Abstract:
A method and apparatus for testing a plurality of optical circuits provides a single broadband light source and means for splitting the light produced by the broadband light source in order to produce a plurality of light beams each of which is directed to a selected one of the plurality of optical circuits.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to apparatus for testing an optical circuit. 
     More particularly, the invention relates to a light source for testing an optical circuit. Light is used to test integrated optic devices. 
     An integrated optic chip (IOC) is made of an electro-optic material whose index of refraction increases or decreases depending on the direction of electric field applied to it. IOC&#39;s are analogous to integrated circuits (IC&#39;s) utilized in semiconductor technology. The signal processing in an IC is totally electric whereas in an IOC it is both optical and electrical. The term “integrated” in “integrated optic chip” implies that the chip has both electrical and optical parts. One or more external electrical signal(s) is applied to one or more electrodes formed on an IOC and the electrical signals change the index of refraction of one or more waveguides adjacent to the electrodes. Changing the index of refraction of a waveguide produces a concomitant change in the intensity and/or phase of light passing through the waveguide. An IOC device is a device which includes one or more IOCs. 
     During the testing of multiple IOC devices, it is common practice to provide a separate laser light source for each IOC device. This procedure is labor intensive, is costly, and can also make it difficult to readily determine when a particular laser is not operating properly. 
     SUMMARY OF THE INVENTION 
     Therefore, it is a principal object of the invention to provide an improved method and apparatus for providing a source of light to test an IOC device or other optical circuit. 
     A further object of the instant invention is to provide a light source of the type described which is relatively inexpensive and which enables variations in the physical properties of the light source to be more readily identified during the testing of an IOC device or other optical circuit. 
     These and other, further and more specific objects and advantages of the invention will be apparent from the following detailed description thereof, taken in conjunction with the drawing, which depicts a light source constructed in accordance with the principles of the invention. 
     Briefly, in accordance with my invention, I provide improved apparatus for directing light into a plurality of optical circuits. The apparatus includes a system for producing broadband light; apparatus for splitting the broadband light into a plurality of beams each comprised of equivalent wavelengths of light; and, apparatus for directing each of the plurality of beams into a different one of the optical circuits. 
     In accordance with another embodiment of my invention, I provide an improved method for directing light into a plurality of optical circuits. The improved method includes the steps of providing a source of broadband light; splitting light from the source into a plurality of light beams each comprised of equivalent wavelengths of light; and, directing each of the plurality of light beams into a different one of said optical circuits. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Turning now to the drawing, which depicts the presently preferred embodiment of the invention for the purpose of illustrating the practice thereof, and not by way of limitation, a source  10  of broadband light includes COMM  14 , power  15 , bias board  11 , laser diode  12 , and coupler/splitter  13 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Laser diode  12  and coupler  13  are interconnected by a loop of erbium-doped fiber. Light from laser diode  12  excites erbium electrons in the fiber loop to a new energy level or orbit. When the electrons decay back to their original energy level or orbit, they emit secondary light. The secondary light is broadband light having a wavelength in the range of 1530 nm to 1560 nm. Broadband light is the amplified spontaneous emission of randomly polarized light. While the range of light wavelengths in broadband light can vary, the range of wavelengths is presently typically about ten to fifty nanometers wide. While the range of wavelengths in the broadband light being utilized is presently from about 1530 nm to 1560 nm, a fiber can be used that is doped with an element(s) or composition other than erbium and that produces a different range of wavelengths, for example 1420 to 1445 nm. The secondary light travels from the erbium fiber  12 A to isolator-splifter unit  13 . Unit  13  includes an isolator which protects laser diode  12  from reflections that travel back through fiber  12 A toward diode  12 . Unit  13  also functions to split the secondary light into a plurality of auxiliary beams each having an equivalent mix of wavelengths in the range of 1530 nm to 1560 nm. Each auxiliary beam is directed from unit  13  down a separate single mode (SM) fiber  16  to a separate polarizer  17 , and is directed from polarizer  17  through a polarization maintaining (PM) fiber  18  into a separate IOC device  19 . I.e., each auxiliary beams from unit  13  is directed to a separate, different IOC device. 
     Output from IOC device  19  travels through single mode fiber  25 , into “bullet” bare fiber adapter  26 , and into multimode fiber  27 . Fiber  27  travels to circuit board enclosure  28 , into and through a RS  232  connector, and to a circuit board  29 . Board  29  is connected to a computer  30 . Computer  30  is used to set controls on board  29  or to otherwise provide board  29  with commands to control the application of direct current to device  19  via circuitry  40  to cable  22  and to control via circuitry  40  the application of RF signals to device  19  via cable  23 . Lead  33  is connected to a thermistor in an aluminum plate contacting and beneath IOC device  19 . 
     Each IOC device has its own separate board  29  which receives output from and controls the testing of the IOC device. The test results for each IOC device are directed by its associated board  29  to computer  30  for storage and analysis. Computer  30  is connected to a monitor  31  and keyboard  32 . 
     The RF cable is connected to device  19  with an SMA (sub miniature adaptor). The SMA is similar to a connector for coaxial cable. The female connector is on device  19 . The male connector is on the end of cable  23 , along with the SMA sleeve which threads over the female connector after the male connector is inserted in the female connector. 
     Device  19  also includes a connector which enables cable  22  to be attached to the connector and device  19 . 
     The circuit board  29  analyzes the input from fiber  27  and sends the results of the analysis to computer  30  for storage. 
     Having described my invention in such terms as to enable those of skill in the art to understand and practice it, and having described the presently preferred embodiments thereof, I claim: