Polarization Hole Burning Research Articles

Optimization of Dual-Wavelength linear cavity Erbium-Doped fiber laser based on pairs of fiber Bragg gratings

There are few reports in the field of linear cavity dual-wavelength fiber lasers about the laser output characteristics when 3-dB fiber loop mirror (FLM) and Fiber Bragg grating (FBG) are used as full reflective mirrors, respectively. Additionally, there is scarce research on further tuning of the FBG parameters (reflectivity and center wavelength interval) to study dual-wavelength fiber lasers. In this paper, we compare the performances of dual-wavelength lasing outputs between the 3-dB FLM-FBG cavity and the FBG-only cavity in a linear-cavity erbium-doped fiber laser (EDFL) based on the polarization hole burning effect. The results show that the optical signal-to-noise ratios (OSNRs) of the dual-wavelength lasing outputs with the FBG-only cavity are approximately 4 ∼ 5 dB higher than those with the 3-dB FLM-FBG cavity. Furthermore, the lasing output performances based on the FBG-only cavity are compared when the reflectivities of the output-mirror FBGs are the same or different. It is observed that the dual-wavelength laser with the same output reflectivity leads to higher OSNR, slope efficiency, and stability. Moreover, by varying the center wavelength interval of pairs of FBGs in the FBG-only cavity to values of 4 nm, 8 nm, and 12 nm respectively. It is shown that wider intervals result in higher OSNRs but lower laser slope efficiency. Finally, we demonstrate a dual- wavelength linear cavity EDFL operating at room temperature with two lasing wavelengths of 1550 nm and 1562 nm. The laser results in OSNRs around 50.62 dB and 50.93 dB; center wavelength variations of less than 0.030 nm and 0.035 nm; output power fluctuations of less than 0.061 mW and 0.059 mW, respectively.

Anti-phase pulsation of counter-propagating dissipative solitons in a bidirectional fiber laser

Due to its unique geometric structure, the bidirectional ultrafast fiber laser is an excellent light source for dual-comb applications. However, sharing the same gain between the counter-propagating solitons also gives rise to complex dynamics. Herein, we report the anti-phase pulsation of counter-propagating dissipative solitons in a bidirectional fiber laser. The in-phase and anti-phase soliton pulsation can be manipulated by adjusting the intracavity birefringence. The periodic modulation of polarization-dependent gain (PDG) caused by polarization hole burning (PHB) in the gain fiber can be responsible for anti-phase pulsation of bidirectional dissipative solitons. These findings offer new, to the best of our knowledge, insights into the complex dynamics of solitons in dissipative optical systems and performance improvement of bidirectional ultrafast fiber lasers.

Multi-wavelength thulium-doped fiber laser at 2.05 μm incorporating a superimposed polarization-maintaining fiber Bragg grating

A switchable multi-wavelength thulium-doped fiber laser with a high optical signal-to-noise ratio (OSNR) and stability is proposed and experimentally demonstrated at 2.05 μm. For the first time, a superimposed polarization-maintaining fiber Bragg grating (SI-PM-FBG) was utilized as a multi-channel narrow bandwidth filter to select the lasing wavelengths in the laser cavity in the 2-μm band. It also introduced polarization hole burning (PHB) to inhibit the strong wavelength competition induced by homogeneous gain broadening in the thulium-doped fiber. By adjusting the two polarization controllers (PCs), four stable switchable single-wavelength operations were obtained. The OSNR reached 72 dB at a pump power of 2.89 W, and the maximum wavelength and power fluctuations were 0.01 nm and 0.162 dB, respectively. Four combinations of dual-wavelength operations were obtained by adjusting the PCs. The polarization states between each dual-wavelength lasing were orthogonal. The stability of the dual-wavelength operation was investigated in detail. The proposed laser also has the capability for three- or four-wavelength operation. The excellent performance enables this fiber laser to be used in atmospheric sensing and free-space optical communication.

Wavelength-switchable ultra-narrow linewidth fiber laser enabled by a figure-8 compound-ring-cavity filter and a polarization-managed four-channel filter.

We propose and demonstrate a high-performance wavelength-switchable erbium-doped fiber laser (EDFL), enabled by a figure-8 compound-ring-cavity (F8-CRC) filter for single-longitudinal-mode (SLM) selection and a polarization-managed four-channel filter (PM-FCF) for defining four lasing wavelengths. We introduce a novel methodology utilizing signal-flow graph combined with Mason's rule to analyze a CRC filter in general and apply it to obtain the important design parameters for the F8-CRC used in this paper. By combining the functions of the F8-CRC filter and the PM-FCF assisted by the enhanced polarization hole-burning and polarization dependent loss, we achieve the EDFL with fifteen lasing states, including four single-, six dual-, four tri- and one quad-wavelength lasing operations. In particular, all the four single-wavelength operations are in stable SLM oscillation, typically with a linewidth of <600 Hz, a RIN of ≤-154.58 dB/Hz@≥3 MHz and an output power fluctuation of ≤±3.45%. In addition, all the six dual-wavelength operations have very similar performances, with the performance parameters close to those of the four single-wavelength operations, superior to our previous work and others' similar work significantly. Finally, we achieve the wavelength-spacing tuning of dual-wavelength operations for photonic generation of tunable microwave signals, and successfully obtain a signal at 23.10 GHz as a demonstration.

Triple-wavelength EDF laser based on phase-shifted fiber grating and 50 μm MMF

We propose and experimentally demonstrate a novel switchable triple-wavelength erbium-doped fiber laser using linear cavity structure. It is composed of two Sagnac loops that act as cavity mirrors in the resonant cavity. The left loop consists of a 3 dB fiber coupler (FC), a three-ring polarization controller (PC), and a phase-shifted fiber grating. The right loop consists of a same 3 dB FC, a same PC and a length of multimode fiber with 50 µm core diameter. The two loops based on different operation principles become two comb filters to jointly excite the multiwavelength output. On the role of the polarization hole burning effect, after adjusting the two PCs, the laser can switch flexibly to output three kinds of different modes from single-wavelength to the triple-wavelength. All lasing lines with a narrow linewidth less than 0.4 nm have the optical signal-to-noise ratio of more than 28 dB.

Quadruple-Wavelength EDF Laser Based on Chirped Fiber Grating and 62.5 μm Multimode Fiber

We propose and experimentally demonstrate a novel switchable quadruple-wavelength CW erbium-doped fiber laser, using a linear cavity structure. It is composed of two Sagnac loops that act as cavity mirrors in the resonant cavity. The left loop consists of a 3 dB fiber coupler (FC), a squeezed polarization controller (PC), and a chirped fiber grating. The right loop consists of a 10 dB FC, the same PC and a length multimode fiber with a core diameter of 62.5 μm. The two loops based on different operation principles become two comb filters to jointly excite the multiwavelength output. On the role of the polarization hole burning effect, after adjusting the two PCs, the laser can switch flexibly to output fourteen kinds of different modes from a single wavelength to the quadruple wavelength. All lasing lines, with a narrow linewidth less than 0.28 nm, have the optical signal-to-noise ratio of more than 20 dB. The laser with good power uniformity shows better stabilities of the wavelength and peak power.

Polarization hole burning and self-rotation of the polarization ellipse in an acetylene-filled hollow-core photonic crystal fiber

We report on the first experimental observation of the polarization ellipse self-rotation (PSR) and the polarization hole burning (PHB) nonlinear optical effects for the acetylene ( C 2 H 2 ) vibrational–rotational transitions in the 1520–1530 nm spectral range. The experiments were performed using a 1-m-long acetylene-filled hollow-core photonic crystal fiber cell at room temperature and gas pressure of 0.4–4 Torr. The PHB effect was experimentally observed as a photo-induced input polarization ellipticity change in the output light. Among all the investigated acetylene transitions P9, P7, P5, and P3, the maximum ellipticity change of ∼ 35 % was observed at zero detuning from the center of the P5 absorption line with the initial optical absorbance about 6. The obtained results are in good agreement with the theoretical predictions of a classical analysis based on the model of the acetylene molecules as gyrators (circular oscillators) with random orientations. For the inhomogeneously broadened acetylene absorption P5 line ( ∼ 500 M H z ), the PSR effect observed for tuning at the sides of the P5 line, as expected, proved to be by factor Δ ω i h / Δ ω h (inhomogeneous-to-homogeneous broadening ratio) lower than the maximum PHB. The PSR constant for these conditions proved to be about 0.1 m − 1 , which is about 2 orders of magnitude lower than that reported earlier for the alkali metal (K, Rb) vapors.

Six-wavelength-switchable narrow-linewidth thulium-doped fiber laser with polarization-maintaining sampled fiber Bragg grating

A compound-cavity-based six-wavelength-switchable single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL) with a homemade polarization-maintaining sampled fiber Bragg grating (PM-SFBG) is proposed and demonstrated. The PM-SFBG in the 2 μm band is studied theoretically and experimentally, and is utilized as a polarization-dependent multi-channel reflecting filter in a multi-wavelength-switchable fiber laser, both for the first time. The SLM lasing in each channel is guaranteed by using a tri-ring sub-cavity. 6 single-wavelength operations are easily obtained and switched each other, and the maximum power and wavelength fluctuations are as low as 0.71 dB and 0.02 nm, respectively. The frequency noise of each lasing wavelength is measured through an unbalanced Michelson interferometry system, and the linewidths for all six lasing wavelengths are among 0.60–1.08 kHz, calculated by the β-separation line method on the basis of the measured frequency noise spectra. Benefiting from the enhanced polarization hole burning effect formed in the gain fiber, 9 switchable dual-wavelength operations with different wavelength intervals and orthogonal polarizations at two lasing wavelengths are obtained with the maximum power and wavelength fluctuations of only 0.95 dB and 0.03 nm, respectively. We believe the proposed TDFL will find great applications as an ideal light source in free space optical communication and optical sensing.

Stable dual-wavelength laser incorporating polarization-maintaining erbium-doped fiber

A stable dual-wavelength erbium-doped fiber laser is proposed and experimentally demonstrated. The mode competition in the gain medium was suppressed by enhancing the polarization hole burning mechanism through incorporation of polarization maintaining erbium-doped fiber and nonlinear polarization rotation. The fiber laser displayed high stability with lasing side-mode suppression ratios of 60.69 and 60.57 dB. Additionally, the negligible peak power fluctuation of 0.01 dB was achieved at 1557.17 and 1560.19 nm with both peak powers of 0.23 mW and 3-dB bandwidth of 0.028 and 0.025 nm, respectively. These findings provide insights for an enhanced seed laser source design for remote dual-wavelength fiber laser applications.

Tunable and switchable multi-wavelength fiber laser based on polarization hole burning effect and Sagnac loop mirrors

In this paper, a stable highly tunable and switchable multi-wavelength fiber laser is presented. It is based on the filtering characteristics of the Sagnac loop mirror and the polarization-dependent devices, the polarization hole burning effect is induced to generate multi-wavelength output with high optical signal-to-noise ratio and narrow 3 dB linewidth, optical signal-to-noise ratio is about 50 dB and linewidth is less than 0.02 nm. The tunable bandwidth is about 30 nm, which covers almost the entire C-band. By the adjusting polarization controller, the number and wavelength spacing of laser emissions can be controlled and switched. The single-wavelength exhibits good power and wavelength stability, the peak power fluctuation is less than 0.04 dB and the wavelength drift is less than 0.04 nm, and the wavelength spacing of the dual-wavelength can be tuned from 0.67 to 27.4 nm. In the proposed structure, multi-wavelength up to 6 laser emissions can be obtained span from 1528 to 1562 nm.

A switchable triple-wavelength erbium-doped fiber laser based on a fiber Bragg grating filter and interleaver

A switchable triple-wavelength erbium-doped fiber laser based on a fiber Bragg grating filter (FBGF) and C-band 50 GHz interleaver is proposed and demonstrated experimentally at room temperature. The FBGF alone can only excite unstable multi-wavelengths. To obtain a stable multi-wavelength output, an interleaver with stationary wavelength spacing and the polarization hole burning effect are used; finally, the laser can switch flexibly to output three different modes from single- or dual- to triple-wavelength. All of the lasing lines with narrow linewidths have the optical signal-to-noise ratio of more than 20 dB, and locate at the wavelength positions in the range of about 1530 nm to 1533 nm. The laser with good light-intensity uniformity shows better stabilities with respect to the wavelength and peak power.

Quintuple-wavelength EDF laser based on multimode fibers with different core diameters

A switchable quintuple-wavelength erbium-doped fiber laser using the linear-cavity configuration is proposed and demonstrated experimentally at room temperature. It is composed of two Sagnac loops that act as the cavity mirrors in the resonant cavity and contain two kinds of multimode fibers with different core diameters (50 and 62.5 µm). The two loops become two comb filters to jointly excite the multi-wavelength output. By using the effects of multimode interference and polarization hole-burning, and after adjusting a polarization controller, the laser can switch flexibly to output nine different kinds of modes from single-wavelength to quintuple-wavelength. All lasing lines with a narrow linewidth of less than 0.25 nm have an optical signal-to-noise ratio of more than 14 dB. The laser has good power uniformity shows good stability with respect to the wavelength and peak power.

Dynamic nuclear polarization and ESR hole burning in As doped silicon.

We present an experimental study of the Dynamic Nuclear Polarization (DNP) of 29Si nuclei in silicon crystals of natural abundance doped with As in the temperature range 0.1-1 K and in a strong magnetic field of 4.6 T. This ensures a very high degree of electron spin polarization, extremely slow nuclear relaxation and optimal conditions for realization of Overhauser and resolved solid effects. We found that the solid effect DNP leads to the appearance of a pattern of holes and peaks in the ESR line, separated by the super-hyperfine interaction between the donor electron and 29Si nuclei closest to the donor. On the contrary, the Overhauser effect DNP mainly affects the remote 29Si nuclei having the weakest interaction with the donor electron. This leads to the appearance of a very narrow (≈3 mG wide) hole in the ESR line. We studied relaxation of the holes after burning, which is caused by the nuclear spin diffusion. Analyzing the dynamics of the hole in the spectrum with a simple one-dimensional diffusion model leads to a value of the diffusion coefficient D = 8(3) × 10-9 G2 s-1. Our data indicate that the spin diffusion is not completely prevented even in the frozen core near the donors. The emergence of the narrow hole after the Overhauser DNP may be explained by a partial "softening" of the frozen core caused by decoupling of the donor electron and remote 29Si nuclei.

Four-wavelength-switchable SLM fiber laser with sub-kHz linewidth using superimposed high-birefringence FBG and dual-coupler ring based compound-cavity filter.

We propose and demonstrate a four-wavelength-switchable erbium-doped fiber laser (4WS-EDFL) with a four-channel superimposed high-birefringence fiber Bragg grating (SI-HBFBG) and a dual-coupler ring based compound-cavity (DCR-CC) filter. Both for the first time, a SI-HBFBG as a four-channel reflective filter is used in a multi-wavelength switchable fiber laser to define wavelength channels and a DCR-CC filter is used to select a single mode from dense longitudinal-modes in a fiber laser. We present in detail how to design, fabricate, and characterize the DCR-CC filter with both theoretical analysis and experimental results, which we believe is the first systematic approach for making a compound-cavity based filter used for selecting single-longitudinal mode (SLM) in a fiber laser. The enhanced polarization hole burning effect in a 2.9 m long erbium-doped fiber, coiled inside a three-loop polarization controller, and the polarization-mismatch-induced losses are introduced into the laser cavity to achieve wavelength-switching operations. We show that the 4WS-EDFL can be switched among fifteen lasing states, including four single-wavelength operations, six dual-wavelength operations, four three-wavelength operations and one four-wavelength operation, all with high stability. For demonstration, in switchable single-wavelength operations, the four SLM lasing outputs measured are all with an optical signal to noise ratio of >80 dB, a linewidth of <700 Hz, a relative intensity noise of ≤-156.7 dB/Hz at frequencies over 3 MHz, an output power fluctuation of ≤0.555 dB and excellent polarization characteristics.

Polarization-dependent pulse dynamics of mode-locked fiber laser with near-zero net dispersion

We demonstrate novel polarization-dependent pulse dynamics in a fiber laser cavity mode-locked by single-wall carbon nanotubes. By managing the net dispersion and polarization state, we obtain two noise-like pulsing procedures with distinctive polarization characteristics. Ultrafast polarization measurements reveal double pulses are produced by the combined effects of double-scroll chaotic polarization attractors and the polarization mode dispersion of single-mode fiber. The corresponding single-shot spectra provide evidence of coherent energy coupling between pulses during the switching process, due to the polarization hole burning of the active medium. The relative results provide new information for the polarization control of ultrafast lasers.

Switchable 0.612-nm-Spaced Dual-Wavelength Fiber Laser With Sub-kHz Linewidth, Ultra-High OSNR, Ultra-Low RIN, and Orthogonal Polarization Outputs

A high-performance switchable 0.612-nm-spaced dual-wavelength erbium-doped fiber (EDF) laser is proposed and experimentally demonstrated. For the first time, we combine a compound-cavity structure (CCS) and an enhanced polarization hole burning (PHB) effect in laser cavity to obtain stable dual-wavelength lasing ( λ 1 and λ 2) and single-longitudinal-mode (SLM) operation at each wavelength without mode hopping. In the CCS, a high-quality triple-ring passive resonator is employed to achieve SLM lasing and a high-birefringence fiber Bragg grating combined with a three-loop polarization controller made with a length of EDF is used to establish a strong PHB effect. Easy switch between dual- and single-wavelength lasing modes is achieved. At a pump power of 150 mW, we obtain dual-wavelength lasing with optical signal-to-noise ratios (OSNRs) of >84 dB for both wavelengths and linewidths of 663 Hz for λ 1 and 768 Hz for λ 2, respectively; we also obtain single-wavelength lasing at λ 1 with an OSNR of >86 dB and a linewidth of 687 Hz or at λ 2 with an OSNR of >88 dB and a linewidth of 678 Hz. For both dual- and single-wavelength operations, the two lasing wavelengths are orthogonally polarized, with a degree of polarization of ∼100%, and their relative intensity noises are <−155 dB/Hz at frequencies over 3 MHz. In addition, the dependence of wavelength, OSNR, and linewidth on pump power and wavelength-tunability on temperature for the proposed fiber laser are also investigated in detail.

Vector soliton rain

Soliton rain is a bunch of small soliton pulses accompanying the main pulse with the period of a round trip. It was found previously that soliton-soliton interaction through the overlapping of their tails or soliton-dispersive wave interaction can result in spikes with an anomalous amplitude satisfying the rogue waves (RW) criteria. Here, we report for the first time on the experimental observation of the polarization dynamics of soliton rain in an erbium–doped fiber laser mode-locked by single wall carbon nanotubes. Unlike the previous study, we have found that the soliton rain dynamics can be driven by polarization hole burning in the orientation distribution of inversion. Completion between holes, filled by the pump wave and rotation of the state of polarization of lasing pulse, is controlled by the pump power and in the cavity polarization controller, which results in repulsion or attraction of the soliton rain pulses and the main pulse. As a result, the different soliton rain patterns including RW can be observed.

High Power Switchable Dual-Wavelength Linear Polarized Yb-Dozped Fiber Laser around 1120 nm

A single-and dual-wavelength switchable polarized Yb-doped double-clad fiber laser around 1120 nm based on a pair of fiber Bragg gratings (FBGs) is demonstrated. The polarization-maintaining (PM) linear cavity is composed of a double clad PM Yb-doped fiber (YDF) and a pair of PM FBGs. The laser can operate in stable dual-wavelength or wavelength-switching modes due to the polarization hole burning (PHB) and the spatial hole burning (SHB) enhanced by the PM linear cavity. In dual-wavelength operation, the two orthogonally polarized wavelengths are centered at 1118.912 nm and 1119.152 nm, with an interval of 0.24 nm and a signal to noise ratio (SNR) of 35 dB. The maximum output power is 14.67 W when the launched LD pump is 24 W corresponding to an optical efficiency of 61.1%. The lasing lines switchover may be realized by adjusting the polarization controller (PC) fitted in the cavity. The two single-wavelengths are 1118.912 nm and 1119.152 nm. When the injected LD pump is 24 W, the highest output powers are 7.68 W and 8.64 W corresponding to optical efficiencies of 32% and 36% respectively. The spectral linewidth of the lasing lines are 0.075 nm and 0.07 nm, and the average numerical values of PER aredB and 19.9 dB, respectively.

Switchable quadruple-wavelength Erbium-doped fiber laser based on a chirped fiber grating and polarization-maintaining fiber

A switchable quadruple-wavelength Erbium-doped fiber laser based on two Sagnac loops with a chirped fiber grating and polarization-maintaining fiber is proposed and demonstrated experimentally at room temperature. The two loops act as comb filters to excite multi-wavelength output. On the basis of the polarization hole burning effect, the laser can switch flexibly to output ten different modes from single-wavelength to quadruple-wavelength. All of the lasing lines with narrow linewidth have the optical signal-to-noise ratio of more than 35dB. The laser with good power uniformity shows better stability with respect to the wavelength and peak power.

Population gratings in saturable optical fibers with randomly oriented rare-earth ions

Formation of the dynamic population gratings in optical fibers with randomly oriented rare-earth ions is analyzed with a special interest to the grating component for readout with the orthogonal light polarization. It is shown that as compared with a simple model case of the collinearly oriented dipole-like centers their random orientation leads to approximately 2-times growth of the effective saturation power Psat when it is estimated from the incident power dependence of the fiber absorption or from that of the fluorescence intensity. An optimal incident power, for which the maximum of the dynamic population grating amplitude for collinear light polarization is observed, also follows this change in Psat, while formation of the grating for orthogonal polarization needs essentially higher light power. The reduced anisotropy of the active centers, which is in charge of the experimentally observed weakening of the polarization hole burning (PHB) and of the fluorescence polarization, compensates in some way the effect of random ion orientation. The ratio between the maximum conventional (i.e. for the interacting waves collinear polarizations) two-wave mixing (TWM) amplitude and the initial not saturable fiber optical density proves to be, however, nearly the same as in the model case of collinearly oriented dipoles. The ratio between the PHB effect and the amplitude of the anisotropic grating, which is responsible for TWM of the orthogonally polarized waves, is also not influenced significantly by the reduced anisotropy of ions.