Micro resonator system for highly stable diode lasers – FBH reaches important milestone in project iMILQ
Fig. 1: SEM picture of an integrated micro resonator system. A 2 µm wide waveguide is positioned in a distance of 0.5 µm from a micro disk of 40 µm diameter. Material system: silicon oxide on silicon.
The "Integrated microresonator stabilized light sources for quantum metrology" (iMILQ) project aims at developing special laser modules that operate at a wavelength of 1064 nm, featuring a very narrow linewidth only in the kHz range. This goal is addressed by coupling a thermally controlled DFB laser optically to a micro resonator; frequency stabilization of the DFB laser and micro resonator will be closed loop controlled. Project partners will furnish the module with optical and electrical ports to enable simple integration into complex optical systems and ensure applicability. Applications include coherent optical (free-space) communication, high-precision interferometric measurements as well as quantum optics precision measurements. The laser module is an advancement of previous larger systems used to demonstrate the functional principle of the arrangement [1].
In this three-year project, a passive optical micro component newly developed at Ferdinand-Braun-Institut (FBH) is deployed for the first time. This component is one of the central parts of the module, consisting of a micro resonator of a few 10 µm in diameter that is coupled to a nearby waveguide. Such micro resonators already proved their high quality in earlier tests, reaching Q-factor values of up to 106. With them, narrowband resonance can be achieved that can be fed back to stabilize the laser. This requires to precisely design the dimensions of the micro resonator disk, the waveguide and their distance to each other since no later adjustments can be accomplished in a monolithic system.
FBH has now reached an important milestone on the way to the micro-integrated system. First micro resonator systems were successfully produced in the cleanroom in silicon oxide on silicon substrate. Fig. 1 shows a SEM picture of such a structure with a disk of 4 µm in diameter and a 2 µm wide waveguide located in a distance of 500 nm: The dark circles are ancillary structures used to underetch the silicon oxide membrane.
iMILQ is funded within the ProFIT program by IBB Berlin over a three-year period. FBH closely cooperates in this project with Humboldt Universität zu Berlin, FBH spin-off Brilliance Fab Berlin, and Picoquant.
Publication
[1] W. Lewoczko-Adamczyk, C. Pyrlik, J. Häger, S. Schwertfeger, A. Wicht, A. Peters, G. Erbert, G. Tränkle, "Ultra-narrow linewidth DFB-laser with optical feedback from a monolithic confocal Fabry-Pérot cavity", Opt. Express 23, pp. 9705-9709 (2015).