Multi-mode optical microcavities have enabled the emergence of compact optical sources such as parametric oscillators and nonlinear combs for quantum information and metrology. Efficient nonlinear interactions take place, owing to a combination of large Q factor, small modal volume and large material index. The control of the frequency spacing of the resonances is also a critical aspect.
Here we demonstrate an effective harmonic potential for photons owning to the concept of bichromatic lattice in a photonic crystal structure. Wide gap semiconductor material, i.e. GaInP, is used here to prevent any detrimental non-linear absorption such as two photons.
The experimental evidence is given through the statistical analysis of the frequency spacing of high-Q resonances over 68 cavities.
For each structure, the complex reflection spectra is measured using Optical Coherent Tomography (OCT) with a resolution of 20 MHz.
The dispersion of the resonator is extracted through a polynomial fit. It appears to be small and more importantly crosses zero as the radius of the holes is changed.
Moreover, each of these resonators have many modes, typically four, with loaded Q factor in the 10^5 to 7x10^5 range and intrinsic Q factor well above one million.
Equi-spaced resonances in a very compact structure should lead to ultra-strong nonlinear interactions, particularly resonantly enhanced Four Wave Mixing and parametric oscillation.
Resonant four-wave-mixing in microcavities has recently proven to be particularly interesting for obtaining ultra-efficient nonlinear wavelength conversion, parametric and frequency combs generation. Contrarily to the commonly used microring or whispering gallery mode cavities, photonic crystal nanocavities have not revealed yet their full potential in this direction. Despite their high-Q and ultra-small modal volume, they are not evidently suited for resonant four wave mixing as they do not naturally exhibit modes at equally spaced frequencies, a necessary condition for energy conservation.
In this work, we designed and fabricated 1D photonic crystal nanobeam cavities which exhibit ultra- high Q modes around 1.55µm equally spaced in frequency. These nanocavities are made of InGaP material bonded on top of a SOI waveguide optical circuitry. The evanescent wave coupling between the cavities and the waveguides can be controlled at will by changing the SOI waveguide width. The large electronic bandgap of InGaP inhibits 2 photon absorption at 1.55µm and allows us to exploit pure Kerr nonlinearity.
The electromagnetic potential inside the cavity is shaped to be spatially parabolic by engineering the hole position along the cavity. Thus, by construction the resonant modes supported by the cavity are equispaced in frequency.
The measured loaded Q factors exceed 105 and the free spectral range (FSR) goes from 150GHz to 1THz depending on the size of the cavity. We demonstrate that the FSR remains quasi constant (flat dispersion). Four wave mixing and parametric generation is observed using CW pump power of few mWs.
From latest nanotechnology advances, low-dimensional matter confinement delivered by nanostructuration or few-layer stacking offer new opportunities for ultimate light absorption performances. In this field, semiconducting 2D materials and photonic crystals have already demonstrated promising flexible optical properties from monoatomic to bulk structuration covering visible to IR spectral range. Today, these emerging materials such as Phosphorene, allow reconsideration of some physical effects such as photoconductivity. Indeed, its exploitation in integrated planar structures become c in terms of efficient local contactless control with a high degree of tunability by optics in association with high dark resistivity, fast carrier dynamics, and sub-wavelength light coupling solutions compatibility. Multiscale modeling and design tools implementing material anisotropic parameters from atomic configuration up to mesoscale, in complement with multiscale optical characterization in a large frequency bandwidth opens routes to new microwave signal processing functionalities such as switching, generation, amplification and emission over a large frequency bandwidth, that could not be achieved by full electronic solutions. This paper will report on latest demonstrations of high performance photoconductive structures for high frequency applications and review state-of-the-art research work in this area, with a specific focus on latest demonstrations for airborne applications.
We briefly review the technology of advanced nonlinear resonators for all-optical gating with a specific focus on the application of high-performance signal sampling and on the properties of III-V semiconductor photonic crystals
Semiconductor optical waveguides have been the subject of intense study as both fundamental objects of study, as well as a path to photonic integration. In this talk I will focus on the nonlinear evolution of optical solitons in photonic crystal waveguides made of semiconductor materials. The ability to independently tune the dispersion and the nonlinearity in photonic crystal waveguides enables the examination of completely different nonlinear regimes in the same platform. I will describe experimental efforts utilizing time-resolved measurements to reveal a number of physical phenomena unique to solitons in a free carrier medium. The experiments are supported by analytic and numerical models providing a deeper insight into the physical scaling of these processes.
Slow light in SOI Slotted Photonic Crystal Waveguides (SPCW) infiltrated by a refractive liquid are investigated. By employing an interferometric technique similar to Optical Coherent Tomography (OCT), we report a group velocity lower than c/20 over a 1 mm-long SPCW. From the OCT measurements, we also infer moderate propagation losses. In the fast light regime (nG <10) propagation loss is about 15 dB.cm-1. Moreover, the coupling to slow modes is efficient. These results show that infiltrated slow light SPCW are a promising route to silicon organic hybrid photonics.
In recent years integrated waveguide devices have emerged as an attractive platform for scalable quantum tech- nologies. In contrast to earlier free-space investigations, one must consider additional effects induced by the media. In amorphous materials, spontaneous Raman scattered photons act as a noise source. In crystalline materials two-photon absorption (TPA) and free carrier absorption (FCA) are present at large intensities. While initial observations noted TPA affected experiments in integrated semiconductor devices, at present the nuanced roles of these processes in the quantum regime is unclear. Here, using single photons generated via spontaneous four-wave mixing (SFWM) in silicon, we experimentally demonstrate that cross-TPA (XTPA) between a classical pump beam and generated single photons imposes an intrinsic limit on heralded single photon generation, even in the single pair regime. Our newly developed model is in excellent agreement with experimental results.
High-resolution infrared absorption spectroscopy of acetylene gas is demonstrated in dispersion-engineered photonic
crystal waveguides under slow light propagation. Individual absorption profiles are obtained for both TE and TM
polarizations for group indices ranging from 1.5 to 6.7. Experimental enhancement factors of 0.31 and 1.00 are obtained
for TE and TM polarization, respectively, and are confirmed by time-domain simulations. We experimentally
demonstrate that molecular absorption is a function of the electric field distribution outside the photonic crystal slab and
the group index under structural slow-light illumination.
Within the EC funded international project OPTHER (OPtically Driven TeraHertz AmplifiERs) a considerable
technological effort is being undertaken, in terms of technological development, THz device design and integration. The
ultimate goal is to develop a miniaturised THz amplifier based on vacuum-tube principles
The main target specifications of the OPTHER amplifier are the following:
- Operating frequency: in the band 0.3 to 2 THz
- Output power: > 10 mW ( 10 dBm )
- Gain: 10 to 20 dB.
The project is in the middle of its duration. Design and simulations have shown that these targets can be met with a
proper device configuration and careful optimization of the different parts of the amplifier. Two parallel schemes will be
employed for amplifier realisation: THz Drive Signal Amplifier and Optically Modulated Beam THz Amplifier.
Most of optoelectronic semiconductor devices, especially quantum well based ones, make use of a grating to
couple the active layer to free space. To go beyond the simplistic coupling role of the grating we propose a
specifically designed metal-dielectric corrugated interface that squeezes normal incidence light in subwalength
scale, taking advantage of the very active work achieved over the last few years in near field electromagnetism.
This structure coherently combines three surface plasmon engineering tools: Bragg reflection, microcavity, and
grating coupling. These electromagnetic properties are demonstrated experimentally in the gigahertz regime, as
a function of design parameters. Light squeezing is observed down to a quarter of a wavelength.
Compactness, massive integration of multiple functions on a single chip and power consumption are crucial for
transmission of large aggregated bit rates at short distance. Efficient implementation of data processing at the
optical level are very attractive. Here we present a technology for implementing ultra-fast switching with recordlow
energy·recovery time product. We developed high-quality photonic crystal micro-resonators based on III-V
semiconductors. The very short carrier lifetime of nano-pattened Gallium Arsenide enabled us to achieve 6 ps
recovery time, thus enabling operations beyond the 100Gb/s rate. For broadband operation, highly nonlinear
waveguides with low insertion loss have been demonstrated.
We present the first steps for the validation of the concept of a new optically driven field emission cathode. The
approach relies on the interaction of surface plasmons with vertically aligned multi-wall carbon nanotubes or metallic
nanowire arrays. The objective is to modulate the field emission current by using the optical field component at the
emitter apex through antenna coupling. Thanks to metallic surface gratings, surface plasmons will be generated and
localized in the vicinity of nanoemitters to increase the interaction. First simulations and preliminary experimental
measurements are presented jointly with perspectives for the wideband modulation of electronic beams up to THz.
In this work we demonstrate for the first time that terahertz (THz) quantum cascade lasers can be realised in a buried-waveguide geometry. In our prototype devices the optical mode is a surface plasmon bound at the interface between the top contact and the semiconductor, providing for both vertical and lateral confinement without the need to define a cavity ridge. Proton-implanted high-resistivity sections are used to define the current channel where electrons can be injected into the active region. This way the electrical and optical confinement can be controlled independently: the former is defined by the non-implanted regions and the latter by the width of the top contact metal strip. Compared to standard ridge waveguides this technique allowed for a narrowing of the device effective cross section without introducing additional losses and improving the thermal conductivity, resulting in an increase of the maximum operating temperature up to 77K in continuous wave at 2.9 THz. In addition, we present preliminary results from buried-waveguide THz quantum cascade lasers obtained by combining a double-metal waveguide geometry with proton implantation. Initial results are promising, yielding record low threshold currents of 19mA at 4.2K in both pulsed and continuous wave operation.
A test bench has been developed at ONERA in order to measure the spectral responses of infrared focal plane arrays (IRFPAs). This test bench can deliver hyperspectral cartographies with rather good resolutions (better than 16 cm-1) on large spectral ranges (from 1.3 μm to 20 μm). The principle of this test bench will be described. Using this technique, tests have been performed on a large format (640x512) IRFPA of quantum-well technology operating in the 8- to 10-μm spectral range. The prototype tested had several small defects that produce spectacular hyperspectral cartographies. To explain the hyperspectral structures observed across the array, an empirical model based on Fourier optics will be presented.
As far as calibrated radiometric imaging is concerned, a complete prediction of oblique incidence effect on the FPA pixels’ response is required. Since a light coupling scheme needs to be used in QWIP detectors, this effect is particularly complicated to understand. This article presents two complementary test benches which allow to quantify the effect of oblique incidence on cooled infrared detectors issued from different technologies. The first test bench performs measurements over a wide angular range with low background emission levels, but gives spectrally integrated measurements. The second one delivers spectrally resolved responses for incident angles lower than 30°. In order to validate both experimental concepts, we studied QWIPs equipped with 2D periodic gratings. Relatively large pixels (100x100μm2) were chosen to ease comparison with models. Calculations based on the modal expansion method reveal that diffraction off an infinite grating does not account very well for the observed spectral responses.
A third-order-mode-emitting laser diode is demonstrated. The AlGaAs/GaAs hetero-structure is engineered to emit a photon pair through intra-cavity modal phase-matched parametric down-conversion. Device operations and twin photon generation experimental issues are discussed.