| 摘要 |
An all-optical reference clock used to generate a stable radio frequency (RF) comb spectrum. The all-optical reference clock includes a fiber ring laser, a tunable mode selection filter and one or more phase locked loop (PLL) control circuits. The fiber ring laser has an effective loop circumference which produces a fundamental frequency mode spacing fl. The all-optical reference clock is configured to output a plurality of equally spaced frequencies which include a frequency fo and the harmonics thereof. The PLL control circuit receives a sample of the spaced frequencies and adjusts the tunable mode selection filter to maintain the desired spacing between the spaced frequencies. In one embodiment, a line-stretching drum, having a variable diameter and controlled by the PLL control circuit, is used to tune the mode selection filter. In another embodiment, a voltage controlled oscillator (VCO) controls a Mach-Zehnder modulator to eliminate undesired frequencies.
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