High Frequency Laser Modulation

Question

I am looking at doing some phase-shift lidar experimentation. To get good accuracy, all the papers suggest that I need to be modulating the laser diode sinusoidally at ~200MHZ. I am finding virtually no laser diodes that have this sort of speed listed as a modulation capability. Does anyone know what the main drawbacks of driving a standard (cheap/plentiful) laser diode at that sort of speed would be? I think from memory that a DVD-R laser is modulated in the realm of 10MHZ, so I was thinking of starting with a laser like that, provided I can find a new one not sourced from a DVD Drive.

Thanks.

Answer 1

Solidstate lasers have internal capacitance (typically junction) and on times. Modulating something quickly with an internal capacitance will tend to just result with a smaller amplitude or not coming on at all. I don't know much about the diodes in a DVD drive, I'd guess it depends on the drive, however, there are plenty available online that do switch faster: https://www.arrow.com/en/products/plt5520-b1-2-3/osram-opto-semiconductors?gclid=Cj0KCQjw-Mr0BRDyARIsAKEFbef1wvwnZJ7LD2As3XJQe2lQ_xlWibDgCYdb348_OCXGmHE6qhXRzKYaArtDEALw_wcB

If you don't already know Digikey and Mouser are the big box stores of choice for this sort of thing, but if you need something special and are willing to pay out your nose, thor labs probably has it.

Answer 2

You can buy surplus telcom lasers at 1300 or 1550nm that can do GHz bandwidth. Look for lasers marked for "direct modulation". They're often so cheap I've seen them given away by the crate when people had surplus.