An all-optical set-reset flip-flop is presented that is based on two coupled lasers with separate cavities and lasing at different wavelengths. The lasers are coupled so that lasing in one of the lasers quenches lasing in the other laser. The flip-flop state is determined by the laser that is currently lasing. A rate-equation based model for the flip-flop is developed and used to obtain steady-state characteristics. Important properties of the system, such as the minimum coupling between lasers and the optical power required for switching, are derived from the model. These properties are primarily dependent on the laser mirror reflectivity, the inter-laser coupling, and the power emitted from one of the component lasers, affording the designer great control over the flip-flop properties. The flip-flop is experimentally demonstrated with two lasers constructed from identical semiconductor optical amplifiers (SOAs) and fiber Bragg gratings of different wavelengths. Good agreement between the theory and experiment is obtained. Furthermore, switching over a wide range of input wavelengths is shown; however, increased switching power is required for wavelengths far from the SOA gain peak.

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All-optical flip-flop based on coupled laser diodes

An all-optical set-reset flip-flop is presented that is based on two coupled identical laser diodes. The lasers are coupled so that when one of the lasers lases, it quenches lasing in the other laser. The state of the flip-flop is determined by which laser is currently lasing. Rate equations are used to model the flip-flop, and it is experimentally demonstrated by the use of antireflection-coated laser diodes and free-space optics. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 157-159, 2000.

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All‐optical flip‐flop based on coupled laser diodes

Optical memories are optical bi(multi-)stable systems whose states can be switched all optically. Acting as a fundamental building block for digital optical signal processing, they have received considerable attention. Many types of optical memories have been explored, which all have in common that they are optical storage elements with two states. Multi-stable optical logic building blocks are interesting for applications in telecommunication systems, since they have potential to process a large number of wavelength channels in parallel. In this thesis, we present two types of multi-stable operation of coupled lasers. The first one is based on coupled ring lasers, which share a single active element and a feedback arm. A single ring laser with feedback can be regarded as an oscillator, since the intensity of the lasing light in the lasing cavity is periodically oscillating. When two such oscillators are coupled together, sharing the same active element and the same feedback arm, they synchronize in a common oscillation frequency if their individual oscillation periodicities are close to each other; otherwise they show bistability between the two oscillators. Switching between different stable states can be realized by injecting external light, in this sense, the system act as an optical memory. Moreover, this concept can easily realize multi-state operation, since only one active element is required. An eight-state optical memory is demonstrated. The second type of multi-stable operation of coupled lasers is based on serially interconnected lasers using the principle of gain quenching. The light from the dominant laser suppresses its neighboring lasers through gain saturation, but still receives amplification by the active element of the suppressed lasers, compensating for coupling losses. This light passes through each of the successive lasers, simultaneously suppressing and being amplified. By this mechanism all the other lasers are suppressed. Only one of the lasers can lase at a time, thus the state of the optical memory is determined by the wavelength of the dominant laser, as same as the first type. A five-state optical memory based on this concept is experimentally demonstrated. Moreover, we use the optical memories as a fundamental logic unit to realize sophisticated optical logic. We present an optical shift register that consists of two serially connected optical memories driven by common clock pulses. The concept is demonstrated at an operation speed of 20 kHz, which is limited by the laser cavities implemented by 10 meter long fiber pigtailed components. Furthermore, we cascade the optical shift register and an optical XOR gate to realize an optical pseudorandom number generator based on optical memories.

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Optical multi-stable operations of coupled lasers

A new class of optical bistable devices, relying on the mutual quenching of two identical lasers, is theoretically analyzed. Conditions for achieving adequate competition between an external injected beam and the intracavity field through a noncoherent coupling (NCC) are discussed. Steady-state and transient behaviors are analyzed and lead to fast electrical or optical switching ( < 100 ps) and low commutation energy (<10 pJ). High efficiency, compactness, and technological compatibility with other integrated devices are expected. In addition, the emissive properties of these devices should considerably simplify their use in cascaded configurations.

Theoretical analysis of a new class of optical bistability due to noncoherent coupling within a twin-laser system

A parallel pattern-recognition system composed of coupled-element tristable optical components is proposed Each elemental component is an optical ring resonator in which three cells of nonlinear refractive-index material are placed between mirrors The basic idea is derived from the symmetry-breaking instability caused by the unbalance between counterpropagating input light fields that excite the nonlinear refractive-index material (the cell) bidirectionally Input spatial patterns composed of the arbitrary combinations of [0, 0, 0], [1, 1, 0], [0, 1, 1], and [1, 0, 1] are found to be recognized at once, yielding the capacity of ⅔ bit/cell

Pattern recognition with a bidirectionally coupled nonlinear-optical-element system.

Competition between external beam amplification and normal laser action is shown to result in a new type of optical bistability in high gain lasers. With one dye laser in a delayed self‐extinction configuration, periodic pulsations are observed, showing the alternation of two quasi‐stable states. With a twin dye laser configuration, only one laser at a time could be above threshold due to their mutual coupling. Switching with subnanosecond rise time has been obtained in a purely optical way.

R. Kuszelewicz

Papers

Demonstration of optical bistability with intensity‐coupled high gain lasers