Abstract
The back-reflection of emitted laser beam (optical feedback, also know as selfmixing) from various external interfaces are sufficient to cause instability, and prohibiting its use in various fields such as communication, spectroscopy, imaging to name a few. So it is desirable to study the laser dynamics and the conditions causing it to be stable in spite of strong optical feedback. With the aid of mathematical formulation, simulation and backed by experimental evidences, it is demonstrated that the frequency deviation of the laser emission due to current (intensity) modulation alters the dynamic state and boundary conditions of the system such that even under large optical feedback strength, the laser may attain stability and retain single modal state. The frequency deviation resulting from former is shown to modify the phase of the system in opposite direction to that induced by the later, showing that there exists an optimal modulation current which compensates the effect of optical feedback and may be used to retain the laser in single modal stationary state. The method thus provides a methodology to avoid optical feedback-induced instability in semiconductor lasers by using the proper amplitude of current (intensity) modulation.
Highlights
Semiconductor lasers are use in diverse fields from communication to spectroscopy to medical imaging, surgery and health to name a few
We introduce the use of CWFM-optical feedback (OF) to induce laser stability even for large C values i.e. high feedback strength
The dynamics of the semiconductor laser under optical feedback in the two distinct cases of classical optical feedback (C-OF) and continuous wave frequency modulated optical feedback (CWFM-OF) have been studied in depth
Summary
Semiconductor lasers are use in diverse fields from communication to spectroscopy to medical imaging, surgery and health to name a few. Agnew et al in [47] carried the detailed investigation on variation in temperature and emission frequency due to thermal effect; Bertling in [49] describes variation of temperature with measurement time; and the thermal coefficient variations with the monitoring time interval after changing the magnitude of injected current is described in [46] Based on these extensive evidences, continuous wave current modulation, advanced laser package to dissipate heat and the fact that temperature stabilizer is used in most of the experimental setup, thermal heating is unlikely to effect the measurements. The frequency modulation coefficient of laser ( f ), is shown to be one of the key factors in determining the laser stability in presence of high C, so it is measured experimentally in Sec. III(III-A) followed by Sec. III-B, that explains the experimental evidences to demonstrate that the frequency deviation caused by the introduction of laser current modulation pulls back the laser from multi modal state to single mode state even under large C values.
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