Multimode Laser Diode Research Articles

Sub-ppb level detection of nitrogen dioxide based on an optimized H-type longitudinal acoustic resonator and a lock-in white-light interferometry demodulation algorithm

This paper presents an optimized H-type longitudinal resonant photoacoustic (PA) cell for nitrogen dioxide (NO2) gas detection. The PA field distributions of the H-type resonant PA cell have been evaluated to optimize the construction of the H-type resonant PA cell, using the finite element method and thermoviscous acoustic theory. The optimized H-type resonant PA cell, together with a high-power continuous-wave (CW) multimode laser diode emitting at around ~ 450 nm and a fiber-optic Fabry-Perot (F-P) acoustic sensor, constitutes a PAS system for NO2 detection. The dynamic cavity length of the fiber-optic acoustic sensor is demodulated by the lock-in white-light interferometry (WLI) demodulation algorithm. Experimental results show that the PA signals are proportional to the concentrations of NO2 for the range of 0-2 ppm (parts per million). The sensitivity is measured to be 0.652 nm/ppm and the minimum detectable limit of NO2 is calculated to be 1.26 ppb (parts per billion).

Diode Laser Ignition of a Poly(Methyl Methacrylate) and Gaseous Oxygen Hybrid Motor

The performance of a diode laser igniter as a restart-capable device has been assessed for single-port, poly(methyl methacrylate) (PMMA)/gaseous oxygen (GOX) hybrid motors. For this testing a prototype version of the igniter has been designed and implemented as a substitute to a traditional methane/GOX torch ignition system. Ignition tests have been conducted at atmospheric ambient conditions using an experimental single-port motor setup. Using three PMMA fuel grains, a total of 46 successful motor ignitions and restarts were achieved. These tests were conducted using a single multimode diode laser with an output power of 10.84 W and a nominal pulse length of 1 s. In addition, a total of 24 successful ignitions and restarts were demonstrated in a vacuum chamber with the same prototype igniter on a flight-scale PMMA/GOX motor under development for smallsat applications. The ignition transient is compared against baseline results from a torch ignition system for atmospheric tests, and the ignition delay performance is considered across all tests.

Experimental Transmission of Digital Data Coded on Electrical Carriers at 2.1 GHz and 4.2 GHz by Using a Microwave Photonic Filter

This paper proposes and demonstrates the use of filtered microwave band-pass windows situated at 2.1 GHz and 4.2 GHz as electrical carriers to transmit digital signals. The use of an appropriate microwave photonic filter (MPF) allows for the generation of the microwave band-pass windows. The key parameters of the filtering effect are the intermodal separation of a multimode laser diode (MLD), the chromatic dispersion parameter of the optical link, and its own length. Experimentally, it is demonstrated that the filtered band-pass windows can be used as electrical carriers to transmit digital signals at frequencies of 50 MHz, 100 MHz, and 150 MHz over 25.31 km of single-mode-standard-fiber (SM-SF). The quality Q-factor, jitter, and bit-error-rate are the parameters that allow for the evaluation of the quality of the digital signal transmission. The obtained results allow for the proposition of this photonic architecture in a passive optical network (PON) to distribute services like Internet Protocol (IP) telephony, internet, streaming video, and high definition television.

Performance improvement of an optoelectronic oscillator by modifying the optical characteristics of a multimode laser diode

This paper presents a substantial improvement on the electrical performance of a microwave optoelectronic oscillator (OEO) by modifying the intermodal separation of a multimode laser diode (MLD). The Free Spectral Range (FSR) of the OEO is controlled by implementing an optical filter that allows manipulating the optical spectrum of an MLD. For this goal, a section of birefringent optical fiber is placed between two crossed polarizers as an optical filter. The intermodal separation of the MLD is varied using a suitable length of birefringent optical fiber. A set of stable microwave signals in the frequency range of 0–12 GHz is obtained. The performance evaluation for the microwave signal centered at 2.93 GHz shows a phase noise as low as −118.06 dBc/Hz at 10 kHz offset frequency and a Q factor of 1.40 × 109 for an optical delay line of 13 km.

Elemental mercury sensing by synchronously sweeping two multimode diode lasers.

We propose a sum-frequency-generation (SFG) laser-based elemental mercury sensing method by mixing two low-cost multimode diode lasers (MDLs). The wavelengths of the two MDLs are synchronously scanned, which enlarges the whole coverage range of wavelength and improves the measurement stability. Correlation spectroscopy was used to eliminate the impact of environmental change and enhance and trace the absorption signal of the sample accurately. A novel data processing method was employed to extract the weak absorption signals from the background efficiently. A sensitivity of ${0.1}\;\unicode{x00B5} {{\rm g/m}^3}$0.1µg/m3 (11 ppt) was achieved for 1-m path length and 10-s integration time. The sensing range was efficiently increased up to ${200}\;\unicode{x00B5} {{\rm g/m}^3}$200µg/m3 using a calibration curve based on a new mathematical analytical formula. Real-time monitoring of the mercury volatilization and diffusion process was experimentally demonstrated with a time resolution of 10 s. The performance of the system shows great practical value for the detection of elemental mercury in industrial applications.

Spectral and spatial dynamics of a multimode GaN-based blue laser diode

ABSTRACTHigh-resolution spectral analysis of a multimode GaN-based blue laser diode was performed as a function of temperature and current both below and above the threshold levels. Maps of longitudinal modes evolution as a function of current and temperature were obtained from the highly resolved emission spectra of the laser diode. The evolution of emitted longitudinal modes with current and temperature exhibited redshifts at rates of 0.0059 nm/mA and 0.0149 nm/°C, respectively. Similarly, the laser gain profile was observed to shift towards longer wavelengths but with rates of 0.022 nm/mA and 0.0439 nm/°C. The longitudinal mode spacing of 0.0540 nm was experimentally evaluated and compared with its equivalent theoretically predicted value.

Multiple passband microwave photonic filter with adjustable bandwidth

We propose a straightforward technique that allows adjusting the bandwidth of microwave filtered signals by using two tunable optical bandpass filters. The principle of operation of the microwave photonic filter that allows the generation of passband windows is described by a full mathematical analysis. The electrical bandwidth of each generated passband window is adjusted by optically filtering a multimode laser diode. We demonstrate that the proposed filter can generate passband windows located at 4.87 GHz and 9.63 GHz exhibiting a bandwidth of 284.54 MHz and 391.24 MHz, respectively. The electrical bandwidth of each passband window can be increased to a maximum value of 1000 MHz by means of an adequate adjustment of the optical bandwidth from 2 nm to 10 nm approximately. A potential application of this proposal resides in the fact that the microwave filtered signals can be used as electrical carriers in optical communication schemes taking advantage of the electrical bandwidth that can be tailored according to a data transmission.

Metamorphosis of self-assembled InAs quantum dot through variation of growth rates

This study investigates the metamorphosis of self-assembled InAs quantum dots (QDs) by varying the InAs growth rate in the range of 0.025–0.15 ML/s. The theoretical approaches for calculating the shape transformation from pyramidal QDs to truncated pyramidal QDs with symmetric/asymmetric slant heights and their outcomes are presented. The cut-off height from the tip of the pyramidal QDs depends on many compression factors, such as thickness of the spacer layer, InAs growth rate, and QD density. From high resolution transmission electron microscopy (HRTEM) images, it was affirmed that the slant heights of the truncated pyramidal QDs were symmetrical and evenly compressed at lower growth rates. However, this is in contrast with the high growth rates, where there is formation of asymmetrical slant heights of the truncated pyramidal QD in conjunction with high randomness in dot size dispersion. We explore the complete metamorphosis of self-assembled QDs in detail along with the effect of growth rate variation. The five different shaped QDs with different aspect ratio (as a result of growth rate variation) were able to tune the emission wavelength from 1201 nm to 1261 nm, which might be applicable for high compact multimode laser diode. Furthermore, we report for the first time on structural characteristics of the metamorphosis of self-assembled InAs QDs through In-plane reciprocal space mapping. The diffused scattering peak from In/Ga intermixing were intensified for high growth rate, indicating diffusion of Ga adatoms into InAs QDs. The hybrid work of experimental and simulations prove that the truncated pyramidal QDs with symmetrical slant heights is important for achieving longer wavelength in comparison with truncated pyramidal QDs with asymmetrical slant heights. It is also shown that the electron confinement is stronger in low growth rate in comparison to the high growth rate. Moreover, calibration of the InAs growth rate is essential as it determines how the next-level vertical multi-stacked strain-coupled InAs QD heterostructures could be designed, in order to meet the state-of-the-art performance of the QD based multimode laser diode.

Feasibility Studies of the Three-Wavelength Mie-Scattering Polarization Scheimpflug Lidar Technique

A three-wavelength Mie-scattering polarization Scheimpflug lidar system, utilizing 808-nm, 520-nm and 405-nm multimode laser diodes as light sources and two CMOS sensors as detectors, is developed for the studies of the aerosol extinction coefficient, depolarization ratio and the Ångström exponent. Atmospheric monitoring has been carried out on a near horizontal path from 23:00 January 14th to 06:00 January 15th, 2019 at Dalian, which is a coast city in Northern China. By studying the depolarization, aerosol extinction coefficient and Ångström exponent, it has been found out that a strong north wind blew away local spherical haze particles and brought external non-spherical large-size particles. The measurement results indicated a promising future of employing the present three-wavelength polarization Scheimpflug lidar system in the applications of atmospheric remote sensing.

Trace gas sensing using diode-pumped collinearly detected spontaneous Raman scattering enhanced by a multipass cell

A simple but highly effective method for enhancement of spontaneous Raman scattering from gases is described. It employs a multimode blue laser diode that receives feedback from a near-concentric bidirectional multipass cavity in such a way as to generate a circulating power on the order of 100 W for a sample volume of 10 m m 3 . The feedback, provided via a volume Bragg grating, reduces the laser bandwidth to 4 c m − 1 . Spectra of spontaneous Raman scattering from ambient atmospheric air, detected collinearly with the pump, were recorded with a limit of detection below 1 ppm. The performance of the setup is further illustrated through detection of acetone, methane, and isotopic carbon dioxide in breath.

Wide-Span Multi-Wavelength High-Power Diode-Laser Pumping of Fiber Raman Laser

A multimode silica-core fiber Raman laser was pumped directly by five wavelength-combined multimode diode lasers. The pump wavelengths were spread over a bandwidth of ~700 cm−1, namely, at 976, 969, 950, 940, and 915 nm. This is larger than the Raman peak shift of 490 cm−1. The output power reached 31.5 W with an overall slope efficiency of 42% at the wavelength of 1018 nm when pumped with the maximum launched power of 175 W. According to simulations, the fiber was under-length and the output power could double in a longer fiber. Our results suggest that pumping with spectrally combined diode lasers is a promising approach to high-power fiber Raman lasers, even when the pump wavelengths are not optimized.

Increasing the THz-QTDS Bandwidth from 1.7 to 2.5 THz Through Optical Feedback

We demonstrate that the bandwidth of a terahertz (THz) quasi time-domain spectroscopy (QTDS) system can be increased by controlled optical feedback into the multimode laser diode. The THz spectral broadening correlates well with the broadening of the optical spectrum. Our results show that the phase of the feedback does not affect the optical or THz bandwidth in general, although certain combinations of feedback power and phase can create additional high-frequency components in the THz spectrum, which are not present otherwise. For the optimal combination of feedback power and phase, the bandwidth of the THz QTDS system is increased from 1.7 to 2.5 THz.

Three-wavelength polarization Scheimpflug lidar system developed for remote sensing of atmospheric aerosols.

Multiple-wavelength polarization lidar techniques have been of great interest for the studies of aerosol backscattering color ratio, Ångström exponent, particle size distribution, hygroscopic growth, etc. Conventional lidar techniques are mainly based on the time-of-flight principle. In this paper, a three-wavelength polarization Scheimpflug lidar (SLidar) system, based on the Scheimpflug imaging principle, has been developed for studying optical properties of atmospheric aerosols. The SLidar system utilizes low-cost, compact, multimode laser diodes as light sources and two complementary metal oxide semiconductor (CMOS) sensors as detectors. The depolarization ratio was measured at the 808 nm band by successively detecting atmospheric backscattering signals from two orthogonally polarized laser beams with a polarization CMOS camera, while the 520 nm and the 405 nm backscattering signals were recorded by a second CMOS camera based on the time-multiplexing scheme. Atmospheric remote measurements were carried out in May and July 2019 on a near-horizontal path. The aerosol extinction coefficient, linear volume depolarization ratio, and the Ångström exponent have been retrieved and evaluated to study aerosol properties during different atmospheric conditions, which were in good agreement with optical properties reported by previous studies.

976 nm all-fiber Raman laser with high beam quality at multimode laser diode pumping

A 976 nm all-fiber Raman laser enabling high beam quality at direct multimode laser diode pumping with low beam quality (M2 > 30) is demonstrated. The laser is performed in a 100/140 multimode graded-index fiber with special in-fiber Bragg gratings that secure generation of the Stokes beam with relatively good quality (M2 ⩽ 2) and high slope efficiency of the pump-to-Stokes conversion (70%) at output powers of up to ~50 W.

Low-cost multimode diode-pumped Tm:YAG and Tm:LuAG lasers

We report a continuous-wave operation of Tm:YAG and Tm:LuAG lasers pumped with a low-cost, multimode AlGaAs laser diode. First, the lifetime and the absorbance behavior of 5 mm, 6 % Tm$^{3+}$-doped YAG and LuAG crystals were thoroughly investigated. A low-cost multimode 3W laser diode at 781 nm was then used as a pump source for the Tm$^{3+}$-doped laser systems. Using three different output couplers, up to 636 mW of output power was obtained from Tm:YAG laser, with a slope efficiency of 29 % at 2017 nm. The maximum output power was 637 mW in the Tm:LuAG laser, with a slope efficiency of 28 % at 2023 nm. The lasing performances showed a decreasing slope efficiency with an increasing level of output coupling, which leads to a high upconversion. Furthermore, using a birefringent filter in the resonators, the laser outputs were tuned from 1942 to 2086 nm in the Tm:YAG resonator and from 1931 to 2107 nm in the Tm:LuAG case.

Semiconductor disk laser in bi-frequency operation by laser ablation micromachining of a laser mirror.

We present bi-frequency continuous wave oscillation in a semiconductor disk laser through direct writing of loss-inducing patterns onto an intra-cavity high reflector mirror. The laser is a Vertical External Cavity Surface Emitting Laser which is optically pumped by up to 1.1 W of 808 nm light from a fibre coupled multi-mode diode laser, and oscillates on two Hermite-Gaussian spatial modes simultaneously, achieving wavelength separations between 0.2 nm and 5 nm around 995 nm. We use a Digital Micromirror Device (DMD) enabled laser ablation system to define spatially specific loss regions on a laser mirror by machining away the Bragg layers from the mirror surface. The ablated pattern is comprised of two orthogonal lines with the centermost region undamaged, and is positioned in the laser cavity so as to interact with the lasing mode, thereby promoting the simultaneous oscillation of the fundamental and a higher order spatial mode. We demonstrate bi-frequency oscillation over a range of mask gap sizes and pump powers.

Diode-pumped 640 nm Pr:YLF regenerative laser pulse amplifier

We demonstrated regenerative laser pulse amplification at 640nm for the first time, to the best of our knowledge, with a mode-locked Pr3+-doped LiYF4 (Pr3+:YLF) oscillator as a picosecond seed pulse. A regenerative amplifier with a Pr3+:YLF crystal was continuously pumped by a multimode InGaN diode laser. At an absorbed pump power of 3.1W, we obtained amplified pulse energy of 13μJ at 10kHz with an excellent spatial beam quality of M2∼1.1, demonstrated second-harmonic generation, and obtained a 320nm pulse energy of 5.9μJ.

Low-cost multi-mode diode pumped Tm:YLF laser: Multi-color & Q-switching operations

In this paper, we report a low-cost multi-mode AlGaAs laser diode pumped broadly-tunable solid-state Tm:YLF laser at room-temperature operating in two different regimes: multi-color and Q-switching. A low-cost multi-mode AlGaAs laser diode, driving 3 W power at 780 nm, was used to excite the 3% Tm3+-ion doped YLF laser. In the continuous-wave regime, 650 mW of output power was obtained at 1942 nm with 41% power efficiency (indicates high cross-relaxation). The output wavelength can be tuned between 1831 and 2031 nm with a birefringent filter (BRF). To the best of our knowledge, this range is the broadest tuning range obtained from a Tm:YLF laser in 2 μm band. Furthermore, multi-color laser operations were observed by translating the crystal inside the cavity (without BRF) i.e. three two-color, two three-color and one four-color were obtained. As far as we know, these results are the first demonstration of three- and four-color 2 μm laser. Additionally, Q-switching regime were obtained by adding a saturable absorber into the cavity. In this regime, the repetition frequencies can be arranged between 16 and 100 kHz with a maximum of 2.7 W peak power and 2.39 μJ pulse energy by translating the saturable absorber along the stability region.

Observation of flat chaos generation using an optical feedback multi-mode laser with a band-pass filter.

We demonstrate experimentally that flat and broadband chaotic signals can be easily generated by combining a multi-mode laser diode subject to optical feedback with a band-pass filter. Measurements are made of the RF spectra of multi-mode and single-mode outputs from an external cavity Fabry-Perot (FP) semiconductor laser before and after the filtering procedure. In this way it is found that in the chaos regime the low-frequency energy of the single-mode output is enhanced by about 25 dB comparing with that of the multi-mode output. Moreover, the associated 3-dB chaos bandwidth can reach around 6 GHz for the single mode case. Numerical demonstrations show mode competition is the physical origin of the low-frequency enhancement in the single-mode chaotic outputs.

Extension of spectral region of sub-terahertz spectroscopic system with multimode laser diodes by simple configuration for photomixing technique

The photomixing technique is applied to a sub-terahertz spectroscopic system with continuous-wave multimode laser diodes (CW-MLDs) to extend the spectral range. I employ two CW-MLDs which have equal spectral widths and slightly different central wavelengths, where sophisticated techniques such as external cavities are not required. I observe that photomixing causes generation of new spectral components of the signal in the frequency region of about 0.5–0.65 THz, while spectral components are limited below about 0.5 THz before the photomixing technique is applied. The generation of spectral components implies that the spectral range covered by the spectroscopic system is extended to higher-frequency regions.