Optical devices employing an optical thresholder

Abstract

An optical device for use with an optical input beam comprises and optical thresholding device having a predetermined threshold level, and is positioned along an optical path defined by the propagation direction of the optical input beam. A source generates a control beam through the optical thresholding device, wherein if the combined intensity of the optical input beam and the control beam is large enough to exceed the threshold level of the thresholding device, the optical beam passes through he thresholding device. The thresholding device attenuates the optical beam as it passes therethrough. In a preferred embodiment, the optical thresholding device is a saturable absorber. When the device is configured as an optical comparator, the intensity of the optical input beam is large enough to exceed the threshold level of the thresholding device, the thresholding device saturates and turns transparent so that the control beam passes through the thresholding device as an optical indicator beam and the optical input beam passes through the thresholding device. When configured as an optical signal attenuator and the intensity of the optical input signal is negligible compared to that of the control beam the combined intensity of the optical input signal and the control beam do not saturate the thresholding device.

What is claimed is:  
     
         1 . An optical device for use with an optical input beam, comprising: 
 an optical thresholding device having a predetermined threshold level, and being positioned along an optical path defined by the propagation direction of the optical input beam;    means for generating a control beam through said optical thresholding device, wherein if the combined intensity of the optical input beam and the control beam is large enough to exceed the threshold level of said thresholding device, the optical beam passes through the thresholding device, said thresholding device attenuating the optical beam as it passes therethrough.    
     
     
         2 . The device according to  claim 1  wherein the control beam and the input beam impinge the optical thresholding device such that they do not interfere with each other.  
     
     
         3 . The device according to  claim 1  wherein the optical thresholding device is a saturable absorber, said optical beam and said control beam saturating the saturable absorber and making it transparent if the combined intensity of said beams is greater than the threshold level of the absorber.  
     
     
         4 . The device according to  claim 3  wherein the saturable absorber provides an optical indicator beam if the optical input beam saturates the absorber.  
     
     
         5 . The device according to  claim 1 , wherein it comprises an optical comparator.  
     
     
         6 . The device according to  claim 1  wherein the intensity of said optical beam and said control beam are below the threshold level, the intensity of said control beam serving to control the transmission of said saturable absorber and hence the attenuation of the intensity of said optical beam.  
     
     
         7 . The device according to  claim 6  wherein it comprises an optical signal attenuator.  
     
     
         8 . An optical comparator for comparing an optical input beam with a threshold level, comprising: 
 an optical source for generating a control beam; and    an optical thresholding device having a predetermined threshold level, said optical thresholding device being positioned along an optical path defined by the propagation direction of the optical input beam and also receiving the control beam, wherein if the intensity of the optical input beam is large enough to exceed the threshold level of a thresholding device, the thresholding device saturates and turns transparent so that the control beam passes through the thresholding device as an optical indicator beam and the optical input beam passes through the thresholding device.    
     
     
         9 . The optical comparator according to  claim 8  wherein said optical thresholding device comprises a saturable absorber.  
     
     
         10 . The optical comparator according to  claim 8  and further including means for decreasing the predetermined threshold level.  
     
     
         11 . The optical comparator according to  claim 10  wherein said means for decreasing comprises a laser for emitting a threshold control beam into said optical thresholding device.  
     
     
         12 . The optical comparator according to  claim 8  wherein the control beam and the input beam impinge said optical thresholding device at an orientation relative to each other so that they do not interfere with each other in the thresholding device.  
     
     
         13 . The optical comparator according to  claim 8  wherein the input beam and the control beam have substantially the same wavelength.  
     
     
         14 . The optical comparator according to  claim 8  and further including a photodetector that is responsive to the optical indicator signal, said photodetector generating an electrical signal indicative of the indicator signal.  
     
     
         15 . The optical comparator according to  claim 14  and further including means for decreasing the predetermined threshold level.  
     
     
         16 . The optical comparator according to  claim 15  wherein said means for decreasing comprises a laser for emitting a threshold control beam into said optical thresholding device.  
     
     
         17 . An optical comparator for comparing an optical input beam with a threshold level, comprising: 
 a semiconductor saturable absorber; and    an electrical measuring system, said semiconductor saturable absorber having a predetermined threshold level, being positioned along an optical path defined by the propagation direction of the optical input beam, and generating charge carriers in response to the input beam, wherein if the intensity of the optical input beam is large enough to exceed the threshold level of a semiconductor saturable absorber, the saturable absorber saturates and turns transparent allowing the optical input beam to pass through the absorber, and said electrical measuring system provides an electrical measurement of the charge carriers generated by the semiconductor saturable absorber as an indicator signal of the input beams intensity.    
     
     
         18 . The device according to  claim 13  wherein said semiconductor saturable absorber is configured as a reversed bias p-i-n structure.  
     
     
         19 . A method of comparing an optical input beam to a threshold, comprising: 
 positioning an optical thresholding device having a predetermined threshold level along an optical path defined by the propagation direction of the optical input beam;    saturating said optical thresholding device if the intensity of the input beam is above the threshold level of the thresholding device, wherein if the intensity of the input beam is above the threshold level of the thresholding device, the thresholding device saturates and turns transparent allowing the input beam to pass therethrough with some attenuation; and    providing an indicator signal when the thresholding device has been saturated by the input beam.    
     
     
         20 . A method of comparing an optical beam to a threshold as recited in  claim 19  and further including selectively lowering the threshold level of said optical thresholding device.  
     
     
         21 . An optical signal attenuator for use with an optical input beam and a control beam comprising: 
 means for generating a control beam; and    an optical thresholding device having inputs for receiving the optical input beam and the control beam and a transmission characteristic that varies with the combined intensity of the optical input beam and the control beam, wherein the intensity of the optical input beam is attenuated as it passes through said optical thresholding device.    
     
     
         22 . The optical attenuator according to  claim 21  wherein the combined intensity of the optical input signal and the control beam is less than that necessary to saturate said optical thresholding device.  
     
     
         23 . The optical attenuator according to  claim 21  wherein the intensity of the optical input signal is substantially less than the intensity of the control beam.  
     
     
         24 . The optical attenuator according to  claim 23  wherein the transmission characteristic varies generally monotonically over a range of intensities of the control beam.  
     
     
         25 . The optical attenuator according to  claim 21  wherein the optical threshold device is a saturable absorber.