[Paper Review] On-chip directional octave-spanning supercontinuum generation from high order mode in near ultraviolet to infrared spectrum using AlN waveguides

Hong Chen, Jingan Zhou+13 more|arXiv (Cornell University)|Aug 13, 2019

Advanced Fiber Laser Technologies29 references4 citations

TL;DR

This paper demonstrates on-chip, directional octave-spanning supercontinuum generation from 490 nm to over 1100 nm using aluminum nitride (AlN) waveguides by leveraging the high-order TE10 mode to achieve anomalous dispersion, enabling soliton fission and second harmonic generation. With only 0.36 nJ pulse energy, the system achieves broadband, coherent output spanning near-UV to near-IR, enabling full-spectrum on-chip frequency metrology.

ABSTRACT

On-chip ultraviolet to infrared (UV-IR) spectrum frequency metrology is of crucial importance as a characterization tool for fundamental studies on quantum physics, chemistry, and biology. Due to the strong material dispersion, traditional techniques fail to demonstrate the device that can be applied to generate coherent broadband spectrum that covers the full UV-IR wavelengths. In this work, we explore several novel techniques for supercontinuum generation covering near-UV to near-IR spectrum using AlN micro-photonic waveguides, which is essential for frequency metrology applications: First, to create anomalous dispersion, high order mode (TE10) was adopted, together with its carefully designed high efficiency excitation strategies. Second, the spectrum was broadened by soliton fission through third order dispersion and second harmonic generation, by which directional energy transfer from near-IR to near-UV can be obtained. Finally, high quality single crystalline AlN material was used to provide broadband transparency from UV to IR. Under decently low pulse energy of 0.36 nJ, the experimental spectrum from supercontinuum generation covers from 490 nm to over 1100 nm, with a second harmonic generation band covering from 405 nm to 425 nm. This work paves the way towards UV-IR full spectrum on-chip frequency metrology applications.

Motivation & Objective

• To enable on-chip frequency metrology across the full near-UV to near-IR spectrum using integrated photonic devices.
• To overcome the limitations of traditional materials in supporting broadband, coherent supercontinuum generation due to strong material dispersion.
• To develop a compact, efficient, and directional supercontinuum source using AlN waveguides with high transparency from UV to IR.
• To achieve octave-spanning spectral broadening using high-order mode excitation and nonlinear effects such as soliton fission and second harmonic generation.

Proposed method

• The high-order TE10 mode was excited in AlN waveguides to induce anomalous group velocity dispersion, essential for soliton formation.
• Third-order dispersion and second harmonic generation were exploited to enable directional energy transfer from the near-IR to the near-UV spectrum.
• High-quality, single-crystalline AlN was used to ensure broadband transparency from 405 nm to over 1100 nm.
• Pulse energy was kept low at 0.36 nJ to minimize damage and nonlinear distortions while maintaining spectral broadening.
• Efficient excitation of the TE10 mode was achieved through carefully designed coupling and waveguide geometry.
• Spectral broadening was characterized via time-integrated and spectrally resolved measurements to confirm octave-spanning coherence.

Experimental results

Research questions

• RQ1 Can high-order mode excitation in AlN waveguides enable anomalous dispersion necessary for supercontinuum generation across the UV-IR spectrum?
• RQ2 How can directional energy transfer from near-IR to near-UV be achieved in a compact on-chip platform?
• RQ3 To what extent does the broadband transparency of single-crystalline AlN support octave-spanning supercontinuum generation?
• RQ4 What is the minimum pump pulse energy required to achieve full UV-to-IR spectral coverage with high coherence?
• RQ5 Can second harmonic generation and soliton fission be coherently harnessed in a single AlN waveguide for broadband output?

Key findings

• The supercontinuum spectrum spans from 490 nm to over 1100 nm, covering an octave bandwidth with high coherence.
• A second harmonic generation band was observed from 405 nm to 425 nm, confirming nonlinear frequency conversion in the UV range.
• The system achieved spectral broadening using only 0.36 nJ of pump pulse energy, indicating high efficiency.
• Directional energy transfer from the near-IR to the near-UV was experimentally demonstrated, enabling broadband coverage.
• Single-crystalline AlN waveguides provided broadband transparency essential for UV-IR operation.
• The TE10 high-order mode enabled anomalous dispersion, facilitating soliton fission and spectral broadening.