Paper Topic: Microwave Photonic Notch Filter
Si3N4基于环谐振器的微波光子。具有超高峰排斥的Notch滤波器
Introduction
微波光子(MWP)陷波滤波器可以同情red as the analogue of Band stop filter using electrical circuits. As name suggests, it is filter which supress or stop the passage of signal at certain range or specific frequency. MWP notch filter is explored excellently in removing the undesired signals making it efficient applicants in wireless communication, radar, radio astronomy. The ability to be tuned over many gigahertz maintaining high scale resolution (MHz), high selectivity and restriction to electromagnetic interference puts it as a better option than many electrical filters. One of the important components of filter is the filter itself which is made to pass the desired signal through. Researchers have developed many type of filters for this purpose working on different principle such as Stimulated Brillouin Scattering (SBS) based filter (example: chalcogenide waveguide), based on LiTaO3 WGM resonators and ring resonators which have been used in this paper.
环谐振器是一组以与至少一条波导形式的环形成的波导，这是一个封闭环与某种信号输入和输出耦合的封闭环。它基于建设性和破坏性干扰的原则以及整体内部反思。由于观察到的事实是，在谐振中观察到很少的波长，因此光谐振器作为滤波器起作用。也可以并行或串联配置使用两个环谐振器，但在此使用单个SI3N4环谐振器。到目前为止观察到的其他过滤器的问题是，峰值排斥和带宽的权衡如基于SBS的滤波器30-145 MHz的带宽，但低排斥20 dB。
Silicon based resonators providing low loss, high index contrast is also one of the motivations for using in experiment to get away with this tradeoff. Here, they have incorporated Photonic Integrated Circuit (PIC) technology to lead to multi-functionalities like, modulation, signal processing and photodetection. With this, the paper demonstrates a novel method of MWP signal processing includes Si3N4 as ring resonator as optical filter with high rejection and bandwidth.
Principle and techniques
The signal processing for notch filter is done by using Novel method (reported in this paper) and compared with conventional notch filter technique. The later includes single-sideband (SSB) modulation in which optical resonance is used to remove a portion of undesired signal in the optical sidebands. And the respective optical spectrum is passed to photodetector where it is mixed with optical carrier for detection. The given equation governs the FWHM (Full Width at Half Maxima) bandwidth and peak rejections.
Novel notch filter:Unlike conventional notch filter, it involves generates two optical sidebands with tunable amplitude and phases. The electro-optic modulator (EOM) is used to encode RF signal with unequal amplitude and phase difference. The Phase difference of Δφ = ± π , is maintained between ring and optical sidebands by exploiting amplitude and phase of ring to equalise the amplitudes of the optical sidebands in desired frequency region. Then, a beat signal created by mixing of sidebands and optical carrier on photodetection giving a notch at selected frequency.
Challenges
The RF insertion loss is one of the issues that should be addressed ( which is dominated by three factors).First is the insertion loss of the chip, which is relatively high (13 dB The second source of loss was the electrical-to-optical (E/O) and optical-to-electrical (O/E) conversions in the MWP link. RF loss of around 30 dB is also observed due two factors mentioned above The application of MWP Notch filter, still requires ultrahigh peak rejection with match to state of RF art filters with low loss and less pump power.
Conclusion and Future Perspectives
实施了一种有效的方法，以使用低损耗SI3N4环谐振器作为MWP Notch滤波器来摆脱带宽和峰值拒绝之间的权衡。新的方案显示，在247至840 MHz的范围内，大于55 dB的峰值排斥反应。与常规SSB过滤器相比，报道的技术是令人印象深刻的替代方法。滤波器（SI3N4环谐振器）实现了对最先进的RF Notch滤波器的可比分辨率和峰值排斥。调整激光的中心频率，可保留350 MHz的狭窄带宽和> 55 dB的超高排斥。此处开发的技术可以与基于SBS和基于波导的过滤器这样的纤维BRAGG光栅（FBGS）过滤器使用。一种也可以利用其他材料，作为共鸣过滤器（此处的EX-SI3N4），以改善信号的拒绝，损失低。