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• A novel methodology to directly characterize the wavelength response (WR) of a DFB laser in wavelength modulation spectroscopy (WMS) is proposed. • This method circumvents the cumbersome etalon signal peak counting process which brings in manual errors easily. • The particle swarm optimization (PSO) algorithm was employed to effectively address the challenges encountered during the multi-parameter fitting process. A novel methodology to directly characterize the wavelength response (WR) of a DFB laser in wavelength modulation spectroscopy (WMS) is proposed. This method circumvents the cumbersome etalon signal peak counting process which brings in manual errors easily. The particle swarm optimization (PSO) algorithm was employed to effectively address the challenges encountered during the fitting process, which involved as many as 7 parameters in the WR. The WR with different combinations of frequencies of scan and modulation, as well as modulation amplitudes were characterized by this method. And it is shown that there exist negligible differences when comparing the results with those by traditional etalon peaking counting method. In order to verify the accuracy of this method, two tunable diode lasers emitting near 7185.59 cm−1 and 7444.35 cm−1 were employed to perform the measurements of temperature above a burner with calibration-free WMS- 2f/1f and direct absorption spectroscopy (DAS), respectively. The temperature measured by two techniques shows great accordance, which indicates the accuracy of WR deduced by the proposed method. [ABSTRACT FROM AUTHOR]

• A multi-laser hybrid sensor is designed based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneous measurement of NH 3 , NO, and flue gas temperature. • In calibration-free wavelength modulation spectroscopy (CF-WMS) measurements, we used a method to obtain the laser wavelength response by a simple fit to the S 2f/1f line pattern of a standard gas with a standard deviation of less than 5 × 10-3 cm-1. • Under static conditions, the relative accuracy of NH 3 and NO detected by the sensor is 4.2% and 2%, respectively, and the maximum relative standard deviation of temperature is 1.3%. • When tested under flowing conditions, the sensor can accurately capture NH 3 , NO, and temperature changes. The relative accuracy of NH 3 and NO is 4.7% and 2.2%, and the relative standard deviation of temperature is 0.9%. The real-time monitoring of NH 3 , NO, and flue gas temperatures is critical to controlling NO x emissions from coal-fired power plants, reducing ammonia slip, and realizing accurate ammonia injection. However, few previous studies have utilized laser absorption sensors to measure these three indicators simultaneously. In this paper, a multi-laser hybrid sensor is designed based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneous measurement of NH 3 , NO, and flue gas temperature. The sensor uses a distributed feedback (DFB) laser to target the NH 3 and the H 2 O lines, and a quantum cascade laser (QCL) is used to target the NO line. In the measurements of NH 3 and NO using calibration-free wavelength-modulated spectroscopy (CF-WMS), we employ a method to obtain the laser wavelength response by fitting the demodulated signal of a standard gas. Additionally, temperature measurements are obtained using the time-division multiplexing (TDM) strategy and direct absorption spectroscopy (DAS) techniques with the help of the absorption spectrum of H 2 O. Under static conditions, the relative accuracy of NH 3 and NO detected by the sensor is 4.2% and 2%, respectively, and the maximum relative standard deviation of temperature is 1.3%. When tested under flowing conditions, the sensor can accurately capture NH 3 , NO, and temperature changes. The relative accuracy of NH 3 and NO is 4.7% and 2.2%, and the relative standard deviation of temperature is 0.9%. The sensor has great potential in optimizing denitrification processes in thermal power plants. [ABSTRACT FROM AUTHOR]

Abstract: The spectral response of PHT-0044 (blue) and BCF-20 (green) scintillating fibers was measured as a function of wavelength using a UV LED. It was observed that significant spectral strength from the PHT-0044 fibers was missing compared to manufacturer''s specifications at the origin of the source, shifting the peak value of the spectrum to significantly higher values in wavelength. In contrast, the corresponding shift for the BCF-20 fibers was minimal. The mechanisms responsible for the observed behavior are discussed herein. Moreover, the attenuation length for each fiber type was extracted and studied as a function of wavelength. Finally, the measured fiber spectra were convolved with the wavelength response from a typical bi-alkali photomultiplier as well as a green-sensitive silicon photomultiplier and compared. [Copyright &y& Elsevier]

A novel polarization-independent wavelength-division-multiplexing (WDM) filter, which exploits the strong polarization dependence of cylindrical microresonators by using them as wavelength-selective polarization splitters is presented. Detailed analysis of the polarization dependence of the filter shows that the filter is indeed virtually polarization-independent and has a wavelength response similar to the wavelength response of a microresonator coupled to two waveguides for a single polarization. [ABSTRACT FROM PUBLISHER]

We developed a periodically poled LiNbO3 wavelength converter with its nonlinear coupling strength changed along the propagation length to improve the quasi-phase-matched (QPM) wavelength bandwidth. The apodization is realized by sampling the QPM grating to attain fabrication easiness. The wavelength response showed a broad and flat-top wavelength conversion characteristic in a second harmonic generation. The QPM bandwidth of the wavelength conversion was 2.2 nm, which is sufficiently broad to convert optical pulses for a 160-Gb/s system. [ABSTRACT FROM PUBLISHER]

A simple and powerful tuning method for a wavelength-division demultiplexer, based on photopolymer holographic grating is proposed. The device was designed to finely tune the transmission wavelengths of the demultiplexer linearly (or arbitrarily) and to obtain various transmission wavelengths depending on the applied strain. This represents the first use of strain for changing the wavelength response of a demultiplexer. The fabrication of the device is a simple process, and has the potential for use as a tunable demultiplexer. [ABSTRACT FROM PUBLISHER]

We demonstrate the wavelength-division multiplexing (WDM) and wavelength-encoding capability of input waveguide grating couplers. The couplers are designed to have a predetermined wavelength response in addition to their conventional function of coupling an incident beam from, e.g., an optical fiber into a planar waveguide. The first example shows the WDM function: separating each of four input wavelengths into a different focus position in the waveguide. The second example shows wavelength encoding: translating a certain wavelength into a desired configuration of focus positions that is different for four different input wavelengths. The couplers were fabricated in an InP waveguide for ~1550-nm wavelength and the separation between the wavelengths was 10 nm. A WDM coupler with a narrower channel separation of 2 nm was also fabricated and successfully demonstrated [ABSTRACT FROM PUBLISHER]

The effect of filter characteristics on the output performance of actively mode-locked fiber ring lasers has been studied experimentally and numerically, with the same 3-dB bandwidth, the filter that has a flatter wavelength response tends to generate narrower soliton-like pulses. [ABSTRACT FROM PUBLISHER]

We present a theoretical study on the effect of the angle of a tilted Bragg grating written in a 2×2 symmetric fused fiber coupler. Coupling coefficients and wavelength response curves show that the grating angle is critical in determining the behavior of the component. For a particular type of coupler, a tilt of 0.40 is sufficient to degrade component performance [ABSTRACT FROM PUBLISHER]

We report on the design and fabrication of 1×32 MMI power splitters through the sol-gel process. The MMI splitter is designed for 1.55-μm wavelength and characterized in terms of tolerance, wavelength response, and polarization sensitivity. The splitter is then UV-imprinted in aluminosilicate material coated on SiO2. It is found that the responses of fabricated and designed splitter are in good agreement, with an excess loss of ~0.75 dB and power uniformity of ~0.95 dB [ABSTRACT FROM PUBLISHER]