Talbot self-imaging has been utilized for arbitrary repetition-rate control of optical pulse trains and frequency combs, which are important for many applications. The fundamental theory of generalized Talbot self-imaging has been presented for the design of temporal and spectral phase operations, while the effects of potential phase modulation distortions and residual dispersions on repetition-rate control in experiments remain to be investigated. In this paper, numerical studies are conducted for evaluating the feasibility of yielding arbitrary repetition-rate control of optical pulse trains and frequency combs, and it provides additional insights into the optimal design conditions for practical implementation of the scheme.
In this paper, we propose and demonstrate a novel Tilted Fiber Bragg grating (TFBG) sensing demodulation scheme based on microwave photonic technique. In the proposed approach, the optical power spectrum from BBS (Broadband source) is shaped by a TFBG and then sent to a dispersive element to perform the linear wavelength-to-time mapping. A nonuniform microwave photonic filter with the center frequency depending on the shaped optical spectrum is obtained at the output of a high-speed photodetector. The central frequency and the envelope of the generated microwave photonic filter will shift according to the change of environment. Theory and a proof-of-principle experiment are implemented to verify the proposed approach.
The in-band full-duplex (IBFD) communication technology transmitting and receiving signals simultaneously on the same frequency, can double the spectrum utilization efficiency and data transmission rate, and has a great potential application in beyond fifth generation (B5G), sixth generation (6G) communications and satellite communications. However, the high-power signal sent from the transmitting antenna will interfere the low-power signal of interest (SOI) that received by the receiving antenna, or even submerge it completely, which is called radio frequency (RF) selfinterference. The RF self-interference is a key issue for the application of IBFD. Compared with the electronic technology, the photonic technology for RF self-interference cancellation (SIC) has the advantages of wide bandwidth and high tuning precision, exhibiting the great potential to realize high interference cancellation depth over broad band. In this paper, the operation principle of photonic RF SIC for IBFD communications is introduced and the recent work in our group is presented, including the photonic RF SIC system composed of separate optoelectronic devices and the silicon photonic integrated RF SIC system.
A photonic RF self-interference cancellation (SIC) scheme for full-duplex communication is proposed and demonstrated experimentally. It is based on phase modulation to convert the RF signal into optical domain. The interference cancellation performance of the photonic RF SIC system under different delay deviation (Δτ) and amplitude deviation (Δα) is analyzed. The cancellation depth of 34.5 dB is measured for 10 GHz signal with bandwidth of 50MHz. According to experimental results, the interference cancellation performance affected by the time delay deviation, the amplitude deviation and the phase response is investigated. The results give a direction for the improvement of system performance.
Photonic enabled RF self-interference cancellation for full-duplex communication by using phase modulation and optical sideband filtering is proposed. Based on the inherent out-of-phase property between the left and right sidebands of phasemodulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. The operational principle of the proposed scheme is theoretically analyzed and the feasibility is experimentally demonstrated. The optical sideband filtering for the phase modulated signals is measured and the RF self-interference cancellation at different carrier frequencies is studied. The results show a good performance of the proposed photonic scheme for RF self-interference cancellation. The full-duplex communication based on the photonic enabled RF self-interference cancellation is also investigated.
A compact dual-loop optoelectronic oscillator (OEO) employing a dual-output Mach–Zehnder intensity modulator (DOMZM) and a balanced photodetector (BPD) is theoretically analyzed and experimentally demonstrated. The fundamental idea of the scheme is based on double loops formed by two complementary output ports of DOMZM and two input ports of BPD, which could be naturally combined without any additional optical coupler or polarization beam splitter devices. This simple structure makes it possible to enhance side-mode suppression ratio (SMSR) and reduce phase noise of the OEO. Compared with the traditional dual-loop OEO (SO-OEO) based on single-output Mach–Zehnder modulator (MZM), optical coupler, and BPD, the advantages of our proposed dual-loop OEO (DO-OEO) with DOMZM and BPD are presented. Experimental results show that a 16-GHz single-mode OEO is obtained with measured SMSR of 72 dB and phase noise of −133.2 dBc/Hz at 10-kHz frequency offset.
A polymer-based multimode interference optical splitter chip has been designed and fabricated. Fiber-waveguide coupling loss as well as the structure of the multimode waveguide are optimized in the design to achieve higher performance. A simple UV-based soft nanoimprint lithography (Soft UV-NIL) technique is adopted in the fabrication. Fluorinated acrylate resins, LFR, with different refractive indices are used in this work. Both the residual layer and waveguide deformation are improved by controlling the fabrication processes. An average of 12.98 dB insertion loss is obtained from 1×4 splitters with 1.08 dB uniformity and 0.05 dB polarization-dependent loss. The validity of the polymer optical splitters fabricated through Soft UV-NIL technique is demonstrated by software simulation as well as experimental works.
A tunable optoelectronic oscillator (OEO) for detecting low-power radiofrequency (RF) signals is proposed and
experimentally demonstrated. The tunable OEO is mainly composed of a tunable laser source, a phase modulator, a
phase-shifted fiber Bragg grating (PS-FBG) and a photodetector. The PS-FBG is used as a notch filter to remove one
sideband of the phase-modulated signal to realize the phase modulation to intensity modulation conversion, which
determines the main oscillation mode of the OEO. The frequency of the RF signal under detection can be estimated by
the frequency difference between the optical carrier from the TLS and the notch of the PS-FBG. The RF signal as low as
-75 dBm is detected with a dynamic range of 80 dB. The RF signals from 1.5 to 4.5 GHz are selectively amplified with a
gain of about 7dB.
A polymer-based multimode interference (MMI) optical splitter chip has been fabricated through UV-based soft imprint lithography (Soft UV-NIL) technique. Propagation loss and bending loss are considered during the chip design in order to decrease the insertion loss. UV curable fluorinated acrylate resin is used due to its low material absorbing loss. 1×4 cascaded MMI splitter is fabricated and measured at 1550 nm optical wavelength and an average 12.38 dB insertion loss is obtained together with an 1.23 dB uniformity.
A microwave photonic link (MPL) with spurious-free dynamic range (SFDR) improvement utilizing the nonlinearity of a distributed feedback (DFB) laser is proposed and demonstrated. First, the relationship between the bias current and nonlinearity of a semiconductor DFB laser is experimentally studied. On this basis, the proposed linear optimization of MPL is realized by the combination of the external intensity Mach–Zehnder modulator (MZM) modulation MPL and the direct modulation MPL with the nonlinear operation of the DFB laser. In the external modulation MPL, the MZM is biased at the linear point to achieve the radio frequency (RF) signal transmission. In the direct modulation MPL, the third-order intermodulation (IMD3) components are generated for enhancing the SFDR of the external modulation MPL. When the center frequency of the input RF signal is 5 GHz and the two-tone signal interval is 10 kHz, the experimental results show that IMD3 of the system is effectively suppressed by 29.3 dB and the SFDR is increased by 7.7 dB.
A novel optical single-sideband (OSSB) signal generation with simultaneous IF signal up conversion technique is proposed to overcome the fiber dispersion problem. With this up-conversion technique, a high frequency OSSB signal is generated by using two low bandwidth intensity modulators in combination with fiber gratings. The low frequency local oscillator (LO) signal is modulated by employing frequency doubling technique or frequency quadrupling technique respectively. The OSSB radio frequency (RF) signal generated by mixing the intermediate frequency (IF) signal and low frequency local oscillator (LO) signal, is transmitted over standard single-mode fiber successfully. The received signal error vector magnitude (EVM) is 5.8% rms and 13% rms.
The filtering properties of a continuously tunable single-passband microwave photonic filter based on stimulated Brillouin scattering (SBS) are investigated. The filter utilizes the advantage of combining phase-modulated RF signal and dual-sideband suppressed-carrier pump signal to achieve the SBS-based tunable narrowband filtering. The effects of pump power on the out-of-band rejection (OBR) and 3-dB bandwidth, the optical fiber structure on the resonant sideband, and input RF signal power on the OBR and 3-dB bandwidth are analyzed theoretically and experimentally. The results show that the pump power has the potential of increasing the OBR and tuning 3-dB bandwidth, whereas the RF signal power has nearly no influence on the two parameters.
KEYWORDS: Signal generators, Singular optics, Modulators, Modulation, Radio optics, Single mode fibers, Microwave radiation, Eye, Signal detection, Optical amplifiers
A novel method is proposed for optical up-converted single-sideband (OSSB) signal generation in radio over fiber links, which can realize optical carrier reuse synchronously. The OSSB signal is generated in order to overcome the fiber dispersion problem by using two intensity modulators in combination with fiber gratings. With this up-conversion technique, a 25 GHz OSSB radio frequency signal is generated by mixing an intermediate frequency signal (5 GHz) and low frequency local oscillator signal (10 GHz). The signal is transmitted over 25 km standard single-mode fiber successfully. And the received signal error vector magnitude is 5.8% root mean square, with eye diagram widely open.
KEYWORDS: Microwave radiation, Single mode fibers, Time division multiplexing, Optical amplifiers, Optical switching, Dispersion, Switches, Modulators, Signal detection, Signal attenuation
We propose a novel photonic technique for unknown microwave frequency measurement by employing an optical group delay line. The 7-bit optical delay line composed of several magneto-optical switches and 1.6 km single-mode fiber is designed as a tunable dispersive medium in the measurement system. In our scheme, the measurable frequency range of 1 to 20 GHz with a measurement error less than ±40 MHz was demonstrated experimentally. Also, we studied the sensitivity of the whole measurement system, and the minimum detectable power reached −50 dBm .
Instantaneous frequency measurement (IFM) of input unknown microwave signals is critical importance for modern radar warning receivers in the field of electronic warfare. The photonic techniques have attracted more and more attentions for IFM due to the advantages of wide bandwidth, low loss, light weight, and immunity to electromagnetic interference. In this paper, a photonic approach to IFM with extended range based on phase modulation is presented. In the proposed measurement system, two optical wavelengths and two segment dispersion fibers are used to construct the frequency-dependent amplitude comparison functions (ACFs). Several ACFs can be jointly utilized to determine the microwave frequency without ambiguities beyond a monotonic region of the conventional one ACF. Then the measurable range of microwave frequency can be extended and the accuracy can be improved by selection of ACF with large slope. The operation principle of the photonic approach is illustrated and the experiment results show that the errors are limited within ±0.15 GHz from 8 to 20GHz frequency measurement range.
A novel technique for instantaneous frequency measurement of unknown microwave signal based on both phase
modulation and intensity modulation is theoretically and experimentally demonstrated. Based on the output microwave
power through dispersive fiber links, three amplitude comparison functions (ACFs) are established, which are combined
to measure the frequency of input microwave signal with improved measurable range and accuracy. In the frequency
estimation process, the measured calibration ACFs are utilized as the look-up table. The experiment results show that
measurement error smaller than 200 MHz can be obtained for the frequency from 0.5 GHz to 20 GHz.
Optical waveguide biosensors are attracting more and more attentions and presenting great potential applications.
Polymer-based optical biosensors are promising for the their unique advantages: low cost, easy fabrication,
possibility of functionalization with chemicals for the detection of biological molecules, and flexible operating
wavelength in both the infrared communication wavelength band (1310-1550nm) and the visible wavelength region
(500-800nm). Operating in the visible wavelength, the optical biosensing can avoid the high optical absorption loss
of water solution, which can hardly be done for Si-based optical sensors. In this paper, an optical biosensor utilizing
polymer-based athermal optical waveguide microring resonator is presented. The athermal design of the microring
resonator can make the resonant wavelength drift with temperature be greatly reduced, and an optical biosensing
platform with high thermal stability can be achieved. The simulation results show that the maximal resonant
wavelength drift is -0.0085nm when the temperature varies from 20°C to 65°C and the maximal wavelength drift
slope is -0.0009nm/K. With the microring resonators fabricated by using a simple UV based soft imprint technique
with self-developed UV-curable polymer PSQ-L materials, experimental investigations on the specific surface
detection of target molecules have been preliminarily performed. The results shows that the optical biosensors
based on the polymer optical microring resonators would have potential applications for label-free surface sensing.
Polymer has been considered to be an ideal material option for integrated photonics devices. To measure these devices,
normally the route of horizontal coupling is chosen to couple the light into or out of the polymer waveguide. Due to the
relatively low refractive index, implementing the surface grating coupler in this material system remains to be a
challenge. In this paper, we present a polymer based surface grating coupler. Rather than expensive CMOS fabrication,
the device is fabricated through a simple and fast UV based soft imprint technique utilizing self-developed low loss
polymer material. The coupling efficiency is enhanced by embedding a thin Si3N4 layer between the waveguide core and
under cladding layer. Around -19.8dB insertion loss from single-mode fiber (SMF) to single-mode fiber is obtained for a
straight waveguide with grating coupler at each end. If collected with multi-mode fiber (MMF), it can be reduced to
around -17.3dB. The 3dB bandwidth is 32nm centered at 1550nm. The proposed surface grating coupler and its easy
fabrication method would be attractive for practical applications.
A novel photonic approach for measuring microwave frequency over a wide bandwidth, based on intensity-modulated link with output microwave interference detection, is proposed. In this simple measurement system, a tunable laser and a fixed-wavelength laser are used with a single-mode fiber as the dispersive medium. By scanning the wavelength of a tunable laser, the frequency of the modulated microwave signal can be obtained directly through analyzing the interference intensity of the microwave signal at the output of the photodetector. The proposed approach is demonstrated experimentally by obtaining the unknown microwave frequency in the range of 1 to 20 GHz with a measurement accuracy of several tens of MHz.
Integrated waveguide microwave photonic filters (MPFs) have the potential to bring down volume, weight, and power consumption of signal processing equipment besides the common advantages of discrete-component-based MPFs. A polysiloxane-liquid polymer-based optical wave-guide microring resonator was designed and fabricated by a simple ultraviolet-based soft-imprint technology, with which the quasi-single-sideband filtering for the 10 to 22 GHz microwave signal was realized and 20 Mbps quadrature phase shift keying signal carried by 14.35 GHz microwave transmission over a 25 km single mode fiber was demonstrated.
Planar integrated optical biosensors are becoming more and more important as they facilitate label-free and real time
monitoring biosensing with high sensitivity. In this paper, the systematic research on one kind of optical biosensor,
based on a resonant principle in a polymer ring resonator, will be presented. Reduced footprint and high sensitivity are
advantages of this kind of biosensor. Rather than expensive CMOS fabrication, the device with high performance is
fabricated through a simple UV based soft imprint technique utilizing self-developed low loss polymer material. The
measurement results for the bulk sensing of a NaCl solution and the surface sensing of a minimal amount of avidin
molecules in a buffered solution will be presented.
The athermal all-polymer waveguide microring resonator is realized by selecting
polymer substrate with proper thermal expansion coefficient to substitute the silicon one. The
designed results show that the maximal resonant wavelength shift is -0.0085nm and the maximal
temperature dependent wavelength shift slope is -0.0009nm/K when the temperature varies from
20°C to 65°C.
Phase noise characteristics of the carrier transmitted by the double-sideband-carrier-suppressed (DSB-CS) modulation system are investigated. On the basis of the established DSB-CS modulation system, the phase noise of the input carrier and the output doubled frequency carrier is measured. The influencing factors on the far-from-carrier phase noise are discussed in detail. The noise current mean-square value of the signal-spontaneous beat noise is first derived in the case that there are two first-order optical sidebands generated by DSB-CS modulation. It is shown that the far-from-carrier phase noise is degraded primarily due to the signal-spontaneous beat noise and the relative-intensity noise.
Recent progress in research on polymer photonics is reviewed in this paper, including new concepts of polymer-based
photonic materials, components and devices. Novel polymer photonic materials developed in our photonic research
group, polysiloxanes (named as PSQ-Ls), are reported, including two kinds of PSQ-Ls, named as PSQ-LL and PSQ-LH.
These polymer photonic materials are of a liquid and can be cured by UV light irradiation or by heat. The
characterization of the optical films and waveguides based on the novel polymer materials, including refractive index,
birefringence, optical loss and thermal stability, is given in detail. By blending PSQ-LL and PSQ-LH, the refractive
indexes can be tuned linearly from 1.4482 to 1.5212 at 1310nm and from 1.4478 to 1.5198 at 1550nm. The birefringence
is below 0.0005 with the variation of PSQ-LL content. These materials exhibit low optical losses of 0.31dB/cm at a
wavelength of 1310nm and 0.70dB/cm at 1550nm, and high thermal stability with 1% decomposition temperatures of
297°C (in air) and 340°C (in N2) for PSQ-LH, and 313°C (in air) and 370°C (in N2) for PSQ-LL. Optical waveguide
components such as micro-ring resonators and waveguide gratings based on PSQ-Ls are fabricated by
photolithography-etching method and by UV imprint technology, respectively. The experimental measurements show
that the polymer-based micro-ring resonators exhibit an excellent resonant filtering function. Potential applications of the
polymer-based micro-ring resonators for optical communications and optical sensing are discussed.
Two kinds of liquid photopatternable inorganic-organic hybrid polymer materials
polysiloxanes, named as PSQ-LL and PSQ-LH, are prepared by a sol-gel process at room
temperature. The refractive indexes of waveguide materials can be tuned linearly from 1.4482 to
1.5212 at 1310nm and from 1.4478 to 1.5198 at 1550nm by blending PSQ-LL and PSQ-LH. These
materials have low optical losses of 0.31dB/cm at 1310nm and 0.80dB/cm at 1550nm, and high
thermal stability with 1% decomposition temperatures of 297°C (in air) and 340°C (in N2) for
PSQ-LH and 313°C (in air) and 370°C (in N2) for PSQ-LL. Typical waveguide structures based on
PSQ-Ls are fabricated by UV imprint technology.
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