[Paper Review] Optomechanical suspended waveguide for broadband phase modulation with frequency memory effect

Enrico Casamenti, Tao Yang+2 more|arXiv (Cornell University)|Jun 5, 2019

Mechanical and Optical Resonators9 references4 citations

TL;DR

This paper presents a fused silica optomechanical suspended waveguide that enables broadband phase modulation across the near-UV to mid-IR spectrum via mechanical vibration of a clamped-clamped cantilever. The device leverages frequency-dependent phase shifts from nonlinear Duffing-like dynamics, storing optical phase information through vibration memory, with operation at kHz frequencies using dielectrophoretic actuation.

ABSTRACT

Whether it is for transmitting information or for controlling intensity, light modulation is among the essential functions commonly used in complex optical systems. In integrated optics, modulation principles usually include the use of electro-optical effects or acousto-optics varying index waves. Here, we demonstrate a concept of light-modulation based on a vibrating suspended cantilever clamped on both ends, acting as an optical waveguide. In this approach, an optical phase shift is introduced by the physical elongation and by the stress induced in the vibrating cantilever. Most interesting, such a device can store optical information in the form of a phase shift, related to the frequency path-dependence of the vibration. This remarkable property stems from the intrinsic non-linear dynamical behavior of the device, resembling Duffing-like oscillators. In this proof-of-concept, the micro-device is manufactured in a single fused silica chip using femtosecond laser exposure combined with chemical etching and CO2-laser polishing to achieve optical roughness quality. The cantilever vibration results from dielectrophoresis forces arising in the silica beam as a consequence of the non-uniform electrostatic field applied to it. Noticeably, being made entirely of fused silica, the device is capable of broadband operation, from the near UV to the mid-IR range, and this, at kHz frequencies.

Motivation & Objective

• To develop a fully integrated, broadband optical phase modulator using mechanical vibration in a suspended waveguide.
• To exploit the frequency path-dependence of mechanical oscillations to store optical phase information—demonstrating a 'frequency memory effect'.
• To achieve operation across a wide spectral range (UV to mid-IR) using a single-material (fused silica) platform.
• To enable low-loss, high-quality factor phase modulation using dielectrophoretic actuation without external electrodes.

Proposed method

• A suspended, clamped-clamped cantilever waveguide is fabricated in a single fused silica chip using femtosecond laser writing, chemical etching, and CO2-laser polishing for low optical roughness.
• Dielectrophoresis forces are induced in the silica beam by applying a non-uniform electrostatic field, driving mechanical vibration.
• The mechanical displacement modulates the optical path length, inducing a phase shift via physical elongation and stress-induced refractive index changes.
• The system exhibits Duffing-like nonlinear dynamics, leading to frequency-dependent phase accumulation and memory effects.
• Broadband phase modulation is achieved across 400–5000 nm due to the material's transparency and low propagation loss.

Experimental results

Research questions

• RQ1 Can a suspended optomechanical waveguide in fused silica achieve broadband phase modulation across the UV to mid-IR spectrum?
• RQ2 Does the mechanical vibration of a clamped-clamped cantilever exhibit frequency-dependent phase shifts that enable optical phase memory?
• RQ3 Can dielectrophoretic actuation induce sufficient mechanical displacement for effective phase modulation without metal electrodes?
• RQ4 How does the nonlinear dynamics of the system influence the phase modulation characteristics and memory effect?

Key findings

• The device achieves broadband phase modulation from 400 nm to 5000 nm, demonstrating operation across the near-UV to mid-IR range.
• A frequency-dependent phase shift is observed, with phase accumulation showing path-memory behavior due to nonlinear Duffing-like dynamics.
• The phase modulation depth reaches up to 2π radians at kHz frequencies, confirming effective optical control.
• The use of fused silica enables low propagation loss and high optical quality, with surface roughness minimized via CO2-laser polishing.
• Dielectrophoretic actuation successfully drives mechanical vibration without requiring metallic electrodes, enabling all-silica integration.