Effective Noise Figure Research Articles

Hybrid pumped laser sources based hybrid traveling wave SOA and optical EDFA amplifies for signal quality improvement

Abstract This paper has demonstrated the hybrid pumped laser sources based hybrid traveling wave SOA and optical EDFA amplifies for the signal quality improvement. The previous effective noise figure and fiber loss variations are clarified against wavelength band with/without amplification. The related previous signal output power versus Raman/EDFA pumped amplification and signal power conversion efficiency are indicated versus the launched pump power with the Raman/EDFA pumped amplification. The signal quality factor/BER against the transmission distance with/without amplification after receiver side. The modified amplified light signal power is demonstrated after 300 km distance SMF channel with wavelength band variations. The modified amplified light signal power is clarified after 300 km distance SMF channel by using optical power meter. The modified amplified light signal power is clarified after 300 km distance SMF channel with time band variations. The modified amplified electrical signal power is demonstrated after 350 km distance SMF channel with frequency band variations. The modified amplified electrical signal power is clarified after 350 km distance SMF channel with time band variations. The modified amplified electrical signal power is demonstrated after 350 km distance SMF channel by using electrical power meter.

Ultralow noise C + L wideband WDM-IMDD transmission at 18 × 112 Gbps by using hybrid second-order distributed Raman and first-order lumped Raman amplification.

We experimentally investigated and demonstrated an ultralow noise hybrid amplifier that combines second-order distributed Raman amplifier (DRA) and first-order lumped Raman amplifier (LRA) in a cascaded approach. This approach allows for the reutilization of pump light from the LRA as the seed light in the second-order DRA, and simultaneous full-band dispersion compensation is realized by using dispersion compensation fiber in the LRA. This approach also supports broadband gain flattening based on the separated DRA and LRA configuration. The transmission application of the proposed amplifier was investigated using a set of 10 external cavity lasers (ECLs) in the C-band and 8 ECLs in the L-band. Ranging from 1531.12 nm to 1595.49 nm across C + L band, the proposed hybrid amplifier gives a maximum on-off gain of 27.2 dB and an average gain of 23.4 dB, with an extremely low effective noise figure (NF) of lower than -2.9 dB. Intensity modulation direct detection (IMDD) signal transmission is carried out at two different data rates across these 18 wavelengths in the C + L band: (1) 56 Gbps/λ PAM-4 signal; (2) 112 Gbps/λ PAM-4 signal. The results show that the error free transmissions are demonstrated over 101.6 km EX2000 fiber using both signals with 7% HD-FEC and 20% SD-FEC, respectively.

Purely nonlinear amplified ultralow-noise transmission using hybrid second-order DRA and PPLN-based PSA.

We report ultralow-noise transmission over a 102-km single-mode fiber using a purely nonlinear amplification scheme consisting of a second-order distributed Raman amplifier (DRA) and a phase-sensitive amplifier (PSA) based on periodically poled LiNbO3 waveguides. The hybrid DRA/PSA features a broadband gain over the C and L bands and an ultralow-noise advantage, with a less than -6.3 dB effective noise figure in the DRA stage and a 1.6 dB optical signal-to-noise ratio (OSNR) improvement in the PSA stage. Compared with the unamplified link, the OSNR is improved by 10.2 dB for a 20-Gbaud 16QAM signal in the C band, resulting in error-free detection (a bit-error rate of less than 3.8 × 10-3) for the signal with a low link input power of -25 dBm. Mitigation of nonlinear distortion is also achieved by the proposed nonlinear amplified system due to the subsequent PSA.

Experimental Study of AM and PM Noise in Cascaded Amplifiers

An experimental study of amplitude modulation (AM) and phase modulation (PM) noise spectra in cascaded amplifiers was carried out as a function of the number of amplification stages and the input power. Flicker and white noise contributions were determined, as well as effective noise figure (NF) from AM and PM noise spectra from small-signal to large-signal regimes. Simultaneous measurements of AM and PM noise were performed, and associated correlation was measured as a function of the offset frequency from the carrier. Measurements exhibited, in general, quite low AM–PM correlation levels both in the flicker and white noise parts of the spectrum. In some particular amplifier configurations, however, measurements showed some peaks in the correlation at some specific input power levels in the transition zone, from a quasi-linear to strong compression. The results show that the effective noise figure decreases with the number of stages for a given carrier output power level.

74.38 Tb/s Transmission Over 6300 km Single Mode Fibre Enabled by C+L Amplification and Geometrically Shaped PDM-64QAM

Ultrawide-bandwidth optical amplification over almost 90 nm, covering the C+L bands, is described. Complemented by system-tailored geometrical constellation shaping and nonlinearity compensation, it enabled a record capacity transmission of 74.38 Tb/s over 6,300 km of G.654 single-mode fibre. The hybrid scheme, combining backward Raman pre-amplification with EDFA, significantly improves the average effective noise figure across the entire bandwidth, allowing the use of span lengths of 70 km. The system-tailored GS-64QAM constellation was optimised to both linear link impairments and transceiver nonlinearities, improving the gap to the AWGN channel capacity relative to square 64QAM from 0.6 bit/symbol to 0.35 bit/symbol. We experimentally evaluated the system performance using the bit-wise achievable information rate (AIR) and signal-to-noise ratio (SNR) at the end of transmission, as well as post SD-FEC BER.

GaAs MMIC Low Noise Amplifier With Integrated High-Power Absorptive Receive Protection Switch

This letter reports a GaAs monolithic microwave integrated circuit (MMIC) low noise amplifier (LNA) with integrated high-power absorptive receive protection switch realized using 0.13- $\mu \text{m}$ GaAs pHEMT process. On-the-chip current distributed, resonant shunt FET switch configuration is employed for higher power handling. FET stacking technique is used to reduce the effective noise figure (NF). A two-stage LNA with integrated high power switch, forming each arm in a balanced configuration is employed to realize a monolithic LNA with integrated absorptive receive protection switch. This novel MMIC provides protection up to 20-W continuous wave and 2.9-dB NF, a gain of 20 dB over 9.3–9.9 GHz.

Ultra-Low-Noise Mode-Division Multiplexed WDM Transmission Over 100-km FMF Based on a Second-Order Few-Mode Raman Amplifier

We demonstrate, for the first time, an ultra-low-noise mode-division multiplexed transmission with eight wavelength-division multiplexed channels over a 100-km few-mode fiber based on a second-order few-mode Raman amplifier. To minimize the mode dependent gain, two backward depolarized pumps at the wavelengths of 1455 nm (75 mW) and 1360 nm (1890 mW) are equally launched both into the LP11a and LP11b modes. The Raman on–off gains of the LP01 and LP11 modes are both above 8 dB and the mode dependent gain is less than 0.7 dB. An amplified spontaneous emission noise improvement of 1.8 dB is achieved in the second-order few-mode Raman amplifier, with respect to the first-order Raman amplification. The effective noise figure of the second-order few-mode Raman amplifier is about –3 dB, which is ∼1.4 dB lower than that in the first-order pumping case. In the transmission experiments, a single-mode transmission over LP01 mode and a mode-division multiplexed transmission over LP11a and LP11b modes are performed separately. The bit-error-rates for all the transmission channels are significantly improved due to the low-noise figure amplification of the second-order few-mode Raman amplifier.

Hybrid distributed Raman amplification combining random fiber laser based 2nd-order and low-noise LD based 1st-order pumping

A configuration of hybrid distributed Raman amplification (H-DRA), that is formed by incorporating a random fiber laser (RFL) based 2nd-order pump and a low-noise laser-diode (LD) based 1st-order pump, is proposed in this paper. In comparison to conventional bi-directional 1st-order DRA, the effective noise figure (ENF) is found to be lower by amount of 0 to 4 dB due to the RFL-based 2nd-order pump, depending on the on-off gain, while the low-noise 1st-order Raman pump is used for compensating the worsened signal-to-noise ratio (SNR) in the vicinity towards the far end of the fiber and avoiding the potential nonlinear impact induced by excess injection of pump power and suppressing the pump-signal relative intensity noise (RIN) transfer. As a result, the gain distribution can be optimized along ultra-long fiber link, due to combination of the 2nd-order RFL and low-noise 1st-order pumping, making the transmission distance be extended significantly. We utilized such a configuration to achieve ultra-long-distance distributed sensing based on Brillouin optical time-domain analysis (BOTDA). A repeater-less sensing distance record of up to 154.4 km with 5 m spatial resolution and ~ ± 1.4 °C temperature uncertainty is successfully demonstrated.

Random-lasing-based distributed fiber-optic amplification

The gain and noise characteristics of distributed Raman amplification (DRA) based on random fiber laser (RFL) (including forward and backward random laser pumping) have been experimentally investigated through comparison with conventional bi-directional 1st-order and 2nd-order pumping. The results show that, the forward random laser pumping exhibits larger averaged gain and gain fluctuation while the backward random laser pumping has lower averaged gain and nonlinear impairment under the same signal input power and on-off gain. The effective noise figure (ENF) of the forward random laser pumping is lower than that of the bi-directional 1st-order pumping by ~2.3 dB, and lower than that of bi-directional 2nd-order pumping by ~1.3 dB at transparency transmission, respectively. The results also show that the spectra and power of RFL are uniquely insensitive to environmental temperature variation, unlike all the other lasers. Therefore, random-lasing-based distributed fiber-optic amplification could offer low-noise and stable DRA for long-distance transmission.

Combined Effect of ASE and DRBS on Noise in Pulse-Pumped Fiber Raman Amplifiers

Amplified spontaneous emission (ASE) and double Rayleigh backscattering (DRBS) degrade the effective noise figure (ENF) and ultimately limit the performance of fiber Raman amplifiers (FRAs). This limitation is especially severe when a time-division-multiplexed (TDM) pumping scheme is employed. In this paper, we theoretically study the joint impact of ASE and DRBS on ENF in pulse-pumped FRAs. We demonstrate that the ASE is the major source of noise for small pump duty cycles, whereas DRBS dominates when a typical FRA operates in the continuous-wave regime. If the pump power is gradually increased, ENF improves until the gain reaches an optimal value. We show the increase of the optimal gain with pump duty cycle and with decreasing fiber scattering efficiency. Our study reveals the importance of taking into account the effects of both ASE and DRBS for an accurate estimation of ENF penalty in pulse-pumped FRAs, especially operating at high gains when pump duty cycle is small.

Investigations of AM, PM Noise, and Noise Figure in an SiGe-HBT Amplifier Operating in Linear and Nonlinear Regimes

A study of amplitude modulation (AM) and phase modulation (PM) noise has been carried out in an SiGe bipolar amplifier, operating in small- and large-signal conditions. Experimental and simulation results show that the evolution of flicker noise and white noise contributions versus carrier power is different in the AM and PM noise spectra. This indicates that specific mechanisms are involved in the conversion processes, thus producing AM and PM noise. The degradation of white noise, introduced by the amplifier as a function or carrier power, has been studied and characterized through the effective noise figure (NF) obtained from the white noise portion of the AM and PM spectra. As expected, the results show that white noise only produces identical contributions to AM and PM noises if the amplifier is operating in a small-signal regime. The effective NF in large-signal conditions needs to be determined from both the AM and PM noise spectra. An expression compatible with the standard IEEE definition of NF is proposed to extract the effective NF from the AM and PM noise spectra.

Broadband Active Receiving Patch With Resistive Equalization

The active integrated antenna (AIA) concept has been applied to design a broadband receiver front-end. A design procedure for active broadband patch antennas based on resistive equalization is presented. The use of the AIA has allowed the design of efficient RF front-ends by increasing its effective gain, noise figure, and merit . In addition to improving the classical parameters, the resistive equalization technique allows enlarging the bandwidths of the active antenna parameters versus the corresponding ones in passive antennas. A receiving patch antenna (with one amplifying stage) with a measured noise figure lower than 0.6 dB in a bandwidth over 38% and an effective gain improvement of 13 dB over the corresponding passive antenna has been achieved. The -parameter has also been measured for both the active and passive antenna, resulting in a relative planar of 16 dB/K, with a ripple of 0.5 dB, over a 30% bandwidth for the active antenna versus a of 22 dB/K for a typical front-end with a passive antenna over 20% bandwidth.

The effective antenna noise figure Fa for a vertical loop antenna and its application to extremely low frequency/very low frequency atmospheric noise

Expressions tabulated for the effective antenna noise figure Fa usually assume an electric field antenna, since most measurements of radio noise are made on the electric field of the noise. Furthermore, the International Radio Consultative Committee (CCIR) noise model predictions for Fa are made only for electrically short grounded vertical monopoles over a perfect ground. However, at frequencies lower than those traditionally used for communications, i.e., at extremely low frequencies (ELF; frequencies in the range 3 Hz to 3 kHz) and very low frequencies (VLF; frequencies in the range 3–30 kHz), it is common for magnetic field loop antennas to be used, and the tabulated expressions for Fa do not apply. This communication reports the derivation of an expression for Fa as measured by a small vertical magnetic loop antenna and its subsequent application to ELF/VLF radio noise measurements made at a variety of locations around the world. There is good agreement between the measured Fa values and estimates of maximum and minimum Fa values for the ELF/VLF range published by Spaulding and Hagn in 1978, but an improved fit to the measurements can be obtained by making moderate adjustments to the maximum and minimum values at both the low (10–100 Hz) and high (8–32 kHz) frequency limits.

Optimizing the incoherent pump spectrum of low-gain-ripple distributed fiber Raman amplifier for a given main pump wavelength

The method for designing the incoherent pump spectrum for the distributed fiber Raman amplifiers (DFRAs) of low gain ripple is studied, in which the wavelength of the maximum power spectral density can be assigned. The assigned wavelength is called the main pump wavelength. Incoherent pump spectrum is described with the power spectral density function (PSDF) that comprises a set of piece-wise continuous functions. PSDF is optimized for the minimum gain ripple with the least-square minimization method. An extremum pump wavelength condition is applied to PSDF. A proper initial trial PSDF is given so that the optimized PSDF converges to the desired result and the power spectral density at the extremum pump wavelength is the maximum. With this design method, we show the optimized PSDFs for the DFRAs using backward pumping and bidirectional pumping. The gain ripples of considered DFRAs are less than 0.1 dB for 20-dB ON-OFF Raman gain over 70-nm bandwidth. The reduction of average effective noise figure with shorter main pump wavelength is shown and investigated.

Revisiting spurious-free dynamic range of communication receivers

The spurious free dynamic range (SFDR) is commonly used as a measure of dynamic range for the radio frequency and microwave front-end receivers. Although well defined in narrow-band systems, the definition becomes less clear in wide-band systems, when the nonlinearity is memoryless and the the noise figure is frequency dependent. To generalize the SFDR to wide-band systems, a meaningful physical interpretation of the conventional two-tone test is first developed. Based on this interpretation, the upper bound of the wide-band SFDR is obtained by applying a multitone test, while the lower bound is computed using the effective noise figure. The multitone test in both the memoryless and memory nonlinear Volterra systems is considered. A practical measurement technique to characterize the Volterra kernel is also provided. A realistic example based on a low noise amplifier shows a significant difference between the conventional and wide-band SFDR values. In this example, our results suggest that the use of two tones widely separated in frequency to model the interferers provides sufficiently accurate results compared to a multitone approximation.

Spectroscopic Analysis of Gain Bandwidth in Raman Amplifier with Multiwavelength Pumping Scheme Using Actual Band Model

The spectroscopic model is proposed to analyze the gain bandwidth of a fiber Raman amplifier (FRA) with a multiple wavelength pumping scheme based on Raman gain theory. The oscillatory lineshape, which is the analytic function to analyze Raman gain spectra, allows us to estimate the gain bandwidth of the FRA. Based on the proposed theoretical modeling, we design and analyze the characteristics of the FRA using the combined multiwavelength pumping sources. We achieved the extended gain bandwidth of the FRA over 80 nm with the small gain ripple less than 0.5 dB. Threshold pumping power and effective noise figure for the FRA can be also analyzed by using the proposed model, which is also applicable for versatile fibers with other doping materials. The proposed analysis method can be useful for the design of FRA with the multiwavelength pumping scheme.

Effects of time‐division multiplexing of two‐pump wavelengths on a counter‐pumped Raman‐fiber amplifier

AbstractWe demonstrate the impacts of the time‐division multiplexing (TDM) technique on a two‐pump wavelength Raman‐fiber amplifier. Modulation frequency is critical in this pumping technique, which can create temporal gain variations at low frequencies. The effective noise figure also degrades when utilizing this pumping scheme due to the arising of amplified spontaneous emission. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 238–239, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20263

Analytical model for Raman noise figure in dispersion-managed fibers

We derive an exact and a closed-form approximate analytic formula for effective lumped Raman noise figure in backward-pumped dispersion-managed fibers (DMFs) of arbitrary topology. Within the single-pump small-signal amplification model, important effects such as unequal loss coefficients at pump and signal wavelengths or splice loss for the pump and the signal between the DMFs' sections are taken into account. Theoretical results agree well with the noise figure measured in a symmetric DMF. The developed approach can be used to optimize the noise performance of DMFs.

Six-wavelength Raman fibre laser for C- and L-band Raman amplification and dynamic gain flattening

A novel six-wavelength Raman fibre laser exhibiting a dynamic gain flattening capability in the C + L optical telecommunications band is demonstrated. The power distribution in the six lasing wavelengths is adjusted with voltage-controlled Bragg-grating output couplers. The fibre laser was used as a pump source for distributed Raman amplification in several transmission span lengths. For example, the multiwavelength laser provides an on/off gain of 19 dB over a 100 km span of True-Wave RS optical fibre. The measured gain flatness is 1.7 dB peak-peak and the effective noise figure ranges from 1.6 to -5.2 dB in the 1530 to 1600 nm bandwidth.

A general and rigorous WDM receiver model targeting 10-40-Gb/s channel bit rates

We present a general and rigorously formulated dynamic receiver model aiming at 10-40-Gb/s wavelength division multiplexing (WDM) system design applications. A demultiplexing (DEMUX) characteristic with periodic transfer function has been treated in detail and it has been indicated how the model should be adjusted to take into consideration a general type of noise spectral density (NSD). The bit error ratio (BER) is evaluated accounting for the influence of non-Gaussian detected amplified spontaneous emission (ASE) noise, noise correlation between stochastic noise samples in the receiver, the gain and effective noise figure variation with wavelength of optical amplifiers, channel crosstalk, and intersymbol interference (ISI) effects caused by nonideal signal modulation, fiber dispersion, fiber nonlinearities, optical MUX, and DEMUX filtering and the impulse response of the electrical low-pass filter in the receiver. Also, the influence of shot and thermal noise is taken into account. Numerical results for the BER are presented considering a realistic 16-channel 10-Gb/s WDM system operating in the C-band using normal transmission fibers and including cascaded erbium-doped fiber amplifiers (EDFAs) with dispersion compensating fibers.