Fiber Fabry-Perot Tunable Filter Research Articles

Bandwidth compensation in swept laser source using the asymmetric sinusoidal modulation

Broadband, high-speed wavelength-swept laser sources can substantially enhance applications in optical coherence tomography (OCT), metrology, fiber-optic sensing, and so on. Fiber Fabry-Perot tunable filters (FFP-TF) are active wavelength selection media for wavelength-swept laser sources because of their wide free spectral range, high finesse values, and more compactness. However, FFP-TF is irreversible and conventionally driven using a sinusoidal electronic waveform, thereby limiting the required acquisition bandwidth. Here, we introduce a new approach based on bandwidth compensation of the continuous-output, asymmetric sinusoidal-mode driving of FFP-TF, where output wavelength is tuned coincidentally to the forward and backward sweeps during the driving cycle. A detailed structure framework and the comparison of the sweep range of the swept laser source under convention sinusoidal and asymmetric sinusoidal-mode driving is discussed. A swept laser source with a sweep rate of 66.7 kHz over a 161 nm range at a center wavelength of 1310 nm is demonstrated. The result shows that the asymmetric sinusoidal-mode is a suitable driving medium for FFP-TF for swept laser sources with increased output bandwidth.

Stable and narrow linewidth linear cavity CW-active Q-switched erbium-doped fiber laser

A stable and narrow-linewidth, continuous wave and active Q-switching erbium-doped fiber laser, incorporating a fiber Bragg grating and a fiber Fabry-Perot tunable filter, was designed and experimentally implemented. Here, we proposed combining three approaches to suppress the mode hopping and improve both the output power stability and narrow the linewidth: first, two narrow-band optical filters, fiber Bragg grating and Fabry-Perot tunable filter were utilized in the laser cavity; second, the cavity configuration was optimized as a function of the output coupling ratio; finally, a 1.5 m long segment of unpumped erbium-doped fiber was inserted in the cavity to act as an induced virtual long and weak fiber Bragg grating. Using a 90% output coupling ratio, and monitoring over 120 min at room temperature, the 3 dB linewidth and power fluctuation of the fiber laser emission at 1550 nm were 16 kHz and 0.0025 dB respectively. Also, an optical signal to noise ratio (OSNR) of 82 dB was obtained. Keeping the same fiber laser configuration, laser pulses were also obtained using the Q-switching technique, realized by using dynamic spectral overlapping between the Bragg grating and the tunable filter. A stable output peak power of 5.6 W was achieved with a pulse width of 450 ns at a repetition rate of 1 kHz.

Lévy spectral intensity statistics in a Raman random fiber laser

The statistical behavior of spectral intensity fluctuations in a Raman gain random fiber laser is investigated for the first time, to the best of our knowledge. Through a fiber Fabry–Perot tunable filter, the intensity of the filtered single wavelength from random laser (RL) spectra is measured at different pump powers. The probability density function (PDF) of spectral intensity values is analyzed. Well below the lasing threshold, the intensity of a single wavelength is stable in the time domain, and the PDF exhibits a typical Gaussian behavior. However, around the threshold, strong fluctuations in intensity emerge. In this case, the statistical distribution is characterized by a power-law-tailed function consistent with a Levy α-stable distribution. We identify the statistical evolution as the injected pump power increases, from a Gaussian to a Levy and then back to a Gaussian distribution, which is similar to the case of RLs with a strong disorder due to the presence of photon scatterers and gain related to electronic transitions in the active medium, indicating the universal existence of such statistical properties in random lasing systems.

Dynamic fiber Bragg grating strain sensor interrogation with real-time measurement

We demonstrate a 1550 nm band resonance Fourier-domain mode-locked (FDML) fiber laser with fiber Bragg grating (FBG) array. Using the FDML fiber laser, we successfully demonstrate real-time monitoring of dynamic FBG strain sensor interrogation for structural health monitoring. The resonance FDML fiber laser consists of six multiplexed FBGs, which are arranged in series with delay fiber lengths. It is operated by driving the fiber Fabry-Perot tunable filter (FFP-TF) with a sinusoidal waveform at a frequency corresponding to the round-trip time of the laser cavity. Each FBG forms a laser cavity independently in the FDML fiber laser because the light travels different length for each FBG. The very closely positioned two FBGs in a pair are operated simultaneously with a frequency in the FDML fiber laser. The spatial positions of the sensing pair can be distinguished from the variation of the applied frequency to the FFP-TF. One of the FBGs in the pair is used as a reference signal and the other one is fixed on the piezoelectric transducer stack to apply the dynamic strain. We successfully achieve real-time measurement of the abrupt change of the frequencies applied to the FBG without any signal processing delay. The real-time monitoring system is displayed simultaneously on the monitor for the variation of the two peaks, the modulation interval of the two peaks, and their fast Fourier transform spectrum. The frequency resolution of the dynamic variation could reach up to 0.5 Hz for 2 s integration time. It depends on the integration time to measure the dynamic variation. We believe that the real-time monitoring system will have a potential application for structural health monitoring.

Continuously tunable wideband semiconductor fiber-ring laser

We demonstrate a wideband tunable semiconductor fiber-ring laser that can be continuously tuned from 1498 nm to 1623 nm. The proposed laser uses a semiconductor optical amplifier (SOA) as a gain medium and a fiber Fabry–Perot tunable filter as a selective wavelength filter. The optimized drive current of the SOA and the output coupling ratio are obtained by experimental research. This laser has a simple configuration, low threshold, flat laser output power and high optical signal-to-noise ratio.

Optimization of excitation of fiber Fabry-Perot tunable filters used in swept lasers using a phase-correction method.

In this paper we investigate a phase-correction method for compensation of the nonlinearity of conventional wavelength-swept laser sources based on a fiber Fabry-Perot tunable filter as a wavelength selective element. A triangular waveform signal is commonly used to drive the filter. We, however, extract the zero crossings from the interferograms and modify the shape of the triangular signal accordingly. This algorithm was tested for different values of the optical path length difference in the interferometer setup. Significant compensation for the nonlinearity of the filter was obtained.

Widely tunable/wavelength-swept SLM fiber laser with ultra-narrow linewidth and ultra-high OSNR

We propose and demonstrate a novel single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 473 Hz and an ultra-high optical signal-to-noise ratio (OSNR) more than 72 dB, or operating at wavelength-swept mode with tunable sweep rate of 10—200 Hz and a sweep range more than 50 nm. The excellent features mainly benefit from a triple-ring subring cavity constructed by three optical couplers nested one another and a fiber Fabry-Perot tunable filter which can be driven by a constant voltage or a periodic sweep voltage for fixed or wavelength- swept operation, respectively. The proposed EDFL has potential applications in high-resolution spectroscopy and fiber optic sensing.

Electro-Optic Swept Source Based on AOTF for Wavenumber-Linear Interferometric Sensing and Imaging

We demonstrate a novel electro-optic swept source for wavenumber-linear interferometric sensing and imaging applications. The electro-optic swept source based on an acousto-optic tunable filter (AOTF) provides high environmental stability and arbitrary drive function sweeping because the electro-optic wavelength selection does not depend on a mechanical moving component to tune the output lasing wavelength. We show improved stability of the suggested electro-optic swept source, compared to a conventional swept source based on a fiber Fabry–Perot tunable filter (FFP-TF). Various types of wavelength sweeping are demonstrated by applying the programmed drive function to the applied radio frequency (RF) of the AOTF. We demonstrated improved image quality of optical coherence tomography (OCT) by using the wavenumber-linear drive function of a simple triangular signal, which has a high wavenumber-linearity with an R-square value of 0.99991.

Active Q-switching of a fiber laser using a modulated fiber Fabry–Perot filter and a fiber Bragg grating

We propose and demonstrate a simple and robust actively Q-switched erbium-doped fiber ring cavity laser. The Q-switching is based on dynamic spectral overlapping of two filters, namely a fiber Bragg grating-based filter and a fiber Fabry–Perot tunable filter. Using 3.5 m of erbium-doped fiber and a pump power of only 60 mW, Q-switched pulses with a peak power of 9.7 W and a pulse duration of 500 ns were obtained. A pulse repetition rate can be continuously varied from a single shot to a few KHz.

Wavelength modulation spectroscopy at 1530.32 nm for measurements of acetylene based on Fabry–Perot tunable filter**Project supported by the National Natural Science Foundation of China (Grant Nos. 61172047 and 61071025).

Sensitive detection of acetylene (C2H2) is performed by absorption spectroscopy and wavelength modulation spectroscopy (WMS) based on Fiber Fabry–Perot tunable filter (FFP-TF) at 1530.32 nm. After being calibrated by Fiber Bragg Grating (FBG), FFP-TF is frequency-multiplexed and modulated at 20 Hz and 2.5 kHz respectively to achieve wavelength modulation. The linearity with 0.9907 fitting coefficient is obtained by measuring different concentrations in a 100 ppmv–400 ppmv range. Furthermore, the stability of the system is analyzed by detecting 50 ppmv and 100 ppmv standard gases for 2 h under room temperature and ambient pressure conditions respectively. The precision of 11 ppmv is achieved by calculating the standard deviation. Therefore, the measuring system of C2H2 detection can be applied in practical applications.

Wavelength-Swept Cascaded Raman Fiber Laser around 1300 nm for OCT Imaging

We experimentally demonstrated a novel wavelength-swept laser using a cascaded Raman gain around 1310 nm. A 1064/1310 wavelength division multiplexing (WDM) coupler and coupled fiber Bragg gratings mirrors at 1064, 1117, 1175, 1240 nm are effectively used to increase the power efficiency in a laser ring cavity with highly non-linear fiber (HNLF) of 2 km. Linear wavelength sweeping is demonstrated with the 100 Hz triangular driving signal to fiber Fabry-Perot tunable filter (FFP-TF) around the 1310 nm region. The measured sweeping range and output power were 27 nm and 2.1 mW, respectively, which are suitable for optical coherence tomography (OCT) imaging.

An optimized strain demodulation method for PZT driven fiber Fabry–Perot tunable filter

An optimized strain-demodulation-method based on piezo-electrical transducer (PZT) driven fiber Fabry–Perot (FFP) filter is proposed and experimentally demonstrated. Using a parallel processing mode to drive the PZT continuously, the hysteresis effect is eliminated, and the system demodulation rate is increased. Furthermore, an AC–DC compensation method is developed to address the intrinsic nonlinear relationship between the displacement and voltage of PZT. The experimental results show that the actual demodulation rate is improved from 15Hz to 30Hz, the random error of the strain measurement is decreased by 95%, and the deviation between the test values after compensation and the theoretical values is less than 1pm/µε.

Large-energy, wavelength-tunable, all-fiber passively Q-switched Er:Yb-codoped double-clad fiber laser with mono-layer chemical vapor deposition graphene.

We demonstrate a large-energy, wavelength-tunable, all-fiber passively Q-switched Er:Yb-codoped laser using a mono-layer chemical vapor deposition (CVD) graphene saturable absorber (SA). By exploiting the large laser gain of Er:Yb double-clad fiber and optimizing the coupling ratio of the output coupler, not only can the mono-layer CVD graphene SA be protected from oversaturation and thermal damage, but also a large pulse energy up to 1.05μJ (corresponding to the average output power of 25.6mW) is thus achieved. Using a tunable fiber Fabry-Perot filter, stable Q-switched pulses can operate with a tunable range from 1530.97 to 1546.92nm, covering a wavelength range of ∼16 nm. The Q-switching states at the different lasing wavelengths have been observed and recorded. The Q-switched repetition rate and the pulse duration (with the minimum one of 2.6μs) have been characterized as well. This is, to the best of our knowledge, the largest pulse energy from an all-fiber graphene Q-switched laser.

A dual-wavelength erbium-doped fiber laser with widely tunable wavelength spacing

A stable dual-wavelength erbium-doped fiber laser (EDFL) with tunable wavelength spacing and equalized output power is proposed and experimentally demonstrated. The fiber laser uses two fiber Fabry-Perot tunable filters (FFPTFs) as the wavelength filter. The main cavity is divided into two sub-cavities with imbalance cavity losses through a 30/70 optical coupler. The tunable wavelength spacing can be achieved by changing the center wavelength of the filters and the equalized dual-wavelength output power can be achieved by properly controlling the variable optical attenuator (VOA) inserted in the lower-loss cavity.

Development of an intra-cavity gas detection system based on L-band erbium-doped fiber ring laser

In this study, a gas detection system based on intra-cavity absorption spectroscopy technique and L-band erbium-doped fiber ring laser is constructed. With a fiber Fabry–Perot tunable filter used for spectral scanning, the system can acquire multiple absorption lines of the detected gas. In order to improve the detection accuracy, reference wavelengths are introduced to calibrate the nonlinearity of the filter, and polynomial fitting is proposed to compensate the impact of temperature variation on gas absorption. When the system is applied to detect the concentration of CO2, the absolute error is less than 400ppm, corresponding to a relative error under 0.52%. The monitoring error of absorption wavelength is no more than 30pm. The system also has the ability to detect other gas species which have absorption lines in L-band.

Wavelength-Division Multiplexing Fiber Bragg Grating Vibration Sensing Demodulation System

A fiber Bragg grating (FBG) sensing network for vibration measurement is proposed and demonstrated in this paper. The light source of the described sensing technique is an erbium-doped fiber laser applying a 980-nm laser diode and a fiber Fabry-Perot tunable filter. The fiber laser has a 40nm tuning range, allowing many vibration sensors to be multiplexed on the same fiber. Reflected light wavelength shift of the FBG sensor caused by strain variation is converted to intensity deviation, which avoids a complex demodulation process. This sensing scheme can effectively increase the demodulation speed of sensing system up to 20 KHz. At least 20 FBGs can be multiplexed alone a fiber.

High resolution and wide scale fiber Bragg grating sensor interrogation system

This paper demonstrates a high resolution and wide scale fiber Bragg grating sensor interrogation system based on fiber Fabry–Perot tunable filter (FFP-TF) and Fabry–Perot ITU filter (FPIF). By automatic control of the driving voltage of the FFP-TF, the wavelength of the laser can be tracked to the −3dB reflectivity spectrum of the FBG. Using FPIF as the reference channel, the measurement resolution of the system is improved by wiping out the nonlinearity of the FFP-TF. A high resolution of better than 2pm within wide strain measurement range was verified by experiments.

Design and experimental research of a high-precision wavelength controller for tunable fiber Fabry-Perot filters

A high-precision wavelength controller is presented in this paper. It is necessary to find out the difference between the central wavelength of a tunable fiber Fabry-Perot (FFP) filter and that of the input laser, while the wavelength controller operates at the states of wavelength-scanning and wavelength-locking modes. Firstly, a dynamic simulation model of tunable FFP filter is established, and the dynamic characteristic of tunable FFP filter modulated by an alternating current (AC) signal is simulated. Then the measuring time at wavelength-scanning mode compared with the theory time is discussed, and this time difference shows the difference between the central wavelength of a tunable FFP filter and that of the input laser. At last, the effects on wavelength-locking precision of time delays, including the time delay of opened-loop circuit, the time constant of the closed-loop circuit and the intrinsic hysteresis of piezoelectric (PZT) element, are analyzed. A wavelength controller of tunable FFP filter is designed and prepared. The experimental results at wavelength-locking mode show that a high locking precision is obtained.

Algorithm for Excitation Optimization of Fabry–Pérot Filters Used in Swept Sources

We investigate the improvement in the nonlinearity of a conventional wavelength swept laser source on the basis of a fiber Fabry-Perot tunable filter using a well-established optimization method, simulated annealing (SA). The signal driving the filter is constructed from many short ramps of different slopes that are interconnected. The values of the slopes are optimized through the SA algorithm to achieve maximum amplitude for the Fourier transformed peaks of the photodetected interferometric signal.

Fiber Fabry-Perot tunable filter based Fourier domain mode locking swept laser source

An all-fiber Fourier domain mode locking (FDML) swept laser source at 1300 nm for swept source optical coherence tomography is reported. The swept laser source is realized with power amplification and laser resonator which includes gain medium, tunable filter and dispersion managed delay line. FDML swept laser can realize high-speed tuning, and phase is stable since its highly stable mode locking operation. The turning range of fiber Fabry-Perot tunable filter (FFP-TF) based FDML swept laser is 130 nm, and the 3 dB bandwidth is 70 nm with an average output power of 11 mW. The tunable speed of FDML laser is 48.12 kHz compared with 8 kHz of short-cavity FFP-TF based swept laser. The axial resolution in OCT imaging of FDML swept laser is 7.8 μm (in tissue), which is improved by 1.9 μm compared with that of short-cavity swept laser.