Tunable Microwave Photonic Filter Research Articles

Wideband-tunable microwave photonic filter using dissipative self-interference microring resonators

We propose and demonstrate a widely tunable microwave photonic filter with controlled frequency agility, bandwidth reconfigurability and flexible switching functions. It is based on the self-interference microring aided by an asymmetric Mach–Zehnder interferometer, breaking the fundamental microring footprint limit and achieving a doubled free spectral range (123.2 GHz) with a strong out-of-band rejection. Simulation results show that a bandpass microwave photonic filter can be tuned across a 60 GHz frequency range with a varied 3-dB bandwidth from 2.13 GHz to 40.7 GHz in a cascaded dual-ring topology. Its RF out-of-band rejection ratio is improved by more than 60 dB in the high frequency region due to a perfect residual phase cancellation. A dual-band notch microwave photonic filter with an extinction ratio of about 50 dB and a frequency tunable range of about 27.7 GHz is also demonstrated, showing its broadly applicability. Our method highlights its suitability to improve chip-scale wideband and high-performance RF receiver systems.

Ultra-Wideband Tunable Microwave Photonic Filter Based on Thin Film Lithium Niobate

In signal processing of the growing semaphore, a microwave photonic filter (MPF) is capable of dealing with high-frequency signals, offering the advantages of high bandwidth, easy tuning, and more. This paper presents an efficient tunable microwave photonic filter that features a wideband tuning capability and narrow-band filtering effect based on the lithium niobate on insulator (LNOI) material platform. A multi-mode waveguide race-track type microring resonator has been designed, along with a thermal electrode that utilizes the thermo-optical effect of lithium niobate to adjust the microring resonator. The packaged device has been tested, with a wideband tunable range of 4.7~38.2 GHz achieved. This allows for cross-band continuous tuning across the C-band to Ka-band range. When supplied with 29.1 mW of electric power, the thermal tuning efficiency reaches 9.2 pm/mW, enabling high-frequency tuning of up to 38.2 GHz. The filter possesses a high resolution, exhibiting a 3 dB bandwidth of 662 MHz.

Ultra-High Peak Rejection, Sub-Gigahertz Narrowband and Bandwidth Tunable Microwave Photonic Filter Based on Silicon Racetrack Resonators

We propose and experimentally demonstrate a notch microwave photonic filter (MPF) with optimized performance (including the sub-gigahertz narrowband, ultra-high rejection ratio and tunable bandwidth) based on two cascaded silicon Mach–Zehnder interferometers (MZI) coupled microring resonators (MRRs). The MRR structure is optimized to obtain a high quality (Q) factor (corresponding to a sub-gigahertz 3dB-bandwidth), adjustable bandwidths and extinction ratios. One ring is designed as the over-coupled state with a π resonant peak phase shift while the other ring performs the under-coupled state with 0 peak phase shift. Under the intensity modulation, an extremely high MPF rejection ratio could be obtained capitalizing the complete interference cancellation technology. Moreover, the MPF bandwidth and central frequency could be flexibly tuned by adjusting the MRR bandwidths and resonant wavelengths, respectively. The experimental results demonstrate the notch MPF response with a narrow 3dB-bandwidth of 185 MHz, an extremely high rejection ratio beyond 70 dB and a 3dB-bandwidth tuning range from 185 MHz to 1.263 GHz. To the best of our knowledge, it is the first time to realize the silicon-based notch narrowband MPFs with the ultra-high rejection ratio (> 70 dB) and a 3dB-bandwidth tuning range from sub-gigahertz to gigahertz level. The proposed silicon-on-insulator-based MPF with competitive performance paves a way for on-chip high-quality microwave signal processing.

Tunable bandpass microwave photonic filter with largely reconfigurable bandwidth and steep shape factor based on cascaded silicon nitride micro-ring resonators.

Bandpass microwave photonic filter (MPF) can be achieved based on the well-known phase to intensity conversion method by using phase modulation and single micro-ring resonator (MRR) notch filter. Since MRR could introduce residual phase in handling one optical sideband, the out-of-band radio frequency (RF) rejection ratio and the shape factor of the bandpass MPF are very limited. Here, by introducing another MRR to handle the other optical sideband, the residual phase can be greatly suppressed, thus the filter's performance can be greatly improved. The proposed bandpass MPF was both verified theoretically and experimentally. Compared with the single MRR, the out-of-band RF rejection ratio and the shape factor were improved by 20 dB and 1.67, respectively. Furthermore, the bandpass MPF's bandwidth is reconfigurable by adjusting the optical carrier's frequency or the two MRRs' amplitude coupling coefficients. The bandpass MPF's center frequency is also tunable by changing the resonant wavelengths of two MRRs in the opposite direction simultaneously. Experimentally, bandwidth reconfiguration from 0.38 GHz to 15.74 GHz, the shape factor optimization from 2 to 1.23, and frequency tuning from 4 GHz to 21.5 GHz were achieved. We believe that the proposed bandpass MPF has great potential for microwave photonic signal processing.

A tunable microwave photonic filter based on hole-assisted graded-index few mode fiber with uniform differential modal group delay

A tunable delay-line microwave photonic filter (MPF) based on hole-assisted graded index few mode fiber (HGI-FMF) is proposed. The HGI-FMF is designed with low mode crosstalk, low nonlinear effect and multiple modal groups. In particular, the designed HGI-FMF shows uniform differential modal group delay (MGD) to form finite impulse response (FIR) MPF. The uniform differential MGD is tunable with wavelength, which results in tunable MPF response. The free spectrum range (FSR) of MPF is continuously tunable from 11.73 GHz down to 10.84 GHz with 120 m designed HGI-FMF as the optical source is tuned from 1530 nm up to 1630 nm. The main sidelobe suppression ratio (MSSR) of the 4-taps filter is larger than 9.93 dB, and the 3 dB bandwidth is around 2.62 GHz.

Automatic Power Control for a Frequency Tunable Optoelectronic Oscillator

Automatic power control for a frequency tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The OEO is implemented by a tunable microwave photonic filter using a phase-shifted fiber Bragg grating (PS-FBG) for frequency-tuning. Taking advantage of the automatic power control (APC), the problem of large power fluctuation in the OEO output signal during the frequency tuning or interfered by the external disturbance can be significantly improved and the functionality of equalization is realized. By adjusting the DC reference voltage of the automatic power control circuit, the tuning of RF signal power is conveniently achieved. To the best of the authors’ knowledge, this is the first time that the output power regulation of OEO has been implemented. For verification, the low-cost OEO at 2–7 GHz is established. Experiment results show that the output power fluctuation of less than 3 dB and a phase noise of −113 dBc/Hz@10 kHz are achieved.

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.

Investigation of a Tunable Microwave Photonic Filter Based on an Acetylene Reference Cell

Introduction.Recently, the development of tunable microwave photonic filters has attracted great scientific and practical interest. Such microwave photonic filters are a good alternative to traditional electrical solutions, due to low losses, wide operating frequency range and such filters can be easily integrated into various telecommunication systems. By using an acetylene reference cell and a laser with tunable wavelength can make it possible to create tunable microwave photonic filter with wide operating frequency range.Aim.Investigation of the characteristic of a tunable microwave photonic filter based on an acetylene reference cell, as well as research possible solution to reduce losses in filter bandwidth; numerical simulation of microwave photonic filter characteristics.Materials and methods.Experimental study was carried out on an experimental prototype of a tunable microwave photonic filter. The filter consisted of a laser with a tunable wavelength, a phase modulator, an acetylene reference cell, an optical fiber connecting the gas cell with a photodetector, and a photodetector. Theoretical study was carried out by modeling of the transmission characteristics of the microwave photonic filter.Results.Experimental transmission characteristics of a tunable microwave photonic filter were obtained. The tuning of the filter bandwidth by tuning laser wavelength was studied. Modeling of transmission characteristics of microwave photonic filter was performed. Possible solution to reduce losses in filter bandwidth was proposed.Conclusion.A tunable microwave photonic filter based on an acetylene reference cell is proposed. Losses in the filter bandwidth was about −30 dB. Using high-power laser and a photodetector with a high photocurrent can reduce losses in the filter bandwidth.

Tunable optoelectronic oscillator based on a high-Q microring resonator

This paper proposes a tunable optoelectronic oscillator (OEO) by using a silicon nitride high-Q microring resonator (MRR) with a Q value of 4.36 × 105. Inserting the high-Q MRR into a phase-modulated link, an 8–38 GHz tunable microwave photonic filter (MPF) is realized with a 3-dB bandwidth of ∼610 MHz. Based on the tunable MPF, a tunable OEO is established. The frequency range of the OEO is 14.60 to 25.65 GHz, and the measured phase noise of the 25.65-GHz oscillation signal is -88 dBc/Hz@10 kHz.

On-chip tunable parity‐time symmetric optoelectronic oscillator

Parity‐time (PT) symmetry breaking offers mode selection capability for facilitating single‐mode oscillation in the optoelectronic oscillator (OEO) loop. However, most OEO implementations depend on discrete devices, which impedes proliferation due to size, weight, power consumption, and cost. In this work, we propose and experimentally demonstrate an on-chip tunable PT‐symmetric OEO. A tunable microwave photonic filter, a PT‐symmetric mode‐selective architecture, and two photodetectors are integrated on a silicon‐on‐insulator chip. By exploiting an on‐chip Mach–Zehnder interferometer to match the gain and loss of two mutually coupled optoelectronic loops, single‐mode oscillation can be obtained. In the experiment, the oscillation frequency of the on-chip tunable PT‐symmetric OEO can be tuned from 0 to 20 GHz. To emulate the integrated case, the OEO loop length is minimized, and no extra-long fiber is used in the experiment. When the oscillation frequency is 13.67 GHz, the single‐sideband phase noise at 10-kHz offset frequency is −80.96 dBc / Hz and the side mode suppression ratio is 46 dB. The proposed on-chip tunable PT‐symmetric OEO significantly reduces the footprint of the system and enhances mode selection.

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 kilohertz microwave photonic bandpass filter based on backscattering in a microresonator.

A tunable microwave photonic bandpass filter (MPBPF) with a kilohertz bandwidth based on the backscattering mode of a silica microsphere resonator is proposed and experimentally demonstrated. In this work, an ultrahigh-quality-factor microsphere resonator is used to generate a radio frequency bandpass response with a bandwidth of 600 kHz. Meanwhile, scattering-induced coupling between the clockwise mode and the counterclockwise mode is introduced to reduce the number of resonance modes, and a single backscattering mode which has a high extinction ratio is obtained. Therefore, an MPBPF with a tuning range of 40 GHz and a rejection ratio of 16.9 dB is realized. This MPBPF possesses advantages such as ultranarrow bandwidth, large tuning range, and compactness, and shows great potential for microwave photonic applications.

Photonic-assisted frequency downconverter with self-interference cancellation and fiber dispersion elimination based on stimulated Brillouin scattering.

A photonic-assisted frequency downconverter with self-interference cancellation and fiber dispersion elimination is proposed for in-band full-duplex (IBFD) radio-over-fiber (ROF) systems based on stimulated Brillouin scattering. In this work, a dual-polarization Mach-Zehnder modulator (DPol-MZM) is employed to cancel the self-interference signal in the optical domain, thus the proposed system has a large operation bandwidth without the limitation of the electrical bottleneck. Meanwhile, a widely tunable microwave photonic filter (MPF) based on stimulated Brillouin scattering (SBS) is constructed to perform carrier-suppressed single-sideband modulation of LO. Therefore, the proposed photonic frequency downconverter is naturally free from fiber dispersion. Furthermore, thanks to the characteristics of the SBS-based MPF, such as large out-of-band rejection ratio, high resolution and wideband tunability, the proposed system has a high flexibility and downconversion efficiency, which is of great significance for IBFD ROF systems.

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.

Widely tunable frequency-doubling optoelectronic oscillator using a polarization modulator and a phase-shifted fiber Bragg grating

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

Tunable narrowband microwave photonic filter based on brillouin fiber oscillator

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

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.

Tunable microwave photonic filters based on double-sideband modulation and linear chirped fibre Bragg gratings

A continuously tunable microwave photonic filter with large dispersion is proposed by using bilaterally modulated and linearly chirped fibre Bragg gratings (LCFBG). A pair of LCFBGS were reverse-inserted into two arms of a Mach–Zehnder interferometer (MZI) to make a dual-tap band-pass filter. The free spectral range (FSR) can be adjusted by setting the basic time difference between two taps, adjusting the wavelength of the optical carrier and reflecting the microwave signal to different physical positions in the LCFBGs. A continuous tunability of the filter is validated. In our scheme, the FSR is adjusted from 33.6 MHz to 37.6 MHz with sub-megahertz accuracy and the adjustable range covering the whole range of over 100 MHz.

Microwave Photonic Filter by Using Recirculating Frequency Shifter to Generate Optical Frequency Comb

In this paper, a continuously tunable microwave photonic filter (MPF) with optical frequency comb (OFC) generated by recirculating frequency shifter (RFS) based on an inphase/quadrature (I/Q) modulator is proposed and experimentally demonstrated. A chirped fiber Bragg grating (CFBG) is inserted into the RFS loop to act as an optical bandpass filter. The central frequencies of two passbands of the MPF in 20 GHz range have been tuned linearly from 7.67 GHz to 9.04 GHz, and 15.34 GHz to 18.03 GHz, respectively by changing the frequency of the driving microwave signal onto the I/Q modulator from 20 GHz to 17 GHz. When the frequency of the driving microwave signal is decreased, OFC with smaller tone spacing is generated, and then the MPF's passbands move to higher frequency. So that, the proposed MPF's passbands with high frequencies can be achieved by applying driving microwave signal with low frequency to generate the OFC. By varying the bandwidth of the CFBG, the number of comb lines can be changed, which results in different bandwidth of the MPF's passband. Furthermore, in our experiment by carefully adjusting bias voltage of the Mach-Zenhder modulator, when the frequencies of driving microwave signal onto the I/Q modulator is 20 GHz and 18 GHz, one passband in the 20 GHz range can be suppressed at the frequency of 15.34 GHz, and 8.52 GHz, respectively.

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.