Multicast optical switch
View Patent ↗A multicast optical switch uses a diffractive bulk optical element, which splits at least one input optical beam into sub-beams, which freely propagate in a medium towards an array of directors, such as MEMS switches, for directing the sub-beams to output ports. Freely propagating optical beams can cross each other without introducing mutual optical loss. The amount of crosstalk is limited by scattering in the optical medium, which can be made virtually non-existent. Therefore, the number of the crossover connections, and consequently the number of inputs and outputs of a multicast optical switch, can be increased substantially without a loss or a crosstalk penalty.
1. A method for multi-casting an optical signal, comprising:
(a) splitting a first optical signal into first and second signal portions using a diffractive bulk optical element;
(b) causing the first and second signal portions to propagate in a bulk optical medium; and
(c) directing the first and second signal portions, respectively, propagated in step (b), to first and second output ports, respectively, using first and second directors.
2. The method of claim 1 , wherein step (a) includes using the diffractive bulk optical element to split each of M optical signals, including the first optical signal, into N signal portions, including the first and second signal portions;
wherein step (b) includes propagating the N portions of each of the M optical signals in the bulk optical medium;
wherein step (c) includes using N directors, including the first and second directors, to direct the N signal portions propagated in step (b) to N output ports including the first and second output ports,
wherein each of the N directors receives a corresponding one of the N portions of each of the M optical signals, and
wherein each of the N output ports is coupled to a corresponding one of the N directors and is configured for outputting a corresponding one of the N portions of a selected one of the M optical signals; and
wherein step (c) includes using each of the N directors to switch the corresponding portion of the selected one of the M optical signals into the corresponding one of the N output ports.
3. The method of claim 2 , wherein in step (a), each of the M optical signals is angularly dispersed;
wherein step (b) includes using an angle-to-offset optical element having a focal length, for coupling each of the angularly dispersed N signal portions to one of the N directors, wherein the N directors are laterally offset from each other, and wherein the angle-to-offset optical element is disposed substantially one focal length away from the diffractive bulk optical element, and substantially one focal length away from the N directors.
4. The method of claim 3 , wherein step (c) includes using at least one of the N directors to provide an adjustable attenuation of the corresponding portion of the one of the M optical signals coupled into the corresponding one of the N output ports.
5. The method of claim 3 , wherein each of the N directors comprise a tiltable MEMS mirror of a MEMS mirror array, wherein step (c) includes reflecting the corresponding one of the N portions of each of the M optical signals at a controllable angle by a corresponding tiltable MEMS mirror of the MEMS mirror array, thereby switching the corresponding portion of the one of the M optical signals into the corresponding one of the N output ports.
6. The method of claim 5 , wherein the angle-to-offset optical element comprises a concave mirror.
7. The method of claim 6 , wherein the diffractive bulk optical element is reflective, the method further comprising disposing the MEMS mirror array and the reflective diffractive bulk optical element on a planar carrier.
8. The method of claim 5 , wherein the M optical signals have a center wavelength λ, wherein in step (a), the M optical signals impinging on the diffractive bulk optical element have a beam waist radius ω DOE , and the N portions of each of the M optical signals impinging on the MEMS mirror array in step (c) have a beam waist radius ω MEMS , wherein the focal length of the angle-to-offset optical element is substantially equal to
f
=
π
ω
DOE
ω
MEMS
λ
.
9. The method of claim 8 , wherein ω DOE ≠ω MEMS .
10. The method of claim 8 , wherein the M optical signals are provided by a first waveguide array comprising M optical waveguides, optically coupled to a first microlens array comprising M microlenses, each of which is optically coupled to a corresponding one of the M optical waveguides of the first waveguide array; and
wherein in step (c), portions of the selected one of the M optical signals are directed by the N directors into the N output ports via a second microlens array comprising N microlenses, wherein the second microlens array is optically coupled to a second waveguide array comprising N optical waveguides, each of which is optically coupled to a corresponding one of the N microlenses of the second microlens array.
11. The method of claim 10 ,
wherein each microlens of the first array has a focal length f 1 and is disposed at a distance s 1 from a proximal tip of a corresponding waveguide of the first waveguide array, f 1 and s 1 satisfying the formula
s
1
=
f
1
(
1
+
ω
DOE
2
ω
wvg
1
2
-
z
R
DOE
2
f
1
2
)
,
wherein z R DOE is a Rayleigh length of the M optical signals impinging on the diffractive bulk optical element, and ω wvg1 is a mode radius of a light mode propagating in the waveguides of the first array; and
wherein each microlens of the second array has a focal length f 2 and is disposed at a distance s 2 from a proximal tip of a corresponding waveguide of the second waveguide array, f 2 and s 2 satisfying the formula
s
2
=
f
2
(
1
+
ω
MEMS
2
ω
wvg
2
2
-
z
R
MEMS
2
f
2
2
)
,
wherein z R MEMS is a Rayleigh length of the N portions of each of the M optical beams, reflected from the MEMS mirror array, and ω wvg2 is a mode radius of a light mode propagating in the waveguides of the second array.
12. The method of claim 2 , wherein M≧4 and N≧8.
13. The method of claim 3 , wherein N≧4, wherein the diffractive bulk optical element angularly disperses each of the M optical signals into N 1 rows and N 2 columns of the N portions of each of the M optical signals, wherein N=N 1 ·N 2 .
14. The method of claim 10 , wherein N≧4, wherein the diffractive bulk optical element angularly disperses each of the M optical signals into N 1 rows and N 2 columns of the N portions of each of the M optical signals, wherein N=N 1 ·N 2 , and
wherein the second waveguide array comprises a multi-row optical fiber array including N 1 rows of N 2 optical fibers.