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

Schwarz, Uli; Pindl, Markus

doi:10.1117/12.591044

Cited by 4 publications

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“…Topics studied so far with this setup are filaments, mode competition, near-field phase dynamics, near-field to far-field propagation, and substrate modes. [20][21][22][23] We start in section two with the description of the time-resolved SNOM setup. In the third section the parameters for tube-etching of the SNOM fiber tips are given.…”

Section: Introductionmentioning

confidence: 99%

Time-resolved scanning near-field microscopy of InGaN laser diode dynamics

et al. 2006

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We combine a scanning near-field microscope (SNOM) with a time-resolved detection scheme to measure the mode dynamics of InGaN laser diodes emitting at 405 nm. Observed phenomena are filaments, mode competition, near-field phase dynamics, near-field to far-field propagation, and substrate modes. In this article we describe in detail the self-built SNOM, specialized for these studies. We also provide our recipe for SNOM tip preparation using tube etching. Then we compare the mode dynamics for a 3 µm narrow and a 10 µm wide ridge waveguide laser diode.

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Section: Introductionmentioning

confidence: 99%

Time-resolved scanning near-field microscopy of InGaN laser diode dynamics

et al. 2006

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Waveguide mode dynamics of blue laser diodes

Pindl

Schwarz

2006

Physica Status Solidi (a)

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We use a scanning near‐field microscope (SNOM) in combination with a time resolved detection scheme to measure the evolution of the near‐field and far‐field of InGaN laser diode (LD) waveguide modes. We observe lateral mode competition, filamentation, and beam steering. Here we compare the lateral mode dynamics for ridge waveguide LDs and oxide stripe LDs which are predominantly index and gain guided, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Experimental and theoretical study of substrate modes in (Al,In)GaN laser diodes

Braun

Lauterbach

Schwarz

et al. 2007

Phys. Status Solidi (c)

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In semiconductor laser diodes, high refractive index epitaxial layers can act as parasitic waveguides and cause severe losses to the mode propagating in the laser waveguide. For (Al,In)GaN laser diodes the parasitic modes are typically caused by the SiC or GaN substrate or buffer layers. Substrate modes have an impact on near-field and far-field of the waveguide mode, on laser threshold, and on gain spectra. We present scanning near-field measurements of the substrate mode and demonstrate that the period of the standing wave in the GaN substrate varies over a wide range and critically depends on the effective refractive index of the waveguide mode.1 Introduction For (Al,In)GaN laser diodes (LD) on bulk GaN substrates the refractive index of the substrate is higher than that of the effective refractive index of the waveguide. Thus any part of the waveguide mode tunneling as evanescent wave through the n-side AlGaN cladding can propagate in the substrate. Reflected under a small angle of incidence from the bottom surface of the substrate it will form a standing wave. This so-called substrate mode causes a periodic modulation of the total loss of the laser mode. We observe this as periodic modulation in the gain spectra measured by the Hakki-Paoli method and by a dependency of the threshold current on the n-cladding layer thickness [1]. The far-field shows side-lobes rising from the substrate mode travelling at an angle to the waveguide which is determined by the effective refractive index of the mode and the refractive index of the substrate. We also observe the standing wave in the substrate by a measurement of the near-field intensity on the cleaved surface of the substrate just below the laser ridge waveguide. This is the most direct observation of the substrate mode.For a quantitative analysis we establish a two-dimensional finite element electromagnetic solver, to simulate periodic variations in the cavity loss that reproduce measurements of the modal gain in terms of absolute value and oscillations amplitude. Details and results of these simulations can be found in [1]. The two-dimensional simulation model shows a periodic interference pattern in the substrate [1], very similar to what can be found in measurements (see Fig. 1). An oscillation period of about 1 µm can be extracted from this pattern. These simulations can be used to optimize the vertical structure (within the constraints given by growth conditions) in order to minimize the impact of the substrate modes [1].Here we concentrate on near-field measurements of the substrate mode intensity distribution. We demonstrate that the spatial period of the substrate mode varies over a wide range and critically depends on the effective refractive index of the waveguide.

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

Cited by 4 publications

References 0 publications

Time-resolved scanning near-field microscopy of InGaN laser diode dynamics

Time-resolved scanning near-field microscopy of InGaN laser diode dynamics

Waveguide mode dynamics of blue laser diodes

Experimental and theoretical study of substrate modes in (Al,In)GaN laser diodes

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