A method and apparatus for measuring spectral information of light from at least one object includes at least one light detector and at least one transparent body. The transparent body has a front side that has an entrance aperture and at least one reflecting surface. The transparent body also has a back side that includes at least one reflecting surface and an exit surface. The detector is positioned near the exit surface. At least one of the front reflecting surface and the back reflecting surface includes a diffractive optical element arranged to receive diverging light from the aperture. A focusing element focuses diffracted light to the exit surface. The apparatus may comprise multiple channels and may also include a device for measuring a distance to the object.
1. An apparatus for measuring spectral information of light from at least one object, comprising:
a transparent body having a front side and a back side, the front side including
an entrance surface having at least one entrance aperture for receiving light, and
at least a first front reflecting surface, and the back side including
at least a first back reflecting surface for reflecting light received from the at least one entrance aperture to the at least one front reflecting surface, and
an exit surface,
at least one of the at least a first front reflecting surface and the at least a first back reflecting surface including a first diffractive optical element, and at least one of the at least a first front reflecting surface and the at least a first back reflecting surface including a first focusing element, the first diffractive element being arranged to disperse diverging light received from the at least one entrance aperture; and
a light detector unit arranged to receive the dispersed light through the exit surface from the at least one reflecting surface on the front side.
2. The apparatus according to claim 1 , wherein a light path through the transparent body from the entrance aperture to the exit surface via the first diffractive optical element and the first focusing element is incident on an aberration correcting element.
3. The apparatus according to claim 1 wherein the front side further includes at least a second front reflecting surface and the back side includes at least a second back reflecting surface, the at least a second front reflecting surface and the at least a second back reflecting being arranged to reflect light propagating from the entrance aperture to the diffractive optical element.
4. The apparatus according to claim 1 , wherein the first diffractive optical element and the light detector unit are arranged in parallel planes.
5. The apparatus according to claim 1 , wherein the entrance surface and the exit surface are parallel.
6. The apparatus according to claim 1 , wherein the at least one entrance aperture includes a rectangular slit.
7. The apparatus according to claim 1 , wherein the at least one entrance aperture includes an exit face of an optical fiber.
8. The apparatus according to claim 1 , wherein the first diffractive optical element is aspheric.
9. The apparatus according to claim 1 , wherein the light detector unit is positioned at a selected distance from the exit surface of the transparent body.
10. The apparatus according to claim 1 , wherein the transparent body is a unitary body.
11. The apparatus according to claim 1 , wherein the transparent body is a composite, transparent body.
12. The apparatus according to claim 1 , wherein the transparent body is covered by light absorbing material.
13. The apparatus according to claim 1 , further comprising at least two spectrometer channel paths between the at least one entrance aperture and the light detector unit.
14. The apparatus according to claim 1 further comprising at least one reference light source to illuminate the at least one object.
15. The apparatus according to claim 1 , further comprising an object distance determining unit having a light spot source for illuminating the at least one object and a distance light detector to detect light from the light spot source reflected by the at least one object.
16. The apparatus according to claim 2 , wherein the first focusing element is an aspheric focusing element, the aspheric focusing element comprising the aberration correcting element.
17. The apparatus according to claim 2 , wherein the aberration correcting element includes one of a tilted exit surface and an aspheric exit surface.
18. The apparatus according to claim 11 wherein the composite, transparent body includes at least first and second body parts, the first body part including the front side and the second body part including the back side.
19. The apparatus according to claim 18 , further comprising light absorbing material disposed between the first and second body parts.
20. The apparatus according to claim 19 , further comprising at least one intermediate body part between the first and second body parts.
21. The apparatus according to claim 12 , wherein the light absorbing material has a refractive index approximately equal to a refractive index of the transparent body.
22. The apparatus according claim 12 , wherein the light absorbing material is coated onto the transparent body.
23. The apparatus according to claim 12 , wherein the light absorbing material is molded into the transparent body.
24. The apparatus according to claim 13 wherein the at least two spectrometer channel paths are parallel.
25. The apparatus according to claim 14 , wherein the at least one reference light source is disposed to illuminate the at least one object in a reflection configuration.
26. The apparatus according to claim 14 wherein the at least one reference light source is disposed to illuminate the at least one object in a transmission configuration.
27. The apparatus according to claim 14 , wherein the transparent body includes at least one measuring channel for measuring light from the at least one object and a reference channel for measuring light from the at least one reference light source.
28. The apparatus according to claim 27 , further comprising a guiding plate disposed to guide light from the at least one reference light source to the reference channel.
29. The apparatus according to claim 27 , further comprising an optical fiber disposed to guide light from the at least one reference light source to the reference channel.
30. The apparatus according to claim 27 , further comprising an analyzer coupled to receive measurement and reference signals from the light detector unit, the analyzer being arranged to produce an output measurement signal using the measurement and reference signals, a variation of the output measurement signal with reference light spectrum being less than a variation in the measurement signal with reference light spectrum.
31. The apparatus according to claim 15 , wherein the light spot source is a substantially monochromatic light source.
32. The apparatus according to claim 15 , wherein the object distance determining unit includes a distance light focusing unit to focus light reflected from the at least one object to the distance light detector.
33. The apparatus according to claim 32 , wherein the distance light focusing unit includes a wavelength bandpass filter allowing passage of light only within a bandwidth of the light spot source.
34. The apparatus according to claim 15 , wherein the distance light detector detects at least one of position and size of a light beam reflected from the at least one object.
35. The apparatus according to claim 15 , wherein the distance light detector is a position sensitive detector or an array detector.
36. The apparatus according to claim 15 wherein the object distance determining unit includes an analyzer coupled to receive a distance measurement signal from the distance light detector and to generate an object distance value representing a distance between the at least one object and the transparent body.
37. The apparatus according to claim 36 , wherein the analyzer is further coupled to receive spectrum measurement signals from the light detector unit and to modify the spectrum measurement signals based on the object distance value.
38. An apparatus for measuring spectral information of light from at least one object, comprising:
a transparent body having a front side and a back side, the front side including
an entrance surface having at least one input means for inputting light from the at least one object, and
at least a first front reflecting surface, and the back side including
at least a first back reflecting surface for reflecting light received from the at least one input means to the at least one front reflecting surface, and
an exit surface,
at least one of the at least a first front reflecting surface and the at least a first back reflecting surface including a first diffracting means for diffracting light, and at least one of the at least a first front reflecting surface and the at least a first back reflecting surface including a first focusing means for focusing light, the first diffracting means being arranged to disperse diverging light received from the at least one input means; and
light detecting means for detecting the dispersed divergent light transmitted out of the exit surface.
39. A method of measuring spectral information of light from an object, comprising:
inputting signal light from the object to a transparent body through an entrance aperture on a first side of the transparent body;
propagating divergent signal light from the entrance aperture to a diffractive element on a second side of the transparent body;
diffracting the divergent signal light with the diffractive element into divergent, separated wavelength components;
reflectively focusing the divergent, separated wavelength components to an exit face using a focusing reflector on the transparent body; and
detecting the focused, separated wavelength components using a detector unit.
40. The method as recited in claim 39 , further comprising reflecting the divergent signal light from the second side to the first side and back to the second side before the divergent signal light is incident on the diffractive element.
41. The method as recited in claim 39 , further comprising:
illuminating the object with reference light to produce the signal light, and
reducing spectral influence of the reference light on a spectrum signal generated by the detector unit.
42. The method as recited in claim 39 , further comprising illuminating the object with distance light and determining a distance between the object and a distance detector using distance light reflected by the object.
43. The method as recited in claim 42 , wherein determining the distance between the object and the distance detector includes determining a light spot size or a light spot position.
44. The method as recited in claim 42 , further comprising adjusting a spectrum signal generated by the detector unit in response to the distance determined between the object and the distance detector.