VCSEL technology for medical diagnostics and therapeutics

Abstract

In the 1990's a new laser technology, Vertical Cavity Surface Emitting Lasers, or VCSELs, emerged and transformed the data communication industry. The combination of performance characteristics, reliability and performance/cost ratio allowed high data rate communication to occur over short distances at a commercially viable price. VCSELs have not been widely used outside of this application space, but with the development of new attributes, such as a wider range of available wavelengths, the demonstration of arrays of VCSELs on a single chip, and a variety of package form factors, VCSELs can have a significant impact on medical diagnostic and therapeutic applications.One area of potential application is neurostimulation. Researchers have previously demonstrated the feasibility of using 1850nm light for nerve stimulation. The ability to create an array of VCSELs emitting at this wavelength would allow significantly improved spatial resolution, and multiple parallel channels of stimulation. For instance, 2D arrays of 100 lasers or more can be integrated on a single chip less than 2mm on a side. A second area of interest is non-invasive sensing. Performance attributes such as the narrow spectral width, low power consumption, and packaging flexibility open up new possibilities in non-invasive and/or continuous sensing. This paper will suggest ways in which VCSELs can be implemented within these application areas, and the advantages provided by the unique performance characteristics of the VCSEL. The status of VCSEL technology as a function of available wavelength and array size and form factors will be summarized.

Implantable semiconductor biosensor for continuous in vivo sensing of far-red fluorescent molecules

“…The elements are monolithically VCSEL technology, developed extensively for the telecommunications industry, is an excellent light source for integrated fluorescence sensing. VCSELs have been commercialized to emit at 670-980nm, 1300nm and longer wavelengths [17], and can be easily integrated with photodetectors [18][19][20]. VCSELs emit light normal to the epitaxial layers of a semiconductor wafer (e.g.…”

Single-mode single-polarization multijunction VCSELs

“…In other words, as long as the device operates in the single-mode regime, it appears that the devices are polarized along the [110] axis. However, as VCSEL becomes multi-mode, the dominant polarization direction starts to switch from [110] to [1][2][3][4][5][6][7][8][9][10] direction. It can be deduced that the fundamental mode is mostly polarized along the [110] direction, while the higher order transverse modes are polarized orthogonally.…”

“…The shape and size of the relief feature is defined using conventional UV lithography techniques. It should be mentioned that the non-circular relief features are defined in the shape of an ellipse, where it is oriented along the crystal axes of [1][2][3][4][5][6][7][8][9][10] and [110]. Figure 1.b shows an SEM image from the top surface of a VCSEL, in which a shallow-etched surface relief feature with both elliptical and circular geometries is shown.…”

“…Over the last two decades, VCSELs have gained notable attraction as a laser light source in variety of sensing and visualization applications and have continued to mature in both materials used in these devices and also their fabrication methods [1]. VCSELs are widely used in a number of application areas that require low to moderate optical output power, from short to long-distance data communication via plastic fibers [2], to variety of spectroscopy and biosensing applications, such as oximetry and toxic gas sensing [3], and also display and visualization applications [4]. In addition to these, VCSELs are being adopted in high-power applications, such as long-distance sensing, especially for automotive LiDAR applications [5].…”

Progress and challenges in electrically pumped GaN-based VCSELs

“…A 2D-VCSEL array would allow for selective stimulation of a nerve without mechanical repositioning of the laser and the individually addressable lasers gives the possibility to stimulate multiple sites simultaneously. This two-dimensional probing of neural networks has been demonstrated with GaN micro-LED arrays 20 , and is desired for example in chochlear implants 21 . Blue LEDs have recently been used in in vivo optogenetic experiments 22 , where VCSELs could offer additional advantages such as a low-divergent circular-symmetric output beam and improved high-speed performance.…”