Pierre Guillemé

Antiphase domain tailoring for combination of modal and 4¯ -quasi-phase matching in gallium phosphide microdisks

We propose a novel phase-matching scheme in GaP whispering-gallery-mode microdisks grown on Si substrate combining modal and 4¯ -quasi-phase-matching for second-harmonic-generation. The technique consists in unlocking parity-forbidden processes by tailoring the antiphase domain distribution in the GaP layer. Our proposal can be used to overcome the limitations of form birefringence phase-matching and 4¯ -quasi-phase-matching using high order whispering-gallery-modes. The high frequency conversion efficiency of this new scheme demonstrates the competitiveness of nonlinear photonic devices monolithically integrated on silicon.

Cathodoluminescence hyperspectral analysis of whispering gallery modes in active semiconductor wedge resonators

Whispering gallery mode resonators are key devices for integrated photonics. Despite their generalization in fundamental and applied science, information on spatial confinement of light in these structures is mostly retrieved from purely spectral analysis. In this work, we present a detailed spectral and spatial characterization of whispering gallery modes in active semiconductor microdisk resonators by use of hyperspectral cathodoluminescence. By comparing our experimental findings to finite element simulations, we demonstrate that the combination of spectral and spatial measurements enables unique identification of the modes and even reveals specific features of the microresonator geometry, such as a wedge profile.

Slow-light microcavities

Optical microcavities with high quality factors Q are of great interest in integrated micro- and nanophotonics. Their narrow resonance and long photon lifetime (τ<inf>cav</inf>) can be used in fundamental physics, sensing applications, microwave signal optical processing or for optical delay line and memory miniaturization [1]. Considering a Lorentzian resonance profile, the quality factor and the photon lifetime of a microcavity with a resonant angular frequency ωο = 2·πε/λ<inf>0</inf> reads: Q = ω<inf>0</inf> τ<inf>cab</inf> = n<inf>G</inf>(ω<inf>0</inf>)LF/λ<inf>0</inf>, (1) where n<inf>g</inf> is the group index of the material constituting the microcavity, F is the finesse and L is the cavity round-trip length. The usual method to obtain ultra-high quality factors consists in optimizing the manufacturing process to reach high finesse values. Following this approach record quality factors up to 10¹¹ have been measured in millimetric CaF2 whispering gallery mode (WGM) resonators [2]. Otherwise, Eq. (1) shows that for a given finesse, the use of resonators made with slow-light materials displaying high group indices can also increase the quality factor. This method has already been successfully implemented in bulky resonators including a highly dispersive slow-light medium [3]. We have recently demonstrated that this approach can be applied to solid-state optical micro-resonators [4]. The slow-light effect was introduced thanks to population oscillations in an Er³⁺ doped WGM fluoride glass microsphere (diameter 100 μm). Since the lifetime of the ⁴I<inf>13/2</inf> level is very long (T ≈ 10 ms) strong group index up to 10⁶ can be obtained. Using a cavity-ring-down method (see Fig. 1) in a pump probe configuration, we have measured a photon lifetime of 2.5 ms at 1530 nm corresponding to a quality factor of 3 × 10¹² [4].

Ultra-long photon lifetime in a slow-light microcavity

Ultrahigh-quality (Q) factor optical micro-resonators with very long photon storage time are important in the aim of integrating optical functions such as filters, tunable delay lines for microwave-photonics or highly sensitive sensor applications. To date, Q-factors up to 1011 have been measured only in millimetre-size crystalline whispering-gallery-mode (WGM) resonators. Semiconductor, Silica or glass WGM micro-resonator Q-factors are limited to 109 due to technological imperfections or residual absorption. We show that by introducing slow light effects in a monolithic WGM micro-resonator it is possible to enhance the photon lifetime by several orders of magnitude and circumvent fabrication limitations. We experimentally demonstrate Erbium-doped fluoride glass micro-resonators with a photon lifetime up to 2.5 ms at room temperature, corresponding to a Q-factor of 3 × 1012 at 1530 nm, by combining WGM resonance effect and population oscillations.

Impact of antiphase boundaries on non-linear frequency conversion in GaP/Si microdisks

GaP is a promising candidate for the development of highly integrated photonic functions on silicon, because of its quasi lattice-matching with Si and its interesting χ(2) non-linear properties. We here present the realization of GaP-based microdisks on Si substrates, and discuss their optical properties. Especially, emphasis is given on the impact of crystal antiphase boundaries generated during the heteroepitaxial growth on second-harmonic generation.