Dispersion-compensative optical assembly

1. An optical assembly comprising:

a first grating device including a compensating grating;

a second grating device including a focusing grating with curved lines and unequal line spacings; and

a grating coupler of a planar waveguide device configured to receive an optical signal that has propagated through the first and the second grating devices,

wherein:

the first grating device is configured to receive a light beam from a fiber; and

the first grating device and the second grating device are configured to mutually compensate their wavelength dispersions such that after propagating through both the first grating device and the second grating device, the optical signals converge and are incident on the grating coupler with different input angles that respectively match optimal incidence angles configured for the different spectral components on the grating coupler.

2. The optical assembly of claim 1 , wherein the first grating device is parallel to the second grating device and wherein the first and second grating devices have a same dispersive power.

3. The optical assembly of claim 1 , wherein the first grating device has parallel straight lines with equal line spacings.

4. The optical assembly of claim 1 , wherein:

the first grating device is configured to receive an optical signal with one of multiple different center wavelengths and to diffract the optical signal toward the second grating device;

the second grating device is configured to receive the optical signal from the first grating device and diffract it toward the grating coupler;

the grating coupler is configured to receive the optical signal from the second grating device and couple it into the planar waveguide device;

a relative displacement of the first grating device and the second grating device is configured to enable the second grating device to direct the optical signal onto the grating coupler; and

the first and second grating devices are configured to cooperate to input the optical signal into the grating coupler at an optimal incidence angle that depends on a center wavelength of the optical signal, the optimal incidence angle being different for each of the multiple different center wavelengths.

5. The optical assembly of claim 4 , wherein:

a spot size of the optical signal that converges on the grating coupler is within an acceptance spot size of the grating coupler; and

a band of converging angles of the optical signal falls within a numerical aperture of the grating coupler.

6. The optical assembly of claim 1 , wherein:

the first grating device is configured to receive a light beam from the fiber, the light beam including a plurality of optical signals with different spectral components; and

the first grating device and the second grating device are configured such that after propagating through both the first grating device and the second grating device, the optical signals converge and are incident on the grating coupler with different input angles that respectively match optimal incidence angles configured for the different spectral components on the grating coupler.

7. The optical assembly of claim 1 , further comprising a mode transformation component configured to convert a Gaussian mode of the optical signal to an exponential mode.

8. The optical assembly of claim 7 , wherein the mode transformation component includes a partial etch phase lens component.

9. The optical assembly of claim 1 , further comprising an optical block having opposing first and second surfaces, the first grating device coupled to or formed on or in the first surface of the optical block and the second grating device coupled to or formed on or in the second surface of the optical block.

10. An optical assembly comprising:

a first grating device that includes a compensating grating and that is configured to:

receive a light beam that includes an optical signal with a particular wavelength from a fiber; and

change a propagation direction of the optical signal according to the particular wavelength of the optical signal; and

a second grating device that includes a focusing grating with curved lines and unequal line spacings and that is configured to:

receive the optical signal outputted from the first grating device;

change the propagation direction of the optical signal according to the particular wavelength of the optical signal; and

direct the optical signal onto a grating coupler of a planar waveguide device, wherein:

a relative displacement of the first grating device and the second grating device is configured to enable the second grating device to direct the optical signal onto the grating coupler; and

the first and second grating devices are configured to mutually compensate their wavelength dispersions and to input the optical signal into the grating coupler at an optimal incidence angle configured for the particular wavelength.

11. The optical assembly of claim 10 , wherein:

a spot size of the optical signal that converges on the grating coupler is within an acceptance spot size of the grating coupler; and

a band of converging angles of the optical signal falls within a numerical aperture of the grating coupler.

12. The optical assembly of claim 10 , wherein:

the light beam includes a plurality of optical signals with different spectral components; and

the first grating device and the second grating device are configured such that after propagating through both the first grating device and the second grating device, the optical signals converge and are incident on the grating coupler with different input angles that respectively match optimal incidence angles configured for the different spectral components on the grating coupler.

13. The optical assembly of claim 10 , wherein the first grating device is parallel to the second grating device and wherein the first and second grating devices have a same dispersive power.

14. The optical assembly of claim 10 , wherein the first grating device has parallel straight lines with equal line spacings.

15. The optical assembly of claim 10 , further comprising at least one of:

an optical block having opposing first and second surfaces, the first grating device coupled to or formed on or in the first surface of the optical block and the second grating device coupled to or formed on or in the second surface of the optical block; or

a focusing device positioned in an optical path of the light beam between the fiber and the first grating device.

16. The optical assembly of claim 10 , further comprising a mode transformation component configured to convert a Gaussian mode of the optical signal to an exponential mode.

17. The method of claim 10 , further comprising converging a spot size of the optical signal to be within an acceptance spot size of the grating coupler when received at the grating coupler.

18. A method, comprising:

receiving a light beam from a fiber at a first grating device that includes a compensating grating, the light beam including a plurality of optical signals each having a different one of a plurality of center wavelengths;

imparting, at the first grating device, angular dispersion to the optical signals of the light beam, including redirecting each of the optical signals toward a second grating device at a corresponding diffraction angle that depends on a corresponding center wavelength of the corresponding optical signal, the second grating device including a focusing grating with curved lines and unequal line spacings;

redirecting, at the second grating device, each of the optical signals toward a grating coupler of a planar waveguide device at a diffraction angle that depends on the corresponding center wavelength of the corresponding optical signal; and

receiving, at the grating coupler, each of the optical signals at a corresponding optimal incidence angle configured for the corresponding center wavelength,

wherein the first grating device and the second grating device mutually compensate their wavelength dispersions.

19. The method of claim 18 , further comprising converting a Gaussian mode of each of the optical signals as output from the fiber to an exponential mode as input to the grating coupler.