Enhancing the photomixing efficiency of optoelectronic devices in the terahertz regime

Abstract

A method to reduce the transit time of majority of carriers in photomixers and photo detectors to < 1 ps is proposed. Enhanced optical fields associated with surface plasmon polaritons, coupled with velocity overshoot phenomenon results in net decrease of transit time of carriers. As an example, model calculations demonstrating > 280× (or ∼2800 and 31.8 µW at 1 and 5 THz respectively) improvement in THz power generation efficiency of a photomixer based on Low Temperature grown GaAs are presented. Due to minimal dependence on the carrier recombination time, it is anticipated that the proposed method paves the way for enhancing the speed and efficiency of photomixers and detectors covering UV to far infrared communications wavelengths (300 to 1600 nm).Recent experimental observation of extraordinary optical transmission through a normal metal film having subwavelength holes[1] has generated intense interest in harnessing the underlying physics for photonic applications. It is widely believed that quasi two-dimensional electromagnetic excitations tightly bound to the metal surface known as Surface Plasmon Polaritons (SPPs) are responsible for the observed near field enhancement of the optical radiation. Exponential decay of field components arising from SPPs (penetrating ∼100, ∼10 nm in dielectric and metal respectively), make them highly attractive for miniature photonic circuits and devices [2]. Currently, several potential applications of SPPs are being explored including wave guiding [3] and near-field microscopy [4]. However, application of SPPs to enhance the speed and efficiency of photo detectors or photomixers has not been attempted due to the complexity of underlying physics and optimal device designs involving complicated dielectric-metal structures.In this letter we propose a simple interdigitated metal structure embedded in a suitable semiconductor material to harness SPPs for improving the speed and efficiency of photomixers and detectors. Such a device can be realized with the existing material growth techniques [5]. As an example, we demonstrate via model calculations, significant (> 280×) improvement in the efficiency of a THz photomixer based on Low Temperature grown GaAs (LT-GaAs). Microwave to THz radiation sources in the 0.1 to 10 THz are being extensively studied for their application in communications, medical imaging, and spectroscopy [6,7,8,9,10]. For many applications-compact, narrow-linewidth, widely tunable continuous wave sources are necessary. In particular, to be used as a local oscillator in communications systems the THz source should produce stable output power > 10 µW [8,11]. Among the various techniques being pursued [6,8,11,12,13] electrical down conversion of optical microwave sources in a suitable photomixer [6,11,12] are appealing due to the easy availability of tunable, narrow-linewidth, and stable solid state lasers. However, until now the output power from these photomixers is limited to < 10 µW in the cru- . When the top and bottom interdigitated structures in (b) are con...

A Review on Terahertz Technologies Accelerated by Silicon Photonics

“…Suitable photomixer devices include PC antennas [ 41 ], uni-travelling-carrier photodiodes (UTC-PDs) [ 42 ], travelling-wave uni-travelling-carrier photodiodes (TW-UTC-PDs) [ 43 ], or n-i-p-n-i-p superlattice photomixers [ 44 ]. However, the efficiency of optical-to-THz conversion is low, which limits the output power of most CW THz signals to the microwatt level [ 9 , 45 ]. The emission in a UTC-PD is typically at frequencies up to 1.5 THz.…”

Millimeter-wave generation using hybrid silicon photonics

“…One promising approach for achieving CW THz sources at room temperature is photomixing in ultrafast photoconductive semiconductor materials, which is possible due to their ultrashort carrier lifetime [375][376][377]. However, the efficiency of photon-to-current conversion is low, which limits the output power of CW THz PMs to the microwatt level [378,379].…”

Terahertz Emitters, Detectors and Sensors: Current Status and Future Prospects

“…Based on model calculations for LT-GaAs photomixer, it has been proposed [Pilla, 2007] that photomixing efficiency can be enhanced by reducing the transit time of majority of carriers in photomixers and photodetectors to < 1 ps. The model indicated that the output terahertz power, P f is proportional to difference frequency of incident lasers (f) which is given by relation Pf α f -2.77 in the 0.5-6.5 THz range.…”