Laser Chip Research Articles

A general White–Box strategy for designing thermoelectric cooling system

AbstractThermoelectric cooling (TEC) is critically important in thermal management of laser modules or chips and potentially for personalized thermoregulation. The formulae for efficiency in standard textbooks can only describe the performance of a TEC module with ideal thermal conditions, that is, fixed terminal temperatures, but are unable to deal with a real TEC system where heat transfer at its interfaces with the heat source and sink are finite and with thermal resistances. Here, we define the TEC system‐level performance indices, that is, the maximum cooling power, temperature difference, and coefficient of performance, by introducing a set of explicit formulae. The external heat transfer conditions are taken into account as dimensionless thermal resistance parameters. With these formulae, the TEC system performances are evaluated elegantly with errors well within ±5% over broad operating conditions. We further optimize the cooling power and the coefficient of performance in practical scenarios and establish a general White–Box design procedure for TEC systems, which enables a transparent design process and straightforward analysis of performance bottlenecks. A set of cooling experiments are performed to validate the analytical model and to illustrate the dependence of system design on realistic thermal conditions. By choosing the suitable TEC module parameter under given external heat transfer conditions, the cooling power can be improved by more than 100%. This work sheds some light on the integral design of TEC systems for broad applications to take full advantage of the advanced thermoelectric materials in the cooling field.image

Research on thermal characteristics of tapered laser chip

The tapered laser with high power and high beam quality is one of the research hotspots in the field of laser. The thermal effect of the tapered laser will reduce the thermal saturation current and produce thermal deformation, which will lead to the decrease of output power. Therefore, the thermal effect of the tapered laser is the main cause of failure. In order to investigate the thermal characteristics of the tapered laser chip, this paper simulates the tapered laser by using COMSOL Multiphysics. The changes of thermal stress under different ridge widths and tapered angles are simulated, and the thermal stress distributions in the ridge and tapered regions are obtained. In addition, a porous heat sink is designed. The simulation results of ordinary radiator and porous radiator are compared, which can be seen that porous heat sink has better heat dissipation capacity than ordinary heat sink. Through the simulation of tapered laser, this paper does research on the thermal characteristics of tapered laser, which can be a useful reference to improving the performance of tapered laser.

Intelligent Micron Optical Character Recognition of DFB Chip Using Deep Convolutional Neural Network

The microcharacter recognition on the distributed feedback (DFB) laser chip is critically essential but a challenging task for the quality control in the incoming chip inspection and optical device manufacturing lines. Hence, this article proposes, designs, and implements a micro-optical character recognition system based on the microscopic imaging system and deep convolutional neural network to facilitate the microcharacter recognition of DFB chips. The proposed micron optical character recognition (MOCR) contains four components, namely, a microscopic imaging system-based visual-based measurement (VBM), character detection, orientation correction, and character recognition. In particular, data augmentation methods considering limited datasets and some chip character features are studied so as to accommodate complex industrial environments and tiny DFB chips. Experiments from the DFB image dataset of a real optical device manufacturing line showed that it reached the accuracy of 98.8%, which took a high speed of over 12.8 fps coping with DFB chip images, and saved 72% of the labor in the inspection position compared to traditional methods. To the best of our knowledge, there are no existing reports focused on MOCR on DFB chips. So, the first realization and successful application of MOCR played a key role in the intelligent manufacturing and quality traceability of DFB chips and devices in the field of optical communications, which is also of great significance for further accelerating the development of the industrial Internet.

Optimizing the efficiency of a laser diode and single-mode fiber coupling using multi-aspherical lenses

The continuous increase in the network access rate requires a higher integration of optoelectronic devices for optical communication. Optical devices require a longer optical path and an enhanced power budget. Therefore, this study designs a three-lens coupled optical path for integrating multiple laser diodes and photodiodes with a high coupling efficiency. The coupling efficiency between the laser diode, aspherical lenses, and single-mode fibre (SMF) is analysed using the physical ray-tracing method. In the simulation results, the maximum coupling efficiency of the system reaches 72.8% by optimising the parameters of the optical path. In the experimental results, the maximum coupling efficiency is 68.01%, indicating the effectiveness of the theoretical approach and proposed design scheme. Furthermore, the simulated results indicate that a higher coupling efficiency (79.41%) would be achieved by increasing the core diameter of the SMF under the same conditions. Additionally, using the same divergence angle of the laser diode (79.04%) or decreasing the focal length of the lens (77.24%) can achieve a higher coupling efficiency. These results provide an important reference point for the design and manufacture of laser chips and SMF.

COMPARATIVE EVALUATION OF EFFICACY OF SCALING AND ROOT PLANING WITH AND WITHOUT CHLORHEXIDINE CHIP AND DIODE LASER IN CHRONIC PERIODONTITIS PATIENTS

Introduction: The motive of the present study is to comparatively measure the competence and effectiveness of diode laser and chlorhexidine chip as adjuncts to the scaling and root planing procedure, in patients with chronic periodontitis.
 Aim: To evaluate the efficacy of diode laser and chlorhexidine chip before and after scaling and root planing in the management of chronic periodontitis. The objective is to compare the efficacy of chlorhexidine chip and diode laser before and after scaling and root planning on clinical parameters.
 Study and design: Randomized clinical trial with split mouth design done in the Department of Periodontics and Implantology.
 Materials and methods: Twenty chronic periodontitis patients having a probing pocket depth of 5mm-7mm on at least one interproximal site in each quadrant of the mouth were selected in the study. After initial treatment, four sites in each patient were randomly subjected to scaling and root planing (control), chlorhexidine chip application (CHX chip group), diode laser (810 nm) decontamination (Diode laser group) or combination of both (Diode laser and chip group). All subjects received a clinical periodontal examination by single examiner who recorded all the variables by manual procedure. Clinical parameters namely Plaque index (PI), Gingival Index (GI), probing pocket depth (PPD) and clinical attachment level (CAL) were assessed at baseline, one month and three months. Results were statistically analysed using one-way ANOVA followed by Post Hoc Analysis.
 Results: The differences in PPD reduction and CAL gain between control group and CHX chip and combination groups were statistically significant (p<0.05) at three months, whereas, the diode laser group did not show any significant difference from the control group.
 Conclusion: Within the limitations in the present study, the following conclusions were derived, i.e., chlorhexidine local delivery alone or in combination with diode laser decontamination is effective in improving oral hygiene, reducing gingival inflammation, reducing probing pocket depth and improving clinical attachment levels when used as adjuncts to scaling and root planing in non-surgical periodontal therapy of patients with chronic periodontitis.
 Keywords: Diode laser decontamination, Local drug delivery, Scaling and root planing.

Multichannel Generations of Orbital Angular Momentum Modes with On‐Demand Characteristics on a Chip

AbstractThe orthogonality among optical beams with different orbital angular momentum (OAM) modes presents a new perspective as independent data‐carrying channels for multiplexing and demultiplexing. In particular, the theoretically infinite topological charge of OAM beam promises the unbounded capacity in communication systems. As a key part for the advancement of OAM technologies, OAM source has attracted considerable interest and experienced a rapid development. Nevertheless, conventional approaches to create OAM modes mainly rely on the use of bulky optical devices and external laser source, preventing their implementation into a miniaturized system. As a contrast, on‐chip generation of OAM beams with a built‐in source stands out with several advantages, including small footprint, compactness, portability, and high‐power efficiency. In this work, a versatile approach to directly produce OAM modes with on‐demand characteristics on a chip is demonstrated. Featuring the judicious combination of the emerging dielectric metasurface with the standard vertical cavity surface‐emitting laser (VCSEL) platform, the approach represents a feasible solution to the wide implementation of wafer‐level OAM emitters for optoelectronic integrations. Prototype laser chips for the generation of both individual OAM beam and OAM array with novel functionalites, such as controllable directionality and spatially varying topological charge and distribution, are systematically presented.

Study on bonding of single bar high power semiconductor lasers

Due to the mismatch between the thermal expansion coefficients of semiconductor laser chip and heat sink, giant thermal stresses will be generated after eutectic bonding. Immoderate thermal stress will cause the devices to produce the smile effect, making the coupling efficiency low. In this paper, we propose an approach to reduce thermal stress and improve the near-field linearity for semiconductor laser arrays. We optimize the eutectic bonding process by controlling the semiconductor laser chip and heat sink in different temperature fields through independent heat sources, to achieve the purpose of matching the shape variables earlier than welding. The heating temperature is determined by Suhir’s deformation formula (Suhir E. Stresses in Bi-metal thermostats. J Appl Mech. 1986;53(3):657–660; Suhir E. Stresses in adhesively bonded Bi-material assemblies used in electronic packaging. MRS Proc. 1986;72). Then, finite element Analysis (FEA) was used for simulation verification.

Focus on lasers, imaging, microscopy, and nanoscience

Focus on lasers, imaging, microscopy, and nanoscience

Integrated MLL chip-based PAM-4/DMT-16QAM photonic-wireless link in W-band for flexible applications.

To accommodate the demand of exponentially increasing global wireless traffic driven by the coming beyond 5G and 6G, wireless communication has stepped into the millimeter wave (MMW) band to exploit large available bandwidth. The future wireless application scenarios require wireless communication systems with high speed, low cost, a small footprint and simple configuration, and the integrated light source-based intensity modulation and direct detection (IM-DD) photonic-wireless system can better meet the demand than the traditional system based on bulky components. In this paper, we experimentally demonstrate a lens-free pulse-amplitude-modulation with four levels (PAM-4) and discrete multi-tone with 16-quadrature amplitude modulation (DMT-16QAM) MMW photonic-wireless transmission system in the W-band using an integrated mode-locked laser (MLL) chip and a mixer-based receiver, which could be applicable for flexible wireless applications. The integrated MLL as an on-chip single light source is used to generate W-band signals and simplify the transmitter. The signal-to-noise ratio of the generated wireless signal is improved by two coherent optical carriers both modulated with data and then beating in the photodiode. In addition, we investigate the IM-DD configuration by employing an envelope detector (ED) to receive the PAM-4 signal for further simplifying the system. The ED-based photonic-wireless system is more suitable for the applications with lower data rate and low cost. For higher data rate, the mixer-based PAM-4/DMT-16QAM systems with up to 31.75 Gbit/s net data rate are more favorable, although the cost is also higher.

Design of Single Anti-Reflection Film for High Power Semiconductor Laser Facet

The catastrophic optical damage (COD) threshold of high power semiconductor laser chip is very important in its application. In this paper, based on the transfer matrix calculation method, a coating model is established to explain the relationship between the design parameters and COD threshold. The influence of the refractive index of the film in the whole range between Air and GaAs medium is analyzed. The influence of the refractive index in the range of 1.1 ~ 3.3 on the reflectivity of the film and on the COD threshold are theoretically simulated. The simulation results show that in the design of actual coating parameters, not only the reasonable PC value, but also the requirement of reducing reflectivity and the trade-off between reflectivity and PC value should be considered. In addition, the possible refractive index parameters of the film, the reflectivity of the corresponding film and the corresponding PC value are reflected in the simulation diagram. This paper provides ideas for the improvement of COD threshold and the reliability of chip facet.

Study and optimization of die-bonding technology for semiconductor lasers based on differential-analysis

This study proposed the method of “differential analysis” based on the study and analysis of the die-bonding technology in semiconductor laser packaging by using the analysis of ray tracing and thermal characteristics to explore the influence of the differential (Δx, the position error between the laser chip and the Submount) on the optical efficiency and heat dissipation performance of the device. Under the influence of the "underhang" effect, the value of Δx was controlled within 12 μm, which can effectively stabilize the output power of the device. Under the influence of the "overhang" effect, the Δx will not have substantial impact on the heat dissipation characteristics of the device. The submount which has the new chamfered structure is designed using this structure, COS (chip on submount) prepared in the semiconductor laser die-bonding technology was shown to exhibit higher stability and reliability.

Threshold gain of coherently coupled aperiodic lattice Y lasers.

By incorporating a holographically designed aperiodic photonic lattice within one of the arms of a Y-coupled Fabry-Perot quantum cascade laser architecture, it has been demonstrated that the multiband mode control exerted by the photonic lattice on emission spectra can, owing to the mutual optical coupling between the arms, be transferred to the second unpatterned arm. However, the underlying theoretical mechanism on how the lattice influences the threshold gain spectral properties of the Y architecture has, until now, remained unstudied. Here, we use the transfer matrix formalism, originally developed for studying aperiodic lattice lasers, to investigate this. A detailed threshold gain spectral study revealed that although the effects of facet feedback of the Y-coupled laser chip are present, due to the enhanced photonic density-of-states at user-specified frequencies, the aperiodic lattice has remarkable control over the Y architecture laser spectra, under the mutual optical coupling between the arms. Finally, indicated by the fringe patterns akin to double-slit interference, of the measured far-field beam profiles, phase-locked terahertz emissions from the Y architecture are demonstrated.

On‐Chip Generation of Structured Light Based on Metasurface Optoelectronic Integration

AbstractMetasurfaces offer complete control of optical wavefront at the subwavelength scale, advancing a new class of artificial planar optics, including lenses, waveplates, and holograms, with unprecedented merits over conventional optical components. In particular, the ultrathin, flat, and compact characteristics of metasurfaces facilitate their integration with semiconductor devices for the development of miniaturized and multifunctional optoelectronic systems. In this work, generation of structured light is implemented at an ultracompact wafer‐level through the monolithic integration of metasurface with standard vertical cavity surface‐emitting lasers (VCSELs). This work opens new perspectives for the design of structured light systems with compactness, lightweight, and scalability. Ultracompact beam structured laser chips with versatile functionalities are experimentally demonstrated, including multichannel beams array generation, on‐chip large‐angle beam steering up to 60°, and wafer‐level holographic beam shaping with a wide field of view (about 124°). The results will promote the development of compact light structuring systems with great potential in 3D imaging, displays, robotic vision, human–computer interaction, and augmented/virtual reality.

High-power SOA-integrated EADFB laser for long-reach passive optical network systems

A high-power optical transmitter module based on an SOA-assisted extended-reach EADFB laser (AXEL) chip was developed at a wavelength of 1.49 µm to improve the loss budget of current passive optical access networks. The fiber-coupled output power of the modulated signal is 10 dBm owing to the post-amplification effect of the integrated SOA with an extinction ratio of 10 dB. Fiber transmission was demonstrated at data rates of 1.25 and 2.5 Gbit/s, assuming GE-PON and G-PON downstream signals, respectively. Error-free transmission over 100-km fiber was achieved with loss budgets of 46 and 43 dB at 1.25 and 2.5 Gbit/s, respectively.

Compact Hybrid-Integrated 4 × 80-Gbps TROSA Module Using Optical Butt-Coupling of DML/SI-PD and Silica AWG Chips

We have developed a compact 4 × 80-Gbps transmitter-receiver optical subassembly (TROSA) module using a chip-to-chip optical butt-coupling method. For a Tx submodule, four directly modulated laser (DML) chips precisely bonded on a silicon DML-carrier are simultaneously butt-coupled to a vertically polished silica-based arrayed waveguide grating (AWG) chip, revealing good optical characteristics insensitive to external optical feedback. A Rx submodule is realized by passive alignment between a 45°-polished AWG and four surface-illuminated (SI)-PD chips, and subsequently integrated with the Tx submodule into a single package case to form the compact TROSA module whose size is only 25 mm × 15 mm × 6.4 mm and compliant to fit into the QSFP-DD/OSFP transceiver. The fabricated TROSA module shows clear Tx optical eye patterns at 80-Gbps PAM4 signals for all channels, achieving the Rx sensitivities within −7.1∼−6 dBm at a bit error rate (BER) of 2.4 × 10−4.

Experimental investigation of the package of diode laser chip based on lateral heat flow suppression

To improve slow axis beam quality of diode laser (LD) and decrease slow axis divergence angle, a new package with lateral heat flow suppression was designed utilizing the difference in thermal conductivity between air and heat sink. The finite element analysis software was used to analyze the temperature distribution with lateral flow suppression package. It is shown that diode laser chip soldered on trough heat sink with width W=120 μm and length L=4000 μm can reduce slow axis divergence angle about 14%, from 12.25° to 10.49°, when working current was 15A. Correspondingly, beam parameter product (BPP) can reduce from 5.344 mm·mrad to 4.5763 mm·mrad and the brightness of slow axis increased about 5.5% than before. According to the result, the lateral flow suppression package can weaken higher order mode caused by thermal lens effect of diode laser so that decrease slow axis divergence angle effectively.

A General White-Box Strategy for Designing Thermoelectric Cooling System

Thermoelectric cooling (TEC) is critically important in thermal management of laser modules or chips and potentially for personalized thermoregulation. The formulae for efficiency in standard textbooks can only describe the performance of a TEC module with ideal thermal conditions, i.e., fixed terminal temperatures, but are unable to deal with a real TEC system where heat transfer at its interfaces with the heat source and sink are finite and with thermal resistances. Here, we define the TEC system-level performance indices, i.e., the maximum cooling power, temperature difference, and coefficient of performance, by introducing a set of explicit formulae. The external heat transfer conditions are taken into account as dimensionless thermal resistance parameters. With these formulae, the TEC system performances are evaluated elegantly with errors well within ±5% over broad operating conditions. We further optimize the cooling power and the coefficient of performance in practical scenarios and establish a general white-box design procedure for TEC systems, which enables a transparent design process and straightforward analysis of performance bottlenecks. A set of cooling experiments are performed to validate the analytical model and to illustrate the dependence of system design on realistic thermal conditions. By choosing the suitable TEC module parameter under given external heat transfer conditions, the cooling power can be improved by more than 100%. This work sheds some light on the integral design of TEC systems for broad applications to take full advantage of the advanced thermoelectric materials in the cooling field.

Study of the Spatial and Current Dynamics of Optical Loss in Semiconductor Laser Heterostructures by Optical Probing

The spatial and temporal dynamics of the optical loss and carrier density in the heterostructure of a semiconductor laser with a segmented contact are studied using an optical pump–probe technique based on the injection of probe radiation with a wavelength of 1560 nm into a semiconductor laser chip under study that is based on an AlGaAs/InGaAs/GaAs heterostructure and emits at wavelength of 1010 nm. It is demonstrated that employing probe light at a wavelength of 1560 nm enables sensitivity in measuring an internal optical loss of no less than 1 cm–1. The segmented design of the current pumping region made it possible to estimate the absolute internal optical loss. It is shown that changing the configuration of the Fabry–Perot eigenmodes of the laser affects the carrier distribution and the internal optical loss both in the current pumping region and in the passive, current unpumped part of the laser chip.

High-efficiency edge-coupling based on lithium niobate on an insulator wire waveguide.

Edge-coupling on single-crystal thin-film lithium niobate on insulator (LNOI) was systematically studied in this paper. An inverse taper-shaped spot-size converter (SSC) to convert the mode field from the laser chip to a nanoscale LNOI waveguide was adopted to improve the coupling efficiency. Structure of the edge coupler was fully investigated and optimized by using the eigenmode expansion method. The single-mode conditions of the LNOI waveguide for three common communication bands were taken into consideration. Further, the length and tip width of the inverse taper, the cross-section dimensions of SiON waveguide, and the sidewall angle were investigated with respect to coupling efficiency. As a result, the maximum coupling efficiency from an edge coupler to laser chip can reach 54%, 48%, and 58% at 1550, 1310, and 850 nm in Z-cut LNOI for quasi-TM mode, respectively. This proposed work gives a better understanding of the function of the edge coupler based on LNOI material and provides an appropriate method for the design of an edge coupler with high efficiency, which could benefit the further application of high-density monolithic integrated optical components.

Experimental investigation of influence of scratch features on GaAs cleavage plane during cleavage processing using a scratching capability index

High-power semiconductor laser cavities are formed via the cleavage plane, and critically influence the reliability and performance of the laser. This paper investigates both the scratching operation and the cleavage operation to improve the quality of the cleavage plane during the entire cleavage process. The scratching capability index (SCI) variable was proposed to evaluate the scratch quality of GaAs. A series of scratching and cleavage experiments were carried out to investigate the effect of the scratch features on the GaAs cleavage plane. Experimental results of the scratching operation showed that a smaller scratching load and higher scratching speed were beneficial for reducing the kerf width and damage area width of GaAs. The cleavage operation on GaAs {100} cleavage planes exhibited crack propagation in the [101] and [100] directions and a slip direction in the crystal direction. The calculated SCI variable correlated well with the scratch and cleavage qualities of GaAs, where a higher scratching SCI correlated with a smoother GaAs cleavage plane during cleavage processing. Thus, the SCI has the potential to relate the scratching parameters with the resulting cleavage plane quality of GaAs, which will help improve the manufacturing of semiconductor laser chips in the future.