Synchronization properties of two coupled multisection semiconductor lasers emitting chaotic light

Abstract

Abstract-We present numerical simulations describing the dynamics of two multisection semiconductor lasers emitting in a chaotic regime coupled in a master-slave configuration. By changing the current of the passive section of the master laser, we observe a change in the maximum correlation between the outputs of the two systems. These devices are promising candidates for on-off phase-shift keying encryption.Index Terms-Chaos communications, multisection lasers. CHAOS-BASED communication can be considered as an alternative technique to encode and transmit information at high bit rate in conventional optical communication systems. Recent experiments in an installed optical fiber network have stressed the potential of this technique [1]. Within a chaotic carrier, the information can be encoded in different ways, the most common ones being chaos shift keying [2], amplitude chaos masking [3], and chaos modulation [1]. As an alternative to these traditional schemes, a new promising encryption method termed on-off phase-shift keying (OOPSK) has been proposed recently [4], [5]. It requires two external cavity semiconductor lasers, matched within a certain precision, operating in a chaotic regime unidirectionally coupled in a master-slave configuration. If the external cavities of the lasers are identical, the two outputs synchronize with a high correlation coefficient. However, if the two cavities differ within subwavelength precision, synchronization quality degrades [4]. By periodically, or aperiodically, changing slightly the external cavity of the master laser, the slave becomes synchronized (high correlation coefficient) or unsynchronized (low correlation coefficient) with the master. These two states, synchronized and unsynchronized, allow us to define two bits, "0" and "1" [5]. The main advantage is that no traces of the message can be guessed either in time or in the frequency domain. Calculations reveal that the maximum rate at which information can be encrypted with the OOPSK method depends on the resynchronization time when the system moves from an unsynchronized stated to a synchronized one. This time depends, as well, on the round-trip time in the external cavity [6]. Consequently, external cavity semiconductor lasers would only allow for bit rates M s [5]. This limitation could be overcome by using much shorter feedback paths.In this letter, we consider the limit of ultrashort optical feedback [7] with delay times of only a few picoseconds. Ultrashort optical feedback can be achieved by integrating the feedback path into the semiconductor laser in the framework of a multisection structure [8]. The result is a compact and robust device which, in addition to the short time scales, is an important requirement for possible applications. Multisection lasers are indeed expected to be essential sources for high bit rate OOPSK encryption.The particular laser structure considered here consists of three sections (see Fig. 1): a single-mode m distributed feedback (DFB) laser, a passive phase-tuning section of higher...

Stability of the nonlinear dynamics of an optically injected VCSEL

“…The latter range from periodic oscillatory output to chaotic behavior [5,6]. The complex nonlinear dynamics arising from optical injection have been investigated using a variety of semiconductor lasers, including edge-emitting Fabry Perot [6], distributed feedback (DFB) [7], multi-section [8] and vertical cavity surface emitting laser (VCSEL) devices [9][10][11][12][13][14][15][16][17][18][19].…”

Mutual optical injection in coupled DBR laser pairs

“…Mutually coupled lasers have been modelled theoretically [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] via coupled nonlinear differential equations for the carrier density, electric field amplitude and phase, where, in addition to the normal parameters found in laser rate equations, coupling strength, coupling time τ and, in some cases [12], optical feedback strength and feedback delay, are introduced. Comparison of 1/τ with the relaxation oscillation frequencies ω RO of the lasers allows mutually coupled systems to be classified into long and short coupling regimes.…”

Information Encoding and Decoding Using Unidirectionally Coupled Chaotic Semiconductor Lasers Subject to Filtered Optical Feedback

“…Message encoding/decoding via a chaos-pass filtering process was demonstrated in 2000 [8], yielding a very fast growth of the field in the last few years [9]- [12]. Nowadays, mechanically stable integrated sources are being proposed and tested [13]- [15].…”

“…The receiver system filters out the message encoded in the transmitted signal, and the information can be extracted by a simple subtraction. Besides the conventional optical feedback scheme, other configurations including optical injection [4], amplified injection [16], amplified optical feedback [13], incoherent optical feedback and injection [17], [18], optoelectronic feedback [19], and multimode lasers [20] [21] have also been investigated.…”