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Vertical Cavity Surface Emitting Laser
Published in Kenichi Iga, Yasuo Kokubun, Encyclopedic Handbook of Integrated Optics, 2018
The vertical cavity surface emitting laser (VCSEL) is a semiconductor laser which has a resonant cavity that is vertically formed with the surfaces of the epitaxial layers. The light output is taken from one of the mirror surfaces, as shown in Figure 1. The present author suggested a VCSEL device in 1977 [1]. The first report came out in 1978 [2]. The VCSEL lasing was demonstrated in 1979, where we used a GalnAsP/InP material for the active region, emitting 1300 nm wavelength light [3]. In 1986, we made a 6mA threshold GaAs device [4]. Then we employed metal organic chemical-vapor deposition (MOCVD) for its crystal growth and the first room temperature continuous wave (CW) laser, using GaAs material was demonstrated in 1988 [5]. Later, in 1989, Jewell and coworkers demonstrated a GalnAs VCSEL exhibiting a 2 mA threshold device [6].
Semiconductor Photonic Devices as Excitable Processors
Published in Paul R. Prucnal, Bhavin J. Shastri, Malvin Carl Teich, Neuromorphic Photonics, 2017
Paul R. Prucnal, Bhavin J. Shastri, Malvin Carl Teich
In summary, VCSEL technology is attractive owing to its many standard advantages [114] including low manufacturing cost, high-coupling efficiency to optical fibers, single-mode operation, and low operating power. However, similar to the SRL proposal in Section 6.2.1, this scheme results in a large base-level intensity on top of spikes. As argued in Ref. [8], a base-level intensity can potentially be debilitating by causing propagating system dependencies. Programming the synaptic weights wij to configure connection strength could interfere with attempts at parameter biasing. Although biological neurons also have a continuously varying state variable (voltage) during an action potential, the actual response is thresholded by voltage-gated reversal potentials that induce only neurotransmitter release between cells during a spike. It is unclear if the semispiking signals emitted by these other lasers could be processed effectively by subsequent units in a network. These lasers would probably require an optical thresholder or a nonlinear O/E/O connection in addition to the units already proposed to work effectively. VCSELs offer an ease of compact integration into 2D and possibly 3D arrays; however, any approach based on optical injection faces other challenges in constructing a scalable interconnect platform. This will be discussed with more detail in Chapter 8.
Gallium arsenide and its ternary alloys (self-assembled quantum dots)
Published in D R Vij, Handbook of Electroluminescent Materials, 2004
Another method of mode confinement is used to make vertical cavity surface emitting lasers (VCSELs), shown in figure 7.14(b)–(d). A VCSEL, as the name suggests, emits light through the surface of the device (as opposed to the edge), and the device geometry more closely resembles a post or pillar (as opposed to a ridge). In a VCSEL, optical (and electrical) confinement is achieved by etching a post structure, implanting the surrounding area with protons degrading its ability to conduct electricity, or by selective oxidation of Al-containing layers above and below the active region. Distributed Bragg reflectors (DBRs) are used as mirrors for VCSELs. For an operation wavelength of λ, a DBR consists of a superlattice made up of alternating, equal thickness, high-index and low-index layers. Each period of the superlattice has a thickness equal to λ/4, and though the reflection from a single layer is not large, when many layers are stacked, the reflectances add in phase and can give total reflection over 99%. If grown correctly, DBRs above and below the active region, separated by a distance λ, confine the optical mode with a peak at the midpoint between the DBRs.
A review of chewing detection for automated dietary monitoring
Published in Journal of the Chinese Institute of Engineers, 2022
Yanxin Wei, Khairun Nisa’ Minhad, Nur Asmiza Selamat, Sawal Hamid Md Ali, Mohammad Arif Sobhan Bhuiyan, Kelvin Jian Aun Ooi, Siti Balqis Samdin
A vertical cavity surface-emitting laser (VCSEL) is a surface-emitting semiconductor light source that emits laser beams in a direction perpendicular to its top surface. Individual VCSEL emitters are small, typically around 10 microns in diameter; they are often grouped into 2D arrays that collectively generate a much higher output power level (VCSEL).