A tunable dual-frequency optoelectronic oscillator (OEO) based on a tunable dual-passband microwave photonic filter (DPMPF) is proposed and demonstrated. The DPMPF is based on phase-to-intensity modulation (PM-IM) conversion and stimulated Brillouin scattering (SBS). Two pump lightwaves are generated through carrier-suppression doublesideband modulation (CS-DSB) in a Mach-Zehnder modulator (MZM) to generate two SBS gain regions in a single mode fiber. Two SBS gain regions act on the phase modulation signal to achieve a dual-passband filter. Through simply varying the frequency of the radio frequency (RF) signal used for CS-DSB, the two central frequencies of the OEO can be tuned with the frequency interval kept constant. In addition, adjusting the frequency of tunable optical source launched to the MZM, the frequency interval of the OEO can be tuned. In the experiment, the dual-frequency OEOs with frequency intervals of 0.2 GHz and 1.2 GHz are achieved, respectively. The frequency tuning range from 3 to 8 GHz is demonstrated. The dual-frequency OEO with the frequency interval tuned is also achieved.
A microwave mixer based on a tunable microwave photonic filter is presented and experimentally demonstrated. The tunable microwave photonic filter consists of a broadband optical source and a dual-parallel Mach–Zehnder modulator employing a variable optical carrier time-shift method. The central frequency of the tunable single-passband filter can be tuned by adjusting an optical variable delay line. The filter can select the wanted mixing components and suppress the other mixing spurs. Experiments are performed and the results show that the out-of-band rejection ratio of the filter is over 45 dB. The up-converted and down-converted signals are successfully selected, and the unwanted mixing spurs are effectively suppressed.
A coherence-free and reconfigurable filter based on semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. A high coherent RF-modulated light source is converted to an incoherent light source by employing the cross-gain modulation of amplified spontaneous emission (ASE) of the SOA. The inversely modulated ASE is sliced by an optical wavelength demultiplexer to realize a stable transversal microwave filter. Reconfigurability of the filter can be achieved by controlling the number and apodization of the taps. The filters with two, three and four taps are experimentally demonstrated.
A reconfigurable microwave photonic filter based on a polarization modulator (PolM) is proposed and experimentally demonstrated. The PolM together with a polarization controller (PC) and a polarization beam splitter (PBS) implements two complementary intensity modulations in two separated branches. Then, optical components are inserted in the two branches to realize a bandpass filter and an allpass filter, respectively. When the two branches are combined by a second PBS, a filter with a frequency response that equals the subtraction of the frequency responses of the allpass filter and bandpass filter is achieved. By adjusting the PCs placed before the second PBS, a notch filter with a tunable notch depth or a bandpass filter can be achieved.
We demonstrate a novel scheme to generate ultra wideband (UWB) doublet pulses by inputting a dark return-to-zero
(RZ) signal into a fiber delay interferometer (FDI). When a dark RZ pulse train with a repetition rate of 0.625 GHz and a
pulse width of 120 ps was inputted into a FDI with a free spectrum range (FSR) of 0.16 nm (~20 GHz, according time
delay is ~50 ps) and an extinction ratio (ER) of 9 dB, by adjusting the control temperature of the FDI, the phase
difference of the input light on the both fiber arms of the FDI is changed and controlled, UWB doublet pulse is directly
generated at the output port of the FDI. The system parameters effects on the output signal were also discussed.
Moreover, we numerically demonstrated that, by carefully optimizing system parameters, UWB quadruplet pulses also
can be generated. This scheme has some distinct advantages including easy integration, convenient tuning, good stability,
and so on. Presented method also accords with the general features in future applied UWB system, namely, single optical
source input, simple configuration and passive device.
A new cascaded microwave photonic filter consisting of two or more infinite impulse response (IIR) filters based on
active loops. is presented. Owing to wavelength conversion, the interference between the modulated optical signals of
different taps from different active loops can be avoided and the stable transmission characteristic of the cascaded filter
can then be achieved. The cascaded filter can increase the free spectral range (FSR) and the Q value significently by
designing the FSR differences of the IIR filters. The cascaded filter with two IIR filters is demonstrated, and the
measured results of a high Q of 3338 and rejection ratio of about 40 dB are obtained. The tunability can also be realized.
We demonstrated experimentally 40 Gbit/s all-optical format conversions between return-to-zero (RZ) and nonreturn-to-
zero (NRZ) using a fiber delay interferometer (FDI) and a single semiconductor optical amplifier (SOA). Firstly, 40 Gbit/s data format conversion from RZ to NRZ is realized using a FDI with temperature control and an optical bandpass filter (BPF). Then, 40 Gbit/s data format conversion from NRZ to RZ is implemented, using four-wave mixing (FWM)
effect of SOA, by injecting synchronously NRZ signal and clock pulses into a single SOA. Presented method has some distinct advantages including multi-channel parallel processing, easy integration, convenient tuning, good stability, and
so on, which has potential to be used in future optical networks that could combine wavelength division multiplexing
(WDM) and optical time domain multiplexing (OTDM) transmission techniques.
We propose and experimentally demonstrate a novel all-optical microwave filter with high quality factor (Q). It is based
on a recirculating delay line (RDL) loop in which a semiconductor optical amplifier (SOA) is followed by a tunable
narrow-band optical filter and a 1x2 10:90 optical coupler. Converted signal used as a negative tap is generated through
wavelength conversion employing the cross-gain modulation (XGM) of the amplified spontaneous emission (ASE)
spectrum of the SOA. The converted signal can circulate in the RDL loop so that the proposed filter realizes a high Q
factor response after photo-detection. The 1x2 10:90 coupler is employed to extract 10% optical power from the loop as
output. A frequency response with a high Q factor of 543, a rejection ratio of 40 dB is experimentally demonstrated.
A tunable and switchable single-longitudinal-mode (SLM) dual-wavelength fiber laser incorporating a reconfigurable
dual-pass Mach-Zehnder interferometer (MZI) filter and its application in microwave generation was proposed and
demonstrated. By incorporating a dual-pass MZI into an erbium-doped fiber ring cavity, tunable and switchable SLM
dual-wavelength operation can be conveniently realized.
An all-optical UWB pulses generation and modulation scheme based on a semiconductor optical amplifier and a DWDM
is proposed and demonstrated, which has potential applications in multiuser UWB-Over-Fiber communications systems.
Using proposed scheme, pulse amplitude modulation (PAM), pulse polarity modulation (PPM) and pulse shape
modulation (PSM) can be conveniently realized.
We experimentally demonstrate all-optical clock recovery (CR) from the nonreturn-to-zero (NRZ) data without any
preprocess measure. Multi-quantum-well (MQW) Fabry-Pérot semiconductor optical amplifier (FP-SOA) plays the dual
role of the data format converter and the clock recovery device. To achieve amplitude equalization of the recovered clock
pulses, a self-nonlinear polarization switching (SNPS) including the FP-SOA itself, two polarization controllers (PCs)
and a polarization beam splitter (PBS) is employed. Using the presented scheme, stable and low jitter 35.80 GHz optical
clock pulses were directly extracted out from input NRZ data. This scheme has some distinct advantages such as being
transparent to data format, free preprocess, free pre-amplification, convenient tuning, good tolerance to long "0s" data,
and good tolerance to wavelength drifting of input data.
A microwave photonic interference mitigation filter is proposed and experimentally demonstrated. The structure is based
on a recirculating delay line loop comprising a semiconductor optical amplifier (SOA) and a tunable narrowband optical
filter. Converted signal used as negative tap is generated through wavelength conversion employing cross-gain
modulation of amplified spontaneous emission spectrum of the SOA. The converted signal circulating in the RDL loop
realizes a high quality factor (Q) response after photo-detection. A bandpass response with negative coefficients
combined with a broadband allpass response achieves a notch response with flat passband.
A novel microwave photonic notch filter structure is proposed and experimentally demonstrated. The structure is based
on a recirculating delay line loop consisting of an optical variable delay line, a semiconductor optical amplifier (SOA)
and a tunable narrowband optical filter. Negative tap is generated using wavelength conversion based on cross-gain
modulation of amplified spontaneous emission spectrum of the SOA. A narrow bandpass response with negative
coefficients and a broadband all-pass response are combined to achieve a narrow notch response with flat passband
which can eliminate interference with minimal impact on the expected signal. Experimental results show good
agreement with theoretical analysis.
An all-optical filter structure for interference suppression of microwave signals is presented. The filter is based on a
recirculating delay line (RDL) loop consisting of a semiconductor optical amplifier (SOA) followed by a tunable
narrowband optical filter, and a fiber Bragg grating connected after the RDL loop. Negative tap is generated in
wavelength conversion process based on cross-gain modulation of amplified spontaneous emission spectrum of the
SOA. A narrow passband filter with negative coefficients and a broadband all-pass filter are synthesized to achieve a
narrow notch filter with flat passband which can excise interference with minimal impact on the wanted signal over a
wide microwave range. Experimental results show that measured and theoretical frequency responses agree well and the
filter is tunable.
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