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14 (a) Transfer function of a lag-lead filter. (b). The open loop transfer function of the JDSU OPLL without and with a lag-lead filter. Eq. (3.47) and the parameters b = 2.6, c f = 1MHz are used in the calculation. The transfer function of the filter is ( ) ( ) 2 1 1 / 1 F s s τ τ = + + with 1 124 s τ μ = and 2 6 s τ μ =
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Optical Phase-Lock loops (OPLLs) have potential applications in phase coherent optics including frequency synthesis, clock distribution and recovery, jitter and noise reduction, etc. However, most implemented OPLLs are based on solid state lasers, fiber lasers, or specially designed semiconductor lasers, whose bulky size and high cost inhibit the a...
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Citations
... are not central to this work and will not be considered here. Some of these metrics are discussed in references [2,73]. ...
... The effect of the FM response can be somewhat mitigated using loop filters. We have developed a number of techniques to improve loop performance, and these are described in detail in reference [73]. We will here describe the salient features of our filter design. ...
This thesis explores the precise control of the phase and frequency of
the output of semiconductor lasers (SCLs), which are the basic building
blocks of most modern optical communication networks. Phase and
frequency control is achieved by purely electronic means, using SCLs in
optoelectronic feedback systems, such as optical phase-locked loops
(OPLLs) and optoelectronic swept-frequency laser (SFL) sources.
Architectures and applications of these systems are studied. OPLLs with
single-section SCLs have limited bandwidths due to the nonuniform SCL
frequency modulation (FM) response. To overcome this limitation, two
novel OPLL architectures are designed and demonstrated, viz. (i) the
sideband-locked OPLL, where the feedback into the SCL is shifted to a
frequency range where the FM response is uniform, and (ii) composite
OPLL systems, where an external optical phase modulator corrects excess
phase noise. It is shown, theoretically and experimentally, and in the
time and frequency domains, that the coherence of the master laser is
"cloned" onto the slave SCL in an OPLL. An array of SCLs, phase-locked
to a common master, therefore forms a coherent aperture, where the phase
of each emitter is electronically controlled by the OPLL. Applications
of phase-controlled apertures in coherent power-combining and
all-electronic beam-steering are demonstrated. An optoelectronic SFL
source that generates precisely linear, broadband, and rapid frequency
chirps (several 100 GHz in 0.1 ms) is developed and demonstrated using a
novel OPLL-like feedback system, where the frequency chirp
characteristics are determined solely by a reference electronic
oscillator. Results from high-sensitivity biomolecular sensing
experiments utilizing the precise frequency control are reported.
Techniques are developed to increase the tuning range of SFLs, which is
the primary requirement in high-resolution three-dimensional imaging
applications. These include (i) the synthesis of a larger effective
bandwidth for imaging by "stitching" measurements taken using SFLs
chirping over different regions of the optical spectrum; and (ii) the
generation of a chirped wave with twice the chirp bandwidth and the same
chirp characteristics by nonlinear four-wave mixing of the SFL output
and a reference monochromatic wave. A quasi-phase-matching scheme to
overcome dispersion in the nonlinear medium is described and
implemented.
In this paper, we report a narrow-linewidth on-chip toroid Raman laser. Under free-running condition, we have obtained the minimum fundamental linewidth of 3 Hz and the maximum unidirectional output power of 223 μW. Lasing under the same condition in continuous-wave mode over 90 min is achieved at an average power level of 21 μW and a standard deviation of 0.17 μW. We further derived the frequency noise spectrum and identified an enhancement of frequency noise due to Kerr non linearity. In addition, we have observed the shifting of relaxation oscillation frequency as a consequence of weak mode splitting.
