Accurate Measurement and Improvement of Laser Phase Noise Performance

  • 18



Name of the Speaker: Mr. Arjun kurur (EE20S137)
Guide: Dr. Deepa Venkitesh
Venue: ESB-244 (Seminar Hall)
Date/Time: August 18th, 2023 (Friday), 10:00 – 11:00 AM

Phase noise is a key parameter that determines the spectral purity of a laser. The exact nature of phase noise decides the performance limits of the various applications of narrow-line lasers such as acoustic sensing, coherent communication and interferometry. Therefore, accurate measurement of the laser phase noise is essential for enhancing the performance of these applications. Although the conventional technique of delayed self-heterodyne gives an estimate of laser phase noise performance through the linewidth, this technique cannot estimate the instantaneous phase/frequency fluctuations.

We discuss two coherent heterodyne approaches which can accurately estimate the instantaneous phase/frequency noise. The detailed experimental implementation of two variants of coherent heterodyne - by referencing with an external laser and by self-referencing is discussed in detail. The benefits and challenges of each method are discussed and the performance of a compact and portable coherent self-heterodyne (CSHD) module is brought out.

We further discuss some experimental trials on the improvement of laser phase noise performance through the Pound-Drever-Hall (PDH) locking method. An absorption line of acetylene is used as the necessary frequency reference and the packaged CSHD module is used to quantify the improvement in the phase noise performance. Preliminary results of the development of a fiber ring resonator that can be employed as a wavelength-independent frequency reference for PDH locking are also discussed.