Nonlinearly enhanced refractive index sensing in coupled optical microresonators

Area of Science:

• Optics and Photonics
• Sensing Technology
• Nonlinear Optics

Background:

• Optical microresonators offer high sensitivity for sensing applications.
• Nonlinear optical effects can enhance sensing performance.
• Coupled resonator systems provide additional control and feedback mechanisms.

Purpose of the Study:

• To investigate the use of nonlinear self-phase modulation (SPM) in coupled optical microresonators for ultrasensitive refractive index sensing.
• To quantify the sensitivity enhancement achieved by SPM and coupled resonators.
• To assess the robustness of the system against laser noise.

Main Methods:

• Utilizing nonlinear self-phase modulation (SPM) within coupled optical microresonator systems.
• Analyzing the resonance frequency shift in response to refractive index perturbations.
• Employing constructive interference and waveguide feedback in a two-resonator configuration.
• Simulating performance using parameters for Silicon (Si) microresonators.

Main Results:

• SPM provides positive feedback, enhancing resonance frequency shifts.
• Coupled resonators further improve sensitivity through constructive interference and feedback.
• Achieved sensitivity is over 100 times greater than single resonators without SPM.
• Demonstrated a minimum detectable refractive index change of 10^-11 RIU with Q-factors of ~10^4.
• The nonlinearly enhanced system shows robustness against laser noise below bistability threshold.

Conclusions:

• Nonlinear SPM in coupled microresonators enables ultrasensitive refractive index sensing.
• The combined approach significantly outperforms traditional single-resonator methods.
• The system is practical for real-world applications due to its noise robustness.