Laser Diode Facet Research Articles

A Wavelength and Spectrum Measurement of an Extremely-Short-External-Cavity Laser Diode by Precisely Controlling Slider Flying Height

In this paper we propose a measurement method that uses a laser diode (LD) attached to a flying slider and a semi-transparent rotating disk mirror for an extremely-short-external-cavity configuration. Not only the wavelength, but also the spectrum and the light output are measured at room temperature with the external cavity length, the reflectivities of the LD facets and the external mirror, and the drive current as parameters. We have confirmed wavelength variation as great as 30 nm by changing the external-cavity length for a 1.3-$mUm wavelength laser diode with an antireflection coating on the LD facet facing the external mirror.

A Tunable Laser Diode With a Photothermally Driven Integrated Cantilever and Related Properties

This paper proposes a photothermally driven tunable laser diode (LD). We demonstrate a micromechanically tunable structure using an edge-emitting LD, a trial fabrication for a monolithic integration with a cantilever and LDs, an enhanced design for widening the wavelength tuning range, and wavelength variation experiments. We describe the design of an antireflection layer and a bimorph layer structure cantilever and expect the deflection to exceed half a wavelength by the temperature increase of 100/spl deg/C. We also confirm a 23-nm wavelength variation by changing the external-cavity length of the LD, which features an antireflection coating on the LD facet facing the external mirror.

Etched facet and semiconductor/air DBR facet of a AlGaInP laser diode prepared by focused ion beam milling

The study of focused ion beam (FIB) milling for making etched facet and semiconductor/air distributed Bragg reflector (DBR) facets of AlGaInP-based red laser diodes (LD) is presented in this letter. For the Ga ion beam current of 100 pA at fixed accelerated voltage 30 kV, FIB milling rate of GaAs was found to be 0.46 μm 3/nC. As a trade-off between high reflectivity and enough technical tolerance, the combination of third Bragg orders of semiconductor wall and air gap was chosen. The deeply etched mirror and distributed Bragg reflector facet consisting of pairs of semiconductor wall/air gap on laser diodes (LD) cavity facets with vertical sidewall on AlGaInP LDs were fabricated by focused Ga ion beam milling. Comparison of the AlGaInP LD with the mirrors between cleaved and FIB made facet was given and discussed.

Radiation characteristics analysis of broad area laser diodes and the proposal of improvement methods

AbstractIn a broad‐area laser diode (LD) having a wide stripe width, a Gaussian pattern is not obtained in the near field (NFP) and the far field pattern (FFP) has multiple peaks, which is known as filamentation. Thus, when used in communications, the losses in the side lobes are large, and antenna directivity problems develop. In this paper, we solve the wave motion equation and the dispersion equation to explain the radiation characteristics during filamentation. In particular, we explain the relationship between the phase distribution at the LD facets and the NFP and FFP. We also investigate the improvements in the radiation characteristics by examining the phase distribution at the facets and the injected current distribution in the direction perpendicular to the wave propagation direction. The results showed that the FFP can be a single peak with a side lobe suppression ratio of −13.4 dB when phase correction having two peaks was performed at the facets. The results also showed effective narrowing of the current distribution. ©2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(3): 40–49, 2002

GaN-Based High Power Blue-Violet Laser Diodes

The epitaxial lateral overgrowth (ELO) technique is an important technology for improving the characteristics of GaN-based laser diodes (LDs). The photoluminescence intensities from GaN and GaInN multiple quantum well active layers in the ELO-GaN wing region were found to be higher than those in the seed region. This indicates that the density of dislocations in the wing region could be reduced significantly. This is evidenced by dislocation densities of less than 106 cm-2 as determined from transmission emission microscopy and etching-pit-density measurements. The cleaved facets of LDs on ELO-GaN and sapphire were observed by atomic forced microscopy. Although the roughness of GaN cleaved facets on sapphire were high (Ra>10 nm), the roughness in the ELO-GaN wing region was found to be as smooth as that of GaAs cleaved facet (Ra<1 nm). The characteristics of LDs on ELO-GaN were found to be superior to those on sapphire as a result of smoother facets and lower dislocation densities.

Correction to "Thermal rollover characteristics up to 150°C of buried-stripe type 980-nm laser diodes with a current injection window delineated by a SiN/sub∞/ layer"

In the above-named letter [ibid., vol. 12, pp. 13-15, Jan. 2000] Fig. 4(b) was incorrect. The correct figure showing the degradation analysis result using EBIC is in the revised Fig. 4. In Fig. 4, the degraded area of the laser diode facet, which is difficult to see in the SEM image of Fig. 4(a), is more clearly observed in the revised Fig. 4(b), which corresponds to the EBIC image.

Optical characterization of visible multiquantum-well semiconductor lasers by collection/excitation modes of scanning near-field optical microscopy

Both collection and excitation modes of scanning near-field optical microscopy were used to study a strained AlGaInP/Ga0.4In0.6P low power visible multiquantum-well laser diode. Collection and excitation modes provide the near-field optical propagating intensity distribution and local photoconductivity information, respectively, at the facet of laser diode. Results show highly localized spatial correlation of the laser diode structure and its optical performance at the facet. Defect level in the energy range of 60–380 meV below the conduction band in the highly n-doped (Al0.7Ga0.3)0.5In0.5P cladding layer was found by the excitation mode using the wavelengths of 543.5 and 632.8 nm. Spatially resolved near-field optical spectra of both stimulated and spontaneous emissions were acquired as well. Longitudinal modes of the stimulated emission of laser diode were observed locally.

Dynamics of the optical damage of output mirrors of ridge semiconductor lasers based on strained quantum-well heterostructures

An investigation of the dynamics of catastrophic optical damage of a laser diode facet showed that the characteristic energy-evolution time of optical damage was 40–80 ns under pulsed operating conditions. When the pulse duration was less than this characteristic time, the damage was governed by the critical energy of a pulse. An estimate of the thickness of an overheated region gave less than 0.6 μm.

Improvement of GaN-based laser diode facets by FIB polishing

420 nm metal organic chemical vapour deposition-grown laser diodes were fabricated using Cl2 reactive ion etching to form the facet mirrors. The diodes were subsequently tested under pulsed conditions before and after focused ion beam (FIB) polishing. Ith was reduced from 1.75 to 1.08 A and the differential quantum efficiency (ηd) increased from 1.3% to 2.5% after FIB.

Stability of sulfur-passivated facets of InGaAs-AlGaAs laser diodes

The facets of GaAs-AlGaAs ridge waveguide (RW) laser diodes were passivated using (NH/sub 4/)/sub 2/S/sub x/. The effectiveness of this procedure was checked by electroluminescence power-voltage-current (P-V-I) measurements that provide information on the changes in the density of surface states. Using this nondestructive method, the degradation of the passivation under ambient atmosphere has been studied. Capping with silicon nitride is found to stabilize the sulfur passivation and avoid degradation.

Gain-switching of laser diodes coupled to optical fibers

Reflections from a fiber positioned at a very short distance from the output facet of a DFB laser diode are shown to induce variations of both mean turn-on time and time jitter under gain switching. Their measured values strongly depend on the phase of the reinjected field even for very small feedback levels. A simple model based on the coupled rate equations for photon and carrier populations is able to describe the experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Antireflection coating for laser diodes

A novel design for an antireflection (AR) coating layer on facets of laser diodes (LDs) is proposed and the validity of the design is confirmed experimentally. The proposed novel AR coating consisting of multilayers is designable such that the characteristic matrix is equivalent to that of the ideal quarter wavelength single layer AR coating. Applying this idea to laser diodes with a lasing wavelength of 1.3 /spl mu/m and equivalent refractive index of 3.2, a very low reflectivity of 0.08% has been realised by the stratified three layers which consist of alumina (Al/sub 2/O/sub 3/, 902 /spl Aring/)/amorphous silicon (/spl alpha/-Si, 83 /spl Aring/)/Al/sub 2/O/sub 3/ (902 /spl Aring/), deposited by electron beam evaporation.

Suppression of multiple pulse formation in actively mode-locked laser diodes by gain quenching

We propose a new method for obtaining high-power short optical pulses without trailing pulses from an actively mode-locked laser diode. To quench the residual optical gain, a part of the output is reflected back into the laser diode with the orthogonal polarization and the appropriate time delay. A numerical analysis using travelingwave rate equations shows that trailing pulses caused by both the excess gain and the residual reflection at the laser diode facet are drastically suppressed.

HIGH POWER LASER DIODE LIFETIME AND DEGRADATION MECHANISMS: A STUDY BY RAMAN MICROPROBE SPECTROSCOPY

For advanced semiconductor lasers, the maximum output power as well as the lifetime is limited by localized facet heating leading to mirror degradation and the occurrence of catastrophic optical damage (COD). The measurement of the laser facet temperature rise behavior, however, is a difficult task because of the small dimension of the lasing region. Utilizing microprobe Raman spectroscopy, we were able to systematically study the laser facet heating behavior with good temperature sensitivity and sub-micron spatial resolution. From these temperature rise data, wc have gained a better understanding of the physics and chemistry of laser diode facet degradation and the mechanisms leading to COD. The relationship of facet temperature to maximum laser output power and lifetime is discussed.

Enhanced uniform phase conjugation in two-section asymmetric laser diodes

Nearly degenerate four-wave mixing in two-section single-mode laser diodes with unequal (asymmetric) facet reflectivities is studied theoretically. It is demonstrated that, under appropriate biasing conditions, the device exhibits a uniform phase-conjugate reflectivity over a frequency detuning range of more than 10 GHz. We can simultaneously achieve enhancement of the four-wave-mixing bandwidth and efficiency by injecting the probe signal at and deriving the conjugate output from the low-reflectivity facet of an asymmetric two-section laser diode.

On the use of the modulated reflectance microscopy in the study of laser diode facets : detection of surface defects

On the use of the modulated reflectance microscopy in the study of laser diode facets : detection of surface defects

Analysis of the spectral linewidth of three-cavity semiconductor laser diodes

The spectral linewidth for a semiconductor laser diode coupled to two external cavities (known as a three-cavity laser diode) is studied in the article. A closed-form expression for the linewidth of this laser is derived by analyzing the number of photons in the laser cavity. It is found that, because of the optical feedback provided by the external cavities, the photon lifetime becomes longer than that of a solitary Fabry-Perot (FP) laser, hence reducing the value of the spectral linewidth. Our theoretical investigations reveal that the linewidth of a three-cavity laser can be reduced further by using external mirrors with high reflectivities and using anti-reflection (AR) coatings on the laser diode facets

Optimum Reflectivity Design of Laser Diode Facets and Recording Medium for an Integrated Flying Optical Head

A reflectivity design of an integrated optical head is presented based on basic design quantities such as laser diode efficiency, write-erase power margin, phase-change medium sensitivity, and permissible read power. We obtain a reflectivity of R1\\fallingdotseq0.7 for the laser diode facet that faces the photodetector, R2=0.01 for the same diode facet that faces the medium, 0.21≥R3h≥0.14 for the medium, and a reflectivity difference between the two medium reflectivity states of R3h-R3l\\fallingdotseq0.05.

Accurate measurement of reflectivity over wavelength of a laser diode antireflection coating using an external cavity laser

A method for measuring laser diode facet antireflection coating over wavelength is presented. The laser diode is coupled to a wavelength-selective external cavity, and laser threshold current over the wavelength region of interest is measured. The coating reflectivity over wavelength is derived from the threshold current data. Reflectivities as low as 1*10/sup -5/ have been measured with good fit over wavelength to an ideal single layer coating. The net external cavity feedback is also determined. An estimate of the accuracy of the reflectivity measurement is made.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Temperature measurements of telecommunication lasers on a micrometre scale

Temperature maps of laser diode facets obtained by photothermal reflectance microscopy are presented. Biased double heterojunction InGaAsP lasers were investigated. The temperature images reveal the influence of laser mode on the spatial distribution of the heat dissipation in the device. Moreover, a study of the modulated reflectance as a function of the injection current is achieved.