All-optical flip-flop with high on-off contrast ratio using two injection-locked single-mode Fabry-Perot laser diodes

Reconfigurable all-optical bistability/tristability in dual injection-locked Fabry-Perot laser diodes

In this Letter, we present a detailed theoretical and experimental investigation of optical bistability and tristability in dual injection-locked Fabry-Perot laser diodes. The proposed device can be reconfigured between the bistable and tristable regimes, simply by adjusting the power level of the injected control optical signal. The tristability presented in the experiment is achieved for relatively low optical input powers between 1.03 and 1.25 mW, with the output signal ratio of up to 7 dB between stable states. Such a device is a potential candidate for designing trits, a bit analogy in ternary computational logic.

Optical RAM and integrated optical memories: a survey

The remarkable achievements in the area of integrated optical memories and optical random access memories (RAMs) together with the rapid adoption of optical interconnects in the Datacom and Computercom industries introduce a new perspective for information storage directly in the optical domain, enabling fast access times, increased bandwidth and transparent cooperation with optical interconnect lines. This article reviews state-of-the-art integrated optical memory technologies and optical RAM cell demonstrations describing the physical mechanisms of several key devices along with their performance metrics in terms of their energy, speed and footprint. Novel applications are outlined, concluding with the scaling challenges to be addressed toward allowing light to serve as both a data-carrying and data-storage medium.

High-extinction ratio and ultra-compact two-bit comparators based on graphene-plasmonic waveguides

Electro-optical 1-bit and 2-bit comparators based on graphene plasmonic waveguides are proposed. Surface plasmon polaritons are stimulated by radiation of a TM-polarized light with a wavelength of 15 µm and their propagation is controlled by applying electrical signals which represent the binary numbers that need to be compared. The results of comparing two numbers are obtained in the form of light at the output ports. Finite-difference time-domain simulation results show that the minimum extinction ratios (ERs) for 1-bit and 2-bit comparators are 9.69 dB and 6.13 dB, respectively. Also, the 1-bit and 2-bit structures have footprints of ${0.42}\;\unicode{x00B5}{\rm m}^2$0.42µm² and ${0.9}\;\unicode{x00B5}{\rm m}^2$0.9µm², respectively. Our studies show that the optical comparators with these ultra-compact dimensions have not been reported so far. The presented structures benefit from high ER and ultra-compact footprint, which make them suitable for use in optical signal processing and photonic computing.

All-optical majority gate based on an injection-locked laser

An all-optical computer has remained an elusive concept. To construct a practical computing primitive equivalent to an electronic Boolean logic, one should utilize nonlinearity that overcomes weaknesses that plague many optical processing schemes. An advantageous nonlinearity provides a complete set of logic operations and allows cascaded operations without changes in wavelength or in signal encoding format. Here we demonstrate an all-optical majority gate based on a vertical-cavity surface-emitting laser (VCSEL). Using emulated signal coupling, the arrangement provides Bit Error Ratio (BER) of 10⁻⁶ at the rate of 1 GHz without changes in the wavelength or in the signal encoding format. Cascaded operation of the injection-locked laser majority gate is simulated on a full adder and a 3-bit ripple-carry adder circuits. Finally, utilizing the spin-flip model semiconductor laser rate equations, we prove that injection-locked lasers may perform normalization operations in the steady-state with an arbitrary linear state of polarization.

Optically tunable microwave, millimeter-wave and submillimeter-wave utilizing single-mode Fabry-Pérot laser diode subject to optical feedback

In this paper, we use optical feedback injection technique to generate tunable microwave, millimeter-wave and submillimeter-wave signals using single-mode Fabry-Pérot laser diode. The beat frequency of the proposed generator ranges from 30.4 GHz to 3.40 THz. The peak power ratio between two resonating modes at the output spectrum of can be less than 0.5 dB by judiciously selecting feedback wavelength. In the stabilization test, the peak fluctuation of photonic signal is as low as 0.19 dB within half hour. Aside from locking regions, where the laser is easily locked by the injection beam, the side-mode suppression ratio is well over 25 dB with the maximum value of 36.6 dB at 30.4 GHz beat frequency. In addition, the minimum beat frequency interval between two adjacent photonic signals is as low as 10 GHz.

Switching time in optically bistable injection-locked semiconductor lasers

Switching between states in a dispersive bistable injection-locked slave laser has been theoretically investigated. We show that the switching can be achieved by relatively small and short (≈10-50 ps) variation of the master laser injection power or frequency, which, besides the variation of the slave laser optical power, leads to significant variation of its photon phase (≈5π/6). By using an analytical model, we calculate the switching time dependence on the magnitude of the injection power and the frequency detuning variation.

Theoretical modeling of an improved all-optical flip flop based on a nonlinear semiconductor distributed feedback laser structure

A new, improved design of an all-optical flip flop is proposed. The waveguiding layer of the device consists of a phase-shifted nonlinear grating. The grating layers of a high refractive index have a negative nonlinear coefficient. A phase-shift section exists at the middle of the waveguiding layer. The optical gain is provided by current injection into an active layer. Nonlinearity in the waveguiding layer is achieved by direct absorption at the edge of the absorption band (Urbach tail). In the "OFF" state, the waveguiding layer forms a weak grating with an optical feedback below the laser threshold. In the "ON" state, the device functions as a distributed feedback (DFB) laser due to an induced strong grating in the nonlinear waveguiding layer. The improvements of the device performance by reducing the set pulse energy and accelerating the switch-off process are discussed. Field simulations in the time domain were performed.

All-optical clocked delay flip-flop using a single terahertz optical asymmetric demultiplexer-based switch: a theoretical study

A flip-flop (FF) is a kind of latch and the simplest form of memory device, which stores various values either temporarily or permanently. Optical FF memories form a fundamental building block for all-optical packet switches in next-generation communication networks. An all-optical clocked delay FF using a single terahertz optical asymmetric demultiplexer-based interferometric switch is proposed and described. Numerical simulation results are also reported.