A photonic-assisted transceiver for microwave Doppler frequency shift (DFS) measurement, which possesses capabilities of generating a frequency-quadruplicated transmitted signal and evaluating the speed and the orientation of the moving object, is proposed and demonstrated by simulating. In the transmitter, the frequency-quadruplicated transmitted signal is obtained by beating the carrier-suppressed ±2nd sidebands. In the receiver, a low-frequency reference signal is introduced to estimate the sign of the DFS. Different from the other DFS measurement solutions based on microwave photonics, the proposed approach takes the advantages of generating a high transmitted signal, employing a low reference signal, and having no use of an optical filter.
Graphene has an extremely weak coupling of electrons to phonons due to its nonionic character of lattice. This remarkable property makes graphene very attractive for hot electron bolometers (HEBs). In this paper, we present the development of a graphene-based terahertz hot electron bolometer (HEB) with Johnson noise readout. The HEB is essentially a graphene microbridge that is connected to a log spiral antenna by Au contact pads. We study the responsivity, noise equivalent power (NEP) and time constant of the graphene-based HEB in a perpendicular magnetic field. In order to understand the thermal transport inside the graphene microbridge, we also measure the graphene-based HEB at different bath temperatures between 3 K and 10 K. Detailed experimental results and analysis will be presented.
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