Optical Science and Engineering ETDs

Publication Date

Summer 7-7-2020


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 the laser cavity. Inside a 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 1e-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 dual frequency combs in fiber lasers is a new field with hitherto unanticipated challenges. This thesis is a first 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 (deadband). 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.

Degree Name

Optical Science and Engineering

Level of Degree


Department Name

Optical Science and Engineering

First Committee Member (Chair)

Jean-Claude M. Diels

Second Committee Member

Ladan Arissian

Third Committee Member

Wolfgang Rudolph

Fourth Committee Member

Arash Mafi

Fifth Committee Member

Matthias Lenzner


Metrology, Interferometry, Fiber laser, Mode-locking, Frequency comb, active laser sensor, Ultrashort pulse

Document Type