Performance analysis of a multi-format compatible all-optical data access method for satellite backbone-networks

As the bit rate of one wavelength channel and the number of channels keep increasing in the telecommunication networks thanks to the advancement of optical transmission technologies, switching is experiencing the transition from the electrical domain to the optical domain. All-optical signal processing, including wavelength conversion, optical logic gates and signal regeneration, etc, is one of the most important enabling technolgies to realize optical switching, including optical circuit switching, optical burst switching and optical packet switching. Semiconductor optical ampli??ers (SOAs) are very promising in all-optical signal processing because they are compact, easy to manufacture and power e??cient. It is therefore very important to develop numerical models for the SOAs to understand their behaviour in di??erent system con??gurations, especially when the interacting pulse duration becomes shorter and shorter with increasing bit rate, where several e??ects that are neglected in previous models have to be accounted for. To investigate high-speed SOA-based all-optical signal processing systems, in this thesis we develop a comprehensive model, which includes both inter- and intra-band carrier dynamics, gain dispersion and group velocity dispersion, in this thesis. Polarization dependent e??ects can also be taken into account through introducing an imbalance factor f. Finite-di??erence beam propagation method is employed to solve the numerical model. Mode-locking lasers o??er a lot of applications in all-optical signal processing systems. In this thesis we investigate a novel mode-locked laser based on nonlinear polarization rotation in an SOA. The pulse narrowing process is demonstrated numerically, achieving good agreement with our experimental results. The pulse performance is largely determined by the ultrafast SOA gain dynamics and the cavity dispersion. The laser can produce a pulse train of sub-picosecond pulse width at a repetition rate of 28 GHz, which is limited by the carrier lifetime, for a moderate SOA current level. For higher currents instabilities occur in the laser. vi One of the drawbacks of the SOA-based devices is the relatively long gain recovery time which results in strong pattern e??ects for high bit rate operaion. In this thesis we extensively investigate a very high bit rate wavelength converter based on a single SOA and an optical bandpass ??lter. The enhancement in operation speed is based on ??ltering an amplitude- and phase-modulated signal. We study the underlying working principle and perform detailed analysis of the high-speed wavelength converter, which leads to optimization rules for high-speed SOA-based wavelength conversion. Moreover, both inverted and non-inverted wavelength conversion at much higher bit rate(1 T b/s), is also predicted. Furthermore, genetic algorithm is introduced in the optimization of the transfer function of the OBF following the SOA. Through optimization, eye opening of more than 33 dB is shown for non-inverted wavelength conversion. The optimized ??lter can be experimentally implemented through a combination of asymmetric Mach-Zehnder interferometer and a Gaussian ??lter. Enlightened by the working principle of the wavelength converter, we proposed and demonstrated experimentally a novel optical logic gate with a very simple structure: an SOA followed by an OBF. This logic gate can realize AND, OR and XOR gate functions based on the same setup but with di??erent operation conditions. This novel device can be integrated.

Underwater wireless optical communication (UWOC) systems have been identified as a suitable replacement technology with high data rates over relatively medium transmission ranges for underwater communication. In the research, we propose a new optical hybrid modulation format for carrying the letters over underwater wireless optical communication (UWOC) system. This hybrid modulation format combines pulse position modulation (PPM) with digital pulse interval modulation (DPIM) to increase the transporting speed. The proposed UWOC system is experimentally investigated in the laboratory over a clean and turbulent water channel. The message was electrically modulated in the transmitter with PPM-DPIM format and then applied to a laser diode. The laser diode emitted light at a wavelength of 650 nm with a power of 60 mW. At the receiver, the photodiode, with its amplifier circuits, sends the received signal to the microprocessor to restore the origin message. The results showed that the received power and signal-to-noise ratio (SNR) decreased with elongating the transmission distance. In addition, the attenuation is raised with increasing distance. The bubbles source is also situated at distances of 25 cm, 50 cm, and 75 cm from the transmitter in turbulent waters. The results showed that locating the bubble source decreases the system's performance. The best results were obtained when the bubble source was 75 cm away from the transmitter. Finally, the hybrid modulation formats (PPM-DPIM) can increase the speed of letter transmission, reduce the bit error rate (BER), and minimize the effect of scattering and attenuation in water channels.

Software-defined radio (SDR) is an emerging technology that offers various advantages over conventional radio designs. The SDR approach uses a common hardware platform, programmed by software modules and firmware, to support many communications standards and operating frequencies. The technology is being promoted by the US Department of Defense to replace tens of thousands of single-protocol, single-purpose radios with a common platform. Military and public safety organisations worldwide are also considering this technology to solve interoperability problems enabling, for example, police and firefighters to easily communicate in the field. In addition, the commercial wireless industry views SDR as a means of reducing development cost and time to market. To fully realize SDR’s promise of an all-encompassing communications device capable of transmitting and receiving over a very wide frequency range requires special attention to the radio frequency (RF) transceiver. Although it is relatively easy to use conventional electronics to build SDRs operating at up to 6GHz, it is increasingly difficult to do so at higher operating frequencies. It needs a hardware platform capable of operating up to about 60GHz to take full advantage of the SDR concept. Ideally, the SDR hardware platform has a continuouslytunable source to act as a local oscillator. It should be possible to modulate this source in any format, perform signal conditioning, and distribute the signal: either by wireless transmission or over an optical network. The prospect of using conventional electronics to develop a commercially-viable source with these properties is limited, so it may be necessary to find another approach. Optical technology can emulate many of the functions normally associated with RF reception and transmission. For example, it is possible to generate microwave signals optically over a very large frequency range—from MHz to THz—using heterodyne techniques such as optical injection locking, optical phaselocked loops, and nonlinear up-conversion. The electrical RF signal is generated by shining two optical inputs, separated by the desired microwave frequency, on to a square-law photodetector that acts as a mixer and generates their beat frequency. In general, when no phase or frequency control is applied, the phase noise of the microwave signal is approximately equal to the sum of the optical linewidths. The key to reducing this typicallyMHz linewidth down to values that are more practical for a communications system is to ensure that the phases of the optical signals are highly correlated. If they are, a very narrow RF linewidth can be achieved, even from large-linewidth optical sources. A carrier is of limited use in a communication system without some form of encoded information. A laser source can be modulated by inserting a baseband optical modulator in the optical path, or by other means. The modulation formats are varied and may act on the frequency, amplitude, or phase of the signal. In general, the bandwidth of the modulator/demodulator is dictated by the format of the protocol or the radio-spectrum channel allocation and is relatively modest, since the high-frequency carrier is already optically generated. This means that digital demodulation can be done directly by the computer, after optical down-conversion, to make it easier to interface with the SDR software. Both the receiver and transmitter need RF filtering for signal conditioning. Techniques for electrical filtering in the optical domain have been examined extensively, but the all-optical microwave filters proposed to date are primarily based on incoherent manipulation of optical carriers with only positive taps. This approach can only create low-pass filters. Many applications, including SDR systems, need bandpass and flat-top filters as well. To overcome this limitation, Yao et. al. recently reported a way to build an all-optical microwave bandpass filter with a simple structure.

The approaches of inexpensive and nanostructured metal oxide semiconductors are widely used for gas sensing. Among them, Tungsten Oxide (WO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> ) has attracted a lot of attentions due to its high sensitivity, structural simplicity, low cost production and high compatibility with nano-fabrication. However, thin film based planar WO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> has a limitation to enhance the sensitivity due to lower surface to volume ratio. To find improvements in sensor sensitivity and response time in terms of cone geometries and to determine optimal driving temperature for ethane (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) gas sensor, hereby this paper reports, for the first time, the nanocone configured WO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> array combined with integration of low powered in-plane microheater.

Electrostatic out-of-plane microactuators have been widely used in applications of variable capacitors, optical attenuators, optical switches and scanning displays due to their small size, low cost, simple and diverse structure, low power consumption and high compatibility with semiconductor process. The large out-of-plane displacement of the microactuator with high reliability is preferred in order to increase the tuning range, tunability and the display size. However, the “pull-in” instability associated with conventional attractive-force electrostatic microactuators significantly limits the out-of-plane displacement and lowers the operation stability. A repulsive-force microactuator has been previously developed which can achieve large out-of-plane rotation and does not suffer from the “pull-in” instability. However, a larger rotation angle of the repulsive-force actuator is highly desired in order to improve its performance in the applications such as increasing the tunability and the scanning angle. In this thesis two novel repulsive-force actuators, i.e., two-row interdigitating-finger and two-width-finger (TWF) actuators are developed which output much larger out-of-plane rotation than the previous repulsive-force actuator without suffering from the “pull-in” instability. The mathematical models are established for both actuators using a hybrid approach. The actuators require only two thin layers and are suitable for surface micromachining process. The measured results show that the two microactuators can achieve rotation angles of 11.5° and 7.5° at 150 V respectively. The improvements are 100% and 35% in comparison to the previous repulsive-force actuator with the same size, stiffness and driving voltage. A 2D scanning micromirror has been developed and fabricated based on the two-row-finger (TRF) actuator. Experimental results show the micromirror has larger rotation angle and faster response speed than those of the micromirror driven by the previous repulsive-force microactuator. The vector scanning display based on the micromirror is demonstrated. An advanced display approach is developed to generate displays with less distortion and higher refreshing rate compared to the previous generic display approach. The automotive Head-up Display (HUD) based on the micromirror and advanced display approach has been constructed for both real and virtual image configurations, which has advantages of small size, low cost, large viewing angle and good visibility over those HUDs in the market.

Orthogonal frequency division multiplexing (OFDM) technology is presented for use in free-space optical (FSO) communications accompanied by the spatial diversity reception. Using quadrature phase shift keying (QPSK) modulation formats, the OFDM signals show robustness to support high spectral efficiency and compatibility with the spatial diversity reception to improve receiver sensitivity. Compared with the single-carrier QPSK signal, the OFDM-QPSK signal with 64 sub-carriers can reduce the BER from 2.87 × 10−3 to 2.98 × 10−4 at the SNR of 6 dB. Using a two-aperture spatial diversity reception with OFDM, the BER can be reduced from 2.45 × 10−3 of a single receiver to 6.10 × 10−4 under moderate turbulence conditions. Under strong turbulence, the BER of the single receiver is 2.14 × 10−2. It can be improved to 1.16 × 10−3 by using four-aperture receivers, and even 6.87 × 10−4 by using six-aperture receivers. The optimized aperture number should be selected according to channel conditions.

We focus on the design of the logical layer on an optical infrastructure for three different architectures: fixed grid WDM with fixed-rate multilevel modulation (WDM-FRMF), fixed grid WDM with time-domain hybrid modulation formats (WDM-TDHFM) and flexible grid (FG). A fairly detailed physical layer modeling is considered in the network design algorithms. Simulations are performed on a 20 nodes network with varying traffic loads. Besides comparing the two paradigms of flexible and fixed grid networks, including both pure and hybrid modulation formats, in terms of their spectral efficiency and number of blocked requests, we show the importance of integrating a detailed physical layer modeling in the network design phase. We mostly focus on the investigation of the impact of changing physical layer design parameters such as fiber type and span length on network level performance.

Capacitive transducers are widely used in fundamental physics experiments, seismology, Earth or planetary observations, and space scientific and technical applications because of their high precision, simple structure, and compatibility with various measurements. However, in real applications, there is a trade-off between their resolution and dynamic range. Therefore, this paper is aimed at enlarging the dynamic range while ensuring high resolution. In this paper, a noise analysis of a capacitive transducer is presented, which shows that the amplitude noise of the carrier wave is the main limiting factor. Hence, a new method of generating a carrier wave with lower-amplitude noise is proposed in the paper. Based on the experimental verification, it is found that the carrier wave produced through the new method performed significantly better than the typical digital carrier wave when they were compared in the same sensing circuit. With the carrier wave produced through the new method, the dynamic range of the capacitive transducer can reach 120.7 dB, which is 18.3 dB greater than for the typical direct digital synthesis (DDS) method. In addition, the resolution of the carrier wave is mainly limited by the voltage reference components.

Hybrid improper ferroelectricity can effectively avoid the intrinsic chemical incompatibility of electronic mechanism for multiferroics. Perovskite superlattices, as theoretically proposed hybrid improper ferroelectrics with simple structure and high technological compatibility, are conducive to device integration and miniaturization, but the experimental realization remains elusive. Here, we report a strain-driven oxygen octahedral distortion strategy for hybrid improper ferroelectricity in La2NiMnO6/La2CoMnO6 double-perovskite superlattices. The epitaxial growth mode with mixed crystalline orientations maintains a large strain transfer distance more than 90 nm in the superlattice films with lattice mismatch less than 1%. Such epitaxial strain permits sustainable long-range modulation of oxygen octahedral rotation and tilting, thereby inducing and regulating hybrid improper ferroelectricity. A robust room-temperature ferroelectricity with remnant polarization of ~ 0.16 μC cm−2 and piezoelectric coefficient of 2.0 pm V−1 is obtained, and the density functional theory calculations and Landau-Ginsburg-Devonshire theory reveal the constitutive correlations between ferroelectricity, octahedral distortions, and strain. This work addresses the gap in experimental studies of hybrid improper ferroelectricity for perovskite superlattices and provides a promising research platform and idea for designing and exploring hybrid improper ferroelectricity.

Novel optical orthogonally modulation scheme for superimposing DPSK signals on dark RZ signals

A new Dynamic Bit Loading (DBL) scheme with the Orthogonal Generalized Frequency Division Multiplexing (OGFDM) is, for the first time, proposed, discussed and assessed. The key concept of this hybrid modulation format depends substantially on the adaptive distribution of the bit stream to be more compatible with the gained capacity of the realistic channel state. Due to the negative impact of employing the fixed schemes of digital modulation on the performance of the conventional telecommunications systems, the influence of using the multi-level modulation system is investigated for the future applications of mobile communications. Utilising the DBL in the physical layer (PHY), a flexible range of modulation formats can be optimally assigned for each applied frequency sub-carrier in accordance with wireless channel circumstances. In addition, depending on the supportive features of the proposed modulation system, the performance in terms of channel capacity can be maximised at the acceptable limit of the Bit Error Rate (BER). As such, an extra enhancement can be achieved in the spectrum efficiency (SE) of the adaptively modulated wireless signal. Thus, an adjustable boost of the transmission range of used modulation formats can be reached with the introduced adaptation system. The performance of the DBL system through a wireless mobile channel under the Additive White Gaussian Noise (AWGN) is evaluated according to a various level of the Signal to Noise Ratio (SNR). Ultimately, regarding the numerical simulation, a MATLAB code is employed to simulate the performance (channel capacity & BER) of the proposed DBL that is fundamentally accommodated by the recent candidate waveform of future mobile technology (OGFDM).

The operational conditions of hydrogen networks in practical refineries commonly fluctuate due to variation of feed properties, loss of catalyst activity, change of market demand, seasonal shift, and improvement of processing technology as well. These fluctuations could affect the operations of the hydrogen networks, which are usually optimized on the basis of fixed operational conditions in practice. In this work, a flexible design method of a multiperiod hydrogen network is proposed. It features the flexible design of multiperiod hydrogen network by considering discrete operational scenarios in multiple periods and possible fluctuation of each operational scenario. The optimal design of the multiperiod hydrogen network with simple structure and low total annual costs can be obtained by the proposed method. Moreover, the bottlenecks restricting the flexibility of each subperiod can also be identified and eliminated. In addition, the proposed method can be readily implemented. A multiperiod hydrogen syste...

The dynamic back-action caused by electromagnetic forces (radiation pressure) in optical and microwave cavities is of growing interest. Back-action cooling, for example, is being pursued as a means of achieving the quantum ground state of macroscopic mechanical oscillators. Work in the optical domain has revolved around millimetre- or micrometre-scale structures using the radiation pressure force. By comparison, in microwave devices, low-loss superconducting structures have been used for gradient-force-mediated coupling to a nanomechanical oscillator of picogram mass. Here we describe measurements of an optical system consisting of a pair of specially patterned nanoscale beams in which optical and mechanical energies are simultaneously localized to a cubic-micron-scale volume, and for which large per-photon optical gradient forces are realized. The resulting scale of the per-photon force and the mass of the structure enable the exploration of cavity optomechanical regimes in which, for example, the mechanical rigidity of the structure is dominantly provided by the internal light field itself. In addition to precision measurement and sensitive force detection, nano-optomechanics may find application in reconfigurable and tunable photonic systems, light-based radio-frequency communication and the generation of giant optical nonlinearities for wavelength conversion and optical buffering.

A simple structure is proposed to generate different modulation formats using a single electroabsorption modulator (EAM). The configuration is based on a Sagnac loop containing two polarization controllers and an EAM which modulates the clockwise and counterclockwise propagating waves inside the Sagnac loop. Measured results demonstrate switchable single-sideband suppression for both reflected and transmitted signals. The second-order harmonic suppression and carrier suppressed modulation are also achieved. A simple analysis explains most of the observed effects.

The semiconductor optical amplifier (SOA) has obvious advantages in all-optical signal processing, because of the simple structure, strong non-linearity, and easy integration. A variety of all-optical signal processing functions, such as all-optical wavelength conversion, all-optical logic gates and all-optical sampling, can be completed by SOA. So the SOA has been widespread concerned in the field of all-optical signal processing. Recently, the polarization rotation effect of SOA is receiving considerable interest, and many researchers have launched numerous research work utilizing this effect. In this paper, a new all-optical flip-flop structure using polarization switch (PSW) based on polarization rotation effect of SOA is presented.