Silicon Photonic Interferometric Modulators PDF Download

Author: David Patel
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Languages : en
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Book Description
"In recent years, the amount of traffic within data centers has increased to a point where electrical interconnects are being replaced by optical interconnects and pluggable modules. Silicon photonics, which uses the existing CMOS fabrication capabilities to develop integrated photonics, offers the ability to make compact devices in high volume with relatively better yield. This makes it a highly desired platform to develop optical transceivers and components for modern data centers. As such, it has recently reached the production phase of the technology development cycle. This thesis studies several devices that are applicablein leading data centers. A detailed analysis and characterization of a silicon Michelson modulator with short 500 um phase shifters and a low VpiLpi of 0.72 V-cm under reverse bias is presented. The optical modulation of reverse biased p-n and forward biased p-i-n junctions is investigated. For reverse bias operation, it is demonstrated that bandwidth can be increased with lower impedance drivers and the driver impedance limits the bitrate achievable. Furthermore, forward bias operation with pre-emphasized signals is shown to have clean eye diagrams up to 40 Gbps. Energy consumption is estimated for all cases of studies and their trade-offs are explained.The work on modulators is further developed by studying series push-pull traveling wave Mach-Zehnder modulators. Measurements of electrodes is compared with simulation validating the methods of increasing impedance and microwave effective index with T-shaped electrodes. Moreover, designs with two and three level implants are compared and it is concluded with measurements that a two level doping design is as good as the design with three level implants, thus reducing the number of masks and processing steps required. Another variation of modulators is the dual-drive modulators. Here, the spacing between electrodes can lead to coupling, which results in different responses depending on whether the modulator is driven single-endedly or differentially. The electro-optic frequency response of a four-port traveling-wave dual-drive modulator with relatively weak coupling amongst the electrodes is measured. It is shown that the electro-optic frequency response of the Mach-Zehnder modulator can be predicted with a 2x2 cascaded matrix model if the Mach-Zehnder modulator is symmetric and differentially driven. In recent years, the increase in data transfers has demanded that more bits be transmitted and received in a given bandwidth. The design and characterization of a silicon-on-insulator traveling-wave multi-electrode Mach-Zehnder modulator is reported in this thesis. This 2-bit electro-optic digital-to-analog converter is formed by dividing a series push-pull Mach-Zehnder modulator into two segments, one for each bit, thus allowing for PAM-4 modulation without using a digital-to-analog converter. The device is operated at speeds up to 50 Gbaud and thus generating 100 Gbps on a single wavelength without signal processing at the transmitter or the receiver. The pre-forward error correction bit error rate is estimated to be lower than the hard-decision forward error correction threshold of 3.8e-3 over 1 km of standard single-mode fiber.Another component that is crucial in optical networks is the optical switch. The optical switch has numerous applications in protection and restoration as well as in certain modern data center architectures. A 4x4 fully non-blocking crossbar switch fabric based on interferometric thermal phase shifters is developed and reported in this thesis. Here, heating is achieved using resistive elements around the silicon waveguide. Switching times of 5 us and 36 mW power consumption in an individual switching element is measured. As a proof of concept, the quality in degradation of switching is demonstrated by routing an input signal to some of the outputs of the switch." --