We propose a third-order intermodulation distortion （IMD3） compensation scheme based on the bidirec- tional modulation of 2-Ch phase modulator （PM）. We realize the destructive combination of IMD3 by using different modulation efficiencies and appropriately adjusting the input optical power ratio to satisfy a fixed relationship with modulation efficiency. The primary advantage of this scheme is that out-of-phase IMD3 is introduced using only one 2-Ch PM, thereby resulting in the cancellation of IMD3. Up to 27-dB suppression in IMD3 is experimentally demonstrated--a feature that will be useful in low-distortion analog or）tical transrni^sirm.
A novel scheme for the generation of background-free pulsed microwave signals is proposed and experimentally demonstrated based on spectral shaping,frequency-to-time mapping,and balanced photodetection.In the proposed scheme,the optical spectral shaper,which consists of a differential group delay(DGD)element,two polarization controllers,and a polarization beam splitter,has two outputs with complementary power transfer functions.By passing a short optical pulse through the spectral shaper and a dispersive element(DE),a pulsed microwave signal is obtained after balanced photodetection.Thanks to the balanced photodetection,the lowfrequency components(i.e.,the background signal)in the electrical spectrum is suppressed,leading to the generation of a background-free pulsed microwave signal.Meanwhile,the spectral power of the obtained microwave signal is enhanced compared to that obtained by single-end detection.Experimental results for the generation of a pulsed microwave signal centered at 12.46 GHz show that the background signal can be suppressed by more than 30 dB,and the spectral power is increased by 5.5 dB.In addition,the central frequency of the obtained background-free pulsed microwave signal can be tuned by changing the DGD introduced by the DGD element,and/or by changing the dispersion of the DE.
The performance of three wireless local-area network(WLAN) media access control(MAC) protocols is investigated and compared in the context of simulcast radioover-fiber-based distributed antenna systems(RoF-DASs) where multiple remote antenna units(RAUs) are connected to one access point(AP) with different-length fiber links.The three WLAN MAC protocols under investigation are distributed coordination function(DCF) in basic access mode,DCF in request/clear to send(RTS/CTS) exchange mode,and point coordination function(PCF).In the analysis,the inter-RAU hidden nodes problems and fiber-length difference effect are both taken into account.Results show that adaptive PCF mechanism has better throughput performances than the other two DCF modes,especially when the inserted fiber length is short.
A tunable and dispersion-insensitive two-tap microwave photonic filter(MPF) with a complex coefficient is proposed and demonstrated.By simply adjusting a polarization controller(PC) in one tap,the filter can be tuned over the entire free spectral range(FSR) while keeping the shape of the filter unchanged.Because the two taps are both single-sideband(SSB) modulated,the filter has high tolerance to fiber dispersion.The transmission response of a system with 25-or 40-km single-mode fiber(SMF) was measured and compared with an MPF with one double sideband(DSB) modulation tap.The proposed MPF shows much better performance for long-distance fiber transmission.
We present a network-level signaling mechanism for user access and service setup in light emitting diode （LED）-based visible light communication （VLC） networks and define the corresponding signaling messages. In this mechanism, lamp selection is an important step for realizing flexible user access and efficient resource allocation. Two basic selection schemes are proposed, and an enhanced bandwidth-based scheme is presented. Simulation results show the different advantages among these schemes.
Microwave photonics(MWPs)uses the strength of photonic techniques to generate,process,control,and distribute microwave signals,combining the advantages of microwaves and photonics.As one of the main topics of MWP,radio-over-fiber(RoF)links can provide features that are very difficult or even impossible to achieve with traditional technologies.Meanwhile,a considerable number of signal-processing subsystems have been carried out in the field of MWP as they are instrumental for the implementation of many functionalities.However,there are still several challenges in strengthening the performance of the technology to support systems and applications with more complex structures,multiple functionality,larger bandwidth,and larger processing capability.In this paper,we identify some of the notable challenges in MWP and review our recent work.Applications and future direction of research are also discussed.
Kun XuRuixin WangYitang DaiFeifei YinJianqiang LiYuefeng JiJintong Lin
An approach to implementing optical single sideband(OSSB)polarization modulation,which is a combination of two orthogonally polarized OSSB modulations with complementary phase differences between the optical carrier and the sideband,is demonstrated based on two cascaded polarization modulators(PolMs).The two PolMs are driven by two RF signals that are 90°out of phase.By properly adjusting the polarization state between the two PolMs,OSSB polarization modulation with large operation bandwidth can be realized.An experiment is performed.OSSB polarization modulation with an operation bandwidth from 2 to 35 GHz is successfully demonstrated.The spectral profile of the OSSB polarization-modulated signal is observed through an optical spectrum analyzer,and its complementary phase properties are analyzed by sending the signal to a photodetector(PD)for square-law detection.Due to the complementary phase differences between the optical carrier and the sideband along the two polarization directions,no microwave frequency component is generated after the PD.The generated OSSB polarization-modulated signal is transmitted through 25 and 50 km single-mode fiber with 50 Mbaud 16 quadrature amplitude modulation baseband data to investigate the transmission performance of the proposed system in radio-over-fiber applications,and very small error vector magnitude degradation is observed.OSSB polarization modulation is also employed to realize a microwave photonic phase shifter.A full-range tunable phase shift is obtained for 2 and 35 GHz microwave signals.
