Towards a fiber-coupled picowatt cryogenic radiometer.

Area of Science:

• Metrology
• Optical Engineering
• Cryogenic Systems

Background:

• Accurate measurement of low optical power is crucial for advanced applications.
• Microscale devices offer potential for miniaturization and enhanced sensitivity in radiometric measurements.
• Electrical substitution radiometry provides a method for calibrating optical power using electrical power.

Purpose of the Study:

• To fabricate and characterize a microscale cryogenic radiometer (PCR) for optical fiber power measurements.
• To assess the performance of the PCR in terms of response inequivalence and repeatability.
• To determine the noise equivalent power (NEP) of the developed system.

Main Methods:

• Fabrication of a micromachined membrane integrating absorber, electrical heater, and thermometer.
• Electrical substitution technique for calibrating optical power measurements.
• Characterization of the PCR's response to varying electrical and optical input powers from fW to nW levels.

Main Results:

• The microscale cryogenic radiometer (PCR) was successfully fabricated on a sub-millimeter membrane.
• Initial measurements showed an 8% response inequivalence between electrical and optical power.
• Repeatability better than ±0.3% (k=2) was achieved for power levels between 15 pW to 70 pW.
• The system demonstrated a noise equivalent power (NEP) of approximately 5×10(-15) W/√Hz at 2 Hz.

Conclusions:

• The microscale cryogenic radiometer is a promising platform for sensitive optical fiber power measurements.
• The demonstrated repeatability suggests the potential for high-precision metrology at picowatt levels.
• Further improvements to the measurement scheme are expected to significantly reduce the NEP, enabling even lower power detection.