The wavelength-sensitive transparent properties of direct-bandgap semiconductor optical diodes (DBSODs) can be utilized for wavelength sensing. A simplified theory is used to describe the operation principles of such wavelength sensing schemes. The principles can be applied to realize different measures,including sensing with or without pilot tone for single wavelength or multiple wavelengths. The simplified theory can also provide an easy way for estimating the wavelength resolution and accuracy. The wavelength resolution is demonstrated to be better than 0.01 nm by detecting the induced junction voltage for a fixed bias. The resolution is limited by the current resolution of the bias source to 0.03 nm when the wavelength is to be discriminated by transparent current detection. The feasibility and limitation of multiwavelength sensing using a single semiconductor optical amplifier are addressed both theoretically and experimentally. The limiting factors, including the power dependency and temperature stability, of the sensing schemes are also investigated.
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