A Simplified Broadband Coupling Approach Applied to Chemically Robust Sol−Gel, Planar Integrated Optical Waveguides

Abstract

A new generation waveguide spectrometer with broadband coupling capabilities has been developed. As opposed to previous devices, this attenuated total reflection (ATR) spectrometer is much simpler in design, is more chemically robust, and transmits light down to at least 400 nm. The attenuated total reflection element consists of a single-mode, planar integrated optical waveguide fabricated by dip-coating a approximately 300 nm thick, sol-gel composite layer on a glass substrate. A commercially available prism is used as the incoupler with an integral holographic diffraction grating acting as the dispersive outcoupling element. The transmission of narrow band-pass filters was used to compare the response of the waveguide spectrometer to that of a conventional transmission instrument. Spectral resolution was assessed by measuring the fwhm of various laser lines, which were found to range from 0.5 to 1.3 nm. The measured limits of detection for the waveguide spectrometer from 400 to 600 nm are 8.0 and 10.1 milliabsorbance units for TE and TM polarizations, respectively. Finally, to demonstrate the application of this technology to a molecular film confined to a solid-liquid interface, visible ATR spectra of an adsorbed submonolayer of horse heart cytochrome c were acquired. A procedure to correct the waveguide spectra for the wavelength dependence in ATR path length is described.

Planar Integrated Optical Waveguide Spectroscopy

“…The spectra in Figure 3c illustrate the significant improvement in bandwidth and performance of the third-generation spectrometer relative to the older first-and second-generation instruments (36). In those cases, achromatic incoupling was unsuccessful at wavelengths <500 nm because of the "steep" dispersion of a 7059 glass IOW in this region of the spectrum (29,34,35).…”

Solid immersion lens at the aplanatic condition for enhancing the spectral bandwidth of a waveguide grating coupler

“…On the other hand, broadband coupling into a single-mode IOW presents challenges due to the dispersive nature of transverse couplers, which must match the effective refractive index of the single-mode waveguide structure. Broadband coupling using a prism coupler, either with an increased angular width of the incoming beam10,13–16 or with an achromatic design,18 have been reported and employed for the spectroscopic interrogation of an adsorbed monolayer. However, prism coupling occurs through an evanescent field, which requires the prism to be placed in close proximity to the waveguiding film, separated by a very small (in the wavelength range) and precisely fixed gap.…”

Monolithic silicon optoelectronic devices for protein and DNA detection

“…The enhancement factor increases as the waveguide thickness decreases while for thickness well below the wavelength tends to saturate due to the Goos-Hänchen shift effects 13 . Bioanalytical microsystems based on such thin optical fibers are very sensitive 14 and can revolutionize portable analytical instrumentation provided the light source and the detector could eventually be monolithically integrated with the bio-activated waveguide. Other than monolithic solutions to integration, such as external mounting or hybrid integration, complicate packaging, require high precision alignment and become impractical and costly.…”