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Photodetectors and Receiver Architectures
Published in Hamid Hemmati, Near-Earth Laser Communications, 2020
Peter Winzer, Klaus Kudielka, Werner Klaus
Here, hf = hc/λ is the energy of a photon and nSP is the amplifier's inversion factor, which characterizes the degree of material inversion achieved by pumping electrons from the lower to the upper (excited) energy states. The ASE occupies the entire spectral region within which optical amplification is possible, which is much wider than any reasonable optical signal bandwidth. Therefore, amplifier noise can be modeled as white noise. A perfect amplifier is fully inverted, corresponding to the lowest possible value of nSP = 1. Values only slightly larger than nSP = 1 can be obtained with commercially available EDFAs. The optical noise power PN (in W) at the output of a “single-mode” amplifier is then given by: PN=2NASEBO,
Basic Optical Fiber Nonlinear Limits
Published in Andrew Ellis, Mariia Sorokina, Optical Communication Systems, 2019
Mohammad Ahmad Zaki Al-Khateeb, Abdallah Ali, Andrew Ellis
We have seen how, throughout the history of optical communications, it has been possible to develop accurate analytical predictions of the nonlinear Kerr products. These applied to single channel systems, with and without optical amplifiers, and to WDM systems with and without dispersion management. The performance of the coherently received optical signals from long-haul optical transmission system is dependent on the SNR value of those signals. SNR of the optical signal is degraded as the signals propagate through the transmission system because of the linear ASE noise accumulated from inline amplifiers, and the nonlinear noise generated from the Kerr effects of the optical fiber. Equation 2.8 provides the basis to calculate the nonlinear power spectral density of Kerr effects generated by the optical signals propagating through discretely amplified optical transmission system.
Telecommunication Applications
Published in Luc B. Jeunhomme, Single-Mode Fiber Optics, 2019
From a practical point of view, however, the broadband ASE noise contribution should be decreased as much as possible by filtering out the ASE noise. Ideally, one should use a filter that blocks out all the noise outside the signal bandwidth (and this can be attained with coherent detection, which permits the use of electronic filters), but in the case of optical filters it seems difficult to achieve such a narrow filter spectral width. The use of a rather large filter width degrades the link gain and decreases the tolerance on the optimum input signal power. For example, typical estimations shows that with a TWLA net gain of 20 dB, a filtering bandwidth equal to the signal bandwidth yields a link gain of more than 19 dB for an input number of signal photons between 5 × 103 and 106, while a filtering bandwidth equal to 3000 times the signal bandwidth yields a maximum link gain of 19 dB, and the tolerance for the number of input signal photons (at a 1-dB link gain compression) is reduced to 105 ≤ Ns ≤ 106 [56].
Reflective semiconductor optical amplifiers-based all-optical NOR and XNOR logic gates at 120 Gb/s
Published in Journal of Modern Optics, 2020
The main source of the noise in the (R)SOA is the ASE effect [24]. The spontaneous emission is generated during the amplification process and amplified during the active region. The optical amplifiers degrade the signal-to-noise ratio (SNR) of the amplified signal due to amplified spontaneous emission (ASE), which adds noise to the output signal. The ASE effect of the whole system is large even if each (R)SOA generates small ASE power because the ASEs are accumulated. The SNR is linked to the noise figure (NF) by NF = (SNR)in/(SNR)out = 2 NSP (G-1)/G, where NSP is the spontaneous emission of the inversion factor [24]. In order to calculate the input and the output SNR, the spontaneous emission must be added [24]. The ASE power in the optical bandwidth (B0) at a central frequency (υ) is given by [24]: Using this equation, the noise effect on the gates’ quality performance is numerically added to the equations of the gates’ output powers numbered (11) for the NOR gate and (17) for the XNOR gate. There are many numerical models for calculating the noise value inside the amplifier. The model based on the spontaneous emission coupling factor is commonly used to calculate the ASE. The different shapes of the ASE spectrum at the two facets when the SOA is saturated [47]. A more direct numerical model to calculate the ASE is described in detail by Connelly [48]. The impact of the ASE can be experimentally measured by adding a few nm wide optical unmodulated signal to the input signals and then measuring the output QF as a function of the signal intensity and bandwidth.
Computer Model for EDFA Dynamics Over 1525–1560 nm Band Using a Novel Multi-Wavelength MATLAB Simulink Test Bed for 8-Channels
Published in IETE Journal of Research, 2018
Reena Sharma, Sanjeev Kumar Raghuwanshi
Some of the ions from the metastable level can decay back to the ground state in the absence of an externally stimulated photon flux. This decay phenomenon is known as spontaneous emission and leads to the amplifier noise called ASE. This undesired recombination gives rise to a broad spectral background of photons that get amplified along with the optical signal. The ASE noise power is given as [14]where optical bandwidth, population inversion factor and amplifier gain.
Studies on rubidium 5S-5d two-photon absorption
Published in Journal of Modern Optics, 2021
Vinay Shukla, Sudip K. Nath, Vaishali Naik, Alok Chakrabarti, Ayan Ray
An important aspect of the Rb 5S→5D transition is non-degenerate frequency conversion. One prominent decay route is 5D5/26P3/25S1/2. This has been utilized in studies of continuous blue light (CBL) generation [4, 29, 30], ASE [12] etc. Most of these studies were carried out with a combination of diode lasers emitting at 780 nm (5S→5P) and 776 nm (5P→5D) except a few [7, 9] where a single laser emitting at 778 nm (5S→5D) has been used to study parametric FWM. However, there exists competition between two different processes: FWM (nonlinear, phase matched, forward directed) and ASE (nonlinear, both forward and backward directed) under direct TPA [19, 20]. The process, which gains most, grows at the expense of pump energy, thus hindering the growth of other process. Under favourable experimental condition, the ASE is suppressed due to a destructive interference between two excitation pathways (between pump and internally generated fields) connecting the ground and excited states. The condition of suppressed ASE and strong FWM can produce a squeezed state of the radiation field [14]. However, here we excited warm Rb vapour with counter-propagating pump beams from a single laser. Theoretically the mismatch of propagation vector nullifies the probability of FWM leaving only ASE as the dominant mechanism present in the medium for populating |4> state, which acts as a leaky reservoir. Figure 3 shows blue fluorescence spectra, which leads to the fact that |3> (cf.Figure 1) is populated. Furthermore, at exact or near two-photon resonance (5S→5D) the effect of hyper Raman scattering, if any, is weak; hence negligible. This overall situation subsequently indicates to ASE as responsible for 5D5/2→6P3/2 decay (infrared radiation 5.2 μm). But the character of following blue radiation (6P3/2→5S1/2, 420nm) under such condition is still to be ascertained.