An optical spectral analyzer for measuring an optical multi-channel signal by separating the multi-channel signal and measuring a plurality of single-channel signals simultaneously. The spectral analyzer can include a demultiplexer configured to receive the multi-channel signal. The multi-channel signal can be a multi-channel wavelength range. The demultiplexer can separate the multi-channel signal into the plurality of single-channel signals including a first single-channel signal and a second single-channel signal. The spectral analyzer can include a plurality of optical paths. The plurality of optical paths can include a plurality of respective detectors for measuring an optical power of the respective single-channel signals. The detectors can convert the optical power of the respective single-channel signals to corresponding electrical signals. In some examples, the spectral analyzer includes a controller configured to obtain the plurality of respective electrical signals simultaneously to correspondingly detect the optical power of the multi-channel signal across the multi-channel wavelength range.