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Si-Waveguide Absorption-Based Methane Sensor

Tool Used: OptSim Circuit

Si-Waveguide Absorption-Based Methane Sensor | 草榴社区

In this OptSim Circuit application note, we will demonstrate an Absorption-based methane sensor using Si waveguide. This methane sensor will:

  • Probe the 1650.96-nm line in methane absorption spectrum (?_???= 0.4347 cm-1)
  • Have the following waveguide parameters:
    • length ? = 10 cm,
    • intrinsic loss ?_?? = 2 dB/cm
    • methane mode overlap Γ = 25.5%
  • Demonstrate 8-dB input/output coupling
  • Demonstrate a measured detection limit of 100 ppmv for 60-second averaging time

OptSim Circuit Cppmv Measurement

OptSim Circuit Cppmv Measurement | 草榴社区
  • Launched power is 10 dBm at 1650.9554 nm
  • Total waveguide power transmission: ?????????Γ??????, where ?=?????/106
  • Receiver noise, assumed to be independent of input signal level, calibrated for 100-ppmv detection limit with 60-second averaging time
  • Receiver calibration based on calculated time-averaged noise-equivalent power (NEP) and absorbance (???):
Formula

OptSim Circuit Allan Deviation Analysis

OptSim Circuit Allan Deviation Analysis | 草榴社区

Indicated blocks produce electrical signal whose average power is the Allan variance in ppmv?:

Formula
where ????,? is the ?th measurement sample (? total) with sampling time ????????

  • Allan deviation (ppmv) versus averaging time matches results from Tombez et al. for 10-dBm launch power
  • Detection limit improves (worsens) for higher (lower) launch power – consistent with assumption that sensor noise is independent of signal power
  • Detection limit optimum at waveguide length = 1/??? [see H. Lin et al., “Mid-infrared integrated photonics on silicon: a perspective”, Nanophotonics 7(2), 393-420 (2018).]
  • Sub-10-ppmv detection limit at optimum length for averaging times ? 91 seconds
  • Detection limit improves as waveguide loss decreases
  • Results assume sensor noise independent of signal power levels