Understanding the effects of laser phase and frequency noise on laser interferometry is significant for evaluating the system performance. To precisely study the performance limit caused by laser frequency noise, here we propose and demonstrate a versatile model based on the Fourier and inverse Fourier transform (FIFT) method. This model, capable of estimating the beat note spectra of different delayed self-interferometry (DSI) with laser sources of arbitrary frequency noise properties, allows for accurate evaluations of the noise performance in a variety of interferometry based systems. Such a model has been experimentally validated using lasers with irregular frequency noise properties such as cavity stabilized fiber laser or laser under optical phase-locking, providing more detailed insight into the evolution of the frequency noise dynamics at different interferometric conditions. With average estimation goodness (AEG) of 0.9716 and computation complexity of O(NlogN), this model offers greater accuracy and lower complexity than conventional methods. It has also been confirmed that this model permits to distinguish the contributions from the laser frequency stability and other noise sources, which could be helpful for the noise analysis and performance optimization of the system.
We present a remote Michelson interferometric phase sensor based on dual-core fiber transmission and linear phase demodulation. The former allows for synchronous transmission of both sensing signal and reference lights, enabling efficient suppression for the environmental disturbances along the transmission link and for the incoherent phase noise between the two lights. The latter is conducted by two optical phase-locked loops, one of which consists of a fiber stretcher that is used to eliminate the residual phase noises, thus stabilizing the operation point while the other relies on a phase modulator that is used to track the remote phase changes, thus achieving a highly linearized phase demodulation. A remote phase sensing over a 20 km fiber link with less than 3% nonlinear phase error over
3
π
range has been readily realized, corresponding to more than 10 times extension in a linear phase demodulation range. The proposed system shows great potential in the field of remote phase sensing for a variety of physical quantities.
We report on a dynamic range enhanced optical frequency domain reflectometry distributed backscattering interrogator based on dual-loop composite optical phase-locked loop (OPLL). Exploiting simultaneously an acousto-optic frequency shifter based an external modulation loop and a piezo based direct modulation loop, the proposed composite OPLL allows offering a larger loop bandwidth and gain, permitting a more efficient coherence enhancement as well as sweep linearization. A high fidelity frequency sweep of ~8.2 GHz at 164 GHz/s sweep rate is generated with a peak-to-peak frequency error as low as ~120 kHz. It leads to a dynamic range enhancement of more than 3 dB for the measured power loss compared to the case when only piezo loop is applied. This corresponds to ~15 km extension for the measurement range of Rayleigh backscattering without any spatial resolution penalties. Fourier transform-limited spatial resolution has been demonstrated at a range window more than about 28 times of the intrinsic coherence length of the adopted fiber laser. The proposed method provides a straightforward optimization of the real-time sweep control and is expected to be a useful tool in industrial and commercial applications.
A coherent dual-wavelength frequency-modulated continuous-wave (FMCW) lidar utilizing dual-heterodyne mixing which permits efficient phase noise cancellation has been proposed. Consistent ranging resolution about 1.4 × 10−6 over distances beyond tens of intrinsic coherence length is achieved.
We present a dual-frequency laser Doppler velocimeter (DF-LDV) relying on a DF laser source (DFLS) generated by optical phase-locking two individual lasers to a common unbalanced Mach–Zehnder interferometer, which allows achieving high stability regardless of the DF separation of the lasers. This DFLS is evaluated using an optical frequency comb, testifying to the generation of DFLS with large DF separation up to terahertz with flexible tunability and high stability. Demonstration of DF-LDV using the DFLS of
∼
1.024
T
H
z
separation has achieved
1.62
×
10
−
2
mm/s velocity resolution even for a slow velocity of
1.8
m
m
/
s
in a mere 5 s acquisition time, confirming the high resolution and efficient speckle noise suppression enabled by the proposed DF-LDV. Featuring high precision, flexibility, and robustness, this method is particularly attractive from the practical point of view.
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