The Influence of Noise Floor on the Measurement of Laser Linewidth Using Short-Delay-Length Self-Heterodyne/Homodyne Techniques

Abstract

Delayed self-heterodyne/homodyne measurements based on an unbalanced interferometer are the most used methods for measuring the linewidth of narrow-linewidth lasers. They typically require the service of a delay of six times (or greater) than the laser coherence time to guarantee the Lorentzian characteristics of the beat notes. Otherwise, the beat notes are displayed as a coherent envelope. The linewidth cannot be directly determined from the coherence envelope. However, measuring narrow linewidths using traditional methods introduces significant errors due to the 1/f frequency noise. Here, a short fiber-based linewidth measurement scheme was proposed, and the influence of the noise floor on the measurement of the laser linewidth using this scheme was studied theoretically and experimentally. The results showed that this solution and calibration process is capable of significantly improving the measurement accuracy of narrow linewidth.

Study on external cavity diode laser with a wide mode-hopping free tuning range

“…At last, the spectral linewidth performance of the proposed ECDL system is illustrated using traditional delayed selfheterodyne (DSH) arrangement with a total length of 20 km single-mode fiber (Corning, SMF28e) and an 80 MHz fibrecoupled acousto-optic modulator (AOM) which is fabricated by the Gooch & Housego [22,23]. The spectral linewidth of the beat signal is depicted in Figure 4A.…”

Low SWaP miniaturized fiber coupled external cavity diode laser (ECDL) with high optical isolation as plug and play solution

“…The frequency spectrum of the beat signal is centered around the AOM modulation frequency and is a measure of the lineshape from which the linewidth can be derived. [8] Figure 2: Measured beat-spectrum of an ECDL in a self-heterodyne setup under the influence of back reflections with 30 dB (green), 50 dB (red), and 70 dB (black) attenuation, which is directly behind the beat-spectrum without any back reflections (blue).…”

“…The resulting correlation of the optical fields in the two interferometer arms leads to oscillations in the spectrum to both sides. In the literature [8,16] the theoretical behavior for a laser with self-superposition and variable delay time within the interferometer arms is described. From there it is possible to fit the measurement data and thus finding the corresponding linewidth of about 6 kHz.…”

High-SMSR wavelength-swept laser with a CL-band mode-hopping free tuning range

“…The highly controllable emission properties of wavelength-swept lasing sources are prior selected semiconductor lasers for a vast array of applications in fields including highresolution spectroscopy [1,2], laser cooling [3], coherent optical orthogonal frequency division multiplexing (CO-OFDM) modulation schemes [4], space strontium optical clock [5][6][7], and optical frequency-domain reflectometry (OFDR) and so on [8][9][10][11][12]. Across these fields, the wavelength-swept lasing sources with higher side-mode suppression ratios (SMSRs) and increased mode-hopping free (MHF) tuning ranges continue to enable new applications.…”