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LCOS-SLM characteristics
Diffraction efficiency
Definition
Diffraction efficiency is defined as the expression that represents the ratio of the 1st-order diffraction light intensity (I1st) to the 0th-order light intensity (Iave) when a phase pattern simulating a brazed diffraction grating is displayed on the LCOS-SLM. In the case of a two-level diffraction grating, however, the average value of the ±1st-order light intensity is viewed as the diffraction light intensity. The 0th-order light intensity is the average value obtained by changing the input gray level from 0 to 255.
Diffraction efficiency = I1st / Iave [%]
Measurement method
The 1st-order diffraction light intensity is measured using a phase modulation optical system as shown in the figure where the polarization direction of the incident light is aligned with the orientation of the liquid crystal molecules. The incident angle θ is set within 10 degrees and the aperture size is set to 10 mm in diameter. Four types of diffraction gratings with 2 to 16 levels are used for the display.
Measurement setup for diffraction efficiency
Phase distribution of diffraction grating
Measurement results
We measured diffraction efficiency using light sources with wavelengths listed in the table below. The results are plotted in the graph below along with the theoretical values. The spatial frequencies of each diffraction grating for display are as follows: 2 levels: 40 lp/mm, 4 levels: 20 lp/mm, 8 levels: 10 lp/mm, and 16 levels: 5 lp/mm.
Wavelength of light sources for diffraction efficiency measurement
Type No. |
Wide wavelength band type |
Specific wavelength type | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
-01 |
-07 |
-08 |
-02 |
-03B |
-05 |
-12 |
-13 |
-15 |
-16 |
-19 |
|
Wavelength of light source (nm) |
633 |
1064 |
1064 |
785 |
1064 |
407 |
940 |
532 |
1550 |
532 |
1950 |
Type No |
High-power laser type |
Laser metal processing type |
|||||
|---|---|---|---|---|---|---|---|
-02L/-02R |
-03BL/-03BR |
-12L/-12R |
-15L/-15R |
-16L/-16R |
-19L/-19R |
-03CL/-03CR |
|
Wavelength of light source (nm) |
785 |
1064 |
940 |
1550 |
532 |
1950 |
1064 |
Measurement results for diffraction efficiency (typical examples) and theoretical values
- Confirmation
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