Showing papers on "Optical Carrier transmission rates published in 2021"

High-Accuracy Multiple Microwave Frequency Measurement With Two-Step Accuracy Improvement Based on Stimulated Brillouin Scattering and Frequency-to-Time Mapping

Abstract: A photonic-assisted multiple microwave frequency measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and a wide frequency measurement range is reported. A frequency sweeping signal is modulated on an optical carrier that is shifted by the Brillouin frequency shift as a frequency sweeping optical probe wave. The unknown microwave frequencies are modulated on the original optical carrier to pump a length of single-mode fiber. Thanks to the SBS effect, the Brillouin gain spectrum is detected by the frequency sweeping optical probe wave. After the optical signal from the probe branch is detected at a photodetector, the amplitude of the direct-current component will be much increased at the exact time when the SBS gain generated by the unknown signal overlaps with a specific optical wavelength of the frequency sweeping optical signal. Therefore, the unknown microwave frequencies are mapped to the time domain. More importantly, by introducing a two-step accuracy improvement, including the reference calibration and the curve smoothing, the measurement accuracy of the proposed approach is greatly improved compared with most of the available approaches. An experiment is performed. Microwave frequency measurement from 6 to 18 GHz is demonstrated with a measurement error of less than ±1 MHz.

Sensitivity-enhanced microwave-photonic optical fiber interferometry based on the Vernier effect.

Abstract: This paper proposes optical carrier microwave interferometry (OCMI)-based optical fiber interferometers for sensing applications with improved measurement sensitivity with the assistance of the Vernier effect. Fabry-Perot interferometers (FPIs) are employed in the proof of concept. A single-FPI-OCMI system is first demonstrated for measurements of variations of temperatures by tracking the spectral shift of the interferogram in microwave domain. By cascading two FPIs with slightly different optical lengths, the Vernier effect is generated in the magnitude spectrum of the system with a typical amplitude-modulated signal. By tracking the shift of the envelope signal, temperature measurements are experimentally demonstrated with greatly enhanced sensitivity. The amplification factor for the measurement sensitivity can be easily adjusted by varying the length ratio of the two cascaded FPIs. In addition to the experimental demonstration, a complete mathematical model of the FPI-OCMI system and the mechanism for the amplified sensitivity due to Vernier effect is presented. Numerical calculations are also performed to verify the analytical derivations.

Multiple radio frequency measurements with an improved frequency resolution based on stimulated Brillouin scattering with a reduced gain bandwidth.

Abstract: A photonic-assisted multiple radio frequency (RF) measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and high frequency resolution is reported. A two-tone signal is a single-sideband (SSB) modulated on an optical carrier via a dual-parallel Mach–Zehnder modulator to construct one SBS gain and two SBS losses for SBS gain bandwidth reduction. The unknown RF signal is also SSB modulated on a carrier that has been modulated by a sweep signal, thus the unknown RF signal is converted to a sweep optical signal along with the sweep optical carrier. The bandwidth-reduced SBS gain spectrum is detected by the sweep optical signals at different specific time, mapping the RF frequencies to the time domain. An experiment is performed. RF frequencies from 0.3 GHz to 7.6 GHz are simultaneously measured with a root mean square error of less than 1 MHz. In addition, the frequency resolution of the measurement can be much lower than 10 MHz, which is now the best result in the RF frequency measurement methods employing the SBS effect.

Ultra-Sensitive Microwave-Photonic Optical Fiber Interferometry Based on Phase-Shift Amplification

Abstract: This paper proposes phase-shift-amplified optical fiber interferometry based on microwave photonics (MWP) for sensing applications with substantially-improved sensitivity. The principal idea of the system combines a destructive interference-based phase-shift amplification technique with optical carrier-based microwave interferometry (OCMI). The phase sensitivity of the OCMI system is significantly improved due to the phase amplifier, and more importantly, can be adjusted by simply varying the amplitude ratio of the two beams used in the interferometer. The amplification of the phase sensitivity is numerically investigated and experimentally demonstrated using a Mach-Zehnder interferometer for temperature and strain measurements. The measurement results accurately match theoretical predictions. Moreover, we demonstrate that light-scattering dots in the optical fiber core, created by tightly-focused femtosecond laser pulses, can be used to precisely tune the amplitude ratio of the two-beam interferometer. We postulate that amplification of several orders of magnitude in phase sensitivity can be achieved in the OCMI system by employing micromachining methods.

High Rate CV-QKD Secured Mobile WDM Fronthaul for Dense 5G Radio Networks

Abstract: A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signal-to-noise ratio for this training signal Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping A low excess noise in the order of 01% to 05% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 132 km Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing

5G NR RoF System Based on a Monolithically Integrated Multi-Wavelength Transmitter

Abstract: We propose and demonstrate the use of a monolithically integrated multi-wavelength transmitter for multiband 5G new radio (NR) radio-over-fiber (RoF) systems, simultaneously operating in the standalone (SA) and non-standalone (NSA) modes The novel integrated photonic circuit, integrating eight tunable and directly modulated distributed feedback lasers, aims to reduce the transmitter complexity and footprint, enabling compact, high-performance and low-cost 5G solutions for frequencies up to 10 GHz We report the implementation of a 4G/5G shared optical mobile fronthaul using two 5G NR and a LTE-A signals, evaluated in two distinct scenarios, as a function of root mean square error vector magnitude (EVMRMS) and in accordance to the 3GPP Release 15 requirements In the first phase, three optical carriers in C-band are independently modulated with three mentioned RF signals, whereas subcarrier multiplexing (SCM) is applied to the second scenario for jointly modulating an optical carrier at 1554 nm Gbit/s throughput is demonstrated for validating the applicability of our monolithically integrated multi-wavelength transmitter either for enabling multiapplication and/or diverse RF standards, using a single wavelength or multiservice exploiting different wavelengths from an unique optical source

High Rate CV-QKD Secured Mobile WDM Fronthaul for Dense 5G Radio Networks

Abstract: A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links. Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization. Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signal-to-noise ratio for this training signal. Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping. A low excess noise in the order of 0.1% to 0.5% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 13.2 km. Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated. Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated. Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively. Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario. These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing.

A High Spectral Efficiency Radio Over Fiber Link Based on Coherent Detection and Digital Phase Noise Cancellation

Abstract: An approach to transmitting two independent microwave vector signals on a single optical carrier with one polarization state based on coherent detection and digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, two independent microwave vector signals are modulated on an optical carrier via a dual-drive Mach-Zehnder modulator (DD-MZM). The modulated optical signals are transmitted over a single-mode fiber (SMF) and sent to a coherent receiver. At the receiver, the optical signals are detected where a local oscillator (LO) optical wave generated by a second free-running laser source is also applied. To recover the two microwave vector signals, a novel digital signal processing (DSP) algorithm is developed and applied to eliminate the joint phase noise terms from the transmitter and the LO laser sources as well as the unstable offset frequency between the two laser sources. An experiment is performed. The transmission of two independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals at 4 GHz with a symbol rate of 1 GSymb/s over a 9-km SMF is demonstrated. The transmission performance in terms of error vector magnitudes (EVMs) and bit error rates (BERs) is also evaluated.

Microwave photonic notch filter with integrated phase-to-intensity modulation transformation and optical carrier suppression

Abstract: We demonstrate for the first time, to the best of our knowledge, an on-chip microwave photonic (MWP) notch filter with high stopband rejection and integrated optical carrier suppression in a phase modulator-based system. The notch filter was achieved through phase modulation to intensity modulation (PM-to-IM) transformation and dual-sideband-processing using a network of three ring resonators (RRs) in a low-loss silicon nitride (Si3N4) platform. We show simultaneous PM-to-IM conversion and optical carrier processing for enhancing the filter performance using a single RR. We achieve filtering with a high stopband rejection of >55dB, an optical carrier suppression up to 3 dB, a radio frequency link gain of 3 dB, a noise figure of 31 dB, and a spurious-free dynamic range of 100dB⋅Hz2/3. These experiments point to the importance of vectorial spectral shaping of an MWP spectrum for advanced functionalities.

Systems and methods for full duplex coherent optics

Abstract: A full duplex communication network includes an optical transmitter end having a first coherent optics transceiver, an optical receiver end having a second coherent optics transceiver, and an optical transport medium operably coupling the first coherent optics transceiver to the second coherent optics transceiver. The first coherent optics transceiver is configured to simultaneously transmit a downstream optical signal and receive an upstream optical signal. The second coherent optics transceiver is configured to simultaneously receive the downstream optical signal from the first coherent optics transceiver and transmit the upstream optical signal first coherent optics transceiver. At least one of the downstream optical signal and the upstream optical signal includes at least one coherent optical carrier and at least one non-coherent optical carrier.

Wide-range optical carrier recovery via broadened Brillouin filters.

Abstract: Stimulated Brillouin scattering has great potential for wide-wavelength-range optical carrier recovery, as it can act as a parametrically defined narrowband gain filter. However, due to the dispersion of the Brillouin frequency shift, prior demonstrations have been limited in wavelength range. Here, we demonstrate that frequency modulating the pump light for a gain filter based on stimulated Brillouin scattering enables optical carrier recovery for a broad range of input wavelengths. We demonstrate highly selective (<150M H z bandwidth) amplification for optical carriers over an 18 nm wide wavelength range in the optical communications C-band, an ∼6× improvement over using an unmodulated pump. Measurements of the noise properties of these spectrally broadened gain filters, in both amplitude and phase, indicate the noise performance and SNR are maintained over a wide wavelength range. Our technique provides a potential solution for highly selective, wavelength agnostic optical carrier recovery.

Highly Stable and Precise Demodulation of an FBG-Based Optical Current Sensor Using a Dual-Loop Optoelectronic Oscillator

Abstract: Electrical current monitoring plays an important role in power transmission system, electric instruments, etc. The stability of the monitoring system is highly demanded. In this paper, a new interrogation scheme for a fiber Bragg grating (FBG) current sensor based on a dual-loop optoelectronic oscillator (OEO) with high stability, high precision and simple structure is proposed and experimentally demonstrated. The wavelength shift of the FBG, which is bonded on a magnetostrictive alloy-strip, is converted into the frequency shift of the microwave signal through the OEO system utilizing the wavelength to frequency mapping mechanism. Different from previous single-loop OEO schemes, a length of ∼1 km single mode fiber is used to form the second loop in the OEO-cavity, which can enhance the mode-selection ability and reduce the total gain requirement of the system. In addition, a fiber-ring-laser (FRL) cavity is adopted by integrating the sensing FBG-head as the wavelength-selective component to improve the quality of the optical carrier signal. The measured side-mode suppression ratio (SMSR) is up to 62.59 dB and the free spectral range (FSR) is five times larger than the single-loop structure, resulting in highly-enhanced stability and so the precision. Most importantly, the frequency fluctuation is as low as 0.277 ppm, which is the minimum to the best of our knowledge. Compensating methods for the influence of the temperature and the hysteresis are also discussed. The proposed scheme provides a feasible solution to promoting the development of OEO-based interrogation technology and its commercial applications.

Extension of Transmitter Bandwidth Using Optical Time-Interleaving Modulator and Digital Spectral Weaver

Abstract: We demonstrate a technology to extend the bandwidth of optical transmitters based on optical time interleaving. An optical time-interleaving in-phase-and-quadrature (IQ) modulator (TI-IQM), which consists of a 1-to-2 optical selector followed by two IQMs, generates optical signals with a bandwidth of each side of the optical carrier that is up to twice that of the electronic sub-signals sent to the IQMs. The sub-signals are generated by a digital spectral weaver followed by digital-to-analog converters and tailored so that the targeted extended-bandwidth signal is obtained as the final optical output from the TI-IQM. We verified the concept in a transmission experiment with 150-GBaud 4, 8, and 16-level quadrature amplitude modulation. We successfully generated optical signals with a bandwidth of each side of optical carrier of around 76 GHz, which is almost twice that of the electronic sub-signals.

Photonic Generation of Phase-Coded Microwave Signals Based on Fourier Domain Mode Locking

Abstract: We report a novel photonic scheme to generate binary phase-coded microwave signals by using two cascaded phase modulators (PMs) based on a Fourier domain mode-locked (FDML) optoelectronic oscillator (OEO). The first PM is driven by a series of electrical coding signals to modulate the phase of the optical carrier. The second PM is a construction of the FDML OEO, which realizes phase-modulation to intensity-modulation conversion together with a phase-shifted fiber Bragg grating. Phase-coded microwave signals can be generated when the period of the electrical coding signal matches with the round-trip time of the OEO. A $\boldsymbol {\pi }$ phase shift of the phase-coded microwave signals can be achieved by properly adjusting the level of the electrical coding signal. The key point of our work is that phase-coded microwave signals can be generated directly from the FDML OEO cavity. Besides, the proposed system has great reconfigurability in terms of center frequency and bit rate. Our scheme is theoretically analyzed and experimentally verified. Phase-coded microwave signals with a bit rate of 420 Mb/s and center frequency of 9.3 GHz, as well as with a bit rate of 2 Gb/s and center frequency of 12.7 GHz are successfully generated in the experiment.

Multiple radio frequency measurement with an improved frequency resolution based on stimulated Brillouin scattering with a reduced gain bandwidth

Abstract: A photonic-assisted multiple radio frequency (RF) measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and high-frequency resolution is reported. A two-tone signal is single-sideband (SSB) modulated on an optical carrier via a dual-parallel Mach-Zehnder modulator to construct one SBS gain and two SBS losses for SBS gain bandwidth reduction. The unknown RF signal is also SSB modulated on a carrier that has been modulated by a sweep signal, thus the unknown RF signal is converted to a sweep optical signal along with the sweep optical carrier. The bandwidth-reduced SBS gain spectrum is detected by the sweep optical signals at different specific time, mapping the RF frequencies to the time domain. An experiment is performed. RF frequencies from 0.3 to 7.6 GHz are simultaneously measured with a root mean square error of less than 1 MHz. In addition, the frequency resolution of the measurement can be much lower than 10 MHz, which is now the best result in the RF frequency measurement methods employing the SBS effect.

Pilot Tone Power Limits of Brillouin Amplified Carrier Recovery for Optical Communications

Abstract: The benefit of Brillouin amplification for optical carrier recovery from pilot tones is evaluated in application to coherent signal detection without a conventional local oscillator (LO) laser. The focus being on the narrow gain bandwidth suppressing broadband spectral noise power relative to the pilot tone. Calculations indicate its use at the receiver with realistic 30 dB gain and 30 MHz gain bandwidth permit lowering the minimum pilot tone to signal power ratio (PSR) for low distortion signal demodulation by up to a24 dB in the case of a 10 GHz wide signal channel, and even larger for broader channels. The ultimate limit being its ratio to the narrowness of the Brillouin gain bandwidth. Low noise Brillouin gain is also accounted for from characterization by a coherent receiver and digital signal processing approach for an optical fiber used as the gain medium in experiments. Its use in optical carrier recovery from a 3 channel WDM 48 Gb/s 64-QAM signal with polarization multiplexed pilot tones demonstrates improvement consistent with predictions in reducing the impact of pilot tone noise to near that for a conventional LO. The estimated low PSR limit for a bit error rate below the hard decision FEC limit was extrapolated as a−38 dB. This rose to a−30 dB with inclusion of 80 km link transmission due to the restricted signal launch power for avoiding nonlinear distortion. The insight highlights the wide-ranging capabilities for enhancing performance in advanced coherent communications.

A Radio over Fiber System Compatible with 3G/4G/5G for Full Spectrum Access and Handover with Multi-Scenarios

Abstract: A Radio over Fiber system based on optical frequency multiplication and multiplexing compatible with 3G/4G/5G systems for full spectrum access and handover with multiple scenarios is proposed and analyzed theoretically as well as simulated numerically. By combining a dual-drive Mach-Zehnder Modulator in Push-Pull modulation-mode with optical frequency multiplication and multiplexing technology, the simultaneous transmission of multiple radio frequency signals in optical carrier is realized. It can be also switchable for full spectrum access of different scenarios and user terminals with Multi-Input Multi-Output wireless capability, based on frequency diversity technology. The BER and eye diagram for the transmission performances have been presented by the simulation experiment. Meanwhile, the feasibility of the scheme has been demonstrated by lots of numerical simulations and accurate theoretical analyses. The method could meet the requirements for communication capacity and transmission rate in both continuous-wide-area coverage and hot-spot high-capacity transmission of 5G system, and for full spectrum access and handover.

Broadband Optoelectronic Frequency Response Measurement Utilizing Frequency Conversion

Abstract: A broadband optoelectronic (O/E) frequency response measurement method utilizing photonics-based frequency conversion is proposed and experimentally demonstrated. It is characterized by a sub-kilohertz frequency resolution and a doubled measurement bandwidth compared with the RF frequency sweeping range and the working bandwidth. A carrier-frequency-shifted optical double-sideband (ODSB) signal is produced by employing a dual-drive Mach-Zehnder modulator (DD-MZM) and stimulated Brillouin scattering (SBS). Then, a photodetector (PD) under test receives and converts the optical signal into a photocurrent. By detecting the frequency up- and down-conversion components generated by the two first-order sidebands and the optical carrier, the O/E frequency responses in the low- and high-frequency regions are achieved. After stitching the two measured responses together, an O/E frequency response with a frequency range that is twice the bandwidth of the input microwave signal is obtained. In an experiment, the O/E frequency response of a commercial high-speed PD is precisely characterized with a frequency resolution up to 5.55 MHz. A frequency bandwidth of 66.8 GHz (0.1–66.9 GHz) is achieved by using a 25-GHz DD-MZM. The measured O/E frequency response is coincident with that measured by a commercial instrument.

A Linearized Analog Microwave Photonic Link With an Eliminated Even-Order Distortions

Abstract: An improved linearized analog microwave photonic link (AMPL) with significant multioctave bandwidth performance is experimentally presented. The proposed AMPL configuration is based on a double dual-parallel Mach–Zehnder modulator and a differential balanced photodetector (BPD). Explicitly, a gallium arsenide (GaAs)-based modulators are used as opposed to the commonly known lithium niobate (LiNbO $_{3}$ ) modulators, due to its robustness in the harsh environment. The system configuration is designed to process a carrier suppressed double-sideband signal through the link, and then at the receiver, a carrier suppressed double-sideband signal is combined with an unmodulated optical carrier, which is transmitted through a polarization maintained (PM) optical fiber. In our experiment, only PM-based optical components are used for better system stability. The developed theoretical model of the proposed system illustrates the elimination of even-order distortions and a high suppression to the third-order intermodulation distortions at the BPD. Consequently, the fundamental signal to interference ratio of 60 dB was experimentally achieved. Furthermore, experimental results, simultaneously, demonstrate a significant increase of second-order spurious-free dynamic range and third-order spurious-free dynamic range by 19.5 and 3.1 dB, respectively, compared to the previously reported AMPL performances based on polarization multiplexing dual-parallel Mach–Zehnder modulator. To the best of our knowledge, this is the highest dynamic range AMPL system performance deploying GaAs electro-optic modulator which has most significant capabilities in managing RF signals and exhibits excessive performance in harsh operating environment in terms of thermal stability, power-handling, radiation resistance and longevity for aerospace, defense, and satellite-to-ground downlink communication system applications.

Michelson interferometer based phase demodulation for stable time transfer over 1556 km fiber links.

Abstract: Time transfer based on phase modulation schemes has attracted extensive attention in recent years. We propose and experimentally demonstrate an adjustable and stable Michelson interferometer (MI) with a DC phase tracking algorithm for two-way time transfer. Time signal with one pulse per second (1 PPS) is loaded on an optical carrier modulated in phase and demodulated by a Michelson interferometer. The whole compact and cost-effective demodulator is symmetrical with a single coupler to split and recombine optical waves, flexible with one photodetector and a bias tee to separate the DC signal and recovery pulses and stable with a phase modulator to compensate for the drift-phase noise. We show the implementation of modulation and demodulation of the time signal and obtain the stability of 2.31 × 10−11 at 1000 s averaging time. We then demonstrate two-way time transfer over 1556 km lab fibers. The experimental result shows time interval stability of 1 PPS with 5.62 × 10−11 at 1000 s averaging time. It has the potential to transfer time signals in long-distance fiber optic links.

Photonic Generation of Multiple Shapes and Sextupled Microwave Signal Based on Polarization Modulator

Abstract: In this article, a photonic technique is proposed for generating the microwave signal of multiple shapes. Furthermore, this is modified to give a microwave signal with frequency multiplying capability, which does not require an optical filter. The proposed methodology is relied on the polarization modulator (PM), the Mach-Zehnder modulator (MZM), and the variable optical delay line (VODL), where the transmission point of PM has been selected by static phase of polarizer controller and MZM by the dc bias voltage. An RF signal of 6-GHz frequency is applied at PM to modulate the optical carrier signal. Frequency-dependent VODL has been used to provide dynamic phase shifts in the harmonics of the modulated signal. Firstly, 12-GHz full-wave rectified (FWR) and 6-GHz half-wave rectified (HWR) sinusoidal signals have been generated using PM and VODL. For the generation of FWR and HWR, respective phase shifts of $- \pi /2$ and $\pi $ have been introduced by VODL. Then, a sextupled microwave signal of 36-GHz frequency has been generated which is further processed for the generation of triangular-shaped HWR of 6-GHz frequency. This has been achieved by modulating one of the split powers of PM with the help of an MZM. The generation of such multishape rectified waveforms has not been reported before. Also, the frequency sextupling capability of the proposed technique defines the multifunctionality of the system. Theoretical analysis of the considered approach has been given which is supported by simulated results and validated by the experimental results.

All-Optical Double Spectral-Efficient RoF Link With Compensation of Dispersion-Induced Power Fading

Abstract: An all-optical radio-over-fiber (RoF) link with double spectral-efficient transmission and compensation of chromatic dispersion-induced power fading is proposed and experimentally demonstrated. At the central office, a commercial dual-polarization quadrature phase-shift keying modulator is utilized to produce a polarization-multiplexed signal composed of two modulated microwave vector signals and an unmodulated optical carrier. At the remote node, by adjusting the polarization controller to introduce a proper phase shift to the unmodulated optical carrier, the two vector signals can be demodulated respectively and dispersion-induced power fading can be compensated simultaneously. The link performance is evaluated by error vector magnitude and bit error rate.

Sensitivity Enhancement for Fiber Bragg Grating Strain Sensing Based on Optoelectronic Oscillator With Vernier Effect

Abstract: Based on a dual-loop optoelectronic oscillator (OEO) with Vernier effect, a scheme of fiber Bragg grating (FBG) interrogation system with an improved scale factor has been proposed and experimentally demonstrated. Functioning as the optical carrier of the OEO, the reflection signal of two cascaded FBGs is divided into two optical beams by using a wavelength division multiplexer (WDM). The two optical beams at different wavelengths travel along single mode fibers with different lengths. After combined together by another WDM, the two optical beams go through a section of dispersion compensation fiber (DCF). The oscillating frequency shift of the OEO is determined by the overall time delay, which is affected by the wavelength change of the sensing FBG. Thus, the wavelength change of the sensing FBG can be converted into the oscillating frequency shift of the OEO. Furthermore, due to the length difference between the two optical beams, an obvious Vernier effect has been generated in the frequency response of the OEO. By detecting the frequency shift of the envelope peak of the frequency response curve, the sensitivity of the sensing interrogation can be enhanced greatly. A proof-of-concept OEO-based FBG sensor for axial strain sensing experiment is performed. The experimental results show that the sensitivity is about 0.31 KHz/μϵ for a single-loop OEO. By employing Vernier effect, the sensitivity can be improved to -11 KHz/μϵ, which is 35 times higher than that of the single-loop OEO.

Stable Radio Frequency Transmission of Single Optical Source Over Fiber Based on Passive Phase Compensation

Abstract: 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.

Bandwidth superposition of linearly chirped microwave waveforms based on a Fourier domain mode-locked optoelectronic oscillator

Abstract: Optoelectronic oscillators (OEOs) are promising for radar, communication and electronic countermeasure systems. Among them, frequency-scanning OEOs with wide instantaneous bandwidth are needed for many advanced applications. In this work, we demonstrate a novel system to generate bandwidth-doubled linearly chirped microwave waveforms (LCMWs) based on bandwidth superposition using a Fourier domain mode-locked OEO (FDML OEO). In the proposed system, bandwidth-doubling is achieved by re-modulating the generated LCMW of the FDML OEO onto a frequency-scanning optical carrier signal with the help of an external Mach-Zehnder modulator. LCMWs with wide frequency scanning instantaneous bandwidth of 10 GHz are experimentally obtained. Meanwhile, these LCMWs are tunable in an ultra-wide frequency range from 1 to 39 GHz. Moreover, they are with high frequency sweep linearity of 0.5%. Our work presents a simple method to generate tunable wide-band LCMWs for potential microwave sources.

SOP Change Robust Optical Modulation Based on Dual Polarization Modulation for Multi-Dimensional Optical Transmission

Abstract: In optical transmission technique using optical polarization, the change of state of polarization (SOP) and the rotation of SOP (RSOP) during optical transmission has a significant impact on the transmission performance. We propose polarized intensity rotational frequency shift keying (PIR-FSK) as a novel modulation technique in change of SOP and RSOP-tolerant optical transmissions. The proposed PIR-FSK signal does not affect the entire intensity of the optical carrier by modulating the sinusoidal signals on each X and Y-polarized optical carrier. Therefore, the proposed PIR-FSK modulation and optical carrier intensity modulation can operate at the same time. Moreover, since the proposed technique does not modulate the signal using the SOP unlike the PolSK, PIR-FSK is not affected by SOP changes that occur during transmission, and the signal does not be degraded even with RSOP. We demonstrated that the signals modulated using the proposed PIR-FSK modulation have higher signal capacity and efficiency compared to the signal modulated using PolSK modulation.

Ranging system based on optical carrier-based microwave interferometry.

Abstract: To compensate for the refractive index errors in optical carrier-based microwave interferometry (OCMI), a ranging system is designed to measure the single-arm optical path of OCMI. A high-speed photodetector and a downconversion method are used to acquire the microwave envelope of the interference signal. A Hilbert transformation is used to realize phase detection. Simulation shows the linear relationship between the phase and optical length in a period. Adjusting the microwave frequency can resolve the phase ambiguity. The experimental results show that when the maximum microwave modulation frequency is set to 1.5 GHz, the standard deviation of the measured data can be limited to the level of 10−5.