Abstract
Designed or patterned structured surfaces, metasurfaces, enable the miniaturization of complex arrangements of optical elements on a plane. Most of the existing literature focuses on miniaturizing the optical detection; little attention is directed to on-chip optical excitation. In this work, we design a metasurface to create a planar integrated photonic source beam collimator for use in on-chip optofluidic sensing applications. We use an iterative inverse design approach in order to optimize the metasurface to achieve a target performance using gradient descent method. We then fabricate beam collimators and experimentally compare performance characteristics with conventional uniform binary grating-based photonic beam diffractors. The optimal design enhances the illumination power by a factor of 5. The reinforced beam is more uniform with 3 dB beam spot increased almost ~ 3 times for the same device footprint area. The design approach will be useful in on-chip applications of fluorescence imaging, Raman, and IR spectroscopy and will enable better multiplexing of light sources for high throughput biosensing.
Highlights
Designed or patterned structured surfaces, metasurfaces, enable the miniaturization of complex arrangements of optical elements on a plane
The promise of silicon photonics is that the technology will enable flexible, low-cost, and scalable approaches for the miniaturization of integrated electronic and photonic systems[1,2,3], enabling on-chip spectroscopic sensing and imaging techniques in the fields of medicine and biology[4,5,6]
Fluorescence imaging/microscopy is a powerful tool for biomedical research; it provides very high sensitivity and specificity for cellular activity detection, making it the gold standard
Summary
Designed or patterned structured surfaces, metasurfaces, enable the miniaturization of complex arrangements of optical elements on a plane. The design approach will be useful in on-chip applications of fluorescence imaging, Raman, and IR spectroscopy and will enable better multiplexing of light sources for high throughput biosensing. With the advent of semiconductor image sensing technology[13, 14], researchers have demonstrated on-chip contact-based fluorescence detection techniques with high throughput and scalability[11]. In addition to the limit of large instrumentation, a major disadvantage of this method is that photonic excitation performed using LED/benchscale lasers is not spatially confined This is predominantly due to diffraction limited beam propagation which results in high background noise, leading to poor signal-to-noise (SNR) ratio and sensitivity
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