Length Of Polarization Maintaining Fiber Research Articles

Cavity-birefringence-based manipulation of long-duration optical pulses in a passively mode-locked fiber laser with large normal dispersion.

Optical pulse manipulation in the large normal dispersion regime through intracavity birefringence management is demonstrated experimentally in an erbium-doped fiber (EDF) laser, for the first time to the best of our knowledge. The EDF laser is passively mode-locked based on a nonlinear amplifying loop mirror (NALM) in a figure-of-eight (f-8) configuration. Different lengths of the same type of polarization-maintaining fiber (PMF) are incorporated into the NALM to vary the net cavity birefringence. For each length of PMF, various polarization states and pump powers were tested and compared to achieve a pulse duration tuning range as large as possible. For comparison, these polarization states and pump powers were also studied by incorporating the PMF into the unidirectional loop of the f-8 cavity. Our results reveal some new features for the management of cavity birefringence that can enable long-duration pulse manipulation in the large normal dispersion regime.

Efficient characterization of phase modulator based on Lyot-Sagnac interferometer

An effective method for evaluating the performance of an electro-optic phase modulator (EOPM) based on the Lyot-Sagnac interferometer is presented and experimentally demonstrated. The Sagnac loop is made up of an EOPM with polarization-maintaining fiber (PMF) pigtails and a length of PMF, which serves as the reference segment. The reference PMF contributes to catalyzing the Vernier effect and magnifying the measurement sensitivity. In order to obtain a better spectrum, numerical investigations are carried out to optimize the parameters in the structure. The experimental results validate the theoretical simulation and display that the envelope of the output spectrum will shift significantly with increasing the modulation voltage. The measurement sensitivity is estimated to be −5.2271 nm/V with linear fit index R2 up to 0.9965 which is amplified by about 87.25 times compared to that of the single Sagnac interferometer. And the measured half-wave voltage and modulation index of the EOPM are around 3.61 V and 0.87 rad/V, respectively. The entire structure is constructed with optical fiber, which is extremely compact and can be extended to plug-and-play scheme for more practical applications.

Abundant dynamics of group velocity locked vector solitons from Er-doped fiber laser based on GO/PVA film

Abstract With the insertion a segment of polarization-maintaining fiber (PMF) inside the cavity, abundant dynamics of group velocity locked vector solitons (GVLVSs) in Er-doped fiber laser have been investigated by using graphene oxide/polyvinyl alcohol (GO/PVA) film as a saturable absorber (SA). The generated Kelly sidebands in emission spectra reveal peak-valley or valley-peak alternation and slightly shift in two orthogonal components, which are the characteristics of GVLVSs. Through proper adjustment of polarization controllers (PCs) inside the EDFLs cavity, versatile vector soliton dynamics such as polarization locked GVLVSs (PL-GVLVSs), polarization rotation GVLVSs (PR-GVLVSs), dual wavelength GVLVSs, bound state GVLVSs, bunch GVLVSs and harmonic mode-locking GVLVSs (HML-GVLVSs) have been observed. The separation between two emission peaks from the dual wavelength GVLVSs was controlled by the Lyot filter and related to the insertion length of PMF inside the cavity. Unlike PL-GVLVSs, the period-doubling phenomenon has been found in two orthogonal components of the PR-GVLVSs. Besides, the bound state GVLVSs were generated showing strongly modulated interference fringes in emission spectrum. For the bunch and HML GVLVSs, the number of solitons inside the cavity increased with the pump power, and it showed the quintuple solitons and the 7th HML-GVLVSs at the highest pump power.

Broadly Tunable Erbium-Doped Fiber Ring Laser Based on Tapered Polarization Maintaining Fiber

A broadly tunable erbium-doped fiber ring laser is proposed and demonstrated based on the tapered polarization maintaining fiber (PMF) Sagnac interferometer, in which the Sagnac and intermodal interferences are superimposed to generate one localized peak over a wide wavelength range in its transmission spectrum. By heating the tapered PMF, the localized peak may be discretely tuned with the temperature at the step, depending on the intermodal interference. Tunability may become continuous when additional stress is exerted longitudinally on the tapered PMF. The tapered PMF Sagnac interferometer is inserted into the laser cavity to achieve broadly and continuously tunable output. Specifically, by optimizing the PMF length and its tapering section to obtain proper channel intervals of the Sagnac and intermodal interference, the lasing wavelength is continuously tuned over 60 nm covering from 1565.1 nm to 1625.2 nm with sidemode suppression ratio higher than 50 dB and power uniformity better than 1 dB. The tuning responses to temperature and axial stress are both linear with sensitivity of −1.1 nm/°C and −29.4 pm/μϵ. Most importantly, the temperature and axial stress affect the Sagnac and intermodal interferences, respectively, which makes it convenient to set the lasing wavelength beforehand during operation.

Polarization Maintaining Fiber Temperature and Stress Gradient Sensitization Sensor Based on Semiconductor-Metal-Polymer Three-Layer Film Coating.

Increasing sensitivity, measuring points, and stability have always been the pursuit of sensors. ZnSe9:CO1 and Ag composite nano films were coated on polarization maintaining fiber (PMF). Then, the coated PMF was nested in capillary and hose which was encapsulated with polydimethylsiloxane (PDMS) and epoxy resin. The integrated capillary sensor and thermoplastic hose sensor were prepared. The gradient sensitization of various measurement parameters such as temperature, stress, and micro bending is realized. The temperature sensitivity is 1.49 nm/°C, the micro bending sensitivity is 1.72 nm/102 g, and the stress sensitivity is 6.27 nm/mε. The sensors maintain good linearity and instantaneous response while having high sensitivity. By adjusting the length of PMF, the number of troughs is increased in the same band range, and different troughs have different sensitivities, which solves the inherent problem of cross sensitivity and realizes multiparameter measurement. Capillary sensors are used for remote safe real-time monitoring of mechanical overheating, and hose sensors are used for real-time monitoring of bridge load and human joint bending. This work is of great significance to the extension of the application range of optical fiber sensor.

Multiwavelength Mode-Locked Fiber Laser Based on an All Fiber Lyot Filter

We report the experimental demonstration of a multiwavelength passively mode-locked fiber laser based on an all-fiber Lyot filter (AFLF). The Lyot filter is composed of two 45°-titled fiber gratings (45°-TFGs) and a length of polarization-maintaining fiber (PMF). The free spectrum range (FSR) and the 3-dB bandwidth of the Lyot filter are 7.5 nm and 3.6 nm, respectively. The laser generates 5-wavelength mode-locked pulses, which have 7.49 nm channel spacing, 192.6 kHz fundamental repetition rate and over 50 dB signal-to-noise ratio (SNR). As increasing the pump power from 178 mW to 407 mW, the pulse width and the average output power increased linearly from 10 ns to 23 ns and from $256\mu \text{W}$ to $621\mu \text{W}$ , respectively. In addition, the fluctuations of center wavelength and laser power are < 0.5 nm and < 0.5 dB respectively within a duration of 1 hour.

PM fiber based sensing tapes with automated 45° birefringence axis alignment for distributed force/pressure sensing.

Polarization maintaining (PM) fibers can be used for distributed force/pressure sensing in which the birefringence axis of the PM fiber should preferably be oriented 45° from the direction of the force/pressure for the maximum sensitivity. However, it is a challenge to achieve such 45° axis orientation for a long length of PM fiber in practice. In this paper, we report the development of what we believe the first equipment and process for making PM fiber based sensing tapes, capable of automatically adjusting the fiber axis orientation 45° with respect to the tape surface. In particular, we develop a machine vision system with the ability of continuously determining fiber axis orientation in real time as the fiber passes by and feeding back the orientation information to a fiber rotation apparatus to automatically adjust its orientation before fixing the fiber on a transparent PET tape with UV epoxy. We show the results of a successfully fabricated 70-m-long PM fiber sensing tape achieving an axis orientation accuracy of 45 ± 3° throughout the whole length of the tape, which is further validated with a distributed polarization crosstalk analyzer (DPXA). Finally, we demonstrate distributed transversal load sensing with 14 force applying weights randomly distributed along the sensing tape using the DPXA, with a polarization crosstalk measurement uniformity of 0.62 dB (standard deviation) using the same applied weight of 100 grams. The same sensing tape can also be used for pressure sensing with properly designed fixtures.

RF Interferometry Measurement of Beat Length in Polarization-Maintaining Fiber

A microwave photonics interferometric (MWPI) method for measuring the beat length in high birefringence polarization-maintaining fiber (PMF) is proposed. The approach is based on the radio frequency (RF) interference between the two polarization modes propagating on the polarization axis in the PMF. The period of the RF interference spectral is determined by the optical path difference of the two polarization modes. According to the principle that the phase difference in one free spectral range (FSR) of the interference spectral is 360 degree, the beat length of the PMF can be calculated by recording the RF interference spectral. Two different lengths of PMF have been tested and the measurement results show that the measurement precision is 0.02 mm. The wavelength dependent beat length has also been measured. Furthermore, the measurement precision of this method and the main source of errors are investigated in detail.

A Sensing Interrogation System for Sagnac Interferometer With Polarization Maintaining Fiber Utilizing Microwave Photonic Filtering Technique

In this paper, a sensing interrogation scheme for Sagnac interferometer (SI) with polarization maintaining fiber (PMF) by using microwave photonic filtering technique has been theoretically analyzed and experimentally demonstrated. In our experiment, the SI acts as the sensing element as well as a spectrum slicer in the single-passband microwave photonic filter (MPF). The central frequency of the MPF’s passband moves to lower frequency when the temperature is increased. Hence, the measurands can be demodulated by monitoring the central frequency of the MPF’s passband in Radio Frequency (RF) domain. Comparing with the interrogation by tracking dip wavelength of the interference patterns in the optical domain and using the product of birefringence and the length of PMF in the SI structure for interrogation, the proposed interrogation system converts the wavelength variations of the interferometer patterns in optical domain to the frequency changes in electronic domain directly by utilizing opto-electronic devices, and thus has an unlimited measurement range, less limitations by resolution limitation of measuring instruments and less cross-sensitivity problems.

Performance improvement of a resonant fiber optic gyroscope with a hybrid photonic crystal fiber ring resonator.

The photonic crystal fiber (PCF) with better thermal stability and polarization-maintaining performance is applied to the resonant fiber optic gyroscope (RFOG). A hybrid fiber ring resonator is fabricated using the conventional polarization-maintaining fiber (PMF) and PCF with close mode field diameters (MFDs) to reduce MFD-mismatch-induced splicing loss. Furthermore, the temperature-dependent birefringence coefficients of the PMF and the PCF are measured to differ almost four times in absolute value and be opposite in sign. The polarization stability of the hybrid PCF-PMF ring resonator is improved by a factor of 7 compared with the PMF ring resonator with the same length of PMF. The RFOG equipped with this hybrid PCF-PMF ring resonator achieves a bias stability of 1.67°/h.

Wavelength-Spacing Adjustable Dual-Wavelength Dissipative Soliton Resonance Thulium-Doped Fiber Laser

A dual-wavelength dissipative soliton resonance thulium-doped fiber laser based on nonlinear optical loop mirror (NOLM) has been demonstrated. In this laser, mode-locking is achieved based on equivalent saturation absorption of the NOLM, while the dual-wavelength operation is attributed to the online birefringent fiber filter composed of a polarizer and a section of polarization-maintaining fiber (PMF). The wavelength spacing of dual-wavelength spectrum can be adjusted through changing the PMF length, and the central wavelengths can be tuned through rotating the polarization controllers. It is also found that at the two central wavelengths of the dual-wavelength pulse, switchable single wavelength mode-locked pulse can be generated. In addition, noise-like pulses with broadband spectra can be generated, when two kinds of mode-locking mechanisms conflict. The dual-wavelength dissipative soliton resonance thulium-doped fiber laser has important potential applications in the laser detection, sensing and other fields. Its rich dynamics also provides a system platform for basic research on laser physics.

Investigation of Multiwavelength Laser Performance based on Temperature Variation of PMF and different SOAs

We demonstrated a multiwavelength performance based on bidirectional Lyot filter at different temperature of polarization maintaining fiber (PMF) and semiconductor optical amplifiers (SOAs). The multiwavelength fiber laser (MWFL) based on bidirectional Lyot filter is not investigated thoroughly on its channel spacing tunability due to birefringence change. A channel spacing of this MWFL is tunable due to birefringence change of the PMF. The birefringence value of is changed by heating the PMF, that leads to narrower channel spacing. From the experimental data, the temperature coefficient based on PMF length of 53.2 m and 10.6 m is 0.49 ×10 -3 nm/°C and 1.35 ×10 -3 nm/°C, respectively, thus shorter PMF is more sensitive to temperature. We also investigated the multiwavelength performance at different SOAs. When the SOA from Qphotonics is changed to the SOA from Alphion, the extinction ratio is reduced from 15 dB to 8 dB. In terms of flatness value, the Qhotonics’s SOA has a flatter multiwavelength spectrum with only 1 dB of peak power difference from 1538 nm until 1541 nm as compared to 2.5 dB when using Alphion’s SOA.

All-polarization-maintaining dual-wavelength mode-locked fiber laser based on Sagnac loop filter.

We demonstrate an all polarization-maintaining (PM) fiber based dual-wavelength mode-locked Er-fiber laser. A nonlinear amplifying loop mirror (NALM) with an intracavity nonreciprocal phase shifter is used for self-started mode-locking. A short segment of PM fiber is angle-spliced to the NALM, functioning as a PM Sagnac loop filter, thus enabling dual-wavelength mode-locking. The wavelength separation is solely determined by the angle-spliced PM fiber length. Stable dual-wavelength mode-locking operation is switchable between 1570/1581 nm and 1581/1594 nm. The two-color pulse trains oscillating in the same cavity have an inherent offset repetition rate of ~1 kHz owing to cavity dispersion, allowing future high precision dual-comb applications with a simple and robust configuration.

Precise measurement of polarization maintaining fiber length based on sawtooth wave phase modulation

A new method of sawtooth wave phase modulation is proposed to improve the measurement accuracy of polarization maintaining fiber length. We convert the measurement of polarization maintaining fiber length into the measurement of time delay. The optical signal is phase-modulated by the sawtooth wave modulation signal with modulation frequency of 2fp. The demodulated error signal is related to the frequency offset of the sawtooth wave and fp. The frequency of the sawtooth wave is adjusted to make the value of the error signal be zero, so that we can obtain the value of fp and calculate the delay time. Using this method, a set of polarization maintaining fiber length measuring system is designed and the fibers of 350 m, 570 m, 600 m, 920 m and 950 m are measured. The measurement accuracy of optical fiber length is about 8 ppm, which is lower than 10 ppm. Compared with other methods of measuring length of the polarization maintaining fiber, the structure and principle of this system are simple, and the experimental results show that this method has high precision and is easy to realize.

Optical fiber hydrogen sensor with single Sagnac interferometer loop based on vernier effect

Abstract An optical fiber hydrogen sensor with single Sagnac interferometer loop based on vernier effect has been proposed. The vernier effect is achieved by angle shift splicing two polarization maintaining fibers (PMFs) in single Sagnac interferometer loop. The hydrogen sensing length of PMF is 2 cm which is coated with Pt-loaded WO3/SiO2 powder. When the Pt/WO3 film is exposed to hydrogen, the redox reaction releases the temperature on the PMF, which induces the wavelength shift of the optical fiber sensor. The temperature sensitivity is −2.44 nm/°C and the hydrogen sensitivity is −14.61 nm/% within the range of 0%–0.8% (vol%), which is 1.85 times higher than the Sagnac sensor without vernier effect. The hydrogen sensitivity is related to the length of the PMF coated with Pt-loaded WO3/SiO2. The sensor is easy to fabricate, selective and high sensitivity.

Measurement error analysis for polarization extinction ratio of multifunctional integrated optic chips.

Measurement error for the polarization extinction ratio (PER) of a multifunctional integrated optic chip (MFIOC) utilizing white light interferometry was analyzed. Three influence factors derived from the all-fiber device (or optical circuit) under test were demonstrated to be the main error sources, including: 1)the axis-alignment angle (AA) of the connection point between the extended polarization-maintaining fiber (PMF) and the chip PMF pigtail; 2)the oriented angle (OA) of the linear polarizer; and 3)the birefringence dispersion of PMF and the MFIOC chip. Theoretical calculations and experimental results indicated that by controlling the AA range within 0°±5°, the OA range within 45°±2° and combining with dispersion compensation process, the maximal PER measurement error can be limited to under 1.4dB, with the 3σ uncertainty of 0.3dB. The variations of birefringence dispersion effect versus PMF length were also discussed to further confirm the validity of dispersion compensation. A MFIOC with the PER of ∼50 dB was experimentally tested, and the total measurement error was calculated to be ∼0.7 dB, which proved the effectiveness of the proposed error reduction methods. We believe that these methods are able to facilitate high-accuracy PER measurement.

Simultaneous measurement of RI and temperature based on the combination of Sagnac loop mirror and balloon-like interferometer

A novel composite interference structure constructed with the combination of Sagnac loop mirror and balloon-like interferometer for simultaneous measurement of refractive index (RI) and temperature is proposed and experimentally demonstrated. A polarization maintaining fiber (PMF) is embedded into the Sagnac loop structure to form a Sagnac loop interferometer, which is highly sensitive to external temperature variations. The balloon-like structure is built with a bend single mode fiber (SMF) to form a modal interferometer, which is sensitive to both external RI and temperature variations. As the two sensing structures are based different interference principles, the two interference spectra do not interfere with each other. By optimizing the bending diameter of the balloon-like interferometer and the length of PMF in the Sagnac loop mirror, separate different resonance wavelengths can be well formed. Hence, the simultaneous measurement of RI and temperature can be realized by monitoring the shift of different resonance wavelengths. Experimental results show that the optimal sensitivities of the RI and temperature can reach up to 218.56nm/RIU and 1.7nm/°C, respectively.

Voltage demodulation and vibration monitoring based on a polarization maintaining fiber loop mirror

Wavelength demodulation for a polarization maintaining fiber loop mirror sensor using an optical spectrum analyzer is not only expensive but also not suitable for vibration monitoring. In this work, we demonstrate a voltage-based polarization maintaining fiber loop mirror sensor demodulation principle. In our experiments, we observed that the light intensity from the output interference spectrum at a certain wavelength increased with increasing strain. To remove the expensive optical spectrum analyzer, we converted the light intensity signals into voltage signals using a photo-detector. The obtained demodulation linear sensitivity was 1.19 mV/µε. Compared with fiber Bragg grating sensors, the sensitivity in our system was improved greatly. Furthermore, the polarization maintaining fiber loop mirror was applied to vibration monitoring. A vibration exciter was attached underneath the specimen for use as a vibration source. A laser displacement sensor was used for comparison. The experimental results show that the polarization maintaining fiber loop mirror performs better at high frequencies than the laser displacement sensor, and that signals below 20 Hz measured by the polarization maintaining fiber loop mirror were distorted as a result of exceeding the measurement range. In addition, we have proposed further decreasing the distortion by reducing the polarization maintaining fiber length and fabricating a polarization maintaining fiber loop mirror sensor with a different dynamic measurement range by adjusting the polarization maintaining fiber length.

A wavelength-tunable fiber laser using a novel filter based on a compound interference effect

A wavelength-tunable erbium-doped fiber laser is proposed and experimentally demonstrated by using a novel filter which is formed from a 2 × 2 3 dB multimode coupler incorporating a segment of polarization maintaining fiber (PMF). By using the filter with 2.1 m lengths of PMF in a ring fiber laser, a stable single wavelength lasing is obtained experimentally. Its 3 dB bandwidth is less than 0.0147 nm and the side mode suppression ratio (SMSR) is higher than 58.91 dB. Experimental results demonstrate that mode competition can be effectively suppressed and the SMSR can be improved due to the compound interference effect aroused by the novel filter. Meanwhile the stability of the output lasing can be enhanced. By appropriately adjusting the polarization controllers (PCs), the output lasing wavelength can be tuned from 1563.51 to 1568.21 nm. This fiber laser has the advantage of a simple structure and stable operation at room temperature.

The Response of Polarization Maintaining Fibers upon Temperature Field Disturbance

The paper deals with the response of polarization maintaining (PM) fibers upon the variation of the temperature field, on condition both polarization axes are excited. Proper use can be applied in the area of optical fiber thermal field disturbance sensor. For a description of polarization properties the coherent Jones and Muller matrices were used. The Poincare sphere was applied to depict the development of the output of the polarization state of PM fibers for wavelengths 633 nm, 1310 nm and 1550 nm were arranged in a proposed sensor setup and were studied in the laboratory. A wide file of results containing dependencies of phase shift variations upon different configurations of measured PM fiber was obtained. The thermal field disturbance of the PM fiber was applied by an object with defined proportions and a defined range of temperatures. Dependencies of phase shift upon the object´s temperature, its distance from the fiber and exposed length of PM fiber were measured.