The following is an excerpt from Wikipedia on the origins of Mimosas
Mimosa IBA Official Cocktail
Type: Wine cocktail
Primary alcohol: Champagne
Standard garnish grenadine, cherries
Standard drinkware Champagne flute
IBA specified ingredients† three parts champagne
two parts orange juice
Preparation Ensure both ingredients are well chilled, then mix together into the glass. Serve cold.
A Mimosa is a cocktail-like drink composed of three parts champagne or other sparkling wine and two parts thoroughly chilled orange juice. It is traditionally served in a tall champagne flute with a morning brunch or to guests at weddings.
The origins of the mimosa are somewhat murky. Allegedly, the drink was invented at the Paris Ritz in 1925, although it bears a striking similarity to another cocktail, the Buck's Fizz, which was introduced in England in 1921, and named after the club in which it was first served. The Buck's Fizz is also traditionally made with champagne and orange juice, although grenadine is sometimes added as well. The name introduced in 1925 comes from the flowers of the mimosa plant, which are yellow and appear slightly frothy from a distance. In Britain, the mixture of orange juice and champagne is still referred to as a Buck's Fizz, while the term mimosa is used in the United States and in most of Europe.
While most bartenders agree that the mimosa should be served in a chilled champagne flute, the exact proportions of the drink are often debated. Some recipes call for a measurement of three parts champagne to one part orange juice, while others prefer a half and half ratio. Both ingredients should be chilled, and some bartenders also serve the drink over ice. Others hotly contest the use of ice, arguing that it dilutes the drink unfavorably. Mimosas are usually served without a garnish, although a twist of orange peel might be considered appropriate.
While a mimosa is traditionally served with champagne, sparkling wines can also be used. For guests who do not wish to consume alcohol, sparkling waters such as Perrier are also acceptable, although you may wish to use coded glasses so that inadvertent consumption of the wrong drink is avoided. In either case, the drink should still be served in a champagne flute so that the bubbles will last longer.