High Reflectivity Fiber Bragg Gratings Research Articles

Low-Cost Dispersion-Tuned Active Harmonic Mode-Locked Laser With a 3-cm Coherence Length

We propose a low-cost dispersion-tuned actively mode-locked laser with long coherence length (up to 3 cm) by combining a wide-band, high reflectivity, and high-dispersion chirped fiber Bragg grating (CFBG) with a reflective semiconductor optical amplifier (RSOA). The dependence of the tuning characteristics on the varying physical length of CFBG in the cavity is studied experimentally and theoretically in the CFBG and RSOA based laser for the first time. The results show that the wavelength tuning range reduces when the harmonic number is increasing. Moreover, the high-dispersion and high-reflectivity CFBG yields high optical signal to noise ratio (>48 dB), narrow spectral width (lower than 0.033 nm), and more than 3-cm coherence length in the harmonically mode-locked laser. This low-cost dispersion tuned mode-locked laser with wide tuning range, stable and small time-bandwidth product, and long coherence length can lead to enhanced applications.

Effect of active fiber birefringence on polarization properties of DBR all-fiber laser

The polarization properties of a distribute Bragg reflective (DBR) all-fiber laser configured with a common single mode high-reflectivity fiber Bragg grating (SM-FBG) and a polarization-maintaining fiber Bragg grating (PM-FBG) are analyzed theoretically and investigated experimentally. Matching the reflective peak of SM-FBG with one of the PM-FBG reflective peaks in an ideal active fiber (without birefringence) would yield a linear polarization light. However, the polarization properties of a fiber laser become very complex when a birefringence is induced into the active fiber. Different polarization properties (linear polarization, elliptical polarization, or circular polarization) of the fiber laser appear with the variation of the birefringence. Two perpendicular axes in the active fiber induced by the birefringence effect must be matched with that of PMFBG to realize the linear polarization output.

100-mW linear polarization single-frequency all-fiber seed laser for coherent Doppler lidar application

A compact short-cavity fiber laser configured with Er 3+/Yb 3+ highly co-doped phosphate glass fiber with stable linear polarization and single frequency output is proposed and investigated experimentally. The fiber laser is composed of a high-reflectivity fiber Bragg grating (HRFBG) and a polarization-maintaining fiber Bragg grating (PMFBG) with the matched wavelengths at 1540.3 nm, which aims at one of the center wavelengths of the atmospheric transmission windows and may be used as the local oscillator (LO) of the coherent Doppler lidar (CDL). The output power of the laser reaches more than 114-mW, the signal-to-noise ratio is larger than 70 dB and the laser linewidth is about 4.1-kHz. Moreover, the linear polarization with 40.5 dB extinction ratio, the power fluctuation of less than ± 0.25% and the frequency fluctuation of less than ± 80 MHz are also obtained. Compared with the DFB fiber laser, the proposed fiber laser is more suitable for the CDL applications.

Time-domain optical reflectometry measurements using a frequency comb interferometer

We characterize the temporal response of fiber-optic components using a fiber-based frequency comb interferometer; measurements are compared and validated against a commercial instrument. The main advantage of the instrument lies in the absence of moving parts or a tunable laser, leading to very fast scanning. A measurement of a mechanical distortion, cycled at 130 Hz, on a fiber Bragg grating (FBG) is presented. A complete profile of the mechanical distortion is taken every 2.5 ms (400 Hz scanning speed) and each "snapshot" is taken in 200 micros. This scanning speed was arbitrarily chosen, and the instrument could be set to scan much faster, up to hundreds of kilohertz. With high-reflectivity FBGs, the same instrument could scan simultaneously the profile of 140 wavelength-multiplexed FBGs at 2 kHz.

Narrow Linewidth Tm3+-Doped Large Core Fiber Laser Based on a Femtosecond Written Fiber Bragg Grating

A diode laser (LD) clad-pumped narrow linewidth all-fiber Tm3+-doped fiber laser is reported with a maximal output power of 27 W at 1.947μm. By successively splicing an LD pigtail fiber, a single-mode Tm3+-doped fiber, and a multi-mode Tm3+-doped fiber, the fiber laser has 70 pm narrow linewidth output, and a high slope efficiency of nearly 47.5% with respect to the launched pump power. The high reflectivity fiber Bragg gratings, which are directly written into the single-mode Tm3+-doped fiber core by the 800 nm femtosecond pulsed laser, act as the high reflectivity coupler. The output laser has diffraction-limited beam quality with a factor M2 of 1.29, when the output laser power is nearly 27 W.

10.1007/s11490-008-3027-1

We report on a wide wavelength tuning in a double-clad ytterbium-doped fiber laser. The laser cavity consists of an array of broadband high-reflection fiber Bragg gratings and a bulk grating as the output coupler and wavelength selection element. The proposed fiber laser configuration combines a low intracavity loss of the fiber Bragg grating mirrors with a wide wavelength tuning of the bulk gratings. We demonstrate a >70-nm wavelength tuning range, limited only by the available fiber Bragg gratings.

Enhanced four-wave mixing in a high-finesse highly nonlinear fiber Fabry–Perot resonator

We have achieved a four-wave mixing process in a high-finesse highly nonlinear fiber Fabry–Perot resonator, where the amplified signal and idler were enhanced in transmission by 6 dB and 10 dB respectively comparing with those in a single fiber. We used a 6 m long low-loss Fabry–Perot resonator with two high-reflectivity fiber Bragg gratings written directly into a highly nonlinear fiber provided by Sumitomo Electric Inc., where the minimised intracavity loss resulted in the finesse in excess of 100. The resonator length was locked for 30 min by means of a modified Pound–Drever–Hall technique. The maximum intracavity power was increased by 14.3 dB by increasing the stimulated Brillouin scattering threshold with periodic phase modulation by a pseudo-random bit sequence, with length matching that of the cavity.

On the Design of Efficient and Accurate Arbitrary-Order Temporal Optical Integrators Using Fiber Bragg Gratings

In this paper, we propose and numerically investigate a simple and practical all-fiber design for implementing first-order and higher order all-optical passive temporal integrators with optimized energetic efficiencies. The proposed solution is based on a high-reflectivity fiber Bragg grating (FBG) providing a reflection spectral response that approaches the frequency transfer function of a time-limited <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> th-order optical integrator ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> = 1, 2, 3 ...). A closed-form analytical expression has been derived for the frequency response to be targeted for implementing an optical integrator of any given integration order operating over a prescribed limited time window. The required grating profile can then be designed using a layer-peeling FBG synthesis algorithm. Our simulations show that for a sufficiently long FBG, a relatively smooth amplitude-only apodization profile is required for any desired integration order even when an FBG peak reflectivity > 99% is targeted. The resulting FBG integrators can provide at least a sixfold increase in energetic efficiency as compared with previously proposed FBG designs while offering a similar or superior performance in terms of processing accuracy. We estimate that ultrafast highly efficient arbitrary-order all-optical temporal integrators capable of accurate operation over nanosecond time windows could be implemented using readily feasible, centimeters-long FBGs.

Broadband Tm-doped superfluorescent fiber source with 11 W single-ended output power

High-power operation of a cladding-pumped Tm-doped broadband superfluorescent fiber source in the two-micron wavelength regime is described. Predominately single-ended operation was achieved using a simple all-fiber geometry without the use of a high reflectivity mirror or fiber Bragg gratings. The source produced >11 W of single-ended amplified spontaneous emission output spanning the wavelength range from approximately 1930 nm to 1988 nm for a launched diode pump power of approximately 40 W at approximately 790 nm, corresponding to a slope efficiency of 38% with respect to launched pump power. The wavelength spectrum of the superfluorescent source spanned the range from approximately 1650 to 2100 nm with a bandwidth (FWHM) of > 100 nm for output power levels of < 20 mW.

73-nm tuning of a double-clad Yb3+-doped fiber laser based on a hybrid array

We report on a wide wavelength tuning in a double-clad ytterbium-doped fiber laser. The laser cavity consists of an array of broadband high-reflection fiber Bragg gratings and a bulk grating as the output coupler and wavelength selection element. The proposed fiber laser configuration combines a low intracavity loss of the fiber Bragg grating mirrors with a wide wavelength tuning of the bulk gratings. We demonstrate a >70-nm wavelength tuning range, limited only by the available fiber Bragg gratings.

Characterization of an Intra-Cavity Pumped P2O5-Doped Silica Raman Fiber Laser

We examine the characteristics of a P2O5-doped Raman fiber laser pumped by a double-clad ytterbium-doped fiber laser in an intra-cavity configuration. The double-clad fiber laser consists of two high reflection fiber Bragg gratings at 1092 nm, with an active length of 17 m, where the output grating is located at the end of the 400m P2O5-doped fiber. The Raman cavity is formed by a 1278-nm-high reflection fiber Bragg grating spliced to the double-clad fiber, and a 50% output coupler. The maximum conversion efficiency at 1278 nm with respect to the input pump power at 915 nm was 26.9%.

Multi-Wavelength-Switchable Double Clad Yb3+-Doped Fiber Laser Based on Reflectivity Control of Fiber Bragg Gratings by Induced Bend Loss

We propose and demonstrate an all-fiber multi-wavelength switchable double-clad Yb3+-doped fiber laser based on the reflectivity cavity control by induced bend loss. The wavelength switching is realized by a variable reflecting mirror that employs a cascaded array of three high reflection (>99%) fiber Bragg gratings at 1064, 1080 and 1096 nm, with a bending controller inserted between each grating. The order of the Bragg gratings is decided according to the gain profile of the Yb3+-doped fiber and the induced bending loss allows us to select the Bragg-wavelength laser operation. The laser is capable of switching continuously from one wavelength to another, and slope efficiencies over 50% are obtained at each wavelength.

Fiber Bragg Gratings With Suppressed Cladding Modes Made in SMF-28 With a Femtosecond IR Laser and a Phase Mask

High reflectivity fiber Bragg gratings (FBG) with strong cladding mode suppression were written in standard telecom fiber (SMF-28) with femtosecond 800-nm laser pulses and a phase mask. No special fiber photosensitization or fiber design was required. Induced index modulations were created by two-beam interference from the phase mask in both the core and cladding region, which resulted in cladding-mode coupling loss <0.1 dB for a high reflecting -30 dB in transmission FBG.

Dynamic Properties of Double-Pass Discrete Raman Amplifier With FBG-Based All-Optical Gain Clamping Techniques

The authors propose and implement a discrete fiber Raman amplifier configured in double-pass scheme together with fiber Bragg grating (FBG)-based all-optical feedback. The double-pass amplifiers achieve more than a 30-dB net gain with affordable pump power and guarantee a large margin for gain clamping. The all-optical gain clamping is provided by the lasing wavelength inside the cavity caused by the high reflectivity FBG and wide-band reflector. A stable gain is obtained for large input signal dynamic range of 30 dB. The gain variation is kept below 0.17 dB and the noise figure is flattened at the same time. Also, the authors investigate the Raman gain and noise figure as a function of signal wavelength with the proposed gain clamping technique.

Novel multimode fiber for narrow-band Bragg gratings

We propose a novel multimode fiber structure with modal propagation characteristics tailored to facilitate the creation of narrow-band high-reflectivity fiber Bragg gratings. The fiber structure proposed consists of concentric cylindrical shells of higher and lower refractive index material. A full vector second-order finite-element method is used to analyze the proposed multimode fiber structure. Simulations of the modal profiles show that high-order modes are localized to particular high-refractive index shells. We present the theoretical characterization of the modal propagation constant as a function of inner shell radius, shell separation, and harmonic-mode parameter. It is shown that a fiber with a minimum inner shell radius of at least 25/spl lambda/ (where /spl lambda/ is the vacuum wavelength), and a minimum shell separation of at least 10/spl lambda/ provides a reasonable tradeoff between fiber size and grating performance. A simulation of the multimode fiber grating shows that a grating with a full-width at half-maximum bandwidth on the order of 10/sup -4//spl lambda/ is theoretically possible, if optical power is launched strictly into modes with angular harmonic parameter p=1.

A novel tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a DFB laser diode and fiber Bragg gratings

We demonstrate experimentally a novel and simple tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a distribution feedback laser diode and high reflection fiber Bragg gratings (FBGs). In this filter, variable time delay is provided by cascaded high reflection fiber Bragg gratings (FBGs), and the tuning of the filter is realized by tuning different FBG to match the fixed carrier wavelength, or adjusting the carrier wavelength to fit different FBG. The incoherent negative tapping is realized by using the carrier depletion effect in a distribution feedback laser diode.