Distributed Feedback Laser Research Articles

Cascadable excitability and inhibition in DFB laser-based photonic spiking neurons

Effective communication between neurons is crucial in both the human brain and neuromorphic computing. Excitatory and inhibitory spiking information are transmitted through axons and dendrites to adjacent neurons. In this paper, we propose a cascaded system for excitability and inhibition in photonic spiking neurons based on distributed feedback (DFB) laser subject to side-mode optical pulse injection (SMOPI). The feasibility of the cascaded system is proved by simulation and experiment. This system offers the advantage of eliminating the need for additional amplifiers. By appropriately adjusting the injection optical power and wavelength detuning between two DFB lasers, neuronal excitability and inhibition can be cascaded successfully. Both temporal encoded spikes and rate encoded spikes are considered. The operating conditions of the two lasers employed in the cascaded system are also analyzed. This work provides a promising technical pathway for the development of photonic spiking neural network (PSNN) chips, leveraging the benefits of low power consumption and high integration.

Pump–probe-alternating photothermal interferometry for two-component gas sensing

We demonstrate a high-sensitivity acetylene/methane gas sensor based on hollow-core fiber photothermal interferometry (PTI) with a pump–probe-alternating technique. This technique utilizes two distributed-feedback lasers as pump and probe beams alternatively for two gas components to facilitate photothermal phase modulation and detection through time-division multiplexing. With a 2.5-cm-long hollow-core conjoint-tube fiber, noise-equivalent concentrations of 370 ppb and 130 ppb are demonstrated for methane and acetylene, respectively. Noise characteristics of the PTI system are analyzed and experimentally tested. The proposed technique eliminates the need for an additional laser in the traditional PTI setup, enabling the construction of a sensitive yet more cost-effective multi-gas component detection system.

Wide range linearization calibration method for DFB Laser in FMCW LiDAR

In this paper, a solution based on a hybrid electro-optic phase-locked loop (HEO-PLL) is proposed to address the nonlinearity of the continuous sweep frequency of the light source in Frequency Modulated Continuous Wave (FMCW) LiDAR. This nonlinearity leads to large measurement errors, low accuracy, and poor system adaptability. The proposed solution uses a HEO-PLL to control the frequency sweep linearity of the distributed feedback (DFB) laser when it undergoes continuous, rapid, and wide-range frequency modulation through current tuning. The system is designed to allow the DFB laser to be used as a high-quality source for FMCW LiDAR. This enhances the resolution and ranging capability of the FMCW LiDAR with the DFB laser as the source, while avoiding issues such as difficult tuning of the loop bandwidth and central frequency and being highly susceptible to temperature and voltage variations caused by the charge pump phase-locked loop.

Low-Threshold 795 nm Oxide-Confined Distributed Feedback Lasers With Surface Gratings

Low-Threshold 795 nm Oxide-Confined Distributed Feedback Lasers With Surface Gratings

Rayleigh backscattering-based simultaneous linewidth narrowing of a multi-wavelength DFB laser array with an arbitrary wavelength spacing.

Simultaneous linewidth narrowing of a multi-wavelength laser array with an arbitrary wavelength spacing based on Rayleigh backscattering is experimentally demonstrated. Rayleigh backscattering from a single 30 m high numerical aperture fiber (HNAF) is employed to simultaneously narrow the linewidths of a DFB laser array consisting of four distributed feedback (DFB) semiconductor lasers with different wavelengths. Experimental results show that the instantaneous linewidths of the four DFB lasers can be simultaneously narrowed from megahertz to kilohertz no matter whether the wavelength spacing between the lasers is equally spaced or not, verifying the self-adaptivity of Rayleigh backscattering on laser linewidth narrowing. The method demonstrated here is also applicable for on-chip waveguides without wavelength dependence, providing a more compact narrow linewidth laser array for the wavelength-multiplexing division system and other promising applications.

Efficient and systematic parameter extraction based on rate equations by DFB equivalent circuit model.

The conventional direct parameter extraction method generally suffers from cumbersome due to redundant experiments. An efficient and systematical parameter extracting solution is proposed based on an equivalent circuit model of distributed feedback (DFB) lasers. The successfully built circuit model includes the necessary intrinsic parameters in the rate equations and the extrinsic parameters to provide a better approximation of the actual laser. This method is experimentally verified through a DFB laser chip measurement of electronic and optical performance under the same conditions. Finally, the nine intrinsic parameters in the rate equations and five extrinsic parameters in the model are efficiently extracted using this technique from a set of experimental characteristics of a DFB laser chip. Modeled and measured results for the laser output characteristics exhibit good agreement when the extracted parameters are used. The method is versatile for other semiconductor lasers that can be modeled using rate equations. Comparison with simulation results of published laser models further validates the reliability of the presented model and extraction method.

Transient analysis of solar pyrolysis and hydrogen yield via interband cascade laser absorption spectroscopy of methane, acetylene, ethylene, and ethane

A mid-infrared laser absorption sensing method has been developed to measure species concentrations of four hydrocarbons and gas temperature over a range of temperatures in mixture compositions relevant to the pyrolytic decomposition of natural gas. The four measured species (methane, acetylene, ethylene, and ethane) are the most abundant hydrocarbons during the pyrolysis of natural gas, and provide a means to monitor decomposition progress and hydrogen yield through molar balance. In this work, time-division multiplexed signals of three distributed-feedback interband cascade lasers are used to make simultaneous measurements of select C-H stretch rovibrational transitions of the target hydrocarbons in the 3.00–3.34 μm range. The sensor was validated over a range of temperatures and pressures (300–1000 K, 0.03–1 atm) at relevant mixture compositions, with correction methods developed to mitigate cross-species interference. The sensor was demonstrated on a solar-thermal pyrolysis reactor, where time-resolved measurements of species mole fractions were performed across a range of insolation conditions to capture the transient response of the reactor.

Frequency stable and low phase noise THz synthesis for precision spectroscopy

We present a robust approach to generate a continuously tunable, low phase noise, Hz linewidth and mHz/s stability THz emission in the 0.1 THz to 1.4 THz range. This is achieved by photomixing two commercial telecom, distributed feedback lasers locked by optical-feedback onto a single highly stable V-shaped optical cavity. The phase noise is evaluated up to 1.2 THz, demonstrating Hz-level linewidth. To illustrate the spectral performances and agility of the source, low pressure absorption lines of methanol and water vapors have been recorded up to 1.4 THz. In addition, the hyperfine structure of a water line at 556.9 GHz, obtained by saturation spectroscopy, is also reported, resolving spectral features displaying a full-width at half-maximum of 10 kHz. The present results unambiguously establish the performances of this source for ultra-high resolution molecular physics.

Influence of sidewall grating etching depth on GaN-based distributed feedback laser diodes

Conventional sidewall gratings in GaN-based distributed feedback (DFB) laser diodes (LD) have a thick p-type layer, which may cause current spreading and carrier-induced anti-guiding effects, severely deteriorating the lasers performance. In this study, we report a novel fabrication technology to not only reduce the remaining p-type layer in the sidewall gratings but also realize close-coupled sidewall gratings. Afterwards, we further investigate the influence of the sidewall gratings etching depth on GaN-based DFB LDs. The results show an almost unchanged current injection efficiency, nearly coincided I–V curve and a near-field emission width for shallow etched structures, which indicate that the current spreading is neglectable in GaN-based ridge structure LDs. Based on this analysis, GaN-on-Si DFB LDs with an emission wavelength of 414 nm, full width at half maxima of 22 pm, and side mode suppression ratio of 19.1 dB were realized.

A Large-Scale Photonic CNN Based on Spike Coding and Temporal Integration

The real-time massive-data intelligent information processing tasks highlight a vital requirement for the novel, intelligent optimization hardware. Convolutional neural networks are highly capable of extracting the hierarchical feature map and enhancing recognition accuracy, with photonics-enabled implementations drawing considerable interest. Here, we propose a large-scale and reconfigurable photonic convolutional neural network (PCNN), based on a hardware-friendly distributed feedback laser diode (DFB-LD). Our approach applies biological time-to-first-spike coding to a DFB-LD neuron to perform a temporal convolutional operation (TCO) for image processing tasks. In PCNN, experimental results demonstrate that we successfully implement the TCO to extract the image features with convolutional kernels of size 11×11. Furthermore, we investigate the temporal pulse shaping of a DFB-LD neuron to build a densely-connected fully connected layer, which synaptic weights can be rapidly adjusted at a rate of 5 GHz, achieving full MNIST and Fashion-MNIST benchmark image classification tasks, with classification accuracies of 98.56% and 87.48%, respectively. This work highlights the potential of neuron-like optical analog computing platforms for real-time and more complex intelligent processing networks.

Research on an Enhanced Detuned-Loading Effect in Integrated Two-Section DFB Lasers with High Modulation Bandwidths.

A novel high-speed directly modulated two-section distributed-feedback (TS-DFB) semiconductor laser based on the detuned-loading effect is proposed and simulated. A grating structure is designed by the reconstruction-equivalent-chirp (REC) technique. A π phase shift is introduced into the reflection grating, which can provide a narrow-band reflection region with a sharp falling slope on both sides of the reflection spectrum, thus enhancing the detuned-loading effect. Owing to its unique dual-falling-edges structure, the bandwidth can be improved even when the lasing wavelength shifts beyond the left falling edge due to a thermal effect in the actual test, in which condition the detuned-loading effect can be used twice, which greatly improves the yield. The modulation bandwidth is increased from 17.5 GHz for a single DFB laser to around 24 GHz when the lasing wavelength is located on the left falling edge of the TS-DFB laser based on the detuned-loading effect, and it can be increased to 22 GHz for the right side. An eight-channel laser array with precise wavelength spacing is investigated, with a side-mode suppression ratio (SMSR) >36 dB. In addition, TS-DFB lasers with uniform reflection gratings are studied, and simulated results show that the modulation characteristic is far inferior to the laser with a phase-shifted grating reflector.

Quasi-2D Dion-Jacobson phase perovskites as a promising material platform for stable and high-performance lasers.

Metal halide perovskites have shown outstanding optoelectronic and nonlinear optical properties; yet, to realize wafer-scale high-performance perovskite-integrated photonics, the materials also need to have excellent ambient stability and compatibility with nanofabrication processes. In this work, we introduce Dion-Jacobson (D-J) phase perovskites for photonic device applications. By combining self-assembled monolayer-assisted film growth with thermal pressing, we obtain a series of compact and extremely smooth D-J phase perovskite thin films that exhibit excellent stability during electron-beam lithography, solvent development, and rinse. Combining spectroscopic and morphological characterizations, we further demonstrate how organic spacers can be used to fine-tune the photophysical properties and processability of the perovskite films. The distributed-feedback lasers based on the D-J phase perovskites exhibit a low lasing threshold (5.5 μJ cm-2 pumped with nanosecond laser), record high Q factor (up to 30,000), and excellent stability, with an unencapsulated device demonstrating a T90 beyond 60 hours in ambient conditions (50% relative humidity).

Single-frequency pulsed fiber laser based on an electro-optic modulator with injection seeding technique.

A single-frequency linearly polarization pulsed fiber laser based on an electro-optic modulator with injection seeding technique is demonstrated. The single-frequency performance of the fiber ring-cavity laser is guaranteed by the seed source, which is a distributed-feedback fiber laser based on the π-phase-shifted fiber Bragg grating. The electro-optic modulator triggers active Q-switching of the laser for pulse generation. The devices used in the fiber laser are all polarization-maintaining to ensure linear polarization laser output. Through parameter optimization, the laser generates a single-frequency linearly polarization pulsed laser with a central wavelength of 1064.22nm, linewidth of 35MHz, and polarization extinction ratio of better than 40dB. This type of fiber laser can be applied in lidar, beam combining, nonlinear frequency conversion, and other fields.

Impact of external carrier noise on the linewidth enhancement factor of a quantum dot distributed feedback laser.

This paper demonstrates that the linewidth enhancement factor of quantum dot lasers is influenced by the external carrier transport issued from different external current sources. A model combining the rate equation and semi-classical carrier noise is used to investigate the different mechanisms leading to the above phenomenon in the context of a quantum dot distributed feedback laser. Meanwhile, the linewidth enhancement factor extracted from the optical phase modulation method shows dramatic differences when the quantum dot laser is driven by different noise-level pumps. Furthermore, the influence of external carrier noise on the frequency noise in the vicinity of the laser's threshold current directly affects the magnitude of the linewidth enhancement factor. Simulations also investigate how the external carrier transport impacts the frequency noise and the spectral linewidth of the QD laser. Overall, we believe that these results are of paramount importance for the development of on-chip integrated ultra-low noise oscillators producing light at or below the shot-noise level.

Erbium-doped fiber amplifier (EDFA)-assisted laser heterodyne radiometer (LHR) working in the shot-noise-dominated regime.

A near-infrared (NIR) laser heterodyne radiometer (LHR) using a 1603 nm distributed feedback (DFB) laser, associated with an erbium-doped fiber amplifier (EDFA), used as a local oscillator (LO) was developed. The EDFA was customized for automatic power control to amplify and stabilize the LO DFB laser power, which allowed to reduce baseline fluctuation and thus make the processed atmospheric transmission spectrum with higher precision. The operation of the EDFA-assisted LHR with a shot-noise-dominated performance was analyzed and experimentally achieved by optimizing the LO power. The performance of the developed LHR was evaluated and verified by measuring an atmospheric CO2 absorption spectrum, and the atmospheric CO2 column abundances were then retrieved based on the optimal estimation method (OEM). The results were in good agreement with the Greenhouse Gas Observation Satellite (GOSAT) data. The EDFA-assisted LHR firstly reported in this Letter has a potential to further improve the measurement precision of atmospheric greenhouse gases using ground-based LHR remote sensing.

An absolute ranging method based on FMCW principle using dual laser interferometry

The FMCW (Frequency Modulated Continuous Wave) laser interferometer can achieve high-precision displacement measurement by calculating the phase of the interference signal. Due to the need for continuous superposition of signal phases, the optical path and power supply cannot be interrupted during the measurement process. To solve this problem, this article proposes a new absolute ranging method—the decimal comparison method. Two distributed feedback lasers with different central wavelengths are used to measure the same target. The digital signal processing technology is used to solve the sampled interference signals, and the initial phase value corresponding to the decimal of interference is taken. Combined with the central wavelength of the two laser sources, the length variation of the F–P cavity corresponding to the number of interference periods is calculated. Finally, the optical path difference of the target is calculated by the established mathematical model. The experimental results show that this method can realize the absolute measurement of laser interferometry and can expand the application range of FMCW interferometry.

Investigation of defect characterization, formation mechanism, and effect in distributed feedback lasers

InP, which exhibits attractive physical characteristics, such as high electron mobility, high conductivity, and high bandgap width, has always been fanatically pursued in high frequency and high speed devices in recent years. However, the inherent high density defects hinder the quality of the epitaxial layer and, even worse, impede the device’s life. Here, we found a kind of defect in the distributed feedback laser layers on an InP based substrate. A focused ion beam was employed in order to dissect the defect. The formation process was characterized using a transmission electron microscope and a high-resolution transmission electron microscope. Closer analysis reveals that defects form a subsurface damage layer between the substrate and the epitaxial layer. The subsurface damage layer already has a potentially destructive lattice, including lots of dislocations and lattice distortions, which leads to anisotropy in the interface layer. As the epitaxial film thickness increases, so does this strain relax, and dislocations form.

Electrically driven organic laser using integrated OLED pumping

Organic semiconductors are carbon-based materials that combine optoelectronic properties with simple fabrication and the scope for tuning by changing their chemical structure1–3. They have been successfully used to make organic light-emitting diodes2,4,5 (OLEDs, now widely found in mobile phone displays and televisions), solar cells1, transistors6 and sensors7. However, making electrically driven organic semiconductor lasers is very challenging8,9. It is difficult because organic semiconductors typically support only low current densities, suffer substantial absorption from injected charges and triplets, and have additional losses due to contacts10,11. In short, injecting charges into the gain medium leads to intolerable losses. Here we take an alternative approach in which charge injection and lasing are spatially separated, thereby greatly reducing losses. We achieve this by developing an integrated device structure that efficiently couples an OLED, with exceptionally high internal-light generation, with a polymer distributed feedback laser. Under the electrical driving of the integrated structure, we observe a threshold in light output versus drive current, with a narrow emission spectrum and the formation of a beam above the threshold. These observations confirm lasing. Our results provide an organic electronic device that has not been previously demonstrated, and show that indirect electrical pumping by an OLED is a very effective way of realizing an electrically driven organic semiconductor laser. This provides an approach to visible lasers that could see applications in spectroscopy, metrology and sensing.

Efficient employment of VCSEL light sources in high speed dispersion compensation system

Abstract This paper demonstrated the efficient employment of vertical cavity surface emitting laser (VCSEL) light sources in high speed dispersion compensation systems. VCSEL are compared with CW laser and distributed feedback laser in the modulated light output power, signal quality factor and minimum data error rates through the fiber system. Light signal base band modulated power is clarified with spectral frequencies after LiNb MZ modulators. Light signal base band modulated amplitude is simulated against base band time frequencies after LiNb MZ modulators. The total light signal index base band modulated power/amplitude value is estimated after LiNb MZ modulators for various light sources. The light signal base band modulated power is demonstrated with both spectral frequencies and time interval after fiber loop control length with compensation system. Total light signal index base band modulated power/amplitude value is estimated numerically after fiber loop control length with compensation system. The modulated electronic signal base band modulated power is indicated with spectral frequencies after PIN receiver. The light signal base band modulated amplitude is studied clearly against base band time frequencies after PIN receiver. The signal quality factor, BER, and modulated lighted output power are clarified and sketched against fiber system lengths for various light sources.

Noise cancellation in distributed feedback laser based interrogation system for twin grating accelerometer

In this paper, we demonstrate a noise cancellation method for suppressing laser frequency noise in distributed feedback laser based system for interrogating a twin fiber Bragg grating based accelerometer. A simple method has been developed by studying the noise characteristics of the sensing photodiode and the reference photodiode, used in standard intensity based wavelength demodulation system. Proposed method could be able to reduce deterministic noise components to about 20% of the original noise components without using any complex feedback mechanism to stabilize the laser.