Doped Silica Fiber Laser Research Articles

Efficiency improvement of multimode Tm3+ doped double cladding silica fiber laser by in-line biconical tapers

Efficiencies improvement of LD (laser diode) pumped multimode large mode area (LMA) Tm3+ doped double cladding silica fiber lasers with different in-line biconial tapers were reported. Two types of multimode Tm3+ doped fiber were used in this experiment. Each type of fiber was made into three fiber lasers, a uniform geometry fiber laser and two tapered fiber lasers with different taper parameters. Biconical tapers located several centimeters from the output end of the multimode fiber lasers were made by heating and stretching method. Although the threshold of the best tapered fiber laser was added 200 mW, the slope efficiency (25.3%) and the maximum output power (1.31 W) of the fiber laser increased by 10.3% and 350 mW respectively, in comparison with the un-tapered one. Pre and post output laser power ratio was 6.3–15.6. Simultaneously, the laser spectrum moved to shorter wavelengths. The same trends of these characteristics were also observed in the other three tapered fiber lasers.

High efficient Tm3+ doped double cladding silica fiber laser with an intracavity biconical taper

A high efficient LD (laser diode) pumped Tm3+ doped double clad silica fiber laser with an intravacity biconical taper was reported. A biconical taper located ∼3 cm from the output end of the fiber laser was fabricated by heating and stretching method with a length 1.5 cm and waist diameter ∼20 µm. The slope efficiency was 49.8% with respected to the launched pump power, and the maximum output power was 1.97 W. Pre and post output laser power ratio was ∼10. This fiber laser was compared with other three biconical tapered fiber lasers (the same fiber with different tapers) and a uniform geometry fiber laser. With intracavity biconical tapers, fiber lasers’ thresholds were ∼1 W higher than the fiber laser without the taper (1.97 W). The pump end’s slope efficiencies of fiber lasers with tapers were 3–5% in contrast with 37.6% of the uniform one. After tapered, the pre and post laser power ratios were much higher than the un-tapered one’s, but not changed much with the launched pump power.

Ld-Clad-Pumped All-Fiber Tm3+-Doped Silica Fiber Laser

The CW 39.4 W all-fiber LD-clad-pumped Tm3+-doped fiber laser output is reported with a slope efficiency of 34% in respect to the pump power. The all-fiber laser is made up by progressively splicing the pigtail fiber, matched FBG fiber and Tm-doped fiber. The reflective FBG and Tm-doped fiber end fresnel reflection build up the laser resonance cavity. Due to the multi-mode FBG as the reflective mirror, the output laser spectrum is multi-peaks at high power output, whereas the total spectrum width is less than 2nm at nearly 1.94 μm.

Double-clad Tm3+-doped silica fiber laser with Bragg grating inscribed directly into active core by femtosecond laser

We report for the first time to inscribe the Fiber Bragg Grating (FBG) in Tm3+-doped multimode double-clad silica fiber by 800 nm femtosecond laser with a phase mask. The 1.35 μm period Bragg grating is written into the fiber core, which is responded to the laser center wavelength located at nearly 1960 nm. Continuous wave total output power of 11.5 W is obtained under the launched pump power of 29.8 W, corresponding to a slope efficiency of 45.0% and a conversion efficiency of 38.6%.

Passively Q-switched Tm^3+, Ho^3+-doped silica fiber laser using a highly nonlinear saturable absorber and dynamic gain pulse compression

We demonstrate a compact core-pumped 2 microm Tm(3+), Ho(3+)- doped all-fiber laser passively Q-switched with an antimony-based saturable absorber. The 20 ns pulses are the shortest Q-switched pulses from a fiber laser operating beyond 1850 nm and were produced at a repetition rate of 57 kHz and pulse energy of 15 microJ using a short-length (4 ns) cavity. The large absorber modulation depth of approximately 70% together with transient gain compression is shown to provide an efficient mechanism for Q-switched pulse shortening.

Passive Q-switching of short-length Tm 3+-doped silica fiber lasers by polycrystalline Cr 2+:ZnSe microchips

We demonstrate passive Q-switching of short-length double-clad Tm 3+-doped silica fiber lasers near 2 μm pumped by a laser diode array (LDA) at 790 nm. Polycrystalline Cr 2+:ZnSe microchips with thickness from 0.3 to 1 mm are adopted as the Q-switching elements. Pulse duration of 120 ns, pulse energy over 14 μJ and repetition rate of 53 kHz are obtained from a 5-cm long fiber laser. As high as 530 kHz repetition rate is achieved from a 50-cm long fiber laser at ∼10-W pump power. The performance of the Q-switched fiber lasers as a function of fiber length is also analyzed.

Fluorescence Emission Centres and the Corresponding Infrared Fluorescence Saturation in a Bismuth-Doped Silica Fibre

We investigate the fluorescence characteristics of bismuth doped silica fibres with and without Al co-dopant which are fabricated by means of modified chemical vapour deposition (MCVD) technique, and find that the fluorescences in the red region (centred around 750 nm) and in the infrared region (centred around 1100 nm) may originate from different emission sites in the fibre. Strong upconversion phenomena are observed in both Al-codoped and non Al codoped bismuth fibres when the fibres are excited by an acoustic-optic Q-switched Nd:YVO4 laser. Both the aspects indicate that the upper energy level absorption reported in the work of the bismuth doped silica fibre lasers may result from the fluorescence emission sites that are not responsible for the infrared emission. It is thus expected that optimizing the compositions and the fabrication conditions of the fibre and then transferring more fluorescence emission centres are helpful for the infrared emission.

Tm^3+/Ho^3+ codoped tellurite fiber laser

Continuous-wave and Q-switched lasing from a Tm(3+)/Ho(3+) codoped tellurite fiber is reported. An Yb(3+)/Er(3+)-doped silica fiber laser operating at 1.6 microm was used as an in-band pump source, exciting the Tm(3+) ions into the (3)F(4) level. Energy is then nonradiatively transferred to the upper laser level, the (5)I(7) state of Ho(3+). The laser transition is from the (5)I(7) level to the (5)I(8) level, and the resulting emission is at 2.1 microm. For continuous wave operation, the slope efficiency was 62% and the threshold 0.1 W; the maximum output demonstrated was 0.16 W. Mechanical Q switching resulted in a pulse of 0.65 microJ energy and 160 ns duration at a repetition rate of 19.4 kHz.

Investigation on the spectral characteristics of bismuth doped silica fibers

We investigated the fluorescence characteristics of the bismuth doped silica fibers with and without Al co-dopant which are fabricated by means of modified chemical vapour deposition (MCVD) technique. It was found that the bismuth and germanium codoped silica fiber exhibited a strong broad infrared emission centring at 1450 nm and covering 1300 nm when excited by the laser diodes working at 808 nm and 976 nm respectively. It was also found that for the Al and bismuth codoped silica fiber, the red (centring around 750 nm) and the infrared fluorescence (centring around 1100 nm) may originate from different emission centers in the fiber. Furthermore, strong up-conversion luminescence was also observed in both Al codoped and non-Al codoped bismuth doped fibers when the fibers were excited by an acoustic-optic Q-switched Nd:YVO 4 laser. It is thus concluded that the upper energy level absorption reported in the work of the bismuth doped silica fiber lasers may result from the fluorescence emission sites not responsible for the infrared emission.

LD-cladding-pumped 50 pm linewidth Tm^3+-doped silica fiber laser

We report on a Tm(3+)-doped fiber laser source operating at 1936.4 nm with a very narrow linewidth (50 pm) laser output. Up to 2.4 W cw laser power was obtained from an 82 cm long Tm(3+)-doped multimode-core fiber cladding pumped by a 792 nm laser diode (LD). The fiber laser cavity included a high-reflective dichroic and a low-reflective FBG output coupler. The multimode fiber Bragg grating (FBG) transmission spectrum and output laser spectrum were measured. By adjusting the distance between the dichroic and the Tm(3+)-doped fiber end, the multipeak laser spectrum changed to a single-peak laser spectrum.

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.

Efficient Tm 3+, Ho 3+-co-doped silica fibre laser diode pumped at 1150 nm

High power and highly efficient operation of a Tm 3+, Ho 3+-doped silica fibre laser that is pumped with diode lasers operating at 1150 nm is demonstrated. Internal slope efficiencies approaching the Stokes limit were produced and the maximum output power was 2.9 W. High power diode lasers operating at 1150 nm are valuable pump sources for a range of fibre lasers offering output in the shortwave infrared spectrum.

Efficient ~2 μm Tm^3+-doped tellurite fiber laser

Laser emission in the range of 1.88-1.99 micrim from a Tm3+ -doped tellurite fiber is demonstrated when pumped with a diode-pumped Er3+/Yb3+-doped silica fiber laser operating at 1.57-1.61 microm. This pump source excites the Tm3+ ions directly into the F43 upper laser level and yields an output power of 280 mW with a slope efficiency of 76% in a 99%-12% laser cavity arrangement and a 32 cm long fiber. This result is very close to the Stokes efficiency limit of approximately 80%. This is, to the authors' knowledge, the first demonstration of high efficiency lasing in a tellurite fiber at wavelengths longer than 1.56 microm.

High PowerTm3+-Doped Fiber Lasers Tuned by a Variable Reflective Output Coupler

Wide wavelength tuning by a variable reflective output coupler is demonstrated in high-power double-cladTm3+-doped silica fiber lasers diode-pumped at∼790 nm. Varying the output coupling from 96% to 5%, the laser wavelength is tuned over a range of 106 nm from 1949 to 2055 nm. The output power exceeds 20 W over 90-nm range and the maximum output power is 32 W at 1949 nm for 51-W launched pump power, corresponding to a slope efficiency of∼70%. Assisted with different fiber lengths, the tuning range is expanded to 240 nm from 1866 to 2107 nm with the output power larger than 10 W.

High-power and highly efficient diode-cladding-pumped Ho^3+-doped silica fiber lasers

We demonstrate high-power operation from a singly Ho3+-doped silica fiber laser that is cladding pumped directly with diode lasers operating at 1150 nm. Internal slope efficiencies approaching the Stokes limit were produced, and the maximum output power was 2.2W. This result was achieved using a low Ho3+-ion concentration and La3+-ion codoping, which together limit the transfer of energy between excited Ho3+ ions.

Discrete wavelength generation using modal interference in a diode-laser-pumped Tm 3+-doped few-mode fibre

By employing a few-mode core fibre in a symmetric cladding-pumped fibre laser arrangement, intermodal interference occurs between the first two symmetric modes that are excited simultaneously. In free-running mode, without the placement of dielectric mirrors, the Tm 3+-doped silica fibre laser oscillates on a number of fringes simultaneously. In a grating-tuned arrangement, the tuning curves comprise of a number of discrete fringes consistent with the theory associated with interference between the two excited symmetric modes propagating the length of the fibre.

High-power and highly efficient Tm^3+-doped silica fiber lasers pumped with diode lasers operating at 1150 nm

An output power of 1.74 W at 2.03 microm was generated at a slope efficiency of 51% when a double-clad Tm(3+)-doped silica fiber laser was pumped with high-power 1150 nm diode lasers. Pump excited state absorption from the upper laser level populates higher energy levels allowing cross relaxation to repopulate the upper laser level at a quantum efficiency greater than unity and to limit losses relating to additional pump excited state absorption. The output power was scaled to 4.77 W when both ends of the fiber were pumped.

Narrow linewidth, 100 W cw Yb^3+-doped silica fiber laser with a point-by-point Bragg grating inscribed directly into the active core

We report on the power scaling to 103 W of a 1.1 microm continuous-wave Yb(3+)-doped silica fiber laser incorporating a point-by-point (PbP) fiber-Bragg grating inscribed directly into the active core using 800 nm femtosecond laser pulses. The spectrum of the laser exhibited a narrow linewidth that broadened to 260 pm at 103 W. The output was frequency doubled using an 11 mm long periodically poled MgO:LiNbO3 crystal to generate 2.1 W of green with an internal conversion efficiency of 10% at high power and 0.81%/W at low power.

Diode-cladding-pumped singly Ho 3+ -doped silica fibre laser

An unsaturated continuous-wave output power of 109 mW was produced from a diode-pumped Ho3+-doped double-clad silica fibre laser that did not require the use of a sensitiser. The laser operated with a slope efficiency of 7% and an emission wavelength of 2.14 µm. Energy transfer upconversion may have adversely affected the performance of the laser.

Passively Q-switched Tm^3+-doped silica fiber lasers

By splicing on a length of Ho(3+)-doped silica fiber onto a diode-pumped double-clad Tm(3+)-doped silica fiber, stable passive Q switching of the Tm(3+)-doped silica fiber laser is demonstrated. The formation of Q-switched pulses was found to depend on both the length and the position of the Ho(3+)-doped silica fiber that was inserted into the fiber laser cavity. For stable Q-switched pulse generation, Ho(3+)-doped silica fiber lengths shorter than twice the absorption depth must be used. For long Ho(3+)-doped silica fiber lengths, randomly generated pulses are observed at operating wavelengths longer than 2090 nm, which are attributed to intracavity pumping of the Ho(3+)-doped silica fiber.