This work focuses on the established self-homodyne coherent receiver (SHCR) method, which is enabled by recent advancements in chip-based coherent receivers. The accuracy of the SHCR method strongly depends on the fiber delay employed. This effect, critical when characterizing narrow-linewidth lasers, is not documented to our knowledge. We present a comprehensive study of this dependence, yielding an optimal fiber delay that maximizes signal-to-noise ratio. The results are validated by comparison with a commercial frequency-noise analyzer, which shows a comparable accuracy between both methods.
Narrow-linewidth lasers are building blocks of coherent communication systems, as lower linewidths enable higherorder modulation formats with lower bit-error rates. For this purpose, diode lasers are in high demand due to their low power consumption, compactness, and potential for mass production. In field-testing scenarios, their output is coupled to a fiber, making them susceptible to external optical feedback (EOF), which is notoriously detrimental to their stability. This challenge is traditionally combated by using, for example, angled output waveguides and optical isolators. The approach reported in this work makes use of EOF in a new way, to reduce and stabilize the laser linewidth. Whereas research in this field has focused on EOF applied to only one side of the laser cavity, this work gives a generalization to the case of feedback on both sides. It is implemented using photonic components available via generic foundry platforms, thus creating a path towards devices with high technology-readiness level. It is numerically observed that the double-feedback case can lead to improved performance with respect to the single-feedback case. In particular, by correctly tuning the phase of the feedback from both sides, a broad region of stability is discovered. This work paves the way towards low-cost, integrated and stable narrow-linewidth integrated lasers.
Achieving ever narrower linewidths in diode lasers has become of paramount importance for coherent communications. Coupling a laser chip to a fiber however introduces external optical feedback (EOF) to the cavity which is notoriously detrimental to the stability of the device, in all but very specific and difficult conditions. A better understanding of the interplay between EOF and the laser dynamics is thus crucial for designing narrow- linewidth diode lasers to be used in field-testing scenarios. The standard formalism of EOF in diode lasers relies on the assumption that feedback is present on one side of the laser cavity. However, given the currently available integration technologies, this assumption is no longer justified. In this work a revision of EOF theory is explored based on the updated assumption that feedback can be introduced from both sides of the laser cavity. This is done by obtaining the dynamic equations of the proposed system, including an expression for the power spectral density and linewidth. Additionally, the stability of the system is discussed. Results show that the proposed revised theory can yield stable laser performance while simultaneously reducing laser linewidth.
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.