http://avalon.law.yale.edu/19th_century/ot1862.asp
Here is a link to a treaty between the United States and the Ottoman Empire in 1862. The text of the treaty refers to them as the "Ottoman Empire."
http://www.fas.nus.edu.sg/hist/eia/documents_archive/karlowitz.php
Perhaps a more revealing example from 1699, the Treaty of Karlowitz, which ended the Ottoman invasion of the southern parts of the Holy Roman Empire, refers to the Ottoman Empire by name several times in the treaty. They also refer to the Ottoman leader a few times as "the Sultan of the Turks." Generally, diplomatically, they were referred to as the Ottoman Empire by the Europeans and the Americans. When speaking of the people which the governed, they would be referred to as the ruler of the 'Turks', despite the diverse ethnic makeup of the empire at the time.