Single Passband Microwave Photonic Filter Research Articles

A single passband microwave photonic filter with enhanced flat top and shape factor based on tunable optical bandpass filter and fiber Bragg gratings

A single passband microwave photonic filter with enhanced flat top and shape factor based on tunable optical bandpass filter and fiber Bragg gratings

High-Q cascaded single-passband microwave photonic filter based on an optical-electrical feedback loop.

A cascaded microwave photonic filter refers to a microwave photonic filter (MPF) with higher performance obtained by cascading a MPF with two different structures. A high-Q cascaded single-passband MPF is proposed experimentally based on stimulated Brillouin scattering (SBS) and an optical-electrical feedback loop (OEFL). In this experiment, the pump light of SBS is provided by a tunable laser. The Brillouin gain spectrum generated by the pump light is used to amplify the phase modulation sideband, and the narrow linewidth OEFL is subsequently used to compress the passband width of the MPF. By carefully adjusting the pump wavelength and tuning the tunable optical delay line, stable tuning can be achieved for a cascaded single-passband MPF with a high-Q value. The results have demonstrated that the MPF has characteristics of high-frequency selectivity and a wide frequency tuning range. Meanwhile, the filtering bandwidth is up to 300kHz, the out-of-band suppression is more than 20dB, the maximum Q-value is 5.333×104, and the center frequency tuning range is 1-17GHz. The cascaded MPF proposed not only achieves a higher Q-value, but also has the advantages of tunability, a high out-of-band rejection ratio, and strong cascaded ability.

High-Sensitivity and High-Resolution RI Sensor With Ultrawide Measurement Range Based on NCF With Large Offset Splicing and MPF Interrogation

A high-sensitivity and high-resolution refractive index (RI) sensor with ultrawide measurement range based on no core fiber (NCF) with large offset splicing and microwave photonic filter (MPF) interrogation is demonstrated theoretically and experimentally for the first time. In the sensor, an inline Mach–Zehnder interferometer (MZI) based on NCF with large offset splicing is used as the sensing head, and a single-passband MPF is designed to interrogate the sensing signal. Compared with the traditional interrogation in optical domain, the MPF interrogation converts the periodic interference pattern in optical spectrum into the nonperiodic bandpass frequency response in radio frequency (RF) domain, so the measurement range is unlimited in principle. Owing to the large offset splicing in the inline MZI structure, the sensitivity of the sensor as high as −1.1054 GHz/RIU is obtained in the experiment. More importantly, MPF interrogation improves the resolution by an order of magnitude to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9\times10$ </tex-math></inline-formula> −7 RIU. Meanwhile, the sensitivity and the resolution of the sensor are easily adjusted by changing the length of dispersive media. The high sensitivity and high resolution of the sensor have potential applications in ultralow concentration biochemical detection field.

Ultra-narrow bandwidth and large tuning range single-passband microwave photonic filter based on Brillouin fiber laser

A scheme to perform ultra-narrow filter bandwidth and high frequency selectivity microwave photonic filter (MPF) with wide tuning range is proposed and experimentally demonstrated. The ultra-narrow bandwidth of the MPF is implemented by a Brillouin laser resonator, which is composed of a cascaded ring Fabry–Pérot (CR-FP) resonator formed by a main cavity with a cavity length of 100 m and a secondary cavity with a cavity length of 10 m. A Brillouin laser resonator is formed by the main cavity to obtain an extremely narrow comb-shaped Brillouin gain spectrum. The Vernier effect of the double ring cavity can effectively suppress the side modes, thereby realizing the narrow linewidth Brillouin laser filtering. Besides, two identical tunable lasers provide the stimulated Brillouin scattering (SBS) pump light and optical carrier signal for this device respectively. After the interaction between the Brillouin gain spectrum and the optical modulation signal, the filter passband can be stably tuned by simply changing the wavelength of SBS pump light. The experimental results show that the microwave photonic filter can be stably tuned in the frequency range of 0–20 GHz, the out-of-band rejection ratio is about 20 dB, and the minimum 3 dB bandwidth is about 114 Hz.

Brillouin-assisted frequency-tuning-range-extended and passband-selected microwave photonic filter based on DPol-DPMZM

A frequency-tuning-range-extended and passband-selected microwave photonic filter (MPF) based on dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM) is proposed and experimentally demonstrated. The upper DPMZM is biased to serve as an equivalent phase modulator, while the lower DPMZM is selectively biased to generate different modulated sideband for pump wave, and then different passband frequency response is selectively realized based on the stimulated Brillouin scattering effect. By using the upper and lower sidebands of carrier-suppression single sideband for pump wave successively, the frequency tuning range of the single-passband MPF can be extended by a value of Brillouin frequency shift, comparing with only one sideband is used. A single-passband MPF with a frequency tuning range of 1.43–19.43 GHz is experimentally obtained, while only a single-tone RF with a frequency range of DC-9 GHz is used. The double-passband MPF with equal passband magnitude and frequency interval tuned is also experimentally achieved.

Ultrahigh spectral resolution single passband microwave photonic filter.

Microwave photonic filters (MPFs) with only one ultra-narrow passband are able to provide high frequency selectivity and wide spectral range, and they are of great importance in radio-frequency (RF) signal processing. However, currently all MPFs are limited by trade-offs between key parameters such as spectral resolution and range, tunability, and stability. Here, we report the first demonstration of a single passband MPF with unprecedented performance including ultrahigh spectral resolution of 650 kHz, 0-40 GHz spectral range, and high stability of center frequency drifting within ±50 kHz. This record performance is accomplished by breaking the amplitude equality of a phase-modulated signal via a Brillouin dynamic grating (BDG) which has an ultra-narrow reflection spectrum of sub-MHz. The results point to new ways of creating high performance microwave photonic systems, such as satellite and mobile communications, radars, and remote-sensing systems.

Trace copper detection using in-line optical fiber Mach-Zehnder interferometer combined with an optoelectronic oscillator.

We experimentally demonstrate a novel optical fiber chemosensor for trace Cu2+ ions detection that is implemented by using an in-line optical fiber Mach-Zehnder interferometer (MZI) in conjunction with an optoelectronic oscillator (OEO). The MZI is fabricated by lateral offset splicing a section of D-shaped fiber between two single-mode fibers. It splices the broadband optical source into a sinusoidal-shaped light, which can form a single passband microwave photonic filter (MPF) by combining the Mach-Zehnder modulator, a segment of fiber and a photodetector. The center frequency of the MPF, determined by the free spectra range of MZI, is affected by the solution concentration. Incorporating the MPF in the OEO sensor, the oscillation frequency is determined by the solution concentration. Therefore, we can estimate the solution concentration by measuring the microwave frequency change. We carry out a proof to concept experiment. High sensitivity Cu2+ ions concentration sensing with sensitivity of 13 Hz/(μM/L) is achieved. The maximum measurement error of concentration obtained is within 1.38 μM/L. The proposed sensor has merits of high interrogation speed, simple operation, high sensitivity and accuracy, offering the potentials in a wide range of biological application scenarios.

High-resolution polymer optical fibre humidity sensor utilizing single-passband microwave photonic filter

Water affinity property of the polymer optical fibre (POF) makes it possible for humidity sensing. In this paper, we propose and experimentally demonstrate a high-resolution POF-based humidity sensor that utilizes microwave photonic interrogation technique. A Mach-Zehnder interferometer (MZI) of one arm inserted with the POF is used as the interrogator, and a single-passband microwave photonic filter is developed for interrogation. The change of the humidity is then converted to the frequency shift of the radio-frequency (RF) filter’s passband. A humidity sensor with sensitivity of 84 MHz/RH% and resolution of 0.0119 RH% is achieved in the experiment. Thanks to the introduction of microwave photonic interrogation technique, the proposed humidity sensor owns the abilities of high resolution and anti-vibration. These advantages make it suitable for the potential applications with high precision requirement or in an unstable environment.

A Sensing Interrogation System for Sagnac Interferometer With Polarization Maintaining Fiber Utilizing Microwave Photonic Filtering Technique

In this paper, a sensing interrogation scheme for Sagnac interferometer (SI) with polarization maintaining fiber (PMF) by using microwave photonic filtering technique has been theoretically analyzed and experimentally demonstrated. In our experiment, the SI acts as the sensing element as well as a spectrum slicer in the single-passband microwave photonic filter (MPF). The central frequency of the MPF’s passband moves to lower frequency when the temperature is increased. Hence, the measurands can be demodulated by monitoring the central frequency of the MPF’s passband in Radio Frequency (RF) domain. Comparing with the interrogation by tracking dip wavelength of the interference patterns in the optical domain and using the product of birefringence and the length of PMF in the SI structure for interrogation, the proposed interrogation system converts the wavelength variations of the interferometer patterns in optical domain to the frequency changes in electronic domain directly by utilizing opto-electronic devices, and thus has an unlimited measurement range, less limitations by resolution limitation of measuring instruments and less cross-sensitivity problems.

High-precision strain-insensitive temperature sensor based on an optoelectronic oscillator.

We have proposed and experimentally demonstrated a high-precision and strain-insensitive temperature sensor based on an optoelectronic oscillator (OEO). The oscillation frequency of the OEO is determined by the single passband microwave photonic filter (MPF) by using stimulated Brillouin scattering (SBS). The sensing fiber, which acts as the SBS gain medium, is exposed to temperature variations. The Brillouin frequency shift (BFS) changes along with the temperature. Since the central frequency of the MPF is a function of the BFS, the oscillation frequency of the OEO is varied. Besides, due to the mode competition in the OEO, the influence of the strain is eliminated. Thus, the temperature variations can be estimated through measuring the oscillation frequency. We carry out a proof-to-concept experiment. Temperature sensing with a high sensitivity of 1.00745 MHz/°C is achieved. The maximum measurement error of temperature obtained is within ± 0.5 °C. The proposed scheme has merits of simplicity and compact configuration. In addition, the proposed temperature sensor can realize quasi-distributed measurement by utilizing wavelength division multiplexing (WDM).

Wideband tunable single passband microwave photonic filter based on optical injection

Optical injection is an effective way to generate a tuned microwave photonic filter (MPF). However, the tuning range of the optical injection-based MPF is limited by the nonlinear dynamics and the nonideal roll-off optical filter. To enlarge the tuning range of the MPF, a polarization modulated optical signal injection distributed feedback semiconductor laser is employed. The method is free from the nonlinear dynamics and the nonideal roll-off optical filter. The experimental result shows that the proposed MPF can be tuned from 0 to 40 GHz by directly tuning the center wavelength of the optical carrier. The tuning range can be increased if polarization modulator and photodetector with larger bandwidth are exploited. To the best of our knowledge, this is the largest frequency tuning range of optical injection-based MPF.

Single passband microwave photonic filter with widely tuning range based on optical injected distributed feedback semiconductor laser

A novel widely tunable single passband microwave photonic filter (MPF) is proposed and experimentally demonstrated, which is based on a carrier-suppressed double sidebands (CS-DSB) optical signal injected into an distributed feedback (DFB) laser. A polarization modulator (PolM) and a polarization beam splitter (PBS) are exploited to generate the CS-DSB optical signal. When the CS-DSB optical signal is injected into the DFB laser, due to the frequency selective gain feature of optical injected DFB laser, one sideband of the CS-DSB optical signal is selected and amplified. Beating the amplified sideband with the optical carrier, the gain spectrum of the DFB laser is mapped to the frequency response of the MPF. The MPF can be tuned by adjusting the wavelength of the DFB laser. Experiment results show that the MPF can be tuned from 0 to 40 GHz by changing the working temperature of the DFB laser.

Fast-Switching Microwave Photonic Filter Using an Integrated Spectrum Shaper

A fast-switching single passband microwave photonic finite impulse response filter (MPF) using an incoherent broadband optical source (BOS) and an integrated spectrum shaper is proposed and experimentally demonstrated. The key component of our proposed MPF is the silica-on-silicon integrated spectrum shaper, which is used to slice the spectrum of the BOS. The performance of the integrated spectrum shaper is measured in terms of time delay, power consistency, and switching speed. A number of spectral shapes with the free spectrum range from 1.88 to 0.058 nm can be flexibly switched by changing the driving voltage of the optical switches. With the dispersion compensating fiber as dispersion medium, a fast-switching MPF with the switching speed up to 1.4-KHz is demonstrated in a wide tunable range from 1 to 12 GHz and the sidelobe suppression is up to 35 dB, which shows a great agreement with the theoretical result.

Microwave Photonic Signal Processing and Sensing Based on Optical Filtering

Microwave photonics, based on optical filtering techniques, are attractive for wideband signal processing and high-performance sensing applications, since it brings significant benefits to the fields by overcoming inherent limitations in electronic approaches and by providing immunity to electromagnetic interference. Recent developments in optical filtering based microwave photonics techniques are presented in this paper. We present single sideband modulation schemes to eliminate dispersion induced power fading in microwave optical links and to provide high-resolution spectral characterization functions, single passband microwave photonic filters to address the challenges of eliminating the spectral periodicity in microwave photonic signal processors, and review the approaches for high-performance sensing through implementing microwave photonics filters or optoelectronic oscillators to enhance measurement resolution.

High-Sensitivity Sensing for Relative Humidity and Temperature Based on an Optoelectronic Oscillator Using a Polyvinyl Alcohol-Fiber Bragg Grating-Fabry Perot Filter

In this paper, a relative humidity (RH) and temperature sensing scheme with high sensitivity based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. A polyvinyl alcohol-Fiber Bragg grating-Fabry Perot (PVA-FBG-FP) filter, in which the PVA film acts as an RH-strain transducer, is employed in the OEO to implement a single passband microwave photonic filter (MPF). In the OEO loop, the oscillating frequency is determined by the center frequency of the PVA-FBG-FP filter and the laser source. When the external RH or temperature changes, the central wavelength of PVA-FBG-FP filter is shifted, leading to the change in the center frequency of the MPF. By simply monitoring the variation of oscillating frequency using an electrical spectrum analyzer or a digital signal processor, the measurements for the RH and temperature can be achieved. In the experiment, the sensitivities of the RH and temperature are measured to be as high as 508.3 MHz/%RH and 1.8118 GHz/°C, respectively.

Bandwidth-reconfigurable single-passband microwave photonic filter based on stimulated Brillouin scattering

A bandwidth-reconfigurable filter is necessary to meet the need of growing communication capacity and signal coverage frequency range. The stimulated Brillouin scattering (SBS) gain spectrum as a filter passband is used to extract desired microwave signals. Due to the fact that the passband is formed by mapping the Brillouin gain spectrum, bandwidth reconfigurability can be implemented by changing Brillouin gain linewidth. In this paper, a scheme using a 5-lines optical comb acting as a Brillouin pump is experimentally demonstrated. The spectrum of the 5-lines optical comb is extended by a binary phase shift keying (BPSK) pulse modulated signal. Experiments have shown that the 3-dB and 20-dB bandwidths of the filter are 196 MHz and 257 MHz, respectively, and its 20-dB shape factor is 1.31. The passband ripple is ~3.5 dBm with stop-band rejection of 20 dBm under 15 dBm optical pump power.

Ultrahigh-Q and tunable single-passband microwave photonic filter based on stimulated Brillouin scattering and a fiber ring resonator.

A scheme to perform ultrahigh-Q and single passband microwave photonic filter (MPF) with tunability is proposed and experimentally demonstrated. The single passband of the MPF is implemented by the stimulated Brillouin scattering (SBS) in an optical fiber. The ultrahigh-Q of the MPF is realized due to the ultra-narrow resonant linewidth of the fiber ring resonator, which compresses the bandwidth of the SBS dramatically. A MPF with a single passband and an ultra-narrow 3dB bandwidth of 825±125 kHz over the wide center frequency tuning range of 2-16GHz are achieved. The MPF also shows high out-of-band suppression exceeding 25dB and small amplitude fluctuation of ±1.8 dB within the tuning range. The maximum Q-factor of the MPF is 17778. To the best of our knowledge, this is the highest Q single-passband MPF reported to date, with wide tunability, high out-of-band suppression, and a simple structure.

Tunable Single-Passband Microwave Photonic Filter Based on Integrated Optical Double Notch Filter

A novel-integration-based technique employing a cascaded pair of microring resonators on silicon-on-insulator platform that can achieve a tunable single-passband microwave photonic filter with improved shape factor and extinction ratio is presented. It is based on an integrated optical double notch filter using a cascaded pair of nonidentical microring resonators, in conjunction with optical phase modulation. This results in minimal net phase being introduced by the overall filter at radio frequencies falling outside the region of the notch stopband, thus enabling nearly full antiphase cancellation of the modulation sidebands, which results in the achievement of an improved filter shape factor and extinction ratio. Additionally, it features a bandwidth that is directly determined by the difference between the bandwidths of the two optical notch filters, rather than by their absolute individual bandwidths. Experimental results have verified the concept, and have demonstrated a single-passband filter having tuning range of 6–17 GHz, a shape factor of 1.78, shape-invariant tuning, and a good out-of-band suppression ratio of approximately 20 dB throughout the entire tuning range.

Wideband tunable optoelectronic oscillator based on a microwave photonic filter with an ultra-narrow passband.

A novel wideband tunable optoelectronic oscillator based on a microwave photonic filter (MPF) with an ultra-narrow passband is proposed and experimentally demonstrated. The single-passband MPF is realized by cascading an MPF based on stimulated Brillouin scattering and an infinite impulse response (IIR) MPF based on an active fiber recirculating delay loop. The measured full width at half-maximum bandwidth of the cascaded MPFs is 150kHz. To the best of my knowledge, this is the first time realizing such a narrow passband in single-passband MPF. The oscillation frequency of the OEO can be tuned from 0 to 40GHz owing to the wideband tunability of the MPF. Thanks to the ultrahigh mode selectivity of the IIR filter, the mode hopping is successfully suppressed. A stable microwave signal at 8.18GHz is obtained with a phase noise of -113 dBc/Hz at 10kHz, and the side mode noise is below -95 dBc/Hz. The signal-to-noise ratio exceeds 50dB during the tuning process.

Analysis of Performance Optimization for a Microwave Photonic Filter Based on Stimulated Brillouin Scattering

A single passband microwave photonic filter (MPF) based on stimulated Brillouin scattering (SBS) is analyzed and experimentally demonstrated. The proposed MPF can be tuned over a dramatically large frequency range, which overcomes the disadvantage in previously reported schemes based on SBS that the frequency tuning range is limited within two folds of the Brillouin frequency shift. The single passband MPF is obtained by enhancing the amplitude of the microwave passband generated by SBS gain while suppressing the amplitude of the microwave passband generated by SBS loss through optimizing the key parameters of the SBS process, including the pump power, the length of high nonlinear fiber, and the polarization states of the pump and signal waves. A theoretical model is established to describe the operation principle of the SBS-based MPF and illustrate the mechanism for the single passband, and an experiment is carried out to verify the theoretical analysis. In the experiment, the central frequency of the single passband MPF can be tuned from 0 to 40 GHz, which is only limited by the bandwidth of the adopted electro-optic modulator and photodetector. The main to secondary sidelobe ratio can reach 55 dB and the full width at half-maximum bandwidth is 16 MHz. The achieved MPF is specifically suitable for applications in ultrahigh selective filtering.