Ultrafast Optical Signal Processing Research Articles

Robust Free Excitons in CH3NH3PbI3 Halide Perovskite Revealed by Four‐Wave Mixing

AbstractDirect bandgap semiconductors possess a unique attribute: the presence of a free exciton state with a high total oscillator strength. This property makes them highly promising for applications in ultrafast optical signal processing and optical computing. One such protocol for optical computing is based on four‐wave mixing (FWM). In this study, the nonlinear optical effect in polycrystalline thin films of halide perovskite MAPbI3 (MA+ = CH3NH) at low temperatures is demonstrated. Through analyzing the spectroscopy of the FWM signal, studying the photoluminescence excitation spectra, and comparing the findings with results from MAPbI3 single crystals, it has been discovered that the strongest nonlinear response is observed at the free exciton resonance and in the region of shallow defect states. Surprisingly, the presence of FWM in cross‐linear excitation geometry has been observed, indicating potential involvement of other nonlinear or many‐body effects. The observations of FWM with free excitons even in highly defective MAPbI3 thin films demonstrate the robustness of the exciton resonance and highlight the practical prospects for utilizing this material in optical computing.

Principle and Recent Development in Photonic Time-Stretch Imaging

Inspiring development in optical imaging enables great applications in the science and engineering industry, especially in the medical imaging area. Photonic time-stretch imaging is one emerging innovation that attracted a wide range of attention due to its principle of one-to-one-to-one mapping among space-wavelength-time using dispersive medium both in spatial and time domains. The ultrafast imaging speed of the photonics time-stretch imaging technique achieves an ultrahigh frame rate of tens of millions of frames per second, which exceeds the traditional imaging methods in several orders of magnitudes. Additionally, regarding ultrafast optical signal processing, it can combine several other optical technologies, such as compressive sensing, nonlinear processing, and deep learning. In this paper, we review the principle and recent development of photonic time-stretch imaging and discuss the future trends.

All-optical Ti3C2Tx modulator based on a sandwich structure.

All-optical modulators based on a MXene-Ti3C2Tx have recently garnered much attention due to their broadband light-matter interactions and ultrafast carrier dynamics. To investigate the modulation characteristics of pump intensity and pump light modulation frequency, we establish an all-optical modulator with a sandwich structure based on MXene-Ti3C2Tx/PVA (polyvinyl alcohol) film. The result shows that this modulator can achieve a high modulation depth of 12.55 dB and a modulation frequency of 50 kHz corresponding to a response time at the microsecond scale. The successful preparation of the modulator is attributed to the saturable absorption characteristics of the MXene-Ti3C2Tx. This modulator has great potential in all-optical communications and ultrafast optical signal processing.

Cascaded chirped quasi-phase-matching grating for broad spectrum generation via a complementary reciprocal lattice vector

Broad spectra are of interest for a variety of applications, including pulse compression and ultrafast optical signal processing. We report a scheme of a cascaded chirped quasi-phase-matching (QPM) grating with a complementary reciprocal lattice vector bandwidth. The large reciprocal lattice vector bandwidth provided by first- and second-order QPM can simultaneously achieve second and third harmonic generations. Combined the effective nonlinear coefficient model with the transfer function method, it reveals that spectrum width increased with increasing fundamental wave bandwidth, reciprocal lattice vector bandwidth, chirp rate, and crystal length. The two-section cascaded chirped QPM grating can offer a reciprocal lattice vector bandwidth as large as 0.3 to 1.26 μm − 1, which corresponds to a broadband spectrum covering 450 to 820 nm upon illumination with a tunable femtosecond laser. The proposed grating could extend supercontinuum generation toward potential spectroscopic applications.

Design of Broadband Flat Optical Frequency Comb Based on Cascaded Sign-Alternated Dispersion Tellurite Microstructure Fiber.

We designed a tellurite microstructure fiber (TMF) and proposed a broadband optical frequency comb generation scheme that was based on electro-optical modulation and cascaded sign-alternated dispersion TMF (CSAD-TMF). In addition, the influence of different nonlinear effects, the ultrashort pulse evolution in the CSAD-TMF with the anomalous dispersion (AD) zones and the normal dispersion (ND) zones were analyzed based on the generalized nonlinear Schrodinger equations (GNLSE) modelling. According to the simulations, when the input seed comb had a repetition rate of 20 GHz and had an input pulse peak power of 30 W, the generation scheme could generate optical frequency combs with a 6 dB spectral bandwidth spanning over 170 nm centered at 1550 nm. Furthermore, the generated combs showed good coherence in performance over the whole 6 dB spectral bandwidth. The highly coherent optical frequency combs can be used as high-repetition-rate, multi-wavelength light sources for various integrated microwave photonics and ultrafast optical signal processing applications.

Highly nonlinear trion-polaritons in a monolayer semiconductor

Highly nonlinear optical materials with strong effective photon-photon interactions are required for ultrafast and quantum optical signal processing circuitry. Here we report strong Kerr-like nonlinearities by employing efficient optical transitions of charged excitons (trions) observed in semiconducting transition metal dichalcogenides (TMDCs). By hybridising trions in monolayer MoSe2 at low electron densities with a microcavity mode, we realise trion-polaritons exhibiting significant energy shifts at small photon fluxes due to phase space filling. We find the ratio of trion- to neutral exciton–polariton interaction strength is in the range from 10 to 100 in TMDC materials and that trion-polariton nonlinearity is comparable to that in other polariton systems. The results are in good agreement with a theory accounting for the composite nature of excitons and trions and deviation of their statistics from that of ideal bosons and fermions. Our findings open a way to scalable quantum optics applications with TMDCs.

Design of a Miniaturized Broadband Silicon Hybrid Plasmonic Temporal Integrator for Ultrafast Optical Signal Processing

A fractional-order silicon hybrid plasmonic temporal integrator with considerably wide full-width at half- maximum (FWHM) bandwidth of ∼1 THz, higher than the previously reported photonic temporal integrators, and noticeably compact footprint of ∼5 μm × 3 μm is proposed. The presented plasmonic temporal integrator is implemented based on a double-ring add-drop resonator structure with ring radii of 1.5 μm. The 3-D finite-difference time-domain (3D-FDTD) simulation results show that the fractional-order of the integrator is 0.64 and it is capable of processing the ultrashort pulses with the duration of 450 fs. The integration time window is estimated as 520 fs, while the achieved energy efficiency is as high as −1.92 dB. The compact size and wide bandwidth of the proposed integrator makes it suitable for ultrafast optical signal processing applications. As an example, the functionality of the designed integrator for solving ordinary differential equations (ODEs) is investigated.

Temporal Imaging Using Dispersive Gradient-Index Time Lenses

We study the temporal imaging with a gradient-index (GRIN) time lens in which both dispersion and time-varying quadratic phase modulation are introduced. The lens is built by using cross-phase modulation between a signal and a parabolic pump pulse in the nonlinear optical fiber with group velocity dispersion. A general theoretical analysis of temporal imaging by the GRIN time lens is performed in detail. Compared to thin lens in previous studies, the introduction of dispersion, benefits periodic self-imaging of both time waveform and frequency spectrum for optical pulses. Interestingly, the temporal and spectral profiles of the input can be exchanged with each other periodically in the GRIN time lens. By combining the GRIN time lens with dispersive elements on both sides, the temporal waveforms of incident optical pulses can be stretched and compressed. For an input signal composed of multiple pulses experiencing different dispersions, the temporal depth imaging of the signal is realized by scanning the timing of the pump pulse applied on the lens. The study may find great applications in ultrafast optical signal processing and measurement.

Impact of two-photon absorption and free-carrier effects on time lens based on four-wave mixing in silicon waveguides

We investigate the influences of two-photon absorption (TPA) and free-carrier effects on a time lens via four-wave mixing in silicon waveguides. It is found that the output waveform is severely modulated and the conversion efficiency is sharply reduced in temporal imaging owing to the impacts of the nonlinear absorption. A silicon–organic hybrid slot waveguide with negligible TPA is proposed for the time lens, which could realize 600× magnification of femtosecond pulses. These results can increase the signal bandwidth from gigahertz to terahertz and give rise to important potential applications for ultrafast optical signal processing in integrated optics, ultrafast optics, and optical communications.

All-optical multi-channel switching at telecommunication wavelengths based on tunable plasmon-induced transparency

As a plasmonic analogue of electromagnetically induced transparency (EIT), plasmon-induced transparency (PIT) has been widely studied duo to the excellent performance on sensing, slow light and enhancing nonlinear effects, which has great potential to be applied on compact optical communication system. Here, we introduce an all-optical PIT multi-channel switching based on the metal–insulator–metal (MIM) plasmonic waveguide device with small footprint. Single/double PIT is investigated both theoretically and numerically by multi-oscillator theory (MOT) and finite-difference time-domain (FDTD), and utilizing the nonlinear medium filled in the cavity, the PIT can be dynamically tunable to achieve various kinds of single/multi-channel switching for telecommunication wavelengths. Besides, utilizing the unprecedented high Kerr coefficient of graphene, the low-power and ultrafast all-optical switching can be made possible. This work provides a novel scheme to realize all-optical switching based on PIT, which can promote on-chip ultrafast optical communication and signal processing.

Active modulation of electromagnetically induced transparency analogue in terahertz hybrid metal-graphene metamaterials

Metamaterial analogues of electromagnetically induced transparency (EIT) have been intensively studied and widely employed for slow light and enhanced nonlinear effects. In particular, the active modulation of the EIT analogue and well-controlled group delay in metamaterials have shown great prospects in optical communication networks. Here we integrate a monolayer graphene into metal-based terahertz (THz) metamaterials, and realize a complete modulation in the resonance strength of the EIT analogue via manipulating the Fermi level of graphene. The physical mechanism lies in the active tuning of the damping rate of the dark mode resonator through the recombination effect of the conductive graphene. This work presents a novel modulation strategy of the EIT analogue in the hybrid metamaterials, and paves the way towards designing very compact slow light devices to meet the future demand of ultrafast optical signal processing.

Ultrafast Optical Signal Processing with Bragg Structures

The phase, amplitude, speed, and polarization, in addition to many other properties of light, can be modulated by photonic Bragg structures. In conjunction with nonlinearity and quantum effects, a variety of ensuing micro- or nano-photonic applications can be realized. This paper reviews various optical phenomena in several exemplary 1D Bragg gratings. Important examples are resonantly absorbing photonic structures, chirped Bragg grating, and cholesteric liquid crystals; their unique operation capabilities and key issues are considered in detail. These Bragg structures are expected to be used in wide-spread applications involving light field modulations, especially in the rapidly advancing field of ultrafast optical signal processing.

Design optimization and fabrication of Mach- Zehnder interferometer based on MIM plasmonic waveguides.

We proposed and designed a compact unbalanced Mach-Zehnder interferometer (MZI) based on metal/insulator/metal (MIM) plasmonic waveguides for ultrafast optical signal processing. The MZI was fabricated by a lithography technique and we provide, for the first time experimental evaluation of the transmission performance of the MZI using MIM PWGs. The experimental results were in good agreement with the numerical simulations. The proposed structure could be considered as a key device for on-chip optical integrated circuits.

Contributed Review: A new synchronized source solution for coherent Raman scattering microscopy

Based on vibrational spectroscopy, coherent Raman Scattering (CRS) microscopy allows label-free imaging of biological and chemical samples with endogenous image contrast. Two-color, synchronized picosecond pulses are typically used for high spectral resolution imaging, which in turn constitutes a dramatic laser source challenge for CRS microscopy. Recently, synchronized time-lens source, inspired from ultrafast optical signal processing, has emerged as a promising laser source solution and has found application in various modalities of CRS microscopy. Time-lens is based on space-time analogy, which uses a "lens" in the time domain to compress long optical pulses or even continuous waves to ultrashort pulses, mimicking a lens in the space domain. Phase and intensity modulators driven with electrical signals are used in the time-lens source for picosecond pulse generation. As a result, the time-lens source is highly versatile and naturally compatible with modulation capabilities. More importantly, if the electrical signals used to drive the time-lens source are derived from other laser sources, such as mode-locked lasers, then synchronization between them can be realized, underlying the physics of a synchronized time-lens source. In this paper, we review recent progress on the basic principle, design of the synchronized time-lens source, and its applications to CRS microscopy of both biological and chemical samples.

An all-optical modulator based on a stereo graphene–microfiber structure

An in-line, all-optical fiber modulator based on a stereo graphene–microfiber structure (GMF) utilizing the lab-on-rod technique was demonstrated in this study. Owing to its unique spring-like geometry, an ultra-long GMF interaction can be achieved, and a modulation depth of ∼7.5 dB (∼2.5 dB) and a modulation efficiency of ∼0.2 dB mW−1 (∼0.07 dB mW−1) were demonstrated for two polarization states. The modulation depth and modulation efficiency are more than one order of magnitude larger than those of other graphene–microfiber hybrid all-optical modulators, although at the cost of a higher insertion loss. By further optimizing the transferring and cleaning process, the upper limit of the modulation depth is mainly determined by the loss from the intrinsic absorption, which depends on the light–graphene interaction. Then, the modulator can quickly switch between the on-state and the off-state with a theoretically maximized modulation depth of tens of decibels. This modulator is compatible with the current fiber-optic communication systems and may be applied in the near future to meet the impending need for ultrafast optical signal processing. A polarization-sensitive all-optical fiber modulator based on a graphene–microfiber structure has been demonstrated by researchers in China. All-optical modulators with high modulation speeds, sufficient modulation depth and wide optical bandwidth are needed to realize ultrafast optical signal processing. Now, Fei Xu and co-workers at Nanjing University have fabricated an all-optical fiber modulator whose modulation depth and efficiency are more than ten times greater than previous all-optical modulators based on graphene and microfibers. These properties originate from its very long interaction length resulting from its spring-like geometry. The researchers consider that even better performance can be achieved by using higher quality graphene and improving the transfer and wrapping of the graphene in the fabrication process. Since the modulator is compatible with existing fiber-optic communication systems, it may find rapid application for ultrafast optical signal processing.

Demonstration of 100 Gbit/s optical time‐division demultiplexing with 1‐to‐4 wavelength multicasting using the cascaded four‐wave mixing in photonic crystal fiber with a single control light source

ABSTRACTDispersion‐flattened highly nonlinear (DF‐HNL) photonic crystal fibers are useful for ultrafast optical signal processing. In this article, 100 Gbit/s‐to‐10 Gbit/s optical time demultiplexing with simultaneous 1‐to‐4 wavelength multicasting is successfully demonstrated by use of the cascaded four‐wave mixing (FWM) in a 50 m DF‐HNL photonic crystal fiber, for the first time. This scheme uses a single control‐pulse light source only and a simple architecture. The wavelength multicasting of the time‐demultiplexed optical signal is achieved on four wavelength channels of which two can have the minimum power penalty of 3.2 dB at 10−9 bit error rate compared to the 10 Gbit/s back‐to‐back measurement. With the cascaded FWM, our proposed scheme can be used to improve the functionality of ultrahigh‐speed optical time‐division multiplexed systems/networks so as to support wavelength multicasting applications in a cost‐effective manner. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2330–2335, 2014

Robust Study of SOA-MZI based Ultrafast Optical Signal Processing for XOR Logic

IJCA is a computer science and electronics journal related with Theoretical Informatics, Quantum Computing, Software Testing, Computer Vision, Digital Systems, Pervasive Computing, Computational Topology etc.

Ultrafast All-Optical Graphene Modulator

Graphene is an optical material of unusual characteristics because of its linearly dispersive conduction and valence bands and the strong interband transitions. It allows broadband light-matter interactions with ultrafast responses and can be readily pasted to surfaces of functional structures for photonic and optoelectronic applications. Recently, graphene-based optical modulators have been demonstrated with electrical tuning of the Fermi level of graphene. Their operation bandwidth, however, was limited to about 1 GHz by the response of the driving electrical circuit. Clearly, this can be improved by an all-optical approach. Here, we show that a graphene-clad microfiber all-optical modulator can achieve a modulation depth of 38% and a response time of ∼ 2.2 ps, limited only by the intrinsic carrier relaxation time of graphene. This modulator is compatible with current high-speed fiber-optic communication networks and may open the door to meet future demand of ultrafast optical signal processing.

Simulation investigation of a 160 Gbit/s all-optical data distributor based on cross-phase modulation in highly nonlinear fiber

Ultrafast-photonic logic circuits are crucial elements to perform ultrafast-optical signal processing functions in the next-generation ultrahigh-speed networks. A 160 Gbit/s all-optical data distributor based on cross-phase modulation in a single highly nonlinear fiber is investigated and demonstrated. The numerical calculation is conducted, and the result shows that the data distributor can be realized in 160 Gbit/s for the data signals of return-to-zero format with logical correctness and high quality. To evaluate the performance of the scheme, the Q-factor of the output signal on signal wavelength, the peak power of signals, the initial delay, and the filter position are calculated and discussed, respectively. The proposed data distributor is suitable for ultrafast applications for the emerging all-optical networks.

20 THz-bandwidth continuous-wave fiber optical parametric amplifier operating at 1 µm using a dispersion-stabilized photonic crystal fiber

We report the experimental demonstration of a continuous-wave all-fiber optical parametric amplifier in the 1 µm band with a record bandwidth of more than 20 THz and a peak gain of almost 40 dB. This is achieved by using a photonic crystal fiber with a high figure of merit and strongly reduced longitudinal dispersion fluctuations. Due to their unique bandwidth and gain characteristics, fiber parametric amplifiers at 1 µm provide an interesting alternative to solid-state or ytterbium-doped fiber amplifiers for ultrafast optical pulse and signal processing.