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A class-B microwave-photonic link using optical frequency modulation (FM) and fiber-Bragg gratings (FBGs) is analyzed and results verified with measurements. Input voltage is converted linearly to FM, and this FM is converted by each FBG to intensity modulation. For small FM index beta, the signal increases as beta3, becoming linear in beta with a frequency offset or carrier leakage, and third-order distortion resulting from the detection process is shown to be worse than that obtained using a Mach-Zehnder intensity modulator at the same modulation index. For large beta( > 10), third-order distortion approaches zero and ideal class-B operation is predicted, and the only shot noise and relative intensity noise (RIN) added is that which arises from the detected signal power.