Wavelength Sensing With Subpicometer Resolution Using Ultrahigh Order Modes

The ultrahigh order modes of a symmetrical metal-cladding optical waveguide, which exhibit strong wavelength dispersion characteristics, are used to track small wavelength changes of the light output of laser diodes. In the case of free-space coupling, the wavelength shift is transformed into an intensity variation of the light reflected on a surface of the waveguide. The sensitivity considering the divergence of the incident light and the thickness of the upper cladding is analyzed. A wavelength resolution of 0.5 pm at a center wavelength of 859.8 nm is demonstrated experimentally