Μm Distributed Feedback Laser Research Articles

Methane gas sensor based on a novel dual‐path multipass cell

AbstractWe have developed a novel dual‐path multipass cell (DP‐MPC) for trace gas detection. The sealed Herriott cell, measuring 16 × 16 × 41.5 cm, has two input/output coupling holes. By adjusting the mirror position and incident angle of the beam, optical paths of 105 and 37.5 m can be obtained, respectively. To test its performance, we setup a methane (CH4) concentration detection system by combining the DP‐MPC with a 1.65 μm distributed feedback laser and carried out a methane gas detection experiment. The Allan variance analysis showed that the limit of detection for the two optical paths were 6 and 30 ppb, respectively.

A sensitive carbon monoxide sensor for industrial process control based on laser absorption spectroscopy with a 2.3 μm distributed feedback laser

Carbon monoxide (CO) is a ubiquitous atmospheric trace gas produced by natural and anthropogenic sources. It can be used as a quantitative marker to help us understand the different production processes. A near-infrared laser absorption spectroscopy of 2.3 μm based in-situ, real-time and continuous CO sensor equipment is developed for the exhaust pipeline of furnace. High sensitivity is accomplished utilizing the ratio between the second and first harmonic signals detection (WMS-2f/1f). The analyzer is housed in an explosion-proof enclosure and installed at both sides of the pipeline with a diameter of 2.1 m. The measured gas temperature inside the pipeline reaches around 400 K. The results primarily show a more linear response and less error, the measurement precision and the minimum detection limit are 0.42 ppm and 1.29 ppm (1σ), simultaneously. Evaluation of the data suggested a dynamic range from 3.87 ppm to 1.3% based on the 3σ rule and maximum absorbance of one. An operator can analyze the industrial production process clearly, that is, the measured CO concentration is negatively correlated with excess oxygen (O2) by observing the measurement results within 10 h. Meanwhile, the measurements of the real targets show that the sensor has great applicability and potential for exhaust pipeline and combustion control systems.

A Laser-Locked Hollow Waveguide Gas Sensor for Simultaneous Measurements of CO2 Isotopologues with High Accuracy, Precision, and Sensitivity.

A laser frequency-locked hollow waveguide (HWG) gas sensor is demonstrated for simultaneous measurements of three isotopologues (12CO2, 13CO2, and 18OC16O) using wavelength modulation spectroscopy with a 2.73 μm distributed feedback laser. The first harmonic (1f) signal at the sampling point where the peak of the second harmonic (2f) signal was located was employed as the locking point to lock the laser frequency to the transition center of 13CO2, while the absorption lines of 12CO2 and 18OC16O were being scanned. Continuous measurements of the three isotopologues of 4.7% CO2 samples over 103 min under free running and frequency locking conditions were performed. The measurement accuracy and precision of the three isotopologues achieved under the frequency locking condition were at least 3 times and 1.3 times better than those obtained under the free running condition, respectively. The Allan variance plot of the developed laser-locked HWG gas sensor shows a detection limit of 0.72‰ for both δ13C and δ18O under the frequency locking condition with a long stability time of 766 s. This study demonstrated the high potential of a novel human breath diagnostic sensor for medical diagnostic with high accuracy, precision, and sensitivity and without frequently repeated calibration.

Three-Dimensional Printed Miniature Fiber-Coupled Multipass Cells with Dense Spot Patterns for ppb-Level Methane Detection Using a Near-IR Diode Laser.

Tunable diode laser absorption spectroscopy (TDLAS) based on a multipass cell (MPC) is a powerful analytical tool and is widely applied to air quality monitoring, industrial process control, and medical diagnostics. However, the conventional MPC as a core component in TDLAS devices has a large size, low utilization efficiency of the mirror surfaces, and tight optical alignment tolerances. In this paper, we design and fabricate a mini-MPC with an optical absorption path length of 4.2 m and dimensions of 4 × 4 × 6 cm3 (open cavity), which, to our best knowledge, is the current smallest MPC in terms of the same optical path length. The mini-MPC generates a seven-nonintersecting-circle dense spot pattern on two 25.4 mm spherical mirror surfaces, providing a high fill factor of 21 cm-2. A fiber-coupled collimator and an InGaAs photodetector are integrated into the mini-MPC via a high-resolution three-dimensional printed frame, hence removing the requirement of active optical alignment. Using a 1.65 μm distributed-feedback laser, the performance of this mini-MPC for methane detection was evaluated in terms of linearity, flow response time, stability, minimum detectable limit, and measurement precision. Continuous measurements of methane near a sewer and in the atmosphere were performed to demonstrate the stability and robustness of the highly integrated mini-MPC-based gas sensor. Our analysis shows that a methane minimum detectable limit of 117 ppbv is achieved, paving the way toward a sensitive, low-cost, and miniature trace gas sensor inherently suitable for large-scale deployment of distributed sensor networks and for handheld mobile devices.

Real-Time Monitoring of 13C- and 18O-Isotopes of Human Breath CO2 Using a Mid-Infrared Hollow Waveguide Gas Sensor.

Real-time measuring of CO2 isotopes (13CO2, 12CO2, and 18OC16O) in exhaled breath using a mid-infrared hollow waveguide gas sensor incorporating a 2.73 μm distributed feedback laser was proposed and demonstrated for the first time based on calibration-free wavelength modulation spectroscopy. The measurement precisions for δ13C and δ18O were, respectively, 0.26 and 0.57‰ for an integration time of 131 s by Allan variance analysis. These measurement precisions achieved in the present work were at least 3.5 times better than those reported using direct absorption spectroscopy and 1.3 times better than those obtained by calibration-needed wavelength modulation absorption spectroscopy. Continuous measurement of three isotopes in the breathing cycle was performed. Alveolar gas from the expirogram was identified, and the 13C/12C and 18O/16O ratios were found to be almost constant during the alveolar plateau, which enables optimization of breath sampling and provides accurate information on metabolic processes. The 13C/12C and 18O/16O isotope ratios at the alveolar plateau of five breath cycles were averaged, yielding δ13C and δ18O values of (-24.3 ± 3.4) and (-30.7 ± 2.6) ‰, respectively. This study demonstrates the feasibility of real-time analysis of 13C- and 18O-isotopes of human breath CO2 in clinical applications and shows its potential for diagnosing respiratory-related diseases with high sensitivity, selectivity, and specificity.

Compact dual-gas sensor for simultaneous measurement of atmospheric methane, and water vapor using a 3.38 μm antimonide-distributed feedback laser diode.

A simple, compact sensor involving a continuous-wave 3.38 μm distributed feedback laser in combination with a novel compact dense-pattern multipass cell was demonstrated for simultaneous measurement of atmospheric methane and water vapor. The calibration-free direct absorption spectroscopy approach was adopted for data generation and processing. Allan deviation analysis indicates that minimum detection limits (1σ) of 11.0 ppb for CH4 and 100 ppm for H2O were achieved with a 1-s integration time at an optimum pressure of 50 Torr. Atmospheric environmental mixing ratios of these two gases were recorded and analyzed. This newly developed mid-infrared dual-gas sensor is very suitable for trace gas sensing in weight-limited unmanned aerial vehicle- or balloon-embedded field observations.

基于2.73 μm分布反馈式激光器同时在线测量呼出气体中的CO2和水汽

基于2.73 μm分布反馈式激光器同时在线测量呼出气体中的CO2和水汽

Effect of gain compression above and below threshold on the chirp characteristics of 1.55 µm distributed feedback laser

We have observed and quantified the adiabatic and transient chirp in a directly modulated laser. The wavelength excursion for both chirp terms is well characterized by the phase rate equation model that describes the chirp behavior. In this study, the effect of gain compression and linewidth enhancement factor, below and above threshold, on the chirp characteristics is investigated by simulation. We have observed the trade-off between the two chirp terms i.e., transient part of the chirp is reduced by the strong damping introduced by gain compression, while as the adiabatic part increases with gain compression. We have observed that above threshold the α-factor increases with bias current, which is attributed to the enhancement of gain compression coefficient. It is shown that the higher the maximum gain, the lower the effects of gain compression and lower the α-factor. Finally, the effects of gain compression on the transmission characteristics are investigated.

基于2.33 μm可调谐激光的石英音叉增强型光声光谱测量CO研究

基于2.33 μm可调谐激光的石英音叉增强型光声光谱测量CO研究

First demonstration of 1.3 μm quarter-wavelength shift distributed feedback (DFB) semiconductor laser based on conventional photolithography

A 1.3 μm distributed feedback (DFB) semiconductor laser with equivalent λ/4 phase shift based on reconstruction equivalent chirp (REC) technique is numerically studied and experimentally demonstrated. The simulation results show that the 1.3 μm DFB laser with equivalent λ/4 phase shift based on the REC technique performs the same as that of actual λ/4 phase shift DFB laser, with nearly the same P-I curves, the internal power distributions and the output ASE spectra. Compared with the traditional λ/4 phase shift DFB laser, the REC based laser only changes the sampling structures with the uniform seed waveguide grating instead of the actual grating structures. As a result, the fabrication of such laser will be very easy. In this paper, we successfully fabricated the 1.3 μm DFB laser based on the REC technique for the first time to the best of our knowledge.

All-fiber passively mode-locked thulium/holmium laser with two center wavelengths

We have demonstrated a self-starting, passively mode-locked Tm/Ho codoped fiber laser that lases at one of two center wavelengths. An amplified 1.56 μm distributed feedback laser pumps a ring laser cavity which contains 1 m of Tm/Ho codoped silica fiber. Mode locking is obtained via nonlinear polarization rotation using a c-band polarization sensitive isolator with two polarization controllers. The laser is able to pulse separately at either 1.97 or 2.04 μm by altering the intracavity polarization during the initiation of mode locking. The codoped fiber permits pulsing at one of two wavelengths, where the shorter is due to the Tm(3+) emission and the longer due to the Ho(3+) emission. The laser produces a stable pulse train at 28.4 MHz with 25 mW average power, and a pulse duration of 966 fs with 9 nm bandwidth.

Multipoint laser Doppler vibrometry with single detector: principles, implementations, and signal analyses

A 20-point laser Doppler vibrometer with single photodetector is presented for noncontact dynamic measurement. A 5×4 beam array with various frequency shifts is generated by a 1.55 μm distributed feedback laser and four acousto-optic devices, and illuminating different points on vibrating objects. The reflected beams are coupled into a single-mode fiber by a pigtailed collimator and interfere with a reference beam. The signal output from a high-speed photodetector is amplified and then digitized by a high-speed analog-to-digital converter with a sampling rate of 1 gigasample per second (1 GS/s). Several methods are introduced to avoid the cross talk among different frequencies and extract the vibration information of 20 points from a one-dimensional signal. Two signal processing algorithms based on Fourier transform and windowed Fourier transform are illustrated to extract the vibration signals at different points. The experimental results are compared with that from a commercial single-point laser vibrometer. The results show simultaneous vibration measurement can be realized on multiple points using a single laser source and a single photodetector.

An efficient and compact difference-frequency-generation spectrometer and its application to (12)CH(3)D/(12)CH(4) isotope ratio measurements.

We have developed an efficient and compact 3.4 μm difference-frequency-generation spectrometer using a 1.55 μm distributed feedback (DFB) laser diode, a 1.06 μm DFB laser diode, and a ridge-waveguide periodically poled lithium niobate. It is continuously tunable in the 30 cm−1 span and is applied to 12CH3D/12CH4 isotope ratio measurements. The suitable pair of 12CH3D ν4 pP(7,6) and 12CH4 ν 2+ν4 R(6) F1(1) lines enabled us to determine their isotope ratio with a precision repeatability of 0.8‰ using a sample and a working standard of pure methane with an effective signal averaging time of 100 ms.

Sub-Doppler resolution 34 μm spectrometer with an efficient difference-frequency-generation source

We have developed a 3.4 mum spectrometer for sub-Doppler resolution molecular absorption spectroscopy. The source is based on the difference frequency generation using a 1.06 microm Nd:YAG laser, a 1.55 microm distributed-feedback laser diode, and a ridge waveguide periodically poled lithium niobate with a conversion efficiency of 9%/W. The generated radiation has a power level of about 300 microW, a linewidth of less than 100 kHz, and a continuous tuning range over 10 cm(-1). The spectrometer allows us to observe six saturated absorption lines of C12H(4) with 0.3-0.4 MHz width and 1.3%-1.7% depth relative to the corresponding linear absorption lines.

1.3 µm Distributed Feedback Laser with Half-Etching Mesa and High-Density Quantum Dots

We propose a quantum dot laser with a new distributed feedback (DFB) structure, namely, a half-etching mesa (HEM) DFB laser that employs a vertical grating structure and requires no regrowth process. The features of the HEM structure are a low coupling coefficient and a low threshold current achieved by suppressing the large scattering loss in the quantum dots (QDs) active layer. This structure is realized by etching vertical gratings only as far as the center of the active layer. We demonstrated fundamental mode control for a 1.3 µm emission with a low coupling coefficient of 22 cm-1 and a threshold current of 35 mA by using high-density and high-uniformity QDs.

Reliability of loss‐coupled 1.55 μm DFB laser diode with automatically buried absorptive InAsP layer

AbstractThe authors achieved loss‐coupled 1.55 μm distributed feedback laser diode incorporating automatically buried absorptive layer implemented by a single step growth that simplifies device fabrication than those of conventional ones. Based on 2800 h of accelerated aging test, estimated lifetime is 1.4 × 106 h at room temperature. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 636–638, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22208

Fiber optic two-color vibration compensated interferometer for plasma density measurements

A fiber optic, heterodyne, two-color interferometer utilizing wavelength division multiplexing technology has been developed for measuring electron density in plasmas. Vibration compensation is accomplished via common path 1.31 and 1.55μm distributed feedback laser interferometers. All beam combining, splitting, frequency modulation, and collimation are accomplished by shared single-mode fiber optic components. Measurements of an argon radio-frequency generated plasma with electron densities of 1020m−3 show effective vibration compensation and typical line-density resolution of approximately 2×1019m−2.

Impact of band gap shrinkage on simulated bifurcation routes in directly modulated semiconductor lasers

A carrier heating model is derived by taking into account the various temperature processes in the active layer of laser diodes. This model is then used to simulate the static and dynamic characteristics of a directly modulated 1.55μm distributed-feedback laser diode. The calculated results are compared with the measured results of this device as obtained in an earlier work [H. F. Liu and W. F. Ngal, IEEE J. Quantum Electron. 29, 1668 (1993)], and this reveals the significant impact of band gap shrinkage on simulated results. This study also shows that the carrier heating model is a self-consistent model that naturally describes the gain suppression phenomena in directly modulated laser diodes.

Study of influence of failure modes on lifetime distribution prediction of 1.55 μm DFB Laser diodes using weak drift of monitored parameters during ageing tests

High performances and high reliability are two of the most important goals driving the penetration of optical transmission into telecommunication systems ranging from 880 nm to 1550 nm. Lifetime prediction defined as the time at which a parameter reaches its maximum acceptable shift, remains the primary result in the estimation of reliability for a technology. In this paper, we demonstrate that bias current of well-mastered actual technologies of single mode 1.55μm Distributed Feedback (DFB) Laser diodes is still a relevant failure indicator to conclude on failure modes although very weak variations are measured (until 6%). Nevertheless, screening complementary parameters such as threshold current and optical efficiency close to operating conditions can assess more information about the failure mechanism. From experimental determination of failure law, statistic computations based on Monte-Carlo approach are detailed to calculate lifetime distributions for the different failure modes over 20 years in operating conditions. Finally, from cumulative failure functions, we highlight the strong interest to take into account of variations of complementary parameters allowing us to perform an improved determination of first times to failure in contrast with only bias current variations.

Selective-area MOCVD growth for distributed feedback lasers integrated with vertically tapered self-aligned waveguide

The growth pressure and mask width dependent thickness enhancement factors of selective-area MOCVD growth were investigated in this article. A high enhancement of 5.8 was obtained at 130 mbar with the mask width of 70 μm. Mismatched InGaAsP (−0.5%) at the maskless region which could ensure the material at butt-joint region to be matched to InP was successively grown by controlling the composition and mismatch modulation in the selective-area growth. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously in separated confined heterostructure 1.55 μm distributed feedback laser, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. A narrow beam of 9° and 12° in the vertical and horizontal directions, a low threshold current of 6.5 mA was fabricated by using this technique.