Polarization-maintaining Research Articles

Temperature Dependence of Faraday Effect-Induced Bias Error in a Fiber Optic Gyroscope.

Improving the performance of interferometric fiber optic gyroscope (IFOG) in harsh environments, such as magnetic field and temperature field variation, is necessary for its practical applications. This paper presents an investigation of Faraday effect-induced bias error of IFOG under varying temperature. Jones matrix method is utilized to formulize the temperature dependence of Faraday effect-induced bias error. Theoretical results show that the Faraday effect-induced bias error changes with the temperature in the non-skeleton polarization maintaining (PM) fiber coil. This phenomenon is caused by the temperature dependence of linear birefringence and Verdet constant of PM fiber. Particularly, Faraday effect-induced bias errors of two polarizations always have opposite signs that can be compensated optically regardless of the changes of the temperature. Two experiments with a 1000 m non-skeleton PM fiber coil are performed, and the experimental results support these theoretical predictions. This study is promising for improving the bias stability of IFOG.

Fiber Optical Coherence Domain Polarimetry for PM Fiber Measurements

Optical coherence domain polarimetry (OCDP) utilizes incoherent light and is based on Michelson interferometer. This paper presents a polarization maintaining (PM) Michelson fiber interferometer utilizing a single PM fiber loop mirror (Sagnac Loop) that replaces the conventional free space mirrors for OCDP systems. This implementation is environmentally robust and alleviates much of the mechanical complications necessary to reduce temperature and vibrations effects. A piezoelectric transducer (PZT) is inserted in one of the arms of the interferometer and driven near its resonance. This enables a detailed measurement of polarization coupling around any point in the device under test. An analytical model is given, based on Pauli matrices algebra, that includes the side effects due to component imperfections. It is shown that the polarization coupling in the PZT has the largest side effect on the OCDP output. Experimental investigations verify the accuracy of the theoretical model. Measurements are done on two PM PANDA fibers of lengths 20 and 150 m, respectively. In addition, the new system successfully measures distributed polarization mode coupling, group birefringence, and group birefringence dispersion for the fiber under test.

All-fiber highly chirped dissipative soliton generation in the telecom range.

A high-energy (0.93nJ) all-fiber erbium femtosecond oscillator operating in the telecom spectral range is proposed and realized. The laser cavity, built of commercially available fibers and components, combines polarization maintaining (PM) and non-PM parts providing stable generation of highly chirped (chirp parameter 40) pulses compressed in an output piece of standard PM fiber to 165fs. The results of the numerical simulation agree well with the experiment. The analyzed intracavity pulse dynamics enables the classification of the generated pulses as dissipative solitons.

Low noise, self-referenced all polarization maintaining Ytterbium fiber laser frequency comb.

We report the implementation of a self-referenced optical frequency comb generated by a passively mode-locked all polarization maintaining (PM) Yb fiber laser based on a nonlinear amplifying loop mirror (NALM). After spectral broadening the optical spectrum spans from 650 nm to 1400 nm, allowing for the generation of an optical octave and carrier envelope offset frequency (fceo) stabilization through a conventional f-2f interferometer. We demonstrate for the first time the stabilization of the fceo of such a PM Yb system with an in-loop fractional frequency stability scaled to an optical frequency of low 10-19 at 1 second averaging time, offering a great potential for applications in optical atomic clock metrology.

Polarization-maintaining, large-effective-area, higher-order-mode fiber.

Higher-order-mode (HOM) fibers guiding light in large-effective-area (Aeff) Bessel-like modes have recently generated great interest for high-power laser applications. A polarization-maintaining (PM) version of HOM fibers can afford the added possibility of coherent beam combination, improved material processing, and polarization multiplexing of high-power fiber lasers. We report a PM-HOM fiber for guiding Bessel-like modes with Aeff ranging from 1200-2800 μm2. The fiber modes exhibit a birefringence value that compares well with that of a conventional single-mode PM fiber (2×10-4), and exhibit a polarization extinction ratio ranging from 13-23dB over meter-long fiber lengths, practical for amplifier systems. This fiber presents a unique platform for next-generation high-power fiber systems, as well as for the fundamental studies on deterministically polarized Bessel-like modes in fibers.

Polarization-Maintaining Optical Components

In a polarization-maintaining (PM) fiber system, the quality of a connection plays a crucial role. In order to offer the best overall performance, PM fibers must be properly oriented inside the connectors and the alignment features on these must guarantee an appropriate orientation across the mating adapter. Due to different mechanical contructions, not all fiber connectors and mating adapters are suitable for PM applications.

Impedance self-matching ultra-narrow linewidth fiber resonator by use of a tunable \u03c0-phase-shifted FBG

In this paper, we present a novel ultra-narrow linewidth fiber resonator formed by a tunable polarization maintaining (PM) π-phase-shifted fiber Bragg grating and a PM uniform fiber Bragg grating with a certain length of PM single mode fiber patch cable between them. Theoretical prediction shows that this resonator has ultra-narrow linewidth resonant peaks and is easy to realize impedance matching. We experimentally obtain 3 MHz narrow linewidth impedance matched resonant peak in a 7.3 m ultra-long passive fiber cavity. The impedance self-matching characteristic of this resonator also makes itself particularly suitable for use in ultra-sensitive sensors, ultra-narrow band rejection optical filters and fiber lasers applications.

>1 kW all-fiberized narrow-linewidth polarization-maintained fiber amplifiers with wavelength spanning from 1065 to 1090 nm

We demonstrate all-fiberized, kilowatt-level, narrow-linewidth, Yb-doped and polarization-maintained (PM) amplifiers with a central wavelength spanning from 1065 to 1090nm. The laser system consists of a tunable single-frequency laser seed and multistage PM fiber amplifiers in the master oscillator power amplifier configuration. The stimulated Brillouin scattering effect is suppressed by phase modulation based on a white noise source. The linewidth (Δλ∼0.12 nm at 1kW), polarization extinction ratio (PER>13 dB) and beam quality (M2∼1.2) are well maintained during the power scaling process, and the slope efficiency of this system is 70.8%.

Linearly-polarized random distributed feedback Raman fiber laser with record power

We demonstrate a linearly polarized random distributed feedback Raman fiber laser with record 86.3 W output power with a piece of 157 m long polarization maintaining (PM) fiber. The maximum optical efficiency of first-order-Stocks light at 1120 nm reaches ~74% while pumping at 1070 nm. The full width at half maximum (FWHM) at maximum output power is ~2 nm and the polarization extinction ratio (PER) is measured to be as high as 22 dB. To the best of our knowledge, this is the highest output power for linearly-polarized random fiber laser.

Incoherently pumped high-power linearly-polarized single-mode random fiber laser: experimental investigations and theoretical prospects.

We present a hundred-watt-level linearly-polarized random fiber laser (RFL) pumped by incoherent broadband amplified spontaneous emission (ASE) source and prospect the power scaling potential theoretically. The RFL employs half-opened cavity structure which is composed by a section of 330 m polarization maintained (PM) passive fiber and two PM high reflectivity fiber Bragg gratings. The 2nd order Stokes light centered at 1178 nm reaches the pump limited maximal power of 100.7 W with a full width at half-maximum linewidth of 2.58 nm and polarization extinction ratio of 23.5 dB. The corresponding ultimate quantum efficiency of pump to 2nd order Stokes light is 86.43%. To the best of our knowledge, this is the first demonstration of linearly-polarized high-order RFL with hundred-watt output power. Furthermore, the theoretical investigation indicates that 300 W-level linearly-polarized single-mode 1st order Stokes light can be obtained from incoherently pumped RFL with 100 m PM passive fiber.

Thermal characterization of Bragg gratings in polarization-maintaining optical fibres: analysis of birefringence and regeneration

This paper presents an analysis of birefringence and regeneration of fibre Bragg gratings (FBGs) in two types of polarization-maintaining (PM) optical fibres, bow tie and internal elliptical cladding (IEC), with different diameters. The thermal regeneration of FBGs in PM fibres with different degrees of saturation (weakly, slightly, and strongly saturated) is presented and the influence of the gratings’ saturation degree on the birefringence of PM fibres is shown. The birefringence values obtained for IEC fibres with 80 µm of diameter were for a strongly saturated seed grating of 5.3 × 10−4 and 6.2 × 10−4 refractive index units after the regeneration. The evolution of the fibre birefringence as a function of the temperature is presented and the results show hysteresis and nonlinear dependence of the birefringence on temperature. The thermal stability of regenerated gratings in PM fibres is demonstrated, and a sensitivity coefficient value of 0.0035 dBm min−1 at 900 °C was obtained. The results obtained show the feasibility of optimization of fibre birefringence; this could allow such fibers to be used as temperature sensors and even improve the birefringence after the grating regeneration.

Optical characteristic variations in gamma ray irradiated polarization-maintaining optical fibers

Polarization-maintaining (PM) optical fibers are introduced in fiber optic communication systems and optical fiber sensors to improve their performances. It is known that characteristics of optical fibers vary for radiation exposures, e.g., a transmission loss increment. It is important to clarify the characteristic variations of PM fibers by radiations in their applications. The radiation induced optical characteristic variation is also useful for an application of optical fibers including PM fibers as radiation sensors. In this paper, optical characteristic variations in gamma ray irradiated PM optical fibers with low modal birefringence were experimentally clarified indenting to apply a polarization optical time domain reflectometry to a distributed radiation sensor. It was confirmed that the transmission losses for both polarization modes in elliptical jacket fibers increased similar to ordinary silica based single-mode fibers, where the difference of transmission losses of two polarization modes was enhanced by the irradiation. We also clarified that the modal birefringence of the elliptical jacket fibers increased for the irradiation for the first time by the beat length measurement using the wavelength sweeping technique.

Ultrafast laser mode-locked using nonlinear polarization evolution in polarization maintaining fibers.

We demonstrate an all-fiber ultrafast ytterbium laser oscillator mode-locked by means of a nonlinear polarization evolution (NPE) method realized in polarization-maintaining (PM) fibers. A sequence of the PM fiber pieces is shown to perform NPE action while maintaining a required temporal overlap of the ordinary and extraordinary pulses propagating through it. We present details of simple numerical simulations showing the advantage of the proposed scheme of segmented PM fibers. The laser utilizing the above mentioned design which generates ultrashort pulses at a 20.54MHz repetition rate with the dechirped pulse duration around 150fs and a pulse energy of 0.85nJ is also presented.

Polarization multiplexing in large-mode-area waveguides and its application to signal enhancement in multiphoton microscopy

Soliton self-frequency shift (SSFS) is an efficient technique of generating broadband tunable femtosecond optical pulses. By using large-mode-area (LMA) waveguides such as photonic-crystal (PC) rods or LMA fibers, SSFS is capable of generating solitons with tens of or even >100 nJ pulse energy, enabling deep-tissue multiphoton microscopy (MPM) with the unprecedented imaging depth. MPM signals are proportional to the repetition rate of the laser. Here, we demonstrate an efficient technique of enhancing MPM signals in LMA waveguides, through polarization multiplexing, in both a PC rod with no polarization-maintaining (PM) structure and a PM LMA fiber. The collinear output soliton pulses with orthogonal linear polarizations show similar pulse energy, pulse width, and spectrum. We also demonstrate the application of this polarization multiplexing technique to MPM signal enhancement in biological tissues. Compared with single-polarization soliton excitation, excitation with polarization-multiplexed solitons can efficiently boost MPM signals in different modalities of MPM.

Polarization-maintaining microfiber-based evanescent-wave sensors

In recent years, polarization-maintaining (PM) microfibers have attracted much research attention mostly due to their ultra-high birefringence and large evanescent field effect. This article starts from introduction of the structures, fabrication methods, and mode characteristics of PM microfibers. Different previously-implemented PM microfiber sensors have been presented. The two polarization modes may have different responses on changes of external parameters for PM microfiber, which allows fabrication of polarization-related devices, such as interferometers or gratings. Some sensing characteristics, such as extremely-high refractive index sensitivity and/or temperature-independent response, have been demonstrated. The sensing applications including detection of refractive index, humidity, magnetic field and specific DNA molecular have been described in detail. This article should be helpful for future development of PM micro/nano fibers and the related sensors.

Environmentally Stable Pulse Energy-Tunable Picosecond Fiber Laser

We have reported a mode-locked pulse energy tunable ytterbium-doped fiber laser constructed by the polarization-maintaining (PM) fibers with a position-tunable focuser and a semiconductor-saturable absorber mirror (SESAM). The narrow bandwidth fiber Bragg grating in the cavity produces self-starting picosecond (ps) mode-locked operation. The linear laser cavity achieved tunable single pulse energy varied from 0.591 to 0.988 nJ, with a 24.7-MHz repetition rate and a 6.03-ps pulse duration at 1064.18 nm. High environmental stability is also confirmed by a high polarization extinction ratio over 17.8 dB.

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.

Fiber self-mixing interferometer with orthogonally polarized light compensation.

A fiber heterodyne self-mixing interferometer with orthogonally polarized light compensation is achieved. This system can adapt to various complex scenes while still keeping ultra-high sensitivity and anti-disturbance capability. Ultra-high sensitivity microchip laser is used as the laser source and polarization maintaining(PM) fiber makes the light path easy to accommodate to complex spaces, such as remote or narrow and small space. Besides, orthogonally polarized light inside PM fiber can eliminate the measurement error on account of environment disturbance. At present, the displacement resolution could be less than 10nm, which shows a great potential in nano-metrology.

Suppression of FM-to-AM modulation by polarizing fiber front end for high-power lasers.

FM-to-AM modulation is an important effect in the front end of high-power lasers that influences the temporal profile. Various methods have been implemented in standard-fiber and polarization-maintaining (PM)-fiber front ends to suppress the FM-to-AM modulation. To analyze the modulation in the front end, a theoretical model is established and detailed simulations carried out that show that the polarizing (PZ) fiber, whose fast axis has a large loss, can successfully suppress the modulation. Moreover, the stability of the FM-to-AM modulation can be improved, which is important for the front end to obtain a stable output. To verify the model, a PZ fiber front end is constructed experimentally. The FM-to-AM modulation, without any compensation, is less than 4%, whereas that of the PM fiber front end with the same structure is nearly 20%. The stability of the FM-to-AM modulation depth is analyzed experimentally and the peak-to-peak and standard deviation (SD) are 2% and 0.38%, respectively, over 3 h. The experimental results agree with the simulation results and both prove that the PZ fiber front end can successfully suppress the FM-to-AM conversion. The PZ fiber front end is a promising alternative for improving the performance of the front end in high-power laser facilities.

Investigation on the Stability of WSe2-PVA Saturable Absorber in an all PM Q-Switched Fiber Laser

In this paper, we demonstrate an all polarization maintaining (PM) Q-switched erbium-doped fiber laser based on tungsten diselenide-polyvinyl alcohol ( $\rm{WSe}_{{2}}\rm{-PVA}$ ) saturable absorber (SA) and investigated the stability of $\rm{WSe}_{{2}}\rm{-PVA}$ SA in the laser. The all PM cavity isolated the environmental perturbation on the cavity birefringence so that the evolution of material properties of $\rm{WSe}_{{2}}\rm{-PVA}$ SA during the Q-switched operation can be investigated based on the laser output. It is found that when heat accumulation reached a certain level in $\rm{WSe}_{{2}}\rm{-PVA}$ SA, PVA in SA would first melt and perturb the transmission of SA; then, WSe2 in SA would be quickly damaged, resulting in a permanent increase of the SA loss. This work will benefit the research on obtaining a long-term stable all PM Q-switched lasers based on 2-D material saturable absorber.