Search

We experimentally demonstrate a few-moded cladding-pumped multi-element fiber amplifier, comprising 4 Er/Yb co-doped signal fibers and 1 multimode pump-delivery fiber all of which are drawn together in a common polymer coating, providing a total spatial path multiplicity of 12. An average WDM signal gain of 18.3 dB and differential modal gain of 1.1 dB were achieved in the spectral range of 1542-1560 nm.

We experimentally demonstrate all-solid 30 and 90 μm core diameter multi-trench fibers. Measurements ensure an effective single-mode operation over a wide range of bend radius in the case of 30 μm core fiber, making it suitable for applications like beam delivery and compact fiber lasers. On the other hand, a 90 μm core fiber ensures an effective single-mode operation and shows good potential for rod-type fiber laser applications. Both fibers were fabricated by the conventional modified chemical vapor deposition process in conjunction with the rod-in-tube technique, hence making them suitable for mass production.

A multi-element Er-doped fiber amplifier (MEEDFA) is demonstrated in which the gain profile is extended into the S and L bands. Each fiber element of the MEEDFA is found to provide a maximum gain of 37 dB and a noise figure of < 4 dB in the C-band. The gain profile of the amplifier is shifted towards longer wavelength by cascading fiber elements. The novel geometry of the multi-element fiber (MEF) could allow for the development of a broadband amplifier in a split-band configuration. The proposed amplifier can operate in the wavelength band of 1520 to 1595 nm (75 nm), with a minimum gain of 20 dB.

International audience; The study of Bismuth (Bi)-doped silica fibers has been performed by using thermally stimulated luminescence. The thermo-luminescence peaks have been spectrally resolved in order to observe the effect of co-dopants on Bi luminescence. A new TSL peak around 625K was observed for the first time in Bi-doped Al-Ge-silicate fibers. This peak is believed to be due to Bi-active centers, and was only observed in Bi-doped samples co-doped with both Al and Ge.

Summary form only given. We utilize polarization-dependent gain to generate single-polarization laser operation in a polarization-maintaining erbium-doped fiber laser (PM EDFL). The PM EDFL was pumped by linearly polarized light. The output polarization from the EDFL was collinear with the pump when the pump was polarized along either of the principal axes of the PM EDFL.

Bending performance of the Multi-trench Fibers (MTFs) has been investigated using the Finite Element Method. Numerical investigations show that MTFs can provide low-loss effective single mode operation under bent configuration, thanks to the resonant coupling of the Higher order Modes (HOMs). Large ratio between the HOMs and the Fundamental Mode (FM) losses can be ensured, although the ratio drops with increasing Effective Area (Aeff) of the FM. MTFs provide better losses ratio between the HOMs and the FM in comparison with other fibers like step-index, W-type, and parabolic fibers.

Erbium-doped multi-element fiber (MEF) amplifiers have been fabricated to simultaneously amplify multiple transmission channels. MEF devices comprise of multiple single-core fibers (elements) combined in a common coating, with each element working as a single fiber in isolation. MEFs containing 3-elements and 7-elements have been fabricated and characterized. Each element of the fabricated MEFs provides nearly 32 dB of gain with a noise figure of5 dB for an input signal level of -23 dBm at 1530 nm. Different permutations of element pairs within the MEFs were checked for crosstalk and none was detected, confirming the simultaneous multi-channel amplification capabilities of MEFs.

We report the fabrication and initial characterization of a waveguide sensor array in the cladding of a flat fiber. The sensor, designed to independently measure the strain on three Bragg grating waveguides, exploits the true three dimensional fabrication technology of ultrafast laser inscription by placing these gratings in a non-planar configuration.

We experimentally validate a numerical model to study multimode erbium-doped fiber amplifiers (MM-EDFAs). Using this model, we demonstrate the improved performance achievable in a step index MM-EDFA incorporating a localized erbium doped ring and its potential for Space Division Multiplexed (SDM) transmission. Using a pure LP01 pump beam, which greatly simplifies amplifier construction, accurate modal gain control can be achieved by carefully tuning the thickness of the ring-doped layer in the active fiber and the pump power. In particular, by optimizing the erbium-ring-doped structure and the length of active fiber used, over 20dB gain for both LP01 and LP11 signals with a maximum gain difference of around 2 dB across the C band are predicted for a pure LP01 pump beam delivering 250mW power at 980nm. Refereed/Peer-reviewed

We present pulsed laser operation in a Nd-doped, Y 3 Al 5 O 12 -based silica fiber. The fiber was fabricated using the rod-in-tube technique with a Nd:YAG crystal rod as the core material and a silica tube for the cladding material. A spectroscopy study revealed that the core region had become amorphous in the process of fiber drawing. Q -switched pulsed laser operation was realized at a wavelength of 1058 nm when the fiber was cladding pumped at a wavelength of 808 nm. The laser delivered 38 μJ of energy in 65 ns pulses. The extracted energy was limited due to the multimodal operation of the fiber. Laser slope efficiency in continuous wave operation reached 52%. The spectroscopic properties of the fabricated fiber are discussed and compared to a Nd:YAG crystal and a Nd:Al-doped silica fiber. Published version

An all-fiber, narrow-linewidth, high power Yb-doped silica fiber laser at 1179 nm has been demonstrated. More than 12 W output power has been obtained, corresponding to a slope efficiency of 43% with respect to launched pump power, by core-pumping at 1090 nm. In order to increase the pump absorption, the Yb-doped fiber was heated up to 125 degrees C. At the maximum output power, the suppression of amplified spontaneous emission was more than 50 dB. Furthermore, theoretical work confirms that the proposed laser architecture can be easily scaled to higher power.

A short Bi doped fiber laser operating in the wavelength region of 1160-1179 nm has been demonstrated. The influence of unsaturable loss on laser performance is investigated. Excited state absorption in Bi doped germano-alumino silicate fiber is reported in the 900-1300 nm wavelength range under 800 and 1047 nm pumping. Bi luminescence and fluorescence decay properties under different pumping wavelengths are also investigated.

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 produced11 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) of100 nm for output power levels of20 mW.

In response to the Comment, we show that Engholm et al. [Opt. Lett. 33, 1216 (2008)] misinterpret the absorption peak at 230 nm and reach mistaken conclusions that contradict their experimental results. Differences in compositions and fabrication details mean that their results are only marginally relevant to our experiments [Opt. Lett. 32, 1626 (2007)]. The excitation of electrons to a charge-transfer band around 230 nm in Yb-doped aluminosilicate glasses leads to conversion from Yb, which, in our opinion, is more likely to account for photobleaching rather than photodarkening.

A simple fabrication technique for a silica suspended-core holey fiber design is presented that features a higher air-filling fraction than most holey fibers, making it ideal for evanescent-field-sensing applications. The holes in the fiber are defined through mechanical drilling of the preform, which is a significantly quicker and more straightforward approach to the customary stacking method. During the draw, the shape of the holes are manipulated so that the final fiber design approximates that of an air-suspended rod with three fine struts supporting the core. Modeling reveals that the modal overlap is greater than 29% at 1550 nm for a core diameter of 0.8 µm, which is significantly higher than any previously reported index-guiding structure used for sensing. A basic gas sensor is demonstrated using acetylene as the sensing medium and the results are reported.

We demonstrate a high-power single-mode cladding-pumped Raman fiber laser. The Raman fiber laser consists of a 1.2 km long germanium-doped double-clad fiber in a linear cavity, which is spliced to a single-mode fiber. The laser is end pumped by a multimode erbium-ytterbium-doped fiber, which is coupled to the inner cladding of the Raman fiber. The embedded core was designed to be single mode at the Raman Stokes wavelength, and up to 10 W of power was obtained at 1660 nm from the single-mode fiber end. The laser has a slope efficiency of 67% and a threshold of 6.5 W.

A high-power Er:YAG laser that is in-band pumped by a high-power cladding-pumped erbium-ytterbium codoped fiber laser operating at 1532 nm is reported. The Er:YAG laser produced 60.3 W of continuous-wave output at 1645.3 nm in a beam with M2 approximately equal to 3 for 82 W of incident pump power and 20 W of TEM00 output with M21.2 for 32.4 W of incident pump power. The slope efficiency with respect to incident pump power at pump powers of20 W was approximately 81%. In the Q-switched mode of operation, a slightly modified resonator configuration incorporating an electro-optic Q switch produced pulses of approximately 4 mJ energy and approximately 100 ns (FWHM) duration, corresponding to a peak power of approximately 42 kW at a repetition rate of 1 kHz for an incident pump power of 16.8 W. The prospects for further improvement in continuous-wave and Q-switched performance are discussed.

A new approach for the prediction of energy-transfer efficiencies in codoped Er-Yb double-clad fiber (EYDCF) is presented. Ab initio calculations have been performed on the basis of migration-assisted energy-transfer models. The two main Yb energy-transfer parameter that is needed in all modelings based on rate equations can be calculated by use of a simple relation. Our approach also permits the prediction of the laser efficiency of EYDCFs, and a comparison of measured and calculated maximum laser slope efficiency shows a good agreement.

We demonstrate the suppression of stimulated Raman scattering in a high power, single-mode Yb-doped fiber amplifier using a W-type core structure. Raman-scattered light is not guided by the core. The amplifier consists of a master oscillator power amplifier (MOPA) system, seeded with 103 ps pulses at 32 MHz repetition rate in the final amplification stage. An average output power of 53 W, which corresponds to 13 kW of peak power, was achieved in the 23 m long W-type double-clad fiber without any significant loss of power due to transfer from the signal wavelength at 1060 nm to the Raman Stokes wavelength at 1114 nm and amplified spontaneous emission from Yb-ions at longer wavelengths (~1070 nm). The power conversion efficiency at 1060 nm was 80% with respect to the absorbed pump power.

An erbium-ytterbium co-doped hollow optical fibre (HOF) laser generating up to 2.5 W of output power in the 1550 nm spectral region with a power conversion efficiency of 26% with respect to the launched pump power is demonstrated. A significant reduction of ytterbium co-lasing at 1060 nm is observed with increasing core thickness in the HOF, which is believed to be correlated with the signal overlap factor at 1550 nm that increases as the core thickness increased.

We show that it is possible to adapt existing software packages developed originally for modeling telecommunication devices and systems to reliably predict and optimize the performance of high-power Ytterbium-doped fiber amplifier and laser systems. The ready availability of a flexible, user-friendly design tool should be of considerable practical interest to scientists and engineers working with this important new laser technology since Ytterbium amplifier and amplifier cascades are often difficult to optimize experimentally due to the three-level nature of the Ytterbium laser transition. As examples of the utility and accuracy of the software, as well as the complexity of the systems and amplifier properties that can be successfully modeled, we present a comparison of experimental and theoretical results for individual core and cladding pumped amplifiers, and also for an ultra-short pulse four-stage amplifier system optimized both to provide a broad gain bandwidth and to minimize nonlinear effects. We also show how high energy 100 ns pulses with complex user definable temporal profiles can be created in a gain-saturated amplifier by suitable pre-shaping of the low-energy input pulses. Furthermore, with appropriate modifications the same software package can be applied to fiber amplifiers based on other rare-earth elements and glass hosts.

Efficient high-power operation of an erbium-ytterbium co-doped fiber laser cladding-pumped by two spatially-multiplexed and polarization combined 975 nm diode-stacks is reported. Up to 188 W of continuous-wave output at 1.57 microm was generated with a beam-quality factor (M;2) of 1.9 and an overall slope efficiency with respect to launched pump power of 41% (and 43% for output powers120W). Tunable operation was demonstrated by use of an external cavity containing a diffraction grating and a maximum output power of 108 W at 1538 nm was generated for a launched pump power of ~ 336 W. The operating wavelength was tunable from 1531 to 1571 nm, with100W output power over a tuning range of 36 nm from 1532 nm to 1568 nm.

An ytterbium-sensitised thulium-doped silica fibre laser that generates up to 75 W of output power in the 2 µm wavelength range when cladding-pumped by a 975 nm diode stack is reported. The slope efficiency is 32% with respect to the launched pump power and the beam quality factor (M) is 1.3.

An Er:Yb codoped fiber amplifier chain for the generation of pulses for coherent lidar applications at a wavelength near 1.5 microm is reported. The final 1.8-m-long power amplification stage had a 50-microm core diameter and yielded a 23-dB energy gain, resulting in 0.29-mJ, 100-ns pulses at a repetition rate of 4 kHz with no Brillouin scattering and an M2 of 2.1.

We report a cladding-pumped ytterbium-doped fibre laser, generating up to 610 W of continuous-wave (cw) output power at 1.1 micron with slope efficiency of 80% and near diffraction-limited beam quality (M2 = 1.3). No undesirable roll-over was observed in output power with increasing pump power.

An Yb-doped fibre laser with a helical core trajectory in the cladding material has been demonstrated for the first time. The laser yields 350 mW of linearly-polarised, single-spatial-mode output at 1047 nm from a multimode core of diameter, 26 µm, and numerical aperture, 0.14, when core-pumped by an Yb:YAG laser at 1030 nm.

A tunable cladding-pumped ytterbium-doped fibre laser is presented. An air-clad inner cladding supported by a micro-structured silica mesh inside a silica jacket is used. A measured inner-cladding NA of 0.4 to 0.5 enables efficient pump launch into a 36 /spl mu/m-diameter inner cladding. The small inner cladding area enables tuning from 1010 to 1120 nm.

The output powers of fibre lasers at 1µm continue to grow and such lasers are now beginning to compete with conventional solid state lasers (for example, Nd:YAG lasers) in many important application areas, e.g., material processing, medicine, range finding, etc. Fibre lasers benefit from a geometry that allows easy thermal management and an easy selection of a high quality output beam. So far a pulse energy of 7.7mJ and 10W average output power has been reported from a large core Yb-doped Q-switched fibre laser [1]. In fact, the maximum extractable energy is limited by the build-up of amplified spontaneous emission or spurious lasing between pulses [2], and thus, large-mode area (LMA) fibres are preferred. Besides the pulse energy, factors to be considered are the average power and the beam quality, which are especially important for applications operating at very high average power levels such as materials processing. In this paper, we investigate Q-switching of LMA cladding-pumped Yb-doped fibre laser in terms of its high-power operation. We designed and fabricated an LMA fibre with a 30µm diameter, 0.07 NA, core, and a 350µm D-shaped inner cladding with 0.49 NA. The continuous wave slope efficiency was ~84% with respect to the absorbed pump power at 975nm. The experimental setup for the Q-switched fibre laser is shown in Fig. 1. A diode-laser stack at 975nm was used as the pump source. The first-order diffracted beam from the acousto-optic modulator was fed back by a dichroic mirror that had a high reflectivity at ~1µm, the diffraction efficiency of which was ~70%. The fibre length was ~9m. The Q-switched pulse energy and the average power are shown in Fig. 2. A maximum pump power of 250W was launched into the fibre. We evaluated the maximum pulse energy to 8.4mJ at ~1.06µm, for a repetition rate of 0.5kHz, though with a large uncertainty because of the high level of amplified spontaneous emission present between pulses. The maximum average power at the repetition rate of 200kHz was 120W with 0.6mJ pulses. The pulse width was ~460nsec at a low repetition rate. These values are the highest that have ever been reported for a Q-switched fibre laser, to the best of our knowledge.

In the past, bismuth doped fiber (BiDF) lasers, operating in the 1160 – 1300 nm wavelength range, have gained much attention as they are promising for many applications; including medical and astronomy. However, the poor lasing efficiency of BiDF laser, compared to the widely used rare-earth doped fiber lasers, requires further investigations. One possible reason that can impair the BiDF laser efficiency is the presence of high unsaturable loss in the fiber, which is temperature dependent [1, 2]. Thus, temperature rise in the BiDF under strong pumping can be a limiting factor for such laser systems. Here, we report the dependence of BiDF laser efficiency on effective cooling of the fiber.

Two-micron lasers are of great interest in a range of applications, from spectroscopy and free space communications, to polymer machining and laser surgery. They also provide an important stepping-stone for wavelength generation further into the mid-infrared via nonlinear frequency conversion. Holmium doped fibre laser systems offer particularly attractive properties as they allow access to the atmospheric transmission window between 2.1 and 2.25 μm. Recently, operational efficiencies for resonantly pumped Ho:silica fibre close to the quantum limit have been demonstrated for core pumped lasers [1]. To further power scale Ho:fibre lasers, development of cladding-pumped fibre configuration is necessary and indeed has enabled scaling of such fibres to >400 W cw average power [2]. Conventional polymer-coated double-clad fibres have high inner-cladding propagation loss at the ∼1.95 μm pump wavelength, resulting from the presence of OH− contamination and absorption in the polymer outer-cladding [3]. Here we report on optimisation of holmium all glass double-clad optical fibre in order to provide efficient operation for cladding pumping at 1.95μm.

In this talk, we discuss all-solid and easily realizable trench-assisted fibers that show tremendous potential for addressing challenges faced by current fiber designs for power scaling.

We present the first demonstration of a multimode (two mode-group) erbium-doped fiber amplifier for Space Division Multiplexed (SDM) applications and demonstrate various design and performance features of such devices. In particular we experimentally demonstrate that differential modal gains can be controlled and reduced both by fiber design and control of the pump field distribution. Using a suitably designed fiber we demonstrate simultaneous modal gains of ~20 dB for different pair-wise combinations of spatial and polarization modes in an EDFA supporting amplification of 6 distinct modes.

We use an approximation for the Brillouin gain in optical fibers to find the antiguiding acoustic refractive index profile that minimizes the gain. We also calculate the Brillouin gain with BPM, with good agreement.

We propose a novel fiber design that shows excellent filtering for higher-order-modes (>6dB/m) and low losses for fundamental mode (72ps/nm-km and effective area >390µm2 with good bend robustness.

High power fiber sources have reached several kilowatts of output power, and are now leading contenders for many applications. Important attractions include control, efficiency, manufacturability, and reliability. We will exemplify opportunities and limitations for these revolutionary sources.

Bi-doped phosphosilicate fibers are fabricated by MCVD-solution doping technique under different oxidation conditions. Fibers are evaluated for unsaturable loss and laser performance. A 22mW all-fiber Bi-laser is demonstrated at 1360nm by LD pumping at 1267nm.

We demonstrate a six spatial-mode, wavelength-routing network interoperable with few-mode, coupled-multi-core, and single-mode fiber spans using a custom 57-port wavelength-selective switch configured for joint-switching of spatial-superchannels. Refereed/Peer-reviewed

We demonstrate an efficient high peak power pulsed cladding-pumped fiber Raman amplifier. The output Stokes peak power is over 200 W. The peak power conversion efficiency exceeds 75% and the on-off peak gain is nearly 65 dB.

The spectroscopic properties of pristine and H 2 -loaded MCVD based Bi-doped aluminosilicate fibers were investigated. Also, the properties of Bi-doped fiber, fabricated by powder-in-tube method, have been compared to MCVD based Bi fiber.

We report what we believe to be the first experimental study of inter-modal cross-gain modulation and associated transient effects as different spatial modes and wavelength channels are added and dropped within a two-mode amplifier for SDM transmission.

We report suppression of photodarkening in Yb-doped nano-crystalline fibers in silica host. The photodarkening induced loss reduced by 20 times compared to Yb-doped aluminosilicate fibers. The laser efficiency of the nano-crystalline fiber was 79%.

We present novel techniques, in-situ solution doping and Chemical-in-Crucible, for manufacturing doped optical fibers with complex structures which offer improved process performance and flexibility over conventional doping processes for high power fiber lasers applications.

A tandem-pumped Yb-doped fiber with a quantum defect of 2% generates 3% of heat. We believe this is a record-low thermal load and the first calorimetric measurement of the heat from a fiber core.

We report a detailed study on the system performance of a two-mode group EDFA. In particular we quantify how the gain spectrum and BER performance are affected by input signal and pump power as required in the execution of our ongoing MDM transmission experiments Refereed/Peer-reviewed

We report the first experimental demonstration of a cladding pumped FM-EDFAsupporting 4 mode groups. The modal gains are measured to be >20dB between 1540nm-1570nmwith a modal differential gain of ~4dB among the mode groups. Refereed/Peer-reviewed

With the breakthrough in ytterbium (Yb) doped fiber laser power scaling to kilowatt levels [1], the search for improved host glass properties has received much attention. A silica host, which is commonly used in high power fiber devices, has the advantage of being low-cost, reliable and able to sustain extremely high optical densities, as compared to other alternative glasses. However, silica is considered to be a poor host in terms of the level of Rare-earth(RE) that can be incorporated into it without the clustering effect of RE ions. This makes it difficult to achieve the high level of RE concentration in silica fibers, that is needed to shorten the device length of high power fiber lasers, which helps to suppress the non-linear effects (such as stimulated Raman and Brillouin scattering) in fibers. In this paper, we investigate Yb doped Y 2 O 3 (or Y 3 Al 6 O 12 ) nanoparticles in a silica rich matrix, as an alternative to the Yb in a ‘standard’, such as aluminium or phosphorous co-doped, silica host for use in high power fiber lasers. Y 2 O 3 is a good host for RE incorporation, and efficient Yb:Y 2 O 3 ceramic lasers have been reported in [2]. It is expected that Y 2 O 3 nanoparticles within a silica host will improve the RE solubility in fibers.

We fabricate the first large-core double-clad Raman fiber and use it for efficient pulsed cladding-pumped fiber Raman amplification. The beam-quality of the output beam improves to diffraction-limited through cascaded Raman scattering.

We show transmission of a 3x112-Gb/s DP-QPSK mode-division-multiplexed signal up to 80km, with and without multi-mode EDFA, using blind 6x6 MIMO digital signal processing. We show that the OSNR-penalty induced by mode-mixing in the multi-mode EDFA is negligible.

Through nonlinear scattering including stimulated Raman scattering and beam cleanup, a pulsed multimode pump beam is converted into a nearly diffraction-limited supercontinuum extending from 1 to 2 µm in a passive cladding-pumped nonlinear fiber converter.

We have fabricated an ytterbium doped all-glass double-clad large mode area holey fiber. A highly efficient cladding pumped single transverse mode holey fiber laser has been demonstrated, allowing continuous-wave output powers in excess of 1W with efficiencies of more than 80%. Furthermore both Q-switched and mode-locked operation of the laser have been demonstrated.