Thermal noise in mid-infrared broadband upconversion detectors

Area of Science:

• Optics and Photonics
• Infrared Detection Technology
• Nonlinear Optics

Background:

• Low-noise mid-infrared (MIR) detection is challenging due to thermal background radiation from detector materials.
• Frequency upconversion detectors (UCDs) offer a promising room-temperature alternative to traditional direct detection schemes, enabling the use of low-noise silicon-based cameras.

Purpose of the Study:

• To rigorously analyze the optical power generated by frequency upconversion of intrinsic black-body radiation within the nonlinear material itself.
• To evaluate noise contributions from the nonlinear material in UCD systems for estimating noise-equivalent power limits.
• To investigate a periodically poled lithium niobate (PPLN) based MIR-UCD operating across its absorption edge (3.5 - 5 µm).

Main Methods:

• Theoretical analysis of optical power generated by frequency upconversion of black-body radiation in nonlinear crystals.
• Experimental investigation using a periodically poled lithium niobate (PPLN) based MIR-UCD.
• Measurement of upconverted thermal radiation power at varying crystal temperatures (room temperature and 120°C) with a continuous-wave (CW) mixing beam.

Main Results:

• The study rigorously analyzed the optical power generated by frequency upconversion of intrinsic black-body radiation in the nonlinear material.
• Measured upconverted thermal radiation power was approximately 30 pW at room temperature (~30°C) and reached ~70 pW at 120°C for a ~60 W CW mixing beam.
• Experimental results showed good quantitative agreement with theoretical predictions.

Conclusions:

• The intrinsic thermal radiation of nonlinear crystals is a significant noise source in MIR-UCDs, particularly near the material's optical absorption edge.
• The analysis provides a quantitative understanding of noise limitations in UCD systems and can be extended to other nonlinear conversion processes.
• This research supports the development of improved UCD systems for low-noise MIR detection.