An optical comb source based on a slab-coupled optical waveguide amplifier (SCOWA) is presented. The laser is
harmonically mode-locked at 10.287 GHz repetition rate and stabilized to an intra-cavity Fabry-Pérot etalon via Pound-
Drever-Hall locking. The Fabry-Pérot etalon serves as a reference for the optical frequency of the comb-lines and
suppresses the fiber cavity modes to allow only a single longitudinal mode-set to oscillate, generating a frequency comb
spaced by the repetition rate. The pulse-to-pulse timing jitter and energy fluctuations are < 2 fs and < 0.03%,
respectively (integrated from 1Hz to 100 MHz). Fundamental to this result is the incorporation of the SCOW amplifier
as the gain medium and the use of an ultra-low noise sapphire-loaded cavity oscillator to mode-lock the laser. The
SCOWA has higher saturation power than commercially available gain media, permitting higher intra-cavity power as
well as available power at the output, increasing the power of the photodetected RF tones which increases their signal-to-noise
ratio. A high visibility optical frequency comb is observed spanning ~3 nm (at -10 dB), with optical SNR > 60 dB
for a cavity with no dispersion compensation. Initial results of a dispersion compensated cavity are presented. A spectral
width of ~7.6 nm (-10 dB) was obtained for this case and the pulses can be compressed to near the transform limit at
A CW injection locked Coupled Opto-Electronic Oscillator (COEO) is presented with a 10.24 GHz spaced optical frequency comb output as well as a low noise RF output. A modified Pound-Drever-Hall scheme is employed to ensure long-term stability of the injection lock, feeding back into the cavity length to compensate for cavity resonance drifts relative to the injection seed frequency. Error signal comparison to an actively mode-locked injection locked laser is presented. High optical signal-to-noise ratio of ~35 dB is demonstrated with >20 comblines of useable bandwidth. The optical linewidth, in agreement with injection locking theory, reduces to that of the injection seed frequency, <5 kHz. Low amplitude and absolute phase noise are presented from the optical output of the laser system. The integrated pulse-to-pulse energy fluctuation was found to be reduced by up to a factor of two due to optical injection. Additional decreases were shown for varying injection powers.
This work discusses the development of a frequency chirped, low repetition rate, semiconductor based mode-locked
laser having reduced noise over previous demonstrations. Specifically, we present a major upgrade on the 100 MHz
harmonically mode-locked Theta (Θ) laser cavity design in the form of the introduction of an intra-cavity fiberized
Fabry-Perot etalon. The initial demonstration of the Theta cavity design offered improved energy per pulse and a linearly
chirped pulse output compared to conventional cavity designs. Nonetheless, it suffered from pulse-to-pulse timing and
energy noise. The noisy operation arises from the harmonic nature of the laser. To mitigate this effect we have inserted a
fiberized etalon within the laser cavity.
The intra-cavity etalon stores and inter-mixes the pulses of the harmonically mode-locked laser, as well as enforces
lasing on a single optical mode-set from the multiple interleaved sets supported by the mode-locked laser due to its
harmonic nature. This leads to the generation of a stable optical frequency comb with 100 MHz spacing and the
suppression of the RF super-mode noise spurs, which results in a reduction of the laser noise. Due to fiber length drift in
both the fiberized laser cavity and the fiberized etalon, a long-term stabilization scheme is necessary. An intra-cavity
Hansch - Couillaud scheme is employed. The laser outputs chirped pulses with 10 nm of bandwidth.
This work provides an in depth analysis of both the development of the Theta cavity with the intra-cavity etalon and
the performance of the developed laser system.
Fast and precise measurements of ultrafast optical waveforms are essential to the development of optical coherent
signal processing. In this paper, multi-heterodyne mixing of stabilized optical frequency combs is presented as a
simple technique for the measurement of ultrafast laser pulses and exotic arbitrary optical waveforms. This
technique takes advantage of both the broadband nature of the frequency comb and the narrow line-width of the
individual comb-lines to produce an array of radio-frequency beat-notes that share the characteristics of the optical
spectrum. Measurements of comb characteristics across THz of bandwidth are enabled by this method, while
maintaining the accuracy at the level of the individual comb-line width. Results show that both frequency
modulation and amplitude modulation combs can be measured using this scheme.
Harmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while
maintaining low optical linewidth via long cavity storage times. Continuous wave (CW) injection locking further
reduces linewidth and stabilizes the optical frequencies. The output can be stabilized long-term with the help of a
modified Pound-Drever-Hall feedback loop. Optical sidemode suppression of 36 dB has been shown, as well as RF
supermode noise suppression of 14 dB for longer than 1 hour. In addition to the injection locking of harmonically mode-locked
lasers requiring an external frequency source, recent work shows the viability of the injection locking technique
for regeneratively mode-locked lasers, or Coupled Opto-Electronic Oscillators (COEO).