Supercontinuum Generation in Media with Sign‐Alternated Dispersion

Abstract

When an ultrafast optical pulse with high intensity is propagating through transparent material a supercontinuum can be coherently generated by self-phase modulation, which is essential to many photonic applications in fibers and integrated waveguides. However, the presence of dispersion causes stagnation of spectral broadening past a certain propagation length, requiring an increased input peak power for further broadening. Overcoming such spectral stagnation will be key to achieve practical integrated supercontinuum devices. We present a concept to drive supercontinuum generation with significantly lower input power by counteracting spectral stagnation via repeatedly alternating the sign of group velocity dispersion along the propagation. We demonstrate the effect experimentally in dispersion alternating fiber in excellent agreement with modeling, revealing almost an order of magnitude reduced peak power compared to uniform dispersion. Calculations reveal a similar power reduction also with integrated optical waveguides, simultaneously with a significant increase of flat bandwidth, which is important for on-chip broadband photonics.

Bandwidth-limited few-cycle pulses by nonlinear compression in a dispersion-alternating fiber

“…where R corresponds to the dispersion ratio. In previous experiments, the dispersion magnitude was matched, but the dispersion slope of both fibers was positive, leading to an increased impact of HOD [5]. In our experiments, avoidance of HOD was accomplished by utilizing standard SMF28…”

“…Ultra-short pulses deliver high peak power within a very short time interval; therefore, pulse compression is a topic of high interest for a manifold of applications such as highharmonic generation [1][2][3], supercontinuum generation [4,5], nonlinear optical microscopy [6], and telecommunication [7]. To generate ultra-short optical pulses, a broad bandwidth is necessary.…”

“…Dispersion-alternating fibers (DAF) combine the advantages of ordinary pulse compression and soliton-effect pulse compression and, therewith, overcome typical limitations for bandwidth generation in optical fibers, such as dispersive temporal defocusing and soliton formation [5,7,40,41]. The alternation of the dispersion sign allows for repetitive sections of SPM-mediated bandwidth generation in the normal dispersion regime with subsequent pulse compression in the anomalous dispersion regime.…”

“…Then, NLPC can be achieved without the use of free-space compressors or soliton formation, and a high compression factor of about 19 to approximately 380 fs pulse duration was achieved [7]. Nonetheless, due to the non-inverted dispersion slopes of the involved fibers, the output pulses suffered from HOD leading to wave-breaking [5,7]. Wave-breaking prohibits the recompression to the bandwidth-limited pulse duration with grating or prism compressors, compensating typically only second-order dispersion.…”

Enhanced Pulse Compression within Sign-Alternating Dispersion Waveguides

“…Supercontinuum generation (SCG) in Kerr nonlinear waveguides is central in numerous applications such as in the generation of sub-cycle pulses [1][2][3][4][5][6], metrology using optical frequency combs [7][8][9][10][11], optical coherence tomography [12][13][14] and as a widebandwidth source for ranging and sensing applications [15,16]. We have recently introduced the concept of repeatedly sign-alternating dispersion along the propagation direction as a means of overcoming stagnation of spectral bandwidth growth across SCG waveguides [17]. Sign-alternating the dispersion maintains spectral bandwidth generation (i.e., an increase in the pulses' 1/e bandwidth) in normal dispersion segments (ND) by countering the bandwidth stagnation that occurs by the loss of peak power and duration increase.…”