Wavelength-stabilized near-field laser

Authors:

• Vitaly A. Shchukin,
• Vladimir M. Kalosha,
• Nikolay Ledentsov Jr.,
• Łukasz Chorchos,
• Nikolay N. Ledentsov

Abstract

Surface-trapped electromagnetic waves can be localized at a boundary between a semiconductor distributed Bragg reflector (DBR) and a homogeneous dielectric medium or air. These waves enable a novel class of both in-plane-emitting and vertically-emitting optical devices including edge-emitting lasers, disk microlasers, near-field fiber-coupled lasers as well as vertical cavity surface emitting lasers (VCSELs). We show that the surface-trapped modes can be controlled by tuning the thickness of a single DBR layer. Diagrams in variables "wavelength - thickness of the control layer" are constructed for both TM and TE optical modes revealing the parameter domains, in which surface-trapped modes exist. The domains contain cusps, in the vicinity of which surface-trapped modes are allowed only in a narrow spectral region, enabling wavelength-stabilized operation of a laser. For an edge-emitting structure designed for lasing at ∼1 μm, the lasing wavelength shifts upon temperature at a rate ∼0.07 nm/K. The fraction of the optical power of the surface-trapped mode accumulated in the air can reach ∼60%. In oxide-confined VCSEL structures the surface-trapped mode can be used for engineering of the interaction with the VCSEL lasing modes. Deposition of an effective (3λ/4)-thick additional layer on top of the top DBR of the VCSEL allows surface-trapped modes to reach the wavelength of the VCSEL lasing modes. Interaction of these two types of generally non-orthogonal optical modes results in the lateral leakage of the VCSEL emission. Mapping of the VCSEL wafers in areas with the variable aperture diameters D shows non-monotonous behavior of side mode suppression ratio (SMRS) versus D oscillating in the range from 7 dB to ∼30 dB with three clearly revealed maxima in the SMSR at particular aperture diameters varied in the range from ∼3 μm to ∼5 μm. Similar oscillatory behavior was previously predicted for a different type of leaky VCSELs. VCSELs with SMSR above 20 dB are tested for data transmission over a multimode fiber (MMF). 40Gb/s open eye data transmission over 1.4 km OM5 MMF without pre-emphasis or equalization is demonstrated is such device.