Bulky fiber spectrum analyzers constrain the application of white light interference-based demodulation of Fabry-Perot interferometric (FPI) sensors in practical measurement scenarios. The key to the ...miniaturization of the fiber Spectrometer is the reconstruction of the fiber spectrum. However, advances in this field are often characterized by a reliance on microelectromechanical systems (MEMS) that cannot have both excellent frequency and resolution. This letter presented a neural network-based systematic scheme to achieve fiber optic sensor's spectral reconstruction with high-frequency and high-resolution potential. The solution can reconstruct the FPI sensor spectrum consisting of hundreds of points based on extremely sparse (even single-digit) sampling points, with MHz-level frequency, and supports custom tuning the reconstructed wavelength range. This solution can provide a novel platform for designing compact, high-performance fiber spectrum analyzers.
We report a novel temperature sensor based on a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) and temperature-to-time mapping. In the proposed scheme, a narrow bandpass electrical ...filter is inserted into the FDML OEO cavity. The temperature information is mapped to the time interval of the output pulses due to the temperature-sensitive bidirectional scanning property of the FDML OEO. Compared with other OEO-based temperature sensors, the proposed scheme avoids the needs of wideband electrical spectrum analyzers, since the temperature-sensitive output pulses can be interrogated using a low-speed oscilloscope working under sub-Nyquist sampling condition. In the proof-of-concept experiment, a high sensitivity of 8.166 μs/°C and resolution of 0.03°C is achieved, demonstrating a good temperature sensing performance.
The complete set of intrinsic dimensionless parameters of a packaged and fiber-pigtailed distributed feedback (DFB) semiconductor laser are extracted from the non-linear operational stability ...boundaries of the optical-injection-locking (OIL) architecture. Specifically, this procedure is done by relating the intrinsic parameters to the injection ratios corresponding to the Hopf bifurcation points at zero detuning, as well as the detuning of the Hopf-Saddle-Node point. The bifurcation points of the injected laser's operational space are found by coupling its output into a high-resolution optical spectrum analyzer. This is enabled by establishing a 30 dB side mode suppression ratio between the central mode and Period 1 oscillations to define the boundaries of Stable Locking. Along with the laser's threshold current and free-running relaxation oscillation frequencies, performing these measurements over a range of pumping values allows for the calculation of the laser's linewidth enhancement factor, irrespective of the device packaging. Utilizing a high pump approximation, the remaining dimensionless parameters are extracted after obtaining the photon lifetime. Using this approach, the operational capabilities of an arbitrarily-packaged laser can be determined, allowing for the analysis of an injected laser's operational space for a variety high-frequency and dynamical applications.
We introduce a slope-assisted Brillouin optical wavemeter. Existing Brillouin-based spectrum analyzers measure the Brillouin gain as the frequency of a pump laser is swept across the frequency band ...of interest. However, this process is slow since only one spectral channel is measured at a time and the spectral resolution is typically limited to the Brillouin gain linewidth. In this work, we introduce a technique that uses both the Brillouin gain and phase to construct a single-shot wavemeter with frequency resolution orders of magnitude below the Brillouin linewidth. We also show that combining information from the Stokes and anti-Stokes interactions allows us to reduce the sensitivity to environmental fluctuations such as temperature, enabling a robust system with frequency noise of 20 Hz/<inline-formula> <tex-math notation="LaTeX">\surd </tex-math></inline-formula>Hz. This noise level enables a measurement of a 200 Hz frequency shift with a 10 ms measurement.
An opticalfiber vector magnetometer based on a thin-cladding polarization-maintaining fiber (TPMF) long-period fiber grating (LPFG) and magnetic fluid (MF) is proposed and experimentally ...demonstrated. The non-circular symmetric fiber structure and asymmetric evanescence field distribution of the LPFG induce a vector surrounding refractive index (SRI) response. Based on the magneto-optical properties of the MF nanoparticles and the directional SRI characteristics of the TPMF-LPFG, the resonance dip wavelength shift of the grating is dependent on the angle between the principal axis of TPMF and the external magnetic field direction when being applied to an external magnetic field. The achieved maximum sensitivity of the wavelength shift was −618 pm/mT when the magnetic intensity changes in the range of 0-10.5 mT. The achieved maximum orientation sensitivity of the sensor was 72 pm/degree, but the magnetic orientation can be detected only within the range of 0-90 degree. The minimum magnetic field intensity that can be detected is about 32.3 μT due to the 0.02 nm wavelength resolution of the optical spectrum analyzer. Our study proves that the high birefringence fiber based LPFG combined with MF can be developed as a high-performance vector magnetometer and such type of sensor is anticipated to find potential applications in magnetic or electric field systems.
This article presents an ON-chip jitter/phase noise measurement (PNM) circuit that is reference-free and self-calibrated in situ in the background. Formula Omitted time to digital converters (TDCs) ...are employed to measure cycle jitters of the signal under test and to digitize the power spectral density of phase noise. As a clean reference clock is not required for the PNM, the sensitivity of PNM is not limited by the reference source. The signal bandwidth of the TDC ranges from 100 kHz to 3.125 MHz, and the measured errors are less than 1 dB by a single-tone phase modulation (PM) test across the frequency range. Compared to the measurement results using a spectrum analyzer (Keysight N9030B), it demonstrates a jitter resolution of 275 fsrms with only 4.8% error, which is at least 3Formula Omitted finer compared to the prior art. This PNM is fabricated via a Taiwan Semiconductor Manufacturing Company (TSMC) 28-nm CMOS process, and the core area is 450 Formula Omitted 453 Formula Omitted. The total power consumption is 15.83 mW.
A high-resolution temperature sensor based on MMF-SMF-MMF (MSM) utilizing the mapping from Fast Fourier transform (FFT) of MSM spectrum to RF spectrum is proposed and experimentally demonstrated. The ...MSM is the sensing element and consists of a single mode fiber (SMF) sandwiched between two short multimode fibers (MMFs). The MSM-based microwave photonic filter (MPF) down-converts the optical spectrum to the RF domain based on the mapping from Fourier transform of MSM spectrum to microwave photonic response. Temperature is extracted from the amplitude variations of the frequency response. Experiments shows that the amplitude variation of response has a quadratic relationship with temperature at 332.3MHz and 594.3MHz due to the differential temperature sensitive coupling coefficient between cladding modes and the core mode of SMF. Compared with the optical spectrum analyzer (OSA) interrogation scheme, the proposed scheme increases temperature resolution by two orders. The interrogation scheme is also suitable for a variety of multimode interferometer with high precision requirement.
When treating root canals of teeth, deformations occur, changes in the geometric characteristics of the surface of endodontic files, which causes their breakages and problems when removing fragments ...of files from the root canals of the tooth. The article offers a method of express analysis of the preliminary assessment of the serviceable state of the endodontic file to exclude its damage in the root canal of the tooth. The method consists in studying the amplitude-frequency characteristics of endodontic files (natural frequencies) using the software of modern smartphones and sound spectrum analyzers for smartphones with the Android operating system. Research results are presented. It is proved that the natural oscillation frequency of new endodontic files ranges from 1260-1280 Hz, and the natural oscillation frequency of deformed endodontic files increases to 1520-1560 Hz or more.
An all-single-mode fiber intracavity displacement sensor based on U-shaped single-mode fiber interferometer (U-SMFI) is demonstrated theoretically and experimentally. The theoretical model for a ...cavity-loss-modulated Er-doped fiber ring laser is proposed to analyze the linewidth-narrowing and signal-to-noise ratio (SNR) enhancement mechanism. The evolutionary process of the spectra is calculated through solving the rate equations to investigate the role that the intracavity spectroscopy plays in narrowing the linewidth and reducing the bandwidth-broadening effect theoretically for the first time. Experimental setup for intracavity displacement sensing via a U-SMFI is established to verify the above principle. According to the experimental results, the linewidth and SNR characteristics have been improved a lot compared with the passive U-SMFI. Moreover, it is indicated that the sensitivity of the intracavity displacement-sensor can be optimized through adjusting the bending radius of the U-SMFI. The mode-hopping phenomenon is investigated and eliminated to make the wavelength stability of the output laser comparable to the highest resolution of the optical spectrum analyzer. When the displacement applied to the U-SMFI with a radius of 5.95 mm is changed from 0 to 200 μm, the sensitivity of the proposed intracavity-sensor is 52.92 pm/μm, which can be enhanced through a further optimization to the radius of the U-SMFI. Our proposed sensor design is expected to emerge as a new and promising alternative approach to achieve high-resolution displacement sensor.
Intensity modulation and direct detection (IM-DD) systems are widely used in short-reach optical networks. Thus, developing a practical and accurate method to characterize nonlinear distortion and to ...estimate system performance is essential, as this is the foundation of IM-DD system design. The amount of nonlinear distortion can be characterized using the noise-to-power ratio (NPR). Although measuring the NPR using a notch requires only a spectrum analyzer, this method cannot be applied to a nonlinear system with non-Gaussian stimuli in general. We employ the method of measuring the NPR using a notch to characterize the nonlinear distortion in directly modulated distributed feedback (DM-DFB) laser-based IM-DD systems. Nonlinear distortion in these IM-DD systems can be attributed to two specific mechanisms: the imperfect power-current characteristic of the DM-DFB laser and the interaction among the modulation, chromatic dispersion (CD), and detection. Experimental results demonstrated that the nonlinear distortion can be accurately characterized with a mean absolute error of 0.47 dB, even when the stimuli are pulse amplitude modulation. The system performance subjected to nonlinearity could be estimated by the equivalent additive noise model. Besides, the method of measuring the NPR using a notch is also effective when the Mach-Zehnder modulator-based IM-DD system has nonnegligible CD. However, it failed in the case of negligible CD. Considering that this method is not always effective, we analyzed the attributes of various nonlinear systems and found that the above method is applicable only to systems dominated by second-order nonlinearity.
