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Chromatic dispersion (CD) is one of the key limitations of increasing the transmission performance for short-reach transmission. The available optical dispersion-compensation techniques are not favored due to their high complexity and other expenses such as power. Reservoir computing is reviewed as a promising technique to provide equalization with memory in an easily trainable fashion, and the properties of the reservoir network are directly linked to system performance. In this article, the digital reservoir computing (RC) based CD-compensation technique is investigated to enhance the transmission performance for digital filter multiple access passive optical network (PON). Numerical results show within 50-km single mode fiber transmission distance for 16 GHz signal bandwidth, the RC-based technique is effective for CD compensation to improve the capacity by 25%.

With the advantages of large electro-optical coefficient, wide transparency window, and strong optical confinement, thin-film lithium niobate (TFLN) technique has enabled the development of various high-performance optoelectronics devices, ranging from the ultra-wideband electro-optic modulators to the high-efficient quantum sources. However, the TFLN platform does not natively promise lasers and photodiodes. This study presents an InP/InGaAs modified uni-traveling carrier (MUTC) photodiodes heterogeneously integrated on the TFLN platform with a record-high 3-dB bandwidth of 110 GHz and a responsivity of 0.4 A/W at a 1,550-nm wavelength. It is implemented in a wafer-level TFLN-InP heterogeneous integration platform and is suitable for the large-scale, multi-function, and high-performance TFLN photonic integrated circuits.

A scheme of integrated sensing and communication in an optical fibre (ISAC-OF) using the same wavelength channel for simultaneous high-speed data transmission and distributed vibration sensing.

A bidirectional wavelength division multiplexing (WDM) analog radio-over-fiber (A-RoF) mobile fronthaul (MFH) link is enhanced using photonic integrated devices. Two key photonic integrated devices are combined in the A-RoF link: an 8-channel InP directly modulated laser (DML) transmitter and a 32×100-GHz silicon array waveguide grating (AWG). The DML transmitter has 8 parallel monolithically integrated distributed feedback lasers, enabling cooperative and reconfigurable downlink analog transmission. Moreover, the 32×100-GHz AWG is featured by low insertion loss (

Short reach optical communications are desperate for cost-effective solutions to improve capacity and compatibility in dealing with massive access and applications. Single sideband-direct detection (SSB-DD) is highly recognized for improving capacity with single PD, but it is confronted with signal-signal beating interference (SSBI). Recently, a DC-Value method has been proposed for optical signal phase retrieval for single carrier signal transmission. To further explore the effectiveness and compatibility of DC-Value method, in this letter for the first time, the orthogonal frequency division multiplexing (OFDM)-based multi-carrier modulation formats are processed by the DC-Value method in the receiver. Simulation results demonstrate that, for both OFDM and Nyquist-shaped single carrier (SC), the DC-Value method is beneficial in applying lower sampling rate to achieve comparable transmission performance than that of Kramers-Kronig receiver. In addition, althrough OFDM holds 2 dB increment of the optimum carrier-signal power ratio (CSPR) than Nyquist-SC, it offers more robustness to fibre transmission.

In this paper, a nonlinear model for Light Emitting Diodes (LEDs) inspired by semiconductor physics, and a corresponding post-compensator are implemented in a Field Programmable Gate Array (FPGA) for real-time Visible Light Communications (VLC). Our experiments demonstrate that the LED model effectively characterizes the dynamic LED nonlinearity, including the memory effects. The output signal of this nonlinear LED model shows a good resemblance with the measured LED output. In addition, a dedicated nonlinear equalizer, say, a post-compensator, inspired by this LED physical model can mitigate the nonlinear distortion substantially. Thereby it facilitates high data rate over the bandwidth-limited LED. It shows that the nonlinear compensator is attractive for practical real-time digital signal processing systems due to its high performance and low complexity.

Chaos generation from a semiconductor laser under band-rejection optical feedback is proposed and investigated numerically and experimentally. The band-rejection feedback performs better than the conventional broadband mirror feedback in concealing the feedback delay time information measured by the time-delay signature (TDS) of optical field and intensity. In this work, the optical band-rejection filter (BRF) is built up based on the transmission of a Bragg grating. The best concealment of delay time information is achieved in the form of simultaneous TDS suppression in optical field and intensity when the BRF is negatively detuned from the free-running laser frequency. Such concealment is due to the suppression of feedback cavity modes by the band-rejection effect. The concealment prefers negative detuning frequency because the laser cavity resonance is red-shifted by optical feedback due to the antiguidance effect. The negatively detuned BRF suppresses the TDS of optical field and intensity by more than an order of magnitude than mirror feedback. The simulation results are qualitatively confirmed by the experimental measurements.

Abstract The random forest, a powerful machine learning algorithm, is introduced to improve the performance of silicon arrayed waveguide grating (AWG)‐based fibre Bragg grating (FBG) wavelength interrogation. The experimental results show the proposed method has high interrogation accuracy with the root mean squared error (RMSE) of 0.73 pm in the whole demodulation range.

In this paper, we propose a stable radio frequency(RF) transmission scheme for optical link based on Dual drive Mach-Zehnder modulator(DDMZM). By frequency mixing, the phase jitter of the output signal caused by environment variation has been automatically compensated. Different from other passive compensation schemes, the reference signal and the pre-compensation signal are modulated on one optical carrier by a DDMZM, and the crosstalk of two RF signals can be depressed by using dispersion compensation and adjusting the bias voltage of DDMZM, without multiple frequency multiplications and divisions. Meanwhile, the noises induced by Rayleigh scattering can be suppressed by using acousto-optic modulator. Our scheme is featured by single laser diode employed and no extra phase jitter induced by wavelength differences, with the advantages of simple structure and cost-effectiveness. In the experiment, we demonstrate 10 GHz RF signal stability transmission over 50 km single mode fiber, the phase jitter mean square error is 0.82 ps during 10 hours.

GNSS carrier-phase-based double-difference positioning has been widely used in various precision positioning systems. This paper proposes a cost-effective scheme for an extensive multi-antenna remote multi-baseline network using a single GNSS-over-fiber system. First, GNSS signals are acquired by multiple remote antennas and transmitted to the local station through long microwave photonic links. Second, the GNSS receivers are reused in time division multiplexing mode via fast multi-port optical switches, providing enhanced temporal resolution and low cost for supporting massive monitoring antennas. Finally, compared with a single baseline, the standard deviation of the three-dimensional coordinate in the multi-baseline network is significantly reduced from millimeter to sub-millimeter level (from 2.9 mm to 0.5 mm). It demonstrates that a smaller number of receivers can support more synchronous observation loops, as well as an asynchronous group of them by fast switching, in this proposed scheme. The main contributions are twofold. First, the GNSS-over-fiber architecture is exploited and extended from single to multiple baselines, extending the spatial coverage. Second, the GNSS receivers are reused via optical switches in a fast surveying campaign, providing enhanced temporal resolution cost-effectively. This work will find applications in the large-scale GNSS baseline network, such as civil engineering and natural environment measurement.

For civil and military applications, the ability to instantaneously capture and process wideband RF (radio-frequency) signal is of great importance. In this paper, a novel photonics-assisted RF channelized receiver aiming for instantaneous broadband RF signal reception is proposed and experimentally demonstrated. The channelizer is composed of two branches. In one branch, an optical frequency comb (OFC) is generated through a phase modulator (PM), while in the other the optical carrier is frequency-shifted via a polarization modulator (PolM) and then modulated by the captured unknown RF signal. Next, the frequency information of the unknown signal is derived from the frequency sum and the power difference of two specific beating tones, while the incorporation of the comb spacing and the amplitude profile of the OFC enable resolving the ambiguity cases. In the experiments, four receiving channels are constructed using five selected comb lines. The reception and analysis of several RF signals including single-tone, multi-tone and linear frequency modulation (LFM) ones within 1-40 GHz are experimentally validated, which can be extended up to 72 GHz in theory. The proposed channelizer is characterized with ambiguous-free capability, low measurement errors less than 2 MHz, and an SFDR of ~92 dB·Hz2/3.

A photonic method to generate hybrid binary digitally modulated radio frequency (RF) signals (i.e. ASK, PSK, and FSK) by using a polarization-division-multiplexed Mach-Zehnder modulator (PDM-MZM) is proposed. The PDM-MZM is driven by two RF signals with different carrier frequencies and two multiplied digital signals. By properly controlling the offsets and the amplitudes of the digital signals, ASK, PSK, and FSK signals can be generated and switched fastly. RF signals at 4/6 GHz and 10/15 GHz with switchable modulation formats are experimentally generated. Moreover, the performances of the generated signals are evaluated in a wireless transmission system and corresponding bit error rate (BER) curves of the signals are presented.

A microwave photonic approach is proposed to achieve a high resolution enhanced by a factor of 2 for the range and velocity measurement. In the transmitter, a V-shaped linear-frequency-modulated (LFM) microwave signal is generated through the frequency doubling enabled by photonics, with large time-bandwidth product for improving the range resolution, whereas in the receiver, the round-trip duration and Doppler frequency shift (DFS) between the transmitted LFM signal and the received echo signal are mapped into two doubled frequency spacings between two pairs of target sidebands by incorporating two cascaded electrooptic modulators. Thus, the distance and velocity of the moving target can be measured from the beat note of the target sidebands, showing a high resolution improved by a factor of 2. Experiments have been implemented and demonstrated in X-band with a bandwidth of 2 GHz. The distance measurement indicates an absolute error less than 3 mm. In addition, the performance of the proposed system in terms of low power level is discussed.

In this paper, a two-dimensional (2-D) vector quantization with vector linear prediction (VLP-VQ) is proposed to improve the transmission performance of the digital mobile fronthaul (MFH). Compared with the conventional vector quantization based on k-means clustering algorithm, the VLP technique can decrease the mean square error of the orthogonal frequency division multiplexing (OFDM) samples by around 5-50% and thereby greatly reduce the quantization noise at the transmitter. In the proof-of-concept experiment, the proposed scheme is demonstrated in a 25-km 10 Gbaud/λ four-level pulse amplitude modulation intensity modulation and direct detection system. In the 5G new radio environment, the experimental results proved the ability of the proposed digital MFH to support 27, 20, 16, and 13 100-MHz OFDM with 4, 16, 64, and 256 quadrature amplitude modulation based antenna-carrier containers at quantization bits per sample of 3, 4, 5, and 6. Compared with the conventional 2-D vector quantization, the error vector magnitude performance of the proposed scheme is significantly improved with the same number of quantization bits.

Herein, we propose and demonstrate that the light-induced optical polymeric waveguides can function as the fully online optical connectors with directional transmission characteristics. The light-induced optical waveguides, which can be used for the optical couplings between single-mode fibers, are fabricated by using a photopolymerizable resin system formed by a 405-nm laser. Subsequently, the transmission characteristics of the light-induced waveguides with different parameters are investigated, and the experimental results reveal that the (directional) transmission characteristics can be modified by controlling the structure of the light-induced waveguides by controlling the illumination time (single-side) or the ratio of the illumination intensity (dual-side). Additionally, the preliminary experimental results reveal that the light-induced optical waveguides can function as the optical connectors. The light-induced waveguide build-up process, which is simple and effective, can be applied to the fabrication of polymer-based optical waveguide modules and for optical interconnections. Simultaneously, this present technique could be a feasible method of incorporating devices such as filters, isolators, and polarizers into fibers, which can potentially contribute to further expansion of integrated optoelectronic system.

A photonic scheme to generate a 4-level frequency hopping (FH) microwave signal is proposed and experimentally demonstrated. The frequency of the generated signal can be fast and flexibly switched by shifting the combinations of two binary signals (i.e., 00, 01, 11, 10). Moreover, the carrier frequencies of the signal can be tuned in a large range. In the experiments, 2/4/6/12, 4/6/8/12, and 6/9/12/18 GHz FH signals are generated with the FH speed up to gigahertz.

A delay-laser-based reservoir computer (RC) usually has its processing speed limited by the transient response of laser dynamics. Here, we study a simple all-optical approach to enhancing the processing speed by introducing optical injection to the reservoir layer of conventional RC that consists of a semiconductor laser with a delay loop. Using optical injection, the laser’s transient response effectively accelerates due to the speeded carrier-photon resonance. In the chaotic time-series prediction task, the proposed RC achieves good performance in a flexible range of injection detuning frequency under sufficient injection rate. Using proper injection parameters, the prediction error is significantly reduced and stabilized when using high processing speed. For achieving a prediction error below 0.006, the optical injection enhances the processing speed by an order of magnitude of about 5 GSample/s. Moreover, the proposed RC extends the advantage to the handwritten digit recognition task by achieving better word error rate.

A photonic generation of microwave frequency shift keying signal (FSK) with large frequency tunability is proposed and experimentally demonstrated. A polarization modulator combined with a polarization maintaining fiber Bragg grating is used to transform a carrier-suppressed double sideband signal to a wavelength-shift-keying one, which is subsequently mixed with a tunable optical source to achieve frequency modulation. A proof-of-concept experiment is demonstrated to obtain an FSK signal at 9.5/12.5 GHz. The carrier frequency has been tuned from 7.2 to 14.8 GHz by adjusting the laser wavelength. Moreover, a radio over fiber transmission link is established to investigate the transmission performance of the generated FSK signal. The bit-error-rate curve of the received FSK signal at 9.5/12.5 GHz for a 5-km single mode fiber and 2-m wireless transmission is presented.

A method to generate a multicarrier phase-coded (MCPC) microwave signal is proposed and experimentally demonstrated. By optimizing the angle between the transverse-electric and transverse-magnetic modes in a phase modulator (PM), an MCPC microwave signal can be generated. Compared with the other reported schemes, the proposed one has an extremely simple structure, since only a PM is required. A proof-of-concept experiment is demonstrated to generate radio frequency signals with the carrier frequency of 5 and 10 GHz simultaneously and the coding rate of 1.25 Gb/s.

An adaptive image restoration algorithm based on 2-D bilateral filtering has been proposed to enhance the signal-to-noise ratio (SNR) of the intrusion location for phase-sensitive optical time domain reflectometry (Φ-OTDR) system. By converting the spatial and time information of the Φ-OTDR traces into 2-D image, the proposed 2-D bilateral filtering algorithm can smooth the noise and preserve the useful signal efficiently. To simplify the algorithm, a Lorentz spatial function is adopted to replace the original Gaussian function, which has higher practicability. Furthermore, an adaptive parameter setting method is developed according to the relation between the optimal gray level standard deviation and noise standard deviation, which is much faster and more robust for different types of signals. In the experiment, the SNR of location information has been improved over 14 dB without spatial resolution loss for a signal with original SNR of 6.43 dB in 27.6 km sensing fiber. The proposed method has the potential to precisely extract intrusion location from a harsh environment with strong background noise.

In this paper, we propose a novel tunable power splitter based on symmetric Mach-Zehnder (MZ) structure to achieve the polarization-insensitive and broadband performance. This good performance is realized by utilizing two 3 dB broadband directional couplers and square waveguides in a conventional symmetric MZ structure. Based on thermo-optic effect, the power splitting ratio of our power splitter for the TE and TM modes can be equally controlled in a wide operating bandwidth of 63 nm. Our results show a low polarization-dependent loss of 0.001-0.089 dB over a wide wavelength range of 1541-1604 nm.

In this paper, we numerically demonstrate that the concealment of time-delay signature (TDS) can be readily achieved via the combined mechanism of phase-conjugate feedback (PCF) and chaotic optical injection. To show the potential advantages of the proposed scheme, its counterpart, i.e., a slave semiconductor laser (SSL) subjected to chaotic optical injection from a master semiconductor laser (MSL) with conventional optical feedback (COF) is studied in parallel. In particular, we consider a fair situation where the MSL in both PCF and COF shows a comparable peak value in the autocorrelation function computed from the intensity time series. Our simulations uncover that combining the mechanism of PCF and chaotic optical injection is beneficial for TDS concealment in the SSL. To better understand this, the effects of some control parameters including injection and feedback are comparably studied. The results further prove that, as the injection or feedback parameters are varied, the proposed PCF-system always exhibits weaker autocorrelation around the feedback delay value when compared to the COF-system. In the meantime, the former system allows for larger bandwidth and, thus, paves way for important applications to secure communication and random-number generation.

Microwave frequency downconversion is optically implemented by using two cascaded polarization modulators (PolMs), characterized by full-frequency-range coverage and high conversion efficiency. In this proposed approach, the incident radio-frequency signal (RF) and the local oscillator signal (LO) are applied to the first PolM at the transmitter and the second one at the receiver, respectively. Effective optical carrier suppression can be achieved using the cascaded PolMs, whereas the optical sidebands induced by the RF and the LO signals remain unchanged. Since no additional optical filter is needed, the lower operation frequency limit in other approaches with an optical filter is eliminated, such that a full-frequency-range coverage is ensured in this approach. Meanwhile, the use of optical carrier suppression (OCS) enables high conversion efficiency for microwave downconversion. In the proof-of-concept experiments, the conversion efficiency is improved by over 20 dB within the frequency range from 2 to 15 GHz, as compared to those of cascaded modulators without OCS. Both the upper and the lower limits of such a frequency range can be greatly extended when test instruments with full frequency range are used.

We investigate the transmission of analog photonic signals based on coupled-mode theory and small-signal analysis and provide general expressions for signal evolution along standard single-mode-fiber links. Such model consists of a set of terms that correspond to polarization effects, chromatic dispersion (CD), and fiber nonlinearity. Based on the proposed complete model, we further investigate two typical cases, including the interaction between polarization effects and CD, as well as CD and Kerr effects. In addition, the limitations of the noise figure and spur-free dynamic range are investigated in dispersive nonlinear links.

An optical fiber temperature and torsion sensor has been proposed by employing the Lyot-Sagnac interferometer, which was composed by inserting two sections of high-birefringence (HiBi) fiber into the Sagnac loop. The two inserted sections of HiBi fiber have different functions; while one section acts as the temperature sensitive region, the other can be used as reference fiber. The temperature and twist sensor based on the proposed interferometer structure have been experimentally demonstrated. The experimental results show that the envelope of the output spectrum will shift with the temperature evolution. The temperature sensitivity is calculated to be −17.99 nm/°C, which is enlarged over 12 times compared to that of the single Sagnac interferometer. Additionally, the fringe visibility of the spectrum will change due to the fiber twist, and the test results reveal that the fringe visibility and twist angle perfectly conform to a Sine relationship over a 360° twist angle. Consequently, simultaneous torsion and temperature measurement could be realized by detecting the envelope shift and fringe visibility of the spectrum.

Phase-sensitive optical time domain reflectometry (Ф-OTDR) attracts much attention due to its capability of telling the type and position of an intrusion simultaneously. In recent decades, coherent Ф-OTDR has been demonstrated to realize long-distance detection. For coherent Ф-OTDR, there are three typical demodulation schemes in the reported studies. However, they still cannot realize real-time monitoring to satisfy practical demands. A simple and effective demodulation method based on self-mixing has been put forward to demodulate the beat signal in coherent Ф-OTDR. It not only saves a local electrical oscillator and frequency locked loop, but also demodulates the beat signal without residual frequency. Several vibrations with different frequency were separately applied at the same location of a 42.5 km fiber. The spatial resolution of 10 m and frequency response range from 8 Hz to 980 Hz have been achieved. The precise location with signal-to-noise ratio of 21.4 dB and broadband measurement demonstrate the self-mixing scheme can demodulate the coherent Ф-OTDR signal effectively.

A high-spectral-efficiency photonic frequency down-conversion approach for wavelength-division-multiplexing radio-over-fiber (WDM-ROF) uplinks is proposed and experimentally investigated. In the approach, an optical frequency comb serves as the carriers of multiple channels, and each comb line is modulated by the upstream radio-frequency (RF) signal via single-sideband modulation. At the central station, the beating between the sideband with upstream signal and its adjacent optical carrier leads to photonic frequency down-conversion without additional optical frequency shifts. Due to the band overlapping or the reduction of guard band between adjacent channels, a high spectral efficiency is achieved for WDM-ROF uplinks. A two-channel experimental uplink is established, where a 15-GHz RF signal carrying quadrature phase shift keying (QPSK) data is successfully down-converted to a 2-GHz intermediate frequency (IF) signal. For the 10-Mb/s QPSK data, the measured eye diagrams and the constellation diagrams clearly show the effectiveness of the frequency down-conversion and the influence of the transmission distance. In fact, the proposed approach is applied to the down-conversion at a high data rate up to several gigabits per second, such as a simulation demonstration at 2.5 Gb/s.

A tunable frequency-doubling optoelectronic oscillator (OEO) is proposed and experimentally demonstrated, of which the novelty lies in the conjunction of the double-sideband suppressed carrier (DSB-SC) modulation and the carrier recovery based on stimulated Brillouin scattering (SBS) effect. Frequency-doubled signals are generated via the DSB-SC modulation, which is realized by using a polarization modulator (PolM) in combination with an optical polarizer. Then, the gain provided by the SBS effect is used to recover the suppressed optical carrier, such that a fundamental-frequency oscillating required in the OEO loop is maintained. In the experiment, frequency-doubled microwave signals at 6.1 and 20 GHz are generated and analyzed. Meanwhile, the stability of the generated signals is also investigated.

A photonic approach to estimating microwave frequency with high-coding-efficiency digital outputs and large measurement range is proposed and experimentally demonstrated. In the proposed approach, an optical filter array that consists of N filters is designed, wherein N - 1 optical phase-shifted filters have an identical free spectral range (FSR) but a phase increment of π/(N - 1) in the transmission responses and one filter has a doubled FSR. The filters are then employed to process the single optical sideband generated by applying a microwave signal to a carrier-suppressed single-sideband (CS-SSB) modulation module, to perform the frequency-to-amplitude conversion and the analog-to-digital conversion simultaneously. After power detection and decision operation, an N-bit digital result in the form of binary code is obtained for microwave frequency measurement within the range of 2 × FSR. A proof-of-concept experiment is performed to verify the proposed approach. A 5-bit binary code with effective number of bits of four is generated to indicate the microwave frequency in the range from 10 to 40 GHz.