Bismuth-doped Fiber Research Articles

Numerical and experimental study on the impact of chromatic dispersion on O-band direct-detection transmission.

The recent emergence of efficient O-band amplification technologies has enabled the consideration of O-band transmission beyond short reach. Despite the O-band being a low chromatic dispersion (CD) window, the impact of CD will become increasingly significant when extending the reach of direct-detection (DD) systems. In this work, we first numerically investigate the 3-dB bandwidth of single-mode fibers (SMF) and the CD-restricted transmission reach in intensity-modulation DD systems, confirming the significant difference between low- and high-dispersion O-band wavelengths. We then carry out experimental transmission studies over SMF for distances of up to 70 km at two different wavelengths, the low-dispersion 1320 nm and the more dispersive 1360 nm, enabled by the use of an O-band bismuth-doped fiber amplifier as a preamplifier at the receiver. We compare three 50-Gb/s optical DD formats, namely, Nyquist on-off keying (OOK), Nyquist 4-ary pulse amplitude modulation (PAM4) and Kramers-Kronig detection-assisted single-sideband quadrature phase shift keying (KK-QPSK) half-cycle subcarrier modulation. Our results show that at both wavelengths, OOK and QPSK exhibit better bit error rate performance than PAM4. When transmitting over 70-km of SMF at the less dispersive wavelength of 1320 nm, 50-Gb/s OOK modulation offers more than 1.5-dB optical power sensitivity improvement at the photodiode (PD) compared to 50-Gb/s QPSK. Conversely, at 1360 nm, the required optical power to the PD can be reduced by more than 3 dB by using QPSK instead of OOK.

Experimental characterization of an o-band bismuth-doped fiber amplifier.

The recent emergence of bismuth-doped fiber amplifiers (BDFAs) offers the potential to transmit high-speed WDM signals over long distances in the O-band spectral region, thereby greatly enhancing the scope of systems utilizing these wavelengths. In this paper, we present a comprehensive experimental study on several basic characteristics of an O-band BDFA based on a phosphosilicate optical fiber, including the frequency-dependent noise figure, gain tilt (static and dynamic), transient response, and polarization dependent gain. We discuss our findings and their implications on the use of BDFA technology in high bit-rate multichannel systems.

Heterodyne photothermal spectroscopy of methane near 1651 nm inside hollow-core fiber using a bismuth-doped fiber amplifier.

We present laser-based methane detection near 1651 nm inside an antiresonant hollow-core fiber (HCF) using photothermal spectroscopy (PTS). A bismuth-doped fiber amplifier capable of delivering up to more than 160 mW at 1651 nm is used to boost the PTS signal amplitude. The design of the system is described, and the impact of various experimental parameters (such as pump source modulation frequency, modulation amplitude, and optical power) on signal amplitude and signal-to-noise ratio is analyzed. Comparison with similar PTS/HCF-based systems is presented. With 1.3 m long HCF and a fiber amplifier for signal enhancement, this technique is capable of detecting methane at single parts-per-million levels, which makes this robust in-fiber sensing approach promising also for industrial applications such as, e.g., natural gas leak detection.

1.3 μm passively Q-Switched bismuth doped fiber laser using Nb2C saturable absorber

A tunable passively Q-switched fiber laser operating at 1.3 μ m was demonstrated using bismuth-doped fiber (BDF) as the gain medium and using niobium carbide (Nb 2 C) as the saturable absorber (SA). The Nb 2 C was prepared using the solution casting method, and then fabricated into a film form for ease of integration into the laser cavity. Stable Q-switched pulses were observed as the pump power was increased from 820 to 1037 mW, generating pulses with increasing repetition rates from 10.1 kHz to 13.8 kHz and decreasing pulse widths from 17.54 to 7.58 μs. The all-fiber laser had a center wavelength at 1314 nm with a broad 3-dB bandwidth of 8.35 nm. The maximum output power and pulse energy of the Q-switched laser were 0.74 mW and 53.7 nJ, respectively. The laser was stable when tested for its long-term stability, where the peak frequency remained consistent at 13.8 kHz and the SNRs were maintained to be more than 60 dB throughout the entire test period. To the best of our knowledge, this is the first demonstration for a passively Q-switched fiber laser operating at 1.3 μ m wavelength region using BDF as the gain medium. • A bismuth-doped phospholicate fiber was used as the amplifying medium for emission in the 1.3 μ m wavelength region. • Q-switched pulses were generated using niobium carbide (Nb 2 C) saturable absorber. • A maximum pulse energy of 53.7 nJ was obtained, with the pulses having a high SNR of more than 60 dB. • The laser was tunable from 1304 to 1320 nm, generating stable Q-switched pulses for a span of 16 nm.

Dynamics of a Q-switched bismuth-doped fibre laser: simulation and comparison with experiment

Using an improved travelling wave model, we have numerically investigated the dynamics of a Q-switched bismuth-doped fibre laser. Comparison of simulation results with previously reported experimental data demonstrates good agreement of the multipeak lasing structure and the shape of the strongest pulses at various levels of pumping. We have assessed the effect of the main laser parameters on output laser characteristics and quantitatively evaluated the effects of the nonsaturable loss in the active fibre and amplified spontaneous emission on output power saturation. Based on analysis of time-dependent light intensity and gain distributions in the gain medium at different instants in time, we have formulated recommendations how to improve output laser characteristics.

Real-time HCl gas detection at parts-per-billion level concentrations utilising a diode laser and a bismuth-doped fibre amplifier

HCl measurements in a cleanroom environment are carried out using a cavity ring-down analyser in order to get an estimate of the HCl concentrations that can be expected to be present in semiconductor manufacturing. HCl is a reactive gas and the materials used for gas sampling and transportation have a significant effect on the measurement response time; hence, data on HCl adsorption to different materials is also provided. Finally, a light source operating at 1742 nm that can be used for HCl detection in a multi-gas analyser based on multipass photo-acoustic spectroscopy is presented. Preliminary results indicate that sub-ppb detection levels are achievable using this approach even for HCl.

1.3\xa0\xb5m dissipative soliton resonance generation in Bismuth doped fiber laser

In this work, a Figure-9 (F9) bismuth-doped fiber laser (BiDFL) operating in the dissipative soliton resonance (DSR) regime is presented. The 1338 nm laser used a BiDF as the active gain medium, while a nonlinear amplifying loop mirror (NALM) in an F9 configuration was employed to obtain high energy mode-locked pulses. The wave breaking-free rectangular pulse widened significantly in the time domain with the increase of the pump power while maintaining an almost constant peak power of 0.6 W. At the maximum pump power, the mode-locked laser delivered a rectangular-shaped pulse with a duration of 48 ns, repetition rate of 362 kHz and a radio-frequency signal-to-noise ratio of more than 60 dB. The maximum output power was recorded at around 11 mW with a corresponding pulse energy of 30 nJ. This is, to the best of the author’s knowledge, the highest mode-locked pulse energy obtained at 1.3 μm as well as the demonstration of an NALM BiDFL in a F9 configuration.

4-Level Alternate-Mark-Inversion for Reach Extension in the O-Band Spectral Region

Alternate-mark-inversion (AMI) has been used in the past to improve the transmission performance of binary intensity modulation formats. In this work, we improved the tolerance of O-band 4-level pulse amplitude modulation (PAM4) transmission to channel impairments through the adoption of an AMI scheme. Improvements in receiver sensitivity were shown in both semiconductor optical amplifier (SOA) and bismuth-doped fibre amplifier (BDFA) equipped links. We confirmed the capability of 4-level AMI to extend the reach in the O-band, which was achieved through the mitigation of nonlinear and dispersive effects. We experimentally demonstrated a 4.28-dB Q-factor improvement for transmission over 60 km of SMF-28e. To offer an insight to the mechanisms leading to the improved tolerance to transmission impairments, we presented numerical simulations that illustrate the underlying method of action of AMI4.

Deterioration of Bismuth-Doped Fiber Lasers Performance Induced by Blue and Green Laser Light Launched into Cladding

Deterioration of Bismuth-Doped Fiber Lasers Performance Induced by Blue and Green Laser Light Launched into Cladding

Bismuth doped fibre amplifier operating in E- and S- optical bands

Bismuth-doped fibre amplifiers offer an attractive solution for expanding the bandwidth of fibre-optic telecommunication systems beyond the current C-band (1530-1565 nm). We report a bismuth-doped fibre amplifier in the spectral range from 1370 to 1490 nm, with a maximum gain exceeding 31 dB, and a noise figure as low as 4.75 dB. The developed system is studied for forward, backward, and bi-directional pumping schemes and three different signal power levels. The forward pumping scheme demonstrates the best performance in terms of the achieved noise figure. The developed amplifier can be potentially used as an in-line amplifier with >20dB gain in the spectral band from 1405 to 1460 nm.

Operation of a Single-Frequency Bismuth-Doped Fiber Power Amplifier near 1.65 µm

The spectral range between 1650 and 1700 nm is an interesting region due to its potential applications in optical telecommunication and optical-based methane sensing. Unfortunately, the availability of compact and simple optical amplifiers with output powers exceeding tens of milliwatts in this spectral region is still limited. In this paper, a single-frequency continuous-wave bismuth-doped fiber amplifier (BDFA) operating at 1651 and 1687 nm is presented. With the improved signal/pump coupling and modified pump source design, the output powers of 163 mW (at 1651 nm) and 197 mW (at 1687 nm) were obtained. Application of the BDFA to the optical spectroscopy of methane near 1651 nm is also described. We demonstrate that the BDFA can be effectively used for signal amplitude enhancement in photothermal interferometry.

Optical Characterisations of Bi-Phosphosilicate Fiber for O Band Amplification

We report on the optical properties of Bi-doped phosphosilicate fiber. The fiber with a core and a clad diameter of 7.75 µm and 125 µm, respectively, is fabricated in-house using the modified chemical vapor deposition (MCVD) with in-situ solution doping technique. The spectroscopic properties of the fabricated fiber are characterized in terms of absorption, emission and lifetime. The lifetime decay is measured to be 800 µs; indicating a good potential optical amplification in the range of 1300 to 1500 nm. A Bismuth-doped fiber amplifier (BDFA) operating within the O-band region was successfully demonstrated. At 1340 nm, a 14.8 dB gain is achieved with 300 mW pumping power.

Ultra-Broadband Bismuth-Doped Fiber Amplifier Covering a 115-nm Bandwidth in the O and E Bands

In this article, we experimentally demonstrate an all-fiber optical amplifier using Bi-doped phosphosilicate fiber (BPSF) operating in both the O-band and the E-band, providing >20 dB gain from 1345 to 1460 nm for an input signal power of −23 dBm. A maximum gain of 31 dB with a noise figure (NF) of 4.8 dB was achieved at 1420 nm for −23 dBm input signal, whereas for an input signal power of −10 dBm it was 26 dB with a NF of 5.3 dB. The in-band OSNR of the proposed Bi-doped fiber amplifier (BDFA) was >22 dB from 1345 to 1460 nm for a −23 dBm input signal. The gain coefficient was found to be 0.04 dB/mW for a −23 dBm input signal. Also, the temperature dependent gain and NF performance of the BDFA within −40 to +60 °C were characterized. The temperature-dependent-gain (TDG) coefficient for a −23 dBm input signal was found to be −0.015 dB/°C at a signal wavelength of 1420 nm where the BDFA gain is maximum, while for an input signal power of −10 dBm it was −0.01 dB/°C at 1420 nm. The TDG coefficient of the proposed BDFA from 1350–1460 nm was in the range from −0.079 to −0.008 dB/°C. The BDFA gain and NF performance were also measured and compared using BPSFs with different unsaturable loss (UL) characteristics.

Multiwavelength Brillouin Generation in Bismuth-Doped Fiber Laser With Single- and Double-Frequency Spacing

Multiwavelength fiber lasers operating in the 1.3 μm wavelength region are of great interest as they complement existing systems in the conventional optical communication band of 1.55 μm. In this work, a multiwavelength Brillouin fiber laser with single- and double-Brillouin frequency spacings operating in 1.3 μm is proposed and demonstrated using a dispersion compensating fiber (DCF) as the Brillouin gain medium. A bismuth-doped fiber serves as the laser gain medium. At the maximum pump power of 1021 mW and with the Brillouin pump set at 11 dBm, up to 7 Brillouin Stokes lines with a wavelength spacing of 0.074 nm are obtained in the single-spaced configuration. In the case of the double-spaced configuration, 14 Stokes lines are generated with a wavelength spacing of 0.15 nm between the even Stokes lines. By tuning the central wavelength of the Brillouin pump, both laser configurations are wavelength-tunable with a range of 93 nm and 19 nm for the single-spaced and double-spaced Brillouin lasers respectively. This is, to the best of the author's knowledge, the first demonstration of a multiwavelength/Brillouin laser using a bismuth-doped fiber as the laser gain medium.

Effect of Drawing Conditions on Optical Properties of Bismuth-Doped High-GeO2–SiO2 Fibers

The effect of drawing conditions on the optical properties of the bismuth-doped high-germania-glass core fibers has been studied. It was found that the gain characteristics of these fibers become better with the increase of the drawing speed from 10 to 100 m/min. The small-signal absorption spectra of the Bi-doped fibers obtained at drawing speeds lower than 1 m/min are characterized by a high level of the unsaturable loss and the presence of an unstructured band situated within a wavelength region of 1100 - 1250 nm. The variation of drawing temperature ranging from 1770 to 1830 °C almost did not affect the optical properties of the fibers studied. It was shown that an optimization of the drawing parameters can significantly increase the performance of the developed bismuth-doped fiber lasers.

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.

Bismuth‐doped fiber as Q‐switcher in hafnium bismuth erbium co‐doped fiber laser

AbstractWe demonstrate a compact, all‐fiber Q‐switched hafnium bismuth erbium co‐doped fiber laser based on bismuth‐doped fiber (BDF) as the saturable absorber (SA). The laser cavity was constructed using a homemade hafnium bismuth erbium co‐doped fiber as gain medium. It was found that stable Q‐switched pulses operating at 1531.74 nm can be readily generated when the 980 nm pump power is raised above the threshold of 96 mW. By increasing the pump power to the maximum power of 198 mW, the repetition rate was tunable from 27.2 to 59.1 kHz while the pulse width reduces from 36.3 to 6.8 μs. At the maximum pump power, the Q‐switched laser produced a pulse energy of 10.1 nJ. The finding provides evidence of the possibility of BDF as an effective SA for Q‐switched laser operating in 1.5 μm region.

Modeling and experimental characterization of a dual-wavelength Bi-doped fiber laser with cascaded cavities

We present a comprehensive theoretical and experimental investigation of a dual-wavelength, bismuth-doped fiber (BDF) laser operating near 1700 nm based on cascaded cavities. The BDF provides optical gain from 1650 nm to 1800 nm when pumped at 1550 nm. The linear laser cavity is defined by a 90% fiber mirror on one end and two fiber Bragg gratings (FBGs) with two lengths of BDF in cascade on the other. The laser can operate at either wavelength alone, or both wavelengths simultaneously by simple adjustment of the pump power. We develop a model based on rate equations and radiation transport equations for two level BDF lasers which we then extend to the case for cascaded cavities. Experimental results agree with simulations.

Characterization of a single-frequency bismuth-doped fiber power amplifier with a continuous wave and modulated seed source at 1687 nm.

In this paper, we report the performance of a bismuth-doped fiber amplifier at 1687 nm. This wavelength region is particularly interesting for laser-based spectroscopy and trace gas detection. The active bismuth-doped fiber is pumped at 1550 nm. With less than 10 mW of the seed power, more than 100 mW is obtained at the amplifier's output. We also investigate the signal at the output when a wavelength-modulated seed source is used, and present wavelength modulation spectroscopy of methane transition near 1687 nm. A significant baseline is observed in the spectra recorded when the fiber amplifier is used. The origin of this unwanted background signal is discussed and methods for its suppression are demonstrated.

Multi-Band Direct-Detection Transmission Over an Ultrawide Bandwidth Hollow-Core NANF

In this article, we report high-speed multi-band direct-detection (DD) transmission over a hollow-core nested antiresonant nodeless fiber (NANF). Thanks to the ultrawide bandwidth of the NANF, we demonstrate dual-band transmission across the O- and C-bands over a ∼1-km length of a hollow-core fiber for the first time. Eight wavelength-division multiplexed (WDM) channels were transmitted using 100-Gb/s/λ Nyquist 4-ary pulse-amplitude modulation (PAM4) signals, which to the best of our knowledge, is the highest aggregate capacity ever transmitted in a DD hollow-core fiber-based transmission system. Optical pre-amplification was adopted for signal reception in both bands, achieved using an in-house built bismuth-doped optical fibre amplifier (BDFA) and a commercial erbium-doped fiber amplifier (EDFA) in the O- and C-band, respectively. We further demonstrate beyond 100-Gb/s/λ adaptively-loaded discrete multitone (DMT) transmission over the S+C+L-bands using the same NANF, without the use of optical amplification. Our experiments show that apart from fiber loss, the use of the NANF did not introduce any additional transmission penalties. The demonstrated results validate the ultrawide bandwidth and excellent modal purity of the fabricated NANF, which allow beyond 100-Gb/s/λ penalty-free transmission over multiple bands, highlighting the potential of this fiber technology for high-speed short- to intermediate-reach applications.