Almost all modern optical communication lines, both local and trunk ones, use the wavelength-division multiplexing principle (WDM or DWDM). We suggest that frequency encoded OCDMA algorithms be used as most suitable tools for local and metropolitan area networks. Coding is performed in this case in the frequency domain, i. e., code sequences can be mapped inside the optical source spectrum. A broadband light source is used in this approach. The spectral amplitude of the light source is modulated with the code that specifies certain components of the spectrum to be on or off. In such a network, different transmitters use different codes which are orthogonal to one another. The receiver can then select the data from the desired transmitter by correlating the spectrally modulated signal with an appropriate code. Furthermore, the channels are independent in the sense of transmitted data bit rates. The coding algorithm we suggest is performed in a narrow spectral band, within one (D)WDM channel, i. e., within a spectral range of 0. 4 to 0. 8 nm. In this case the available communication lines can be used. However, due to the fact that such lines use amplitude modulation for information encoding, the signal with a spectral encoding will be nearly inaccessible for an unauthorized user.