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.
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 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.
We report on a quantitative quasi-distributed vibration sensing (DVS) system enabled by phase-sensitive optical frequency domain reflectometry (φ-OFDR), which allows for multiple vibration events over consecutive spatial resolutions. To achieve effective crosstalk suppression and mitigation of the instability during the phase extraction, fiber with embedded ultra-weak grating arrays has been adopted as the sensing fiber. It exhibits a particularly customized low spatial duty cycle, that is, high ratio between the size of the gratings and their spacing and the spacing is additionally designed to match the integer multiple of the theoretical spatial resolution. In combination with a rectified frequency-modulated continuous-wave optical probe enabled by the optical phase-locked loop, it allows to achieve quantitative quasi-DVS for multiple events over consecutive sensing spatial resolution as high as ∼2.5 cm along the distance over ∼2200 m. The ability to simultaneously retrieve arbitrary multi-point vibration events over spatially consecutive sensing spatial resolutions with consistently linear response and sensitivity up to a few nano-strain level even at long distances has shown great potentials for the application of φ-OFDR from a practical point of view.
We present and establish a versatile analytical model that allows overall analysis and optimization for the phase noise performance of the delay interferometer based optical phase-locked loop (OPLL). It allows considering any type of lasers with arbitrary frequency noise properties while taking into account the contributions from various practical noise sources, thus enabling comprehensive investigation for the complicated interaction among underlying limiting factors. The quantitative analysis for their evolution along with the change of the delay of the interferometer unveils the resulting impact on the fundamental limit and dynamics of the output phase noise, leading to a well-balanced loop bandwidth and sensitivity thus enabling the overall optimization in terms of closed-loop noise performance. The tendencies observed and the results predicted in terms of coherence metrics in numerical verification with different lasers have testified to the precision and effectiveness of the proposed model, which is quite capable of acting as a design tool for the insightful analysis and overall optimization with guiding significance for practical applications.
We report a phase modulation coherent linear phase demodulation (PM-CLPD) analog photonic link (APL) based on an optical phase-locked loop (OPLL). In this work, we mainly focus on the analysis for the impact of different noise sources on the noise floor in particular under different received optical powers. It was found that due to the limited commonmode noise rejection of the balanced detector, an appropriate received optical power should be made of choice in order to prevent the potential dynamic range deterioration. With this scope, experimental investigations have been carried to verify such specified condition at certain system configurations. In addition, to solve the problem of noise deterioration caused by optical amplification in traditional APL, a common optical amplification scheme is incorporated to facilitate the common-mode noise reduction, making the system less sensitive to the extra noise induced deterioration. By taking into account these aspects, an improvement as large as 10dB is demonstrated for the overall system noise floor.
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