A high efficiency input/output coupler for small silicon photonic devices

Coupling light from an optical fibre to small optical waveguides is particularly problematic in semiconductors, since the refractive index of the silica fibre is very different from that of a semiconductor waveguide. There have been several published methods of achieving such coupling, but none are sufficiently efficient whilst being robust enough for commercial applications. In this paper experimental results of our approach called a Dual-Grating Assisted Directional Coupler, are presented. The principle of coupling by this novel method has been successfully demonstrated, and a coupling efficiency of 55% measured

Coexistence of multiuser entanglement distribution and classical light in optical fiber network with a semiconductor chip

Building communication links among multiple users in a scalable and robust way is a key objective in achieving large-scale quantum networks. In realistic scenario, noise from the coexisting classical light is inevitable and can ultimately disrupt the entanglement. The previous significant fully connected multiuser entanglement distribution experiments are conducted using dark fiber links and there is no explicit relation between the entanglement degradations induced by classical noise and its error rate. Here we fabricate a semiconductor chip with a high figure-of-merit modal overlap to directly generate broadband polarization entanglement. Our monolithic source maintains polarization entanglement fidelity above 96% for 42 nm bandwidth with a brightness of 1.2*10^7 Hz/mW. We perform a continuously working quantum entanglement distribution among three users coexisting with classical light. Under finite-key analysis, we establish secure keys and enable images encryption as well as quantum secret sharing between users. Our work paves the way for practical multiparty quantum communication with integrated photonic architecture compatible with real-world fiber optical communication network

Quasi-lossless data transmission with ultra-long Raman fibre laser based amplification

The project consists of an experimental and numerical modelling study of the applications of ultra-long Raman fibre laser (URFL) based amplification techniques for high-speed multi-wavelength optical communications systems. The research is focused in telecommunications C-band 40 Gb/s transmission data rates with direct and coherent detection. The optical transmission performance of URFL based systems in terms of optical noise, gain bandwidth and gain flatness for different system configurations is evaluated. Systems with different overall span lengths, transmission fibre types and data modulation formats are investigated. Performance is compared with conventional Erbium doped fibre amplifier based system to evaluate system configurations where URFL based amplification provide performance or commercial advantages

Advanced techniques for the improvement of optical transmission systems

This thesis presents the experimental investigation into two novel techniques which can be incorporated into current optical systems. These techniques have the capability to improve the performance of transmission and the recovery of the transmitted signal at the receiver. The experimental objectives are described and the results for each technique are presented in two sections: The first experimental section is on work related to Ultra-long Raman Fibre lasers (ULRFLs). The fibre lasers have become an important research topic in recent years due to the significant improvement they give over lumped Raman amplification and their potential use in the development of system with large bandwidths and very low losses. The experiments involved the use of ASK and DPSK modulation types over a distance of 240km and DPSK over a distance of 320km. These results are compared to the current state of-the-art and against other types of ultra-long transmission amplification techniques. The second technique investigated involves asymmetrical, or offset, filtering. This technique is important because it deals with the strong filtering regimes that are a part of optical systems and networks in modern high-speed communications. It allows the improvement of the received signal by offsetting the central frequency of a filter after the output of a Delay Line Interferometer (DLI), which induces significant improvement in BER and/or Qvalues at the receiver and therefore an increase in signal quality. The experimental results are then concluded against the objectives of the experimental work and potential future work discussed

Rare-earth ion doped chalcogenide waveguide amplifiers

Chalcogenide glass waveguide devices have received a great deal of attention worldwide in the last few years on account of their excellent properties and potential applications in mid-infrared (MIR) sensing and all-optical signal processing. Waveguide propagation losses, however, currently limit the potential for low power nonlinear optical processing, and the lack of suitable on chip integrated MIR sources is one of the major barriers to integrated optics based MIR sensing. One approach to overcome the losses is to employ rare-earth ion doped waveguides in which the optical gain can compensate the loss, in such a way that the conversion efficiency of nonlinear effects is increased significantly. For infrared applications, the long wavelengths potentially attainable from rare-earth ion transitions in chalcogenide hosts are unique amongst glass hosts. New rare-earth ion doped chalcogenide sources in the MIR range could benefit molecular sensing, medical laser surgery, defence etc. Despite these promising applications, until now, no one has succeeded in fabricating rare-earth ion doped chalcogenide amplifiers or lasers in planar devices. This work develops high quality erbium ion doped chalcogenide waveguides for amplifier and laser applications. Erbium ion doped As2S3 films were fabricated using co-thermal evaporation. Planar waveguides with 0.35 dB/cm propagation loss were patterned using photolithography and plasma etching on an erbium ion doped As2S3 film with an optimised erbium ion concentration of 0.45x1020 ions/cm3. The first demonstration of internal gain in an erbium ion doped As2S3 planar waveguide was performed using these waveguides. With different film deposition approaches, promising results on intrinsic lifetime of the Er3+ 4I13/2 state were achieved in both ErCl3 doped As2S3 films (2.6 ms) and radio frenquency sputtered Er3+:As2S3 films (2.1 ms), however, no waveguide was fabricated on these films due to film quality issues and photopumped water absorption issues. The low rare-earth ion solubility of As2S3 is considered the main factor limiting its performance as a host. Gallium-containing chalcogenide glasses are known to have good rare-earth ion solubility. Therefore, a new glass host material, the Ge-Ga-Se system, was investigated. Emission properties of the bulk glasses were studied as a function of erbium ion doping. A region between approximately 0.5 and 0.8 at% of Er3+ ion was shown to provide sufficient doping, good photoluminescence and adequate lifetime to envisage practical planar waveguide amplifier devices. Ridge waveguides based on high quality erbium ion doped Ge-Ga-Se films were patterned. Significant signal enhancement at 1540 nm was observed and 50 % erbium ion population inversion was obtained, in waveguides with Er3+ concentration of 1.5x1020 ion/cm3. To the Author's knowledge, this is the highest level of inversion ever demonstrated for erbium ions in a chalcogenide glass host and is an important step towards future devices operating at 1550 nm and on the MIR transitions of erbium ions in chalcogenide glass hosts. Photoinduced absorption loss caused by upconversion products in the waveguides is the remaining hurdle to achieving net gain. Further research is needed to find suitable compositions that possess high rare-earth ion solubility whilst avoiding the detrimental photoinduced losses

High capacity photonic integrated switching circuits

As the demand for high-capacity data transfer keeps increasing in high performance computing and in a broader range of system area networking environments; reconfiguring the strained networks at ever faster speeds with larger volumes of traffic has become a huge challenge. Formidable bottlenecks appear at the physical layer of these switched interconnects due to its energy consumption and footprint. The energy consumption of the highly sophisticated but increasingly unwieldy electronic switching systems is growing rapidly with line rate, and their designs are already being constrained by heat and power management issues. The routing of multi-Terabit/second data using optical techniques has been targeted by leading international industrial and academic research labs. So far the work has relied largely on discrete components which are bulky and incurconsiderable networking complexity. The integration of the most promising architectures is required in a way which fully leverages the advantages of photonic technologies. Photonic integration technologies offer the promise of low power consumption and reduced footprint. In particular, photonic integrated semiconductor optical amplifier (SOA) gate-based circuits have received much attention as a potential solution. SOA gates exhibit multi-terahertz bandwidths and can be switched from a high-gain state to a high-loss state within a nanosecond using low-voltage electronics. In addition, in contrast to the electronic switching systems, their energy consumption does not rise with line rate. This dissertation will discuss, through the use of different kind of materials and integration technologies, that photonic integrated SOA-based optoelectronic switches can be scalable in either connectivity or data capacity and are poised to become a key technology for very high-speed applications. In Chapter 2, the optical switching background with the drawbacks of optical switches using electronic cores is discussed. The current optical technologies for switching are reviewed with special attention given to the SOA-based switches. Chapter 3 discusses the first demonstrations using quantum dot (QD) material to develop scalable and compact switching matrices operating in the 1.55µm telecommunication window. In Chapter 4, the capacity limitations of scalable quantum well (QW) SOA-based multistage switches is assessed through experimental studies for the first time. In Chapter 5 theoretical analysis on the dependence of data integrity as ultrahigh line-rate and number of monolithically integrated SOA-stages increases is discussed. Chapter 6 presents some designs for the next generation of large scale photonic integrated interconnects. A 16x16 switch architecture is described from its blocking properties to the new miniaturized elements proposed. Finally, Chapter 7 presents several recommendations for future work, along with some concluding remark

Advances in Solid State Circuit Technologies

This book brings together contributions from experts in the fields to describe the current status of important topics in solid-state circuit technologies. It consists of 20 chapters which are grouped under the following categories: general information, circuits and devices, materials, and characterization techniques. These chapters have been written by renowned experts in the respective fields making this book valuable to the integrated circuits and materials science communities. It is intended for a diverse readership including electrical engineers and material scientists in the industry and academic institutions. Readers will be able to familiarize themselves with the latest technologies in the various fields