Catastrophic Optical Damage Threshold Research Articles

Multiphysics analysis of chip and resonator designs for increased damage threshold of external cavity high-power laser diodes.

We present a detailed analysis of multiphysics simulation results to evaluate the threshold for catastrophic optical damage (COD) of high-power laser diodes under misaligned external optical feedback. Three different chip designs are investigated: the non-injecting mirror concept, the non-absorbing mirror concept and the introduction of an additional energy barrier within the waveguide near the front facet. Furthermore, a modification of the external resonator that promises a lower sensitivity towards misalignments is considered. The dependence of the COD threshold on the additional design parameters (bandgap change, modification length, focal length) and the impact of the different approaches on electro-optical efficiency as well as beam quality are analyzed. Compared to the initial design, the different chip design concepts promise an increase of the achievable output power by 8%, 27% and 27% respectively, whereas the modified resonator fully prevents feedback-induced failure.

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.

High-power edge-emitting laser based on a parity-time-structured Bragg reflection waveguide.

A parity-time-structured Bragg reflection waveguide is proposed and analyzed for realizing a high-power laser. A single transverse mode with the optical field confined mainly in the low-index core is discussed to improve the catastrophic optical damage threshold for high output power. The designed scheme can potentially mitigate the heat buildup by moving the injection from the central narrow core to the outer large-area claddings, while suppressing the coupler mode transversely. The structure can achieve high output power with a short cavity length, low lasing threshold, and high power conversion efficiency.

High‐power single spatial mode superluminescent diodes at 675 nm

The optimisation of AlGaInP/GaInPAs MQW heterostructure metal-organic chemical vapour deposition growth as well as the improvements of active channel formation and P-contact deposition technologies is shown to enable a significantly increased external differential efficiency up to 0.5 mW/mA and catastrophic optical damage threshold up to 50 mW of spatially single-mode superluminescent diodes (SLDs) at central wavelength of 675 nm. Life time tests demonstrated high reliability of new SLDs at continuous wave output power of up to 30 mW. The dependencies of spectral and power characteristics of these SLDs on active channel dimensions are presented. To the best of knowledge, these are the most powerful and broadband SLDs at 675 nm.

Asymmetric Heterostructure With Reduced Distance From Active Region to Heatsink for 810-nm Range High-Power Laser Diodes

An asymmetric heterostructure design has been proposed to meet high-power laser diode (LD) requirements, such as a high catastrophic optical damage threshold, a low internal loss, low thermal and electrical resistances and a low vertical beam divergence. The asymmetry has been designed to shift the optical field in heterostructure waveguide toward the n-side, where losses are lower than those at the p-side. The main features of the design are: 1) a thin anti-guiding layer inserted between the “active” [containing quantum well (QW)] and the passive waveguides to elongate field penetration toward the n-side and to increase degree of freedom in design; and 2) reduced p-cladding layer thickness (thanks to the shift of the optical field toward the n-side) aimed at reducing the diode resistances due to shortened QW to heatsink distance. The characteristics of pulsed and CW operation of high-power LDs based on the asymmetric GaAsP/AlGaAs/GaAs heterostructure are presented. A lower temperature increase of the active region of asymmetric LDs compared with equivalent symmetric LDs has been evidenced by time-resolved spectra and thermovision characteristics.

Increase in the optical damage threshold of a ZnSe-passivated front mirror of a laser diode

The operation of single-mode diode lasers with a front mirror passivated by ZnSe films of different thicknesses is studied in the pulsed regime (pulse duration τ = 0.2 – 10 μs). It is found that in the case of short (0.2 μs) pulses, the catastrophic optical damage threshold grows almost linearly as the film thickness on the front mirror increases from 0.1 to 0.5 μm. It is shown that lasers with mirrors passivated by 'thick' (0.4 – 0.6 μm) ZnSe films can operate stably in the case of 'long' (2 – 10 μs) pulses. It is assumed that in this pulsed regime the ZnSe film provides an additional heat removal from the hot zone of the front mirror, and consequently increases the optical damage threshold.

Radiation parameters of ridge lasers at high pump currents

Quantum-well ridge GaAs/AlGaAs heterostructure lasers are studied at high pump currents. It is shown that their catastrophic optical damage (COD) is preceded, as a rule, by a giant kink caused by the collapse of a waveguide in a horizontal plane. It is found that, by increasing the coating thickness of the output end-face of a diode by preparing an intermediate ZnSe layer between the cleaved output end-face of the diode and a coating forming the output mirror of the laser, it is possible to increase the COD threshold by a factor of 1.5–2. This optical strengthening occurs because the ZnSe layer provides an additional channel for heat sink from the overheated output face.

The role of monolithic integration in advanced laser products

The design and performance of single-mode high-power (>100 mW) semiconductor lasers suitable for integration into large arrays are reported. In 830 nm lasers, quantum well intermixing (QWI) has been used to increase the bandgap of the waveguide in the facet region by 120 meV, and the catastrophic optical damage threshold of uncoated devices increased by a factor of >3 as a result. The passive waveguides are relatively cool, bringing high reliability, improving the single-mode waveguide stability and enabling high-temperature operation. Furthermore, the passive waveguides relax the cleaving and packaging alignment tolerances, giving a high yield process suitable for manufacture. A far-field reduction layer is included in the lasers giving a fast axis divergence of <20° FWHM. Arrays in which each emitter operates at several 100 mW, have excellent uniformity of laser parameters such as kink power, operating power and optical beam profile.

High-power superluminescent diodes with non-injection output sections

Superluminescent diodes based on a separate-confinement (GaAl)As heterostructure are studied in the 850-nm spectral region. A contact p+-GaAs layer in the output sections of a narrow active channel of width 4 μm was removed and a metal contact was not deposited. These sections played the role of saturable absorbers. This design provided a significant increase in the catastrophic optical damage threshold and ensured 250 mW of output cw power at the diode facet. The power coupled out through a single-mode fibre in the case of a simplest coupling achieved 110 mW.

High-efficiency AlGaAs-based laser diode at 808 nm with large transverse spot size

Lasers diodes having a large transverse spot size have been fabricated from a modified graded index separate confinement heterostructure with an active region consisting of two 70 /spl Aring/ Al/sub 0.15/In/sub 0.10/Ga/sub 0.75/As strained quantum wells. The catastrophic optical damage threshold for these large transverse mode devices is increased by more than two times over that of conventional devices while still maintaining good device performance.

An AlGaAs window structure laser

Extremely high optical power density emission was achieved with an AlGaAs "window structure" laser in CW operation as well as pulsed operation by increasing the threshold of the catastrophic optical damage (COD) on mirrors. A Zn diffused "window stripe" laser consists of the Zn diffused p-type light emitting region with low effective energy gap in the central part and the n-type window regions with high effective energy gap at both ends of the cavity. The maximum available optical power in pulsed operation was at least one order of magnitude higher than the COD threshold in conventional structures. 80 mW optical power in CW operation was achieved in the Zn diffused window stripe laser with a 5 μm wide stripe. Furthermore, gradual degradation due to the photoenhanced mirror oxidation has been reduced significantly under long term CW operation.