A 1320 nm experimental optical phase-locked loop
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 , 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 , . 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 ,  or external cavity semiconductor  lasers. Nevertheless, by careful microoptical design , first homodyne  and, subsequently, heterodyne ,  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. "
Article: Microwave photonics[Show abstract] [Hide abstract]
ABSTRACT: The low-loss wide-bandwidth capability of optoelectronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. This paper describes the development of microwave photonic devices, describes their systems applications, and suggests likely areas for future developmentIEEE Transactions on Microwave Theory and Techniques 04/2002; 50(3-50):877 - 887. DOI:10.1109/22.989971 · 2.24 Impact Factor
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ABSTRACT: In this dissertation I describe the frequency stabilization of the diode laser pumped Non Planar Ring Oscillator (NPRO) and discuss its use in coherent optical communication systems. The requirements necessary to achieve stability at the sub-Hz level are emphasized and the experiments resulting in a relative stability of 330 mHz are included. Optical interferometers with extremely high finesse are used as frequency discriminators in the stabilization experiments discussed here. The development and characterization of one such interferometer with a finesse of 27,500 and an optical transmission bandwidth of 25 kHz is also presented. The spectral density of frequency noise associated with the NPRO was measured from 10 Hz to 100 kHz and an unambiguous pole in the spectrum was observed. This structure was assumed to be due to thermal filtering of the pump laser power fluctuations and theoretical modeling supported this hypothesis. This model also demonstrated that a significant reduction in the spectral density can be achieved when a shot noise limited laser is used as the optical pump in the NPRO. The magnitude of the spectral density of frequency noise was ~115 Hz/ surdHz at 100 Hz and ~3Hz/ surdHz at 10 kHz. The diode laser pumped solid state laser, with its ability to be frequency stabilized to the sub-Hz level, is an ideal source for use in a coherent optical communications link. An optical phase locked loop (OPLL) at 1.06 mum for use in a coherent homodyne receiver was developed using two NPROs, and an extended theory describing its performance is presented. This analysis emphasizes the advantages offered by the NPRO, as compared to the diode laser, when used in a homodyne communications receiver.
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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 laserJournal of Lightwave Technology 04/1990; DOI:10.1109/50.50726 · 2.97 Impact Factor