Optical interference bandpass filter
An optical filter includes a substrate and a filter film attached on the substrate. The filter film has alternate layers of high reflective layers and low reflective layers to form a plurality of Fabry-Perot resonators. A basic optical thickness of the high reflective layers and the low reflective layers is one fourth a central wavelength (λ 0 /4) of incident ray, and each of the Fabry-Perot resonators has two high reflector films and a spacer between the high reflector films. The spacers in the Fabry-Perot resonator, which is most proximal to the substrate, and in the Fabry-Perot resonator, which is most distal to the substrate, have an optical thickness respectively in a range between four times the basic optical thickness and fourteen times the basic optical thickness.
1. An optical filter, comprising:
a substrate;
a filter film attached on the substrate having alternating layers of high reflective layers and low reflective layers to form a plurality of Fabry-Perot resonators, wherein a basic optical thickness of the high reflective layers and the low reflective layers is one fourth a central wavelength (λ 0 /4) of incident ray, and where each of the Fabry-Perot resonator high reflective layers has two high reflector layer films and
said low reflective layers have a low reflective layer spacer where said low reflective layer spacers are between the high reflector layer films;
wherein the low reflective layer spacers in the Fabry-Perot resonator which is most proximal to the substrate, and in the Fabry-Perot resonator which is most distal to the substrate, have an optical thickness respectively in a range between four times the basic optical thickness and fourteen times the basic optical thickness and
wherein a sequence of the optical filter is:
H(LH)^2 AL (HL)^3; H(LH)^3 4L (HL)^3; H(LH)^4 6L (HL)^4; H(LH)^3 6L (HL)^3; H(LH)^4 6L (HL)^4; H(LH)^3 6L (HL)^3; H(LH)^4 6L (HL)^4; H(LH)^3 4L (HL)^3; H(LH)^3 BL (HL)^2 H; Ns
wherein H indicates a high reflective layer with a basic optical thickness (λ 0 /4);
L indicates a low reflective layer with a basic optical thickness (λ 0 /4);
Ns indicates the substrate;
4≦A≦14, and 4≦B≦14;
A indicates times the basic optical thickness of the low reflective layer spacer which is most proximal to the substrate; and
B indicates times the basic optical thickness of the low reflective layer spacer which is most distal to the substrate.
2. The optical filter as defined in claim 1 , wherein the optical thickness of the low reflective layer spacer in the Fabry-Perot resonator which is most proximal to the substrate, is selected from the group consisting of four times the basic optical thickness, six times the basic optical thickness, eight times the basic optical thickness, ten times the basic optical thickness, twelve times the basic optical thickness, and fourteen times the basic optical thickness.
3. The optical filter as defined in claim 2 , wherein the optical thickness of the low reflective layer spacer in the Fabry-Perot resonator which is most distal to the substrate, is selected from the group consisting of four times the basic optical thickness, six times the basic optical thickness, eight times the basic optical thickness, ten times the basic optical thickness, twelve times the basic optical thickness, and fourteen times the basic optical thickness.
4. The optical filter as defined in claim 1 , wherein the central wavelength of the incident rays is 1530 nanometers.
5. The optical filter as defined in claim 1 , wherein an index of refraction of the low reflective layer is in a range between 1.38 and 1.44.
6. The optical filter as defined in claim 5 , wherein the low reflective layer spacers are made of silica.
7. The optical filter as defined in claim 1 , wherein an index of refraction of the high reflective layer is in a range between 2.1 and 2.7.
8. The optical filter as defined in claim 7 , wherein the high reflective layers are made of tantalum oxide.
9. The optical filter as defined in claim 1 , wherein the A is selected from the group consisting of 4, 6, 8, 10, 12, and 14, and the B is selected from the group consisting of 4, 6, 8, 10, 12.