Holmium-doped Fiber Amplifier Research Articles

Thermo-optical simulation of holmium-doped fiber amplifiers for high-power applications

Thermo-optical simulation of holmium-doped fiber amplifiers for high-power applications

Detailed scrutiny of FWM in holmium-doped fiber amplifier (HOFA) in WDM systems

Abstract Four wave mixing (FWM) in wavelength division multiplexed (WDM) systems is prominent performance degrading nonlinearity and limits the total capacity of the system. FWM is explored in different fiber optical amplifiers such as erbium-doped fiber amplifier (EDFA), Raman fiber amplifier (RFA), and also in semiconductor optical amplifier (SOA). Reported studies in HOFA revealed that nonlinear effects in these amplifiers are low; however, in present study, in this research article WDM-HOFA system has been simulated and studied FWM in detail at different HOFA parameters such as input power, length, core radius, doping radius, numerical aperture (NA), Ho ion density, and effects of co- and counter-pumping. Gain and noise figure (NF) are also investigated at aforementioned parameters, and performance is evaluated in terms of optical signal to noise ratio (OSNR) at 2,030 nm wavelength window. It is observed that least FWM obtained at 3 m Ho fiber length, 2 µm core radius and doping radius, 15.6 × 1023 m−3 Ho ion doping, 0.1 NA, −10 dB input power, 0.8 GHz channel spacing, and 4 WDM channels. However, better gain and NF comes at different values of these parameters, and as a result, there is trade-off between FWM and gain, NF.

10 W-class, narrow-linewidth, linearly polarized, low-noise Holmium-doped Fiber Amplifier at 2095 nm

10 W-class, narrow-linewidth, linearly polarized, low-noise Holmium-doped Fiber Amplifier at 2095 nm

Pair induced quenching in high concentration Holmium-doped fiber amplifiers

The spectrum required for future optical communication systems is being extended towards the C-, L- and U-bands, resulting in a significant interest in the spectral region around 2 μm wavelength. Since Holmium doped fiber amplifiers (HDFAs) provide amplification in this spectral region, they have become a focus of researchers working on doped fiber amplifiers. A major factor resulting in the performance degradation of HDFAs is the inhomogeneous energy transfer within Ho3+ ion-pairs in high-concentration Holmium-doped fibers (HDFs), an effect generally known as pair-induced quenching (PIQ). In this paper, we study the luminal and temporal dynamics of pulses of different repetition rates at 2.05 μm in high-concentration HDFs considering the effects of ion-pairs. Input pulses having repetition rates of 25 GHz and 500 kHz are generated using wavelength tunable actively mode-locked Holmium-doped fiber laser (AML-HDFL) based on a single ring cavity and bidirectional pumping. The characteristics of the pulses propagating through high-concentration HDF are analyzed based on different metrics such as average power, peak power, pulse energy, full-width at half maximum (FWHM), and time delay without and with ion-pairs for values of fraction of ion-pairs k = 0 and k = 10%, respectively. The results obtained at optimized length of HDF show that ion-pairs significantly degrade the average power, peak power, and energy of the output pulses for both of the repetition rates. For both k = 0 and k = 10%, the FWHM and shape of the output pulses remain same in the presence of the ion-pairs while, time delay of 4 ps and 19 ns is observed in the output pulses at repetition rates of 25 GHz and 500 kHz, respectively. The effects of increasing the pump and signal power on the average power and energy of the output pulses for k = 0 and k = 10% are also discussed for both repetition rates. This analysis provides important guidelines for designers of 2 μm fiber lasers and amplifiers based on high-concentration HDFs.

Ultra-Low-Noise, Single-Frequency, All-PM Thulium- and Holmium-Doped Fiber Amplifiers at 1950 nm and 2090 nm for Third-Generation Gravitational Wave Detectors

Ultra-Low-Noise, Single-Frequency, All-PM Thulium- and Holmium-Doped Fiber Amplifiers at 1950 nm and 2090 nm for Third-Generation Gravitational Wave Detectors

Design and Analysis of Holmium-Doped Fiber Amplifier for WDM System in 1990 – 2100 nm Wavelength Range at Higher Bit Rates

Design and Analysis of Holmium-Doped Fiber Amplifier for WDM System in 1990 – 2100 nm Wavelength Range at Higher Bit Rates

Novel pumping scheme of Holmium doped fiber amplifiers operating around [formula omitted] using [formula omitted] lasers exploiting cascaded fiber lasers

The optical communication window around 2μm is attracting significant research attention for future optical communication systems as an extension to the C-, L-, and U-bands. One of the research topics in the 2μm region is optical amplifiers. Holmium-doped fiber amplifier (HDFA) is a suitable candidate for amplifying signals in this region. However, the pump laser for Holmium-doped fiber (HDF) is expensive and not widely available. In this work, we propose through numerical simulations, a novel pumping scheme to pump the HDF using commercially available 1.48μm lasers by exploiting cascaded fiber lasers made up of Erbium-doped fiber (EDF) and Thulium-doped fiber (TDF). The first fiber uses a commercially available 1.48μm laser to pump a piece of EDF to generate a 1.62μm continuous wave (CW) laser. This 1.62μm CW laser is used to pump a piece of TDF in the second fiber laser to create a 1.95μm CW laser that is used to pump the HDF. The HDFA can be used to amplify modulated optical signals in the 2μm wavelength range. A small-signal gain of 52.5 dB, 46.2 dB, and 32.6 dB can be achieved for input signal powers of −30 dBm, −15 dBm, and 0 dBm, respectively, at 2.032μm using a 5 W laser diode pump at 1.48μm. A noise figure (NF) of 7.5 dB, 6.6 dB, and 5.58 dB has been observed for input signal power of −30 dBm, −15 dBm, and 0 dBm, respectively at 2.032μm.

Performance Optimization of Holmium Doped Fiber Amplifiers for Optical Communication Applications in 2–2.15 μm Wavelength Range

In this paper, we address the performance optimization of Holmium doped fiber amplifier (HDFA) for optical communications in 2–2.15 μm wavelength range based on a single in-band forward pump source. The performance of the HDFA is analyzed with the help of theoretical simulations by considering an optimized length of Holmium doped fiber (HDF), doping concentration of Ho3+, and pump power. The impact of signal wavelength and power on gain, amplified spontaneous emission (ASE) noise, and noise figure (NF) of the amplifier is investigated. Furthermore, we investigate the variations in the gain of the amplifier, its output power, and NF by varying the power and wavelength of the pump source. After optimizing the parameters of the amplifier, the peak gain observed is around 56.5 dB, the 3 dB saturated output power obtained is 33.3 dBm, and the output power is 3 W at signal wavelength of 2.0321 μm for HDF having an optimized length of 12 m and pump power of 3.5 W. Minimum NF of around 8.2 dB is observed at 2.0321 μm for signal power of −5 dBm. The impact of ion-ion interaction on the performance of HDFA is also investigated. A reduction of 24.2 dB and 0.051 W is observed in peak gain and output power of HDFA, respectively by considering the ion-ion interaction.

Novel Highly Efficient In-Band Pump Wavelengths for Medium Slope Efficiency Holmium-Doped Fiber Amplifiers

We report the design and performance of medium slope efficiency (64%) Holmium-doped fiber amplifiers (HDFAs) with novel alternative in-band pump wavelengths in the 1720-2000 nm spectral region. We demonstrate through simulations that pump wavelengths of 1840-1860 nm can yield significantly improved output power, gain, and optical-optical conversion efficiency compared to the previous technical and industry standard pump wavelength of 1940 nm. Our simulations are verified by experimental data.

2090 nm 200 W Peak Power 50 ns Pulsed PM Ho-Doped Fiber Amplifier Pumped at 1860 nm

We report the design and performance of a 2 μm dual-stage polarization maintaining (PM) holmium-doped fiber amplifier (HDFA) operating in either continuous-wave (CW) or pulsed regime. The amplifier is pumped at 1860 nm, which offers a better efficiency than a 1940 nm pump. In CW regime, we measured more than 1 W of output power at both 2051 nm and 2090 nm signal wavelengths. In pulsed mode, we tested the amplifier over a broad range of pulse widths (50-500 ns) and pulse repetition frequencies (PRFs) (50-1500 kHz). The PM HDFA delivered up to 200 W of peak power and 10 μJ of pulse energy with an excellent stability, while integrated inside a compact module.

Influence of upconversion transition process on the performance of inband pumped holmium-doped silica fiber amplifiers

In this report, a theoretical model of in-band pumped holmium-doped silica fiber amplifiers (HDFAs) is presented. This model is developed to consider the influence of energy transfer up-conversion (ETU) on the HDFAs performance. The advantage of this model is to investigate the properties of HDFAs as a function of holmium-doped fiber length and doping concentration. A good agreement is observed between the simulation results and the previous experimental findings. Our simulation results show the negative impact of ETU process to deteriorate the HDFAs performance and this process may have bigger effect at high holmium doped concentration. This is the first time to our knowledge that the influence of upconversion process is theoretically investigated on the performance of in-band pumped HDFAs.

Thermal effects on tapered holmium-doped fiber amplifiers

The temperature response of a tapered holmium-doped fiber amplifier and its impact in the performance of fiber lasers and temperature fiber sensors has numerically been analyzed. Different pump schemes and different longitudinal shapes of the tapered-doped fiber were investigated, and it was found that a parabolic shape of the tapered fiber amplifier in a co-propagating pump scheme shows the highest sensitivity to temperature changes. In particular, the temperature sensitivity of the amplified signal was 2.5 × 10 − 4 ° C for 1 W of pump power and 1 m of doped fiber length. In addition, this sensitivity can be increased up to 10 times for fiber lengths shorter than 1 m and pump powers lower than 300 mW. Our results can be used to describe the temperature response of tapered fiber amplifiers in the mid-infrared spectral region and contribute with new information for the development of fiber lasers and fiber temperature sensors.

Shared Pump Two-Stage Polarization-Maintaining Holmium-Doped Fiber Amplifier

We propose and report the experimental demonstration of a shared pump architecture for a two-stage, broadband, high-gain polarization-maintaining Ho-doped fiber amplifier (HDFA). The gain as high as 59 dB, a noise figure of 10 dB, a dynamic range of >43 dB, and an output power of 4.1 W are achieved at a signal wavelength $\lambda _{ {s}}$ of 2051 nm. The multiwavelength performance of the HDFA is measured for $\lambda _{ {s}} = {2004} - {2108}$ nm. Initial comparisons of simulations with our experimental results show a relatively good agreement for $\lambda _{\mathbf {s}} > {2051}$ nm.

Two-Stage Performance of Polarization-Maintaining Holmium-Doped Fiber Amplifiers

We report the experimental demonstration and record performance of two-stage broadband, high gain polarization-maintaining (PM) Ho-doped fiber amplifiers (HDFAs) at a signal wavelength of λs = 2051 nm. We begin by presenting a new PM Ho-doped fiber with core diameter 8 μm, a PANDA structure, a cutoff wavelength of 1650 nm, and a peak absorption of 57 dB/m at 1951 nm. Next, we consider architectures for high gain PM HDFAs. Here we demonstrate G = 60 dB with a dynamic range of >40 dB and noise figures as low as 10 dB. We then investigate configurations for high output power PM HDFAs. With one stage, we measure P out = 3.45 W and an optical–optical slope efficiency η = 69%. With two stages, we obtain P out = 6.7 W and η = 80%. The potential bandwidth of the high power PM HDFA is BW = 100 nm (7.5 THz). An optical signal-to-noise ratio of 58 dB/0.1 nm is achieved, and the polarization extinction ratio is >20 dB. Initial comparisons of simulations of gain and output power with our experimental results show relatively good agreement.

Development of highly nonlinear polarization-maintaining fibers with normal dispersion across entire transmission window

A determined polarization state of light is required in nonlinear optics applications related to ultrashort and single-cycle light pulse generation. Such short timescales require up to one full octave of the spectral width of light. A fiber-based, pulse-preserving and linearly polarized supercontinuum can meet these requirements. We report on the development—from linear simulations of the fiber structure, through fabrication of physical fibers to their versatile characterization—of polarization-maintaining, highly nonlinear photonic crystal fibers, intended for femtosecond pumping at a wavelength of 1560 nm. A full octave of linearly polarized light around this wavelength would enable the covering of amplification bandwidths of the three major fiber amplifiers, from ytterbium-doped systems up to thulium- and holmium-doped fiber amplifiers, with a coherent, linearly polarized seed signal. At the same time, an all-normal chromatic dispersion profile over an entire transmission window, and a small dispersion of nonlinearity in the developed fibers, would facilitate use of commercially available femtosecond fiber lasers as pump sources for the developed fibers.

Towards a Supercontinuum Generation in an All-Fiberized Holmium-Doped ZBLAN Fiber Amplifier

A supercontinuum (SC) was first generated in a holmium-doped ZBLAN (ZrF4−BaF2−LaF 3−AlF3−NaF) fiber amplifier (HDZFA) with a spectral coverage of 2.03–2.9 μm, then was further red-shifted to 3.7 μm by cascading a piece of passive ZBLAN fiber. The amplifier consisted of a 2050-nm pulsed fiber laser and a piece of holmium-doped ZBLAN fiber (HDZF), which was in-band pumped by a 1950-nm continuous wave thulium-doped fiber laser. A fusion splicing was achieved between passive silica fiber and the HDZF. The spectral and power characteristics of the amplifier were carefully investigated. The SC obtained in the amplifier showed a spectrum ranging from 2.03 to 2.9 μm with an output power of 248 mW and a maximal slope efficiency of 43.3%. The spectral broadening in the amplifier was halted by a strong absorption induced by an excited state absorption (ESA) of Ho3+ in the range ∼2.7–2.8 μm. An SC with 20-dB spectral coverage of 2.05–3.71 μm was finally obtained by cascading a piece of passive single-mode ZBLAN fiber after the amplifier, with the purpose of overcoming the ESA-induced loss of holmium ions. To the best of our knowledge, this research is the first demonstration of an SC generation in an HDZFA.

Spectrally flat supercontinuum generation in a holmium-doped ZBLAN fiber with record power ratio beyond 3 μm

A spectrally flat mid-infrared supercontinuum (MIR-SC) spanning 2.8–3.9 μm with a maximum output power of 411 mW was generated in a holmium-doped ZBLAN fiber amplifier (HDZFA). A broadband fiber-based SC covering the 2.4–3.2 μm region was designed to seed the amplifier. Benefiting from the broadband seed laser, the obtained SC had a high spectral flatness of 3 dB over the range of 2.93–3.70 μm (770 nm). A spectral integral showed that the SC power beyond 3 μm was 372 mW, i.e., a power ratio of 90.6% of the total power. This paper, to the best of our knowledge, not only demonstrates the first spectrally flat MIR-SC directly generated in fluoride fiber amplifiers, but also reports the highest power ratio beyond 3 μm obtained in rare-earth-doped fluoride fiber until now.

Design and Performance Analysis of Holmium-Doped Fiber Amplifier Operating at 2µm band

Design and Performance Analysis of Holmium-Doped Fiber Amplifier Operating at 2µm band

Transformation of the supercontinuum spectra by the Ho-doped fiber amplifier

A multicascade femtosecond supercontinuum source based on a holmium-doped fiber amplifier was demonstrated. Maximum average power was approximately 400 mW and concentrated in the range from 1950 to 2150 nm. The shape of the output spectrum was controlled by the pump of the holmium-doped fiber amplifier.

A holmium-doped fiber amplifier at 2.1 μm

An all-fiber holmium-doped power amplifier is demonstrated for the first time, to the best of our knowledge. A maximum amplified power of 1.65 W is achieved for an input signal power of 35 mW. The slope efficiency is estimated to be 23% for pumping at 1.12 μm. A maximum gain of 18.5 dB is achieved for an input signal of 18 mW.