| 摘要 |
Devices for measuring one or more properties of a light signal is disclosed. More particularly the invention relates to devices for wavelength and power demodulation based on the use of quantum well electroabsorption photodiodes. In one aspect the invention provides and power and wavelength demodulation system based on a quantum well electroabsorption (QWEA) filtering detector. The input optical signal passes through an optical beam splitter with part of the signal input into a filtering detector which is a multiple quantum well electroabsorption (MQW EA) photodiode having a tunable bandgap and the other part into a reference detector. The input light signal is impinged on the QW diode perpendicular to the plane of the quantum wells. Th e output of filtering detector is amplified by an amplifier and the output of the reference detector is input into another amplifier. The output from referenc e detector amplifier serves as a measurement of the power of the input optical signal. The outputs of the amplifiers are input into an analog divider circu it where the signals are ratioed. A ratiometric voltage signal, Vratio, is obta ined by ratioing the filtered output of filtering detector and the unfiltered refere nce output to provide optical intensity self-referencing (immunity to input power fluctuations). This Vratio output signal is continuously compared with a ref erence voltage signal, Vref, and the difference of Vratio and Vref is input into a feedback control circuit. The output voltage Vout of the feedback control circuit is used to bias the QW EA photodiode so that in closed loop operation the QW EA photodiode is continuously wavelength tuned to maintain Vratio equal to Vref .
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