Distributed Feedback Laser Diode Research Articles

Measurement of Atmospheric CO2 Column Concentrations Based on Open-Path TDLAS.

Monitoring of CO2 column concentrations is valuable for atmospheric research. A mobile open-path system was developed based on tunable diode laser absorption spectroscopy (TDLAS) to measure atmospheric CO2 column concentrations. A laser beam was emitted downward from a distributed feedback diode laser at 2 μm and then reflected by the retroreflector array on the ground. We measured the CO2 column concentrations over the 20 and 110 m long vertical path. Several single-point sensors were distributed at different heights to provide comparative measurements for the open-path TDLAS system. The results showed that the minimum detection limit of system was 0.52 ppm. Some similarities were observed in trends from the open-path TDLAS system and these sensors, but the average of these sensors was more consistent with the open-path TDLAS system values than the single-point measurement. These field measurements demonstrate the feasibility of open-path TDLAS for measuring the CO2 column concentration and monitoring carbon emission over large areas.

Monolithic Double Resonator for Quartz Enhanced Photoacoustic Spectroscopy

A new approach for Quartz Enhanced Photoacoustic Spectroscopy is presented, based on an acoustic excitation from the outside of the prongs of a quartz tuning fork, to increase the sensitivity of the sensor. For this purpose, we introduce a monolithic acoustic double-resonator (double-mR) in a T-shape configuration, using 3D printing. It was modelized and experimentally characterized using a 1392 nm distributed feedback laser diode, targeting a water vapor absorption line. The setup showed a two-factor enhancement of the signal, compared to a classical off-beam QEPAS approach and confirmed the strong interest of photolithographic printing techniques for acoustic developments.

A methane telemetry sensor based on near-infrared laser absorption spectroscopy

In order to detect methane leakage accurately and prompt, a methane telemetry sensor is demonstrated based on near infrared absorption spectroscopy and optimized wavelength modulation technology. The distributed feedback diode laser is applied as the light source to cover the selected absorption line of 6046 cm−1 to reduce the interference of CO2 and H2O. The waveform generator and the digital quadrature lock-in amplifier are constructed by the FPGA to produce driving signals and extract WMS-1f and 2f signals. And the “2f/1f” method is adopted to eliminate the environment influence such as light intensity fluctuations and improve the signal-to-noise ratio. This methane sensor has the characteristics of fast response and strong resistance to environmental interference and has great application prospect.

Integration of a high-efficiency Mach-Zehnder modulator with a DFB laser using membrane InP-based devices on a Si photonics platform.

We demonstrate a wafer-level integration of a distributed feedback laser diode (DFB LD) and high-efficiency Mach-Zehnder modulator (MZM) using InGaAsP phase shifters on Si waveguide circuits. The key to integrating materials with different bandgaps is to combine direct wafer bonding of a multiple quantum well layer for the DFB LD and regrowth of a bulk layer for the phase shifter. Buried regrowth of an InP layer is also employed to define the waveguide cores for the LD and phase shifters on a Si substrate. Both the LD and phase shifters have 230-nm-thick lateral diodes, whose thickness is less than the critical thickness of the III-V compound semiconductor layers on the Si substrate. The fabricated device has a 500-µm-long DFB LD and 500-µm-long carrier-depletion InGaAsP-bulk phase shifters, which provide a total footprint of only 1.9 × 0.31 mm2. Thanks to the low losses of the silica-based fiber couplers, InP/Si narrow tapers, and the phase shifters, the fiber-coupled output power of 3.2 mW is achieved with the LD current of 80 mA. The MZM has a VπL of around 0.4 Vcm, which overcomes the VπL limit of typical carrier-depletion Si MZMs. Thanks to the high modulation efficiency, the device shows an extinction ratio of 5 dB for 50-Gbit/s NRZ signal with a low peak-to-peak voltage of 2.5 V, despite the short phase shifters and single-arm driving.

All-optical microwave oscillator based on feedback modulation within distributed feedback laser diode

An all-optical microwave oscillator is proposed and experimentally demonstrated, in which a distributed feedback laser diode (DFB-LD) acts as light source and optical-optical modulator simultaneously. By employing stimulated Brillouin scattering (SBS) process for oscillation frequency selection and active optical comb filter for side-modes suppression, single-mode photonic microwave signal generation can be achieved through a pure optical oscillation. In the experiment, a stable 10.87-GHz photonic microwave signal is obtained. The signal quality is evaluated by measuring the side-mode suppression ratio and single side-band phase noise of the signal. The corresponding values are 42 dB and −85 dBc / Hz at 10 kHz, respectively. This scheme explores the innovative application potentiality of DFB-LD, which will benefit on-chip photonic microwave systems.

Development of a laser heterodyne spectroradiometer for high-resolution measurements of CO2, CH4, H2O and O2 in the atmospheric column.

We have developed a portable near-infrared laser heterodyne radiometer (LHR) for quasi-simultaneous measurements of atmospheric carbon dioxide (CO2), methane (CH4), water vapor (H2O) and oxygen (O2) column absorption by using three distributed-feedback diode lasers as the local oscillators of the heterodyne detection. The developed system shows good performance in terms of its high spectral resolution of 0.066 cm-1 and a low solar power detection noise which was about 2 times the theoretical quantum limit. Its measurement precision of the column-averaged mole fraction for CO2 and CH4 is within 1.1%, based on the standard deviation from the mean value of the retrieved results for a clean sky. The column abundance information of the O2 is used to correct for the variations and uncertainties of atmosphere pressure, the solar altitude angle, and the prior profiles of pressure and temperature. Comparison measurements of daily column-averaged atmospheric mole fractions of CO2, CH4 and H2O, between our developed LHR and a greenhouse gas observing satellite, show a good agreement, which proves the reliability of our developed system.

Electrically injected parity-time symmetric distributed feedback laser diodes (DFB) for telecom applications

Abstract The new paradigm of parity-time symmetry in quantum mechanics has readily been applied in the field of optics with numerous demonstrations of exotic properties in photonic systems. In this work, we report on the implementation of single frequency electrically injected distributed feedback (DFB) laser diodes based on parity-time symmetric dual gratings in a standard ridge waveguide configuration. We demonstrate enhanced modal discrimination for these devices as compared with index or gain coupled ones, fabricated in the same technology run. Optical transmission probing experiments further show asymmetric amplification in the light propagation confirming the parity-time symmetry signature of unidirectional light behavior. Another asset of these complex coupled devices is further highlighted in terms of robustness to optical feedback.

Investigation of optical short pulse generation using intensity modulation for LiDAR and free-space communications

A simple optical pulse generation scheme for pulsed light detection and ranging (LiDAR) and free-space communications is proposed and experimentally and numerically demonstrated, in which continuous-wave light emitted by a distributed feedback-laser diode (DFB-LD) is modulated by a lithium-niobate Mach–Zehnder intensity modulator to generate optical short pulses, and an Er-doped fiber amplifier (EDFA) is used to boost transmitting light power. Possibilities of intensity modulators for high speed communications being used to generate optical short pulses for low speed pulsed LiDAR are investigated. The influences of bias voltage of intensity modulator and bit rate of modulation signal on the generated optical pulses are discussed. The pulse width obtained by using the return to zero signal with 33% duty cycle on bit rate of 2.5 and 5 Gbit/s is respectively 128.0 and 63.2 ps, and the corresponding nominal accuracy of pulsed LiDAR is respectively 19.2 and 9.5 mm, and low repetition frequency required by pulsed LiDAR is achieved by coding to high-speed modulation signal. The system performance for free-space communications and pulsed LiDAR is evaluated, respectively. We believe that the proposed scheme is suitable for the integrated system of pulsed LiDAR and free-space communications.

Tunable optoelectronic oscillator based on optically injected distributed-feedback semiconductor laser diode under subharmonic microwave modulation

Tunable optoelectronic oscillator based on optically injected distributed-feedback semiconductor laser diode under subharmonic microwave modulation

Dynamic Device Characteristics and Linewidth Measurement of InGaN/GaN Laser Diodes

We report on the characterization and analysis of a GaN-based distributed feedback laser diode (DFB-LD) with 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order laterally etched sidewall gratings centered at a wavelength of 420 nm. We also compare the device parameters with two commonly used Fabry-Perot (FP) devices operating at 450 nm and 520 nm. Intrinsic properties of the devices were extracted, including damping factor, carrier and photon lifetimes, modulation efficiency, differential gain, and parasitic capacitance. These parameters showed that the DFB exhibits a lower damping rate and parasitic capacitance while demonstrating a higher modulation efficiency, indicating that the DFB shows good potential for communications applications. Additionally, spectral linewidth of a GaN DFB is reported. To the authors' knowledge, this is the first demonstration of parameter extraction and spectral linewidth measurement for GaN-based DFB-LDs.

Monitoring the Fractional Distillation Purification of Inorganic Hydrides by Diode Laser Absorption Spectroscopy

We present our findings on the use of diode laser spectroscopy (DLS) for monitoring СО2, Н2О, СН4, C2H2, C2H4, NH3, and other gas impurities during low-temperature fractional distillation purification of gaseous hydrides. We demonstrate a lineup of instruments and techniques for continuously monitoring impurities during purification of hydrides: NH3, AsH3, РН3, and SiH4. The IR sources used are distributed feedback diode lasers (DLs) having a single mode output fiber pigtail and covering the near-IR spectral region, from 0.7 to 2.0 μm, where overtone and combination absorption bands of the impurities of interest are located. The systems offer high sensitivity and speed in impurity concentration measurements. Owing to their small size and low energy consumption, they can readily be integrated into a process equipment (components of fractionation columns) and enable prolonged continuous monitoring of the purity of hydrides. We describe gas concentration measurement techniques that use conventional high-resolution differential absorption spectroscopy and new, modulation correlation approaches for monitoring a weak molecular absorption by an impurity of interest against a strong selective absorption background of a matrix substance (hydride under study). We present results of technological experiments concerned with the low-temperature fractional distillation of hydrides and the degree of impurity removal from them as monitored by DLS.

Simple and compact diode laser system stabilized to Doppler-broadened iodine lines at 633 nm

We present a compact iodine-stabilized laser system at 633 nm, based on a distributed-feedback laser diode. Within a footprint of 27×15cm2, the system provides 5 mW of frequency-stabilized light from a single-mode fiber. Its performance was evaluated in comparison to Cs clocks representing primary frequency standards, realizing the SI unit Hz via an optical frequency comb. With the best suited absorption line, the laser reaches a fractional frequency instability below 10-10 for averaging times above 10 s. The performance was investigated at several iodine lines, and a model was developed to describe the observed stability on the different lines.

Dual-frequency laser comprising a single fiber ring cavity for self-injection locking of DFB laser diode and Brillouin lasing.

Low-noise lasers are a powerful tool in precision spectroscopy, displacement measurements, and development of advanced optical atomic clocks. While all applications benefit from lower frequency noise and robust design, some of them also require lasing at two frequencies. Here, we introduce a simple dual-frequency laser leveraging a ring fiber cavity exploited both for self-injection locking of a standard semiconductor distributed feedback (DFB) laser and for generation of Stokes light via stimulated Brillouin scattering. In contrast to the previous laser configurations, the system is supplied by a low-bandwidth active optoelectronic feedback. Importantly, continuous operation of two mutually locked frequencies is provided by self-injection locking, while the active feedback loop is used just to support this regime. The fiber configuration reduces the natural Lorentzian linewidth of light emitted by the laser at pump and Stokes frequencies down to 270 Hz and 110 Hz, respectively, and features a stable 300-Hz-width RF spectrum recorded with beating of two laser outputs. Translating the proposed laser design to integrated photonics will dramatically reduce cost and footprint for many laser applications such as ultra-high capacity fiber and data center networks, atomic clocks, and microwave photonics.

A Flexible Bidirectional Fiber-FSO-5G Wireless Convergent System

A flexible bidirectional fiber-free-space optical (FSO)-fifth-generation (5G) wireless convergent system with 1-Gb/s/4.5-GHz sub-6 GHz and 10-Gb/s/28-GHz millimeter-wave (MMW) (downstream), as well as 10-Gb/s/24-GHz MMW (upstream) 5G hybrid data signals is built, employing a vertical cavity surface emitting laser (VCSEL)-based wavelength selector and a remotely injection-locked distributed feedback laser diode (DFB LD) for presentation. It is the first to adopt a VCSEL-based wavelength selector to adaptively provide 5G applications and an injection-locked DFB LD to perform a phase modulation-to-intensity modulation transformation with an optical-to-electrical conversion. Good bit error rate performance and acceptable eye diagrams are achieved over 25 km single-mode fiber transport, 600 m FSO link, and 10 m/4 m RF wireless transmission. Such demonstrated fiber-FSO-5G wireless convergent system is a promising one toward optical-based long-haul networks at comparatively high-speed operations. It exhibits an excellent convergence not only due to its development for incorporating optical fiber with optical/5G wireless networks, but also due to its enhancement for flexible two-way high-speed and long-haul communications.

Distributed-feedback blue laser diode utilizing a tunnel junction grown by plasma-assisted molecular beam epitaxy

In this paper, we demonstrate a novel approach utilizing tunnel junction (TJ) to realize GaN-based distributed feedback (DFB) laser diodes (LDs). Thanks to the use of the TJ the top metal contact is moved to the side of the ridge and the DFB grating is placed directly on top of the ridge. The high refractive index contrast between air and GaN, together with the high overlap of optical mode with the grating, provides a high coupling coefficient. The demonstrated DFB LD operates at λ=450.15 nm with a side mode suppression ratio higher than 35dB. The results are compared to a standard Fabry-Perot LD.

Quartz-Tuning-Fork-Enhanced Spectroscopy Based on Fast Fourier Transform Algorithm

In this paper, a gas sensing technique based on quartz-crystal-tuning-fork enhanced spectroscopy (QCTFES) and wavelength modulation spectroscopy (WMS) is reported. To explore the capabilities of this technique, detection of trace methane (CH4) was demonstrated using a near infrared distributed feedback diode laser near 1.653 μm and a single pass gas absorption cell with an optical length of 20 cm. For signal processing, a fast and effective signal analysis method based on Fast Fourier transform (FFT) algorithm is proposed for extracting the absorption intensity signal of the QCTFES-WMS, instead of a lock-in amplifier used for harmonic signal demodulation in traditional QCTF based detection techniques. Primary laboratory results indicate that an excellent linearity response of CH4 concentration and optical power levels are founded, and a detection limit of 64 ppm is achieved for a 1s averaging time, which can be further improved to 9 ppm with an averaging time of 250 s. Improvements in sensitivity and detectivity can be significantly improved if a higher power laser source is available. Compared to traditional WMS technique based semiconductor photodetectors, the room-temperature QCTF-based WMS shows significant advantages of super-broadband wavelength response, much cheap and tiny.

Near-GHz scanned-wavelength-modulation spectroscopy for MHz thermometry and H$$_2$$O measurements in aluminized fireballs of energetic materials

This manuscript presents the development of a two-color laser-absorption-spectroscopy (LAS) sensor capable of providing calibration-free measurements of temperature and H $$_2$$ O at 1 MHz in particle-laden combustion environments. This sensor employs scanned-wavelength-modulation spectroscopy with first-harmonic-normalized second-harmonic detection (scanned-WMS-2f/1f) with two distributed-feedback (DFB) tunable diode lasers (TDLs) emitting near 1392 nm and 1469 nm. The wavelength of each laser was modulated at 35 or 45.5 MHz to frequency multiplex the lasers and, more importantly, enable simultaneous wavelength scanning across the peak of each H $$_2$$ O absorption transition at 1 MHz. This method provides an absolute, in situ wavelength reference which improves measurement accuracy and robustness. Methods to characterize the lasers’ wavelength and intensity modulation at frequencies above 10 MHz are presented. Measurements of temperature and H $$_2$$ O mole fraction within 0.3–2.5% and 2–10%, respectively, of known values were acquired in a static-gas cell at temperatures of 700–1200 K. The sensor was applied to measure the path-integrated temperature and H $$_2$$ O column density in fireballs produced by igniting 0.75 g of grade 3, class B HMX with and without H-5 micro-aluminum powder (20% by mass). Temperature measurements were acquired in the fireballs with a 1– $$\sigma$$ precision of 50 K, 30 K, and 15 K for measurement rates of 1 MHz, 250 kHz, and 25 kHz, respectively. The results are the first to demonstrate that calibration-free measurements of gas properties can be acquired at 1 MHz using WMS-2f/1f.

Simulation of Monolithically Integrated Semiconductor Laser Subject to Random Feedback and Mutual Injection

Aiming at the problems of limited bandwidth and periodicity of chaotic laser, a monolithically integrated chaotic semiconductor laser subject to random feedback and mutual injection is proposed. The chaotic laser consists of two distributed feedback laser diodes (DFB-LD), two semiconductor optical amplifiers (SOA) and a passive optical waveguide. Optical injection of two coupled DFB-LDs achieves chaotic signal shaping and bandwidth enhancement. Random grating along the passive waveguide provides stochastic feedback to suppress the time delay signature (TDS). A theoretical model is established based on the Lang-Kobayashi model to explore the dynamics of the proposed chaotic laser. A chaotic signal with TDS of 0.06 and bandwidth of 13.12 GHz is obtained by simulation. Furthermore, the effects of parameters including feedback ratio, mutual injection ratio, and detuning frequency on the TDS and bandwidth of chaotic signal are investigated. The results show that the broadband chaotic laser signal with TDS suppression can be obtained by controlling parameters reasonably.

Comparison of digital lock-in amplifier and fast fourier transform algorithms for quartz-tuning-fork enhanced spectroscopy

A near-infrared methane (CH4) gas sensor system was implemented using a quartz crystal tuning fork (QCTF) based photoelectric detector and a fiber-coupled distributed feedback diode laser emitting at 1.653 μm. Wavelength-modulation with second-harmonic (2f) detection method was investigated. For signal processing, two different demodulation algorithms, i.e. Fast Fourier Transformation (FFT) and digital lock-in amplifier (DLIA), were developed and completely compared for harmonic signal extraction. Experimental results show that the SNR of WMS-2f signals using the proposed FFT algorithm can be improved by 2.5 times on average than the common DLIA method, which agrees well with the theoretical value of 2.7 times achieved with the simulated spectra data. In comparison, the proposed FFT algorithm shows better performance on signal processing efficiency and simplification, when a QCTF was used as a photoelectric detector or an acoustic transducer.

Diffuse-reflection-based single-ended laser absorption sensor for H2O temperature and concentration in kerosene-fuelled combustor

The design, optimization and demonstration of a compact, single-ended laser absorption sensor based on a diffuse-wall-reflected signal is presented for temperature and H2O concentration measurements in a kerosene-fuelled aero-combustor. The challenges of laser measurements in such harsh, practical combustion environments involve strong beam-steering, low signal-to-noise ratio (SNR), and constrained optical access. We present here a detailed characterization and optimization procedure of a single-ended optical configuration using a holed off-axis parabolic mirror as the pitch and catch optics, and the coked wall surface of the combustor as a diffuse reflector. A near-infrared distributed-feedback diode laser near 1.4 µm scanned at 1 kHz for direct absorption detection was used to access two H2O transitions for concentration and temperature measurement. An optical system design and adaptive Savitzky–Golay signal processing algorithm were used for noise suppression and SNR amelioration. The sensor was demonstrated under practical conditions in a kerosene-fuelled swirl combustor. High signal fidelity was achieved and allowed for a single-scan H2O concentration detection limit of 122 ppm MHz−1/2, despite a low reflected laser intensity level of ~50 µW. In situ, time-resolved measurements detected temperatures ranging from ~1100 K to 1300 K, and H2O concentration ranging from ~8% to 12% as global equivalence ratio varied between 0.2 and 0.45. The results revealed an expected trend while demonstrating much faster response and less delay versus a comparative thermocouple. This successful field manifestation provides direct proof for the robustness and reliability of a diffuse-reflection-based single-ended sensor system in engine combustion chamber environments.