Multimode interference devices for focusing in microfluidic channels

Abstract

Low-cost, compact, automated optical microsystems for chemical analysis such as micro-flow cytometers for identification of individual biological cells require monolithically-integrated microlenses for focusing in microfluidic channels, to enable high-resolution scattering and fluorescence measurements. The multimode interference device (MMI), which makes use of self-imaging in multimode waveguides, is shown to be a simple and effective alternative to the microlens for microflow cytometry. MMIs were designed, realized and integrated with microfluidic channels in a silica-based glass waveguide material system. Focal spotsizes of 2.4 µm for MMIs have been measured at foci as far as 43.7 µm into the microfluidic channel.

All-Fiber Strain and Curvature Sensor Based on No-Core Fiber

“…In this letter, a simple but sensitive fiber-optic sensor based on multimode interference (MMI) effects is demonstrated [1], [14]- [17]. Here we use a little thinner no-core fiber (NCF) to instead the traditional MMF.…”

Monolithically-integrated cytometer for measuring particle diameter in the extracellular vesicle size range using multi-angle scattering

“…Basic fibre-compatible waveguides were required to connect the chip inputs to waveguide lenses and the microfluidic channel and to collect the light from the microfluidic channel and guide it to the chip outputs. The basic waveguide design chosen was that used previously 25,26 with the waveguide cross sectional dimensions and refractive index shown in Fig. 1(a).…”

Integrated optical waveguides and inertial focussing microfluidics in silica for microflow cytometry applications

“…To allow efficient coupling to commercial single-mode optical fibres, the refractive index of the waveguide core material was chosen to be similar to that of the fibre core (Δn ≈ 0.7%) and the waveguide height was chosen to be 2 µm to offer good matching to the fibre mode [14]. The waveguides are grouped into arrays along the length of the fluidic channel.…”

“…Whilst polymer based system are often cheaper and quicker to fabricate, glass based integration systems are appealing as they can offer superior optical performance and mechanical stability making them attractive as a cost effective replacement to high precision laboratory instruments. The material stability offers the potential to include advanced integrated optical components which are sensitive to dimensional changes, such as kinoform lenses [13], multimode interference devices [14] and spectrometers [15] for light focussing, collection and analysis.…”

“…To demonstrate a relevant application, an example device is fabricated and used for fluorescence and transmission based detection of flowing polystyrene microspheres (beads) commonly used in bead-based immunoassays [26]. In the future it is envisaged that more specialised designs could be used for the analysis of cells and extracellular vesicles [27,28], building on previous work which has developed integrated lenses in the same material system [14]. The optical beam shape and inertial focussing behaviour of beads in the microfluidic channel are characterised.…”