Mingyu Li

Optical waveguide double-ring sensor using intensity interrogation with a low-cost broadband source

A highly sensitive optical waveguide sensor based on simple intensity interrogation with a broadband light source is proposed and investigated. It consists of two cascaded microring resonators with the same or slightly different free spectral ranges. The variation of the refractive index of the analyte sample results in a large shift in the envelope function of the transmission peaks of the sensor, and, consequently, a large change in the transmitted power. The low-cost sensing scheme can achieve an ultrahigh sensitivity of 2 × 10⁴ dB/RIU. Experimental results on the intensity interrogated double-ring sensor using a broadband source are presented, demonstrating its operation principle and potential for low-cost practical applications.

Cascaded silicon-on-insulator double-ring sensors operating in high-sensitivity transverse-magnetic mode

We demonstrate ultrahigh-sensitivity silicon photonic sensors based on two cascaded double-ring resonators operating in transverse-magnetic mode. Both wavelength interrogation and intensity interrogation methods are experimentally investigated and the sensitivities reached 24,300 nm/RIU and 2430 dB/RIU, respectively. We also show that the double-ring sensors can be simply cascaded to realize simultaneous detection of multiple species, which is very promising for low-cost array applications.

High-sensitivity optical biosensor based on cascaded Mach–Zehnder interferometer and ring resonator using Vernier effect

We demonstrate an ultrahigh sensitivity silicon photonic biosensor based on cascaded Mach-Zehnder interferometer (MZI) and ring resonator with the Vernier effect using wavelength interrogation. Experimental results show that the sensitivities reached 2870 nm/RIU and 21,500 nm/RIU for MZI sensor and MZI-ring sensor, respectively. A biosensing application was demonstrated by monitoring the interaction between goat and antigoat immunoglobulin G (IgG) pairs. The measured results show that 1 ng/ml IgG resulted in 0.035 nm and 0.5 nm wavelength shift for MZI sensor and MZI-ring sensor, respectively. This high performance sensor is promising for medical diagnostic applications.

CMOS-Compatible Integrated Spectrometer Based on Echelle Diffraction Grating and MSM Photodetector Array

We demonstrate an integrated spectrometer-on-a-chip composed of an echelle diffraction grating (EDG) and metal-semiconductor-metal (MSM) waveguide photodetector array based on silicon-on-insulator (SOI). In the passive section, silicon oxynitride (SiON) is chosen as the material for the waveguide core and is deposited after selectively removing the top silicon layer of the SOI wafer. The buried silicon dioxide layer of the SOI wafer functions as the lower cladding for the SiON core waveguide. In the active section, the MSM photodetector array is fabricated on the top silicon layer of the SOI waveguide with a pitch width of 7.5 μm. With the butt-coupling structure, a responsivity of 0.41 A/W is obtained at 850 nm. Based on the CMOS-compatible fabrication process, we have fabricated a 60-channel spectrometer with a chip size of 9 mm × 6 mm operating around 850 nm. The measured channel spacing is 0.494 nm, with an adjacent channel crosstalk around 18 dB. The channel nonuniformity is less than 1.5 dB. The CMOS-compatible spectrometer with integrated silicon photodetector array can provide a low-cost solution for high-resolution on-chip spectral analysis for visible and near-infrared light with the wavelength below 1100 nm.

Analysis of Wavelength and Intensity Interrogation Methods in Cascaded Double-Ring Sensors

Optical waveguide sensors based on cascaded double-ring resonators are analyzed theoretically and experimentally, for both wavelength interrogation and intensity interrogation methods. It is shown that for the wavelength interrogation, the sensitivity can be increased by over three orders of magnitude by combining the intensity ratio detection of two central peaks, compared with the simple digital operation mode of the central peak wavelength shift detection of the transmission spectrum. While the detection limit of the wavelength interrogation method is several times smaller than that of intensity interrogation method, the latter has advantages of simplicity and low cost which can outweigh the sensitivity reduction for many practical applications. Experimental results showed good agreements with the theoretical analysis.

Experimental investigation of waveguide sensor based on cascaded-microring resonators with vernier effect

An optical sensor based on two cascaded microring resonators is fabricated in silicon-on-insulator waveguide. A Q-factor of 2×104 is measured and the increase of refractive index sensitivity by using Vernier effect is investigated experimentally.

Ultrasensitive Detection of Testosterone Using Microring Resonator with Molecularly Imprinted Polymers

We report ultrasensitive and highly selective detection of testosterone based on microring resonance sensor using molecularly imprinted polymers (MIP). A silicon-on-insulator (SOI) micoring resonator was modified by MIP films (MIPs) on a surface. The MIPs was synthesized by thermopolymerization using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinking agent. The concentration of detected testosterone varies from 0.05 ng/mL to 10 ng/mL. The detection limit reaches 48.7 pg/mL. Ultrahigh sensitivity, good specificity and reproducibility have been demonstrated, indicating the great potential of making a cost effective and easy to operate lab-on-Chip and down scaling micro-fluidics devices in biosensing.

Optical Sensor Based on Vernier-Cascade of Ring Resonator and Echelle Diffraction Grating

An optical sensor based on the Vernier-cascade of a ring resonator and an echelle diffraction grating (EDG) demultiplexer is proposed and analyzed. Due to the difference between the free spectral range of the ring and the channel spacing of the EDG demultiplexer, the refractive index change of the analyte fluid on the ring can be detected by the power distribution among the channels of the EDG. By combining a coarse measurement and a fine measurement, a refractive index sensitivity in the order of 10-6 RIU can be achieved. An optical sensor system can be realized by using a low-cost broadband light source and a detector array.

High-sensitivity and wide-range optical sensor based on three cascaded ring resonators

We demonstrate a three cascaded micro-ring resonators based refractive index optical sensor with a high sensitivity of 5866 nm/RIU, the measurement range of which is significantly improved 24.7 times comparing with the traditional two cascaded micro-ring resonators.

Silicon nanowire waveguide sensor based on two cascaded ring resonators

We report the latest experimental results of cascaded double ring sensor. To improve the sensitivity, nanowire waveguide sensor operating in TM polarization is designed and fabricated, with the help of the e-beam lithography system. The measured transmission spectrum shows good agreement with theoretical analysis.