A 1320 nm experimental optical phase-locked loop

Bellcore, Red Bank, NJ, USA
IEEE Photonics Technology Letters (Impact Factor: 2.11). 12/1989; 1(11):395 - 397. DOI: 10.1109/68.43391
Source: IEEE Xplore

ABSTRACT An experimental balanced optical second-order phase-locked loop constructed using 1320 nm diode laser pumped miniature Nd:YAG lasers is discussed. The loop is stable and has a phase error of less than 1.8 degrees when the received signal power is -65 dBm or more. The phase error appears to be dominated by the lasers' frequency noise as long as the signal power is more than -60 dBm.< >

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    • "Although simple in principle and demonstrated for narrow-linewidth gas lasers at an early stage in laser development [43], the practical realization of OPPLs is limited by the requirement that the loop delay should be small enough to ensure that phase fluctuations of the optical sources are accurately cancelled [44], [45]. The requirement for subnanosecond loop delays to lock nonline narrowed semiconductor lasers led to much early work being carried out with narrow-linewidth solid-state [46], [47] or external cavity semiconductor [48] lasers. Nevertheless, by careful microoptical design , first homodyne [49] and, subsequently, heterodyne [50], [51] loops were successfully realized using nonline narrowed semiconductor lasers with linewidths of an order of 10 MHz, yielding reference source limited phase noise of better than 83 dBc/Hz at offsets of a few megahertz, as shown in Fig. 4. "
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    ABSTRACT: The frequency and intensity noise spectra, as well as the frequency modulation (FM) response, of 1320-nm laser-diode-pumped miniature Nd:YAG ring lasers have been measured. The frequency noise spectrum has a resonance peak at the relaxation oscillation frequency of the laser (between 123 and 150 kHz) and is flat beyond 200 kHz with a spectral density of 613 rad<sup>2</sup>-Hz, much smaller than that of semiconductor lasers; the corresponding laser linewidth is less than 49 Hz. The relative intensity noise is -140 dB/Hz at the valley and has a resonance peak at the relaxation oscillation frequency of the laser. The FM response is flat from DC to 110 kHz and is in the 0.65-3 MHz/V range; the modulation frequency is limited by the relaxation oscillation frequency of the laser
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