Optical Flip-flop Research Articles

Microwatt Volatile Optical Bistability via Nanomechanical Nonlinearity.

Metastable optically controlled devices (optical flip-flops) are needed in data storage, signal processing, and displays. Although nonvolatile memory relying on phase transitions in chalcogenide glasses has been widely used for optical data storage, beyond that, weak optical nonlinearities have hindered the development of low-power bistable devices. This work reports a new type of volatile optical bistability in a hybrid nano-optomechanical device, comprising a pair of anchored nanowires decorated with plasmonic metamolecules. The nonlinearity and bistability reside in the mechanical properties of the acoustically driven nanowires and are transduced to the optical response by reconfiguring the plasmonic metamolecules. The device can be switched between bistable optical states with microwatts of optical power and its volatile memory can be erased by removing the acoustic signal. The demonstration of hybrid nano-optomechanical bistability opens new opportunities to develop low-power optical bistable devices.

Controllable optical bistability based on rotation in semiconductor micro-cavity

In this paper, we discuss a possibility to realize the optical bistability in a rotating semiconductor micro-cavity system. To study the mean cavity photon number profile, we have obtained stationary solution by solving Heisenberg–Langevin equations of motion. In a rotating semiconductor micro-cavity system, bistability is observed when the cavity is driven externally in one direction but not the other direction. The bistable behavior is possible for strong coupling regime, and this can be controlled by hopping strength, decay rates and pump power. The photon profile also shows tunable zero intensity window. The system may be useful to design all-optical switch and optical flip–flop i.e., optical memory element, which would be faster in applications and compact in size.

Investigations with all optical sequential circuit at higher data rate

Abstract All optical signal processing is one of the growing area, finds relevance where fast computing speed is one of the vital concern. Optical sequential logic system is the backbone of the ultrafast processing network. Accordingly, this article explores proposed optical sequential schemes for the JK and T-type optical flip flop’s investigation at higher data rate. The outputs have been verified for the JK and T-type flip flops. Numerical simulations showed ER of 11.6 and 10 dB for the executed designs. Design have been investigated for variation in pump current, data rate (10–100 Gbps), peak power, bias voltage yielded the optimal performance with ER of over 12 dB. This schematic is simple excludes expensive optoelectronic translation and outcomes are well helpful for the design of complex sequential logic operations.

Terahertz Spoof Surface Plasmonic Logic Gates.

SummaryLogic gates are important components in integrated photonic circuitry. Here, a series of logic gates to achieve fundamental logic operations based on linear interference in spoof surface plasmon polariton waveguides are demonstrated at terahertz frequencies. A metasurface-based plasmonic source is adopted to couple free-space terahertz radiation into surface waves, followed by a funnel-shaped metasurface to efficiently couple the surface waves to the waveguides built on a domino structure. A single Mach-Zehnder waveguide interferometer can work as logic gates for four logic functions: AND, NOT, OR, and XOR. By cascading two such interferometers, NAND and NOR operations can also be achieved. Experimental investigations are supported by numerical simulations, and good agreement is obtained. The logic gates have compact sizes and high intensity contrasts for the output “1” and “0” states. More complicated functions can be envisioned and will be of great value for future terahertz integrated computing.

Reconfigurable nonlinear nonreciprocal transmission in a silicon photonic integrated circuit

We present a programmable silicon photonic integrated circuit (PIC) that can be configured to show nonlinear nonreciprocal transmission at high optical input power. Nonreciprocal transmission in PICs is of fundamental importance in various fields. Despite diverse approaches to generate nonreciprocal transmission, the research on efficient control of this effect is still scarce. The silicon PIC presented here has programmable linear and nonlinear behavior using integrated phase shifters. In the nonlinear regime (high optical power), the device can be configured to be either reciprocal or nonreciprocal between opposite propagation directions with over 30 dB extinction ratio and only 1.5 dB insertion loss. More importantly, the high/low transmission direction can be dynamically reconfigured. Furthermore, nonreciprocal transmission based on nonlinearities usually requires the optical field in both propagation directions to be high, in order to induce a large extinction ratio. For our circuit, only the forward-propagating light needs to have high power to enjoy low-loss transmission while the backward propagating light will always suffer a high rejection. Besides this nonreciprocal behavior, the circuit also offers the ability for all-optical functions, such as switching, optical compute gates, or optical flip-flops, thanks to its unique controllable nonlinear behavior. This work can trigger new research efforts in nonreciprocal photonics circuits.

All-optical switching and flip-flop based on dynamically controlled bistability in a V-type atomic system

We have proposed a scheme for all-optical switching and flip-flop based on controllable optical bistability in a simple three-level V-type atomic system assisted by an incoherent pump field. Due to the auxiliary incoherent pump, the atomic population is redistributed in the three levels, and then the absorption-dispersion property and the Kerr nonlinearity of the medium are different from those of the conventional V-type electromagnetically induced transparency system. The results show that both the thresholds and the area (or shape) of the hysteresis loop can be controlled efficiently via the adjustment of either the incoherent pump field or the coupling field. As a result, with a constant cavity input, the output of the optical cavity can be switched between the low- and high-power states of different bistable curves by tuning the optical fields. Based on this effect, we realize all-optical steady-state switching and set-reset flip-flop operation by adding a pulse sequence (positive pulse or set-reset pulse) onto either the incoherent pump field or the coupling field. Such a simple and effective technique of optical switching and flip-flop can find application in all-optical signal processing systems.

10 Gb/s optical random access memory (RAM) cell.

Optical random access memories (RAMs) have been conceived as high-bandwidth alternatives of their electronic counterparts, raising expectations for ultra-fast operation that can resolve the ns-long electronic RAM access bottleneck. However, experimentally demonstrated optical RAMs have been limited to up to 5GHz only, failing to validate the speed advantages over electronics. In this Letter, we demonstrate the first all-optical RAM cell that performs both Write and Read functionalities at 10Gb/s, reporting on a 100% speed increase compared to state-of-the-art optical RAM demonstrations. To achieve this, the proposed RAM cell deploys a monolithically integrated InP optical Flip-Flop and a Semiconductor optical amplifier-Mach-Zehnder Interferometer (SOA-MZI) On/Off switch configured to operate as a strongly saturated differentially-biased access gate. Error-free operation is demonstrated at 10Gb/s for both Write and Read operations with 6.2dB and 0.4dB power, respectively, achieving the fastest reported RAM cell functionalities.

Performance analysis of different designs of all-optical D flip flop

All optical flip flops play an important role in optical networks as well as in the field of optical computing. Optical memories are used for storing decisions in photonic packet routers temporarily. In this paper all optical D-flip flop is designed based on all optical gates. The nonlinear effects such as XGM (Cross Gain Modulation), XPM (Cross Phase Modulation) and FWM (Four Wave Mixing) are used to design all optical gates. We designed the D flip flop based on two logic that are NAND-NAND logic and NAND-NOR logic. The performance of both the designs is analyzed and the functionality of all optical D-flip-flop is verified using the truth table. It is proved that NAND-NAND logic is more effective than NAND-NOR logic.

A new scheme of an all optical frequency encoded dibit based latch with its simulated result

Super fast all optical memory and optical logic gates are the basic building blocks for optical computation and communication systems. Realization of a very fast memory cell in the optical domain is very challenging. Recently different theoretical proposals based on combinational and sequential logic circuits for developing all optical flip flops as well as memory cells have been reported by different authors. Here, the authors have proposed a new scheme of an all optical frequency encoded dibit based latch circuit using a reflective semiconductor optical amplifier and an add/drop multiplexer with its proper simulation. The use of the dibit representation technique along with the optical frequency encoding technique makes the system very fast, reduces the bit error problem, and increases the signal to noise ratio.

All-optical tree-based greedy router using optical logic gates and optical flip-flops

Due to ever-increasing throughput demands, the lookup in conventional IP routers based on longest prefix matching is becoming a bottleneck. Additionally, the scalability of current routing protocols is limited by the size of the routing tables. Geometric greedy routing is an alternative to IP routing which replaces longest prefix matching with a simple calculation employing only local information for packet forwarding. For the first time, in this paper we propose a novel and truly all-optical geometric greedy router based on optical logic gates and optical flip-flops. The circuit of the router is constructed through the interconnection of SOAs and directional couplers. The successful functionality of the proposed router is verified through simulation. The circuit enables high data rate throughput.

Integrated Optical Content Addressable Memories (CAM) and Optical Random Access Memories (RAM) for Ultra-Fast Address Look-Up Operations

Electronic Content Addressable Memories (CAM) implement Address Look-Up (AL) table functionalities of network routers; however, they typically operate in the MHz regime, turning AL into a critical network bottleneck. In this communication, we demonstrate the first steps towards developing optical CAM alternatives to enable a re-engineering of AL memories. Firstly, we report on the photonic integration of Semiconductor Optical Amplifier-Mach Zehnder Interferometer (SOA-MZI)-based optical Flip-Flop and Random Access Memories on a monolithic InP platform, capable of storing the binary prefix-address data-bits and the outgoing port information for next hop routing, respectively. Subsequently the first optical Binary CAM cell (B-CAM) is experimentally demonstrated, comprising an InP Flip-Flop and a SOA-MZI Exclusive OR (XOR) gate for fast search operations through an XOR-based bit comparison, yielding an error-free 10 Gb/s operation. This is later extended via physical layer simulations in an optical Ternary-CAM (T-CAM) cell and a 4-bit Matchline (ML) configuration, supporting a third state of the “logical X” value towards wildcard bits of network subnet masks. The proposed functional CAM and Random Access Memories (RAM) sub-circuits may facilitate light-based Address Look-Up tables supporting search operations at 10 Gb/s and beyond, paving the way towards minimizing the disparity with the frantic optical transmission linerates, and fast re-configurability through multiple simultaneous Wavelength Division Multiplexed (WDM) memory access requests.

Design of frequency-encoded data-based optical master-slave-JK flip-flop using polarization switch

An optical data processing and communication system provides enormous potential bandwidth and a very high processing speed, and it can fulfill the demands of the present generation. For an optical computing system, several data processing units that work in the optical domain are essential. Memory elements are undoubtedly essential to storing any information. Optical flip-flops can store one bit of optical information. From these flip-flop registers, counters can be developed. Here, the authors proposed an optical master-slave (MS)-JK flip-flop with the help of two-input and three-input optical NAND gates. Optical NAND gates have been developed using semiconductor optical amplifiers (SOAs). The nonlinear polarization switching property of an SOA has been exploited here, and it acts as a polarization switch in the proposed scheme. A frequency encoding technique is adopted for representing data. A specific frequency of an optical signal represents a binary data bit. This technique of data representation is helpful because frequency is the fundamental property of a signal, and it remains unaltered during reflection, refraction, absorption, etc. throughout the data propagation. The simulated results enhance the admissibility of the scheme.

Symmetry Breaking of Counter-Propagating Light in a Nonlinear Resonator

Spontaneous symmetry breaking is a concept of fundamental importance in many areas of physics, underpinning such diverse phenomena as ferromagnetism, superconductivity, superfluidity and the Higgs mechanism. Here we demonstrate nonreciprocity and spontaneous symmetry breaking between counter-propagating light in dielectric microresonators. The symmetry breaking corresponds to a resonance frequency splitting that allows only one of two counter-propagating (but otherwise identical) states of light to circulate in the resonator. Equivalently, this effect can be seen as the collapse of standing waves and transition to travelling waves within the resonator. We present theoretical calculations to show that the symmetry breaking is induced by Kerr-nonlinearity-mediated interaction between the counter-propagating light. Our findings pave the way for a variety of applications including optically controllable circulators and isolators, all-optical switching, nonlinear-enhanced rotation sensing, optical flip-flops for photonic memories as well as exceptionally sensitive power and refractive index sensors.

Numerical Simulation of an All Optical Flip-Flop Based on a Nonlinear Distributed Bragg Reflector Laser Structure

A new design for an all optical flip flop is introduced. It is based on a nonlinear Distributed Bragg Reflector (DBR) semiconductor laser structure. The device does not require a holding beam. An optical gain medium confined between 2 Bragg reflectors forms the device. One of the Bragg reflectors is detuned from the other by making its average refractive index slightly higher, and it has a negative nonlinear coefficient that is due to direct absorption at Urbach tail. At low light intensity in the structure, the detuned Bragg reflector does not provide optical feedback to start a laser mode. An optical pulse injected to the structure reduces the detuning of the nonlinear Bragg reflector and a laser mode builds up. The device is reset by detuning the second Bragg reflector optically by an optical pulse that generates electron-hole pairs by direct absorption. A mathematical model of the device is introduced. The model is solved numerically in time domain using a general purpose graphics processing unit (GPGPU) to increase accuracy and to reduce the computation time. The switching dynamics of the device are in nanosecond time scale. The device could be used for all optical data packet switching/routing.

An Improved Design for an All-Optical Flip-Flop Based on a Nonlinear 3-Sections DFB Laser Cavity

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 Signal Processing Based on Self-Induced Polarization Control in Optical Fibers

In this contribution, we review our recent progress on the all-optical control of the state-of-polarization of light in optical fibers upon propagation in a system called Omnipolarizer. More precisely, in this device we exploit the unexpected capability of light to self-organize its own state-of-polarization, upon propagation in optical fibers, into universal and environmentally robust states. The underlying physical mechanism consists in a nonlinear cross-polarization feedback interaction between an arbitrary polarized incident signal and its own counter-propagating replica generated at the fiber end by means of a reflective element. Depending on the power ratio between the two waves, e.g., the reflective coefficient, this nonlinear self-repolarization phenomenon offers a rich variety of dynamics for which we have highlighted three main working regimes identified by first a bistable operating regime, a polarization alignment process as well as a genuine chaotic behavior. We have fully characterized these three operating regimes with an excellent agreement between numerical and experimental results. Moreover, beyond the fundamental aspect of these first studies, we have then exploited this self-induced repolarization phenomenon in order to implement several proof-of-principles for all-optical signal processing. In particular, we have successfully demonstrated the spontaneous repolarization of a 10-Gb/s return-to-zero optical signal without noticeable impairments. The bistability and associated hysteresis properties of the Omnipolarizer have been also exploited to implement an optical flip-flop memory as well as a 10-Gb/s polarization-based data packet router. Finally, we have taken advantage of the chaotic dynamics of our device to demonstrate an all-optical scrambler enabling truly chaotic polarization diversity for 10-Gb/s on/off keying wavelength division multiplexing applications.

Bistable 1060-nm High-Power Single-Mode DFB Laser Diode

We report a novel high-power bistable distributed feedback (DFB) semiconductor laser diode operating near 1060 nm, which is realized by inserting a high-bandgap electron barrier layer and a grating layer in a super large optical cavity laser design. Optical and electrical bistable characteristics are both observed for this device. An on-state optical output power of 98 mW and an on-off extinction ratio of 22 dB were demonstrated between the bistable states. A qualitative physical model based on carrier population profile shift is used to explain the switching effect. Optical flip-flop operation was also demonstrated.

Spontaneous mirror-symmetry breaking in coupled photonic-crystal nanolasers

Multi-cavity photonic systems, known as photonic molecules (PMs), are ideal multi-well potential building blocks for advanced quantum and nonlinear optics. A key phenomenon arising in double well potentials is the spontaneous breaking of the inversion symmetry, i.e. a transition from a delocalized to two localized states in the wells, which are mirror images of each other. Although few theoretical studies have addressed mirror-symmetry breaking in micro and nanophotonic systems, no experimental evidence has been reported to date. Thanks to the potential barrier engineering implemented here, we demonstrate spontaneous mirror-symmetry breaking through a pitchfork bifurcation in a PM composed of two coupled photonic crystal nanolasers. Coexistence of localized states is shown by switching them with short pulses. This offers exciting prospects for the realization of ultra-compact, integrated, scalable optical flip-flops based on spontaneous symmetry breaking. Furthermore, we predict such transitions with few intracavity photons for future devices with strong quantum correlations.

All-optical S-R flip flop using 2-D photonic crystal

The photonic crystals (PhC) draw significant attention to build all optical logic devices and considered one of the solutions for the opto-electronic bottleneck via speed and size. The paper presents a novel all optical SR flip flop memory based on two optical NOR gates using 2D PhC. The design of optical Flip Flop is based on four nonlinear photonic crystal ring resonator and T-type waveguide. The total size of the proposed optical memory flip flop is equal to 30 μm × 30 μm. The structure has lattice constant ‘a’ is equal to 630 nm and bandgap range from 0.32 to 044. The flip flop design has a switching time in few Picoseconds and low power input of 50 mW. The PhC structure has a square lattice of silicon rod with refractive index of 3.39 in air. The overall design and the results are discussed through the experimental implementation and the numerically simulation to confirm its operation and feasibility.

ALL OPTICAL OVSF CODE GENERATOR REALIZATION USING OPTICAL FLIP FLOP AND OPTICAL HARDLIMITTERS

The orthogonal variables spreading factor (OVSF) provides variables data rates to flexible support many applications with different bandwidth. This paper presents an optical OVSF code generator using all optical gates and a set of all optical flip-flops based on two coupled polarization switches (PSWs). The optical OVSF code generator helps to use the OVSF code technique in optical communications. The general objective is to make the OVSF code tree suitable to support a lot of users in the optical communication links. The overall design and the results are discussed through the realization and the computing numerical simulation to confirm its operation and feasibility. The proposed scheme has been theoretically demonstrated for a spreading factor of 4 and 8.