Characterization of phase noise in semiconductor lasers

Abstract

Phase noise in semiconductor lasers has been investigated by many authors in the range of low frequencies (<1 MHz). In this letter we present for the first time phase noise measurements extended up to frequencies greater than 1 GHz. Experimental results showing the power spectral density Sφ̇(ω) of the instantaneous frequency φ̇(t) and the variance σ2[Δτφ(t)] of the phase shift Δτφ(t) are presented. The peculiar behavior of Sφ̇(ω), which presents a sharp peak at the same frequency of the amplitude noise peak, can account for the excessive broadening of the linewidth of single-mode injection lasers.

A comparison of small signal modulation parameter extraction techniques for vertical-cavity, surface-emitting lasers

“…The phase noise of a laser is not spectrally flat, but instead has a resonance at the relaxation oscillation frequency [10] similar to the peak observed in the RIN spectrum. This resonance manifests itself as a pair of spectral side bands, adjacent to each lasing mode in the optical spectrum.…”

120° Phase Difference Interference Technology Based on 3 × 3 Coupler and its Application in Laser Noise Measurement

“…In a high-frequency domain (>100 kHz), there is only white noise, and the minimum linewidth of about δν 1 = 2 kHz is calculated. Meantime, the inset figure shows the linewidth of the same laser measured by the self-delay heterodyne (SDH) method [14] with heterodyne frequency of 80 MHz and optical fiber delay length of 45 km. The Lorentz fitted linewidth at −20 dB from the spectrum measured by the SDH method is about 51.7 kHz, so the laser linewidth is about δν 2 = 2.6 kHz, and the fitted linewidth would not vary with the observation time.…”

“…To measure the phase and frequency noise, many methods have been proposed, such as beat note method [10], recirculating delayed self-heterodyne (DSH) method [11], DSH technique based on Mach-Zehnder interferometer with 2 × 2 coupler [12,13], or Michelson interferometer (MI) with 2 × 2 coupler [14]. These methods can obtain good measurement results but need some strict conditions.…”

Spectral filtering within the Schawlow-Townes linewidth of a semiconductor laser

“…This notion has been appreciated in fiber optics [2], laser physics [3,4], and laser spectroscopy [5][6][7]. As an example, in fiber-optic interferometric sensors [8] and signal processors [9], the optical performance is mainly limited by an excessive amount of intensity noise, which results from interferometric conversion of laser phase noise.…”

“…Since the phase-induced intensity noise is directly proportional to the input power it can severely limit the dynamic range of these systems. Conversion of phase noise into intensity noise may also be used on purpose: Phase-noise characteristics of a laser can be studied [3] and manipulated [4] by means of dispersive elements. In laser spectroscopy an atom instead of an interferometer acts as the resonant system; the phase fluctuations of the laser source can then lead to fluctuations in the resonance fluorescence of the laser-excited atoms [5,7,10].…”