Solid-core Photonic Bandgap Fiber Research Articles

Large Mode Area Solid-Core Photonic Bandgap Yb-Doped Fiber With Hetero-Structured Cladding for Compact High-Power Laser Systems

We report on the design, realization and testing in pulsed amplification regime of a double-cladding, large mode area, polarization maintaining, solid core photonic bandgap fiber with Yb-doped core obtained from a Sol-Gel -made material. A specific hetero-structuration of the cladding has been applied to efficiently reject the higher-order modes, making the fiber single-mode in practice. When used as the last stage of a high power fiber amplifier, more than 90 W average power has been extracted at 1.03 μm wavelength with a slope efficiency of 75 % with respect to the absorbed pump power. These performances were obtained for a 6 m-long piece of fiber bent on a radius smaller than 12.5 cm. A mode field diameter of 35 μm is reported for the amplified beam with very good spatial quality and polarization extinction ratio.

Amplification of orbital angular momentum modes in an erbium-doped solid-core photonic bandgap fiber

Abstract A new kind of erbium-doped solid-core photonic bandgap fiber (ED-SC-PBGF) for amplification of orbital angular momentum (OAM) modes is proposed and investigated. The configurations of annular erbium-doped profile with special design and multi pump modes are used to amplify the signal modes evenly. Using an optimized ED-SC-PBGF pumped with l = 1 and 2 modes, differential mode gains of 0.9 dB and gain of more than 20 dB can be achieved for l = 1 and 2 OAM signal modes across the full C-band. This OAM-in-fiber amplification techniques would have potential application in ultra-long distance and high capacity OAM optical communication systems and other systems that utilize high power OAM light.

μJ-level Raman-assisted fiber optical parametric chirped-pulse amplification.

We experimentally demonstrate the amplification of chirped pulses in a fiber optical parametric chirped pulse amplifier up to 1μJ. This high energy level originates from combined Raman and parametric processes in a specially designed solid core photonic bandgap fiber. Output pulses are recompressed up to 560fs. These performances make this all-fiber system compatible with first stages of bulk amplification chains.

Design and fabrication of a heterostructured cladding solid-core photonic bandgap fiber for construction of Mach-Zehnder interferometer and high sensitive curvature sensor.

A heterostructured cladding solid-core photonic bandgap fiber (HCSC-PBGF) is designed and fabricated which supports strong core mode and cladding mode transmission in a wide bandgap. An in-line Mach-Zehnder interferometer (MZI) curvature sensor is constructed by splicing single mode fibers at both ends of a HCSC-PBGF. Theoretical analysis of this heterostructured cladding design has been implemented, and the simulation results are consistent with experiment results. Benefiting from the heterostructured cladding design, an enhanced curvature sensing sensitivity of 24.3 nm/m-1 in the range of 0-1.75 m-1 and a high quality interference spectrum with 20 dB fringe visibility are achieved. In order to eliminate the interference of longitudinal strain and transverse torsion on the result of the curvature sensing experiment, we measure the longitudinal strain and transverse torsion sensing properties of HCSC-PBGF, and the results show that the impact is negligible. It is obvious that this high-sensitivity and cost-effective all fiber sensor with a compact structure will have a promising application in fiber sensing.

All fiber M-Z interferometer for high temperature sensing based on a hetero-structured cladding solid-core photonic bandgap fiber.

We proposed and experimentally demonstrated a high temperature fiber sensor using a hetero-structured cladding solid-core photonic bandgap fiber (HCSC-PBGF) for the first time to our knowledge. A hetero-structured cladding solid-core photonic bandgap fiber is designed and fabricated that supports vibrant core mode and cladding mode transmission. Then, an all fiber M-Z interference sensor is constructed by splicing single mode fiber at both ends of HCSC-PBGF without any other micromachining. The transmission characteristics of HCSC-PBGF are analyzed with a full-vector beam propagation method and a full-vector finite element method, and the simulation results are consistent with experiment results. The sensitivity of this fiber sensor is as high as 0.09 nm/°C when operating from room temperature to 1000 °C, and the fringe contrast keeps stable and clear. It is obvious that this all fiber sensor will have great application prospects in fiber sensing with the advantages of a compact structure, high sensitivity, and cost-effectiveness.

Fiber-based ultrashort pulse delivery for nonlinear imaging using high-energy solitons.

We present an approach for fiber delivery of femtosecond pulses relying on pulse breakup and soliton self-frequency shift in a custom-made solid-core photonic bandgap fiber. In this scheme, the fiber properties themselves ensure that a powerful Fourier-transform-limited pulse is emitted at the fiber output, hence doing away with the need for complex precompensation and enabling tunability of the excitation. We report high-energy soliton excitation for two-photon fluorescence microspectroscopy over a 100-nm range and multimodal nonlinear imaging on biological samples.

Measurement of higher order chromatic dispersion in a photonic bandgap fiber: comparative study of spectral interferometric methods

Chromatic dispersion of a 37 cm long, solid-core photonic bandgap (PBG) fiber was studied in the wavelength range of 740-840 nm with spectral interferometry employing a Mach-Zehnder interferometer and a high resolution spectrometer. The interferometer was illuminated by a Ti:sapphire laser providing 20 fs pulses. A comparative study has been carried out to find the most accurate spectral phase retrieval method that is suitable for measuring higher order chromatic dispersion. The stationary phase point, the minima-maxima, the cosine function fit, the Fourier transform, and the windowed Fourier transform methods were tested. It was shown that out of these five techniques, the Fourier-transform method provided the dispersion coefficients with the highest accuracy, and it could also detect rapid phase changes in the vicinity of leaking mode frequencies within the transmission band of the PBG fiber.

A 98 W 1178 nm Yb-doped solid-core photonic bandgap fiber oscillator

A high-power ytterbium-doped solid-core photonic bandgap fiber laser directly oscillating at 1178 nm is reported. The sharp-cut bandpass distributed filtering effect of photonic bandgap fiber can suppress amplified spontaneous emission (ASE) in the conventional high-gain spectral region. The oscillator is composed of a high reflection fiber Bragg grating spliced with a 39 m gain fiber and a Fresnel fiber end surface. A model based on rate equations is investigated numerically. A record output power of 98 W is achieved with a slope efficiency of 54%. The laser linewidth is 0.5 nm. The spectrum at 98 W indicates that ASE and parasitic lasing are suppressed effectively.

Refractive Index Sensors Based Resonant Coupling in Solid-Core Photonic Band-Gap Fibers

A novel refractive index sensor based on the resonant coupling mechanism is proposed. The sensor consists of a standard index-guiding solid fiber core and several periodically distributed micro fluidic channels. When the channels are infiltrated with high-index fluid, the resonant coupling between the core mode and cladding modes makes the sensing fiber to be a stop-band filter. Since the filtering effect introduced by the photonic band-gap of the cladding is sensitive to the refractive index of the measurand, numerical results reveal that the sensitivity of the sensor could reach 17250nm/RIU, which is much higher than traditional refractive index fiber sensors.

Single-Mode, Large Mode Area, Solid-Core Photonic BandGap Fiber With Hetero-Structured Cladding

We theoretically and experimentally analyze the benefit of hetero-structured cladding in Solid-Core Photonic BandGap fibers so as to increase the loss ratio between high order modes and fundamental mode. This property is applied to the realization of 19-cells core fibers practically single-mode around 1050 nm. When designed to operate in the 4th BandGap, a new design is proposed which permits to obtain mode field diameter of 44 μm whereas, for operation in the 3rd BandGap, a mode field diameter of 33 μm is obtained with 20 cm bending radius. The impact of the shape of hetero-structure on single-mode behavior is discussed.

Higher-order core-guided modes in two-dimensional photonic bandgap fibers

We numerically and theoretically investigate the core modes of two-dimensional solid-core photonic bandgap (PBG) fibers based on hexagonal arrays of high-index circular rods. Such fibers guide light in discrete bandgaps, and the number of core-guided modes depends on the order of the bandgap as well as the position within the bandgap. We first classify the different core-guided modes in such fibers and we discuss the links among band structure, losses, and number and type of modes. We demonstrate that, similar to the case of bandgapless Kagome and ring-based fibers, solid-core bandgap fibers can have core-guided modes that are within photonic bands of the cladding. We discuss the classification of core modes in such fibers, and highlight analogies and differences with that of index-guiding fibers. Through an asymptotic expansion of an analytic model of a fiber’s photonic bands, we show that, in the limit of higher-order gaps (i.e., short wavelengths), the number of modes in the middle of gaps tends to a constant that is independent of refractive index contrast, as is the case for index-guiding photonic crystal fibers. We also discuss the evolution of the effectively single-mode propagation regime with geometrical parameters of structures having constant or variable band diagrams. For small- and large-core PBG fibers, we compute the exact number of core-guided modes within the center of the transmission band. We discuss their evolution with gap orders and coupling strength between high-index inclusions in the cladding. We find good agreement of the core-guided mode number in the center of the gaps computed with our theoretical model and with a numerical method for short wavelengths.

High power Yb-doped photonic bandgap fiber oscillator at 1178 nm

An ytterbium-doped solid-core photonic bandgap fiber oscillator in an all-fiber format is investigated for high power at an extreme long wavelength. The photonic bandgap fiber is spliced with two fiber Bragg gratings to compose the cavity. The sharp-cut bandpass distributed filtering effect of the photonic bandgap fibers efficiently suppresses amplified spontaneous emission in the conventional high-gain region. Fine adjustment of the short cut-off wavelength by coiling with tighter diameter is performed to suppress parasitic lasing. A record output power of 53.6 W with a slope efficiency of 53% at 1178 nm was demonstrated.

Benefits of Photonic Bandgap Fibers for the Thermal Stabilization of Optoelectronic Oscillators

This work reports on the analysis of optoelectronic oscillators (OEO) realized with various kinds of microstructured optical fibers (MOF) as delay lines. More precisely, the thermal dependence of the group delay is measured through the analysis of the thermal variation of the frequency of the OEO and compared with a theoretical model that includes the effect of temperature on refractive index, strains, and deformation. It is shown that, whereas the presence of air in air/silica fibers guiding via modified total internal reflection (M-TIR) has only little interest, it allows a net decrease of the thermal variation of the group delay in the case of hollow core photonic bandgap (HC-PBG) fiber. In addition to the effect of material, we show that this decrease is related to the PBG mechanism itself, which is a property also exploited in a solid-core photonic bandgap (SC-PBG) fiber.

Sub-30-fs Pulse Generation From Dispersion-Managed Yb:Fiber Ring Laser Incorporating Solid-Core Photonic Bandgap Fiber

We demonstrate a Yb:fiber ring laser incorporating a piece of solid-core photonic bandgap fiber for intra-cavity group delay dispersion compensation. The output pulse was as short as 29 fs after a prism pair compression with a spectral bandwidth of 41 nm. The output power was 150 mW at a repetition rate of 130 MHz.

Manipulating the Propagation of Solitons with Solid-Core Photonic Bandgap Fibers

We review the dynamics of soliton self-frequency shift induced by Raman gain in special solid-core photonic bandgap fibers and its consequences in terms of supercontinuum generation. These photonic bandgap fibers have been designed to allow nonlinear experiments in the first bandgap without suffering from significant loss even when working close to the photonic bandgap edge. We studied experimentally, numerically, and analytically the extreme deceleration of the soliton self-frequency shift at the long-wavelength edge of the first transmission window. This phenomenon is interpreted as being due to a large variation of the group-velocity dispersion in this spectral range and has been obtained with no significant power loss. Then, we investigated experimentally and numerically the generation of supercontinuum in this kind of fibers, in both spectral and temporal domains. In particular, we demonstrated an efficient tailoring of the supercontinuum spectral extension as well as a strong noise reduction at its long-wavelength edge.

Solid-core photonic bandgap fibers for cladding-pumped Raman amplification

Cladding-pumped solid-core photonic bandgap Raman fiber amplifiers are analyzed theoretically as possible candidates for power scaling. An example fiber design with a mode field diameter of 46 µm and a cladding diameter of 250 µm is calculated to exhibit 0.12 dB/km of confinement loss at the first Stokes wavelength and >10 dB/m at the second Stokes wavelength for a pump wavelength of 1.567 µm while maintaining low loss and large mode area in realistic coiling configurations. A Raman amplifier based on this fiber with 85 kW of output power, 78% optical conversion efficiency, a maximum heat load of 130 W/m, and a length of 235 m is simulated.

Design of solid core photonic bandgap fibers for visible supercontinuum generation

We present a numerical study of two dimensional solid core photonic bandgap fiber design criteria for their particular application to blue/visible supercontinuum generation. By exploiting their strong frequency-dependent dispersion when compared to index guiding micro-structured fibers, we highlight the design of solid core photonic bandgap fibers to fulfill group index matching conditions between the first ejected optical soliton and the trapped dispersive wave generated in the visible wavelength range. We study how these matching conditions depend on the opto-geometrical parameters of the micro-structured cladding, and we use frequency-domain numerical simulations to determine the expected supercontinuum spectral characteristics for selected cases. We investigate design criteria to generate short wavelengths by pumping in such photonic bandgap fibers in different pulse duration regimes and we identify a novel class of short wavelength (blue/visible) supercontinuum generation in the 3rd bandgap of a typical structure by pumping into the 2nd bandgap through a high attenuation spectral region.

Significant reduction of power fluctuations at the long-wavelength edge of a supercontinuum generated in solid-core photonic bandgap fibers

We show that the infrared edge of supercontinua generated in solid core photonic bandgap fibers is characterized by a very different temporal behavior than the one obtained in standard fibers. In particular, pulse-to-pulse spectral power fluctuations are significantly reduced near the bandgap edge, and the statistical distribution is quasi-gaussian. The spectral dynamics of this process and statistical properties are investigated experimentally and confirmed by numerical simulations. The reduction of power fluctuations originates from the cancellation of the soliton self-frequency shift near the bandgap edge.

Extreme deceleration of the soliton self-frequency shift by the third-order dispersion in solid-core photonic bandgap fibers

We report an experimental study of the nonlinear propagation of femtosecond pulses in solid-core photonic bandgap fibers. An extreme deceleration of the soliton self-frequency shift accompanied by a spectral compression is observed near the photonic bandgap edge. In practice, this extreme deceleration is equivalent to a suppression of the soliton self-frequency shift and so to a stabilization of the soliton frequency. The physical origin of this phenomenon is discussed with the help of numerical simulations. Finally, a simple model is proposed to identify the main physical mechanism responsible for the extreme deceleration of soliton self-frequency shift. In the case of our fiber design, it is mainly due to the strong third-order dispersion experienced by the soliton as it approaches the photonic bandgap edge.

Effective area limit of large-mode-area solid-core photonic bandgap fibers for fiber laser applications

We investigate the bending characteristics of solid-core photonic bandgap fibers (SC-PBGFs) aiming to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for high-power Yb-doped fiber lasers and amplifiers. Through detailed numerical simulations based on the finite element method (FEM), we evaluate the impacts of the order of photonic bandgap on the bending performance and point out the limits of core size enlargement in the SC-PBGFs with a 1-cell core structure due to the increment of bending loss. In addition, under practical constraints, we find that the SC-PBGFs having a 7-cell core can achieve sufficient differential bending loss between the fundamental mode and the higher-order modes and a much larger effective area limit as compared with previously-reported index-guiding LMA fibers.