Abstract:
Techniques to speed the manufacturing process of devices such as optical signal transmitters, transponders, or transceivers by utilizing automated extinction ratio adjustment.

Description:
FIELD 
   The subject matter disclosed herein generally relates to techniques to manufacture fiber optic devices. 
   DESCRIPTION OF RELATED ART 
   Establishing an extinction ratio of optical signals transmitted by a light source of an optical signal transmitter is an important step in the fabrication of such optical signal transmitter. An extinction ratio may be defined as a ratio of two optical power levels, P 1 /P 2 , of a signal generated by an optical signal source, where P 1  is the optical power level generated when the light source is “on,” and P 2  is the power level generated when the light source is “off.” 
     FIG. 1  depicts a conventional system that may be used to determine an extinction ratio of optical signals output by an optical signal transmitter. A conventional technique to establish a desired extinction ratio may involve an assembly worker using an optical scope  120  to read an extinction ratio of optical signals from optical signal transmitter  110 . The assembly worker may manually tune the impedance level of a potentiometer, which changes the bias current of the optical signal transmitter  110  until a desired extinction ratio is reached. After the desired extinction ratio is reached, the assembly worker may then replace the potentiometer with a resistor that has an impedance value equal to the impedance level of the potentiometer. It is desirable for the fabrication of optical signal transmitters to be as fast as possible. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a conventional system that may be used to determine an extinction ratio of optical signals output by an optical signal transmitter. 
       FIG. 2  depicts in block diagram form an embodiment of the present invention in a test and adjust system, in accordance with an embodiment of the present invention. 
       FIG. 3  depicts in block diagram format an example implementation of a transmitter, in accordance with an embodiment of the present invention. 
       FIG. 4  depicts an example manner to generate a bias current, in accordance with an embodiment of the present invention. 
   

   Note that use of the same reference numbers in different figures indicates the same or like elements. 
   DETAILED DESCRIPTION 
     FIG. 2  depicts in block diagram form an embodiment of the present invention in test and adjust system  200 . One implementation of test and adjust system  200  may include personal computer (PC)  210 , evaluation board  220 , transmitter  230 , and optical scope  240 . 
   One implementation of PC  210  may include a central processing unit (CPU), input/output (I/O) interface device, and memory. PC  210  may intercommunicate with the evaluation board  220  using a coaxial, parallel, serial cable, or wireless connection and may utilize the RS232, Peripheral Component Interconnect (PCI), Universal Serial Bus (USB), Ethernet (IEEE 802.3), IEEE 1394, and/or other communications protocols. 
   Evaluation board  220  may provide intercommunication between transmitter  230  and PC  210 . For example, evaluation board  220  may include a bus to provide intercommunication between transmitter  230  and PC  210 . The bus of evaluation board  220  may utilize, for example, an inter-IC (I 2 C), Peripheral Component Interconnect (PCI), Universal Serial Bus (USB), Ethernet (IEEE 802.3), IEEE 1394, and/or other communications protocols. PC  210  may command transmitter  230  to output binary signals in optical signal format to optical scope  240 . In some implementations, the PC  210  may transmit to optical scope  240  a binary signal pattern that PC  210  commands transmitter  230  to output. Optical scope  240  may measure the extinction ratio of optical signals output by transmitter  230 . 
   In accordance with an embodiment of the present invention, PC  210  may program an extinction ratio characteristic of optical signals output by transmitter  230 . For example, a suitable extinction ratio may be one that minimizes a bit error rate of optical signals transmitted by the transmitter  230 , enables the optical signals to reach a desired distance, and minimizes the dispersion penalty. In one embodiment, a person may program PC  210  with a desired extinction ratio. 
     FIG. 3  depicts in block diagram format an example implementation of transmitter  230 , in accordance with an embodiment of the present invention. Transmitter  230  may include multiplexer (MUX)  312 , driver  314 , laser module  316 , and bus  318 . 
   A transport layer component  311  may provide electrical signals to MUX  312 . Transport layer component  311  may provide electrical signals in a format in accordance with Synchronous Optical Network (SONET), Optical Transport Network (OTN), and/or Synchronous Digital Hierarchy (SDH). With respect to such electrical signals, transport layer component  311  may perform media access control (MAC) management in compliance for example with Ethernet; framing and wrapping in compliance for example with ITU-T G.709; and/or forward error correction (FEC) processing, for example in accordance with ITU-T G.975; and/or other layer  2  processing. 
   MUX  312  may receive electrical signals in parallel format and provide such electrical signals in a serial format. Driver  314  may receive the electrical signals from MUX  312  in serial format and amplify such signals. Laser module  316  may convert electrical signals from driver  314  into optical format. Laser module  316  may transmit optical signals, for example, to an optical network which may comply, for example, with SONET, OTN, and/or SDH. 
   In accordance with an embodiment of the present invention, optical signals output by laser module  316  may have an extinction ratio that is tunable by PC  210 . Bus  318  may provide communication between evaluation board  220  and laser module  316 . Bus  318  may utilize for example an inter-IC (I 2 C), Peripheral Component Interconnect (PCI), Universal Serial Bus (USB), Ethernet (IEEE 802.3), IEEE 1394, and/or other communications protocols. In accordance with an embodiment of the present invention, bus  318  may provide a communications path for PC  210  to set the extinction ratio of optical signals output by laser module  316 . 
   In accordance with an embodiment of the present invention,  FIG. 4  depicts one of many possible implementations of laser module  316 . Laser module  316  may include potentiometer  410 , impedance element  415 , laser diode  420 , operational amplifier  425 , capacitive element  430 , and transistor  435 . 
   Impedance element  415  may couple a positive or high bias voltage to the positive input terminal of operational amplifier  425 . Impedance element  415  may be implemented as a fixed impedance device such as a resistor or circuit arrangement providing a desired resistance value. Potentiometer  410  may couple the positive input terminal of operational amplifier  425  to ground or a negative bias voltage. A suitable implementation of potentiometer  410  is a digital potentiometer available from Xicor of San Jose, Calif. In accordance with an embodiment of the present invention, PC  210  may tune the impedance level of potentiometer  410 . 
   Capacitive element  430  may couple the output terminal of operational amplifier  425  to a negative input terminal of operational amplifier  425 . 
   In one implementation, transistor  435  may be implemented as a BJT transistor, although other types and combinations of transistors may be used. The base terminal of transistor  435  may be coupled to the output terminal of operational amplifier  425 . Laser diode  420  may couple a positive bias voltage to the collector terminal of transistor  435 . The laser diode  420  may output optical signals to a single-mode optical fiber (not depicted), which may carry the optical signals to a network. The emitter terminal of transistor  435  may be coupled to ground or a negative bias voltage. 
   A change of the impedance value of potentiometer  410  may change the output voltage from the operational amplifier  425 . A change in the output voltage of operational amplifier  425  may change the magnitude of the laser bias current. A change in the magnitude of the laser bias current may change the extinction ratio of the optical signal generated by transmitter  230 . In accordance with an embodiment of the present invention, PC  210  may adjust the impedance value of potentiometer  410  using bus  318 . 
   The drawings and the forgoing description gave examples of the present invention. The scope of the present invention, however, is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of the invention is at least as broad as given by the following claims.