Driving a laser diode

Hi all,

I've searched the forum and read all the related posts, but still felt it pertinent to make a new post with the specific information for my project.

I'm looking to create a mini demonstration of free-space optical communication using an arduino to send serial data to a laser diode, which will transmit to a receiver and do serial into another arduino.

My laser diode is here: http://www.thorlabs.us/thorcat/QTN/L1550P5DFB-SpecSheet.pdf

Operating current typical is 20mA, at 1.1v. I obviously don't want to damage the arduino or the diode, so what would be the best way to drive this?


Arduino output with current limit resistor: (5V - 1.1)/.02A = 195 ohm, so use a 200 ohm. What's the 2nd diode in the package for?

Thanks for the reply, CrossRoads!

I think the photodiode is there to check if the laser diode is working? It's interesting to me that they're in the same package, but we can disregard for this purpose, we'll only be using the laser diode.

The photodiode I'll be using on the receiving end is this: http://www.thorlabs.us/thorcat/TTN/FGA01-SpecSheet.pdf

I'll have to figure out how to bring the output signal up to proper TTL levels for the arduino to read. Thanks another problem to solve!

The purpose of the photodiode - as I understand it - is to measure the output of the laser, and to adjust the current based on that (how that works or how you design the circuit, I don't know).

Run the Vo from the circuit into input of a comparator - connect the other input to a variable DC source (trimpot between +5 & Gnd). Then you adjust the trimpot to where Vo trips the comparator and flips the output from 0 to 5V, or 5V to 0, depending on what you have connected where; Vo on + > then trimpot on -, output goes high. Vo on - > trimpot on +, output goes low.