A comprehensive model for photomixing in ultrafast photoconductors

A comprehensive model for photomixing phenomenon in a dc-biased ultrafast photoconductor is proposed. The dependence of the carrier lifetime and carrier velocity on the electric field is taken into account, and the significance of carrier transport and carrier generation and recombination mechanisms in a terahertz photomixer are evaluated. A method for calculating the nonuniform induced electric field due to excess charge density resulting from unequal electron and hole recombination lifetimes is presented.     

Frequency- and time-varying scattering parameters of a photo-excited superconducting microbridge

The extended scattering parameters for linear time varying devices are used to model a high-temperature superconducting (HTS) bridge under time-harmonic optical irradiation. It is shown that this structure acts as a time-varying low-pass filter, which its transfer function characteristic changes periodically with time. This behavior makes this configuration ideal for applications where a time-varying filter is on demand.     

A submilliwatt terahertz high-temperature superconductive photomixer array source: analysis and design

A continuous-wave terahertz photomixer array source made of a high-temperature superconductor material is proposed, and its radiation characteristic is studied. Employing photomixer/antenna elements in an array configuration increases the available terahertz power. It is shown that a submilliwatt terahertz power is achievable from a typical array structure. The beam steering capability of the proposed device is also investigated.     

Analysis and design of a photoconductive integrated photomixer/antenna for terahertz applications

A new terahertz (THz) photoconductive photomixer/antenna device is presented. A continuous-wave THz signal is generated in a dc-biased photoconductive film by employing optical heterodyne scheme, and at the same time, the size of the film on the grounded dielectric substrate is designed to have an efficient broadside radiation. Incorporating the photoconductive film as the photomixing media and the radiation element not only eliminates source to antenna coupling problem but also makes the proposed device attractive for THz array source configurations. Analytical expressions for the photocurrent and the radiation power are derived under high dc bias condition, and the effects of the device configuration on its performance is studied. Two possible photomixer configurations, namely longitudinal and transversal, are introduced and their photomixing efficiencies and radiation power are compared. The typical nW output power is achievable by mW laser pump power for frequencies up to 10 THz.     

Modeling and analysis of high-temperature superconductor terahertz photomixers

Photomixing phenomenon in superconductors is studied. For a photo-excited superconductor film the fundamental equations for the carriers motion inside the superconductor material have been used in connection with the two-temperature model to find an analytic expression for the generated terahertz (THz) photocurrent inside the film. The dependency of the resulting photocurrent on the material and laser parameters, temperature, and photomixer configuration for a photomixer made of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// high-temperature superconductor is studied.     

Physical modeling and frequency-response analysis of a high-temperature Superconducting terahertz photomixer

A physical modeling and a rigorous theoretical analysis consisting of the two-temperature model and the generalized transmission-line model is used to evaluate a photo-induced terahertz continuous-wave voltage from a dc current-biased high-temperature superconducting (HTS) transmission line by optical heterodyne photomixing. The electrical and optical frequency-response analyses show the amplitude of this voltage increases with increasing beat frequency and decreasing optical frequency of laser beams. Its maximum frequency is found to be limited by the gap frequency of the HTS material, which is consistent with the available experiments reported in the literature. The developed model along with our numerical simulation reveal the ways to produce a coherent traveling-wave and high-power terahertz signal with proper choice of an HTS material, bias condition, geometrical configuration, and parameters of the transmission line and characteristics of two laser beams. This HTS photomixer can play an important role in terahertz transceivers as broadly tunable local oscillators with low-noise/low-power consumption characteristics.     

Analysis and design of a continuous-wave terahertz photoconductive photomixer array source

An array of photoconductive photomixer/antenna elements as a continuous-wave terahertz source is proposed, and its radiation characteristic is studied. Employing photomixer/antenna elements in an array configuration increases available terahertz power, while each of the array elements consumes optical power less than its maximum sustainable power. A few microwatt terahertz power is achievable from a typical array structure. It is shown that the radiated beam can be steered by changing the angle between the two exciting laser beams.     

Semi-Analytical Calculation of Terahertz Signal Generated from Photocurrent Radiation in Traveling-Wave Photonic Mixers

A semi-analytical method based on distributed source transmission line model is proposed to analyze a traveling-wave terahertz photomixer integrated with a coplanar stripline waveguide. Multilayer spectral domain method along with complex image technique have been applied to calculate the distributed voltage source element in the transmission line representation. To find the coupled terahertz signal along the coplanar stripline, the transmission line equations are solved. The results obtained from the proposed method are verified by the full wave analysis.