Polarization-maintaining Fiber Research Articles

Watt-level deep-UV subnanosecond laser system based on Nd-doped fiber at 229 nm.

We report an efficient deep-UV master-oscillator power amplifier (MOPA) laser system at 229 nm that generates 350 ps pulses at 2 MHz repetition rate with an average power of 1.2 W. The use of a polarization-maintaining large mode area neodymium-doped fiber operating on the 4F3/2→4I9/2 transition allows high-power laser emission of up to 28 W near 915 nm in the sub-nanosecond regime with low spectral broadening. Two nonlinear frequency conversion stages (LBO + BBO crystals) in a single-pass configuration directly convert the IR laser emission to deep UV. This laser demonstrates the great potential of Nd3+-doped fiber lasers to produce high-power deep-UV emission.

3.2 kW, 0.22 nm narrow-linewidth MOPA configuration fiber laser with a homemade polarization-maintaining Yb-doped fiber

In this work, a narrow-linewidth linearly polarized fiber amplifier with a record output power of 3.2 kW was achieved based on a homemade polarization-maintaining Yb-doped fiber corresponding to a slope efficiency of 79% and a 3 dB linewidth of 0.2227 nm. By examining various numerical aperture (NA) PMYDFs, the experimental investigation on expanding mode instability (MI) threshold in PM fiber amplifiers was put on display. And the results reveal that the MI threshold is enhanced by more than 370 W for every 0.004 decrease in core numerical aperture. Increasing the seed linewidth from 0.0454 nm to 0.0976 nm by adding 200 m polarization maintaining Ge-doped fiber the stimulated Brillouin scattering threshold increased from 805 W to above 3.2 kW. By applying the MI suppression method, a double-eight-shaped aluminum plate was adopted to coil the gain fiber, and the MI threshold increased by more than 1100 W.

Large-mode-area soliton fiber oscillator mode-locked using NPE in an all-PM self-stabilized interferometer.

In this work, we investigate an approach to scale up the output pulse energy in an all-polarization-maintaining 17.3 MHz Yb-doped fiber oscillator via implementation of a 25 µm core-diameter large-mode-area fiber. The artificial saturable absorber is based on a Kerr-type linear self-stabilized fiber interferometer, enabling non-linear polarization rotation in polarization-maintaining fibers. Highly stable mode-locked steady states in the soliton-like operation regime are demonstrated with 170 mW average output power and a total output pulse energy of ∼10n J distributed between two output ports. An experimental parameter comparison with a reference oscillator constructed with 5.5 µm core-sized standard fiber components reveals an increase of pulse energy by a factor of 36 with simultaneously reduced intensity noise in the high-frequency range >100k H z.

Polarization maintaining harmonically mode-locked fiber laser with suppressed supermode noise due to continuous wave injection

We report on experimental studies of a SESAM mode-locked Er-doped fiber laser completely spliced from polarization-maintaining fiber components. With the fiber mode spot properly aligned to the SESAM, the laser operates harmonic mode-locking (HML) available in a whole range of pump powers up to ∼355mW with the supermode suppression level (SSL) less than 25 dB. Importantly, the HML laser generates the pulses in a linear polarization state and enables the pulse repetition rate (PRR) up to ∼1145 MHz. In our experiments we show that an optical injection of an external continuous wave (CW) into the laser cavity improves the stability of the laser operation in HML regime resulting in an increase of the SSL by 20–30 dB. Besides, the CW injection is able to expand the range of pump powers available with HML laser providing an increase of the maximal laser PRR up to ∼2195 MHz. Importantly, the implemented optical injection does not affect high purity of the laser polarization state. The presented numerical simulations enable qualitative explanations of the effects observed experimentally.

Tunable and switchable dual-wavelength SLM narrow-linewidth fiber laser with cascaded passive double-ring cavity narrowband filters

In this article, we have proposed and demonstrated a tunable, switchable dual-wavelength linear cavity fiber laser, which has a passive dual ring cavity structures (DRCs) and polarization-maintaining fiber Bragg grating (PM-FBG), and can be used for the operation of single-longitudinal mode(SLM), narrow-linewidth, and orthogonal single polarization. The passive DRCs, consisted of four 2 × 2 optical couplers (OCs), work as the narrow-band filter and mirror. The tunable and switchable wavelength of the fiber laser is realized by stretching PM-FBG and adjusting the polarization controller (PC). The optical signal-to-noise ratio (OSNR) at the dual-wavelength operating state can be more than 45 dB in the tunable range. While the OSNR of fiber laser at the each-wavelength operating state can reach 50 dB with the maximum wavelength and power fluctuation of 0.01 nm and 1.2 dB, during the monitoring time of 40 min. In addition, the measured laser linewidths are 375 Hz and 420 Hz, respectively. Meanwhile, the states of polarization are orthogonal single polarization, and the degree of polarization (DOP) is close to 100 %.

Polarization-maintaining large-mode-area solid-core anti-resonant fiber for high-power fiber lasers

A polarization-maintaining large-mode-area solid-core anti-resonant fiber is investigated in this work with double-layer anti-resonant elements for improved capability on fundamental mode guidance and higher order mode suppression, and structural and material asymmetry on inner-layer cladding tubes for high birefringence. Mode coupling between fundamental core mode in one polarization direction and mode on two high-index inner cladding tubes is used to enhance the fiber birefringence under large core diameter. Eventually, an optimized design of polarization-maintaining large-mode-area solid-core anti-resonant fiber with the currently largest mode field area of 3026 μm2 and birefringence of 1.20 × 10−5 can be anticipated with the confinement losses for all the higher order modes exceeding 10 dB/m. Moreover, confinement loss below 0.1 dB/m can still be obtained for the fundamental core mode in both polarization direction even under the mode-coupling effect. Active polarization-maintaining anti-resonant fiber is analyzed and the refractive index of the central rare-earth-doped region is optimized for the first time for both well guided signal and pump laser. Large pump absorption coefficient can thus be anticipated from the multimode laser core-pumped active large-mode-area fiber, which facilitates short active fiber length needed for sufficient laser gain. The fiber proposed here offers great potential for the development of high-performance fiber laser sources including high-power single-frequency fiber amplifiers and high-peak-power ultrashort pulsed fiber amplifiers.

Dynamics of frequency detuning in a hybrid Er-doped mode-locked fiber laser

Frequency detuning of mode-locked fiber lasers displays many remarkable nonlinear dynamical behaviors. Here we report for the first time the evolution of pulses from mode-locking through period pulsation to Q -switched mode-locking for three fundamental cases. Our experiments are performed in a hybrid actively and passively amplitude-modulated all-fiber polarization-maintaining mode-locked fiber laser, where the amplitude modulation frequency artificially deviates from the fundamental frequency of the cavity. We design and numerically simulate the laser with coupled Ginzburg–Landau equations. The experimentally observed dynamics of the mode detuning process is discussed with the assistance of the fitted model and numerical simulations, showing the generalizability of the optical mode detuning variation process. Our work provides fundamental insights for understanding perturbations in nonlinear optical resonant cavities and expands the ideas for studying chaotic path theory in hybrid mode-locked fiber lasers.

High Sensitivity Temperature Sensor Based on Harmonic Vernier Effect

A high-sensitivity temperature sensor based on the harmonic Vernier effect is proposed and verified by experiments. The main component of the sensor is a Sagnac interferometer consisting of two sections of polarization maintaining fibers (PMFs) spliced with an intersection angle of 45° between their fast axes. The harmonic Vernier effect is achieved by setting the length of one of the PMFs an integral multiple (i-times) of the length of the other plus a detuning factor. Compared with the Sagnac interferometer based on the fundamental Vernier effect, the temperature sensitivity of the harmonic Vernier effect is higher, reaching i+1 times of that of the fundamental Vernier effect (i is the order of the harmonic).

Highly birefringent one-air-hole panda fiber.

This Letter proposes a highly birefringent one-air-hole panda fiber, which is fabricated by corroding a single stress zone of the traditional panda-type polarization-maintaining fiber (PMF). An additional geometric asymmetry is induced in the fiber to increase the birefringence effect and enhance the light-matter interaction, which improves the performance of the sensor and the device applications of the special fiber. A theoretical and experimental analysis of the one-air-hole panda fiber demonstrates that the birefringence of the fiber can be of the order of 10-3, which is one order of magnitude higher than that of the traditional panda-type fiber. The corroded region provides a microchannel to be filled with a functional material to compose optical fiber sensors; a sample of a salt solution was filled into the microchannel to measure the refractive index with a sensitivity of 3760 nm/RIU (refractive index units).

Oscillating soliton molecules induced by strong vector-mode coupling

Soliton molecules, composed of closely spaced pulses with strong internal interactions, have been in-depth studied in fiber lasers due to their fascinating evolution dynamics and potential applications in high-speed optical communications. Here we demonstrate a type of oscillating soliton molecules in a mode-locked fiber laser constituted by single-mode and polarization-maintaining fibers. Ascribing to the unequal coupling between two orthogonal-polarized vector modes, the constituent pulses of soliton molecules possess different intensities and further result in a dual-roundtrip and large-period oscillation. Numerical simulations reproduce the critical experimental phenomena and show that two vector modes display diverse departing behavior in polarization-maintaining fiber. This work sheds light on the role of strong birefringence on vector solitons, providing a flexible nonlinear system to generate and study oscillating soliton molecules.

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.

Temperature response of a fiber end-face integrated lithium niobate crystal probe based on pyroelectric and thermo-optic effects via polarization state modulation

This paper presents the temperature response in a fiber end-face integrated lithium niobate (LN) crystal probe. It is a reflective probe. The fiber end-face integrated with components such as a focusing lens, a quarter waveplate, a cube of LN crystal and a gold mirror. Thanks to the pyroelectric and thermo-optic effects of the LN, the temperature response with a steep change in a narrow range of temperature is observed and it might be exploited in temperature measurement applications. The ambient temperature is mapped to the output light via polarization state modulation (PSM) method. Experimentally, the change of exit beam polarization is measured as the variation of the S1. The experimental results show that the variation of the S1 per unit interaction length which is the sensitivity reaches 5.37 K−1cm−1 in the temperature range of 309.95 K to 316.15 K. It is 447 times higher than that in a polarization-maintaining fiber (PMF). The temperature accuracy is 0.86 K in the range of 311.15 K to 316.15 K which is estimated via the standard deviation between the experimental data and fitting cure. In terms of size, the sensitive material lithium niobate cube has a side length of 2 mm and the total length including all the assembled optical components is 1.7 cm. Due to the compact size and optic signal transmission, the probe might be used in biological domain such as measuring core temperature and in industrial fields such as remote monitoring.

Wavelength and pulse width programmable mode-locked Yb fiber laser.

To the best of our knowledge, this study is the first demonstration of a mode-locked polarization-maintaining Yb fiber laser that incorporates a liquid-crystal-on-silicon-based electrically programmable filter into the cavity. The intracavity filter continuously tunes pulse characteristics, such as a wavelength tunable range of 1018-1065 nm and pulse width tunable range of 0.3-2.6 ps. Further, numerical simulations of the laser oscillator results were consistent with the experimental results and confirmed the mode-locked pulse generation regime. The proposed technique is expected to have great potential as a seed laser for multifunctional ultrashort-pulse lasers.

Compact and high-reliability fiber-optic open-loop gyroscope enabled by an in-fiber polarizer.

The performance of an open-loop fiber-optic gyroscope is strongly dependent on the optical characteristics of its polarizer. Here we report the implementation of an in-house fabricated 45° tilted-fiber-grating-based polarizer, for the first time on an ultra-fine diameter polarization-maintaining fiber platform in an open-loop fiber-optic gyroscope. This special in-line polarizer is proven to have the merits of high extinction ratio, broad spectrum, bendability, stretchability, temperature insensitivity, and high reliability, all of which make it a perfect match for practical fiber optic gyros that need to be packaged compactly without affecting performance. Our prototype fiber optic gyroscope has a compact volume of only ϕ35 × 20 mm2, achieving a bias instability of less than 0.1 °/h, full temperature bias stability of less than 1 °/h, and scale factor linearity of better than 200 ppm. This compact and high-performance fiber gyro enabled by TFG polarizer may promise great potential in the field of automation and control.

Thermal Sensitivity of Birefringence in Polarization-Maintaining Hollow-Core Photonic Bandgap Fibers

Polarization-maintaining (PM) fiber is the core sensitive component of a fiber optic gyroscope (FOG); its birefringence temperature stability is crucial for maintaining accuracy. Here, we systematically investigated the structural thermal deformation and the resulting birefringence variation in typical PM hollow-core photonic bandgap fibers (HC-PBGFs) for FOG according to varying fiber structure parameters. To verify the application potential of PM HC-PBGFs in FOG, we compared the thermal sensitivity of birefringence (TSB) with that of the commonly used Panda PM fiber, which was tested to 5.07 × 10−5/100 °C. For rhombic-core fibers, the TSB was determined by the structure of the cladding and could be tuned as low as low as 10−7/100 °C, two orders of magnitude smaller than that of the panda PM fibers. For hexagonal-core fibers, the birefringence variation depended mainly on the drift of the surface modes (SMs) caused by the deformation of the core. A slight drift in SMs could cause a dramatic birefringence variation in hexagonal-core fiber, and the TSB could be as high as 10−4/100 °C, much higher than that of panda PM fiber. This study lays the foundation for the development of high birefringence temperature-stable HC-PBGFs and their applications in FOG.

Tilted fiber grating polarizer in a 40-µm polarization-maintaining fiber.

The optical polarizer is a crucial component widely used in many optical systems and applications. Fiber-optic polarizers have the merits of excellent compatibility and ease of integration with other fiber components. We report an in-line polarizer enabled by a 45° tilted fiber grating inscribed into a specialty fiber for the next generation fiber-optic gyroscope, i.e.,a 40-µm ultra-fine-diameter tiger-type polarization-maintaining fiber with which the size of fiber-optic sensors can be miniaturized. The results show that a 40-mm-long polarizer operates at a center wavelength of around 830nm with high-performance characteristics, such as a polarization extinction ratio exceeding 30dB, a low insertion loss of less than 1.5dB, and a large 3-dB optical bandwidth more than 60nm. This kind of fiber-optic polarizer may have a broad scope across applications and systems such as fiber lasers and sensors, especially high-precision fiber-optic gyroscopes.

Theoretical and experimental investigations of dispersion-managed, polarization-maintaining 1-GHz mode-locked fiber lasers.

High-repetition-rate (up to GHz) femtosecond mode-locked lasers have attracted significant attention in many applications, such as broadband spectroscopy, high-speed optical sampling, and so on. In this paper, the characteristics of dispersion-managed, polarization-maintaining (PM) 1-GHz mode-locked fiber lasers were investigated both experimentally and numerically. Three compact and robust 1-GHz fiber lasers operating at anomalous, normal, and near-zero dispersion regimes were demonstrated, respectively. The net dispersion of the linear cavity is adjusted by changing types of PM erbium-doped fibers (EDFs) and semiconductor saturable absorber mirrors (SESAMs) in the cavity. Moreover, the long-term stability of the three mode-locked fiber lasers is proved without external control. In order to better understand the mode-locking dynamics of lasers, a numerical model was constructed for analysis of the 1-GHz fiber laser. Pulse evolution simulations have been carried out for soliton, dissipative-soliton, and stretched-pulse mode-locking regimes under different net dispersion conditions. Experimental results are basically in agreement with the numerical simulations.

Strain and temperature discrimination measurement sensor using MMF-PMF-THF fiber structure built in Sagnac loop

A strain and temperature discrimination Sagnac interferometric fiber sensor is proposed and demonstrated experimentally. A segment of polarization maintaining fiber (PMF) is sandwiched between the multi-mode fiber (MMF) and twin hole fiber (THF) to build a sensing component. Then proposed MMF-PMF-THF fiber configuration is connected to a 3 dB optical fiber coupler to construct a Sagnac loop. The experimental results have demonstrated that the fringe contrast reaches up to 22.3 dB. The strain and temperature sensitivities are 43 pm/με and −1.36 nm/0C respectively. The temperature error and strain error are ± 0.77 °C and ± 24.5με respectively.

Comments about birefringence dispersion, with group and phase birefringence measurements in polarization-maintaining fibers

A recent JEOS-RP publication proposed Comments about Dispersion of Light Waves, and we present here complementary comments for birefringence dispersion in polarization-maintaining (PM) fibers, and for its measurement techniques based on channeled spectrum analysis. We start by a study of early seminal papers, and we propose additional explanations to get a simpler understanding of the subject. A geometrical construction is described to relate phase birefringence to group birefringence, and it is applied to the measurement of several kinds of PM fibers using stress-induced photo-elasticity, or shape birefringence. These measurements confirm clearly that the difference between group birefringence and phase birefringence is limited to 15–20% in stress-induced PM fibers (bow-tie, panda, or tiger-eye), but that it can get up to a 3-fold factor with an elliptical-core (E-core) fiber. There are also surprising results with solid-core micro-structured PM fibers, that are based on shape birefringence, as E-core fibers.

Planar fiber-chip-coupling using angle-polished polarization maintaining fibers

We report on our latest developments of a planar fiber-chip-coupling scheme, using angle polished, polarization maintaining (PM) fibers. Most integrated photonic chip components are polarization sensitive and a suitable way to launch several wavelength channels with the same polarization to the chip is the use of PM fibers. Those impose several challenges at processing and handling to achieve a stable, permanent, and low-loss coupling. We present the processing of the fibers in detail and experimental results for our planar and compact fiber-chip-coupling technique.