Discrete Raman Amplifier Research Articles

All-Raman-Amplified, 73 nm Seamless Band Transmission of 9 Tb/s Over 6000 km of Fiber

We report wavelength-division-multiplexed transmission of ninety 128-Gb/s polarization-multiplexed quadrature-phase-shift-keyed channels in a seamless 73 nm band over 60 × 100 km of ultra-large-area fiber. Co- and counter-pumped all-Raman amplification in the fiber spans, single-stage discrete Raman amplifiers, and broadband wavelength selective switch and channel equalizer were utilized to achieve optical signal-to-noise-ratio margin of more than 3 dB after 6000 km transmission of the 9 Tb/s capacity.

Comparison of Semiconductor Optical Amplifier and Discrete Raman Amplifier Performance in DWDM Systems

In the last decade due to the growing demand on high capacity transmission, DWDM transmission systems have evolved rapidly. The growth of transmission speed and the decrease in channel spacing has resulted in stricter requirements to the elements used in optical signal transmission process, including optical amplifiers. In this article we take one of the most popular DWDM solutions – a 10 Gbit/s 16 channel NRZ-OOK 50 GHz DWDM transmission system, and implement a SOA and a RA as a single in-line amplifier, in order to estimate and compare their performance, and to identify and estimate the main factors that limit the total transmission quality in both cases. Ill. 6, bibl. 6, tabl. 1 (in English; abstracts in English and Lithuanian).DOI: http://dx.doi.org/10.5755/j01.eee.123.7.2392

Entirely passive reach extended GPON using Raman amplification

In previous investigation of extended GPON system, we employed 1240 nm and 1427 nm dual pumps within optical line terminal (OLT) equipments at central office (CO) to provide distributed Raman gains of upstream 1310 nm and downstream 1490 nm signals. These pump wavelengths were selected to ensure compatibility with the standard GPON wavelengths and reduce the unwanted pump-to-signal interactions. In this paper, we propose a new system scheme for an entirely-passive extended reach GPON to further enhance the system performance by eliminating the pump-to-signal interactions. In this scheme, a 1240 nm laser is employed to provide counter-pumping distributed Raman amplification of the upstream 1310 nm signal, and a discrete Raman amplifier is integrated with the 1490 nm transmitter to booster the downstream signal power and to improve the link loss budget. An operation over 60-km of zero-water-peak Allwave® fiber with a 1:128 way splitter is experimentally demonstrated at 2.5 Gbit/s. The system performance of such purely passive GPON extender is investigated in the paper. The system transmission limitation of upstream signal due to Raman ASE noises is discussed, and the non-linear impairment on downstream signal due to high launch power into feeder fiber is also examined.

Design methodology for multi-pumped discrete Raman amplifiers: case-study employing photonic crystal fibers

This paper proposes a new design methodology for discrete multi-pumped Raman amplifier. In a multi-objective optimization scenario, in a first step the whole solution-space is inspected by a CW analytical formulation. Then, the most promising solutions are fully investigated by a rigorous numerical treatment and the Raman amplification performance is thus determined by the combination of analytical and numerical approaches. As an application of our methodology we designed an photonic crystal fiber Raman amplifier configuration which provides low ripple, high gain, clear eye opening and a low power penalty. The amplifier configuration also enables to fully compensate the dispersion introduced by a 70-km singlemode fiber in a 10 Gbit/s system. We have successfully obtained a configuration with 8.5 dB average gain over the C-band and 0.71 dB ripple with almost zero eye-penalty using only two pump lasers with relatively low pump power.

Gain-clamped discrete Raman amplifier with suppressed low-frequency relative intensity noise pump-to-signal transfer

We demonstrate an optically gain-clamped discrete Raman amplifier with a suppressed low-frequency relative intensity noise transfer from pump sources to an input amplified signal, which is accomplished by employing a cascaded second-order Raman fiber resonator as an optical amplification. The input signal dynamic range for a 3-dB gain compression is controllable without affecting the clamping level. In addition, we find that the Raman net gain is unsusceptible to fiber parameters such as the gain and attenuation coefficients at the pump, first-, and second-order Stokes lines. These characteristics fit our proposed gain-clamped discrete Raman amplifier for practical deployment although it works at the expense of the efficiency.

Multi-pump discrete Raman amplifier for CWDM system in the O-band

We demonstrate theoretically that discrete Raman amplifiers operating in the O-band region (1260–1360 nm) are more efficient than in any other band if we consider the fiber attenuation. Compared with the C-band (1530–1565 nm), the net gain is 3 dB higher. We present also theoretically two types of discrete Raman amplifiers which can be used in the O-band with a course wavelength division multiplexing system. The first amplifier has a bandwidth of 70 nm that was designed with four pump lasers operating at 12XY nm. The second one has a bandwidth of 100 nm and needed six pump lasers to obtain a flattened gain across the O-band. In addition, we have analyzed the gain saturation in both optical amplifiers.

Low-Noise Fiber Raman Amplifiers Based on a Raman Ring Fiber Oscillator

We propose two discrete fiber Raman amplifier schemes using Raman ring fiber oscillator, a two-stage scheme, and a forward pumping scheme, to reduce double Rayleigh backscattering noise at high gains over 20 dB. Both schemes have low noise characteristics compared to a previous scheme. Bit-error-rate measurements at 10 Gb/s show power penalty free operation for the two-stage scheme at a gain of 25 dB.

Analysis of distributed temperature sensing based on Raman scattering using OTDR coding and discrete Raman amplification

The behaviour of distributed temperature sensors based on spontaneous Raman scattering and coded OTDR (optical time domain reflectometry) is studied both theoretically and experimentally; in particular a high performance scheme has been implemented using amplitude modulation according to Simplex coding, direct detection and additional use of lumped Raman amplification to further extend the sensing range. An efficient and cost-effective distributed temperature sensing system operating along 30 km of dispersion-shifted fibre with 17 m spatial resolution and 5 K temperature resolution is theoretically demonstrated and experimentally achieved using 255 bit Simplex coding and low-power commercially available laser diodes (80 mW CW power). Use of lumped Raman amplification to produce high-power coded pulses allows further 10 km distance enhancement, resulting in a total measurement range of 40 km.

Dynamic Response of Discrete Fiber Raman Amplifiers to Multi-channel Randomly Variable Packet Traffic

Dynamic Response of Discrete Fiber Raman Amplifiers to Multi-channel Randomly Variable Packet Traffic

Characteristics of S-band (1490-1512 nm) Discrete Raman Amplifier Using High Raman Gain Fiber

We have developed a high Raman gain fiber that is applicable to Raman amplification over a wide wavelength region. Since this fiber has sufficiently low OH-loss, favorable amplification characteristics for S-band are expected. Using 2 km of this fiber, an S-band discrete Raman amplifier of single stage configuration is fabricated with three laser diodes, and gain characteristics are investigated for 30 S-band WDM signals (1490-1512nm) with 100-GHz spacing. Amplifier input/output of-9.5dBm/+4.5dBm and-20dBm/-3.5dBm×30ch with 1-dB flatness without any gain-flattening filters are achieved by total 680mW pump power.

Threshold level and gain of forward stimulated Brillouin scattering in a forward pumped s-band discrete DCF fibers Raman amplifier

Amplification effect of forward stimulated Brillouin scattering (SBS) lines on the forward pumped s-band discrete DCF fiber Raman amplifier (FRA) has been studied. Pump threshold power of the forward first order Stokes SBS (FSB1-), second order Stokes SBS (FSB2-) and third order SBS (FSB3-) in the forward pumped FRA are 1.5 mW, 1.4 mW and 1.7 mW, respectively. The Stokes SBS lines are amplified by FRA and fiber Brillouin amplifier (FBA) at the same time. Gain of amplification is given as GA=GR · GB, where GR is Raman gain and GB is Brillouin gain. Saturation gain of FSB1-, FSB2- and FSB3- are about 52 dB, 65 dB and 65 dB, respectively. The saturation Raman gain of 10 km DCF forward FRA is about 14 dB, so Brillouin gain of FSB1-, FSB2- and FSB3- are about 38 dB, 51 dB and 51 dB, respectively. The forward cascaded SBS lines have been observed.

Fiber Bragg gratings for dispersion compensation in optical communication systems

Dispersion compensating fibers (DCF) are the most widely used technology for dispersion compensation. A DCF without Raman amplification introduces extra loss in the system, thus increasing the need for gain in the discrete amplifiers and degrading the noise performance. The idea to additionally use the DCF as a Raman gain medium was originally proposed by Hansen et al. in 1998. [1] This was quickly followed by Emori et al., who demonstrated a broadband, loss less DCF using multiple-wavelength Raman pumping. [2] DCF is a good Raman gain medium, due to a relatively high germanium doping level and a small effective area. To get sufficient gain with a reasonable pump power, a discrete Raman amplifier has to contain several kilometers of fiber, adding extra dispersion to the system that must be handled in the overall dispersion management. Dispersion compensating Raman amplifiers integrates two key functions: dispersion compensation and discrete Raman amplification into a single component.

Impact of the pump reflector in double‐pass discrete Raman amplifiers

AbstractWe present the experimental investigation of a counter‐pumped double‐pass discrete Raman amplifier with and without a pump reflector. The pump reflector is constructed with high‐reflectivity fiber Bragg grating. Gain improvement is obtained as a result of pump recycling, in comparison to the conventional double‐pass Raman amplifier. Noise‐figure degradation is found for large signals in the proposed Raman amplifier due to the enhanced double‐Rayleigh scattering and bidirectional pumping caused by the pump reflector. The impact of pump‐to‐signal relative intensity noise in the experimental work is minimized by utilizing Fabry–Perot pump lasers. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 777–779, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21473

Experimental validation of double-pass discrete Raman amplifier limitation for large signals

In this letter, we present a report on the experimental validation of double-pass discrete Raman amplifier (DRA) limitation for large signals. It has been proven that the limitation of double-pass Raman amplifier for large signals is due to stimulated Brillouin scattering (SBS) even though with a modulated signal at 10-Gb/s data. The multichannel amplification shows that this limitation can be relaxed due to energy distribution among the channels, the SBS threshold is enhanced. An average gain of 19.2 dB is obtained in four-channel amplification without any significant SBS effects. The double-pass DRA is found suitable for large signals to be deployed in wavelength division multiplexing systems

Dispersion-compensating fibers

This paper reviews properties and use of conventional single-mode dispersion-compensating fibers (DCFs). The quality of the dispersion compensation expressed as residual dispersion after compensation is treated. Properties of actual DCFs for discrete compensation including loss and nonlinear effects are discussed. Fiber design with special emphasis on design tradeoffs is considered. The Raman properties of DCFs and their use as a discrete Raman amplifier are also discussed. Finally, DCF for use in dispersion-managed cables (DMCs) is addressed, including optimum fiber design and comparison of different configurations.

High-performance discrete amplifier based on a second-order fiber Raman oscillator

We propose a second-order counterpumped Raman ring fiber oscillator for high gain and low noise discrete Raman amplification with enhanced robustness to wavelength-division-multiplexing channels add-drop operations. Bit-error-rate measurement at 10 Gb/s shows negligible penalties up to 20-dB net gain.

Behaviour of a wideband double-pass discrete Raman amplifier with simultaneous reflection of signals and multi-pump

The behaviour of a high efficient double-pass discrete Raman amplifier with 80nm bandwidth was studied theoretically and experimentally. In this Raman amplifier, by using a one-end gilt fibre as the broadband reflector, signals and multi-pump are simultaneously reflected to propagate through the gain fibre for a second time in the opposite direction of the input. An increase in net gain of more than 150% has been achieved compared with that in the typical co-pumped Raman amplifier. The advantages of this new configuration have been studied by comparing with the currently existing Raman amplifier configurations. Also, the influencing factors for the gain increase have been analysed, including the pump-to-pump Raman interactions and the length of gain fibre.

Performance of two-stage discrete fiber Raman amplifiers with and without all-optical gain clamping

Using numerical simulations, we analyze the properties of two-stage discrete fiber Raman amplifiers without and with all-optical gain clamping. In both cases a two-stage amplifier can be designed to have the same gain characteristics as a single-stage amplifier with improved noise performance by use of either the same total length of gain fiber (but with increased pump power) or total pump power (but with increased total length of gain fiber).

Composite broad-band fiber Raman amplifiers using incoherent pumping

This report presents an investigation of composite fiber Raman amplifiers (i.e., a distributed fiber Raman amplifier followed by a discrete fiber Raman amplifier) with in-coherent pumping, compared to conventional coherent pumping. It is shown that a flatter gain, noise figure and optical signal-to-noise ratio (OSNR) over 100-nm bandwidth can be achieved simultaneously by using two counter-incoherent pumps, compared to using six counter-coherent pumps. Moreover, it is found that a further improvement in gain, noise figure and OSNR flatness can be obtained in composite fiber Raman amplifiers with bi-directional incoherent pumping. The flatness of both gain and OSNR with a ripple of 1 dB is predicted by using one co-incoherent pump and one counter-incoherent pump.

Reflective type Raman amplification for loss compensation in dispersion compensating fiber

We demonstrate the characteristics of the reflective type discrete Raman amplifier in the dispersion compensating fiber which is composed of a circulator and a Faraday rotator mirror. With the same dispersion compensation, the gain of the reflective type is higher than that of the conventional single-pass type. Moreover, the forward pumping is better than the backward pumping in the reflective type dispersion compensating Raman amplifier. We also show that, by using the reflective type configuration, the polarization mode dispersion of the dispersion compensating fiber can be almost compensated.