Praseodymium-doped Fluoride Fiber Amplifier Research Articles

Compact and efficient O-band bismuth-doped phosphosilicate fiber amplifier for fiber-optic communications

During last decades there has been considerable interest in developing a fiber amplifier for the 1.3-upmu m spectral region that is comparable in performance to the Er-doped fiber amplifier operating near 1.55 upmu m. It is due to the fact that most of the existing fiber-optic communication systems that dominate terrestrial networks could be used for the data transmission in O-band (1260–1360 nm), where dispersion compensation is not required, providing a low-cost increase of the capacity. In this regard, significant efforts of the research laboratories were initially directed towards the study of the praseodymium-doped fluoride fiber amplifier having high gain and output powers at the desired wavelengths. However, despite the fact that this type of amplifiers had rapidly appeared as a commercial amplifier prototype it did not receive widespread demand in the telecom industry because of its low efficiency. It stimulated the search of novel optical materials for this purpose. About 10 years ago, a new type of bismuth-doped active fibers was developed, which turned out to be a promising medium for amplification at 1.3 upmu m. Here, we report on the development of a compact and efficient 20-dB (achieved for signal powers between -40 and -10 dBm) bismuth-doped fiber amplifier for a wavelength region of 1300–1350 nm in the forward, backward and bi-directional configurations, which can be pumped by a commercially available laser diode at 1230 nm with an output power of 250 mW. The compactness of the tested amplifier was provided by using a depressed cladding active fiber with low bending loss, which was coiled on a reel with a radius of 1.5 cm. We studied the gain and noise figure characteristics at different pump and signal powers. A record gain coefficient of 0.18 dB/mW (at the pump-to-signal power conversion efficiency of above 27%) has been achieved.

Experimental investigation of gain transients in praseodymium-doped fluoride fiber amplifiers

We experimentally analyze power excursions on a surviving data channel due to praseodymium-doped fluoride fiber amplifier (PDFFA) gain transients. These transients are a result of the equivalent time-varying power for adding or dropping up to 15 wavelength division multiplexed (WDM) signals from a 16-channel WDM system at 1310 nm. We find that power excursions for the surviving 10-Gbit/s data channel increase with an increase in the number of channels added or dropped from the system. Bit error rate (BER) measurements on the surviving channel indicate that a power penalty of up to 3.5 dB as compared to the steady-state condition results from a 15-channel add-drop event. These results provide indication of the applicability of PDFFA amplification to dynamic reconfigurable optical networks in future DWDM systems that incorporate wavelengths in the 1310-nm region.

Gain Characterization of All-Optical Gain-Clamped PDFFA for WDM Networks Using the Feedback Theory

Using feedback theory, we analyze the gain of an all-optical gain-clamped praseodymium-doped fluoride fiber amplifier (AOGC PDFFA) for eight-channel multiwavelength operation. We demonstrate by numerical simulation that gain stabilization is achieved when the open-loop gain is higher than the feedback path attenuation. If this condition is fulfilled, the gain stabilizes to a value equal to the feedback path attenuation and is not influenced by the pump power, input signal power, number of channels, doped fiber length, or any other doped fiber parameter. In our setup the AOGC PDFFA noise figure is 0.12 dB lower than the open-loop PDFFA noise figure.

Gain Stabilization in All-Optical Gain-Clamped Cascade of Praseodymium-Doped Fluoride Fiber Amplifiers

The authors present theoretical results of an analysis of an all-optical gain-clamped (AOGC) praseodymium-doped fluoride fiber amplifier (PDFFA) for protecting surviving channels in an amplified wavelength division multiplexed (WDM) network with six cascaded PDFFAs. The theoretical analysis is based on application of a large-signal numerical model that takes into account propagation of pump, signal, and downstream and upstream amplified spontaneous emission and includes time variation effects in a four-level laser system. It is shown that power excursions caused in an eight-channel WDM network by loss addition of six channels could be lower than 1 dB and free of relaxation oscillations if the AOGC PDFFA is strongly inverted and the total loss of the ring resonator is appropriately set.

Development of an efficient praseodymium-doped fiber amplifier

This paper describes the development of an efficient praseodymium-doped fluoride fiber amplifier (PDFA) using newly developed PbF/sub 2/-InF/sub 3/-based fluoride single-mode fiber. First, the spectroscopic properties of Pr/sup 3+/ in PbF/sub 2/-InF/sub 3/-based and ZrF/sub 4/-based fluoride glass are compared and then the fabrication of high-NA PbF/sub 2/-InF/sub 3/-based fluoride single-mode fiber is presented. The gain coefficients obtained with the developed fiber are 0.36 dB/mW with a forward pumping scheme and 0.4 dB/mW with a bidirectional pumping scheme. We use this newly developed fiber to construct two types of an efficient PDFA module. We realized a 19-in rack size PDFA module with a master oscillator/power amplifier laser diode (MOPA-LD) and a plug-in type PDFA module with a wavelength-stabilized 1.017-/spl mu/m LD and describe their amplification characteristics.

Modelling of the temporal response of -doped fluoride fibre amplifiers

This paper presents a theoretical modelling and a numerical evaluation of the performance in the kHz regime of a typical praseodymium-doped fluoride fibre amplifier. The transient response of the amplifier is studied and amplifier characteristics such as saturation-induced second- and third-order distortion and interchannel interference, which become important in real telecommunication systems, are analysed in detail for amplitude-modulated signals.

Upconversion mechanisms of a praseodymium-doped fluoride fibre amplifier

We develop a simple method leading to the determination of important parameters for the praseodymium-doped fluoride fibre amplifier (PDFFA), such as the non-radiative energy transfer upconversion coefficient or pump-excited state absorption cross section . We apply this method to five ZBLAN bulks of different concentration (from 10 000 down to 500 wt ppm) and to a ZBLAN: 500 wt ppm single-mode fibre. The resulting non-radiative energy transfer upconversion coefficients are at 500 wt ppm and at 1000 wt ppm. When the pump wavelength is set at 1017 nm, is very weak: less than . We measured that the population varies according to the pump power raised to the power 2.7. We conclude that the upconversion mechanism leading to the excitation of states in the PDFFA is different from all that which has been previously suggested and we propose a three-photon process. The application of our method requires the measurement of radiative emission branching ratios from levels and that we compare to the values calculated with the Judd - Ofelt analysis. We show that this analysis has to be used very cautiously with ions. Finally, we discuss the distribution of ions in ZBLAN glass. The fitting of fluorescence decay curves from level with the Inokuti-Hirayama model shows that the distribution of ions in ZBLAN is nearly homogeneous and no clustering effects are detected. Nevertheless, the non-exponential fluorescence decay curve of level even at very low concentrations is explained by the fact that the ions do not all have exactly the same environment in the glass.

Subpicosecond pulse generation from a 1.3 [micro sign]m DFB laser gain-switched at 1 GHz

Pulses from a 1.3 µm gain-switched DFB laser are amplified using a praseodymium doped fluoride fibre amplifier, and then compressed to as short as 240 fs using higher-order soliton compression. Techniques for pedestal minimisation are investigated.

Transmission of 5 ps solitons at 1.32 [micro sign]m over 50 km of standard fibre using praseodymium doped fluoride fibre amplifiers

The authors report the amplification of 5 ps duration pulses from a gain-switched 1.32 µm DFB laser using a praseodymium doped fluoride fibre amplifier, and their subsequent soliton transmission over 50 km of standard telecommunications fibre.

Crosstalk in 1.3 μm praseodymium fluoride fiber amplifiers

Praseodymium-doped fluoride fiber amplifiers have been demonstrated to provide good gain, output power, and noise performance in the second telecommunications window. This paper presents a study of the crosstalk performance of these amplifiers. A theoretical analysis is presented from which a numerical model is developed and is used to predict the crosstalk performance of a typical amplifier. Experimental results, using two separate signals within the gain band, show good agreement between measurement and theory, indicating that it is unlikely that crosstalk will present a problem in anticipated amplifier applications. From the measured crosstalk, an upper limit is placed on the lower level lifetime, indicating that the population of this level will have a negligible effect amplifier gain. A novel technique for measuring the upper state lifetime in an amplifier, based on pump power dependence of crosstalk, is described and experimental results which are in agreement with fluorescent decay are presented.

Second Window Optical Amplifiers: Comparison of Different Pumping Wavelengths and Fibers

Praseodymium-doped fluoride fiber amplifiers at 1300 nm with different configurations and pumping sources have been developed. Performances obtained with various pumping wavelengths and active fibers are compared. The best results obtained with pumping at 1047 nm are 32.4 dB internal gain and 13.4 dBm saturation power.

A review of recent system demonstrations incorporating 1.3-μm praseodymium-doped fluoride fiber amplifiers

This paper provides a review of recent system demonstrations incorporating 1.3-/spl mu/m praseodymium doped fluoride fiber amplifiers (PDFFA's), following a brief historical perspective on the amplifiers development, the analogue and digital systems experiments, which have been conducted to date incorporating these new amplifiers, are described. Beyond this review material recent systems experiments conducted at BT Labs are also described. These experiments investigate the application of high performance PDFFA's to both, analogue, FM-SCM transmission, and high-speed (5 and 10 Gb/s), digital transmission systems. The results of a recent 10-Gb/s field transmission experiment are also presented. This paper also provides a perspective on the potential significance of 1.3-amplifiers to both long-haul point-to-point transmission systems and to optical fiber access networks based on passive optical network structures. >

Analysis of gain dynamics in Pr/sup 3+/-doped fluoride fiber amplifiers

A large-signal model for a four-level laser system which includes time variation effects has been used to study low frequency response characteristics, two-channel crosstalk and transient effects in praseodymium-doped fluoride fiber amplifiers (PDFFA). Pump power modulation results in a low-pass transfer of modulation to signals amplified in the PDFFA. Low-frequency compression of the PDFFA input/output signal transfer characteristic has been observed. Due to a relatively long lifetime of the /sup 1/G/sub 4/ metastable level, multichannel crosstalk lower than 30 dB has been calculated for modulation frequencies higher than 600 kHz. Response of the PDFFA toward a low-frequency signal square pulse exhibits a characteristic overshoot that originates from the PDFFA saturation by the amplified signal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimization of Pr 3+-doped fiber amplifier design for different pump wavelengths

The dependence of praseodymium-doped fluoride fiber amplifiers gain on pump wavelength has been analyzed with a large signal numerical model. The main scope of the analysis was to determine the amount of gain improvement which can be obtained for pump wavelengths in the range from 970 to 1060 nm by varying the active fiber length. It was found that an increase in gain of several dB can be achieved by selecting an active fiber which is considerably longer than the optimum length for pumping at the absorption maximum. The influence of background loss on the gain improvement is also discussed.

Multichannel FM-TV transmission using an engineered 1.3 µm praseodymium-doped fluoride fibre amplifier

The authors report the first use of a praseodymium-doped fluoride fibre amplifier (PDFFA) in a 24 TV channel FM-SCM transmission experiment. 24 analogue FM-SCM-TV channels were amplified by a PDFFA without any observable degradation in picture quality. By using a single PDFFA as a post-amplifier, transmission over 100 km of ‘standard’ 1.3 µm optimised fibre was demonstrated with a total loss budget of 45 dB. By using the same PDFFA as an inline amplifier, a loss budge of 53 dB was achieved.

Distortion and noise properties of a praseodymium-doped fluoride fiber amplifier in 1.3 /spl mu/m AM-SCM video transmission systems

The distortion and noise of a praseodymium-doped fluoride fiber amplifier (PDFA) are measured in two 40-channel AM-SCM video transmission systems. While it is already known that with direct modulation a PDFA leads to increased composite second-order distortion (CSO) and cross-modulation distortion (XM), this letter introduces an external modulation scheme that completely eliminates both problems. One PDFA is examined and found to yield low distortion and high CNR, but this is offset by a low-frequency noise. This noise is significant and the resulting picture quality is "annoying" in subjective tests.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Quarter-watt output at 1.3 mu m from a praseodymium-doped fluoride fiber amplifier pumped with a diode-pumped Nd:YLF laser

The characteristics of a praseodymium-doped fluoride fiber amplifier (PDFFA) pumped using a high-power diode-pumped Nd:YLF laser operating at 1.047 mu m are described. High small signal gains (29.5 dB) and the highest saturated output yet reported for PDFFAs (250 mW) have been achieved using this commercial diode-pumped source. The spectral characteristics have also been examined in both the large and small signal regimes. It is concluded that there is no significant penalty associated with pumping PDFFAs in the long wavelength wing of their pump band, even though this pump wavelength is almost 40 nm away from the peak of the absorption band. >

High output power from an efficient praseodymium-doped fluoride fiber amplifier

A praseodymium doped fluoride fiber amplifier (PDFFA) exhibiting efficient operation in both the large- and the small-signal regimes is described. The amplifier, based on a high NA fluoride fiber, exhibited a maximum small-signal gain of 29 dB and a low-pump small-signal. efficiency of 0.13 dB/mW. In the saturated regime a maximum output power of 212 mW was achieved. In this format, the signal-out versus pump-in characteristic, exhibited a slope efficiency of 30%, representing the most efficient conversion from pump to signal yet reported. Detailed spectral characterization reveals small-signal gain in excess of 20 dB over a wavelength range of almost 50 nm and in excess of 100 mW of saturated output available over a 30-nm wavelength range. >

One-LD-pumped Pr3+-doped fluoride fibre amplifier module with signal gain of 23 dB

The authors have developed a one-LD-pumped praseodymium-doped fluoride fibre amplifier module, based on an efficient, double-pass configuration with an optical circulator. They demonstrate a high gain coefficient of 0.40 dB/mW and a signal gain of 23 dB at 1.30 μm.

Design Considerations for Pr3+-Doped Fluoride Fiber Amplifier

A large-signal model for a four-level laser system has been used to study the small-signal and large-signal properties of a praseodymium-doped fluoride fiber amplifier. The model takes into account the LP 01 mode radial field distribution in step-index single-mode fiber and experimentally obtained stimulated emission, signal excited state absorption and pump absorption cross-sections. It has been found that the optimum cutoff wavelength is 750 nm and is independent of numerical aperture and input pump power. The numerical aperture should be made as high as possible