Jean-François Lampin

Terahertz radiation from heavy-ion-irradiated In0.53Ga0.47As photoconductive antenna excited at 1.55μm

We investigate terahertz (THz) emission from heavy-ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm. The carrier lifetime in the highly irradiated In0.53Ga0.47As layer is less than 200 fs, the steady-state mobility is 490cm2V−1s−1, and the dark resistivity is 3Ωcm. The spectrum of the electric field radiating from the Br+-irradiated In0.53Ga0.47As antenna extends beyond 2 THz. The THz electric field magnitude is shown to saturate at high optical pump fluence, and the saturation fluence level increases with the irradiation dose, indicating that defect center scattering has a significant contribution to the transient mobility.

Metal-metal terahertz quantum cascade laser with micro-transverse-electromagnetic-horn antenna

A 2.8 THz metal-metal quantum cascade laser operating with a microtransverse-electromagnetic-horn antenna has been demonstrated. By comparing the far-field radiation pattern to a standard ridge cavity with a cleaved facet, a striking improvement of the directionality is observed. The effectiveness of the horn antenna is critically dependent on the control of the lateral modes in the laser cavity.

Continuous wave terahertz generation up to 2THz by photomixing on ion-irradiated In0.53Ga0.47As at 1.55μm wavelengths

We report the generation of continuous terahertz waves from microwave frequencies of up to 2THz obtained by photomixing two optical waves at 1.55μm wavelengths in ion-irradiated In0.53Ga0.47As interdigitated photomixers. A 200nm thick silicon nitride coating is used for antireflection and passivation layer, improving the reliability and the heat tolerance of the photomixer. In such devices, output powers greater than 40nW at 0.5THz and 10nW at 1THz have been achieved. Considering the observed saturation of the output power with the increase of bias voltage, the optimum excitation conditions regarding optical power and bias voltage are discussed.

Ultrawide-Bandwidth Single-Channel 0.4-THz Wireless Link Combining Broadband Quasi-Optic Photomixer and Coherent Detection

Free space communications with huge data capacity have become a key point for the development of mobile access, services, and network technologies convergence. Wireless links using emerging terahertz technologies, also referred to as T-ray communications, have become an intensive research field within last years since T-rays at the millimeter/submillimeter frontier remain more robust in terms of scintillation, dielectric obstacles, and fog compared with near-infrared signals. Using a passive THz hot-spot which can be fed by fiber optic networks, we investigate up bit rates up to 46 Gbps for a THz wireless transmission system at 400-GHz carrier frequency. Using a THz photomixer integrated with a specific broadband antenna and heterodyne electronic detection, we investigate the eye diagrams using 1-μW received power, highlighting the high sensitivity and ultra-wideband behavior of the whole THz system.

Milliwatt-level output power in the sub-terahertz range generated by photomixing in a GaAs photoconductor

It is shown from accurate on-wafer measurement that continuous wave output powers of 1.2 mW at 50 GHz and 0.35 mW at 305 GHz can be generated by photomixing in a low temperature grown GaAs photoconductor using a metallic mirror Fabry-Perot cavity. The output power is improved by a factor of about 100 as compared to the previous works on GaAs photomixers. A satisfactory agreement between the theory and the experiment is obtained in considering both the contribution of the holes and the electrons to the total photocurrent.

Injection-locking of terahertz quantum cascade lasers up to 35GHz using RF amplitude modulation

We demonstrate that the cavity resonance frequency — the round-trip frequency — of terahertz quantum cascade lasers can be injection-locked by direct modulation of the bias current using an RF source. Metal-metal and single-plasmon waveguide devices with roundtrip frequencies up to 35GHz have been studied, and show locking ranges above 200MHz. Inside this locking range the laser round-trip frequency is phase-locked, with a phase noise determined by the RF-synthesizer. We find a square-root dependence of the locking range with RF-power in agreement with classical injection-locking theory. These results are discussed in the context of mode-locking operation.

Detection of picosecond electrical pulses using the intrinsic Franz–Keldysh effect

We report time-resolved measurements of ultrafast electrical pulses propagating on a coplanar transmission line using the intrinsic Franz–Keldysh effect. A low-temperature-grown GaAs layer deposited on a GaAs substrate allows generation and also detection of ps pulses via electroabsorption sampling (EAS). This all-optical method does not require any external sampling probe. A typical rise time of 1.1 ps has been measured. EAS is a good candidate for use in THz characterization of ultrafast devices.

Generation and detection of terahertz pulses using post-process bonding of low-temperature-grown GaAs and AlGaAs

We present an electro-optical method to measure very high frequency characteristics of planar electronic devices. This method allows one to generate and detect subpicosecond electrical pulses on a coplanar stripline using photoconduction and electroabsorption sampling in transferred low-temperature-grown epitaxial layers. The epitaxial lifted-off films are directly van der Waals bonded on the transmission line under test. Good switching efficiency and short electrical rise time (<490 fs) are measured. A bandwidth of 2.5 THz with 60 dB of dynamic range is obtained. This confers to the technique a large field of applications in ultrahigh-speed electronic measurements.

Experimental evidence of backward waves on terahertz left-handed transmission lines

Left-handed transmission lines have been characterized by electro-optic sampling. The transmission lines used a coplanar strip technology periodically loaded by series capacitances and shunt inductances printed by electron-beam lithography onto a low-κ substrate. The experiments by optoelectronic sampling were conducted using low-temperature-grown GaAs and AlGaAs patches for probing the time-domain transmission properties. The devices exhibit a high-frequency response above 100 and up to 400 GHz which shows direct evidence of a backward propagation by tracking the time dependence of transmitted signals and phase analysis.

Two-photon absorption in InP substrates in the 1.55μm range

The nonlinear optical absorption has been studied in three different InP substrates (semi-insulating Fe-doped, n-type S-doped, and p-type Zn-doped) by subpicosecond pump-probe differential transmission experiments at 1.6μm. A strong negative differential transmission peak is observed at zero delay, induced by an autocorrelation effect: it is related to two-photon absorption, but not to the occurrence of transitions involving any midgap level (noticeably the Fe-related one). The experimental two-photon absorption coefficient β for InP stands in the range between 24 and 33cm∕GW.