Bandpass Microwave Photonic Filter Research Articles

Widely Tunable Optoelectronic Oscillator Using a Dispersion-Induced Single Bandpass MPF

A widely frequency tunable optoelectronic oscillator (OEO) based on a dispersion-induced single bandpass microwave photonic filter (MPF) is proposed and demonstrated. The MPF is implemented using a broadband optical source, a dual-output Mach–Zehnder modulator ( $1\times 2$ MZM) with unbalanced output fiber lengths into the upper and lower arms of the $1\times 2$ MZM, and a linearly chirped fiber Bragg grating. Through adjusting the difference between the two output fiber lengths after the $1\times 2$ MZM, the oscillation frequency of the OEO can be tuned by incorporating the MPF into an optical domain dual-loop OEO. A proof-of-concept experiment is performed. A microwave signal with a frequency tunable from 4.078 to 13.05 GHz is generated and its performance is investigated.

Tunable optoelectronic oscillator using a polarization division multiplexing emulator and a polarization modulator

This paper proposes a frequency-tunable optoelectronic oscillator (OEO) based on a single bandpass microwave photonic filter (MPF), which is implemented by a polarization division multiplexing emulator (PDME) with a tunable time delay difference between the two polarization states, a polarization modulator (PolM), a broadband optical source (BOS), and a linearly chirped fiber Bragg grating (LCFBG). The center frequency of the MPF can be shifted by adjusting the time delay difference between the two polarization states of the PDME. By incorporating the MPF into an OEO, the oscillation frequency of OEO is tuned. The proposed OEO is experimentally demonstrated. Frequency-tunable oscillation signals from 2.45 to 12.72 GHz are generated with their performance being investigated.

All-Fiber-Optics-Based Microwave Photonic Filter With Tunable Center Frequency and Passband Plus Notch

We propose and demonstrate a microwave photonic band-pass filter (MPF), which features a single light source, with continuously and independently tunable center frequency and bandwidth. The center frequency and bandwidth can be adjusted by tuning the variable optical delay line and the position of a spatial filter, respectively. Using a balanced photodetector, the baseband, which is ineradicable in some conventional designs, and the common-mode noise are canceled in our proof-of-concept experiment. Alternatively, a notch with continuously tunable frequency can also be added in the MPF. The experimental measurements of the frequency response of this MPF are demonstrated, which have a good agreement with the theoretical simulations.

Multifunctional microwave photonic signal processor based on dual-parallel Mach–Zehnder modulator and stimulated Brillouin scattering

We report a multifunctional microwave photonic signal processor based on dual-parallel Mach–Zehnder modulator and stimulated Brillouin scattering. The signal processor acts as a microwave photonic filter (MPF) and microwave photonic phase shifter (MPS) simultaneously. The MPF and MPS can be tuned separately. Experimental results demonstrate that the central frequency of the bandpass MPF is tunable from 3 to 18 GHz while the MPS in the passband of the MPF is continuously adjustable over 360 deg.

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.

Linear and nonlinear microwave responses of a microwave photonic filter based on a photonic crystal microcavity

We propose and demonstrate an ultracompact bandpass microwave photonic filter (MPF) based on a silicon photonic crystal (PhC) microcavity. Taking the fabricated PhC microcavity as an example, we comprehensively investigate both the linear and nonlinear microwave responses of the MPF based on silicon waveguide devices. Two cases are discussed in the experiment, i.e., the optical carrier wavelength is located on the left or right side of the notch resonant wavelength of the PhC microcavity. The experimental results agree well with the theoretical analyses. For the former case, the central frequency of MPF increases monotonically when fixing the optical carrier wavelength and increasing the optical carrier power. For the latter case, the nonlinear response at a fixed optical carrier wavelength shows a decrease first and then an increase in the central frequency of MPF when increasing the optical carrier power. A jump of the response is observed in the switching process. Moreover, we also observe an interesting bistable microwave response in the experiment under an optical carrier power of around −2.6 dBm in the latter case.

A Tunable Single Passband Microwave Photonic Filter of Overcoming Fiber Dispersion Induced Amplitude Fading

A tunable single passband microwave photonic filter (MPF) of overcoming fiber dispersion induced amplitude fading of the microwave passband is proposed and demonstrated. The passband amplitude of the MPF can be kept invariant for different central frequencies. The scheme is realized based on a dual-drive Mach–Zehnder modulator (DDMZM) and a broadband optical source sliced by a delay interferometer. The DDMZM is single-electrode driven and the microwave signal is modulated onto the optical carrier with simultaneous phase and intensity modulation formats. The ratio of the two modulation formats can be controlled by adjusting the bias of DDMZM to compensate the dispersion-induced amplitude fading at any passband of the MPF. In the experiment, the proposed MPF can be tuned between 0 and 30 GHz and the rejection ratio exceeds 30 dB.

Wideband tunable optoelectronic oscillator based on the deamplification of stimulated Brillouin scattering.

A wideband tunable optoelectronic oscillator (OEO) based on the deamplification of stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. A tunable single passband microwave photonic filter (MPF) utilizing phase modulation and SBS deamplification is used to realize the tunability of the OEO. Theoretical analysis of the MPF and phase noise performance of the OEO are presented. The frequency response of the MPF is determined by the + 1st sideband attenuation due to SBS deamplification and phase shift difference between the two sidebands due to chromatic dispersion and SBS. The close-in (< 1 MHz) phase noise of the proposed OEO is shown to be dominated by the laser frequency noise via phase shift of SBS. The conversion of the laser frequency noise to the close-in phase noise of the proposed OEO is effectively reduced compared with the OEO based on amplification by SBS. Tunable 7 to 40 GHz signals are experimentally obtained. The single-sideband (SSB) phase noise at 10 kHz offset is -128 dBc/Hz for 10.30 GHz signal. Compared with the OEO based on SBS amplification, the proposed OEO can achieve a phase noise performance improvement beyond 20 dB at 10 kHz offset. The maximum frequency and power drifts at 10.69 GHz are within 1 ppm and 1.4 dB during 1000 seconds, respectively. To achieve better close-in phase noise performance, lower frequency noise laser and higher pump power are preferred. The experimental results agree well with the theoretical models.

Optoelectronic Oscillator Based Sensor Using an On-Chip Sensing Probe

An integrated photonic sensor based on an optoelectronic oscillator with an on-chip sensing probe that is capable of realizing highly sensitive and high-resolution optical sensing is presented. The key component is an integrated silicon-on-insulator based microring resonator which is used to implement a microwave photonic bandpass filter (MPBF) to effectively suppress the side modes of the optoelectronic oscillator (OEO) by more than 30 dB, thus generating a peak RF signal that maps the detected optical change into a resulting shift in the oscillating frequency. As an application example, the proposed optical sensor system is employed to detect small changes in temperature, and experimental results demonstrate a highly sensitive optical temperature sensor with an achieved sensitivity of 7.7 GHz/°C. Moreover, the proposed sensing system revealed a 0.02 °C measurement resolution, which is a tenfold improvement to the modest resolution of 0.23 °C of the conventional MPBF system without the OEO loop, rendering it highly suitable for diverse high-resolution sensing applications.

Demodulation of an optical fiber MEMS pressure sensor based on single bandpass microwave photonic filter.

In this paper, a demodulation method for optic fiber micro-electromechanical systems (MEMS) extrinsic Fabry-Perot interferometer (EFPI) pressure sensor exploiting microwave photonics filter technique is firstly proposed and experimentally demonstrated. A single bandpass microwave photonic filter (MPF) which mainly consists of a spectrum-sliced light source, a pressurized optical fiber MEMS EFPI, a phase modulator (PM) and a length of dispersion compensating fiber (DCF) is demonstrated. The frequency response of the filter with respect to the pressure is studied. By detecting the resonance frequency shifts of the MPF, the pressure can be determined. The theoretical and experimental results show that the proposed EFPI pressure demodulation method has a higher resolution and higher speed than traditional methods based on optical spectrum analysis. The sensitivity of the sensor is measured to be as high as 86 MHz/MPa in the range of 0-4Mpa. Moreover, the sensitivity can be easily adjusted.

All-Optical Virtual Private Network in OFDM-PON Using Microwave Photonic Filter

We propose and demonstrate a novel all-optical virtual private network (VPN) using a microwave photonic filter, which enables inter-communications among optical network units in a passive optical network system. In our scheme, an optical coupler based recirculating delay line is used at optical line terminal as an optical subsystem to implement a microwave photonic-bandpass filter (MP-BPF). The periodic passbands of an MP-BPF are used to transmit VPN signal, whereas stopbands are used for conventional upstream transmission. The proposed system has two critical issues, optical phase-induced intensity noise in the MP-BPF and Rayleigh back-scattering interference by a single-fiber loop back link. To overcome the issues, an RF clipping tone based spectrum-broadening technique is applied to uplink transmitter. The proposed all-optical VPN system is tolerant to wavelength of VPN optical carrier, and enables multi-VPN data transmission using multi-passbands of MP-BPF.

A Linearized Tunable Single Bandpass Microwave Photonic Filter

In this letter, a tunable single bandpass microwave photonic filter (MPF) with an improved spurious free dynamic range (SFDR) based on a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. A phase-modulated double-sideband (DSB) signal is sent to a PS-FBG; when one of the sidebands falls in the notch of the reflection band of the PS-FBG, the reflected signal is converted to an intensity-modulated single-sideband (SSB) signal which leads to a single passband of the MPF. By tuning the wavelength of the optical carrier, the center frequency of the passband can be tuned correspondingly. The SFDR is improved by employing polarization mixing technique in a LiNbO3 phase modulator and a polarization diversity receiver. Experimental results show that the passband width and the frequency-tunable range of the single bandpass MPF are 80 MHz and 5.5 GHz, respectively. An SFDR improvement of 13.1 dB is successfully achieved.

Tunable bandpass microwave photonic filter with ultrahigh stopband attenuation and skirt selectivity.

we propose and demonstrate a bandpass microwave photonic filter (MPF) with ultrahigh stopband attenuation and skirt selectivity based on a simple signal cancellation technique. By injecting two phase modulated signals located on opposite sides of two resonant gain peaks of a Fabry-Pérot semiconductor optical amplifier (FP-SOA), two microwave frequency responses can be generated by the two input signals, respectively. The two frequency responses will add together within the passband but cancel each other out within the stopband, thus generating a MPF with simultaneous ultrahigh stopband attenuation and skirt selectivity. In the experiment the obtained MPF exhibits single passband in the range from 0 to 18 GHz and is tunable from 4 to 16 GHz by adjusting the laser wavelengths. During the tuning process the maximum stopband attenuation is 76.3 dB and the minimum 30-dB to 3-dB bandwidth shape factor is 3.5.

Flat-top bandpass microwave photonic filter with tunable bandwidth and center frequency based on a Fabry–Pérot semiconductor optical amplifier

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 (SPM) are exploited to achieve flat-top and bandwidth tuning, respectively. Wideband and continuous tuning of the center frequency is achieved by altering the bias current of the FP-SOA. Experimental results demonstrate a flat-top single-passband MPF with its center frequency tunable from 6.0 to 18.3 GHz by adjusting the bias current from 54.05 to 107.85 mA. The 3-dB bandwidth of the passband when centered at 10.0 GHz is shown to be variable from 680 to 1.43 GHz, by increasing the injected optical power from -1 to +5 dBm. During the bandwidth tuning, the amplitude ripple within the passband is maintained at less than ±0.5 dB. Excellent main to secondary sidelobe ratio exceeding 45 dB is achieved when the MPF is centered at 18.3 GHz.

An Optoelectronic Oscillator for High Sensitivity Temperature Sensing

An optoelectronic oscillator (OEO) for high sensitivity temperature sensing is proposed and experimentally demonstrated. The oscillation frequency of the OEO is determined by a single passband microwave photonic filter (MPF) in the OEO loop, which is implemented using a broadband light source, a Mach–Zehnder interferometer (MZI), a dispersion compensating fiber, and a photodetector. One arm of the MZI is used as a sensing arm, which is exposed to temperature variations and the other arm is used as a reference arm. When the temperature is changed, the length difference between the two arms is changed, which leads to the change of the free spectral range of the MZI. Since the central frequency of the MPF is a function of the FSR, the oscillation frequency of the OEO is affected by the temperature variations. By measuring the frequency change, the temperature change to the sensing arm is estimated. The proposed approach is experimentally evaluated. High sensitivity temperature sensing with a sensitivity of 3.7 MHz/°C is experimentally demonstrated.

Dual-band bandpass tunable microwave photonic filter based on stimulated Brillouin scattering

A dual-band bandpass microwave photonic filter (MPF) based on stimulated Brillouin scattering (SBS) is theoretically analyzed and experimentally demonstrated. Two separated tunable laser sources (TLSs) are employed to generate two passbands by implementing phase modulation to amplitude modulation conversion by using SBS induced sideband amplification. The center frequencies of both passbands can be independently tuned ranging from 1 GHz to 19 GHz. High resolution with 3 dB bandwidth less than 30 MHz and large out-of-band rejection about 40 dB under 25 mW optical pump power are achieved.

Distributed optical signal processing for microwave photonics subsystems.

We propose and experimentally demonstrate a novel and practical microwave photonic system that is capable of executing cascaded signal processing functions comprising a microwave photonic bandpass filter and a phase shifter, while providing separate and independent control for each function. The experimental results demonstrate a single bandpass microwave photonic filter with a 3-dB bandwidth of 15 MHz and an out-of-band ratio of over 40 dB, together with a simultaneous RF phase tuning control of 0-215° with less than ± 3 dB filter shape variance.

Tunable Single Bandpass Microwave Photonic Filter With an Improved Dynamic Range

A tunable single bandpass microwave photonic filter (MPF) with an improved spurious free dynamic range (SFDR) using a dual-parallel Mach–Zehnder modulator (DP-MZM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. The DP-MZM is employed to generate an equivalent phase-modulated (EPM) signal with an adjustable optical carrier to sideband ratio. The PS-FBG is used as an optical notch filter to remove one sideband of the EPM signal to convert the EPM signal to a single-sideband intensity-modulated signal. At the output of a photodetector, a microwave signal is detected. The entire operation is equivalent to a single passband MPF. The tunability is achieved by tuning the wavelength the optical carrier. The SFDR of the MPF is improved due to the gain enhancement by a partial suppression of the optical carrier. An experiment is performed. A single bandpass MPF with a passband width of 150 MHz and a frequency-tunable range of $\sim 5.5$ GHz with an improved SFDR by 11 dB is demonstrated.

Wideband tunable single bandpass microwave photonic filter based on FWM dynamics of optical‐injected DFB laser

A wideband tunable single bandpass microwave photonic filter (MPF) based on the four-wave mixing (FWM) nonlinear dynamics of a distributed feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Utilising the wavelength-selective optical gain of the optical-injected DFB laser, phase-modulation to intensity-modulation conversion is obtained, leading to the realisation of a single bandpass MPF. By changing the injection parameters, an MPF with a frequency tuning range of 27.72 GHz has been achieved. The minimum 3 dB bandwidth and the out-of-band suppression ratio are measured to be 61.2 MHz and 25 dB, respectively.

A Novel Approach to Realizing a Widely Tunable Single Passband Microwave Photonic Filter Based on Optical Injection

In this paper, a novel approach to realize a single passband microwave photonic filter (MPF) with wideband tunability based on an optical-injected distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. The fundamental principle is based on the wavelength-selective amplification of the DFB laser under optical injection. The frequency tunability, insertion loss, and out-of-band suppression ratio of the proposed MPF are investigated in the experiment. By varying the injection locking parameters, MPFs with the frequency tuned from 11 to 41 GHz are achieved, and the insertion losses and out-of-band suppression ratios are around 20 dB. They are useful in applications where high frequency and wideband tunability are required.