Modifying the coherence of vertical-cavity surface-emitting lasers using chaotic cavities
Omar Alkhazragi, Ming Dong, Liang Chen, Liang Dong, Tien Khee Ng, Junping Zhang, Hakan Bağcı, Boon S. Ooi
Abstract
Vertical-cavity surface-emitting lasers (VCSELs) have been widely adopted in a variety of applications in recent years, with even more applications currently under research and development as a result of the emergence of visible-light VCSELs. Most of these applications make use of the ease of fabrication of large two-dimensional arrays of lasers, a feature unique to VCSELs that makes them scalable and versatile. However, applications that rely on the uniformity of the emitted beam in the transverse plane, such as illumination, projection, holography, and displays, suffer from the coherence artifacts (speckles) that reduce the quality of the formed images when coherent lasers are used. In this work, we show that, by using a chaotic-cavity D-shaped mesa, the coherence of broad-area VCSELs can be substantially reduced (the number of mutually incoherent modes is almost doubled, and the spectral full width at half-maximum is increased from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>1.1</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>4.5</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:math> ), and the maximum achievable optical power is increased by up to 60%. The simplicity of implementing the reported design, which requires no additional fabrication steps, makes it a promising solution for applications that would benefit from the lower speckle density of the emitted light as well as those that rely on lower temporal coherence, such as time-domain optical coherence tomography and fiber-optic gyroscopes.