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Inline weld depth measurement for high brilliance laser beam sources using optical coherence tomography
摘要： As a result of the rapidly growing importance of applications in electro mobility that require a precisely defined laser weld depth, the demand for inline process monitoring and control is increasing. To overcome the challenges in process data acquisition, this paper proposes the application of a novel sensor concept for deep penetration laser beam welding with high brilliance laser sources. The experiments show that optical coherence tomography (OCT) can be used to measure the weld depth by comparing the distance to the material surface with the distance to the keyhole bottom measured by the sensor. Within the presented work, the measuring principle was used for the first time to observe a welding process with a highly focused laser beam source. First, a preliminary experimental study was carried out to evaluate the influence of the angle of incidence, the material, and the weld joint geometry on the quality of the sensor signal. When using a multimode fiber laser with a focus diameter of 320 μm, the measurements showed a distinct behavior for aluminum and copper. The findings about the measurement signal properties were then applied to laser beam welding with a single-mode fiber laser with a spot diameter of only 55 μm. The spot diameter of the OCT measuring beam was about 50 μm and thus only slightly smaller than that of the single-mode processing beam. A wide variety of tests were carried out to determine the limits of the measurement procedure. The results show that the application of OCT allows inline monitoring of the weld depth using both a multimode and a highly focused single-mode laser beam. In addition, various influences on the signal were identified, e.g., the material-specific melt pool dynamics as well as several characteristic reflection and absorption properties.
关键词： high brilliance laser beam sources,weld depth measurement,optical coherence tomography,laser beam welding
更新于2025-11-28 14:24:20
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Polarization induced non-reciprocal phase controlled all-fiber loop mirror based inclinometer
摘要： An optical fiber inclinometer based on non-reciprocal phase change effect in a single-mode fiber loop mirror (FLM) is proposed. The phase of light waves in FLM is controlled by two-phase shifters (PSs). The relationship between the inclination angles and phase differences of the two-PSs, and transmitted light power was derived by Jones calculus. The signature of the birefringence obtained through simulation on the output light has been confirmed by experimentation. From the results, it was found that when the birefringence of the two-PSs are different, two measurement sensitivities (17.07 × 10?3 deg?1 and 21.37 × 10?3 deg?1) can be realized with one angle measurement system. We also report a method for changing measurable ranges, and measurement sensitivity. Since the angle can be directly measured from the transmitted light power, the results of this work contribute to the realization of simple and low-loss inclinometers using standard single-mode fiber.
关键词： Optical fiber inclinometer,Tilt measurement,Fiber optics,Sagnac interferometer,Fiber loop mirror
更新于2025-11-28 14:24:03
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Large-Dynamic Frequency Response Measurement for Broadband Electro-Optic Phase Modulators
摘要： A novel method for characterizing the frequency responses of broadband electro-optic phase modulators (PMs) by employing stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. In the proposed method, the SBS amplifies the +1st-order sideband and attenuates the -1st-order sideband of the phase-modulated signal from a PM under test. Thereby, the phase-modulated signal is converted into an optical single-sideband (OSSB) modulation signal. After square-law photodetection, the overall frequency responses are obtained. Removing the frequency responses of the SBS gain and the photodetector (PD) from the overall responses, the responses of the PM are thus achieved. Benefitting from the amplification of the SBS, the proposed method possesses a large dynamic range. Sub-Hz resolution and broadband measurement range are also achievable. A commercial broadband PM is experimentally characterized from 10 MHz to 50 GHz with a resolution of 5 MHz. According to the amplification of the SBS, the dynamic range is enhanced by 17.74 dB. The measurement result is verified by the conventional method utilizing optical spectrum analysis.
关键词： stimulated Brillouin scattering,Electrooptic modulation,Phase modulation,microwave photonics,optical variables measurement
更新于2025-11-28 14:24:03
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A Method for Expansion of Z-Directional Measurement Range in a Mode-Locked Femtosecond Laser Chromatic Confocal Probe
摘要： A method is proposed to expand the Z-directional measurement range of a fiber-based dual-detector chromatic confocal probe with a mode-locked femtosecond laser source. In the dual-detector chromatic confocal probe, the Z-directional displacement of a measurement target is derived from the peak wavelength in the normalized intensity ratio from the two light intensities obtained by the two identical fiber detectors. In this paper, a new method utilizing the main-lobe and side-lobes of axial responses acquired from both the normalized intensity ratio Ia and the invert normalized intensity ratio In, which is the inverse of Ia, is proposed to obtain the seamless relationship between the peak wavelength and the Z-directional displacement of a measurement target. Theoretical calculations and experimental investigation are carried out to demonstrate the feasibility of the proposed measurement range expansion method.
关键词： measurement range expansion,side-lobe,femtosecond laser,chromatic confocal probe
更新于2025-11-28 14:24:03
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An optical angle sensor based on chromatic dispersion with a mode-locked laser source
摘要： This paper proposes a new optical angle sensor, in which a mode-locked laser is employed as the light source, and chromatic dispersion of a collimator objective is utilized to detect the angular displacement of a target of interest. In the proposed method, each of the optical modes in the femtosecond laser beam reflected from the reflector mounted on a target of interest is separated from the others by chromatic dispersion of a collimator objective to generate a group of focused laser beams that can be utilized as the scale for measurement of an angular displacement of the target. By detecting the change in peak frequency in optical spectra obtained by the photodetector, a small angular displacement can be measured. In this paper, as the first step of research, a prototype optical setup is developed, and some basic experiments are carried out to demonstrate the feasibility of the proposed method for measurement of angular displacement.
关键词： Chromatic dispersion,Angular displacement,Angle measurement,Optical frequency comb,Laser autocollimation
更新于2025-11-28 14:24:03
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Temperature fiber sensor based on single longitudinal mode fiber laser in 2?μm band with Sagnac interferometer
摘要： A single longitudinal mode (SLM) ?ber laser with a ring cavity based on Sagnac interferometer (SI) for temperature sensing in the 2-μm band is proposed and demonstrated. The simulation and experimental results show that the transmission spectrum of the SI ?lter is sensitive to temperature change. Based on this distinguishing feature, the correlation between the laser wavelength drift and temperature variation can be established. Experimental results show that the proposed laser operates stably at the resonant wavelength of 1988.21 nm and the optical signal-to-noise ratio is approximately 55 dB at ambient temperature. Through continuous measurement for 100 min, the ?uctuation of the output laser power is lower than 0.74 dB, and the resonant wavelength shift is less than the minimum resolution of the spectrometer of 0.05 nm. This indicates that it has good stability for a certain period of time. At the same time, the laser operates stably in SLM state. A temperature sensitivity of 2.09 nm/°C is obtained in experiment. Notably, the proposed ?ber laser sensor possesses the merits including high sensitivity, low cost and simple structure, which are bene?cial to its practical application.
关键词： Fiber optics sensors,Temperature measurement,Sagnac interferometer,Fiber laser,2-μm band
更新于2025-11-28 14:23:57
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Demonstration of linewidth measurement based on phase noise analysis for a single frequency fiber laser in the 2 <i>μ</i> m band
摘要： Linewidth measurement based on phase noise analysis using a 3 × 3 coupler has been applied in the 1550 nm band. One of the obvious advantages of this method compared with the common delayed self-heterodyne method is the low loss caused by the short delay line used. Taking full advantage of this particular characteristic, the linewidth of the single frequency (SF) fiber laser in the 2 μm band can also be measured. However, a specifically experimental demonstration of this method in the 2 μm band is absent to date. In this paper, a high-performance SF thulium-doped fiber laser (TDFL) was proposed and employed for the demonstration. The TDFL operates at the center wavelength of 1942.03 nm with high stability. By means of the phase noise analysis-based linewidth measurement system with a fiber delay line of only 50 m, the linewidth of the proposed TDFL is successfully measured. When the measuring time is 0.001 s, the linewidth is ~47 kHz. Furthermore, the noise characteristics of the SF laser were simultaneously studied by this method.
关键词： 2 μm band,phase noise,single frequency fiber laser,linewidth measurement
更新于2025-11-28 14:23:57
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Absolute distance measurement based on spectral interferometry using femtosecond optical frequency comb
摘要： We demonstrated an absolute distance measurement method based on the frequency folding e?ect using the spectral interferometry of femtosecond optical frequency comb. And the investigation was carried out on the ranging accuracy in?uence of the phase noise in the traditional complicated phase unwrapping method via band-pass ?lter and Fourier Transform. To reduce the e?ects of the phase noise, we proposed the non-?ltered and di?erential envelop phase demodulation method, and its robustness was illustrated with a standard deviation of 75 nm for the stability of single point measurements. Further, through the extension of the non-ambiguity range, we achieved a resolution of better than 30 ??m in a long distance measurements range of 70 m, yielding a relative precision of 3.1 × 10 ? 7.
关键词： Spectral interferometry,Optical frequency comb,Absolute distance measurement
更新于2025-11-28 14:23:57
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Simultaneous Measurement of Refractive Index and Temperature Based on a Peanut-Shape Structure In-Line Fiber Mach–Zehnder Interferometer
摘要： We proposed a peanut-shape structure in-line fiber Mach–Zehnder interferometer (MZI) for simultaneous measurement of refractive index (RI) and temperature. Two kinds of demodulation methods were investigated and compared. The wavelength-related and phase-related character matrices of the in-line fiber MZI were determined for simultaneous measurement of RI and temperature, respectively. For the wavelength-related measurement, the highest temperature and RI sensitivities were 0.0709 nm/°C and ?47.3620 nm/RIU, respectively. The phase-related measurement was with a lower measuring errors compared to the wavelength-related measurement, and the highest temperature and RI sensitivities were ?0.0632rad/°C (0.0764 nm/°C) and 77.0995rad/RIU (?93.2429 nm/RIU), respectively. The minimum measuring errors of temperature and RI were 0.3800 °C and 0.0004 RIU, respectively.
关键词： Mach–Zehnder interferometer,simultaneous measurement of refractive index and temperature,Optical fiber sensor,peanut-shape structure
更新于2025-11-28 14:23:57
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Extrinsic Fabry Perot interferometer fiber sensor for simultaneous measurement of hydrazine vapor and temperature
摘要： A novel optical fiber sensor of hydrazine (N2H4) vapor and temperature is proposed and demonstrated. The perylene diimide derivative (TClPDI) is deposited on the enlarged optical fiber end face as sensitive film, and an extrinsic Fabry Perot resonator is formed with fiber bragg grating (FBG) and fiber end face. The film device exhibits high sensitivity and reproducibility to hydrazine vapor with liner concentration dependent characteristic, which owes to the change of refractive index under hydrazine vapor. The enhancement sensitivity and temperature monitoring could be obtained due to the FBG. The results show that a hydrazine vapor sensitivity of 0.01 dB m/ppm, a temperature sensitivity of 9.8 pm/?C could be achieved. In addition, the effect of enlarged fiber end face on the form of TClPDI film was investigated, the sensing mechanism of the film device to hydrazine vapor was studied. The sensor has the advantages of all optical system, tiny, high repeatability, high reliability and two parameters sensing, showing high potential for practical application.
关键词： Tautomerism,Simultaneous measurement,The change of RI,FBG-FP,Two-parameter
更新于2025-11-28 14:23:57