Jérôme Faist

ETH Zurich | ETH Zürich · Department of Physics

In many precision sensing applications, the final detection sensitivity is tightly related to the intensity noise of the laser source, which might represent the ultimate limit to the sensor performance. In this framework, we present here the intensity noise characterization of three different mid-infrared semiconductor devices (two quantum cascade...

We present the simulation, design, fabrication, and characterization of planarized double metal quantum cascade lasers based on InGaAs/GaAsSb. Intended for astrophysical heterodyne measurements and having the cavity embedded in benzocyclobutene, the devices are equipped with thermal bridges on either side of the ridge, in order to improve the heat...

Ring quantum cascade lasers have recently gained considerable attention, showing ultrastable frequency comb and soliton operation, thus opening a way to integrated spectrometers in the midinfrared and terahertz fingerprint regions. Thanks to a self-consistent Maxwell-Bloch model, we demonstrate, in excellent agreement with the experimental data, th...

Frequency-modulated (FM) combs form spontaneously in free-running semiconductor lasers and possess a vast potential for spectroscopic applications. Despite recent progress in obtaining a conclusive theoretical description, experimental FM combs often exhibit non-ideal traits, which prevents their widespread use. Here we explain this by providing a...

Source radiation (radiation reaction) and vacuum field fluctuations can be seen as two inseparable contributions to processes such as spontaneous emission, the Lamb shift, or the Casimir force. Here, we propose how they can be individually probed and their space-time structure revealed in electro-optic sampling experiments. This allows us to experi...

Frequency combs are powerful tools for many applications and high performances are achieved by stabilizing these lasers. For operation in the mid-infrared, quantum cascade lasers (QCL) are ideal candidates as they present numerous advantages. However, stabilized QCL-combs lack of a detailed characterization of their noise properties due to the sens...

Astronomical heterodyne spectrometers such as upGREAT on the SOFIA telescope use a powerful Quantum Cascade Laser (QCL) as Local Oscillator (LO) to observe the atomic oxygen line at 4.7 THz. The free-running laser, although temperature stabilized, is prone to broad effective linewidth and frequency drifts and lacks an absolute frequency reference....

Frequency‐modulated (FM) combs feature flat intensity spectra with a linear frequency chirp, useful for metrology and sensing applications. Generating FM combs in semiconductor lasers generally requires a fast saturable gain, usually limited by the intrinsic gain medium properties. Here, it is shown how a spatial modulation of the laser gain medium...

Synthetic lattices in photonics enable the exploration of light states in new dimensions, transcending phenomena common only to physical space. We propose and demonstrate a quantum walk comb in synthetic frequency space formed by externally modulating a ring-shaped semiconductor laser with ultrafast recovery times. The initially ballistic quantum w...

Frequency-modulated (FM) combs form spontaneously in free-running semiconductor lasers and possess a vast potential for spectroscopic applications. Despite recent progress in obtaining a conclusive theoretical description, experimental FM combs often exhibit non-ideal traits, which prevents their widespread use. Here we explain this by providing a...

We present a planarized waveguide cavity with an integrated broadband output coupler that improves both the output power and far-field properties of THz quantum cascade laser frequency combs. The laser mirror reflectivity can be tuned by the shape of the end facet, which is obtained with an efficient inverse design algorithm, where the structure is...

While the opportunity to perform fast and broadband spectroscopy in the Mid-IR portion of the electromagnetic spectrum is very appealing, it requires the use of compatible light-sources. Here, we strongly modulate a Mid-Infrared Quantum Cascade Laser at a frequency in the RF domain, which is low compared to the natural repetition frequency of the d...

We present a dual-comb spectrometer based on quantum cascade lasers operating at 7.7 µm with a stabilization scheme that enables coherent averaging. We show that by illuminating a low cost near-infrared light source of the front facet of the quantum cascade laser, we can tightly lock one comb line of the dual-comb spectrum, resulting in narrow line...

Frequency combs (FC) generated by quantum cascade lasers (QCLs) are a promising tool for precision spectroscopy and gas sensing. Recently, ring QCLs have emerged as a new platform for generating FC with unique advantages over Fabry-Perot geometry. While the bandwidth of such Fabry-Perot devices is determined by the device geometry and dispersion, r...

Locking multiple modes into a frequency comb is key for multiple metrological applications, and a great effort has been therefore invested in this challenge over the last decade. The most common techniques are based on either nonlinearities or modulation of the cavity, while the latter is considered the more controllable method to produce frequency...

We present a surface emitting THz quantum cascade laser frequency comb with an adjustable chromatic dispersion compensation via a mechanically tunable GTI cavity. Surface emission and high optical feedback into the laser cavity are achieved by a planarized ridge waveguide design with low reflectivity facets and two broadband patch array antennas fo...

Frequency comb lasers with fast gain recovery times naturally favor the emission of frequency mod-ulated periodic signals, which are useful for multiple applications in spectroscopy and communications. Models and phase measurements predict an ultrashort strong intensity spike at the instantaneous frequency discontinuity of the cavity cycle. Here we...

Using near-infrared light, we tightly-lock a mid-infrared quantum cascade laser frequency comb to another laser, achieving a residual integrated phase noise of 200 mrad. This high coherence is pertinent for highly-sensitive dual-comb spectroscopy and metrology.

We present a systematic study of the optical design, fabrication, and characterization of quantum cascade laser devices with a frequency around 4.7 THz, intended for use as local oscillators in the GREAT heterodyne receiver aboard SOFIA [1], [2]. The measured devices exhibit consistent spectral performance, with approximately 75% of them having the...

It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling strength. In...

THz quantum cascade lasers (QCLs) based on double metal waveguides feature broadband and high-temperature devices for their use in spectroscopy and sensing. However, their extreme field confinement produces poor output coupling efficiencies and divergent far-fields. Here, we present a planarized THz QCL with an inverse-designed end facet reflector...

Synthetic lattices in photonics enable the exploration of light states in new dimensions, transcending phenomena common only to physical space. We propose and demonstrate a Quantum Walk Laser in synthetic frequency space formed by externally modulating a ring-shaped semiconductor laser with ultrafast recovery times. In this device, the initially ba...

A low-cost single frequency laser emitting in the mid-infrared spectral region and dissipating minimal electrical power is a key ingredient for the next generation of portable gas sensors for high-volume applications involving chemical sensing of important greenhouse and pollutant gases. We propose here a Quantum Cascade Surface Emitting Laser (QCS...

We demonstrate terahertz chiral metamaterial cavities that break time-reversal symmetry by coupling the degenerate linearly polarized modes of two orthogonal sets of nano-antenna arrays using the inter-Landau level transition of a two-dimensional electron gas in a perpendicular magnetic field, realizing normalized light-matter coupling rates up to...

We demonstrate the use of a low power near-infrared laser illuminating the front facet of a quantum cascade laser (QCL) as an optical actuator for the coherent control of a mid-infrared frequency comb. We show that with appropriate current control of the QCL comb and intensity modulation of the near-infrared laser, a tight phase lock of a comb line...

Phase modulation is demonstrated in a quantum Stark effect modulator designed to operate in the mid-infrared at wavelength around 10 µm. Both phase and amplitude modulation are simultaneously resolved through the measurement of the heterodyne signal arising from the beating of a quantum cascade laser with a highly stabilized frequency comb. The hig...

Quantum-cascade-laser (QCL) frequency combs are compact semiconductor light sources operating in the mid-IR and terahertz frequencies. Achieving subpicosecond laser pulses with high peak power is of vital importance for performing nonlinear time-resolved spectroscopy as well for exploring nonlinear phenomena. Therefore, investigation and characteri...

THz quantum cascade lasers (QCLs) based on double metal waveguides feature broadband and high-temperature devices for use in spectroscopy and sensing. However, their extreme field confinement produces poor output coupling efficiencies and divergent far-fields. Here, we present a planarized THz QCL with an inverse-designed end facet reflector couple...

Quantum cascade lasers (QCLs) constitute an intriguing opportunity for the generation of on-chip optical dissipative Kerr solitons (DKSs). Originally demonstrated in passive microresonators, DKSs were recently observed in mid-infrared ring QCL paving the way for their achievement even at longer wavelengths. To this end, we realized defect-free tera...

In processes such as spontaneous emission, the Lamb shift or the Casimir force, source radiation (radiation reaction) and vacuum-field fluctuations can be seen as two inseparable contributions. Here, we propose how they can be individually probed and their space-time structure revealed in electro-optic sampling experiments. This allows to experimen...

We demonstrate the use of a low power near-infrared laser illuminating the front facet of a quantum cascade laser (QCL) as an optical actuator for the coherent control of a mid-infrared frequency comb. We show that by appropriate current control of the QCL comb and intensity modulation of the near-infrared laser, a tight phase lock of a comb line t...

Frequency-modulated (FM) combs feature flat intensity spectra with a linear frequency chirp, useful for metrology and sensing applications. Generating FM combs in semiconductor lasers generally requires a fast saturable gain, usually limited by the intrinsic gain medium properties. Here, we show how a spatial modulation of the laser gain medium can...

Ring quantum cascade lasers have recently gained considerable attention, showing ultrastable frequency comb and soliton operation, and thus opening a way to integrated spectrometers in the mid-infrared and terahertz fingerprint regions. Thanks to a self-consistent Maxwell-Bloch model, we demonstrate, in excellent agreement with the experimental dat...

Fast (sub-second) spectroscopy with high spectral resolution is of vital importance for revealing quantum chemistry kinetics of complex chemical and biological reactions. Fourier transform (FT) spectrometers can achieve high spectral resolution and operate at hundreds of ms time scales in rapid-scan mode. However, the linear translation of a scanni...

Intramolecular or position-specific carbon isotope analysis of propane (13CH3-12CH2-12CH3 and 12CH3-13CH2-12CH3) provides unique insights into its formation mechanism and temperature history. The unambiguous detection of such carbon isotopic distributions with currently established methods is challenging due to the complexity of the technique and t...

The picosecond carrier dynamics observed in quantum cascade lasers (QCLs) poses a fundamental obstacle for the formation of intracavity pulses. On the other hand, the ultrafast gain response makes the QCL ideally suited for high frequency modulation of its pump current. In this work, we leverage this property and use short electrical excitations to...

We study the performance of a hot-electron bolometer (HEB) operating at THz frequencies based on superconducting niobium nitride films. We report on the voltage response of the detector over a large electrical detection bandwidth carried out with different THz sources. We show that the impulse response of the fully packaged HEB at 7.5 K has a 3 dB...

In recent years, optical frequency combs with a frequency modulated output have attracted considerable attention. While first observed decades ago in externally modulated lasers, a whole class of semiconductor lasers has since been identified to spontaneously enter such a regime of self frequency modulation. The temporal properties of these sources...

The linewidth enhancement factor (LEF) describes the coupling between amplitude and phase fluctuations in a semiconductor laser and has recently been shown to be a crucial component for frequency comb formation in addition to linewidth broadening. It necessarily arises from causality, as famously formulated by the Kramers–Kronig relation, in media...

Bridging the “terahertz gap“ relies upon synthesizing arbitrary waveforms in the terahertz domain enabling applications that require both narrow band sources for sensing and few-cycle drives for classical and quantum objects. However, realization of custom-tailored waveforms needed for these applications is currently hindered due to limited flexibi...

We demonstrate an asynchronous optical sampling technique for the temporal characterization of frequency modulated combs. On the basis of a mid-infrared quantum cascade laser frequency comb, we measure both its instantaneous intensity and optical frequency.

We report THz optical soliton formation in defect-less ring QCL featuring anomalous dispersion. Free-running spectra with sech ² envelopes are presented together with SWIFT measurement showing ∼ 12 ps pulses in the reconstructed emission time-profile.

It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, coupling to propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling...

Recently, there has been a growing interest in integrated THz photonics for various applications in communications, spectroscopy and sensing. We present a new integrated photonic platform based on active and passive elements integrated in a double-metal, high-confinement waveguide layout planarized with a low-loss polymer. An extended top metalliza...

Quantum Cascade Lasers (QCL) constitute an intriguing opportunity for the production of on-chip optical Dissipative Kerr Solitons (DKS): self-organized optical waves which can travel while preserving their shape thanks to the interplay between Kerr effect and dispersion. Originally demonstrated in passive microresonators, DKS were recently observed...

We report comb operation of RF injected ring Quantum Cascade Lasers. A coupled waveguide approach is implemented for dispersion compensation while passive bullseye antenna improves the device power extraction and far field. Phase sensitive measurements are presented which hints at the presence of soliton state.

We present a new planarized waveguide geometry for THz quantum cascade laser frequency combs with improved waveguide losses, RF and thermal dissipation properties. Ridge devices display broadband free-running comb states, and the THz emission can be further broadened by RF injection. Tapered waveguide devices feature a strong field-enhancement effe...

We will discuss, theoretically and experimentally, the existence of a limit to the possibility of arbitrarily increasing electromagnetic confinement in polaritonic systems, where strongly sub-wavelength fields can excite a continuum of high-momenta propagative magnetoplasmons. This leads to peculiar nonlocal polaritonic effects, as certain polarito...

Optical frequency combs based on semiconductor lasers are a promising technology for monolithic integration of dual-comb spectrometers. However, the stabilization of offset frequency f ceo remains a challenging feat due the lack of octave-spanning spectra. In a dual-comb configuration, the uncorrelated jitter of the offset frequencies leads to a no...