Wavelength-tunable vertical cavity surface emitting laser for swept source optical coherence tomography system

Abstract

A wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) with the use of micro-electromechanical system (MEMS) technology is provided as a swept source for Optical Coherence Tomography (OCT). The wavelength-tunable VCSEL comprises a bottom mirror of the VCSEL, an active region, and a MEMS tunable upper mirror movable by electrostatic deflections. The bottom mirror comprising a GaAs based distributed Bragg reflector (DBR) stack, and the active region comprising multiple stacks of GaAs based quantum dot (QD) layers, are epitaxially grown on a GaAs substrate. The MEMS tunable upper mirror includes a membrane part supported by suspension beams, and an upper mirror comprising a dielectric DBR stack. The MEMS tunable quantum dots VCSEL can cover an operating wavelength range of more than 100 nm, preferably with a center wavelength between 250 and 1950 nm, and the sweeping rate can be from a few kHz to hundreds of kHz, and up to a few MHz.

What is claimed: 
     
         1 . A microelectromechanical system (MEMS) tunable vertical cavity surface-emitting laser (VCSEL) comprising one or more layers of quantum dots. 
     
     
         2 . The MEMS tunable VCSEL of  claim 1 , wherein the one or more layers of quantum dots comprise InAs or InGaAs quantum dots, and are separated by InGaAs barrier layers. 
     
     
         3 . The MEMS tunable VCSEL of  claim 1 , having an upper and a lower DBR, wherein the DBR is GaAs or AlGaAs-based. 
     
     
         4 . The MEMS tunable VCSEL of  claim 1 , wherein the one or more layers of quantum dots are in an active region grown continuously on the DBR. 
     
     
         5 . The MEMS tunable VCSEL of  claim 1 , having a tunable range of greater than 100 nm. 
     
     
         6 . A tunable VCSEL for swept source optical coherence tomography comprising:
 a MEMS tunable VCSEL,   wherein said MEMS tunable VCSEL comprises:
 a bottom half VCSEL part, and an upper mirror part, wherein said bottom half VCSEL part includes: 
 a bottom DBR that is epitaxially grown on a GaAs substrate, 
 and an active layer comprised of a plurality of layers of quantum dots that are epitaxially grown on the top of said bottom DBR, 
 and said upper mirror part includes: 
 a vertically movable membrane supported by beams; 
 an upper DBR provided on said vertically movable membrane, as an upper reflector for light; 
 electrodes supplying a voltage between said vertically movable membrane and said handle substrate to change a cavity length of a cavity formed between said upper DBR layer and said bottom DBR layer. 
   
     
     
         7 . The tunable VCSEL of  claim 6 , wherein said active layer comprises multiple layers comprising more than one size of quantum dot. 
     
     
         8 . The tunable VCSEL of  claim 6 , wherein said active layer comprises multiple layers comprising more than one composition of quantum dot. 
     
     
         9 . The tunable VCSEL of  claim 6 , wherein said active layer comprises multiple layers consisting of quantum dots having a second quantized energy state. 
     
     
         10 . The tunable VCSEL of  claim 6 , wherein said active layer comprises multiple layers consisting of InAs or InGaAs quantum dots. 
     
     
         11 . The tunable VCSEL of  claim 6 , wherein the active layer comprises multiple layers of quantum dots having a center wavelength in the range of 250-1950 nm. 
     
     
         12 . The tunable VCSEL of  claim 6 , wherein the active layer comprises multiple layers of quantum dots having a center wavelength in the range of 850-1700 nm. 
     
     
         13 . The tunable VCSEL of  claim 6 , wherein the active layer comprises multiple layers of quantum dots having a center wavelength in the range of 1100-1350 nm. 
     
     
         14 . An optical coherence tomography system comprising the tunable VCSEL of  claim 1 .