Modulated Laser Diode Research Articles

679/339.5 nm radiation generation of pr: YLF laser pumped by fiber coupled blue laser diode module

679/339.5 nm radiation generation of pr: YLF laser pumped by fiber coupled blue laser diode module

Effective bandwidth of optical pre-emphasis by photon-photon resonance in hybrid modulation laser diode

Effective bandwidth of optical pre-emphasis by photon-photon resonance in hybrid modulation laser diode

High beam quality, high brightness dense spectral beam combining of 650 nm laser diode module

Dense spectral beam combining (DSBC) of a laser diode module at a wavelength of 650 nm was realized for what we believe to be the first time. In this paper, the optimal spectral locking interval range for the 650 nm wavelength band was obtained by stimulation. A DSBC device containing 19 single emitters was designed and built according to the optimal spectral interval. The output power of the combining beam reached 17.74 W, and the stable spectral width was 4.75 nm. The beam quality factors (M2) in the fast-axis and slow-axis directions were basically the same as that of the single emitter, and even slightly optimized in the slow-axis direction. The beam brightness of the DSBC beam was about 123.395 MW·cm−2·sr−1, which was about fourteen times higher than that of the single emitter output.

Enhanced vibration measurement through frequency modulated laser diode self-mixing interferometry

Enhanced vibration measurement through frequency modulated laser diode self-mixing interferometry

High-peak-power nanosecond pulse laser at 915 nm based on all-fiber structure

We demonstrate an all-fiber high-peak-power nanosecond pulse laser operating at 915 nm. The nanosecond pulse laser source is consisting of a 915 nm modulated laser diode and 4-stage Nd-doped fiber amplifiers. A maximum output power of 2.01 W is achieved with a peak power of 2.2 kW. The peak-to-peak fluctuation is less than ±0.2 % and the RMS is 0.084 %. Additionally, the beam quality at output power of 2.01 W is measured to be Mx2 = 1.09, My2 = 1.08, indicative of excellent beam characteristics in the output signal. To the best of our knowledge, it is the first report about high-peak-power Nd-doped fiber laser at 915 nm based on all-fiber structure. This work provides a good candidate for the Automotive Lidar with high imaging resolution and detection accuracy.

Review on the chirping characteristics of directly modulated laser diodes under high transmission speeds in optical fiber networks

Review on the chirping characteristics of directly modulated laser diodes under high transmission speeds in optical fiber networks

Review on the chirping characteristics of directly modulated laser diodes under high transmission speeds in optical fiber networks

Review on the chirping characteristics of directly modulated laser diodes under high transmission speeds in optical fiber networks

Study on laser spot size measurement by scanning-slit method based on back-injection interferometry

Spot size is an important parameter of the laser, which not only represents the resolution of laser, but is also involved in the calculation of other parameters. Nowadays, CCD imaging systems, scanning imaging systems, and other sensors are used to measure the laser spot size. But they are all lacking flexibility when measuring the spot size in different locations, not to mention their high cost. In this study, a new spot size measurement device based on laser back-injection interferometry was presented. The photodiode integrated with the laser diode was used to collect the feedback laser, then the laser spot size was calculated by the feedback current. A commercial CCD imaging system was used to provide the laser spot size as a reference. Results show that our spot size measurement device could measure the spot size (Full Width Half Maximum) of 5 laser diode modules both in the x (Gaussian-like profile) and y (top-hat-like profile) direction through scanning-slit. Though there are variations between the scanning-slit results and spot sizes from the CCD imaging system due to the diffuse and specular reflection, the accuracy of the spot size measurement device ranges from 96.07 % to 99.46 %, which proves the reliability of our device. It is believed that our device could provide an alternate method for laser spot size measurement, which is cost-effective, easy to operate, and accurate.

Design and Implementation of a Power Semiconductor-Based Switching Mode Laser Diode Driver.

Fiber lasers are commonly used in many industrial applications, such as cutting, welding, marking, and additive manufacturing. In a fiber laser system, the driver of a pumping source using a laser diode (LD) module and its dynamic control capability directly affect the performance of the fiber laser system. The commercial design of pumping source drivers for high-power fiber lasers is mainly based on a linear-type DC power supply, which has two major drawbacks, i.e., lower efficiency and bulk. In this regard, this paper proposes for the first time a new design approach with a programmable switching mode laser diode driver using a power semiconductor device (PSD)-based full-bridge phase-shifted (FB-PS) DC-DC converter for driving a 200 W optical power laser diode module. In this paper, the characteristics of a laser diode module and the system configuration of the proposed laser diode driver are first introduced. Then, a current control scheme using the concept of phase angle shifting to achieve a fast dynamic current tracking feature is explained. The proposed current control technique with a fully digital control scheme is then addressed. Next, dynamic mathematical models of the laser diode driver system and controllers are derived, and the quantitative design detail of the controller is presented. To confirm the correctness of the proposed control scheme, a simulation study on a typical control case is performed in PSIM 9.1 software environment. To verify the effectiveness of the proposed LD driver, a digital signal processor is then used as the control core to construct a hardware prototype implementation for performing experimental tests. Results obtained from simulation and hardware tests show highly satisfactory driving performances in the laser diode's output current command tracking control.

Efficacy of Diode Laser 940 nm in Dentine Hypersensitivity Reduction: A Clinical Trial

Background: Dentin hypersensitivity is a discomfort arising from unprotected dentin as a response to heat, cold, touch, or pressure stimuli. Various treatment modalities, including laser light, have been used to manage such a problem. This study aims to evaluate the efficacy of diode laser 940 nm, with different powers in managing dentin hypersensitivity. Materials and Methods: A cross-sectional study was conducted from 1 January–5 April 2023 on a cohort of patients presented to the dental department clinics of our college with dentine hyper-sensitivity. A 10-second continuous mode diode laser light 940 nm at two different powers was used to evaluate its desensitizing effect for managing dentin hypersensitivity for six patients with a total number of teeth treated, 38 teeth. A jet of air/water was applied for a specific period and a certain distance from the tooth surface. Scores were documented for evaluating responses using the VAS scale. Results: A statistically significant decrease in dentine hypersensitivity was found immediately after one treatment session and after a 14-day follow-up period. Conclusions: It was established that using a diode laser (940 nm) successfully resolved instant and longstanding dentin hypersensitivity pain.

Implementation and performance analysis of combined SOD and PWM control in diode based laser beam machining process on leather specimen

Due to a variety of benefits over traditional cutting techniques, the usage of laser technology has risen substantially in recent times. In the present study, an effort was made to investigate the effects of different control approaches in laser power diode based cutting process on leather specimens. Since kerf Width (KW) and material removal Rate (MRR) can impact the process efficiency, these outcomes were used in this study. The leather specimens were cut using 20 W laser diode with various approaches such as open loop standoff distance (SOD) control, closed loop SOD control, open loop pulse width modulation (PWM) control, closed loop PWM control and combined closed loop SOD and PWM control. The synthesized diode LBM process can effectively remove the material from leather specimen under various control approaches such SOD control, PWM control and combined control methodology. The high power with less spot size under pulsed mode can produce higher power density. Due to the ability of controlling beam shape and size under 20 W laser diode module, the combined control could produce lower kerfwidth and higher MRR. Since the combined control of SOD and PWM can also control peak pulse energy and power density at the same time, it can produce better performance measures as compared with other mode of control. Owing to the ability of controlling peak pulse energy and pulse width, the combined control of SOD and PWM produces larger MRR.

Influence of scattering effects on the interaction between longitudinal modes in laser diodes

Influence of scattering effects on the interaction between longitudinal modes in laser diodes

All-solid-state CW Pr3+:YLF green laser at 522 nm end-pumped by a high-power fiber-coupled 444 nm blue LD module

Continuous wave (CW) green lasers have a lot of important applications in many fields, including holography, interferometry, atom cooling and trapping, and quantum optics, and they are usually achieved by frequency-doubling 1 µm lasers based on the Nd3+ gain media. In this paper, we present an all-solid-state CW green laser with an output wavelength of 522 nm, which was directly attained by employing a Pr3+:YLF crystal pumped with a high-power fiber-coupled blue laser diode (LD) module as the gain medium. Due to the negative thermal lens effect of the Pr3+:YLF crystal, the designed laser resonator had to be lengthened with the increase in the incident pump power. As a result, when a 0.5% doped Pr3+:YLF crystal was employed as the gain medium and the incident pump power was 12 W, the length of the resonator was optimized to 311.3 mm and the maximum output power of 522 nm green laser was up to 886 mW. The obtained conversion efficiency and beam quality M2 were 11.25% and 1.15, respectively. The long-term power stability within 4.5 h was better than ±1.5% at an output power of 700 mW. The obtained watt-level green laser can also be used to generate high power CW deep UV laser for laser processing of silicon and organic materials, inspection, etc.

Potential application of a green fiber laser in laser display systems.

This study explores the application of optical fiber lasers in display systems by integrating a P r3+-doped green all-fiber laser into a laser projection display system. As a control group to compare the results, a 520nm semiconductor green laser diode module was integrated, similar to the experimental group. The color gamut and speckle performances were studied and compared. The results showed that the experimental group performed slightly better in the color gamut volume. The speckle contrast decreased rapidly in the experimental group when power increased. To our knowledge, this is the first study to apply a fiber laser to a laser display system. The results shed light on developing laser display systems with fewer or no speckle reduction elements.

An injection-locking diode laser at 671 nm with a wide tuning range up to 6 GHz

We present a compact injection-locking diode laser module to generate 671 nm laser light with a high output power up to 150 mW. The module adopts a master–slave injection-locking scheme, and the injection-locking state is monitored using the transmission spectrum from a Fabry–Pérot interferometer. Beat frequency spectrum measurement shows that the injection-locked slave laser has no other frequency components within the 150-MHz detection bandwidth. It is found that without additional electronic feedback, the slave laser can follow the master laser over a wide range of 6 GHz. All the elements of the module are commercially available, which favors fast construction of a complete 671-nm laser system for the preparation of cold 6Li atoms with only one research-grade diode laser as the seeding source.

28.1: Invited Paper: A Review of Optical source by using μLED and Single mode Laser Diodes for HMD, AR/VR Glasses

Expansion of devices to access the virtual world is expected due to much attention to Metaverse in recent years. In particular, head mount display (HMD), smart glasses and AR glasses have been attracting attention as next‐generation mobile devices that will replace smart phones. Laser diodes and μLEDs are developed in various research institutes and companies as light sources for those devices. In this paper, we describe the development status of the laser diodes and the μLEDs, the technical problems of optimal adaptation to smart glasses, and introduce one of the solutions when using the laser diodes.

A tabletop experiment for speed of light measurement using a Red Pitaya STEMlab board

The speed of light is an important fundamental constant in physics, and so determining its value is a common undergraduate laboratory experiment. Methods to measure the light speed can help students practice their experimental skills and become familiar with the concepts of modern precision measurement techniques. In this paper, we demonstrate that a tabletop optical setup, comprised of an affordable Red Pitaya STEMlab board and a low-cost laser diode module, can be used to accurately determine the speed of light by measuring the frequency response of the phase shift between intensity-modulated light beams reflected by two end mirrors separated by 50 cm. By using the STEMlab built-in Bode analyzer to automatically scan the modulation frequency over the range from 10 to 40 MHz, the frequency response of phase is measured and recorded. These phase shift data are then used to calculate the speed of light with an uncertainty of less than 0.5%. With the help of the Red Pitaya board, the number of required electronic instruments for our setup is reduced. All of the required components are commercially available, and no electronic construction work is necessary so that teachers and students can implement the experiment in a plug-and-play manner.

Novel laser hair removal in all skin types.

Laser has been long accepted as a solution for excess or unwanted hair growth yet traditional lasers are not always ideal for safe and effective outcome for all skin types and hair characteristics. A diode laser module combining three wavelengths (755, 810, and 1064 nm) in a single pulse was developed to provide a fast and long-term solution for subjects with various profiles. To evaluate the safety and efficacy of a Triple wavelength diode laser module for hair removal treatment in all skin types (Fitzpatrick I-VI). This was a prospective, dual centered, single-arm study. Subjects were treated with a novel diode laser module. Thirty-six subjects were enrolled, sixteen with Fitzpatrick skin types I-IV (46%) and twenty with Fitzpatrick skin types V-VI (54%). Treatment areas were axilla and bikini lines. Subjects underwent 4 treatment sessions at 6 weeks ± 5 days intervals and attended a follow-up visit 3months after the last treatment session. 2D digital photographs were taken at baseline and at the follow-up visit, and a hair count was conducted by three blinded evaluators. A significant reduction in hair count between baseline and the 3-month follow-up visit was observed in both axilla and bikini lines for all skin types. The mean hair reduction was 41.5± 19.4% and 48.1± 20.9% in the axilla and bikini line, respectively. A significant hair reduction was also observed within skin type groups; mean hair reduction 45.5± 16.9% and 40.3± 17.2% in skin types I-IV and V-VI, respectively, indicating similar efficacy for both light and dark skin types. No serious adverse events were reported. This study demonstrates that the Soprano Titanium laser platform is safe and effective for hair removal treatment in all skin types.

Novel Wide-Range Frequency Offset Estimation and Compensation for Burst-mode CPFSK Upstream Signaling in TDM-Based Digital Coherent PON

The burst-mode continuous phase frequency shift-keying (CPFSK) transmitter that combines a directly modulated laser diode, an electro absorption modulator and a semiconductor optical amplifier is attractive as a cost-effective transmitter for phase modulation formats for digital signal processing (DSP)-based coherent passive optical network (PON) upstream signaling. However, since highly accurate wavelength controllers for the transmitters in optical network units (ONUs) create excessive cost burdens, large carrier frequency offsets (CFOs) must be expected. Thus, a CFO compensation method with wide compensation range is required. This paper proposes a novel CFO estimation and compensation method for burst-mode CPFSK signals in upstream PON signaling. The proposed method is based on a simple blind algorithm and does not require any training symbols. We demonstrate wide CFO compensation range, from −12 to 14 GHz, with high receiver sensitivity, less than −42.5 dBm for 10 Gbit/s binary CPFSK signals. This range far exceeds that of the conventional CFO compensation method using a blind algorithm. Moreover, the proposed method can enhance the convergence of finite impulse response (FIR) filters. The feasibility of the proposed CFO compensation technique is successfully demonstrated for burst-mode CPFSK signals.

Laser projection system for polymer transverse strain measurements in tensile testing

A self-built laser projection system for optical transverse strain measurements in tensile testing is presented. The setup based on laser diode modules, charge-coupled device array detectors, and standard optomechanical components is proposed to be a low-cost system for testing polymer samples. The optical setup is mobile and can easily be mounted on a tensile test machine. Circular cross-sectional changes in polymer diameter were detected with 10-μm resolution and stress-strain curves obtained by a tensile test machine. The article describes signal processing using the open-source programming language R, and the transverse deformation of the polymer sample is evaluated in two perpendicular planes. The results obtained by the optical system may be used to accurately describe the models of energy-based mechanical properties of polymers for complex load conditions.