Optical apparatus which uses a virtually imaged phased array to produce chromatic dispersion
View Patent ↗An optical apparatus for producing chromatic dispersion. The apparatus includes a virtually imaged phased array (VIPA) generator, a mirror and a lens. The VIPA generator receives an input light at a respective wavelength and produces a corresponding collimated output light traveling from the VIPA generator in a direction determined by the wavelength of the input light, the output light thereby being spatially distinguishable from an output light produced for an input light at a different wavelength. The mirror has a cone shape, or a modified cone shape. The lens focuses the output light traveling from the VIPA generator onto the mirror so that the mirror reflects the output light. The reflected light is directed by the lens back to the VIPA generator. In this manner, the apparatus provides chromatic dispersion to the input light. The modified cone shape of the mirror can be designed so that the apparatus provides a uniform chromatic dispersion to light in the same channel of a wavelength division multiplexed light.
1. An apparatus comprising:
a virtually imaged phased array (VIPA) generator receiving an input light at a respective wavelength and producing a corresponding collimated output light traveling from the VIPA generator in a direction determined by the wavelength of the input light;
a reflecting surface reflecting the output light back to the VIPA generator;
a lens or mirror focusing the output light traveling from the VIPA generator onto the reflecting surface so that the reflecting surface reflects the output light, the reflected light being directed by said lens or mirror back to the VIPA generator; and
an angular dispersive element between the VIPA generator and said lens or mirror, the reflecting surface having different curvatures at different positions along a direction perpendicular to a plane which includes the traveling directions of collimated output light from the VIPA generator for input light at different wavelengths, the angular dispersive element having an angular dispersion direction which is perpendicular to said plane, curvature c(y) of the reflecting surface being as follows:
c
(
y
)
=
K
8
f
4
y
4
+
K
Θ
2
f
3
y
3
+
K
Θ
2
-
(
f
-
a
)
2
f
2
y
2
where
y=is a light focusing position on the reflecting surface,
Θ=is an input angle of the input light to the VIPA generator in air,
f=is a focal length of the lens or mirror,
a=is a depth of a center beam waist of the VIPA generator, and
K is a constant so that chromatic dispersion equals −2n 4 K/cλ, with c being the speed of light, λ being wavelength, and n being a refractive index of material forming the VIPA generator.
2. An apparatus as in claim 1 , wherein the angular dispersive element is a grating.
3. An apparatus as in claim 2 , further comprising:
a quarter wave plate canceling polarization dependence of the grating.
4. An apparatus as in claim 2 , wherein the reflecting surface is movable to change a dispersion amount.