Development of Tl+/Na+ ion-exchanged single-mode waveguides on silicate glass for visible-blue wavelengths applications

Abstract For more than thirty years, ion-exchange (IE) on glass technology has been successfully used to provide reliable and low losses Integrated Optics devices. Historically, optical telecommunications have been the first targeted application, the technologies were therefore optimized to cover the [0.98–1.6] μm spectral range. However nowadays most of the progresses are driven by the fast development of sensing applications and among them biological ones. Since, most biological species present absorption bands in the visible, there is a demand to shift the IE technologies to this spectral range, but none of them has provided so far a satisfactory solution. Ag+/Na+ IE processes have proven to be highly dependable thanks to their low-loss in the near IR. However, the Ag+ absorption in the visible strongly limits their interest for sensing. For this reason, a disruptive technology based on Tl+/Na+ IE has been investigated. A dedicated silicate glass has thus been developed and a first signal transmission in the visible blue light at λ=0.405 μm is presented. The device has been fabricated by mean of a thermal IE that has been carried-out at 300 °C during 20 min in a 0.5KNO3–0.5TlNO3 molten salt bath. In order to create channel waveguides, an alumina mask has been previously deposited and patterned. The mode-profile image at λ=0.405 μm of a waveguide obtained through a 0.5 μm mask window exhibits a single-mode behavior, demonstrating the promising feasibility of integrated circuitry at such wavelengths. The propagation losses measured with the first device reach 9±1 dB/cm at the working wavelength but could be minimized in the future by reducing the thallium concentration of the salt bath and by improving the glass quality.