Laser Diode Facet Research Articles

Optimization of technology of diode laser mirror processing to maximize the threshold of catastrophic optical degradation

In this paper, optimization works on the technology of passivation and optical coatings of laser diode facets are described. The main goal is to increase the optical power at which the catastrophic optical mirror damage occurs. The coatings and passivation processes have been done in an ion source-aided electron-beam evaporator. The essence of passivation was to remove native oxides and produce a native thin nitride layer with simultaneous saturation of the dangling atomic bonds. The procedure has been realized with the help of nitrogen or forming gas (N2 + H2) beam. As a result, we present sets of technological parameters allowing to increase the catastrophic optical mirror damage threshold of diode lasers.

Balanced detection for self-mixing interferometry.

We propose a new detection scheme for self-mixing interferometry using two photodiodes for implementing a differential acquisition. The method is based on the phase opposition of the self-mixing signal measured between the two laser diode facet outputs. The subtraction of the two outputs implements a sort of balanced detection that improves the signal quality, and allows canceling of unwanted signals due to laser modulation and disturbances on laser supply and transimpedance amplifier. Experimental results demonstrate the benefits of differential acquisition in a system for both absolute distance and displacement-vibration measurement. This Letter provides guidance for the design of self-mixing interferometers using balanced detection.

On the formation of cleaved mirror facets of GaN-based laser diodes—A comparative study of diamond-tip edge-scribing and laser scribing

The formation of cleaved mirror facets of GaN-based laser diodes on c-plane GaN substrates is investigated using either diamond-tip edge-scribing or laser scribing with a skip-and-scribe method. The yield of properly cleaved facets was significantly improved to around 80% when using the laser skip-and-scribe method instead of diamond scribing. In addition, the cleavage planes of laser scribed samples showed fewer terraces than those of diamond scribed samples. The performance of broad area laser diodes with proper facet quality is shown to be independent of the scribing methods studied.

Chemically assisted ion beam etching of laser diode facets on nonpolar and semipolar orientations of GaN

We demonstrate a vertical (<1° departure) and smooth (2.0 nm root mean square line-edge roughness (LER)) etch by chemically assisted Ar ion beam etching (CAIBE) in Cl2 chemistry that is suitable for forming laser diode (LD) facets on nonpolar and semipolar oriented III-nitride devices. The etch profiles were achieved with photoresist masks and optimized CAIBE chamber conditions including the platen tilt angle and Cl2 flow rate. Co-loaded studies showed similar etch rates of ∼60 nm min−1 for and m-plane orientations. The etched surfaces of LD facets on these orientations are chemically dissimilar (Ga-rich versus N-rich), but were visually indistinguishable, thus confirming the negligible orientation dependence of the etch. Continuous-wave blue LDs were fabricated on the semipolar plane to compare CAIBE and reactive ion etch (RIE) facet processes. The CAIBE process resulted in LDs with lower threshold current densities due to reduced parasitic mirror loss compared with the RIE process. The LER, degree of verticality, and model of the 1D vertical laser mode were used to calculate a maximum uncoated facet reflection of 17% (94% of the nominal) for the CAIBE facet. The results demonstrate the suitability of CAIBE for forming high quality facets for high performance nonpolar and semipolar III-N LDs.

Precision UV laser scribing for cleaving mirror facets of GaN-based laser diodes

Laser scribing with a nanosecond-pulsed UV laser operating at 355 nm was used to create precise perforation for die separation of GaN-based laser diodes. Machining depth of single- and multiple-pass scribing was investigated. For pulse energies between 1 and 45 µJ at a pulse repetition frequency of 20 kHz and single scan at 100 mm/min, scribe depths from 15 to 180 µm were obtained. Processing parameters were adjusted to minimize the formation of microcracks due to laser-induced local heating. By using the laser skip-and-scribe technique, the propagation of the cleavage plane could be controlled, irregular breaking could be minimized, and die yield could be improved. Smooth mirror facets with low density of terraces were formed by cleaving. In the vicinity of the laser-treated zone, no detrimental effects on the crystal quality of the multi-quantum wells could be detected by cathodoluminescence. The electro-optical characteristics of broad-area laser diodes fabricated by the laser-assisted process were similar to the ones fabricated using the conventional diamond-tip edge-scribing technique that suffers from low die yield. Our results demonstrate that nanosecond-pulsed UV laser scribing followed by cleaving is a powerful technique for the formation of mirror facets of GaN-based laser diodes.

Evaluation of structural and microscopic properties of tetragonal ZrO2 for the facet coating of 980 nm semiconductor laser diodes

ZrO2 based antireflection coatings are expected to show a high laser induced damage threshold in the facet coating applications of laser diodes. A single layer of undoped ZrO2 and multilayers of ZrO2/SiO2 are deposited at 80 °C by an e-beam evaporation technique on GaAs and Si substrates. ZrO2 layers deposited under the optimized conditions are of a tetragonal nature and the grain size increases with reduced atomistic configuration mismatch between the surfaces of the layer and substrate. The electron/optical density profiles of the tetragonal ZrO2 single layer and multilayers of ZrO2/SiO2 are obtained from x-ray reflectivity measurements which confirm a uniform surface without any evidence of interfacial diffusion. The refractive index spectrum of tetragonal ZrO2 is found to be different from its other stable monoclinic allotropes. This is due to the possible differences in the atomistic structure of tetragonal ZrO2 that might be caused by oxygen vacancies and impurities. The measured values of refractive index, surface and interface roughness are used to engineer the layer structures for achieving 2 and 90% reflectivity at 980 nm at the front and the rear facets of laser diodes. The slope efficiency of the facet coated laser diode increases from 0.5 to 0.91 W A−1 without any measurable difference in the threshold current density.

The Characteristics of Facet Coatings on Diode Lasers

The effect of the output power with different facet passivation methods on 980 nm graded index waveguide structure InGaAs/AlGaAs laser diodes was studied. The output power of the 980 nm laser diodes with Si passivation, and ZnSe passivation at the front and the back facet were compared. The test results show that output power of the ZnSe passivation method is 11% higher than Si passivation method. The laser diode with the Si passivation film is failure when current is 5.1 A, the laser diode with the ZnSe passivation film is not failure until current is 5.6 A And we analyzed the failure reasons for each method. In conclusion, the method of coated ZnSe passivation on the laser diode facet can effectively increase the output power of semiconductor lasers.

In situ control and monitoring of photonic device intermixing during laser irradiation

Apparatus and method for the in situ control of photonic device intermixing processes are described. The setup utilises an optical fiber splitter which delivers photons to selectively anneal the photonic device and simultaneously measures the emission spectra from the device to monitor the intermixing process in real time. The in situ monitoring of a laser annealing process for the modification of a semiconductor laser diode facet is demonstrated using the instrumentation. A progressive blueshift in the emission wavelength of the device can clearly be observed in real time while high energy photons are delivered to anneal the device facet, hence enabling the control on the degree of intermixing required. This instrumentation is also ideal for broadening of emission spectra in quantum dot and quantum well based light emitting devices such as superluminescent diodes and broadband laser.

Laser Diode Feedback Signal for Position Sensing Using Self-Mixing Interference

We modified a digital versatile disk (DVD) pickup head as a DVD actuator with a laser diode package for sensing. Tuning a tilting coil in the DVD actuator causes the tilt of a laser diode to compensate misalignment between a target surface and the laser diode facet. Experimental results show that tuning the tilting coil compensates misalignment between both surfaces to achieve effective self-mixing signal. Furthermore, we present the conformity between the output voltage and the target surface displacement from a laser diode package using the self-mixing effect. The resolution in linear region of self-mixing signal is 100 mV/nm.

Formation of nitride laser cavities with cleaved facets on transferred laser diodes on GaAs substrates

AbstractSmoothly cleaved facets with high reflectivities have been demonstrated on GaN laser diodes after the devices were transferred onto GaAs substrates. The GaN based laser diode structure was first fabricated by metal organic chemical vapor deposition (MOCVD) on c‐plane sapphire substrates. The samples were then mounted onto thin GaAs substrates using wafer‐bonding technology. Laser lift‐off (LLO) technique was applied to remove the original sapphire substrate and transfer the GaN laser structure onto GaAs substrates. Since the cubic substrates have well‐defined laser cavity cleavage facet, the GaN structures bonded onto the substrates also formed smooth facets after cleavage. The cleaved facets of GaN laser diodes have been characterized using atomic force microscopy (AFM) with less than 2 nm roughness. The present study demonstrated the feasibility of transferring GaN laser structures onto other more appealing substrates for formation of laser cavities. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Plasmonic Laser Antennas and Related Devices

This paper reviews recent work on device applications of optical antennas. Localized surface plasmon resonances of gold nanorod antennas resting on a silica glass substrate were modeled by finite difference time-domain simulations. A single gold nanorod of length 150 or 550 nm resonantly generates enhanced near fields when illuminated with light of 830 nm wavelength. A pair of these nanorods gives higher field enhancements due to capacitive coupling between them. Bowtie antennas that consist of a pair of triangular gold particles offer the best near-field confinement and enhancement. Plasmonic laser antennas based on the coupled nanorod antenna design were fabricated by focused ion beam lithography on the facet of a semiconductor laser diode operating at a wavelength of 830 nm. An optical spot size of few tens of nanometers was measured by apertureless near-field optical microscope. We have extended our work on plasmonic antenna into mid-infrared (mid-IR) wavelengths by implementing resonant nanorod and bowtie antennas on the facets of various quantum cascade lasers. Experiments show that this mid-IR device can provide an optical intensity confinement 70 times higher than that would be achieved with diffraction limited optics. Near-field intensities ~ 1 GW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were estimated for both near-infrared and mid-IR plasmonic antennas. A fiber device that takes advantage of plasmonic resonances of gold nanorod arrays providing a high density of optical ldquohot spotsrdquo is proposed. Results of a systematic theoretical and experimental study of the reflection spectra of these arrays fabricated on a silica glass substrate are also presented. The family of these proof-of-concept plasmonic devices that we present here can be potentially useful in many applications including near-field optical microscopes, high-density optical data storage, surface enhanced Raman spectroscopy, heat-assisted magnetic recording, and spatially resolved absorption spectroscopy.

Degradation Analysis and Degradation Suppression Technology Caused by Light Absorption at Active Layer Facet of GaInAsP Laser Diode

Electrostatic discharge induced degradation is one of the serious reliability problems of GaInAsP/InP laser diode. The authors have conducted an analysis on electrostatic discharge induced degradation, and clarified the principal degradation mechanism. Main cause of degradation is heating by light absorption at the active layer facet. This phenomenon is similar to the catastrophic optical damage that occurs in a GaAs-based high power laser diode. This problem is more serious in recent tendency to high power demand. Therefore degradation suppression technology is extremely important. We focused on facet coating that is one of key process to suppress facet degradation. And we demonstrated that the facet degradation is successfully suppressed by inserting an aluminum ultra-thin layer between the semiconductor and dielectric coating films. This effect is caused by reduction in surface recombination. This degradation suppression technology has potential to be applied to not only GaInAsP/InP laser diode but arbitrary InP-based laser diode.

Optical Near-Field Generation and Detection By Using a Metal–Dielectric Film Fabricated From Silver Paste and Spherical Fused Silica

A novel optical near-field generator and detector are fabricated by using a metal-dielectric film composed of silver metal and spherical fused silica. The generators formed on the facets of laser diodes convert lasing light into the optical near-field. The detectors formed on InGaAs and InP epitaxial layers clearly respond to the optical near-field converted from propagating light. This shows the applicability of metal-dielectric film to optical near-field generators and detectors.

Optimization of facet coating for highly strained InGaAs quantum well lasers operating at 1200 nm

The optical output power of a laser diode can be enhanced by anti-reflection (AR) and high-reflection (HR) facet coatings, respectively, at the front and back facet. AR and HR coatings also serve the purpose of protection and passivation of laser diode facets. In this work, we have designed and optimized a single layer λ/4 thick Al 2O 3 film for the AR coating and a stack of λ/4 thick Al 2O 3/ λ/4 thick Si bi-layers for the HR coating for highly strained InGaAs quantum-well edge emitting broad area (BA) laser diodes. Effect of the front and back facet reflectivities on output power of the laser diodes has been studied. The light output versus injected current ( L–I characteristics) measurements were carried out on selected devices before and after the facet coatings. We have also carried out the numerical simulation and analysis of L–I characteristics for this particular diode structure. The experimental results have been compared and verified with the numerical simulation.

Atomic force microscopy analysis of cleaved facets in III-nitride laser diodes grown on free-standing GaN substrates

The cleaved {11¯00} mirror facets of III-nitride ridge waveguide laser diodes grown on free-standing GaN substrates have been characterized using atomic force microscopy. The measurements indicate that the exposed facets are atomically smooth and therefore they have a much lower roughness than has been reported for cleaved surfaces of III-nitride heterostructures grown on other substrates. Individual heterostructure layers—including InGaN quantum wells only 3nm thick—could be identified from small variations in the height of the exposed surface. These variations are attributed primarily to the partial relaxation of strained layers at the free surface.

Ion Cleaning of Facets for Improving the Reliability of HighPower 980 nm Semiconductor Lasers

We report a simple and available way of improving the reliability ofhigh power InGaAs 980 nm lasers by cleaning the facets using Ar ionbefore the protecting films have been coated. The Ar cleaning can removethe impurity and the oxide on the air-cleaved facets of laser diodes. Itis proven that the way has marked effect on reducing the gradualdegradation rate of laser diodes and improving thecatastrophic–optical–damage threshold.

Facet degradation of GaN heterostructure laser diodes

We investigated the degradation of cleaved facets of (Al,In)GaN laser diodes in different atmospheres. We found that operation in water-free atmospheres with sufficient oxygen shows a slow degradation. Operation in atmospheres with water vapor causes a fast degradation and an oxidation on the facet. This deposition is a permanent damage to the laser diode. If the laser diode is operated in pure nitrogen, we find a thick deposition on the facet, which shows high absorption. This deposition can be removed by either high optical output powers or by operation in atmospheres with sufficient oxygen. We also explain the influence of these coatings to the degradation behavior and see these coatings as the reason for unstable kinks in the L–I characteristics during operation.

Near-field and far-field dynamics of (Al,In)GaN laser diodes

Near- and far-field dynamics of edge-emitting (Al,In)GaN laser diodes are measured simultaneously with a 100 nm spatial and a 5 ns temporal resolution using a scanning near-field microscope. We reconstruct the phase distribution at the laser diode facet. Beam steering and near-field mode dynamics are interpreted in terms of thermal and carrier induced change of refractive index in the waveguide.

MOVPE Grown 1360-nm GaInNAs Quantum-Well Laser With Multibarrier Structures

We present a promising method to achieve a high-performance GaInNAs quantum-well (QW) laser emitting 1.36 /spl mu/m by metal-organic vapor phase epitaxy. It was found that the insertion of GaNAs-InGaAs layers to GaInNAs QW-GaAs barrier is very effective to control the emission wavelength and improve the optical property of QW. As the thickness of the GaNAs and InGaAs layers was decreased, the wavelength emitted from QW became longer. The optical efficiencies of the proposed QW structure were confirmed by the lasing performance in edge-emitting laser. The threshold current density and slope efficiency per facet of a 1360-nm laser diode are measured to be 892 A/cm/sup 2/ and 0.135 W/A, respectively.

Nano patterning on optical fiber and laser diode facet with dry resist

Semiconductor micro and nanofabrication lithography techniques for application in microelectronics as well as in micromechanics and optoelectronics can gain significantly from using a dry resist process, since it enables the deposition of a very uniform lithographically sensitive layer on a potentially very small area. This would otherwise be extremely difficult to achieve by using a traditional spin coated resist, such as poly(methylmethacrylate) (PMMA). We demonstrate the use of an electron sensitive sterol based evaporated electron beam resist to fabricate high-resolution features (down to 100 nm) on a small surface area. This electron beam resist has a sensitivity comparable to PMMA and is deposited using a simple thermal evaporation. Two practical applications are explored: first, this resist makes it possible to fabricate a Fresnel zone plate lens on the tip of an optical fiber in order to demonstrate the principle and the potential of highly efficient coupling of diode laser emission into the fiber; second, we use this evaporated electron beam resist in order to pattern an optical diffractive element on the facet of a semiconductor laser.