We propose and experimentally demonstrate a pulse radar signal generation based on the Fourier domain mode-locked optoelectronic oscillator (FDML-OEO). In this method, two low-frequency control signals generated by a direct digital synthesizer (DDS) are adopted to control the tunable laser source (TLS) and the bias voltage of Mach-Zehnder modulators (MZM) respectively. The broadband pulse signals are generated by directly truncating the broadband signals on the basis of a FDML-OEO by controlling the frequency and amplitude of the bias voltage of the MZM. In the experiment, the broadband radar pulse signals with tunable duty cycle and the center frequency are demonstrated. In particular, the center frequency of signals are tuned by changing the initial phase of pulse driving signal and the triangular wave or the wavelength of TLS, which have greatly potential in improving the detection capability of the radar system.
A phase-coded microwave signal generation method based on parallel Mach-Zehnder modulator (MZM) with tunable frequency multiplication factor is proposed and demonstrated. By controlling the modulation index and the optical power ratio of the parallel MZMs, phase-coded microwave signals with frequency multiplication factors of 1, 3 and 5 are obtained. The feasibility of this approach is demonstrated by theoretical analysis and simulation, in which binary phase-coded signals with carrier frequency of 1GHz, 3GHz or 5GHz are respectively generated under 1GHz radio frequency (RF) signal input.
A single sideband phase modulated radio over fiber link with improved spurious-free dynamic range is propsed, in which an optical processor is used for IMD3 suppression. A theoretical analysis is presented and the simulation experiment results indicate that the SFDR is up to 126.3 dB·Hz4/5.
We propose a fiber Bragg grating sensor interrogation system based on a Fourier domain mode-locked optoelectronic oscillator (FDML-OEO). The FDML is achieved by synchronizing the period of the driving current of the laser with the round-trip time of the OEO loop. By employing a narrow band electrical filter with the central frequency located within the sweeping frequency of the FDML-OEO, pulsed microwave output can be obtained. The wavelength shift of the phase-shift fiber Bragg grating (PS-FBG) can be interrogated by measuring the pulse interval variation. The experimental results indicate that the pulse interval of the generated signal has a linear relationship with the axial strain applied to the PS-FBG and a sensitivity as high as 0.42 μs/με is achieved.
A simple single sideband (SSB) analog optical link with enhancement spurious free dynamic range (SFDR) is proposed. By coupling the independent optical carrier and +1st, +2nd order phase-modulated optical sidebands to be demodulation, the suppression of IMD3 is achieved. An theoretical model is established and the simulation results show that the carrier-to-interference ratio (CIR) presents a 32dB improvement and the corresponding improved SFDR is 123.5 dB·HZ2/3 , which is 18.6 dB larger than that of conventional single sideband phase-modulated link. In particular, the proposed SSB link can avoid the periodic power attenuation caused by dispersion, presenting great potential usage in modern radar system.
A photonic approach to generate triangular frequency modulated microwave waveform (TFMMW) using frequency-scanning (FS) laser and dual-output dual-parallel Mach-Zehnder modulator (DO-DPMZM) is proposed and demonstrated. In the scheme, a DO-DPMZM followed by a time delayer and a polarization beam combiner is utilized to generate orthogonally polarized -1rst-order sideband and +1rst-order sideband with time delay. After that, a TFMMW with large time-bandwidth product (TBWP) can be generated by photoelectric balanced detection. In the simulation experiments, Ka band TFMMW with TBWP of 9830.4 is generated and its ambiguity function is investigated
An optical length measuring method exploiting microwave interrogated cascaded fiber Mach-Zehnder interferometer (MZI) is proposed. The frequency response of the filter with respect to the fiber length change of MZI is studied and an length measuring sensitivity of 2.580 GHz/mm is obtained. The proposed sensing configuration is with high sensitivity, easy to implement and shows the capability for other parameters measurement such as temperature, strain, and vibration.
An approach for photonic generation dual-chirp microwave waveform (DCMW) with frequency and bandwidth multiplication without filtering is proposed and demonstrated. A continuous-wave (CW) optical signal is sent to a polarization division multiplexing modulator. In the modulator, one part of the CW optical signal is modulated by the radio-frequency (RF) driving signals to generate ±2 nd-order single-frequency sidebands, while another one is modulated by the baseband chirped signals to generate ±2 nd-order chirped sidebands. After that, a frequency-doubled and bandwidth-quadrupled DCMW can be generated by photoelectric balanced detection. In the simulation experiments, by using a RF driving signal at 5GHz and a baseband single-chirp signal with bandwidth of 0.5GHz as the input electrical signals, a DCMW with central frequency of 10GHz and bandwidth of 2GHz is generated.
Generation of phase-coded chirped microwave waveforms by an improved frequency-sweeping optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In the proposed system, an upgraded frequency-sweeping OEO has function to generate not only a linearly chirped microwave waveform (LCMW) but also to output an optical sideband and the latter is then modulated in phase by a binary phase-coded electrical signal. By beating the phase modulated signal and a portion of the frequency-sweeping laser light at a high-speed photodetector, a phase-coded chirped microwave waveform is generated. In order to realize large time-bandwidth product (TBWP), the key significance of the improved frequency-sweeping OEO is that a near-zero-dispersion single-mode-fiber (SMF) introduced into the loop which can not only avoid the limitation of high frequency oscillation caused by dispersion, but also construct long OEO delay loop to realize large time duration. Finally, phase-coded chirped microwave waveform with a bandwidth of 6 GHz and a TBWP of 130,392 is experimentally demonstrated.
Photonic generation approach of linearly chirped microwave waveform(LCMW) with tunable frequency and bandwidth multiplication factor(FBMF) based on parallel Mach-Zehnder modulator(MZM) is proposed. Theoretical analysis show that LCMW with FBMF of 4, 8 and 12 can be obtained by properly adjusting the amplitude of linearly chirped microwave drive signal and direct current(DC) drive signal. The scheme greatly reduce the frequency and bandwidth of electrical linearly chirped microwave drive signal. Due to no filter is employed, so the generation LCMW has a large frequency and bandwidth tunable range. Furthermore, the feasibility of the approach is demonstrated by the simulation based on OptiSystem platform.
KEYWORDS: Modulators, Microwave photonics, Modulation, Intermodulation, Phase shift keying, Radio optics, Single mode fibers, Signal attenuation, Phase modulation, Local area networks
A novel phase modulator-based microwave photonics link (MPL) with improved spurious-free dynamic range (SFDR) is proposed, in which a parallel optical sideband processing path is used to generate the opposite third-order intermodulation distortion (IMD3) for destructive combination. By controlling the magnitude of the generated IMD3 term via attenuator in one path, the suppression of IMD3 term was achieved. A theoretical analysis is presented and the simulation experiment results indicate that the SFDR is up to 128.582 dB•HZ2/3, which has an improvement of 23.66 dB compared with the nonlinearized link.
In this paper, a multi-passband microwave photonic filter (MPF) based on multiple dispersive devices has been proposed and experimentally demonstrated. The Mach-Zehnder interferometer (MZI) divides the broadband light source (BBS) into multiple optical taps, and with the combination of different dispersion mediums such as chirped fiber Bragg grating (CFBG) and single mode fiber (SMF) to delay the optical tap, a MPF with multiple passbands can be simply achieved. The number of the passbands can be easily controlled by changing the number of the dispersion medium. In the experiment, the frequency response result of the four passbands is obtained by accessing two CFBGs and two SMFs. In addition, by adjusting the wavelength interval of the interference spectrum with a variable optical delay line (VODL), all passbands of the filter can be simultaneously tuned. The filter has broad application prospects in the fields of modern wireless and satellite communication, optoelectronic oscillator and optical sensing.
In this paper, a tunable dual-bandpass microwave photonic filter (MPF) based on a single broadband light source (BBS) has been proposed and experimentally demonstrated. By cascading two chirped fiber Bragg gratings (CFBG) with different reflection bandwidth and chirp parameter, the different delay of the modulated light signal in the system is introduced and consequently, a MPF with two different passbands can be realized. Two different passbands with the frequency of 6.75 GHz and 16.01 GHz is obtained in the experiment. By changing the free spectral range (FSR) of the Mach Zehnder interferometer (MZI) through an optical tunable delay line (OTDL), the central frequency of the two passbands can be changed. The dual-bandpass MPF presented in this paper is easy to implement and has good tunability and stability.
A Ka-band microwave photonic imaging radar demonstrator with 10.02 GHz-bandwidth is proposed and experimentally demonstrated. Continuous linear frequency waveform is optically generated in the transmitter and processed in the receiver. The range resolution of the demonstrator is tested to be 1.68 cm. Out-field tests while demonstrator works at inverse synthetic aperture radar (ISAR) and synthetic aperture radar (SAR) mode are carried out to image different targets.
An ultra-short DBR fiber laser based device for arterial pulse wave monitoring is proposed and demonstrated. As the sensing element, the 10mm length laser cavity is mounted onto a soft plastic plate and then embedded into textile. Deformation of the textile, involving the transverse force subjected by the laser cavity, is proportional to the vibration caused by the arterial pulse. The sensing principle is based on the linear relationship between the beat frequency of the laser and the transverse force. Laboratory studies demonstrate that the sensor could achieve real-time and accurate measurement of the weak and dynamical arterial pulse signal.
A distributed Bragg reflector fiber laser-based respiration movement monitoring system has been proposed and experimentally demonstrated. To fabricate the sensing element for respiration monitoring, a fixture that consists of a plastic plate, a section of elastic textile is employed to experience and transfer the belly expansion induced pressure onto the cross-section of the laser cavity. By tracing the change of the beat signal that generates between two polarization lasing modes, the information of the respiration movement can be extracted in real time. Experimental studies have demonstrated that the system is able to detect both respiration waveform and rate simultaneously. Moreover, the recorded results show that the different gestures as well as the physiology conditions can be distinguished by monitoring the amplitude and period change of the waveform. It is anticipated that the proposed fiber laser-based sensor would be highly suitable for respiratory monitoring.
A novel data processing algorithm named “2-FFT” for multi-point disturbances detection and location in an in-line Sagnac sensing system is proposed and demonstrated. When multiple disturbances are applied onto the sensing fiber at the same time, the frequency response curve of the modulated phase will be superposed by each null frequency curve of the single disturbance. However, by applying a second-time FFT to the frequency spectrum, the location corresponding to each disturbance point could be simply extracted and determined. Based on the theoretical and the experimental investigation, the “2-FFT” algorithm is demonstrated to be reasonable and efficient.
A micro Fabry-Perot (MFP) filter is proposed and fabricated by twisting a section of microfiber into two Sagnac loop mirrors. With the co-operation of this MFP filter and a section of highly nonlinear fiber, we propose and experimentally demonstrate a multi-wavelength Erbium-doped fiber ring laser (EDFRL) based on the inhomogeneous loss mechanism. When the pump current is set at 450mA, 22-lasering wavelengths with the identical wavelength space of 0.22nm and side-mode suppression ratio (SMSR) above 30dB are achieved. Within the period of one hour’s monitoring, the fluctuation of the output power is less than 0.943dB.
A microfiber Fabry-Perot interferometer (FPI) which employs two fiber Bragg Gratings (FBGs) as reflection mirrors and
a short length microfiber as its cavity is proposed and fabricated. Theoretic study shows that the reflection spectrum of
such microfiber FPI is consisted of two parts - interference fringes induced by FPI and reflection band induced by FBGs.
Temperature affects both parts while ambient refractive index only influences the first part, i.e. microfiber FPI has
different response to temperature and RI. Therefore, Dual-parameter measurement is experimentally demonstrated by
tracking the FSR variation and the central wavelength shift of the reflection spectrum of microfiber FPI.
A high sensitive temperature sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally
demonstrated. Temperature measurement is achieved by immerging a section of microfiber into the refractive index (RI)
liquid with a high thermo-optic coefficient. A slight change of ambient temperature will lead to the enhanced variation
of the liquid index. Due to the evanescent field of microfiber, microfiber effective refractive index will be changed, and
subsequently the optical length. Thus, by measuring the free spectral range (FSR) of the MZI, the temperature sensor can
achieve a high sensitivity of 6.44nm/°C at the temperature of 20.6°C.
A dual-polarization distributed Bragg reflector (DBR) fiber grating laser for liquid level measurement is proposed and
experimentally demonstrated. The laser cavity is used as the sensing device. The liquid level is obtained by measuring
the beat frequency generated between the two lasing polarizaion modes. The result shows the beat frequency shifts
linearly with the water level and a sensitivity of 241 kHz/mm has been obtained. The sensor is simple, easy to fabricate
and with high sensitivity to liquid level variation, which could be very helpful in practical applications.
A highly sensitive liquid-level sensor based on weak uniform fiber Bragg grating (FBG) with narrow-bandwidth is proposed and demonstrated. The resonance wavelength of FBG varies as a result of the change of axial strain. According to this characteristic, a precise approach utilizing fiber grating as sensing element to measure height of liquid is achieved. The grating is directly bonded to a float which can transfer buoyancy into axial strain on the fiber. Measurement of liquid level can be realized by monitoring the central wavelength shift of the sensing FBG. The experimental results show that for a liquid-level variation of 25 mm, a high sensitivity of 5.9×10−6 m/pm with a good linearity of 0.991 is achieved. Within bidirectional change of liquid level, crossing sensitivity and long term stability taken into account, the system is of good reliability and stability.
A distributed fiber-optic sensor system is proposed and demonstrated for long-distance intrusion-detection, which
employs the hybrid time/wavelength division multiplexing (TDM/WDM) architecture. By utilizing 20 time zones and 6
wavelengths, the system contains up to 120 fiber sensing units (OSU), of which the distributed sensing distance is from 0
to 500m. So the whole sensing distance of this system could reach 60 km. The system has been demonstrated to run
stably exceed six months with the false alarm rate of less than 4%.
In this paper, a method for realizing a stable multi-wavelength EDFL at room temperature is analyzed theoretically and
obtained experimentally. We have proposed a multi-wavelength fiber ring cavity laser by using EDF as the gain medium.
A F-P and a band-pass filter are inserted into the cavity to achieve the selection of multi-wavelength. Meanwhile, by
inserting a nonlinear optical loop mirror (NOLM) in the linear cavity, which can suppresses the mode competition owing
to the homogeneous broaden line in EDF and eliminates the unstable single wavelength lasing, stable output can be
obtained at room temperature. As a result, power-stable, broad bandwidth and uniform multi-wavelength operations with
narrow line-width and high side mode suppression ratio are obtained at room temperature. In addition, we also
demonstrate a kind of tunable multi-wavelength EDFL based on multi-channel FBG (M-FBG). Four-wavelength output
with the flatness and SNR of almost 1dB and more than 50dB is achieved and the output wavelength can be changed by
applying stress on the M-FBG.
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