Advanced Technologies For Next Generation Optical Transceivers In Long Haul Transport Links And Short Reach Interconnects

"The burgeoning capacity demand for both optical transport links over metro / long-haul distances (> 100km) and short reach optical interconnects (100m-20km) for inter- and intra-datacenter networking is driving the notion of a digital signal processing (DSP) based optical transceiver. In optical transport, flexible optical transceivers employ coherent detection and DSP to enable mitigating various fiber transmission impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD), Kerr nonlinearity, laser phase noise and frequency offset. In addition, these flexible transceivers need to be agile enough to adapt to the increasingly dynamic network traffic needs (e.g. varying capacity and reach requirements, dynamic wavelength assignments). On the short reach side, cheap and power efficient optics is a necessity for datacenter applications and hence intensity modulation / direct-detection (IM/DD) prevails over coherent detection. For such IM/DD transceivers, photonic integration is envisioned to play a significant role in reducing the cost along with DSP that potentially allows increasing the delivered bit rates with cheap electronics and reduced number of optical components (and consequently footprint).In the first part of the thesis, we propose and verify, both analytically and experimentally, a myriad of DSP algorithms suitable for implementation in flexible optical coherent transceivers for transport networks. The proposed DSP algorithms tackle impairments such as laser phase noise, frequency offset, polarization rotation, fiber Kerr nonlinearity and sampling frequency offset. For each of the proposed algorithms, we provide a performance comparison with the standard counterparts in the literature highlighting the advantages of our approaches together with the underlying tradeoffs. Next, we develop and experimentally verify a rigorously derived analytical model for performance evaluation of a flexible coherent optical front-end that can operate colorlessly in a wavelength division multiplexing (WDM) scenario, i.e. without the need for a WDM demultiplexing filter prior to the receiver. The accuracy of the developed model was proved by finding a close match between model predictions and experimental results. We finally show that the model can be used as a useful system design tool to predict the system performance at various operating scenarios.In the last part of the thesis, we propose a DSP algorithm to enable polarization division multiplexing (PDM) in IM/DD transceivers for short reach optical interconnects. This doubles the achievable bit rate with the same speed of the electronic components and with the same number of light sources by exploiting the two orthogonal polarization states per source. The proposed DSP algorithm is based on a multiple-input and multiple-output (MIMO) finite impulse response (FIR) filter that operates on the Stokes parameters of the received field, which can be obtained via a direct-detection receiver front-end, to invert the random rotations that occurred along the fiber. The proposed DSP was verified experimentally using an IM/DD transceiver that employs a single 1310 nm laser whose both polarizations were modulated by a packaged silicon photonic (SiP) intensity modulator. A record bit rate of 224 Gb/s was transmitted over 10 km with a BER below the forward-error-correcting (FEC) threshold." --