Stimulated Brillouin scattering for fiber-optic links

Abstract

An attenuator/filter is disclosed that is inherently tuned and provides for a stimulated Brillouin scattering effect having a predetermined threshold that fixes the output thereof at a predefined power level. The stimulated Brillouin scattering effect is disclosed as being provided by either a fused silica optical fiber or a fiber-optic ring resonator both of which act as a filter to allow selected frequencies to pass. The SBS threshold is selected to improve the sideband to carrier power ratio which, in turn, determines the modulation depth for the modulated signal.

What I claim is: 
     
       1. An attenuator and filter for reducing, passing and blocking incident optical signals comprising carrier waves having sidebands each having a preselected power level, said attenuator and filter comprising a Brillouin medium having a threshold for creating backward traveling Stoke's waves when subjected to a predetermined power level of incident optical signal, said threshold being selected to increase the sideband to carrier wave power ratio. 
     
     
       2. The attenuator and filter according to claim 1, wherein said predetermined power level is in excess of about 5 milliwatts (mW). 
     
     
       3. The attenuator and filter according to claim 1, wherein said incident optical signal is generated by a laser source having an operating wavelength of about 1550 nm with a linewidth less than about 100 kHz. 
     
     
       4. The attenuator and filter according to claim 3, wherein said Brillouin medium is a dispersion shifted single mode optical fiber comprised of fused silica and has a length of about 25 km. 
     
     
       5. The attenuator and filter according to claim 3, wherein said Brillouin medium is a fiber-optic ring resonator. 
     
     
       6. A method of increasing the power ratio of sidebands to their incident optical carrier waves comprising the steps of: (a) providing a Brillouin medium having a threshold for creating backward traveling Stoke's waves when subjected to a predetermined power level of incident optical signals; and   (b) selecting said threshold at a power level so that optical carrier signals above this threshold are attenuated and the sidebands of said optical carrier waves are allowed to pass.   
     
     
       7. The method of claim 6, wherein said selecting step further comprising selecting the threshold to establish a depth of modulation of the information carried by said incident optical signals. 
     
     
       8. The method of claim 6, wherein said predetermined power level has a value greater than about 5 milliwatts (mW) but less than 50 milliwatts (mW). 
     
     
       9. The method of claim 6, wherein said predetermined power level has a value of about 10 milliwatts. 
     
     
       10. The method according to claim 6, wherein said Brillouin medium is a dispersion shifted single mode optical fiber comprised of fused silica and having a length of about 25 km. 
     
     
       11. The method according to claim 6, wherein said Brillouin medium is a fiber-optic ring resonator. 
     
     
       12. An attenuator and filtering system for reducing, passing and blocking optical signals generated by an optical transmitter and received by an optical receiver, said optical transmitter having a source providing optical carrier waves in excess of about 5 milliwatts (mW) with sidebands thereof and an electro-optical modulator, said optical receiver having a photodetector responsive to received optical carrier waves and said sidebands thereof, said attenuator and filtering system being interposed between said optical transmitter and said optical receiver and comprising a Brillouin medium having a threshold for creating backward traveling Stoke's waves when subjected to a predetermined power level in excess of about 5 milliwatts (mW), said threshold being selected to establish a predetermined ratio of said sidebands and said carrier waves. 
     
     
       13. The attenuator and filtering system according to claim 12, wherein said threshold is further selected to determine the depth of modulation of the information carried by said carrier wave and said sidebands and received by said photodetector.