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Optical nonlinear processes in linearly uncoupled resonators are being actively studied as a convenient way to engineer and control the generation of non-classical light. In these structures, one can take advantage of the independent combs of resonances of two linearly uncoupled ring resonators for field enhancement, with the phase-matching condition being significantly relaxed compared to a single resonator. However, previous implementations of this approach have shown a limited operational bandwidth along with a significant reduction of the generation efficiency. Here, we experimentally demonstrate that a Mach–Zehnder interferometer can be used to effectively linearly uncouple two resonators and, at the same time, allows for their efficient nonlinear coupling. We demonstrate that this structure can lead to an unprecedented control over the rings' interaction and can operate over more than 160 nm, covering the S-, C-, and L-telecom bands. In addition, we show that the photon pair generation efficiency is increased by a factor of four with respect to previous implementations.

In this work, we experimentally demonstrate confined modes in a Bloch surface wave (BSW) ring resonator. We fabricate and characterize a ring resonator with a radius R = 105 μm on a truncated periodic porous silicon multilayer. We show resonant modes around 1.5 μm with quality factors exceeding 103. These results suggest that this platform is promising to develop integrated optical resonators based on BSWs.In this work, we experimentally demonstrate confined modes in a Bloch surface wave (BSW) ring resonator. We fabricate and characterize a ring resonator with a radius R = 105 μm on a truncated periodic porous silicon multilayer. We show resonant modes around 1.5 μm with quality factors exceeding 103. These results suggest that this platform is promising to develop integrated optical resonators based on BSWs.

A theoretical study of second-harmonic generation in planar microcavities with periodic dielectric mirrors is made. Strong enhancement of the nonlinear conversion is predicted when double resonance for the pump and harmonic fields, as well as phase matching, are achieved. For a given structure design, the finite angle of incidence is used as a tuning parameter and the splitting between cavity modes with different polarizations is used to compensate the material dispersion. Examples are given for GaAs cavities with AlGaAs∕Alox dielectric mirrors.

We report the measurement of low-power continuous-wave four-wave mixing in porous silicon microring resonators operating in the 1550 nm telecom band. Resonantly enhanced stimulated four-wave mixing has been measured in rings with 25 μm radius and quality factor around 5000 for pump powers as low as a few hundreds of microwatts. A waveguide nonlinear parameter γ = 20 W–1 m−1 has been determined. These results suggest further research on porous silicon for low-power nonlinear optics, possibly taking advantage of its tunable porosity.

Using rigorous electro-optical calculations, we predict a significant efficiency enhancement in thin-film crystalline silicon (c-Si) solar cells with rough interfaces. We show that an optimized rough texture allows one to reach the Lambertian limit of absorption in a wide absorber thickness range from 1 to 100 μm. The improvement of efficiency due to the roughness is particularly substantial for thin cells, for which light trapping is crucial. We consider Auger, Shockley-Read-Hall (SRH), and surface recombination, quantifying the importance of specific loss mechanisms. When the cell performance is limited by intrinsic Auger recombination, the efficiency of 24.4% corresponding to the wafer-based PERL cell can be achieved even if the absorber thickness is reduced from 260 to 10 μm. For cells with material imperfections, defect-based SRH recombination contributes to the opposite trends of short-circuit current and open-circuit voltage as a function of the absorber thickness. By investigating a wide range of SRH parameters, we determine an optimal absorber thickness as a function of material quality. Finally, we show that the efficiency enhancement in textured cells persists also in the presence of surface recombination. Indeed, in our design the efficiency is limited by recombination at the rear (silicon absorber/back reflector) interface, and therefore it is possible to engineer the front surface to a large extent without compromising on efficiency.

We propose a luminescent solar concentrator (LSC) characterized by a strong enhancement of the concentration factor in which the area covered by photovoltaic cells is independent of the area over which sunlight is collected. We name this device cascade-LSC (c-LSC), as sunlight is both geometrically and spectrally concentrated by cascading absorption and emission into different LSCs. We demonstrate a prototype and measure the generated photocurrent. The results are in good agreement with those predicted by our numerical model based on Monte Carlo simulations.

We report on the design, fabrication, and electro-optical characterization of a light emitting device operating at 1.54 ?m, whose active layer consists of silicon oxide containing Er-doped Si nanoclusters. A photonic crystal (PhC) is fabricated on the top-electrode to enhance the light extraction in the vertical direction, and thus the external efficiency of the device. This occurs if a photonic mode of the PhC slab is resonant with the Er emission energy, as confirmed by theoretical calculations and experimental analyses. We measure an increase of the extraction efficiency by a factor of 3 with a high directionality of light emission in a narrow vertical cone. External quantum efficiency and power efficiency are among the highest reported for this kind of material. These results are important for the realization of CMOS-compatible efficient light emitters at telecom wavelengths. © 2014 AIP Publishing LLC.

There is a conceptual mistake in the extraction of the Rabi splitting from the simulated data shown in Fig. 2. In fact, the Rabi splitting should be evaluated from the dispersion as a function of wave vector, which, for our structure, yields a corrected value of 5.4 meV instead of 6 meV. Therefore, in the abstract the corrected text should be: “the exciton photon coupling is more than 40% larger as compared to....” The text at the bottom of the first column in pp. 121118–2 should read as “the predicted resonance splitting is about 5.4 meV. This value is more than 40% larger....” In the caption of Fig. 2 we correct as “ b attenuated total reflectance ATR spectrum for the angle of incidence at which the exciton and the photon resonances have the same energy, i.e., dashed line in a .”

We present a strategy for label-free biosensing using porous silicon diffraction gratings. The gratings are fabricated using a cost-effective, high-throughput stamping technique. Unlike traditional diffraction-based biosensors that rely on microcontact printing or lithography to create gratings for the localization of analytes on the top surface of the grating, in our structure analytes are free to infiltrate the porous network and increase the effective refractive index of the grating. The large surface area of porous silicon available for molecular binding offers the potential for enhanced diffraction response compared to nonporous gratings with limited surface area. Small molecule detection of 3-aminopropyltriethoxysilane is demonstrated.

We propose a biosensor based on the diffraction of Bloch surface waves (BSWs) in periodic dielectric stacks. Significant enhancement of diffraction efficiency by a biomolecule grating placed on the multilayer is predicted when a BSW is excited through a prism in the Kretschmann configuration. Numerical calculations for BSW in a Si∕SiO2 dielectric stack show an increase of diffraction intensity up to three orders of magnitude with respect to the case of surface plasmon wave enhancement. The mechanism that leads to large field confinement and the absence of absorption losses in the dielectric system make this solution flexible and suitable to different grating periods.

We have realized silicon-on-insulator photonic crystal (PhC) waveguides with intense 1.54 mu m emission at room temperature. The slabs contain a thin layer of SiO2 with Er3+ doped silicon nanoclusters embedded at the center of the Si core and are patterned with a triangular lattice of holes. An enhancement by more than two orders of magnitude of the Er3+ near-normal emission is observed when the transition is in resonance with an appropriate mode of the PhC slab. The results are in very good agreement with calculated photonic bands and emission spectra. These findings are important for the realization of Si-compatible efficient light emitters at telecom wavelengths. (c) 2006 American Institute of Physics.