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1.
Opt Lett ; 47(15): 3912-3915, 2022 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-35913346

RESUMO

A physics-based deep learning (DL) method termed Phynet is proposed for modeling the nonlinear pulse propagation in optical fibers totally independent of the ground truth. The presented Phynet is a combination of a handcrafted neural network and the nonlinear Schrödinger physics model. In particular, Phynet is optimized through physics loss generated by the interaction between the network and the physical model rather than the supervised loss. The inverse pulse propagation problem is leveraged to exemplify the performance of Phynet when in comparison to the typical DL method under the same structure and datasets. The results demonstrate that Phynet is able to precisely restore the initial pulse profiles with varied initial widths and powers, while revealing a similar prediction accuracy compared with the typical DL method. The proposed Phynet method can be expected to break the severe bottleneck of the traditional DL method in terms of relying on abundant labeled data during the training phase, which thus brings new insight for modeling and predicting the nonlinear dynamics of the fibers.

2.
Opt Lett ; 47(10): 2382-2385, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35561356

RESUMO

Chaotic optical communication technology is considered as an effective secure communication technology, which can protect information from a physical layer and is compatible with the existing optical networks. At present, to realize long-distance chaos synchronization is still a very difficult problem, mainly because well-matched hardware cannot always be guaranteed between the transmitter and receiver. In this Letter, we introduce long short-term memory (LSTM) networks to learn a nonlinear dynamics model of an opto-electronic feedback loop, and then apply the trained deep learning model to generate a chaotic waveform for encryption and decryption at the transmitter and receiver. Furthermore, to improve the security, we establish a deep learning model pool which consists of different gain trained models and different delay trained models, and use a digital signal to drive chaos synchronization between the receiver and transmitter. The proposed scheme is experimentally verified in chaotic-encrypted 56-Gbit/s PAM-4 systems, and a decrypted performance below 7%FEC threshold (BER = 3.8×10-3) can be achieved over a 100-km fiber transmission.

3.
Opt Express ; 30(7): 11306-11316, 2022 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-35473078

RESUMO

Conventional Brillouin optical time-domain analyzer (BOTDA) with a frequency-modulated probe (FMP) could avoid non-local effects, while still suffering from the acoustic crosstalk between different frequencies. The induced Brillouin frequency shift (BFS) measurement errors over the whole sensing fiber link reduce system certainty subsequently. A BOTDA scheme with a bidirectional frequency-modulated probe (BFMP) is proposed to overcome such an effect. It utilizes BFMP to generate the crosstalk of the same magnitude and opposite direction to compensate each other. Experimental results indicate that the pulse interval of the coded sequence could be reduced to ∼500 ns to improve the measurement efficiency and BFS estimation errors (∼2.2 MHz) over 117.46-km sensor link are eliminated simultaneously.

4.
Opt Lett ; 47(6): 1442-1445, 2022 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-35290334

RESUMO

An optical frequency comb (OFC)-assisted covert wireless communication system with multiple access and enhanced capacity is proposed and experimentally demonstrated. In the scheme, signals in multiple channels are spread and mixed together to use a single transmitter and then received by individual receivers according to multiple access channels. The mixed signal is highly contaminated by noise to achieve high concealment in both the time and frequency domains, and then effectively recovered as different channels using the OFC assisted analog deep denoising technique. In experiments, mixed signals of 16 access channels with a signal-to-noise ratio (SNR) from -18 to -5 dB are accommodated, showing high covertness and 16× capacity enhancement (16×10 Mbit/s). Mutual interference among different channels is also analyzed and greatly eliminated by phases optimization in the spectral-spreading process. This scheme can greatly improve the time and spectrum utilization efficiency, which will be of great significance for enabling multiple access, large capacity, and high security for wireless communications.

5.
Opt Express ; 30(5): 6690-6699, 2022 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-35299448

RESUMO

A microwave photonic link to transmit four independent microwave vector signals modulated on a single optical carrier based on coherent detection and digital signal processing (DSP) is proposed and experimentally demonstrated. At the transmitter, a continuous-wave (CW) light wave is modulated by four independent microwave vector signals with an identical center microwave frequency at a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM), to generate four intensity-modulated optical signals, with two signals sharing one of the two orthogonal polarization states. After transmission over a single-mode fiber (SMF), the optical signals are applied to a polarization- and phase- diversity coherent receiver to which a light wave from a second laser source as a local oscillator (LO) is also applied. To eliminate the joint phase noise and the unstable offset frequency from the transmitter and the LO laser sources and to perform polarization demultiplexing, a digital noise cancellation algorithm and a polarization demultiplexing algorithm are developed. The proposed approach is evaluated experimentally. For four independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals at 4 GHz with a symbol rate of 0.5 GSymbol/s, error-free transmission over a 9-km SMF is achieved when the received optical power at the coherent receiver is higher than -21 dBm with forward error correction (FEC).

6.
Opt Express ; 29(21): 33926-33936, 2021 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-34809193

RESUMO

The measurement accuracy of a Brillouin optical time domain analysis (BOTDA) fiber sensor is determined by the signal-to-noise ratio (SNR) of the received sensing signal. Here, a new hybrid aperiodic coding method is proposed to improve the SNR. In the proposed method, two pre-discovered short seed aperiodic codes (SA-codes) are used to construct a new hybrid aperiodic code (HA-code) in a nested way. The HA-code inherits the good denoising capabilities of the two SA-codes and features a high coding gain. In the proof-of-concept experiment, a SNR improvement up to 8 dB is obtained, which improves the measurement certainty to 1.67 MHz over a 117.46 km sensing range under a spatial resolution of 2.6 m.

7.
Opt Express ; 29(16): 25868-25875, 2021 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-34614906

RESUMO

Radio-over-fiber (RoF) transmission is a quite reliable technology to support the current and future demands of rapidly progressing broadband wireless network with large capacity and high spectral efficiency. In this paper, we report and demonstrate a digital RoF transmission system using two-dimensional discrete cosine transform with vector quantization (2D-DCT-VQ). By employing the 2D-DCT-VQ technique, the spectral efficiency can be greatly improved, while the system performance is comparable to the traditional approach without compression. The proposed method is experimentally demonstrated in a 20-km 5-Gbaud/λ four-level pulse modulation intensity-modulation/direct-detection optical link. In the orthogonal frequency-division multiplexing -modulated downlink illustrated experimentally, the transmission rate rises by 69.49% on account of the compressed samples by using the proposed method.

8.
Opt Express ; 29(17): 27340-27349, 2021 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-34615152

RESUMO

The erbium-doped-fiber-amplifier (EDFA), generally served as a pre-amplifier, could effectively raise the signal-to-noise ratio (SNR) of a Brillouin optical time-domain analysis (BOTDA) sensor. However, it also induces a distortion in the Brillouin gain spectrum and Brillouin frequency shift measurement errors due to the slow transient effect (STE) in the coded-BOTDA. We propose a distributed depletion mapping (DDM) method to overcome such an effect. A continuous light wave with a particular wavelength is injected to map the STE-induced depletion to compensate for the distortion. The proposed scheme is experimentally demonstrated along a 120-km sensing fiber with 2-m spatial resolution. Experimental results show that the conventional tail-alignment (TA) method cannot compensate for the STE over the whole fiber link, while the proposed DDM method compensates for over 7.69-MHz measurement errors.

9.
Opt Express ; 29(20): 32333-32348, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-34615307

RESUMO

Highly reliable wireless train-ground communication immune to the electromagnetic interferences (EMIs) is of critical importance for the security and efficiency of high-speed railways (HSRs). However, the rapid development of HSRs (>52,000 km all over the world) brings great challenges on the conventional EMIs mitigation strategies featuring non-real-time and passive. In this paper, the convergence of radio-over-fiber distributed antenna architecture (RoF-DAA) and reinforcement learning technologies is explored to empower a real-time, cognitive and efficient wireless communication solution for HSRs, with strong immunity to EMIs. A centralized communication system utilizes the RoF-DAA to connect the center station (CS) and distributed remote radio units (RRUs) along with the railway track-sides to collect electromagnetic signals from environments. Real-time recognition of EMIs and interactions between the CS and RRUs are enabled by the RoF link featuring broad bandwidth and low transmission loss. An intelligent proactive interference avoidance scheme is proposed to perform EMI-immunity wireless communication. Then an improved Win or learn Fast-Policy Hill Climbing (WoLF-PHC) multi-agent reinforcement learning algorithm is adopted to dynamically select and switch the operation frequency bands of RRUs in a self-adaptive mode, avoiding the frequency channel contaminated by the EMIs. In proof-of-concept experiments and simulations, EMIs towards a single RRU and multiple RRUs in the same cluster and towards two adjacent RRUs in distinct clusters are effectively avoided for the Global System for Mobile communications-Railway (GSM-R) system in HSRs. The proposed system has a superior performance in terms of circumventing either static or dynamic EMIs, serving as an improved cognitive radio scheme to ensuring high security and high efficiency railway communication.

10.
Light Sci Appl ; 10(1): 172, 2021 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-34456335

RESUMO

High-speed physical key distribution is diligently pursued for secure communication. In this paper, we propose and experimentally demonstrate a scheme of high-speed key distribution using mode-shift keying chaos synchronization between two multi-longitudinal-mode Fabry-Perot lasers commonly driven by a super-luminescent diode. Legitimate users dynamically select one of the longitudinal modes according to private control codes to achieve mode-shift keying chaos synchronization. The two remote chaotic light waveforms are quantized to generate two raw random bit streams, and then those bits corresponding to chaos synchronization are sifted as shared keys by comparing the control codes. In this method, the transition time, i.e., the chaos synchronization recovery time is determined by the rising time of the control codes rather than the laser transition response time, so the key distribution rate is improved greatly. Our experiment achieved a 0.75-Gbit/s key distribution rate with a bit error rate of 3.8 × 10-3 over 160-km fiber transmission with dispersion compensation. The entropy rate of the laser chaos is evaluated as 16 Gbit/s, which determines the ultimate final key rate together with the key generation ratio. It is therefore believed that the method pays a way for Gbit/s physical key distribution.

11.
Opt Lett ; 46(14): 3488-3491, 2021 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-34264246

RESUMO

The Brillouin collision rate in a Brillouin optical correlation domain analysis fiber sensor is ultimately limited by the sensing fiber length, which restricts the single point sampling rate in dynamic strain measurement. Here, a time-gated long-phase-sequence-coded pump method is proposed to overcome this limitation. The Brillouin collision rate is limited only by the phonon lifetime, since it governs the building and decaying time of the acoustic wave. For a sensing fiber length of ∼1km, a Brillouin collision rate as high as 1 MHz is experimentally realized. This further results in a single-point sampling rate of 1 kHz for dynamic strain sensing with a spatial resolution of ∼2cm and a measurement uncertainty of <33.5µÎµ.

12.
Opt Lett ; 46(12): 2824-2827, 2021 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-34129550

RESUMO

The instability of optical phase chaos synchronization between semiconductor lasers under master-slave open-loop configuration is investigated. The phase difference between the master and slave lasers is obtained and analyzed in experiment by heterodyne detection and Hilbert transform, and in simulation by solving the rate equations. The results show that the phase difference only maintains in a short duration time and then jumps to another value. A statistical analysis shows that both duration time and jumping values are random, proving that the phase chaos synchronization is unstable. A theoretical analysis shows that the instability of phase synchronization is caused by the jumping of the external cavity mode in the master laser.

13.
Opt Express ; 29(8): 12478-12490, 2021 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-33985006

RESUMO

We propose a frequency splicing code-based Brillouin optical time domain collider (FSC-BOTDC) for fast dynamic sensing. By delicately designing the frequency splicing code (FSC), multiple collision modes with controllable characteristics are realized for probing multiple target areas with a high sampling rate. Moreover, the sensing system is simpler and more robust than the previous BOTDC. In the experiment, the FSC-BOTDC with 10-time enhanced sampling rate is implemented for single and multiple target areas measurements. Results demonstrate that tailorable measurements can be achieved by the tunable FSC. Furthermore, the FSC-BOTDC is executed to measure periodic mechanical vibrations over 7.9-km sensing range with the sampling rate of 625 Hz.

14.
Opt Express ; 29(8): 12750-12762, 2021 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-33985025

RESUMO

Recent demonstrations of chaos-based secure communication have proven the feasibility of secured transmission of high-speed (tens of Gbit/s) signals over certain distances (∼100-km), which bring hope for secure communication from theoretical analysis to practical applications. So far, the chaos-based secure communication system with chaos-masking (CMS) encryption is considered as one of the most important and feasible schemes. In this paper, an optical chaotic carrier generated by an opto-electronic oscillator is used to encrypt 112-Gbit/s message by CMS encryption for data transmission over a 1040-km single-mode-fiber. The message is successfully decrypted by combining coherent detection and our proposed blind decryption algorithms, which can successfully separate the chaotic carrier and the message with the bit-error-rate (BER) below the forward error correction (FEC) threshold. Experimental results show that the coherent detection combined digital signal processing algorithms may be a possible way to promote the practical applications of chaotic optical communication in the future. In addition, this paper reveals that the security of the CMS encryption may be not high enough for those systems requiring rigorous confidentiality. Subsequently, we further discuss the bottlenecks encountered in current high-speed chaotic optical communication systems and analyze how to improve and weight the security and practicability.

15.
Opt Lett ; 46(7): 1668-1671, 2021 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-33793514

RESUMO

In this Letter, a chirped-pulse conversion algorithm (CPCA) is proposed to convert a normal probe pulse into an equivalent chirped probe pulse by convolving a chirp factor on the received signal in coherent phase-sensitive optical time-domain reflectometry (Φ-OTDR). With this algorithm, the Rayleigh interference pattern (RIP) demodulation once applied to chirped-pulse Φ-OTDR can be adopted to quantify the dynamic strain in the traditional coherent Φ-OTDR. Since the equivalent chirped pulse is generated by digital processing, complex and costly chirp modulation is not required. The proposed scheme is capable of fully quantifying perturbations with spatial resolution of 4 m, a sensing range of 8 km, frequency response of 5 kHz, and strain resolution of 56pε/√Hz.

16.
Opt Lett ; 46(4): 757-760, 2021 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-33577507

RESUMO

The employment of coherent detection in a Brillouin optical time domain analysis (BOTDA) fiber sensor brings benefits, including signal-to-noise ratio enhancement, non-local effect reduction, and sensing speed improvement. Recently, it was found that the performance of a coherent-detection BOTDA fiber sensor suffers from phase fluctuations introduced by the fiber group delay jitter. Here, we propose a phase fluctuation cancellation approach based on optical subcarrier multiplexing. In a proof-of-concept experiment, the phase stability for in-phase/quadrature demodulation reaches a standard deviation value of as small as 0.4 mrad. The variations in the Brillouin gain and phase spectra caused by the phase fluctuation are then effectively alleviated, resulting in an enhancement of the Brillouin frequency shift measurement certainty along the whole sensing fiber.

17.
Opt Express ; 28(25): 37919-37935, 2020 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-33379616

RESUMO

We propose a scheme of high-speed physical key distribution based on dispersion-shift-keying chaos synchronization in two semiconductor lasers without external feedback (response lasers), which are driven by a common external-cavity semiconductor laser (drive laser). In this scheme, the dispersion introduces a laser field beating-induced nonlinear transformation to the outputs of drive laser and renders the correlation elimination between the drive and response lasers improving the security of key distribution. Moreover, the commonly driven lasers without external feedback constitute an open-loop synchronization configuration and yield a short synchronization recovery time of a subnanosecond supporting the implementation of high-speed key distribution. With these two merits, we numerically demonstrate a 1.2 Gb/s secure key distribution with a bit error ratio below 3.8×10-3.

18.
Appl Opt ; 59(36): 11273, 2020 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-33362050

RESUMO

This publisher's note corrects the Funding section in Appl. Opt.59, 9540 (2020)APOPAI0003-693510.1364/AO.404741.

19.
Appl Opt ; 59(30): 9540-9547, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-33104674

RESUMO

The polarization splitter-rotator (PSR) plays a significant role in telecom, Datacom, and quantum circuits to meet significant requirements for polarization processing and multiplexing. We design an ultracompact PSR based on a silicon asymmetrical directional coupler (ADC). One waveguide of the ADC is gradually etched in two levels along the coupling region and the S-bend. A trapezoidal taper on the top of the dual-etched waveguide is first formed to satisfy the phase-matching condition for the TM-TE mode conversion, such that the TM mode is cross-coupled from the input waveguide without etching. Then, the etching width gradually increases in the S-bend and the following to achieve a single-mode waveguide for further removal of the residual TM mode. In this way, a high extinction ratio can be achieved for the polarization mode splitting in an ultracompact silicon ADC. For the designed PSR with a total length of about 24 µm, the simulation results reveal that the minimum extinction ratio is greater than 30, 20, or 15 dB within the bandwidth of 33, 100, or 150 nm, respectively, while the maximum polarization conversion loss is less than 0.4, 0.9, or 1 dB.

20.
Opt Lett ; 45(17): 4762-4765, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32870851

RESUMO

We propose and numerically demonstrate a scheme of coherent optical chaos communication using semiconductor lasers for secure transmission of optical quadrature amplitude modulation (QAM) signals. In this scheme, a laser intensity chaos and its delayed duplicate are used to amplitude-quadrature modulate a continuous-wave light to generate a chaotic carrier. High-quality chaotic carrier synchronization between the transmitter and receiver is guaranteed by laser intensity chaos synchronization, avoiding laser phase fluctuation. Decryption is implemented by a 90 deg optical hybrid using the synchronous chaotic carrier as local light. Secure transmission of an optical 40 Gb/s 16QAM signal is demonstrated by using a laser intensity chaos with a bandwidth of 11.7 GHz. The system performances are evaluated by analyzing a bit error ratio with different masking coefficients, signal rates, synchronization coefficients, parameter mismatches, and dispersion compensation. It is believed that this scheme can pave a way for high-speed optical chaos communication.

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