Design of feedback insensitive InP ring laser

The optical isolators used to protect semiconductor lasers against optical feedback cannot be integrated. Therefore we propose to fabricate a laser that has a strongly reduced sensitivity to feedback. Simulations show that such a device can be realized by employing a ring laser in which the clockwise and counterclockwise modes are not coupled. To achieve unidirectional lasing, this work proposes to use an intra cavity weak optical isolator based on two phase modulators that are driven 90 degrees out of phase. Simulations show up to 3% of intensity feedback can be tolerated without any distinguishable effect on the laser light

Design of feedback insensitive InP ring laser

The optical isolators used to protect semiconductor lasers against optical feedback cannot be integrated. Therefore we propose to fabricate a laser that has a strongly reduced sensitivity to feedback. Simulations show that such a device can be realized by employing a ring laser in which the clockwise and counterclockwise modes are not coupled. To achieve unidirectional lasing, this work proposes to use an intra cavity weak optical isolator based on two phase modulators that are driven 90 degrees out of phase. Simulations show up to 3% of intensity feedback can be tolerated without any distinguishable effect on the laser light

Toward a feedback-insensitive semiconductor laser

We present a route toward design and fabrication of a conceptually new type of optical feedback insensitive integrated semiconductor ring laser with a weak optical isolator included in the ring. Although the approach has not resulted in the clear advantages that were aimed at, this detailed account of the process we believe is valuable to readers active in the field. After a summary of optical-feedback sensitivity in semiconductor lasers, we review various attempts toward reducing this sensitivity and discuss the feasibility of the concept of weak intra-cavity isolation. The design, model and theory of the novel integrated ring laser device are presented. The observed 5 dB of isolation and 3 dB increase of tolerance for external optical feedback demonstrate the feasibility of the intra-cavity isolation concept. However, the observed output performance of the single-mode laser, both with and without activated intra-cavity isolation, suggests the presence of a spurious intra-cavity reflection, strongly coupling the directional modes. Due to this coupling, the sensitivity to external optical feedback is comparable to that of a Fabry-Pérot type laser. Therefore, an alternate route is indicated toward a less complex laser cavity with potentially less intra-cavity reflection and better tolerance for external optical feedback

Feedback-insensitive integrated laser

Semiconductor lasers are highly susceptible to external optical feedback. Since the optical isolators used to prevent this effect cannot be integrated, we propose to fabricate an integrated feedback-insensitive laser. Two designs for integrated ring lasers are studied in detail. Theoretical analysis based on rate equations, simulation results and preliminary measurement results will be presented

Rate-equation theory of a feedback insensitive unidirectional semiconductor ring laser

For our recently designed continuous-wave and single-frequency ring laser with intra-cavity isolator, we have formulated a rate-equation theory which accounts for two sources of mutual back-scattering between the clockwise and counterclockwise modes, i.e. induced by side-wall irregularities and due to inversion-grating-induced spatial hole burning. With this theory we first confirm that for a ring laser without intra-cavity isolation, from sufficiently large pumping strength on, the inversion-grating-induced bistable operation (i.e. either clockwise or counterclockwise) will overrule the back-reflection-induced coupled-mode operation (i.e. both clockwise and counterclockwise). We then analyze the robustness of unidirectional operation in case of intra-cavity isolation against the intra-cavity back-reflection mechanism and grating-induced mode coupling and derive for this case an explicit expression for the directionality in the presence of external optical feedback, valid for sufficiently strong isolation. The predictions posed in the second reference remain unaltered in the presence of the mode coupling mechanisms here considered

Feedback-insensitive integrated laser

Semiconductor lasers are highly susceptible to external optical feedback. Since the optical isolators used to prevent this effect cannot be integrated, we propose to fabricate an integrated feedback-insensitive laser. Two designs for integrated ring lasers are studied in detail. Theoretical analysis based on rate equations, simulation results and preliminary measurement results will be presented

Theoretical analysis of a feedback insensitive semiconductor ring laser using weak intracavity isolation

External optical feedback can severely deteriorate the performance of semiconductor lasers. This paper proposes an integrated laser design that can withstand tens of percent of off-chip feedback, without requiring the integration of magneto-optic materials. The proposed laser consists of a ring cavity with a weak intracavity optical isolator. Sufficient gain difference between clockwise and counter-clockwise modes leads to unidirectional laser oscillation. Any reflected light is returned to a mode that is below threshold. This significantly reduces interactions between the feedback and the lasing mode. A rate-equation analysis is presented to show that the rin changes less than a factor 2 when less than -0.1 dB of the light is fed back into the laser and when intracavity isolation is 10 dB. Linewidth and optical output power change approximately 0.1% for these values

Multi-stable operation of a semiconductor ring laser due to spatial hole-burning

We have theoretically analyzed multi-stability of a symmetric ring laser operating in one single longitudinal mode in the presence of coherent back scattering and inversion-grating-induced mutual coupling of the clockwise and counter-clockwise modes. Our model takes into account the inversion grating created by the standing-wave pattern of the interfering counter-propagating fields and avoids the frequently used ad-hoc introduction of cross and self-saturation coefficients. Our study confirms that linear coupling due to waveguide irregularities or weak interface reflections leads to an effective pump strength below which the clock and anti-clock wise modes are symmetrically coupled whereas above which the grating-induced coupling leads to multi-stability

Feedback insensitive integrated semiconductor ring laser concept using weak intracavity isolation

External optical feedback can influence semiconductor laser performance to a great extent. Strong optical isolators with reasonable insertion loss are not available in a photonic integrated circuit due to material incompatibilities, preventing the use of an isolator external to the laser cavity to suppress any feedback effects. In this work the feedback sensitivity of a semiconductor ring laser with an intra-cavity isolation of less than 10 dB is studied using a rate equation analysis. It is found that the relative intensity noise and linewidth are insensitive to feedback strengths over -10 dB