Section Of Polarization-maintaining Fiber Research Articles

Pure-quartic soliton in a birefringence-managed fiber laser

Pure-quartic soliton (PQS) fiber lasers with a great variety of operating regimes have aroused considerable interest in high-energy ultrashort pulses and novel soliton patterns. Here, we numerically investigate the generation and dynamic properties of birefringence-managed pure-quartic soliton (BMPQS) in a positive fourth-order dispersion (FOD) fiber laser consisting of single-mode fibers and a section of polarization-maintaining fiber. The formation mechanism of the chirp-free BMPQS is dominated by the phase-matching effect, which arises from the co-actions of the birefringence, positive FOD, and nonlinear effects. It is observed that a higher FOD coefficient leads to energy transfer between the spectral sidebands inside the BMPQS. Moreover, the evolution of the BMPQS with the increase of the pump power confirms the phase-matching theory. Finally, the BMPQS molecule can be obtained with further increasing the pump power. This work offers a new avenue to create chirp-free pulses in positive FOD fiber lasers and enriches the sub-families of PQSs.

Sagnac mirror loop with two polarization maintaining fibers for twist measurement by tracking adjacent dips with tunable measurement range

The transmission characteristics of Sagnac fiber loop interferometer which consists two sections of polarization-maintaining fiber (PMF) spliced at different offset angles were analyzed. Based on the simulation results, an application for twist measurement where PMFs were spliced at different offset angles was designed. When the lengths of two PMFs are equal, a clear spectrum can be obtained for twist or torsion sensing. A phenomenon that the dips would split or merge with twist angle alteration can be used for sensing. Measurement range and sensitivity can be adjusted by changing the PMFs offset angle. The sensitivity was improved by calculating the distance between two adjacent dips, being 0.73 nm/° or 8.37 nm/(rad/m) when the offset angle was 75°.

Highly sensitive and stable fiber-laser pressure-sensing system based on an unequal-arm Mach-Zehnder cascaded with a Sagnac structure

We propose, analyze, and experimentally demonstrate a highly sensitive and stable fiber-laser pressure-sensing system based on an unequal-arm Mach-Zehnder interferometer (MZI) merged with a Sagnac interferometer (SI). The unequal-arm MZI structure consists essentially of two single-mode fibers of different lengths, and the SI structure uses a section of polarization-maintaining fiber, which acts as a sensing head. Moreover, in the proposed sensing system, the MZI and SI structures both act as a cascade filter. Given the asymmetric MZI and cascade filter structure laser mode hopping is effectively suppressed, so minor variations in environmental parameters cause a stable shift of the interference spectrum. The experimental results show that the proposed system can be used to make accurate pressure measurements. The −3 dB linewidth of the reflection interference peak produced by the proposed system is less than 0.02 nm, and the signal-to-noise ratio (SNR) can exceed 45 dB. With a 1-m-long sensor head, the proposed system provides a pressure sensitivity of 29.275 nm/MPa, and the interference spectrum of the sensing system fluctuates less than ±0.02 nm over 1 h. The proposed sensing system thus offers the attractive characteristics of good sensing linearity and stability, high SNR, and high sensitivity.

Selective transverse mode emission from all polarization-maintaining fiber lasers

We demonstrated all polarization-maintaining fiber (PMF) lasers which could offer selective transverse mode emission by polarization rotation technique (PRT). Offset and cross splicing between PMF sections was used to generate higher order mode and to yield a birefringence induced mode filter. PRT was used to select the output beam profile. Both linear cavity and ring cavity were explored. Experimentally, 360° rotating LP11 mode and OAM vortex beam with ±1 topological charge has been realized from an all PMF linear cavity laser and a ring cavity laser respectively.

Nonlinear Polarization Evolution Mode-Locked YDFL Based on All-PM Fiber Cavity

Polarization-maintaining (PM) all-fiber cavity is always essential to realize stable ultrafast-pulse generation. With the help of five sections of PM fibers with independently specific splicing angles, we successfully obtain a femtosecond pulse output from a PM Ytterbium-doped fiber laser (YDFL) mode-locked by the nonlinear polarization evolution (NPE) technique. Using a hybrid component, the PM all-fiber cavity can be greatly simplified. Ultrafast-pulses with 24.5-MHz repetition rate, 20-nm spectral bandwidth, and 260-fs pulse duration after external compression can be steadily generated. In comparison with the non-PM fiber cavity, the proposed YDFL has excellent long-term environmental stability, making it ideal for various practical applications.

A fiber optic temperature sensor based on interference fringe contrast demodulation

We propose and verify a fiber optic temperature sensor whose demodulation method is measuring the spectra contrast, which is quantified by the amplitude of the fast Fourier transform (FFT) of interference fringes within a certain small wavelength range. A section of polarization-maintaining fiber (PMF) is spliced in the sensing arm of the Mach-Zehnder interferometer (MZI). Due to the birefringence of the PMF, a visible envelope is formed in the interference fringes. Within a certain range of optical frequency (i.e. wavelength), the change of birefringence caused by external temperature will drive the envelope drift, and the amplitude of interference fringe after fast Fourier transform will also change correspondingly. By measuring the change of amplitude, the purpose of demodulating external temperature can be realized. Experimental results show high sensitivity better than 2.1 dB/°Cwith a high accuracy of 0.00048 °C, comparing with the envelope drift measuring results 1.62 nm/°C with resolution of 0.012 °C. The resolution of this scheme is increased by two orders of magnitude compared with measuring the envelope drift. Moreover, merits of our sensor in terms of immune to phase shift of reference arm and the power fluctuation of light source benefit our practical application for such as electric power system monitoring.

A simple fiber lateral stress sensor based on polarization-maintaining fiber embedded Michelson interferometer assisted by silicon rubber sheets

A simple fiber lateral stress sensor is proposed based on polarization-maintaining fiber (PMF) embedded Michelson interferometer (MI). A section of PMF is spliced in the sensing arm of the MI to form the basis of the sensing element. Here the output spectrum will be derived from a two-part interference spectrum: fine part from optical path difference (OPD) of the MI and envelope one from birefringence of the PMF. The PMF is wound into a spiral shape sandwiched by two square silicon rubber sheets, that is the sensing element. Thanks to the low elasticity modulus of silicon rubber material, the experiment show high stress sensitivity of 1.93 nm/kPa in 2.1 kPa stress range by demodulating the envelope shifting. Compared with conventional Sagnac type sensor, the proposed sensor has merits of convenient for application, flexible form, and so on. And this is beneficial for electric power system monitoring

Switchable multiwavelength thulium-doped fiber laser with cylindrical vector beam emission

We experimentally demonstrate a switchable multiwavelength thulium-doped fiber laser with cylindrical vector beam (CVB) emission, which is the first report, to our best knowledge, on the generation of CVBs in a 2 µm wavelength band. The Sagnac loop filter, made up of a 50:50 coupler, a section of polarization-maintaining fiber and a polarization controller, serves as a periodical filter and accounts for the excitation of multiwavelength channels. The mode-selective coupler consisting of both tapered single-mode and four-mode fibers has been designed and fabricated as a mode converter from LP01 to LP11 mode with a purity of >80%. By adjusting the polarization controllers, laser outputs with 1–3 switchable wavelengths have been realized in the spectrum ranging from 1988–1998 nm. The laser could find miscellaneous applications in wavelength/mode-division multiplexing system, etc.

Fiber-based polarization-sensitive optical coherence tomography of a minimalistic system configuration.

We present a very simple method of constructing a polarization-sensitive optical coherence tomography (PS-OCT) system. An ordinary fiber-based swept-source OCT system was reconfigured for PS-OCT by adding a long section of polarization-maintaining fiber in the sample arm. Two polarization modes of a large group-delay difference formed spatially distinguished polarization channels. The depth-encoded information on the polarization states was retrieved by an amplitude-based analysis. We found that our method provides an economic scheme of PS-OCT. It demonstrates that an ordinary OCT system can be easily reconfigured for PS-OCT imaging if it has sufficient margins in the imaging range.

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.

Research on tunable multiwavelength fiber lasers with two-section birefringence fibers and a nonlinear optical loop

Two types of tunable multiwavelength fiber lasers based on two-section polarization maintaining fibers (PMFs) cascaded/in parallel and nonlinear optical loop are proposed and experimentally demonstrated. Two-section cascaded PMFs and two polarization controllers (PCs) form the two-stage Lyot filter, which can generate comb spectrum to achieve multiwavelength output. When two sections of PMFs are in parallel, PCs in two paths are adjusted to change the beam’s polarization to suppress the light of one branch, and then the light of the other branch passes through the cavity. Additionally, a nonlinear optical loop acts as an intensity-dependent component, which can suppress the mode competition to maintain a stable output of multiwavelength lasing. The nonlinear optical loop is made by a 3 dB coupler, a PC3, and a 200 m high nonlinear fiber. Two types of tunable multiwavelength fiber lasers can achieve tuning of the channel space and the number of lasing wavelengths by adjusting PC1 and PC2. The channel space of the multiwavelengh laser can be tuned at nearly 0.4, 0.68, and 0.92 nm. Meanwhile, the spectral range of multiwavelength lasing can be controlled by PC3 in the nonlinear optical loop, and the tuning range of two multiwavelength lasers is about 2.28 and 1.45 nm, respectively.

Tunable and stable multi-wavelength erbium-doped fiber laser based on a double Sagnac comb filter with polarization-maintaining fibers

In this paper, a tunable and stable multi-wavelength erbium-doped fiber laser that employs a double polarization-maintaining Sagnac loop comb filter is proposed and experimentally demonstrated. The two nested Sagnac loops are used as the comb filter, which was fabricated using two 3-dB couplers, two polarization controllers (PC), and two sections of polarization-maintaining fibers (PMFs) with lengths of 1.2m and 1.8m, respectively. In the proposed laser, a stable and tunable single-, double-, and triple-wavelength lasing was obtained experimentally in the spectral range of 1528–1564nm, the side mode suppression ratio (SMSR) was higher than 38dB, and the wavelength shifts and power fluctuations were less than 0.04nm and 4.7dB, respectively, for a duration of 10min at a room temperature of 26°C. Furthermore, the laser can emit quadruple-wavelengths through adjustment of the two PCs in the experiment.

Simplified tunable fiber comb filter based on polarization-diversity loop configuration

A simple tunable fiber comb filter composed of two quarter-wave plates and a section of polarization-maintaining fiber is proposed. The states of polarization are investigated through theoretical analysis, and we present the means for continuous wavelength tunability using analytic expression. The optimal angle combination of each birefringent device could be deduced so that an arbitrary wavelength could be a channel center of the comb filter without transmission loss, which is verified experimentally.

Tunable multi-wavelength thulium-doped fiber laser incorporating two-stage cascaded Sagnac loop comb filter

A tunable multi-wavelength narrow-linewidth thulium-doped fiber laser employing two-stage cascaded Sagnac loop mirrors is proposed and experimentally demonstrated. The designed fiber laser is composed of a pump source, wavelength division multiplex, circulator, thulium-doped fiber, polarization controllers (PCs), couplers and polarization-maintaining fibers (PMFs). Two cascaded Sagnac loops are used as the cavity reflector and filter, and the proposed filter is fabricated using two sections of PMFs with 2-m and 1-m lengths, respectively. In the experiment, the laser threshold is 110 mW, and laser can emit single, double, triple, quadruple and quintuple wavelengths in the spectral range of 1873–1901 nm through the simultaneous adjustment of the two PCs. The power fluctuations and 3-dB linewidth are less than 2.1 dB and 0.2 nm, respectively, over 10 min at room temperature, and the side-mode suppression ratio is greater than 20 dB. The proposed laser will be useful in various fields, such as spectral analysis, fiber sensing and optical communication.

Fiber torsion sensor based on a twist taper in polarization-maintaining fiber.

A novel optical fiber torsion sensor head is proposed. A section of polarization-maintaining fiber (PMF) is spliced between single mode fiber (SMF), and a twist taper is fabricated by a commercial electric-arc fusion splicer in the middle of the PMF. The asymmetric characteristics are obtained by the twist taper so that a fiber torsion sensor with directional discrimination is fabricated. Due to the characteristics of the asymmetric structure, the torsion sensitivity for the twist rate from 0 rad/m to -8 rad/m reaches 2.392 nm/rad·m-1, and for the twist rate from 0 rad/m to 8 rad/m reaches 1.071 nm/rad·m-1 respectively.

Distributed group birefringence measurement in a polarization-maintaining fiber using optical frequency-domain reflectometry

We propose to use optical frequency-domain reflectometry to measure distributed group birefringence along a section of polarization-maintaining fiber. Frequency dependence of the propagation constant difference along the fiber between the fast and slow modes can be determined. The scanning frequency bandwidth has influences on the measurement of the phase modal birefringence and beat length. Besides phase modal birefringence and beat length can be measured, distributed group birefringence along the fiber is obtained with a spatial resolution of 7.8cm.

Temperature-independent fiber inclinometer based on orthogonally polarized modes coupling using a polarization-maintaining fiber bragg grating.

A reflection fiber inclinometer is proposed and experimentally demonstrated based on two linearly polarized (LP) modes coupling. The configuration consists of a section of polarization-maintaining fiber (PMF) containing a fiber Bragg grating (FBG) splicing with single mode fiber (SMF). Bending the PMF in the upstream of FBG can induce an additional birefringence of PMF, which results in the intensity changes of two LP modes owing to orthogonal polarization coupling. The experimental results represent that the device shows different bending responses at the angle range from 0° to 40°and from 64° to 88°, respectively. Moreover, the temperature change just shifts the wavelengths of LP modes reflected and does not influence their intensities, which effectively avoid the temperature cross-sensitivity and make it a good candidate for measuring inclinometer and temperature simultaneously.

A fiber-based polarization–rotation filter utilized to suppress the FM-to-AM effect in a large-scale laser facility

The frequency modulation to amplitude modulation (FM-to-AM) effect is one of the few remaining scientific issues in a large-scale laser facility which could prevent fusion ignition. A fiber-based polarization–rotation filter which consists of a fiber polarizer, a section of polarization-maintaining fiber, a half-wave plate and a polarization beam splitter is proposed to suppress the FM-to-AM effect. Theoretical analysis and experimental demonstration in the preamplifier module of the SG-III laser facility prove the effectiveness of this filter.

A polarization-maintaining fiber loop mirror based sensor for liquid refractive index absolute measurement

A fiber sensor based on polarization-maintaining fiber loop mirror (FLM) for liquid refractive index absolute measurement is described. Two sections of polarization maintaining fibers (PMFs) with different length were inserted into the FLM. One section of PMF was chemical etched for liquid refractive index measurement and the other one for reference. Liquid refractive index absolute measurement can be obtained by detecting the interference wavelength difference corresponding to the two sections of PMFs. High sensitivity of 63.82±0.04nm/RIU (refractive index unit) and a resolution of 3.14×10−4RIU were obtained for the proposed liquid refractive index sensor.

A Photonic UWB Generator Reconfigurable for Multiple Modulation Formats

In this letter, we propose and demonstrate a simple and flexible optical ultra-wideband (UWB) pulse generator that can be reconfigured for pulse-position modulation, biphase modulation, and pulse-shape modulation. The system is implemented using a dual-drive Mach-Zehnder modulator and an electrically reconfigurable asymmetric Mach-Zehnder interferometer (AMZI). The AMZI consists of a polarization modulator (PolM), a polarization controller (PC), a section of polarization-maintaining fiber, and an optical polarizer. By adjusting the PC and the drive voltage to the PolM, the system is reconfigured to generate UWB signals with different modulation formats. An experiment is performed, which verifies the proposed technique.