Near-field imaging of light propagation in photonic crystal waveguides: Explicit role of Bloch harmonics

Abstract

We employ a collection scanning near-field optical microscope ͑SNOM͒ to image the propagation of light at telecommunication wavelengths along straight and bent regions of silicon-on-insulator photonic crystal waveguides ͑PCWs͒ formed by removing a single row of holes in the triangular 410-nm-period lattice along the ⌫M direction of the irreducible Brillouin zone. We obtain high quality SNOM images of PCWs excited in the wavelength range of 1520-1570 nm, which indicate good PCW mode confinement and low propagation loss. Using averaged cross sections of the intensity distributions before and after PCW bends, bend loss is evaluated and found to noticeably increase with the increase of the light wavelength from ϳ1 dB at 1520 nm to ϳ6 dB at 1570 nm. We analyze light intensity variations along PCWs measured with the SNOM at different distances from the sample surface. Considering the interference between a quasihomogeneous background field and Bloch harmonics of the PCW mode, we account for spatial frequency spectra of the intensity variations and determine the propagation constant of the PCW mode at 1520 nm. The possibilities and limitations of SNOM imaging for the characterization of PCWs are discussed.

Near-field characterization of low-loss photonic crystal waveguides

“…15 Quite recently, we have employed a collection scanning near-field optical microscope ͑SNOM͒ for imaging of the propagation of light at telecommunication wavelengths along straight and bent regions of silicon-on-insulator PCWs. 16,17 High-quality SNOM images were obtained allowing us to directly evaluate the bend loss and characterize the PCW mode confinement. Furthermore, by considering spatial frequencies in light-intensity variations along the PCW we have estimated the propagation constant and determined the dispersion of the PCW mode.…”

Local probing of Bloch mode dispersion in a photonic crystal waveguide

“…Indeed recently, PhCW dispersion has been addressed by local evanescent field probing. This was demonstrated by either investigating the evanescent field coupling between a tapered optical fiber and a PhCW [13] or by local near-field probing of the intensity distribution in a PhCW [14]. Unfortunately, in both cases only a small portion of the total band diagram was obtained.…”

Nonlinear Bloch modes in two-dimensional photonic lattices

“…In particular, depending on the local dispersion and a local value of the wave vector, an optical beam (or pulse) experience normal, anomalous or even vanishing diffraction (or dispersion) [3,4,5]. Experimentally, the Blochwave character of electromagnetic waves in photonic crystal waveguides has been deduced indirectly by detecting the out-of-plane leakage of light [6], by investigating the evanescent field coupling between a tapered optical fiber and a photonic crystal waveguide [7], and more directly by local near-field probing of the intensity distribution in a waveguide [8]. The full band structure of a photonic crystal waveguide has been recovered very recently by employing a near-field optical microscope and probing both the local phase and amplitude of the light propagating through a single-line defect waveguide [9,10].…”