Optical particle manipulation by application-specific densely packed VCSEL arrays

Abstract

Densely packed arrays of vertical-cavity surface-emitting lasers (VCSELs) are presented, serving as low-cost and small-sized laser sources in optical particle manipulation systems. A novel, self-aligned fabrication process enables both a pitch in the 20 µm m range and a selective surface etch for enhanced transverse single-mode emission. Homogeneous array performance and single-mode output powers of up to 3.8 mW are observed. By inserting the arrays into an optical tweezers setup with external optics, multiple optical traps are easily created. Non-mechanical particle translation by switching between individually addressable devices as well as continuous particle deflection in a one-dimensional optical lattice are demonstrated.

VCSEL-based optical trapping for microparticle manipulation

“…We have fabricated oxide-confined VCSEL arrays with small center-to-center distance of down to 24 µm and a gap of only 2 µm between adjacent mesas. 24 This geometry necessitates a dry-etching process for steep mesa side walls. Furthermore, the surface relief technique should be included, where an exact alignment of relief and oxide aperture is mandatory.…”

“…Furthermore, with a tilted linear array of permanently emitting VCSELs, continuous deflection of flowing particles was achieved. 24,25 The working principle is as follows: 26,27 The linear array creates a tilted, linear optical lattice at the sample stage. If the trapping force is smaller than the fluidic drag force, a particle passing the lattice is not retained, but deflected at each trap.…”

“…While the particle velocity in our former experiments in Ref. 24 was initiated by a movement of the whole sample stage, this scheme was translated to a microfluidic flow in Ref. 25 initial experiments toward a drastic miniaturization of this scheme: The external optical elements are removed and laser arrays and microfluidic channel are merged in an integrated optical trap.…”

A microtip self-written on a vertical-cavity surface-emitting laser by photopolymerization

“…The potentialities which have already been demonstrated as well as the flexibility of these laser devices have recently strongly contributed to the rise of extended applications related to microsystems and in particular to biomedical instrumentation. [1][2][3][4] Using VCSELs instead of standard laser diodes provides some inherent advantages for several applications, for example, the systems can be smaller and use two-dimensional source arrays such that multiple, simultaneous experiments can be performed in parallel and at low cost and low power consumption. However, despite a limited far-field beam divergence ͑ϳ10°-25°͒, these sources have more and more to be associated with micro-optical elements to enhance their optical performances, to increase their coupling efficiency to optical fibers or to meet stringent collimation requirements in microsystem applications.…”