Highly-coherent stimulated phonon oscillations in a multi-core optical fiber

Abstract

Opto-mechanical oscillators that generate coherent acoustic waves are drawing much interest, in both fundamental research and applications. Narrowband oscillations can be obtained through the introduction of feedback to the acoustic wave. Most previous realizations of this concept, sometimes referred to as “phonon lasers”, relied on radiation pressure and moving boundary effects in micro- or nano-structured media. Demonstrations in bulk crystals required cryogenic temperatures. In this work, stimulated emission of highly-coherent acoustic waves is achieved in a commercially-available multi-core fiber, at room temperature. The fiber is connected within an opto-electronic cavity loop. Pump light in one core is driving acoustic waves via electrostriction, whereas an optical probe wave at a different physical core undergoes photo-elastic modulation by the stimulated acoustic waves. Coupling between pump and probe is based entirely on inter-core, opto-mechanical cross-phase modulation: no direct optical feedback is provided. Single-frequency mechanical oscillations at hundreds of MHz frequencies are obtained, with side-mode suppression that is better than 55 dB. A sharp threshold and rapid collapse of the linewidth above threshold are observed. The linewidths of the acoustic oscillations are on the order of 100 Hz, orders of magnitude narrower than those of the pump and probe light sources. The relative Allan’s deviation of the frequency is between 0.1–1 ppm. The frequency may be switched among several values by propagating the pump or probe waves in different cores. The results may be used in sensing, metrology and microwave-photonic information processing applications.

Opto-Mechanical Interactions in Multi-Core Optical Fibers and Their Applications

“…Conclusions are drawn in Section V. The description below is intended primarily for readers who are familiar with fiber-optics, but may not be specialists in opto-mechanics. Parts of the results appear in separate, earlier publications [25], [28], however the reader may benefit from the more unified perspective provided below. Some results were presented only briefly in a recent conference [29].…”

“…Steady-state oscillations require that the sequence of electroopto-mechanical conversions within the feedback loop should reproduce the initial modulation voltage [28]:…”

Forward Stimulated Brillouin Scattering Analysis of Optical Fibers Coatings

“…Forward stimulated Brillouin scattering (F-SBS) is a nonlinear optical effect that couples between two copropagating optical fields and an acoustic wave that are guided in a common medium [6][7][8][9][10][11][12][13][14][15][16][17][18]. F-SBS has been studied in standard optical fibers since 1985 [6].…”

“…F-SBS has been studied in standard optical fibers since 1985 [6]. Unlike the more widely employed effect of backwards SBS, the acoustic modes that mediate forward Brillouin scattering in fibers are predominantly transverse [6][7][8][9][10][11][12][13][14][15][16][17][18]. These modes are guided by the whole fiber cross-section, and their transverse profiles span the entire cladding and reach its outer boundary [6][7][8].…”

Shaping nonlinear optical response using nonlocal forward Brillouin interactions

“…By comparison, integrated photonic systems allow additional structural degrees of freedom which can be used to tailor both the optical and acoustic modes that participate in the nonlocal interaction [17,18]. These devices can be the basis for new signal processing schemes such as filters [18], transducers [17], oscillators [20], and modulators [21] for both optical and microwave applications. The description and analysis of the underlying processes will enable the design and optimization of future technologies based on these devices.…”