All-optical polarization-based temporal cloaking

Abstract

Summary form only given. Due to a growing demand of security in transmission systems, recent research have been focus on the ability to manipulate a light beam in such a way to hide, namely to cloak, an event over a finite time or localization in space. The main idea is to create a hole or a gap in the spatial or time domain so as to allow for an object or a data to be kept hidden for a while and then to be restored [1-2]. Here we experimentally demonstrate a new type of temporal cloaking based on the ability for an arbitrary polarized light beam to self-organize and trap its state of polarization (SOP) in an optical fiber and then, to self-scramble in a reverse manner. We analyze the performance of our system by alternatively spying and then cloaking a 10Gbit/s signal propagating in an optical fiber and threaten by an attempt of hacking though an optical parametric based copying process. We successfully show that a quasi-annihilation of the probing operation (cloaking mode) or alternatively an error-free copying process (spying mode) can be achieved, both modes being independent from the incident SOP. The principle is illustrated in Fig. 1a. After travelling through a transmission system, an incident signal reaches the cloaking/spying zone with an arbitrary SOP. At this point, a continuous wave (cw) probe is then used to attempt a copy of the transmitted signal through a fiber optical parametric amplifier (FOPA). Since parametric process in optical fiber is highly polarization dependent, the conversion efficiency towards the copy wave (i.e. the idler) is strongly dependent on the incident signal SOP, which in usual situation where SOP randomly fluctuates, does not allow any kind of stable processing. Nevertheless, a successful cloaking or spying operation could be performed if one can trap the incident signal SOP orthogonal or parallel to the probe state. Here, this operation of polarization trapping is realized by means of an all-optical Omnipolarizer (OP) [3] in which self-organization of light SOP is spontaneously achieved by means of a counter-propagating four-wave mixing between the signal beam and its own backward replica generated through a reflective-loop [3]. As a consequence, in the cloaking zone, if the OP traps the signal SOP orthogonally to the probe state, no idler is generated and the signal remains hidden. At the opposite, if the OP locks the incident signal SOP parallel to the probe state, a maximal idler is then generated and the signal is kept hacked independently of its input SOP. Finally, to keep a transparent operation for the user, polarization randomness of the signal is restored thanks to a second Omnipolarizer, in which a high power backward replica induces the self-polarization process to become chaotic, leading to the unexpected behavior of the device to play the role of all-optical scrambler.Γ