Abstract
Polymer-based single-microring biosensors usually have a small free spectral range (FSR) that hampers the tracing of the spectrum shifting in the measurement. A cascade of two microring resonators based on the Vernier effect, is applied in this article in order to make up for this defect. A small FSR difference between the reference microring and the sensing microring is designed, in order to superpose the periodic envelope signal onto the constituent peaks, which makes it possible to continuously track the spectrum of the sensor. The optical polymer material, Ormocore, which has a large transparent window, is used in the fabrication. The biosensor is fabricated by using an UV-based soft imprint technique, which is considered to be cost-effective and suitable for mass production. By optimizing the volume ratio of Ormocore and the maT thinner, the device can be fabricated almost without a residual layer. The device works at a wavelength of 840 nm, where water absorption loss is much lower than at the infrared wavelengths. A two-step fitting method, including single-peak fitting and whole-envelope fitting, is applied in order to trace the spectral shift accurately. Finally, the two-cascaded-microrings biosensor is characterized, and the obtained FSR is 4.6 nm, which is 16 times larger than the FSR of the single microring biosensor demonstrated in our previous work. Moreover, the sensitivity can also be amplified by 16-fold, thanks to the Vernier effect.
Highlights
IntroductionIntegrated photonics have been widely known as key components in optical communication [1,2,3,4]
Integrated photonics have been widely known as key components in optical communication [1,2,3,4].In recent years, they have attracted a lot of interest for biosensors, because of their unique features, such as high sensitivity, being label free, and allowing for real-time monitoring [5,6]
The evanescent tail of waveguide modes that can interact with the external environment is usually utilized in integrated photonics biosensors, and various structures have been demonstrated, such as Mach–Zehnder interferometers (MZIs) [7], Young interferometers [8], microring resonators [9,10], photonic crystals [11,12], and plasmonic structures [13,14,15]
Summary
Integrated photonics have been widely known as key components in optical communication [1,2,3,4] In recent years, they have attracted a lot of interest for biosensors, because of their unique features, such as high sensitivity, being label free, and allowing for real-time monitoring [5,6]. In order to ensure that the envelope period falls within the wavelength range of the measurement devices, small FSRs for both microrings are required This means that a large roundtrip by the microring is needed, which is not suitable for the SOI or SiN platforms. It is usually considered to be simple and suitable for mass production, as no high pressures or temperatures are necessary, and roller-to-roller can be applied [25]
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