Paul M. Ferm

Femtosecond response of electro‐optic poled polymers

We investigate the ultrafast electro‐optic response and sensitivity of a poled side chain polymer film via the electro‐optic sampling technique. A 760 fs rise‐time electrical transient is observed corresponding to a bandwidth of 460 GHz. We believe this to be device limited and not due to limitations in the speed of response of the polymer.

Viewing-angle-enhancement system for LCDs

An enhanced liquid crystal display (LCD) design with minimal contrast ratio or color shift with increased viewing angle and with improved performance in high brightness environments has been developed. Contrast ratios of greater than 50 :1 have been demonstrated at ±60° (vertical and horizontal) on an active matrix LCD. The operating principles of the key components of this new design will be described.

Infrared‐induced desorption of HD from lithium fluoride

Low intensity ir radiation at 2–15 μm desorbs HD from 1.5–4.2 K lithium fluoride (LiF) via four distinct channels. The channel most studied here involves coverages of one monolayer or less and 9–15 μm radiation, causing HD to desorb with a translational energy TB of 21 K. This process, which is attributed to a single phonon ejecting HD from its lowest bound state, is precisely linear in the radiation intensity, and its efficiency increases with increasing wavelength, reaching a maximum of ≊4×10−5 molecules per photon at 15 μm. At multilayer coverages and a surface temperature of 4.2 K, at which HD has a significant vapor pressure, we observe a photoinduced thermal desorption signal (TB=4.0–4.8 K), arising from a very small (≊0.005 K) perturbation of the crystal temperature. The evidence for thermal desorption of this channel strongly contrasts with the other three channels, which are nonthermal. A third channel involves radiation between 2.71 and 4.4 μm, which causes a very weak signal with TB≊20 K. While...

High‐speed InP/GaInAs heterojunction phototransistor on InP‐on‐Si grown by organometallic vapor phase epitaxy

We have fabricated the first heterojunction phototransistor (HPT) on InP‐on‐Si. These phototransistors, based on the InP/GaInAs heterojunction, have optical gains as high as 125 A/W at 1300 nm and dark currents as low as 300 pA, for a 48×64 μm HPT. The bandwidth was determined from impulse photoresponse measurements to be 4.4 GHz. The intrinsic bandwidth was estimated from the zero bias capacitance (0.2 pf) to be as high as 16 GHz.

Loss measurements in electro-optic polymer waveguides

We report loss measurements in polymer-bound Disperse Red I slab and photodelineated channel waveguides. Losses resulting from electronic charge-transfer and vibrational carbon- hydrogen stretch overtone absorptions, trans to cis isomerization, exposure to visible or ultraviolet (UV) light and changes in dye pendant group number density are investigated. A waveguide absorption spectrometer is described which can measured waveguide losses (alpha) ((lambda) ) from 600 - 1800 nm. Absorption losses are compared to the wavelength dependent electro-optic coefficient r33((lambda) ) and a figure-of-merit r33((lambda) )/(alpha) ((lambda) ) is determined for the material.

Polymeric Electro-Optic Materials and Devices: Meeting the Challenges of Practical Applications

Over the past five years, a new class of electro-optic polymeric materials has evolved which provides for the first time the capability to fabricate simple and inexpensive electro-optic devices on a variety of substrates. More importantly, these materials possess optical dielectric constants (or refractive indexes) comparable to radio-frequency dielectric constants allowing for fabrication of devices in which the electric field and the optical field propagate at the same velocity. Finally, the low dielectric constant of these materials relative to inorganic ionic crystals provides for operation of devices at much higher efficiency. Although the above facts have been clear for some time, the practical applications of these materials cannot be realized until materials can be created which satisfy a host of practical requirements and until device architectures and fabrication techniques appropriate for these materials can be developed. We will describe here research directed toward both of these ends.

Optical characterization of azo dye-based electro-optic polymer films

We have investigated the photochemistry and optical properties of an azo dye-based electro- optic (EO) copolymer, methacrylate-bound Disperse Red 1/methylmethacrylate (MA1). We present a complete picture of the optical properties of the copolymer at wavelengths ranging from 200 nm to 1800 nm with detection sensitivity over 6 orders of magnitude. We describe intrinsic measurements of absorption loss and also describe how temperature and radiation affect absorption loss. Photochemical investigations reveal details concerning photodelineation of waveguides in MA1. Irreversible photodegradation of the azo chromophore proceeds with both visible and ultra-violet radiation and a quantum yield of 2 X 10-5 is found for 475 nm radiation in MA1.