MultiParameter Sensing in a Multimode SelfInterference MicroRing Resonator by Machine Learning A universal multiparameter sensing scheme based on a selfinterference microring resonator (SIMRR) is proposed. Benefit from the special intensity sensing mechanism, the SIMRR allows multimode sensing in a wide range of wavelengths but immune from frequency noise. To process the multiple mode spectra that are dependent on multiple parameters, we adopt the machine learning algorithm instead of massive asymptotic solutions of resonators. Employing the proposed multimode sensing approach, a twoparameter SIMRR sensor is designed. Assuming that two gases have different wavelength dependence of refractive indices, the feasibility and effectiveness of the twoparameter sensing strategy are verified numerically. Moreover, the dependence of parameter estimation accuracy on the laser intensity noises is also investigated. The numerical results indicate that our scheme of multiparameter sensing in a multimode SIMRR holds great potential for practical highsensitive sensing platforms compared with the singlemode sensing based on whispering gallery mode (WGM) resonators.

A WideRange and CalibrationFree Spectrometer Which Combines Wavelength Modulation and Direct Absorption Spectroscopy with Cavity Ringdown Spectroscopy A widerange, calibrationfree tunable diode laser spectrometer is established by combining wavelength modulation and direct absorption spectroscopy (WMDAS) with continuous wave cavity ringdown spectroscopy (CWCRDS). This spectrometer combines the benefits of absolute concentration measurements, wide range, and high speed, using WMDAS with enhanced noise reduction in CWCRDS. The accurate baseline ringdown time, xcfx840, is calculated by the absorption peak (measured by WMDAS) and the ringdown time containing gas absorption information (measured by CWCRDS at the center wavelength of the spectral line). The gas concentration is obtained without measuring xcfx840 in real time, thus, greatly improving the measuring speed. A WMDASCWCRDS spectrometer at 1.57 xcexbcm for CO detection was assembled for experimental validation of the multiplexing scheme over a concentration ranging from 4 ppm to 1.09% (0.1 MPa, 298 K). The measured concentration of CO at 6374.406 cmxe2x88x921 shows that the dynamic range of this tunable diode laser absorption spectrometer is extendable up to five orders of magnitude and the corresponding precision is improved. The measurement speed of this spectrometer can extend up to 10 ms, and the detection limit can reach 35 ppb within 25 s.