Demonstration of the coupling of optofluidic ring resonator lasers with liquid waveguides

Abstract

Optofluidic lasers are of particular interest for lab-on-a-chip-type devices, with broad spectral tunability, convenient microfluidic integration, and a small footprint. Optofluidic ring resonator (OFRR) lasers are advantageous in terms of size but typically generate nondirectional emission that is of minimal practical use. We introduce two unique geometries for soft-lithography-based OFRR lasers--side-coupled rings and spiral rings--both of which can be produced in polydimethyl siloxane substrates with contact molding. These rings utilize evanescent and direct butt-coupling, respectively, to effectively couple the OFRR laser emission into microfluidic channels. A laser threshold of a few to tens of microJ/mm(2) is achieved.

Tunable single mode lasing from an on-chip optofluidic ring resonator laser

“…Similarly, we calculate the total coupling coefficient between the lower OFRR and the waveguide ͑i.e., total fractional loss per round trip of the lower OFRR͒ to be on the order of 10 −3 , corresponding to a Q ϳ 7 ϫ 10 6 . Therefore, based on the Q-factor ͑ϳ5000͒ experimentally observed in a single PDMS based OFRR in our previous studies, 18 we infer that each ring in the current coupled OFRR system should have a similar Q-factor ͑ϳ5000͒, which provides sufficient side mode suppression to achieve single mode operation, as shown in Fig. 2͑a͒.…”

“…15,16 Very recently, on-chip polydimethylsiloxane ͑PDMS͒ based OFRRs were also demonstrated. 17,18 Since the entire PDMS device can be fabricated by simple replica molding processes, costeffective mass production of the OFRR lasers becomes possible.…”

“…This Q-factor value is close to what was observed previously, in which the ring resonator has a similar contact region with a waveguide. 18 While the coupling between the two OFRRs affects the single mode operation of the OFRR laser, the size of the OFRRs does not deteriorate the properties of the lasing. As illustrated in Fig.…”

Evanescent-Wave Pumped and Gain Coupled Whispering-Gallery-Mode Fibre Laser

“…As the evanescent field of a WGM in a circular cavity extends into the gain medium, the gain can be coupled into the WGM that provides optical feedback required by lasing oscillations. To optically excite the gain molecules around a circular cavity, laser beams are usually pumped from the outside of the gain medium [1][2][3][4][5], this pumping configuration, called side-pumping scheme, suffers a low 196 pump efficiency, because the pump energy is absorbed by all of excited molecules, and only a small number of molecules residing in the WGM evanescent field contributes to the optical gain. To solve this problem, evanescent-wave pumping scheme has been used in circular cavities in recent years, such as bare optical fiber [6], capillary [9], and microfiber knot [11], which reduces lasing threshold from 200 J /pulse in the side-pumping scheme [1] to 9.2 J /pulse [9] and further to 100 nJ /pulse [11].…”

Study of disklike microdroplet cavities directly coupled to liquid-core waveguides

“…Many types of liquid cavities such as Fabry-Perot resonators [1,2], circular feedback Bragg gratings [3], microspheres, and microrings [4][5][6][7] were reported with a wide range of applications in molecule diagnosis or laser emission. Most of the cavity structures are made by microfabrication processes and the optical performance is affected by the fabrication quality, including etching-induced surface roughness.…”