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US-12625310-B2 - Optical filter

US12625310B2US 12625310 B2US12625310 B2US 12625310B2US-12625310-B2

Abstract

The present invention provides an optical filter having a narrow bandpass, high transmittance in the bandpass, low transmittance outside the bandpass, little change in optical properties even when the incident angle of light changes and thus, being advantageous in terms of yield and cost per hour. In addition, the present invention may provide a LiDAR system including the optical filter and an application of the optical filter and the LiDAR system.

Inventors

  • Jung Yeol SHIN
  • Tae Jin SONG
  • Seong Yong Yoon
  • Jin Hwan Kim

Assignees

  • LMS CO., LTD.

Dates

Publication Date
20260512
Application Date
20230601
Priority Date
20220901

Claims (20)

  1. 1 . An optical filter comprising: a reflective layer including a first layer and a second layer, formed in the reflective layer, respectively, wherein the first layer is an amorphous silicon layer having a measured Raman peak of 495 cm −1 or more and 500 cm −1 or less, and the second layer has a lower refractive index than a refractive index of the amorphous silicon layer, and wherein the optical filter shows a transmission band having a bandwidth within a range of 20 nm to 150 nm within a wavelength range of 700 nm to 2,000 nm and has an average transmittance of 5% or less in a wavelength band other than the wavelength forming the transmission band within a wavelength range of 700 nm to 2,000 nm.
  2. 2 . The optical filter of claim 1 , wherein a central wavelength of the transmission band is in a range of 800 nm to 1,650 nm.
  3. 3 . The optical filter of claim 2 , wherein a highest transmittance within the transmittance band is 90% or more.
  4. 4 . The optical filter of claim 1 , wherein an absolute value of L 1 in the following Equation 1 is 0.6 or less, and an absolute value of L 2 in the following Equation 2 is 0.6 or less: L 1 =0.01×(λ 1 −λ 2 ); and [Equation 1] [Equation 2] L 2 =0.01×(λ 3 −λ 4 ), wherein in Equation 1, λ 1 is a shortest wavelength of the optical filter exhibiting a transmittance of 10% in a wavelength region of 700 nm to 2,000 nm, and λ 2 is a shortest wavelength of the optical filter exhibiting a transmittance of 80% in the wavelength region of 700 nm to 2,000 nm; and in Equation 2, λ 3 is a longest wavelength of the optical filter exhibiting a transmittance of 10% in the wavelength region of 700 nm to 2,000 nm, and λ 4 is a longest wavelength of the optical filter exhibiting a transmittance of 80% in the wavelength region of 700 nm to 2,000 nm.
  5. 5 . The optical filter of claim 1 , wherein an absolute value of AXON in the following Equation 3 is 5% or less: [Equation 3] Δλ ON =100×(λ ON. 30 −λ ON. 0 )/λ ON. 0 , where in Equation 3, λ ON. 0 is the shortest wavelength of the optical filter exhibiting a transmittance of 50% in a wavelength region of 700 nm to 2,000 nm and an incident angle of 0°, and λ ON. 30 is the shortest wavelength of the optical filter exhibiting a transmittance of 50% in the wavelength region of 700 nm to 2,000 nm and an incident angle of 30°.
  6. 6 . The optical filter of claim 1 , wherein an absolute value of Δλ OFF of the following Equation 4 is 5% or less: [Equation 4] Δλ OFF =100×(λ OFF. 30 −λ OFF. 0 )/λ OFF. 0 , where in Equation 4, λ OFF. 0 is the longest wavelength of the optical filter exhibiting a transmittance of 50% in a wavelength region of 700 nm to 2,000 nm and an incident angle of 0°, and λ OFF. 30 is the longest wavelength of the optical filter exhibiting a transmittance of 50% in the wavelength region of 700 nm to 2,000 nm and an incident angle of 30°.
  7. 7 . The optical filter of claim 1 , wherein the absolute value of Δλ C of the following Equation 5 is 5% or less: [Equation 5] Δλ C =100×(λ C. 30 − C. 0 )/λ C. 0 where in Equation 5, λ C. 0 is a central wavelength of the transmission band of the optical filter at an incident angle of 0°, and λ C. 30 is a central wavelength of the transmission band of the optical filter at an incidence angle of 30°.
  8. 8 . The optical filter of claim 1 , wherein an absolute value of AB in the following Equation 6 is 30% or less: [Equation 6] ΔB=100×(B 30 −B 0 )/B 0 , where in Equation 6, B 0 is a bandwidth of the transmission band of the optical filter at an incident angle of 0° and B 30 is a bandwidth of the transmission band of the optical filter at an incidence angle of 30°.
  9. 9 . The optical filter of claim 1 , wherein the absolute value of ΔL 1 in the following Equation 7 is 3 or less, and an absolute value of ΔL 2 in the following Equation 8 is 3 or less: Δ L 1 =( L 1.30 −L 1.0 )/ L 1.0 ; and [Equation 7] [Equation 8] ΔL 2 =(L 2.30 −L 2.0 )/L 2.0 , where in Equation 7, L 1.30 is a value of L 1 of Equation 1 obtained at an incident angle of 30°, L 1.0 is a value of L 1 of Equation 1 obtained at an incident angle of 0° and L 2.30 in Equation 8 is a value of L 2 of Equation 2 obtained at an incident angle of 30°, L 2.0 is a value of L 2 of Equation 2 obtained at an incident angle of 0°: L 1 =0.01×(λ 1 −λ 2 ); and [Equation 1] [Equation 2] L 2 =0.01×(λ 3 −λ 4 ), where in Equation 1, λ 1 is a shortest wavelength of the optical filter exhibiting a transmittance of 10% in a wavelength region of 700 nm to 2,000 nm, and λ 2 is a shortest wavelength of the optical filter exhibiting a transmittance of 80% in the wavelength region of 700 nm to 2,000 nm; and in Equation 2, λ 3 is a longest wavelength of the optical filter exhibiting a transmittance of 10% in the wavelength region of 700 nm to 2,000 nm, and λ 4 is a longest wavelength of the optical filter exhibiting a transmittance of 80% in the wavelength region of 700 nm to 2,000 nm.
  10. 10 . The optical filter of claim 1 , wherein the first layer has a refractive index of 3.3 or more at a wavelength of 940 nm and a refractive index of 3.1 or more at a wavelength of 1550 nm.
  11. 11 . The optical filter of claim 1 , wherein the first layer has an extinction coefficient K of zero at any one of a thickness within a thickness range of 60 nm to 300 nm and a wavelength within a wavelength range of 800 nm to 900 nm.
  12. 12 . The optical filter according to claim 10 , wherein a ratio n 1 /n 2 of the refractive index n 1 of the first layer and a refractive index n 2 of the second layer is 1.3 or more.
  13. 13 . The optical filter of claim 1 , wherein the first layer and the second layer are alternately stacked on each other in the reflective layer, and the reflective layer further includes a third layer, and a ratio n 1 /n 3 of the refractive index n 1 of the first layer and a refractive index n 3 of the third layer is 1.3 or more.
  14. 14 . The optical filter of claim 1 , wherein R in the following Equation 9 is in a range of 14 to 20: [Equation 9] R=4×T/λ C , wherein in Equation 9, T is a thickness of the reflective layer having a unit in mm and λ C is a central wavelength of the transmission band of the optical filter.
  15. 15 . The optical filter of claim 1 , wherein an average thickness of the first and second layers in the reflective layer is each independently within a range of 80 nm to 400 nm.
  16. 16 . The optical filter of claim 1 , wherein R H of the following Equation 10 is 30% or more: [Equation 10] R H =100×T H /(T H +T L ), wherein in Equation 10, T H is a total thickness of the first layer in the reflective layer, and T L is a total thickness of the second layer in the reflective layer.
  17. 17 . The optical filter of claim 1 , wherein R HO of the following Equation 11 is in a range of 55 to 80: [Equation 11] R HO =T HO /(T HO +T LO ), wherein T HO is an optical thickness of the first layer in the reflective layer, T LO is an optical thickness of the second layer in the reflective layer, and the optical thickness of the first layer is a product of a total thickness of the first layer in the reflective layer and the refractive index of the first layer, and the optical thickness of the second layer is a product of a total thickness of the second layer in the reflective layer and the refractive index of the second layer.
  18. 18 . The optical filter of claim 1 , wherein a total number of layers of the first and the second layers in the reflective layer is in a range of 20 to 150 layers, and a ratio (L 1+2 /L T ) between the total number of the layers of the first and second layers (L 1+2 ) in the reflective layer and a number of layers of entire sub-layers (L T ) is in a range of 0.85 to 1.
  19. 19 . The optical filter of claim 18 , wherein a ratio (T 1 /T 2 ) between a total number of layers of the first layer (T 1 ) and a total number of layers of the second layer (T 2 ) in the reflective layer is in a range of 0.5 to 1.5.
  20. 20 . A LiDAR system comprising the optical filter of claim 1 .

Description

FIELD The present invention relates to an optical filter, a LiDAR (Light Detection and Ranging) system including the optical filter, and its application. BACKGROUND A LiDAR (Light Detection and Ranging) system is a system that can detect the distance, direction, speed, temperature, material distribution and concentration characteristics of an object by shining a laser on the target. To detect the laser reflected from the target, an optical filter is utilized. The optical filter is specifically a band pass filter, and it transmits the laser reflected from the target to a recognition sensor (e.g., an image sensor, etc.), simultaneously blocks ambient light substantially, and thus, it is possible to increase the recognition sensitivity of the reflected laser. In other words, the optical filter serves to transmit the laser reflected from the target but substantially to block ambient light. Therefore, since the optical filter must transmit only the laser reflected from the target as much as possible, it must have a bandpass including at least a part of the wavelength region of the laser. Also, the bandpass must have a high level of transmittance in the wavelength region while the bandpass is narrow and thus, it should exhibit a high level of transmission barrier outside the bandpass. For the optical filter, it is common to form a dielectric layer by alternatively stacking a high refractive indexed layer and a low refractive indexed layer on both surfaces of a substrate where TiO2 is used as the high refractive indexed layer, and SiO2 is used as the low refractive indexed layer. In this case, to form a narrow and high transmittance bandpass and to exhibit the transmission barrier outside the bandpass, a rather large number of stacked layers should have been formed. Such a conventional optical filter with a bandpass filter is disclosed in a prior art: U.S. Pat. No. 9,588,269. However, in a case of an optical filter having a large number of layers, it generally has high transmittance within the bandpass and low transmittance outside the bandpass, but the overall thickness of the optical filter becomes thick, and thus, there is a problem of bending due to thermal expansion. In addition, if the number of layers is large, it is disadvantageous in terms of yield per hour or cost. In addition, for the optical filter having a large number of layers as described above, the central wavelength of the bandpass is greatly changed with respect to the change in the incident angle of the reflected laser. This is the so-called shift phenomenon, which increases the amount of ambient light transmitted by the shift; decreases the signal-to-noise ratio (SNR); and reduces the amount of light transmitted over the required angle of incidence. To transmit the reflected laser, the bandpass shall be relatively widened, so there is a problem in that the detection sensitivity is relatively low. Accordingly, it is necessary to secure an optical filter that has a narrow bandpass, high transmittance in the bandpass, low transmittance outside the bandpass, and reduces the overall number of layers, thereby improving the above-described problem. SUMMARY Δn object of the present invention is to provide an optical filter having a narrow bandpass, high transmittance in the bandpass, and low transmittance outside the bandpass. Another object of the present invention is to provide an optical filter that has little change in optical properties even when the incident angle of light is changed, and is advantageous in terms of yield per hour and cost. Furthermore, another object of the present invention is to provide a LiDAR system including the optical filter and the application of the optical filter and LiDAR system. According to an embodiment of the invention, there is provided that an optical filter comprises a reflective layer including a plurality of a first layer and a plurality of a second layer are formed in the reflective layer, respectively. The first layer is an amorphous silicon layer and the second layer has a lower refractive index than a refractive index of the amorphous silicon layer. The optical filter shows a transmission band having a bandwidth within a range of 20 nm to 150 nm within a wavelength range of 700 nm to 2,000 nm and has an average transmittance of 5% or less in a wavelength band other than the wavelength forming the transmission band within a wavelength range of 700 nm to 2,000 nm. In an embodiment, a central wavelength of the transmission band is in a range of 800 nm to 1,650 nm for the optical filter layer in the present invention. In an embodiment, a highest transmittance within the transmittance band is 90% or more for the optical filter layer in the present invention. In an embodiment, an average transmittance within the transmittance band is 70% or more for the optical filter layer in the present invention. In an embodiment, an absolute value of L1 in the following Equation 1 is 0.6 or less, and an absolute value of L