RESUMO
In this paper, we report on waveguide-type modified uni-traveling-carrier photodiodes (MUTC-PDs) providing a record high output power level for non-resonant photodiodes in the WR3.4 band. Indium phosphide (InP) based waveguide-type 1.55 µm MUTC-PDs have been fabricated and characterized thoroughly. Maximum output powers of -0.6 dBm and -2.7 dBm were achieved at 240â GHz and 280â GHz, respectively. This has been accomplished by an optimized layer structure and doping profile design that takes transient carrier dynamics into account. An energy-balance model has been developed to study and optimize carrier transport at high optical input intensities. The advantageous THz capabilities of the optimized MUTC layer structure are confirmed by experiments revealing a transit time limited cutoff frequency of 249â GHz and a saturation photocurrent beyond 20â mA in the WR3.4 band. The responsivity for a 16 µm long waveguide-type THz MUTC-PD is found to be 0.25 A/W. In addition, bow-tie antenna integrated waveguide-type MUTC-PDs are fabricated and reported to operate up to 0.7 THz above a received power of -40 dBm.
RESUMO
A novel photonic-assisted 2-D Terahertz beam steering chip using only two tuning elements is presented. The chip is based on an array of three leaky wave antennas (LWAs) with a monolithically integrated beamforming network (BFN) on a 50â µm-thick indium phosphide substrate. The THz beam angle in elevation (E-plane) is controlled via optical frequency tuning using a tunable dual-wavelength laser. An optical delay line is used for azimuth (H-plane) beam control. The simulated beam scanning range is 92° in elevation for a frequency sweep from 0.23â THz to 0.33â THz and 69.18° in azimuth for a time delay of 3.6 ps. For the frequency range from 0.26â THz to 0.32â THz, it is confirmed experimentally that the THz beam scans from -12° to +33°, which is in good agreement with the numerical simulations. The beam direction in azimuth scans with a total angle of 39° when applying a delay difference of 1.68 ps. A good agreement is found between theoretically predicted and experimentally determined THz beam angles with a maximum angle deviation below 5°. The experimental scanning angles are limited due to the mechanical constraints of the on-wafer probes, the on-chip integrated transition and the bandwidth of the THz receiver LNA. The mechanical limitation will be overcome when using a packaged chip.
RESUMO
THz communications is envisaged for wide bandwidth mobile communications eventually reaching data capacities exceeding 100 Gbit/s. The technology enabling compact chip-integrated transceivers with highly directive, steerable antennas is the key challenge at THz frequencies to overcome the very high free-space path losses and to support user mobility. In this article, we report on mobile and multi-user THz communications using a photonic THz transmitter chip featuring 1D beam steering for the first time. In the proposed approach, 1D THz beam steering is achieved by using a photodiode excited leaky-wave antenna (LWA) in the transmitter chip. The on-chip LWA allows to steer the directive THz beam from 6° to 39° within the upper WR3-band (0.28-0.33 THz). The antenna's directivity is 14 dBi which is further increased to 23 dBi using an additional hemicylindrical Teflon lens. The 3-dB beam width and coherence bandwidth of the fabricated THz transmitter chips with lens are 9° and 12 GHz, respectively. The proposed approach allows steering the THz beam via the beat frequency of an optical heterodyne system at a speed up to 28°/s. Without using a THz amplifier in the transmitter chip, a data rate of 24 Gbit/s is achieved for a single user for all beam directions and at short wireless distances up to 6 cm. The wireless distance is successfully increased to 32 cm for a lower data rate of 4 Gbit/s, still without using a transmitter amplifier. Also, multi-user THz communications and the overall capacity of the developed THz transmitter chip is studied revealing that up to 12 users could be supported together with a total wireless data capacity of 48 Gbit/s. Fully integrated 2D transmitter chips are expected to reach wireless distances of several meters without additional amplifiers.