Chromatic Dispersion Induced Power Fading Research Articles

Photonic-assisted multi-format dual-band microwave signal generator without background noise.

We report a photonic approach to generate background-free multi-format dual-band microwave signals based on a single modulator, which is suitable for high-precision and fast detection of radars in complex electromagnetic environments. By applying different radio-frequency signals and electrical coding signals to the polarization-division multiplexing Mach-Zehnder modulator (PDM-MZM), the generation of dual-band dual-chirp signals or dual-band phase-coded pulse signals centered at 10 and 15.5 GHz is experimentally demonstrated. Furthermore, by choosing an appropriate fiber length, we verified that the generated dual-band dual-chirp signals are not affected by chromatic-dispersion induced-power fading (CDIP); meanwhile, by autocorrelation calculations, we got high pulse compression ratios (PCRs) of 13 of the generated dual-band phase-encoded signals, showing that the generated phase-encoded signals can be emitted directly without extra pulse truncation operation. The proposed system features a compact structure, reconfigurability and polarization independence, which is promising for multi-functional dual-band radar systems.

Optical Field Recovery in Jones Space

Optical full-field recovery allows for fiber impairments compensation such as chromatic dispersion and polarization mode dispersion (PMD) in the digital signal processing. For cost-sensitive short-reach optical networks, some advanced single-polarization (SP) optical field recovery schemes are recently proposed to avoid chromatic dispersion-induced power fading effect and improve the spectral efficiency for larger potential capacity. Polarization division multiplexing (PDM) can further double both the spectral efficiency and the system capacity of these SP carrier-assisted direct detection (DD) schemes. However, the so-called polarization fading phenomenon induced by random polarization rotation is a fundamental obstacle that prevents SP carrier-assisted DD systems from polarization diversity. In this paper, we propose a receiver of Jones-space field recovery (JSFR) to realize polarization diversity with SP carrier-assisted DD schemes. Different receiver structures and simplified recovery procedures for JSFR are explored theoretically. The proposed JSFR pushes SP DD schemes towards PDM without an extra optical signal-to-noise ratio (OSNR) penalty. In addition, the JSFR shows good tolerance to PMD since the optical field recovery is conducted before polarization recovery. In the concept-of-proof experiment, we demonstrate 448-Gb/s reception over 80-km single-mode fiber using the proposed JSFR based on 2 × 2 couplers. Furthermore, we qualitatively compare the optical field recovery in Jones space and Stokes space in terms of the modulation dimension and hardware complexity.

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

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.

Reconfigurable Photonic generation and transmission of multi-format radar signals

In this paper, photonic generation and transmission technique for multi-format microwave waveform is proposed. In the center office, a broadband optical source (BOS) is utilized as optical carrier. And the main component is a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM) followed by a polarization division multiplexed emulator (PDME). The DPol-DDMZM consists of two sub-DDMZMs to generate two orthogonally polarized optical signals. The system we proposed is conveniently reconfigured to generate different waveforms. By applying phase modulation (PM) to the orthogonal polarization states, a polyphase-coded microwave waveform with a tunable center frequency multiplication factor can be generated. By tuning the differential group delay (DGD) of the two polarizations by the PDME, the multiplication factor can be easily adjusted. In addition, if the carrier is suppressed at the upper and lower DDMZM, broadband dual-chirp microwave signal can be generated, transmitted over fiber and detected at a base station. The chromatic dispersion induced power fading is eliminated. The approach is investigated by simulations. Polyphase-coded signal with a repetition rate of 4 Gbit/s is demonstrated. And dual-chirp signal with a bandwidth of 8 GHz is carried out. Besides, the practical feasibility of the system is further studied by analyzing the power of the BOS, the relative time delay of PDME and the photonic integrated circuit (PIC) replica of the generator.

Photonic generation of quadruple bandwidth dual-band dual-chirp microwave waveforms with immunity to power fading.

A photonic method to generate and transmit quadruple bandwidth dual-band dual-chirp microwave waveforms with immunity to fiber chromatic dispersion induced power fading is proposed and experimentally demonstrated, which is suitable for Doppler blind-speed elimination, small target detection, and multiband detection in multiband radar systems. A dual-polarization dual-parallel Mach-Zehnder modulator is utilized to realize carrier-suppressed harmonic single-sideband modulation of a radio frequency carrier and carrier-suppressed DSB modulation of a baseband single-chirped waveform at two orthogonal polarization states. After photoelectronic conversion, dual-band bandwidth-quadrupling dual-chirp waveforms are generated. Moreover, different from traditional DSB-based dual-chirp signal generation, the generated dual-chirp microwave waveforms can be transmitted over fiber without power fading, which is significant in dual-band radars for one to multiple base station transmissions.

Incoherent Laser Heterodyned Long-Reach 60-GHz MMWoF Link With Volterra Filtered 16-QAM OFDM Beyond 13 Gbps

By remotely heterodyning two independent laser carriers, the long-reach 60-GHz millimeter-wave-over-fiber (MMWoF) link is demonstrated for the Volterra series filtered quadrature amplitude modulation orthogonal frequency division multiplexing (QAM-OFDM) transmission with nonlinear noise suppression, which enables 13-Gbps data delivery through 50-km single-mode fiber (SMF) and 3-m free-space links. A wavelength tunable colorless laser diode transmits the Volterra filter equalized QAM-OFDM data to remotely couple with a localized single-mode laser carrier at the optical receiving end of the MMWoF system. Such an incoherently coupled dual-mode carrier facilitates the optical single-carrier modulation to suppress chromatic dispersion induced power fading effect of the SMF transmitted QAM-OFDM data. The 2nd+3rd-order nonlinear noise induced by direct modulation, heterodyne conversion, and phase fluctuation of the incoherently coupled dual-mode carrier is corrected with the Volterra filter equalization to upgrade the decoded signal-to-noise ratio (SNR) by >2 dB. After remotely heterodyning the downstream and the localized carriers with mutual incoherence in between, the 16-QAM OFDM transmission at a data rate up to 13.2 Gbps is successfully delivered over 3-m wireless link, which reveals the FEC certificated error vector magnitude of 14.1%, SNR of 17 dB, and bit error rate of 1.7 × 10−3.

Experimental Demonstration of Complex-Valued DSB Signal Field Recovery via Direct Detection

The recent decade has witnessed the evolution and enormous demand of the high-capacity data center interconnect (DCI), in such application scenarios spectral efficiency, optical field recovery and cost-effectiveness are highly desirable. Compared to coherent detection, direct detection does not require local oscillators, resulting in a simpler transceiver structure and thus a lower-cost solution for DCIs. To overcome chromatic dispersion induced power fading, field recovery enabled by direct detection has drawn extensive research interests. To date, various proposed direct detection schemes concentrate mainly on single sideband (SSB) modulation. Compared to double sideband (DSB) modulation, however, one sideband of SSB is unfilled and hence SSB poses higher requirement on the receiver bandwidth. Besides, the complexity and cost of implementing precisely aligned optical filtering poses burden for adopting SSB. Accordingly, we recently proposed a novel direct detection scheme called carrier assisted differential detection (CADD), which can realize the field recovery of complex-valued DSB signals with the aid of an optical carrier. In this letter, we carry out the first-time experimental demonstration of the CADD receiver. 54-Gb/s OFDM signals are transmitted over 160-km standard single-mode fiber with digital chromatic dispersion compensation at the receiver, indicating the ability to reconstruct optical field of DSB signals. For signal-signal beat interference (SSBI) which extensively exists in direct detection, experimental results show that merely two iterations of cancellation are sufficient to mitigate SSBI. More importantly, compared to various SSB based receiver schemes, the requirement of receiver bandwidth for DSB based CADD scheme is relaxed by 41%.

Dual-chirp microwave waveform transmitter with elimination of power fading for one-to-multibase station fiber transmission

We present a photonic approach to generate and transmit a dual-chirp microwave waveform with antidispersion performance. Traditionally, the microwave signal generated based on double-sideband (DSB) modulation suffers from power fading significantly. We propose a DSB-based dual-chirp microwave waveform transmitter that can eliminate the chromatic dispersion-induced power fading (CDIP) over fiber transmission. The CDIP elimination, rather than compensation, ensures that the working bandwidth of the dual-chirp waveform is not limited by the periodical power fading. The proposed signal modulation scheme makes the signal transmitter free from the direct current bias drifting of the modulator. Moreover, thanks to the phase modulation, the generated waveform is background-free. The proposed dual-chirp waveform transmitter features a compact structure, polarization independence, and CDIP elimination, which has great potential in radars for one-to-multibase station fiber transmission.

An analog photonic down-conversion link with simultaneous IMD3 distortion suppression and dispersion-induced power fading compensation

A novel analog photonic down-conversion link based on a polarization modulator and a phase modulator with simultaneous linear optimization and chromatic dispersion-induced power fading compensation is proposed and experimentally demonstrated. By introducing an appropriate phase shift to the optical sidebands, chromatic dispersion-induced power fading is compensated, and third-order intermodulation distortion terms are eliminated in the same time. The scheme exhibits wide operating frequency range due to its no use of filters and frequency-dependent electrical or optical devices. The scheme is robust, as the operation of the polarization modulator and the phase modulator are independent of signal amplitude and bias voltage. Experimental results show that, for a 25-km transmission link, an improvement of more than 15.5 dB in spurious-free dynamic range is achieved and the dispersion-induced power fading is compensated at the same time. In addition, benefiting from the power compensation and significant suppression of IMD3, a 16QAM vector signal is demonstrated to have a good demodulation performance.

Photonic Microwave Up-Conversion Link With Compensation of Chromatic Dispersion-Induced Power Fading

An effective scheme of frequency doubling up-conversion is proposed and demonstrated, which achieves the generation of high-frequency microwave signal and the compensation of chromatic dispersion-induced power fading (CDIPF). The system structure is based on a cascading of a Sagnac loop and a Mach–Zehnder modulator (MZM), where a phase modulator is used in the Sagnac loop. In the loop, only the clockwise propagating light wave is modulated by a small local oscillator signal, leaving the counter-clockwise propagating light wave unmodulated because of the velocity mismatch. The output signal is divided into two parts, one traveling into an MZM and the other entering an optical phase shifter. The intermediate frequency signal is supplied to the MZM, which is biased at its minimum point and then the carrier-suppressed double sideband is achieved. With the adjustment of the optical phase shift, the CDIPF can be compensated at any frequency. In the simulation, by comparing the frequency responses of the proposed link with and without dispersion compensation, we successfully demonstrate the performance of power fading compensation for 60- and 80-km link. Consequently, the spurious-free dynamic range is effectively improved by 13.54 dB at 22.6 GHz for 60-km link.

Effects of frequency chirping and finite extinction ratio of optical modulators in microwave photonic IFM receivers

Frequency-to-power mapping approach based on chromatic dispersion is frequently used in microwave photonic (MWP) instantaneous frequency measurement (IFM) receivers. In this technique, carrier frequency of an unknown microwave signal is estimated according to a specific relationship between the unknown microwave frequency and the ratio of two optical or microwave power functions which is known as amplitude comparison function (ACF). The ACF can be constructed using chromatic dispersion-induced power fading functions of intensity- or phase-modulated optical signals transmitting through dispersive mediums. Practical non-ideal intensity modulators have finite extinction ratio and suffer from frequency chirping. Despite previously published numerous works, the contribution of these parameter in MWP IFMs have not been already studied. In this paper, effects of chirp parameter and finite extinction ratio of intensity modulators on the performance of chromatic dispersion-based MWP IFM receivers are theoretically investigated. It is shown that in general the ACFs of these MWP IFM receivers depend on the chirp parameter of their intensity modulators which is a function of unknown amplitude of the microwave signal whose frequency is intended to be measured and varies with time. This problem cannot be resolved by calibrations and degrades the measurement accuracy. Besides, it is shown that ACFs are different for different finite extinction ratios which degrades the measurement accuracy. Finally, we propose using Mach–Zehnder interferometer (MZI)- and Sagnac interferometer (SI)-based intensity modulators with zero chirp in these MWF IFMs. Analytical results are verified by computer simulations using OptiSystem software.

Decision-Feedback Frequency-Domain Volterra Nonlinear Equalizer for IM/DD OFDM Long-Reach PON

A low-complexity third-order decision-feedback frequency-domain Volterra nonlinear equalizer (DF-FD-VNLE) with superior nonlinearity-compensation performance is proposed and experimentally demonstrated for OFDM long-reach PONs. High optical launch power up to 18 dBm is implemented to mitigate the chromatic dispersion induced power fading and increase the power budget. By reconstructing and subtracting the nonlinear noise in frequency domain with the knowledge of the nonlinear channel, the proposed DF-FD-VNLE outperforms the conventional time-domain VNLE (TD-VNLE) and feed-forward FD-VNLE (FF-FD-VNLE), resulting in better received signal-to-noise ratio (SNR) performance. The nonlinearity-compensation performance of the DF-FD-VNLE can be further improved with the usage of a FF-FD-VNLE or more than one iteration. Complexity and experimental analyses show that similar complexity and higher SNR can be achieved by using the one-iteration DF-FD-VNLE with FD linear equalization (FD-LE), compared with that of the FF-FD-VNLE. Compared with conventional TD-VNLE, the required number of real-valued multiplication (RNRM) of the one-iteration DF-FD-VNLE with FF-FD-VNLE (FD-LE) is reduced by a factor of as much as 82.19% (89.61%) at a memory length of 14 and a truncation factor of 3. Based on the one-iteration DF-FD-VNLE with FF-FD-VNLE, around 53.79 Gb/s single wavelength OFDM IM-DD transmission over 60.8-km SSMF is successfully demonstrated at a BER of 3.8 × 10−3 and a received optical power (ROP) of −2 dBm, achieving 15% capacity improvement compared to the conventional TD-VNLE.

Quasi-Color-Free LD-Based Long-Reach 28-GHz MMWoF With 512-QAM OFDM

By using a 512-quadrature amplitude modulating-orthogonal frequency division multiplexing (512-QAM OFDM) data stream with universal filtered multicarrier (UFMC) process to directly encode a quasi-color-free laser diode (QCFLD) with dual-mode carrier, a long-reach 28-GHz millimeter-wave over fiber (MMWoF) link over 50-km single-mode fiber (SMF) is demonstrated for future fiber network with 5G wireless link. At the fiber-wired optical transmission stage, the dual-mode QCFLD can support raw data rates up to 54, 42, and 24 Gbit/s after 0, 25, and 50-km SMF transmissions. The data-rate degradation results from chromatic dispersion induced power fading effect. The 28-GHz MMW carrier optically heterodyned at remote node with a carrier-to-noise ratio of 53.5 dB is generated after 25-km SMF propagation, which achieves 6-m free-space transmission at 16 Gbit/s. Lengthening the SMF to 50 km still allows the MMWoF for wireless transmission at 16-Gbit/s over 5 m and 14-Gbit/s over 10 m. To favor the 5G wireless access with high data capacity, the UFMC processed QAM-OFDM was further adopted for noise suppression via sidelobe filtering operation. By lengthening the cyclic prefix and the filter window for the OFDM, the tradeoff between data quality and net-data-rate ratio without and with UFMC process is discussed. With UFMC, the MMWoF transmission capacity can deliver 3-GHz wide 32-QAM UFMC processed OFDM data at 15 Gbit/s over 50 km in SMF and 10 m in free space. Even within a limited subcarrier bandwidth as narrow as 140 MHz for practical 5G users, the 512-QAM UFMC data can be allocated to provide a raw data rate of 1.26 Gbit/s.

Bidirectional 50 Gb/s/λ WDM-PON based on optical intensity modulation and direct detection

We experimentally demonstrate an optical intensity modulation transmitter with a half-cycle 32 QAM Nyquist subcarrier modulation and direct detection receiver-based channel-reuse wavelength-division-multiplexing passive optical network. Chromatic dispersion-induced power fading in the direct detection system is avoided with fiber Bragg grating filter-based vestigial-sideband filtering. The inter-symbol interference is mitigated with a digital signal processing-based overlap frequency-domain equalizer and iterative distortion-cancellation technique. A frequency division multiplexing-based wavelength management method is employed for the tunable laser used in a colorless optical network unit to achieve a bidirectional 50 Gb/s/λ transmission over a 40 km-long standard single-mode-fiber on a 100 GHz WDM grid. The transmission performance is also measured with different central wavelength shifts between upstream and downstream in the channel-reuse system.

Efficient Photonic Microwave Mixer With Compensation of the Chromatic Dispersion-Induced Power Fading

The conversion gain of a photonic microwave mixer is often limited by the large carrier of the modulated optical signal, and may be further deteriorated by the chromatic dispersion-induced power fading after transmission over fiber. To solve this problem, an efficient photonic microwave mixer based on a dual-electrode Mach–Zehnder modulator is proposed in this paper. The carrier of the modulated optical signal is suppressed by bidirectional use of the modulator in a Sagnac loop, and a 21.9-dB improvement of the conversion gain is achieved in the experiment. In addition, the frequency response of the mixer after transmission over fiber can be tuned by simply adjusting the direct current bias of the modulator. This feature is applied to compensate the dispersion-induced power fading of the mixing product. In the proof of concept experiment, a vector signal centered at 2.4 GHz is up-converted to 16 GHz and transmitted over 25-km single mode fiber. After power compensation, the constellation diagram, error vector magnitude and receiver sensitivity are significantly improved, and are almost as good as that without fiber transmission.

IMDD-based bidirectional 20 Gb/s/λ WDM-PON with Nyquist 4 PAM employing Rayleigh backscattering noise detection-based self wavelength management

We experimentally demonstrate an optical intensity modulation transmitter with a Nyquist 4 level pulse amplitude modulation and direct detection (DD) receiver-based channel-reuse wavelength-division-multiplexing passive optical network (WDM-PON). A Rayleigh backscattering noise detection-based wavelength management method is employed for the tunable optical transmitter used in colorless optical network unit to achieve bidirectional 20 Gb/s/λ transmission over 45-km standard single-mode-fiber on a 100-GHz WDM grid. Chromatic dispersion induced power fading in the DD system is avoided with fiber Bragg grating filter-based vestigial-sideband filtering. The inter-symbol interference is cancelled with digital signal processing-based overlap frequency-domain equalizer. The transmission performance is also measured with different optical signal to Rayleigh backscattering noise ratio and different central wavelength shift between upstream and downstream in the channel-reuse system.

All optical up-converted signal generation with high dispersion tolerance using frequency quadrupling technique for radio over fiber system

A novel all optical up-converted signal generation scheme with optical single-sideband (OSSB) technique for radio over fiber (RoF) application is presented and experimentally demonstrated using low-bandwidth devices. The OSSB signal is generated by one low-bandwidth intensity LiNbO3 Mach-Zehnder modulator (LN-MZM) under frequency quadrupling modulation scheme and one low-bandwidth LN-MZM under double sideband carrier suppressed modulation (DSB-CS) scheme. The proposed all OSSB generation scheme is capable of high tolerance of fiber chromatic dispersion induced power fading (DIPF) effect. Benefiting from this novel OSSB generation scheme, a 26GHz radio frequency (RF) signal up-conversion is realized successfully when one sideband of the optical LO signal is reused as the optical carrier for intermediate frequency (IF) signal modulation. The received vector signal transmission over long distance single-mode fiber (SMF) shows negligible DIPF effect with the error vector magnitude (EVM) of 15.7%rms. In addition, a spurious free dynamic range (SFDR) of the OSSB up-converting system is measured up to 81dBHz2/3. The experiment results indicate that the proposed system may find potential applications in future wireless communication networks, especially in microcellular personal communication system (MPCS).

Compensation of chromatic dispersion-induced power fading using optimised chirped fibre Bragg grating for millimetre-wave radio-over-fibre system

Compensation of fibre dispersion-induced power fading in an externally modulated sub-carrier multiplexed radio-over-fibre transmission link using the chirped fibre Bragg grating (CFBG) has been investigated. The results show that periodic power fading caused by fibre chromatic dispersion is significantly reduced and the optimum transmission distance can be increased by proper design of grating parameters and optimum selection of apodisation profile. The investigation also reveals that carrier-to-noise ratio and bit-error rate of 156 Mbps DPSK signal are also significantly improved using the CFBG with asymmetric apodisation profile as the dispersion compensator.