All-optical XOR logic gate for 40Gb/s DPSK signals via FWM in a silicon nanowire

Third-Order Optical Nonlinearities of 2D Materials at Telecommunications Wavelengths

All-optical signal processing based on nonlinear optical devices is promising for ultrafast information processing in optical communication systems. Recent advances in two-dimensional (2D) layered materials with unique structures and distinctive properties have opened up new avenues for nonlinear optics and the fabrication of related devices with high performance. This paper reviews the recent advances in research on third-order optical nonlinearities of 2D materials, focusing on all-optical processing applications in the optical telecommunications band near 1550 nm. First, we provide an overview of the material properties of different 2D materials. Next, we review different methods for characterizing the third-order optical nonlinearities of 2D materials, including the Z-scan technique, third-harmonic generation (THG) measurement, and hybrid device characterization, together with a summary of the measured n₂ values in the telecommunications band. Finally, the current challenges and future perspectives are discussed.

Seven-channel all-optical reconfigurable canonical logic units multicasting at 40 Gb/s based on a nonlinearity-enhanced silicon waveguide

All-optical canonical logic unit (CLU) is the basic building block of high-speed optical logic operation and complex optical computing. By utilizing the parallelism of optical signals, multichannel multicasting of all-optical CLUs can expand the capacity of the computing system effectively. Here, we propose and experimentally demonstrate the 40 Gb/s all-optical reconfigurable two-input CLUs generated in seven wavelength channels via four-wave mixing (FWM) in the nonlinearity-enhanced silicon waveguide. By introducing reverse-biased PIN junctions to reduce nonlinear loss, the output power of converted light can be increased over 10 dB. Moreover, pumped by two optical signals and a continuous wave beam, a full set of reconfigurable CLUs is multicasted in seven parallel wavelength channels. All logic signals with error-free performance are realized. Attributing to the rate transparency of FWM and parallel multicasting of logic functions, the proposed scheme offers more flexibility and expandability in future high-speed optical logic processing and complex optical computing.

Recent advances in integrated optical directed logic operations for high performance optical computing: a review

Optical directed logic (DL) is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic functions. This review first provides an overview of the concept and working principle of DL. The developing trends of DL computing are then discussed in detail, including the fundamental optical DL gates, combinational optical DL operations, reconfigurable logic computing, low power optical logic computing, and programmable photonic network. The concluding remarks provide an outlook on the DL future development and its impacts in optical computing.

Demonstration of various optical directed logic operations by using an integrated photonic circuit

Optical directed logic is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic operations. In this Letter, we propose and demonstrate an integrated photonic circuit which can implement five different optical logic operations by utilizing two optical modes. The proposed device is fabricated on a silicon-on-insulator substrate by using electron beam lithography and inductively coupled plasma etching processes. The static experimental results show that the fabricated device can implement five different operations correctly-XOR, XNOR, NOR, NOT, and AND-from which we can see that the signal-to-noise ratios are larger than 17.6 dB over the entire C band for all five logic functions. At last, all five logic operations with the speed of 10 Kbps are demonstrated. The proposed device with simple structure, large bandwidth, and versatility would be a promising candidate for information processing in optical mode division multiplexing networks.

Releasing the light field in subwavelength grating slot microring resonators for athermal and sensing applications

Silicon-on-insulator (SOI) platforms have attracted increasing interest for photonic integrated devices with an ultra-small footprint. The distinct feature is the strong light confinement in the silicon region due to a high refractive-index-contrast. In contrast, releasing the light field out of the silicon region is also of great significance for providing a useful supplement to existing light guiding mechanisms and for facilitating versatile applications. Here, subwavelength grating slot (SWGS) microring resonators, which can effectively release light out of the silicon region for athermal and sensing applications, are proposed and demonstrated. The mechanism of releasing light relies on the combination of a surface enhanced supermode in a slot waveguide and a Bloch mode in a subwavelength grating waveguide. Four types of racetrack microring resonators (strip, slot, strip-SWGS, and slot-SWGS) were fabricated for comparison. The slot-SWGS microring resonator shows the best performance for athermal and sensing applications. The demonstrations may be useful for new releasing-light-enabled devices and applications.

Raman mediated ultrafast all-optical NOR gate

A new device architecture has been proposed in this paper implementing the all-optical cascadable logic NOR functionality. The device functions based on stimulated Raman scattering (SRS) in silicon nanocrystal embedded slotted photonic crystal waveguide (SPCW). Substantial miniaturizations both in operating power and overall footprint of the device have been achieved owing to the ultrahigh SRS gain of silicon nanocrystal and strong spatio-temporal confinement of the SPCW. Successful operation of the device has been demonstrated at a pulse rate that is as high as 125 Gbps.

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.

Automated logic synthesis for electro-optic logic-based integrated optical computing

Integrated optical computing attracts increasing interest recently as Moore's law approaches the physical limitation. Among all the approaches of integrated optical computing, directed logic that takes the full advantage of integrated photonics and electronics has received lots of investigation since its first introduction in 2007. Meanwhile, as integrated photonics matures, it has become critical to develop automated methods for synthesizing optical devices for large-scale optical designs. In this paper, we propose a general electro-optic (EO) logic in a higher level to explore its potential in integrated computing. Compared to the directed logic, the EO logic leads to a briefer design with shorter optical paths and fewer components. Then a comprehensive gate library based on EO logic is summarized. At last, an And-Inverter Graphs (AIGs) based automated logic synthesis algorithm is described as an example to implement the EO logic, which offers an instruction for the design automation of high-speed integrated optical computing circuits.

Integrated all-optical programmable logic array based on semiconductor optical amplifiers

The all-optical programmable logic array (PLA) is one of the most important optical complex logic devices that can implement combinational logic functions. In this Letter, we propose and experimentally demonstrate an integrated all-optical PLA at the operation speed of 40 Gb/s. The PLA mainly consists of a delay interferometer (DI) and semiconductor optical amplifiers (SOAs) of different lengths. The DI is used to pre-code the input signals and improve the reconfigurability of the scheme. The longer SOAs are nonlinear media for generating canonical logic units (CLUs) using four-wave mixing. The shorter SOAs are used to select the appropriate CLUs by changing the working states; then reconfigurable logic functions can be output directly. The results show that all the CLUs are realized successfully, and the optical signal-to-noise ratios are above 22 dB. The exclusive NOR gate and exclusive OR gate are experimentally demonstrated based on output CLUs.

All-optical retro-modulation for free-space optical communication

This work presents device and system architectures for free-space optical and optical wireless communication at high data rates over multidirectional links. This is particularly important for all-optical networks, with high data rates, low latencies, and network protocol transparency, and for asymmetrical networks, with multidirectional links from one transceiver to multiple distributed transceivers. These two goals can be met by implementing a passive uplink via all-optical retro-modulation (AORM), which harnesses the optical power from an active downlink to form a passive uplink through retroreflection. The retroreflected optical power is modulated all-optically to ideally achieve terabit-per-second data rates. The proposed AORM architecture, for passive uplinks, uses high-refractive-index S-LAH79 hemispheres to realize effective retroreflection and an interior semiconductor thin film of CuO nanocrystals to realize ultrafast all-optical modulation on a timescale of approximately 770 fs. The AORM architecture is fabricated and tested, and ultimately shown to be capable of enabling multidirectional free-space optical communication with terabit-per-second aggregate data rates.

Ultracompact CMOS-compatible optical logic using carrier depletion in microdisk resonators

We present a CMOS-compatible optoelectronic directed logic architecture that achieves high computational throughput (number of operations per second per unit area) by its ultracompact form factor. High speed-to-power performance is also achieved, by the low capacitance and high junction-to-mode overlap of low-radii SOI vertical pn junction microdisk switches. By using wavelength-division multiplexing and two electrical control signals per disk, each switch performs (N)OR, (N)AND, and X(N)OR operations simultaneously. Connecting multiple switches together, we demonstrate higher-order scalability in five fundamental N-bit logic circuits: AND/OR gates, adders, comparators, encoders, and decoders. To the best of our knowledge, these circuits achieve the lowest footprint of silicon-based multigigabit-per-second optical logic devices in literature.

All-optical logic gates based on cross phase modulation effect in a phase-shifted grating

In this paper, we perform a theoretical study of the all-optical logic gates based on the techniques of cross phase modulation (XPM) in a phase-shifted grating. Here the pumps are used to control the switching of a weak continuous wave (cw). In order to understand the transferring process of the information from the pump light to the cw light, we first study the switching characteristic of the device. Then, by changing the combination between two pumps, in a fiber grating with zero phase shift we have realized NOT, AND, and NAND gates, and in a phase-shifted grating with the phase shift π, the other various logic operations can be realized such as NAND gates and OR gates; when selecting Δφ=3/2π, we can realize XOR gates and XNOR gates. Thus the change of the phase shift of the phase-shifted grating will yield various logic gates.

High-speed all-optical NAND/AND logic gates using four-wave mixing Bragg scattering

A high-speed all-optical NAND logic gate is proposed and experimentally demonstrated using four-wave mixing Bragg scattering in highly nonlinear fiber. NAND/AND logic functions are implemented at two wavelengths by encoding logic inputs on two pumps via on-off keying. A 15.2-dB depletion of the signal is obtained for NAND operation, and time domain measurements show 10-Gb/s NAND/AND logic operations with open eye diagrams. The approach can be readily extended to higher data rates and transferred to on-chip waveguide platforms.

40 Gb/s reconfigurable optical logic gates based on FWM in silicon waveguide

Here we experimentally demonstrate reconfigurable logic gates via four-wave-mixing (FWM) in silicon waveguide with an operating speed of up to 40 Gb/s. After demodulated by a 40-GHz delay interferometer (DI), four non-return-to-zero differential phase shift keying (NRZ-DPSK) signals with carefully selected wavelengths are launched into the waveguide at the same time. Thanks to the effective FWM in silicon nano-waveguide, a full set of the two-input logic minterms can be generated simultaneously, and arbitrary combinational logic functions are able to be realized by properly combining these minterms.

Flexible and re-configurable optical three-input XOR logic gate of phase-modulated signals with multicast functionality for potential application in optical physical-layer network coding

Optical logic gate, especially exclusive-or (XOR) gate, plays important role in accomplishing photonic computing and various network functionalities in future optical networks. On the other hand, optical multicast is another indispensable functionality to efficiently deliver information in optical networks. In this paper, for the first time, we propose and experimentally demonstrate a flexible optical three-input XOR gate scheme for multiple input phase-modulated signals with a 1-to-2 multicast functionality for each XOR operation using four-wave mixing (FWM) effect in single piece of highly-nonlinear fiber (HNLF). Through FWM in HNLF, all of the possible XOR operations among input signals could be simultaneously realized by sharing a single piece of HNLF. By selecting the obtained XOR components using a followed wavelength selective component, the number of XOR gates and the participant light in XOR operations could be flexibly configured. The re-configurability of the proposed XOR gate and the function integration of the optical logic gate and multicast in single device offer the flexibility in network design and improve the network efficiency. We experimentally demonstrate flexible 3-input XOR gate for four 10-Gbaud binary phase-shift keying signals with a multicast scale of 2. Error-free operations for the obtained XOR results are achieved. Potential application of the integrated XOR and multicast function in network coding is also discussed.

Experimental demonstration on two-input optical high-base hybrid doubling and subtraction functions in graphene

Optical signal processing is considered to be a promising technique to overcome the speed limitation of electronics and accelerate next-generation high-speed optical networks. Among various optical signal processing operations, optical arithmetic functions have attracted increasing interest. Here, by exploiting the degenerate four-wave mixing progress in graphene and adopting (differential) quadrature phase-shift keying signals, we experimentally demonstrate 10 Gbaud two-input (A, B) hybrid quaternary arithmetic functions of doubling and subtraction (2A-B, 2B-A) in the optical domain. The measured optical signal-to-noise ratio penalties at a bit-error rate of 2 × 10⁻³ are about 7.4 dB for 2A-B and 7 dB for 2B-A.

Electro-optic directed XOR logic circuits based on parallel-cascaded micro-ring resonators

We report an electro-optic photonic integrated circuit which can perform the exclusive (XOR) logic operation based on two silicon parallel-cascaded microring resonators (MRRs) fabricated on the silicon-on-insulator (SOI) platform. PIN diodes embedded around MRRs are employed to achieve the carrier injection modulation. Two electrical pulse sequences regarded as two operands of operations are applied to PIN diodes to modulate two MRRs through the free carrier dispersion effect. The final operation result of two operands is output at the Output port in the form of light. The scattering matrix method is employed to establish numerical model of the device, and numerical simulator SG-framework is used to simulate the electrical characteristics of the PIN diodes. XOR operation with the speed of 100Mbps is demonstrated successfully.

All-optical logic gates based on nonlinear plasmonic ring resonators

A nonlinear plasmonic T-shaped switch based on a square-shaped ring resonator is simulated by the finite-difference time-domain numerical method. Three optical logic gates-a NOT, with one T-shaped switch, and AND and NOR gates, each with two cascaded T-shaped switches-are proposed. The nonlinear Kerr effect is utilized to show the performance of our proposed logic gates. The values of transmission at the ON and OFF states of NOT and NOR gates are 70% and less than 0.6% of the input lightwave, respectively, while these values for the AND gate are 90% and less than 30%, respectively.

Integration of photonic nanojets and semiconductor nanoparticles for enhanced all-optical switching

All-optical switching is the foundation of emerging all-optical (terabit-per-second) networks and processors. All-optical switching has attracted considerable attention, but it must ultimately support operation with femtojoule switching energies and femtosecond switching times to be effective. Here we introduce an all-optical switch architecture in the form of a dielectric sphere that focuses a high-intensity photonic nanojet into a peripheral coating of semiconductor nanoparticles. Milli-scale spheres coated with Si and SiC nanoparticles yield switching energies of 200 and 100 fJ with switching times of 10 ps and 350 fs, respectively. Micro-scale spheres coated with Si and SiC nanoparticles yield switching energies of 1 pJ and 20 fJ with switching times of 2 ps and 270 fs, respectively. We show that femtojoule switching energies are enabled by localized photoinjection from the photonic nanojets and that femtosecond switching times are enabled by localized recombination within the semiconductor nanoparticles.

The terabit-per-second rates of optical fibres exceed the capability of electronics, but all-optical switches are needed to alleviate the bottleneck in these networks. Here, Born et al. describe such a switch using dielectric spheres, yielding femtojoule switching energy and femtosecond switching times.

Low-power continuous-wave four-wave mixing wavelength conversion in AlGaAs-nanowaveguide microresonators

We experimentally demonstrate enhanced wavelength conversion in a Q∼7500 deeply etched AlGaAs-nanowaveguide microresonator via degenerate continuous-wave four-wave mixing with a pump power of 24 mW. The maximum conversion efficiency is -43  dB and accounts for 12 dB enhancement compared to that of a straight nanowaveguide. The experimental results and theoretical predictions agree very well and show optimized conversion efficiency of -15  dB. This work represents a step toward realizing a fully integrated optical devices for generating new optical frequencies.

Reconfigurable dual-channel all-optical logic gate in a silicon waveguide using polarization encoding

A reconfigurable dual-channel all-optical logic gate is proposed and experimentally demonstrated using four-wave mixing in a silicon waveguide for polarization encoding signals. Six logic functions, XNOR, AND, NOR, XOR, AB¯, and A¯B are implemented at two different wavelength channels by adjusting the polarization states of two 10 Gb/s non-return-to-zero polarization-shift keying (NRZ-PolSK) signals modulated by 10-bit on-off keying (OOK) sequences. The eye diagrams of the logic signals are clearly observed, and the logic functions are well demonstrated as the two incident NRZ-PolSK signals are both modulated by the OOK sequences, which originate from 2(31)-1 pseudo-random binary sequences.

CMOS compatible integrated all-optical radio frequency spectrum analyzer

We report an integrated all-optical radio frequency spectrum analyzer based on a ~4 cm long doped silica glass waveguide, with a bandwidth greater than 2.5 THz. We use this device to characterize the intensity power spectrum of ultrahigh repetition rate mode-locked lasers at repetition rates up to 400 GHz, and observe dynamic noise related behavior not observable with other techniques.

All-optical XOR logic gate using intersubband transition in III-V quantum well materials

A monolithically integrated all-optical exclusive-OR (XOR) logic gate is experimentally demonstrated based on a Michelson interferometer (MI) gating device in InGaAs/AlAsSb coupled double quantum wells (CDQWs). The MI arms can convert the pump data with return-to-zero ON-OFF keying (RZ OOK) to binary phase-shift keying (BPSK) format, then two BPSK signals can interfere with each other for realizing a desired logical operation. All-optical format conversion from the RZ OOK to BPSK is based on the cross-phase modulation to the transverse electric (TE) probe wave, which is caused by the intersubband transition excited by the transverse magnetic (TM) pump light. Bit error rate measurements show that error free operation for both BPSK format conversion and XOR logical operation can be achieved.

Cascaded all-optical operations in a hybrid integrated 80-Gb/s logic circuit

We demonstrate logic functionalities in a high-speed all-optical logic circuit based on differential Mach-Zehnder interferometers with semiconductor optical amplifiers as the nonlinear optical elements. The circuit, implemented by hybrid integration of the semiconductor optical amplifiers on a planar lightwave circuit platform fabricated in silica glass, can be flexibly configured to realize a variety of Boolean logic gates. We present both simulations and experimental demonstrations of cascaded all-optical operations for 80-Gb/s on-off keyed data.

XOR and XNOR operations at 12.5 Gb/s using cascaded carrier-depletion microring resonators

We report the implementation of the XOR and XNOR logical operations using an electro-optic circuit, which is fabricated by CMOS-compatible process in the silicon-on-insulator (SOI) platform. The circuit consists of two cascaded add-drop microring resonators (MRRs), which are modulated through electric-field-induced carrier depletion in reverse biased pn junctions embedded in the ring waveguides. The resonance wavelength mismatch between the two nominally identical MRRs caused by fabrication errors is compensated by thermal tuning. Simultaneous bitwise XOR and XNOR operations of the two electrical modulating signals at the speed of 12.5 Gb/s are demonstrated. And 20 Gb/s XOR operation at one output port of the circuit is achieved. We explain the phenomena that one half of the resonance regions of the device are much more sensitive to the round-trip phase shift in the ring waveguides than the other half resonance regions. Characteristic graphs with logarithmic phase coordinate are proposed to analyze the sensitivity of the demonstrated circuit, as well as several typical integrated optical structures. It is found that our circuit with arbitrary chosen parameters has similar sensitivity to MRRs under the critical coupling.

Raman mediated all-optical cascadable inverter using silicon-on-insulator waveguides

In this Letter, we propose an all-optical circuit for a cascadable and integrable logic inverter based on stimulated Raman scattering. A maximum product criteria for noise margin is taken to analyze the cascadability of the inverter. Variation of noise margin for different model parameters is also studied. Finally, the time domain response of the inverter is analyzed for different widths of input pulses.

All-optical 10 Gb/s AND logic gate in a silicon microring resonator

An all-optical AND logic gate in a single silicon microring resonator is experimentally demonstrated at 10 Gb/s with 50% RZ-OOK signals. By setting the wavelengths of two intensity-modulated input pumps on the resonances of the microring resonator, field-enhanced four-wave mixing with a total input power of only 8.5 dBm takes place in the ring, resulting in the generation of an idler whose intensity follows the logic operation between the pumps. Clear and open eye diagrams with a bit-error- ratio below 10(-9) are achieved.

Three-input optical addition and subtraction of quaternary base numbers

We present an approach to implementing three-input addition and subtraction of quaternary base numbers in the optical domain using multiple non-degenerate four-wave mixing (FWM) processes in a single highly nonlinear fiber (HNLF) and differential quadrature phase-shift keying (DQPSK) signals. By employing 100-Gbit/s three-input return-to-zero DQPSK (RZ-DQPSK) signals (A, B, C), we demonstrate 50-Gbaud/s three-input quaternary hybrid addition and subtraction (A + B-C, A + C-B, B + C-A). Moreover, by adding a conversion stage from C to -C via conjugated degenerate FWM, we also demonstrate 50-Gbaud/s three-input quaternary addition (A + B + C). The power penalties of three-input quaternary addition and subtraction (A + B-C, A + C-B, B + C-A, A + B + C) are measured to be less than 6 dB at a bit-error rate (BER) of 10(-9). In addition, no significant degradations are observed for RZ-DQPSK signals (A, B, C or -C) after the operations of quaternary addition and subtraction.