Swept wavelength-to-time mapping for optical wavelength measurement

Optical wavelength measurement is imperative in a wide range of applications, such as optical metrology, sensing, wireless communication, and so on. In this paper, we propose and demonstrate a novel microwave photonic optical wavelength measurement method based on swept wavelength-to-time mapping, where the optical wavelength is mapped to the time domain information of a microwave photonic link with the help of a swept signal. Wavelength of the optical signal under test can therefore be measured by simply measuring the time domain information. To achieve swept wavelength-to-time mapping, a bi-directional frequency-swept optical signal for reference is first constructed. The reference optical signal and the optical signal under test is then combined and launched into a photodetector for optical-to-electrical conversion. A pair of microwave pulses can be observed, which is obtained by filtering the recovered photocurrent using an electrical bandpass filter with narrow passband. The occurrence time of the filtered pulses are related to the optical wavelength under test due to the bi-directional frequency-scanning property of the reference optical signal, thus swept wavelength-to-time mapping is enabled. Only a low-speed oscilloscope is needed for optical wavelength measurement by monitoring the time-domain information of the microwave pulses in the proposed method, which provides a cost-effective approach for microwave photonic optical wavelength measurement.