Feedback control is used to maintain Mach-Zehnder modulators at a desired bias point,

since heating and aging effects in its electro-optic materials cause a drift in its transfer function

over time. Considering that the desired bias point in the MZM transfer curve varies among

different applications, the control method should have an adjustable setpoint. The proposed

method seeks to achieve this with the minimum number of components possible.

SIMULINK models were used to obtain a better understanding of MZM biasing. Then,

after comparing available commercial products and a literature review, it was decided to apply

a known technique whereby a low-frequency dither signal is applied to the MZM DC input,

the output of the MZM is measured and a PID controller adjusts the MZM DC voltage to

maintain a constant ratio of the dither tone’s 2nd harmonic and fundamental. This method is

independent of optical power and allows the bias to be set to any point in the transfer curve.

To eliminate the need for standalone filters for each frequency and an additional IC for

obtaining the power ratio, digital filtering, processing and PID control are all done within a

microcontroller. A prototype board was built and the bias control measurements are presented.

The application of this method to Si MZM is also briefly discussed

Data centers today account for about 2.5 % of the total electricity usage in the United States. The portion of that power that is consumed by the internal network is increasing dramatically, as server-to-server traffic grows over 23 % every year. As aresult, there is great demand for scalable power-efficient intra data center (IDC) optical communication links. IDC links today are based on intensity-modulation direct-detection modulation formats (IMDD). Thus far, the scaling of IMDD links has been achieved by increasing the number of signal amplitude levels, by moving to higher baud rates, and by adding multiple wavelengths or fibers. However, each of these scaling paths is severely constrained. Whereas IMDD systems only utilize the intensity of signal, coherent detection (CD) also leverages the two polarizations and two quadratures of the fiber optic channel, and thus is more scalable. CD also improves sensitivity by up to 20 dB by mixing the received signal with a strong local oscillator. CD has been employed in long-haul links for many years, yet these systems rely on power-hungry high-speed analog-to-digital converters (ADC) and digital signal processing (DSP) and thus may be unsuitable for IDC links. A compelling alternative to DSP-based CD is analog coherent detection (ACD), in which polarization demultiplexing, carrier recovery, and phase demodulation are performed using analog circuits. This work focuses on the co-design of analog circuits and opto-electric devices that enable low-power ACD-based IDC links. First, a discussion of a proposed next-generation ACD IDC link architecture is outlined as motivation for the low-power circuit designs. Three monolithic 50 Gb/s opto-electric receiver topologies in SiGe BiCMOS technology are analyzed and compared. Then, a 100 Gb/s QPSK hybrid receiver in 45 nm CMOS is described. The co-design of a driver 56 Gb/s and traveling-wave Mach-Zehnder modulator (TW-MZM) is also presented. Finally, the thesis describes a TW-MZM equalization technique based on a tunable termination mismatch.