M.Sc Thesis

M.Sc StudentSepton Tali
SubjectStable Laser Reference System for Spectral Characterization
of Narrow Linewidth QD-DFB Lasers
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Gad Eisenstein


Linewidth is a measure of the frequency stability of any kind of oscillator, and it is

a defining characteristic of coherent lasers. Narrow linewidth laser technology, particularly

for lasers operating at 1550nm wavelength, has progressed to the point where

highly stable sources are commercially available with linewidths on the order of 1-100

kHz. In order to achieve a higher level of stability, the laser must be augmented by an

external frequency stabilization system. An optical frequency comb is a laser source

whose spectrum consists of a series of discrete, equally spaced frequency lines. By

Locking one of the comb lines to a narrow linewidth laser serving as an optical reference,

the phase noise of the comb is reduced significantly and can be used for precision

frequency measurements. This form of a stabilized comb is also the most basic version

of an optical clock. This master thesis reports on the design and characterization of a

setup for an ultra-narrow linewidth laser. Using the Pound-Drever-Hall technique,

the system significantly reduces the linewidth of an input laser with an un-stabilized

linewidth of 5 kHz. The system utilizes a high-finesse Fabry-Perot cavity, which is

thermally isolated as a frequency reference to measure the time-varying frequency of

the input laser, and an electronic feedback loop working to correct the frequency error.

Testing has proven the Pound-Drever-Hall system to be highly stable and capable of

operating continuously for days. The ultra- narrow linewidth system was used as a reference frequency for the stabilization of an optical frequency comb, and the superior precision and stability of the combined system is exploited for the characterization of narrow linewidth Quantum Dot DFB lasers. Future work would include incorporating the system into a Rubidium based optical atomic clock, and experiments in broadcasting of high precision optical clock signals over fiber to long distance.