35 dB optical gain at 2.716 mu m in erbium doped ZBLAN fibre pumped at 0.642 mu m

An optical gain of 35 dB at 2.716 mu m signal wavelength has been measured in an erbium doped ZBLAN fibre. A pump-wavelength scanning determined the pump wavelength for maximum gain. This pump wavelength was found to be 0.642 mu m. The maximum absorption wavelength for this Er/sup 3+/ doped fibre is 0.649 mu m. It was deduced that the excited state absorption process improves the gain performance of such fibres at the signal wavelength considered.<>     

Design and performance of an erbium-doped silicon waveguide detector operating at 1.5 /spl mu/m

A new concept for an infrared waveguide detector based on silicon is introduced. It is fabricated using silicon-on-insulator material, and consists of an erbium-doped p-n junction located in the core of a silicon ridge waveguide. The detection scheme relies on the optical absorption of 1.5-/spl mu/m light by Er/sup 3+/ ions in the waveguide core, followed by electron-hole pair generation by the excited Er and subsequent carrier separation by the electric field of the p-n junction. By performing optical mode calculations and including realistic doping profiles, we show that an external quantum efficiency of 10/sup -3/ can be achieved in a 4-cm-long waveguide detector fabricated using standard silicon processing. It is found that the quantum efficiency of the detector is mainly limited by free carrier absorption in the waveguide core, and may be further enhanced by optimizing the electrical doping profiles. Preliminary photocurrent measurements on an erbium-doped Si waveguide detector at room temperature show a clear erbium related photocurrent at 1.5 /spl mu/m.     

Full characterization of packaged Er-Yb-codoped phosphate glass waveguides

We present a procedure for the characterization of packaged Er-Yb-codoped phosphate glass waveguides. The procedure is based on precise measurements of the output optical powers when the waveguide is diode-laser pumped at 980 nm. The dependence of these optical powers on the input pump power is then fitted to the results from a numerical model that describes in detail the propagation of the optical powers inside the waveguide. The best fit is obtained for the following parameters: the signal wavelength scattering losses are /spl alpha/(1534)=8.3/spl times/10/sup -2/ dB/cm, the Yb/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 5.4/spl times/10/sup -25/ m/sup 2/ and 7.0/spl times/10/sup -25/ m/sup 2/, the Er/sup 3+/ absorption and emission cross sections (/spl ap/980 nm) are 1.6/spl times/10/sup -25/ m/sup 2/ and 1.2/spl times/10/sup -25/ m/sup 2/, the Yb/sup 3+/--Er/sup 3+/ energy-transfer coefficient is 1.8/spl times/10/sup -23/ m/sup 3//s and the cooperative-upconversion coefficient is 8/spl times/10/sup -25/ m/sup 3//s. An approximate method is introduced that allows the determination of the absorption and emission cross section distributions for the erbium /sup 4/I/sub 13/2//spl hArr//sup 4/I/sub 15/2/ transition from the amplified spontaneous emission power spectrum.     

A compact high-performance optical waveguide amplifier

A glass waveguide amplifier was constructed in an Er/sup 3+/- and Yb/sup 3+/-doped phosphate glass. The waveguide channels were defined via a field-assisted Ag/sup +/ diffusion process. A net gain of 4.1 dB was measured at 1534 nm in a 3-mm length waveguide.     

High gain, broadband, 1.6 mu m Er/sup 3+/ doped silica fibre amplifier

Results demonstrating small signal gain in excess of 25 dB between 1.57 mu m and 1.61 mu m in Er/sup 3+/ doped silica fibre pumped at 1.55 mu m are presented. An optimum small signal gain of 0.33 dB per mW of pump power and a saturated output of 45 mW for 160 mW of pump power have been achieved.<>     

Numerical analysis of optical amplification in Er/sup 3+/-Yb/sup 3+/ codoped Ti:LiNbO/sub 3/ strip waveguides

Optical amplification at 1530 nm in 980-nm pumped Er/sup 3+/-Yb/sup 3+/-diffused Ti:LiNbO/sub 3/ strip waveguides was numerically analyzed on the basis of rate equation model of Er/sup 3+/-Yb/sup 3+/ system and pump/signal power propagation equations. The model includes total eight energy levels of the Er/sup 3+/-Yb/sup 3+/ system and simultaneously takes into account the excited state absorption (ESA) and upconversion processes within the Er/sup 3+/ ions as well as possible energy transfer processes between Yb/sup 3+/ and Er/sup 3+/ ions. A comparison of numerical results from the eight-level model and highly simplified five-level model has indicated that the /sup 4/S/sub 3/2/ manifold of Er /sup 3+/ ion must be included in the rate equation model. Dependences of threshold pump power and amplification gain on pump power (for gain only), Yb/sup 3+/ surface concentration and waveguide length were calculated and discussed. The characteristics of pump power evolution along the waveguide axis and population density distribution, as well as the influences of energy transfer coefficient from Yb/sup 3+/ to Er/sup 3+/, 550-nm (Er/sup 3+/), and 1060-nm (Yb/sup 3+/) fluorescence lifetime and above-mentioned detrimental processes including ESA, upconversion, and cross-relaxation processes on numerical result were studied. The role of Yb/sup 3+/ is demonstrated. A novel design idea that Yb/sup 3+/ is only incorporated at the end of the waveguide is proposed.     

1.65 /spl mu/m-band optical amplification with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping

In order to expand the available bandwidth for wavelength division multiplexing transmission systems, a 1.65 /spl mu/m-band optical fibre amplifier with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping has been demonstrated. The positive gain, 3.8 dB, is the first ever achieved by means of (/sup 2/H/sub 11/2/, /sup 4/S/sub 3/2/) /spl rarr/ /sup 4/I/sub 9/2/ stimulated emission transition.     

Soliton amplification and transmission with Er/sup 3+/-doped fibre repeater pumped by GaInAsP diode

Optical solitons in 1.5 mu m dispersion-shifted optical fibres have been successfully amplified and transmitted over 30-50 km with an Er/sup 3+/-doped single-mode fibre repeater. The Er repeater was pumped by a GaInAsP Fabry-Perot-type, high-power laser diode, and a gain as high as 10 dB was obtained in the soliton power regime for an Er pump power of 50 mW.<>     

Amplification and lasing at 1.3 mu m in praseodymium-doped fluorozirconate fibres

Light emission from the /sup 1/G/sub 4/ to /sup 3/H/sub 5/ transition around 1.3 mu m of Pr/sup 3+/ has been studied in fluoride glass (ZBLAN) fibres. Pumping at 1064 nm yields extracted laser power of a few mW at 1.294 mu m. Gain curves centred at 1.295 mu m have been obtained, with gross gains of more than 15 dB at 1.319 mu m. Changes of the output ASE with pumping conditions are explained by excited state absorption or energy transfer from the /sup 1/G/sub 4/ upper level of the transition.<>     

用于波导放大器的Er3+/Yb3+共掺磷酸盐玻璃的性能研究

通过优化熔融条件和玻璃组份,成功开发出一种新的Er3+/Yb3+ 共掺磷酸盐玻璃,其在沸水和熔盐中均表现出很好的化学稳定性.通过分析室温下Er3+/Yb3+ 共掺磷酸盐玻璃的吸收光谱,计算得到了Er3+ 离子在波长1533 nm处的峰值发射截面和杜得奥菲而特强度参数;其中Er3+ 离子在波长1533 nm 处的峰值发射截面为0 72×10-20 cm2,大于Schott的IOG1玻璃中Er3+离子的峰值发射截面0 67×10-20 cm2.通过改变离子交换的条件,获得了1 55μm单模光波导的制作条件;制作的波导传输损耗均小于1 dB/cm.初步的离子交换实验表明,Er3+/Yb3+共掺磷酸盐玻璃WM4完全适合波导放大器的制作.     

Gain-flattened Er/sup 3+/-doped fiber amplifier for a WDM signal in the 1.57-1.60-/spl mu/m wavelength region

A gain-flattened Er/sup 3+/-doped silica-based fiber amplifier (EDFA) has been constructed for a 1.58-/spl mu/m band WDM signal. This EDFA exhibits uniform amplification characteristics with a gain excursion of 0.9 dB for a four-channel WDM signal in the 1.57-1.60 /spl mu/m wavelength region. The average signal gain and the noise figure for the WDM signal are 29.5 dB and less than 6.3 dB, respectively. The use of this EDFA in parallel with a 1.55-/spl mu/m band EDFA will expand the WDM transmission wavelength region.     

1.58-/spl mu/m broad-band erbium-doped tellurite fiber amplifier

This paper describes the development of a 1.58-/spl mu/m broad-band and gain-flattened erbium-doped tellurite fiber amplifier (EDTFA). First, we compare the spectroscopic properties of various glasses including the stimulated emission cross sections of the Er/sup 3+4/ I/sub 13/2/ /sup 4/I/sub 15/2/ transition and the signal excited-state absorption (ESA) cross sections of the Er/sup 3+4/ I/sub 13/2/ - /sup 4/I/sub 9/2/ transition. We detail the amplification characteristics of a 1.58-/spl mu/m-band EDTFA designed for wavelength-division-multiplexing applications by comparing it with a 1.58-/spl mu/m-band erbium-doped silica fiber amplifier. Furthermore, we describe the 1.58-/spl mu/m-band gain-flattened EDTFA we developed using a fiber-Bragg-grating-type gain equalizer. We achieved a gain of 25.3 dB and a noise figure of less than 6 dB with a slight gain excursion of 0.6 dB over a wide wavelength range of 1561-1611 nm. The total output power of the EDTFA module was 20.4 dBm and its power conversion efficiency reached 32.8%.     

Laser diode pumped Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fluoride fiber amplifiers operating at 1.3 mu m

Both Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped singlemode fibres with high numerical apertures are pumped by laser diodes with InGaAs/GaAs strained quantum well structures. A net gain of 5.2 dB is obtained from Pr/sup 3+/-doped fluoride fibre pumped by laser diodes operating at 1.1017 mu m and a net gain of 3.2 dB is obtained from Pr/sup 3+/-Yb/sup 3+/-codoped fibre pumped by laser diodes operating at 0.98 mu m. The pumping efficiency difference between Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fibre is discussed.<>     

High-power 0.98 mu m GaInAs strained quantum well lasers for Er/sup 3+/-doped fibre amplifier

High-power GaInAs strained quantum well lasers with an emission wavelength of 0.98 mu m, suitable for Er/sup 3+/-doped fibre amplifier pumping, have been fabricated. A threshold current of 15 mA and a peak output power as high as 85 mW have been obtained for the ridge waveguide structure with AR/HR facet coating. Highly efficient pumping for the 1.536 mu m signals has been confirmed.<>     

Theoretical analysis of gain characteristics of Er/sup 3+/-Tm/sup 3+/-codoped tellurite fiber amplifier

The rate and power propagation equations of Er/sup 3+/ and Tm/sup 3+/-codoped tellurite fiber amplifier pumped by 800-nm laser are presented and solved to analyze the dependences of gain at both 1470 and 1530 nm on the codoping concentration of Er/sup 3+/ and Tm/sup 3+/, fiber length, and input signal power. The numerical results show that with pump power of 200 mW and fiber length of 1.5 m, the gain at both 1470 and 1530 nm may reach 12.0 dB when the codoping concentration of Er/sup 3+/ and Tm/sup 3+/ reach 4.0/spl times/10/sup 25/ ions/m/sup 3/, 3.2/spl times/10/sup 25/ ions/m/sup 3/, respectively. The fiber length and codopant concentrations are proposed to make the two channels equivalently amplified.     

Enhancement of fluorescence emission and signal gain at 1.53 µm in Er3+/Ce3+ co-doped tellurite glass fiber

Er3+/Ce3+ co-doped tellurite glasses with composition of TeO2-GeO2-Li2O-Nb2O5 were prepared using conventional melt-quenching technique for potential applications in Er3+-doped fiber amplifier (EDFA). The absorption spectra, up-conversion spectra and 1.53 µm band fluorescence spectra of glass samples were measured. It is shown that the 1.53 µm band fluorescence emission intensity of Er3+-doped tellurite glass fiber is improved obviously with the introduction of an appropriate amount of Ce3+, which is attributed to the energy transfer (ET) from Er3+ to Ce3+. Meanwhile, the 1.53 µm band optical signal amplification is simulated based on the rate and power propagation equations, and an increment in signal gain of about 2.4 dB at 1 532 nm in the Er3+/Ce3+ co-doped tellurite glass fiber is found. The maximum signal gain reaches 29.3 dB on a 50 cm-long fiber pumped at 980 nm with power of 100 mW. The results indicate that the prepared Er3+/Ce3+ co-doped tellurite glass is a good gain medium applied for 1.53 µm broadband and high-gain EDFA.     

GaAs/GaAlAs multiquantum well waveguides for all-optical switching at 1.55 mu m

The first measurements of selfphase modulation and nonlinear absorption in a GaAs/GaAlAs multiquantum well (MQW) waveguide near the half-bandgap resonance are reported. An intensity-dependent refractive index coefficient n/sub 2/ of 9*10/sup -14/ cm/sup 2//W and a two-photon absorption coefficient of 0.15 cm/Gw at 1.55 mu m wavelength for TM light were obtained. This corresponds to an intensity-independent figure of merit of 24 rad phase change in one nonlinear absorption length, high enough to allow the implementation of subpicosecond all-optical switches at 1.55 mu m wavelength.<>     

Optimum parameter design of Er/sup 3+/-doped fiber for optical amplifiers

The parameters of Er/sup 3+/-doped fiber which optimize the signal gain of a fiber amplifier pumped by a 1.48- mu m laser diode are theoretically determined using the rate equation for a three-level laser system. The basic parameters specified are the relative-index difference and the cutoff wavelength. The optimum cutoff wavelength of a completely Er/sup 3+/-doped core fiber with a step-index profile is 0.8 mu m regardless of the value of the relative-index difference. The optimum cutoff wavelength depends on the Er/sup 3+/-doped area radius.<>     

A high gain, high output saturation power Pr/sup 3+/-doped fluoride fiber amplifier operating at 1.3 mu m

A high net gain of 30.1 dB at 1.309 mu m and an output saturation of 13 dBm are obtained using a Pr/sup 3+/-doped fluoride fiber amplifier pumped at 1.017 mu m. The critical Pr/sup 3+/ concentration at which concentration quenching begins to occur was obtained by fluorescence lifetime measurement. The Pr/sup 3+/ concentration should be less than 1000 ppm to suppress the concentration quenching by cross relaxation. A high signal output power of 17.8 dBm was extracted from the Pr/sup 3+/-doped fluoride fiber. The Pr/sup 3+/-doped fluoride amplifier shows good potential for use in 13. mu m telecommunication systems.<>     

Tunable gain equalization using a Mach-Zehnder optical filter in multistage fiber amplifiers

Tunable signal gain equalization is demonstrated in three-stage Er/sup 3+/-doped fiber amplifiers using a waveguide type Mach-Zehnder (MZ) optical fiber. A 29-channel multiplexed system is examined where signal wavelengths are positioned from 1.548 to 1.555 mu m. By adjusting the MZ transmittance with the external control current, tunable gain equalization is achieved at the output of each amplifier.<>