Novel Continuously Tunable Microwave Photonic Bandpass Filter

A new technique for tuning the passband frequency of a microwave photonic bandpass filter is presented. It is based on controlling the polarization state of the signal in an amplified recirculating delay line loop with a polarizer at the output. A fixed wavelength laser can be used as an optical source. The filter has a sharp passband, which can be tuned continuously while maintaining the same passband width. Experimental results demonstrate continuous tuning capability of the high-resolution bandpass filter.     

全新布里渊散射可切换微波光子滤波器

提出了一个新的基于布里渊散射效应的微波光子滤波器。该滤波器可通过调谐系统中光滤波器的中心波长,实现高解析度带通滤波器与陷波滤波器之间的灵活切换,并且通过调谐产生受激布里渊散射的泵浦光的波长可实现滤波器通带或阻带的中心频率在很大频率范围内连续调谐。该滤波器为全光结构,因此具有非常大的调谐范围（调谐上限仅受限于试验中使用的矢量网络分析仪的显示频率上限）。系统中采用相位调制器,因此没有偏置电压漂移问题。实验结果展示了一个带通与陷波滤可灵活切换的高解析度微波光子滤波器,并且通带和阻带的中心频率在9～26.5 GHz范围内连续可调谐,其中带通滤波器的通带具有极窄3 dB带宽,约28 MHz（由光纤本身布里渊增益区线宽所决定）。     

Reflective Amplified Recirculating Delay Line Bandpass Filter

A new microwave photonic filter structure that can achieve a high factor, high stopband rejection, and high skirt selectivity bandpass filter response simultaneously is presented. It is based on reflecting the signal back into a single amplified optical recirculating delay line and comprises coherent summation of the multiple signals that constitute each tap and incoherent summation of the successive taps. This introduces a new class of filter operation and effectively enables the realization of a higher order bandpass filter characteristic in a very simple structure. Experimental results are presented that demonstrate a multiple-tap high- bandpass filter response that also displays high stopband rejection level and high skirt selectivity.     

Microwave photonic filter with single bandpass response

A new microwave photonic filter that solves the problem of realising a single bandpass RF response is presented. The filter is based on using phase modulation together with a pair of gratings, and eliminates the baseband response and periodic spectral response of typical FIR filters. Experimental results demonstrate a single passband square-type bandpass filter response, and operation to high frequencies.     

Photonic bandpass filters with high skirt selectivity and stopband attenuation

A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown.     

Tunable Photonic Microwave Bandpass Filter With Negative Coefficients Implemented Using an Optical Phase Modulator and Chirped Fiber Bragg Gratings

A continuously tunable photonic microwave bandpass filter with positive and negative coefficients implemented using an optical phase modulator and chirped fiber Bragg gratings (FBGs) is proposed and experimentally demonstrated. The positive and negative coefficients are generated through optical phase-modulation to intensity-modulation conversion by reflecting the phase-modulated optical carrier from linearly chirped FBGs (LCFBGs) with positive and negative dispersions. The tunability of the filter is realized by changing the wavelength of the optical carrier such that it is reflected at different physical locations in the LCFBGs. A two-tap microwave bandpass filter with a free spectral range tunable from 1.14 to 4.55 GHz is experimentally demonstrated.     

Double Coupler Amplified Recirculating Delay Line Microwave Photonic Bandpass Filter

Theoretical and experimental investigations on a double coupler amplified recirculating delay line (ARDL) microwave photonic bandpass filter are presented. These show that the system involves both coherent and incoherent summation of optical signals. This enables a higher order filter transfer function to be realized, which results in a high-performance frequency response that cannot be achieved by the conventional single coupler ARDL structure. Experimental results are presented that demonstrate a sharp, high skirt selectivity and high stopband rejection level bandpass filter response.     

Microwave photonic notch filter with complex coefficient based on four wave mixing

A microwave photonic notch filter with a complex coefficient is proposed and demonstrated based on four wave mixing (FWM). FWM effect of two single-frequency laser beams occurs in a highly nonlinear fiber (HNLF), and multi-wavelength optical signals are generated and used to generate the multi-tap of microwave photonic filter (MPF). The complex coefficient is generated by using a Fourier-domain optical processor (FD-OP) to control the amplitude and phase of the optical carrier and phase modulation sidebands. The results show that this filter can be changed from bandpass filter to notch filter by controlling the FD-OP. The center frequency of the notch filter can be continuously tuned from 5.853 GHz to 29.311 GHz with free spectral range (FSR) of 11.729 GHz. The shape of the frequency response keeps unchanged when the phase is tuned.     

Microwave photonic bandpass filter based on spectrumslicing and phase modulator

A tunable microwave photonic bandpass filter with high mainlobe-to-sidelobe ratio (MSR) based on a phase modulator and a dispersive device is proposed. The multi-tap characteristics of the filter are realized by slicing a broadband source using a Mach-Zehnder interferometer (MZI) which results in a high MSR of 25 dB. The tunability of the filter is realized by an optical variable delay line (OVDL) in one arm of the MZI, which changes the wavelength spacing of the sliced broadband source and results in a tunable free spectrum range (FSR) of the filter. The central frequency of the bandpass filter is tunable from 10.7 GHz to 27 GHz by changing the wavelength spacing from 0.145 nm to 0.054 nm.     

All-optical tunable filters built with discontinuity-assisted ringresonators

Numerically simulated performance is presented in a new type of bandstop and bandpass filters, built with discontinuity-assisted ring resonator (DARR)-loaded couplers. The operating characteristic of the bandpass filter is similar to that of a long grating with a centered cavity or a photonic crystal with a defect. The filters are tuned by varying the refractive index or the length of the waveguide forming the ring or the cavity. Selectivity and tuning range are controlled by the coupling coefficient of the couplers, by the order of resonance in the rings, and by the reflection coefficient of the discontinuities. A design procedure and the effect of loss are also presented     

Photonic reconfigurable microwave filter with negative coefficients

A photonic implementation of a reconfigurable microwave transversal filter is proposed. The implementation allows the filter taps to be both positive and negative. This allows for greater flexibility in the design of the filter so that bandpass and lowpass filters with flatter passbands could be realised. A four-tap version of the filter is demonstrated.     

80 Gbit/s wavelength conversion using semiconductor optical amplifier and optical bandpass filter

A wavelength converter is presented that is made out of a semiconductor optical amplifier and an optical bandpass filter. Error-free inverted wavelength conversion is demonstrated at a bitrate of 80 Gbit/s. This approach can be exploited at higher bitrates. A clear open eye indicating error-free wavelength conversion at 160 Gbit/s is also presented. This wavelength converter has a simple configuration and allows photonic integration.     

Photonic Microwave Bandpass Filter With Negative Coefficients Using a Polarization Modulator

A novel photonic microwave bandpass filter with negative coefficients implemented using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed filter, a lightwave from a tunable laser source (TLS) is sent to a PolM, with the incident lightwave adjusted to have its polarization direction aligned at an angle of plusmn45deg to the principal axes of the PolM. A microwave signal is applied to the PolM through its RF port. Thanks to the polarization modulation in the PolM, two complementary microwave signals with identical amplitudes carried by two optical carriers with orthogonal polarizations are generated. The two complementary optical microwave signals are then sent to an optical delay line consisting of one section or two sections of polarization-maintaining fiber (PMF), with the polarization directions aligned with the fast and slow axes of the PMF. A photonic microwave bandpass filter with two or four taps is obtained     

Coherence-Free Microwave Photonic Bandpass Filter Using a Frequency-Shifting Recirculating Delay Line

A new microwave photonic filter that realizes a high-resolution bandpass filter response with coherence-free operation and without the limitations of phase-induced intensity noise is presented in this paper. It is based on a frequency-shifting recirculating delay line, which can simultaneously achieve a multitap, high-resolution filter and a very large suppression of noise, while also enabling the use of a conventional narrow-linewidth laser source without suffering from coherent interference effects. Experimental results demonstrate a filter $Q$ value of 200 and an SNR improvement of 40.3 dB compared to conventional recirculating delay line structures.      

变容管电调微波带通滤波器

本文叙述采用梳状线结构的变容管电调微波带通滤波器的设计理论和方法。推导出梳状线带通滤波器的输入、输出耦合网络的参数条件,以补偿带通滤波器的谐振器之间电磁耦合随不同调谐频率的变化;并给出使带通滤波器的绝对带宽或通带回波损耗在调谐频率范围内变化最小时,梳状线谐振器的电长度应满足的相应条件,由此来保证电调带通滤波器在较宽的调谐频率范围内具有较高的通带回波损耗,且保持带通滤波器的响应形状和绝对带宽基本不变。此外,还讨论了由电调变容管的Q值引起的带通滤波器的通带有功损耗问题。文中给出了具体的设计公式。最后,给出了一个L波段变容管电调带通滤波器的研制实例和测试结果。     

Tunable Bandpass Filter With Solid-Core Photonic Bandgap Fiber and Bragg Fiber

A tunable spectral bandpass filter which includes two fibers with different bend loss edges-a solid-core photonic bandgap fiber with short wavelength bend loss edge and a Bragg fiber with long wavelength bend loss edge-is presented in this letter. The central wavelength and the bandwidth can be widely tuned around 1100 nm by controlling the bend diameters of the two fibers respectively. It can be a low-loss in-line fiber device due to its all solid structure and standard splice connection.     

Fiber-optic tunable microwave transversal filter

A fiber-optic finite impulse response filter with continuously tunable unit time delays is developed and studied. The filter consists of eight taps with progressively longer segments of high-dispersion fiber, but completed with dispersion-shifted fiber to nominally identical overall lengths. The time delays through each tap are tuned by varying the wavelength of the optical carrier. The constructed 8-tap filter exhibits bandpass characteristics with a Q of 30. The bandpass band is continuously tuned over a full octave from under 9 GHz to over 18 GHz with a single low-voltage control signal that demonstrates the technique's applicability to adaptive systems     

微带带通滤波器的设计方法

本文采用函数变换经验公式法计算滤波器元件值.以X频段微带带通滤波器为例,阐述其方法的具体运用,其计算结果与文献[1]的设计值比较,表明本文方法计算简单、精度高.     

Novel Coherence-Free RF/Microwave Photonic Bandpass Filter

A new structure for realizing an equivalent multitap bandpass filter response without coherent interference and phase noise limitations is presented. It is based on intensity modulating a continuous-wave light multiple times to obtain many taps, and also enables windowing to be employed. Experimental results are presented that demonstrate a multiple-tap bandpass filter with high rejection ratio and with no coherence and phase-induced intensity noise limitations.      

Continuously tunable bandpass filtering using high-index inclusion microstructured optical fibre

A tunable bandpass filter is demonstrated by applying a variable thermal gradient to a microstructured fibre with high index inclusion, thus chirping its local anti-resonances. The width of its transmission bands can be continuously varied and transmission completely suppressed. The experiment is compared with numerical simulations.