Single Erbium-doped Fiber Research Articles

Dual-comb Spectroscopy for Laminar Premixed Flames with a Free-running Fiber Laser

ABSTRACT Dual-comb spectroscopy (DCS) has emerged as an important new technique for high-resolution molecular spectroscopy. However, this powerful tool has not been widely utilized in combustion diagnostics due to the difficulty of maintaining the mutual coherence between the two comb sources. In this work, we demonstrated a free-running fiber-laser-based DCS for in situ and non-intrusive H2O and C2H2 measurements in laminar premixed flames. This picometer-resolution dual-comb spectroscopic system was developed by using a single erbium-doped fiber laser at 1.5 μm along with a multipass optical configuration for the enhanced absorption measurement. Because of the mutual coherence of the two comb pulse trains emitted from the same laser cavity, DCS could be performed without using any phase-locking systems. Absorption spectra of CH4/O2/air flames over the spectral range 6503 cm−1 – 6535 cm−1 were measured at different reactant flow rates and heights above the burner, showing a good agreement with the spectral simulation of high-temperature H2O using the HITEMP database. A noise equivalent (1σ) absorption coefficient of 9.5 × 10−5 cm−1 was achieved using the current DCS system. Besides, the dual-comb measurement of a C2H4/air sooting flame was also performed at the equivalence ratio Ф = 2.94 and compared with the spectral simulation of high-temperature H2O and C2H2. All the spectral data were retrieved by 1500 averages of interferograms to increase the spectral signal-to-noise ratio (SNR), but a single interferogram could be acquired at 0.83 ms using the current free-running dual-wavelength fiber laser.

Measurement of fiber non-linearity based on four-wave mixing with an ASE source

A new four-wave mixing scheme to practically measure the non-linear coefficient of fibers is introduced. A single erbium-doped fiber amplifier is used to create the two wavelengths for the four-wave mixing inputs, which are pre-spectrally sliced via fiber Bragg grating filters. The proposed scheme avoids the Brillouin backscattering, rendering this a more accurate method to determine fiber nonlinearities than conventional coherent FWM systems. Furthermore, the generated FWM seed beams are pure and ultra-narrow, and can therefore be treated as coherent light. Consequently, accurate degeneracy factor can also be taken into consideration.

Highly Accurate Compensation Technique for 10-GHz Pulse Intensity Fluctuation Using SPM-Based All-Optical Intensity Limiter

We report a trial of 10-GHz and highly accurate pulse-by-pulse intensity limiting with a single erbium-doped fiber amplifier for low-power-consumption driving optical limiting. A self-phase modulation-based optical limiter with an appropriate pre-chirping made it possible, which provides high limiting accuracy of less than 0.1 dB at a 10-GHz bit rate. The limiting function was tested in a simulation and an experiment for 10-GHz bit sequence with intensity fluctuation. When fed a 1.6-dB sinusoidal intensity modulation at 2 GHz, the experimental setup successfully achieved optical limiting with 0.1-dB accuracy.

Experiment and theoretical explanation of optical bistability in a single erbium-doped fiber ring laser

Optical bistability phenomenon in a single fiber ring laser employing erbium-doped fiber (EDF) as gain medium is observed in our experiment. In the EDF amplifiers, the photons of pump light cannot completely transfer into that of signal light because of various attenuation factors. This part of loss (useless pump loss) and active spontaneous emission (ASE) can both lower the small-signal gain of the EDF, and can eventually result in the bistability phenomenon. The range of this bistability has a complicated relationship with the length of the EDF, the erbium-ion doping concentration, the cavity loss and the useless loss coefficient of the pump light.

A theoretical analysis of amplification characteristics of bi-directional erbium-doped fiber amplifiers with single erbium-doped fiber

Based on the discussion of the structure scheme of bi-directional EDFA (Bi-EDFA) with single erbium-doped fiber (EDF) which can efficiently suppress the internal reflections, a rate equation model for the Bi-EDFA is developed to calculate the signal gain, pump absorption and output noise spectrum. The effects of numbers of signals, pumps of arbitrary direction, amplified spontaneous emission (ASE) and inherent loss are taken into account. Using this model, the influence of EDF length, input signal power, pump style and pump power on the gain characteristics of the Bi-EDFA is analyzed. The forward and the backward noise figures versus bi-directional input signal power for different pump styles are also investigated. With these results, the optimal design for Bi-EDFAs in optical fiber communication systems and networks can be achieved.

Average inversion level, modeling, and physics of erbium-doped fiber amplifiers

We present a detailed study of a set of models for characterizing the gain, the input and output powers of single erbium-doped fiber amplifiers (EDFAs) and networks of EDFAs. The time dependent gain is described by a single ordinary differential equation for the average inversion level of an EDFA with arbitrary number of signal channels with arbitrary power levels and propagation directions. In steady state, this ordinary differential equation becomes a transcendental equation from which many important parameters are derived. Through perturbation analysis of the time dependent model, the output perturbation can be expressed explicitly in terms of the input perturbations, which is useful for tone calculations. Therefore, this set of models can be applied to the steady state, and to large- and small-signal transient states in wavelength-division multiplexed (WDM) optical communication networks with EDFAs. The models are applied to analyze fast power transients in networks of EDFAs.

Bidirectional transmission at 622 Mb/s utilizing erbium-doped fiber amplifiers

Amplification of two bidirectional 622-Mb/s optical signals was demonstrated using a single erbium-doped fiber amplifier (EDFA). Bidirectional amplification was examined with the EDFA operating as a midspan repeater and as a pre/post amplifier at one terminal end of a 95-km fiber span. Without using any isolators in the EDFA, bidirectional optical amplification through a single EDFA was achieved while simultaneously improving system gain relative to a unidirectional link without an EDFA. The system gain improvement was 9.5 and 7 dB in the pre/post configuration, and 25.5 and 20.3 dB in the midspan configuration, when the signal wavelengths were 1537 and 1545 nm, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>