We realize a strongly dispersive material with large tunable group velocity dispersion (GVD) in a commercially-available photonic crystal fiber. Specifically, we pump the fiber with a two-frequency pump field that induces an absorbing resonance adjacent to an amplifying resonance via the stimulated Brillouin processes. We demonstrate all-optical control of the GVD by measuring the linear frequency chirp impressed on a 28-nanosecond-duration optical pulse by the medium and find that it is tunable over the range ± 7.8 ns(2)/m. The maximum observed value of the GVD is 10(9) times larger than that in a typical single-mode silica optical fiber. Our observations are in good agreement with a theoretical model of the process.
We realize a strongly dispersive material with large tunable group velocity dispersion (GVD) in a commercially-available photonic crystal fiber. Specifically, we pump the fiber with a two-frequency pump field that induces an absorbing resonance adjacent to an amplifying resonance via the stimulated Brillouin processes. We demonstrate all-optical control of the GVD by measuring the linear frequency chirp impressed on a 28-nanosecond-duration optical pulse by the medium and find that it is tunable over the range ± 7.8 ns(2)/m. The maximum observed value of the GVD is 10(9) times larger than that in a typical single-mode silica optical fiber. Our observations are in good agreement with a theoretical model of the process.
Slow light study is discussed in various methods of generation, materials and approaches. In this study, the control of group velocity, Vg and group velocity dispersion (GVD) of a pulse propagating in optical fiber is simulated and demonstrated. The slow light generation, which is closely related to Vg of a light pulse for this study is based on stimulated Brillouin scattering (SBS), the most efficient approach as reported by previous researchers. By using Matlab R2011b software, the slow light generation is simulated for the slow light structure in the form of hollow conical shape resonator, focusing on the geometrical parameters. The simulation work is extended to the control of Vg and GVD, to investigate the influences of refractive index of the materials and wave number of the light pulses. While most of slow light researches neglect the effect of dispersion, this study explicitly includes the second term of the wave number’s expansion to represent GVD. Therefore, the experimental work investigates the creation of a strongly dispersive material with large chirp and small group delay via SBS in a highlynonlinear optical fiber as opposed to previous SBS experiments which mainly focus on the creation of a slow light material with minimum dispersion and chirp. To demonstrate the control of Vg and GVD, a two-frequency pump field which consists of two distributed feedback lasers with the relative frequency separation nearly twice the Brillouin frequency and a slow light medium in the form of a 2-km high nonlinear single mode optical fiber are employed. For input field with slowly varying amplitude, the experiment obtained output pulses with large GVD and decreased intensity. All-optical control of the GVD is demonstrated by measuring the linear frequency chirp impressed on a 28-nanosecond-duration optical pulse and it is tunable over the range of ± 7.8 ns2 m-1. In addition, the maximum observed value of GVD is 109 times larger than that obtained in a typical single-mode silica optical fiber. The simulation results for Gaussian pulses as input signal are in good agreement with the experimental ones, and therefore the control of Vg and GVD for different shapes of input pulses using the developed system can be predicted.
We propose a method of effectively extending the stimulated Brillouin scattering (SBS) gain bandwidth in a single-mode optical fiber to reduce group-velocity-dispersion (GVD)-dependent pulse spread of SBS slow light. This can be done by overlapping doublet SBS gain spectra synthesized from a single pump laser. Numerical calculations are performed to verify our proposed method. We find that there exists the optimum spectral separation between two center frequencies of the doublet SBS gain spectrum with respect to the inherent spectral width of the pump laser, which makes it possible to effectively reduce the signal pulse broadening due to GVD. We show that the maximum time delay of the amplified signal pulse can be approximately two times longer than that by a previously reported method using a single broadband pump laser.
All-optical group velocity manipulation of light, so-called slow and fast light, has drawn extensive attention due to its potential applications in the fields of optical signal processing, light storage, light-matter interaction enhancement, hypersensitive sensing and temporal cloak. Tremendous approaches of slow and fast light generation have been widely demonstrated by the creation of the sharp spectral resonances in the past decade. Specifically, superluminal propagation (larger-than-light velocity c) through the optical media has been proposed and validated in anomalous dispersion media. One effective approach is employing stimulated Brillouin scattering to harness the narrowband spectral resonance and thus generate slow and fast light in the optical fiber. In particular, Brillouin lasing oscillation has been experimentally demonstrated to generate fast and superluminal propagation in ten-meter optical fibers. Afterwards, the propagating distance over hundreds of meters has been experimentally demonstrated by the suppression of multiple-longitudinal-mode operation. However, the delay-bandwidth product or the fractional advancement is still fundamentally limited in conventional fast and slow light system. For example, the maximum advancement as well as the fractional temporal advancement are practically restricted due to the Brillouin gain saturation and multiple longitudinal mode lasing operation under high pump power in the Brillouin lasing resonance-based fast and superluminal system. In this paper, we experimentally validate the extension of time advancement of superluminal propagation based on Brillouin lasing oscillation for the first time. By employing two stages of single-frequency Brillouin lasing fiber ring resonators, Stokes lasing resonance was effectively created in each fiber ring cavity to deliver Brillouin-induced loss resonance at the center frequency of pump, which essentially leads to fast light and superluminal propagation of the pump light. Consequently, Gaussian signal pulses with the pulse width of 500 ns experiences cascaded Brillouin-induced fast light and even negative group-velocity superluminal propagation. The temporal advancement was basically extended to 365.8 ns which is twice than that of single stage fast light and superluminal system. Correspondingly, the fractional advancement was increased from 0.36 to 0.73. The maximum group velocity was 6.3 times larger than the light speed c in vacuum while negative-group- velocity propagation can be found in the range of −9.9 to −0.2 by increasing the total input power from 593.2 to 812.0 mW. Furthermore, the group index can be manipulated in the range of 1.5 to −4.0 by simply varying the total input pump power. It indicates superluminal signals can be cascaded to essentially extend the propagation distance and enlarge the temporal advancement. The scheme exhibits robustness in cascading Brillouin spectral loss resonance for temporal advancement enhancement as well as propagating distance extension. More importantly, the cascading design could basically eliminate the fundamental limitation introduced by Brillouin gain saturation and multiple longitudinal lasing mode under high power operation in single stage Brillouin fast and superluminal system. Further optimization could also be implemented by utilizing the nonstandard specialty fibers as Brillouin gain medium to achieve an efficient Brillouin lasing resonance for an enhanced advancement efficiency. Additionally, the combination with the cascading technique and long-cavity single-frequency Brillouin lasing resonance could enable the feasibility of distance-limitless and large-advancement superluminal propagation, paving a way for promising applications in sensing and temporal cloak.
We have demonstrated that stimulated Brillouin scattering can be used to generate all-optical slow-light pulse delays of greater than a pulse length for pulses as short as 16 ns in a single-mode fiber. Since the induced delay is generated for wavelengths detuned from the pump field by the Brillouin frequency, tuning near an electronic resonance of the material is not required and thus delays can be induced at telecommunication wavelengths. This represents a significant improvement over previous demonstrations of slow light in solids and is an important step towards developing an all-optical tunable delay line for telecommunications. In addition, these results strongly suggest that analogous delays can be achieved using stimulated Raman scattering at telecommunication data rates.
Future quantum networks will rely on the ability to coherently transfer optically encoded quantum information between different wavelength bands. Bragg-scattering four-wave mixing in optical fiber is a promising route to achieving this, but requires fibers with precise dispersion control and broadband transmission at signal, target, and pump wavelengths. Here, we introduce a photonic crystal fiber with a germanium-doped core featuring group velocity matching at 1550 nm, the telecoms C-band, and 920 nm, within the emission range of efficient single photon sources based on InAs quantum dots. With low chromatic walk-off and good optical guidance even at long wavelengths, large lengths of this fiber are used to achieve nanometer-scale frequency shifts between wavelengths around 920 nm with up to 79.4% internal conversion efficiency, allowing dissimilar InAs dots to be interfaced. We also show how cascading this frequency conversion can be used to generate a frequency comb away from telecoms wavelengths. Finally, we use the fiber to demonstrate tunable frequency conversion of weak classical signals around 918 nm to the telecoms C-band.
We report the first demonstration of group delay tuning with stimulated Raman scattering-induced dispersion in a hydrogen-filled hollow-core optical fiber.A pump laser induces a sharp refractive index change near the S 0 (0) Raman transition of hydrogen molecules, enabling the control of the group velocity of signal pulses around the Stokes wavelength.Experiments with an 80-m-long hollow-core fiber filled with 2.5 bar hydrogen achieved continuous tuning of the pulse delay up to 1.42 ns by varying the Raman amplification from 0 to 10 dB.The tunable pulse delay is realized by changing the pump power as well as the hydrogen pressure.This work provides a new technique for controlling the pulse propagation in optical fibers with high flexibility.