Free space excitation of coupled Anderson-localized modes in photonic crystal waveguides with polarization tailored beam

Abstract

We experimentally demonstrate free space excitation of coupled Anderson-localized modes in photonic crystal (PhC) line-defect waveguides (W1) with polarization tailored beams. The corresponding light beam is tightly focused on a pristine W1, and out-of-plane scattering is imaged. By integrating the scattering spectra along the guide, at the W1 modal cut-off, Anderson-localized cavities are observed due to residual W1 fabrication-disorder. Their spectral lines exhibit high quality Q factors up to 2 × 105. The incident beam polarization and scattering intensities of the localized modes characterize the efficiency of free-space coupling. The coupling is studied for linearly and radially polarized input beams and for different input coupling locations along the W1 guide. The proposed coupling scheme is particularly attractive for excitation of PhC waveguide modes and Anderson-localized cavities by beam steering and scanning microscopy for sensing applications.

Single Virus Detection on Silicon Photonic Crystal Random Cavities

“…1d). The polarization direction of the linearlypolarized laser light was adjusted to the direction parallel to the waveguide to achieve a better coupling to the waveguide 34 . The residual fabrication disorder inherent in the silicon PhC induces both backscattering and out-of-plane scattering for the light propagating along the W1 waveguide, especially in the vicinity of the cut-off frequency where the radiation losses of the slowly guided Bloch-TE waveguide mode 46 increase 50,51 .…”

“…The polarization direction of the linearly polarized laser light was adjusted to the direction parallel to the waveguide to achieve a better coupling to the waveguide. [34] The residual fabrication disorder inherent in the silicon PhC induces both backscattering and out-ofplane scattering for the light propagating along the W1 waveguide, especially in the vicinity of the cut-off frequency where the radiation losses of the slowly guided Bloch-TE waveguide mode [44] increase. [48,49] As a result, one can vertically collect the scattered light using an objective to measure the spectrum of the localized modes for those k-vector components that lie within the numerical aperture (NA) of the objective.…”

“…[29,30] The PhC random cavities are excited by a free space beam (Figure 1a). Nanoparticle sensing with Anderson-localized, random PhC cavities [30] provides several advantages as compared to the use of other, more carefully engineered PhC defect cavities [31] or PhC heterostructure cavities: [32,33] (1) The silicon PhC sensor consists only of the W1 waveguide without requiring any other pre-fabricated optical structures such as defect cavities or coupler(s); (2) the residual and unavoidable fabrication disorder which usually limits a sensor's performance here localizes the light in the high Q/V random cavities; (3) the excitation of the random cavities along the guide using the free-space beam [34] requires only minimal initial beam alignment; (4) many particles can be detected without saturating a microcavity response, and (5) the freespace excitation allows for ease of integration with an aqueous sample cell and, in the future, with simple microfluidics.…”

“…[42]), the Anderson‐localized random cavities have previously been used for example in InGaAsP random lasers [ 37 ] and for quantum electrodynamics in GaAs PhC waveguides [ 35 ] to demonstrate the strong coupling with a single emitter. [ 36,43 ] Previously, we have demonstrated Q > 10 5 in silicon PhC W1 waveguide slabs in the telecom wavelength range at a similar level of nanoscale disorder, [ 34,41 ] and predicted that the Anderson‐localized random PhC microcavity sensor could provide a platform suitable for various biosensing applications. Despite this potential for biosensing and nanoparticle detection in particular, there have been very few reports that use the Anderson‐localized W1 random cavity modes for sensing applications.…”

Guiding robust valley-dependent edge states by surface acoustic waves

“…The SAW valley-dependent properties revealed here could inspire further applications in e.g. on-chip acoustic sensing, 36 phonon-photon interactions 37,38 and acoustic signal processing. [39][40][41] 9…”