Abstract: An apparatus is used for spectral beam combining laser wavelengths into a combined beam. The apparatus has an integrated, sealed optical assembly that can be installed and replaced in the field. The optical assembly has a housing composed of a material, such as fused silica, transparent to the laser wavelengths. Transmissive gratings are disposed on ends of the housing and have their datums facing the sealed interior. V-grooves on a shelf at one end of the housing are disposed at an angle relative to the first grating. Fiber ends of a fiber array have end caps affixed in the V-grooves and aligned to the datums of the first grating. The fiber ends transmit the laser wavelengths in an array of beams toward the first grating, which diffracts the laser wavelengths to the second grating. In turn, the second grating transmits the laser wavelengths as a combined beam from the second end of the housing.