Double-clad Yb3 Research Articles

Characterisation and laser performance of a Yb:LuAG double-clad planar waveguide grown by pulsed laser deposition

We report on the fabrication of a crystalline multi-layer lutetium aluminium garnet planar waveguide, with a ytterbium-doped core, via hetero-epitaxial pulsed laser deposition on an undoped yttrium aluminium garnet substrate. Physical and optical characterization of the device revealed good crystallinity of the grown films and mode propagation investigations confirmed waveguiding properties. The measured fluorescence lifetime and calculated absorption and stimulated emission cross section spectra are found to be comparable with those reported for Yb:LuAG crystals grown by traditional methods. When end-pumped by a diode-laser bar, the crystalline double-clad Yb:LuAG planar waveguide lased using a quasi-monolithic cavity configuration. An output power of > 3 W with a 20% slope efficiency was obtained, limited by a waveguide propagation loss of 1.2 dB cm−1. This first demonstration of a multi-layer LuAG double-clad planar waveguide laser shows great potential for realising compact high-power waveguide lasers and amplifiers.

Efficient wavelength-tunable operation of tandem-pumped Yb fiber lasers

Highly efficient operation of double-clad Yb fiber lasers with fixed-wavelength and wavelength-tunable resonator configurations tandem-pumped by tunable Yb fiber lasers is reported. When wavelength selection was achieved using volume Bragg gratings in an external feedback cavity, the tandem-pumped Yb fiber laser produced maximum output powers of 7.0, 6.8, and 6.4 W at 1070 nm, corresponding to slope efficiencies of 88.2, 87.8, and 89.5%, for pump wavelengths of 1020, 1025, and 1030 nm, respectively. The wavelength-tunable fiber laser employing volume Bragg gratings and diffraction gratings was tuned from 1055 to 1112 nm with a linewidth of ~0.3 nm (FWHM), which was in good agreement with the calculated gain spectra. Optimization of tandem-pumped Yb fiber lasers and the prospect for further improvement in performance are considered.

双包层掺镱光纤激光器连续和调Q运转的实验研究

With fiber Bragg grating as resonant cavity,it was realized for the continuous and Q-switched function of double-clad Yb3+-doped fiber laser whose end pumped by a semiconductor laser of 980 nm wavelength.The experimental results of continuous laser showed that the gain fiber exists an optimal length when the pump power is fixed and laser power output biggest;As the pump power increases,the best gain fiber length increases too.The stable passive Q-switching function of the fiber laser was realized by using graphene dispersion liquid as a saturable absorber and inserting it between gain fiber and fiber Bragg grating.At the pump power of 2.87 W,the pulse sequence with minmum pulse width of 33 ns and repetition rate of 38.5 KHz was obtained.As the pump power increased further,the instable Q-swithed mode locking occurred.

Distributed Scheme Versus MOFPA Array on the Power Scaling of a Monolithic Fiber Laser

A couple of amplifying arrays for the power scaling of the fiber lasers under diverse pumping modes are studied. The multifiber series distributed side-pumping arrangement and the cascade amplifier chains in the form of the end-pumped master oscillator fiber power amplifier (MOFPA) scheme are investigated accordingly. Those are numerically modeled based on the propagation rate equations associated with stimulated Brillouin scattering (SBS) as well as the consideration of coupling and splicing losses for large mode area fibers. The continuous wave double-clad Yb:silica fiber laser amplifier is analyzed in various amplifying stages for several cavity lengths at forward pumping regime. Despite the distributed mode exhibits a desirable beam quality, however, it suffers a low SBS threshold. On the other hand, high output power is achieved in the MOFPA configuration far from the onset of SBS.

Suppression of self‐pulsing in Yb fibre lasers coupled with external Fabry‐Pérot cavity

A simple technique to suppress self-pulsing behaviour in a fibre laser employing a two-mirror Fabry-Perot external feedback cavity is reported. Feedback provided by the external Fabry-Perot cavity enforces the fibre laser to oscillate in the selected longitudinal modes, resulting in robust laser operation without self-pulsing. This technique has been successfully applied to a double-clad Yb fibre laser, yielding a stable continuous-wave output of up to 9.8 W at 1050 nm. The advantages of this technique and the prospects of further improvement are discussed.

Electronic and thermal refractive index changes in Ytterbium-doped fiber amplifiers

We develop a theoretical framework to analyze the mechanism of refractive index changes (RIC) in double-clad Yb³⁺ doped optical fibers under resonant core or clad pumping, and with signal amplification. The model describes and compares thermal and electronic contributions to the phase shifts induced on the amplified signal at 1064 nm and the probe signal at 1550 nm, i.e. located inside and outside of the fiber amplification band, respectively. The ratio between the thermal and electronic phase shifts is evaluated as a function of the pump pulse duration, the gain saturation, the amplified beam power and for a variety of fiber parameters.

Tunable double-clad ytterbium-doped fiber laser based on a double-pass Mach–Zehnder interferometer

We have demonstrated an adjustable double-clad Yb 3+-doped fiber laser using a double-pass Mach–Zehnder interferometer. The laser is adjustable over a range of 40 nm from 1064 nm to 1104 nm. By adjusting the state of the polarization controller, which is placed in the double-pass Mach–Zehnder interferometer, we obtained central lasing wavelengths that can be accurately tuned with controllable spacing between different tunable wavelengths. The laser has a side mode suppression ratio of 42 dB, the 3 dB spectral width is less than 0.2 nm, and the slope efficiencies at 1068 nm, 1082 nm and 1098 nm are 23%, 32% and 26%, respectively. In addition, we have experimentally observed tunable multi-wavelengths lasing output.

Narrow-linewidth, Yb 3+ -doped, hybrid microstructured fibre laser operating at 1178 nm

A narrow-linewidth fibre laser operating at 1178 nm that employs a double-clad Yb3+-doped hybrid microstructured fibre, is demonstrated. The fibre suppresses amplified spontaneous emission by the photonic bandgap effect, and parasitic lasing at shorter wavelength range (1030–1100 nm) was prevented. A narrow-linewidth (<0.05 nm), CW output of 0.5 W at 1178 nm with a slope efficiency of 14%, was measured.

Efficient double-clad Yb 3+-doped silica fibre laser pumped by an unfocused diode laser

A moderate output power Yb 3+-doped double-clad fibre laser pumped by an unfocused diode laser is reported. This pumping configuration omits micro positioned lenses used in fibre coupled laser diodes, thus making the system significantly less complex and more robust. The maximum launch efficiency was ∼80% and the maximum output power was >5 W with a measured FWHM of 18 pm.

Critical pump power and cross-section calculation for Yb3+-doped novel inner-clad structures

Rare-earth doped fiber lasers are now considered suitable sources for the 1.0-, 1.5-, and even 2.0-μm regions in a relatively large number of applications. In particular, Yb3+-doped fiber lasers have received strong interest due to its high quantum efficiency, broad tunability, and available high output power. In this work, we present results on a newly developed code for the simulation of the critical power that is required when designing double-clad high-power Yb3+-doped fiber lasers, which are based on novel inner-clad structures. From our results, we can also estimate σep, σel, σap, and σal for the aforementioned free-running laser cavities. Finally, we will formulate our predictions for feasible fiber laser cross sections.

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.

Analytical characterization of an end pumped rare-earth-doped double-clad fiber laser

Few steps of derivations on the rate equations have made it clear that the key issue of obtaining an analytical expression for the output laser power, from a double-clad Yb 3+-doped fiber laser, is how to integrate the products between the radiation power and its respective loss coefficient for both the pump and laser waves. After examining the approximations adopted in previous studies, instead of nullifying the population density of the upper-level atom, we used its average value in the pump equation, so that the cavity length range, that the analytical result can be applied, is extended. Consequently, we have shown that the output laser power can be expressed as η ( P p − P th ) when pumped by a power of P p . And the analytical expressions for the differential pump efficiency η and the threshold pump power P th have also been derived.

Design and fabrication of triangular inner cladding double-clad ytterbium doped fibre for high power lasers

To improve the performance of double clad high power fibre lasers, inner cladding design plays a significant role. A triangular inner cladding and silica structure second cladding with large air holes to acquire high inner cladding numerical aperture are designed. Single mode and high power output of the fibre lasers need the double clad Yb doped fibre with large core. A fibre with annular refractive index distribution core and low numerical aperture to acquire a large mode area fibre core is designed and fabricated. Furthermore co-doping with aluminium (Al) has been used to improve the solubility of ytterbium (Yb) into silicate network and the core absorption coefficients of two Yb doped fibres are compared with different Al concentration experimentally.

Output dynamics and stabilisation of a multi-mode double-clad Yb-doped silica fibre laser

The intensity dynamics of the double-clad Yb fibre laser have been characterised. Stabilisation of the fibre laser intensity by using uniform bi-directional pumping is demonstrated. For the single-end-pumped Yb fibre laser, the output becomes more stable for the shorter fibre length due to the higher threshold of stimulated Brillouin scattering, SBS, and Kerr effects and the reduction of saturated absorber effects caused by any unpumped fibre section. By additional pumping in a double-end-pumped configuration, the output power can be scaled higher before detecting high intensity pulses initiated by SBS in the Yb fibre laser due to the reduction of saturable absorption effect. It is confirmed that uniform pumping enhances the stability of the laser output.

The analytical investigation of the super-Gaussian pump source on the thermal, stress and thermo-optics properties of double-clad Yb:glass fiber lasers

Fiber lasers have attracted considerable attention when their power can realistically be scaled to kilowatt level and beyond. In this paper, we assumed that the fiber core and first clad are exposed to a pump source with a super-Gaussian profile of order four. The effects of this non-uniform heat deposition on thermal, stress and thermooptics properties such as temperature-dependent change of refractive index and thermally induced stress have been comprehensively studied and their equations analytically derived.

Temperature-dependent fluorescence characteristics of an ytterbium-sensitized erbium-doped silica fiber for sensor applications

The characteristics of temperature-dependent fluorescence of an ytterbium (Yb 3+)-sensitized erbium (Er 3+)-doped silica fiber are presented. A 10-cm long double-clad Yb 3+/Er 3+-codoped fiber is diode-pumped at 915 nm and the individual fluorescence intensities from Yb 3+ and Er 3+ ions are measured with varying the fiber temperature. The ratio of the dual fluorescence intensities varies exponentially with temperature in the range of room temperature to ∼300 °C. This dual-dopant system has dual emission bands that emit comparable fluorescence powers. Particularly, the self-referencing fluorescence intensity ratio is insensitive to external perturbations in the fiber, which is useful for sensors that are used in a harsh environment without any use of additional referencing techniques. This scheme allows a compact, long-life, and low-cost temperature sensor and can also be combined with a wide range of existing fiber-optic multiplexing schemes that can simultaneously detect multiple physical parameters.

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.

Double-clad Yb3+-doped fiber lasers with virtually non-circular cladding geometry

We report on cladding pumped Yb3+-doped fiber lasers with novel virtual-non-circular cladding geometries. The geometry of the inner-cladding is in fact circular with D-shaped holes, that form virtual-D (one hole), and virtual-square (four holes) structures for the inner-cladding. The laser performance of this structure is assessed at several wavelengths and lengths, showing efficiencies as high as those obtained with other geometries for the inner-cladding.

Efficient operation of double-clad Yb3+-doped fiber lasers with a novel circular cladding geometry.

A highly efficient double-clad Yb3+-doped fiber laser with a novel cladding geometry is described. A round double-clad fiber with a small D-shaped hole for breaking a circular symmetry in a cladding combines the advantages of ease of manufacture and handling round fibers with efficient absorption of pump light. Fiber lasers with a double-D cladding shape and a D-hole cladding are compared. We report what are to our knowledge the highest slope efficiencies of 73% and 69%, respectively, pumping at 915 nm. Output powers in excess of 13 W are demonstrated.

End-pumped, passively Q-switched Yb:YAG double-clad waveguide laser

We present a diode-pumped, double-clad Yb:YAG waveguide laser that contains an integrated section of a Cr(4+): YAG saturable absorber for passive Q switching. Using two 4-W polarization-coupled, broad-striped diode-pumped lasers, we obtained 30-microJ pulses of 1.6-ns duration at repetition rates of as much as 77 kHz. The slope efficiency was ~50% with respect to absorbed pump power, with a maximum output average power of 2.3 W and a peak power of ~18 kW . The output beam was single lobed, with M(2) values as great as 1.5x1.3 . We also demonstrate a passively Q -switched Nd:YAG waveguide laser of similar design, operating at 1.064 microm and 946 nm.