OSE Dissertation Defense by Ms. Hanieh Afkhamiardakani on Generation of Correlated Dual Frequency Combs with PM Fiber Lasers for High-Precision Metrology

Departmental News

Ms. Hanieh Afkhamiardakani

Posted: June 17, 2020

Date: Tuesday, July 7, 2020 

Time:  10:30 AM to 12:30 PM

Location:  Zoom at https://unm.zoom.us/j/91430911537

Committee Members:

Dr. Jean-Claude Diels, Physics and Astronomy (Committee Chair)
Dr. Ladan Arissian, Electrical and Computer Engineering
Dr. Matthias Lenzner, Physics and Astronomy
Dr. Wolfgang Rudolph​, Physics and Astronomy and Electrical and Computer Engineering
Dr. Arash Mafi, Physics and Astronomy


Intracavity Phase Interferometry (IPI) using two correlated, counter-propagating frequency combs (pulse trains) in mode-locked lasers has evolved into a powerful technique for high-precision metrology. In this method a physical parameter to be measured imparts a phase shift onto a pulse circulating in a laser cavity. Inside the laser cavity, that phase shift becomes a frequency shift (phase shift/round-trip time) applied to the whole frequency comb created by this pulse as it exits the cavity at each round-trip. This frequency shift is measured by interfering this comb with a reference comb created by a reference pulse circulating in the same mode-locked laser cavity. A phase sensitivity better than 10^(-8) radians allowed this method to successfully measure minuscule changes in flow velocity, electric field, magnetic field, rotation, acceleration, and displacements, using discrete element lasers. Although fiber lasers appear to be ideal for environment insensitive, robust, reliable and compact implementation of IPI, previous attempts have so far been unsuccessful. This is partly due to the fact that generating frequency combs in fiber lasers is a new field with hitherto unanticipated challenges. This thesis is a rst step in identifying and solving some of the basic problems. For instance, the large intensity in the core, coupled with the nonlinear index of glass, result in a cumulative nonlinear index on axis which dwarfs the signal to be measured. The large saturable gain changes in an unpredictable way the repetition rate of the laser impeding the creation of frequency combs with identical repetition rate. The huge amount of phase coupling between pulses crossing at the saturable absorber eliminates the small signal response (dead-band). The study and resolution of these hurdles culminates in a successful observation of a beat signal in a polarization maintaining mode-locked fiber laser operating with orthogonally polarized pulses.