Abstract: The present invention includes a photodiode having a first p-type semiconductor layer and an n-type semiconductor layer coupled by a second p-type semiconductor layer. The second p-type semiconductor layer has graded doping along the path of the carriers. In particular, the doping is concentration graded from a high value near the anode to a lower p concentration towards the cathode. By grading the doping in this way, an increase in absorption is achieved, improving the responsivity of the device. Although this doping increases the capacitance relative to an intrinsic semiconductor of the same thickness, the pseudo electric field that is created by the graded doping gives the electrons a very high velocity which more than compensates for this increased capacitance.

Abstract: The present invention is a fiber optic waveguide adapted for focusing a beam of light at an obtuse angle to the optical axis. A focusing end of the fiber optic is polished at an angle such that the surface normal does not coincide with the optical axis, which is defined by the path of the beam of light through the fiber optic waveguide. The angle ? is necessarily greater than 0 degrees and less than 90 degrees. The present invention further includes a focusing lens coupled to the outside of the fiber optic waveguide at its focusing end. The focusing lens may be a ball lens, and it is attached to the exterior of the cladding layer by an adhesive material.

Abstract: The present invention includes a semiconductor epitaxial structure optimized for photoconductive free space terahertz generation and detection; and amplifier circuits for photoconductively sampled terahertz detection which may employ the optimized epitaxial structures.

Abstract: A system and method for using terahertz radiation to detect and monitor a substance undergoing a change in phase from a liquid phase to a solid phase or vice-versa is disclosed. By employing terahertz radiation in either the pulsed mode or in the continuous-wave (CW) mode, the system can non-invasively monitor these changes. The system uses the principle that matter in a liquid state will absorb and attenuate terahertz radiation to a larger degree than matter in a semisolid or solid state. Most terahertz radiation absorption occurs due to the rotational motions of molecules, i.e. either whole molecules or groups of atoms rotating about molecular bonds.

Abstract: An industrially hardened terahertz electromagnetic transmitter and receiver module (29) is disclosed. The electromagnetic wave module has an optic (30) which relays an optical pulse from the delivery fiber (32) to the terahertz device. The relay optic (30) allows for a greatly reduced optical spot size as compared to the output of the optical fiber. Thus, the sensitivity of the overall system is enhanced by improving the efficiency of the terahertz device. The relay optic (30) allows the small spot of light to be aligned to the electromagnetic transmitter or receiver with sub-micron precision.

Abstract: The present invention includes a semiconductor epitaxial structure optimized for photoconductive free space terahertz generation and detection; and amplifier circuits for photoconductively sampled terahertz detection which may employ the optimized epitaxial structures.

Abstract: An electromagnetic radiation emitter which utilizes a precompensator, pulsed light signal, optical fiber cable, and a terahertz radiation generator. The present invention incorporates an optical precompensator to correct for the stretching of an optical signal as it travels through an optical fiber cable. The dispersion characteristics of the precompensator will be equal and opposite to the dispersion characteristics of the optical fiber cable, maintaining the fidelity of optical pulses as they travel through and exit the optical fiber cable striking a device that generates terahertz electromagnetic radiation.

Abstract: A semiconductor p-i-n photodiode having a substrate, an n layer coupled to the surface of said substrate, an i layer coupled to the surface of said n layer, and a carbon doped p layer coupled to the surface of said i layer.