CW-THz vector spectroscopy and imaging system based on 1.55-mu m fiber-optics

We present a continuous-wave terahertz (THz) vector spectroscopy and imaging system based on a 1.5-mu m fiber optic unitraveling- carrier photodiode and InGaAs photo-conductive receiver. Using electro-optic (EO) phase modulators for THz phase control with shortened optical paths, the system achieves fast vector measurement with effective phase stabilization. Dynamic ranges of 100 dB.Hz and 75 degrees dB.Hz at 300 GHz and 1 THz, and phase stability of 1.5 per minute are obtained. With the simultaneous measurement of absorbance and relative permittivity, we demonstrate non-destructive analyses of pharmaceutical cocrystals inside tablets within a few minutes. (C) 2014 Optical Society of America111513sciescopu

Terahertz Communications at 300 GHz Using UTC-PD Transmitter and MMIC Receiver

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50-Gb/s Direct Conversion QPSK Modulator and Demodulator MMICs for Terahertz Communications at 300 GHz

We demonstrate direct quadrature modulator and demodulator monolithic microwave integrated circuits for future terahertz communications at 300 GHz based on the quadrature phase-shift keying (QPSK) modulation format. For the modulating and demodulating signal, we employed half-Gilbert cell mixers, which provide balanced signaling and moderate performance in conversion efficiency with a simple circuit configuration. In order to maintain the balance performance of the modulator and demodulator, passive baluns and couplers are implemented with thin-film microstrip lines, which exhibit less insertion loss than inverted microstrip lines (IMSLs), while the active mixers are based on IMSLs for short interconnections. The half-Gilbert-cell mixers have a wide enough operation bandwidth for high-throughput communications of more than 10% at 300 GHz. According to the static constellation of the modulator, imbalance is expected to be less than approximately +/- 0.6 dB angle 4 degrees. A nonchip back-to-back experiment was conducted at up to 60 Gb/s, and 50-Gb/s operation was verified with a low bit error rate on the order of 10(-8) or less. The results demonstrate that the QPSK modulation scheme can be applied to double the data rate at terahertz frequencies.115247sciescopu

Continuous-wave THz homodyne spectroscopy and imaging system with electro-optical phase modulation for high dynamic range

We present a terahertz (THz) continuous-wave coherent homodyne spectroscopy and imaging system based on THz phase control using electrooptic (EO) phase modulation for fast measurement without mechanical delay movement. After describing the degradation effects of detection signal by the optical laser noise and parasitic amplitude modulation, we propose the push-pull EO phase modulation with optical delay control for dynamic range enhancement. Using wideband unitraveling-carrier photodiode and InGaAs photoconductive antenna, spectroscopy up to a 1.5-THz frequency range and imaging are demonstrated.111619sciescopu

A 325 GHz Quadrature Voltage Controlled Oscillator With Superharmonic-Coupling

We present a 325 GHz quadrature voltage controlled oscillator (QVCO) using 0.25 mu m InP HBT technology and superharmonic coupling of two differential Colpitts VCOs. The individual VCOs exhibit about -5-dBm single-ended output power and 10 GHz frequency tuning range. The quadrature oscillation is successfully demonstrated with dc power consumption of 92.4 mW and phase imbalance less than +/- 12 degrees at around 325 GHz.1178sciescopu

Fully Integrated ASK Receiver MMIC for Terahertz Communications at 300 GHz

An ASK receiver MMIC operating at 300 GHz for future terahertz communications is presented. In the receiver IC, we fully integrated all necessary components-a receiving dipole antenna, high gain RF amplifier, envelop detector for demodulating ASK signal and output differential data amplifier-in a 1000x2500 mu m(2) area. A silicon lens was used to compensate for the small gain of the on-chip antenna. To ensure reliable and stable operation, we designed the MMIC with a thin-film microstrip line, which is expected to suppress crosstalk between the on-chip antenna and the RF amplifier through the substrate and silicon lens. The packaged receiver module with the silicon lens is expected to provide approximately 24-dBi beam directivity. Measured RF and baseband bandwidths are around 30 and 15 GHz, respectively, when a single bias of 3.3 V and total current of around 86 mA are applied. With the receiver module, simple wireless data transmission was conducted for up to 24 Gbps in the 300-GHz band. At 12.5 Gbps, error-free data transmission bit error rate < 10(-9)) over 0.3 m was achieved with the transmission power of - 16-dBm and a 25-dBi transmitting antenna. With -10-dBm transmission power, measured Q-factors of the received eye patterns were larger than 6 for up to 20 Gbps, which implies that the bit error rate will be less than 10(-9).115052sciescopu

300-GHz Step-Profiled Corrugated Horn Antennas Integrated in LTCC

This paper presents 300-GHz step-profiled corrugated horn antennas, aiming at their integration in low-temperature co-fired ceramic (LTCC) packages. Using substrate integrated waveguide technology, the cavity inside the multi-layer LTCC substrate and a surrounding via fence are used to form a feeding hollow waveguide and horn structure. Owing to the vertical configuration, we were able to design the corrugations and stepped profile of horn antennas to approximate smooth metallic surface. To verify the design experimentally, the LTCC waveguides and horn antennas were fabricated with an LTCC multi-layer process. The LTCC waveguide exhibits insertion loss of 0.6 dB/mm, and the LTCC horn antenna exhibits 18-dBi peak gain and 100-GHz bandwidth with more than 10-dB return loss. The size of the horn antenna is only, 5 x 5 x 2.8 mm(3) which makes it easy to integrate it in LTCC transceiver modules.112826sciescopu