Weak-signal conversion from 1550 to 532  nm with 84% efficiency

Area of Science:

• Quantum optics
• Nonlinear optics
• Photonics

Background:

• Efficient frequency conversion is crucial for quantum technologies and optical sensing.
• Previous methods often reported efficiencies that did not account for all system losses.
• Sum-frequency generation (SFG) is a key nonlinear optical process for frequency upconversion.

Purpose of the Study:

• To experimentally demonstrate high-efficiency frequency conversion of a dim, continuous-wave (CW) light field.
• To accurately quantify photon-number conversion efficiency, including all optical losses.
• To validate a numerical model for SFG in a resonant cavity.

Main Methods:

• Sum-frequency generation (SFG) using a periodically poled type I potassium titanyl phosphate (PPKTP) crystal.
• Implementation within a standing-wave optical cavity to enhance nonlinear interaction.
• Pumping the crystal with an intense 810 nm light field to drive the SFG process.
• Careful accounting for all optical losses prior to photoelectric detection.

Main Results:

• Achieved an external photon-number conversion efficiency of (84.4±1.5)% for converting 1550 nm light to 532 nm.
• The reported efficiency includes all losses, such as those from frequency filters and cavity coupling.
• Experimental results show excellent agreement with theoretical predictions from a numerical model.
• The model predicts a potential conversion efficiency of up to 93% with optimized cavity parameters.

Conclusions:

• Demonstrated a record high, loss-corrected photon-number conversion efficiency for dim light upconversion.
• The use of a resonant cavity with a PPKTP crystal is highly effective for efficient SFG.
• The validated numerical model can guide future optimization of frequency conversion systems for quantum applications.