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A new all optical flip-flop based on a 3-sections nonlinear semiconductor DFB laser structure is proposed and simulated. The operation of the device does not require a holding beam. Electrical current injection into an active layer provides optical gain to the laser mode. The wave-guiding layer consists of a linear grating section centered between 2 detuned nonlinear grating sections. The average refractive index in the nonlinear sections is slightly higher than the refractive index of the middle section. A negative nonlinear refractive index coefficient exists along the nonlinear sections. In the “OFF” state, the DFB structure does not provide enough optical feedback to lase due to the detuned sections. At high light intensity in structure, “ON” state, detuning decreases and the DFB structure allows for a laser mode that sustains the decrease in detuning to exist. The nonlinearity is provided by direct photon absorption at the Urbach tail. Numerical simulations using GPGPU computing show nanoseconds transition times between “OFF” and “ON” states.

All-optical data packet routing and processing requires an all optical data memory element to store optical information related to the optical data packet, [

In this work, an improved design is introduced. The device design is symmetric and requires less injected current. A novel all-optical flip-flop based on a 3-sections nonlinear DFB laser structure is proposed. The device allows for a bistable operation as is [

The device schematic is shown in

two nonlinear sections of constant refractive index. Hence the structure shown in this article is easier in fabication. Second, the structure shown in [

Schematic of the device is shown in

this case, is reduced and the optical laser mode is not allowed to build up. In this work,

The laser mode in the device is modeled as 2 counter propagating modes. Coupled mode equations are used to model laser mode in the device [

Equations (1) and (2) represent the coupled mode equations of the laser mode and the “Set” pulse. Equation (3) presents the “Reset” pulse. Equations (4) and (5) describe detuning, loss and coupling coefficients (

c is the velocity of light in vacuum, and

It was assumed, in the simulations,

The system of differential equations is solved using Rung-Kutta technique. The length of the device is divided into 80 sections.

General purpose graphics processing unit (GPGPU) computing is used to perform long simulation time (150 nanosecond). This is done by distributing the computation load along the length of the device among 80 parallel threads that compute the forward and backward fields in the next time step simultaneously. The parallel computation decreases the computation time. The numerical simulations use a PC (processor: intel Core i3-4130 CPU at 3.40 GHz ´ 4, and 32 GB RAM) and graphics processing unit (GPU) Nvidia GeForce GTX 670. The program is coded using Cuda C, [

In the following sections, optical bi-stability and ON/OFF switching dynamics in time domain are investigated by solving the mathematical model numerically.

In the following simulations, the output optical laser power is

the meduim. The output power is normalised to

lightaqua Symbols | Description | Value |
---|---|---|

Device length | 375 mm | |

Current injected into the device | 0.040313 Ampere | |

Average ref. index | 3 | |

Group velocity | ||

Line-width enhancement | −0.5 | |

Gain saturation | ||

Overlap factor | 0.35 | |

Cavity volume | ||

Non-radiative recomb | 1 nsec | |

in nonlinear sections | ||

Non-radiative recomb | 3 nsec | |

in active region | ||

Radiative Recombination | ||

Auger recombination | ||

Differential gain at | ||

Differential gain at | ||

Transparency carrier density | 1023 m^{−3} |

the Electric fields are normalised to

Optical output mode power versus electrical current injected bi-stability is calculated as follow. The injected current to the device is increased from 0 to 0.08 Ampere in 75 nanosecond linearly. Then, the current is decreased linearly till it reaches 0 in an another 75 nanosecond. Optical bi-stability loop is shown in ^{−1}) due to direct absorption) at ^{−1}). This central part, at low light intensity in the device, does not provide enough optical feedback to produce a laser mode. This is due to the high escaping rate of photons at

The output optical powers at the ON and at the OFF states are simulated for 150 nsec to insure the stability of the output in each state.

The device is switched ON by a Set pulse at

A part of the input pulse energy (photons) is absorbed in the nonlinear wave-guiding sections. It generates electron-hole pairs that reduce the refractive index in each nonlinear section. This decrease in refractive index decreases the detuning in these sections. Hence, the reflection band of each nonlinear section starts to overlap with the reflection band of the middle phase-shifted grating. The optical feedback (reflections) from both nonlinear sections increases, an optical laser mode builds up in the central part of the nonlinear grating section. The optical power of the laser mode maintains the changes in the refractive index in both nonlinear sections.

Set-Reset operation is simulated in time domain for 22.5 nsec. At t = 22.5 nsec from the start of simulation time, an input optical pulse (Set pulse) at

The output optical power is shown in

Multiple Set/Reset operations are simulated for 150 nsec.

The input pulses are shown in

in the time interval between the RESET pulse and the next SET pulse, and after the multiple operations elapse. This is the same value in the OFF state. During the RESET operations

In this work, a new, improved all-optical flip-flop based on a nonlinear 3-sections DFB laser structure was investigated. The device has advantages over work shown in [

is used to solve the mathematical model using parallel computing to be able to decrease the integration step and to be able to reduce the simulation time. The switching dynamics are investigated and show switching between different states in nanosecond time scale. The device is switched ON with a

Hossam Zoweil, (2016) An Improved Design for an All-Optical Flip-Flop Based on a Nonlinear 3-Sections DFB Laser Cavity. Optics and Photonics Journal,06,87-100. doi: 10.4236/opj.2016.65012