xshou
Member level 2

laser diode matching
An optical guy asked me to see if there is any other way to do laser diode termination. Application is SONET OC192 DML.
Conventionally, just tline and a series resistor with laser diode to make a 50Ohm termination. This approach has the catch of dissipating most power in the resistor.
A modified version is to use a wire-wound resistor to do a complex impedance matching since normally laser diode has some parasitc cap.
The guy hope he can use quarter wavelength Tlines to transform laser diode low impendance into 50Ohm, without the extra resistor. However, I feel uncomfortable with this idea since the matching would occur only in narrow band(I would give a guess of 1G~8G). However, SONET data contains frequency component as low as 40KHz. Severe BW limitation and ISI shall appear in this approach.
Heard a company called hytek claimed to have something called "backmatching", which does not require 50Ohm termination from laser side. No details online.
Any suggestion?
An optical guy asked me to see if there is any other way to do laser diode termination. Application is SONET OC192 DML.
Conventionally, just tline and a series resistor with laser diode to make a 50Ohm termination. This approach has the catch of dissipating most power in the resistor.
A modified version is to use a wire-wound resistor to do a complex impedance matching since normally laser diode has some parasitc cap.
The guy hope he can use quarter wavelength Tlines to transform laser diode low impendance into 50Ohm, without the extra resistor. However, I feel uncomfortable with this idea since the matching would occur only in narrow band(I would give a guess of 1G~8G). However, SONET data contains frequency component as low as 40KHz. Severe BW limitation and ISI shall appear in this approach.
Heard a company called hytek claimed to have something called "backmatching", which does not require 50Ohm termination from laser side. No details online.
Any suggestion?