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Temperature and Aging Compensation of Laser Drive Circuits

IP.com Disclosure Number: IPCOM000111110D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Radcliffe, JK: AUTHOR [+2]

Abstract

The circuit described provides a means of controlling bias and modulation currents to compensate for temperature and aging variations in a laser diode used for optical communications. After the currents are set at the time of manufacture, the bias current required to run the laser at constant average optical power is monitored and used to adjust the modulation current.

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Temperature and Aging Compensation of Laser Drive Circuits

      The circuit described provides a means of controlling bias and
modulation currents to compensate for temperature and aging
variations in a laser diode used for optical communications.  After
the currents are set at the time of manufacture, the bias current
required to run the laser at constant average optical power is
monitored and used to adjust the modulation current.

      It has been shown that both the threshold current and the
differential quantum efficiency of a laser diode are functions of the
ratio of the operating temperature to a parameter of the laser known
as the characteristic temperature.  Furthermore, over the temperature
and operating range of interest laser aging effects may be
represented as changes in the characteristic temperature.  Therefore,
any control system that adequately compensates for temperature also
compensates for aging.

      Examination of a large number of lasers has shown that the
modulation current may be related to the laser bias current by the
approximate relationship:

I(Sub)m = S(1 + .035I(Sub)b)
where

I(Sub)m is laser modulation current
I(Sub)b is laser bias
S is a constant adjusted during manufacturing trim operations

      The  laser's  average  output power and the parameter S are set
during the manufacturing trim of the laser operating  point.    After
that,  a  simple Automatic Power Control (APC) circuit controls Ib to
keep the average output power constant  as  the  laser  changes  with
temperature  and  age.    A  control  circui...