Fig. 1: Experimental setup of the integrated ECTL stabilized to an integrated coil reference cavity. | Nature Communications

Fig. 1: Experimental setup of the integrated ECTL stabilized to an integrated coil reference cavity.

From: Hybrid integrated ultra-low linewidth coil stabilized isolator-free widely tunable external cavity laser

Fig. 1

a Schematic of the experimental setup where the external cavity tunable laser (ECTL) is PDH-locked to an integrated 10 m coil reference cavity without an optical isolator. Hybrid integration of a reflective semiconductor optical amplifier (RSOA) provides a gain element. The high quality factor (Q) silicon nitride (Si3N4) rings serve as an external cavity and provide instantaneous linewidth narrowing, and the large-mode volume Si3N4 coil resonator provides a frequency reference for linewidth reduction and laser stabilization. b The frequency noise spectral energy (offset from the carrier) of the free-running ECTL (Sf(v) blue) and the noise reduction, particularly of the low-frequency noise components, resulting from stabilizing the ECTL to the 10 m coil reference cavity (orange). c Image of the hybrid-integrated ECTL, the RSOA is visible in the top left, the red-dashed lines highlight the Si3N4 waveguides, and gold pads indicate the metal heaters. d Schematic cross-section of the 80 nm thick Si3N4 low-loss waveguide platform. e Image of the 10 m coil resonator. “Photonic integrated beam delivery for a rubidium 3D magneto-optical trap” by Isichenko et al., used under CC BY 4.0/Panel a adapted from original52.

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