Chuan-Tao Zheng

Pocket-Sized Nondispersive Infrared Methane Detection Device Using Two-Parameter Temperature Compensation

ABSTRACT With the correction on Beer–Lambert law, a low-cost, low-power, and miniaturization methane detection device is reported by using a two-parameter temperature compensation method. The adopted methane sensor contains a midinfrared light source, an optical path, and a midinfrared dual-channel detector. Control and processing circuits are developed to extract gas concentration, and experiments are carried out to derive detection performances. Two characteristic parameters of the device are achieved through calibration, and their relations with temperature are obtained for accurate compensation. The device is powered by batteries with a total current less than 100 mA, and the power consumption is less than 0.6 W. Both the sensitivity and the minimum detection limit under low concentration range can reach to 50 parts per million. The device also reveals high stability owing to the compensation on temperature variation. Compared with the preexisting wall-mounted devices, this device does well meeting the requirement of detecting explosive gases in a more convenient handheld style.

Low-power and high-speed thermo-optic switch using hybrid silica/polymer waveguide structure: design, fabrication and measurement

Response speed and power consumption are improved for a Mach–Zehnder interferometer (MZI) thermo-optic (TO) switch, by using a hybrid silica/polymer waveguide structure and optimizing both the thickness of the silica under cladding and that of the PMMA-GMA upper cladding. Fabrication techniques, including chemical vapor deposition (CVD), spin-coating and wet-etching, are adopted to develop the switch sample. Under 1550 nm wavelength, the driving powers under ON and OFF states are measured to be 0 and 13 mW, respectively, indicating a switching power of 13 mW. The fiber-to-fiber insertion loss under the ON state is 15 dB, the extinction ratio between the ON state and the OFF state is 18.3 dB, and the rise time and fall time are 73.5 and 96.5 µs, respectively. Compared with the TO switches based on Si/SiO2 or all-polymer waveguide structure, the proposed device possesses both low power consumption and fast response speed, by virtue of the large TO coefficient of the polymer core, thin upper/under claddings and the large thermal conductivity of silica.

Fourier Modeling and Numerical Characterization on a High-Linear Bias-Free Polymer Push-Pull Poled Y-Fed Coupler Electro-Optic Modulator

A high-linear bias-free polymer Y-fed coupler electro-optic (EO) modulator with push-pull poled two section waveguides is proposed. Using Fourier transformation, a novel formulation technique is presented to numerically model and characterize the device performances. As an EO modulator, the half-wave voltage is 2.6852 V, and the 3-dB modulation bandwidth is ~ 143 GHz. As an EO switch, the insertion loss and crosstalk are <; 3.548 and <; -30 dB, respectively, and the 10%-90% rise time and fall time are both ~ 3.90 ps, indicating a cutoff switching frequency up to 128.2 GHz. As the modulation coefficient is within the range of 1%-10%, the distortion suppression on the third-order intermodulation distortion signals is as high as 60-90 dB, suggesting favorable linearity. This analytical technique is also efficient to theoretically predict the performances of a device with Y-fed coupler structure.

Infrared Dual-Gas CH4/C2H6Sensor Using Two Continuous-Wave Interband Cascade Lasers

An infrared dual-gas sensor system for the simultaneous detection and monitoring of methane (CH₄) and ethane (C₂H₆) at parts-per-billion by volume (ppbv) concentration levels was developed using two room temperature, distributed feedback interband cascade lasers, and two miniature multipass cells with an effective absorption length of 54.6 m. Laser direct absorption spectroscopy was used to detect CH₄ utilizing the 3038.5-cm^-1 absorption line, and second-harmonic wavelength modulation spectroscopy method was used to detect C₂H₆ using the 2996.88-cm^-1 absorption line. The 1σ CH₄ detection limit is ~2.7 ppbv with a 1-s averaging time and exhibits a minimum value of ~1.7 ppbv for a 9-s averaging time; the 1σ C₂H₆ detection limit is ~2.6 ppbv with a 3.4-s averaging time and shows an optimum averaging time of 65 s corresponding to a stability of ~0.36 ppbv. Using the dualgas sensor system, 24 h monitoring of the two atmospheric gases was performed in the Greater Houston area, TX, USA.

Wireless Mid-Infrared Spectroscopy Sensor Network for Automatic Carbon Dioxide Fertilization in a Greenhouse Environment

In this paper, a wireless mid-infrared spectroscopy sensor network was designed and implemented for carbon dioxide fertilization in a greenhouse environment. A mid-infrared carbon dioxide (CO2) sensor based on non-dispersive infrared (NDIR) with the functionalities of wireless communication and anti-condensation prevention was realized as the sensor node. Smart transmission power regulation was applied in the wireless sensor network, according to the Received Signal Strength Indication (RSSI), to realize high communication stability and low-power consumption deployment. Besides real-time monitoring, this system also provides a CO2 control facility for manual and automatic control through a LabVIEW platform. According to simulations and field tests, the implemented sensor node has a satisfying anti-condensation ability and reliable measurement performance on CO2 concentrations ranging from 30 ppm to 5000 ppm. As an application, based on the Fuzzy proportional, integral, and derivative (PID) algorithm realized on a LabVIEW platform, the CO2 concentration was regulated to some desired concentrations, such as 800 ppm and 1200 ppm, in 30 min with a controlled fluctuation of <±35 ppm in an acre of greenhouse.

Silica/Polymer TIR Optical Switches and a Proposal for Nonblocking Four-Port Routers

We have fabricated a wavelength-insensitive silica/polymer total-internal-reflection thermooptic switch element using photolithography and wet etching techniques. A switching power of 70 mW is required to drop the crosstalk below -20 dB. Under through and reflection states, the propagation losses of the 0.47-cm long core switch element are measured to be 1.8 and 3.6 dB, respectively. The 10%-90% rise time and the 90%-10% fall time are 0.35/0.38 and 0.52 ms, respectively. Using 11 switch elements, we have proposed a nonblocking four-port optical router. The propagation loss range is ~5.4-23.4 dB along all routing paths. Both the switch and the router show potential applications of wideband signal switching and routing in multiprocessor-based optical networks-on-chip.

FABRICATION OF A POLYMER-ON-SILICA HYBRID THERMO-OPTIC SWITCH WITH FAST RESPONSE TIME AND LOW POWER CONSUMPTION

A polymer-on-silica Mach–Zehnder interferometer (MZI) TO switch is experimentally demonstrated using core polymer material with large thermo-optic (TO) coefficient. In the hybrid structure, the negative photoresist SU-8 and silica are used as core and lower cladding, respectively. Wet-etching technique is adopted to optimize fabrication process and diminish sidewall roughness and scattering loss. Compared to our two previously reported works, this switch exhibits better performance with lower power consumption of less than 4.8 mW, higher extinction ratio of 22.5 dB, shorter rise time of 141 μs and fall time of 87 μs, due to the larger thermal conductivity of silica relative to polymer in the proposed hybrid configuration.

Nanosecond Bias-Free Mach–Zehnder Electro-Optic Switch Based on Dye-Doped Polymer DR1/SU-8 and Microstrip Line Electrode

Abstract A bias-free Mach–Zehnder interferometer electro-optic switch is demonstrated with a dye-doped polymer Disperse Red 1 (Tokyo Chemical Industry, Co., LTD, Tokyo, Japan)/SU-8 (MicroChem Corp., Newton, Massachusetts, USA) and microstrip line electrode. The device is carefully designed and optimized for bias-free function and high-speed switching using the three-dimensional beam-propagation method and extended point-matching method, and the switch is seriously fabricated by a wet-etching technique and inductively coupled plasma etching technique for good control of dimension parameters. The measured rise time and fall time at 1,550 nm are both at the level of ~10 ns. Owing to the bias-free function and nanosecond response speed, this switch exhibits potential applications of high-speed optical routing and exchanging.

Fast response 2 \times 2 thermo-optic switch with polymer/silica hybrid waveguide

A polymer/silica hybrid 2 \times 2 multimode-interference Mach–Zehnder interferometer thermo-optic (TO) switch is designed and fabricated. Instead of polymer, silica is used as under-cladding to accelerate heat release because of its large thermal conductivity. The developed switch exhibits low power consumption of 6.2 mW, low crosstalk of about –28 dB, and short response time. The rise and fall times of 103 and 91 \mu s for this hybrid switch are shortened by 40.8% and 52.4%, respectively, compared with those of the fabricated TO switch (174 and 191 \mu s) using polymer as both upper- and under-claddings.

Investigation of a novel wide-spectrum polymer electro-optic switch with high extinction ratio over 40 dB covering S-C-L band

A novel kind of wavelength-insensitive wide-spectrum polymer electro-optic (EO) switch is proposed by employing two symmetric active Mach-Zehnder interferometers (MZIs), a passive middle directional coupler and a pair of passive phase-generating couplers. Extinction ratio compensation condition under off-state and insertion loss compensation condition under on-state are derived to expand wavelength spectrum. With sufficient consideration of the wavelength dispersion of material and waveguide, optimization, and simulation were performed. The switch exhibits a switching voltage of 4.96 V with each MZI EO region length of 5000 μ m. An S-C-L band (1460 to 1625 nm) covering a wide-spectrum more than 165 nm was obtained, and within this range, an extremely high extinction ratio more than 40 dB and an insertion loss within 1.8 to 11.9 dB were reached. This spectrum was more than 8 times of that of the traditional MZI EO switch (only 20 nm).The proposed device can function normally at any wavelength, and is an ideal candidate for a broadband photonic switching element in next-generation nonwavelength selective optical networks-on-chip.