A beam splitter formed by laminating a plurality of optical films on a glass substrate having a refractive index of 1.51.+-.0.10. The optical films are first, second, third, fourth, and fifth layers laminated in this order from the glass substrate. The first layer has a refractive index of 1.44.+-.0.10 and an optical film thickness of 0.05-0.15; the second layer has a refractive index of 1.68.+-.0.10 and an optical film thickness of 0.01-0.10; the third layer has a refractive index of 1.44.+-.0.10 and an optical film thickness of 0.50-0.60; the fourth layer has a refractive index of 2.23.+-.0.10 and an optical film thickness of 0.25-0.35; and the fifth layer has a refractive index of 1.44.+-.0.10 and an optical film thickness of 0.25-0.35. The optical film thickness means a relative value represented by n.times.d/.lambda. where n denotes a refractive index; d denotes an actual film thickness, and .lambda. denotes a wavelength deciding the center of a wavelength band. The beam splitter can reduce the polarization dependency of a branching ratio with a beam incident angle of 22.5.degree..
Described herein is an optical multilayered-film filter which provides less interference and a good optical characteristic and is high in productivity. The optical multilayered-film filter wherein dielectric thin films are stacked on each other in a multilayer form in a single direction, comprises a refractive-index inclined laminated portion in which refractive indices of dielectric thin-film layers are successively inclined and changed in a laminating direction, and an alternately-laminated portion in which a dielectric thin-film layer having a high refractive index and a dielectric thin-film layer having a low refractive index are alternately laminated on each other.
A polarizing filter has a laminate structure: wherein one to four layers of first dielectric thin films 1 and one to four layers of second dielectric thin films 2 are alternately laminated on a transparent flat substrate 10 to form the laminate structure, the layers of second dielectric thin films 2 having a refractive index lower than that of the first dielectric thin films 1 with respect to the wavelength of incident light; wherein one layer of the third dielectric thin film 3 having a refractive index intermediate between the refractive indices of the first and second dielectric thin films with respect to the wavelength of incident light is laminated on a surface of the laminate structure.In an optical device using the polarizing filter, the angle of incidence is set to be in a range of from 20 to 70 degrees.
A polarizing filter has a laminate structure: wherein one to four layers of first dielectric thin films 1 and one to four layers of second dielectric thin films 2 are alternately laminated on a transparent flat substrate 10 to form the laminate structure, the layers of second dielectric thin films 2 having a refractive index lower than that of the first dielectric thin films 1 with respect to the wavelength of incident light; wherein one layer of the third dielectric thin film 3 having a refractive index intermediate between the refractive indices of the first and second dielectric thin films with respect to the wavelength of incident light is laminated on a surface of the laminate structure. In an optical device using the polarizing filter, the angle of incidence is set to be in a range of from 20 to 70 degrees.
An optical data link using a single optical fiber for bi-directional optical communication. Bi-direction optical transceivers couple to the single optical fiber having two optical channels of communication. An optical subassembly in each optical transceiver to multiplex an optical transmit signal and demultiplex an optical receive signal within the bi-direction optical transceiver. The optical subassembly includes an optical block with an optical filter to reflect at least one wavelength of light and to allow passage of another wavelength of light. Embodiments of the optical block with the optical filter are described.
