Yiying Gu

The February–March 2000 Eruption of Hekla, Iceland from a Satellite Perspective

An 80,000 km 2 stratospheric volcanic cloud formed from the 26 February 2000 eruption of Hekla (63.98° N, 19.70° W). POAM-III profiles showed the cloud was 9-12 km asl. During 3 days this cloud drifted north. Three remote sensing algorithms (TOMS SO 2 , MODIS & TOVS 7.3 μm IR and MODIS 8.6 μm IR) estimated ∼0.2 Tg SO 2 . Sulfate aerosol in the cloud was 0.003-0.008 Tg, from MODIS IR data. MODIS and AVHRR show that cloud particles were ice. The ice mass peaked at ∼1 Tg ∼10 hours after eruption onset. A ∼0.1 Tg mass of ash was detected in the early plume. Repetitive TOVS data showed a decrease of SO 2 in the cloud from 0.2 Tg to below TOVS detection (i.e.<0.01 Tg) in ∼3.5 days. The stratospheric height of the cloud may result from a large release of magmatic water vapor early (1819 UT on 26 February) leading to the ice-rich volcanic cloud. The optical depth of the cloud peaked early on 27 February and faded with time, apparently as ice fell out. A research aircraft encounter with the top of the cloud at 0514 UT on 28 February, 35 hours after eruption onset, provided validation of algorithms. The aircrafts instruments measured ∼0.5-1 ppmv SO 2 and ∼35-70 ppb sulfate aerosol in the cloud, 10-30% lower than concentrations from retrievals a few hours later. Different SO 2 algorithms illuminate environmental variables which affect the quality of results. Overall this is the most robust data set ever analyzed from the first few days of stratospheric residence of a volcanic cloud.

UV-soft Imprinted Tunable Polymer Waveguide Ring Resonator for Microwave Photonic Filtering

A tunable polymer waveguide ring resonator is proposed and demonstrated for microwave photonic filtering. The ring resonator consists of a Mach-Zehnder interferometer (MZI) as the tunable coupler and two micro-heaters as the thermo-optic phase shifters. It was fabricated with inorganic-organic hybrid optical material polysiloxane-liquid series by a novel and simple UV-soft selective imprint technique. The coupling conditions, over-, critical- and under-coupling, were obtained with the micro-heater on the arm of MZI and the maximum notch depth of about 18 dB was achieved. The resonant wavelength was also tuned with the micro-heater on the ring waveguide. The dispersion induced power fading of radio over fiber link was overcome by the tunable ring resonator with its notch filtering function.

Optical biosensors utilizing polymer-based athermal microring resonators

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.

Quasi-single-sideband radio over fiber transmission with a polymer-based waveguide microring resonator

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.

A Novel Low-Power-Consumption All-Fiber-Optic Anemometer with Simple System Design

A compact and low-power consuming fiber-optic anemometer based on single-walled carbon nanotubes (SWCNTs) coated tilted fiber Bragg grating (TFBG) is presented. TFBG as a near infrared in-fiber sensing element is able to excite a number of cladding modes and radiation modes in the fiber and effectively couple light in the core to interact with the fiber surrounding mediums. It is an ideal in-fiber device used in a fiber hot-wire anemometer (HWA) as both coupling and sensing elements to simplify the sensing head structure. The fabricated TFBG was immobilized with an SWCNT film on the fiber surface. SWCNTs, a kind of innovative nanomaterial, were utilized as light-heat conversion medium instead of traditional metallic materials, due to its excellent infrared light absorption ability and competitive thermal conductivity. When the SWCNT film strongly absorbs the light in the fiber, the sensor head can be heated and form a “hot wire”. As the sensor is put into wind field, the wind will take away the heat on the sensor resulting in a temperature variation that is then accurately measured by the TFBG. Benefited from the high coupling and absorption efficiency, the heating and sensing light source was shared with only one broadband light source (BBS) without any extra pumping laser complicating the system. This not only significantly reduces power consumption, but also simplifies the whole sensing system with lower cost. In experiments, the key parameters of the sensor, such as the film thickness and the inherent angle of the TFBG, were fully investigated. It was demonstrated that, under a very low BBS input power of 9.87 mW, a 0.100 nm wavelength response can still be detected as the wind speed changed from 0 to 2 m/s. In addition, the sensitivity was found to be −0.0346 nm/(m/s) under the wind speed of 1 m/s. The proposed simple and low-power-consumption wind speed sensing system exhibits promising potential for future long-term remote monitoring and on-chip sensing in practical applications.

Sagnac Interferometer-Assisted Microwave Photonic Link With Improved Dynamic Range

In this paper, we propose a simple method to improve the spurious-free dynamic range (SFDR) of a microwave photonic link (MPL). The proposed method is based on a Sagnac interferometer structure; signal output of the Sagnac interferometer consists of two kinds of optical components: the clockwise (CW) modulated optical signal and the counter clockwise (CCW) unmodulated optical carrier. An appropriate situation is then created to satisfy the phase and power ratio condition of the two counter propagating light waves. Eventually, in photodiode, part of the third-order intermodulation distortion (IMD3) component is generated by the CW light wave and another part is generated by the CW sidebands beating with the CCW optical carrier. Under appropriate circumstances, these two kinds of IMD3s have same amplitude but opposing phase; hence, the IMD3 can be cancelled, and an enhanced SFDR is achieved. An experiment is conducted, and results show that, as compared with a conventional MPL, the SFDR of the proposed link is improved by 10.3 dB, and for a 16-quadrature amplitude modulation (QAM) 10-MSym/s signal centered at 15 GHz, the error vector magnitude is reduced by 5.9%.

Dynamic Range Improvement of a Microwave Photonic Link Based on Brillouin Processing

A novel method to improve the spurious-free dynamic range (SFDR) of a microwave photonic link based on stimulated Brillouin scattering (SBS) processing is proposed and experimentally demonstrated. In the proposed system, an optical single-sideband with suppressed carrier (SSB-SC) signal is generated using a dual-parallel Mach–Zehnder modulator (MZM) by biasing its two sub-MZMs at minimum transmission point and the parent MZM at quadrature transmission point. In order to generate SBS, the SSB-SC signal is amplified and injected into a length of dispersion-shifted fiber where the MPL’s double-sideband optical signals are transmitted. Due to the SBS effect, a phase shift is induced to MPL’s optical carrier band, and hence, the third-order intermodulation distortion (IMD3) components originated from two different sources can cancel each other. Experimental results show that the SFDR of the link is improved by 10.3 dB, and the IMD3 is reduced by more than 23 dB.

Filtering properties of the tunable microwave photonic filter with stimulated Brillouin scattering

Abstract. 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.

Photonic approach to microwave frequency measurement with extended range based on phase modulation

We propose and demonstrate a photonic approach to instantaneous frequency measurement with an extended range based on phase modulation. In the measurement system, two optical wavelengths and two dispersion fiber segments are used to construct the frequency-dependent amplitude comparison functions (ACFs). Several ACFs can be utilized jointly to determine the microwave frequency without ambiguities beyond a monotonic region of the lone conventional ACF. The measurable range of microwave frequency can be extended and the accuracy can be improved by selecting an ACF with a large slope. The experimental results show that the errors are limited within ±140 MHz of a frequency measuremental range from 8 to 20 GHz.

Novel photonic broadband microwave frequency measurement based on intensity-modulated link with output microwave interference detection

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.