I assume you must be asking about what's now called the "Ottoman Decline Thesis" - the idea that after the death of Suleiman the Magnificent in 1566 the Ottoman Empire entered a period of stagnation and decline from which it was never able to recover until its dissolution in the twentieth century. This is not something which professional historians believe in any longer. To quote Jane Hathaway, The Arab Lands under Ottoman Rule, (2008), pp. 8-9.

Historians of the Ottoman Empire have rejected the narrative of decline in favor of one of crisis and adaptation: after weathering a wretched economic and demographic crisis in the late sixteenth and early seventeenth centuries, the Ottoman Empire adjusted its character from that of a military conquest state to that of a territorially more stable, bureaucratic state whose chief concern was no longer conquering new territories but extracting revenue from the territories it already controlled while shoring up its image as the bastion of Sunni Islam.

Now it's obviously much more complicated than this, but the simple answer to your question is that the Ottoman empire did not decline and fall behind Europe after the sixteenth century. Numerous historical studies have been produced showing that the empire was very much a dynamic and versatile state throughout the seventeenth century. Its defeats in war against the Habsburgs at the end of the century were a result not of military inferiority, but of having to fight on multiple fronts at once against numerous enemies - the Ottomans were at war simultaneously with the Habsburgs, Venice, Poland-Lithuania and Russia.

On this see Rhoads Murphey, Ottoman Warfare: 1500-1700, (New Brunswick: Rutgers University Press, 1999), 10. and Gábor Ágoston, Guns for the Sultan: Military Power and the Weapons Industry in the Ottoman Empire, (Cambridge: Cambridge University Press, 2005) pp. 200-201.