Abstract
We demonstrate in simulation and experiment that the out-of-plane, far-field scattering profile of resonance modes in photonic crystal nanobeam (PCN) cavities can be used to identify resonance mode order. Through detection of resonantly scattered light with an infrared camera, the overlap between optical resonance modes and the leaky region of k-space can be measured experimentally. Mode order dependent overlap with the leaky region enables usage of resonance scattering as a "fingerprint" by which resonant modes in nanophotonic structures can be identified via detection in the far-field. By selectively observing emission near the PCN cavity region, the resonant scattering profile of the device can be spatially isolated and the signal noise introduced by other elements in the transmission line can be significantly reduced, consequently improving the signal to noise ratio (SNR) of resonance detection. This work demonstrates an increase in SNR of ∼ 19 dB in out-of-plane scattering measurements over in-plane transmission measurements. The capabilities demonstrated here may be applied to improve characterization across nanophotonic devices with mode-dependent spatial field profiles and enhance the utility of these devices across a variety of applications.
Highlights
Nanophotonic devices such as ring resonators, photonic crystals, plasmonic structures and FabryPerot cavities enable numerous optical applications, including signal processing [1,2,3], optical nanomanipulation [4, 5], sensing [6,7,8], quantum computing [9, 10] and optomechanics [11,12,13], in platforms compatible with dense integration and on-chip implementation
Experimental identification of mode order in nanophotonic devices has been done by either relating measured modal features to simulated results [14, 15], or through direct, near-field measurements such as near-field scanning optical microscopy (NSOM) [16]
While comparison of measured modal features to simulated results is widely used for determining mode order, devices with high spatial or temporal optical confinement are highly sensitive to small changes in device dimensions such that small deviations between simulated and fabricated geometric dimensions can lead to large shifts in resonant features
Summary
Nanophotonic devices such as ring resonators, photonic crystals, plasmonic structures and FabryPerot cavities enable numerous optical applications, including signal processing [1,2,3], optical nanomanipulation [4, 5], sensing [6,7,8], quantum computing [9, 10] and optomechanics [11,12,13], in platforms compatible with dense integration and on-chip implementation The appeal of these devices largely hinges on their ability to spatially and temporally localize light. NSOM is able to circumvent these issues through direct field measurements of excited optical modes; it is a relatively complex technique which is not yet widely available for measurement of guided wave photonic structures
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