Reconfigurable Microwave Photonic Filter Research Articles

Low-Power, Reconfigurable Brillouin RF Photonic Bandstop Filters

Stimulated Brillouin Scattering (SBS) has been widely used to realize narrowband as well as wideband microwave photonic bandstop filters. However, most Brillouin based wide-band bandstop filters require large powers and have high complexity. In this letter, we propose a novel approach to realize a wideband, reconfigurable and tunable Brillouin-based microwave photonic bandstop filter using RF phase engineering. We demonstrate bandstop filters with suppression of >15 dB for moderate bandwidths and maximum bandwidth reconfigurability up to 1 GHz by using two pumps with powers of 8.2 dBm and 9.3 dBm. Further, we also demonstrate switching from a bandpass to a bandstop filter with simple phase manipulations. This letter presents numerical simulations, analysis, and experimental results for the proposed filter. Compared to conventional Brillouin systems, the proposed filter is extremely power-efficient.

Reconfigurable and tunable few-mode fiber-based microwave photonic filter

We propose a reconfigurable and tunable few-mode fiber-based microwave photonic filter. LP01 mode and LP11 mode are simultaneously excited by a few-mode long-period fiber grating. The free spectral range of the two-tap microwave photonic filter varies with the length of the few-mode fiber. LP01 mode, LP11 mode and LP21 mode are simultaneously excited by cascading different few-mode long-period fiber gratings and reflected at the same wavelength by different few-mode fiber Bragg gratings, which allows LP01 mode, LP11 mode and LP21 mode to be transmitted with equal differential delay. The free spectral range of the three-tap microwave photonic filter varies with the length of the few-mode fiber. A reconfigurable and tunable few-mode fiber-based microwave photonic filter can be implemented by changing the number of excited modes and the length of the few-mode fiber.

Tunable and Reconfigurable Microwave Photonic Bandpass Filter Based on Cascaded Silicon Microring Resonators

A tunable and reconfigurable bandpass microwave photonic filter (MPF) is demanded in scenarios where different center frequencies and bandwidths are required. Here, we propose and demonstrate a silicon-on-insulator (SOI)-based microwave photonic bandpass filter, whose center frequency and bandwidth can be adjusted. The MPF is implemented by using four cascaded microring resonators (MRRs) that fabricated based on SOI wafer. Each MRR combines the design of multi-mode waveguides and tunable coupling regions, thereby exhibiting simultaneous high frequency selectivity and excellent reconfigurability. The center frequency can be tuned by adjusting the resonant wavelengths of the MRRs, and the bandwidth can be reconfigured by adjusting the coupling coefficients as well as the resonant wavelengths of the MRRs. The operation state of each MRR can be monitored and thus the MPF can be adjusted precisely. In the experiment, the bandwidth and center frequency of the MPF are adjusted from 0.7 to 2 GHz and from 5.2 to 35.8 GHz, respectively. During the adjustment, the rejection ratio of the MPF remains above 40 dB. The link performance, including the link gain, noise figure and spurious-free dynamic range, are also charactered. The achieved MPF can be potentially applied to radar, sensor networks, and wireless communications.

Reconfigurable Microwave Photonic Filter Based on Space-Division Multiplexing Powered by Artificial Neural Networks

Space-division multiplexing (SDM) techniques bring new approaches for various applications in microwave photonic signal processing. In this work, an all-fiber reconfigurable microwave photonic filter (MPF) is realized based on SDM techniques using multicore fiber (MCF) and multimode fiber (MMF). The multimode interference (MMI) generated from the proposed MCF-MMF-MCF structure can be manipulated in dimensions of space and wavelength simultaneously, thus configuring the power distribution in all the taps of the MPF. The trained artificial neural network can accurately predict the operating wavelength and spatial input core for a target power distribution. In a low-cost, light-weight, and compact way, SDM fibers combined with MMI allow for greater flexibility and diversity in the response of the reconfigurable MPF.

Microcomb-driven silicon photonic systems

Microcombs have sparked a surge of applications over the past decade, ranging from optical communications to metrology1–4. Despite their diverse deployment, most microcomb-based systems rely on a large amount of bulky elements and equipment to fulfil their desired functions, which is complicated, expensive and power consuming. By contrast, foundry-based silicon photonics (SiPh) has had remarkable success in providing versatile functionality in a scalable and low-cost manner5–7, but its available chip-based light sources lack the capacity for parallelization, which limits the scope of SiPh applications. Here we combine these two technologies by using a power-efficient and operationally simple aluminium-gallium-arsenide-on-insulator microcomb source to drive complementary metal–oxide–semiconductor SiPh engines. We present two important chip-scale photonic systems for optical data transmission and microwave photonics, respectively. A microcomb-based integrated photonic data link is demonstrated, based on a pulse-amplitude four-level modulation scheme with a two-terabit-per-second aggregate rate, and a highly reconfigurable microwave photonic filter with a high level of integration is constructed using a time-stretch approach. Such synergy of a microcomb and SiPh integrated components is an essential step towards the next generation of fully integrated photonic systems.

Reconfigurable microwave photonic filter based on a quantum dash mode-locked laser.

We demonstrate a reconfigurable microwave photonic (MWP) filter using a quantum dash (QDash) mode-locked laser (MLL) that can generate an optical frequency comb (OFC) with ∼50 comb lines and a free spectral range of 25 GHz. Thanks to the large number of comb lines, the MWP filter responses can be easily programmed by tailoring the OFC spectrum. We implement MWP filter responses with Gaussian, sinc, flat-top, and multiple peaks, as well as demonstrate that tuning of the central frequency. We achieve a minimum 3 dB bandwidth of ∼100 MHz for a sinc-shaped MWP filter, while the maximum out-of-band rejection can be up to ∼30 dB with Gaussian apodization. Our results show that the QDash-MLL is a promising OFC source for developing integrated and reconfigurable MWP filters.

Generation of Reconfigurable Linearly Chirped Microwave Waveforms Based On Fourier domain Mode-Locked Optoelectronic Oscillator

We propose and experimentally demonstrate an approach to generating reconfigurable linearly chirped microwave waveforms (LCMWs) based on a Fourier domain mode-locked (FDML) optoelectronic oscillator (OEO), in which a tunable and reconfigurable microwave photonic filter (MPF) based on a high-Q microring resonator (MRR) is used for mode selection. The MPF can be electrically tuned to achieve Fourier domain mode-locking by using a micro-heater deposited on the MRR. Adjusting the state of polarization of the optical carrier, the MPF is reconfigured and multi-band and multi-format LCWMs can be generated based on the FDML OEO. In the experiment, a dual-chirp LCMW with a bandwidth of 12 GHz consisting of an up-chirped waveform from 7 to 13 GHz and a down-chirped waveform from 19 to 13 GHz is realized, with a time-bandwidth product (TBWP) as high as 1.004×10⁶. By reconfiguring the MPF, we can also obtain LCMWs with a single chirp at C-band (from 4 to 8 GHz), X-band (from 8 to 12 GHz) and Ku-band (from 13 to 19 GHz), respectively. Further, the bandwidth and center frequency of the LCMWs and the dual-chirp LCMWs can be changed by adjusting the magnitude of the driving signal and the laser wavelength, respectively. This kind of reconfigurable LCMWs can be applied to advanced multi-band radar and wireless communication systems.

Numerical Study of a Reconfigurable Multiband Microwave Photonic Filter Using a Tunable Fabry-Perot Filter

Microwave photonic filters (MPFs) with the capabilities of bandwidth reconfigurability and frequency tunability in the GHz range are of great interest in high-speed communications systems. In this paper, we propose a new reconfigurable multiband microwave photonic filter (MPF) using a tunable Fabry–Perot Filter (FPF). It is demonstrated by numerical simulations that the modification of the intermodal separation (δλ) of a multimode laser diode (MLD) by tunable FPF allows for the reconfigurable multi-passband of the MPF. Our simulation results show that our new filter system is promising to communications systems.

Optical phase effects in reconfigurable microwave photonic filters with multiple wavelength input

Microwave photonic filters with a multiple wavelength input are analyzed. A comprehensive model assessing the impact of the phase characteristic of the optical stage is presented from which optimized design rules have been derived. Examples with one, 2 and 3 lasers are provided along with experimental results supporting our findings.

Panda-type few-mode fiber-enabled microwave photonic filter with a reconfigurable finite impulse response.

Leveraging various physical dimensions of optical signals allows significant scaling of the transmission capacity for optical communications. Here we experimentally demonstrate a reconfigurable microwave photonic filter (MPF) enabled by both mode and polarization division multiplexing arising in a Panda-type few-mode fiber. The LP01x, LP01y, LP11x, and LP11y modes are used to realize optical true-time delay lines of the MPF, thus achieving a four-tap finite impulse response (FIR) with a free spectral range of around 2.22 GHz. Due to the employed delay between two orthogonal polarizations, the number of taps arising in its FIR can be doubled. Moreover, the reconfigurable FIR of the MPF can be achieved by loading the corresponding phase pattern onto a spatial light modulator. Finally, the low-pass FIR can be switched to the bandpass FIR due to the introduction of polarization modulation, indicating the flexible manipulation of the FIR for the multi-dimensional division multiplexing enabled MPF.

Design and optimization of a microwave photonic filter exploiting differential mode group delay of a multi-mode fiber

A reconfigurable and application-specific tunable microwave photonic filter having finite impulse response is proposed. The filter exploits the differential mode group delays of linearly polarized modes in a multi-mode fiber to achieve single and multiple high-frequency passband response. The filter taps are realized using a single continuous wave laser source and differential delays among modes that are propagated through a single spool of graded index multi-mode fiber. Depending upon the application requirement, different values of free spectral range of the microwave photonic filter are obtained by employing fiber spools of different lengths. The reconfigurability of the microwave photonic filter is achieved by varying the number of linearly polarized modes. It has been shown that the passband ripple can be reduced by employing higher order spatial modes and unequal power ratio among different modes. The proposed filter enables application-specific free spectra range tunability and reconfigurability along with added advantages of easy implementation and passband optimization.

Manipulation microwave photonic filter response of single microring by using optical frequency combs

We proposed a reconfigurable microwave photonic filter combining the multiple resonances of single microring resonator and optical frequency combs. By manipulating the number of comb lines, the frequency spacing of the comb lines and the relative power between the comb lines, the MPF can be reconfigured from a notch filter with ultra-high rejection ratio to a flat bandstop filter. The mechanism of the reconfigurable microwave photonic filter was clarified theoretically. And in experiments, a notch filter with an ultra-high RF rejection ratio exceed 60 dB and a flat stopband filter with a 10 dB rejection ratio and a stopband ripple less than 0.53 dB were easily reconfigured by manipulating the optical frequency comb lines.

Tunable and reconfigurable microwave photonic filter based on Fourier domain optical processor and cascaded fiber rings

A tunable and reconfigurable microwave photonic filter (MPF) based on a Fourier domain optical processor (FD-OP) and cascaded fiber rings is proposed and demonstrated. A stable and multiple wavelengths source can be realized by using a broadband source and a waveshaper. The multiple wavelengths source with different wavelength spacings is achieved by programming the waveshaper. Two fiber rings of the same structure are cascaded together to achieve a high main sidelobe suppression ratio (MSSR) and a high Q factor. The FD-OP is induced to add additional phase shifts to achieve tunability. When the number of taps is 60, by introducing cascaded two-fiber rings and the FD-OP, the MSSR is 59.356 dB, the maximum Q factor is 470.895 and the 3dB bandwidth of the filter is 0.019 GHz. The simulating results show that the center frequency continuously tuned from 4.47–13.41 GHz. The tunability and reconfigurability of the MPF are well realized.

Discretely programmable microwave photonic filter based on temporal Talbot effects.

We propose and experimentally demonstrate a reconfigurable microwave photonic filter based on temporal Talbot effects. The microwave signal is first uniformly sampled by a train of optical pulses through electro-optic intensity modulation. The sampled optical pulses are then directed to a Talbot-based optical signal processor, consisting of an electro-optic temporal phase modulator and a chromatic dispersion line. The Talbot-based microwave photonic filter (TMPF) exploits the inherent properties of the Talbot self-imaging effect for mitigating pulse-to-pulse intensity fluctuations of optical pulses to transmit some fluctuation frequencies and mitigate or entirely block other microwave spectral components. The output microwave signal is finally reconstructed from the processed optical pulses and the resultant RF response is measured by a network analyzer. The TMPF exhibits an RF response with periodic, symmetric-profile passbands whose center frequency and free spectral range (FSR) are defined by the sampling rate and the dispersion value. The filter passbands can be reconfigured electrically, in discrete steps, by adjusting the modulation function of the phase modulator, i.e., without the need for manual adjustment of the optical components. This enables the capability of selection of specific passbands among the primary passbands. The phase modulation function is provided using an arbitrary waveform generator, with the potential for fast tuning of the filter's spectral response. The bandwidth of the filter passband can also be easily customized by adjusting the sampling pulse's temporal width using an optical bandpass filter. Examples of filter performance in various passband configurations are also presented in the time domain to further validate the operation of the filter.

Reconfigurable Microwave Photonic Filter Based on Long Period Gratings Inscribed in Multicore Fibers

We propose and experimentally demonstrate a reconfigurable finite impulse response microwave photonic filter (FIR-MPF) based on long period gratings (LPGs) inscribed in multicore fibers. By exploiting two dimensions of optical wavelength and space, intentional inter-core signal switching is realized. For the diversity of optical wavelength, we tune the operation wavelength to change the inter-core power coupling according to the wavelength-dependent characteristic of LPGs. On the other hand, for the diversity of space, we use directional bending of LPGs to achieve switchable spatial channel allocation. Both configurations can implement three different two-tap FIR-MPFs individually. We show a promising solution for reconfigurable radio frequency signal processing in potential with low cost and high efficiency.

Reconfigurable and switchable microwave photonic filter based on stimulated Brillouin scattering

A bandwidth reconfigurable and passband switchable filter is proposed and experimentally demonstrated. Based on the same structure, the filter can realize a single broadened response, two passbands with tunable bandwidth or multiband filter. A single broadened response adopts binary phase-shift keying modulation, in which the bandwidth is related to the modulation data pattern. By using the programmable single-sideband suppression carrier signals, the position of the optical lines can be settled down properly and the corresponding arbitrary passbands are constructed. The proposed filter is flexible, which offers possibilities to process multitype microwave signals simultaneously.

Reconfigurable microwave photonic filter based on polarization modulation and an optical filter

We present a reconfigurable microwave photonic filter (MPF) based on polarization modulation and a tunable optical bandpass filter (TOBPF). The MPF is possible to switch between a low-pass and bandpass responses by simply setting a polarizer. Furthermore, the cutoff frequency of the low-pass MPF, the central frequency, and the bandwidth of the bandpass MPF are widely tunable by adjusting the TOBPF. The proposed MPF is theoretically analyzed and experimentally verified.

Advanced RF and microwave functions based on an integrated optical frequency comb source.

We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, wideband tunability, and highly reconfigurable filtering shapes. These results show that our approach is a competitive solution to implementing reconfigurable, high performance and potentially low cost RF and microwave signal processing functions for applications including radar and communication systems.

A reconfigurable microwave photonic filter with flexible tunability using a multi-wavelength laser and a multi-channel phase-shifted fiber Bragg grating

We propose a photonic scheme to realize a reconfigurable microwave photonic filter (MPF) with flexible tunability using a multi-wavelength laser (MWL) and a multi-channel phase-shifted fiber Bragg grating (PS-FBG). The proposed MPF is capable of performing reconfigurability including single bandpass filter, two independently bandpass filter and a flat-top bandpass filter. The performance such as the central frequency and the bandwidth of passband is tuned by controlling the wavelengths of the MWL. In the MPF, The light waves from a MWL are sent to a phase modulator (PM) to generate the phase-modulated optical signals. By applying a multi-channel PS-FBG, which has a series of narrow notches in the reflection spectrum with the free spectral range (FSR) of 0.8 nm, the +1st sidebands are removed in the notches and the phased-modulated signals are converted to the intensity-modulated signals without beating signals generation between each two optical carriers. The proposed MPF is also experimentally verified. The 3-dB bandwidth of the MPF is broadened from 35 MHz to 135 MHz and the magnitude deviation of the top from the MPF is less than 0.2 dB within the frequency tunable range from 1 GHz to 5 GHz.

Chip-based Brillouin radio frequency photonic phase shifter and wideband time delay.

We report a chip-based true-time-delay unit based on stimulated Brillouin scattering that uses an on-off Brillouin gain of 52 dB to enable 4 ns delay over a bandwidth of 100 MHz and a phase shift of ∼200°. To verify these operations, we use a two-tap microwave filter configuration and observed changes in the free spectral range of the filter and shift in the spectrum of the filter. The realization of these functionalities on chip-scale devices is critical for phased-array antennas, multibeam satellites, delay lines, arbitrary waveform generation, and reconfigurable microwave photonic filters.