SU-8 Waveguide Research Articles

UV-sensitive photofunctional device using evanescent field absorption between SU-8 polymer optical waveguide and photochromic dye

We presented an ultraviolet (UV)-sensitive photofunctional device using a principle of evanescent field coupling occurring between SU-8 waveguide and photochromic dye (spirooxazine). The feasibility as a UV sensor was evaluated. When the 5-mm sensing area was irradiated with UV for 3 s, the absorption and the output intensity of the UV sensor was 0.0396 /spl sim/ 0.114 absorbance/mW and 1 /spl sim/ 10 mW, respectively. The UV sensor had linearity by variation of sensing area. The sensitivity of the proposed sensor was higher than the spectrophotometers method and optical fiber sensors.

A SU-8/PDMS Hybrid Microfluidic Device with Integrated Optical Fibers for Online Monitoring of Lactate

A microfluidic device with integrated optical fibres was developed for online monitoring of lactate. The device consists of a SU-8 waveguide, microfluidic channels and grooves for the insertion of optic fibres. It was fabricated by one-step photolithography of SU-8 polymer resist. Different channel widths (50-300 microm) were tested in terms of detection sensitivity. A wide range of flow rates were applied to investigate the influence of flow rate on signal fluctuations. The separation between optical fibre sensor and microfluidic channel and the width of fluidic channel have been optimized to maximize the detection sensitivity. It was revealed that 250 microm of channel width is the optimum light path length for a compromise between detection sensitivity and interference of ambient light. The independence of detection signals on flow rates was demonstrated within the range of flow rate (0.5-5 ml/hr) tested. Compared with conventional lactate detection, the device is proved to have high accuracy, relatively low limit of detection (50 mg/L) and reasonably fast response time (100 sec). The fabrication of device is simple and low cost. The present work has provided some fundamental data for further system optimization to meet specific detection requirements.

End-fire coupling of a SU-8 waveguide to a silicon mesa photodiode: Integrability in an optical analysis microsystem

This work deals with mesa silicon photodiodes and SU-8 ridge waveguides fabrication and their coupling by means of an end-fire configuration. Both photodiodes and waveguides are electrically and optically characterized and are expected to be used as optical power measurement devices for integration in a miniaturized optical analysis system. The integrability of the devices is studied through an analysis of the further steps necessary to build a complete optical analysis microsystem and the feasibility of such device is empirically anticipated.

Integration of microfluidic and microoptical elements using a single-mask photolithographic step

We present a design and process to fabricate an integrated microfluidic/microoptical device—the microfluidic optical waveguide sensor (“μFlOWs”). Optical waveguides and fluidic microchannels have been defined using only a single photolithographic masking step. This integration has been demonstrated with three device types: (A) a hybrid structure with embedded SU-8 waveguides and polydimethylsiloxane (PDMS) channels; (B) a structure using only SU-8 for both the waveguides and microchannel walls and (C) a structure as a modification to the all-SU-8 structure. Testing has demonstrated the ability of the waveguides to transmit light to and receive light from the microchannels, which contain a fluorescent dye that emits upon laser excitation. This type of strategy can find effective use in a variety of bio-assay experiments.

PMMA to SU-8 bonding for polymer based lab-on-a-chip systems with integrated optics

An adhesive bonding technique for wafer-level sealing of SU-8 based lab-on-a-chip microsystems with integrated optical components is presented. Microfluidic channels and optical components, e.g. waveguides, are fabricated in cross-linked SU-8 and sealed with a Pyrex glass substrate by means of an intermediate layer of 950k molecular weight poly-methylmethacrylate (PMMA). Due to a lower refractive index of PMMA (n = 1.49 at λ = 600–900 nm) this bonding technique preserves waveguiding in the cross-linked SU-8 structures (n = 1.59 at λ = 633 nm) in combination with good sealing of the microfluidic channels. The bonding strength dependence on bonding temperature and bonding force is investigated. A maximum bonding strength of 16 MPa is achieved at bonding temperatures between 110 °C and 120 °C, at a bonding force of 2000 N on a 4 inch wafer. The optical propagation loss of multi-mode 10 µm (thickness) × 30 µm (width) SU-8 waveguides is measured. The propagation loss in PMMA bonded waveguide structures is more than 5 dB cm−1 lower, at wavelengths between 600 nm and 900 nm, than in similar structures bonded by an intermediate layer of SU-8. Furthermore 950k PMMA shows no tendency to flow into the bonded structures during bonding because of its high viscosity.

Monolithic coupling of a SU8 waveguide to a silicon photodiode

We present quantitative results of light coupling from SU8 waveguides into silicon p-n photodiodes in monolithically integrated structures. Multimode, 12 μm thick, and 20 μm wide SU8 waveguides were fabricated to overlap 40×180 μm2 photodiodes, with three different waveguide-photodiode overlap lengths. The attenuation due to leaky-mode coupling in the overlap area was then calculated from photocurrent measurements. The overlap attenuation ranged from a minimum of 2.2 dB per mm overlap length to a maximum of about 3 dB/mm, comparing favorably with reported nonpolymeric waveguide-Si photodiode attenuations.

An integrated optical oxygen sensor fabricated using rapid-prototyping techniques.

This paper details the design and fabrication of an integrated optical biochemical sensor using a select oxygen-sensitive fluorescent dye, tris(2,2'-bipyridyl) dichlororuthenium(ii) hexahydrate, combined with polymeric waveguides that are fabricated on a glass substrate. The sensor uses evanescent interaction of light confined within the waveguide with the dye that is immobilized on an SU-8 waveguide surface. Adhesion of the dye to the integrated waveguide surface is accomplished using a unique process of spin-coating/electrostatic layer-by-layer formation. The SU-8 waveguide was chemically modified to allow the deposition process. Exposure of the dye molecules to the analyte and subsequent chemical interaction is achieved by directly coupling the fluid channel to the integrated waveguide. The completed sensor was linear in the dissolved oxygen across a wide range of interest and had a sensitivity of 0.6 ppm. A unique fabrication aspect of this sensor is the inherent simplicity of the design, and the resulting rapidity of fabrication, while maintaining a high degree of functionality and flexibility.