Frequency comb offset detection using supercontinuum generation in silicon nitride waveguides

Area of Science:

• Photonics and Optical Engineering
• Laser Physics
• Materials Science

Background:

• Carrier-envelope-offset (CEO) frequency stabilization is crucial for precision spectroscopy and optical frequency combs.
• Traditional methods often require high optical power or complex setups.
• Supercontinuum generation (SCG) in waveguides offers a compact platform for nonlinear optical processes.

Purpose of the Study:

• To demonstrate direct CEO frequency detection using SCG in a CMOS-compatible silicon nitride (Si(3)N(4)) waveguide.
• To evaluate the efficiency and performance of Si(3)N(4) waveguides for f-to-2f interferometry.
• To compare the performance of Si(3)N(4) waveguides with conventional photonic crystal fibers for CEO detection.

Main Methods:

• Generation of a coherent supercontinuum spanning over 1.5 octaves in a Si(3)N(4) waveguide.
• Self-referencing of SESAM modelocked diode-pumped Yb:CALGO lasers using standard f-to-2f interferometry.
• Direct detection of CEO beat signals without amplification for 100-MHz and 1-GHz lasers.

Main Results:

• Successful direct CEO frequency detection was achieved in Si(3)N(4) waveguides.
• High signal-to-noise ratios (SNR) exceeding 25 dB and 30 dB were obtained with low coupled pulse energies (30 pJ and 36 pJ).
• Si(3)N(4) waveguides reduced the required peak power for CEO beat detection by over an order of magnitude compared to photonic crystal fibers.

Conclusions:

• CMOS-compatible Si(3)N(4) waveguides are highly effective for direct CEO frequency detection.
• This approach significantly lowers the power requirements for stabilizing modelocked lasers.
• The findings pave the way for more accessible and compact optical frequency comb systems.