A power splitter with a wideband arbitrary splitting ratio, which provides flexibility and adaptability in forming photonic devices such as microring resonators and Mach–Zehnder interferometers, proves to be essential in photonic integrated circuits (PICs). We designed and fabricated a directional coupler-based power splitter with a wideband arbitrary splitting ratio and a microring resonator with a wideband uniform extinction ratio (ER) based on artificial gauge field (AGF) optimization. The neural network-aided inverse design method is applied to complete the target. Less than 0.9 dB power splitting variation and 1.6 dB ER variation have been achieved experimentally over a 100-nm bandwidth. Wideband performance, design efficiency, and device compactness are obtained by utilizing this optimization, which indicates great potential and universality in PIC applications.
We present a newly developed high performance fiber optics sensor for quasi-static strain measurement. The sensor consists of a piece of π-phase shifted FBG for static strain sensing, and fiber Fabry-Perot interferometer for reference, interrogated by an improved sideband interrogation method with real-time feedback loops. Strain resolution of 0.12 nano-strain was achieved with sampling rate up to 1 kS/s in laboratory experiments. Compared with previous sensor systems, the proposed method shows great improvement in the sensing rate as well as the resolution.
In this invited talk, we will present the advances in research and development activities of optical reflectometry in our laboratory. The performance of phase-sensitive coherent OTDR, which is developed for distributed vibration measurement, is reported with the results of field tests. The performance of time-gated digital OFDR, which is developed for optical access network diagnostics, is also reported. We will also discuss how to increase the frequency sweep span of the linearly-swept optical source, a very important part for improving the performance of optical reflectometry.
We developed a novel optical coherent domain reflectometer (OCDR) technique with large measurement range by using of dual frequency modulation. The probe and local oscillator beams are frequency modulated independently, and the sensing position can be adjusted digitally via the time delay between the driving signals for the two modulators. Meanwhile, the frequency tuning spans of the two paths are different to enable heterodyne detection. In the demonstrational experiments, a spatial resolution of 3.9 m over a range of 24.6 km fiber was achieved with 35 MHz tunable range of the modulator, and the spatial resolution keeps a constant over the whole measurement range.
We reported an optical fiber based temperature sensor with mK-order resolution, wide temperature range and excellent long term stability. The sensor composes of a fiber Bragg grating (FBG) as the sensing element, an HCN gas cell for absolute frequency reference. A distributed feedback diode laser with current modulation is used as the light source. To overcome the frequency-sweep nonlinearity of the laser, an auxiliary Fabry-Perot interferometer with free spectrum range of 10 MHz is employed. A cross-correlation algorithm is employed to calculate the center frequency difference between the FBG and the gas cell. With the proposed configuration, a temperature resolution of 0.41 mK was demonstrated in experiment. To the best knowledge, this is the first time that an mK order temperature resolution has been achieved by optical fiber sensor.
We demonstrate a method for high spatial resolution optical frequency domain reflectometry (OFDR) by utilizing degenerated four-wave-mixing (FWM) for broadening the frequency sweeping. High order sideband is obtained from an optical comb and is consequently utilized as the pump for the FWM. An idler wavelength is produced after the FWM and 21-times broadened optical frequency sweeping is achieved compared with the radio frequency (RF) sweeping. 0.75-cm spatial resolution is obtained with RF frequency sweeping span of 638.4 MHz.
High-order and cascaded four-wave-mixing (FWM) is utilized for enhancing the strain sensitivity of an FBG sensor based on all-optical frequency chirp magnification. 7.6-pm/με strain sensitivity is obtained for a conventional FBG sensor, which has been magnified by a factor of six.
Two simple and low-cost methods for achieving selective filling of air-core photonic bandgap fibers (PBGFs) are
proposed and demonstrated. In the first method, liquid paraffin was filled into a PBGF by capillary force. By a two-step
filling-cleaving process, all cladding air-holes are finally blocked but the air-core remains open. In the second method,
lateral erosion method by hydrofluoric acid was first used to make the cladding air-holes laterally open. Then, the
laterally filled liquid paraffin made all cladding air-holes blocked and left only air-core open. With these two methods,
the central hollow-core of the PBGF can be selectively filled, which allows for the fabrication of novel hybrid
functional-material-silica PBGF for various applications.
A stable multiwavelength erbium-doped fiber laser is proposed and demonstrated successfully. Through carefully
adjusting the state of the polarization controller, the stable two three-wavelength with a spacing of 0.8 nm and one four-wavelength
with a spacing of 0.4 nm fiber laser have been obtained. A nonlinear optical loop mirror (NOLM) with 70-m
long Photonic Crystal Fiber (PCF) is employed to ensure stable room-temperature multiwavelength operation. The
measured power fluctuation of each wavelength is less than 0.2 dB and the peak power differences among the main
oscillation wavelengths are less than 1.0 dB. Another desirable characteristic is that it needs a relatively low pump power
of 100 mW. The signal-to-noise ratio is ~35 dB. And it is better than that inserting single-mode fiber (SMF) ever
reported.
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