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The use of optical fiber for signal distribution and remote operation of a set of parallel inspection units based on THz time-domain spectroscopy is presented and analyzed. A centralized approach with optical source-sharing simplifies the implementation and cost of nondestructive inspection platforms, where several sensing units have to work in the same facility, such as factories and security controls. The cost of such a distribution system is evaluated, its feasibility experimentally demonstrated, and key features relevant to the system performance are discussed., This work was supported in part by the Spanish Ministry of Economy and Competitiveness through Project TEC2012-35797 and FPU Grant 12/02847.

A processing technique for the determination of the average refractive index and thickness of a two-layer system is presented. It is based on a single measurement with a standard terahertz time-domain spectrometer and the multilayer system thickness. The technique relies on the interference caused by the main pulse with the echoes produced in each material. This approach allows noninvasive inspection of double-layer compound products. (C) 2014 Optical Society of America, The authors thank the Spanish Ministerio de Economia y Competitividad for partially supporting this work through project TEC2012-35797. Federico Sanjuan also thanks Dr. Jorge Tocho and Dr. Alberto Lencina for their encouragement and support.

A method for obtaining the average refractive indexes of a birefringent material in the terahertz region in a single measurement with a standard terahertz time-domain spectrometer is presented. The method is based on processing the frequency-domain interference between terahertz pulses and echoes through the Fourier transform of the terahertz spectrum. The technique also allows the determination of the optical axis orientation of the material by making two measurements with different angles of the sample optical axis. (C) 2014 Optical Society of America, The authors thank the Erasmus Mundus scholarship and the Consejo Nacional de Investigaciones Cientificas y Tecnicas (Conicet) that support the work of Federico Sanjuan at Universitat Politecnica de Valencia and the Spanish Ministerio de Economia y Competitividad for partially supporting this work through project TEC2012-35797. Federico Sanjuan also thanks Dr. Jorge Tocho for his encouragement and support.

A distributed system for remote generation and detection of terahertz pulses using an active optical fiber link and photoconductive antennas optimized for telecom wavelengths is experimentally demonstrated. Frequencies beyond 1 THz after 1×16 division and 100 m fiber transmission are obtained. It shows the capability of fiber-based spectroscopy setups for cost-reduction in facilities where several sensing platforms are needed such as industrial in-line product inspection, transport security checkpoints, etc.

Enhanced multiple four-wave mixing (FWM) processes in nonlinear fiber by phase modulation of the pump carrier are investigated for harmonic mixing multiplication of microwave signals. The enhancement of cascaded FWM by phase modulation in the case of small spacing between pump carriers (10 GHz) is studied. Experimental results show that microwave signals in the V-band can be generated from a tone in the C-band through external amplitude modulation and optical nonlinear harmonic multiplication. A harmonic multiplication factor of 13 has been demonstrated using the proposed technique. The upconverted microwave signals show no additional degradation in phase noise due to the photonic nonlinear processes besides the inherent phase noise increment due to the multiplication process., This work was supported in part by the Spanish Ministerio de Economia y Competitividad through Project TEC2009-08078 and Project TEC2012-35797.

Time-domain modulation of a pulsed laser spectrum to synthesize different pulse shapes is proposed. The generated pulses are time-stretched and injected into a semiconductor optical amplifier biased by the photo-detection of a time-shaped version of the pulses generated by the optical source. Different frequencies of the original spectrum can therefore be suppressed or amplified leading to pulse shaping. Experimental results proving the concept are reported.

A terahertz shaping system based on optical fiber components as opposed to traditional free-space solutions is proposed. It is based on the time-domain modulation of the optical source spectrum. Standard singlemode fiber distributes and disperses the pulse before filtering its spectral components by means of the cross-gain and cross-phase modulation effects taking place in an interferometric semiconductor optical amplifier structure. Experimental measurements are obtained, showing the tunability of the system as well as its reconfigurability. © 2012 Optical Society of America., This work has been partially supported by the Spanish Ministerio de Economia y Competitividad (TEC2009-08078). Jesus Palaci is supported by the Formacion de Personal Investigador grant program of the Universidad Politecnica de Valencia.

The manipulation of the operating conditions of photoconductive antennas by means of an additional continuous wave (CW) is reported. It is used to control a fiber-based terahertz (THz) time-domain-spectroscopy system at telecom wavelengths. The injection of an optical CW into the transmitter allows the control of the THz amplitude without causing major degradation to the system performance. This, for instance, can be exploited to perform modulation of the THz signal., This work was supported by the Spanish Ministerio de Economia y Competitividad through project TEC2012-35797. The work of Alexander Bockelt is supported by the Formacion de Profesorado Universitario (FPU) grant program of the Ministerio de Economia y Competitividad.

All-fibre control of a terahertz time-domain spectroscopy system based on photoconductive antennas fed with optical sources in the telecom band is demonstrated. A semiconductor optical amplifier (SOA) is used to obtain continuously tunable delays on 100 fs optical pulses. Additionally, the modulation required to carry out lock-in detection can be simultaneously performed avoiding mechanical choppers or high-voltage alternate biasing of the transmitter antenna., This work was supported by the Spanish Ministerio de Ciencia e Innovacion TEC2009-08078. J. Palaci's work is supported by an FPI-UPV grant programme of the Universitat Politecnica de Valencia.