Laser Module Research Articles

Food 3D Printing with Starch Suspension

: 3D food printing is a method of making a novel three-dimensional processed food based on digital data by applying additive manufacturing technology to food materials [1]. Food 3D printers are expected to serve foods with controlling nutrients and textures suitable for an individual's health. There are many different types of food 3D printers such as screw type, syringe type, inkjet type, etc. But there are few 3D printers capable of printing hard textured foods. We aim to develop a food 3D printer capable of printing hard textured food with starch suspension [2]. In the printing process, the starch suspension is irradiated with a blue laser, and irradiated spot is gelatinized by heat generated by photothermal conversion. Experiments: The Food 3D printer is based on a commercially available 3D printer Geetech i3 pro B. The extruder unit of Geetech i3 pro B is replaced by a blue laser (wavelength 450 nm) module (alfawise 5500mm ). The maximum laser output is 5.5W. We select a visible blue laser that is common and safe. As the first experiment, We print a pyramid shape (shown in Fig.1) using starch suspension as a printing material. The pyramid has composed of five layers and the thickness of each layer is 0.5 mm. The bottom layer is a 10mm square and the higher layer has shorter edges. Fig.2 shows a schematic diagram of the modeling method. The starch suspension (50 % wt in water) is poured (added) into the container and leveled to make 0.5mm thickness. The liquid surface of the Suspension is irradiated with laser and gelatinized. 3D printing is performed by repeating those processes. Tartrazine (0.03% wt) is added for enhancing the absorption of the blue laser. The laser scan speed is set at 5.0 mm/s. Results: Fig.3 shows a Photo of the 3D printed pyramid structure. We successfully 3D printed pyramid structure with starch suspension. The 3D printed pyramid structure is larger than the original pyramid 3D data. We assume that the gelatinized starch absorbed water and swelled during and after the 3d printing process.

Application of Dual-Frequency Self-Injection Locked DFB Laser for Brillouin Optical Time Domain Analysis.

Self-injection locking to an external fiber cavity is an efficient technique enabling drastic linewidth narrowing of semiconductor lasers. Recently, we constructed a simple dual-frequency laser source that employs self-injection locking of a DFB laser in the external ring fiber cavity and Brillouin lasing in the same cavity. The laser performance characteristics are on the level of the laser modules commonly used with BOTDA. The use of a laser source operating two frequencies strongly locked through the Brillouin resonance simplifies the BOTDA system, avoiding the use of a broadband electrooptical modulator (EOM) and high-frequency electronics. Here, in a direct comparison with the commercial BOTDA, we explore the capacity of our low-cost solution for BOTDA sensing, demonstrating distributed measurements of the Brillouin frequency shift in a 10 km sensing fiber with a 1.5 m spatial resolution.

Free-electron qubits and maximum-contrast attosecond pulses via temporal Talbot revivals

We use laser light and a transmission electron microscope to modulate a free-electron beam into high-contrast electron pulses and free-electron qubits by using temporal Talbot revivals. At large enough propagation distances, the discrete energy sidebands from a laser modulation acquire special phases and group delays that optimize or cancel their time-domain interference, producing a revival or alternatively a pulse train at close to 100% modulation depth. A sequence of two laser interactions at an optimized propagation distance allows us to coherently control adjacent energy sidebands in amplitude and phase in the way of a qubit. The use of continuous-wave laser light provides these modulations at almost the full brightness of the beam source. Free electrons under large-distance laser control are therefore a promising tool for ultrafast material characterizations or investigations of free-electron quantum mechanics.

Effect of energy on Ti plate fabrication by vacuum selective laser melting for uniformity of grain size

Grain size homogenization by controlling heat input using modulated pulses in additive manufacturing was verified. A Ti plate was fabricated with a modulated pulsed laser by vacuum selective laser melting. 20-layer fabrication was performed with modulated pulsed laser and continuous wave laser. As a result of cross-sectional observation, it was found that the variation of the grain size was smaller when the modulated pulsed laser was used. These experimental results suggest that it is possible to control the grain size by using a modulated pulsed laser.

Modulation Performance Enhancement of Directly Modulated Injection-Locked Semiconductor Lasers Using an Equivalent Electrical Circuit

We propose an equivalent electrical circuit model to evaluate the direct modulation performance of optically injection-locked (OIL) semiconductor lasers. We modeled the equivalent circuit of the OIL laser based on alternating complex envelope representations, simulated it using the Simulation Program with Integrated Circuit Emphasis (SPICE), and analyzed the frequency response of the OIL laser. Although the frequency response of the OIL laser is better than that of a free-running laser, its 3-dB modulation performance is degraded by the relaxation oscillation that occurs during direct modulation of the semiconductor laser. To overcome this limitation and maintain the maximum modulation performance within the entire locking range, we also designed an electrical filter to preprocess the electrical modulation signal and compensate for the non-flat modulation output of the OIL laser. The damping ratio of the directly modulated OIL laser increased by 0.101 (280%) and its settling time decreased by >0.037 (44%) when the electrical compensation circuit was added, exhibiting a flat 3-dB modulation bandwidth of 28.79 GHz.

Reservoir Computing Based on Mutually Injected Phase Modulated Semiconductor Lasers as a Monolithic Integrated Hardware Accelerator

In this paper we propose and numerically study a neuromorphic computing scheme that applies delay-based reservoir computing in a laser system consisting of two mutually coupled phase modulated lasers. The scheme can be monolithic integrated in a straightforward manner and alleviates the need for external optical injection, as the data can be directly applied on the on-chip phase modulator placed between the two lasers. The scheme also offers the benefit of increasing the nodes compared to a reservoir computing system using either one laser under feedback or laser under feedback and optical injection. Numerical simulations assess the performance of the integrated reservoir computing system in dispersion compensation tasks in short-reach optical communication systems. We numerically demonstrate that the proposed platform can recover severely distorted 25 Gbaud PAM-4 signals for transmission distances exceeding 50km and outperform other competing delay-based reservoir computing systems relying on optical feedback. The proposed scheme, thanks to its compactness and simplicity, can play the role of a monolithic integrated hardware accelerator in a wide range of application requiring high speed real time processing.

Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography.

We present a complete characterization of the width and depth of a very narrow fatigue crack developed in an Al-alloy dog bone plate using laser-spot lock-in thermography. Unlike visible micrographs, which show many surface scratches, the thermographic image clearly identifies the presence of a single crack about 1.5 mm long. Once detected, we focus a modulated laser beam close to the crack and we record the temperature amplitude. By fitting the numerical model to the temperature profile across the crack, we obtain both the width and depth simultaneously, at the location of the laser spot. Repeating the process for different positions of the laser spot along the crack length, we obtain the distribution of the crack width and depth. We show that the crack has an almost constant depth (0.7 mm) and width (1.5 µm) along 0.7 mm and features a fast reduction in both quantities until the crack vanishes. The results prove the ability of laser-spot lock-in thermography to fully characterize quantitatively narrow cracks, even below 1 µm.

Generation of a dual optical frequency comb by large signal modulation of a semiconductor laser.

In this paper, we present and theoretically investigate a simple and power efficient scheme for dual optical frequency comb generation residing on a single directly modulated semiconductor laser driven by two superimposed current waveforms. Our detailed model estimates dual combs comprising teeth pairs within 20 dB margin spanning up to 116 GHz with power per teeth pair up to 8.8 µW. In addition, we report dual combs with 40 GHz span comprising ultraflat teeth pairs, with flatness of the order of 1 dB.

Synchronous coherent population trapping and its magnetic spectral response in rubidium vapor

This paper reports experimental investigations of the spectral response of synchronous coherent population trapping (CPT) for magnetometry applications. Synchronous CPT is demonstrated using resonant two-photon excitation with a modulated bichromatic laser field in the $^{87}\mathrm{Rb} {D}_{1}$ manifold. Spectra containing multiple magnetic resonances are produced due to two-photon excitations created by various frequency components of the modulated beam. Theoretical modeling based on the atomic density-matrix equations is used to simulate the spectral response of synchronous CPT. Our results show potential advantages of synchronous CPT over synchronous optical pumping for magnetic field measurement. Magnetic resonance signals produced by synchronous CPT can be used in eliminating the dead-zone problem and also in determining the magnetic field direction.

High Sensitivity Frequency Modulation Spectroscopy and the Path to Single Molecule Detection.

Advances in optical spectroscopy rely on improved detection techniques that reduce noise to fundamental detection limits. When properly applied, frequency modulation laser spectroscopy (FM spectroscopy or FMS) approaches the quantum limit for detection. Having demonstrated that double modulation FMS could achieve such sensitivity in absorption spectroscopy, researchers raced to the goal of measuring the absorption of an individual molecule. In 1989, Moerner and Kador performed the first optical detection and probing of single dopant molecules in solids, spawning the field of single-molecule spectroscopy. In this Perspective, we trace the development of FMS from its initial demonstration in 1979 to Moerner's remarkable achievement with an emphasis on the double modulation methods needed to achieve high sensitivity measurement of very small absorptions.

Ultralow longitudinal emittance storage rings

Low longitudinal emittance means small energy spread and short bunch length, which makes high-power short-wavelength coherent radiation possible. In a storage ring, due to quantum excitation, the equilibrium longitudinal emittance is mainly the overall contribution of all bend-related elements, such as bends, undulators and laser modulators. By introducing longitudinal Twiss function and analyzing the 6D one-turn map in 3D Twiss form, the longitudinal emittance contribution of all these elements is theoretically studied in this paper, and a general method for minimizing the storage ring equilibrium longitudinal emittance is proposed. An integrated optimization of longitudinal beta function shows, the longitudinal emittance scales as the third power of bending angle, and can be as low as subpicometer with a beam energy of 400 MeV in an ultimate state.

Graphene-coupled silica microtoroid for optical polarization controlling and electro-optic modulation

Whispering gallery (WG) microcavities have been applied for a variety of optoelectronic devices due to their extraordinary characteristics of high quality factor ( Q ) and small mode volume, crucial to accurately tune the quality factor for realizing the high-speed optical modulation and short pulse laser. In this paper, we propose and theoretically analyze a hybrid, graphene-coupled silica microtoroid device and realize optical polarization control and electro-optic modulation due to the polarization-dependent absorption of graphene on the different cavity WG modes. By changing the gap distance between graphene and the microtoroid, the influence of graphene absorption on the different polarization modes is diverse due to the different electric field distributions of modes in the microtoroid, therefore demonstrating the different resonant wavelength shifts and quality factor variations. The transmission depth variation of the second-order transverse electric mode upon changing the gap distance between graphene and microtoroid is 4.5 dB more than that of the second-order transverse magnetic mode, verifying that the polarization control is because of the polarization-dependent absorption of graphene. Furthermore, by applying the voltage on the graphene flakes, electro-optic modulation with a high contrast of 21.7 dB is demonstrated based on this hybrid graphene-coupled silica microtoroid.

Visible Light Communication System Technology Review: Devices, Architectures, and Applications

Visible light communication (VLC) is an advanced, highly developed optical wireless communication (OWC) technology that can simultaneously provide lighting and high-speed wireless data transmission. A VLC system has several key advantages: ultra-high data rate, secure communication channels, and a lack of interference from electromagnetic (EM) waves, which enable a wide range of applications. Light-emitting diodes (LEDs) have been considered the optimal choice for VLC systems since they can provide excellent illumination performance. However, the quantum confinement Stark effect (QCSE), crystal orientation, carrier lifetime, and recombination factor will influence the modulation bandwidth, and the transmission performance is severely limited. To solve the insufficient modulation bandwidth, micro-LEDs (μ-LEDs) and laser diodes (LDs) are considered as new ideal light sources. Additionally, the development of modulation technology has dramatically increased the transmission capacity of the system. The performance of the VLC system is briefly discussed in this review article, as well as some of its prospective applications in the realms of the industrial Internet of Things (IoT), vehicle communications, and underwater wireless network applications.

Compact full‐color laser beam scanning image projector based on a waveguide‐type RGB combiner

AbstractA packaged red‐green‐blue (RGB) laser module based on a waveguide‐type combiner is demonstrated. The module has characteristic features such as (a) a compact size and lightweight, (b) almost perfectly aligned RGB laser beams owing to a single waveguide output, and (c) a configuration with only a few mechanical elements. The typical package size is 10 × 5 × 5 mm for an outside focusing lens type and 11 × 4.8 × 3 mm for an inside focusing lens type. Light intensity monitors and a temperature monitor are also equipped for the inside focusing lens type.Furthermore, a compact RGB laser beam scanning module is demonstrated. Clear full‐color high‐definition video images are obtained. Thus, these modules based on waveguide‐type combiners can provide compact imaging projectors with clear images. Compact Lidar scanners and laser sources for various sensors are also candidate applications.

High-precision and robust localization system for mobile robots in complex and large-scale indoor scenes

High-precision and robust localization is the key issue for long-term and autonomous navigation of mobile robots in industrial scenes. In this article, we propose a high-precision and robust localization system based on laser and artificial landmarks. The proposed localization system is mainly composed of three modules, namely scoring mechanism-based global localization module, laser and artificial landmark-based localization module, and relocalization trigger module. Global localization module processes the global map to obtain the map pyramid, thus improve the global localization speed and accuracy when robots are powered on or kidnapped. Laser and artificial landmark-based localization module is employed to achieve robust localization in highly dynamic scenes and high-precision localization in target areas. The relocalization trigger module is used to monitor the current localization quality in real time by matching the current laser scan with the global map and feeds it back to the global localization module to improve the robustness of the system. Experimental results show that our method can achieve robust robot localization and real-time detection of the current localization quality in indoor scenes and industrial environment. In the target area, the position error is less than 0.004 m and the angle error is less than 0.01 rad.

Chirping removes recoil effect on fluorescence signal of optical pumping by synchronous frequency modulation

Recoil effect is one of the limiting factors of signal amplitude in many spectroscopic applications due to creating light shift or AC Stark effect. Doppler shift of the Recoil velocity of the pumped atoms reduces their absorption efficiency. Synchronous Frequency Modulation or chirping of the pump laser enhances optical pumping and amplitude of the fluorescence signal. Results of this paper demonstrate significant enhancement of the fluorescence signal and the symmetry of the signal.

Influence of Laser Modulation Frequency on the Performance of Terahertz Photoconductive Switches on Semi-Insulating GaAs Exhibiting Negative Differential Conductance

In typical terahertz time-domain spectroscopy systems, the use of the lock-in technique is necessary because of the low current induced at the receiver so that the laser pump beam must be modulated (chopped) at a frequency much lower than the laser repetition rate. This work shows that, in the case of semi-insulating GaAs (SI-GaAs) antennas, this modulation has an important effect on the antenna current and consequently, on the radiated electromagnetic pulse. There exists a threshold bias (whose value depends on the chopping frequency) where an abrupt increase in the current and consequently, in the terahertz emission takes place. The calculated energy of the pulse below and above the threshold shows that the energy doubles. The exact bias voltage at which this occurs changes with the laser modulation frequency when this is below 350 Hz, but at higher frequencies, the threshold remains almost constant. The experiments show that the responsibility for this behavior is the S-shape negative differential conductance exhibited by SI-GaAs originated by a slow field-enhanced charge trapping mechanism, which is also an important source of noise at the receiver of the system.

Machine learning-based data processing technique for time-domain thermoreflectance (TDTR) measurements

Machine learning (ML) has emerged as an increasingly important research tool and has shown great potential for efficient and high-throughput experimental data processing. Meanwhile, ultrafast laser-based time-domain thermoreflectance (TDTR) has been developed into a powerful thermal characterization technique and has been widely applied to measure thermal properties of both bulk and thin-film materials. In this work, artificial neural network-based ML models have been trained for data processing in TDTR experiments. One generally applicable ML model could be trained to process the experimental data of different samples measured using different modulation frequencies and laser spot sizes. Our results suggest that ML is not only fast and efficient in data processing but also accurate and powerful, capable of detecting minute features in the experimental signals and thus enabling extraction of multiple (three or more) parameters simultaneously from the experimental data. The ML model also enables high-speed estimation of the uncertainties of multiple parameters using the Monte Carlo method.

Advanced Laser Technology for Quantum Communications (Tutorial Review)

AbstractQuantum communications is the art of exchanging and manipulating information beyond the capabilities of the conventional technologies using the laws of quantum mechanics. With applications ranging from quantum computing to cryptographic systems with information‐theoretic security, there is strong incentive to introduce quantum communications into many areas of the society. However, an important challenge is to develop viable technologies meeting the stringent requirements of low noise and high coherence for quantum state encoding, of high bit rate and low power for the integration with classical communication networks, and of scalable and low‐cost production for a practical wide‐deployment. This tutorial presents recent advances in laser modulation technologies that have enabled the development of efficient and versatile light sources for quantum communications, with a particular focus on quantum key distribution (QKD). Such approaches have been successfully used to demonstrate several QKD protocols with state‐of‐the‐art performance. The applications and experimental results are reviewed and interpreted in the light of a complete theoretical background, allowing the reader to model and simulate such sources.

Femtosecond laser direct writing of Nd:YLF cladding waveguides for efficient 1047-nm laser emission

In this work, to the best of our knowledge, the first demonstration of 1047-nm Q-switched mode-locked Nd:YLF cladding waveguide lasers fabricated by femtosecond laser direct writing (FsLDW) is reported. Modulated by Gr-ReS2-Gr heterostructure film, the fabricated waveguide laser delivers laser pulses with a pulse duration of as short as 31 ps at a fundamental repetition rate of up to 9.55 GHz. The maximum output power under the pulsed regime is determined to be 300 mW with a slope efficiency of 31.77%. The result in this work indicates promising applications of Gr-ReS2-Gr heterostructure film for modulation of ultrafast pulsed laser and compact Nd:YLF waveguide lasers for integrated photonics.