1 Low power continuous-wave nonlinear optics in silica glass integrated waveguide structures (2103.00351v1)

Abstract: Photonic integrated circuits (PICs) are a key component [1] for future telecommunication networks, where demands for greater bandwidth, network flexibility, low energy consumption and cost must all be met. The quest for all optical components has naturally targeted materials with extremely large nonlinearity, including chalcogenide glasses (ChG) [2] and semiconductors, such as silicon [3] and AlGaAs [4]. Yet issues such as immature fabrication technologies for ChG, and high linear and nonlinear losses for semiconductors, motivate the search for other materials. Here we present the first demonstration of nonlinear optics in integrated silica based glass waveguides using continuous wave (CW) light. We demonstrate four wave mixing (FWM), with low (7mW) CW pump power at a wavelength of 1550nm, in high index doped silica glass ring resonators capable of performing in photonic telecommunications networks as linear filters [5]. The high reliability, design flexibility, and manufacturability of our device raises the possibility of a new platform for future low cost nonlinear all optical PICs.

• The paper demonstrates efficient four-wave mixing in high-index doped silica glass waveguides using only 7 mW CW pump power at 1550 nm.
• The paper employs CMOS-compatible fabrication to achieve a 200-fold higher nonlinearity than standard fibers, ensuring low optical losses and high conversion efficiency.
• The paper highlights the potential of scalable, low-cost photonic integrated circuits for high-bandwidth telecommunications through advanced nonlinear optics.

Low Power Continuous-Wave Nonlinear Optics in Silica Glass Integrated Waveguide Structures

This paper presents an inaugural demonstration of nonlinear optics in silica glass integrated waveguides under continuous-wave (CW) operation. This investigation, centered on high index doped silica glass micro-ring resonators, opens potential pathways for the development of low-cost nonlinear all-optical photonic integrated circuits (PICs) crucial for future telecommunication systems.

The core contribution of this work is the achievement of four-wave mixing (FWM) with remarkably low CW pump power (7 mW) at a 1550 nm wavelength, showcasing effective wavelength conversion. High index doped silica glass exhibits notable advantages, such as low linear and nonlinear optical losses and compatibility with advanced fabrication techniques. These characteristics suggest that this material could serve as a promising platform for the development of efficient integrated photonic devices.

Key Findings and Results

• Enhanced Nonlinear Performance: The paper reports a substantial nonlinearity parameter (γ), approximately 200 times greater than that of standard communication fibers. The high γ value is achieved through enhancement of the Kerr nonlinearity (n₂) and compact mode confinement within the waveguides, which utilize a high core-cladding refractive index contrast (∆n = 17%).
• Device Performance: The resonator design ensures notable field enhancement, achieving external conversion efficiencies comparable to silicon-based devices at lower pump power levels and significantly surpassing them at higher pump powers where silicon devices experience saturation due to multi-photon absorption.
• Compatibility and Fabrication: The integrated waveguides were fabricated using CMOS-compatible processes, ensuring low sidewall roughness and low temperature requirements, a marked advantage over other materials like silicon oxynitride that require high temperature annealing.
• Experimental Validation: The experiments underlined the negligible dispersion in the device, indicated by an on-resonance idler power during FWM processes. Furthermore, it was demonstrated that there was no multi-photon absorption up to peak power levels of 13 dBm, although the experiments were pump-power limited.

Practical and Theoretical Implications

From a practical perspective, the results point to the potential for integrating a larger number of nonlinear devices onto a single chip without significant efficiency losses, largely attributed to the low-loss characteristics of the silica glass waveguides. This could facilitate the development of highly efficient, scalable PICs for telecommunications networks that require high bandwidth performance.

Theoretically, the paper provides a framework for further research into the effective use of high index glasses. Specifically, the paper notes that materials such as silicon oxinitride could potentially offer similar nonlinear optical properties if low losses are maintained.

Future Directions

The work suggests several avenues for further investigation. Future research could explore optimized configurations of the resonator structures to enhance field confinement, further reducing mode field areas and thus increasing the efficiency of nonlinear interactions. Additionally, the exploration of other high index doped glass materials under similar fabrication conditions could broaden the range of suitable materials for high-performance PICs. Expanding the bandwidth and increasing processing speed are also crucial steps in advancing the utility of these integrated devices for broader optical signal processing applications.

In summary, this paper advances the understanding and application of silica glass in low power nonlinear optics, positioning it as a viable material for a range of future telecommunications applications. With further research, such integrated waveguide structures could become a mainstay in the development of advanced photonic technologies.