Wavelength Channels Research Articles

Optical channel aggregation based on modulation format conversion by coherent spectral superposition with electro-optic modulators

Spectrally efficient modulation formats become essential for optical network scaling as the demand for routed data streams exceeds the present wavelength-division multiplexing systems’ throughput. However, achieving high spectral efficiency at high data rates requires complex and bandwidth-intensive electronics. In this study, we propose an all-optical aggregation scheme that combines multiple low spectral efficiency optical wavelength channels from an optical frequency comb based transmitter into fewer channels with higher spectral efficiency. Our method utilizes coherent spectral superposition and optical vector summation, eliminating the need for optical nonlinearities and relying on linear signal processing with an electro-optic modulator. By adjusting the phase of the radio frequency signal driving the modulator, we can easily achieve the required optical phase tuning for vector addition in the I-Q plane. Through experimental demonstrations, we show that the proposed approach enables the generation of 10 GBd PAM-4 and 10 GBd quadrature phase shift keying (QPSK) signals by aggregating two 10 GBd binary phase shift keying signals. Similarly, we aggregate two 10 GBd QPSK signals into one 10 GBd quadrature amplitude modulation-16 (QAM-16) signal. The experiments employ both conventional and sinc-shaped Nyquist signals. Our in-line, all-optical aggregation concept significantly enhances operational capacity while reducing complexity. It offers a promising solution for realizing flexible integrated optical transmitters for advanced modulation format signals using lower-quality electronics. Additionally, it aligns with the requirements of future dynamically reconfigurable optical networks that leverage spectral traffic aggregation. Given its reliance on linear signal processing with an electro-optic modulator, the integration of the method into any integrated photonic platform is straightforward.

3.61 Pbit/s S, C, and L-Band Transmission With 19-Core Single-Mode Fiber

We experimentally demonstrate a 3.61 Pbit/s generalized mutual information (GMI) estimated throughput by space division multiplexing (SDM) and wavelength division multiplexing (WDM) combined transmission over 19-core single-mode fiber. Covering 17 THz bandwidth with a 25-GHz grid in S, C, and L band, 680 wavelength channels are used to deliver 24.5 GBaud probabilistically constellation-shaped (PCS) 256 quadrature amplitude modulation (QAM) and PCS-64QAM signals. The measured data rate shows a great potential for S/C/L-band transmission to dramatically enhance the achievable data rate in multi-core fibers.

Spectral Relaxation Imaging Microscopy II: Complex Dynamics.

The dynamics of condensed matter can be measured by the time-dependent Stokes shift of a suitable fluorescent probe. The time-dependent spectral correlation function is typically described by one or more spectral relaxation correlation times, which, in liquid solvents, characterize the timescales of the dipolar relaxation processes around the excited-state probe. The phasor plot provides a powerful approach to represent and analyze time and frequency-domain data acquired as images, thus providing a spatial map of spectral dynamics in a complex structure such as a living cell. Measurements of the phase and modulation at two emission wavelength channels were shown to be sufficient to extract a single excited-state lifetime and a single spectral relaxation correlation time, supplying estimates of the mean rate of excited-state depopulation and the mean rate of spectral shift. In the present contribution, two more issues were addressed. First, the provision of analytic formulae allowing extraction of the initial generalized polarization and the relaxed generalized polarization, which characterize the fluorescence spectrum of the unrelaxed state and the fully relaxed state. Second, improved methods of model discrimination and model parameter extraction for more complex spectral relaxation phenomena. The analysis workflow was illustrated with examples from the literature.

10×10 Gbs directly modulated DFB laser array based on the REC technique.

We proposed and experimentally demonstrated a directly modulated distributed feedback (DFB) laser array with a transmission rate of 100Gbps (10c h a n n e l s×10G b p s). The grating design is based on the reconstruction equivalent chirp (REC) technique, which enables precise control of the channel wavelength spacing to 100GHz, as specified in the ITU-DWDM standard. DFB laser arrays incorporating the REC technique demonstrate excellent consistency performance, with a side-mode suppression ratio exceeding 48dB, threshold current of approximately 20mA, and modulation bandwidth of greater than 13GHz at a bias current of 100mA. We evaluated the laser's performance by loading a 10Gbps nonreturn-to-zero signal onto the laser using direct modulation and transmitting it over a 10km single-mode fiber. Based on our experimental results, the proposed DFB laser array is promising to be utilized in the next generation of low-cost, 100Gbps DWDM communication systems.

Inverse design of an ultra-compact dual-band wavelength demultiplexing power splitter with detailed analysis of hyperparameters.

Inverse design has been widely studied as an efficient method to reduce footprint and improve performance for integrated silicon photonic (SiP) devices. In this study, we have used inverse design to develop a series of ultra-compact dual-band wavelength demultiplexing power splitters (WDPSs) that can simultaneously perform both wavelength demultiplexing and 1:1 optical power splitting. These WDPSs could facilitate the potential coexistence of dual-band passive optical networks (PONs). The design is performed on a standard silicon-on-insulator (SOI) platform using, what we believe to be, a novel two-step direct binary search (TS-DBS) method and the impact of different hyperparameters related to the physical structure and the optimization algorithm is analyzed in detail. Our inverse-designed WDPS with a minimum feature size of 130 nm achieves a 12.77-times reduction in footprint and a slight increase in performance compared with the forward-designed WDPS. We utilize the optimal combination of hyperparameters to design another WDPS with a minimum feature size reduced to 65 nm, which achieves ultra-low insertion losses of 0.36 dB and 0.37 dB and crosstalk values of -19.91 dB and -17.02 dB at wavelength channels of 1310 nm and 1550 nm, respectively. To the best of our knowledge, the hyperparameters of optimization-based inverse design are systematically discussed for the first time. Our work demonstrates that appropriate setting of hyperparameters greatly improves device performance, throwing light on the manipulation of hyperparameters for future inverse design.

A Wavelength Tunable Multi-Section PIC as an Upstream Transmitter for TWDM Networks

In this paper, we demonstrate a novel multi-section directly modulated laser transmitter for upstream operation in the application of time wavelength division multiplexing (TWDM) architecture. The photonic integrated circuit (PIC) is fabricated using a regrowth-free process that favors simplified and fast manufacturing. The PIC is based on a master-slave configuration, with an addition of a variable optical attenuator (VOA) section between them, and a semiconductor optical amplifier (SOA) at the output. The VOA enables control of the optical injection from the master to the directly modulated slave laser improving the transmission performance. The integrated SOA section at the output is used to boost or turn off the optical output power of the transmitter, thereby enabling burst mode operation. Experimental results show that the PIC can be tuned to four wavelength channels on a 100 GHz frequency grid. We also demonstrate that each channel achieves error-free performance (bit error ratio < 10e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> ), when modulated with 10 Gbps signal and transmitted over 25 km and 50 km fiber. The SOA-based output disable feature of the PIC delivers more than 60 dB attenuation.

Efficient Blue-Green Light Phased Array Based on High-Contrast Grating as a Demultiplexer

Wavelength division multiplexing (WDM) technology has been proven to effectively increase the capacity of optical communications in the infrared light band. However, to date, the WDM systems in the visible band only support limited quantity of wavelength channels, with coarse channel spacing of over 20 nm. This is because there are no available multi/demultiplexers (MUX/DeMUX) with fine wavelength spacing for visible light. In this work, we use a high-contrast grating (HCG) structure to effectively separate the blue-green wavelengths with fine spacing. An efficient blue-green light phased array based on HCG aperture is demonstrated to work as the DeMUX in a WDM system. The HCG aperture presents more efficient main-lobe radiation than typical one-dimensional waveguide surface grating arrays with fishbone antennas. The measured main-lobe loss of optical phased array (OPA) with HCG is over 15 dB lower than that of OPA with fishbone antennas, because HCG provides maximum scatterings for blue-green light. A wavelength spacing as small as 4 nm is validated in a blue-green WDM system, which is the finest channel spacing for WDM in visible band to the best of our knowledge.

Spectral characteristic of multi-wavelength random fiber laser using a microfiber knot resonator

We demonstrate a U-band multi-wavelength random Raman fiber laser (RRFL) based on a microfiber knot resonator (MKR). The RRFL has a forward-pump half-open cavity, wherein a 10-km single mode fiber provides both Rayleigh backscattering feedback and Raman gain. A MKR with a 0.18 nm free spectral range is used as the broadband comb filter. Up to 40 and 38 wavelength channels within 3 dB bandwidth were achieved from the intracavity and the end of the RRFL, respectively. The laser showed a good stability with maximum 0.38 and 0.1 dB peak power fluctuation within an hour at the two outputs, respectively. The spectral evolution with two envelopes was observed, and the impact of the MKR was discussed. The MKR is a small-size all-fiber and wavelength-insensitive broadband filter, which suits well with the broadband operation of the RRFL. The proposed RRFL has a simple structure and good potential tunability and provides guidance for flexible multi-wavelength lasers in the U-band and other wavebands, which have great potential in applications.

Optical label-based cost-effective DWDM optical network performance monitoring using low-bandwidth PD with novel SRS mitigation DSP

Large-scale dense wavelength division multiplexing (DWDM) multi-channel performance monitoring is one of the indispensable technologies for the flexible optical networks. The existing Labelbased monitoring scheme requires expensive optical demultiplexing components/equipment to avoid the influence of stimulated Raman scattering (SRS), which is not only costly and bulky, but also could not monitor the wavelength channels simultaneously. In this paper, a low-cost, high-accuracy monitoring scheme based on Optical Label Method is proposed for DWDM networks, where the optical channel power and node identification (ID), as the main monitoring targets that both can indicate or evaluate the channel connection status, could be efficiently monitored. In the scheme, a novel digital signal processing (DSP) method of SRS mitigation is proposed and demonstrated, and an asynchronous code-division multiple access (A-CDMA) based digital label encoding and decoding method is adopted to distinguish the node ID so that channel initial added node can be accurately verified, thereby wavelength connection status can be reliably monitored by combining the channel power and node ID information. The simulation results show that each wavelength channel power and node ID can be accurately monitored only by low bandwidth photoelectric detector (PD) under the condition of 80 wavelengths and 10 spans at C-band.

Massively scalable Kerr comb-driven silicon photonic link

The growth of computing needs for artificial intelligence and machine learning is critically challenging data communications in today’s data-centre systems. Data movement, dominated by energy costs and limited ‘chip-escape’ bandwidth densities, is perhaps the singular factor determining the scalability of future systems. Using light to send information between compute nodes in such systems can dramatically increase the available bandwidth while simultaneously decreasing energy consumption. Through wavelength-division multiplexing with chip-based microresonator Kerr frequency combs, independent information channels can be encoded onto many distinct colours of light in the same optical fibre for massively parallel data transmission with low energy. Although previous high-bandwidth demonstrations have relied on benchtop equipment for filtering and modulating Kerr comb wavelength channels, data-centre interconnects require a compact on-chip form factor for these operations. Here we demonstrate a massively scalable chip-based silicon photonic data link using a Kerr comb source enabled by a new link architecture and experimentally show aggregate single-fibre data transmission of 512 Gb s−1 across 32 independent wavelength channels. The demonstrated architecture is fundamentally scalable to hundreds of wavelength channels, enabling massively parallel terabit-scale optical interconnects for future green hyperscale data centres.

Scaling comb-driven resonator-based DWDM silicon photonic links to multi-Tb/s in the multi-FSR regime

The use of chip-based micro-resonator Kerr frequency combs in conjunction with dense wavelength-division multiplexing (DWDM) enables massively parallel intensity-modulated direct-detection data transmission with low energy consumption. Resonator-based modulators and filters used in such systems can limit the number of usable wavelength channels due to practical constraints on the maximum achievable free spectral range (FSR). In this work, we introduce the design of multi-Tb/s comb-driven resonator-based silicon photonic links by leveraging the multi-FSR regime. We demonstrate the viability of the link architecture with yield estimates that are supported by extensive wafer-scale measurements of 704 micro-resonators fabricated in a commercial complementary metal–oxide–semiconductor foundry. We show that a 2.80 Tb/s link is realizable with a ≥6σ yield (∼99.999%), and that aggregate bandwidths of 3.76 Tb/s and 4.72 Tb/s are possible if yield targets are relaxed (3σ and 1σ, respectively). All designs represent a 1.94−3.28× boost to aggregate link bandwidth while maintaining BER≤10−10 performance, with a theoretical bandwidth of 10.51 Tb/s being possible for sufficiently robust resonators. We use high-speed BER measurements to inform co-optimization of data rate and aggressor spacing (λag), limiting any additional loss-based power penalties to off-resonance insertion loss (IL) and routing loss. This work demonstrates that, through the multi-FSR regime, there is a clear path toward Kerr comb-driven ultra-broadband, high bandwidth silicon photonic links that can support next-generation data centers and high-performance computers.

A Multiple Scattering Theory Approach: Numerical Model for Haze Detection Using Horizontal Scanning LIDAR

Haze is hazardous to human health. Although horizontal scanning LIDARs have been used to monitor air pollution sources, they have not been used for haze detection. In this work, we present a numerical model for haze detection using horizontal scanning LIDAR by incorporating multiple scattering theory. This model could evaluate whether multiple scattering theory is suitable for analyzing horizontal scanning LIDAR readings to detect haze without assembling LIDARs. We demonstrate this using a hypothetical LIDAR that has maximum horizontal range of 1 km as case study example. In our assessment, Python™ was used to develop simulation algorithm based on single and multiple scattering LIDAR equations. Relative humidity was below 80% which corresponded to potential haze. Visibility data at different haze levels were incorporated for analysis. We then evaluated errors in hypothetical LIDAR readings associated with multiple scattering. Lastly, we calculated ratios of multiple scattering returns in haze relative to clear weather as haze level indicators. Numerical assessment showed that multiple scattering effects were negligible for both wavelength channels (532 nm and 808 nm) at receiver field-of-view (RFOV) of 1.5 mrad, but introduced significant errors when RFOV is 10 mrad. Average ratio of multiple scattering returns evaluated against threshold of 1 could directly reflect the severity of haze. Although this approach was not suitable for heavy and severe haze, it sufficed for practical applications. Overall, the case study demonstrated the feasibility of incorporating multiple scattering theory when analyzing horizontal scanning LIDAR readings to detect haze without experimental verification.

Stationary flow driven by non-sinusoidal time-periodic pressure gradients in wavy-walled channels

The classical problem of secondary flow driven by a sinusoidally varying pressure gradient is extended here to address periodic pressure gradients of complex waveform, which are present in many oscillatory physiological flows. A slender two-dimensional wavy-walled channel is selected as a canonical model problem. Following standard steady-streaming analyses, valid for small values of the ratio ε of the stroke length of the pulsatile motion to the channel wavelength, the spatially periodic flow is described in terms of power-law expansions of ε, with the Womersley number assumed to be of order unity. The solution found at leading order involves a time-periodic velocity with a zero time-averaged value at any given point. As in the case of a sinusoidal pressure gradient, effects of inertia enter at the following order to induce a steady flow in the form of recirculating vortices with zero net flow rate. An improved two-term asymptotic description of this secondary flow is sought by carrying the analysis to the following order. It is found that, when the pressure gradient has a waveform with multiple harmonics, the resulting velocity corrections display a nonzero flow rate, not present in the single-frequency case, which enables stationary convective transport along the channel. Direct numerical simulations for values of ε of order unity are used to investigate effects of inertia and delineate the range of validity of the asymptotic limit ε≪1. The comparisons of the time-averaged velocity obtained numerically with the two-term asymptotic description reveals that the latter remains remarkably accurate for values of ε exceeding 0.5. As an illustrative example, the results of the model problem are used to investigate the cerebrospinal-fluid flow driven along the spinal canal by the cardiac and respiratory cycles, characterized by markedly non-sinusoidal waveforms.

Bidirectional Cladding-Pumped Multicore EDFA and its Optimization for Energy Efficiency by Tuning Pump Condition

This work investigates the feasibility of improving the energy efficiency of a cladding-pumped multicore (MC) EDFA by utilizing bidirectional (BD) pumping. We combined a conventional forward-cladding-pumped MC-EDFA with backward cladding pumping and tuned the pump-gain characteristics and gain shape by controlling the optical pump power ratio of its forward and backward pumps. Since EDFAs have wavelength dependence, output power equalization by each wavelength channel is extremely important for amplifying the wavelength division multiplexing (WDM) signal. The standard method of current equalization is to adjust the attenuation by the output power of each wavelength channel. The main issue with the current standard equalization is the indispensable optical power loss caused the reduced optical amplification efficiency of the EDFA. Our previous work demonstrated that the optical power loss due to equalization can be reduced by controlling the optical power ratio of the forward and backward pumps. This leads to improved energy efficiency of the signal amplification and equalization of both the WDM and spatial division multiplexing (SDM). <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we report our detailed investigation into the tuning amplification characteristics of the BD-MC-EDFA. Our main focus was the gain, noise figure (NF), and gain shape of a 7-core BD-MC-EDFA prototype when forward and backward optical pump power was changed. Under 8 W of total optical pump power, the percentage of 60% forward cladding optical pump power was found to be optimal for efficiency considering the minimum output optical power loss due to equalization. This condition translates into a 1.7% pump conversion efficiency (PCE) improvement, which corresponds to a 24% reduction of the total optical pump power compared to conventional MC-EDFA with only forward cladding pumping. Although the NF deteriorated by 1.0 dB in wavelength average in the 4.5-THz signal bandwidth in exchange for the efficiency improvement, degradation of the 34.2-GBaud polarization multiplexed 16 quadrature amplitude modulation (PM-16QAM) signal amplified by the BD-MC-EDFA operated under the optimized condition was negligible.

A 32-Channel C-Band Hybrid Wavelength/ Polarization Division (de)multiplexer on Silicon

A 32-channel hybrid (de)multiplexer on silicon is designed and experimentally demonstrated to enable polarization division multiplexing (PDM) and wavelength division multiplexing (WDM) for improving the capacity of optical communication links. The hybrid (de)multiplexer is realized by monolithically integrating a polarization rotator and splitter (PRS) and two 16-channel microring resonators (MRRs) arrays. The through and cross ports of the PRS are connected to the bus waveguide of the MRR arrays, respectively. In order to ensure a larger free spectrum range (FSR) to cover all wavelength channels, the radius of the microring is about 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m and the wavelength-channel spacing is 1.6 nm. For the hybrid (de)multiplexer, the crosstalk between the adjacent channels and the non-adjacent channels are -20 dB and -25 dB, respectively. When TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{0}$</tex-math></inline-formula> mode input, the insertion loss is 1.5 dB - 3.8 dB, the crosstalk between the through and cross port is less than -24 dB. When TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{0}$</tex-math></inline-formula> mode inputs, the insertion loss is 1.9 dB - 4.5 dB and the polarization crosstalk is less than -22 dB. In order to eliminate the influence of the fabrication errors and temperature on resonance wavelength, a TiN thermal tuning electrode is added to calibrate the deviation of the wavelength.

FPGA-Based Demonstration of WDM-PAM4-PON System With Low-Complexity CMA

We propose and experimentally demonstrate a low-complexity constant modulus algorithm (CMA) based on FPGA for 4-channel wavelength-division-multiplexing passive optical network (WDM-PON) employing 4-level pulse amplitude modulation (PAM4). The FPGA processes the 4 wavelength channels sequentially. In order to reduce the logic resources required by parallel equalization algorithm, an optimization based on parallel structure of constant mode algorithm (PCMA) was proposed in this paper. Different from the classic all-parallel structure CMA, our proposed PCMA adopts a new tap update structure, which only needs to update few sets of taps. With the help of the proposed structure, the resource of DSP is reduced to 21% on average. The PAM4 signal with a net rate of 110.24Gb/s transmission over 25-km SSMF can be achieved with the bit error rate (BER) less than 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .

Observation of Helium in Mercury's Exosphere by PHEBUS on Bepi‐Colombo

AbstractOn 1 October 2021, Bepi‐Colombo performed its first flyby of Mercury. During the maneuver, the short wavelength channel (55–155 nm) of “Probing the Hermean Exosphere by UV Spectroscopy” (PHEBUS) was activated for a total duration of 1 hr. The helium resonance line at 58.4 nm was clearly observed during the whole sequence. At large distance from the planet, the emission was due to helium atoms in the interplanetary medium (interplanetary UV glow). Just after crossing the terminator of the planet and entering the dawn side of the exosphere, PHEBUS observed a clear additional emission due to scattering of solar photons by helium atoms in the exosphere of Mercury. The first detection of the 58.4 nm line in the exosphere of Mercury was reported by Broadfoot et al. (1976, https://doi.org/10.1029/gl003i010p00577) following the Mariner 10 flybys in 1974. The PHEBUS observation of exospheric helium emissions is the first for this element since the UVS measurements. In this paper, we present the results of our analysis of the PHEBUS data at 58.4 nm. Calibration of both instruments are compared with observations of the interplanetary glow, showing that the measurements of both instruments are accurate. However, we find that the exospheric density of helium atoms deduced from the PHEBUS data is 4.5–7.5 times lower than the previous estimate from UVS on Mariner 10. Possible explanations are considered. We show that some of the helium atoms present in the exosphere of Mercury could originate from the local interstellar cloud.

Integrated programmable spectral filter for frequency-multiplexed neuromorphic computers.

Artificial neural networks (ANN) are a groundbreaking technology massively employed in a plethora of fields. Currently, ANNs are mostly implemented through electronic digital computers, but analog photonic implementations are very interesting mainly because of low power consumption and high bandwidth. We recently demonstrated a photonic neuromorphic computing system based on frequency multiplexing that executes ANNs algorithms as reservoir computing and Extreme Learning Machines. Neuron signals are encoded in the amplitude of the lines of a frequency comb, and neuron interconnections are realized through frequency-domain interference. Here we present an integrated programmable spectral filter designed to manipulate the optical frequency comb in our frequency multiplexing neuromorphic computing platform. The programmable filter controls the attenuation of 16 independent wavelength channels with a 20 GHz spacing. We discuss the design and the results of the chip characterization, and we preliminary demonstrate, through a numerical simulation, that the produced chip is suitable for the envisioned neuromorphic computing application.

Two-Color iSCAT Imaging of Ag Nanoparticles Resolves Size and Ambient Refractive Index Changes.

The ability to discern noble metal nanoparticles (NPs) with different sizes and in ambient media with different refractive indices has important applications in imaging and sensing. Here a two-color (405 nm, 445 nm) interferometric scattering (iSCAT) detection scheme is applied to characterize the wavelength-dependent iSCAT contrast of Ag NPs with nominal diameters of 10, 20, 40, and 60 nm and to distinguish between NPs of different sizes. The iSCAT contrast also depends on the ambient refractive index and the relative iSCAT contrast on both channels revealed a spectral red-shift for 40 and 60 nm Ag NPs when the ambient refractive index was increased from n = 1.3892 to n = 1.4328. With the selected wavelength channels, the spectral resolution of the two-color imaging strategy was, however, insufficient to resolve spectral shifts induced by refractive index changes for 10 and 20 nm Ag NPs.

Real-time Fourier-domain optical vector oscilloscope

To meet the constant demands of high-capacity telecommunications infrastructure, data rates beyond 1 terabit per second per wavelength channel and optical multiplexing are widely applied. However, these features pose challenges for existing data acquisition and optical performance monitoring techniques because of bandwidth limitation and signal synchronization. We designed an approach that would address these limitations by optically converting the frequency limit to an unlimited time axis and combining this with a chirped coherent detection to innovatively obtain the full-field spectrum. With this approach, we demonstrated a real-time Fourier-domain optical vector oscilloscope, with a 3.4-terahertz bandwidth and a 280-femtosecond temporal resolution over a 520-picosecond record length. In addition to on-off keying and binary phase-shift keying signals (128 gigabits per second), quadrature phase-shift keying wavelength division-multiplexed signals (4 × 160 gigabits per second) are simultaneously observed. Moreover, we successfully demonstrate some high-precision measurements, which indicate them as a promising scientific and industrial tool in high-speed optical communication and ultrafast optical measurement.