Multiple input spectrometer
A concurrently measuring multiple light input spectrometer with a shared or common optical path is described. The spectrometer can help eliminates errors from dark offsets, can reduce impact of ambient optical and electrical noise, and can mitigate temperature effects. Additionally, it can help readily provide wavelength calibration. By using just two inputs, spectrometer can provide true spectral measurement of the test object by continuous measurement of the spectra of the source and the spectra of the source light after interacting with the test object. More generally, including an individual photodetector (instead of an array of multiple photodetectors) associated with each input can help address solving the problems that may get introduced by using multiple photodetectors for a particular input.
1 . A spectroscopic device for analyzing at least two independent input light sources, the device comprising:
a spectroscopy optics housing, enclosing spectroscopy optics and including a baffle defining a first aperture arranged to receive and transmit into the housing first input light from a first input light source, the baffle also defining a second aperture, spaced apart from the first aperture, and arranged to receive and transmit into the housing second input light from a second input light source that is independent from the first input light source, the housing enclosing:
a commonly-shared optical dispersive system to spatially disperse the first input light and the second input light, respectively received from the first input light source and the second input light source, into corresponding spectral components;
an optical modulator, arranged to provide at least two individually modulated different spectral bin light components that are modulation encoded, using respective different time-varying modulation functions for each of the first and second input light from the corresponding first and second input light sources; and
a first and a second light transducer, arranged to receive modulated light from the optical modulator corresponding to an individual one of the first and second input light sources, and to respectively produce a corresponding first and second electrical response signal in response thereto; and
signal processing circuitry, coupled to the first and second light transducers to receive and digitize the first and second electrical response signals, and, using information about the respective different time-varying modulation functions, decoding the first and second electrical response signals to recover information about a respective response parameter of the individually modulated different spectral bin light components to provide a spectral bin response of the corresponding first and second input light from the corresponding first and second input light sources.
2 . The device of claim 1 , wherein one of the first input light or the second input light is further split using a beam splitter after optical modulation and measured by a corresponding one of the first and second light transducers after being transmitted or reflected from an optical wavelength standard to determine a wavelength corresponding to different spectral bin components.
3 . The device of claim 1 , wherein the first input light corresponds to illumination light used for spectroscopic measurement and that has not interacted with a test object, and the second input light corresponds to illumination light after transmission, reflection, scattering, or other interaction with the test object.
4 . The device of claim 1 , wherein the first and second light transducers are located downstream in an optical pathway from a spectral combiner that is configured to spectrally combine the individually modulated different spectral bin light components.
5 . The device of claim 1 , wherein the optical modulator includes a patterned disk configured to produce time varying modulation functions in response to rotation of the disk.
6 . The device of claim 1 , wherein the signal processing circuitry is configured to perform division of computed spectra of the first input light from the first input light source and the second input light from the second input light source.
7 . The device of claim 1 , wherein the first and second apertures respectively include first and second slits for the corresponding one of the first and second input light respectively provided by the first and second input light source, wherein the first and second slits are displaced from each other by an opaque region of the baffle to provide slightly different wavelength mapping for the first slit with respect to the second slit.
8 . The device of claim 1 , wherein the individual first and second light transducers respectively have different signal gains for producing the corresponding first and second electrical response signals respectively corresponding to first input light from the first aperture and to second input light from the second.
9 . The device of claim 1 , wherein the signal processing circuitry performs analog-to-digital conversion of the first and second electrical response signals synchronously to modulation by the optical modulator.
10 . The device of claim 1 , wherein the spectroscopic device is configured for measurement of color.