Semiconductor gain medium with multimode and single mode regions

Abstract

A semiconductor gain medium has an optical cavity comprising a multimode region permitting propagation of light with a diverging phase front and a single mode region. An optical cavity is formed by optical feedback within the medium. Preferably, the feedback comprises a combination of a cleaved facet and a grating. The gain medium may be an amplifier or, in addition to the amplifier, may include a resonator cavity, or operate as an unstable resonator.

What is claimed is:  
     
       1. A semiconductor gain medium comprising: 
       a multimode region having a gain portion and providing light propagation with a diverging phase front to a first reflector comprising a cleaved facet;  
       at least one single mode region having a first end coupled to a first end of said multimode region opposite said first reflecting surface  reflector and having at a second end a second reflector comprising a grating reflector formed in said single mode region; and  
       an optical cavity formed between said first and second reflectors.  
     
     
       2. The semiconductor gain medium of claim  1  wherein the first end of said multimode  region having the gain portion is a  flared region extending from said multimode region first end . 
     
     
       3. The semiconductor gain medium of claim  1  wherein said optical cavity establishes a resonant optical cavity. 
     
     
       4. The semiconductor gain medium of claim  1  further comprising means for applying a tuning current to said grating reflector. 
     
     
       5. The semiconductor gain medium of claim  1  further comprising means for applying a pump current to at least a portion of said single mode region. 
     
     
       6. The semiconductor gain medium of claim  1  further comprising means for applying a phasing current to a portion of said single mode region. 
     
     
       7. The semiconductor gain medium of claim  1  further comprising means for applying a tuning current to said grating reflector to adjust the wavelength response of said grating reflector and means for applying a phasing current to a portion of said single mode region to adjust the optical path length of said optical cavity to match the phase of the light propagating in said optical cavity to a selected wavelength. 
     
     
       8. The semiconductor gain medium of claim  1  further comprising means for differential pumping said multimode  region having the gain portion.