Polarization-maintaining Photonic Crystal Fiber Research Articles

Monolithic all-PM femtosecond Yb-fiber laser stabilized with a narrow-band fiber Bragg grating and pulse-compressed in a hollow-core photonic crystal fiber

We report on an environmentally stable self-starting monolithic (i.e. without any free-space coupling) all-polarization-maintaining (PM) femtosecond Yb-fiber laser, stabilized against Q-switching by a narrow-band fiber Bragg grating and modelocked using a semiconductor saturable absorber mirror. The laser output is compressed in a spliced-on hollow-core PM photonic crystal fiber, thus providing direct end-of-the-fiber delivery of pulses of around 370 fs duration and 4 nJ energy with high mode quality. Tuning the pump power of the end amplifier of the laser allows for the control of output pulse bandwidth and duration. Our experimental results are in good agreement with the theoretical predictions.

Amplification and ASE suppression in a polarization-maintaining ytterbium-doped all-solid photonic bandgap fibre

We demonstrate suppression of amplified spontaneous emission at the conventional ytterbium gain wavelengths around 1030 nm in a cladding-pumped polarization-maintaining ytterbium-doped all-solid photonic crystal fibre. The fibre works through combined index and bandgap guiding. Furthermore, we show that the peak of the amplified spontaneous emission can be shifted towards longer wavelengths by rescaling the fibre dimensions. Thereby one can obtain lasing or amplification at longer wavelengths (1100 nm - 1200 nm) as the amount of amplification in the fibre is shown to scale with the power of the amplified spontaneous emission.

Pressure sensor realized with polarization-maintaining photonic crystal fiber-based Sagnac interferometer

A novel intrinsic fiber optic pressure sensor realized with a polarization-maintaining photonic crystal fiber (PM-PCF) based Sagnac interferometer is proposed and demonstrated experimentally. A large wavelength-pressure coefficient of 3.42 nm/MPa was measured using a 58.4 cm long PM-PCF as the sensing element. Owing to the inherently low bending loss and thermal dependence of the PM-PCF, the proposed pressure sensor is very compact and exhibits low temperature sensitivity.

Study on the Fabrication Process of Polarization Maintaining Photonic Crystal Fibers and Their Optical Properties

In this paper, we describe the fabrication process and the characteristics of polarization maintaining photonic crystal fibers (PM-PCFs). The PM-PCF is fabricated by stack-and-draw method, i.e., stacking silica capillary tubes (making a PM-PCF preform) and drawing to optical fiber. Firstly, a PM-PCF preform is formed by stacking two kinds of capillary tubes around a solid silica rod and jacketing these stacked tubes with an outer silica tube (out-jacket tube). Later, the desired preform is drawn to a fiber in a high temperature drawing tower. We also compare the polarization properties such as polarization dependent loss, birefringence, and differential group delay of the fabricated PM-PCF with those of the conventional PANDA PM fiber.

Fusion Splicing Photonic Crystal Fibers and Conventional Single-Mode Fibers: Microhole Collapse Effect

We investigate the microhole collapse property of different photonic crystal fibers (PCFs) and its effect on the splice loss using an electric arc fusion splicer. The physical mechanism of the splice loss for different kinds of PCFs is studied, and a guideline for splicing these PCFs and conventional single-mode fibers (SMFs) is proposed. We demonstrate a low-loss fusion splicing of five different PCFs with SMFs, including large-mode PCF, hollow-core PCF, nonlinear PCFs, and polarization-maintaining PCF.

Analysis of temperature-dependent birefringence of a polarization-maintaining photonic crystal fiber

We have analyzed the temperature-dependent birefringence of a polarization-maintaining photonic crystal fiber. The temperature-coefficient of birefringence, dB/dT, for a commercially available polarization-maintaining photonic crystal fiber was found to be approximately −2.0×10−9 K−1. This is 35 times smaller than that of a standard polarization-maintaining fiber, which was approximately −7.0×10−8 K−1. Based on numerical analysis of the fiber structures, we determined that the temperature-dependence of the birefringence of the polarization-maintaining photonic crystal fiber is mainly due to a combination of temperature-dependent structure and index change. Due to thermal expansion of the silica, the photonic crystal structure of the fiber deforms, resulting in the shifting of the photonic band gap, which results in the birefringence change. Temperature-dependent refractive index change of the silica also causes a shift in the photonic band gap and thus a birefringence change. The numerically calculated dB/dT of the photonic crystal fiber was found to be approximately (−4±2)×10−9 K−1, and is in excellent agreement with the experimental results.

All polarization‐maintaining type Yb mode‐locked fiber laser with photonic crystal fiber

AbstractWe have demonstrated a polarization‐maintaining (PM) Yb mode‐lock highly stable fiber laser with high beam quality. The characteristics of side‐hole type PM Yb‐doped fiber (YDF) were examined. The splicing connection between PM‐YDF and PANDA fiber was optimized. We optimized the laser oscillation output and improved the efficiency of the fiber length in the Fabry‐Perot cavity. We demonstrated an all PM single‐mode fiber ring cavity. Mode‐locking was produced by inserting a semiconductor saturable absorption mirror (SESAM). A PM photonic crystal fiber (PCF) was used for dispersion compensation in the cavity. Stable mode‐lock operation with 500‐ps pulses at 7.2 MHz was observed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(5): 27–32, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20326

Temperature-insensitive strain sensor with polarization-maintaining photonic crystal fiber based Sagnac interferometer

A fiber-optic strain sensor is demonstrated by using a short length of polarization-maintaining photonic crystal fiber (PM-PCF) as the sensing element inserted in a Sagnac loop interferometer. Spectrum shift in response of strain with a sensitivity of 0.23pm∕με is achieved, and the measurement range, by stretching the PM-PCF only, is up to 32mε. Due to the ultralow thermal sensitivity of the PM-PCF, the proposed strain sensor is inherently insensitive to temperature, eliminating the requirement for temperature compensation.

Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm

Use of photonic crystal fibers (PCFs) in the field of sensing is relatively new. We propose the application of a PCF for pressure sensing. The fiber analyzed is a polarization-maintaining PCF that has negligible sensitivity to temperature, making it an ideal candidate for pressure sensing in harsh environments. On the basis of theoretical and experimental analysis, PCF is proposed to be applied as a temperature-compensated pressure sensor. Detailed theoretical analysis and the experiment carried out are described to show the concept of the sensor.

Highly birefringent elliptical-hole photonic crystal fiber with squeezed hexagonal lattice

We propose a novel polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core and a cladding with squeezed-hexagonal-lattice elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental modes in such PCFs. Numerical result shows that very high modal birefringence with a magnitude of the order of 10(-2) around 1550 nm has been obtained. Furthermore, large normal dispersion appears over a wide range of wavelengths in both orthogonal polarizations.

Highly Birefringent Elliptical-Hole Photonic Crystal Fiber With Two Big Circular Air Holes Adjacent to the Core

In this letter, we propose a novel design for a polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core, two big circular air holes near the core, and a cladding with elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental mode in such a PCF. The numerical result shows that very high modal birefringence with magnitude of order of 10-3 has been obtained, which are higher than the birefringence induced by adding two big air holes near the core or using elliptical air holes in cladding separately

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Spectral Broadening in a Polarization-Maintaining PhotonicCrystal Fibre by Femtosecond Pulses from an Optical Parametric Amplifier

The spectral broadening with the bandwidth of 83 nm(1.2486–1.3318 μm) in the 1.3 μm region is achieved in a0.2-m-long, polarization-maintaining photonic crystal fibre (PCF) withan average core radius of 1.8 μm, pumped by optical pulses at thewavelength 1.269 μm, with the duration 250 fs and the repetitionrate 250 kHz from an optical parametric amplifier. The polarizationcharacteristics of the output spectra are also investigated.

Supercontinuum Generation Using a Polarization-MaintainingPhotonic Crystal Fibre by a Regeneratively Amplified Ti:Sapphire Laser

Supercontinuum with an ultra-broad bandwidth in the range from 380 nmto 1750 nm was generated by injecting 250 kHz 200 fs optical pulsesproduced by a regeneratively amplified Ti:sapphire laser into a2.5-m-long polarization-maintaining photonic crystal fibre (PCF). It isindicated that the mechanism for the supercontinuum generation in theanomalous dispersion region of the PCF are directly related to theRaman effect, the fission of higher-order solitons, nonsolitonicradiation, and the coinstantaneous effect of four-wave mixing. Thefrequency components beyond 1.4 μm were also observed. It isinterpreted that the energy of solitons is shifted beyond the OHabsorption with a higher input power.

Polarization-maintaining photonic crystal fibre

Photonic crystal fibres (PCFs) offer new possibilities of realizing highly birefringent fibres due to a higher intrinsic index contrast compared to conventional fibres. In this paper, we analyse theoretically the modal properties of a kind of polarization-maintaining PCF, namely the elliptical hole photonic crystal fibre (EHPCF) with a central small elliptical hole introduced in the core region. We demonstrate the possibility of achieving large birefringence with zero walk-off in the single-mode regime. This PCF also exhibits unusual dispersion properties. Several hundred nanometres of ultra broadband flattened dispersion near the wavelength 1.55μm is achieved in this EHPCF with a central small hole of dc=0.4Λ.

Near-Elliptic Core Polarization-Maintaining Photonic Crystal Fiber: Modeling Birefringence Characteristics and Realization

We investigate the modal birefringence behavior of a near-elliptic core index-guiding photonic crystal fiber (PCF) by using the first-order perturbation correction technique of mode analysis combined with semivectorial mode-field convergence method. The algorithm requires simple formulation, yields reasonably accurate results, and is efficient as needed for a design analysis; it is also applicable to any index-guiding regular structure/PCFs. The efficacy of our design tool has been verified with otherwise known solutions. Using this as a design recipe, we have realized PCFs with high birefringence characteristics.

Sagnac loop interferometer based on polarization maintaining photonic crystal fiber with reduced temperature sensitivity

A Sagnac loop interferometer based on polarization-maintaining photonic crystal fiber was built and analyzed. Mainly the temperature dependence of the Sagnac loop filter function was measured and analyzed. By measuring the filtering function of the Sagnac loop as a function of the temperature over 200 degrees C, we deduced an unambiguous temperature dependent birefringence coefficient, d n/dT = 2.0 x 10-9 /K. Over the full temperature swing, the maximum peak shifts was less than 10% of the filter period. For comparison, a standard Sagnac loop was built with the exact same length and experimental condition, where we deduced d n/dT = 7.0 x 10-8 /K.

Supercontinuum generation at 155 m in a dispersion-flattened polarization-maintaining photonic crystal fiber

We demonstrate the generation of symmetrical supercontinuum of over 40 nm in the 1.55 m region (1540 - 1580 nm) by injecting 1562 nm, 2.2 ps, 40 GHz optical pulses into a 200 m-long, dispersion-flattened polarization-maintaining photonic crystal fiber. The chromatic dispersion and dispersion slope of the fiber at 1.55 m are -0.23 ps/km/nm and 0.01 ps/km/nm2, respectively. This is the first report of 1.55 m band supercontinuum generation in a dispersion-flattened and polarization-maintaining photonic crystal fiber.

Structural rocking filters in highly birefringent photonic crystal fiber.

We report what we believe is the first example of efficient rocking filter formation in polarization-maintaining photonic crystal fiber. Very high coupling efficiencies (as much as -23.5-dB suppression of the input polarization) and loss of < 0.02 dB were achieved for fibers as short as 11 mm. The filters, which we prepared by periodic mechanical twisting and heating with a scanned CO2 laser beam, are highly compact, and they are expected to be temperature stable.

Design and Fabrication of Dispersion Controlled and Polarization Maintaining Photonic Crystal Fibers for Optical Communications Systems

ABSTRACTRecent progress on photonic crystal fibers (PCFs) is reviewed aiming at their application to high performance optical communications sytems. The optical properties, for example dispersion characteristics, can be set by selecting the appropriate combination of air hole diameter and air hole pitch. A noteworthy characteristic of PCFs is their strong birefringence, which suggests optical components with better polarization maintaining characteristics.This paper describes the characteristics of dispersion controlled PCFs and polarization maintaining PCFs. It describes theoretical analyses and experimental results of fabricated PCFs that have short wavelength zero dispersion at 810 nm, polarization maintaining capability with birefringence of 1 × 10−3, polarization maintaining dispersion flattened functions, and absolute single polarization state support with polarization dependent loss of 1 dB/m at 1550 nm. A supercontinuum generation experiment with PM-PCF in the 1550 nm region is shown with symmetrical spectral broadening to over 40 nm. The potential of PCFs will be discussed with reference to the next generation optical communications systems.