Nonlinear photonics with applications in lightwave communications

  • Umair Ahmed Korai Baloch

Student thesis: Doctoral Thesis


This doctoral dissertation investigates the use of nonlinear photonics in targeted Lightwave communication applications. Different highly nonlinear optical materials have been considered for the investigation of Lightwave communications data carriers, with a focus on the optical carrier pulsewidth. A state-of-the-art novel method has been developed to measure pico-second optical carrier pulses using highly nonlinear optical fiber. This method is based on the nonlinear optical loop mirror (NOLM), with consideration focused on the third order nonlinearity. Silicon is considered to be one of the most attractive materials for photonics integrated circuit technology (PIC) due to its compatibility with complementary metal oxide semiconductor (CMOS). As such, the method has been applied to the SOI platform Mach-Zehnder interferometer (MZI), also by considering the third order nonlinearity. In the NOLM approach, the picosecond optical data carrier pulsewidth is measured by using an optical power meter. Simulations for both the self-phase and cross-phase modulation schemes are carried out, and as expected, the cross phase modulation gives an increment in the sensitivity twice that of the self-phase modulation. Due to very high repetition rates of the order 10 GHz, the effect of counter propagating non-linear interactions in the NOLM are also considered in the theoretical evaluation. In the experimental validation, the pulses from an active fiber mode-locked laser at a repetition rate of 10 GHz were incrementally temporally dispersed using an SMF-28 fiber. The optical data carrier pulses over a range of 2-10 ps were successfully measured with a resolution of 0.25 ps. By extrapolating the theoretical evaluation and by selecting different physical parameters for the setup, the method was found to exhibit an extended range of 0.25 to 40 ps.;The concept described above is then extended to the investigation of nonlinear SOI devices using an MZI, thus miniaturizing the setup. In this investigation, the silicon waveguide has been simulated for self-phase and cross-phase modulation by solving the nonlinear Schrodinger equations using the split step method. Silicon has strong two photon absorption at telecommunication wavelengths, i.e. 1550 nm, and therefore all nonlinear losses (i.e. TPA and free carriers generated through TPA) are included in the split step simulations. The results obtained show that the on-chip nonlinear MZI (based on the SOI platform) can also be used for the measurement of optical data carrier pulse-widths of up to 10 ps. In the last part of this doctoral dissertation, a novel design for a temperature insensitive MZI is presented. Temperature dependence is one of the main challenges in the design of the SOI platform due to the large thermo-optic coefficient of its core material. A change in temperature can cause the device properties to deviate significantly, and can also alter the nonlinear properties of the device. Therefore, a design of an all-passive athermal MZI device based on the SOI platform has been developed and investigated. The MZI's temperature compensation is achieved by optimizing the relative length of the wire and subwavelength grating arms, and by tailoring the thermal response of the subwavelength structure. The simulation results of the athermal MZI design indicated that an overall temperature sensitivity of 7.5 pm/K could be achieved over a 100 nm spectral range near the 1550 nm region.
Date of Award28 Feb 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorIvan Glesk (Supervisor) & Vladimir Stankovic (Supervisor)

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