Investigation on microwave photonic filter group delay performance

Investigation on the group delay performance of microwave photonic filters is presented. Analysis and simulation results show symmetrical distribution on the delayed optical signals in the impulse response is required to obtain a constant group delay performance. Experimental results for both symmetrical and asymmetrical tap distribution microwave photonic notch filters are presented showing the group delay response with ?25 ps and around 1 ns ripples, respectively.     

Wideband tunable optoelectronic oscillator based on a single-bandpass microwave photonic filter and a recirculating delay line

A wideband tunable optoelectronic oscillator(OEO) based on a tunable single-bandpass microwave photonic filter(MPF) and a recirculating delay line is proposed and experimentally demonstrated. The MPF is formed by cascading a finite impulse response filter and an infinite impulse response filter, which can enhance the quality factor of the MPF and suppress the side modes of the OEO. The frequency response of the tunable MPF is theoretically analyzed. By placing the MPF into the OEO, tunable microwave signals from 10.3 GHz to 26.7 GHz and a 100 MHz step tunability are experimentally demonstrated. The phase noise is-113 dBc∕Hz@10 kHz. The results agree well with the theory.     

A photonic approach for microwave/millimeter-wave frequency measurement using stimulated brillouin scattering in single mode fiber

A photonic approach for microwave/millimeter-wave (MMW) frequency measurement is proposed and demonstrated based on stimulated Brillouin scattering (SBS) of a 20-km standard single mode fiber (SSMF). After the MMW signal is modulated to a laser source with two sidebands using optical carrier suppression (OCS) modulation, its frequency can be easily measured by monitoring the SBS-induced amplification with a power meter. Due to the 1-pm resolution of a tunable pump laser source, a frequency measurement range of 1–40 GHz is demonstrated in our experiment with a frequency resolution of 125 MHz. We believe the frequency measurement range can be further extended to satisfy photonic radar front-end processing application.     

Wideband frequency tunable optoelectronic oscillator based on a dispersion compensated microwave photonic filter

A wideband tunable optoelectronic oscillator (OEO) based on a dispersion compensated phase modulated microwave photonics filter (MPF) is proposed and experimentally demonstrated. The MPF, consisting of a tunable laser source (TLS), a phase modulator, a fiber Bragg grating Fabry–Perot filter and a photodetector, is used as the oscillating mode selection device. Dual-loop configuration is employed to make sure the OEO operates at a single oscillating mode. Theoretically analysis is carried out to demonstrate the tuning range limitation due to the phase-modulation to intensity-modulation conversion caused by long single mode fiber (SMF). To overcome this disadvantage and expand the signal tuning range, a dispersion compensation fiber is introduced followed by the SMF to compensate the fiber dispersion. By simply adjusting the wavelength of the TLS, an ultra-wideband tunable microwave signal with the frequency tuning range from 2 to 44 GHz is obtained. The phase noise is also investigated and measured to be less than ? 110 dBc/Hz at an offset of 10 kHz within the whole frequency range.     

Multiple-bipolar-tap tunable spectrum sliced microwave photonic filter

A spectrum sliced microwave photonic signal processor structure, which is all-fiber based and features simplicity, together with the ability to realize tunability, reconfigurability, bipolar taps, and multiple-tap rf filtering, is presented. It is based on thermally controlled optical slicing filters induced into two linearly chirped fiber Bragg gratings. Experimental results demonstrate the realization of versatile microwave photonic filters with frequency tunable, reconfiguration, and bipolar-tap generation capabilities.     

Effects of grating characteristics to the performance of fiber-Bragg-grating delay line based microwave photonic filters

In this paper, both theoretical investigation and experimental verification of microwave photonic filter based on a fiber-Bragg-grating (FBG) delay line and a broadband light source have been carried out, in which the effects of spectrum and dispersion characteristics of the FBGs on the frequency response of the microwave photonic filter have been taken into consideration. Theoretical and experimental results agree well, and both results show that FBG's characteristics affect not only the free spectrum range (FSR) of microwave photonic filter's response, but also results in the frequency dependent power degrading.     

Performance limitation of chirped-fiber-Bragg-grating-based photonic microwave notch filter due to group delay and reflectivity ripples

We investigated the performance limitation of a frequency-tunable photonic microwave notch filter incorporating a chirped fiber Bragg grating (FBG) as a group delay line. In particular, we carried out theoretical and experimental studies to analyze the impact of the reflectivity ripple (RR) and group delay ripple (GDR) in the chirped FBG on the output notch performance. The results of experimental and theoretical analyses performed on a photonic microwave notch filter in which an S-bending-based linearly chirped FBG was incorporated, revealed that the notch depth and notch frequency were significantly affected by imperfections in the chirped FBG. The notch depth was found to be decreased by the RRs, whereas significant fluctuations in the notch frequency were caused by the GDRs. On the basis of the obtained results, we conclude that the RR and the GDR are the fundamental factors that degrade the performance of chirped FBG-based photonic microwave filters.     

A novel tunable cascaded IIR microwave photonic filter

A new tunable cascaded infinite impulse response (IIR) microwave photonic filter is presented, based on a novel configuration in which a semiconductor optical amplifier (SOA) is inserted between two active recirculating delay line (RDL) loops. Due to wavelength conversion with cross-gain modulation (XGM) in SOA, interferences between light beams traveling different paths are canceled, ensuring a stable transmission. By employing this configuration, a cascaded IIR microwave photonic filter is firstly achieved. The free spectral range (FSR) and the Q factor are both increased significantly by adopting “vernier effect” technique in the IIR filter. The structure is also tunable by adjusting the length of one RDL loop.     

A MZI-based photonic instantaneous microwave frequency measurement simplified by an optical polarizer

A novel photonic scheme of microwave signal frequency measurement with adjustable measurement range and resolution is proposed and experimentally demonstrated. The proposed scheme is based on simultaneous optical phase modulation and intensity modulation with interferometric detection. A low-pass frequency response is achieved by a Mach–Zehnder interferometer (MZI) while a bandpass frequency response is produced by a polarizer placed on the back instead of in front of the MZI. The microwave frequency can be estimated by the measured amplitude comparison function (ACF) obtained from the ratio of the two frequency responses. This scheme is simple, cost-effective as it requires no extra laser sources or modulators in the basic analog modulation link. The measurement errors as shown in experimental results can be kept in 0.1 GHz over a frequency range of 0.1–8.5 GHz.     

光纤光栅群时延纹波对微波光子滤波性能的影响

建立了一种研究光纤光栅群时延纹波(GDR)对微波光子滤波性能影响的理论模型,探讨了群时延纹波对相干光源型和非相干光源型微波光子滤波器性能的影响。基于该理论模型,分别在随机分布的GDR和实测GDR影响下,分析了微波光子滤波器幅频响应、相频响应的演变趋势。相干光源型滤波器中,GDR主要影响体现为陷波点频率的偏移,而非相干光源型滤波器中GDR则导致幅频响应形状和线性相位畸变;而在多抽头情形下,GDR导致边模抑制比下降和消光比劣化。     

光纤光栅群时延纹波对微波光子滤波性能的影响

建立了一种研究光纤光栅群时延纹波(GDR)对微波光子滤波性能影响的理论模型,探讨了群时延纹波对相干光源型和非相干光源型微波光子滤波器性能的影响。基于该理论模型,分别在随机分布的GDR和实测GDR影响下,分析了微波光子滤波器幅频响应、相频响应的演变趋势。相干光源型滤波器中,GDR主要影响体现为陷波点频率的偏移,而非相干光源型滤波器中GDR则导致幅频响应形状和线性相位畸变;而在多抽头情形下,GDR导致边模抑制比下降和消光比劣化。     

Novel method for fiber chromatic dispersion measurement based on microwave photonic technique

In this letter,we propose and demonstrate a simple and novel method for fiber chromatic dispersion(CD) measurement based on microwave photonic technique.The radio frequency(RF) signal is modulated simultaneously on two light-waves with different wavelengths,and the light-wave carrying RF signals transmit through the dispersive medium under test.CD can be obtained by monitoring the power changing of the interference RF signals after photo detector.The CD values of the single-mode and dispersion compensation fibers are both measured within the wavelength range from 1 525 to 1 605 nm,which verifies the feasibility of this method.     

A monolithic microwave delay line

A microwave acoustic delay line ordinarily has three parts. These are electromagnetic coupling circuit, transducer, and delay medium. In the device considered here, these three parts are coalesced into a single, simple, unstructured block of material, which has been termed an integral delay line. This type of delay line is suitable for use in both waveguide and coax systems, and both cases are described.     

Fault-tolerant polarization-insensitive photonic delay line architectures using two-dimensional digital micromirror devices

A binary multichannel photonic delay line (PDL) module is introduced that gives balanced loss switched states and a polarization-insensitive operation via the use of binary operation Digital Micromirror Devices (DMDs). Experimental demonstration of a DMD-based PDL architecture is performed for a 6.84-ns time delay design. Experimental results include a 25-beam feed interchannel crosstalk test indicating a <−60 dB optical interchannel crosstalk level for a 0.381 mm interchannel distance in the multichannel PDL. An average optical signal-to-leakage noise ratio of 35.33 dB is measured for this PDL. A butterfly design PDL optical architecture is proposed for minimizing loss and improving assembly accuracy. These DMD-based variable PDLs can be used in applications ranging from radio frequency (RF) fiber-optic signal processing systems to adaptive optics for astronomical and laser radar arrays.     

Photonic approach to microwave frequency measurement with extended range based on phase modulation

We propose and demonstrate a photonic approach to instantaneous frequency measurement with an extended range based on phase modulation.In the measurement system,two optical wavelengths and two dispersion fiber segments are used to construct the frequency-dependent amplitude comparison functions(ACFs).Several ACFs can be utilized jointly to determine the microwave frequency without ambiguities beyond a monotonic region of the lone conventional ACF.The measurable range of microwave frequency can be extended and the accuracy can be improved by selecting an ACF with a large slope.The experimental results show that the errors are limited within ±140 MHz of a frequency measuremental range from 8 to 20 GHz.     

1维微波光子晶体频率选择性反射面

研究了一种由多层介质交替排列的1维微波光子晶体,应用传输矩阵法计算和分析了该结构周期数、波的入射角、介质的相对介电常数以及介质层厚度等对其频率选择特性的影响,并具体给出了一个可行的设计方案。所设计的频率选择表面在3.2～4.0 GHz频率范围内,反射系数大于0.99,在9.5～9.7 GHz频率范围内透射系数大于0.98。     

A large bandwidth photonic delay line using passive cascaded silicon-on-insulator microring resonators

This paper investigated the design and the characterization of a photonic delay line based on passive cascaded silicon-on-insulator (SOI) microrings.We considered the compromise of group delay,bandwidth and insertion loss.A 3-stage double channel side-coupled integrated spaced sequence of resonator (SCISSOR) device was optimized by shifting the resonance of each microring and fabricated with electron beam lithography and dry etching.The group delay was measured to be 17 ps for non-return-to-zero signals at different bit rates and the bandwidth of 78 GHz was achieved.The experiment result agreed well with our simulation.     

1维微波光子晶体频率选择性反射面

研究了一种由多层介质交替排列的1维微波光子晶体,应用传输矩阵法计算和分析了该结构周期数、波的入射角、介质的相对介电常数以及介质层厚度等对其频率选择特性的影响,并具体给出了一个可行的设计方案。所设计的频率选择表面在3.2~4.0 GHz频率范围内,反射系数大于0.99,在9.5~9.7 GHz频率范围内透射系数大于0.98。