Near-field characterization of photonic crystal waveguides

Abstract

In the past few years, the development of photonic crystal waveguides and structures has progressed immensely revealing many interesting optical phenomena and demonstrating numerous potential applications. We show how a scanning near-field optical microscope (SNOM) in the collection mode can be used to investigate these powerful new optical structures, in particular photonic crystal waveguides (PhCWs). Unlike conventional far-field techniques, a SNOM can detect truly guided light propagating inside the structure without relying on scattering, and SNOM imaging is thereby not restricted by the diffraction limit of half of the wavelength used. In contrast to the regular input-output measurements, the SNOM collects local optical information which is not integrated or averaged because the light has propagated through the entire photonic structure, including possible in-and out-coupling waveguides. We show how intensity detection can be used to map mode profiles, determine losses locally, gain insight into the Bloch nature of the propagating light, and investigate more complex photonic crystal-based structures. Phase-sensitive detection allows the Bloch nature to be investigated in more detail as all the Bloch harmonics belonging to a single Bloch mode can be unravelled. Time-resolved SNOM measurements (pulse tracking measurements) allow pulse propagation to be visualized and phase and group velocities to be determined independently with the need for modelling. For certain optical frequencies ultraslow light can be observed. The possibilities and limitations of SNOM imaging for the characterization of PhCWs are discussed.

Superfocusing and Light Confinement by Surface Plasmon Excitation Through Radially Polarized Beam

“…However, the use of such microscope keeps growing during the last 10 years especially due to its ability to make very local detection of the light distribution surrounding very small samples. Thus, quantum dots [3][4][5][6], photonic crystals [7][8][9][10][11][12][13], or nonlinear materials (Raman, fluorescence, ...) [14][15][16][17] are currently characterized thanks to optical near-field microscopes working with conventional tips (coated or uncoated tapered optical fibers). Apertureless nearfield optical microscopes are often used by exploiting the tip effect, also named the "antenna effect", that leads to a large light confinement at the tip apex (see [18] and references therein).…”

Light propagation in a free-standing lithium niobate photonic crystal waveguide

“…As described in Ref. 13, the collected signal results from interferences between multiple beams. In the crystallographic coordinate system ͑X axis being the surface normal, Y and Z axis lying in the PhC plane with Z parallel to the WG͒, the field probed by the SNOM tip E t can be expressed as…”

Discrete diffraction in waveguide arrays: A quantitative analysis by tunneling optical microscopy

“…16 and references therein͒. 16 In general, repro-ducible near-field probes are desired for quantitative analysis by STOM. This circumstance can affect the imaging process and must be carefully taken into account in the case of phase-sensitive detection.…”

“…15,16 A topography of the sample surface, in which the waveguides appear as buried stripes at the surface, is depicted in Fig. The impulse response of the array at 980 nm has been accurately measured using a STOM system.…”