Polymer-based waveguides and optical switching

The fabrication and linear optical characterization of a Bragg reflector in a planar polymeric waveguide, suitable for an all-optical switching device, is reported. Surface corrugation gratings with a grating constant of 349 nm were produced in different polymeric films of poly(phenylene-vinylene), polydiacetylene and polystyrene by excimer laser photoablation. Furthermore, the gap in the linear transmission spectrum of the modulated waveguide was measured and compared with the result of numerical simulations. A good agreement can only be found if a non-uniform grating with a small chirp is assumed. This small deviation from the uniform grating cannot be resolved with a scanning electron microscope. However, this linear optical investigation helps to further improve the fabrication process and opens the possibility to yield a well-defined grating with a prescribed modulation strength, which is a vital requirement for the proper operation of a nonlinear all-optical switch.     

Adiabatic polymer-glass-waveguide all-optical switch

We propose an adiabatic all-optical switch that is composed of an asymmetric Y-branch ion-exchanged glass waveguide with a strip of nonlinear polymer loaded on top of one branch. The properties of nonlinear wave propagation in the device are investigated in detail. By extending the effective-index method to the analysis of nonlinear waveguides, we calculate the nonlinear dispersion curves in successive sections to explain the evolution of normal modes in the device. As the multivalued propagation constants exist in the tapered directional coupler region, the device possesses an abrupt switching behavior and nonreciprocal properties. To demonstrate nonlinear switching behaviors in the Y-branch waveguide further, we employ a beam propagation method to simulate optical-field propagation. The inputs by three different ports are investigated, and the results agree well with the dispersion-curve analysis.     

Integrated Mach-Zehnder-based 2x2 all-optical switch using nonlinear two-mode interference waveguide

The Mach-Zehnder interferometer (MZI) is a common structure for integrated all-optical switches. We proposed and designed an all-optical 2x2 switch that is based on the MZI, multimode interference, and a nonlinear two-mode interference waveguide. The beam propagation method is used to simulate and analyze the device. The results show that the switching action is done properly.     

Study of a Mach–Zehnder-type ultrafast all-optical switch based on a periodically patterned microring resonator

A novel Mach–Zehnder-type ultrafast all-optical switch is proposed, based on a periodically patterned microring resonator. The periodic patterns in the ring resonator provide both strong confinement and slow light properties, and enhance the nonlinear Kerr effect. The special design achieves the goal of deceasing the length and area of the device. This device possesses the practical advantages of low power consumption, low latency, high speed data processing ability, and integration potential. The pump power for the switching is reduced to 5 mW. It is a promising device for future all-optical network nodes.     

Integrated all-optical logic and arithmetic operations with the help of a TOAD-based interferometer device--alternative approach

Interferometric devices have drawn a great interest in all-optical signal processing for their high-speed photonic activity. The nonlinear optical loop mirror provides a major support to optical switching based all-optical logic and algebraic operations. The gate based on the terahertz optical asymmetric demultiplexer (TOAD) has added new momentum in this field. Optical tree architecture (OTA) plays a significant role in the optical interconnecting network. We have tried to exploit the advantages of both OTA- and TOAD-based switches. We have proposed a TOAD-based tree architecture, a new and alternative scheme, for integrated all-optical logic and arithmetic operations.     

Highly efficient all-optical control of surface-plasmon-polariton generation based on a compact asymmetric single slit

By engaging a compact asymmetric single slit coated with a photorefractive polymer, surface-plasmon-polariton (SPP) generation was efficiently controlled by a pump beam. In the structure, the nonlinear light-matter interaction is enhanced because of the cavity effect, which increases the sensitivity of SPPs to the surrounding dielectric. By variation of the real part of the refractive index together with an interferometric configuration, high on/off switching ratios are achieved. Moreover, the SPP generation and modulation processes are integrated in the same asymmetric single slit, which makes the device ultracompact. Experimentally, a high on/off switching ratio of >20 dB and phase variation of >π were observed with the device lateral dimension of only about 2 μm.     

Optical polarization switching in a Fabry-Perot étalon that utilizes the photoinduced Kerr effect

We present an all-optical polarization switching of an asymmetric Fabry-Perot étalon containing a nonlinear Kerr medium in reflection type. Reflectance of a signal wave breaks up into two orthogonal polarization components as a result of photoinduced birefringent effects and shows distinct features of intensity stability and a high extinction ratio in polarization switching-modulation and memory operations.     

Numerical simulation of a novel all-optical flip-flop based on a chirped nonlinear distributed feedback semiconductor laser structure using GPGPU computing

A novel all-optical flip-flop based on a chirped nonlinear distributed feedback laser structure is proposed. The flip-flop does not require a holding beam. The optical gain is provided by a current injection into an active layer. The nonlinear wave-guiding layer consists of a chirped phase shifted grating accompanied with a negative nonlinear refractive index coefficient that increases in magnitude along the wave-guide. In the ‘OFF’ state, the chirped grating does not provide the required optical feedback to start lasing. An optical pulse switches the device ‘ON’ by reducing the chirp due to the negative nonlinear refractive index coefficient. The reduced chirp grating provides enough feedback to sustain a laser mode. The device is switched ‘OFF’ by cross gain modulation. GPGPU computing allows for long simulation time of multiple SET–RESET operations. The ‘ON/OFF’ transitions delays are in nanoseconds time scale.     

All-optical bistable switching based on photonic crystal slab nanocavity using nonlinear Kerr effect

In this paper, we propose all-optical bistable switching based on a two-dimensional (2D) photonic crystal slab nanocavity using the nonlinear Kerr effect with improved optical properties such as on/off ratio and switching power. The nonlinear properties of different kinds of nanocavity-based L3 structures are characterized. Using the 2D finite-difference time-domain method, we present a new structure of nanocavities for all-optical switching. The device has on/off ratio greater than 15?dB and power smaller than 375?mW for input optical pulses in the range of picoseconds.     

All-optical controllable channel-drop filters in two-dimensional square-lattice photonic crystals

A novel all-optical controllable channel-drop filter in photonic crystals (PC) of square lattice is presented. We show that using a resonant-cavity-based add-drop filter with a wavelength-selective reflection feedback and a single-control switching module which is based on nonlinear PC microcavities, the dropped channel can be routed to the drop port or returned to the bus waveguide. Using the temporal coupled-mode theory and two-dimensional nonlinear finite-difference time-domain method, the performance of the proposed device is investigated and the simulation results show the validity of the proposed design.     

Optical bistability in metal-insulator-metal plasmonic waveguide with nanodisk resonator containing Kerr nonlinear medium

We numerically investigate the optical bistability effect in the metal-insulator-metal waveguide with a nanodisk resonator containing a Kerr nonlinear medium. It is found that the increase of the refractive index, which is induced by enhancing the incident intensity, can cause a redshift for the resonance wavelength. The local resonant field excited in the nanodisk cavity can significantly increase the Kerr nonlinear effect. In addition, an obvious bistability loop is observed in the proposed structure. This nonlinear structure can find important applications for all-optical switching in highly integrated optical circuits.     

Ultrafast low-threshold all-optical switch implemented by arrays of ring resonators coupled to a Mach-Zehnder interferometer arm: based on 2D photonic crystals

Using an array of m x n nonlinear ring resonators (m = 1, 3, 5, and n = 1, 2, 3) coupled to the upper arm of a Mach-Zehnder interferometer (MZI), we have proposed an all-optical switch structure. Using a 5 x 3 array, we have shown the possibility of designing an all-optical switching device with a threshold intensity as low as 15 mW/m(2) and switching window of approximately 35 ps. While using m x 1 arrays, we have achieved switching windows smaller than 10 ps, at the expense of higher switching thresholds, ranging from 37 to 55 mW/m(2). The whole structure is based on a square lattice photonic crystal of lattice constant a = 600 nm, formed by rods of radius r = 90 nm in an air background. The linear rods' refractive index is taken to be the same as that of Si(0.75)Ge(0.25); i.e., n(r) = 3.6, whereas the nonlinear rod's refractive index and Kerr index parameter are taken to be n(0) = 1.4 and n(2) = 10(-14) m(2)/W. The center wavelength at which the nonlinear rings are designed to make the resonance is taken to be lambda(0) = 1550 nm in free space.     

All-optical switch using optically controlled two mode interference coupler

In this paper, we have introduced optically controlled two-mode interference (OTMI) coupler having silicon core and GaAsInP cladding as an all-optical switch. By taking advantage of refractive index modulation by launching optical pulse into cladding region of TMI waveguide, we have shown optically controlled switching operation. We have studied optical pulse-controlled coupling characteristics of the proposed device by using a simple mathematical model on the basis of sinusoidal modes. The device length is less than that of previous work. It is also seen that the cross talk of the OTMI switch is not significantly increased with fabrication tolerances (±δw) in comparison with previous work.     

All-optical switching in an asymmetric silicon Fabry-Perot étalon based on the free-carrier plasma effect

We demonstrate all-optical switching at 1.3 and 1.5 μm in the reflection mode of an asymmetric silicon Fabry-Perot étalon by a control beam at 0.85 μm. Both switch-on and switch-off operations are demonstrated at different locations of the etalon. Based on the free-carrier plasma effect, a modulation depth as large as 10% is obtained and a frequency response as high as 0.5 GHz is achieved.     

Photonic crystal fibre based all-optical modulation format conversions between NRZ and RZ with hybrid clock recovery from a PRZ signal

Several all-optical modulation format-converting schemes are described for non-return-to-zero (NRZ) and return-to-zero (RZ) modulation formats that make use of spectral filtering of either self-phase modulation (SPM) or cross-phase modulation (XPM) broadened signal spectrum in a highly-nonlinear dispersion-flattened photonic-crystal fibre. Format conversions have been performed between the most widely used modulation formats - NRZ and RZ. In addition, a hybrid clock recovery scheme is proposed to obtain the data rate of the NRZ signal for NRZ-to-RZ format conversion. All format-converting schemes are based on the extraction of the spectral components in a nonlinear phase modulation broadened signal spectrum. In NRZ-to-RZ format conversion, a periodic pulse train, at a repetition rate similar to the NRZ data rate, is used as a control that induces a nonlinear phase shift to the NRZ probe signal and broadens its spectrum. The spectral components, contributed by different time instances of the control pulse, can be extracted as the converted RZ signal output. In RZ-to-NRZ format conversion, the RZ signal serves as a control that induces a nonlinear phase shift to a continuous wave probe light, where a logic-inverted NRZ signal can be extracted by filtering out the chirped components. Format conversions between NRZ and RZ signals at 9.95328 GB/s (OC-192) are demonstrated. As the proposed optical signal-processing schemes make use of the fibre nonlinearity (SPM/XPM), it is possible to extend it to a high-speed operation <160 Gb/s. Therefore the proposed format-converting schemes can serve as a format converter between the optical time-division multiplexed networks and the wavelength division multiplexed networks     

Information throughput of photorefractive spatial solitons in the telecommunication range

Photorefractive spatial solitons are attractive elements because they can be used as controllable optical interconnectors for all-optical devices. To our knowledge, until now their properties were investigated in terms of energy transportation. We suggest considering photorefractive spatial solitons as optically induced information channels. The experimental technique to measure the information throughput of photorefractive spatial solitons in accordance with Shannon's definition was developed and demonstrated by us. We experimentally demonstrated that in the wavelength range of 1520-1630 nm it can be estimated as large as approximately 90 Tbits/s. We also experimentally demonstrate a measurement of the group-velocity dispersion and show the limitation of the pulse transfer rate of the induced waveguides to approximately 6.2 THz.     

All-optical switching in plant blue light photoreceptor phototropin

We theoretically analyze all-optical switching in the recently characterized LOV2 domain from Avena sativa (oat) phot1 phototropin, a blue-light plant photoreceptor, based on nonlinear intensity-induced excited-state absorption. The transmission of a cw probe laser beam at 660 nm corresponding to the peak absorption of the first excited L-state, through the LOV2 sample, is switched by a pulsed pump laser beam at 442 nm that corresponds to the maximum initial D state absorption. The switching characteristics have been analyzed using the rate equation approach, considering all the three intermediate states and transitions in the LOV2 photocycle. It is shown that for a given pump pulse intensity, there is an optimum pump pulsewidth for which the switching contrast is maximum. It is shown that the probe laser beam can be completely switched off (100% modulation) by the pump laser beam at 50 kW/cm² for a concentration of 1 mM with sample thickness of 5.5 mm. The switching characteristics are sensitive to various parameters such as concentration, rate constant of L-state, peak pump intensity and pump pulse width. At typical values, the switch-off and switch-on time is 1.6 and 22.3 mus, respectively. The switching characteristics have also been used to design all-optical not and the universal nor and nand logic gates     

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.     

EIT-based MZ-MMI all-optical switch

We propose a new control structure for all-optical switching in multimode inference (MMI)-based Mach–Zehnder interferometer (MZI) devices. This structure is composed of an MZI doped by three-level nanocrystals for the realization of electromagnetically induced transparency (EIT) in the lower arm. We use two different intensities of control field for two states of the proposed switch. Using a control field in both of the two switching states is necessary, where the EIT region is transparent. By changing the intensity of the control field, the refractive index of the doped region changes, which makes the phase difference between the two arms of the MZI. Hence, the switching operation takes place. Simulation results show that the extinction ratio of the device is ?32dB in the worst case.     

All-optical switching in a distributed-feedback GaInAsP waveguide

The characteristics of all-optical switching in a waveguide device with a distributed-feedback structure were experimentally investigated. The device was composed of a strip-loaded GaInAsP/InP waveguide and a distributed-feedback structure, which was fabricated by a combination of reactive-ion etching and electron-beam exposure. In the experiments, several optical switching operations were demonstrated. In particular, the all-optical set-reset operation and threshold operation were obtained.