Wavelength tunable laser

Abstract

A wavelength tunable laser comprising a laser diode and a closed external cavity formed by one or more optical resonators either horizontally or vertically coupled to adjacent waveguides. The optical resonator primarily functions as a wavelength selector and may be in the form of disk, ring or other closed cavity geometries. The emission from one end of the laser diode is coupled into the first waveguide using optical lens or butt-joint method and transferred to the second waveguide through evanescent coupling between the waveguides and optical resonator. A mirror system or high reflection coating at the end of the second waveguide reflects the light backwards into the system resulting in a closed optical cavity. Lasing can be achieved when the optical gain overcomes the optical loss in this closed cavity for a certain resonance wavelength which is tunable by changing the resonance condition of the optical resonator through reversed biased voltage or current injection. Multiple optical resonators may be used to reduce the lasing threshold and provide higher power output. With monolithic integration, more optical devices can be integrated with the tunable laser into the same substrate to produce optical devices that are capable of more complex functions, such as tunable transmitters or waveguide buses.

1 . In a tunable laser system comprising a laser and a resonator having an adjustable refractive index induced tunable resonance wavelength, a method for tuning the wavelength of the tunable laser system comprising: 
 adjusting the refractive index of the resonator by applying an electrical signal to the resonator such that the resonance wavelength of the resonance corresponds to a selected wavelength;    coupling light emissions from the laser into the resonator through evanescent coupling, whereby substantially only the light emissions having a wavelength at the resonance wavelength of the resonator are coupled into the resonator; and    coupling light at the resonance frequency of the resonator from the resonator back into the laser.    
   
   
       2 . The method of  claim 1 , wherein the electrical signal comprises a voltage.  
   
   
       3 . The method of  claim 1 , wherein the electrical signal comprises a current.  
   
   
       4 . The method of  claim 1 , wherein the laser comprises a laser diode.  
   
   
       5 . The method of  claim 4 , further comprising applying a current to the laser diode below a lasing threshold of the laser diode to generate the light emissions.  
   
   
       6 . The method of  claim 5 , further comprising applying enough current to the laser diode so that light at the resonance frequency of the resonator has enough gain to overcome optical losses associated with the system.  
   
   
       7 . The method of  claim 6 , wherein the laser diode has opposing first and second end facets, the light emissions are emitted from the second end facet of the laser diode, light at the resonance frequency of the resonator is coupled from the resonator back into the laser diode through the second end facet, and the method further comprises increasing the current applied to the laser diode until light at the resonance frequency of the resonator becomes lasing and is outputted from the first end facet of the laser diode.  
   
   
       8 . The method of  claim 1 , further comprising: 
 coupling light at the resonance frequency of the resonator from the resonator into a waveguide;    reflecting the light coupled into the waveguide back toward the resonator; and    coupling the reflected light from the waveguide back into the resonator.    
   
   
       9 . The method of  claim 8 , wherein the light in the waveguide is reflected using a mirror.  
   
   
       10 . The method of  claim 8 , wherein the light in the waveguide is reflected using a reflective coating on the waveguide.  
   
   
       11 . The method of  claim 8 , wherein light is coupled into the waveguide through evanescent coupling.  
   
   
       12 . The method of  claim 1 , further comprising adjusting the resonance frequency of the resonator to another selected frequency by changing the electrical signal applied to the resonator.  
   
   
       13 . In a tunable laser system comprising a laser and a waveguide-coupled resonator, the waveguide-coupled resonator comprising first and second waveguides and a resonator having an adjustable refractive index induced tunable resonance wavelength, a method for tuning the wavelength of the tunable laser system comprising: 
 adjusting the refractive index of the resonator by applying an electrical signal to the resonator such that the resonance wavelength of the resonance corresponds to a selected wavelength;    coupling light emissions from the laser into the first waveguide;    coupling the light emissions from the first waveguide into the resonator through evanescent coupling, whereby substantially only the light emissions having a wavelength at the resonance wavelength of the resonator are coupled into the resonator;    coupling light at the resonance frequency of the resonator from the resonator into the second waveguide;    reflecting the light coupled into the second waveguide back toward the resonator;    coupling the reflected light from the second waveguide back into the resonator;    coupling light at the resonance frequency of the resonator from the resonator back into the first waveguide; and    coupling light at the resonance frequency of the resonator from the first waveguide back into the laser.    
   
   
       14 . The method of  claim 13 , wherein the electrical signal comprises a voltage.  
   
   
       15 . The method of  claim 13 , wherein the electrical signal comprises a current.  
   
   
       16 . The method of  claim 13 , wherein the light in the second waveguide is reflected using a mirror.  
   
   
       17 . The method of  claim 13 , wherein the light in the second waveguide is reflected using a reflective coating on the second waveguide.  
   
   
       18 . The method of  claim 13 , wherein the laser comprises a laser diode.  
   
   
       19 . The method of  claim 18 , further comprising applying a current to the laser diode below a lasing threshold of the laser diode to generate the light emissions.  
   
   
       20 . The method of  claim 19 , further comprising applying enough current to the laser diode so that light at the resonance frequency of the resonator has enough gain to overcome optical losses associated with the system.  
   
   
       21 . The method of  claim 20 , wherein the laser diode has opposing first and second end facets, the light emissions are emitted from the second end facet of the laser diode, light at the resonance frequency of the resonator is coupled from the first waveguide into the laser diode through the second end facet, and the method further comprises increasing the current applied to the laser diode until light at the resonance frequency of the resonator becomes lasing and is outputted from the first end facet of the laser diode.  
   
   
       22 . The method of  claim 13 , further comprising adjusting the resonance frequency of the resonator to another selected frequency by changing the electrical signal applied to the resonator.