Fabrication of an integrated high-quality-factor (high-Q) optofluidic sensor by femtosecond laser micromachining

Abstract

We report on fabrication of a microtoroid resonator of a high-quality factor (i.e., Q-factor of ~3.24 × 10(6) measured under the critical coupling condition) integrated in a microfluidic channel using femtosecond laser three-dimensional (3D) micromachining. Coupling of light into and out of the microresonator has been realized with a fiber taper that is reliably assembled with the microtoroid. The assembly of the fiber to the microtoroid is achieved by welding the fiber taper onto the sidewall of the microtoroid using CO2 laser irradiation. The integrated microresonator maintains a high Q-factor of 3.21 × 10(5) as measured in air, which should still be sufficient for many sensing applications. We test the functionality of the integrated optofluidic sensor by performing bulk refractive index sensing of purified water doped with tiny amount of salt. It is shown that a detection limit of ~1.2 × 10(-4) refractive index unit can be achieved. Our result showcases the capability of integration of high-Q microresonators with complex microfluidic systems using femtosecond laser 3D micromachining.

Femtosecond laser three-dimensional micro- and nanofabrication

“…Over the past decade, an impressive number of highly integrated optofluidic systems have been designed and fabricated, for which a variety of innovative functionalities for biological and chemical applications (e.g., determining the functions of living microorganisms, sensing the concentrations of liquid samples, detecting, sorting and manipulating single cells, rapid screening of algae populations, and observation of microorganisms in nanoaquaria) have been successfully demonstrated. 32,33,[35][36][37][38][39] Figure 31 shows a microfluidic network fabricated in commercially available silica glass by water-assisted 3D femtosecond laser drilling. 119 An 800 nm, 120 fs femtosecond laser operating at 1 kHz was used to induce optical breakdown from the backside of the glass sample which was in contact with distilled water.…”

“…[21][22][23][24][25][26][27][28] To date, femtosecond laser internal processing has been widely applied to the fabrication of photonic integrated circuits, free-space microoptics, and microfluidic/optofluidic chips. [29][30][31][32][33][34][35][36][37][38][39] However, femtosecond laser bonding of glasses has recently attracted significant attention as an emerging technique for optoelectronics, medical and biochips, and MEMS packaging, 13,14,40,41 which are important for a number of applications.…”

[INVITED] Ultrafast laser micro-processing of transparent material

“…This method has advantages in fabricating large scale microfluidic structures and achieving smooth inner walls, which can be even used as mirrors and lenses [60][61][62][63][64]. Functional devices like biochips and sensors have been successfully generated by the integration of the microchannels, microoptical elements and fluid control microcomponents such as a microvalve and a micropump in the microfluidics [52][53][54][65][66][67][68].…”

Femtosecond Laser Fabrication of Monolithically Integrated Microfluidic Sensors in Glass

“…These components can also be fabricated using FsLDW. By integrating a microfluidic structure and an optical resonator, a microcavity-based sensor was reported [128]. Attachment of a fiber taper to the sidewall of a microtoroid was realized by welding using CO 2 laser irradiation.…”