I've noticed that fiber-optic SFP modules from Cisco and the like often specify a range of power outputs, such as -3 to -9 dBm. What determines the actual power output we should expect to see from such modules? Is it determined dynamically, or configurable statically, or is it just a manufacturing tolerance and we can't expect to know exactly how much power a given module will emit before we install it?
An example specification is here: http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet0900aecd8033f885.html - see "Table 2. Main Optical Parameters".