Efficient Photon Sources Research Articles

Large-scale error-tolerant programmable interferometer fabricated by femtosecond laser writing

We introduce a programmable eight-port interferometer with the recently proposed error-tolerant architecture capable of performing a broad class of transformations. The interferometer has been fabricated with femtosecond laser writing, and it is the largest programmable interferometer of this kind to date. We have demonstrated its advantageous error tolerance by showing an operation in a broad wavelength range from 920 to 980 nm, which is particularly relevant for quantum photonics due to efficient photon sources existing in this wavelength range. Our work highlights the importance of developing novel architectures of programmable photonics for information processing.

Quasi-BIC Modes in All-Dielectric Slotted Nanoantennas for Enhanced Er3+ Emission.

In the quest for new and increasingly efficient photon sources, the engineering of the photonic environment at the subwavelength scale is fundamental for controlling the properties of quantum emitters. A high refractive index particle can be exploited to enhance the optical properties of nearby emitters without decreasing their quantum efficiency, but the relatively modest Q-factors (Q ∼ 5-10) limit the local density of optical states (LDOS) amplification achievable. On the other hand, ultrahigh Q-factors (up to Q ∼ 109) have been reported for quasi-BIC modes in all-dielectric nanostructures. In the present work, we demonstrate that the combination of quasi-BIC modes with high spectral confinement and nanogaps with spacial confinement in silicon slotted nanoantennas lead to a significant boosting of the electromagnetic LDOS in the optically active region of the nanoantenna array. We observe an enhancement of up to 3 orders of magnitude in the photoluminescence intensity and 2 orders of magnitude in the decay rate of the Er3+ emission at room temperature and telecom wavelengths. Moreover, the nanoantenna directivity is increased, proving that strong beaming effects can be obtained when the emitted radiation couples to the high Q-factor modes. Finally, via tuning the nanoanntenna aspect ratio, a selective control of the Er3+ electric and magnetic radiative transitions can be obtained, keeping the quantum efficiency almost unitary.

Strong Er3+ radiative emission enhancement by quasi-BIC modes coupling in all-dielectric slot nanoantenna arrays

We have designed and realized all-dielectric lossless nanoantennas, in which a thin SiO2 layer doped with erbium ions is placed inside slotted silicon nanopillars arranged in a square array. The modal analysis has evi-denced that the slotted nanopillar array supports optical quasi-BIC resonances with ultra-high Q-factors (up to Q∼109), able to boost the electromagnetic local density of optical states in the optically active layer. Up to 3 orders of magnitude photoluminescence intensity increment and 2 orders of magnitude decay rate enhancement have been measured at room temperature when the Er3+ emission at about λ=1540 nm couples with the quasi-BIC resonances. Furthermore, by tailoring the nanopillar aspect ratio, the slot geometry has been exploited to obtain selective enhancements of the electric or magnetic dipole contribution to Er3+ radiative transitions in the NIR, keeping the emitter quantum efficiency almost unitary. Finally, by computing the angularly resolved elec-tromagnetic field enhancement inside the nanoslot, the nanoantenna directivity has been designed, proving that strong beaming effects can be obtained. Our findings have a direct impact on the development of bright and effi-cient photon sources operating at telecom wavelength that are of primary importance for quantum nanophotonic applications.

Down-conversion processes inab initiononrelativistic quantum electrodynamics

The availability of efficient photon sources with specific properties is important for quantum-technological applications. However, the realization of such photon sources is often challenging and hence alternative perspectives that suggest different means to enhance desired properties while suppressing detrimental processes are valuable. In this work we highlight that ab initio simulations of coupled light-matter systems can provide such alternative avenues. We show for a simple model of a quantum ring that by treating light and matter on equal footing, we can create and enhance pathways for down-conversion processes. By changing the matter subsystem as well as the photonic environment in experimentally feasible ways, we can engineer hybrid light-matter states that enhance at the same time the efficiency of the down-conversion process and the nonclassicality of the created photons. Furthermore, we show that this also leads to a faster down-conversion, potentially avoiding detrimental decoherence effects.

Phase Controlled Bistability in Silicon Microring Resonators for Nonlinear Photonics

Resonance shift and bistability in a silicon microring resonator operating at higher optical power levels pose serious difficulties, especially in nonlinear four wave mixing process. A solution of parking a laser wavelength around any of the resonances of a microring resonator and operating at any power levels is explored by integrating a microheater. We have shown with the existing theoretical model that the previous history of phase detuning in a silicon microring resonator determines the effective gain in stimulated four wave mixing process. The experimental results have been shown to be closely matching with the simulation results. For a microring resonator of radius 50 $\mu$ m, an improved stimulated four wave mixing gain of $\sim$ 11.6 dB has been observed while thermo-optically blue-shifting resonances in comparison to that of red-shifting resonances, for a launched pump power of 8.4 mW operating at a slightly off-resonant wavelength $\lambda _p$ . The proposed technique can be used in designing actively controlled efficient photon sources in a large-scale integrated quantum photonic circuit operating at $\lambda \sim$ 1550 nm.

Feasibility of Ultraviolet-Light-Emitting Diodes as an Alternative Light Source for Photocatalysis

The objective of this study was to determine whether ultraviolet-light-emitting diodes (UV-LEDs) could serve as an efficient photon source for heterogeneous photocatalytic oxidation (PCO). An LED module consisting of 12 high-power UV-A (lambda max = 365 nm) LEDs was designed to be interchangeable with a UV-A fluorescent black light blue (BLB) lamp for a bench scale annular reactor packed with silica-titania composite (STC) pellets. Lighting and thermal properties of the module were characterized to assess its uniformity and total irradiance. A forward current (I(F)) of 100 mA delivered an average irradiance of 4.0 mW cm(-2) at a distance of 8 mm, which is equivalent to the maximum output of the BLB, but the irradiance of the LED module was less uniform than that of the BLB. The LED and BLB reactors were tested for the oxidization of ethanol (50 ppm(v)) in a continuous-flow-through mode with 0.94 sec residence time. At the same average irradiance, the UV-A LED reactor resulted in a lower CO2 production rate (19.8 vs. 28.6 nmol L(-1) s(-1)), lower ethanol removal (80% vs. 91%), and lower mineralization efficiency (28% vs. 44%) than the UV-A BLB reactor. Ethanol mineralization was enhanced with the increase of the irradiance at the catalyst surface. This result suggests that reduced ethanol mineralization in the LED reactor relative to the BLB reactor at the same average irradiance could be attributed to the nonuniform irradiance over the photocatalyst, that is, a portion of the catalyst was exposed to less than the average irradiance. The potential of UV-A LEDs may be fully realized by optimizing the light distribution over the catalyst and utilizing their instantaneous "on" and "off" feature for periodic irradiation. Nevertheless, our results also showed that the current UV-A LED module had the same wall plug efficiency (WPE) of 13% as that of the UV-A BLB, demonstrating that UV-A LEDs are a viable photon source both in terms of WPE and PCO efficiency.