Tunable spectroscopic source with power stability and method of operation

Abstract

A laser system for a spectroscopic catheter system utilizes an overmoded cavity in order to reduce mode hoping induced power fluctuations during wavelength scanning. In the preferred embodiment, a semiconductor gain medium is used to reduce cost. A fiber pigtail is used to define the laser cavity, which has a tight cavity mode spacing of less that 15 Gigahertz. A diffraction grating is used as the tuning element. A cylindrical lens is used to reduce alignment tolerances and thereby increase manufacturability.

1 . A tunable laser source having stable output power during wavelength scanning, the source comprising: 
 a laser cavity including:    a wavelength selector for scanning a passband over a scan band, and    a laser gain chip providing gain to longitudinal modes of the laser cavity within a gain bandwidth provided by the passband; and    wherein the laser cavity is characterized by a cavity longitudinal mode spacing that is more than two times smaller than the gain bandwidth.    
   
   
       2 . A tunable laser source as claimed in  claim 1 , wherein the wavelength selector comprises a diffraction grating.  
   
   
       3 . A tunable laser source as claimed in  claim 1 , wherein the wavelength selector comprises a bulk diffraction grating.  
   
   
       4 . A tunable laser source as claimed in  claim 1 , wherein the wavelength selector comprises a Bragg grating.  
   
   
       5 . A tunable laser source as claimed in  claim 1 , wherein the laser cavity further comprises an optical fiber pigtail coupling the laser gain chip and the wavelength selector.  
   
   
       6 . A tunable laser source as claimed in  claim 1 , further comprising an output coupler for coupling laser light out of the laser cavity.  
   
   
       7 . A tunable laser source as claimed in  claim 6 , wherein the output coupler provides the laser light to a catheter for insertion into a patient.  
   
   
       8 . A tunable laser source as claimed in  claim 1 , wherein the laser gain chip comprises a semiconductor optical amplifier.  
   
   
       9 . A tunable laser source as claimed in  claim 1 , wherein the laser gain chip comprises a reflective semiconductor optical amplifier.  
   
   
       10 . A tunable laser source as claimed in  claim 1 , wherein an optical length of the laser cavity is greater than 10 centimeters.  
   
   
       11 . A tunable laser source as claimed in  claim 1 , wherein an optical length of the laser cavity is greater than 50 centimeters.  
   
   
       12 . A tunable laser source as claimed in  claim 1 , wherein an optical length of the laser cavity is greater than 1 meter.  
   
   
       13 . A tunable laser source as claimed in  claim 1 , wherein the cavity mode spacing is less than 15 Gigahertz.  
   
   
       14 . A tunable laser source as claimed in  claim 1 , wherein the cavity mode spacing is less than 1.5 Gigahertz.  
   
   
       15 . A tunable laser source as claimed in  claim 1 , wherein the gain bandwidth is greater than 10 Gigahertz.  
   
   
       16 . A tunable laser source as claimed in  claim 1 , wherein the gain bandwidth is greater than 50 Gigahertz.  
   
   
       17 . A tunable laser source as claimed in  claim 1 , wherein the gain bandwidth is greater than 100 Gigahertz.  
   
   
       18 . A tunable laser source as claimed in  claim 1 , further comprising at least two laser gain chips.  
   
   
       19 . A tunable laser source as claimed in  claim 1 , wherein the laser gain chip is contained within a pigtailed hermetic package.