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     

Photonic Generation of Chirped Microwave Pulses Using Superimposed Chirped Fiber Bragg Gratings

A novel approach to generating linearly chirped microwave pulses in the optical domain based on spectral shaping and linear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed system, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is spectrum-shaped by an optical filter that consists of two superimposed chirped fiber Bragg gratings (SI-CFBGs) with different chirp rates. The SI-CFBGs form a Fabry-Perot cavity with a cavity length linearly dependent on the resonance wavelength, thus a spectral response with an increased or decreased free spectral range is generated. A chirped microwave pulse with the pulse shape identical to the shaped spectrum is obtained at the output of a high-speed photodetector thanks to the frequency-to-time mapping in a dispersive device. The proposed technique is experimentally demonstrated, a linearly chirped microwave pulse with a central frequency of 15 GHz and a chirp rate of 0.0217 GHz/ps is experimentally generated.     

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.     

Continuously Tunable Microwave Photonic Filter With Negative Coefficients Using Cross-Phase Modulation in an SOA-MZ Interferometer

A notch filter with negative tap is proposed based on exploiting cross-phase modulation in a semiconductor optical amplifier Mach-Zehnder interferometer. This configuration shows a high operation bandwidth and reduces the chirp of the modulated signal compared to prior proposed configurations based on cross-gain modulation. We compare the operation of the structure when optic delay lines or dispersive fibers are used to generate the optical taps. Moreover, a continuous free-spectral range tuning is shown.     

Simple Reconfigurable Photonic Microwave Filter Using an Arrayed Waveguide Grating and Fiber Bragg Gratings

We demonstrate a photonic microwave finite impulse response filter with reconfiguration and tuning capabilities. The filter is based on spectral slicing of a broadband source and optical fiber as a wideband dispersive medium. An arrayed waveguide grating and fiber Bragg gratings are used to select and vary the weight of the optical taps to achieve reconfiguration and tuning     

Tunable All-Optical Microwave Filters Based on Fiber Loop and Chirped Fiber Bragg Gratings

All-optical microwave filters are important parts of fiber-optic microwave/millimeter wave processing systems. In this paper, two novel passive tunable all-optical microwave filters based on fiber loop and chirped fiber Bragg gratings (CFBGs) are demonstrated, where the frequency response of the both filters can be continuously tuned by adjusting the wavelength of the input light. The required free spectral range (FSR) of the filters can be obtained by carefully controlling the length of fiber loop and the positions of the CFBGs in the fiber loop. Experimental results prove the feasibility of the proposed filtering structures.     

A Tunable Photonic Microwave Filter With a Complex Coefficient Using an Optical RF Phase Shifter

A novel tunable photonic microwave filter with complex coefficients is proposed and experimentally demonstrated. The complex coefficient is generated using a wideband tunable optical RF phase shifter that consists of two electrooptic intensity modulators. The phase of the RF signal is shifted by simply adjusting the bias voltages applied to the two electrooptic intensity modulators, and the phase shift remains constant over the microwave spectral region of interest. A two-tap photonic microwave filter with one tunable complex coefficient, with a wide and continuous tuning range, is experimentally demonstrated.     

Multitap Photonic Microwave Filters With Arbitrary Positive and Negative Coefficients Using a Polarization Modulator and an Optical Polarizer

A novel multitap photonic microwave filter with arbitrary positive and negative coefficients implemented using an electrooptic polarization modulator (PolM) and an optical polarizer is proposed and experimentally demonstrated. In the proposed filter, the optical polarizer is connected at the output of the PolM with its transmission axis aligned at an angle of 45 to one principal axis of the PolM. By adjusting the polarization direction of the input lightwave to be 45 or 135 to one principal axis of the PolM, an inverted or noninverted intensity-modulated optical microwave signal is obtained at the output of the optical polarizer, which leads to the generation of a negative or positive coefficient. A time delay difference between adjacent taps is generated by using a wavelength-dependent delay line. A five-tap photonic microwave filter with arbitrary positive and negative coefficients is demonstrated. The reconfigurability of the filter is also investigated.     

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.     

Chirped Microwave Pulse Generation Using a Photonic Microwave Delay-Line Filter With a Quadratic Phase Response

We propose an optical approach to generating chirped microwave pulses using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response. If a chirp-free broadband microwave pulse is inputted into the filter, a chirped microwave pulse is generated thanks to the quadratic phase response of the filter. To design a PMDLF with a quadratic phase response, complex tap coefficients are required, which is hard to implement in the optical domain. In this letter, a PMDLF with equivalent complex coefficients implemented based on a nonuniformly spaced delay-line structure is demonstrated. Since only positive coefficients are required, the filter is easy to implement. A design example is provided. A five-tap PMDLF to generate a chirped microwave pulse with a chirp rate of 13.2 GHz/ns is then experimentally demonstrated.     

以环行器和光纤光栅为腔镜的可调谐窄线宽激光器

实验报道了一种结构简单有效的波长可调谐掺铒光纤激光器.该激光器为线型腔结构,由环行器(DC)、掺饵光纤(EDF)、光纤布拉格光栅(FBG)和波分复用(WDM)组成.利用环行器作为全反射腔镜,光纤布拉格光栅作为波长选择性腔镜,通过对光纤光栅施加轴向应力改变其布拉格波长来实现光纤激光器的波长可调谐输出.利用此结构.室温下实验获得了中心波长在1543.5～1549.5 am连续可调,边模抑制比(SMSR)大于50 dB的连续激光输出,激光输出线宽保持在0.01 nm以下.     

Tunable Transmission Resonant Filter and Modulator With Vertical Gratings

Resonant filters in waveguides with vertical gratings have been realized on a silicon-on-insulator wafer. Two identical uniformly distributed Bragg reflectors with vertical gratings are separated by a quarter wavelength phase offset. Experimental studies show a broad stopband and a narrow transmission band which shifts with changing substrate temperature that is also illuminated by an external laser pump beam at 514-nm wavelength. Experimental results on a low-frequency thermal modulation using an external light source are also presented     

Negative Tap Photonic Microwave Filter Based on a Mach–Zehnder Modulator and a Tunable Optical Polarizer

A negative tap photonic microwave filter based on a Mach-Zehnder modulator (MZM) and a tunable optical polarizer is proposed. In the proposed filter, the output light from the MZM, after experiencing a time delay difference between the two orthogonal modes in a polarization-maintaining fiber, is sent to the tunable optical polarizer. By adjusting the dc bias of the MZM and the polarization angle of the tunable polarizer with respect to the two orthogonal modes, two positive or one positive and one negative coefficient are generated. A theoretical analysis is presented which is verified by experiments. A two-tap microwave filter with two positive or one positive and one negative coefficient is demonstrated.     

基于偏振控制的Sagnac环负系数微波光子滤波器

为了克服正抽头系数低通滤波的限制,满足光载无线通信(ROF)、无线通信等系统对带通滤波器的需要,提出了一种新的负系数带通微波光子滤波器结构。系统采用了一种偏振敏感的电吸收调制器,其横向电场(TE)和横向磁场(TM)方向上具有不同的调制系数,在小信号调制下仍为线性调制。通过旋转偏振控制单元的波片,改变其快轴与TE方向的夹角,可以得到任意偏振态的转换。当偏振控制单元由两个旋光方向相反的法拉第旋光片和一个1/2波片组合时实现了负系数滤波,和一个1/4波片组合时得到了正系数滤波。     

Tunable Photonic Microwave Notch Filter With Negative Coefficient Based on Polarization Modulation

A novel tunable photonic microwave notch filter with negative and positive coefficients is proposed and experimentally demonstrated. The coefficients can be achieved by polarization modulation along with an electrical signal. The two polarization-modulated signals, which have a relative time delay, are combined, and detected by a photodetector. The transfer response of the filter shows a very stable operation irrespective of the coherence length of the source used. Moreover, the free spectral range of the filter, which shows a sharp notch, can be changed by using a tunable differential group delay generator over the range of 3.16-4.31 GHz     

Dynamic Single／Dual—channel Filter with Tunable Fiber Bragg Gratings

The shift mechanism of Bragg wavelength with stress variation for a fiber grating is investigated in detail.The influence of strain change on reflection and bandpass is theoretically analyzed.By applying stress, the dynamic single/dual-channel filter with tunable fiber Bragg gratings is achieved.     

基于掺Er光纤放大器的可调谐微波光子滤波器

提出了一种基于掺Er光纤放大器(EDFA)的光纤环结构可调谐微波光子滤波器.在光纤环结构中引入掺Er光纤(EDF),通过增加泵浦功率提供增益来补偿器件损耗,从而增加了信号的有效采样数,大大改善了滤波器的性能.在泵浦功率为42.7 mW时,实现了通带3 dB带宽为0.15 MHz、Q值为100和抑制比为20 dB的微波光子滤波器.进一步通过在光纤环结构中引入可调光纤延迟线(TODL),实现了可调谐微波滤波器.     

基于叠印啁啾光纤布拉格光栅的宽谱微波光子信道化接收方法

提出了利用叠印啁啾光纤布拉格光栅(S-CFBG)实现宽谱微波信号光子信道化接收的方法。利用一个S-CFBG产生光频梳(OFC),接收的微波信号被强度调制器调制到OFC的各个载波上。第二个S-CFBG对不同的边带进行滤波,利用波分复用(WDM)解复用器进行信道分离,实现对宽谱微波信号频率的实时测量。该方法还可以同时检测不同射频(RF)载波上所携带的数据信息,无需传统的电本振源阵列,简化了系统结构。建立了测量范围为0～20GHz,测量精度为0.5GHz的宽谱微波信号信道化接收仿真系统。实现了不同RF频率上携带信息的实时同步检测,并对接收误码性能进行了分析。     

Tunable Fiber Laser With Ultra-Narrow Linewidth Using A Tunable Phase-Shifted Chirped Fiber Grating

We experimentally demonstrate a tunable $C$ -band erbium-doped fiber ring laser with ultra-narrow linewidth using a tunable phase-shifted linearly chirped fiber Bragg grating (PS-LCFBG) as an intracavity ultra-narrowband filter. The center wavelength of the PS-LCFBG with an ultra-narrow bandwidth of ${≪}$10 pm is thermally tuned by scanning a current-controlled resistance wire along its length. The laser has an ultra-narrow linewidth of ${≪}$1.52 kHz, a tuning range of ${sim}$ 15.5 nm, a good sidemode suppression ratio of ${>}$30 dB, an output power of ${sim}$10 dBm, a small power variation of ${≪}$ 0.2 dB, and a small wavelength variation of ${≪}$0.01 nm. The laser structure is simple and cost-effective.      

Novel Technique for Implementing Incoherent Microwave Photonic Filters With Negative Coefficients Using Phase Modulation and Single Sideband Selection

We propose a novel configuration to implement microwave photonic filters featuring positive and negative coefficients which is based on the use of a single phase modulator to modulate an array of optical sources followed by a filtering stage to choose the optical carrier and higher or lower radio-frequency sideband depending on the sign of the desired coefficient. Experimental results are presented which prove the feasibility of this concept for a two tap notch filter. Filter tunability is also demonstrated.