Bidirectional Optical Amplifier Research Articles

Raman and erbium-doped fiber amplifiers hybrid bidirectional optical amplifier with low noise figure for fiber-optic radio frequency synchronization

Raman and erbium-doped fiber amplifiers hybrid bidirectional optical amplifier with low noise figure for fiber-optic radio frequency synchronization

Microwave Frequency Dissemination over a 250 km Fiber Link with Stability at the 10−18 Level

In this paper, a microwave phase compensation scheme is adopted. It utilizes microwave signals of different frequencies for round-trip signal transmission over a 250 km fiber optic link to mitigate the impact of parasitic reflections. Additionally, dispersion compensation fibers are employed to compensate for the dispersion in the fiber optic link. Bidirectional optical amplifiers are utilized to compensate for the losses in long-distance fiber optic links and reduce optical path asymmetry. By implementing these methods, the transmission stability of the fiber optic microwave frequency transmission system achieves 5.6 × 10−15 at 1 s and 2.8 × 10−18 at 100,000 s.

Controlling of the bidirectional amplifier chain for optical frequency distribution based on a two-dimensional noise detector.

In the paper we present a solution for controlling the chain of bidirectional optical amplifiers, intended for long-haul fiber links used to distribute signals produced by optical atomic clocks. The solution is based on a dedicated two-channel noise detector, which allows independent measurement of the noise contributions related to interferometric signal fading and additive wideband noise. New signal quality metrics, based on two-dimensional noise detector, allows to distribute properly the needed gain among the chained amplifiers. Experimental results performed both in laboratory conditions and on a real 600 km-long link, confirming proper operation of proposed solutions, are presented.

Protection Scheme for a Wavelength-Division-Multiplexed Passive Optical Network Based on Reconfigurable Optical Amplifiers

This paper demonstrates a wavelength-division-multiplexed passive optical network (WDM-PON) scheme based on novel reconfigurable optical amplifiers (ROAs). The measured switching characteristics of the ROA3 constructed with a 2 × 2 crossbar optical switch and a four-port reversible optical circulator (OC) and a conventional EDFA can meet the requirements of most network management and surveillance. The self-made four-port reversible OC’s response time is less than 2 ms, and its insertion losses are about 1 dB or less for all the transmission paths and switching states. An optimal design of ROAs is proposed and evaluated for bidirectional optical amplifier protection, in which ROA3 has an EDF length of 7.5 m long with a 1480 nm pump laser and possesses a backward or forward pumping configuration with the corresponding pump power of 200 mW or 50 mW. We verified the scheme’s feasibility through a simulation of WDM-PON systems with 40 downstream and upstream channels. This scheme enables the intelligent protection switching in practical operation scenarios for high-capacity multi-wavelength networks.

Optimization of time and frequency fiber-optic links exploiting bi-directional amplifiers, based on real-time performance measurement

Long-distance fiber-optic time and frequency transfer links exploit bi-directional optical amplifiers whose gains need to be optimized to limit the noise propagating along with the desirable signals. Unlike the usual optimization of such links that are based on simulations or on a trial and error approach, we propose here a technique where the link is initially set-up with a pre-set algorithm, using optical powers measured in the amplifiers installed along the link. After that the final optimization is performed based on jitters measured in the end terminals of the link with a dedicated hardware. All the required parameters (i.e. the optical powers and jitters) are measured in a real-time in a live link. Various methods of assessment of the link performance, using the jitter measurements performed either in one or both end terminals, as well as various optimization criteria (like minimax, square root of sum of RMS jitters or analysis of a single-end jitter measurements), are investigated. The developed procedures were tested experimentally in the laboratory and also during a field trial in a real fiber telecom infrastructure. Obtained results (55% jitter reduction, 7 dB SNR improvement, comparing to the link state after its initial set-up) suggest that the proposed solutions allow optimizing effectively the link performance and may be used to supplement or replace simulation methods, particularly on initial start-up or when reconfiguring the link (e.g. due to a link route modification or after a fiber break).

Electrical Regeneration for Long-Haul Fiber-Optic Time and Frequency Distribution Systems.

In recent years fiber-optic-based long-haul installations for time and frequency (T&F) distribution have become operational at various sites. The common practice to cope with large attenuation of long fiber path is to use bidirectional optical amplifiers. This, however, becomes insufficient in case of very long links and/or long spans between amplifiers, because of unavoidable deterioration of the signal-to-noise ratio (SNR). In this article, we present a solution where the optical signal amplification is combined with optical-electrical-optical (OEO) regeneration, performed in a few points along the link. We analyze the impact of replacing some optical amplifiers with OEOs and demonstrate the resulting improvement in terms of SNR of the received optical signal and the phase noise at the output of the T&F distribution system. Laboratory experiments performed with both spooled and metropolitan-area fibers (total length up to 900 km) confirmed the theoretical predictions and showed that placing the OEO regenerators in appropriate points along the link allows reaching the required SNR.

Optimization method for universal NOLM-based phase-preserving amplitude regenerator with application to Att-NALM scheme

We theoretically investigate the conditions of achieving phase-preserving amplitude regeneration for the universal nonlinear optical loop mirror (NOLM) structure and present a method of determining the optimal working point for amplitude shaping. A normalized amplitude-phase transfer parameter is introduced to measure the phase-preserving performance at the working points of multilevel regeneration. Then, a new NOLM (so-called Att-NALM) structure, consisting of an optical attenuator and a bidirectional optical amplifier, is taken into account by the optimization method. The optimal working point can respectively be designed on the first or second plateau of the optical power transfer function for phase-preserving and amplitude regeneration of QPSK/8PSK or two-amplitude 8QAM signal. Our simulation shows that, the corresponding error vector magnitude (EVM) has a maximal reduction with the noise reduction ratio of 5.44dB, 4.7dB and 3.7dB for only amplitude noise, and 1.86dB, 1.58dB and 1.4dB for simultaneous amplitude and phase noise, respectively. We also list the design parameters of the existing NOLM structures for phase-preserving amplitude regeneration.

Bidirectional optical amplifier for time transfer using bidirectional WDM transmission

In this letter, we propose a bidirectional optical amplification scheme for fiber-optic time transfer based on bidirectional wavelength-division multiplexing (WDM) transmission. The proposed scheme employs single unidirectional erbiumdoped fiber amplifier (Uni-EDFA) for commercial optical networks to implement bidirectional optical amplification. Since including isolators, the effect of backscattering due to the accumulated amplification can be efficiently suppressed by the proposed amplifier. The proposed scheme is validated over different length fiber links in laboratory. Experimental results show that the proposed amplifier can support fiber-optic time transfer over several thousands of kilometers with an additional bidirectional delay difference fluctuation at picosecond magnitude.

Modeling and Optimization of Bidirectional Fiber-Optic Links for Time and Frequency Transfer.

In this paper, a bidirectional fiber-optic link is considered, composed of two end terminals, connected by a number of fiber spans and bidirectional optical amplifiers. The end terminals exchange time and frequency information by sending and receiving intensity modulated optical signals in both directions, which is required to compensate the fluctuation of the propagation delay of the transmission medium. In such a link for its optimal performance, the gains of the bidirectional optical amplifiers need to be adjusted to minimize the noise resulting from Rayleigh backscattering and amplified spontaneous emission. A model of the link is proposed using a transmission matrixes approach, which allows estimating the signal-to-noise ratio (SNR) at the ends of the main link (i.e., connecting the end terminals) and at the extraction (tapping) nodes located along the main link. The transmission matrixes of a fiber span and Er-doped fiber amplifier are presented and required formulas are derived. In addition, wavelength selective isolators are considered, which allow intentional breaking of the propagation of backscattered signals and are effective in improving the SNR when long fiber spans are involved. The model is experimentally verified in a laboratory link composed of four bidirectional amplifiers and five fiber spans of total length up to 420 km, showing the agreement between the measured and calculated SNRs not worse than 2 dB.

High-Precision Ultralong Distance Time Transfer Using Single-Fiber Bidirectional-Transmission Unidirectional Optical Amplifiers

This paper demonstrates a fiber-optic time transfer over a 6000 km noncalibrated fiber link using proposed single-fiber bidirectional-transmission unidirectional optical amplifiers (SFBT-UOAs). The proposed SFBT-UOA employs a 2 × 2 optical switch to enable the time-division-multiplexed time signals for both directions to pass through the same UOA in different time slots. The bidirectional delay symmetry is guaranteed to the maximum extent by allowing the time signals to be transmitted back and forth using the same wavelength over a single fiber. Meanwhile, the noises suffered in the systems employing single fiber bidirectional optical amplifiers (SF-BOAs), such as double Rayleigh backscattering, are effectively suppressed. Consequently, high-precision fiber-optic time transfer can be implemented over ultralong distance by adopting the proposed SFBT-UOAs. Moreover, the SFBT-UOA can support the conventional network services via wavelength division multiplexings (WDMs) and, therefore, offers the potential to perform high-precision time transfer over long-haul commercial fiber links. Over 6000 km, the measured time deviations of fiber-optic time transfer in the laboratory are less than 190 ps/s and 61 ps/105 s, respectively. The calculated combined uncertainty is not beyond 70 ps, which agrees well with the experimental verification over the noncalibrated fiber link.

Frequency Transfer in Electronically Stabilized Fiber Optic Link Exploiting Bidirectional Optical Amplifiers

In this paper, we present the experimental result for the fiber optic frequency transfer link with optical regenerators exploiting the same Er-doped fiber for amplifying the signals in both directions. The measurements performed at the distance of 124 km with one amplifier and 224 km with three amplifiers showed that the presented solution is adequate for transferring the frequency signals generated by cesium clocks, hydrogen masers, and cesium fountain clocks. The Allan deviation around 9 ·10-18 and 5.5 ·10-17 was found for the averaging time of 105 s for 124- and 224-km-long links, respectively.

System for precise dissemination of frequency standard via optical fiber

AbstractA precise frequency dissemination system using optical fiber is studied. The purpose of the system is to transmit a frequency standard with little deterioration to many distant users. It is composed of a phase compensation transmitter, bidirectional optical amplifiers, optical amplified distributor, and receiver. The goal of the system is to achieve stable transmission of hydrogen maser‐class signals. For short‐term stability, the required optical received power to realize an Allan deviation of 1 × 10–13 (average time of 1 s) is shown. For long‐term stability, a new compensation method using a third wavelength transmission is effective to suppress phase fluctuation induced by temperature changes in the fiber. Experimental results show a stability of 8 × 10–17 at 105 s in a fiber link of 160 km in all with one bidirectional amplifier. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(3): 45–54, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10372

Performance Evaluation of Bidirectional Optical Amplifiers for Amplified Passive Optical Network Based on Broadband Light Source Seeded Optical Sources

We have evaluated the performances of bidirectional optical amplifiers which were suited for the cost-effective implementation of amplified bidirectional passive optical networks (PONs). First, we measured the maximum gains of two simple bidirectional optical amplifiers implemented without using any optical components for the suppression of reflected signals. From the results, the maximum gains of two simple bidirectional amplifiers with a broadband light source (BLS) seeded optical source were limited to be 27 dB due to the reflection-induced in-band crosstalk, when the reflectance coefficients were measured to be -33 dB in both directions. Then, we have also implemented a bidirectional optical amplifier with two band splitters for the amplified bidirectional PON where the two different wavelength bands were allocated to the downstream and upstream signals transmission. In our measurement, we confirmed that the maximum gain of bidirectional optical amplifier with two band splitters could be increased to more than 30 dB owing to the efficient suppression of in-band crosstalk.

Precise Frequency Comparison System Using Bidirectional Optical Amplifiers

Precise frequency comparisons are becoming more urgent given the recent rapid progress in next-generation frequency standards. This paper describes a new type of bidirectional optical amplifier that overcomes the fiber loss limits that have prevented accurate frequency comparisons between widely separated places; such comparison is realized by bidirectionally transmitting wavelength-division-multiplexed (WDM) signals along a single fiber. The proposed optical amplifier has an optical isolator in each two-way channel divided by wavelength filters to suppress the optical reflection that causes amplification instability. The additional insertion optical loss due to this method is about 1.5 dB. The optical gain greater than 30 dB is obtained for both signals with good optical isolation of 65 dB. A radio-frequency reference signal can directly be sent by simple intensity modulation and direct detection (IM-DD) devices in the 1550-nm region widely used in telecommunication networks. Phase comparisons of the received signals and the frequency standards at each terminal are used for frequency comparisons. The amplifier is tested in the field using two hydrogen masers. A 120-km fiber with loss of 52.5 dB is used to connect the National Metrology Institute of Japan (NMIJ) to the University of Tokyo. Because of this loss, an amplifier is needed to realize sufficient receiving power. The frequency stability of the system with a 10-MHz direct transmission is evaluated by returning the optical signal from a halfway point [55 km from the NMIJ] where the amplifier is installed. The result is 2.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> (Allan deviation) with the averaging time of 7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s. The laboratory result is 8.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-17</sup> (¿ = 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s). The amplifier's long-term stability is promising for stable frequency dissemination in addition to precise frequency comparisons.

Precise Dissemination System of Frequency Standard via Optical Fiber

A precise frequency dissemination system using optical fiber is studied. The purpose of the system is to transmit frequency standard with little deterioration to distant many users. It is composed of a phase compensation transmitter, bidirectional optical amplifiers, optical amplified distributor, and receiver. The system target is to achieve a stable transmission of hydrogen maser class signals. For short term stability, it is shown the required optical received power to realize the Allan deviation of 1×10-13 (averaging time of 1 s). For long term stability, a new compensation method using third wavelength transmission is effective to suppress phase fluctuation induced by fiber temperature change. Experimental result shows stability of 8×10-17 at 105 s in a fiber link of 160 km in total with one bidirectional optical amplifier.

Bidirectional WDM-DPSK transmission by using SOAs

We demonstrate the longest bidirectional and unrepeatered semiconductor optical amplifier (SOA)-based transmission of 16 differential phase-shift keying (DPSK), 100-GHz-spaced channels at 10 Gb/s over standard single-mode fiber. Key techniques are: the use of DPSK constant-envelope modulation format to prevent nonlinear distortions in the SOAs; a new type of wavelength-division-multiplexing-DSPK demodulator to strongly enhance the signal tolerance to chromatic dispersion. After 120-km transmission, 1.8- to 3-dB power penalty was found for the 16 channels

Optical network unit based on a bidirectional reflective semiconductor optical amplifier for fiber-to-the-home networks

An optical access network transceiver based on a reflective semiconductor optical amplifier operating as modulator and photodetector is demonstrated. Device characterization and modulation/detection tests show the system proper operation at 1.25 Gb/s to 30-km reach. This optical network unit design is a simple and capable solution for future fiber-to-the-home networks.

Simple and reliable bidirectional optical amplifier suitable for variable traffic pattern networks

We proposed a simple and flexible bidirectional optical amplifier (BOA) that consists of one erbium-doped fiber amplifier (EDFA) and an arrayed waveguide grating (AWG). This BOA is especially suitable for networks having asymmetric traffic patterns since the circuit configuration of BOA can be modified easily by manipulation of AWG ports connection. We constructed the BOA and demonstrated its performance for 10-Gb/s symmetric traffic over 80-km single-mode fiber. The proposed BOA worked well with negligible relative intensity noise by virtue of intrinsic tolerance of backscattering in an AWG.

Low-cost bidirectional optical amplifier using a unidirectional Er-doped fiber amplifier and a fiber Mach-Zehnder interferometer

We propose a cost-effective bidirectional optical amplifier consisting of a single unidirectional Er-doped fiber amplifier and a fiber Mach-Zehnder interferometer (MZI). We demonstrated its feasibility by observing the optical spectra and measuring bit error rates when four optical signals were bidirectionally transmitted at 2.5 Gb/s over a 160-km single-mode fiber. A net gain of 17 dB and a power penalty of 0.5 dB were obtained.

Repeatered Bidirectional 10 Gb/s–240 km Fiber Transmission Experiment

We report the design and performance evaluation of a novel circulator-based bidirectional optical amplifier. Using this amplifier as a mid-span repeater, we have demonstrated successful bit error rate (BER<10−13) transmission at 10 Gb/s over 240 km of dispersion shifted fiber in both directions for channel wavelengths at 1557.5 and 1559 nm.