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Tunable laser sources with a wide wavelength tuning range, mode-hop-free (MHF) operation, and high spectral purity are essential for applications such as high-resolution spectroscopy, coherent detection, and intelligent fiber sensing. In this paper, we present a wide-range tunable laser source that operates without mode hopping, based on external cavity feedback using a semiconductor gain chip as the laser gain medium. The wavelength, power, and spectral characteristics of the laser are experimentally measured. A wide MHF continuous wavelength tuning range from 1480 nm to 1620 nm with a side-mode suppression ratio of more than 61.65 dB is achieved. An output optical power of more than 11.14 dBm with good power stability can also be realized in the full C+L band. This proposed external-cavity tunable laser source features a narrow intrinsic linewidth and MHF tunable radiation with a maximum sweep speed of 200 nm/s, enabling practical applications such as high-resolution vector spectrum analysis. [ABSTRACT FROM AUTHOR]

Tunable laser sources with a wide wavelength tuning range, mode-hop-free (MHF) operation, and high spectral purity are essential for applications such as high-resolution spectroscopy, coherent detection, and intelligent fiber sensing. In this paper, we present a wide-range tunable laser source that operates without mode hopping, based on external cavity feedback using a semiconductor gain chip as the laser gain medium. The wavelength, power, and spectral characteristics of the laser are experimentally measured. A wide MHF continuous wavelength tuning range from 1480 nm to 1620 nm with a side-mode suppression ratio of more than 61.65 dB is achieved. An output optical power of more than 11.14 dBm with good power stability can also be realized in the full C+L band. This proposed external-cavity tunable laser source features a narrow intrinsic linewidth and MHF tunable radiation with a maximum sweep speed of 200 nm/s, enabling practical applications such as high-resolution vector spectrum analysis.

Polarization maintaining fibers (PMF) are used in various fields of photonics and telecommunications, so the study of the propagation of optical radiation in such fibers and the determination of the parameters of these fibers is an important task. Therefore, for example, to work with a Mach–Zehnder interferometer, it is important to know the time delay or the difference in arm lengths. One of the methods that solve this problem is optical frequency domain reflectometry, which has a high spatial resolution, sensitivity, and measurement speed. A new method for determining the difference in the lengths of PMF during measurements by the method of optical reflectometry in the frequency domain is presented. If the fibers under study are adjusted at an angle of 45° to the optical axes of the output fibers of the reflectometer, then the detected signal exhibits beat frequencies caused by intermode interference of light fields with orthogonal polarizations. The beat frequencies obtained by analyzing the detected signal contain information about the delay time and the total length of the studied optical fibers. A model is proposed that explains the physical nature of the occurrence of beat frequencies, demonstrates the high accuracy of agreement between numerical calculations and experimental results, and shows the influence of certain parameters on the position and magnitude of these frequencies on the reflectogram. To improve the accuracy of determining the parameters of the studied optical fibers, various methods were used to compensate for the nonlinearity of the laser tuning using an asymmetric interferometer. [ABSTRACT FROM AUTHOR]

The traditional optical frequency domain reflectometry usually requires a separate auxiliary interferometer to compensate for laser nonlinear tuning effect. In order to break through this limitation, this paper proposes a simplified optical frequency domain reflectometry system by integrating an in-fiber auxiliary interferometer before the sensing fiber. We experimentally characterized the laser nonlinear tuning effect, and then verified the feasibility of the proposed system in compensating the laser nonlinear tuning effect by both simulation and experiment. Finally, the capabilities of the distributed sensing of our proposed system was confirmed by the temperature and strain sensing experiments. [ABSTRACT FROM AUTHOR]

A data processing method for correcting the frequency sweeping nonlinearity of a tunable laser in an optical frequency domain reflectometry system is presented. The proposed method calibrates the positions of all the data points by the time-scale factor determined by the zero-crossing points of the auxiliary interferometer. Then, the signal of the main interferometer is interpolated with the calibrated results. In experiments, a spatial resolution of 0.17 mm over a measurable range of 155 m has been obtained even when the optical path difference of the auxiliary interferometer is shorter than that of the main interferometer. This method could resolve the problem that measurable range is limited by the length of delay fiber in the auxiliary interferometer and significantly decrease the requirement of sampling rate.

A new hardware configuration to correct nonlinear tuning affects in optical frequency domain reflectometry (OFDR) is proposed. Unlike conventional correction methods, the new configuration does not require a separate auxiliary interferometer detection, which may eliminate the need for an extra detection device and an acquisition channel. In the proposed method, an intentional beat signal is introduced at the beginning of the OFDR spectrum, which is treated as an auxiliary interferometer to acquire tunable laser phase information for the nonlinear tuning correction. The proposed method may reduce the overall system cost, reduce the data acquisition time and computational load, and make system configuration simpler by eliminating the need for extra components. In this article, the feasibility of the proposed configuration is demonstrated by correcting nonlinear tuning affects using simulations and experiments in a ∼50 m long optical fiber. Distributed strain and temperature sensing are also performed in a 50 m optical fiber with the proposed new configuration. [ABSTRACT FROM AUTHOR]

• A MEMS high-temperature sensitive diaphragm is combined with the fiber microstructure to make the sensing probe. • The F–P acceleration sensor can successfully avoid the fading phenomenon of FBG sensor at high temperature of above 400°C. • A signal demodulation system is proposed based on fast automatically tracking the quiescent operation point. Vibration measurement at high temperature is of great significance to monitoring the operation of major projects and mechanical equipment. As the temperature resistance of electrical vibration sensors is usually below 600°C, it cannot meet the requirements of some high-temperature measuring conditions. This paper studies a high-temperature Fabry–Perot (F–P) acceleration sensing system with general single-mode fiber. A high-temperature sensitive diaphragm is machined based on micro-electromechanical system (MEMS) technology and it is combined with the fiber microstructure to enable the sensing probe to be packaged under high temperatures. According to the temperature characteristic of the length of the F–P cavity, a signal demodulation system was proposed based on the rapid automatic tracking of the quiescent operation point. The complete optical fiber F–P acceleration sensing system conducted real-time vibration detection of high temperature casting in the foundry factory. The experimental result indicates that the optical fiber high-temperature acceleration sensor showed a better vibration response in the working frequency of 100–1000 Hz and the relative error of the frequency measurement is less than 1.56% under normal temperatures and a high temperature of 800°C. [ABSTRACT FROM AUTHOR]

A novel, simple, and short cavity design of single longitudinal mode (SLM) tunable erbium-doped fiber ring laser using a graphene-based saturable absorber is proposed and demonstrated as a tunable signal source. The SLM output is then mixed with another output signal from a tunable laser source (TLS) to generate tunable radio frequency (RF) signals. The tunable SLM fiber ring laser uses a short length of 1 m highly doped erbium-doped fiber as the gain medium. Graphene is used as a saturable absorber to generate the SLM operation, as opposed to the commonly used unpumped erbium-doped fiber. The tuning range of the fiber ring laser is determined by a tunable fiber Bragg grating, which can be tuned from 1547.88 to 1559.88 nm. A continuous wavelength spacing tuning range of 0.020-0.050 nm is obtained between the output of the SLM fiber ring laser and the TLS which is then mixed in a 6 GHz bandwidth optical-to-electrical convertor. This generates a corresponding RF signal of between 2.4 and 5.9 GHz with a low variation in output power. The current RF signal generation is limited by the frequency bandwidth of the optical-to-electrical convertor. [ABSTRACT FROM PUBLISHER]

This paper discusses a Single Wavelength Interrogation (SWI) technique used to measure fast changing pressure related signals and over a large operational temperature range. The novel technique is based on a fiber-optic pressure and temperature hybrid sensor, and a feedback stabilization technique for a tunable laser source. The fiber-optic hybrid sensor consists of a miniature diaphragm based all-silica Extrinsic Fabry-Perot Interferometric (EFPI) Fiber-Optic Pressure Sensor (FOPS) which additionally incorporates a Fiber Bragg Grating (FBG) temperature sensor. The FBG temperature sensor is used as a feedback element to stabilize the output wavelength of the tunable laser source to operate always in the linear range of the EFPI FOPS. [ABSTRACT FROM PUBLISHER]

To realize extremely wideband wavelength-tunable femtosecond (fs) pulse generation, we propose a dispersion-flattened comblike profiled fiber that is a pulse compressor comprised of low dispersion-slope highly nonlinear fiber and zero dispersion-slope nonzero dispersion-shifted fiber (ZDS-NZDSF). We also apply ZDS-NZDSF to a soliton converter to reshape and compress a seed pulse train generated from a tunable laser source and an intensity modulator. Using the proposed scheme, we successfully generate 100-fs optical pulse from the seed pulse with the varied wavelengths of 1530, 1570, and 1610 nm [ABSTRACT FROM PUBLISHER]

The results of an investigation of the performance of a time-division-multiplexed (TDM) fiber Bragg grating (FBG) sensor array using a tunable laser source are reported. The system performance is found limited by the extinction ratio of the optical pulse modulator used for pulse amplitude modulation. Formulas that relate the crosstalk to the extinction ratio of the optical pulse modulator, the modulation parameters of the tunable laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 FBG sensors with 3 με resolution can be realized with a commercially available single Mach-Zehnder type optical pulse modulator of -35-dB extinction ratio [ABSTRACT FROM PUBLISHER]

An original laser technique producing high power, tunable, 1 ps pulses starting from a single standard nanosecond laser is described. Time resolved absorption spectra of dye solutions are shown as an example of application. [ABSTRACT FROM AUTHOR]

Field configuration of multi-function on a single compact photonic integrated circuit introduces considerable system flexibility compared with traditional dedicated single function devices. Here we report a monolithic integrated operation-mode-reconfigurable laser (OMR-laser) based on InP platform with a co-cavity structure. For the first time a detailed study of an OMR-laser is presented. By configuring the bias voltages applied to each sections, continuous wave, Q-switching and pulse wave operations are achieved. The results indicate that the OMR-laser is cost effective and a promising candidate for, e.g., a LiDAR system. [ABSTRACT FROM AUTHOR]

A novel photonic microwave bandpass filter with negative coefficients implemented using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed filter, a lightwave from a tunable laser source (TLS) is sent to a PolM, with the incident lightwave adjusted to have its polarization direction aligned at an angle of plusmn45deg to the principal axes of the PolM. A microwave signal is applied to the PolM through its RF port. Thanks to the polarization modulation in the PolM, two complementary microwave signals with identical amplitudes carried by two optical carriers with orthogonal polarizations are generated. The two complementary optical microwave signals are then sent to an optical delay line consisting of one section or two sections of polarization-maintaining fiber (PMF), with the polarization directions aligned with the fast and slow axes of the PMF. A photonic microwave bandpass filter with two or four taps is obtained [ABSTRACT FROM PUBLISHER]

• Two novel EDFRL architectures based on loop EDFA and double-pass EDFA designs are proposed. • Wide tuning ranges (C+L band) are achieved using proposed configurations. • Extremely flat output power levels with very high OSNRs (~60 dB) are obtained within the tuning range. • High stability for laser output power and oscillation wavelength are achieved. This study presents two novel tunable erbium doped fiber ring laser (EDFRL) configurations based on loop EDFA design and double-pass EDFA design, respectively to achieve an ultra-wideband tuning range and stable single-longitudinal-mode lasing operation. A micro-electro-mechanical system (MEMS) based optical tunable band pass filter was utilized as the wavelength selection element. Output spectral and power characteristics of these EDFRLs were experimentally analyzed and discussed. The EDFRLs had moderate and stable output power level (~ -3 dBm) over 70 nm tuning range that covers C+L band. Moreover, the proposed EDFRLs could also suppress the undesired multi-longitudinal-modes successfully and have a high (~ 60 dB) OSNR level in whole tuning range. [ABSTRACT FROM AUTHOR]

We present a 1-Tb/s (100×12.4 Gb/s) transmission of 12.5-GHz-spaced ultradense (UD) wavelength-division-multiplexing (WDM) channels over a standard single-mode fiber of 1200 km. The UD-WDM channels are aligned within ±100-MHz errors using their beat frequency signals with a tunable laser source. The UD-WDM channels are modulated in nonreturn-to-zero format and amplified using erbium-doped fiber amplifiers to demonstrate the upgradability of existing WDM networks. [ABSTRACT FROM PUBLISHER]

We present a beat-frequency-locking method that uses a tunable laser source (TLS) for the alignment of ultradense (UD) wavelength-division-multiplexing (WDM) channels. The beat-frequency signals between UD-WDM channels and the TLS are used to align the UD-WDM channels within microwave accuracies. As a demonstration, we align 64 UD-WDM channels in 12.5-GHz channel spacing with less than ±100-MHz errors. [ABSTRACT FROM PUBLISHER]