Distributed Feedback Laser Research Articles

High‐Power, Narrow‐Linewidth, and Low‐Noise Quantum Dot Distributed Feedback Lasers

AbstractSingle‐frequency semiconductor lasers represent a critical role in optical communications, light detection and ranging systems, photonics integrated circuits, etc. Here, combining atom‐like quantum dot (QD) materials and advanced lateral gratings, a high‐power, ultra‐low‐noise 1.3 µm InAs/GaAs QD distributed feedback laser is demonstrated. Stable single‐longitudinal‐mode output power of 100 mW from 25 ℃ to 85 ℃ is achieved with a maximum side mode suppression ratio of 62.6 dB, and the variations of threshold current and slope efficiency over the temperature range are slight, indicting a high temperature stability. A record‐narrow intrinsic linewidth of 1.62 kHz is achieved at 55 ℃ with a white noise level of merely 515 Hz2 Hz–1, and a minimum averaged relative intensity noise of only –166 dB/Hz between 0.1 GHz and 20 GHz is obtained at 25 ℃. Furthermore, a strong tolerance to external optical feedback (〉 –14 dB) is demonstrated in the range from 25 ℃ to 85 ℃, with a maximum value of –8 dB at 85 ℃. This high‐quality single‐frequency laser fabricated with simplified processes and compact size paves the way for its future large‐scale applications such as high‐capacity optical communication, high‐precision optical detection, high‐speed optical interconnections, etc.

A fiber-solid hybrid 1319 nm single-frequency MOPA Laser for sodium Doppler lidar

The narrow linewidth nanosecond pulse 1319 nm laser used to generate 589 nm laser is the core technology of sodium Doppler lidar. Here, a high gain fiber-solid hybrid amplifier seeded by a 1319 nm distributed-feedback laser diode (DFB-LD) is proposed to achieve high-power amplification of small signal 1319 nm pulse laser. A pulsed 1319 nm laser with a repetition frequency of 500 Hz, a pulse duration of 500 ns, an energy of 10.3 mJ and a linewidth of 1.9 MHz was developed by utilizing a three-stage fiber coupled end-pumped amplifier and a two-stage Innoslab amplifier, and the beam quality factor M2 is less than 1.6, the gain of the solid amplification system exceeds 28 dB.

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.

High-entropy-rate broadband chaos generation by using short-resonant-cavity DFB semiconductor laser with optical feedback.

Semiconductor lasers with delayed optical feedback are a promising source of optical chaos for practical applications, owing to simple configurations that are easy to integrate and synchronize. However, for traditional semiconductor lasers, the chaos bandwidth is limited by the relaxation frequency to several gigahertz. Here, we propose and experimentally demonstrate that a short-resonant-cavity distributed-feedback (SC-DFB) laser can generate broadband chaos only with simple feedback from an external mirror. The short distributed-feedback resonant cavity not only enhances laser relaxation frequency but also makes the laser mode more susceptible to external feedback. Experiments obtained a laser chaos with 33.6 GHz bandwidth and a spectral flatness of 4.5 dB. The corresponding entropy rate is estimated as more than 33.3 Gbit/s. It is believed that the SC-DFB lasers will promote development of chaos-based secure communication and physical key distribution.

A laser absorption sensor for fuel slip monitoring in high-humidity flue gases from ammonia combustion

Ammonia has been recently recognized as a promising carbon-free fuel to help decarbone both the power and industrial heating sectors. However, fuel slip during ammonia combustion is of high concern because of the high toxicity of the chemical, motivating the development of sensitive sensors for real-time monitoring of ammonia emission in combustion flue gases. In this work, a near-infrared absorption spectroscopic sensor was developed for trace ammonia (NH3) measurements in high-humidity flue gas environments with water vapor (H2O) mole fractions up to 40%. The focus on high humidity is motivated by the facct that ammonia combustion generally leads to flues gases with notably higher water vapor concentations as compared to conventional hydrocarbons. The sensor used a distributed feedback laser to target the NH3 absorption line near 6612.73 cm−1. Proof-of-concept tests were conducted in a high-temperature multi-pass cell with a controlled temperature of 500 K and pressure of 1 atm. A custom-designed variable humidity generator was used to provide a reference NH3/N2 mixture with a controlled H2O mole fraction (10%–40%) to simulate ammonia combustion flue gases. Direct absorption spectroscopy and wavelength modulation spectroscopy were both used to ensure a relatively large dynamic range. H2O-induced broadening effects on the measured absorption profile were quantified. The developed sensor was firstly validated against NH3/N2 mixtures with different H2O concentrations, with a lower detection limit of 76 ppb achieved. Real-time measurements of NH3 slip in the flue gases from CH4/NH3/air flames and CH4/NH3 co-firing industrial furnace were performed as a demonstration of the sensor for time-resolved ammonia monitoring with sufficient accuracy, sensitivity, and time response.

Critical dispersion of chirped fiber Bragg grating for eliminating time delay signature of distributed feedback laser chaos

Optical chaos has attracted widespread attention owing to its complex dynamic behaviors. However, the time delay signature (TDS) caused by the external cavity mode reduces the complexity of optical chaos. We propose and numerically demonstrate the critical dispersion of chirped fiber Bragg grating (CFBG) for eliminating the TDS of laser chaos in this work. The critical dispersion, as a function of relaxation frequency and bandwidth of the optical spectrum, is found through extensive dynamics simulations. It is shown that the TDS can be eliminated when the dispersion of CFBG is above this critical dispersion. In addition, the influence of dispersive feedback light and output light from a laser is investigated. These results provide important quantitative guidance for designing chaotic semiconductor lasers without TDS.

Precision vibration measurement using differential phase-modulated homodyne interferometry

A novel precision vibration measurement using differential phase-modulated homodyne interferometry is presented. The orthogonal linearly polarized phase-modulated single frequency laser source is constructed by using a distributed feedback (DFB) fiber laser and a fiber-coupled electro-optic phase modulator (EOM). An auxiliary monitoring signal is used to differentially compensate the optical path drift and common-mode noise of the fiber. By pre-scanning the wavelength of DFB laser to introduce enough phase changes, ellipse fitting can be realized without moving the object more than half a wavelength. Therefore, the periodic nonlinearity of the phase generated carrier (PGC) demodulation is compensated. Experimental setup was built and the real-time signal processing was realized based on field programmable gate array (FPGA). The experiments of pulse vibration, sinusoidal vibration and comparison with commercial laser vibrometer were performed to verify the feasibility of the proposed method. The experimental results show that the average deviation of vibration amplitude is about 0.97 nm in the frequency range of 0.5 kHz to 10.0 kHz, which indicates that the proposed method has significant application for precision vibration measurement.

High-temperature absorption cross-sections and interference-immune sensing method for formaldehyde near 3.6-µm

Absorption cross-sections of formaldehyde (CH2O) were measured at elevated temperatures near 3.6 µm, a region of strong intensity due to the overlapping QQ5 branch of the v1 band and the PQ7 branch of the v2+v4 combination band. 1,3,5-trioxane was shock-heated in an argon bath gas to produce controlled mixtures of formaldehyde over a range of temperatures (900–1500 K) and pressures (0.4–4.8 atm). Spectrally-resolved absorption measurements of formaldehyde were obtained using a rapidly-tunable distributed-feedback interband cascade laser scanned at 40 kHz over 2778.1–2778.9 cm−1 behind reflected shock waves. The resulting absorption cross-sections were fit with functions reflecting the temperature and pressure dependence of the targeted features, enabling spectral reconstruction at any temperature and pressure within the range of the study. By exploiting the strong temperature and pressure sensitivity of the cross-sections, it is demonstrated that CH2O concentration, temperature, and pressure can be inferred from a measured absorbance spectrum. Cross-sections of common combustion species were also measured over the selected wavelength range to validate that the region is largely free of narrow-band interference. Further, the multi-parameter spectral fitting method is shown to correct for baseline interference and demonstrated in experiments involving transient gas properties.

Suppressing DFB Lasers Relaxation Oscillations by High-Order Continuous Shaping Current With CNN Prediction

A technique of continuous shaping current waveform to suppress relaxation oscillations (ROs) of distributed feedback (DFB) laser for a high-performance optic system is demonstrated. To effectively suppress ROs, expressions for the shaping current waveform are theoretically derived based on the rate equations and different polynomials for the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> , 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , and 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order Fourier basis functions are introduced. The convolutional neural network (CNN) is employed to predict the multi-parameter values that determine the results of the shaping input current, which exempt from the difficult and time-consuming process of parameter selection. Prior to training, preprocessing of the data obtained from DFB laser forward simulation using min-max normalization aims to improve the training efficiency of the CNN. The shaping current signals obtained from the CNN predicted parameters are put into the equivalent circuit model for the DFB laser to verify the effectiveness of the shaping current technique and CNN parameter optimization. Afterwards, the shaping current waveform is verified in a time division multiplex passive optical network (TDM-PON) utilizing the DFB laser model as a directly modulated source achieving remarkable performance with low cost. The results show that the high-order continuous shaping current modulated technique can successfully suppress the ROs and enhance the performance of the optic system.

III-V-on-Si DFB Laser With Co-Integrated Power Amplifier Realized Using Micro-Transfer Printing

A C-band III-V-on-Si distributed feedback (DFB) laser with co-integrated power amplifier was realized using micro-transfer printing. The DFB laser exhibits single mode operation around 1540 nm at 20°C. By driving the DFB laser and co-integrated power amplifier simultaneously, up to 14 dBm waveguide-coupled output power with over 28 dB side mode suppression ratio was achieved at an overall bias current of 270 mA.

Fused Triangulene Dimers: Facile Synthesis by Intramolecular Radical‐Radical Coupling and Application for Near‐Infrared Lasers

AbstractLarge graphene‐like molecules with four zigzag edges are ideal gain medium materials for organic near‐infrared (NIR) lasers. However, synthesizing them becomes increasingly challenging as the molecular size increases. In this study, we introduce a new intramolecular radical‐radical coupling approach and successfully synthesize two fused triangulene dimers (1 a/1 b) efficiently. X‐ray crystallographic analysis of 1 a indicates that there is no intermolecular π‐π stacking in the solid state. When the more soluble derivative 1 b is dispersed in polystyrene thin films, amplified spontaneous emission in the NIR region is observed. Using 1 b as the active gain material, we fabricate solution‐processed distributed feedback lasers that exhibit a narrow emission linewidth at around 790 nm. The laser devices also exhibit low thresholds with high photostability. Our study provides a new synthetic strategy for extended nanographenes, which have diverse applications in electronics and photonics.

Frequency modulation laser spectroscopy method for methane isotopologue ratio and total concentration measurements at 1661 nm

Source identification and accurate measurements of methane gas concentration are key tools necessary for climate change management. Here we present a method for methane isotopologue ratio measurement using a laser-based frequency modulation (FM) spectroscopy technique in the near infrared at 1661 nm. We provide line shape analysis and discuss a fitting algorithm for accurate isotopologue ratio metrology and investigate and minimize the effects of residual amplitude modulation on the experimentally produced FM signal line shape. This FM technique is further evaluated for future development of a cavity-enhanced and noise-immune system capable of isotopologue ratio as well as ultrasensitive trace gas measurements, all accessible using a single distributed feedback laser.

Fused Triangulene Dimers: Facile Synthesis by Intramolecular Radical-Radical Coupling and Application for Near-Infrared Lasers.

Large graphene-like molecules with four zigzag edges are ideal gain medium materials for organic near-infrared (NIR) lasers. However, synthesizing them becomes increasingly challenging as the molecular size increases. In this study, we introduce a new intramolecular radical-radical coupling approach and successfully synthesize two fused triangulene dimers (1 a/1 b) efficiently. X-ray crystallographic analysis of 1 a indicates that there is no intermolecular π-π stacking in the solid state. When the more soluble derivative 1 b is dispersed in polystyrene thin films, amplified spontaneous emission in the NIR region is observed. Using 1 b as the active gain material, we fabricate solution-processed distributed feedback lasers that exhibit a narrow emission linewidth at around 790 nm. The laser devices also exhibit low thresholds with high photostability. Our study provides a new synthetic strategy for extended nanographenes, which have diverse applications in electronics and photonics.

On multiplexing in physical random number generation, and conserved total entropy content

In the current article, we use a random supercontinuum based on a random Raman distributed feedback laser to investigate the generation of random numbers by spectrally demultiplexing the broad supercontinuum spectrum in parallel channels. By tuning the spectral separation between two independent channels, we test the most typically used statistical tests’ abilities to identify the required minimum spectral separation between channels, especially after the use of post-processing steps. Out of all the tests that were investigated, the cross-correlation across channels using the raw data appears to be the most robust. We also demonstrate that the use of post-processing steps, either least significant bits extraction or exclusive-OR operations, hinders the ability of these tests to detect the existing correlations. As such, performing these tests on post-processed data, often reported in literature, is insufficient to properly establish the independence of two parallel channels. We therefore present a methodology, which may be used to confirm the true randomness of parallel random number generation schemes. Finally, we demonstrate that, while tuning a single channel’s bandwidth can modify its potential randomness output, it also affects the number of available channels, such that the total random number generation bitrate is conserved.

Hybrid integrated narrow-linewidth semiconductor lasers.

Integrated narrow-linewidth lasers are the key devices in compact coherent optical systems of metrology, sensing, and optical microwave generation. Here, we demonstrate a hybrid integrated laser based on an optical negative feedback scheme. The laser is composed of a commercial distributed feedback (DFB) laser diode and an on-chip micro-resonator with a Q-factor of 0.815 million. The feedback optical field is coupled back to the laser cavity through the back facet. Therefore, the laser can maintain the lasing efficiency of the DFB laser diode. The linewidth of the DFB laser diode is compressed from 2MHz to 6kHz, corresponding to the linewidth reduction factor of 25.2dB. The theoretical result shows that the laser performance still has a huge improvement margin through precise control of the detuning between laser frequency and the micro-resonator, as well as the phase delay of the feedback optical field. The hybrid narrow-linewidth laser diode has wide application prospects in coherent optical systems benefitting from the low cost and volume productivity.

Multimode Lasing in All-Solution-Processed UV-Nanoimprinted Distributed Feedback MAPbI3 Perovskite Waveguides

In this work, we present an all-solution fabrication approach for external second-order 1D distributed feedback (DFB) gratings using soft UV-nanoimprint lithography (UV-NIL) above archetypical methylammonium lead iodide (MAPbI3) perovskite films. This high-throughput method can be carried out in an ambient environment and requires only slightly elevated temperatures as low as 70 °C, gentle imprint pressure, and the use of compatible UV-NIL resin. Under stripe-shaped optical excitation, we observe simultaneously occurring optical phenomena in our high-gain strong-scattering perovskite films, namely amplified spontaneous emission, random lasing, and 1D DFB lasing. In pursuit of distinguishing these mechanisms, we explore far-field emission patterns and output polarization. Additionally, the DFB lasing is hardly attenuated when a thin absorbing indium tin oxide (ITO) film, commonly used as an electrode in fully contacted electrical devices, is inserted between the perovskite film and the DFB grating. As a result, we reproducibly achieve single and multimode, low-threshold (below 100 μJ·cm–2), narrow linewidth (below 0.2 nm), and strongly polarized (extinction ratio above 50) optically pumped DFB lasing for MAPbI3 waveguides with and without an adjacent ITO layer. We believe that the proposed resonator integration approach can be extended toward complete electrically active devices, enabling an alternative integration scheme to achieve current-injection lasing.

Microcavity- and Microlaser-Based Optical Barcoding: A Review of Encoding Techniques and Applications.

Optical microbarcodes have recently received a great deal of interest because of their suitability for a wide range of applications, such as multiplexed assays, cell tagging and tracking, anticounterfeiting, and product labeling. Spectral barcodes are especially promising because they are robust and have a simple readout. In addition, microcavity- and microlaser-based barcodes have very narrow spectra and therefore have the potential to generate millions of unique barcodes. This review begins with a discussion of the different types of barcodes and then focuses specifically on microcavity-based barcodes. While almost any kind of optical microcavity can be used for barcoding, currently whispering-gallery microcavities (in the form of spheres and disks), nanowire lasers, Fabry-Pérot lasers, random lasers, and distributed feedback lasers are the most frequently employed for this purpose. In microcavity-based barcodes, the information is encoded in various ways in the properties of the emitted light, most frequently in the spectrum. The barcode is dependent on the properties of the microcavity, such as the size, shape, and the gain materials. Various applications of these barcodes, including cell tracking, anticounterfeiting, and product labeling are described. Finally, the future prospects for microcavity- and microlaser-based barcodes are discussed.

Seawater Temperature Measurement System Based on Wavelength Sweeping and Cross Correlation Algorithm

A real-time seawater temperature measurement system based on a wavelength swept distributed feedback laser is developed. The π phase shifted Fiber Bragg grating with a narrow bandwidth of 12 pm is used as the sensing probe. The wavelength is swept by linearly and periodically modulating the driving current of laser with a sawtooth wave signal. The absorption line of H13C14N gas cell provides a standard wavelength to calibrate the swept wavelength in real time to reduces the measurement error induced by the noises or drifts of the laser. Resonance difference between the measurement and the reference in time domain is obtained via a series of digital signal processing such as normalization, derivation, low-pass filtering and cross-correlation operation. Experimental results show that, the sensitivity of the sensor is 16.22 pm/°C, the dynamic range is about 55 °C, the resolution is as high as 0.002 °C, and the thermal response time is ~50 ms. The sensor system is compact, simple, high-resolution and large-dynamic range that has potential application for ocean temperature monitoring.

Characterization of optical phase-locked two distributed-feedback fiber lasers for 87Rb atom interferometry

We report the optical phase-locking of two 1560 nm distributed-feedback (DFB) fiber lasers converted to 780 nm with a frequency difference of 6.834 GHz for 87Rb. The fiber laser exhibits a narrow linewidth and low-intensity noise, which are advantageous for a Raman pulse laser in an atomic gravimeter. However, the piezoelectric actuator of the DFB laser causes a low feedback rate in an optical phase-locking loop (OPLL). To overcome this limitation, we used an acousto-optic modulator as an additional actuator to increase the modulation bandwidth of the OPLL and achieved a residual phase noise of approximately -127 dBrad2/Hz in the offset frequency range from 10 Hz to 1 kHz. The sensitivity limit estimated using the sensitivity function and experimental parameters of 87Rb atomic gravimeter shows that our OPLL system can be used in state-of-the-art gravimeters.

Development of a Stable Oxygen Sensor Using a 761 nm DFB Laser and Multi-Pass Absorption Spectroscopy for Field Measurements.

An optical sensor system based on wavelength modulation spectroscopy (WMS) was developed for atmospheric oxygen (O2) detection. A distributed feedback (DFB) laser with butterfly packaging was used to target the O2 absorption line at 760.89 nm. A compact multi-pass gas cell was employed to increase the effective absorption length to 3.3 m. To ensure the stability and anti-interference capability of the sensor in field measurements, the optical module was fabricated with isolation of ambient light and vibration design. A 1f normalized 2f WMS (WMS-2f/1f) technique was adopted to reduce the effect of laser power drift. In addition, a LabVIEW-based dual-channel lock-in amplifier was developed for harmonic detection, which significantly reduced the sensor volume and cost. The detailed detection principle was described, and a theoretical model was established to verify the effectiveness of the technique. Experiments were carried out to obtain the device's sensing performances. An Allan deviation analysis yielded a minimum detection limit of 0.054% for 1 s integration time that can be further improved to 0.009% at ~60 s. Finally, the reliability and anti-interference capability of the sensor system were verified by the atmospheric O2 monitoring.