Dual-wavelength Fiber Ring Laser Research Articles

Temperature measurement with error suppression based on dual-wavelength fiber ring laser sensor

The sensors based on intracavity intensity modulation of fiber ring laser (FRL) have shown excellent performance in sensing resolution and detection limit, but suffer from large measurement errors. The measurement errors mainly result from the power fluctuation of pump source and environmental interference. Therefore, the methods of error suppression are of great significance for FRL sensors. In this paper, a temperature measurement method with error suppression is performed by a dual-wavelength FRL with an intracavity Sagnac interferometer. The sensing principle of single- and dual-wavelength FRL sensors have been analyzed. By the sensing manner of intensity difference of two excited wavelengths, the measurement error has been decreased from 0.443% to 0.066% compared with the single-wavelength configuration. The temperature sensitivity and measurement stability have been further discussed. This method can be extended to similar FRL sensors to suppress measurement errors.

Compact Dynamic In-Fiber Acoustically-Induced Mach-Zehnder Interferometer Based on Phase Mismatch and Its Application in a Tunable and Switchable Dual-Wavelength Laser

A compact and robust in-fiber acoustically-induced Mach-Zehnder interferometer (AI-MZI) was demonstrated based on the phase mismatch in an acoustic wave driving fiber Bragg grating (FBG). The fiber structure of the AI-MZI was easy to fabricate and of a uniform diameter with larger refractive index difference in its arm part, which helped to reduce the length of the arm. In the experiment, the total length of the AI-MZI was less than 7 cm and the response time was about 120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s. The bandpass isolation and resonant center wavelength could be optimized by changing the power and frequency of the radio frequency source, respectively. As its application, a tunable and individually switchable dual-wavelength fiber ring laser was realized and characterized. The proposed structure gains advantages of robustness, easy fabrication, compact size and fast tuning speed accordingly. At the same time, it provides another practical way to use an FBG to introduce phase mismatch into an acousto-optic fiber grating.

Simultaneous Measurement of Temperature and Relative Humidity Using a Dual-Wavelength Erbium-Doped Fiber Ring Laser Sensor

A fiber ring laser sensor setup utilizing fiber Bragg gratings (FBGs) for simultaneous measurement of ambient temperature and relative humidity (RH) is presented. Two FBGs are incorporated as tunable filters for a dual-wavelength laser emission, where one FBG was coated with polyimide (PI) in order to achieve sensitivity to RH changes, while the other bare FBG was used for temperature sensing. An increase in RH would induce a strain on the grating, which results in a variation in the resonance wavelength of the PI-coated FBG. This causes a shift in the laser emission wavelength. Being insensitive to RH changes, the bare FBG was employed to measure temperature. The dual-wavelength fiber ring laser sensor created, and thus allows to determine simultaneous measurement of RH and temperature. The RH sensitivities observed by the PI-coated FBG to RH and temperature are 3.6 pm/%RH and 12.15 pm/°C. The temperature sensitivity of the bare FBG was observed to be 9.6 pm/°C. The main advantage of the proposed setup is an optical signal to noise ratio (OSNR) higher than 55 db 3 dB bandwidth less than 0.02 nm, which points out efficient capabilities for both precise sensing and remote detection applications.

Highly sensitive dual-wavelength fiber ring laser sensor for the low concentration gas detection

A highly sensitive low concentration gas sensor based on dual-wavelength Erbium-doped fiber ring laser (EDFRL) is designed and demonstrated. The dual-wavelength lasing output is introduced by a tunable Fabry-Perot (F-P) filter and a fiber Bragg grating (FBG) due to the mode competition as they both share a same EDF gain medium. One wavelength at 1530.37 nm serving as the sensing element is inserted by a hollow core photonic crystal fiber (HCPCF) gas cell which can bring in much more power change when the cavity loss slightly varies while the other wavelength at 1532.38 nm acting as a reference. Experimental results show that the sensor can achieve a good linear response (R2 = 0.9864) to acetylene concentration variation and a minimum detection limit (MDL) of 10.42 ppmV at 20 s response time, which is the lowest to our best knowledge and improving 6.44 times than that of single-wavelength EDFRL based. Moreover, the absolute detected error induced by the power fluctuation (< 0.1 dB) is less than 1.78% over more than 300 s of observation.

Tunable dual-wavelength ytterbium-doped fiber ring laser based on a Sagnac interferometer

A tunable dual-wavelength ytterbium-doped fiber ring laser based on Sagnac interferometer is proposed and experimentally demonstrated. Due to a broad gain bandwidth of ytterbium-doped fiber, a tuning range of 17.9 nm for single-wavelength lasing output and 8.4 nm for dual-wavelength lasing have been achieved with side-mode suppression ratio higher than 38 dB. In addition, experimental results indicate that the lasing output has favorable wavelength and power stability with the maximum wavelength shift and the peak power fluctuation less than 0.06 nm and 0.94 dB, respectively. Such a wide tunable ytterbium-doped fiber ring laser around the wavelength of 1 µm with simple structure has potential applications in metrology, medical treatments or laser cooling, where the laser wavelength need adjusted accurately.

Convertible Dark Pulse and Bright Pulse Fiber Ring Laser by Adjusting the Polarization

A wavelength tunable, dark pulse, and bright pulse-switched dual-wavelength fiber ring laser is reported. Through adding high nonlinear optical fiber as a nonlinear medium in the fiber ring cavity, the double-wavelength dark-bright pulse pair can be formed. The separation of dark-bright pulse pair can be achieved by polarization beam splitter. The dark pulse and bright pulse with orthogonal polarization correspond to different wavelengths, respectively. Then, via tunable optical filter and polarization controller to filter out the wavelength we need and adjust the polarization, we achieved the interconversion of dark pulse and bright pulse in the same wavelength and the tunableness of wavelengths of dark pulse and bright pulse in our laser.

Single longitudinal mode fiber ring laser

In this work, a dual-wavelength fiber ring laser working on the SLM regime is proposed and experimentally verified. A proof-of-concept device has been tested employing high precision small-sized SLM fiber lasers to complement the feedback produced by a passive FBG. The ring laser output inherits the spectral benefits of its SLM seed lasers but maintaining some power-related properties of ring cavities. These spectral benefits can also be achieved for a single wavelength, simplifying the requirements regarding power equalization between different wavelengths to obtain the SLM regime. The experimental results exhibit a remarkably good wavelength stability and SLM operation of a fiber ring laser with several meters of cavity length, both with single and multi-wavelength configurations.

Fiber ring laser based on MMF-PMFBG-MMF filter for three parameters sensing.

A dual-wavelength fiber ring laser based on multimode fiber-polarization maintaining fiber Bragg grating-multimode fiber (MMF-PMFBG-MMF) filter for simultaneously axial strain, temperature and refractive index (RI) sensing is proposed and experimentally demonstrated. In the ring laser, stable dual-wavelength lasing is determined by the MMF-PMFBG-MMF filter with two polarization states. The fiber birefringence affected by axial strain is far less than the effect of the temperature. Through monitoring the variations of each wavelength shift and output power, the simultaneous measurement for the axial strain, temperature and RI is realized. In our experiment, the proposed fiber laser sensor exhibits an axial strain sensitivity of 1.16 × 10-3nm/με and an RI sensitivity of 81.2dB/RIU. Meanwhile, the temperature sensitivities of two wavelengths are experimentally measured to be 9.74 × 10-3nm/°C and 9.2 × 10-3nm /°C, respectively.

Development of dual-wavelength fiber ring laser and its application to step-height measurement using self-mixing interferometry.

A dual-wavelength erbium-doped fiber (EDF) ring laser was developed and its application to step-height measurement using two-wavelength self-mixing interferometry (SMI) was demonstrated. The fiber laser can emit two different wavelengths without any laser mode competition. It is composed of two EDF laser cavities and employs fiber Bragg gratings to determine which wavelengths are emitted. The step heights can be measured using SMI of the two wavelengths, and the maximum height that can be measured is half the synthetic wavelength of the two wavelengths. A step height of 1mm was constructed using two gauge blocks and then measured using the laser. The measurement was repeated ten times, and the standard deviation of the measurements was 2.4nm.

High resolution refractive index sensing with dual-wavelength fiber laser

A novel refractive index (RI) sensor has been demonstrated based on a simple dual-wavelength fiber ring laser by incorporating two fiber Bragg grating (FBG) filters. The grating filters are made of two FBGs with different cladding thicknesses. By inserting the filters into the fiber ring cavity, a stable dual-wavelength fiber laser can realize at room temperature. The cladding-etched FBG (thinned) acted as the RI sensing elements, while the normal one as temperature reference. As the RI increases, the laser wavelength corresponding to the thinned FBG moves toward longer wavelength, while that corresponding to the normal FBG is unchanged. Then, RI changes can be determined by measuring the separation of the two lasing wavelengths. Moreover, compared with the conventional thinned FBG-based sensors, the fiber laser sensor has a narrow bandwidth, which is beneficial to high precision sensing. The RI measurement resolution of proposed sensor is about $1.44\times 10^{{ {-5}}}$ RIU.

All-fiber dual wavelength femtosecond ring laser by using FBG

In this paper we demonstrate an all-fiber dual wavelength ring laser by using chirp fiber Bragg grating (CFBG). A dual wavelength centered at 1500nm and 1550nm was operated simultaneously in one beam. Pulse widths are measured at 258fs and 253fs, and output power is −19dBm. In order to generate width spectrum for dual wavelength femtosecond laser, we use extra cavity. Fiber Bragg grating is phase matching and can make passive mode locking. This laser is tunable and stable, and the loss is very low due to its all-fiber structure. To the best of our knowledge this is first dual-wavelength femtosecond fiber ring laser that uses CFBG.

A Dual-Wavelength Rational Harmonic Mode-Locked Fiber Ring Laser With Different Repetition Frequencies

A dual-wavelength rational harmonic mode-locked fiber ring laser with different repetition frequencies is theoretically analyzed and experimentally demonstrated. In this scheme, two wavelength channels are inserted into the laser loop to form two resonant cavities. By tuning the length of each channel, required rational harmonic mode-locking conditions can be achieved, and dual-frequency mode-locked signals are simultaneously generated at different wavelengths. In addition, the supermode suppression ratio is further improved due to the mode competition caused by this dual-cavity configuration. In the experimental demonstration, when the fourth-order (or fifth-order) harmonic mode-locked signal is generated in Cavity 1, the first-, second-, and third-order (or fourth-order) harmonic mode-locked signals, respectively, can be generated in Cavity 2 by tuning its length. The measured radio frequency spectra and waveforms show that the signals have high quality. Compared with a conventional rational harmonic mode-locked laser (RHMLL), more than 10 dB supermode suppression ratio improvement is obtained. Since this system can flexibly implement multiwavelength and multifrequency signal generation without adding much cost, it may have wide applications in optical communication system, photonic microwave signal generation, and optical waveform synthesizers.

Three-channel dual-wavelength fiber laser based on a digital micromirror-device processor and photonic crystal fiber

A stable three-channel dual-wavelength fiber ring laser is proposed and experimentally demonstrated. The digital micromirror-device (DMD) processor can select and recirculate any dual waveband from the gain spectrum of the erbium-doped fiber at each channel. The uniform and stable dual-wavelength oscillation is obtained by a highly nonlinear photonic crystal fiber, which causes two degenerate the four-wave-mixing processes. By loading different reproducibility diffraction gratings on the optoelectronic DMD processor, the laser can be operated stably in a three-channel dual-wavelength scheme at room temperature. The power fluctuation of each laser channel is less than -0.02 dB.

Single Polarization, Dual Wavelength Fiber Laser Based on a 3-Stage All Fiber Lyot Filter

We have demonstrated a switchable dual wavelength fiber ring laser with a high degree of polarization output by using an intracavity 3-stage all fiber Lyot filter. The filter is formed by concatenating four 45° tilted fiber gratings separated by polarization maintaining fibers with a length ratio of 1:2:4 (20, 40, and 80 cm), giving a compact integrated configuration with reduced bandwidth. Switchable dual wavelength or single wavelength output at 1533.5 and 1563.3 nm has been achieved. The output lasing is considerably stable owing to the in-phase mode-selecting function of the multistage Lyot filter, and has a very high degree of polarization higher than 99.9%.

A Dual-Wavelength Fiber Ring Laser Incorporating an Injection-Coupled Optoelectronic Oscillator and Its Application to Transverse Load Sensing

A novel configuration for a dual-wavelength fiber ring laser with improved lasing stability realized through the use of an injection-coupled optoelectronic oscillator (OEO) is proposed and demonstrated, and its application to transverse load sensing is studied. The OEO-coupled dual-wavelength laser has two mutually coupled loops: the fiber ring loop and the OEO loop. In the fiber ring loop, a polarization-maintaining phase-shifted fiber Bragg grating is incorporated to generate two optical wavelengths with the wavelength spacing determined by the birefringence of the polarization-maintaining (PM) fiber. In the OEO loop, a microwave signal with its frequency also determined by the birefringence of the PM fiber is generated, which is fed into the fiber ring loop to injection lock the dual wavelengths. Due to the injection locking, a very stable dual-wavelength operation is established. The use of the dual wavelengths for high-resolution and high-speed transverse load sensing is then implemented. The sensitivity of the transverse load sensor is measured as high as +9.7573 and -9.7350 GHz/(N/mm), along the fast and slow axes, respectively. The high frequency purity and stability of the generated microwave signal permits very reliable and high accuracy measurement and the microwave frequency interrogation allows the system to operate at an ultra-high speed.

Tunable and switchable dual-wavelength Er-doped fiber ring laser using ASEs

A tunable and switchable dual-wavelength Er-doped fiber ring laser using simultaneously forward and backward amplified spontaneous emissions is proposed and demonstrated experimentally at room temperature. A polarization-maintaining fiber Sagnac interferometer is used as a comb filter. This laser has eleven different output modes in the range of 1559–1566nm that can be switched flexibly from one to another. Single- and dual-wavelength lasers with a 3-dB linewidth of 0.7nm and optical signal-to-noise ratios of more than 28dB have a small tunable range. Spacing of dual-wavelength laser can be changed from 1.8nm to 0.8nm with the wavelength׳s increment. The laser shows good wavelength and peak power stabilities.

Switchable dual-wavelength fiber ring laser featuring twin-core photonic crystal fiber-based filter

A simple configuration for the generation of a switchable dual-wavelength fiber ring laser is presented. The proposed configuration employs a short twin-core photonic crystal fiber acting as a Mach-Zehnder interferometer at room temperature. A polarization controller is further utilized to enable switchable dualwavelength operation.

A switchable single- and dual-wavelength erbium fiber ring laser in single-longitudinal-mode operation

A simple stable single-longitudinal-mode (SLM) single- and dual-wavelength erbium-doped fiber ring laser using an arrayed waveguide grating as the wavelength filter is proposed and demonstrated. SLM operation is guaranteed by a saturable-absorber-based auto-tracking filter. A 40/60 optical coupler is used to form two imbalanced loss cavities in the fiber laser initially, and single- and dual-wavelength operation can be changed by properly modifying the variable optical attenuator. The side mode suppression ratios of the laser outputs are higher than 60 dB. Through switching the two fiber optical switches, the dual-wavelength spacing is tuned from the narrowest 0.82 nm to the widest 12.05 nm, which offers potential uses in the generation of terahertz (THz) radiation.

A stable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser with superimposed FBG and an in-line two-taper MZI filter

A simple approach to fabricate a stable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser with one superimposed fiber Bragg grating (FBG) is proposed and demonstrated. The superimposed FBG is fabricated by the dual-exposure method for wavelength selection. A home-made in-line two-taper Mach–Zehnder interferometer is incorporated to balance the intra-cavity loss for the wavelengths. The SLM operation is guaranteed by a feedback fiber loop and saturable absorber. A stable dual-wavelength SLM fiber ring laser with a wavelength spacing of approximately 8.53 nm is experimentally realized. The optical signal-to-noise ratio of the laser output is over 50 dB and the linewidth of each wavelength measured by the delayed self-heterodyne method is 9.67 kHz and 9.07 kHz, respectively. The proposed scheme offers the possibility for difference frequency generation of terahertz radiation.

Self-mixing interference in dual-wavelength fiber ring laser using cascaded fiber Bragg gratings

Self-mixing interference in dual-wavelength fiber ring laser (FRL) with serial connection of fiber Bragg gratings (FBGs) is presented. Wavelength division multiplexing and active sensing is achieved by extracting single wavelength and adding feedback to the system. The expression of the optical output power of dual-wavelength fiber ring laser is analyzed when optical feedback is introduced. The gain competition and the intensities alternation among the applied channels are discussed. We apply the developed system for displacement measurements of two moving objects and investigate the influence on output signals under different feedback conditions. The experimental results show that this system has improved efficiency to expand the channels and maintains many advantages of self-mixing interference, validating the feasibility for implementation in a dual-channel displacement sensor at the same time.