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We consider an optical code-division multiple-access (OCDMA) network that supports multiple traffic classes. Each class has different processing gain and performance requirements. In this paper, a new method is proposed to analyze the cutoff rates for a multiclass, multirate optical frequency-hopping code-division multiple-access system using fiber Bragg gratings and direct detection. This approach exploits the linear structure of passive OCDMA systems and the nominal time required to accomplish the encoding-decoding operations in such systems. A system model is presented and analyzed, based on a newly introduced bit-overlap procedure. An expression for the cutoff rate of a single-class system is derived. In addition, for a multiclass system, an expression that relates the cutoff rates of the offered classes is introduced, and it is called the service curve. It is shown that for a required quality of service guarantee …