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Abstract
We discuss the design and characterization of a micro ring laser with on-chip filtered optical feedback. The laser and feedback section have been fabricated on a generic photonic integration platform using only standard building blocks. The filtering process in the feedback scheme is based on the reflection from a distributed Bragg reflector. We include several control pads in the feedback section which allows us to control separately the wavelength, the strength and the phase of the filtered feedback. By controlling the phase of the feedback, we can fine-tune the longitudinal mode selection and wavelength of the laser output, while changing the strength of the feedback allows us to control the power distribution between the two directions of the micro ring laser. Numerical simulations reproduce our experimental observations.
Highlights
Optical feedback is one of the well known approaches to change and/or control the output of semiconductor lasers [1,2,3]
The filtering process in the feedback scheme is based on the reflection from a distributed Bragg reflector
As can be seen from this figure, the laser emits in a single longitudinal mode at 1551.3 nm with a large side mode suppression ratio (SMSR). This is in stark contrast with the highly multi-mode spectrum that we obtained in Fig. 3(c) at the same laser pump current but without pumping of the feedback semiconductor optical amplifiers (SOAs), illustrating the wavelength selection caused by the filtered feedback
Summary
Optical feedback is one of the well known approaches to change and/or control the output of semiconductor lasers [1,2,3]. The FOF section in our design is based on DBR mirrors and implements cross-feedback between the two directions of the SRL, such that the feedback can be used both to control the emission wavelength and to enhance one of the directional modes. To get a Bragg wavelength of 1550 nm, we used a grating pitch of 237.5 nm while a nominal value of 50 cm−1 is used for the grating coupling coefficient At both sides of the SOAs in the feedback arms, there is an isolation waveguide such that the phase shifter, the SOA and the DBR are electrically isolated and can be individually controlled. The spectrally filtered light reflected by the DBRs will pass back through the SOA and the phase section, and this beam is coupled back in the SRL via the MMI coupler. The wavelength tuning can be achieved either by changing the DBR’s Bragg wavelength or by changing the feedback parameters in the feedback arms
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