C
colin
- Jan 1, 1970
- 0
Hi,
Im having problems with optical feedback with a pointer type 5mw visible
laser diode,
its modultaed with 1ghz wich is fed via AC coupling and a dc circuit bias
circuit controls the diode current with feedback from the internal
photodiode.
I have to drive the diode quite hard to get it over 1ghz and RF seems to be
interfering
with the optical feedback, increasing the brightness substantualy, the laser
current is increasing.
It also tends to latch on brightly very occasionaly and wont turn off untill
the RF modulation is reduced.
Im not sure if this is due to RF pickup in the 2 transistor circuit as this
would tend to reduce the brightness,
or if the rf picked up on the photodiode is modulating it. The diode has 3v
reverse bias accross it so it shouldnt be rectifing the RF unless its is
seeing more than 3v.
--o---o----------o---------o------- 0v
| | | |
| - .-. |
| ^ pd | | |
| | | | |
| | '-' |
| | | V laser
| .-. .-----o -
--- | | | | |
--- | | V | |
| '-' - | |
| | | | |
| | | | | ||
| | | |< o----||- AC drive
'---o----)---| | ||
| | |\ |
| | | |/
.-. | o---o---|
| | | | | |>
| | | | | |
'-' | | | |
| .-. .-. | .-.
'-->| | | | --- | |
| | | | --- | |
'-' '-' | '-'
| | | |
-----------o-----o---o-----o------- -5v
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Colin =^.^=
Im having problems with optical feedback with a pointer type 5mw visible
laser diode,
its modultaed with 1ghz wich is fed via AC coupling and a dc circuit bias
circuit controls the diode current with feedback from the internal
photodiode.
I have to drive the diode quite hard to get it over 1ghz and RF seems to be
interfering
with the optical feedback, increasing the brightness substantualy, the laser
current is increasing.
It also tends to latch on brightly very occasionaly and wont turn off untill
the RF modulation is reduced.
Im not sure if this is due to RF pickup in the 2 transistor circuit as this
would tend to reduce the brightness,
or if the rf picked up on the photodiode is modulating it. The diode has 3v
reverse bias accross it so it shouldnt be rectifing the RF unless its is
seeing more than 3v.
--o---o----------o---------o------- 0v
| | | |
| - .-. |
| ^ pd | | |
| | | | |
| | '-' |
| | | V laser
| .-. .-----o -
--- | | | | |
--- | | V | |
| '-' - | |
| | | | |
| | | | | ||
| | | |< o----||- AC drive
'---o----)---| | ||
| | |\ |
| | | |/
.-. | o---o---|
| | | | | |>
| | | | | |
'-' | | | |
| .-. .-. | .-.
'-->| | | | --- | |
| | | | --- | |
'-' '-' | '-'
| | | |
-----------o-----o---o-----o------- -5v
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Colin =^.^=