Fiber Loop Mirror Research Articles

Enhanced multiwavelength generation in Brillouin fiber laser with pump noise suppression technique

A new multiwavelength Brillouin fiber laser (BFL) that provides a large number of Stokes lines with improved optical signal-to-noise ratio has been proposed and demonstrated. The BFL cavity is only formed by a nonlinear fiber loop mirror (NOLM) with 500 m long highly nonlinear fiber (HNLF). The BFL with improved performance is based on the suppression of the Brillouin pump noise floor utilizing a narrow tunable bandpass filter. The generation of Stokes lines covering up to a 33.67 nm wavelength range is achieved by setting the Brillouin pump signal within the HNLF’s zero dispersion wavelength and with power of 250 mW. This is owing to the combination of the stimulated Brillouin scattering and four-wave mixing effect in the NOLM structure.

Switchable and multi-wavelength linear fiber laser based on Fabry–Perot and Mach–Zehnder interferometers

In this manuscript, switchable and multi-wavelength erbium-doped fiber laser arrangement, based on Fabry–Perot (FPI) and Mach–Zehnder (MZI) interferometers is presented. Here, the FPI is composed by two air-microcavities set into the tip of conventional single mode fiber, this one is used as a partially reflecting mirror and lasing modes generator. And the MZI fabricated by splicing a segment of photonic crystal fiber (PCF) between a single-mode fiber section, was set into an optical fiber loop mirror that acts as full-reflecting and wavelength selective filter. Both interferometers, promotes a cavity oscillation into the fiber laser configuration, besides by curvature applied over the MZI, the fiber laser generates: single, double, triple and quadruple laser emissions with a signal to noise ratio (SNR) of 30dB. These laser emissions can be switching between them from 1525nm to 1534nm by adjusting the curvature radius over the MZI. This laser fiber offers a wavelength and power stability at room temperature, compactness and low implementation cost. Moreover the linear laser proposed can be used in several fields such as spectroscopy, telecommunications and fiber optic sensing systems.

Simultaneous measurement of torsion, strain and temperature using a side-leakage photonic crystal fiber loop mirror

A fiber optic sensor for simultaneous measurement of multi-parameter is proposed. The fiber sensor is realized by a fiber loop mirror based on a piece of homemade side-leakage photonic crystal fiber. Affected by the group birefringence of the side-leakage photonic crystal fiber, which induced by the elliptical germanium-doped core and the linear side-leakage defect, the fiber loop mirror has different wavelength responses to torsion, strain and temperature at different interference fringe valleys. By monitoring the wavelength shifts of three selected valleys in the transmission spectrum, simultaneous measurement of torsion, strain and temperature is achieved. The maximal sensitivities to torsion, strain and temperature are 151.14pm/°, 1pm/με and 71pm/°C, respectively.

High-birefringence microfiber Sagnac interferometer based humidity sensor

A relative humidity (RH) sensor based on a microfiber Sagnac loop interferometer is proposed and demonstrated. The sensor is formed by fusion splicing a high-birefringence elliptical microfiber into a fiber loop mirror without any humidity sensitive coating to the structure. Interferometric fringe with visibility of around 30dB can be achieved in the transmission spectrum due to phase difference between the two polarization modes travelling through the microfiber region. The proposed structure presents high sensitivity up to ∼201.25pm/%RH, within an RH range from 30%RH to 90%RH. Moreover, we realize the sensitivity enhancement (up to ∼422.2pm/%RH) by inserting a reference Panda fiber into the fiber loop. The sensitivity is two to five times of magnitude higher than the counterparts in the literature. The measured response time is around 60ms, which is much better than the previously-reported devices.

Torsion Sensor Based on Polarization-Maintaining Photonic Crystal Fiber Loop Mirror with an Output Port Probe

Torsion Sensor Based on Polarization-Maintaining Photonic Crystal Fiber Loop Mirror with an Output Port Probe

A Fibre Bragg Grating Interrogation Technique Based on High Birefringence Fibre Loop Mirror and WDM

In this paper, a fibre Bragg grating (FBG) interrogation technique based on high Birefringence fibre loop mirror (Hi-Bi FLM) and wavelength division multiplexer (WDM) is proposed and demonstrated. The approximate linear edge of the transmittance of the Hi-Bi FLM, which is a sinusoidal function of wavelength, is used to interrogate the sensing FBGs and WDMs is used to realize wavelength discrimination .Suitable for both static and dynamic sensing, this interrogation method has the advantages of all fibre design and high stability.

The rule of bias current of semiconductor laser in chaos communications

The dynamics of chaotic behavior of semiconductor laser diode with optical feedback from single mode fiber loop mirror has been experimentally studied. In the represented configuration the feedback strength was constant while the control parameter with laser injection current was variable, we found a wide range of optical intensity oscillation dynamics such as limit cycles, quasiperiodic and chaos oscillations. These dynamics were analyzed by time series and their extracted FFT power spectrums, phase diagrams (attractors), inter-spike intervals (ISI), these measurements enhanced by bifurcation diagram which clarified the chaotic regimes. Efficient bandwidth of chaotic signals has been calculated and observed to be increased with injection current. The complexity of chaotic system was measured by Shannon’s entropy function.

Temperature and refractive index sensor using a high-birefringence fiber loop mirror and single mode-coreless-single mode fiber structure

ABSTRACTA novel fiber optic sensor for the simultaneous measurement of refractive index and temperature is reported. The sensor consists of a high-birefringence fiber loop mirror and a section of single mode-coreless-single mode fiber structure. The single mode-coreless-single mode fiber structure served as a refractometer while the high-birefringence fiber loop mirror was used to measure temperature. The multimode interference valley of the single mode-coreless-single mode fiber structure was sensitive to the surrounding refractive index of liquids (96.42 nm/refractive index unit) and had almost no response to temperature fluctuations. The high-birefringence fiber loop mirror was highly sensitive to temperature (1.98 nm/°C) but was insensitive to changes in refractive index. The theoretical and experimental results demonstrated simultaneous measurement of temperature and refractive index. The optimum resolution was 2.07 × 10−4 refractive index units and 0.01°C.

High resolution polarization-independent high-birefringence fiber loop mirror sensor.

In this work, two all polarization-maintaining (PM) high-birefringence (Hi-Bi) fiber loop mirrors (FLM) which are immune to external polarization perturbations are validated both theoretically and experimentally. Simplified and stable versions of classical FLMs were attained using a PM-coupler and by fusing the different Hi-Bi fiber sections with an adequate rotation angle between them. Since the polarization states are fixed along the whole fiber loop, no polarization controllers are needed. This simplifies the operation and increases the stability of the systems, which were also validated as ultra-high resolution sensors, experimentally obtaining a resolution of 6.2∙10-4 °C without averaging.

Linearly polarized random fiber laser with ultimate efficiency.

Linearly polarized pumping of a random fiber laser made of a 500-m PM fiber with PM fiber-loop mirror at one fiber end results in generation of linearly polarized radiation at 1.11 μm with the polarization extinction ratio as high as 25 dB at the output power of up to 9.4 W. The absolute optical efficiency of pump-to-Stokes wave conversion reaches 87%, which is close to the quantum limit and sets a record for Raman fiber lasers with random distributed feedback and with a linear cavity as well. Herewith, the output linewidth at high powers tends to saturation at a level of 1.8 nm.

Low-Complexity TOAD-Based All-Optical Sampling Gate With Ultralow Switching Energy and High Linearity

We present experimentally a low-complexity ultralow switching energy and high-linearity all-optical sampling gate based on a terahertz optical asymmetric demultiplexer, constructed by placing a polarization-insensitive multiple-quantum-well semiconductor optical amplifier (PI-MQW-SOA) asymmetrically within a fiber loop mirror. Using a picosecond pulse train as the trigger clock, we analyze, in detail, the influence of the sampling pulse power and the offset of the PI-MQW-SOA from the loop midpoint on the shape, width, and amplitude of the sampling window, respectively. Furthermore, the switching energy and linearity of this sampling gate under different widths of sampling windows are specifically investigated. Results demonstrate that our sampling gate possesses a switching energy as low as 25 fJ and a high linearity above 0.99.

Stable and switchable single-longitudinal-mode dual-wavelength erbium-doped fiber laser based on a fiber ring filter

A switchable dual-wavelength and single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) based on a fiber ring filter (FRF) is proposed and demonstrated through a detailed experimental verification. In the design, the simple linear-cavity EDFL is composed of one 976-nm laser diode (LD), one fiber loop mirror (FLM), two cascaded fiber Bragg gratings (FBGs), and an EDF. To improve the laser stability, the FRF is spliced into a specially designed EDFL, which is fabricated from an EDF and two couplers with splitting ratios of 50:50 and 30:70, respectively. Both single- and dual-wavelength lasers can be realized by adjusting the variable attenuator (VA) between the two FBGs. In the proposed EDFL, the 1540-nm laser and the 1545-nm laser, respectively, incur laser-frequency shifts at room temperature of less than 3 pm and 2 pm over a period of 60min. The single-wavelength 1540- and 1545-nm lasers show single-longitudinal-mode (SLM) operation within the frequency range of 0–500MHz, as measured by the delayed self-heterodyne method using a 50-km single-mode fiber, and the 3-dB linewidths of the output of two lasers are about 2.8kHz and 2.5kHz, respectively.

Novel torsion sensor using a polarization maintaining photonic crystal fiber loop mirror

ABSTRACTA novel torsion sensor employing a short length of polarization maintaining photonic crystal fiber was inserted into the fiber loop mirror with an output probe. The sensing scheme was described theoretically by a Jones matrix and experimentally demonstrated. The results showed that the sensitivity of the intensity loss in response to the twist angle may be up to 0.0394 dB/° and a resolution of 0.025° was achieved. This torsion sensor is attractive due to its compact size, insensitivity to temperature, and suitability for longer distance transmission than conventional sensors.

A switchable femtosecond and picosecond soliton fiber laser mode-locked by carbon nanotubes

We propose a switchable dual-scale nanotube-mode-locking fiber laser based on a fiber loop mirror and fiber Bragg grating. The loop mirror not only works as a broadband reflector, but also a birefringence-induced filter. By adjusting the polarization controller in the loop, the operation wavelength can be switched between 1530 and 1560 nm. The femtosecond soliton at 1560 nm has a bandwidth of 5.5 nm and pulse duration of 680 fs, while the picosecond soliton is centered at 1529.5 nm with the bandwidth of 0.11 nm and pulse duration of 23.3 ps. The dual-scale solitons display more than 30 times a difference of pulse width, as well as distinct spectral bandwidth, repetition rate, and pulse energy. Our study provides the flexibly switchable ultrashort pulse sources at femtosecond and picosecond scales, which are suitable for practical applications.

Multiwavelength Linear-Cavity SOA-Based Laser Array Design for Multiparameter and Long-Haul Sensing

A multiwavelength linear-cavity laser array for long-distance sensing is designed and experimentally demonstrated. It is a semiconductor optical amplifier (SOA) integrating a $1\times N$ optical switch, formed by a $2\times 2$ fiber loop mirror and fiber Bragg grating (FBG) as cavity ends. We investigate the laser system output characteristics and evaluate the sensor performance for different sensing distances incorporating the FBGs. The results show that this SOA-based laser sensor array possesses a dynamic sensing distance of up to 35 km at a 350-mA injection current. Stress/strain detection and reliable linear-cavity fiber laser sensing operation were successfully achieved.

Temperature insensitive refractive index sensor based on a combination interference structure

A sensing head consisting of fiber loop mirror inscribed with a highly birefringence photonic crystal fiber (HiBi-PCF) was proposed and experimentally demonstrated. The HiBi-PCF was completely collapsed near the splicing points, thus the cladding mode in the HiBi-PCF would be excited, which was sensitive to the refractive index (RI) of surrounding medium. Owing to the low thermo-optic and thermo-expansion coefficient of the HiBi-PCF, the sensing head in our design was temperature insensitive. High sensitivity of 306.6±0.2nm/RIU (refractive index unit) and a resolution of 6.5×10−5RIU have been achieved for the proposed liquid refractive index sensor.

Fiber optic displacement sensor based on a double-reflecting OTDR technique

In this work, it is proposed a technique to implement an intensity sensor based on the generation of a double-reflecting (ghost) signal in optical time domain reflectometry (OTDR). The intensity sensor is supported by a singlemode-multimode-singlemode (SMS) fiber structure combined with a fiber loop mirror (FLM). The results of the displacement sensitivity show linear behavior for both the first-reflecting and double-reflecting signals with linear slopes of approximately −4.5 dB/mm and −6 dB/mm, respectively. The displacement resolution achieved is ∼0.28 mm. It is also found that the system is able to read periodic displacement variations in the millisecond time scale applied to the sensing head. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1312–1315, 2015

Multiwavelength Raman fiber laser based on polarization maintaining fiber loop mirror and random distributed feedback

We experimentally demonstrate a configuration to realize multiwavelength generation in a Raman fiber laser structure. The system includes a fiber loop mirror (FLM) containing a piece of polarization maintaining (PM) single mode fiber, and a 1 km-long passive fiber which is core pumped by a 1120 nm pump laser providing Raman amplification and random distributed feedback via Rayleigh scattering. Up to 1 W multiwavelength laser output is realized due to interference between modes supported by the FLM. As a consequence, a 35 nm bandwidth multiwavelength spectrum from 1155 to 1190 nm with ~0.75 nm spacing (OSNR ~10 dB) is obtained.

Direct generation of 2 W average-power and 232 nJ picosecond pulses from an ultra-simple Yb-doped double-clad fiber laser.

We report the generation of 2.06W average-power and 232nJ picosecond mode-locked pulses directly from an ultra-simple Yb-doped fiber laser. A section of Yb-doped double-clad fiber pumped by a 976nm laser diode provides the large gain, and the linear cavity is simply formed by a 1064nm highly reflective fiber Bragg grating and a fiber loop mirror (FLM) using a 5/95 optical coupler. The asymmetric FLM not only acts as the output mirror for providing ∼20% optical feedback, but also equivalently behaves as a nonlinear optical loop mirror (NOLM) to initiate the mode-locking operation in this cavity. Stable mode-locking is therefore achieved over a pump power of 3.76W. The mode-locked pulses show the dissipative soliton resonance (DSR), which has the pulse duration of 695ps to ∼1 ns, and the almost unchanged peak power of ∼200 W as increasing the pump power. In particular, this laser can emit 232nJ high-energy DSR pulses with an average output power of >2 W. This is, to the best of our knowledge, the first demonstration of such an ultra-simple, mode-locked fiber laser that enables watt-level, high energy, picosecond DSR pulses.

Temperature insensitive curvature sensor based on a combination interference structure and an intensity demodulation method

ABSTRACTIn this article, a sensing head consisting of fiber loop mirror inscribed with a highly Birefringence photonic crystal fiber (HiBi‐PCF) was proposed and experimentally demonstrated. The fully collapsed air holes of the PCF at the spice regions allow the coupling of PCF core and cladding modes that makes a Mach–Zehnder interferometer. The couple efficiency of the core mode to the cladding mode will be decreased as the curvature on the HiBi‐PCF part is increased. The curvature variation on the HiBi‐PCF part can be obtained by detecting the fringe visibility of the interference patterns. Experimental results show that the curvature sensor with maximal sensitivity of 10.171 dB/m−1 within a measurement range of 0–0.48 m−1 is obtained. Owing to the low thermo‐optic and thermo‐expansion coefficient of the HiBi‐PCF and with the using of intensity demodulation method, the proposed sensor can overcome the temperature and curvature cross‐sensitivity effects. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:806–809, 2015