Papers
Topics
Authors
Recent
Gemini 2.5 Flash
Gemini 2.5 Flash
173 tokens/sec
GPT-4o
7 tokens/sec
Gemini 2.5 Pro Pro
46 tokens/sec
o3 Pro
4 tokens/sec
GPT-4.1 Pro
38 tokens/sec
DeepSeek R1 via Azure Pro
28 tokens/sec
2000 character limit reached

An octave spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide (1405.4205v1)

Published 16 May 2014 in physics.optics

Abstract: We demonstrate an octave-spanning frequency comb with a spectrum covering wavelengths from 1,540 nm up to 3,200 nm. The supercontinuum is generated by pumping a 1-cm long dispersion engineered silicon wire waveguide by 70 fs pulses with an energy of merely 15 pJ. We confirm the phase coherence of the output spectrum by beating the supercontinuum with narrow bandwidth CW lasers. We show that the experimental results are in agreement with numerical simulations.

Citations (200)

Summary

An Octave-Spanning Mid-Infrared Frequency Comb in Silicon Nanophotonic Waveguides

The paper presents a significant advancement in the generation of mid-infrared frequency combs utilizing silicon nanophotonic wire waveguides. The researchers successfully demonstrate an octave-spanning frequency comb, with a spectral range extending from 1,540 nm to 3,200 nm. This achievement is primarily facilitated by pumping a 1-cm-long, dispersion-engineered silicon wire waveguide with femtosecond (fs) pulses possessing an energy of only 15 picojoules (pJ).

Core Methodology and Device Architecture

The silicon waveguide under discussion is fabricated in a silicon-on-insulator (SOI) platform consisting of a 390-nm thick silicon device layer supported by a 2-µm buried oxide layer. The waveguide is precisely engineered with a rectangular cross-section whereby slight over-etching optimizes dispersion properties. Leveraging the high nonlinear refractive index of silicon, significant optical confinement is achieved, leading to a nonlinear parameter of 38 (W·m)-1. The authors employ a femtosecond mode-locked Ti-Sapphire laser to pump the waveguide near its zero dispersion wavelength, culminating in the broadband supercontinuum generation.

Results and Analysis

A significant outcome of this experimentation is the generation of phase-coherent supercontinuum output verified through free-running beat note measurements with narrow-bandwidth CW lasers. This coherence is an essential property for precision applications such as frequency metrology and direct frequency comb spectroscopy. Through simulations, the researchers establish that the coherence is uniform across the entire bandwidth, corroborating the experimental data. The results indicate the potential of these silicon nanophotonic structures to sustain frequency comb structures with exceptional spectral width due to their inherent dispersion properties and high-refractive index contrast.

Implications and Future Prospects

The demonstrated approach presents two major implications for the future of mid-infrared photonics. Theoretically, it underscores the viability of leveraging silicon as a medium for broadband frequency combs, which could significantly streamline and compact future optical systems compared to traditional chalcogenide-based systems. Practically, due to the inherently high nonlinearity and capacity for precise dispersion engineering of silicon waveguides, the technique paves the way for widespread CMOS-compatible photonic circuits operating in the mid-infrared spectrum.

Additionally, the potential for scaling and extending the supercontinuum generation to broader spectra—limited by the oxide layer—is particularly fascinating. With advancements in dispersion engineering and innovations such as the silicon-on-sapphire platforms, the bandwidth could be further expanded up to 8,500 nm. This expansion could be pivotal in precision measurement applications, boosting the resolution and sensitivity of systems used in various scientific and industrial fields.

In conclusion, this paper marks a significant stride toward developing efficient and compact mid-infrared frequency comb systems using silicon nanophotonics. Future research exploring improved designs, alternative platforms, and real-world applications could catalyze revolutionary changes in frequency metrology and spectroscopic methods.