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Impact of Finite Frequency Deviation on the Performance of Dual-Filter Heterodyne FSK Lightwave Systems
STATE UNIV OF NEW YORK AT BUFFALO DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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A detailed theoretical analysis is given for the impact of finite frequency deviation on the sensitivity of dual-filter heterodyne Frequency Shift Keying FSK lightwave systems. Our analysis provides closed-form signal-to- noise ratio SNR results for estimating the bit-error-ratio BER performance of the system. These closed-form results provide an insight into the impact of finite frequency deviation 2 Delta fd, laser linewidth Delta v, bit rate Rb, and IF filter bandwidths on the system performance. It is shown that there is a well-defined relationship between the choice of frequency deviation and the tolerable amount of laser phase noise. When there is no phase noise, a frequency deviation of 2 Delta fd 0.72Rb, is sufficient for 1 dB sensitivity penalty with respect to infinite frequency deviation case whereas for a linewidth of Delta v 0.5ORb the required frequency deviation increases to 2 Delta fd 3. 42Rb for the same sensitivity penalty. The sensitivity degradation can be very severe for a fixed linewidth as the frequency deviation gets smaller for a linewidth of 20 the sensitivity penalty is only 0.54 dB when the frequency deviation is infinite whereas it is 3.48 dB when the frequency deviation is 2 Delta fd Rb. We also quantify the impact of finite frequency deviation on optimum IF filter bandwidths. For a fixed linewidth, the optimum IF filter bandwidth decreases as frequency deviation becomes smaller for Delta v 0.5Rb the optimum IF filter bandwidth reduces from 7Rb to 3Rb when 2 Delta fd reduces from very large values to 3Rb.
APPROVED FOR PUBLIC RELEASE