This paper proposes a wavelength sensor based on the optical directional coupler. The finite-difference time-domain (FDTD) is used in analysis of the field intensity of the light propagating thorough the structure. The device with the width of 0.4 μm and the thickness of 0.4 μm, corresponding with the coupling length of 40μm, would provide the linear relationship between the coupling efficiency against the wavelength. The device can be employed to sense the wavelength in a range between 1.5 μm and 1.6 μ, with continuous resolutions. The wide wavelength could be also done by paralleling the light to a number of wavelength-sensing modules with particularly required bands. Therefore, the proposed structure could be employed as the wavelength sensing for most optical communications, optoelectronics and laser applications.
