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The multicore fiber amplifier, as a key component in spatial division multiplexing (SDM) communication systems, presents higher technical difficulty compared to traditional multi-channel single core fiber amplifiers, which has sparked widespread attention. To achieve balance, efficiency, miniaturization, and cost-effectiveness in the performance of multi-core optical fiber amplifiers, we propose an innovative triple cladding 13-core Er/Yb co-doped microstructured fiber (13CEYDMOF). The proposed fiber features an outer cladding with peanut-shaped air holes, which enables uniform excitation of the 13 cores using a single multimode laser pump source within the inner cladding. This approach also prevents damage or aging of the fiber's outer coating due to the pump laser. Furthermore, the design of Peanut-Shaped Air Holes effectively increases the numerical aperture (NA) of the inner cladding while reducing the outer diameter of the fiber, enhancing the fiber's mechanical flexibility. To address the coupling difficulties caused by air holes, we bi-directionally pump the 13CEYDMOFA by utilizing a combined technique of the side winding and end pumping. The experimental results show that the 13CEYDMOFA can achieve an average gain of 23.8 dB, a noise figure (NF) of ∼4.6 dB, and an inter-core gain difference of less than 2 dB in the wavelength range of 1529–1565 nm. The in-line amplified transmission experiment demonstrates that the 13CEYDMOFA is well suited for the 13 spatial channels transmission. To the best of our knowledge, this is the first time to realize high performance telecommunication band amplification in a multicore microstructure fiber. [ABSTRACT FROM AUTHOR]

We improve the output of a MOPA system that emits single-frequency high-energy optical pulses using a large mode area Er-doped fiber amplifier pumped by a cascaded Raman fiber laser with a low 150 Hz repetition frequency. It is found that the unwanted light generated in the cascaded Raman fiber laser at the same time as the pump light saps the gain of the amplifier and degrades its output characteristics. By combining the removal of unwanted light with a pulse pump technique, the pulse energy is improved from less than 1.0 mJ to 1.2 mJ with at the same time a SNR of 30 dB compared to 19 dB before the improvement. The percentage of power in the signal also improves from 61.0% to over 90.7%.

In this paper, we report a simulation study on the performance enhancement of Praseodymium doped silica fiber amplifiers (PDFAs) in O-band (1270-1350 nm) in terms of small signal gain, power conversion efficiency (PCE), and output optical power by employing bidirectional pumping. The PDFA performance is examined by optimizing the length of Praseodymium doped silica fiber (PDF), its mode-field diameter (MFD) and the concentration of Pr3+. A small-signal peak gain of 56.4 dB, power conversion efficiency (PCE) of 47%, and output optical power of around 1.6 W (32 dBm) is observed at optimized parameters for input signal wavelength of 1310 nm. Minimum noise figure (NF) of 4.1 dB is observed at input signal wavelength of 1310 nm. Moreover, the effect of varying the pump wavelength and pump power on output optical power of the amplifier and amplified spontaneous emission (ASE) noise is also investigated, respectively. Finally, the impact of ion-ion interaction (up-conversion effect) on small-signal gain of the amplifier is also studied by considering different values of up-conversion coefficient. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the highest spectral brightness for the pulsed fiber lasers to the best of our knowledge in a compact high power and pulse energy laser system consisting of a DFB laser diode as a master oscillator and a high-power fiber amplifier based on a double-clad active tapered fiber (T-DCF). Due to the unique properties of T-DCF, this system provides more than 1 MW of peak power and pulse energy of more than 60 μJ at a frequency of 500 kHz while maintaining a spectral width of less than 0.1 nm. The spectrum broadening limits the further power scaling of the laser system. The system is capable of delivering up to 150 W average power at 10 MHz pulse repetition rate with 0.14 nm linewidth. We also demonstrate the second harmonic generation of 532 nm with over 30 W at 10 MHz repetition rate and 14.5 W at 500 kHz. The experimental results reveals that the narrow linewidth system based on a DFB laser diode and a T-DCF amplifier is an excellent and robust solution for material processing and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Optical amplification beyond C- and L-bands may be a promising solution to increase the capacity of transmission systems. In this paper we reviewed different amplification technologies, including semiconductor optical amplifiers (SOA), Raman amplifiers and doped fiber amplifiers briefly discussing their advantages and disadvantages. We found that while a variety of amplification solutions are available, they have not been implemented in practical systems because, until recently, C- and L- bands EDFA amplified systems provided sufficient capacity, and the lack of a complete optical components ecosystem. The O-band (1260–1360 nm) may be a notable exception since it has been used for decades for unamplified point-to-point transmission near fiber zero dispersion wavelength. Overall capacity demand and power budget reduction caused by the bit rate increase of pluggable modules promises to make O-band amplification an attractive solution. We present simple broadband O-band bismuth doped fiber amplifier (BDFA) with characteristics similar to, or above commercially available EDFAs. We demonstrated that BDFAs can amplify the entire O-band and a single stage amplifier can deliver 20 dB gain, 18 dBm output power and 5.5 dB noise figure over the 3-dB bandwidth greater than 60 nm. We illustrated the application of BDFAs by transmitting signals from a commercial 400 Gb/s 8-channel LAN-WDM transponder, operating within the IEEE standardized band, over 50 km of legacy G.652 fiber. We also demonstrated high power BDFA capable of delivering more than 700 mW of optical power without inducing measurable nonlinear distortion to intensity modulated signal propagating over a dispersive fiber waveguide. [ABSTRACT FROM AUTHOR]

We report the characterization of a cladding-pumped multicore fiber with annular erbium doping for low gain compression over the C-band (1528.8 nm to 1563.9 nm). The fiber aims to minimize saturation effects by placing the erbium doping in the cladding where the signal intensity is lower. The challenge of ensuring adequate erbium ion solubility in the cladding, without unduly raising its refractive index, was answered by using aluminophosphosilicate for the doped region. Before assembling the eight-core amplifier with fan-in and fan-out, we needed to determine the optimum fiber length to meet the gain compression target when the eight cores are loaded, for a given pump power injected in the cladding. We thus performed a thorough experimental characterization of a single core. This allowed the determination of all the relevant fiber parameters needed to do numerical simulations and predict the multicore fiber amplifier performance under the fully loaded scenario. For the first time, these numerical results are compared to the experimental results of a fully loaded multicore amplifier with cladding pumping and erbium doping in the cladding. We discuss the amplifier performance in terms of gain compression when the input power signal is varied, as would be the case in dynamic optical networks. We also examine the core-to-core gain variations and the sensitivity of the design to fabrication variations. Results show that significant reduction in gain compression of multicore cladding-pump amplifiers can be achieved with the proposed annular doping design in the cladding, although improvement in the fabrication uniformity of the core will be required for practical applications. Lastly, we discuss how this erbium doped fiber design can also lead to improved power conversion efficiency (PCE) in cladding-pumped amplifiers. [ABSTRACT FROM AUTHOR]

In this work, we carry out a systematic study on the evolution of relative intensity noise (RIN) in a high-power narrow-linewidth fiber laser system based on phase-modulated single-frequency seed laser. The experimental results clarify that enhancement of the RIN mainly occurs when the seed laser gets amplified from low power to medium power. In addition, further power scaling could lead to reduction of the RIN until it reaches saturation on the condition that the transverse mode instability (TMI) effect is effectively suppressed. Apart from the power scaling process, the phase-modulation would also lead to enhancement of the RIN at specific frequencies corresponded to the modulation frequency. More importantly, the contrast experiments reveal that the TMI effect could lead to obvious enhancement of the RIN of the signal laser during amplification well below the TMI threshold defined by the traditional method. Therefore, apart from degeneration of the RIN during amplification, potential enhancement of the RIN induced by the phase-modulation or the TMI effect below its traditional threshold should be carefully considered and controlled to achieve high-power low-noise fiber laser. Overall, our experimental results could provide a well reference for design of high-power low-noise fiber lasers and high-power narrow-linewidth fiber lasers. [ABSTRACT FROM AUTHOR]

We report the design and performance of a 2 $\mu$ m dual-stage polarization maintaining (PM) holmium-doped fiber amplifier (HDFA) operating in either continuous-wave (CW) or pulsed regime. The amplifier is pumped at 1860 nm, which offers a better efficiency than a 1940 nm pump. In CW regime, we measured more than 1 W of output power at both 2051 nm and 2090 nm signal wavelengths. In pulsed mode, we tested the amplifier over a broad range of pulse widths (50–500 ns) and pulse repetition frequencies (PRFs) (50–1500 kHz). The PM HDFA delivered up to 200 W of peak power and 10 $\mu$ J of pulse energy with an excellent stability, while integrated inside a compact module. [ABSTRACT FROM AUTHOR]

Sixty-one lasing fiber channels are passively combined in a monolithic optical resonator array to produce an output power above 200 W at two-micrometer wavelength with the central intensity enhanced by a factor of 8 compared to incoherent beam combination. The 61-channel lasing mode corresponds to a transitional state with 75-degree phase shift between neighboring cores and has a far-field peak intensity 4.6 times below theoretical prediction for a fully coherent array. A 7-channel mode corresponds to the anti-phase supermode of the Talbot cavity, which has no central lobe in the far field. The monolithic laser cavity is formed by a fiber array, which is drawn and fusion-spliced to an endcap serving as a Talbot cavity mirror without air gaps. The central intensity enhancement, which is achieved without spectral or polarization selectivity, improves as the number of channels increases. This is an important step towards a passively combined multichannel all-solid-state laser system. [ABSTRACT FROM AUTHOR]

We report the design and performance of medium slope efficiency (64%) Holmium-doped fiber amplifiers (HDFAs) with novel alternative in-band pump wavelengths in the 1720–2000 nm spectral region. We demonstrate through simulations that pump wavelengths of 1840–1860 nm can yield significantly improved output power, gain, and optical-optical conversion efficiency compared to the previous technical and industry standard pump wavelength of 1940 nm. Our simulations are verified by experimental data. [ABSTRACT FROM AUTHOR]

This paper presents a rigorous theoretical analysis of a thulium doped fiber amplifier (TDFA) operating at around 1900 nm. The performance of the amplifier is analyzed based on the concentration of Tm3+ ions, TDF length, and the pumping power, respectively. A broadband gain of around 41 dB is demonstrated for a Tm3+ doped fiber length of 10 m, and an optimized pump power of 400 mW, while employing an in‐band pumping scheme. The minimum noise figure of 4.15 dB is achieved within a broad bandwidth of around 120 nm. [ABSTRACT FROM AUTHOR]

We report the design and performance of a packaged broadband PM hybrid HDFA/TDFA in the 2000–2100 nm band using all-single-clad doped fibers. Internalsmall signal G = 49.1 dB, small signal NF = 6.5 dB, and Pout = 3.54 W are achieved at λs = 2051 nm. The simulated 3 dB output power bandwidth is 98 nm. Comparisons of experimental data and simulations show good agreement. We investigate through simulations an all-Holmium two stage PM optical amplifier design for comparison to the hybrid PM HDFA/TDFA. [ABSTRACT FROM AUTHOR]

Space-division multiplexing (SDM) attracts attention to cladding-pumped optical amplifiers, but they suffer from a low pump power conversion efficiency. To address this issue, ytterbium (Yb3+) and erbium (Er3+) co-doping is considered as an effective approach. However, it changes the gain profile of Er3+-doped fiber amplifiers and induces the gain difference between optical wavelengths in the C-band, significantly limiting the effective band of the dense wavelength-division multiplexed (DWDM) system. This paper is devoted to a detailed study of a cladding-pumped Er3+/Yb3+ co-doped fiber amplifier (EYDFA) through numerical simulations aiming to identify a configuration, before assembling a similar EYDFA in our laboratory premises that ensures the desired performance. The simulation model is based on a commercial double cladding EYDF whose parameters are experimentally extracted and fed to the EYDFA setup for the system-level studies. We investigate the wavelength dependence of the amplifier's characteristics (absolute gain, gain uniformity, noise figure) and bit error rate (BER) performance for several DWDM channels and their optical power. The obtained results show that a 7 m long EYDF and co-propagating pump direction is preferable for the EYDFA with a 3 W pump source at 975 nm and with the given gain medium characteristics for WDM applications. For instance, it ensures a gain of 19.7–28.3 dB and a noise figure of 3.7–4.2 dB when amplifying 40 DWDM channels with the input power of −20 dBm per channel. Besides, we study EYDFA gain bandwidth and the maximum output power when operating close to the saturation regime and perform a sensitivity analysis showing how the doped fiber's absorption and emission cross-sections impact the amplification process through energy transfer from Yb3+ to Er3+. Finally, we quantify the power penalty introduced by the EYDFA; the results show that it is not higher than 0.1 dB when amplifying 40 × 10 Gbps non-return-to-zero on-off keying signals from −20 dBm/channel. [ABSTRACT FROM AUTHOR]

In this article, we experimentally demonstrate an all-fiber optical amplifier using Bi-doped phosphosilicate fiber (BPSF) operating in both the O-band and the E-band, providing >20 dB gain from 1345 to 1460 nm for an input signal power of −23 dBm. A maximum gain of 31 dB with a noise figure (NF) of 4.8 dB was achieved at 1420 nm for −23 dBm input signal, whereas for an input signal power of −10 dBm it was 26 dB with a NF of 5.3 dB. The in-band OSNR of the proposed Bi-doped fiber amplifier (BDFA) was >22 dB from 1345 to 1460 nm for a −23 dBm input signal. The gain coefficient was found to be 0.04 dB/mW for a −23 dBm input signal. Also, the temperature dependent gain and NF performance of the BDFA within −40 to +60 °C were characterized. The temperature-dependent-gain (TDG) coefficient for a −23 dBm input signal was found to be −0.015 dB/°C at a signal wavelength of 1420 nm where the BDFA gain is maximum, while for an input signal power of −10 dBm it was −0.01 dB/°C at 1420 nm. The TDG coefficient of the proposed BDFA from 1350–1460 nm was in the range from −0.079 to −0.008 dB/°C. The BDFA gain and NF performance were also measured and compared using BPSFs with different unsaturable loss (UL) characteristics. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a high fidelity narrowband picosecond pulse two-stage fiber amplification scheme with inter-stage filtering technique using fiber Bragg grating. This technique can not only narrow the bandwidth of the pulses broadened by self phase modulation in the first-stage fiber amplifier, but also reshape the pulse temporal profile to near Gaussian shape, which reduces the spectral broadening slope of the pulses in the second-stage fiber amplifier and improves the narrowband fiber amplification ability. Using this technique, pulse energy of 10 nJ is achieved from a 0.2-nJ initial pulse by only using standard single mode fiber amplifiers while retaining 10 ps pulse width and 0.4 nm root mean square bandwidth. This technique may provide a simple and effective solution for high fidelity fiber amplification of low-energy ps seed pulse from fiber oscillators. [ABSTRACT FROM AUTHOR]

We report the experimental performance of a packaged dual-stage all-single-clad broadband polarization maintaining (PM) Tm-doped silica fiber amplifier (TDFA) with a high signal output power of 2.2 W at 1909 and 1951 nm. Our novel design incorporates an uncooled 940 nm multimode semiconductor pump laser source. Combined high gain of >46 dB, wide operating bandwidth of 1875–2000 nm, low noise figure of 7 dB, high OSNR of >54 dB/0.1 nm, and a PER of >20 dB are achieved with our TDFA. [ABSTRACT FROM AUTHOR]

In this tutorial, a classical Langevin equation, a classical Markov equation, and a quantum Langevin equation are used to model the amplification and attenuation of an optical signal. Equations are derived for the photon-number moments (mean and variance). All three approaches produce the same moment equations. In the first approach, the moments of the noise sources must be specified (using physical insight), whereas in the second and third approaches, they are determined self-consistently and satisfy the shot-noise rule: The number variance is driven at a rate that equals the sum of the moduli of the rates in the mean equation. [ABSTRACT FROM AUTHOR]

The phase of modes in three-core optical fibers under high thermal load is studied by means of the combined thermal and optical models. In particular, the effects of thermal dissipation in the doped cores, as a result of quantum defect heat generation, and the relative material refractive index variation are investigated. The induced index gradient can influence the guided mode propagation in multiple adjacent cores, even if their distance is enough to decouple them optically, showing a remarkable dephasing of the different fiber output beams. This effect brought by the thermal phenomenon inherent in the amplification process has to be carefully accounted for when designing multi-core high-power optical lasing and amplifying devices. The mode dephasing results also provide useful information for future evaluation of thermo-optic coupling effects that may occur along the fiber under high power regime. [ABSTRACT FROM AUTHOR]

We report the broadband spectral performance of a three-stage, high gain, single mode, high output power (25 W) polarization-maintaining (PM) hybrid Ho-doped and Tm-doped fiber amplifier at signal wavelengths of λs = 2004–2108 nm. The three-stage amplifier consists of a two stage high gain Ho-doped PM single clad preamplifier stage followed by a Tm-doped PM double clad power amplifier. We employ narrow linewidth (<2 MHz), single frequency, discrete mode, packaged InGaAs/InP based laser sources to study the performance of our amplifier in a master oscillator-power amplifier (MOPA) configuration. Measurements are made over a broad wavelength range that is determined by careful selection of the properties of the Ho-doped and Tm-doped fibers in the three amplifier stages. No nonlinear effects, such as stimulated Brillouin scattering (SBS) or stimulated Raman scattering (SRS), are observed at any signal wavelength in our measurements. We compare the experimental results with steady-state simulations of both the Ho-doped preamplifier and the TDFA booster and find good agreement between data and simulations for gain, noise figure, output power, and output optical spectra. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on higher order mode suppression due to differential gain in large mode area step index fiber amplifiers with confined Yb doping using spatially and spectrally resolved imaging (S2). A novel active fiber with Yb doping confined to the central 30% of the core area is fabricated and its performance is directly compared to a fiber with a conventional homogeneously doped core with almost identical parameters. At high pump rates, S2 and beam pointing stability measurements clearly demonstrate fundamental mode operation of the confined doping few mode fiber, even under imperfect launching conditions and environmental perturbations. In addition, we discuss the mode content as a function of gain in co-pumped fiber amplifiers with and without confined rare earth core doping using a power propagation model for fibers with similar parameters to those used in our experiments. Our simulation results as well as amplification experiments indicate the great potential of the confined doping concept for single mode high power operation. [ABSTRACT FROM AUTHOR]

Cladding-pumped optical fiber amplifiers are of increased interest in the context of space-division multiplexing but are known to suffer from low power efficiency. In this context, ytterbium (Yb) co-doping can be an attractive solution to improve the performance of erbium (Er) doped fiber amplifiers. We present a detailed direct comparison between Er/Yb-co-doping and Er-doping using numerical simulations validated by experimental results. Two double-cladding fibers, one doped with Er only and the other one co-doped with Er and Yb, are designed, fabricated and characterized. Using the experimentally extracted parameters, we simulate multi-core fiber amplifiers and investigate the interest of Er/Yb-co-doping. We calculate the minimum gain of the amplifiers over a 35-nm spectral window considering various scenarios. [ABSTRACT FROM AUTHOR]

We propose and report the experimental demonstration of a shared pump architecture for a two-stage, broadband, high-gain polarization-maintaining Ho-doped fiber amplifier (HDFA). The gain as high as 59 dB, a noise figure of 10 dB, a dynamic range of >43 dB, and an output power of 4.1 W are achieved at a signal wavelength $\lambda _{ {s}}$ of 2051 nm. The multiwavelength performance of the HDFA is measured for $\lambda _{ {s}} = {2004} - {2108}$ nm. Initial comparisons of simulations with our experimental results show a relatively good agreement for $\lambda _{\mathbf {s}} > {2051}$ nm. [ABSTRACT FROM AUTHOR]

We report the experimental demonstration and record performance of two-stage broadband, high gain polarization-maintaining (PM) Ho-doped fiber amplifiers (HDFAs) at a signal wavelength of λs = 2051 nm. We begin by presenting a new PM Ho-doped fiber with core diameter 8 μm, a PANDA structure, a cutoff wavelength of 1650 nm, and a peak absorption of 57 dB/m at 1951 nm. Next, we consider architectures for high gain PM HDFAs. Here we demonstrate G = 60 dB with a dynamic range of >40 dB and noise figures as low as 10 dB. We then investigate configurations for high output power PM HDFAs. With one stage, we measure Pout = 3.45 W and an optical–optical slope efficiency η = 69%. With two stages, we obtain Pout = 6.7 W and η = 80%. The potential bandwidth of the high power PM HDFA is BW = 100 nm (7.5 THz). An optical signal-to-noise ratio of 58 dB/0.1 nm is achieved, and the polarization extinction ratio is >20 dB. Initial comparisons of simulations of gain and output power with our experimental results show relatively good agreement. [ABSTRACT FROM AUTHOR]

Space-division multiplexing (SDM) attracts attention to cladding-pumped optical amplifiers, but they suffer from a low pump power conversion efficiency. To address this issue, ytterbium (Yb3+) and erbium (Er3+) co-doping is considered as an effective approach. However, it changes the gain profile of Er3+-doped fiber amplifiers and induces the gain difference between optical wavelengths in the C-band, significantly limiting the effective band of the dense wavelength-division multiplexed (DWDM) system. This paper is devoted to a detailed study of a cladding-pumped Er3+/Yb3+ co-doped fiber amplifier (EYDFA) through numerical simulations aiming to identify a configuration, before assembling a similar EYDFA in our laboratory premises that ensures the desired performance. The simulation model is based on a commercial double cladding EYDF whose parameters are experimentally extracted and fed to the EYDFA setup for the system-level studies. We investigate the wavelength dependence of the amplifier’s characteristics (absolute gain, gain uniformity, noise figure) and bit error rate (BER) performance for several DWDM channels and their optical power. The obtained results show that a 7 m long EYDF and co-propagating pump direction is preferable for the EYDFA with a 3 W pump source at 975 nm and with the given gain medium characteristics for WDM applications. For instance, it ensures a gain of 19.7–28.3 dB and a noise figure of 3.7–4.2 dB when amplifying 40 DWDM channels with the input power of −20 dBm per channel. Besides, we study EYDFA gain bandwidth and the maximum output power when operating close to the saturation regime and perform a sensitivity analysis showing how the doped fiber’s absorption and emission cross-sections impact the amplification process through energy transfer from Yb3+ to Er3+. Finally, we quantify the power penalty introduced by the EYDFA; the results show that it is not higher than 0.1 dB when amplifying 40 × 10 Gbps non-return-to-zero on-off keying signals from −20 dBm/channel.

The spectral range between 1650 and 1700 nm is an interesting region due to its potential applications in optical telecommunication and optical-based methane sensing. Unfortunately, the availability of compact and simple optical amplifiers with output powers exceeding tens of milliwatts in this spectral region is still limited. In this paper, a single-frequency continuous-wave bismuth-doped fiber amplifier (BDFA) operating at 1651 and 1687 nm is presented. With the improved signal/pump coupling and modified pump source design, the output powers of 163 mW (at 1651 nm) and 197 mW (at 1687 nm) were obtained. Application of the BDFA to the optical spectroscopy of methane near 1651 nm is also described. We demonstrate that the BDFA can be effectively used for signal amplitude enhancement in photothermal interferometry.

We demonstrate a thulium-doped fiber ring laser (TDFRL) integrated with an amplifier, which has a watt-level single-frequency output at 2 $\mu\text{m}$ with a 120-nm wavelength tunability. The TDFRL is constructed based on a hybrid ring-linear resonator configuration. An unpumped TDF is incorporated as a self-constructed saturable absorption grating. A blazed grating aligned in a Littrow configuration is employed for broadband wavelength-selective feedback. The characteristics of the laser output mode are analyzed by using an all-fiber scanning ring resonator.

A compact, high-average-power, sub-picosecond, two-color (1025 and 1085 nm) fiber-coupled, chirped pulse amplification Yb:fiber laser is reported. Two colors are selected from a continuum using a chirped fiber Bragg grating, which are then amplified in a two-stage Yb:fiber amplifier system. The preamplifier is fully fiber-coupled, improving significantly the stability and efficiency compared to the former bulk-optic system. The system delivers two-color pulses with the total average power of 2.3 W (1.9 W at 1025 nm and 0.4 W at 1085 nm) at a 65 MHz repetition rate. The FWHM duration of the final compressed output pulses of each color is 900 and 600 fs. The amplified spectrum showed insignificant spontaneous emission between the colors, indicating that the separation could be further increased. [ABSTRACT FROM AUTHOR]

A supercontinuum (SC) was first generated in a holmium-doped ZBLAN (ZrF4−BaF2−LaF 3−AlF3−NaF) fiber amplifier (HDZFA) with a spectral coverage of 2.03–2.9 μm, then was further red-shifted to 3.7 μm by cascading a piece of passive ZBLAN fiber. The amplifier consisted of a 2050-nm pulsed fiber laser and a piece of holmium-doped ZBLAN fiber (HDZF), which was in-band pumped by a 1950-nm continuous wave thulium-doped fiber laser. A fusion splicing was achieved between passive silica fiber and the HDZF. The spectral and power characteristics of the amplifier were carefully investigated. The SC obtained in the amplifier showed a spectrum ranging from 2.03 to 2.9 μm with an output power of 248 mW and a maximal slope efficiency of 43.3%. The spectral broadening in the amplifier was halted by a strong absorption induced by an excited state absorption (ESA) of Ho3+ in the range ∼2.7–2.8 μm. An SC with 20-dB spectral coverage of 2.05–3.71 μm was finally obtained by cascading a piece of passive single-mode ZBLAN fiber after the amplifier, with the purpose of overcoming the ESA-induced loss of holmium ions. To the best of our knowledge, this research is the first demonstration of an SC generation in an HDZFA. [ABSTRACT FROM AUTHOR]

We report experimental and simulated performance of a tandem (dual-stage) Tm-doped silica fiber amplifier with a high signal output power of 2.6 W in the 2-μm band. Combined high dynamic range, high gain, low noise figure, and high optical signal to noise ratios are achieved with our design. [ABSTRACT FROM AUTHOR]

We report the design of an ultrashort pulse amplifier based on using a chalcogenide gain fiber with a praseodymium doped core for operating in the 4--5 µm range on the ( ³F2,³H6 )→ ³H5 and ³H5→³H4 transitions. A detailed numerical simulation with allowance for dispersive and nonlinear effects for two pumping schemes: four-level at 1.55 µm and three-level at 2 µm with different fiber optical losses, pulse repetition rates, and central signal wavelengths is presented. The preferable case is cascade amplification on both laser transitions with overlapping emission cross sections for seeding pulses at 4.3 µm pumped at 1.55 µm. In this case, a gain of more than 30 dB can be achieved. The pulse energy can be increased from 10 pJ up to>10 nJ for the repetition rate of order 1MHz even for the loss level of 3 dB/m. The produced ps pulses have broadband spectra with Fourier transform limitation of order 100 fs. Further amplification may be limited by fiber damage. [ABSTRACT FROM AUTHOR]

We present multimode fiber lasers for tandem pumping of high power Er-, Tm-, and Yb-doped lasers. These pump sources are based on especially developed multimode Er- and Yb-doped double-clad fibers. Er-doped lasers with record pump conversion efficiency >48% at 1565 nm and more than 41% at 1535 and 1590 nm were realized. Yb-doped fiber laser at 1020 nm with record high 85% pump conversion efficiency was demonstrated. Also, we propose novel design of compact and cost-effective multimode laser scheme. The potential of power scaling of proposed lasers to the 1–10-kW level and their advantages as resonant pump sources are discussed. [ABSTRACT FROM PUBLISHER]

We demonstrate a thulium-doped fiber ring laser (TDFRL) integrated with an amplifier, which has a watt-level single-frequency output at 2 \mu\textm with a 120-nm wavelength tunability. The TDFRL is constructed based on a hybrid ring-linear resonator configuration. An unpumped TDF is incorporated as a self-constructed saturable absorption grating. A blazed grating aligned in a Littrow configuration is employed for broadband wavelength-selective feedback. The characteristics of the laser output mode are analyzed by using an all-fiber scanning ring resonator. [ABSTRACT FROM PUBLISHER]

We report an all-fiber pulsed source based on parametric conversion followed by thulium amplification able to deliver picosecond pulses at a repetition rate selectable between 2 and 5 GHz, of which central wavelength can be freely selected in the 2-μm region. A very versatile Nyquist pulse shaping of the parametric pump, which allows for the electrical control of the pulse train, enables such a freedom in the repetition rate selection, as well as some control in the pulse duration. We also show that data can be embedded in the output pulse train resulting in a high-quality Gb/s return-to-zero transmitter. Such a programmable short-wave infrared laser is of high interest for sensing or nonlinear optics applications around 2000 nm that require a fine adjustment in both the spectral and temporal domains. [ABSTRACT FROM PUBLISHER]

A Yb-doped linearly polarized fiber ring oscillator continuously tunable from 1000 to 1099 nm is built and amplification over the whole range is investigated with emphasis on the short wavelength regime of 1000–1025 nm. With an all-fiber single-mode polarization-maintaining master oscillator power amplifier, over 10 W output from 1010 to 1090 nm and over 30 W from 1014 to 1080 nm are achieved. At wavelength <1020 nm, bandpass filters are inserted for suppressing amplified spontaneous emission. The source can be used in a variety of applications, including laser cooling of Yb-doped solids. [ABSTRACT FROM PUBLISHER]