Figures 6 and 7 show the frequency dependence of gain and noise figure for both EDFA and EYDWA optical amplifiers, respectively. Homogeneous upconversion tends to cause more degradation in the performance of the EDFA amplifier than in the EYDWA amplifier. Figure 8 shows the change in profit as a function of the HUC coefficient [15].
Equalization of gain with optimization of EDFA parameters
Good gain surface requires continuous control of the input power to adjust it to its optimal value [15].
Gain equalization through the use of a GFF filter
The figures below show a schematic representation of the spectrum emitted at the output of the EDFA and the output of the GFF gain equalization filter. We can see that the spectrum received at the output of the EDFA has a different total value.
Conclusion
1 Mascara Iniwɛrisite, LEPO Laboratoire de Sidi Bel Abbes, Alzeri jamana na. 2 Sidi Bel Abbes Iniwɛrisite, LEPO laboratuwari Sidi Bel Abbes, Alzeri 3 Mascara Iniwɛrisite, Alzeri.
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Introduction
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technique for representing information, which reduces the complexity of the receiver's digital processing unit while combating harmful channel effects with simple correction algorithms. However, some of the immediate consequences of these compelling benefits in OFDM are: the limitation of spectral efficiency due to the introduction of CP, the detrimental impact of high peak-to-average power ratio (PAPR) and serious susceptibility to transmitter impairments [4 . , 5]. Transmitter impairments, such as phase noise (PHN), carrier frequency offset (CFO) and the effect of phase unbalance in quadrature (IQ), must be significantly addressed to make the best possible use. of limited radio spectrum to further increase throughput as well as user capacity.
While there are many transceiver limitations to consider when designing a digital communications system, there is a compelling case for focusing precisely on the PHN. In contrast, while the imbalance of CFO and IQ is deterministic, PHN is random disturbances in the phase of the carrier signal. In addition, the multi-carrier systems such as OFDM suffer a much loss in signal-to-noise ratio (SNR) due to PHN than single-carrier systems.
Phase noise
This is the result of a longer duration of the multicarrier symbol and the loss of orthogonality between the subcarriers. The simulated samples of PHN modeled as Wiener process and celebrated O-U process, for FRO and PLL VCO, respectively, are shown in Figure 2. Although the time-varying PHN process of FRO can be characterized with β alone, PLL requires VCO more parameters to characterize as given in Table 1, assuming the VCO is noisier than the reference oscillator.
OFDM
Phase noise in OFDM
- Common phase error
- Intercarrier interference
Note further that with modulus indexing, the lowest-order spectral components of PHN are given by gap0, p1, pN 1, p2, pN 2, etc. ICI is present because PHN causes the energy of individual subcarriers to spread on top of all others. subcarriers [20-23]. Figure 5 shows two 22 MHz bandwidth systems where the first system uses the PHN-free ideal oscillator with a carrier frequency of 2420.5 MHz, while the second system uses a noisy FRO with a carrier frequency of 2433.5 MHz and spectrum row, which causes results in power leakage in the first band, producing Intermittent Interference (ICI). The rotation of the constellation is produced due to CPE, while the cloudy constellation is the influence of ICI.
The effect of PHN on BER of the OFDM system is shown in Figure 7 only for receiver FRO PHN (PHN deviation = .06 rad2) and for transceiver FRO PHN (PHN deviation = .06 rad2) and is compared with the BER of pure AWGN channel. OFDM symbols are generated using 16-quadrance amplitude modulation (QAM) and 64-point IFFT and then prefixed by CP of length 16 samples. Effect of phase noise in MC communication system (spectral regrowth (in-band-ICI)(out-of-band-MUI)).
OFDMA
Practically, in the frequency domain, the allocation is not done at the level of subcarriers but in the group of subcarriers. To explain the basic principle of OFDMA transmitter, we are considering here that one user uses one subcarrier in the given time slot, i.e., the number of users (U)=N. At the receiver side (base station), the received signal is the sum of the users' signal U, which acts as an OFDM signal.
These symbols are then OFDMA modulated by subchanneling and an SC modulator (in the case of U ¼N) or an OFDM modulator if a single user is using a group of subcarriers. An OFDMA system requires accurate clock and carrier synchronization to ensure orthogonality between modulated signals from different mobile terminals. This is achieved by the immediate transmission of synchronization signals from the receiver to all mobile terminals.
Each terminal OFDM modulator drives the carrier frequency and clock signal from these downlink signals.
Phase noise in OFDMA
This MUI is induced by the spectral spreading of the energy from each user's subcarriers on top of other users' subcarriers. The presence of the transceiver PHN degrades the performance of the OFDM system due to the rotation effect CPE and spectral regrowth ICI. Yadav for his valuable suggestions and comments that helped to improve the presentation of the book chapter.
This ever-increasing demand is pushed by the constant increase in the number of connected users, devices, processes and data (vs. Internet of Everything IOE). One of the most promising variants of SDM that has recently shown great potential is based on exploiting orbital angular momentum (OAM) modes as data carriers. This demand is fueled by the rapid and renewed increase in the number of connected users, devices, processes and data (e.g.
CDM is based on an increase in the number of cores embedded in the same cladding of optical fiber [8]. SAM provides only two different modes (available data channels). 2) Orbital Angular Momentum (OAM), which is linked to the spiral aspect (twisted light) of the wavefront.
Space division multiplexing (SDM) system
- Emission side
- SDM-optical fiber transmission
- Receiver side
This facilitates a better understanding of the influence of each fiber parameter on fiber performance measurements and smoothes the transition from the design phase to the fabrication process (eg MCVD as modified chemical vapor deposition) and to the placement operation. to the ground later (eg FTTH as Fiber to the Home and FTTX as fiber to x). Next, we focus on the potential of using OAM modes over optical fibers (OAM-SDM) as a promising candidate that tends to realize the full potential for SDM technology. Photonic beacon, waveguide optics interface with photonic lattice integrated coupler, narrow multicore fibers, wave coupling (e.g. in the case of MCFs, isolated channels connect each core to an SMF of special) and free space optics approaches such as phase plates, mirrors, beam splitters and special lenses [20].
In principle, the selection rule between these techniques is based on the embedded SDM fiber (ie, FMF, MMF MCF) and the requirement of minimum loss, low susceptibility to crosstalk, compactness, and low complexity and flexibility. According to CDM, the first technology used as fiber SDM is based on the use of a single-core fiber bundle (fiber ribbon), where parallel single-mode fibers are packed together to form a fiber bundle or ribbon cable. In principle, there are two main categories of MCF: weakly coupled MCF (= unbonded MCF) and strongly coupled MCF (= coupled MCF), depending on the value of the coupling coefficient 'K'. which is used to characterize crosstalk).
On the contrary, due to low XT in uncoupled MCF, it is not necessary to mitigate the XT impacts via complex MIMO (see Table 1). In principle, the selection of these devices is based on the following requirements: high responsivity, bandwidth, noise characteristics, low cost, and so on [34].
OAM-SDM system over fibers: potential and challenges
- OAM beams
- Devices and components for OAM-SDM over fibers
- OAM-SDM-fibers: potentials and challenges
By modulating the phases of the Gaussian beams, we can generate a wide range of OAM modes. The use of OAM modes in optical fiber was a challenge for the optical communication community. The investigation of already existing fibers in the OAM context has been carried out by performing a comprehensive analysis of the OAM modes in the standard index multimode fiber (GIF) (i.e. OM3) in [97].
In the beginning, the Ramachandran group demonstrated the multiplexing/transmission and demultiplexing of OAM modes over a dedicated vortex fiber [80]. A transmission capacity of 10.56 Tbit/s has been demonstrated over an ACF with 12 OAM modes using WDM technology (OAM-SDM-WDM) [107]. As a first experiment, the use of IPGIF as an OAM fiber was successfully demonstrated based on the transmission of two OAM modes over 1 km.
In [116], we proposed reverse raised cosine fiber IRCF (Figure 7g) for supporting moderate and robust OAM modes. The transfer of OAM modes via MCFs has been demonstrated with the aim of further increasing the capacity of an SDM links (i.e. improving the available data channels).
Perspectives and future research orientations
1 Faculty of Sciences of Monastir, Laboratory of Electronics and Microelectronics, Department of Physics, University of Monastir, Monastir, Tunisia. 2 Faculty of Sciences of Bizerte, Laboratory of Artificial Intelligence and Data Engineering Applications, Computer Department, University of Carthage, Bizerte, Tunisia.
Conclusions
Mode division multiplexing using an orbital angular momentum mode sorter and MIMO-DSP over a graded-index few-mode optical fiber. Comparison of mode crosstalk and mode-dependent loss of laterally shifted orbital angular momentum and Hermite-Gaussian modes for optical communication in free space. Efficient generation and sorting of orbital angular momentum eigenmodes of light by thermally tuned q-plates.
High-purity generation and energy-efficient multiplexing of optical orbital angular momentum (OAM) modes in a ring fiber for spatial division multiplexing systems. Efficient generation and multiplexing of optical orbital angular momentum modes in a ring fiber by using multiple coherent inputs. Integration of 5 × 5 Dammann gratings to detect orbital angular momentum states of beams ranging from −24 to +24.
Scalable mode-division multiplexed transmission over a 10-km ring-core fiber using high-order orbital angular momentum modes.
