Lens cap for optical module, optical module, and method for manufacturing lens cap for optical module

The invention provides a lens cap for an optical module, an optical module, and a method for manufacturing a lens cap for an optical module which can prevent an optical output variation and secure airtightness. The lens cap for an optical module includes: a barrel of a metal material; and a press lens of glass and held in the barrel. The coefficient of linear expansion of the glass is 6 to 8 ppm/K, and the coefficient of linear expansion of the metal material is at least 10 ppm/K at 150 DEG C to 800 DEG C and no more than 8 ppm/K at up to 100 DEG C or below.