Wavelength Modulation Research Articles

Spatio-spectral 4D coherent ranging using a flutter-wavelength-swept laser

Coherent light detection and ranging (LiDAR), particularly the frequency-modulated continuous-wave LiDAR, is a robust optical imaging technology for measuring long-range distance and velocity in three dimensions (3D). We propose a spatio-spectral coherent LiDAR based on a unique wavelength-swept laser to enable both axial coherent ranging and lateral spatio-spectral beam scanning simultaneously. Instead of the conventional unidirectional wavelength-swept laser, a flutter-wavelength-swept laser (FWSL) successfully decoupled bidirectional wavelength modulation and continuous wavelength sweep, which overcame the measurable distance limited by the sampling process. The decoupled operation in FWSL enabled sequential sampling of flutter-wavelength modulation across its wide spectral bandwidth of 160 nm and, thus, allowed simultaneous distance and velocity measurement over an extended measurable distance. Herein, complete four-dimensional (4D) imaging, combining real-time 3D distance and velocity measurements, was implemented by solid-state beam scanning. An acousto-optic scanner was synchronized to facilitate the other lateral beam scanning, resulting in an optimized solid-state coherent LiDAR system. The proposed spatio-spectral coherent LiDAR system achieved high-resolution coherent ranging over long distances and real-time 4D imaging with a frame rate of 10 Hz, even in challenging environments.

Reverse design of multifunctional demultiplexing devices

A novel direct binary search algorithm based on rotation (RDBS) is proposed in this paper. A 1*2 ultra-compact 2.4*3.6µm2 multimode wavelength demultiplexer (DEMUX) is designed in reverse, which is roughly two orders of magnitude smaller than the size of a conventional waveguide device. It can simultaneously perform wavelength demultiplexing and mode conversion. This DEMUX separates the 1310 and 1550 nm wavelengths while converting the input light from the fundamental transverse electric mode (TE0) to the first-order transverse electric mode (TE1). The simulation results using RDBS show that the insertion loss(IL) of the upper channel (wavelength 1310 nm) is −0.9644 dB, the IL of the lower channel (wavelength 1550 nm) is −0.9752 dB, and the crosstalk values(CT) are −10.079 dB and −9.261 dB, respectively.

High-Precision Multipass Fiber-Optic Photoacoustic Gas Analyzer Based on 2f/1f Wavelength Modulation Spectroscopy.

A self-calibration fiber-optic photoacoustic (PA) gas analyzer based on 2f/1f wavelength modulation spectroscopy (WMS) is proposed, which utilizes gas and solid multipass absorption enhancement. The laser light is incident obliquely on the cell wall, and one end of the cell is equipped with a highly reflective mirror. The gas analyzer takes full advantage of the miniature multipass PA cell, which enhances the absorption of gas and solid simultaneously. As a result, the double absorption enhancement of 1f and 2f PA signals are realized. A dual-channel lock-in white-light interferometer based on fiber-optic PA demodulation is designed to simultaneously extract the 1f and 2f PA signals detected by the silicon cantilever. The experimental results of methane gas detection show that the minimum detection limit (MDL) of the PA gas analyzer is 20 ppb when the integration time is 60 s. Moreover, the detection error of gas concentration is within 3% when the laser power is reduced by half. The fiber-optic PA gas analyzer eliminates the influence of changes in the laser power and optical path loss, which can be used for the high-precision detection of trace gases.

Research on Multi-point Measurement System of Mine Gas Based on TDLA

Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology combines the advantages of wavelength modulation technology and direct absorption spectroscopy technology, and the system achieves highly sensitive and full-range detection of methane gas concentrations. In the system, only the pure optical methane probe is positioned under the mine, which establishes connectivity with the host computer on the surface through the optical fiber. This setup enables the simultaneous detection of 16 channels of methane gas through time-sharing multiplexing technology. Experimental results demonstrate a measurement error of less than ±6.0×10−4 at low concentrations (0∼1%) and within ±6% of the true value at high concentrations under normal temperature and pressure conditions. The full-range linear fit attains 0.9998. According to the one-fold standard deviation, the minimum detection lower limit of the system stands at 68.36 ppm and the measured gas concentrations across different channels of the methane probes remain consistent inhe same environment. This technology provides a new solution for continuous, accurate, and multi-point monitoring of mine gas.

Effect of junction temperature on 1.3 µm InAs/GaAs quantum dot lasers directly grown on silicon

Laser junction temperature (Tj) is an essential parameter that directly affects the light power and lifetime of semiconductor lasers. Here, we investigate the effect of Tj on an InAs/GaAs quantum dot (QD) laser grown on a Si(001) substrate. Under 1% low pulsed current (1 µs pulse width and 100 µs period), the pure temperature-induced mode shift rate is 0.084 nm/°C. By increasing the duty cycle and measuring the corresponding mode wavelength shift, the laser’s Tj under the continuous-wave (Tj-CW) mode is predicted to be from 31.1 to 81.6 °C when the injection current increases from 100 to 550 mA. Next, the average thermal resistance is 36.2 °C/W. Moreover, the non-negligible increase in Tj-CW is analyzed to significantly reduce the mean-time-to-failure of Si-based QD laser, especially for cases under high CW injection currents. These results provide an accurate reference for the thermal analysis of silicon-based QD lasers and point the way to high performance on-chip light sources by improving the laser heat accumulation.

Design of anti-temperature interference liquid level sensor based on π-phase-shifted LPFG near phase-matched turning points

A new, to the best of our knowledge, type of liquid level sensor with π-phase-shifted long-period fiber grating operating near the phase-matched turning point is proposed. The sensor introduces a π-phase shift at the center of the grating, which can generate three attenuation peaks due to the mode interference effect in the transmission spectrum of the sensor operating near the phase-matched turning points. According to the different liquid level and temperature sensing characteristics of three attenuation peaks, simultaneous detection of liquid level and temperature can be realized through wavelength modulation and intensity modulation detection. In this paper, the structural parameters of this liquid level sensor, such as grating period and grating length, are designed optimally based on the fiber grating coupled mode theory, and the wavelength spacing of the attenuation peaks on both sides and the intensity of the center attenuation peak are analyzed in relation to the liquid level and temperature. The simulation results show that the liquid level sensitivity is 5.58 nm/mm and −1.316dB/mm for wavelength modulation and intensity modulation, respectively, for the liquid level variation range of 0 to 18 mm; and the temperature sensitivity of wavelength modulation and intensity modulation is −0.139nm/∘C and 0.171 dB/°C, respectively, over the temperature variation range of 20°C to 80°C. Therefore the simultaneous detection of liquid level and temperature can be realized by establishing a measurement inversion matrix. Compared with other liquid level sensors, this sensor is expected to be widely used in the field of liquid level sensing due to its simple structure, high liquid level sensitivity, large liquid level measurement range, and narrow monitoring peak bandwidth.

Molecular Engineering Enables Multi‐Color Room Temperature Phosphorescence of Carbon Dots Composites Derived In Situ, Facilitating their Utilization for Advanced Information Encryption

AbstractLong‐life room temperature phosphorescent (RTP) materials hold significant potential in the fields of optoelectronic devices, information encryption, and bio‐imaging due to their excellent optical properties. However, achieving multi‐color tunable RTP materials has proven challenging. In this study, molecular engineering strategies are employed to select precursor molecules with varying degrees of conjugation such as phthalic anhydride (PA), naphtho[2,3‐c] furan‐1,3‐dione (23NA), and naphthalic anhydride (NA). By combining these guest molecules with a host boric acid matrix through a one‐step microwave method, carbon dots (CDs)composites (PA@BA, 23NA@BA and NA@BA) exhibiting excellent RTP properties are successfully prepared. As the degree of precursor conjugation increased gradually, the phosphorescence color modulation of the composites demonstrates satisfactory transitions from blue to yellow. Notably, CDs are derived in situ within the boric acid matrix while covalent and hydrogen bonds formed between CDs and borate matrix effectively suppress nonradiative leaps and facilitate composite RTP activation. Furthermore, the boric acid matrix acts as insulation against oxygen diffusion and prevents quenching of triplet excitons by external factors. The rationality behind phosphorescence emission mechanism and wavelength modulation is further conformed by density functional theory (DFT) calculations. Finally, CDs composites are successfully applied for advanced message encryption of text and images.

Theoretical analysis of bulk acoustic wave resonators with emerging ε -Ga2O3 piezoelectric film

In this paper, the theoretical analysis of 2.3 GHz bulk acoustic wave (BAW) resonators with emerging ε-Ga2O3 piezoelectric films was investigated. By using the finite element method to calculate the dispersion curve of the BAW resonator based on ε-Ga2O3, we designed and optimized the Bragg reflector structure as well as the metal frame to suppress transverse energy leakage. When the width of the raised metal frame is an odd multiple of the quarter wavelength of the S1 Lamb mode, the vibration displacement at the boundary of the resonators is significantly suppressed, and the acoustic energy is concentrated as much as possible in the effective area of the resonators, resulting in improvement of the Qp and Qmax. Therefore, the ε-Ga2O3 based BAW resonators with Bode Qmax (∼1488), electromechanical coupling coefficient k2eff (∼15%), and the figure of merit (FoM) coefficient (∼223) are simulated and designed. Detailed theoretical analysis provides the key theoretical guidance and design scheme for the realization of ε-Ga2O3 BAW filters. The above-mentioned results imply that the emerging ε-Ga2O3 piezoelectric semiconductors have application prospects in BAW resonators and radio frequency front-end fields.

Near-Infrared Off-Axis integrated cavity output spectroscopic sensor system for ammonia leakage measurement in cold store using embedded Multi-Core processor

A near-infrared off-axis integrated cavity output spectroscopic (OA-ICOS) sensor system for ammonia (NH3) leakage detection was developed. A distributed feedback (DFB) laser was used to target the absorption line of NH3 at 6612.167 cm−1. Experiments were conducted to evaluate the performance of the sensor system. When the averaging time is 0.8 s, the detection limit (1σ) of NH3 is ∼ 1.21 parts-per-million by volume (ppmv) using wavelength modulation spectroscopy (WMS). The 10–90 % response time of the NH3 sensor system is ∼ 7.2 s. Based on the developed local monitoring and control platform (LMCP), cloud server, remote monitoring and control end (RMCE), the unattended NH3 leakage detection experiments were carried out in a cold store located in Jilin City. The experimental results confirmed the rapid detection capability of the reported sensor system for NH3 leakage as well as the capability of remote monitoring and control.

Near-infrared H2S telemetry system under non-cooperative target with a novel mixed heterodyne optical structure scheme for high efficiency

A gas leakage telemetry system under non-cooperative target was designed and developed based on laser absorption spectroscopy technology, targeting the combination frequency absorption band of Hydrogen sulfide (H2S) gas molecules. A distributed feedback (DFB) laser centered at 1578 nm was adopt, with mature packaging process and high market maturity. The returned signal of diffuse reflection is extremely weak, decreasing exponentially with the increase of telemetry distance, and direct detection technology is difficult to achieve ideal performance at telemetry distance and lower detection limit. Thus, heterodyne detection technology was introduced to significantly amplify diffuse reflection signal and improve the signal-to-noise ratio (SNR) of telemetry system. For further detection sensitivity, wavelength modulation spectroscopy (WMS) technology was combined to suppress background noise through the electrical modulation of DFB laser. Alternating signal was applied to the laser to alter its output characteristics during the process of laser oscillation. Compared with exterior modulation methods, this interior modulation method does not require additional modulator, which avoids optical loss and is more economical. Combining the advantages of fiber structure and space optical path structure, a novel mixed heterodyne optical structure which was more applicable to this system was independently designed after the specific analysis of main noise sources. Then, the effect of heterodyne detection technology was verified in contrast of direct detection technology. Sensor performance was validated through calibration and stability experiments. The limit of detection (LoD) reached a minimum of 3.44 parts-per-million (ppm·m) with a 98 s averaging time. And the packaged system was fully capable of detecting the hazardous critical concentration of H2S and acting as an alarm mechanism.

Quantum cascade laser absorption sensor for in-situ, real-time and sensitive measurement of high-temperature SO2 and SO3

We report a mid-infrared quantum cascade laser absorption sensor capable of measuring SO2 and SO3 simultaneously and sensitively at elevated temperatures. In the sensor development, the intense transitions of SO2 and SO3 in the mid-infrared region of 1129 cm−1 and 1398 cm−1 were exploited by two quantum cascade lasers. A high-temperature multipass cell was adopted to increase the absorption path length to 10 m. The quantitative concentrations of SOx were directly obtained from the calibration-free wavelength modulation spectroscopic method, which was validated at varied temperature and pressure conditions. From Allan deviation analysis, we achieved a minimum detection limit of 8 parts per billion (ppb) for SO2 and 3 ppb for SO3, with an average time of 100 s. Lastly, we successfully demonstrated the real-time and sensitive measurement of SO2 and SO3 during the oxidation reaction of SO2 by O3 at 460 K. Our laser sensor shows great potential for in-situ and real-time monitoring of SOx from combustion emissions.

Suppression of Randomness in Electrically Pumped Random Lasing from a ZnO Film-Based Light-Emitting Device on Silicon.

We report on the suppressed randomness in electrically pumped random lasing (RL) from a light-emitting device (LED) based on a metal-insulator-semiconductor (MIS) structure of Au/SiOx (x < 2)/ZnO on a silicon substrate, by means of patterning the light-emitting ZnO polycrystalline film into a number of square blocks separated by streets that are filled with the SiOx insulator. It is found that the RL modes can be remarkably reduced by shrinking the blocks in the absence of interblock optical coupling. Meanwhile, with the imposition of interblock optical coupling by shrinking the streets, the RL modes can be further reduced, and more importantly, the strongest mode wavelength is stabilized around 380 nm, where the ZnO film exhibits the largest optical gain.

A Biosensing Platform Based on Metamaterials BioNEMS for Lab-on-Chip Systems.

An optical nanoelectromechanical platform relied on a SRR metamaterial system is presented in this paper as a label-free biosensor. This structure includes a flexible BioNEMS (Bio-Nano-Electro-Mechanical Systems) transducer and a proposed SRR metamaterials for detection of biological changes. Metamaterial cells consist of two parts which are coupled with an air gap distance. A functionalized BioNEMS beam supports one part of the proposed metamaterial cells. When patient samples including target analytes is exposed to the NEMS beam surface, the specific bio-interactions are happened and the energy (surface stress type) is released on the surface. This energy, which is induced only to the one side of the movable beam, causes a differential surface stress and thus displaces the nanomechanical beam. As a result, the air distance between two separated cells of the metamaterial unit is changed. This leads to varying the cell coupling effect which excites plasmon modes in a different wavelength. Therefore, biological quantities can be measured by detecting the resonance wavelength changes. Moreover, analyzing the device by various approaches results its functional characteristics as follows: detection sensitivity of 4251 nm/RIU, figure of merit (FOM) of 500.1 RIU -1 , mechanical sensitivity of [Formula: see text]/Nm -1 and resonant frequency of 17.1 kHz. Consequently, this mechanism is important for label-free biosensing due to its high potential for sensitive and quantitative detection of target analytes which leads to accurate diagnosis of diseases or identification of drugs.

Advanced inorganic nanomaterials for high-performance electrochromic applications.

Electrochromic materials and devices with the capability of dynamic optical regulation have attracted considerable attention recently and have shown a variety of potential applications including energy-efficient smart windows, multicolor displays, atuto-diming mirrors, military camouflage, and adaptive thermal management due to the advantages of active control, wide wavelength modulation, and low energy consumption. However, its development still experiences a number of issues such as long response time and inadequate durability. Nanostructuring has demonstrated that it is an effective strategy to improve the electrochromic performance of the materials due to the increased reaction active sites and the reduced ion diffusion distance. Various advanced inorganic nanomaterials with high electrochromic performance have been developed recently, significantly contributing to the development of electrochromic applications. In this review, we systematically introduce and discuss the recent advances in advanced inorganic nanomaterials including zero-, one-, and two-dimensional materials for high-performance electrochromic applications. Finally, we outline the current major challenges and our perspectives for the future development of nanostructured electrochromic materials and applications.

Highly sensitive detection of oxygen based on light-induced thermoelastic spectroscopy with a high power diode laser

Oxygen (O2) is a fundamental element in the atmosphere. It is important to detect it in various fields. In this paper, a sensitive O2 sensor based on light-induced thermoelastic spectroscopy (LITES) with a high power diode laser is reported. A distributed feedback (DFB) diode laser emitting at 760 nm with output power of 16.8 mW was employed as the light source. The O2 absorption line at 13144.54 cm-1 was selected for the investigation. Wavelength modulation spectroscopy (WMS) technique and second harmonic signal demodulation (2f) were adopted to improve the sensing performance. For the concentration dynamic range from 20% to 80%, a linear relationship between the amplitude of 2f signal and O2 concentration was demonstrated. Allan deviation analysis was conducted to evaluate the long-term stability of the sensor system and the minimum detection limit (MDL) was measured to be 583 ppm at the optimum integration time of 100 s. Further improvement of this O2-LITES sensor system was also discussed.

Mid-infrared auto-correction on-chip waveguide gas sensor based on 2f/1f wavelength modulation spectroscopy.

Compared to the most commonly used on-chip direct absorption spectroscopy (DAS) gas detection technique, the second harmonic (2f) based on-chip wavelength modulation spectroscopy (WMS) proposed by our group has the faculty to suppress noise and improve performance, but the accuracy of 2f WMS is easily affected by optical power variation. A mid-infrared auto-correction on-chip gas sensor based on 2f/1f WMS was proposed for decreasing the influence of the variation of optical power. The limit of detection of methane (CH4) obtained by a chalcogenide waveguide with a length of 10 mm is 0.031%. Compared with the 2f WMS, the maximum relative concentration error of the auto-correction on-chip gas sensor was decreased by ∼5.6 times. The measurement error is ≤2% in a temperature variation range of 30°C. This auto-correction sensor without a complicated manual calibration is helpful to the high accuracy measurement for on-chip integrated gas sensing.

A Firefly Algorithm-Based Spectral Fitting Technique for Wavelength Modulation Spectroscopy Systems

A Firefly Algorithm-Based Spectral Fitting Technique for Wavelength Modulation Spectroscopy Systems

Re-injection off-axis integrated cavity output spectroscopy for the simultaneous detection of N2O, H2O and CO with a mid-infrared QCL laser.

Off-axis integrated cavity output spectroscopy (OA-ICOS) has attracted much interest because it potentially allows highly sensitive field measurements with robust optical alignment. In this paper, a novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of multi-component gases N2O, H2O and CO in the atmosphere based on a mid-infrared quantum cascade laser (QCL) and OA-ICOS. In order to improve the energy utilization and increase the signal-to-noise ratio (SNR) of the signal, a new type of optical path structure of the laser re-injection method is adopted. Furthermore, the system performance can be effectively improved by using a new intervention method of injecting radio frequency (RF) white noise into a laser driver to suppress cavity mode noise and combining the wavelength modulation method (WMS). We compared the sensitivity of the second harmonic signal demodulation between the re-injection method and the standard OA-ICOS, and the SNR increased by 2.68 times compared to the latter. Analysis of the spectral measurements with Allan variance indicates that within an integration time of 1 s, the measurement accuracy of N2O, H2O, and CO is 6.71 ppb, 13.945 ppm, and 1.81 ppb, respectively, and within an integration time of 820 s, the measurement accuracy of N2O, H2O, and CO can be further improved to 1.26 ppb, 2.089 ppm, and 172 ppt, respectively. Our approach represents an underlying analytical method that provides guidelines for monitoring of representative gases in the atmosphere, industrial processes, emergency safety, etc.

A Fast Measurement Method Based on Linearly Swept Wavelength Modulation and Frequency Tracking Demodulation for Photoacoustic Spectroscopy

A Fast Measurement Method Based on Linearly Swept Wavelength Modulation and Frequency Tracking Demodulation for Photoacoustic Spectroscopy

A Wavelength Modulation Spectroscopy Gas Concentration Detection Method Based on Linear Convolution

A Wavelength Modulation Spectroscopy Gas Concentration Detection Method Based on Linear Convolution