A novel optoelectronic switch array for communication network

The advancement of communication technology and growth of internet traffic have continuously driven the fast evolution of networks. Compared to the traditional optoelectronic switch, all-optical switch provides high throughput, rich routing functionalities, and excellent flexibility for rapid signal exchange in fiber optical network. Among various all-optical switches, thermal actuated ring switch provides the advantages of high accuracy, easy actuation, and reasonable switching speed. However, when scale up, thermal ring switch may encounter issues related to fabrication error, non-accurate wavelength response, and large terminal numbers in the control circuit. Planar-lightwave-circuit switch (PLC-SW), employing thermo-optic (TO) effect of silica glass for light switch, is a very promising technique for communication applications because of low insertion loss, high extinction ratio, long-term stability, and high reliability. There have been many matrix switches designed based on the TO effect with low-loss, polarization insensitive operation, and good fabrication repeatability. For example, 8×8 matrix switches were fabricated by using a single Mach- Zehnder (MZ) switching unit and demonstrated well performance in transmission systems, so as an 8×8 matrix switch and a 16×16 matrix switch by the similar MZ switching unit. 32×four-channel client reconfigurable optical add/drop multiplexer on planar lightwave circuit. However, when scaled up, thermal ring switch may encounter issues related to large terminal numbers in the control circuit, fabrication error and non-accurate wavelength response. For example, if conventional driving circuits are employed for a 16×28 or even larger switch array, 448 or more terminals will be required for control. Such a large number of terminals would complicate the module structure and occupy a large area. On the other hand, when a DC-current is applied for balancing wavelength offset from fabrication error, the input power will result in a temperature elevation of the neighboring switches, thus changes the related refractive indexes and therefore deviate wavelengths. To solve the aforementioned issues, this chapter proposes a ring resonator with silicon nitride as the core layer and silicon dioxide as the cladding layer was designed and fabricated on silicon substrate, a novel architecture of high selection speed three dimensional (3D) data registration for driving large-array optoelectronic packet switches. The 3D driving architecture can successfully reduce the total numbers of control pads into 31 for 448 switches as well as the scanning time up to 67 % reduction with a higher signal rising speed and smaller circuit area. All the sub-circuits, including power control, digital I/O, analog-to-digital converter, power drivers were integrated into a single IC. On the other hand, instead of DC current control, wavelength lock is realized by amplitude and frequency modulated heating pulses for stabilization of temperature and fine-tune of wavelength from fabrication imperfection and environment fluctuation. This planar-lightwave-circuit has been designed, fabricated, and characterized. It is demonstrated not only the functionality in optical packet switches but also the consistency between simulation and experiment results. In this research, we design the tuneable micro ring resonators and propose the employment of an integrated ASIC system CMOS technology control circuit to compensate the fabrication error and tune as well as lock the wavelength in a thermalactuated ring-type optical switch through a frequency modulation scheme. The use of a standard and commercial CMOS technology for designing micro resonators entails a set of limitations, such as layer thicknesses, and available materials in an inalterable process sequence. From the MEMS design point of view, those restrictions will limit the electrical properties of fabricated micro-resonators. On the other hand, MEMS integration into a CMOS technology presents unique advantages, like reduction of the parasitic capacitance due to the possibility to monolithically integrate the circuitry, in addition to an expected reduction of the overall production costs. Additional functionalities can also be added in this circuit by tailoring externally the roundtrip loss or coupling constants of the ring. The design concept can be easily scaled up for large array optical switch system without much change in the terminal numbers thanks to the three dimensional hierarchy of control circuit design, which effectively reduces the terminal numbers into the cubic root of the total control unit numbers. The integrated circuit has been designed, simulated, as well as fabricated, and demonstrated a decent performance with Free Spectral Range (FSR) equal to 1.5nm at 1534 nm and very accurate wavelength modulation to 0.3 nm within 0.01 nm fluctuation for thermal actuated ring type optoelectronic switch.