We propose to all-optically encrypt and decrypt high-speed optical signals using the stimulated Brillouin scattering (SBS) effect in optical fiber for the first time. The spectral-shaped SBS gain or loss distorts the broadband optical signal so as to realize optical encryption. A corresponding SBS loss or gain with the same spectral shape and amplitude recovers the distorted signal to implement optical decryption. We experimentally demonstrate the SBS encryption/decryption process on 10.86 Gb s −1 non-return-to-zero-on-off-keying (NRZ-OOK) data using phase-modulated Brillouin pumps to generate a spectral-shaped SBS gain/loss encryption key, and no power penalty is observed for the best decryption case. The proposed all-optical encryption/decryption method is completely compatible with existing fiber-optic communication systems.
We propose to all-optically encrypt and decrypt high-speed optical signals using the stimulated Brillouin scattering (SBS) effect in optical fiber for the first time. The spectral-shaped SBS gain or loss distorts the broadband optical signal so as to realize optical encryption. A corresponding SBS loss or gain with the same spectral shape and amplitude recovers the distorted signal to implement optical decryption. We experimentally demonstrate the SBS encryption/decryption process on 10.86 Gb s −1 non-return-to-zero-on-off-keying (NRZ-OOK) data using phase-modulated Brillouin pumps to generate a spectral-shaped SBS gain/loss encryption key, and no power penalty is observed for the best decryption case. The proposed all-optical encryption/decryption method is completely compatible with existing fiber-optic communication systems.
Slow light due to stimulated Brillouin scattering in fibers is a promising technique to realize all-optical data storage and synchronization. For delaying high-speed data, we demonstrate an approach to solve the problem of narrowband Brillouin gain by phase-modulating the Brillouin pump. The bit rate of the phase-modulating signal determines the Brillouin gain bandwidth. A 1.25-Gb/s nonreturn-to-zero pseudorandom binary sequence data is delayed by 520 ps with a phase-modulated pump operating at 2.5-Gb/s bit rate. We have also observed the pattern-dependent delay and distortion of the data caused by the filtering characteristics of Brillouin amplification, and we have suppressed the distortion by detuning the carrier of the signal away from the Brillouin gain peak
Dynamic control of the speed of a light signal, based on stimulated Brillouin scattering in optical fibers, was theoretically studied and also experimentally demonstrated as the core object of this thesis. To date, slow light based on stimulated Brillouin scattering has shown the unmatched flexibility to offer an efficient timing tool for the development of all-optical future router. Nevertheless, the seeming perfect Brillouin slow light suffered from three major obstacles: naturally narrow signal bandwidth, strong change of signal amplitude, and significant signal distortion. The essential contribution of this work has been mostly dedicated to resolve all those impairments so as to make Brillouin slow light a completely operating all-optical delay line for practical applications. Actually, high capability of tailoring the spectral distribution of the effective Brillouin resonance makes possible to resolve partially or completely all those problems. First of all, a broadband spectral window was passively obtained in between two Brillouin gain/loss resonances by simply appending two segments of fibers showing different Brillouin frequency shifts. The global Brillouin gain of the concatenated fibers manifests a gain/loss doublet resonance showing a broad window in between gain/loss peaks. In practice, this configuration has a crucial advantage that it removes the need of the pump modulation, generally used to create a polychromatic pump source. Therefore, a broadband Brillouin slow and fast light was simple realized with a reduced distortion. Secondly, the signal amplification or attenuation associated to the signal delay was completely compensated by superposing Brillouin gain and loss resonances with identical depth but different width. As a result, the Brillouin gain led to effectively a spectral hole in the center of the broadband absorption and opened a transparent window while the sharp change in the refractive index was preserve. This way it makes possible to realize zero-gain Brillouin slow light. This configuration was also exploited to produce Brillouin fast light with a total absence of signal loss, simply by swapping the spectral position of the two pumps. At last, a signal was continuously delayed through a Brillouin fiber delay line without any distortion. Due to the strong induced dispersion, pulse broadening is a major difficulty in all slow light systems and it is impossible to compensate such broadening using a linear system. Therefore, a conventional Brillouin slow light system was combined with a nonlinear optical fiber loop mirror that gives a nonlinear quadratic transmission. Using this configuration, the inevitable pulse broadening was completely compensated at the output of the loop and a signal was delayed up to one symbol without any distortion. Brillouin slow light systems were further studied in the spectral domain. For a given Brillouin resonance the spectrum of a light pulse was optimized to better match the Brillouin bandwidth. When the time envelope of a pulse was properly shaped, it was clearly observed that the spectral width of the pulse became minimized while preserving the pulse duration. This way the maximum time delay through Brillouin slow light could be enhanced for a fixed pulse width. Brillouin fast light was even realized in total absence of any pump source, which is a plain requirement for the generation of Brillouin slow or fast light. This self-generated delay line, key contribution of this thesis, relies on both spontaneous and stimulated Brillouin scattering in optical fibers. In this implementation, a light signal was strongly boosted above the so-called Brillouin threshold, so that most power of the signal was transferred to a backward propagating wave, namely the generation of amplified spontaneous Stokes wave. Since the center frequency of the intense Stokes wave is below the signal frequency by exactly Brillouin shift of the fiber used, this wave led to a Brillouin loss band centered at the signal frequency. Consequently, the signal experienced fast light propagation and the propagation velocity of the signal was self-controlled, simply by varying the signal input power. This technique has many practical advantages such as its high simplicity of the configuration and an invariant signal power in the output of this delay line. Additionally, this system self-adapts the signal bandwidth as the spectrum of the amplified Stokes wave matches the spectral distribution of the signal. An alternative method to generate all-optical delay line was proposed instead of slow light. This scheme makes use of the combination of wavelength conversion and group velocity dispersion. This type of delay line was mainly aimed at improving the storage capability of delaying element. The wavelength of a signal was simply and efficiently converted at a desired wavelength using cross gain modulation in semiconductor optical amplifiers. Then the converted signal was delivered to a high dispersive medium and arrived at the end of the medium with relative time delay due to the group velocity dispersion. A fractional delay of 140 was continuously produced through this delay line for a signal with a duration of 100 ps, preserving signal bandwidth and wavelength. The effect of slow light on linear interactions between light and matter was experimentally investigated to clarify the current scientific argument regarding slow light-enhanced Beer-Lambert absorption. It was predicted that real slowing of the light group velocity could enhance the molecular linear absorptions so as to improve the sensitivity of this type of sensing. However, the experimental results unambiguously show that material slow light (slow light in traveling wave media) does not enhance the Beer-Lambert absorption.
The manipulation of the group velocity of optical signals (slow and fast light) has many possible applications in telecommunications, sensing, nonlinear optics, and so on. The exploitation of the effect of stimulated Brillouin scattering (SBS) is of special interest for the alteration of the group velocity in optical fibers, since it just requires standard telecom equipment and low-to-moderate optical power. However, each delay in one single, low-gain SBS-based slow-light system is accompanied by a pulse broadening. This is a result of the inherent Kramers–Kronig relations among the gain, the phase change, and the accompanied group velocity. For an ideal flat gain, the phase change is nonideal, and for an ideal phase change the gain curve leads to a broadening. Furthermore, if the gain bandwidth is adapted to the signal by broadening, the delay will be reduced. Thus the signal broadening can be reduced by several methods for one single low-gain slow-light system, but it cannot be zero. Here, we will show how a zero-broadening SBS-based slow light can be achieved with several methods. The basic idea is a reshaping of the original pulse in a second stage by saturation of the SBS system, or by the superposition of two gains. As will be shown, all of these systems show an almost ideal overall gain and phase function over the bandwidth of the pulses. Thus, SBS-based slow light with a delay bandwidth product of 1 bit and zero distortion is possible.
We have experimentally demonstrated superluminal propagation through a 500 m optical fiber using stimulated Brillouin scattering (SBS), which is the longest superluminal propagating distance reported so far, to the best of our knowledge. Brillouin-induced loss resonance for fast light generation of pump signals is achieved in a single frequency Brillouin lasing oscillator with a highly nonlinear fiber as the SBS medium. The single frequency operation is realized by embedding the saturable absorber fiber loop with an unpumped erbium-doped fiber. Consequently, signals with a pulse width of 710 ns experience a maximum advancement of 1330 ns. Furthermore, the effects of pulse width and the duty cycle of pump signals are also investigated.
We analyse the stimulated Brillouin scattering （SBS） slow light using double broadband pumps in a single mode fiber. A new SBS gain spectrum tailoring method is proposed using two Gaussian-shaped broadband pumps with different powers and spectral widths, and the central frequency interval of them is carefully set at two Brillouin frequency shifts to make sure that the gain of one pump has the same center with the loss of the other. The top of the gain spectrum of the strong pump beam can be counteracted by the loss spectrum of the weak pump beam to construct a flat top gain spectrum. We give the optimized conditions of the laser powers and spectral widths between two broadband pumps to obtain a flat gain. Distortions of signal pulse under this flat top gain are studied and compared with that obtained using a single broadband pump. We find that the flat top gain profile can effectively reduce the pulse distortions.