Gain characteristics of tellurite-based erbium-doped fiber amplifiers for 1.5-microm broadband amplification

Widely tunable S-band ring-cavity Tm3+-doped fluorotellurite fiber laser

Tm3+-doped fluorotellurite fibers (TDFTFs) are fabricated by using a rod-in-tube method. A 2.1 m long TDFTF is used as the gain medium, in which both ends of the TDFTF are connected to a short piece of a silica fiber by direct fusion splicing. By inserting the above TDFTF and a tunable optical bandpass filter into a ring cavity and employing a 1400/1570 nm dual-wavelength pumping technique, tunable lasing from 1460 to 1526 nm is obtained, which almost covers the whole S-band. To the best of our knowledge, this is the first report of tunable Tm3+-doped fiber laser with a tunable range almost covering the whole S-band. Furthermore, by removing the tunable optical bandpass filter from the ring cavity, free-running multi-wavelength lasers at 1500 and 1901 nm are achieved. Our results show that TDFTFs are promising gain media for constructing S-band fiber lasers.

Bandwidth extension to 1627 nm of over 20 dB gain in an erbium-doped silica fiber via two-photon absorption

In this study, PbS/Er co-doped fibers (PEDFs) were fabricated by atomic layer deposition (ALD) combined with modified chemical vapor deposition (MCVD). A pumping scheme based on two-photon absorption at 1310 nm of PEDF is proposed for L + band amplification. Through the theoretical analysis, the local environment of Er3+ is changed due to the co-doping of PbS, which improves the two-photon absorption efficiency near 1300 nm. Compared with the 980 nm pump, the PEDFs excited by the 1310 nm pump show better amplification performance in the L + band. And in a bi-directional pumping system, PEDF achieves over 22 dB of gain in the whole L band. In particular, the bandwidth of over 20 dB gain was extended to 1627 nm with a noise figure as low as 4.9 dB. To the best of our knowledge, this is the first time that a high-gain bandwidth of L band amplification has been extended to 1627 nm. The results of unsaturated loss also show that PbS co-doping improves the two-photon absorption efficiency of PEDF to broaden the amplification bandwidth of L + band. These results demonstrate that an effective L + band amplification method is practically provided for future ultra-wideband optical communications.

Numerical analysis of optical confinement in silica and tellurite multicore fibers for near-infrared image transportation

We analyzed light confinement in circular step-index cores of tellurite and silica fibers through numerical calculations and also examined crosstalk between the fundamental modes of cores in multicore fibers. Our analysis showed that tellurite fibers have a pixel density about 2.2 times higher and a brightness about 1.4 times brighter than silica fibers. As a result, tellurite multicore image fibers have the potential to provide improved resolution and brightness for near-infrared image transportation compared with silica fibers.

Lasing at 2.72 µm in an Er3+-doped high-purity tungsten-tellurite glass fiber laser

This Letter reports the experimental realization, for the first time to our knowledge, of lasing in an erbium-doped tellurite fiber at 2.72 µm. The key to the successful implementation was the use of advanced technology for obtaining ultra-dry preforms of tellurite glasses, as well as the creation of single-mode Er³⁺-doped tungsten-tellurite fibers with an almost imperceptible absorption band of hydroxyl groups, with a maximum of ∼3 µm. The linewidth of the output spectrum was as narrow as 1 nm. Our experiments also confirm the possibility of pumping the Er-doped tellurite fiber with a low-cost high efficiency diode laser at 976 nm.

Broadband gain performance in the mid-IR using supercontinuum: 2.7 µm gain in high-purity Er3+doped tungsten tellurite glass fibers

This paper presents an experimental study of broadband mid-IR amplification that is carried out, for the first time, to the best of our knowledge, in an erbium-doped tungsten tellurite fiber. A simple, robust supercontinuum source based on a tapered germanate fiber is developed as a seed input in the region of 1.5-3 µm. We show that gain by a factor of 5 on one pass can be achieved in the 2.7 µm range by pumping a low-cost, high-efficiency diode laser at 976 nm using high-purity tellurite glass fibers.

Third-order cascaded Raman shift in all-solid fluorotellurite fiber pumped at 1550 nm

In this Letter, we demonstrate a third-order cascaded Raman shift in an all-solid fluorotellurite fiber pumped by a 1550 nm nanosecond laser. The fluorotellurite glass with a composition of TeO₂-BaF₂-Y₂O₃ (TBY) has a usable Raman shift of ∼785 cm^-1 and a Raman gain coefficient of ∼1.65 × 10^-12 m/W at 1550 nm, which is approximately 25.4 times larger than that of silica glass. By using a 5.38 m fluorotellurite fiber as the Raman gain medium and a 1550 nm nanosecond laser as the pump light, a third-order cascaded Raman shift is obtained via spontaneous cascaded Raman amplification in the fluorotellurite fiber, causing the generation of the first-, second-, and third-order Stokes emissions that peak at 1765, 2049, and 2438 nm, respectively. For an average pump power of ∼491.5 mW, the output power of the generated first-, second-, and third-order Stokes light is approximately 14.1, 67.4, and 31.6 mW, respectively. The corresponding conversion efficiency is approximately 2.87%, 13.70%, and 6.43%, respectively. Our results show that fluorotellurite fibers are promising Raman gain media for constructing cascaded Raman fiber lasers with a wide range of wavelengths.

Extending the L-band amplification to 1623 nm using Er/Yb/P co-doped phosphosilicate fiber

The gain bandwidth of the erbium-doped fiber amplifier limits the enhancement of the transmission capacity in optical fiber communication systems. This Letter reports an erbium-ytterbium co-doped phosphosilicate fiber, which is expected to increase transmission capacity by extending the L-band gain bandwidth to 1623 nm. The fiber was fabricated by modified chemical vapor deposition combined with solution doping technology. The mechanism of bandwidth-expansion by inhibiting the signal excited-state absorption was investigated. When the signal power and pump power were maintained at -3.7dBm and ∼720mW at 1480 nm, the 20 dB gain range was extended out to 1623 nm. Additionally, the noise figure at 1623 nm decreased to 6.01 dB, with 23 dBm saturated output power. The results show that the erbium-ytterbium co-doped phosphosilicate fiber has a great potential for extending L-band amplification.

Enhanced 1.5 μm emission from Yb3+/Er3+ codoped tungsten tellurite glasses for broadband near-infrared optical fiber amplifiers and tunable fiber lasers

Strong 1.5 μm emission with full width at half maximum (FWHM) of 64 nm has been obtained in 3 mol% Yb₂O₃ and 1 mol% Er₂O₃ codoped tungsten tellurite glass under the excitation of a 980 nm laser diode. Spectroscopic properties of Yb³⁺/Er³⁺ codoped tungsten tellurite glasses as a function of Yb³⁺ and Er³⁺ contents are systematically investigated by absorption spectra, emission spectra and lifetime measurement. The structure of tungsten tellurite glass is characterized by Raman spectrum. In addition, emission cross section and gain coefficient of Er³⁺ ions near 1.5 μm are determined and respective maximum values attain 1.06 × 10^-20 cm² and 4.07 cm^-1. Moreover, gain bandwidth and figure of merit associated with gain properties in tungsten tellurite glass are calculated and compared with other reported glasses. These results indicate that Yb³⁺/Er³⁺ codoped tungsten tellurite glasses with better gain properties are promising candidates in constructing broadband optical fiber amplifiers and tunable fiber lasers in the optical telecommunication window.

Structural, thermal and broadband NIR emission properties of Nd3+/Pr3+/Ag NPs co-doped tellurite glass

Nd³⁺/Pr³⁺ co-doped tellurite glasses containing metallic Ag NPs were synthesized by melt-quenching and heat-treating techniques. The amorphous structural nature, fundamental vibrational units and good thermal stability of the prepared tellurite glasses were confirmed by X-ray diffraction (XRD) pattern, Raman spectrum and differential scanning calorimeter (DSC) curve, respectively. The precipitated Ag NPs in a glass matrix with an average diameter ∼5 nm were revealed by transmission electron microscopy (TEM) image, and the radiative property of Nd³⁺ and Pr³⁺ ions was evaluated from the absorption spectrum by Judd-Ofelt theory. Under the excitation of 488 nm Xenon lamp, two broadband near-infrared emissions covering 800-1100 nm and 1250-1650 nm ranges were observed from the fluorescence spectrum. The former originated from the transitions of Pr³⁺:³P_1,0→¹G₄, Pr³⁺:¹D₂→³F_4,3, Nd³⁺:⁴F_3/2→⁴I_11/2 and Nd³⁺:⁴F_3/2→⁴I_9/2, while the latter was contributed by the Pr³⁺:¹G₄→³H₅, Pr³⁺:¹D₂→¹G₄, Pr³⁺:³F₃→³H₄ and Nd³⁺:⁴F_3/2→⁴I_13/2 transitions. With the introduction of Ag NPs, the emission intensity of two broadband near-infrared emissions was further enhanced, in which the peak emission intensity of 1250-1650 nm band was increased by about 56% and the FWHM is up to 250 nm. The obtained results indicate that Nd³⁺/Pr³⁺/Ag NPs co-doped tellurite glass has great potential in realizing ultra-broadband near-infrared emission covering O-, E- and S-bands simultaneously.

Ultrafast All-Optical Signal Modulation Induced by Optical Kerr Effect in a Tellurite Photonic Bandgap Fiber

Ultrafast all-optical signal modulation induced by optical Kerr effect (OKE) was demonstrated in an all-solid tellurite photonic bandgap fiber (PBGF) which was designed and fabricated based on TeO2–Li2O–WO3–MoO3–Nb2O5 (TLWMN, high-index rods), TeO2–ZnO–Na2O–La2O3 (TZNL, background), and TeO2-ZnO-Li2O-K2O-Al2O3-P2O5 (TZLKAP, cladding) glasses. At the input of a control pulse with high intensity, OKE occurred in the tellurite PBGF and the transmission bands of the tellurite PBGF shifted. The signal at 1.57 μm transmitting in the fiber core can be ultrafast all-optically modulated by the ultrafast single pulse (200 kW, 200 fs) under OKE, where the modulation speed can reach 50 GHz, faster than some commercial LiNbO3 modulators. The results in this paper can be applied to multi-monitors, local area network, detectors, multi-sources, etc.

Compound Glass Microsphere Resonator Devices

In recent years, compound glass microsphere resonator devices have attracted increasing interest and have been widely used in sensing, microsphere lasers, and nonlinear optics. Compared with traditional silica resonators, compound glass microsphere resonators have many significant and attractive properties, such as high-Q factor, an ability to achieve high rare earth ion, wide infrared transmittance, and low phonon energy. This review provides a summary and a critical assessment of the fabrication and the optical characterization of compound glasses and the related fabrication and applications of compound glass microsphere resonators.

High power narrow-linewidth linearly-polarized 1610 nm Er:Yb all-fiber MOPA

We developed a narrow-linewidth linearly-polarized all-PM-fiber MOPA at the wavelength of 1610 nm. The MOPA consists of a DFB laser diode seed source and three amplifier stages with three different gain fibers. The first amplifier stage employed an Er doped fiber and the second and third amplifier stages employed Er:Yb co-doped fibers. The maximum output power was 8 W. Linewidth of 25 MHz and polarization extinction ratio of 28 dB was obtained. At the maximum output power, no ASE component around 1.55 μm or 1μm was observed.

Role of ion migrations in ultrafast laser written tellurite glass waveguides

We report on a strong cross migration of ions in a Tellurite (Te) based glass to form waveguides using a high repetition rate femtosecond laser. The tellurite glass matrix was modified using oxides of P, Na and Zn elements of which Te and Na ions play an important role to form waveguides upon laser irradiation. Tellurium was observed to migrate causing a positive index change zone whereas sodium cross migrates to the tellurium deficient zone forming a relatively low index change region. We have used micro-Raman analysis to scan across the waveguide cross-section to understand the state of the glass network and the relation between ion migration and glass densification for waveguiding. We have found that there is an increase in TeO3 units and reduction of TeO4 units in the Te rich zones enabling densification. This work will help guide the new commercial glass manufacturing industries that aim at producing mid-infrared transparent glasses like tellurite, tellurides and chalcogenides for the production of waveguide based devices.

Spectroscopic properties and energy transfer parameters of Er3+-doped fluorozirconate and oxyfluoroaluminate glasses

Er³⁺- doped fluorozirconate (ZrF₄-BaF₂-YF₃-AlF₃) and oxyfluoroaluminate glasses are successfully prepared here. These glasses exhibit significant superiority compared with traditional fluorozirconate glass (ZrF₄-BaF₂-LaF₃-AlF₃-NaF) because of their higher temperature of glass transition and better resistance to water corrosion. Judd-Ofelt (J-O) intensity parameters are evaluated and used to compute the radiative properties based on the VIS-NIR absorption spectra. Broad emission bands located at 1535 and 2708 nm are observed, and large calculated emission sections are obtained. The intensity of 2708 nm emission closely relates to the phonon energy of host glass. A lower phonon energy leads to a more intensive 2708 nm emission. The energy transfer processes of Er³⁺ ions are discussed and lifetime of Er³⁺: ⁴I_13/2 is measured. It is the first time to observe that a longer lifetime of the ⁴I_13/2 level leads to a less intensive 1535 nm emission, because the lifetime is long enough to generate excited state absorption (ESA) and energy transfer (ET) processes. These results indicate that the novel glasses possess better chemical and thermal properties as well as excellent optical properties compared with ZBLAN glass. These Er³⁺- doped ZBYA and oxyfluoroaluminate glasses have potential applications as laser materials.

Spectroscopy and visible frequency upconversion in Er3+-Yb3+: TeO2-ZnO glass

The UV-Vis-NIR absorption studies of the Er(3+)/Er(3+)-Yb(3+) doped/codoped TeO2-ZnO (TZO) glasses fabricated by the melting and quenching method has been performed. The spectroscopic radiative parameters viz. radiative transition probabilities, branching ratios and lifetimes have been determined from the absorption spectrum by using Judd-Ofelt theory. The near infrared (NIR) to visible frequency upconversion (UC) have been monitored by using an excitation of 976 nm wavelength radiation from a CW diode laser. The effect of codoping with Yb(3+) ions on the intensity of the UC emission bands from the Er(3+) ions throughout visible region has been studied. The mechanism responsible for the observed upconversion emissions in the prepared samples have been explained on the basis of excited state absorption and efficient energy transfer processes.

Broadband amplification and highly efficient lasing in erbium-doped tellurite microstructured fibers

We report broadband amplification and highly efficient lasing in erbium-doped tellurite microstructured fibers. A broad positive net gain bandwidth of 113 nm (1524-1637 nm) is obtained in a 17 cm long erbium-doped tellurite microstructured fiber upon a pump power of 94 mW at 1480 nm. An all-fiber lasing at 1561 nm with maximum unsaturated power of 140 mW and slope efficiency of 53.7% is achieved from the fiber by employing a linear cavity. In addition, the influence of the fiber length on amplification and lasing is investigated and laser oscillation at 1535 nm is realized in a 4.3 cm long fiber.

Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers

In this Letter, we present a comprehensive comparison of the performance of a zirconia-based erbium-doped fiber amplifier (Zr-EDFA) and a bismuth-based erbium-doped fiber amplifier (Bi-EDFA). The experimental results reveal that a Zr-EDFA can achieve comparable performance to the conventional Bi-EDFA for C-band and L-band operations. With a combination of both Zr and Al, we could achieve a high erbium-doping concentration of about 2800 ppm (parts per million) in the glass host without any phase separations of rare earths. The Zr-based erbium-doped fiber (Zr-EDF) was fabricated using in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber through a solution-doping technique along with modified chemical vapor deposition. At a high input signal of 0 dBm, a flat gain at average value of 13 dB is obtained with a gain variation of less than 2 dB within the wavelength region of 1530-1575 nm and using 2 m of Zr-EDF and 120 mW pump power. The noise figures are less than 9.2 at this wavelength region. It was found that a Zr-EDFA can achieve even better flat-gain value and bandwidth as well as lower noise figure than the conventional Bi-EDFA.

Optimization of pump efficiency of Er(3+)-Ce(3+)doped telluride fiber amplifier

We propose a simplified numerical model to simulate the erbium/cerium codoped telluride fiber amplifier, and the feasibility of this model is verified by comparing the numerical results with the experiment data. Based on this numerical model, the research of the erbium/cerium codoping concentration and fiber length indicates that 45?dB gain can be achieved at a pump power of 130?mW for a 15?cm length telluride fiber.

Raman scattering boson peak and differential scanning calorimetry studies of the glass transition in tellurium-zinc oxide glasses

Raman scattering and differential scanning calorimetry (DSC) measurements have been carried out on four mixed tellurium-zinc oxide (TeO(2))(1 - x)(ZnO)(x) (x = 0.1, 0.2, 0.3, 0.4) glasses under variable temperature, with particular attention being given to the respective glass transition region. From the DSC measurements, the glass transition temperature T(g) has been determined for each glass, showing a monotonous decrease of T(g) with increasing ZnO content. The Raman study is focused on the low-frequency band of the glasses, the so-called boson peak (BP), whose frequency undergoes an abrupt decrease at a temperature T(d) very close to the respective T(g) values obtained by DSC. These results show that the BP is highly sensitive to dynamical effects over the glass transition and provides a means for an equally reliable (to DSC) determination of T(g) in tellurite glasses and other network glasses. The discontinuous temperature dependence of the BP frequency at the glass transition, along with the absence of such a behaviour by the high-frequency Raman bands (due to local atomic vibrations), indicates that marked changes of the medium range order (MRO) occur at T(g) and confirms the correlation between the BP and the MRO of glasses.

Highly ytterbium-doped bismuth-oxide-based fiber

Thermally stable highly ytterbium-doped bismuth-oxide-based glasses have been investigated. The absorbance increased linearly with Yb(2)O(3) concentration, reaching 7800 dB/m with 3 mol-% of Yb(2)O(3). An ytterbium-doped bismuth-oxide-based fiber has also been fabricated with a fiber loss of 0.24 dB/m. A fiber laser is also demonstrated, and it shows a slope efficiency of 36%.

Study of broadband near-infrared emission in Tm3+-Er3+ codoped TeO2-WO3-PbO glasses

In this work, we report the near-infrared emission properties of Tm(3+)-Er(3+) codoped tellurite TeO(2)-WO(3)-PbO glasses under 794 nm excitation. A broad emission from 1350 to 1750 nm corresponding to the Tm(3+) and Er(3+) emissions is observed. The full width at half-maximum of this broadband increases with increasing [Tm]/[Er] concentration ratio up to a value of ~ 160 nm. The energy transfer between Tm(3+) and Er(3+) ions is evidenced by both the temporal behavior of the near-infrared luminescence and the effect of Tm3+ codoping on the visible upconversion of Er(3+) ions.

Widely tunable ring-cavity tellurite fiber Raman laser

We report a widely tunable ring-cavity tellurite fiber Raman laser covering the S+C+L+U band. A tunable range (1495-1600 nm, limited by the tunable optical bandpass filter) over 100 nm is obtained by using a single-mode tellurite fiber with high Raman gain coefficients (55 W(-1)km(-1)) and large Raman shift (approximately 22.3 THz) as the gain medium. Furthermore, the free-running 1665 nm Raman fiber laser is achieved from the ring cavity by removing the tunable optical bandpass filter, which shows that such a tellurite fiber has potential for constructing a widely tunable fiber Raman laser covering the S+C+L+U band. A high optical signal-to-noise ratio of over 60 dB for almost all of the tunable range is also demonstrated.

Spectroscopic properties of the 1.4 microm emission of Tm3+ ions in TeO2-WO3-PbO glasses

In this work, we report the spectroscopic properties of the infrared 3H4-->3F4 emission of Tm3+ ions in two different compositions of glasses based on TeO2, WO3, and PbO for three Tm2O3 concentrations (0.1,0.5, and 1 wt%). Judd-Ofelt intensity parameters have been determined and used to calculate the radiative transition probabilities and radiative lifetimes. The infrared emission at around 1490 nm corresponding to the 3H4-->F4 transition has two noticeable features if compared to fluoride glasses used for S-band amplifiers. On one hand, it is broader by nearly 30 nm, and on the other, the stimulated emission cross section is twice the value for fluoride glasses. Both the relative intensity ratio of the 1490 nm emission to 1820 nm and the measured lifetime of the 3H4 level decrease as concentration increases, due to the existence of energy transfer via cross-relaxation among Tm3+ ions. The analysis of the decays from the 3H4 level with increasing concentration indicates the presence of a dipole-dipole quenching process assisted by energy migration.

Laser-diode-excited intense luminescence and green-upconversion in erbium-doped bismuth-germanate-lead glasses

We investigate the spectroscopic properties of the 1.5-microm emission from the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions in bismuth-germanate-lead glasses for applications in broadband fiber amplifiers. The emission peak locates at 1532nm with a full width at half-maximum (FWHM) of approximately 65nm. The measured lifetime and the calculated emission cross-section of this transition are 3.3ms and 8.66x10(-21)cm(2), respectively. IR-to-green-upconversion occurs simultaneously upon excitation of the 1.5-microm emission with a commercially available 980nm laser diode. Effects of PbF(2) content on the thermal stability, structure and spectroscopic properties of Er(3+)-doped bismuth-germanate-lead glasses have been examined. We find that the substitution with PbF(2) provides a couple of potentials: shortening the UV cutoff band and decreasing the phonon energy of host glasses. Codoping of Yb(3+) significantly enhances both the green-upconversion and 1.5-microm emission intensity by means of a nonradiative Yb(3+)-->Er(3+) energy transfer. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the (2)H(11/2) level, which is an emitting level of the green-upconversion of Er(3+). The results indicate the possibility towards the development of bismuth-germanate-lead based glasses as photonics devices.

Optical microsphere amplification system

We demonstrated a compact optical amplification system using a fiber taper and rare-earth-doped microsphere. Both the signal and pump beams were injected into the microsphere via the fiber taper to increase the spatial matching between two whispering gallery modes. As the pump power was increased, the resonance dip in the transmission spectra due to intrinsic attenuation in the microsphere became filled and then transited to the resonance gain peak. An amplification factor of up to 2.5 was realized with a microsphere of 63 microm in diameter.

Spectroscopic Properties of Er3+/Yb3+-codoped PbO–Bi2O3–Ga2O3–GeO2 Glasses

We investigate the spectroscopic properties of the 1.5-microm emission from the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions in PbO-Bi(2)O(3)-Ga(2)O(3)-GeO(2) glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width at half-maximum of approximately 45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 x 10(-20) cm(2) and a large FWHM x sigma(e)(peak) product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-microm emission with a commercially available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the (2)H(11/2) of Er(3+). The results indicate the possibility towards the development of lead-bismuth-gallate-germanate based glasses as photonics devices.

Judd-Ofelt analysis of Tm and energy transfer studies between Tm and Er codoped in lithium tellurite network

Optical properties of Tm(3+) and Er(3+) and Tm(3+)+Er(3+) codoped tellurite glass have been studied using different wavelengths from a Ti-Sapphire laser as excitation source. The energy transfer from one rare earth to other on excitation with different wavelengths has been studied. The Judd-Ofelt theory has been used to calculate various optical parameters suitable for laser oscillation.

Spectroscopic properties and thermal stability of Er3+ -doped TeO2-B2O3-Nb2O5-ZnO glass for potential WDM amplifier

A series of novel 70TeO2-(15-x)B2O3-xNb2O5-15ZnO-1wt.% Er2O3 (TBN x=0, 3, 6, 9, 12 and 15 mol%) tellurite glasses were prepared. The thermal stability, absorption spectra, emission spectra, and the lifetime of the (4)I(13/2) level of Er(3+) ions were measured and investigated. Three Judd-Ofelt intensity parameters Omega(t) (t=2, 4 and 6) (Omega(2)=(5.42-6.76)x10(-20)cm(2); Omega(4)=(1.37-1.73)x10(-20)cm(2); Omega(6)=(0.70-0.94)x10(-20)cm(2)) of Er(3+) ions were calculated by Judd-Ofelt theory. It is found that the Omega(6) first increases with the increase of Nb2O5 content from 0 to 6 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section (sigma(e)(peak)=(0.77-0.91)x10(-20)cm(2)) of Er(3+): (4)I(13/2)-->(4)I(15/2) transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=65-73 nm) of the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions were measured. The results indicate that these new TBN glasses can be used as a candidate host material for potential broadband optical amplifiers.

Spectral properties of Er3+/Yb3+ codoped tungsten-tellurite glasses

The spectral properties of Er3+/Yb3+ codoped tungsten-tellurite (WT) glasses have been investigated. The measured absorption spectra are analyzed by Judd-Ofelt theory. The compositional change of intensity parameter omega2 is attributed to the change in the covalency between the Er3+ and oxygen ions, the asymmetry in the local structures around the Er3+ ions can be neglected. The lifetimes of 4I(13/2) level of Er3+ in WT glasses are measured and comparable with other TeO2-based glasses. The stimulated emission cross-section is calculated based on McCumber theory. The fluorescence full width at half maximum (FWHM) and the emission cross-section (sigma(peak)) of the 4I(13/2) --> 4I(15/2) transition of Er3+ in different glass hosts have been compared. The suitability of such WT glasses as host materials for 1.5 microm broadband amplification is discussed.

Double-clad Cr4+:YAG crystal fiber amplifier

A novel double-clad Cr4+:YAG crystal fiber is demonstrated by use of a codrawing laser-heated pedestal growth method. Up to 10 dB of gross gain at a wavelength of 1.52 microm is achieved at a pump power of 0.83 W, which, to our knowledge, is the first Cr4+-doped fiber amplifier in the optical fiber communication band.