James E. Toney

Detection of Energized Structures With an Electro-Optic Electric Field Sensor

An electro-optic, solid-state electric field sensor system for noncontact detection of energized objects at power frequency (60 Hz) was investigated. In laboratory testing, the sensor system was found to have a minimum detectable field amplitude of 4 mV/m/Hz1/2, which was further reduced by a factor of 2 through vector averaging over 20 cycles. In an experimental setup emulating the realistic scenario of an energized conducting structure (such as a street light or metal fence post), the detection of a 1-m object energized at 1 VAC at a distance of 2 m was demonstrated.

Advanced Materials and Device Technology for Photonic Electric Field Sensors

Photonic methods for electric field sensing have been demonstrated across the electromagnetic spectrum from near-DC to millimeter waves, and at field strengths from microvolts-per-meter to megavolts-per-meter. The advantages of the photonic approach include a high degree of electrical isolation, wide bandwidth, minimum perturbation of the incident field, and the ability to operate in harsh environments. Aerospace applications of this technology span a wide range of frequencies and field strengths. They include, at the high-frequency/high-field end, measurement of high-power electromagnetic pulses, and at the low-frequency/low-field end, in-flight monitoring of electrophysiological signals. The demands of these applications continue to spur the development of novel materials and device structures to achieve increased sensitivity, wider bandwidth, and greater high-field measurement capability. This paper will discuss several new directions in photonic electric field sensing technology for defense applications. The first is the use of crystal ion slicing to prepare high-quality, single-crystal electro-optic thin films on low-dielectricconstant, RF-friendly substrates. The second is the use of two-dimensional photonic crystal structures to enhance the electro-optic response through slow-light propagation effects. The third is the use of ferroelectric relaxor materials with extremely high electro-optic coefficients.

Electro-optic devices in Thin Film Lithium Niobate (TFLN™)

Recent R&D projects have placed SRICO at the forefront of Thin Film Lithium Niobate (TFLNTM) technology to create advanced photonic, electro-optic devices and nonlinear optical devices. This talk will address the method of producing TFLNTM and results of novel devices fabricated using thin film lithium niobate. Key avionics and defense applications include phased array radar, free space optical communications, mobile communications, satellite communications, antenna remoting, wideband electronic warfare receivers, optical time delay modules, and surveillance activities.

Environmental stress effects on fiber optic cable end faces

The PC and PC-NC termini studied here showed tolerable changes in optical transmittance under temperature cycling, vibration testing or mating/de-mating cycles with periodic cleaning. The flat-NC termini studied here showed much greater average change, and much greater variability, from all stimuli than the other types. We hypothesize that this is due to variation in fiber height, and was in contrast to expected variations fiber height for the PC-NC termini as well. There are substantial differences between the designs of the PC-NC and the flat-NC termini which could cause the discrepancy: 1) end face shape, 2) very short fiber attachment region inside the flat-NC terminus, 3) possible inconsistent fiber coating adhesion, or 4) stress caused from use of tight buffered cable with the flat-NC terminus. Failure analysis did not detect epoxy failure. The mate/demate test results highlight the importance of regular cleaning to prevent end face damage.

ZnO-diffused lithium niobate waveguide polarization controller

The linear electro-optic effect in lithium niobate is capable of realizing a variety of polarization transformations, including TE-to-TM and left-to-right circular polarization conversion. While most LiNbO3 components are designed for operation in the third telecommunications window around 1.55 μm wavelength, current interest in quantum information processing and atomic physics, where the wavelengths of interest are in the visible and near-infrared, has placed new demands on endless polarization control devices. At short wavelengths, traditional Ti-diffused LiNbO3 waveguides suffer from photorefractive degradation at optical power levels well below 1 mW. Proton exchanged waveguides have much higher power handling capability but can only guide light polarized parallel to the optic axis, and therefore are not applicable to polarization control. Zinc oxide diffusion is an alternative waveguide fabrication technology that guides both e- and o-waves with much higher power handling capability than Ti:LiNbO3 waveguides. ZnO:LiNbO3 waveguides exhibit a highly circular mode field with lower anisotropy than Ti-diffused waveguides. We report on the modeling, fabrication and testing of a polarization controller in ZnO-doped, x-cut lithium niobate operating at a wavelength of 780 nm.

Engineered thin film lithium niobate substrate for high gain-bandwidth electro-optic modulators

This paper reports the demonstration of a high-speed electro-optic modulator in crystal ion sliced thin film lithium niobate (TFLN™). Experimental results indicate potential to realize a 100 GHz TFLN™ modulator at 1550 nm with V_π = 2.5V.

Noncontact electro-optic near field probe for surface electric field profiling

An integrated electro-optic electric field sensor probe for measurement of near-surface electric fields from 20 mV/m to 30 kV/m, and from low audio to VHF frequencies was demonstrated. The sensor has a single-fiber geometry to enable measurements with high spatial resolution in the near field. One dimensional electric field profile measurements were performed with millimeter spatial resolution. The dynamic range of the sensor system exceeded 100 dB in a 1 Hz bandwidth, with a minimum detectable field of 20 mV/m/root-Hz at 100 MHz, and a 1 dB compression field greater than 30 kV/m.

Integrated RF photonic devices based on crystal ion sliced lithium niobate

This paper reports on the development of thin film lithium niobate (TFLN™) electro-optic devices at SRICO. TFLN™ is formed on various substrates using a layer transfer process called crystal ion slicing. In the ion slicing process, light ions such as helium and hydrogen are implanted at a depth in a bulk seed wafer as determined by the implant energy. After wafer bonding to a suitable handle substrate, the implanted seed wafer is separated (sliced) at the implant depth using a wet etching or thermal splitting step. After annealing and polishing of the slice surface, the transferred film is bulk quality, retaining all the favorable properties of the bulk seed crystal. Ion slicing technology opens up a vast design space to produce lithium niobate electro-optic devices that were not possible using bulk substrates or physically deposited films. For broadband electro-optic modulation, TFLN™ is formed on RF friendly substrates to achieve impedance matched operation at up to 100 GHz or more. For narrowband RF filtering functions, a quasi-phase matched modulator is presented that incorporates domain engineering to implement periodic inversion of electro-optic phase. The thinness of the ferroelectric films makes it possible to in situ program the domains, and thus the filter response, using only few tens of applied volts. A planar poled prism optical beam steering device is also presented that is suitable for optically switched true time delay architectures. Commercial applications of the TFLN™ device technologies include high bandwidth fiber optic links, cellular antenna remoting, photonic microwave signal processing, optical switching and phased arrayed radar.

Quasi-phase-matched electro-optic modulators for high-speed signal processing

This paper reports on the design, fabrication and testing of quasi-phase-matched (QPM) lithium niobate electro-optic modulators optimized for the 40-60 GHz frequency range. The device used a single-drive, coplanar-waveguide (cpw) electrode structure that provided a good balance between impedance and RF loss, and a DC Vπ.L product of approximately 10 V.cm. Ferroelectric domain engineering enabled push-pull operation with a single drive, while achieving low chirp. A custom developed pulsed poling process was used to fabricate periodic domain QPM structures in lithium niobate. QPM periods were in the range of 3 mm to 4.5 mm, depending on the design frequency. The pulse method enabled precise domain definition with a minimum of overpoling. Low-loss diffused optical waveguides were fabricated by an annealed proton exchange (APE) process. By operating in both co-propagating and counter-propagating modes, the QPM devices can be used to implement dual band RF bandpass filters simultaneously covering both 10-20 GHz and 40-60 GHz frequency bands. Arrays of QPM device structures demonstrated in this work form the basis for a reconfigurable RF photonic filter. The RF photonic QPM technology enables efficient concurrent antenna remoting and filtering functionality. Applications of the technology include fiber radio for cellular access and finite impulse response filters for wideband electronic warfare receivers.

Efficacy of manual fiber optic cleavers used on coated optical fibers

This work compares the performance of two manual fiber cleavers, which are specifically intended to solve the problem of field cleaving fibers in the presence of durable coatings such as polyimide.