Edge-coupled membrane terahertz photonic transmitters based on metal–semiconductor–metal traveling-wave photodetectors

Abstract

Ultra-high-speed photodetectors and printed-circuit antennas construct photonic transmitters. In this letter, we demonstrate a terahertz ͑THz͒ photonic transmitter: edge-coupled membrane photonic transmitters based on metal-semiconductor-metal traveling-wave photodetectors, which are fabricated with low-temperature-grown GaAs photoabsorption layers. With a membrane-based and edge-coupled structure, the demonstrated photonic transmitters can eliminate the requirement of Si lenses and attain an over 20 times higher optical-to-THz power conversion efficiency 2ϫ10 Ϫ4 than vertical illuminated photonic transmitters with Si lenses at the same operation frequency.

Electron relaxation and transport dynamics in low-temperature-grown GaAs under 1 eV optical excitation

“…1,2 Even though most applications have been restricted to the ϳ800 nm range, more and more attention has focused on their potential use for the telecommunications regime ͑1.3-1.55 m͒ [3][4][5][6][7] by utilizing midgap defect state to conduction band absorption or two-photon absorption. Recently, ultrahigh speed high power-bandwidth performance has been demonstrated around 1.3 m with LTG GaAs metal-semiconductor-metal ͑MSM͒ traveling-wave photodetectors ͑TWPDs͒.…”

Traveling-Wave Photodetectors With High Power–Bandwidth and Gain–Bandwidth Product Performance

“…Distinct bandwidth degradation behavior, which can be attributed to hot electron effects of photogenerated carriers [30], [31], have also been observed. By utilizing the good speed and output power performances of MSM-TWPD, we have also demonstrated the novel structure of an LTG-GaAs-based terahertz photonic transmitter [32]. By utilizing the fully distributed microwave guiding property of the MSM-TWPD, short carrier-trapping time of LTG-GaAs, and a membrane antenna structure, high conversion efficiency ( 1.1 10 ) can be achieved at 650-GHz frequency [33].…”

“…By utilizing the fully distributed microwave guiding property of the MSM-TWPD and a membrane antenna structure, we have also demonstrated a novel terahertz photonic transmitter [32], [33] with high conversion efficiency. Compared with other millimeter-or submillimeter-wave emission techniques such as Gunn diodes [54], p-type Ge-based or quantum cascade terahertz lasers [55], [56], and resonant tunneling diodes [57], photonic transmitters have the advantages of simplicity, compactness, wide tunability, and room temperature operations.…”

“…To test the performance of our fabricated device, the light source that we used was a mode-locked Ti:sapphire laser with 100-fs optical pulsewidth and 82-MHz repetition rate. By passing the broadband femtosecond optical pulses through etalons, we can increase the repetition rate of the light source to terahertz frequency range and trigger the photonic transmitters by coupling this high-repetition-rate light into the edge-coupled MSM-TWPD [32], [33]. The top view of our device is shown in Fig.…”

“…The RF choke filter, which acts as an inductance [41], avoids the high-frequency ac current (with a resonant frequency of the slot line antenna) leaking into the dc probe pad. We removed the GaAs substrate and mounted the membrane of the fabricated device on a glass substrate, which has a much lower dielectric constant than GaAs substrates and can thus allow the radiation of terahertz energy into the substrate or free space without using a Si lens [32], [33]. Fig.…”