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Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, Silicon is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities, like second harmonic generation nor the linear electro-optic effect (i.e. Pockels effect). Nonetheless, by means of strain gradients, generated by depositing a stressed layer (typically SiN) on silicon waveguides, this restriction vanishe. Hence, for years, many attempts on characterizing the second order nonlinear susceptibility tensor through Pockels effect have been performed. However, due to the semiconductor nature of silicon, its analysis has been wrongly carried out. Indeed, carriers in Si, at the Si/SiN interface and in SiN have a screening effect when performing electro-optic modulation, which have led to overestimations of the second order nonlinear susceptibility and eventually rose a controversy on the real existence of Pockels effect in strained silicon waveguides. Here, we report on unambiguous experimental characterization of Pockels effect in the microwave domain, by taking advantage of the inherent limitation of carrier effect in high frequency range. Recent results on high-speed measurements will be presented and discussed. Both charge effects and Pockels effect induced under an electric field will be also analysed.

International audience; Near-infrared germanium (Ge) photodetectors monolithically integrated on top of silicon-on-insulator substrates are universally regarded as key enablers towards chip-scale nanophotonics, with applications ranging from sensing and health monitoring to object recognition and optical communications. In this work, we report on the highdata-rate performance pin waveguide photodetectors made of a lateral hetero-structured silicon-Ge-silicon (Si-Ge-Si) junction operating under low reverse bias at 1.55 mu m. The pin photodetector integration scheme considerably eases device manufacturing and is fully compatible with complementary metal-oxide-semiconductor technology. In particular, the hetero-structured Si-Ge-Si photodetectors show efficiency-bandwidth products of similar to 9 GHz at -1 V and similar to 30 GHz at -3 V, with a leakage dark current as low as similar to 150 nA, allowing superior signal detection of high-speed data traffic. A bit-error rate of 10(-9) is achieved for conventional 10 Gbps, 20 Gbps, and 25 Gbps data rates, yielding optical power sensitivities of -13.85 dBm, -12.70 dBm, and -11.25 dBm, respectively. This demonstration opens up new horizons towards cost-effective Ge pin waveguide photodetectors that combine fast device operation at low voltages with standard semiconductor fabrication processes, as desired for reliable on-chip architectures in next-generation nanophotonics integrated circuits.

With the fast growing demand of data, current chip-scale communication systems based on electrical links suffer rate limitations and high power consumptions to address these new requirements. In this context, Silicon Photonics has proven to be a viable alternative by replacing electronic links with optical ones while taking advantage of the well-established CMOS foundries techniques to reduce fabrication costs. However, silicon, in spite of being an excellent material to guide light, its centrosymmetry prevents second order nonlinear effects to exist, such as Pockels effect an electro-optic effect extensively used in high speed and low power consumption data transmission. Nevertheless, straining silicon by means of stressed thin films allows breaking the crystal symmetry and eventually enhancing Pockels effect. However the semiconductor nature of silicon makes the analysis of Pockels effect a challenging task because free carriers have a direct impact, through plasma dispersion effect, on its efficiency, which in turn complicates the estimation of the second order susceptibility necessary for further optimizations. However, this analysis is more relaxed working in high-speed regime because of the frequency limitation of free carriers-based modulation. In this work, we report experimental results on the modulation characteristics based on Mach-Zehnder interferometers strained by silicon nitride. We demonstrated high speed Pockels-based optical modulation up to 25 GHz in the C-band.

Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, silicon is a centrosymmetric crystal, i.e. silicon doesn’t have Pockels effect. Nevertheless, breaking the crystal symmetry of silicon can be used to overcome this limitation. In this work, the crystal modification is achieved by depositing a SiN high-stress overlayer. Recent results on high-speed measurements will be presented and discussed. Both charge effects and Pockels effect induced under an electric field will be also analyzed.

With the increasing demand of data, current chip-scale communication systems based on metallic interconnects suffer rate limitations and power consumptions. In this context, Silicon photonics has emerged as an alternative by replacing the classical copper interconnects with silicon waveguides while taking advantage of the well-established CMOS foundries techniques to reduce fabrication costs. Silicon is now considered as an excellent candidate for the development of integrated optical functionalities including waveguiding structures, modulators, switches… One of the main challenges of silicon photonics is to reduce the power consumption and the swing voltage of optical silicon modulators while increasing the data rate speed. However, silicon is a centrosymmetric crystal, vanishing the second order nonlinear effect i.e. Pockels effect which is intrinsically a high speed effect. To overcome this limitation, mechanical stresses on silicon to break the crystal symmetry can be used depositing a strained overlayer. In this work, we have studied the effect of the stress layer in the modulation characteristics based on Mach-Zehnder interferometers. The deposition of silicon nitride as the stress layer and its optimization to induce the maximum effect will be presented.

We demonstrate sub-wavelength electromagnetic resonators operating in the THz spectral range, whose resonant properties and optical response can be engineered using lumped elements, similarly to what is done in electronic circuits and antennas. We discuss the device concept, and we experimentally study the tuning of the resonant frequency as a function of variable capacitances and inductances. The advantages of this ‘circuit-tunable’ platform to realize novel THz meta-devices featuring an ultra-small semiconductor core are then discussed. As an application, we show that these micro-resonators have a strong potential for ultra-fast THz detection, when combined to a tiny quantum well photodetector active core. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

International audience; Terahertz (THz) and sub-THz frequency emitter and detector technologies are receiving increasing attention, underpinned by emerging applications in ultra-fast THz physics, frequency-combs technology and pulsed laser development in this relatively unexplored region of the electromagnetic spectrum. In particular, semiconductor-based ultrafast THz receivers are required for compact, ultrafast spectroscopy and communication systems, and to date, quantum-well infrared photodetectors (QWIPs) have proved to be an excellent technology to address this, given their intrinsic picosecond-range response. However, with research focused on diffraction-limited QWIP structures (λ∕2), RC constants cannot be reduced indefinitely, and detection speeds are bound to eventually meet an upper limit. The key to an ultra-fast response with no intrinsic upper limit even at tens of gigahertz (GHz) is an aggressive reduction in device size, below the diffraction limit. Here we demonstrate sub-wavelength (λ∕10) THz QWIP detectors based on a 3D split-ring geometry, yielding ultra-fast operation at a wavelength of around 100 μm. Each sensing meta-atom pixel features a suspended loop antenna that feeds THz radiation in the ∼20 μm 3 active volume (V eff ∼3 × 10 −4 λ∕2 3). Arrays of detectors as well as single-pixel detectors have been implemented with this new architecture, with the latter exhibiting ultra-low dark currents below the nA level. This extremely small resonator architecture leads to measured optical response speeds-on arrays of 300 devices-of up to ∼3 GHz and an expected device operation of up to tens of GHz, based on the measured S parameters on single devices and arrays.

The performances increase at low temperature make the SiGe HBT a masterpiece for cryogenic circuits. The time-progressive enhancement of fT and fMAX toward the THz frequency at room and at cryogenic temperatures is presented along with STMicroelectronics and IBM successive HBTs generations. The influence of the Ge content and graduality into the base is discussed, highlighting the keys for best high-frequency cryogenic operation. This is shown with eight different cases and addressed on fT, fMAX, the transit time, the minimum noise figure and the equivalent noise resistance.

Broadband spectrometers based on transmission coplanar waveguides have recently found much success for extracting the frequency dependent magnetic permeability. Here, we describe a simpler instrument based on a coplanar waveguide terminated by an open-circuit. This geometry and the associated standing wave ensure that the permeability is measured in the low excitation regime. We demonstrate a scheme to transform reflexion parameters into permeability spectra, and compare our evaluation method to measurements performed using the standardized transmission geometry.

International audience; We report on the design, fabrication, and characterization of InP-based 1.55 μm wavelength large diameter (50 μm) electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs). The hybrid device consists of a half vertical cavity surface emitting laser (1/2-VCSEL) structure assembled with a concave dielectric external mirror. The 1/2-VCSEL is monolithically grown on InP substrate and includes a semiconductor Bragg mirror and a tunnel junction for electrical injection. Buried (BTJ) and ion implanted (ITJ) tunnel junction electrical confinement schemes are compared in terms of their thermal and electrical characteristics. Lower thermal resistance values are measured for BJT, but reduced current crowding effects and uniform current injection are evidenced for ITJ. Using the ITJ technique, we demonstrate Room-Temperature (RT) continuous-wave (CW) single transverse mode laser operation from 50-μm diameter EP-VECSEL devices. We show that the experimental laser optical output versus injected current (L–I) curves are well-reproduced by a simple analytical thermal model, consistent with the thermal resistance measurements performed on the 1/2-VCSEL structure. Our results indicate that thermal heating is the main mechanism limiting the maximum CW output power of 50-μm diameter VECSELs, rather than current injection inhomogeneity.

This work presents a fabrication process validation for planar and 3D microcoils (microsolenoids) as three-axis magnetic sensors. The devices are elaborated on flexible substrates (Kapton ® and Peek ® ) to allow its location as close as possible to the surface to be characterized. The fabrication process is based on copper micromoulding. For planar microcoils, the process implements only one step of micromoulding: photolithography of a 18 μm thick photoresist and copper growth by electrodeposition through the patterned photoresist. Matrices of 1–80 turns planar microcoils with an external size of less than 2 mm, a thickness of 5–15 μm, a width of 5–20 μm and 5–10 μm track spacing have been realized. For microsolenoids, the process, more original, implements only two steps of micromoulding. The second one uses a 3D photolithography process of a 18 μm thick photoresist and a copper electrodeposition with an overflow technique. The fabricated microsolenoids are comprised of 10 or 13 wires whose sizes are 30 μm in length, 18 μm in height and 8 or 10 μm in width and spacing. The electrical tests show high values of inductance for planar devices (up to 1 μH) and values of about 1 nH for microsolenoids. For both types of devices the Q -factors are about 20.

It has been demonstrated recently that the magnetization of a nano magnet can be switched by spin-transfer effect within 200 ps. This result is promising for the application of spin-transfer effect to magnetic random access memory. Contrary to thermally-assisted reversal, the switching process slows down with increasing temperature. We analyze these results in terms of a phenomenological model which takes into account the incoherent precession of the magnetization. The results suggest that coherent precession is a key to realize ultra fast switching.

Microwave noise performance of SiGe-based heterostructure field effect transistors (HFETs) is presented. Noise parameters for devices with buried channel fabricated on several virtual substrates are discussed. The impact of such strain relieved buffers on device noise performance is estimated by a proper noise de-embedding technique. Then, the noise properties measured in the 2.5-18-GHz frequency range are compared with those of other technologies. Noise parameters of SiGe HFETs are simulated using Pospieszalski's and Van Der Ziel's noise models. Some detrimental effects like access resistances and self-heating effects that negatively impact the microwave noise behavior are discussed and some alternatives to overwhelm them are proposed.

We study the speed limitations of the magnetization switching resulting from spin transfer in pillar-shaped CoFe/Cu/CoFe spin valves. The quasi-static critical currents are I c - = - 2 mA for the antiparallel (AP) to parallel (P) configuration and I c + = + 4.6 mA for the P to AP transition. Current pulses of duration down to 100 ps and amplitude of 4Ic trigger switching at 300 K. The switching is probabilistic for lower current pulses. The P to AP transition speed is not much temperature dependant from 50 to 300 K. In contrast, the AP to P transition is thermally inhibited and is much faster at 150 K than at 300 K. This thermal inhibition highlights the importance of the macrospin coherency and of the thermally excited spin waves with finite wave vector parallel to the magnetization. Our results validate spin-transfer switching for fast memory applications.

International audience; We investigate surface plasmon waves propagating on planar Goubau lines, so-called Goubau modes, using a guided-wave terahertz spectroscopy system based on a freely positionable electrooptic probe. We show the radial nature of the Goubau mode and its confinement around the Goubau line over a few tenths of microns (λ/10).

Recent advances in silicon photonics have aided the development of on-chip communications. Power consumption, however, remains an issue in almost all integrated devices. Here, we report a 10 Gbit per second waveguide avalanche germanium photodiode under low reverse bias. The avalanche photodiode scheme requires only simple technological steps that are fully compatible with complementary metal oxide semiconductor processes and do not need nanometre accuracy and/or complex epitaxial growth schemes. An intrinsic gain higher than 20 was demonstrated under a bias voltage as low as -7 V. The Q-factor relating to the signal-to-noise ratio at 10 Gbit per second was maintained over 20 dB without the use of a trans-impedance amplifier for an input optical power lower than -26 dBm thanks to an aggressive shrinkage of the germanium multiplication region. A maximum gain over 140 was also obtained for optical powers below -35 dBm. These results pave the way for low-power-consumption on-chip communication applications.

We present 40 Gbit/s optical modulators based on different types of phase shifters (lateral pn, pipin, and interleaved pn junction phase). Those structures were processed both on 200 and 300mm SOI wafers, available in large-scale microelectronic foundries. Both Ring Resonators (RR) and Mach Zehnder (MZ) modulators were fabricated. As an example, MZ modulator based on 0.95 mm long interleaved pn junction phase shifter delivered a high ER of 7.8 dB at 40 Gbit/s with low optical loss of only 4 dB. Ring modulator was also fabricated and characterized at high-speed, exhibiting 40 Gbit/s.

The integration of germanium quantum-well devices and low-loss waveguides with silicon substrates shows promise for realizing low-loss, on-chip photonic interconnects.

A fully MESFET hybrid sampling system has been built and tested. The circuit includes an FET sampling gate, an FET sampling pulse generator, and an FET test step generator. These functions have been studied separately using a large-signal model and picosecond instrumentation. The parameters of each of them are optimized to obtain the best performances. Measurements with the GaAs FET sampler are performed and a time-domain resolution better than 28 ps corresponding to a bandwidth of 12 GHz is obtained. In particular, the measurements performed on the MESFET sampling system are in good agreement with those obtained on the conventional S4 reference sampling head.

We report on the demonstration of an intersubband (ISB) coupled quantum-well modulator operating at room temperature and telecommunication wavelength using a GaN-AIN quantum-well structure. The optical modulation is shown to result from electron tunneling between the wells. Stark shifting of the ISB absorption is observed. The maximum modulation depth is 0.79% at lambda= 2.3 mum and 0.18% at lambda= 1.37 mum for a mesa device with only 151-nm interaction length. We show that by reducing the mesa size down to 15 times 15 mum2, optical modulation bandwidth as large as 3 GHz can be obtained.

We report the demonstration of intersubband modulators operating at telecommunication wavelengths at room temperature based on GaN/AlN quantum wells. We first investigate electro-optical modulators making use of electron tunneling in coupled quantum wells. Electro-absorption modulation with opposite sign induced by the electron tunneling between the reservoir and active quantum wells is observed at λ = 1.3–1.6 µm and λ = 2.2 µm. We show that by reducing the mesa size down to 15 × 15 µm2, optical modulation bandwidth as large as 3 GHz can be obtained. We then investigate waveguide intersubband modulators relying on the depletion of the ground electronic state of a 3 quantum well active region. Modulation depths as large as 14 dB in the wavelength range of 1.2–1.6 µm are obtained under –9 V/+7 V voltage swing. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In NMR imaging, internal coil losses and patient-induced losses are the two dominant noise sources. Using small-sized antennas can increase the SNR when imaging small areas at the surface of the body. But this improvement is limited because the internal coil losses become dominant over the patient induced losses and set an actual limit to the SNR. The use of HTS material at low temperature with small-sized antennas should considerably improve the image quality. We describe a multi-turn transmission line resonator made from a sandwich YBaCuO-Sapphire-YBaCuO. Intrinsic parameters of YBaCuO have been determined by HF characterisation (45 MHz-45 GHz) using a network analyser. The antenna NMR-coil performances have been evaluated by RF measurements using a dual-loop technique and an dedicated cryocooler. The RF measuremens can be interpreted extrapolating the HF thermal behaviour. A gain in SNR of about 9 can be expected at the skin surface corresponding to the ultimate limit set by the patient -induced losses.

Materials with a periodically structured dielectric constant may exhibit forbidden photonic band gaps (PBG), that is, frequency domains where electromagnetic fields cannot propagate. The position and width of forbidden gaps can be controlled via the geometrical parameters of the structures and the contrast between the different permittivities. PBG materials have potential applications to a variety of devices in the microwave domain such as waveguides, couplers, reflectors and antenna substrate. This work reports on first experimental and theoretical studies of microwave guides and ring couplers based on PBG materials. Experiments are performed in the 27-75 GHz frequency range. Different coupling situations are given in illustration.

The contribution of conduction electron scattering to magnon relaxation in Permalloy thin films [2-20 nm] was studied by resistivity measurements and by high frequency permeability measurements using network analyzer ferromagnetic resonance. Both effective Gilbert damping alpha of the magnetization and electrical resistivity rho were measured from room temperature down to 10 K. We observe that an increase of the resistivity does not necessarily lead to an increase of the effective damping. Indeed, increases up to 50% of the resistivity in the studied temperature range are not accompanied by any change of the damping parameter alpha. We discuss our findings by sorting out the different conduction electron scattering channels that lead to spin-flip, and that hence contribute to the overall damping. We conclude that alloy disorder scattering is the main channel that leads to correlated contributions to damping and resistivity

A two-stage 8–12 GHz (X-band) cryogenically-cooled Low-Noise Amplifier (LNA) has been developed with a commercial pseudomorphic HEMT on AsGa substrate. In a first step, different commercial transistors have been fully characterized from 300 K to 20 K using a new method to measure the four noise parameters. Preliminary results have allowed the selection of the best device. This enabled the design of the two-stage LNA with the help of a microwave CAD software.

We propose an electrooptic sampler at 1.55 /spl mu/m (wavelength), which uses an ion-irradiated InP-based photoconductor for the optical-to-electrical conversion and a fiber-mounted LiTaO/sub 3/ crystal as the electric-field sensor. A measurement bandwidth of 210 GHz is obtained with a signal-to-noise ratio higher than 17 dB. These results are found to be independent of the amplitude of the 2.1-ps excitation pulse, which reaches values as high as 0.81 V. Large signal characterization of InP-based components are thus allowed. The performance of our system is validated by test measurements performed on coplanar waveguides made on semi-insulating InP substrates.

First demonstrations of high speed silicon optical modulators fabricated on 300 mm silicon-on-insulator (SOI) wafers in CMOS foundry are presented. Both ring resonator and Mach Zehnder structures show 10 Gbit/s modulation. Small signal electro-optical bandwidth up to 20 GHz has been achieved, demonstrating the possibility of 40 Gbps data-rate transmission.

Electroluminescence spectroscopy of short gate high‐electron‐mobility transistors (HEMTs) on InP substrates is performed at cryogenic temperatures. Electroluminescence is a reliable tool to investigate impact ionization as compared to studies based on gate current which depend on the weakness of the intrinsic gate current intensity. In on‐state biased devices, a low energy (0.7–0.9 eV) recombination band is observed which is related to radiative recombination of carriers created by impact ionization in the low band gap InGaAs channel. The evolution of the luminescence intensity versus bias applied to the device shows that the electroluminescence intensity and impact ionization depend on two competing parameters: the electric field in the gate–drain access area and the drain current intensity. We show that the so‐called ‘‘kink’’ effect, which is a noticeable increase of the output conductance and which is observed at relatively moderate drain bias (600–750 mV) in our devices, is not correlated with impact ...

This paper is about the dc and microwave characterization of the first high electron mobility transistors (HEMT's) realized using X-ray lithography processing. This full field patterning technology is proposed as a way to produce transistors with sub-200 nm gate lengths and high operating frequency. Fully operational devices are demonstrated and characterized. The dc parameters are determined to be comparable to those obtained on similar devices processed with electron beam lithography. A maximum intrinsic transconductance of 575 mS/mm is obtained. This shows that the X-ray radiation does not cause any significant damage to the substrates and that the process developed is viable. Devices with different geometries were tested at microwave frequencies. A current gain cutoff frequency of 70 GHz is measured for the device with the shortest gate-length whereas a maximum oscillation frequency as high as 105 GHz is measured for devices having the lowest gate resistance.

Sub-ns magnetization switching has been triggered by spin momentum transfer in pulsed current in pillar shaped CoFe∕Cu∕CoFe trilayers. By analyzing the change in magneto-resistance induced after the application of individual short current pulses (100ps–10ns), we measured the probability of magnetization reversal as a function of the current pulse magnitude, polarity and duration, at various temperatures between 150 and 300K. At all studied temperatures, the reversal process can take place within a few 100ps. The energy cost of the reversal scales favorably with the switching speed and decreases in the 1pJ range when using 100ps current pulses at 300K. Significantly higher switching speeds are obtained at lower temperatures, which is opposite to a thermal activation of the reversal.

An improved broadband inductive technique for the measurement of magnetization dynamics in thin ferromagnetic films is presented. The technique is demonstrated using 9.3 nm thick Permalloy films, and allows for time and frequency domain measurements to be made in parallel. Free oscillations after short duration pulses (200 ps ) and broadband response to radio frequency fields up to 6 GHz have been observed, and can be precisely matched to existing theories. This opens the way for detailed studies of the relaxation mechanisms above 1 GHz .

Electroluminescence of pseudomorphic InGaAs high‐electron‐mobility transistors (HEMTs) on GaAs and of standard AlGaAs/GaAs HEMTs with ultrashort gate lengths is investigated at room and cryogenic temperatures. The spectral distribution of the emitted radiation is analyzed in the 0.7–1.6 eV energy range. In the case of pseudomorphic transistors, three different recombination lines originating from distinct layers are observed: a broad luminescence band around 0.8–0.9 eV; a doublet arising from confined subbands in the InGaAs layer; and a single peak coming from the GaAs substrate. The energy position and the temperature dependence of these different lines under various biases give valuable information on the physical mechanisms which occur under high‐electric‐field nonstationary transport: lattice self‐heating (≊150 K at high‐bias conditions), origin of the impact ionization in the channel of the quantum‐well layer, and perpendicular transfer of hot holes which recombine with the barrier DX centers thus leading to the broad luminescence band. These characteristics are supported by comparison with analog standard HEMTs and with electrical measurements.

A 2.2 ps full-width-at-half-maximum impulse response is measured for ion-irradiated InGaAs photoconductive switches triggered by ultrashort 1.55 μm laser pulses. Correspondingly, the −3 dB bandwidth is estimated to be ∼120 GHz. Measurements of the electrical signals delivered by photoconductive switches are performed using an electro-optic sampling technique. As is shown, the ion irradiation reduces the carrier lifetime to less than 1 ps. The sheet resistance is 0.6×105 Ω/square. The photoconductive switch responsivity is found to exhibit a nonlinear dependence with optical power. The results are qualitatively interpreted.

Pump-probe experiments have been used to measure the (sub-) picosecond carrier lifetimes in Au+- and proton-irradiated InGaAs samples, subsequently annealed at various temperatures. For both types of irradiation, the carrier lifetime increases with the annealing temperature. After 600 °C annealing, the defects are totally recovered in proton-irradiated samples, whereas they are still present in Au+-irradiated samples. The defect annealing kinetics observed in proton-irradiated samples is described well by a Frenkel pair recombination model, thereby indicating the dominance of isolated point defects. In contrast, the model is not adapted to describe the thermal behavior of Au+-irradiation-induced defects that are clusters of point defects as observed via transmission electronic microscopy. It is clearly shown that heavy-ion irradiated InGaAs exhibits a much higher thermal stability than proton-irradiated InGaAs.

Experimental results of a silicon modulator based on carrier depletion in a PIPIN diode integrated in a Mach-Zehnder interferometer, are presented. At 40 Gbit/s, the modulator exhibits 6.6 dB extinction ratio and 6 dB optical loss.

We report a Germanium lateral pin photodiode integrated with selective epitaxy at the end of silicon waveguide. A very high optical bandwidth estimated at 120GHz is shown, with internal responsivity as high as 0.8A/W at 1550nm wavelength. Open eye diagram at 40Gb/s was obtained under zero-bias at wavelength of 1.55μm.

Silicon-based photonics has generated a lot of interest in recent years, mainly for optical telecommunications and optical interconnects in microelectronic circuits. The rationales of silicon photonics are the reduction of photonic system cost and the increase of the number of functionalities on the same integrated chip by combining photonics and electronics. Numerous developments on photonic and optoelectronic building blocks have been made including waveguides, modulators, lasers, and photodetectors. In this paper, we will present recent results on ultrafast optical modulators and germanium photodetectors integrated in silicon on insulator (SOI) waveguides. The modulator presented here is based on a 400nm thick PIPIN diode. The considered silicon rib waveguide width is 660 nm with a 100 nm etching depth. A p-doped slit is inserted in the intrinsic region of the lateral pin diode and acts as a source of holes. High p and n- doped regions are placed on both sides of the rib region to define the pin diode. As a large part of the waveguide is not doped and because metallic contacts are deposited on both sides of the waveguide, low propagation loss is obtained while keeping a high modulation efficiency. Such a design is favorable to high speed operation as the capacitance and access resistances are low. The principle of such a modulator is the following: at equilibrium, holes are confined in the doped slit inside the rib waveguide. A good overlap between the carrier density variation zone (doped slit) and the guided mode then occurs. Under a reverse bias, holes are swept out which leads to an effective index variation. This index variation creates a phase shift of the guided mode. The phase shifter is inserted in both arms of a 4.6 mm long asymetric Mach-Zehnder interferometer and electrodes are used to bias one arm. The measured insertion loss was about 6 dB and dynamic extinction ratio as large as 6 dB was achieved at 40Gbit/s. This good compromise between high extinction ratio and low loss is due to the use of the PIPIN diode instead of more classical PN diodes. In addition insertion loss can be reduced down to 4.5 dB using 1mm long active region, with an extinction ratio larger than 3 dB. For the receiver part, the monolithic integration of photodetectors in SOI waveguides requires an active material compatible with the Si CMOS technology. Germanium (Ge) is from this point of view a natural candidate for light absorption around 1.55µm. In our approach, Ge is selectively grown at the end of a SOI waveguide in a silicon recess, in order to achieve butt coupling integration. Such a configuration allows a very short absorption length. Indeed, 95 % of the light intensity is absorbed over lengths of about 4 µm at 1.31 µm and less than 7 µm at 1.55 µm, respectively. 40Gbit/s data transmission was obtained under zero-bias, which means that there is no power dissipation in the photodetector due to DC reverse biasing. The responsivity was about 0.8A/W at a wavelength of 1.55µm. In conclusion, our recent results on silicon optical modulators and photodetectors integrated in silicon waveguides show 40Gbit/s data transmission.

40 Gbit/s low-loss silicon optical modulators are demonstrated. The devices are based on the carrier depletion effect in a pipin diode to generate a good compromise between high efficiency, speed and low optical loss. The diode is embedded in a Mach-Zehnder interferometer, and a self-aligned fabrication process was used to obtain precise localization of the active p-doped region in the middle of the waveguide. Using a 4.7 mm (resp. 0.95 mm) long phase shifter, the modulator exhibits an extinction ratio of 6.6 dB (resp. 3.2 dB), simultaneously with an optical loss of 6 dB (resp. 4.5 dB) at the same operating point.

International audience; The dispersion relation and confinement of terahertz surface plasmon modes propagating along planar Goubau lines are studied using guided-wave time domain spectroscopy. We demonstrate the radial nature of the surface plasmon mode known as the Goubau mode and the transverse confinement of the electric field over a few tenths of microns (~l/10). We experimentally and computationally observed a transition of the shape of the THz pulses from unipolar to bipolar as the propagation distance increases, indicating that the Goubau line acts as a high-pass filter. The deviation of the dispersion relation curve from a linear law above 600 GHz is discussed