Abstract
Chaos generation from a semiconductor laser under band-rejection optical feedback is proposed and investigated numerically and experimentally. The band-rejection feedback performs better than the conventional broadband mirror feedback in concealing the feedback delay time information measured by the time-delay signature (TDS) of optical field and intensity. In this work, the optical band-rejection filter (BRF) is built up based on the transmission of a Bragg grating. The best concealment of delay time information is achieved in the form of simultaneous TDS suppression in optical field and intensity when the BRF is negatively detuned from the free-running laser frequency. Such concealment is due to the suppression of feedback cavity modes by the band-rejection effect. The concealment prefers negative detuning frequency because the laser cavity resonance is red-shifted by optical feedback due to the antiguidance effect. The negatively detuned BRF suppresses the TDS of optical field and intensity by more than an order of magnitude than mirror feedback. The simulation results are qualitatively confirmed by the experimental measurements.
Highlights
Optical chaos from semiconductor lasers are of particular interest due to unique properties such as broad bandwidth, noise-like but synchronizable waveform, and high dimension [1]–[6]
Such a delay time information results in a weak periodic property in both intensity and phase dynamics, which can be extracted by using information processing techniques such as time-dependent exponent, neural network analysis, permutation entropy, delayed mutual information (DMI), or autocorrelation function (ACF) [24]–[27]
Different from conventional mirror feedback, a region of stable states is observed under relatively strong ξf at negative ∆f due to locking the red-shifted laser cavity resonance to one of the band-rejection filter (BRF) side lobes. Such red-shifted resonance is induced by optical feedback through the antiguidance effect, which leads to an asymmetry of dynamical mapping with respect to ∆f [51]
Summary
Optical chaos from semiconductor lasers are of particular interest due to unique properties such as broad bandwidth, noise-like but synchronizable waveform, and high dimension [1]–[6]. Chaotic dynamics from a feedback scheme inherently contains an information about the characteristic delay time within the external feedback cavity. For suppressing the TDS in intensity dynamics, the pioneer approach was numerically demonstrated using mirror feedback, where the intensity TDS was covered by the lasers relaxation resonance under short delay [24]. Besides using feedback cavity with identical delay, approaches using dispersive feedback cavity were numerically and experimentally demonstrated, where the intensity TDS was flattened and suppressed due to the group-velocity dispersion [37]–[42]. Filtered optical feedback is a much simpler approach towards perturbing both intensity and phase dynamics. The band-rejection filter (BRF) effectively suppresses the feedback cavity modes conceals the delay time information in the form of simultaneous TDS suppression in intensity and phase dynamics. Numerical simulations are conducted using the fourth-order Runge-Kutta method with time step 2.38 ps for time span of 1.25 μs
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