Quantum mechanical phenomena are revolutionizing classical engineering fields such as signal processing or cryptography. When randomness plays an important role, like in cryptography where random bit sequences guarantee certain levels of security, quantum mechanical phenomena allow new ways of generating random bit sequences. Such sequences have a lot of applications in the communication sector and beyond. They can be generated deterministically (e.g. by using polynomials, resulting in pseudo-random sequences) or in a non-deterministic way (e.g. by using physical noise sources like external devices or sensors, resulting in random sequences). Important characteristics of such binary sequences can be modelled by gap processes in conjunction with the probability theory. Recently, all-optical approaches have attracted a lot of research interest. In this work, an adaptation of the quantum key distribution (QKD) setup is utilized for generating randomised bit sequences. The simulation results show that all-optically generated sequences very well resemble the theoretically ideal probability density characteristic. Furthermore, m-sequences show very promising results as well as Gold sequences. Additionally, the level of burstiness, i. e. the distribution of one’s and zero’s throughout the sequence, is studied for the different sequences. The results lead to the finding that generator polynomials with concentrated non-zero coefficients lead to more bursty bit sequences.

Quantum mechanical phenomena are revolutionizing classical engineering fields such as signal processing or cryptography. When randomness plays an important role, like in cryptography where random bit sequences guarantee certain levels of security, quantum mechanical phenomena allow new ways of generating random bit sequences. Such sequences have a lot of applications in the communication sector, e.g., regarding data transmission, simulation, sensors or radars, and beyond. They can be generated deterministically (e.g., by using polynomials, resulting in pseudo-random sequences) or in a non-deterministic way (e.g., by using physical noise sources like external devices or sensors, resulting in random sequences). Important characteristics of such binary sequences can be modelled by gap processes in conjunction with the probability theory. Recently, all-optical approaches have attracted a lot of research interest. In this work, an adaptation of the quantum key distribution setup is utilized for generating randomised bit sequences. The simulation results show that all-optically generated sequences very well resemble the theoretically ideal probability density characteristic. Additionally, an experimental optical setup is developed that confirms the simulation results. Furthermore, m-sequences show very promising results as well as Gold sequences. Additionally, the level of burstiness, i.e., the distribution of ones and zeros throughout the sequence, is studied for the different sequences. The results enable the finding that generator polynomials with concentrated non-zero coefficients lead to more bursty bit sequences.

In recent years, the surge in capacity demands and cost-effectiveness have been beyond the ability of single-mode fiber (SMF) operating optical networks. In this work, the capacity crunch is dealt with by utilizing an optical multiple-input and multiple-output (MIMO) technology integrated with higher-order modulations (HOMs) as they lead to higher spectral efficiency. The low cost is achieved using intensity modulation / direct detection (IM/DD) system with a multi-mode fiber (MMF) transmission link. Contrary to an SMF channel, a highly dispersion-impaired MMF is equalized using a jointly designed pre- and post-equalization (PPE) filter, which consists of just two-taps pre-equalizer. A numerical optimization is defined to optimize the pre-and post-equalizer coefficients within the provided power and cost budgets. This work is the first investigation of a singular value decomposition (SVD) based joint-PPE scheme with a 1km long MMF link. The obtained results reveal that the signal-to-noise-ratio (SNR) gains of 5.48 dB and 10.57 dB at 10– 4 bit-error rate (BER) for PAM-2 and PAM-4 compared to post-equalization only (PE-only) respectively. From the results, the SVD-assisted joint-PPE yields benefit in the presence of an MMF channel.

In optical fiber communication, recent advances in multiple-input and multiple-output (MIMO) systems using space-division multiplexing have helped achieve higher spectral efficiency and data rates. Propagating higher-order modulation formats over MIMO systems further strengthens the capacity of the transmission link. In the optical-MIMO system, the dispersion impairments originating from a 1.4 km long multi-mode fiber (MMF) are mitigated using the proposed joint-transceiver equalization technique. A numerical convex optimization algorithm is used to compute and optimize the pre- and post-equalization (PPE) coefficients jointly restricted by cost and power budgets. The potential of the proposed joint-PPE technique is tested on an MMF link, which is severely degraded by dispersion compared to a single-mode fiber channel. From the experimental results, the average optical received power gain necessary to reach 10−4 bit-error rate is improved by nearly 2.5 dB using the joint-PPE compared to the post-equalization only based on the minimum mean-squared error principle. When the efficiency of the conventional zero-forcing (ZF) principle-based PPE and the joint-PPE is compared, the joint-PPE scheme outperforms the ZF-PPE by approximately 1.5 dB. The enhancement in the transmission quality is observed with experimentally measured eye diagrams using the joint-PPE scheme. Under the analyzed scenarios, computer simulation also confirms the hypothesis, which establishes the effectiveness of the proposed joint-transceiver equalization over the conventional ZF-PPE scheme. Moreover, the simulated performance benefits of the joint-PPE are evaluated using the singular value decomposition (SVD) technique. Improvement of ≈3.86 dB in the average optical received power gain required to reach 10−4 bit-error rate is witnessed with the PAM-4 format. Overall, the joint-transceiver equalization technique is proven to be beneficial in optical MIMO systems.

Dimensionality reduction is an important step for various applications where usage of the internet and multimedia systems is involved which requires huge bandwidth and storage space. This paper presents Big Bang-Big Crunch (BB-BC) optimization algorithm based two new approaches to feature selection for dimensionality reduction. In first approach, PCA is used to extract the features (eigenvectors) and defines feature set based on computation of knee point and BB-BC optimization algorithm, in turn selects an optimal subset from the predefined feature set. In the second approach, PCA is used only for feature extraction and BB-BC optimization algorithm is used for optimal feature selection from all extracted features. Olivetti Research Laboratory (ORL) face database has been used for performing the experiment and recognition rate is the parameter to be optimized for face recognition as an application area. The experimentation proves BB-BC as a powerful soft computing technique to solve such NP hard problems.

This work presents a novel simultaneous optical data transmission and sensing concept. For this combined system, neither additional components nor spectral segregation is required. In contrary to other combined systems, the complexity does not increase in the presented approach. The sensor system is a code-division multiplex (CDM)-wavelength-division multiplex (WDM) system that is able to interrogate thousands of serial fiber-Bragg gratings (FBGs) within a single optical fiber. Simultaneously, this fiber is also used as the data transmission medium. In the proposed system, the performance limitations due to the shared broadband light source are mitigated by using different post-equalization schemes. The proof of concept is verified using an experimental setup, which demonstrates the interrogation of 1000 sensors and concurrent data transmission at a bit rate of 1 Gbps using a 1.6 km FBG sensor network employing a unified broadband light source.

Multiple-input and multiple-output (MIMO) technology have attracted a lot of research due to the rising demands of higher capacity and data rates. To actively address these challenges in the area of optical fiber communication, the spatial division multiplexing techniques with an optical MIMO system by using multi-mode fibers are applied. While restraining the transmitter's complexity and allowing multi-level signaling, a linear pre- and post-equalization (PPE) is proposed for an optical MIMO system. A numerical optimization solver provides an aid to jointly optimize the proposed PPE scheme according to the maximum power constraint. In contrast to existing research, the joint-PPE scheme is implemented for a multi-mode fiber system, which is adversely affected by the modal dispersion. In the analyzed scenario, the experimental measurement results confirm that the joint-PPE scheme is advantageous with multi-mode fiber links. While using the proposed joint-PPE scheme, the required optical received power to reach a bit-error rate of 10(-3) is reduced by 3.8 % and 2.7 % in comparison to the zero-forcing and the minimum mean square error post equalizers respectively.

A joint pre- and post-equalization scheme is proposed for an optical intensity modulation and direct detection (IM/DD) system. At the transmitter, a linear feed-forward pre-equalizer with just two, three, or four filter taps is suggested to limit the transmitter's complexity and to allow the use of multi-level modulation. Finally, this concept is combined with a zero-forcing post-equalizer at the receiver. By utilizing numerical optimization to design the multi-level signals, the intersymbol-interference originating from the channel is mitigated pre-equalizer taps, a reduction of 3 % in received power compared to a conventional zero-forcing design is achieved. The equalization scheme is tailored for an optical IM/DD system. Therefore, the specific power constraints of such a setup are taken into account in the equalizer design process. In contrast to existing research, the approach is tested for a multi-mode fiber system, which is affected by increased inter-symbol interference due to modal dispersion. The simulation results show that by shifting a small portion of the equalization complexity to the transmitter side, the required optical power to reach a bit-error rate of 10(-3) is reduced by 7.3% for zero-forcing and 6.8% for minimum mean square error post-equalizers. the noise increase by the post-equalizer is reduced by 6.9 % when including the pre-equalizer with just two filter taps. Compared to an equalization scheme that solely relies on a zero-forcing post-equalizer, the suggested joint pre- and post-equalization scheme is able to improve the bit-error rate performance by an average of 7.15 %. A testbed experiment with a 250 m multi-mode fiber channel and a data rate of 2.5 Gbps operating at 1550 nm confirms these simulation results.

The multiple-input and multiple-output (MIMO) technology is a promising area of research to cope up with the demands of higher data rates and capacity. In the optical communication domain, the combination of space-division multiplexing (SDM) with higher-order modulation (HOM) formats over an optical MIMO system actively addresses these challenges. By allowing multi-level signaling with limited increment in the transmitter’s complexity, a jointly designed pre- and post-equalization (PPE) for an optical MIMO system with a multi-mode fiber (MMF) link is proposed. Cost-effectiveness of the system is incorporated by utilizing intensity modulation/direct detection (IM/DD) with HOM formats such as pulse-amplitude modulation (PAM) schemes. With the aid of a numerical optimization algorithm, the proposed joint-PPE filter coefficients are optimized with respect to the MMF channel and the transmit power constraint. In contrast to existing research on the single-mode fiber (SMF) based optical systems, the effectiveness of the proposed joint-PPE filter is analyzed on an MMF link, which is considerably degraded by the modal dispersion. In the analyzed experimental scenario, the proposed joint-PPE scheme confirms to be beneficial as compared to the post-equalization only (PE-only) in terms of bit-error rate (BER) performance. Furthermore, the required average received optical power to reach a BER 10−4 by the joint-PPE scheme is improved by 2 dB with comparison to the minimum mean-squared error (MMSE) PE-only.

In optical fiber communication, the concept of multiple-input and multiple-output (MIMO) transmission using multimode fiber has gained a lot of attention due to an enhanced fiber capacity. This paper outlines a joint pre- and post-equalization (PPE) scheme for an optical intensity modulation and direct detection MIMO system. For restraining the transmitter's complexity and allowing multi-level modulation for performance benefits, a simple few-tap linear feed-forward equalizer in conjunction to the zero-forcing based post-equalizer is proposed. Using a mathematical optimizer, the pre- and post-equalizers are jointly designed and optimized, which yield a performance gain of 19.95 % compared to the post-equalization only, with a constraint subjects to the maximum transmit power of the laser source. This work offers one of the first investigations regarding the benefit of joint-PPE schemes in an optical MIMO system with a multimode fiber channel, where the inter-symbol interference is assertive due to modal dispersion along with crosstalk. The usefulness of the joint-PPE scheme is tested over two distinct frequency-selective channels using computer simulations. In terms of the bit-error rate (BER) performance, the joint-PPE scheme outperforms the post-equalization only and provides a gain of approximately 2 dB at 10−3 BER.

In optical communication, the higher-order modulation (HOM) schemes have attracted a lot of attention as they provide higher data rates within a defined bandwidth. Due to shot noise, the received data is affected by different noise variances depending upon the received power levels. In such systems, an equidistant constellation is not always optimal. Therefore, a geometric constellation shaping (GCS) approach is proposed. The purpose of this contribution is to investigate the potential of GCS with pulse amplitude modulation (PAM) to improve the bit-error rate (BER) performance. Moreover, this work aims to identify the conditions, e.g. the constellation size, where the GCS enhances the performance of an intensity modulated and direct detected (IM/DD) system. The GCS is realized with the aid of nonlinear optimization. In the analyzed scenarios, the simulation results show that GCS is not beneficial in terms of the BER performance for low constellation sizes. In contrast, GCS for high constellation sizes can significantly improve the BER. The experimental measurement results suggest that GCS can be advantageous.