Shaping the spectral correlation of bi-photon quantum frequency combs by multi-frequency excitation of an SOI integrated nonlinear resonator

: We reveal the generation of a broadband (> 1.9 THz) bi-photon quantum frequency comb (QFC) in a silicon-on-insulator (SOI) Fabry-Pérot micro-cavity and the control of its spectral correlation properties. Correlated photon pairs are generated through three spontaneous four-wave mixing (SFWM) processes by using a co-polarized bi-chromatic coherent input with power P1 and P2 on adjacent resonances of the nonlinear cavity. Adjusting the spectral power ratio r = P1/(P1 + P2) allows control over the influence of each process leading to an enhancement of the overall photon pair generation rate (PGR) μ(r) by a maximal factor of μ(r = 0.5)/μ(r = 0) ≈ 1.5, compared to the overall PGR provided by a single-pump configuration with the same power budget. We demonstrate that the efficiency aND of the non-degenerate excitation SFWM process (NDP) doubles the efficiency a1 ≈ a2 of the degenerate excitation SFWM processes (DP), showing a good agreement with the provided model

Shaping the spectral correlation of bi-photon quantum frequency combs by multi-frequency excitation of an SOI integrated nonlinear resonator

We reveal the generation of a broadband (> 1.9 THz) bi-photon quantum frequency comb (QFC) in a silicon-on-insulator (SOI) Fabry–Pérot micro-cavity and the control of its spectral correlation properties. Correlated photon pairs are generated through three spontaneous four-wave mixing (SFWM) processes by using a co-polarized bi-chromatic coherent input with power P1 and P2 on adjacent resonances of the nonlinear cavity. Adjusting the spectral power ratio r = P1/(P1 + P2) allows control over the influence of each process leading to an enhancement of the overall photon pair generation rate (PGR) µ(r) by a maximal factor of µ(r = 0.5)/µ(r = 0) ≈ 1.5, compared to the overall PGR provided by a single-pump configuration with the same power budget. We demonstrate that the efficiency aND of the non-degenerate excitation SFWM process (NDP) doubles the efficiency a1 ≈ a2 of the degenerate excitation SFWM processes (DP), showing a good agreement with the provided model

Fully on-chip photonic turnkey quantum source for entangled qubit/qudit state generation

Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust and scalable chip formats, with applications in long-distance quantum-secured communication, quantum-accelerated information processing and nonclassical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers, making them impractical prototype devices that are not reproducible, hindering their scalability and transfer out of the laboratory into real-world applications. Here we demonstrate a fully integrated quantum light source that overcomes these challenges through the integration of a laser cavity, a highly efficient tunable noise suppression filter (>55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon-pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically pumped InP gain section and a Si3N4 low-loss microring filter system, and demonstrates high performance parameters, that is, pair emission over four resonant modes in the telecom band (bandwidth of ~1 THz) and a remarkable pair detection rate of ~620 Hz at a high coincidence-to-accidental ratio of ~80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), as verified by quantum interference measurements with visibilities up to 96% (violating Bell’s inequality) and by density matrix reconstruction through state tomography, showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables scalable, commercially viable, low-cost, compact, lightweight and field-deployable entangled quantum sources, quintessential for practical, out-of-laboratory applications such as in quantum processors and quantum satellite communications systems

Single-Photon Level Dispersive Fourier Transform: Ultrasensitive Characterization of Noise-Driven Nonlinear Dynamics

Dispersive Fourier transform is a characterization technique that allows directly extracting an optical spectrum from a time domain signal, thus providing access to real-time characterization of the signal spectrum. However, these techniques suffer from sensitivity and dynamic range limitations, hampering their use for special applications in, e.g., high-contrast characterizations and sensing. Here, we report on a novel approach to dispersive Fourier transform-based characterization using single-photon detectors. In particular, we experimentally develop this approach by leveraging mutual information analysis for signal processing and hold a performance comparison with standard dispersive Fourier transform detection and statistical tools. We apply the comparison to the analysis of noise-driven nonlinear dynamics arising from well-known modulation instability processes. We demonstrate that with this dispersive Fourier transform approach, mutual information metrics allow for successfully gaining insight into the fluctuations associated with modulation instability-induced spectral broadening, providing qualitatively similar signatures compared to ultrafast photodetector-based dispersive Fourier transform but with improved signal quality and spectral resolution (down to 53 pm). The technique presents an intrinsically unlimited dynamic range and is extremely sensitive, with a sensitivity reaching below the femtowatt (typically 4 orders of magnitude better than ultrafast dispersive Fourier transform detection). We show that this method can not only be implemented to gain insight into noise-driven (spontaneous) frequency conversion processes but also be leveraged to characterize incoherent dynamics seeded by weak coherent optical fields

DISPOSITIFS ET COMPOSANTS PHOTONIQUES INTÉGRÉS POUR DES APPLICATIONS OPTIQUES LINÉAIRES, NON LINÉAIRES ET QUANTIQUES

Photonic technologies hold the potential to replace electronic technologies in near futureby solving most of the drawbacks of the electronic circuits. Generation andmanipulation of photons in an integrated waveguide-based platform are preferredover bulk-optical components, mainly due to their compactness, stability, scalability,connectivity, reproducibility, and low power consumptions. Sophisticated fabricationtechniques have enabled to design low-loss intricate planar and non-planararchitectures consisting of several twists and turns. Optical directional couplers(DCs), polarization beam splitters (PBSs), microring resonators (MRRs), etc. aresome of the indispensable components of the photonic circuits having a plethoraof applications in the linear, nonlinear, and quantum optical applications. Silicon(Si) has been the preferred material to design the photonic components due to thehigh refractive-index, low-loss, low-cost, and high nonlinearity.A corpus of works has been done to shrink the overall device footprint duringthe last few decades. At the beginning of the dissertation, a novel scheme tominiaturize the existing designs of optical DCs and PBSs based on off-centered,asymmetric, and hybrid dielectric slot waveguides is discussed. Slot dimensionsand positions are optimized to achieve maximum coupling coefficient (> 88% enhancement)between two adjacent silicon wire-waveguides. The scheme leads tothe device-length of 0.9 um, and 1.1 um, for the DC and the PBS, respectively,which is a significant improvement over their contemporary counterparts. Toobtain ripple-free broadband band-pass or band-rejection filters, serially coupledMRRs have been utilized which occupy large space on a chip. To overcome thisissue, non-concentric (off-axis) nested MRR has been proposed in this thesis workthat reduces the filter-size without compromising its performance, thereby enablinghigh-density photonic integration on-chip. High thermo-optic coefficient ofSi is the Achilles heel of the silicon-on-insulator MRR based electro-optic modulators(EOMs). Off-axis MRR also helps to mitigate the thermal red-shift in the spectral response of an MRR which facilitates its applicability to achieve athermalEOM. By further improvement in non-concentric nested MRRs, it is possible to attainand maintain high quality-factor and high extinction-ratio with a fabricationtolerance of 10-20%. Initial experiments on nested MRRs confirm the theoreticalpredictions. Such nested congurations will be highly efficient in bio-sensing andquantum applications for a broad ambient temperature range.The Kerr nonlinearity of the microresonators has been exploited through anarrow line-width continuous-wave laser source for the generation of equispacedcoherent frequency lines known as the optical frequency comb (FC). Most of thenonlinear materials used to generate FC, including Si, exhibit nonlinear lossesand free-carrier effects in the telecom wavelength range. In the next part of thethesis, an analytical model of FC in the presence of nonlinear losses, free-carrierabsorption, and dispersion effects has been developed, which capacitates us toexplain several experimental results previously obtained. Further, numerical simulationsexplore that, using dual-pump, it is possible to generate tunable FCand synchronous all-optical buffers, which are robust to the writing-jitters, 3rd orderdispersion, and Raman effect. Apart from linear and nonlinear applications,integrated optical devices provide an efficient testbed for the realization of theinvincible quantum technologies. In the final portion of the dissertation, efficientpumping schemes have been discussed to generate continuous variable bipartiteand multipartite entanglement in different waveguide-pairs, simultaneously, usingan integrated 5X5 periodically poled lithium niobate waveguide array throughspontaneous parametric down conversion.French not availabl

Dr Narinder Singh Kapany: Forgotten 'Father of Fiber-Optics'

34-37After the demise of eminent Indian radio-astronomer Prof. Govind Swarup, the scientific community worldwide now mourns another great loss, Dr Narinder Singh Kapany

Bistability and Self-Pulsation in Free-carrier Driven Optical Microcavities with All Nonlinear Losses

Continuous-wave pumped micro-optical resonators have been vastly exploited to produce frequency comb (FC) utilizing Kerr effect. Most of the materials used to build photonic platforms exhibit nonlinear losses such as, multi-photon absorption, free-carrier absorption and free-carrier dispersion which can strongly affect the nonlinear characteristics of the devices viz. micro-resonators. In this work, we have developed analytical formulation to make quick estimation of the steady-state behavior, optical bistability, and self-pulsation phenomena in presence of nonlinear losses. Higher-order (>3) characteristic polynomial of intra-cavity power describing the steady-state homogeneous solution of the modified Lugiato Lefever Equation are discussed in detail. We derive the generalized analytical expressions for the threshold of normalized pump detuning to initiate the optical bistability, a necessary condition for the FC generation