Welcome to Flyer Talk lahiruwan

Lufthansa's minimum connection time (MCT) for LH-LH at FRA is 1 hour. However for Sri Lankan to Lufthansa the MCT is likely to be longer (for starters I think Sri Lankan uses the other terminal).

If you are on separate tickets then misconnection risk is yours, Lufthansa is under no obligations if you miss your onward flight - ie your ticket may be cancelled (depending on fare rules) requiring purchase of a last minute ticket (at high fares). On separate tickets you are will only be able to check in at Colombo for the flight to Frankfurt and will need to check in for Lufthansa at Frankfurt. Any checked luggage might be able to be through checked for Lyon (assuming Sri Lankan and Lufthansa have interline agreement and 1:40 is above the MCT) or might not.

If you are on a single ticket and 1:40 is above the MCT for Sri Lankan to Lufthansa at Frankfurt, then you will be protected in the event of misconnection. If you are on a single ticket and 1:40 is below the MCT for Sri Lankan to Lufthansa then you should be advised of this fact and will not have protection for misconnection if you insist on those flights.

Personally I'd allow more time and take a later flight to Lyon. Frankfurt is a huge airport and it will take some time to transfer (especially if unfamiliar with the layout as it is rather confusing). You will clear immigration at Frankfurt (whether airside or landside transfer) and a security check (or more than one if navigate the wrong way through the terminals). If you have checked bags and can only check them as far as Frankfurt then you'll need to allow additional time to claim your bags, transfer between terminals landside and then re-check in.