Dual-passband Microwave Photonic Filter Research Articles

Improving the Sensitivity of Temperature Measurement Based on a Dual-Passband Microwave Photonic Filter

In this article, a dual-passband microwave photonic filter (MPF) is proposed and experimentally demonstrated for high-precision temperature sensing. A pair of parallel Mach–Zehnder interferometers (MZIs) sharing the same sensing arm is used to splice the broadband optical light source (BOS). Since the interference spectrum in the optical domain is a combination of two MZIs with different free spectrum ranges (FSRs), an MPF with two passbands is successfully generated in the microwave domain. The kernel of this scheme is precisely controlling the length of the sensing arm between the lengths of the upper arm and lower arm. When the temperature applied to the sensing arm changes, the FSR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${s}$ </tex-math></inline-formula> of two MZIs vary contrarily, resulting in the two passbands of the MPF shifting in the opposite direction. By tracking the central frequency difference between two passbands, the sensitivity can be enhanced. Experimental results show that with the increased temperature, the first passband moves to the lower frequency range, whereas the second passband shifts to the higher frequency range. The central frequency of an arbitrary passband is proportional to the temperature. The sensitivity is 16.81 ± 4.73 MHz/° by tracking the central frequency of a single passband, while, by recording the central frequency difference between two passbands, the sensitivity can be improved to 33.55 ± 4.17 MHz/°, which is twice over a single passband.

High-Speed Switchable Dual-Passband Microwave Photonic Filter With Dual-Beam Injection in an SMFP-LD

In this paper, a high-speed switchable dual-passband microwave photonic filter (MPF) using a single mode Fabry-Perot laser diode (SMFP-LD) is proposed and experimentally demonstrated. Benefiting from the wavelength selective amplification in the SMFP-LD, the +1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> sideband of two external beams injected after phase modulation can be amplified in the gain spectrum of the SMFP-LD. Hence, an MPF with two tunable passbands is generated. The switching of the generated passbands is obtained through the switching signal of 1 Gbps applied to the modulator, which controls the power of one of the external beams. By properly setting the external beams’ injection parameters, the passbands of MPF can switch from single passband to no passband, single passband to dual passband, and one passband to another passband. In this experiment, the maximum center frequency and tuning range of the passbands is 45.0 GHz and 35.0 GHz, respectively. The out-of-band rejection ratio and 3 dB bandwidth of the proposed filter are 29.62 dB and 83 MHz, respectively.

Dual-Passband Microwave Photonic Filter Based on a Directly Modulated Microcavity Laser

An approach to achieving a highly selective and stable dual-passband microwave photonic filter (MPF) is presented. The dual-passband MPF is realized based on the phase-to-intensity modulation conversion by stimulated Brillouin scattering (SBS). The core of the proposed scheme is a two-tone pump generation by a directly modulated microcavity laser instead of two individual lasers or electro-optic modulators (EOMs), which makes the system relatively simple and stable. The center frequency of the MPF can be tuned from 0 to 20 GHz by adjusting the modulation frequency of the microcavity laser, where the center frequencies of the two passbands are related. The 3-dB bandwidth and the out-of-band rejection ratio of each passband are about 38 MHz and lager than 28.5 dB, respectively. The frequency stability of the MPF is also verified experimentally.

Frequency-Sweep-Range-Reconfigurable Complementary Linearly Chirped Microwave Waveform Pair Generation by Using a Fourier Domain Mode Locking Optoelectronic Oscillator Based on Stimulated Brillouin Scattering

A Fourier domain mode locking (FDML) optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is proposed to generate complementary linearly chirped microwave waveform (LCMW) pairs with flexibly-reconfigurable frequency sweep range and excellent frequency sweep linearity. The FDML OEO involves an SBS-based dual-passband microwave photonic filter with its two passbands linearly and fast scanning in the opposite direction at an identical frequency sweep rate, which is realized by using a single laser source to obtain a fast frequency sweep probe light and a two-tone pump light through electro-optic modulation. A proof-of-concept experiment is carried out to demonstrate the proposed scheme. In the experiment, frequency-sweep-range-reconfigurable complementary LCMW pairs with period of 20.5 μs are generated in the range of 5 GHz to 18 GHz, where the maximum time-bandwidth product and chirp rate are 82000 and ±0.195 GHz/µs, respectively. Most importantly, the frequency sweep linearity is measured to be 1.76%, which is much better than the results obtained in the existing FDML OEOs.

A Tunable Dual-Passband Microwave Photonic Filter Based on Optically Injected Distributed Feedback Semiconductor Lasers and Dual-Output Mach-Zehnder Modulator

In this paper, a novel approach to achieving a wideband tunable dual-passband microwave photonic filter (MPF) is proposed based on optical-injected distributed feedback (DFB) semiconductor lasers and a dual-output Mach–Zehnder modulator (DOMZM). The fundamental concepts for realizing the MPF are the wavelength-selective amplification effect and the period-one oscillation state under optically injected DFB lasers. These effects provide a widely tunable range of center frequency, along with high flexibility and low insertion loss. The proposed MPF is experimentally demonstrated, showing that the dual-passband center frequency in the MPF can be tuned independently from 19 to 37 GHz by adjusting the detuning frequency and injection ratio. Meanwhile, the insertion loss of the system is about 15 dB when there is no optical or electrical amplifier in the MPF link. The out-of-band suppression ratio of the MPF is more than 20 dB, which can be improved by adjusting the power of the two optical signals.

Passband-Switchable and Frequency-Tunable Dual-Passband Microwave Photonic Filter

A passband-switchable and frequency-tunable dual passband microwave photonic filter (MPF) implemented using a broadband optical source (BOS) in a delay-line configuration is proposed and experimentally demonstrated. In the proposed MPF, the BOS is sliced by a Mach-Zehnder interferometer (MZI), in which a phase modulator (PM) is incorporated in the upper arm. The phase-modulated light signal combined with an unmodulated light at the output of the MZI is sent through a dispersive delay line and detected at a photodetector (PD). The entire operation is equivalent to a microwave bandpass filter with its central frequency determined by the time delay difference between the two arms of the MZI. To implement a dual passband MPF, a second lower arm with a different arm length corresponding to a different time delay is added. The independent switchability of the passband is realized by controlling the polarization state of the light wave in each of the lower arms to be parallel or orthogonal with that of the upper arm. The independent frequency tunability is achieved by tuning the time delay of each of the lower arms. The proposed MPF is experimentally evaluated. A dual-passband MPF with independent passband switchability and independent frequency tunability is demonstrated. The results show that each of the two passbands can be switched on and off with an extinction ratio of about 20 dB. The passband frequency can also be continuously tuned with a tunable range from 1 to 18 GHz.

Tunable dual-passband microwave photonic filter with a fixed frequency interval using phase-to-intensity modulation conversion by stimulated Brillouin scattering.

An approach to realizing a highly selective and stable tunable dual-passband microwave photonic filter (MPF) is proposed and experimentally demonstrated, in which two passbands have a fixed frequency interval. The MPF is achieved based on phase-to-intensity modulation (PM-IM) conversion by stimulated Brillouin scattering (SBS). The kernel of the proposed scheme is generating a two-tone pump by first frequency-downshifting the optical carrier through self-induced SBS in a spool of single-mode fiber (SMF), and then modulating it in carrier-suppressed double-sideband modulation mode. Making use of Brillouin frequency shift difference between the SMF and the high nonlinear fiber used for PM-IM conversion, two passbands with a fixed frequency interval equal to 2 times the Brillouin frequency shift difference between the two fibers can be achieved. Through simply varying the modulation frequency, the two passbands can be synchronously shifted back and forth. In the experiment, a tunable dual-passband MPF with a fixed frequency interval of 2.434GHz is demonstrated in the frequency range of 0-9.644GHz, where the out-of-band rejection ratio and the 3-dB bandwidth of the passbands are measured to be larger than 20dB and smaller than 57MHz, respectively.

Freely Tunable Dual-Passband Microwave Photonic Filter Based on Phase-to-Intensity Modulation Conversion by Stimulated Brillouin Scattering

An approach to achieving a highly selective and stable microwave photonic filter (MPF) with two passbands independently tunable is presented. The dual-passband MPF is realized based on phase-to-intensity modulation conversion by stimulated Brillouin scattering. In the proposed scheme, a freely tunable two-tone pump is generated by passing the optical carrier through two cascaded dual-parallel Mach-Zehnder modulators (DPMZMs), with one acting as a frequency shifter with assistance of an electrical 90° hybrid and the other one working at carrier-suppressed double-sideband modulation mode to generate two-tone pump. The two passband locations of the MPF can be freely set by adjusting the frequencies of the two single-tone signals applied to the two DPMZMs. In the experiment, a dual-passband MPF with flexible passband tunability and shape-invariant tuning is demonstrated in the frequency range of 0-9.644 GHz, where the out-of-band rejection ratio and the 3-dB bandwidth of the passbands are measured to be larger than 25 dB and smaller than 55 MHz, respectively. The proposed MPF scheme also has the ability to tailor the shape and the width of the two passbands, which is a promising solution to achieve a freely programable dual-passband MPF.

Switchable Microwave Photonic Filter Between Dual-Notch and Dual-Passband Responses

We present a microwave photonic filter (MPF) which is switchable between dual-notch and dual-passband responses. In the MPF, a dual-drive Mach–Zehnder modulator is used to generate a quasi-single-sideband or phase-modulated signal by controlling the bias of the modulator. The first-order sidebands of the modulated signal are processed by stimulated Brillouin scattering in optical fiber to build or destroy the amplitude balance of the sidebands. In this way, a dual-notch or dual-passband MPF is finally obtained. The center frequencies of the notches or passbands are symmetric about the Brillouin frequency shift. The frequency spacing between the two notches or two passbands is determined by the frequency spacing of the dual-wavelength pump. The experimental results show that the MPF can be freely switched between dual-notch and dual-passband response with wideband tunability.

On-Chip Sensor for Simultaneous Temperature and Refractive Index Measurements Based on a Dual-Passband Microwave Photonic Filter

We propose and experimentally demonstrate an on-chip optical sensor based on a dual-passband microwave photonic filter (MPF) incorporating a silicon photonic integrated microdisk resonator (MDR). Two whispering gallery modes supported by the MDR that are experiencing different wavelength shifts are employed for simultaneous temperature and refractive index (RI) measurements. To increase the interrogation speed and resolution, the MDR is incorporated in an MPF to produce two microwave passbands. By applying a broadband linearly chirped microwave waveform to the MPF, two filtered microwave waveforms with their temporal locations or equivalently central frequencies corresponding to the wavelength shifts of the notches are generated. The measurement of the temporal locations or equivalently the central frequencies is performed at high speed and high resolution using a digital signal processor. To increase the signal-to-noise ratio of the filtered microwave waveforms, a noise reduction algorithm based on phase-only filtering is proposed and employed. The on-chip optical sensing system is experimentally demonstrated. The sensing system can provide high temperature and RI interrogation resolutions of 2.4 × 10−5 °C and 9.1 × 10−8 RIU at a high interrogation speed of 1 MHz.

Simultaneous Measurement of Temperature and Transversal Loading by Using a Modified Fiber Mach-Zehnder Interferometer

In this paper, a fiber-optic sensing interrogation system for simultaneous measurement of temperature and transversal loading based on a modified fiber Mach-Zehnder interferometer (FMZI) has been theoretically and experimentally demonstrated. In our experiment, the modified FMZI is taken as the sensing element as well as the spectrum slicer for a dual-passband microwave photonic filter (MPF). One arm of the FMZI is used as the temperature sensing fiber, and portion of the fiber in the second loop of the FMZI is utilized for measuring the transversal loading variation. As the temperature increases, the central frequencies of the passbands of the MPF move to the higher frequency. The peak amplitude of the lower passband decreases while the higher one increases with the increment of transversal loading. Thus, simultaneous measurement of temperature and transversal loading can be implemented by tracking the central frequencies and the peak amplitude of the passbands.

Optical Fiber Bragg Grating Pressure Sensor Based on Dual-Frequency Optoelectronic Oscillator

A dual-frequency optoelectronic oscillator (OEO) for high sensitivity pressure sensing is proposed and experimentally demonstrated. The oscillation frequency of the OEO is determined by a dual-passband microwave photonic filter in the OEO loop, which is implemented using phase shifted fiber Bragg gratings (PSFBGs) written in side-hole fiber to perform phase-modulation to intensity-modulation conversion. When the PSFBGs are experiencing a pressure, the wavelength difference between the two notches of the PSFBGs is slightly changed, which leads to a large frequency change of the two oscillating frequencies. Since the beat frequency between the two microwave signals is linearly proportional to the pressure, the high sensitivity pressure measurement can be realized through monitoring the beat frequency. The proposed approach is experimentally evaluated. High sensitivity pressure sensing with a sensitivity of 418.8 MHz/MPa is experimentally demonstrated. In addition, the sensing is insensitive to the variations of the environmental temperature.

High sensitivity axial strain and temperature sensor based on dual-frequency optoelectronic oscillator using PMFBG Fabry-Perot filter.

A dual-frequency optoelectronic oscillator (OEO) incorporating a polarization-maintaining fiber Bragg grating (PMFBG) Fabry-Perot filter for high-sensitivity and high-speed axial strain and temperature sensing is proposed and experimentally demonstrated. In the OEO loop, two oscillation frequencies are determined by a PMFBG Fabry-Perot filter with two ultra-narrow notches and two laser sources which operate as a dual-passband microwave photonic filter. The fiber birefringence affected by axial strain is far less than the temperature. Through monitoring the variations of two oscillating frequencies and beat frequency, the simultaneous measurement for the axial strain and temperature is realized. The sensitivities of the proposed OEO sensor for axial strain and temperature are experimentally measured to be as high as 100.6 or 100.5 MHz/με and -41 MHz/°C, respectively.

Microwave Photonic Bandpass Filter Based on Carrier-Suppressed Single Sideband Injected Distributed Feedback Laser

A novel microwave photonic filter (MPF) based on carrier-suppressed single sideband (CS-SSB) injected distributed feedback (DFB) laser is proposed. The proposed MPF system exploits the frequency selective gain feature of optical injected DFB lasers, which can be tuned by adjusting the optical injection parameters or the working conditions of the laser. Therefore, the proposed MPF system can be tunable. The proposed system is verified by a proof-of-concept experiment, and the results show that the passband of the proposed MPF can be tuned by tuning the injection ratio and bias current of the slave laser, where the tuning range of 9–39 GHz is realized. At the same time, the out-of-band rejection of the proposed MPF can reach to 32 dB. Moreover, a dual-passband MPF response is also realized by the proposed system with a couple of master lasers, and the two passbands can be tuned independently from 10 to 39 GHz.

Tunable Dual-Passband Microwave Photonic Filter Based on Stimulated Brillouin Scattering

A novel ultra-narrow dual-passband microwave photonic filter (MPF) with wide tunability based on stimulated Brillouin scattering (SBS) is presented. The proposed dual-passband MPF is implemented via the usage of carrier suppressed modulation of an electrooptic modulator (EOM). The passband separation of the dual-passband filter is determined by the oscillation radio frequency (RF) that is applied onto the EOM, where the frequency change of the RF oscillator results in two times the bandpass frequency shift with a central frequency that is symmetric with respect to the SBS frequency shift. A complete theoretical model based on the combined effects of the Brillouin gain and loss in a dual-wavelength Brillouin pump structure is presented to characterize the filter RF responses. Experimental results show a widely tunable dual-passband MPF that has an ultra-narrow bandwidth of 20.1MHz with over 35 dB out-of-band rejection ratio and a 20-3-dB bandwidth shape factor of 2.5.

Tunable Dual-Passband Microwave Photonic Filter Using Orthogonal Polarization Modulation

A microwave photonic filter (MPF) with two independently tunable passbands using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. By applying two orthogonally polarized optical waves from two tunable laser sources (TLSs) to the PolM, two phase-modulated optical signals that are orthogonally polarized are generated, which are sent to the PS-FBG that acts as an optical notch filter to suppress one sideband of the orthogonally polarized phase-modulated signals. Thus, the two phase-modulated signals are converted to two intensity-modulated single-sideband signals. The overall operation corresponds to a dual-passband MPF with the central frequencies of the two passbands independently tunable by changing the wavelengths of the optical carriers from the two TLSs. The proposed MPF is experimentally evaluated. A dual-passband MPF with a bandwidth for each passband of 140 MHz and a frequency tunable range of $\sim 6$ GHz is demonstrated. The insertion loss and the dynamic range of the filter are also studied and measured experimentally.

Switchable and tunable microwave frequency multiplication based on a dual-passband microwave photonic filter.

In this paper, a novel approach to implement switchable and tunable microwave frequency multiplication has been proposed and experimentally demonstrated. High order harmonics of microwave signal with external modulation technique can be selected by using a novel switchable dual-passband microwave photonic filter (MPF) based on a modified fiber Mach-Zehnder interferometer (FMZI) and a dispersive medium. By adjusting the polarization controllers in the modified FMZI, the passbands of the MPF can switch between lower frequency, higher frequency or dual-passband states, and by changing the length of the variable optical delay line (VODL) in the modified FMZI, the central frequencies of these passbands can also be tuned. Therefore, tunable and switchable microwave signal frequency multiplication can be achieved. The experimental results show that by modulating a driving signal with frequency of 2.5 GHz, a signal with frequency of 7.5 GHz, which is three times of the driving frequency, the other one with the frequency of 15 GHz, which is six times of the driving frequency can be generated and freely switchable between two frequencies and dual frequency states by simply adjusting the polarization controllers in the modified FMZI.

A tunable dual-passband microwave photonic filter based on optical slicing and dual-path fiber delay lines

In this article, a dual-passband microwave photonics filter (MPF) based on spectrally sliced broadband optical source (BOS) and a dual-path fiber delay line has been proposed and experimentally demonstrated. Continuous optical samples are obtained when a BOS is sliced by a fiber Mach–Zehnder interferometer (FMZI). Dual-passband frequency response has been realized by utilizing two dispersive fiber delay lines with different length and recombining two groups of delayed samples on the photodiode (PD). The proposed dual-passband MPF is stable and the central frequencies of the passbands can be tuned continuously by either changing the free spectral range of the FMZI or the length of dispersive fiber delay lines. Furthermore, multi-passband MPF with desirable passband central frequencies can be achieved by using the proposed technique, which shows good application potentials in the wireless communication and measurement systems.

Microwave Photonic Filter With Two Independently Tunable Passbands Using a Phase Modulator and an Equivalent Phase-Shifted Fiber Bragg Grating

A dual-passband microwave photonic filter (MPF) implemented based on phase-modulation to intensity-modulation (PM-IM) conversion using a phase modulator and an equivalent phase-shifted fiber Bragg grating (EPS-FBG) is proposed and experimentally demonstrated. The key component in the system is the EPS-FBG, which is designed and fabricated based on the equivalent phase-shift technique. The unique feature of the EPS-FBG is that equivalent phase shifts are introduced to both of the ±1st channels, leading to a notch in each of the two channels. Thus, by implementing PM-IM conversion in the two channels, two passbands are produced. The central frequency of each passband is determined by the wavelength different between the notch and the optical carrier. In the design and fabrication, two phase shifts are introduced to the EPS-FBG to decrease the shape factor, which is defined as the ratio between the 20- and 3-dB bandwidths. In addition, a stimulated Brillouin scattering (SBS) assisted filter is incorporated in the system for carrier suppression to increase the spurious-free dynamic range (SFDR) and decrease the noise figure (NF) of the MPF. An experiment is performed. A dual passband filter with a 3-dB bandwidth and a shape factor of 167.3 MHz and 3.8, and 143.3 MHz and 3.3 for the 1st and 2nd passband is achieved. The frequency tunable ranges of the 1st and 2nd passbands are 5.4 and 7.4 GHz, respectively, with the magnitude variations of about ±0.5 dB during the turning. Due to the SBS-assisted filter, the SFDRs are increased by 7 dB and the NFs are decreased by 10 dB.