All-optical Flip-flop Operation Research Articles

Switchable All-Optical Flip-Flop and Inverter Operations in Quantum Well Microring Laser

We experimentally demonstrate all-optical flip-flop and inverter operations using two adjacent lasing wavelengths in a quantum-well microring laser, and that the state is switched between the flip-flop and inverter operations by changing the phase in the outer cavity composed of busline waveguides. We also propose multimodal rate equations for a microring laser taking into account clockwise and counter-clockwise light propagations. By comparing experimental results and simulated results based on the rate equations, the principle of the switching between the flip-flop and inverter operations is clarified.

An All Optical Approach to Construct J-K Flip-Flop by Proper Exploitation of Nonlinear Material

Optical signal is the best suitable one for data processing and digital signal communication for its inherent parallelism and tremendous operational speed. Conventional electronic or optoelectronic devices are unable to fulfill this due to less speed and time delay. In the case of perfect electronic flip-flop, at the time of switching turned ON, there is noticeable propagation delay on the order of nanoseconds. In the case of an opto-electronic flip-flop, although the propagation delays time is much less than those of a pure electronic flip-flop about 10 to 100 times less, there are many disadvantages still have. Some of these disadvantages are delay of response time due to the use of spatial light modulators, an O/E converter that does not operate at all frequencies or wavelengths, and the unavailability of such materials. An optical input encoding methodology may be the alternative for the performance of two inputs all-optical flip-flop operations. These operations may be conducted in all-optical mode and will be parallel in nature. All the operations may be conducted with proper exploitation of some nonlinear materials. In this communication author reported an optical encoding technique for the construction of clocked J-K flip-flop with two inputs. All the operations are conducted by the proper exploitation of nonlinear materials.

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.

Nonlinear model analysis of all-optical flip-flop and inverter operations of microring laser

We explore a theoretical model of bistability at two adjacent lasing wavelengths from an InGaAs/InGaAsP multiple quantum well (MQW) microring laser. We show that nonlinear effects on the phase and amplitude play significant roles in the lasing operations of the microring laser. Numerical simulations indicate that all-optical flip-flop operations and inverter operations can be observed within the same device by controlling the injection current. The validity of our analysis is confirmed by a comparison of the results for numerical simulations with experimental results of the lasing spectrum. We believe that the analysis presented in this paper will be useful for the future design of all-optical signal processing devices.

All-optical flip-flops based on dynamic Brillouin gratings in fibers.

A method to generate an all-optical flip-flop is proposed and experimentally demonstrated based on dynamic Brillouin gratings (DBGs) in polarization maintaining fibers. In a fiber with sufficiently uniform birefringence, this flip-flop can provide extremely long storage times and ultra-wide bandwidth. The experimental results demonstrate an all-optical flip-flop operation using phase-modulated pulses of 300ps and a 1m long DBG. This has led to a time-bandwidth product of ∼30, being in this proof-of-concept setup mainly limited by the relatively low bandwidth of the used pulses and the short fiber length.

All-optical flip-flop operation based on bistability in V-cavity laser.

We theoretically analyzed and experimentally demonstrated an injection-locking based all-optical flip-flop memory using a simple and compact tunable V-cavity laser (VCL). A bistable region in the tuning characteristics of the VCL is employed for the flip-flop operation. The state of the VCL can be set and reset by injecting signal pulses at two different wavelengths. The pulse power for both set and reset signal is only about 1 pJ. Short response times of about 150 ps are measured for storing and erasing.

All‐optical flip‐flop contrast enhancement based on bistable polarisation rotation within Fabry–Perót SOA

Switching-contrast enhancement of over 28 dB for all-optical flip-flop (AOFF) operation of a Fabry–Perot semiconductor optical amplifier (SOA) is experimentally demonstrated. Although the two stable flip-flop states of such a device are typically distinguished by their optical power, it is demonstrated that each stable state can also exhibit a unique state of polarisation (SOP). This bistable polarisation rotation (BPR) is leveraged to achieve extreme contrast enhancement by aligning the AOFF reset-state SOP to the blocking axis of a linear polariser, producing a contrast of 36.6 dB. This contrast-enhancement technique is applicable to other AOFFs based on resonant-type SOAs (RT-SOAs) and Kerr-nonlinear media, substantially improving their applicability to advanced photonic-switching applications.

Bit Error Rate Measurements of All-Optical Flip-Flop Operations of a 1.55-μm Polarization Bistable VCSEL

We measured the bit error rate (BER) of all-optical flip-flop operations using a 1.55-μm polarization bistable vertical-cavity surface-emitting laser (VCSEL). Polarization bistable flip-flop operations were obtained by injecting optical set and reset pulses with independently adjusted wavelengths toward the two VCSEL lasing modes, whose polarizations are orthogonal to each other. Acquired waveforms showed clearly opened eyes, and BERs less than 1 × 10−9 were measured up to 1 Gb/s although the optical set and reset pulse power was much lower than the VCSEL output power. We also demonstrated all-optical flip-flop operations by injecting optical set and reset pulses with the same wavelength, which were generated by a single laser diode. In this case, we obtained polarization bistable flip-flop operations up to 500 Mb/s with almost the same BER values that were obtained when the wavelengths of the set and reset pulses were adjusted independently. The optical input pulse powers were higher than for the case using input pulses with two different wavelengths, but still lower than the VCSEL output power.

Fast all-optical multistate flip-flop operation realized by a single self-sustained micro-ring laser memory cell

We investigate all-optical multistate flip-flop operation realized by a single self-sustained micro-ring laser memory cell based on a time-domain multi-mode nonlinear model. Each state is written by the corresponding 100 ps-width input non-return-to-zero (NRZ) pulse carrying the directional and wavelength information, and the cell remains in the written state until another trigger arrives. The effects of key parameters including the detuning frequency and injection power ratio on the injection locking and flipping regions of different modes in both directions of the micro-ring device are studied. By optimizing the operation conditions, we simulate the minimal switching speed for each mode. The fast switching speed of less than 20 ps and up to ten mode flip-flop operation indicate that this single optical memory cell can support ten states at a data rate of at least 10 Gbps, which is particularly valuable for the realization of future all-optical networking and functional sub-system technology.

Dynamics of 1.55 μm Wavelength Single-Mode Vertical-Cavity Surface-Emitting Laser Output under External Optical Injection

We review the temporal dynamics of the laser output spectrum and polarization state of 1.55 μm wavelength single-mode (SM) vertical-cavity surface-emitting lasers (VCSELs) induced by external optical beam injection. Injection of an external continuous-wave laser beam to a gain-switched SM VCSEL near the resonance wavelength corresponding to its main polarization-mode output was critical for improvement of its laser pulse generation characteristics, such as pulse timing-jitter reduction, linewidth narrowing, pulse amplitude enhancement, and pulse width shortening. Pulse injection of pulse width shorter than the cavity photon lifetime into the SM VCSEL in the orthogonal polarization direction with respect to its main polarization mode caused temporal delay of the polarization recovery after polarization switching (PS), and its delay was found to be the minimum at an optimized bias current. Polarization-mode bistability was observed even in the laser output of an SM VCSEL of a standard circularly cylindrical shape and used for all-optical flip-flop operations with set and reset injection pulses of very low pulse energy of order of the 3.5~4.5 fJ.

All-Optical Flip-Flop Operation at 1-mA Bias Current in Polarization Bistable Vertical-Cavity Surface-Emitting Lasers With an Oxide Confinement Structure

Polarization bistable vertical-cavity surface-emitting lasers (VCSELs) with an oxidation confinement structure were fabricated for low power consumption operation. Threshold current of the VCSEL was reduced to 0.22 mA. The VCSEL operated in a single longitudinal and transverse mode and in one of two orthogonal linear polarization modes. All-optical flip-flop operation based on polarization bistability was achieved at a record low bias current of 1.15 mA, which is about one tenth of our previously developed polarization bistable VCSEL without a current confinement structure.

All-optical flip-flop operation based on asymmetric active-multimode interferometer bi-stable laser diodes

We demonstrate fast and low energy all optical flip-flop devices based on asymmetric active-multimode interferometer using high-mesa waveguide structure. The implemented devices showed high speed all-optical flip-flop operation with 25 ps long pulses. The rising and falling times of the output signal were 121 ps and 25 ps, respectively. The required set and reset pulse energies were only 7.1 fJ and 3.4 fJ, respectively.

1-GHz All-Optical Flip-Flop Operation of Conventional Cylindrical-Shaped Single-Mode VCSELs Under Low-Power Optical Injection

All-optical set-reset flip-flop operations of conventional circular cylindrical-shaped 1.55-μm wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) have been demonstrated at a switching frequency of 1 GHz based on polarization bistability observed via injection current variation. The energy of set and reset pulses was lower than 4.5 fJ at a bias current of the VCSEL of 4 mA. Polarization bistable VCSELs will be useful for high-speed optical signal processing applications.

New alternative approach to all-optical flip-flop with nonlinear material

Due to its inherent parallelism and tremendous operational speed, optical signal is the most suitable for data processing and digital communication in various fields. Conventional electronic and opto-electronic systems are unable to fulfill this arena, because of their low speed and time delay. In the case of pure electronic flip-flop, when a switch is turned ON, there is notable propagation delay on the order of nanoseconds. For an opto-electronic flip-flop although the propagation delay time is much less than that of an electronic flip-flop (about 10 to 100 times less), there are many disadvantages. Some of these disadvantages are delay of response time due to the use of spatial light modulators, an O/E converter that does not operate at all frequencies or wavelengths, and the unavailability of such materials. An optical input encoding methodology is proposed for the performance of all-optical flip-flop operations possible for two inputs. These operations were conducted in all-optical mode and are parallel in nature. All the operations are treated with proper exploitation of some nonlinear materials.

All-optical Flip-flop Operation Based on Polarization Bistability of Conventional-type 1.55-㎛ Wavelength Single-mode VCSELs

We report, for the first time to our knowledge, observation of polarization bistability from 1.55-µm wavelength single-mode VCSELs of a conventional cylinder-shape under control of their driving current, and demonstration of all-optical flip-flop (AOFF) operations based on the bistability with optical set and reset pulse injection at a 50 MHz switching frequency. The injection pulse energy was less than 14 fJ. The average on-off contrast ratio of the flip-flopped signals was about 7 dB. These properties of the VCSELs will be potentially useful for future high-speed all-optical signal processing applications.

All-Optical Flip-Flop Operation in a Standard Tunable DBR Laser Diode

A novel concept for all-optical flip-flop operation in a distributed Bragg reflector laser is presented. Using pulses at the same wavelength but with a different duration and amplitude, flip-flop operation is obtained experimentally with switching times of 50 ps and pulse energies of 2-4 pJ.

Polarization-bistable vertical-cavity surface-emitting lasers: application for optical bit memory

AbstractWe summarize recent results on polarization-bistable vertical-cavity surface-emitting lasers (VCSELs) and their application to optical buffer memory. All-optical flip-flop operation with very low switching energies and high repetition rates is achieved. An optical buffer memory consisting of a two-dimensional array of polarization-bistable VCSELs, in which the bit state of the optical signal, “0” or “1”, is stored as a lasing linear polarization state of 0 or 90°. Input data stored as the polarization states of the first VCSEL are transferred to the polarization states of the second VCSEL. In our experiments with 980 nm polarization-bistable VCSELs, 10 Gbit/s optical buffering, 2-bit optical buffering, and a shift register function have been successfully demonstrated.

All-optical flip-flop operation of VCSOA

An all-optical flip-flop, the memory of which is based on dispersive bistability in a single vertical cavity semiconductor optical amplifier, is demonstrated experimentally. Flip-flop control is achieved using two mechanisms: cross-phase modulation to set the flip-flop and cross-gain modulation of the holding beam within a remote SOA to reset it. Optical control signals are sub-milliwatt in power and derived from a single 5 ns, 1539 nm initial pulse. Flip-flop operation at 1542 nm is polarisation insensitive to control signals and achieved with an on-off contrast greater than 3 dB.

All-optical flip-flops based on DFB laser diodes and DFB-arrays

We present numerical and experimental results on a number of different all-optical flip-flops which are based on DFB laser diodes or DFB-arrays. All these flip-flop concepts show potential for fast switching with low switching energy and high extinction ratio. They are moreover very robust in the sense that the switching pulses (and the injected CW beam in some cases) can be of arbitrary wavelength and that the bistability characteristics can be tuned by simple variation of the current injected into the devices. Two different designs for all-optical flip-flop operation will be discussed in detail. The first one is a DFB or DBR laser diode coupled to a semiconductor optical amplifier, in which the bidirectional coupling between laser and amplifier causes the bistability. The second concept is based on bistable behaviour in a single AR-coated DFB laser, with low coupling coefficient and in which a CW signal is injected. These all-optical flip-flops can easily be extended to optically switchable multistate devices with any number of stable states. Such multistate devices are briefly discussed at the end.

Dynamic Operation of All-Optical Flip-Flops with Distributed Bragg Reflectors for Self-Routing of 10-Gbit/s Optical Packets

We present the dynamic all-optical flip-flop (AOFF) operation of a multimode interference (MMI) bistable laser diode (BLD) with distributed Bragg reflector (DBR) mirrors, which allow single-mode lasing and on-chip integration with other waveguide devices. The DBR-MMI-BLD has been operated by 10-ns-wide optical set/reset pulse, resulting in 320 ps rising time and 470 ps falling time. Self-routing of 10 Gbit/s optical packets has also been demonstrated using the Mach–Zehnder interferometer (MZI) semiconductor optical amplifier (SOA) all-optical switch driven by the DBR-MMI-BLD AOFF. The 10 Gbit/s optical packets were switched in the optical domain by cross-phase modulation of the SOA. The extinction ratio of the all-optical switch was 8 dB, and an error-free operation was obtained with 1.8 dB power penalty.