Optical Time Delay Research Articles

光纤延迟环型射频存储技术的优化研究

光纤延迟环型射频存储技术的优化研究

Photonic generation of triangular-shaped waveform signal with adjustable symmetrical coefficient

ABSTRACTA configuration for triangular-shaped microwave signal generator is proposed and analysed. In the proposed model, a single-drive Mach–Zehnder modulator operated under the push–pull mode is firstly driven by a sinusoid signal. The lightwave is then split into two branches and converted by a balanced photodetector. According to the analysis, the output photocurrent contains infinite sinusoidal harmonics of the driven frequency. By adjusting three variables (modulation index, bias state and optical time delay), the power of the first three harmonics can be arbitrarily controlled. Such a property can be used in triangular-shaped microwave generation with adjustable symmetrical coefficient δ. The theory and discussion are proposed in this work. A fitting error η is defined to evaluate the waveform quality. With a defined η < 6%, the symmetrical coefficient can be adjusted within a range of 20% ≤ δ ≤ 80%.

Fano resonance in MDM plasmonic waveguides coupled with split ring resonator

Fano resonance results from the coherent interference between a narrow discrete state and a wide continuous spectrum, which is useful for the integrated optical devices. In this paper, Fano resonance in some ultra compact metal-dielectric-metal (MDM) plasmonic waveguides is studied in detail. The structures are composed of a bus waveguide, a stub resonator, a split ring resonator (SRR), or an SRR connected to a tooth resonator (TSRR). The simulation results indicate that the two Fano resonances FR1 and FR2 can be excited, which are sensitive to some of the structural parameters and the refractive index of the dielectric medium in SRR and TSRR. A novel and interesting result is that, for the TSRR, when the rotation angle of its connected tooth cavity is 90° or 45°, the independent tunability of the resonant wavelength of the two Fano resonances can be achieved. In addition, as for the application of refractive index sensor, the sensitivity and the figure of merit (FOM) are both higher. Due to the sharp change of transmission phase shift, larger dispersion will accompany with the Fano resonance. It is shown that the maximum group index can be larger than 14 with optical delay time of about 0.1ps. So the proposed waveguide structures may be suitable for the applications of nanoscale filters, refractive index sensors, and slow-light devices and so on.

Adaptive optical self-interference cancellation for in-band full-duplex systems using regular triangle algorithm.

In this paper, we propose an adaptive optical self-interference cancellation using regular triangle algorithm for in-band full-duplex systems. By using this algorithm, the manual adjustment of the tunable optical time delay line and attenuator is replaced with the adaptive program to change the delay and attenuation for achieving optimal cancellation point. The adjustment process is simplified as a convex function problem. We choose to attain the optimal cancellation point by directly and continuously sampling the power of the signal after cancellation and in turn adjust the time delay and attenuation according to the algorithm. In this way, the two paths in the self-interference cancellation system are precisely and automatically matched. By using our proposed algorithm, the interference signal over 300-MHz wideband is diminished to the noise floor, attaining 20-25 dB cancellation depth adaptively. Compared with other existing algorithms in both the experiment and simulation, our proposed regular triangle algorithm reaches the optimal point faster with 10-30% less number of samples from the near start region, and lowers 40-60% less number of samples from the farther start region.

High-accuracy optical time delay measurement in fiber link [Invited

Optoelectronic components and subsystems such as optically controlled phased array antennas, distributed radar networks, interferometric optical fiber hydrophones, and high-speed optoelectronic chips demand high-accuracy optical time delay measurement with large measurement range and the capability for single-end and wavelength-dependent measurement. In this paper, the recent advances in the optical time delay measurement of a fiber link with high accuracy are reviewed. The general models of the typical time delay measurement technologies are established with the operational principle analyzed. The performance of these techniques is also discussed.

Temporal and Spatial Coherent Pulse Combining by Multi-path Interferometric Scheme

In this investigation, we propose a compact temporal and spatial coherent pulse combining module to be applied to the divided chirped pulse amplification. Our temporal coherent pulse dividing/combining module has effectively long optical time delay line, which leads to a few ns delay time, because of the multi-path interferometric scheme and the single module can act a role of both dividing and combining pulses. For the coherent pulse combining, the locking of optical coherence by single-detector electronic-frequency tagging technique was adopted and the sub-pulses were successfully combined to achieve the single combined pulse. In order to estimate the power stability, the intensity signals were collected for approximately 13 h and Allan deviation was calculated. As the result, the stability of pulse combining was 2.97 × 10−2 (2.97%) at 1 s integration time.

Nanosensing and slow light application based on Fano resonance in waveguide coupled equilateral triangle resonator system

Plasmonic Fano resonance effect is investigated in a novel metal-insulator-metal waveguide structure, which consists of a stub MIM waveguide and a triangle shaped resonator. The transmission properties of the proposed plasmonic waveguide structure are numerically investigated by the two dimensional finite-difference-time -domain (FDTD). The coupling between the stub resonator and the triangle resonator results in a Fano resonance. The transmission characteristics and the slow light effect, sensing performance of the proposed plasmonic structure are studies in detail. By proper design, the sensitivity and the optical delay time of the proposed structure can be up to 800 nm/RIU and 0.053 ps. The above characteristics indicate the proposed plasmonic structure may have application in slow light device, plasmonic filter, all optical switch and nanosensing.

IIR Microwave Photonic Filters Based on Homogeneous Multicore Fibers

We propose and experimentally demonstrate two types of infinite impulse response (IIR) microwave photonic filters (MPFs) with different configurations, named cascaded configuration and parallel configuration. Both configurations are based on the homogeneous multicore fiber (MCF) in which the intercore power coupling is enabled by the tapering technique. The quality factors (Q factors) of cascaded and parallel IIR-MPFs are 143 and 136, respectively, which is much higher than that of one single IIR filter. The geometric structure of the tapered MCF and the number of spatial cores open new dimensions to manipulate the performance of MPFs. Theoretically, higher Q factor and rejection ratio can be obtained by using more cores of MCF to build more cascaded or parallel filters. These two types of IIR-MPFs show good reconfigurability and tunability by adjusting optical power and time delay through simulations. We anticipate that microwave photonics systems will benefit from these two types of IIR-MPFs in terms of compactness, reconfigurability, tunability, and performance stability.

Dynamically Tunable Plasmon-Induced Transparency Based on an H-Shaped Graphene Resonator

We propose a dynamically adjustable plasmon-induced transparent (PIT) plane device consisting of a periodic H-shaped graphene resonator (HSGR). For the symmetrical pattern, only dipole resonance is observed at a normal incidence excited with electric field along the $x$ -direction. Once the asymmetry is introduced into the structure, the magnetic dipole mode that is not accessible in the symmetric structure can be excited, and the interference between the continuum and the leaky modes in HSGR forms a PIT window in original dipole resonance absorption band. The spectrum responses of HSGR can be flexibly regulated by transforming geometric parameters of U-shaped cavity as well as the Fermi energy of graphene. Besides, an optical delay time more than 0.04 ps and a figure-of-merit value 17.78 are obtained in our design structure. Our studies may open up avenues for fabricating compact equipment in appealing bio-chemical sensors and slow-light devices.

Tunable plasmon-induced absorption in an integrated graphene nanoribbon side-coupled waveguide.

By designing a novel graphene plasmonic band-pass filter with two gold ribbons, we have numerically and analytically investigated the transmission properties of plasmon-induced absorption (PIA) in a compact graphene nanoribbon side-coupled waveguide. The formation and evolution of the PIA window are dependent on the superposition of super resonances and the near-field coupling intensity between the designed two resonators. Interestingly, the induced absorption window not only can be engineered longitudinally in intensity, but also dynamically tuned horizontally in the resonant wavelength by changing the Fermi energy of the graphene layers. Optical time delay near 1.0ps can be realized in the PIA window, which exhibits excellent slow light features. Double PIA resonance is also discussed. This result may have potential applications in graphene plasmonic switching and buffering.

Optical Signal Time Delay Generation Based on Micro Ring Resonators for Quantum Non Demolition Detection

Optical Signal Time Delay Generation Based on Micro Ring Resonators for Quantum Non Demolition Detection

Theoretical demonstration of all-optical switchable and tunable UWB doublet pulse train generator utilizing SOA wavelength conversion and tunable time delay

An all-optical ultrawide band (UWB) doublet pulse train signal generator is proposed and theoretically simulated by utilizing an inverse wavelength conversion base on the cross-gain modulation (XGM) effect in a semiconductor optical amplifier (SOA) and controllable time delay in two optical delay lines (ODLs). The proposed scheme is not only optically switchable in the polarity of pulse by switching the polarity of input pulse but also tunable in signal pulse width and radiofrequency (RF) spectrum by tuning the ODLs.

Analysis of optic disc damage by optical coherence tomography in terms of therapy in non-arteritic anterior ischemic optic neuropathy.

This study aimed to assess the relationship between the rate of nerve fiber loss in non-arteritic anterior ischemic optic neuropathy (NAION) and time delay before therapy. Total 24 patients received the same treatment within or after 2wk (early and late groups). There were significantly lower level of destruction of nerve fibers (P=0.0014) and significantly better visual field sensitivity (P=0.039) in early group. The results indicate that therapy should be started within 2wk. The degree of ischemic damage due to NAION correlates well with retinal nerve fiber layer thickness and the ischemia-induced decrease in visual field sensitivity.

Guideline of choosing optical delay time to optimize the performance of an interferometry-based in-band OSNR monitor.

We propose and experimentally demonstrate a guideline of choosing optical delay time in an interferometry-based optical signal-to-noise ratio (OSNR) monitor to achieve the optimal monitoring performance by calculating the normalized autocorrelation function of the channel noise. According to the position of the first zero point of the calculated autocorrelation function, the delay time is determined; consequently the OSNR monitoring range up to 29 dB (within an error≤±0.5 dB) is achieved for 112 Gb/s PM-QPSK signal with a channel filter bandwidth of 100 GHz. The experimental results also show that the guideline is applicable to channel filters with different bandwidths and shapes. In simulation, the guideline is proven to be valid in OSNR monitoring for a 28 Gbaud PM-16QAM signal and a 50 Gbaud PM-QPSK signal.

Subwavelength grating enabled on-chip ultra-compact optical true time delay line.

An optical true time delay line (OTTDL) is a basic photonic building block that enables many microwave photonic and optical processing operations. The conventional design for an integrated OTTDL that is based on spatial diversity uses a length-variable waveguide array to create the optical time delays, which can introduce complexities in the integrated circuit design. Here we report the first ever demonstration of an integrated index-variable OTTDL that exploits spatial diversity in an equal length waveguide array. The approach uses subwavelength grating waveguides in silicon-on-insulator (SOI), which enables the realization of OTTDLs having a simple geometry and that occupy a compact chip area. Moreover, compared to conventional wavelength-variable delay lines with a few THz operation bandwidth, our index-variable OTTDL has an extremely broad operation bandwidth practically exceeding several tens of THz, which supports operation for various input optical signals with broad ranges of central wavelength and bandwidth.

Graphene-based fine-tunable optical delay line for optical beamforming in phased-array antennas.

The design of an integrated graphene-based fine-tunable optical delay line on silicon nitride for optical beamforming in phased-array antennas is reported. A high value of the optical delay time (τg=920 ps) together with a compact footprint (4.15 mm2) and optical loss <27 dB make this device particularly suitable for highly efficient steering in active phased-array antennas. The delay line includes two graphene-based Mach-Zehnder interferometer switches and two vertically stacked microring resonators between which a graphene capacitor is placed. The tuning range is obtained by varying the value of the voltage applied to the graphene electrodes, which controls the optical path of the light propagation and therefore the delay time. The graphene provides a faster reconfigurable time and low values of energy dissipation. Such significant advantages, together with a negligible beam-squint effect, allow us to overcome the limitations of conventional RF beamformers. A highly efficient fine-tunable optical delay line for the beamsteering of 20radiating elements up to ±20° in the azimuth direction of a tile in a phased-array antenna of an X-band synthetic aperture radar has been designed.

Simultaneous optical monitoring of BL Lacertae object S5 0716+714 with high temporal resolution

We have monitored the BL Lacertae object S5 0716+714 simultaneously in the B, R and I bands on three nights in November 2014. The average time resolution is quite high (73s, 34s, 58s for the filters B, R and I), which can help us trace the profile of the variation and search for the short inter-band time delay. Intra-day variability was about 0.1 mag on the first two nights and more than 0.3 mag on the third. A bluer-when-brighter color behavior was found. An clear loop path can be seen on the color-magnitude diagram of the third night, revealing possible time delays between variations at high and low energies. It is the first time that the intra-day spectral hysteresis loop has been found so obviously in the optical band. We used the interpolated cross-correlation function method to further confirm the time delay and calculated the values of lag between light curves at different wavelengths on each night. On the third night, variations in the R and B bands is approximately 1.5 minutes lagging behind the I band. Such optical time delay is probably due to the interplay of different processes of electrons in the jet of the blazar.

Determination of hydrocarbon levels in water via laser-induced acoustics wave

Hydrocarbon contamination in water is a major environmental concern in terms of foreseen collapse of the natural ecosystem. Hydrocarbon level in water was determined by generating acoustic wave via an innovative laser-induced breakdown in conjunction with high-speed photographic coupling with piezoelectric transducer to trace acoustic wave propagation. A Q-switched Nd:YAG (40mJ) was focused in cuvette-filled hydrocarbon solution at various concentrations (0–2000ppm) to induce optical breakdown, shock wave generation and later acoustic wave propagation. A nitro-dye (ND) laser (10mJ) was used as a flash to illuminate and frozen the acoustic wave propagation. Lasers were synchronised using a digital delay generator. The image of acoustic waves was grabbed and recorded via charged couple device (CCD) video camera at the speed of 30 frames/second with the aid of Matrox software version 9. The optical delay (0.8–10.0μs) between the acoustic wave formation and its frozen time is recorded through photodetectors. A piezo-electric transducer (PZT) was used to trace the acoustic wave (sound signal), which cascades to a digital oscilloscope. The acoustic speed is calculated from the ratio of acoustic wave radius (1–8mm) and optical time delay. Acoustic wave speed is found to linearly increase with hydrocarbon concentrations. The acoustic signal generation at higher hydrocarbon levels in water is attributed to supplementary mass transfer and impact on the probe. Integrated high-speed photography with transducer detection system authenticated that the signals indeed emerged from the laser-induced acoustic wave instead of photothermal processes. It is established that the acoustic wave speed in water is used as a fingerprint to detect the hydrocarbon levels.

Power Balance and Control in Optically Controlled Phased Array Antenna, Based on Optical True Time Delay

There is clear difference in each fiber-optic link's power output, in the large scale optically controlled phased array antenna. In order to realize the optical power balance and control between the various channels, the equilibrium or control power of each optical signal needs to be considered, and it will reduce the optical beam forming network generat- ed side-lobe beam, which results in the performance improvement of the system. In this paper, the methods of optical power equalization and control is proposed, which is used in the forming network of the optical beam. The method can re- alize the optical power's equalization and control of each optical signal. In the end of this paper, the verification and re- sults are provided. Some researchers advance a new theory very early, which is using optical fiber as delay medium in the signal processing of microwave and millimeter waves. The tech- nology of Optical True Time-Delay is appeared, and it is the earliest application, which is used in microwave photonic filter and optically controlled phased array antenna. The technological idea of OCPAA, which is based on OTTD, is as follows: the electrical signal, with its frequency greatly lower than the optical frequency, can be loaded into the opti- cal wave. Then the loaded optical wave can be delayed, and the electrical signal can be extracted from it by optical detec- tor. The extracted electrical signal and the original electrical one have identical characters, but there are some time-delay on phase position between the two signals. The True Time Delay(TTD) system based on this technological process is called the OTTD system. The integration of OTTD and phased array antenna tech- nique has overcome two technical bottlenecks in the conven- tional phased array radar, i.e., the restriction of large instan- taneous bandwidth and the beam deflection. The pure elec- trical real time delay unit has been replaced by the optical real time delay unit in optically controlled phased array an- tenna system, which makes the new OCPAA system have the virtue of low cost, light weight, small size, low power consumption and strong capability of anti-electromagnetic interference. In addition, OTTD has extensive application in optical switching technique and wireless communication technology. Compared to conventional electronic beam forming net- work, the optical beam forming network based on OTTD has many advantages, such as low power consumption, small size, large bandwidth, anti-electromagnetic interference and effectively restriction of beam deflection, etc. Thus, many OTTD systematic configuration models have been invented. However, after experiments, due to various factors, e.g. large amount of photovoltaic components and parts in optical beam forming network with its inconsistent wavelengths response, the gain difference of diversed wavelength signals caused by Erbium-Doped Fiber Amplifier (the gain uneven- ness), the inconsistent insertion loss of filters at different wavelength positions, as well as the inconsistent photoelec- tric detectors response, the optical power input in photoelec- tric detectors through channels are not equal. The optical power unequalization results in the functional deterioration of microwave in space distribution, for example, the low main-lobe peak, the high sidelobe level, and the accuracy decrease of beam-pointing. As a result, it is necessary to pre- cise control the optical signal power in each channel for the smooth operation of optical beam forming network.

Simultaneous Suppression of Time-Delay Signature in Intensity and Phase of Dual-Channel Chaos Communication

In this paper, we propose a novel dual-channel optical chaos system with a time-delay (TD) feature simultaneously suppressed in all observables, i.e., in both intensity and phase. A hybrid optical and electro-optic feedback for a single vertical-cavity surface-emitting laser (VCSEL) is verified to induce simultaneous TD suppression for the polarization-resolved components of the chaotic output. A comprehensive mathematical model is developed to incorporate the optical and electro-optic time delays into the rate equations of the VCSEL. The suppression of TD signature is then examined by means of autocorrelation function and delayed mutual information. The results show that the output chaotic signal has the TD feature well eliminated in both the intensity and phase over certain regions of parameter space identified using the peak signal to mean ratio technique. The independent evolution of the two orthogonal VCSEL modes renders the polarization-resolved output modes appropriate for the enhanced dual-channel chaos applications. To the best of our knowledge, this is the first time that a dual-channel chaos communication system is reported with simultaneous suppression of the TD feature in all the transmitted observables.