A simple and intelligent technique of reducing the zero-order diffraction in an optical spectrographic processor is discussed and the corresponding nonbias optical architecture, by which spectrograms can indeed be obtained, is proposed. Reduction of zero-order diffraction in a Fourier optical system arises from the removal of the dc bias, which is usually needed when a conventional optical spectrographic processor is utilized. We have shown that discrimination sensitivity of the optical spectrograms is significantly enhanced and the dynamic range (DR) requirement for the spectrogram capturing device is also notably reduced due to the removal of the dc bias. In addition, energy utilization efficiency in the optical signal processing is drastically improved by our nonbias architecture. Simulated demonstration is provided.