High-resolution wavelength monitoring using differential/ratio detection of junction voltage across a diode laser

High-resolution, compact, and power-insensitive wavelength monitoring can be realized by using a low-cost diode laser as the wavelength sensor. The wavelength resolution can be improved by more than an order with the help of the Fabry-Perot resonance inside the cavity of a diode laser, as well as by differential or ratio detection. Wavelength resolution of 0.01 nm can he obtained with much relaxed requirement on the detection circuitry. The wavelength monitoring with such resolution ran tolerate up to 15 dB of power variation on the incident light power.