Monolithic semiconductor passively mode locked lasers (MLL) are very attractive components for many applications
including high bit rate telecommunications, microwave photonics and instrumentation. Owing to the three dimensional
confinement of the charge carriers, quantum dot based mode-locked lasers have been the subject of intense investigations
because of their improved performance compared to conventional material systems. Indeed, the inhomogeneous gain
broadening and the ultrafast absorption recovery dynamics are an asset for short pulse generation. Moreover, the weak
coupling of amplified spontaneous emission with the guided modes plus low loss waveguide leads to low timing jitter.
Our work concentrates on InAs quantum dash nanostructures grown on InP substrate, intended for applications in the
1.55 μm telecom window. InAs/InP quantum dash based lasers, in particular, have demonstrated efficient mode locking
in single section Fabry-Perot configurations. The flat optical spectrum of about 12 nm, combined with the narrow RF
beat note linewidth of about 10 kHz make them a promising technology for optical frequency comb generation.
Coherence between spectral modes was assessed by means of spectral phase measurements. The parabolic spectral phase
profile indicates that short pulses can be obtained provided the intracavity dispersion can be compensated by inserting a
single mode fiber.
The effect of controlled optical feedback has been investigated for InAs/InP laser structures operating in the 1.55
μm fiber window. Mode locked lasers in particular show extremely small phase noise when subjected to optical
feedback, implying a very low timing jitter which is of interest for many applications.
Monolithic semiconductor mode-locked lasers (MLLs) are rising considerable interest for such diverse applications as
very high speed optical time division multiplexing sources (40-160 GHz), all-optical signal processing, and low noise
sampling for signal monitoring of optical networks.
In a large number of these applications, MLLs may be subjected to optical feedback generated by unwanted reflections
in optical systems which may greatly degrade laser performance. A number of experimental studies have been performed
to evaluate the sensitivity of MLLs to optical feedback showing an increase of phase noise [1-5]. Quantum-dash (Qdash)
based Fabry Perot lasers have been shown to exhibit an improved tolerance to feedback [6].
In this work, optical feedback tolerance is investigated for a monolithic quantum-dash-based passive mode-locked laser
emitting at 1.58 μm. The two-section device generates ~5 ps pulses at a repetition rate of 17 GHz. The onset of the
coherence collapse (CC) regime is experimentally determined by measuring the broadening of the longitudinal modes in
the optical spectrum. Depending on bias condition, the CC regime is reached for values of feedback ranging from -35 dB
to -29 dB at which emitted pulses were slighly broadened. The radio-frequency (RF) linewidth was simultaneously
assessed and a drastic reduction of the RF linewidth with increasing feedback strength is evidenced. This indicates a
reduction of the phase noise, thus implying a low "high frequency" timing jitter. We in particular observed an RF
linewidth narrowing down to a value of less than 1 kHz under optical feedback.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.