Electrical – Help designing a circuit to drive a 1550nm DFB LD and use it to modulate an RF signal

circuit-designlaser-diodelaser-driverModulationRF

I need to modulate an RF signal (random sine wave acting as data) using the 1550nm DFB Laser Diode, I need a control circuit to drive the Laser Diode and inject the data to modulate the LD carrier wave. I won't mind if you provide me with the complete circuit just as long as you can explain to me step by step the purpose of each part of it, I'm sure this break down will help those that read this to benefit from this question.

The carrier would be the optical wave and the source signal will be an analog continuous wave, i will be using a function generator to create this wave. This means i will modulate the optical wave using the analog wave and carry the modulated wave through a single mode fiber, at the other end i will have a Photo diode and an oscilloscope to see my original signal.

I will be using a function generator to create the RF signal so there is no restriction to the frequency i can use, it can be low or high. The specs of the LD say that the max operating voltage is 1.7V and the max operating current is 90mA. Since i am not sure what else is needed i can provide more information if necessary,the LD is WSLP-1550-008m-9-DFB.

Thanks in advance.

Datasheet
https://www.dropbox.com/s/00ga6umtnw6re3d/WSLP-1550-008m-9-DFB.pdf?dl=0

Best Answer

What modulation scheme do you intend to use? (Amplitude modulation, Frequency modulation, Pulse-density modulation, etc.).

What type of waveform is your input signal? (sinewave, pulse, triangle, etc.). Are you trying to convey the input's amplitude, frequency, duty-cycle, and/or phase?

For OOK and other pulse-modulation schemes, the laser-diode/LD current would switch from full off to full on (0mA and 75mA for your LD. The 90mA is an absolute max. spec.), at a frequency or width determined by the modulation signal. For FM, the LD would be driven with a pulse train whose frequency changes according to the modulation signal. For AM, the LD would be biased at 50%, and DC-modulated by the input signal.

For OOK, I would use a simple switched current source:

schematic

simulate this circuit – Schematic created using CircuitLab

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