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We propose a flat-top bandpass microwave photonic filter (MPF) with flexible tunability of the bandwidth and center frequency based on optical nonlinearities in a Fabry–Pérot semiconductor optical amplifier (FP-SOA). Phase-inverted modulation induced by cross-gain modulation (XGM) and optical spectral broadening induced by self-phase modulation (SP...
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Citations
... FP-SOAs by means of predetermined and well defined facet reflectivities enable multiple passes of the signal to be amplified inside the amplifier cavity. This facilitates higher achievable amplification values at the expense of narrowband gain due to the wavelength selectivity determined by the cavity resonances [24], [25]. In our case, the negative bias of the detector-section is crucial to avoid multiple passes of the injected light in the cavity of the SOA-detector and thus operation of the detector as FP-SOA. ...
Heterodyne detection based on interband cascade lasers (ICL) has been demonstrated in a wide range of different applications. However, it is still often limited to bulky tabletop systems using individual components such as dual laser setups, beam shaping elements, and discrete detectors. In this work, a versatile integrated ICL platform is investigated for tackling this issue. A RF-optimized, two-section ICL approach is employed, consisting of a short section typically used for efficient modulation of the cavity field and a long gain section. Such a laser is operated in reversed mode, with the entire Fabry–Pérot waveguide utilized as a semiconductor optical amplifier (SOA) and the electrically separated short section as detector. Furthermore, a racetrack cavity is introduced as on-chip single-mode reference generator. The field of the racetrack cavity is coupled into the SOA waveguide via an 800 nm gap. By external injection of a single mode ICL operating at the appropriate wavelength, a heterodyne beating between the on-chip reference and the injected signal can be observed on the integrated detector section of the SOA-detector.
... The Fabry-Perot (FP) cavity is a basic and important optical device that plays an important role in the design of various types of optical devices and exhibits wide applications. To date, many researchers have devoted considerable effort to the nonlinear dynamic effects of the FP cavity and have developed many novel optical devices, such as interferometers, 1,2 resonators, 3,4 lasers, 5,6 amplifiers, 7,8 optical bistability, 9,10 and other applications. 11,12 In addition, the FP cavity can be combined with other materials or structures to realize a variety of optical devices through the resonance of different optical modes to enhance the field, resulting in refractive index sensing. ...
We numerically investigate the ultrafast dynamic nonlinear mechanism of an Fabry‐Perot (FP) cavity with femtosecond (fs) pumping by the transmission change of an incident signal pulse. The nonlinear effect simulated by a two‐level system model can decrease the dielectric constant. Therefore, the temporally transmitted pulse is compressed owing to the faster phase velocity, and a sloped change in the transmission spectra is observed, which can be explained by the mechanism of pulse deformation. In addition, we stretched a certain part of the temporally transmitted pulse to further demonstrate the deformation of the pulse mechanism. This dynamic nonlinear mechanism based on the FP cavity can not only be used to design new optical devices with ultrafast response times, such as pulse modulators and passive amplifiers, but can also be easily constructed and integrated, which has great practical applications.
... So typical tunable MPFs based on optical filters are introduced into the OEO loop to realize wideband frequency tuning. However, comparing with electronic filter, optical filter usually has a relatively larger bandwidth (typically ∼ GHz or hundreds of MHz) [9,10,11], which prohibited single-mode selection in OEO. Therefore, in order to obtain single-mode oscillation, usually short optical fiber delay must be used, which limits the phase noise of the generated signal. ...
The ability to achieve low phase noise single-mode oscillation within an optoelectronic oscillator (OEO) is of fundamental importance. In the frequency-tunable OEO, the wide microwave photonic filter (MPF) bandwidth is detrimental to select single-mode among the large number of cavity modes, thus leading to low signal quality and spectral purity. Stable single–mode oscillation can be achieved in a large time delay OEO system by harnessing the mechanism from parity-time (PT) symmetry. Here, a PT-symmetric tunable OEO based on dual-wavelength and cascaded phase-shifted fiber gratings (PS-FBGs) in a single-loop is proposed and experimentally demonstrated. Combining the merits of wide frequency tuning of PS-FBG-based MPF and single mode selection completed by the PT-symmetric architecture of the OEO, where the gain and loss modes carried by dual-wavelengths to form two mutually coupled resonators in a single-loop, signals range from 1 GHz to 22 GHz with the low phase noise distributed in −122∼ −130 dBc/Hz at 10 kHz offset frequency are obtained in the experiment.
... As an important building block of MWP technology, microwave photonic filters (MPFs) have attracted a lot of research interests in RF signals processing and have been widely applied in the field of wireless communications, radar, beamforming and radio astronomy [3], [4]. To date, MPFs based on fiber components such as Fabry-Perot filter [5][6][7], fiber Bragg grating [8], [9] and stimulated Brillouin scattering (SBS) [10][11][12] have been reported. However, these MPFs based on the bulky fiber components are relative unstable and lack of reconfigurability [8]. ...
A stopband and passband switchable microwave photonic filter based on the integrated tunable dual ring coupled Mach-Zehnder interferometer has been demonstrated. By using the optical single sideband modulation, the switchable stopband and passband optical responses of the optical filter are one-to-one mapping to the RF spectra. And the center frequency and bandwidth of the switchable microwave photonic filter are both reconfigurable. A frequency tuning range of 4 GHz~25 GHz is obtained, and the bandwidth tuning ranges of the passband and stopband MPFs are 4.54 GHz~9.72 GHz and 3.65 GHz~6.35 GHz, respectively. In addition, a RF rejection ratio about 20 dB is achieved. Compared with the switchable MPFs implemented by non-integrated devices, the proposed switchable MPF provides a simple and low cost way to process radiofrequency signals.
In this paper, an acousto-optic tunable flat top filter is proposed by using one-dimensional coupled-cavity photonic crystal, and two kinds of materials, i.e. magnesium fluoride and tellurium dioxide, are selected. Based on the theory of acousto-optic effect, the thickness and refractive index of one-dimensional coupled cavity photonic crystal acousto-optic medium are changed by varying the ultrasonic frequency. After the parameters of acousto-optic medium are changed, the central wavelength of flat top filter of transmission spectrum shifts toward the short wave direction, thus realizing tunable filtering function. Based on the transfer matrix method and the theory of acousto-optic effect, the theoretical model of the flat top filter is established. The rectangularity, passband bandwidth, insertion loss and tunability of flat top filter are simulated by COMSOL software. The results show that the tuning effect can be achieved by applying a certain frequency of ultrasound in the case of different ultrasonic amplitudes. The decreasing trends of transmittance are basically identical in the process of changing ultrasonic frequency in the case of different amplitudes. When the central wavelength of the flat top filter increases from 1510 nm to 1514 nm, the transmissivity corresponding to the central wavelength increases sharply from 37% to 90%; when the central wavelength of the flat top filter continuously increases to 1562 nm, the transmittance corresponding to the central wavelength increasing gently from 90% to 97% in the case of different amplitudes. Considering the transmissivity required to exceed 90% in the passband of flat top filter and the cost of ultrasonic generator, the ultrasonic wave with an amplitude of 0.4 nm is selected as the research object. The flat top filter with 5–6 nm central wavelength and 1514–1562 nm tunable flat top filter can be realized by applying ultrasonic wave with the frequency in a range of 6–11 MHz. In the tunable range, the highest insertion loss is only 2.23 dB, the lowest is only 0.78 dB, and the lowest rectangularity is 1.4. In a practical flat top filter with machining error within 5 cm, the deviation of center wavelength, rectangularity, insertion loss and passband bandwidth of flat top filter are all very small. The flat top filter has the characteristics of easy design and integration, flat passband, wide tunable range, stable passband bandwidth, low insertion loss and high quality factor. It has important applications in optical communication fields such as optical switch, tunable fiber laser and fiber sensing.
A tunable bandpass microwave photonic filter can be achieved by using a notch ring resonator with optical phase modulation. However, the filter’s out of band rejection ratio and shape factor are limited due to the ring resonator’s residual phase, which can seriously degrade the filter’s performance. By using dual optical carriers and setting their wavelengths oppositely detuned from two resonant frequencies of a notch ring resonator, the residual phase induced by the ring resonator at radio frequencies falling outside the region of the notch stopband is reduced, thus the out-of-band rejection ratio and shape factor of the microwave photonic filter are greatly improved. The proposed microwave photonic filter was both verified theoretically and experimentally. Compared with single optical carrier method, the out-of-band rejection ratio of the filter can be enhanced from 17.7dB to 31.5dB, and the filter’s shape factor is improved from 3.05 to 1.78. Besides, the filter’s frequency and bandwidth can be tuned by varying the wavelengths of the two optical carriers and the ring resonator’s coupling coefficients. Finally, a tunable bandpass microwave photonic filter with frequency tuning range of 2~14GHz, 3dB bandwidth tuning range of 0.673~2.798GHz is demonstrated.
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.
