Stefan Hunsche

T-ray tomography

We demonstrate tomographic T-ray imaging, using the timing information present in terahertz (THz) pulses in a reflection geometry. THz pulses are reflected from refractive-index discontinuities inside an object, and the time delays of these pulses are used to determine the positions of the discontinuities along the propagation direction. In this fashion a tomographic image can be constructed.

THz near-field imaging

We present first results of near-field imaging with ultrashort, broadband far-infrared pulses. By focusing the radiation into a tapered metal tip with a small exit aperture and scanning a sample in the near field of this aperture, sub-wavelength spatial resolution better than λ/4 is demonstrated.

Measurement of residual chromatic dispersion of a 40-Gb/s RZ signal via spectral broadening

In this letter, we examine the spectrum of a 40-Gb/s return-to-zero (RZ) data stream, which has been broadened by self-phase modulation in a nonlinear fiber. Spectra were recorded as the residual chromatic dispersion at the input of the nonlinear fiber was varied using a tunable dispersion element. We show that spectral broadening can provide a useful measure of the residual chromatic dispersion of the data stream.

THz-imaging: a new method for density mapping of wood

SummaryThis paper presents a new technique for fast and non-intrusive density mapping of wood based on far-infrared spectroscopy. The transmission of a piece of beech 1.7 mm thick is investigated between 0.1 and 2.5 THz. In this spectral range we find wood to be fairly transparent, but density inhomogeneities and structural details such as annual rings become visible in the transmission profile. The measured absorption correlates well with the wood density independently obtained by the gravitometric-volumetric method. Thus it finally becomes possible to transform the THz images into 2-dimensional density maps.

Q-factor monitoring using FEC for fault-management applications

Feature Issue on Optical Performance Monitoring (OPM). We examine the use of forward-error-correction coding for Q-factoring monitoring in fault-management applications. The sensitivity of this technique is measured for accumulated dispersion values up to -982 ps/nm, demonstrating the potential for use in embedded monitoring without dispersion compensation.

THz imaging in the near-field

Time-domain terahertz spectroscopy (THz-TDS), based on optoelectronic generation and detection of sub-picosecond electrical transients in photoconducting antennae, has become an extremely valuable tool for spectroscopy in the far-infrared spectral region,1 Recently, we have extended THz-TDS to realtime “T-ray” imaging by reducing the acquisition time of THz waveforms by four orders of magnitude.