Abstract

Sine wave rugate index profiles may be superimposed on a slowly varying average index in such a way as to reduce sidelobes over broad spectral regions and at the same time maintain the strength of the stopband reflectance.

© 1989 Optical Society of America

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References

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  1. W. H. Southwell, “Gradient-Index Antireflection Coatings,” Opt. Lett. 8, 584–586 (1983).
    [CrossRef] [PubMed]
  2. W. H. Southwell, “Spectral Response Calculations of Rugate Filters Using Coupled-Wave Theory,” J. Opt. Soc. Am. A 5, 1558–1564 (1988).
    [CrossRef]

1988 (1)

1983 (1)

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Figures (8)

Fig. 1
Fig. 1

Rugate-index profile with 100.5 cycles. na = 2, np = 0.1, and the substrate index = 1.52. (The substrate is on the left in all the figures in this paper. Wavelengths and thicknesses are in units of microns.)

Fig. 2
Fig. 2

Broadband reflectance for the rugate shown in Fig. 1. Since there are no index matching layers, the sidelobes are high everywhere. The peak optical density is 3.25.

Fig. 3
Fig. 3

Rugate with quarterwave matching layers.

Fig. 4
Fig. 4

Reflectance of the rugate with quarterwave matching layers. Sidelobes are suppressed only near the peak. Optical density of the peak is 2.8.

Fig. 5
Fig. 5

Rugate with six-cycle quintic matching regions.

Fig. 6
Fig. 6

Reflectance of the rugate with six-cycle quintic matching layers. The OD is 3.0.

Fig. 7
Fig. 7

Rugate with six-cycle quintic matching layers superimposed with rugate cycles.

Fig. 8
Fig. 8

Reflectance of the rugate with six-cycle quintics with superimposed rugate cycles (rugated quintics). The addition of the superimposed rugates boosted the OD from 3.0 to 3.4 with no increase in thickness or loss of sideband suppression.

Equations (5)

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n = n a + 1 2 n p sin ( 4 π n a d / λ ) ,
OD = log ( T ) ,
n = n L + ( n H n L ) ( 10 t 3 15 t 4 + 6 t 5 ) ,
t = d / T ,
O t = 0 . 5 ( n L + n H ) T .

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