fabricate a VCSEL

The optical reflectivity methods in order to fabricate a VCSEL

The optical reflectivity methods in order to fabricate a VCSEL

Introduction

Today, most near-field nanoprobes consist of specially processed optical fibres, which are difficult to fabricate with high reproducibility and in large number. To overcome this handicap, we propose a miniaturised near-field sensor. One of the novelties is to use the optical feedback properties of a vertical-cavity surface-emitting laser (VCSEL) cavity as an active principle of detection. The other novelty is that the architecture of a compound-cavity VCSEL with a GaAs micromachined tip, offering a nanometer-scale resolution of near-field probes, constitutes the first tentative to miniaturise an SNOM microscope. First, we investigate the effects of external optical feedback on the threshold and spectral characteristics of VCSELs. Second, theoretical analysis and experimental evidence demonstrate the practicability of VCSEL feedback as a detection principle for SNOM microscopy. Finally, we propose a compact architecture of an SNOM sensor with a microtip integrated on top of the VCSEL and report the preliminary results of fabrication of the integrated device.

Fabrication of nanostructures is of great interest both from a fundamental and a technological point of view. Fundamental interests include, for example, quantum dots and quantum wires, attracting much interest due to their possible applications in devices such as vertical-cavity surface-emitting lasers (VCSELs) . Technological applications, for example, include the fabrication of probes for near-field microscopy with improved form and nano-scale resolution. Thus, the optical near-field sensors have attracted much interest since it demonstrated sub-wavelength resolution unlimited by optical diffraction. Fluorescence spectroscopy of nanometer objects such as quantum dots and its efficiency as a read/write head in optical memory systems were demonstrated. Particularly, recent advances in batch fabrication of probes with sub-wavelength aperture and laser techniques have pushed the conventional near-field scanning optical microscopes (SNOMs) to be applied routinely to a wide range of applications such as high-density optical recording.

Since the mid-1980s, VCSELs have received a considerable attention due to their inherent advantages, rivalling conventional edge-emitting laser diodes in efficiency and surpass them by a low threshold operation and a symmetrical narrow beam cross-section with small divergence . With the laser emission from the wafer surface, it is possible to fabricate two-dimensional laser arrays with high fill factor. In addition, the very short cavity length makes the operation of VCSELs inherently single longitudinal mode, avoiding mode hops typical of conventional diode lasers. From a manufacturing aspect, in VCSEL technology based on epitaxial growth, the labour-intensive cleaving or dry etch steps used in making edge-emitting laser facets are eliminated. This last fact increases the compatibility with standard IC technologies and permits high-volume and low-cost VCSEL manufacturing by batch processing. On the other hand, VCSELs have been extensively investigated because of their potential in integration with MEMS elements such as micromachined-deformable membranes. Thus, the realisation of micromechanically wavelength-tuned laser was demonstrated. More recently, Heisig et al. reported the integration of a VCSEL on a GaAs cantilever for SNOM applications.

Explanation Optical feedback influence on conventional edge-emitting lasers is a well-known problem, ...