Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

High performance single frequency fiber grating-basederbium/ytterbium-codoped fiber lasers

The device characteristics of Er³⁺,Yb³⁺ single frequency fiber lasers are reported. A 5-cm long 1550-nm distributed feedback fiber laser with 4 mW output power is shown to have excellent specifications in terms of optical linewidth, signal-to-noise ratio (SNR), relative intensity noise, side-mode suppression and polarization purity. For higher power applications, a 1.5 cm single frequency Er³⁺,Yb³⁺ grating-based fiber laser with 60 mW output power and a net efficiency of 12% is demonstrated     

Tuning of a Tm3+:Ho3+: silica fiber laser at2 μm

Thermal tuning of a Tm³⁺:Ho³⁺:SiO₂ glass fiber laser was investigated. As a function of fiber length and temperature, the emission wavelength can be varied between 1960 and 2032 nm. The bandwidth of the laser emission is about 2 mm. Besides the wavelength also the change of threshold and slope efficiency with temperature and fiber length and the fiber absorption were measured     

Bidirectional 10-GHz optical comb generation with an intracavityfiber DFB pumped Brillouin/erbium fiber laser

We present multiwavelength and bidirectional operation of a novel Brillouin/erbium fiber ring laser. Multiwavelength operation is seeded by an Er³⁺:Yb³⁺ fiber distributed-feedback (DFB) laser inserted into the ring cavity. We realized lasing at up to eight wavelengths separated by 10.6 GHz     

1.55-μm Ce,Er:ZBLAN fiber laser operation under 980-nm pumping:experiment and simulation

Fiber laser operating property at 1.55-μm band in a newly developed Ce,Er:ZBLAN fiber by a continuous-wave laser diode pumping at 980 nm is presented. The output characteristics of the Ce,Er:ZBLAN fiber laser system are analyzed in detail based on the rate equations model by taking into account the energy transfer between Ce³⁺ and Er ³⁺ ions, as well as the upconversion mechanisms. The promotion role of the Ce in the erbium-doped ZBLAN for the 1.55-μm band fiber laser operation has been realized     

Operation of diode laser pumped Tm3+ ZBLAN upconversionfiber laser at 482 nm

Lasing at 482 nm is observed in Tm³⁺-doped ZBLAN glass fiber pumped with single-mode InP semiconductor diode lasers. Up to 5 mW of 482 nm light is obtained with <40 mW of absorbed pump power from a single 1135 nm pump diode laser. The optimum pump wavelength is measured to be 1135-1340 nm. More efficient laser operation is observed in fiber with 2500 ppm Tm³⁺ compared to 1000 ppm Tm³⁺ because of the reduced length of the fiber laser cavity possible with increased doping. Improved slope efficiencies are also demonstrated when the fiber laser is co-pumped with up to 5 mW from a 1220 nm diode laser. The relative intensity noise (RIN) of the fiber laser displays a maximum of -90 dB/Hz at relaxation oscillation frequencies of a few tens of kHz. The measurement of RIN is limited by shot-noise of -152 dB/Hz above 2 MHz. At higher frequencies, self mode-locking was observed in the fiber laser, which may indicate the existence of saturable absorbers in the fiber core. The presence of such bleachable absorbers is indicated by the observed increase in threshold after upconversion lasing at 482 mm     

Mid-wave IR and long-wave IR laser potential of rare-earth dopedchalcogenide glass fiber

The mid-wave IR and long-wave IR laser potential of rare-earth ions in chalcogenide glass fiber is reviewed. Spectroscopic data for the mid-wave and long-wave IR transitions for Pr³⁺, Dy³⁺ , and Tb³⁺ in chalcogenide glass is presented and used as a basis for discussion of laser potential in these glasses     

400-nm-Bandwidth Emission From a Cr-Doped Glass Fiber

Cr⁴⁺-doped glass fiber by a laser-heated pedestal growth method is reported. By analyzing the absorption spectra, the transitions of Cr³⁺ and Cr⁴⁺ in the fibers are identified. With appropriate pumping wavelength and divalent doping concentration, both Cr³⁺ and Cr⁴⁺ emission bands can be excited simultaneously, and become comparable in their fluorescent intensities. As a result, more than 400-nm-width emission peaked at 1144 nm was generated at room temperature. As much as 12muW of amplified spontaneous emission was obtained by pumping with a 900-nm Ti : sapphire laser     

Energy recycling versus lifetime quenching in erbium-doped 3-μmfiber lasers

Based on recently published spectroscopic measurements of the relevant energy-transfer parameters, we performed a detailed analysis of the population mechanisms and the characteristics of the output from Er ³⁺-singly-doped and Er³⁺, Pr³⁺-codoped ZBLAN fiber lasers operating at 3 μm, for various Er³⁺ concentrations and pump powers. Whereas both approaches resulted in similar laser performance at Er³⁺ concentrations <4 mol.% and pump powers <10 W absorbed, it is theoretically shown here that the Er³⁺-singly-doped system will be advantageous for higher Er³⁺ concentrations and pump powers. In this case, energy recycling by energy-transfer upconversion from the lower to the upper laser level can increase the slope efficiency to values greater than the Stokes efficiency, as is associated with a number of Er³⁺-doped crystal lasers. Output powers at 3 μm on the order of 10 W are predicted     

Diode-array pumping of Er3+/Yb3+ Co-dopedfiber lasers and amplifiers

Single-mode double-clad Er³⁺/Yb³⁺ co-doped fibers are shown to be suitable for diode array pumping at around 960 nm. A fiber laser with 96-W output power at 1.53 μm and a power amplifier exhibiting a small signal gain of 24 dB and a saturated output power of +17 dBm are reported     

CW operation of a 1.064-μm pumped Tm-Ho-doped silica fiber laser

The results from experiments relating to the CW operation of a Tm-Ho-doped silica fiber laser which is pumped with the fundamental output from a Nd:YAG laser are presented. The measured maximum output power from the fiber laser of 11 mW was generated at a slope efficiency of approximately 1.8% for a fiber length of 0.574 m and an output coupling of 10%. An output wavelength of 2170 nm (one of the longest lasing wavelengths to be achieved with the use of a silica host material) was also generated from the Tm-Ho-doped fiber laser when the fiber length was extended to 1.240 m and a 5% output coupling incorporated. The reduced efficiency and increased threshold for the Nd:YAG-pumped Tm-Ho-doped silica fiber laser when compared to previous reports of Ti:sapphire pumping is discussed in detail with the aid of a comprehensive numerical model. The numerical model solves the rate equations for the Tm-Ho-doped silica fiber laser system by taking into account the cross relaxation, energy transfer, and upconversion mechanisms, and it utilizes all published spectroscopic parameters relevant to Tm-Ho-doped silica and Tm-Ho:ZBLAN glass materials. It is established that the excited state absorption relevant to Nd:YAG pumping severely depletes the ³H₄ energy level of Tm³⁺ and consequently hinders the energy transfer process to the ⁵I₇ energy level of Ho³⁺. Optimum dopant concentrations are also established for both Nd:YAG and Ti:sapphire pump schemes     

Fabrication and properties of polymer optical fibers containingNd-chelate

Graded-index poly(methyl methacrylate) optical fibers (GI POF) containing a Nd-chelate have been fabricated. The absorption spectrum of the fiber exhibited several strong bands in the visible and infrared regions. We have observed infrared fluorescence (0.90, 1.06, and 1.3 μm) of the Nd³⁺ ion of the fiber at room temperature when it was pumped with an Ar⁺-pumped dye laser at 580 nm     

Cumulative waveform distortion in cascaded optical amplifierrepeaters for multigigabit IM/DD systems

An analysis was conducted of a cumulative pattern-dependent waveform distortion in cascaded semiconductor laser and Er³⁺-doped fiber amplifiers. At 2.5 Gb/s, cumulative waveform distortion limits the number of cascaded amplifiers to about 20 for the semiconductor amplifiers. The Er³⁺-doped fiber amplifier is relatively unaffected-over 100 stages can be cascaded. The Er³⁺ amplifier is seen to be the better choice for long-haul multigigabit systems     

Efficient integrated Nd3+ fiber laser

An efficient, integrated, low-threshold, tunable, laser-diode pumped Nd³⁺ fiber laser has been fabricated. The integrated fiber laser incorporated two highly reflecting intracore Bragg reflectors, which were formed holographically by transversely exposing the core to a UV two-beam interference pattern. When the fiber laser was diode pumped, a maximum output of 2.3 mW was observed at 1.088 μm, and a slope efficiency of 41% was measured     

Er3+-doped fiber amplifier pumped by 0.98 μm laserdiodes

The performance of an Er³⁺-doped fiber amplifier pumped by 0.98 μm InGaAs laser diodes (LDs) is reported. By using a fiber with low Er³⁺ content and optimizing the fiber length, a maximum signal gain of 37.8 dB at 30-mW pump power was realized at a signal wavelength of 1.536 μm. A maximum gain coefficient of 1.9 dB/mW at 14 mW pump power was achieved. It was found that the fiber amplifier pumped by the 0.98-μm LDs is twice as efficient as that pumped by 1.48-μm LDs, from the viewpoint of both required fiber length and the attained gain     

Laser diode-pumped holmium-doped fluorozirconate glass fiber laserin the green (λ~544-549 nm): power conversion efficiency, pumpacceptance bandwidth, and excited-state kinetics

The green (544-549 nm) Ho-doped fluorozirconate (ZBLAN) glass fiber laser, pumped in the red (λ~6;15 nm) by a high-power (~30 mW) InGaAlP laser diode or a ring dye-laser, has been characterized with regard to power conversion efficiency, fiber core-diameter and length, cavity output coupling, and pump acceptance bandwidth. Fibers doped with ~1200 ppm (by weight) of Ho and having core diameters of 1.7, 3, and 11 μm, and lengths ranging from 12.5 to 86 cm, have been studied in Fabry-Perot resonators having output couplings ranging from 1.545 to 96%. For a 1.7-μm core-diameter fiber, 21 cm in length, the threshold-launched pump power for the diode-pumped fiber laser is 1.9 and 3.5 mW for cavity output couplings of 1.5% and 24%, respectively. These values are the lowest for any upconversion-pumped fiber laser reported to date. Also, the noise and threshold-pumping power properties of the diode-pumped fiber laser are superior to those for its dye-laser-pumped counterpart. The highest laser slope efficiency (>22% with respect to launched pump power) was measured for a 3-μm core-diameter fiber and a cavity output coupling of 24%. The spectral interval over which the launched threshold pump power for this laser is <10 mW is almost 20 nm (637-656 nm). Studies of the fiber laser waveform as a function of pump power reveal competition for population between the ⁵S² and ⁵F₄ states and among the Stark sublevels of the ⁵F₄ manifold. Also, measurements of the output power on individual laser lines of the ⁵F₄, ⁵S₂→ ⁵I₈ (ground) transitions of Ho³⁺:ZBLAN as a function of pump power demonstrate the existence of a loss mechanism at the fiber laser wavelength, presumably due to absorption from ground or the ⁵I_y, ⁶S₂ or ⁵F₄ excited states of the ion     

Spectroscopic properties and efficient diode-pumped laser operationof neodymium-doped lanthanum scandium borate

We report on the spectroscopic properties and laser performance of Czochralski-grown LaSc₃(BO₃)₄ (LSB) crystals with high neodymium concentrations up to 2.5·10²¹ cm^-3. The low-concentration quenching of the upper laser level of neodymium and the polarization dependence of the spectra indicate that LaSc₃(BO₃)₄ crystalizes in a huntite-type structure like Nd³⁺:YAl₃(BO₃)₄ (NYAB). With diode laser pumping at 808 nm, a multimode Nd³⁺:LaSc₃ (BO₃)₄ (NLSB) laser at 1063 nm is demonstrated. Optical slope efficiency was 64% with respect to absorbed pump power. The possibility of second-harmonic generation in the laser crystal is discussed     

Efficient gain-switched operation of a Tm-doped silica fiber laser

We present the results from experiments relating to a gain-switched Tm-doped silica fiber laser in which a gain-switched Nd:YAG laser is used to pump the ³H₅ energy level of the Tm³⁺ dopant ion. This fiber laser configuration is the first example to our knowledge of a moderate energy gain-switched fiber laser which is pumped with a low-repetition-rate high-energy pulsed laser. For a near-optimized cavity, the gain-switched fiber laser produces a maximum pulse energy of 1.46 mJ at a maximum linear slope efficiency of 20% and a total optical-to-optical efficiency (with respect to the launched energy) of 19%. At low pump energies, the slope efficiency is approximately 40%, however, saturation of the output pulse energy is observed with the increase in the launched pump energy. We also present results from a numerical model that simulates ³H ₅-band pumping and includes all of the known pump excited-state absorption (ESA) mechanisms and, in addition, four cross-relaxation mechanisms have also been included. The calculations establish that the pump ESA mechanism contributes only a small loss factor to the overall efficiency of the laser when the Tm-doped silica fiber laser is pumped at low pump energies, however, as the pump energy is increased, losses due to pump ESA limit the amount of output energy from the fiber laser. The loss mechanism is mainly attributed to pump ESA from the ³H₄ upper laser level to the combined ³F_2,3 energy level at low launched pump energies because of the large absorption cross section for this transition and the relatively long lifetime of the ³H₄ energy level. For harder pumping conditions, the majority of the excited state population resides in the ¹G₄ level, inhibiting in some laser configurations gain-switching of the fiber laser until cessation of the pump pulse itself     

High-gain and high-efficiency diode laser pumped fiber amplifier at1.56 μm

Gain of an erbium-doped amplifier was optimized for operation at 1.56 μm, resulting in gains of up to 20 dB and slope efficiencies of 0.66 dB/mW. The amplifier is plug compatible with existing fiber networks. The gains of up to 20 dB were achieved using 1.48-1.49 μm laser diode pump sources with powers of 30 mW launched into the input of the system. The erbium-doped fiber used had an Er³⁺ concentration of roughly 30 p.p.m. in a GeO₂-Al₂O ₃SiO₂ host, and a core diameter of 7.0 μm