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Comparison Of Signal To Noise And Carrier To Noise Methods Of Characterizing Optical Memories

Many optical recording media companies characterize media properties using carrier to noise measurement methods. While this method is easily accomplished with off-the-shelf measurement equipment, it has proven to be a very unreliable method of characterizing the performance of optical recording materials. Optical recording data channel is known to have several unique features relating to nonlinearities and multiplicative noise sources which makes the use of carrier to noise ratio measurements ambigious or inaccurate. Alternative measures of making performance measurements using signal to noise ratio parameters provides substantially greater accuracy, eliminate the ambiguities and provide better insight into the operating properties of the recording material. Signal to noise ratio measurements (SNR) are made using a digitizer and software processing of the data channel output. SNR measurements are useful to both media and drive companies unlike CNR measurements which are useful only as a qualitative measure presented by media companies. The purpose of this paper is to evaluate the differences between CNR and SNR measurement and to show the substantial improvement in characterization accuracy which can be achieved by SNR measurements.