Clarinet is one of the instruments played in operas. The clarinet became popular in the late 18th century and 19th century. Caldara's opera "ifigenia in Aulide" in 1718 is mostly likely the first to use the clarinets in an opera. In 1720, Jean Adam Joseph Faber used the clarinet in orchestra, he is known to be the first to use arpeggios on the chalaumeu in an orchestra.
Clarinet writing style, the use of different registers like the arpeggio and notes became popular in opera around 1730. Many clarinetists played solos at operas. Clarinet has evolved over time to become a very important instrument in performances all around the world.
The addition of the clarinet was not overly influential to the opera. However, because clarinets are so versatile, they are important nonetheless. Operas, like any musical production, require a certain level of emotion conveyed.
Clarinets are perfect for this requirement because they can have a soft and demure tone while in the next minute switch over to something that can convey an aggressive or even angry tone.