Wavelength selective switch

1 . A wavelength selective switch comprising:

one or more input ports;

one or more output ports;

a polarization controller that adjusts a polarization state of light incident from the input ports;

a dispersive element that demultiplexes wavelength-multiplexed light incident from the input ports; and

a deflection element that controls deflection of the demultiplexed light,

wherein the dispersive element is a liquid crystal diffraction element having a liquid crystal alignment pattern where an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction.

2 . The wavelength selective switch according to claim 1 ,

wherein the deflection element is a polarization control phase modulator that changes a phase of incident light based on an applied voltage to control deflection of the incident light.

3 . The wavelength selective switch according to claim 2 ,

wherein the liquid crystal diffraction element is a transmissive type.

4 . The wavelength selective switch according to claim 3 ,

wherein a difference Δn in refractive index of a liquid crystal compound used in the transmissive liquid crystal diffraction element, a film thickness d of the transmissive liquid crystal diffraction element, and a wavelength λ of incidence light satisfy Expression (1),

λ

/

2

-

λ

/

10

≤

Δ

⁢

n

×

d

≤

λ

/

2

+

λ

/

10.

(

1

)

5 . The wavelength selective switch according to claim 2 ,

wherein the liquid crystal diffraction element is a reflective type.

6 . The wavelength selective switch according to claim 5 ,

wherein a film thickness d of the reflective liquid crystal diffraction element, an average refractive index nLC of a liquid crystal compound, and a wavelength λ of incidence light satisfy Expression (2),

d

≥

(

6

×

λ

)

/

nLC

.

(

2

)

7 . The wavelength selective switch according to claim 2 ,

wherein a light refraction member is bonded to the liquid crystal diffraction element.

8 . The wavelength selective switch according to claim 7 ,

wherein a λ/4 plate is provided between the liquid crystal diffraction element and the light refraction member.

9 . The wavelength selective switch according to claim 8 , further comprising:

a first bonding layer that is provided between the liquid crystal diffraction element and the λ/4 plate; and

a second bonding layer that is provided between the λ/4 plate and the light refraction member,

wherein a difference between a refractive index of the first bonding layer and a refractive index of the liquid crystal diffraction element is 0 to 0.1,

a difference between the refractive index of the first bonding layer and a refractive index of the λ/4 plate is 0 to 0.1,

a difference between a refractive index of the second bonding layer and the refractive index of the λ/4 plate is 0 to 0.1, and

a difference between the refractive index of the second bonding layer and a refractive index of the light refraction member is 0 to 0.1.

10 . The wavelength selective switch according to claim 1 ,

wherein the liquid crystal diffraction element is a transmissive type.

11 . The wavelength selective switch according to claim 10 ,

wherein a difference Δn in refractive index of a liquid crystal compound used in the transmissive liquid crystal diffraction element, a film thickness d of the transmissive liquid crystal diffraction element, and a wavelength λ of incidence light satisfy Expression (1),

λ

/

2

-

λ

/

10

≤

Δ

⁢

n

×

d

≤

λ

/

2

+

λ

/

10.

(

1

)

12 . The wavelength selective switch according to claim 11 ,

wherein a light refraction member is bonded to the liquid crystal diffraction element.

13 . The wavelength selective switch according to claim 10 ,

wherein a light refraction member is bonded to the liquid crystal diffraction element.

14 . The wavelength selective switch according to claim 1 ,

wherein the liquid crystal diffraction element is a reflective type.

15 . The wavelength selective switch according to claim 14 ,

wherein a film thickness d of the reflective liquid crystal diffraction element, an average refractive index nLC of a liquid crystal compound, and a wavelength λ of incidence light satisfy Expression (2),

d

≥

(

6

×

λ

)

/

nLC

.

(

2

)

16 . The wavelength selective switch according to claim 15 ,

wherein a light refraction member is bonded to the liquid crystal diffraction element.

17 . The wavelength selective switch according to claim 14 ,

wherein a light refraction member is bonded to the liquid crystal diffraction element.

18 . The wavelength selective switch according to claim 1 ,

wherein a light refraction member is bonded to the liquid crystal diffraction element.

19 . The wavelength selective switch according to claim 18 ,

wherein a λ/4 plate is provided between the liquid crystal diffraction element and the light refraction member.

20 . The wavelength selective switch according to claim 19 , further comprising:

a first bonding layer that is provided between the liquid crystal diffraction element and the λ/4 plate; and

a second bonding layer that is provided between the λ/4 plate and the light refraction member,

wherein a difference between a refractive index of the first bonding layer and a refractive index of the liquid crystal diffraction element is 0 to 0.1,

a difference between the refractive index of the first bonding layer and a refractive index of the λ/4 plate is 0 to 0.1,

a difference between a refractive index of the second bonding layer and the refractive index of the λ/4 plate is 0 to 0.1, and

a difference between the refractive index of the second bonding layer and a refractive index of the light refraction member is 0 to 0.1.