High End FiberOptic Transmitter and Reciever Circuit Design

[Aemornion]

Hello Everyone,
I joined this forum in the hopes obtaining some circuit design assistance relating to fiber optic Transmitters and Recievers.

I have obtained some higer end Rx/Tx units and I am having some difficulty figuring out how to drive them.
I am tryng to drive Serial (9600) data through them.
Their are various reasons I am not converting to RS232 and then fiber. The most prominant is power requirments and space.

I was able to get this to work with the low end industrial fiber Rx/Tx modules. But in the end result I am forced to use 1350 and 1550 nm fiber forcing me to acquire these particular modules.

The end result will be a microcontroller running inside a high voltage test unit. Which has existing fibers I need to maintain.

I have attached the data sheets for the Tx/Rx modules.

I have a pretty good grasp on the Tx module.
It has a reverse photo diode, So i was planning on using a bjt tied to a differential opamp.
The signal is input via a NAND gate to a voltage divider, and decoupling cap to the cathode of the laser. When the signal is active the laser cathode will fall low, allowing for a current to flow. Then that current is regulated by a BJT. the regulation occures via the reverse photodiode, is compared to a reference via a differential op-amp and output to the bjt to maintan a constant laser power.

Does this seem sane?

For the Rx module I am lost
It has 5 pins
#1 VR : PD bias
#2 OUT+ : Positive output
#3 OUT- : Negative output
#4 Vdd : Preamp bias
#5 GND : Case ground
I would prefer to get it to a single output and not a differential output.
But I am lost in how to go about properly biasing the preamp and photodiode etc.

Any help/suggestions are greatly appreciated.


My data rate does not need to be astronomically high, All I am trying to to is read voltage and temp data. but later we might try and add more functionality. So keeping it with a digital communication like serial would be preferable.

Thank you for any help and assistance which is offered.
Cheers

 

[KlausST]

Hi,

i´m sorry i can´t haelp you with your fiber optic devices. This is because you didn´t write the device names and vendor and i can´t get access to your attachements. Please check if the attachements working OK.

*******

If you can switch from high end fiber cable to POF then i can recommend AVAGO´s HFBR system.
I have good experience with it in high EMV industrial environment. Up to Mbauds up to some 10 meters.
It´s easy to use.


Klaus

 

[Aemornion]

Klaus,
Thank you for the reply, and thanks for pointing out the error with the file upload.
It looks like my work machine had the pdf's encrypted or something.
My Apologies.

The files have been successfully uploaded to the EDABoard Forum servers, they are available in the initial post as attachments.

The modules are made by Sumitomo electric.
You have to email and request the data sheets, so the link above is the best way for now.
I have the weblink at work for the general unit info which ill post it tomorrow.
I could not find it on their site just now.

Unfortunately, I don't think I can move to an 850nm system. We have a large collection of existing fiber for data collection in a different capacity, which are all the 1350 and 1550 wavelengths and I already have 10 each of the Tx and Rx modules. So I really want to explore trying to use what I have on hand before moving away from them completely. That fully integrated module does seem very tempting though. =)

Thank you for your help.
Cheers

 

[KlausST]

Hi,

Did you try to contact the manufacturer regarding your problems?

Klaus

 

[Aemornion]

Klaus,

Yes, tried contacting them and got absolutly no where. Not a very plesant group.

Ill keep digging around and hopefully Ill figure something out.


Cheers