Ph.D Thesis

Ph.D StudentYadin Yoav
SubjectSpectrally Efficient Optical Communications Systems -
Design and Analysis
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Meir Orenstein
Full Thesis textFull thesis text - English Version


Fiber-optic communications are widely used for high data-rate digital transmission systems. Low fiber attenuation and the ability to multiplex and simultaneously amplify many channels over a single fiber enable the transmission of high data rates over long distances. Thus, optical systems are typically used for long and medium range communications. Research has also focused on enabling cost-effective optical solutions for short-reach applications, including board-to-board, chip-to-chip, and ultimately intra-chip optical interconnects.

Modern wavelength division multiplexing optical communications systems utilize most of the available amplifier bandwidth. However, these systems use simple on-off-keying modulation, which has relatively poor spectral efficiency. In order to further increase the system capacities, advanced modulation schemes which offer enhanced spectral efficiency are required.

Increased spectral efficiency can be achieved by modulating the phase of the electromagnetic field as well as its amplitude. Differential phase shift keying has attracted interest recently due to its enhanced receiver sensitivity and tolerance to fiber nonlinearities. The performance analysis of optical phase modulated systems is not straightforward. Due to nonlinear effects, the phase of the transmitted signal is distorted during propagation. The combination of nonlinearities and amplifier noise introduces phase noise, limiting the performance of phase-modulated systems.

In this work we analyze the noise characteristics of phase-modulated fiber-optic transmission systems and their impact on system performance. The theoretical analysis is verified using Monte-Carlo simulations, and used to compare different modulation schemes. The insights gained from this analysis are used to propose and analyze new modulation and demodulation techniques.

Optical solutions have significant advantages for short-reach interconnections applications due to the high data rates, low loss and low crosstalk which characterize optical transmission systems. Long-haul fiber-optic solutions are not applicable for optical interconnections due to the high cost of the components. Therefore, a new approach must be developed, enabling high-speed transmission over short distances without the need for costly components.

The large data rates required for optical interconnects, combined with the limited bandwidth of optical components, prohibit the use of a single physical channel. Parallel transmission is needed to achieve the required data rates while keeping the per-channel data rates at an acceptable level.

In this work we propose a new approach for optical interconnects. Parallel transmission of several channels is obtained by exploiting the modal diversity of multimode waveguides, thus eliminating the need to physically route several waveguides. Several variants of this approach, using different modulation schemes, are presented, analyzed, and compared.