Ultra-low loss integrated visible photonics using thin-film lithium niobate (1902.08217v2)

Abstract: Integrated photonics is a powerful platform that can improve the performance and stability of optical systems, while providing low-cost, small-footprint and scalable alternatives to implementations based on free-space optics. While great progress has been made on the development of low-loss integrated photonics platforms at telecom wavelengths, visible wavelength range has received less attention. Yet, many applications utilize visible or near-visible light, including those in optical imaging, optogenetics, and quantum science and technology. Here we demonstrate an ultra-low loss integrated visible photonics platform based on thin film lithium niobate on insulator. Our waveguides feature ultra-low propagation loss of 6 dB/m, while our microring resonators have an intrinsic quality factor of 11 million, both measured at 637 nm wavelength. Additionally, we demonstrate an on-chip visible intensity modulator with an electro-optic bandwidth of 10 GHz, limited by the detector used. The ultra-low loss devices demonstrated in this work, together with the strong second- and third-order nonlinearities in lithium niobate, open up new opportunities for creating novel passive, and active devices for frequency metrology and quantum information processing in the visible spectrum range.

Ultra-Low Loss Integrated Visible Photonics Using Thin-Film Lithium Niobate

The paper under discussion presents a significant advancement in the domain of integrated photonics, focusing on the visible spectrum. The authors demonstrate an ultra-low loss photonics platform based on thin-film lithium niobate (TFLN) that operates at visible wavelengths. This platform is crucial for various applications such as optical imaging, optogenetics, and quantum technologies which demand precision and stability in optical systems.

Key Contributions

The paper outlines the successful creation of waveguides and microring resonators with exceptionally low propagation loss and high intrinsic quality factors, catering specifically to visible wavelengths centered around 637 nm. The microring resonators achieved an intrinsic quality factor of 11 million, and the waveguides exhibited a propagation loss of just 6 dB/m, which are noteworthy benchmarks for photonics technology at visible wavelengths.

The integrated photonic platform also incorporates an on-chip visible intensity modulator with an electro-optic bandwidth of 10 GHz. This capability is essential for applications requiring rapid signal manipulation and modulation in the visible light range, such as frequency-modulation spectroscopy and related laser technologies.

Methodology and Results

• Fabrication Process: The authors utilized lithium niobate on an insulator substrate, applying techniques such as electron beam lithography and inductively coupled reactive ion etching for precise pattern transferring. The structures were finalized with silicon dioxide cladding to ensure protection and stability.
• Characterization: The devices were characterized for optical losses, with microring resonators employing a pulley coupling scheme to effectively manage narrow coupling gaps at visible wavelengths. The resonators sustained high quality factors as measurements were conducted incrementally from 634 nm to 850 nm.
• Device Performance: A detailed assessment of the electro-optic modulator evidenced a half-wave voltage (${V_{\pi}}$) of 8 V for a 2 mm long device at 850 nm, translating into a competitive voltage-length product of 1.6 Vcm. Furthermore, the modulator demonstrated a robust electro-optic response up to the bandwidth of 10 GHz, dictated by the detector's limit.

Implications and Future Prospects

This work validates the applicability of lithium niobate in integrated photonic platforms for visible light, surpassing the conventional materials that are typically passive and limited in bandwidth. Practical implications include enhanced active light manipulation and wavelength conversion capabilities within a compact and efficient platform.

The implications for quantum information processing are particularly promising, as the demonstrated low-loss, high-Q devices can support advanced metrology and quantum state manipulation. The authors posit that the integration with quantum emitters and active manipulation of light at visible wavelengths will drive further innovation in quantum computing and information.

In conclusion, the research underscores lithium niobate's potential to cater to emerging needs in visible photonics, encouraging studies that further explore its nonlinear optical properties and integration with other quantum elements. This platform could lead to compact, scalable solutions enhancing both traditional and futuristic photonic applications.