Angle-tunable transmissive grating

Abstract

A tunable transmissive grating comprises a transmissive dispersive element, a reflective element, and an angle θ formed between the two elements. A first optical path is formed according to the angle θ, wherein light dispersing from the dispersive element is directed onto the reflective element and reflects therefrom. At least one element is rotatable about a rotational center to cause a second optical path and thereby tune the wavelength of the light reflecting from the reflective element. Both elements can be rotatable together around a common rotational center point according to certain embodiments, and/or each element can be independently rotated around a rotational axis associated only with that element. According to some embodiments, the relative angle θ formed between the elements is held constant; however, in other embodiments θ can vary.

Description

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a transmissive grating and fixed entrance and exit beam directions, showing the angles α, β, and γ used for associated grating equations.

FIG. 2 illustrates a monochrometer using a tunable transmissive grating according to an embodiment of the invention.

FIG. 3 illustrates a monochrometer using a tunable transmissive grating with collimators according to an embodiment of the invention.

FIG. 4 shows an example of a further embodiment of the invention.

FIG. 5 shows an example of a laser cavity using a tunable transmissive grating according to an embodiment of the invention.

FIG. 6 shows an example of a tunable diode laser cavity using a tunable transmissive grating according to an embodiment of the invention.

FIG. 7 illustrates a relationship between grating efficiency expressed as output power and tunable wavelength in a diode laser cavity using a tunable transmissive grating according to an embodiment of the invention, where the angle of the grating-mirror assembly to achieve the tuning to a specific wavelength is also depicted.

FIG. 8 illustrates an efficiency curve for a grating used in one embodiment of the invention, showing comparison of the efficiency with the grating rotating with the mirror to tune the wavelength versus efficiency with the grating fixed while the mirror rotates to tune the wavelength.

Claims

1. An apparatus for tuning wavelengths of light through a transmissive dispersive element, comprising: a transmissive dispersive element, anda reflector, at least one of said dispersive element and reflector being movable such that said movement alters a wavelength of light transmitted by the dispersive element and reflected by the reflector.

2. The apparatus of claim 1 further comprising a light input path and a light output path, the dispersive element and the reflector being oriented at a fixed angle such the joint rotation of the dispersive element and reflector relative to a stationary input path causes a change in wavelength of light on a stationary output path.

3. The apparatus of claim 1 further comprising: a first optical path such that an input light beam having a input vector projects onto the dispersive element, the dispersive element having a central axis, said beam then dispersing along a dispersion vector from the dispersive element onto the reflector and said beam then reflecting from the reflector along an output path having an output vector, the reflector having a central axis;an angle α formed between the input vector and a normal to the central axis of the dispersive element; andan angle β′ formed between the output vector and the normal to the central axis of the dispersive element, the apparatus being configured such that a movement of at least one of the element and the reflector produces a second optical path, while keeping the sum of angles α and β′ constant.

4. The apparatus of claim 3, further comprising: an angle θ is formed between the central axis of the dispersive element and the central axis of the reflector; the apparatus being configured such that a movement of at least one of the element and the reflector produces a second optical path, while keeping the angle θ constant.

5. The apparatus of claim 1 wherein the apparatus is configured such that a change in wavelength of a light beam reflecting from the reflector is tunable by a rotational movement of at least one of the dispersive element and the reflector.

6. The apparatus of claim 1 wherein the apparatus is configured such that a change in wavelength of a light beam reflecting from the reflector is tunable by a rotational movement of the dispersive element and the reflector through the same angle.

7. The apparatus of claim 2 wherein the movement of the dispersive element and the reflector is a rotation about a rotational axis.

8. The apparatus of claim 5 wherein the rotational movement of the dispersive element and the reflector is a rotation about a rotational axis fixedly attached to the dispersive element and the reflector.

9. The apparatus of claim 8 wherein the rotational movement of the dispersive element and the reflector is a rotation about a rotational axis comprising a rigid joint fixedly adjacent to a side of the dispersive element and a side of the reflector.

10. The apparatus of claim 1 wherein the transmissive dispersive element is a transmissive grating.

11. The apparatus of claim 1 further comprising: a joint attaching the dispersive element to the reflector, the joint including a rotational axis such that an angular position is formed between the dispersive element and reflector;a first angular position and a second angular position of the reflector and dispersive element;a first optical path such that light dispersing from the dispersive element is directed onto the reflector at the first relative angular position; anda second optical path such that light dispersing from the dispersive element is directed onto the reflector at the second angular position.

12. The apparatus of claim 1 wherein the apparatus further comprises a monochrometer.

13. The apparatus of claim 1 wherein the apparatus further comprises a tunable laser cavity.

14. The apparatus of claim 1 wherein the apparatus comprises a double or triple spectrometer.

15. The apparatus of claim 10 wherein the transmissive grating is one a Volume Holographic Transmission (VHT) or a Fused Silica (FS) grating.

16. An apparatus for tuning wavelengths of light through a transmissive dispersive element, comprising: a grating having a grating normal;a reflector;a first relative angular position θ formed between the the grating and the reflector;a first optical path such that light dispersing from the dispersive element is directed onto the reflector and reflects at the first relative angular position θ;a first relative angular position β′ formed between the grating normal and the light reflecting from the reflector according to the first optical path;a second relative angular position β′ formed between the grating normal and the light reflecting from the reflector; anda second optical path such that light dispersing from the dispersive element is directed onto the reflector and reflects at the second relative angular position β′.

17. The apparatus of claim 16 wherein a change in wavelength of a light beam reflecting from the reflector is tunable by the relative angular change between the grating normal and the light reflecting from the reflector.

18. The apparatus of claim 17 wherein the apparatus is configured such that a movement of at least one of the dispersive element and the reflector, the movement comprising a rotation about a rotational axis, causes a relative angular change between the grating normal and the light reflecting from the reflector.

19. The apparatus of claim 16 wherein the relative movement between the dispersive element and the reflector is a rotation about a rotational axis.

20. The apparatus of claim 16 wherein the relative movement between the dispersive element and the reflector is a rotation about a rotational axis rigidly attached to sides of the dispersive element and the reflector.

21. The apparatus of claim 16 wherein the relative movement between the dispersive element and the reflector is a rotation about a rotational axis, said axis being an intersection of a plane projecting from the dispersive element and a plane projecting from the reflector and said axis being the same for both the first and second relative angular positions.

22. A method of tuning the wavelength of an output beam in an optical instrument, comprising the steps of providing a transmissive dispersive element and a reflector to provide a tuning device; andproviding relative movement between an input light path and the tuning device to alter a wavelength of light emitted by the tuning device.

23. The method of claim 22 further comprising: fixedly joining a lateral edge of the dispersive element to a lateral edge of the reflector, the fixed joint comprising a rotational axis and a relative angular position θ formed between the dispersive element and reflector;positioning the rotational center in a first rotational position;providing an input light beam;optically coupling the light beam along a first optical path onto the element and the reflector, wherein the input light beam having an input path vector projecting onto the dispersive element, said beam then dispersing along a dispersion vector from the dispersive element onto the reflector and said beam then reflecting from the reflector along an output path vector, an angle α being formed between the input vector and the normal to a central axis of the dispersive element, an angle β′ is formed between the output path vector and the normal to the central axis of the dispersive element; androtating the reflector and element together about the rotational axis.

24. The method of claim 23 further comprising rotating the element and the reflector together about the rotational axis to produce a second optical path, the input light beam being projected onto the dispersive element and directed onto the reflector while keeping θ constant and the sum of angles α and β′ constant, said rotation tuning the wavelength of the output light beam along the output path vector.

25. The method of claim 22 further comprising providing a dispersive element including a grating and a reflector including a mirror.