Multicore Erbium-doped Fiber Amplifier Research Articles

Capacity Expansion in Submarine Cable Systems With Bidirectional Transmission Using 4-Core-or-More MCF and MC-EDFA

Bidirectional transmission in a multicore fiber (MCF) reduces core-to-core crosstalk, changing optimal MCF design and multicore submarine cable systems, compared with conventional unidirectional transmission systems. We first demonstrate analytically the increase in capacity with bidirectional transmission in submarine systems. From the perspective of the capacity of one MCF, we show that bidirectional transmission enables an optimum design based on a 6-core MCF with a standard cladding diameter, taking advantage of the reduction of XT. For multicore submarine cable systems, we demonstrate that 6-core MCF systems with bidirectional transmission offer the highest cable capacity for regional Asian systems in the range of 3,000 km. We further discuss a multicore erbium doped fiber amplifier (MC-EDFA) system even for bidirectional transmission to improve the energy efficiency in submarine systems, and we show that 6-core MCF systems offer the highest capacity up to 6,000 km because of MC-EDFA. We also show a 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> larger capacity for a 3,000 km 6-core MCF system, and 43 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> larger capacity for a 9,000 km 4-core MCF system in bidirectional transmission with MC-EDFA, compared with the conventional repeater amplifier in FIFO devices. In addition, we investigated the potential increase in the cable capacity with the future cable system assumption, especially concerning cable supply voltage.

Cable Capacity and Cost/Bit Modeling of Submarine MCF Systems With MC-EDFA Alternatives

We model and examine various amplification options for trans-oceanic repeatered submarine systems using multicore fiber (MCF) transmission in the context of relative cable capacity and relative system cost/bit. First, we compare the optical performance of various configurations of parallel standard single-core erbium-doped fiber amplifiers (SC-EDFAs) and multicore erbium-doped fiber amplifiers (MC-EDFAs), including both the C/L-bands and core/cladding pump designs. Key amplifier parameters governing expected capacity and cost/bit performance include noise figure, amplifier bandwidth, relative electrical-to-optical conversion efficiency, and relative amplifier cost. We make our best estimates of these parameters through modeling, analysis, and component cost estimates and assess the sensitivity of the results to the nominal values. We find that MC-EDFAs using either core- or cladding-pumping might offer lower cost/bit than parallel SC-EDFAs but cladding-pumping may reduce cable capacities due to the higher noise figure and potentially smaller amplifier bandwidth.

Large area Bragg grating for pump recycling in cladding-pumped multicore erbium-doped fiber amplifiers.

We demonstrate for the first time that a Bragg grating can be written over a large area inside the cladding of a multicore erbium-doped fiber amplifier to increase the power conversion efficiency (PCE) by recycling the output pump power. Our results indicate that a Bragg grating covering ∼25% of the cladding area allows us to recycle 19% of the output pump power which leads to a relative increase of the PCE by 16% for an input pump power of 10.6 W in the specific case of an eight-core erbium-doped fiber with a length of 20.3 m and one core loaded with an input signal power of 1.5 dBm.

Power Consumption Analysis of Optical Repeater Subsystem in Multicore Fiber Link

The power consumption of optical repeater subsystems in a multicore fiber (MCF) link is analyzed via the simulation of an erbium-doped fiber amplifier (EDFA) considering the power consumption of an ancillary function and an EDFA. Ancillary power consumption is attributed to nonessential functions that are required only for the subsystem to operate. In the analysis, the ancillary power consumption of optical repeater subsystems that employ multicore (MC) EDFAs is compared with subsystems that employ multiple conventional single-core (SC) EDFAs to determine whether an MC-EDFA has an advantage over the use of the number of cores ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_c$</tex-math></inline-formula> ) of SC-EDFAs in an MCF link. In a subsystem with a cladding-pumped MC-EDFA, the required sharable ancillary power consumption such that the total power consumption of the repeater subsystem with a cladding-pumped MC-EDFA is smaller than that with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_c$</tex-math></inline-formula> of SC-EDFAs, is several tens of watts in the C-band, whereas it is less than 10 W in the L-band. This required sharable ancillary power consumption is converted to a ratio of required sharable ancillary power consumption to ancillary power consumption of a conventional subsystem. The ratios for the C-band is 30–100 %, and most of the ratio values for the L-band are less than 40 % with minimum values of 0 %. However, the L-band cladding-pumped MC-EDFA has a 3-dB poorer noise figure compared to that for SC-EDFA, which makes the L-band cladding-pumped MC-EDFA achieve a higher output power to maintain the optical signal to noise ratio and may introduce the degradation caused by nonlinear optical effects. In contrast, the required sharable ancillary power consumption for a subsystem with a core-pumped MC-EDFA is a few watts and less than 10 W for the C- and L-bands, respectively. This implies that most of the required sharable ancillary power consumption ratio values for the C- and L-bands are less than 10 % and 40 %, respectively. In terms of power consumption, a cladding-pumped MC-EDFA has less advantage over the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_c$</tex-math></inline-formula> of SC-EDFAs, and a core-pumped MC-EDFA may have an advantage over the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_c$</tex-math></inline-formula> of SC-EDFA if the size of a core-pumped MC-EDFA is reduced to a value smaller than the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_c$</tex-math></inline-formula> of the SC-EDFA by integrating MCF amplifier components.

Effect of pitch on gain-noise figure and crosstalk performance of different core structure Multicore Erbium-Doped Fiber Amplifier: A comparative analysis

A detailed analysis of 7-cores Erbium-Doped Fiber Amplifier has been done to assess the effect of different core and pitch arrangement on the fiber amplifier's performance. The investigation is performed within the C-band communication wavelengths to compare the performance of Y-structure, T-structure, circular and linear structure of the core. The comparison is also extended further by including the performance of a widely used hexagonal structure. A thorough analysis is conducted by examining the profiles of gain, noise figure, and mode of transmission. The inter-core crosstalk (IC-XT) is also calculated for all the core structures and pitch, making this research effort conclusive. Maximum gain has been observed for the Y-shape/structure core arrangement, whereas minimum IC-XT has been observed for the hexagonal structure. However, an encouraging observation is that the percentage decrease in crosstalk due to an increase in pitch is significantly higher for Y-structure than hexagonal. Therefore, the authors believe that this detailed investigation gives significant insight to design efficient multicore EDFA in current research and development.

Characteristics of Randomly Coupled 12-core Erbium-Doped Fiber Amplifier

A randomly coupled 12-core erbium-doped fiber amplifier (EDFA) operating in the C- or L-band is investigated. We experimentally demonstrate that both C and L-band operation can be supported with the 12-core EDFA by adjusting the erbium-doped fiber (EDF) length. Evaluations of the amplification characteristics of the proposed EDFA showed that a modal gain of more than 20 dB or 15 dB, a noise figure of about 5 dB or 6 dB, and a mode-dependent loss penalty of less than 1 dB or 2 dB were respectively obtained over the whole C-band (1530-1565 nm) or L-band (1570-1605 nm) with 8- or 60-m EDF. Transmission experiments showed the applicability of our EDFAs for inline amplified transmission systems. We also examined the impact of MDL on the power efficiency of the randomly coupled multi-core EDFA for achieving power-efficient long-distance SDM transmission.

A parametric study to create an optimal design of seven-cores hexagonal structured erbium-doped fiber amplifier

Abstract Numerical analysis for calculating the gain and noise figure (NF) of 7-cores hexagonal structured Multicore Erbium-Doped Fiber Amplifier (MC-EDFA) is carried out. In addition to this, a mode analysis has been carried out for the same geometric structure of the Erbium-Doped Fiber (EDF). The effect of different core radius, signal wavelengths are analyzed and the results are laid down in the form of gain and NF of the MC-EDFA, propagating mode, normalized frequency, maximum and minimum modal intensity in order to analyze the modal field confinement in the MC-EDFA. Along with this, the inter-core crosstalk has also been investigated for 7-cores Erbium-Doped Fiber Amplifier (EDFA). Results other than gain and NF, calculated with respect to the operating wavelength range from 1525 nm to 1565 nm are compared with the calculated gain for each core radius of the MC-EDFA so as to obtain an optimum set of conditions for designing a superior MC-EDFA. Thus, it is ascertained that the performance of a 7-cores MC-EDFA can be significantly improved by designing it with reference to optimum value of core radius and signal wavelength.

Gain Control in Multi-Core Erbium-Doped Fiber Amplifier With Cladding and Core Hybrid Pumping

This paper investigates gain controllability of cladding- and core-pumping hybrid-pumped single-stage and double-stage multi-core (MC) erbium-doped amplifiers (EDFAs) for changes in the input signal power per channel and number of channels. During the gain control, the core-pumping power is adjusted, whereas the cladding-pumping power is kept constant. Static characteristics are experimentally measured, and both kinds of hybrid-pumped MC-EDFAs are gain controlled with a small gain change for both the input signal changes. Dynamic characteristics are investigated by calculating the gain transient response of a surviving channel of the gain-controlled hybrid-pumped MC-EDFAs for signal channel dropping, and the response characteristics are compared with those of reference EDFAs whose erbium-doped fiber (EDF) has the same core parameters as those of EDF used in a conventional practical EDFA. It is shown that there is no significant difference in dynamic gain controllability between the hybrid-pumped MC-EDFAs and reference EDFAs even though the cladding-pumping power is not adjusted and kept constant. The results for the static and dynamic gain control characteristics suggest that constant cladding-pump power has little impact on gain controllability of the hybrid-pumped MC-EDFAs.

Hybrid cladding-pumped multicore EDFA/Raman amplification for space division multiplexing transmission systems.

We propose and demonstrate a hybrid cladding-pumped multicore erbium-doped fiber amplifier (EDFA) and distributed Raman amplification for space division multiplexing transmission systems. The cladding-pumped multicore EDFA is used to efficiently amplify signals in multiple cores simultaneously, while Raman pumping is used to control loss in each core individually. We construct an in-line amplified 7-core transmission line, and show that distributed Raman amplification can compensate loss variation between cores. Furthermore, we transmit 46 WDM PDM-16QAM signals over a long distance of greater than 1000 km and demonstrate good transmission performance.

Applicability of a model with average inversion level to a cladding-pumped multicore erbium-doped fiber amplifier

This paper investigates the applicability of a model of a cladding-pumped multicore erbium-doped fiber amplifier (CP-MC-EDFA) that employs the average inversion level of an erbium ion. The model is modified to include the effects of multiple cores for modifications of the background loss coefficient of the pump light. The model is validated experimentally by measurements of the pump power, gain transient, and intercore cross-gain modulation of a cladding-pumped 12-core EDFA in which the pump light is uniformly distributed in the inner cladding. The calculated and measured pump power, gain transient response, and gain change caused by the intercore cross-gain modulation agree well, suggesting the modified model is useful for characterizing a CP-MC-EDFA.

Multilane Photonic Spectral Processor Integrated in a Spatial and Planar Optical Circuit for a Space-Division Multiplexing Network

We developed a multilane photonic spectral processor array integrated with a spatial and planar optical circuit platform. This device enables individual control of the optical power in the spatial and wavelength domains by controlling the phase pattern on liquid crystal on a silicon spatial light modulator and the heater electricity of a waveguide-based variable attenuator. We constructed a prototype device including an array of seven spectral processors. We transmitted 100-Gbps DP-QPSK signals over seven spans with a small optical-signal-to-noise ratio penalty of 0.05 dB, which suggests that the device can work in actual networks. As an application, we demonstrated gain equalizing of a multicore erbium-doped fiber amplifier (MC-EDFA). The device equalized the gain spectra of the MC-EDFA to an accuracy of ±0.8 dB over 30 nm.

Pump Power Reduction in Optical Fiber Amplifier for WDM-Interleaved Multi-Core/Multi-Fiber System

The effect of reducing the pump power in a multi-core erbium-doped fiber amplifier (MC-EDFA) designed for a wavelength-division-multiplexing-interleaved multi-core/multi-fiber system is investigated. An analysis of the asymptotic behavior of the pump power ratio of the MC-EDFA and discrete single-core EDFAs, derived by using the analytical EDFA model with an average inversion level, shows a remarkable effect of the pump power reduction in an MC-EDFA when the input signal power or the amplifier gain is small. Experimental results are consistent with the analysis of the pump efficiency. The allowable excess losses of optical components in an MC-EDFA are also investigated by using the analytical expression of an EDFA.

Coherent beam combining of a narrow-linewidth long-pulse Er3+-doped multicore fiber amplifier.

Active phase locking of a multicore erbium-doped fiber amplifier is demonstrated for 180 ns narrow-linewidth pulses at 1545 nm. A spatial light modulator is used at the input of the amplifier to control the optical phase of 7 beams injected in the hexagonally-arranged cores, ensuring efficient combining through a SPGD algorithm. At the output, combining is performed using a diffractive optical element. This experiment establishes multicore amplifiers as a promising way to scale the energy of Brillouin-limited pulsed amplifiers for LIDAR applications. We also present a simple lensless technique to measure phase shifts between pairs of adjacent channels that could be implemented in future active coherent combining systems.

51.1-Tbit/s MCF Transmission Over 2520 km Using Cladding-Pumped Seven-Core EDFAs

Multicore erbium-doped fiber amplifiers (MC-EDFAs) are essential components to achieve long-haul multicore fiber (MCF) transmission. An attractive technique for reducing the number of components and power consumption is the cladding–pumping scheme in MC-EDFAs in which all cores are simultaneously pumped using a single high-power multimode laser diode. In this paper, we experimentally demonstrate long-haul MCF transmission using cladding-pumped seven-core EDFAs. We confirm that 73 × 128-Gbit/s Nyquist-pulse-shaped dual-polarization quadrature phase-shift keying signals are successfully transmitted over 2520-km seven-core fiber.

Space division multiplexed multicore erbium-doped fiber amplifiers

We report on the recent development of multicore fiber amplifiers suitable for amplifying space division multiplexed signals. We have constructed 7-core amplifiers, where the cores could be pumped individually or simultaneously through the cladding, and studied the amplification and noise properties of these amplifiers. In the core-pumped amplifier, the net average gain was 25 dB, and noise figure was less than 4 dB. Using side-coupled cladding pumping, gain over 25 dB was obtained in each of the cores over a 40-nm bandwidth covering the C-band. We have further studied numerically the amplification and noise properties of a few-moded single/multicore erbium doped fiber amplifier with a doped region that extends beyond the few-mode core. We show that when excited by a multimoded pump, this can provide nearly uniform gain in C-band for modes such as, LP01, LP11, LP21, and LP02 over a wide range of pump power. Differential modal gain (DMG) between LP01, and LP02 was ~ 0.5 dB for a small signal gain of 32 dB at 1550 nm signal wavelength. The dependence of modal gain on the size of the doped core has also been studied.

Ultra-Long-Haul High-Capacity Super-Nyquist-WDM Transmission Experiment Using Multi-Core Fibers

This paper describes promising techniques for approaching the capacity-distance product over 1 Exabit/s×km in the transoceanic-class optical fiber transmission. One is the Super-Nyquist wavelength-division multiplexing (WDM) technique based on poly-binary-pulse shaping with maximum likelihood sequence estimation, in which it is possible to multiplex optical signals with WDM spacing of less than the signal baudrate. Another technique is the space-division multiplexing technique based on multi-core fibers (MCFs) with multi-core Erbium-doped fiber amplifiers (EDFAs), in which the fiber capacity can be increased when the number of cores of MCF is increased. Finally, we present a demonstration of 140.7-Tbit/s, 7 326-km transmission of 201-channel 25-GHz-spaced Super-Nyquist-WDM 100-Gbit/s optical signals using seven-core fibers and full C-band seven-core EDFAs.

Spatial Superchannel Routing in a Two-Span ROADM System for Space Division Multiplexing

We report a two-span, 67-km space-division-multiplexed (SDM) wavelength-division-multiplexed (WDM) system incorporating the first reconfigurable optical add-drop multiplexer (ROADM) supporting spatial superchannels and the first cladding-pumped multicore erbium-doped fiber amplifier directly spliced to multicore transmission fiber. The ROADM subsystem utilizes two conventional 1 × 20 wavelength selective switches (WSS) each configured to implement a 7 × (1 × 2) WSS. ROADM performance tests indicate that the subchannel insertion losses, attenuation accuracies, and passband widths are well matched to each other and show no significant penalty, compared to the conventional operating mode for the WSS. For 6 × 40 × 128-Gb/s SDM-WDM polarization-multiplexed quadrature phase-shift-keyed (PM-QPSK) transmission on 50 GHz spacing, optical signal-to-noise ratio penalties are less than 1.6 dB in Add, Drop, and Express paths. In addition, we demonstrate the feasibility of utilizing joint signal processing of subchannels in this two-span, ROADM system.

Cladding-pumped erbium-doped multicore fiber amplifier

A cladding pumped multicore erbium-doped fiber amplifier for simultaneous amplification of 6 channels is demonstrated. Peak gain over 32 dB has been obtained at a wavelength of 1560 nm and the bandwidth measured at 20-dB gain was about 35 nm. Numerical modeling of cladding pumped multicore erbium-doped amplifier was also performed to study the properties of the amplifier. The results of experiment and simulation are found to be in good agreement.

Amplification and noise properties of an erbium-doped multicore fiber amplifier

A multicore erbium-doped fiber (MC-EDF) amplifier for simultaneous amplification in the 7-cores has been developed, and the gain and noise properties of individual cores have been studied. The pump and signal radiation were coupled to individual cores of MC-EDF using two tapered fiber bundled (TFB) couplers with low insertion loss. For a pump power of 146 mW, the average gain achieved in the MC-EDF fiber was 30 dB, and noise figure was less than 4 dB. The net useful gain from the multicore-amplifier, after taking into consideration of all the passive losses, was about 23-27 dB. Pump induced ASE noise transfer between the neighboring channel was negligible.