Analytical approximation solutions for 3-D optical waveguides: Review

The rectangular dielectric waveguide is the most commonly used structure in integrated optics, especially in semi-conductor diode lasers. Demands for new applications such as high-speed data backplanes in integrated electronics, waveguide filters, optical multiplexers and optical switches are driving technology toward better materials and processing techniques for planar waveguide structures. The infinite slab and circular waveguides that we know are not practical for use on a substrate because the slab waveguide has no lateral confinement and the circular fiber is not compatible with the planar processing technology being used to make planar structures. The rectangular waveguide is the natural structure. In this review, we have discussed several analytical methods for analyzing the mode structure of rectangular structures, beginning with a wave analysis based on the pioneering work of Marcatili. We study three basic techniques with examples to compare their performance levels. These are the analytical approach developed by Marcatili, the perturbation techniques, which improve on the analytical solutions and the effective index method with examples.

New temperature fluctuation method for direct determination of thermal activation energy of deep levels in semiconductors

A new method is suggested where the thermal activation energy is measured directly and not as a slope of an Arrhenius plot. The sample temperature T is allowed to fluctuate about a temperature T0. The reverse-biased sample diode is repeatedly pulsed towards zero bias and the transient capacitance C1 at time t1 is measured The activation energy is obtained by monitoring the fluctuations in C1 and T. The method has been used to measure the activation energy of the gold acceptor level in silicon.

A ternary Schmitt trigger

A new ternary circuit, namely, a ternary Schmitt trigger, is presented. This novel circuit which is based on the well-known lambda diode, is suitable for integration using CMOS technology. The circuit has been simulated using the SPICE 2G Program. The results of the simulation are presented. The circuit offers a high degree of design flexibility. This circuit is expected to be a very useful functional block in the processing of ternary and pseudoternary signals.

Weak rectifying behaviour of p-SnS/n-ITO heterojunctions

This work explores the electrical properties of p-SnS/n-ITO heterojunction at different temperatures. The p-type SnS film was deposited on n-type ITO substrate using the thermal evaporation technique and its junction properties were studied using two probe method. The as-grown p-n junction exhibited weak rectifying behaviour with a low Saturation current of the order of similar to 10(-6) A. While increasing temperature, the saturation current of the junction is increased and however, its series resistance decreased. At all temperatures the junction exhibited three types of transport mechanisms depending on applied bias-voltage. At lower voltages the junction showed nearly ideal diode characteristics. The junction behaviour with respect to bias-voltage and temperature is discussed with the help of existing theories and energy band diagram.

Metal-insulator-semiconductor capacitors with bismuth oxide as insulator

Metal-insulator-semiconductor capacitors using aluminum Bi2O3 and silicon have been studied for varactor applications. Reactively sputtered Bi2O3 films which under suitable proportions of oxygen and argon and had high resistivity suitable for device applications showed a dielectric constant of 25. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Static RAM cell for ternary logic

A novel CMOS static RAM cell for ternary logic systems is described. This cell is based on the lambda diode. The operation of the cell has been simulated using the SPICE 2G program. The results of the simulation are given.

Molybdenum trioxide (MoO3)/silicon photodiodes

Molybdenum trioxide (MoO3) has been deposited onto single-crystal p-type silicon by neutralized ion-beam sputter techniques. The results indicate that the diode behavior is a function of oxygen partial pressure during the reactive sputtering. Film thickness, deposition rate, index of refraction, resistivity, and integrated transmission have been measured under AM1 illumination. It appears that thin films of MoO3 could serve as an n-type transparent semiconductor for photovoltaic applications. Applied Physics Letters is copyrighted by The American Institute of Physics.

Some properties of indium-tin oxide-films

Thin films of indium-tin oxide have been deposited by DC diode sputtering from an indium-tin alloy target in an argon, hydrogen and oxygen atmosphere. Films with sheet resistance of 11 ohms/square and 80% light transmission have been obtained. The effect of cathode composition and gas mixture on sheet resistance and optical transmission properties of the films have been studied.

High Resolution Surface Imaging Using a Carbon Nanotube Array with Pointed Height distribution

In this paper we discuss a new technique to image the surfaces of metallic substrates using field emission from a pointed array of carbon nanotubes (CNTs). We consider a pointed height distribution of the CNT array under a diode configuration with two side gates maintained at a negative potential to obtain a highly intense beam of electrons localized at the center of the array. The CNT array on a metallic substrate is considered as the cathode and the test substrate as the anode. Scanning the test Substrate with the cathode reveals that the field emission current is highly sensitive to the surface features with nanometer resolution. Surface features of semi-circular, triangular and rectangular geometries (projections and grooves) are considered for simulation. This surface scanning/mapping technique can be applied for surface roughness measurements with nanoscale accuracy. micro/nano damage detection, high precision displacement sensors, vibrometers and accelerometers. among other applications.

Design Optimization of Field Emission From A Stacked Carbon Nanotube Array

Fluctuation of field emission in carbon nanotubes (CNTs) is riot desirable in many applications and the design of biomedical x-ray devices is one of them. In these applications, it is of great importance to have precise control of electron beams over multiple spatio-temporal scales. In this paper, a new design is proposed in order to optimize the field emission performance of CNT arrays. A diode configuration is used for analysis, where arrays of CNTs act as cathode. The results indicate that the linear height distribution of CNTs, as proposed in this study, shows more stable performance than the conventionally used unifrom distribution.

Precise measurement of hyperfine structure in the 2P(1/2) state of Li-7 using saturated-absorption spectroscopy

We report a precise measurement of the hyperfine interval in the 2P(1/2) state of Li-7. The transition from the ground state (D-1 line) is accessed using a diode laser and the technique of saturated-absorption spectroscopy in hot Li vapor. The interval is measured by locking an acousto-optic modulator to the frequency difference between the two hyperfine peaks. The measured interval of 92.040(6) MHz is consistent with an earlier measurement reported by us using an atomic-beam spectrometer Das and Natarajan, J. Phys. B 41, 035001 (2008)]. The interval yields the magnetic dipole constant in the P-1/2 state as A = 46.047(3), which is discrepant from theoretical calculations by > 80 kHz.

Novel approach for simultaneous measurement of strain and temperature using a single tapered fiber Bragg grating

A novel approach for simultaneous measurement of strain and temperature with a single tapered fiber Bragg grating is proposed. This method is based on the fact that the reflectivity at central wavelength of FBG reflection changes with chirp (strain gradient). A diode laser is locked to the central wavelength of FBG reflection. Central wavelength of the FBG shifts with temperature. Change in reflectivity & wavelength of the diode laser were used to measure strain and temperature on the FBG respectively.

Simultaneous measurement of strain and temperature with a pair of matched fiber Bragg gratings

A novel approach for simultaneous measurement of static/dynamic strain and temperature with a pair of matched fiber Bragg grating(FBG)s is proposed. When a diode laser locked to the mid reflection frequency of reference FBG is used to illuminate the sensor FBG, reflected intensity changes with strain on sensor FBG. Reference FBG responds with temperature on sensor FBG and is immune to strain, hence, wavelength of the diode laser acts as a signature for temperature measurement. Theoretical sensitivity limit for static strain and temperature are 1.2n epsilon / root Hz and 0.0011 degrees C respectively. Proposed sensor shows a great potential in high sensitive strain measurements with a simplified experimental setup.

High sensitive Static fiber Bragg grating strain sensing using lasers locked to relative frequency reference

A novel high sensitive fiber Bragg grating (FBG) strain sensing technique using lasers locked to relative frequency reference is proposed and analyzed theoretically. Static strain on FBG independent of temperature can be measured by locking frequency of diode laser to the mid reflection frequency of matched reference FBG, which responds to temperature similar to that of the sensor FBG, but is immune to strain applied to the same. Difference between light intensities reflected from the sensor and reference FBGs (proportional to the difference between respective pass band gains at the diode laser frequency) is not only proportional to the relative strain between the sensor and reference FBGs but also independent of servo residual frequency errors. Usage of relative frequency reference avoids all complexities involved in the usage of absolute frequency reference, hence, making the system simple and economical. Theoretical limit for dynamic and static strain sensitivities considering all major noise contributions are of the order of 25 (p epsilon) / root Hz and 1.2 n epsilon / root Hz respectively.

Growth and characterization of single crystal cored fibers of organic nonlinear optical materials

The recent development of several organic materials with large nonlinear susceptibilities, high damage threshold and low melting points encouraged researchers to employ these materials in fiber form to efficiently couple diode laser pumps and obtain enhanced second harmonic generation (SHG). In this paper we report the growth of single crystal cored fibers of 4-nitro-4'-methylbenzylidene aniline, ethoxy methoxy chalcone and (-)2-((alpha) -methylbenzylamino)-5- nitropyridine by inverted Bridgman-Stockbarger technique. The fibers were grown in glass capillaries with varying internal diameters and lengths and were characterized using x-ray and polarizing microscope techniques. The propagation loss at 632.8 nm and 1300 nm were measured and SHG was studied using 1064 nm pump.