A spectral filter (1100; 1200; 1300; 1400; 1500; 1600; 1700) comprising: a plurality of first reflective layers (131, 132; 431; 432; 531, 533; 851, 852) spaced apart from each other and facing each other; and at least a first cavity (144; 348; 444; 544; 644; 744; 844) having a first thickness, a second cavity (143; 347; 443; 543; 643; 743; 843) having a second thickness, a third cavity (142; 346; 442; 542; 642; 742; 842) having a third thickness and a fourth cavity (141; 345; 441; 541; 641; 741; 841) having a fourth thickness provided between the plurality of first reflective layers (131, 132; 431; 432; 531, 533; 851, 852), wherein the first to fourth thicknesses are different from one another decreasing from the first thickness subsequently to the fourth thickness, the first thickness of the first cavity (144; 348; 444; 544; 644; 744; 844) determined according to a first center wavelength, the second thickness of the second cavity (143; 347; 443; 543; 643; 743; 843) determined according to a second center wavelength, the third thickness of the third cavity (142; 346; 442; 542; 642; 742; 842) determined according to a third center wavelength, and the fourth thickness of the fourth cavity (141; 345; 441; 541; 641; 741; 841) determined according to a fourth center wavelength, wherein each of the first cavity (144; 348; 444; 544; 644; 744; 844), the second cavity (143; 347; 443; 543; 643; 743; 843), the third cavity (142; 346; 442; 542; 642; 742; 842), and the fourth cavity (141; 345; 441; 541; 641; 741; 841) includes a plurality of etch stop layers (151, 152; 351-353; 451, 452) having a constant fifth thickness and the first cavity (144; 348; 444; 544; 644; 744; 844) has two or more dielectric layers of a plurality of dielectric layers (161, 162; 361-363, 461, 462) having a sixth thickness, the second cavity (143; 347; 443; 543; 643; 743; 843) has one or more dielectric layers of the plurality of dielectric layers (161, 162; 361-363, 461, 462) having a seventh thickness, the third cavity (142; 346; 442; 542; 642; 742; 842) has one or more dielectric layers of the plurality of dielectric layers (161, 162; 361-363, 461, 462) having an eighth thickness, and the fourth cavity (141; 345; 441; 541; 641; 741; 841) has no or one dielectric layer of the plurality of dielectric layers (161, 162; 361-363, 461, 462) having a ninth thickness, wherein the sixth thickness, the seventh thickness, the eighth thickness and the ninth thickness differ from each other according to the first center wavelength of the first cavity, the second center wavelength of the second cavity, the third center wavelength of the third cavity and the fourth center wavelength of the fourth cavity. a plurality of first reflective layers (131, 132; 431; 432; 531, 533; 851, 852) spaced apart from each other and facing each other; and at least a first cavity (144; 348; 444; 544; 644; 744; 844) having a first thickness, a second cavity (143; 347; 443; 543; 643; 743; 843) having a second thickness, a third cavity (142; 346; 442; 542; 642; 742; 842) having a third thickness and a fourth cavity (141; 345; 441; 541; 641; 741; 841) having a fourth thickness provided between the plurality of first reflective layers (131, 132; 431; 432; 531, 533; 851, 852), wherein the first to fourth thicknesses are different from one another decreasing from the first thickness subsequently to the fourth thickness, the first thickness of the first cavity (144; 348; 444; 544; 644; 744; 844) determined according to a first center wavelength, the second thickness of the second cavity (143; 347; 443; 543; 643; 743; 843) determined according to a second center wavelength, the third thickness of the third cavity (142; 346; 442; 542; 642; 742; 842) determined according to a third center wavelength, and the fourth thickness of the fourth cavity (141; 345; 441; 541; 641; 741; 841) determined according to a fourth center wavelength, wherein each of the first cavity (144; 348; 444; 544; 644; 744; 844), the second cavity (143; 347; 443; 543; 643; 743; 843), the third cavity (142; 346; 442; 542; 642; 742; 842), and the fourth cavity (141; 345; 441; 541; 641; 741; 841) includes a plurality of etch stop layers (151, 152; 351-353; 451, 452) having a constant fifth thickness and the first cavity (144; 348; 444; 544; 644; 744; 844) has two or more dielectric layers of a plurality of dielectric layers (161, 162; 361-363, 461, 462) having a sixth thickness, the second cavity (143; 347; 443; 543; 643; 743; 843) has one or more dielectric layers of the plurality of dielectric layers (161, 162; 361-363, 461, 462) having a seventh thickness, the third cavity (142; 346; 442; 542; 642; 742; 842) has one or more dielectric layers of the plurality of dielectric layers (161, 162; 361-363, 461, 462) having an eighth thickness, and the fourth cavity (141; 345; 441; 541; 641; 741; 841) has no or one dielectric layer of the plurality of dielectric layers (161, 162; 361-363, 461, 462) having a ninth thickness, wherein the sixth thickness, the seventh thickness, the eighth thickness and the ninth thickness differ from each other according to the first center wavelength of the first cavity, the second center wavelength of the second cavity, the third center wavelength of the third cavity and the fourth center wavelength of the fourth cavity.