A system for determining a wavelength of a narrow-band light beam, the system comprising: a first photodetector having a first spectral response over a domain of wavelengths including the wavelength of the narrow-band light beam, the first photodetector configured to generate a first output signal i d1 indicative of a first photocurrent induced by a projection of a first portion of the narrow-band light beam thereon, wherein the first spectral response is monotonically increasing throughout the domain of wavelengths including the wavelength of the narrow-band light beam; a second photodetector having a second spectral response over the domain of wavelengths including the wavelength of the narrow-band light beam, the second spectral response different from the first spectral response, the second photodetector configured to generate a second output signal i d2 indicative of a second photocurrent induced by a projection of a second portion of the narrow-band light beam thereon, wherein the second spectral response is monotonically decreasing throughout the domain of wavelengths including the wavelength of the narrow-band light beam; a third photodetector having the first spectral response over the domain of wavelengths including the wavelength of the narrow-band light beam, the third photodetector configured to generate a first reference output signal, i r1 indicative of a first dark current of the third photodetector; and a fourth photodetector having the second spectral response over the domain of wavelengths including the wavelength of the narrow-band light beam, the fourth photodetector configured to generate a second reference output signal, i r2 indicative of a second dark current of the fourth photodetector; and a calculation engine configured to determine a ratio of the first and second photocurrents, wherein the determined ratio is a monotonic function of wavelength over the domain of wavelengths including the wavelength of the narrow-band light beam, thereby indicative of the wavelength of the narrow-band light beam; characterized in that the first photocurrent is equal to a first difference between the first output signal and the first reference signal i d1 -i r1, and the second photocurrent is equal to a second difference between the second output signal and the second reference signal i d2 -i r2. a first photodetector having a first spectral response over a domain of wavelengths including the wavelength of the narrow-band light beam, the first photodetector configured to generate a first output signal i d1 indicative of a first photocurrent induced by a projection of a first portion of the narrow-band light beam thereon, wherein the first spectral response is monotonically increasing throughout the domain of wavelengths including the wavelength of the narrow-band light beam; a second photodetector having a second spectral response over the domain of wavelengths including the wavelength of the narrow-band light beam, the second spectral response different from the first spectral response, the second photodetector configured to generate a second output signal i d2 indicative of a second photocurrent induced by a projection of a second portion of the narrow-band light beam thereon, wherein the second spectral response is monotonically decreasing throughout the domain of wavelengths including the wavelength of the narrow-band light beam; a third photodetector having the first spectral response over the domain of wavelengths including the wavelength of the narrow-band light beam, the third photodetector configured to generate a first reference output signal, i r1 indicative of a first dark current of the third photodetector; and a fourth photodetector having the second spectral response over the domain of wavelengths including the wavelength of the narrow-band light beam, the fourth photodetector configured to generate a second reference output signal, i r2 indicative of a second dark current of the fourth photodetector; and a calculation engine configured to determine a ratio of the first and second photocurrents, wherein the determined ratio is a monotonic function of wavelength over the domain of wavelengths including the wavelength of the narrow-band light beam, thereby indicative of the wavelength of the narrow-band light beam; characterized in that the first photocurrent is equal to a first difference between the first output signal and the first reference signal i d1 -i r1, and the second photocurrent is equal to a second difference between the second output signal and the second reference signal i d2 -i r2.