that the orientation of the crystal in one arm of the Mach-Zehnder interferometer is inverted to provide push-pull optical modulation for an applied electric field. Optical fibers are connected to the input and output of the sensor device. The basic device is an all-dielectric intensity modulator. The ability to operate the sensor without the use of any metal antenna permits its use in extremely high field conditions without any danger of damaging the sensor. The optical fiber connections provide optical isolation to the instrumentation to protect the instrumentation from possible overload conditions. The electrode-less sensor is designed specially for measuring high field strengths similar to the conditions in electromagnetic pulse, high power microwave and high voltage power lines. Sensitivity improvements are possible by using carrier suppression techniques.

Revolutionary optical sensor for physiological monitoring in the battlefield

SRICO has developed a revolutionary approach to physiological status monitoring using state-of-the-art optical chip technology. The company’s patent pending Photrode is a photonic electrode that uses unique optical voltage sensing technology to measure and monitor electrophysiological parameters. The optical-based monitoring system enables dry-contact measurements of EEG and ECG signals that require no surface preparation or conductive gel and non-contact measurements of ECG signals through the clothing. The Photrode applies high performance optical integrated circuit technology, that has been successfully implemented in military & commercial aerospace, missile, and communications applications for sensing and signal transmission. SRICO’s award winning Photrode represents a new paradigm for the measurement of biopotentials in a reliable, convenient, and non-intrusive manner. Photrode technology has significant applications on the battlefield for rapid triage to determine the brain dead from those with viable brain function. An ECG may be obtained over the clothing without any direct skin contact. Such applications would enable the combat medic to receive timely medical information and to make important decisions regarding identification, location, triage priority and treatment of casualties. Other applications for the Photrode include anesthesia awareness monitoring, sleep medicine, mobile medical monitoring for space flight, emergency patient care, functional magnetic resonance imaging, various biopotential signal acquisition (EMG, EOG), and routine neuro and cardio diagnostics.

Use of a rapid thermal annealing system to initiate indiffusion for fabrication of Ti:LiNbO 3 optical channel waveguides

A rapid thermal annealing (RTA) system has been used to initiate indiffusion of Ti into LiNbO(3) for fabrication of optical channel waveguides. Four separate processes are investigated, each with different RTA temperature vs time variations followed by furnace heating. The sample processed with a fast initial ramp of temperature vs time to 875 degrees C yielded the lowest waveguide propagation loss of 1 dB/cm at a wavelength of 632.8 nm, compared with samples processed with other RTA variations and with a sample undergoing only furnace processing. Use of a dry O(2) ambient during RTA resulted in a smoother waveguide surface with no outdiffusion, when compared with use of a wet O(2) ambient.

Fabrication Of Ti:LiNbO3 Optical Channel Waveguides Using A Rapid Thermal Annealing System

We have investigated use of rapid thermal annealing (RTA) to initiate in-diffusion of Ti into LiNb03 to form optical channel waveguides using several different RTA processes. Each process is characterized by a different RTA temperature versus time variation followed by a common furnace heating step. One set of samples has undergone a slow ramp RTA temperature versus time variation, a second set has undergone a two step variation, a third set has undergone a very rapid ramp, and a fourth set has undergone no RTA processing. Samples processed with the fast RTA ramp of temperature versus time to 875C yielded the lowest channel waveguide propagation loss of about 1 dB/cm measured at a wavelength of 632.8 nm.

Characterization of Ti:LiNbo 3 Optical Channel Waveguides Fabricated using Rapid Thermal Annealing

Rapid thermal annealing has been used to initiate diffusion of Ti in LiNbO 3 for the fabrication of optical waveguides. The sample with the most rapid initial ramp of temperature to 875 C was found to have the lowest propagation loss of 1 dB/cm. In order to more fully understand these channel waveguides, we have utilized Raman microprobe spectroscopy. Preliminary results suggest that the presence of the Ti in the LiNbO3 lattice dramatically alters the Raman response.

High-power, integrated photonic, electric-field sensor

A Mach-Zehnder interferometer designed as an electric field transducer operates without metal electrodes by incorporating a novel substrate configuration. The lithium niobate device uses reverse poling of one of the interferometer arms, which provides opposing optical phase changes in the two interferometer arms when placed in an electric field. The fabricated devices exhibit a measured minimum detectable field of 0.22 V/m(root)Hz and frequency response greater than 6 GHz. Theoretical calculations show that fields in excess of 330 kV/m can be detected before appreciable distortion occurs.

Linearized electro-optic directional coupler modulator in stoichiometric lithium niobate

This paper reports on a novel optical linearized directional coupler modulator in stoichiometric lithium niobate (SLN). The linearized design has important applications in analog and RF communications systems where fiber optic link performance depends critically on the spurious-free dynamic range of the modulator. Newly available SLN has several distinct advantages over the congruently grown crystals commonly used for high speed integrated optic devices, including higher electrooptic coefficient and better ferroelectric properties. The higher electrooptic coefficient yields lower drive voltage, while the enhanced ferroelectric properties enable better velocity-matched electrode structures using domain inverted waveguides. This paper addresses the operation of the linearized directional coupler design, and the critical advantages of the SLN substrate for implementing high-speed operation using velocity-matching.

An Electrode-Less Integrated Mach-Zehnder Interferometer Electric Field Sensor

Advances in the development of a newly configured Mach-Zehnder interferometric electric field sensor device utilizing the electro-optic effect are reported. The integrated optical lithium niobate device operates solely by immersion in an electric field, using no metallic electrodes. Reverse poling of one arm of the interferometer results in additive optical phase changes in the interferometer arms when the device is placed in an electric field. Recently fabricated devices have exhibited a measured minimum detectable field of 34 mV/m per √Hz and a frequency response of greater than 10 GHz.

Extraordinary-mode refractive-index change produced by the linear electro-optic effect in LiNbO 3 and reverse-poled LiNbO 3

To examine aspects of an integrated photonic electric-field sensor, we calculate electro-optically induced refractive-index change in regular and reverse-poled LiNbO(3). Specifically, for y-propagating extraordinary modes, we determine how index change depends on electric-field magnitude and direction. To accomplish this, changes in index-ellipsoid shape and orientation are found by the use of a numerical eigenvalue procedure to diagonalize the impermeability tensor; then, refractive index is calculated by the use of a vector reference-frame transformation and a small perturbation approximation. A general formula is inferred from calculations for specific field directions. Electro-optic coefficients for reversepoled LiNbO(3) are obtained by application of a tensor reference-frame transformation to those of LiNbO(3). The index-calculation procedure has utility beyond the problem that is considered.