Philipp G. Kornreich

Focusing by electrical modulation of refraction in a liquid crystal cell

The creation of a field-controlled variation of the index of refraction in a liquid crystal cell has been analyzed and experimentally verified. To obtain a spherical lens utilizing a simple electrode structure and capable of focusing arbitrary incoming polarizations requires four flat nematic liquid crystal cells. With electrodes fabricated well within the current capability of photolithography, near diffraction-limited performance in terms of the optical transfer function is predicted. The focusing capability of a liquid crystal lens was demonstrated using a single cell with linear transparent electrodes. A plano-convex cylindrical lens for a single incoming polarization was thus created. While the cell had a crude electrode structure, it affirmed all the major qualitative predictions. The fringing along the edge of the electrodes required for eventually obtaining near diffraction-limited performance was observed.

Adaptive spherical lens

This paper reports the creation of a tandem liquid crystal cell arrangement capable of simulating the performance of a spherical lens. Electrical modulation of the index of refraction creates focusing behavior. The modulation is induced by a set of electrodes whose individual voltages are arranged to provide a cylindrical exit wave front for a uniform plane-wave input. Two such cells with orthogonal electrodes arranged in cascade create spherical lens performance. Experimental evidence using a lens with a relatively small number of electrodes is presented. Applications for such structures, once improved, would include real-time focus adjustment for optical disk readers and hand-held photographic equipment as well as aberration compensation for long path-length optical systems.

Light amplification by a Cd3P2 cylinder fiber

We have fabricated fibers with an a few nm thick Cd3P2 semiconductor layer at the clear glass core glass cladding boundary. We have measured a gain of approximately 7.1 dB in a 4 mm long piece of this Semiconductor Cylinder Fiber (SCF) at a wavelength of 1550 nm. The fiber section was pumped from the side with a 38 mW laser operating at a wavelength of 980 nm. We have reason to believe that the test wavelength of 1550 nm is near the short wavelength end of about a few hundred nm wide gain curve. The SCFs have applications as broad band Fiber Light Amplifiers.

Thin‐film thermocouple gauge

The importance of the thermocouple gauge in vacuum technology is well established. In this paper we present the fabrication and the calibration of a miniature thermocouple gauge using Cu–Cr thin films. The thermocouple gauge consists of a thin‐film Cr heater and a thin‐film Cu–Cr differential thermocouple on a glass substrate. The thin‐film Cu–Cr thermocouple was calibrated using a standard K‐type thermocouple. At constant temperature the change in the input power is a monotonic function of the change in the pressure. The measurement was repeated for several gases at a constant heater temperature of 100 °C. Experimental results show that our device can be used for a wide range of measurements. Owing to its small size, fabrication simplicity, and compatability with the existing thin‐film processing it is rather easy to incorporate our device with other integrated circuits.

Passive Detection of Motion Transverse to the Optical Viewing Axis

The passive detection of velocities of objects moving transverse to the optical viewing axis is discussed from the standpoint of the spatial Fourier transform of the image. A simple algorithm is developed which yields the velocity, as a function of time, of an object moving against a complicated background. This algorithm relies on monitoring magnitude and phase of two prominent spatial Fourier components. Measurement of the Fourier components is most simply accomplished with the direct electronic Fourier transform (DEFT) sensor. This device employs coupling between the image intensity, surface acoustic waves, and electron current in a CdS film to decompose the image into Fourier components. Experimental results show strong confirmation between theory and experiment. The paper concludes with a brief comparison of the DEFT implementation versus other systems in terms of speed, sensitivity, and cost.

A traveling-wave high electron mobility transistor

A traveling-wave high electron mobility transistor (THEMT) is proposed. The device is unique in that it includes an integral distributed load resistor and uses a HEMT as the active device. A rigorous analysis of the device is carried out, using a small-signal equivalent circuit model for an incremental section of the device. Losses and reflected waves are not neglected, as has been done in other work. Treating the device as a four-port network, closed-form expressions for S-parameters are derived. Theoretical calculations, using equivalent circuit parameter values for a HEMT reported in the literature, show that the proposed device is capable of exponential increase in gain with device width. Power gain of more than 10 dB at 50 GHz and remarkably flat response in the frequency range 10-100 GHz are shown to be achievable for a 1-mm-wide device. >

Intercore-cladding uniaxial dielectric thin film optical fibers

Light propagation through optical fibers consisting of a glass core coated with a high refractive index uniaxial dielectric thin film, in turn surrounded by a glass cladding, is presented. The dispersion equations are derived, and mode classifications are established for transverse and hybrid modes. Simulation results of lithium niobate thin film with bulk material dispersion are given as an example of uniaxial film. It is shown that modes are guided mainly in the film and the structure is capable of strong light confinement. Investigation of power flow along the propagation direction shows that the higher the film thickness, the higher the power density in the film.

Cd3P2 Cylinder Fibers

We are currently working on Semiconductor Cylinder Fibers (SCF), fibers with a thin semiconductor layer at the glass core glass cladding boundary. We hope that these fibers can eventually be used as both S aturable Absorbers (SA) and Fiber Light Amplifiers (FLA). We use a rod and tube method for fabricating these fibers. The three fabrication process steps, semiconductor deposition, collapse, and fiber drawing have been working well since the summer of 1 999. We have mathematical models for the fabrication process steps that allows us to calculate the required temperatures and pressures used. The fabrication process is very reproducible.

Thermocouple gauge for partial pressure measurements

We here present the design and testing of a thermocouple gauge with unique properties. Operating the gauge at different temperatures allows one to measure the partial pressure of different gases in a vacuum system. The gauge system consists of two parts, the detector and the control circuitry. The detector consists of a filament and a heat shield. A differential thermocouple measures the temperature difference between the filament and the heat shield. The control part consists of circuitry that keeps the temperature difference between the filament and heat shield constant by controlling the filament power. The gauge has been calibrated with a Mcleod gauge and with various gases, such as He, Ar, N2, and CO2 gas. This gauge measures pressure without ionizing the gases. Experimental results show that the gauge is very sensitive down to 10−4 Torr.

Mathematical model of the absorption and gain in a Cd3P2 cylinder fiber

A theoretical analysis of the light absorption and gain mechanisms in a Cd 3 P 2 Semiconductor Cylinder Fiber is presented. The results of these calculations are in good agreement with previously published experimental data. Cd 3 P 2 has two direct energy gaps, which both influence the gain mechanism. Pump light can be used to reduce the absorption. Stronger pump light that generates more charge carriers will produce net gain (gain above absorption compensation). The fiber exhibits gain over a very wide light wavelength bandwidth.