We measured pulsed THz emission from high-mobility MBE grown InGaAs/InAlAs multi-nanolayer structures. The detected average THz power was 32 μW at 32 mW optical excitation power. The bandwidth of the THz pulses exceeds 4 THz.

We demonstrate pulsed THz emission and detection in low temperature (LT) MBE grown Be-doped InGaAs/InAlAs multi-nanolayer structures for an excitation wavelength of 1030 nm. We obtained spectra with a bandwidth of up to 3 THz. Furthermore, we performed differential transmission experiments to investigate the material's relaxation time constants.

We present scalable large area terahertz (THz) emitters based on a nanoscale multilayer InGaAs/InAlAs heterostructure and a microstructured electrode pattern. The emitters are designed for pump lasers working at the telecommunication wavelength of 1.55 μm. Electric THz fields of more than 2.5 V cm⁻¹ are reached with moderate pump powers of 80 mW, the corresponding spectrum extends up to 3 THz. The saturation characteristics have been investigated for different pump laser spot sizes. For small pump powers of less than 50 mW the emitted THz field is nearly independent of the spot size, for higher pump powers and small spot sizes a clear saturation of the generated THz pulse can be observed. Hence the use of scalable emitters is especially promising for high power fibre laser systems. The spectral content of the generated radiation is nearly independent of the parameters spot size, pump power, and bias voltage, which allows for stable operation in spectroscopic applications.

The influence of localization and disorder in (GaIn)As/(AlIn)As heterostructures with spatially separated photoconductive and recombination regions designed as a material for THz antennas for telecom applications at 1.55μm is investigated by photoluminescence spectroscopy. The emission is studied as a function of lattice temperature for a series of samples with different growth temperatures. Strain-induced disorder is identified as the main contribution to carrier localization. In addition, inhomogeneous broadening as well as PL intensity is strongly influenced by the impurity density in the barrier material. The optimal configuration as THz antenna material is achieved at a growth temperature of 375°C.

We present a photonic integrated circuit, which enables the full control of the THz signal in continuous wave photomixing THz systems via standard electronics. The device comprises two DFB-lasers and an optical phase modulator on a single chip. Due to a unique bidirectional operation technique, the chip provides the optical beat signal for both THz emitter and THz receiver and allows for manipulation of the THz phase via the optical phase modulator. To evaluate the performance of our solution, we realize a coherent cw THz system based on our photonic integrated circuit and compare it to discrete lasers and standard components. As the results show, both setups feature an identical signal-to-noise ratio, reaching 50 dB at a frequency of 1 THz for an integration time of 500 ms. This is the best reported performance of CW photomixing systems running at 1.5 mu m optical wavelength.

We report on scalable large-area terahertz emitters and detectors based on In0.53Ga0.47As/In0.52Al0.48As heterostructures for excitation with 1.55 μm radiation. Different geometries involving three different electrode gap sizes are compared with respect to terahertz (THz) emission, bias field distribution, and Joule heating. The field distribution becomes more favorable for THz emission as gap size increases, while Joule heating exhibits the opposite dependence. Devices with three different gap sizes, namely 3 μm, 5 μm, and 7.5 μm, have been investigated experimentally, the emitter with a gap size of 7.5 μm showed the best performance. The scalable devices are furthermore employed as detectors. The scalable electrode geometry enables spatially integrated detection, which is attractive for specific applications, e.g., where an unfocused THz beam has to be used.

We present a photomixing based continuous wave terahertz single pixel imaging system with quasi instantaneous amplitude and phase detection, allowing us to scan a terahertz image at 1 THz with 0.45 million measurement points in less than 8 min, which is as fast as previously demonstrated at lower frequencies (0.3 THz).

An integrated photonic chip allows for full control of the THz signal in cw THz photomixing systems. This THz control unit does provide direct access to the THz amplitude and phase via standard electronics as well as continuous tuning of the beat frequency over a frequency range larger than 1 THz.

Terahertz systems can profit from technologies developed originally for telecom applications. Recent developments on telecom-based key devices are summarized and ways towards CW systems with highest flexibility and excellent performance at reasonable costs are sketched.

Highly efficient mesa-structured 1.5 μm photoconductive antennas, direct detection without lock-in amplifier, and a voice-coil mirror drive with accurate position sensor are merged to a fast and precise system. A pulse trace of 25 ps is measured every 50 ms, and integration over 15 s results in a superior 75 dB dynamic range and a bandwidth of 5 THz.

We present first results of pulsed THz emission from low temperature (LT) MBE grown Be-doped InGaAs/InAlAs multi-nanolayer structures at an excitation wavelength of 1030 nm. The spectra obtained reach 3 THz. We further investigate the material's relaxation time constants by differential transmission experiments.

In-fibre wavelength selective modulation of the optical phase enables the electro-optic control of the terahertz phase in continuous-wave photomixing terahertz systems without any free-space optics. Using a fully fibre-coupled terahertz setup, a coherent scan of a frequency range of 1.5 THz with 100 MHz resolution in less than 24 s is demonstrated. This sample rate of 1.6 ms/sample is more than 20 times faster than any previous broadband scans reported.

We present first results on photoconductive switches based on MBE grown InGaAs/InAlAs multi-nanolayer structures with separated trapping and photoconductive layers, the later exhibiting high carrier mobility. The high mobility significantly increases the optical power-to-THz conversion efficiency, while the emitted THz bandwidth exceeds 3 THz.

Low cost and compact transmitters are key components for short reach and datacom applications in fiber communication systems. Bit rates of 40 Gbit/s are beyond the speed limitation of conventional directly modulated lasers. Lasers with an integrated electro-absorption modulator (EML) represent one possible solution. An attractive alternative are Passive Feedback Lasers (PFL). Here, the modulation bandwidth is significantly increased by an integrated feedback section. Underlying physics and functionality of the PFL are presented as well as the successful realization at wavelengths in the 1300 nm and 1550 nm regions. The performance of these PFLs is demonstrated in system experiments.