A wide-spectrum confocal detection optical system with switchable wavelength

[0030] Refer to figure 1 As shown, a switchable wide-spectrum confocal detection optical system consists of a first spherical lens 1, a second spherical lens 2, a third spherical lens 3, a fourth spherical lens 4, and a fifth spherical lens 5 and a parallel plate glass 6, the order of the optical materials of the first spherical lens 1, the second spherical lens 2, the third spherical lens 3, the fourth spherical lens 4, and the fifth spherical lens 5 are: ZK10, ZF6 and ZK6 (double cemented lenses), LAF5, ZK6, ZF6, while the first spherical lens 1 is a convex-concave positive lens, the second spherical lens 2 is a negative positive doublet lens, and the third spherical lens 3 is convex-concave The positive lens and the fourth spherical lens 4 are convex-concave positive lenses, the fifth spherical lens 5 is a concave-convex negative lens, the parallel plate glass 6 is made of ordinary glass K9, and the parallel plate glass 6 is located on the fifth lens 5 and the CCD target surface 7. In the meantime, by switching the wavelength band used by the parallel plate glass 6, the diaphragm 8 is fixed between the third spherical lens 3 and the fourth spherical lens 4. The first spherical lens 1, the second spherical lens 2, and the third spherical lens group 3 form the optical front group. The fifth spherical lens 5 and the parallel plate glass 6 form the rear group. The first spherical lens 1, the second Two spherical lenses 2, the third spherical lens 3, the fourth spherical lens 4, and the fifth spherical lens 5 are coated with 450-950nm antireflection coating, and the parallel plate glass 6 is respectively coated with 450-700nm and 760- 950nm antireflection coating.

[0031] The constraints related to the selection of optical lens materials are as follows:

[0032] n ( λ ) = a + b λ 2 + c λ 4 + . . . - - - ( 5 )

[0033] In the formula, n(λ) is the refractive index of the optical material at the wavelength λ; a, b, and c are constants, and different optical materials have different values.

[0034] f ′ = - n ( r 2 - r 1 ) + ( n - 1 ) d n - 1 - - - ( 6 )

[0035] In the formula, is the image-side focal length of the single lens; n is the refractive index of the selected optical material for the single lens; r1 and r2 are the front and back curvature radii of the single lens; d is the thickness of the single lens.

[0036] f = f 1 f 2 Δ - - - ( 7 )

[0037] In the formula, f is the composite focal length of the two optical groups; f1 and f2 are the object focal lengths of the two optical groups respectively; △ is the distance from the image-side focal point of the first optical group to the object-side focal point of the second optical group.

[0038] P Fλ = n F - n λ n F - n C - - - ( 8 )

[0039] In the formula, PFλ is the relative dispersion coefficient of the optical material; nF and nC are the refractive index of the optical material calculated according to the formula in condition (5) for F light and C light respectively; nλ is the refractive index of the optical material at wavelength λ .

[0040] The purpose of selecting the above constraints is as follows:

[0041] The condition (5) can be used to calculate the change of the selected optical material's refractive index with wavelength. Due to the wide spectrum from visible light to near-infrared, the refractive index of the optical material will have a certain range of change instead of a constant.

[0042] Condition (6) and Condition (7) are formulas for calculating the focal length of the single lens and the lens group, respectively. It can be seen that the focal length is closely related to the optical refractive index, and it can be seen from the condition (5) that the refractive index of the optical material changes with the wavelength. Therefore, in order to ensure that the optical system is in the range of the entire visible light to the near-infrared band If the focal length change is small, it is necessary to select optical materials whose refractive index is not too sensitive to wavelength changes. However, the types of optical materials are limited. It can also be seen from condition (6) and condition (7) that the structural parameters (radius of curvature, thickness) of the single lens and the distance between the lens groups can be adjusted to reduce the pressure on the selection of optical materials, and ultimately ensure the entire system The change in focal length with wavelength is limited to a certain range.

[0043] Condition (8) is used to calculate the relative dispersion coefficient of the optical material. Generally, the focal length of a wide-spectrum system is longer, and the secondary spectrum of a telephoto system is more difficult to correct than an ordinary system. This requires selecting optical material groups with similar relative dispersion coefficients to correct the secondary spectrum. Due to the wide spectral band of this system, calculate the refractive index and dispersion value of several glasses at wavelengths of 480nm, 580nm, 650nm, 780nm, 850nm, 920nm, and calculate the residual amount of the secondary spectrum at the calculation place, through reasonable allocation of system parameters To correct the secondary spectrum and chromatic aberration.

[0044] The main feature of this wide-spectrum confocal optical system is: according to the detection requirements of long-distance targets and actual use, the designed spectrum is 450-950nm, and the spectrum can pass between 450-700nm and 760-950nm Change the filter to switch the band, and the detection optical system of the confocal surface after switching is suitable for use in environments with standard visibility, misty weather and low sensitivity.

[0045] In order to meet the system requirements, a few groups of optical materials were initially selected according to condition (8); then according to conditions (6) and (7), the structural parameters of the optical materials and the optical group were compromised, and the structural parameters of the system were continuously optimized ; Finally, under the premise of selecting common materials, the purpose of confocal and secondary spectrum correction is achieved, and excellent imaging effects in each spectral region are obtained.

[0046] Table 1 and figure 2 , image 3 , Figure 4 , Figure 5 and Image 6 It is an example of the present invention. In the table, R is the radius of curvature of each lens; d is the distance between each optical surface; nd is the d-light refractive index of the selected optical material; vd is the d-light dispersion coefficient of the selected optical material.

[0047] The focal length of the system is EFFL: 73mm, the field of view is: 9°, F/#: 1.75. The image-side rear intercept of both bands is 4mm, and the total length of the system is ≤100mm. The processing performance of the entire optical system lens is good, and the imaging quality of the wide-spectrum confocal detection optical system is good through actual experiments, which can meet the detection of targets under long-distance conditions.

[0048] Table 1: Data of each lens

[0049] Serial number R Object surface (mm) d(∞)mm nd Vd 1 60.81 7 1.622 56.69 2 424 4 / / 3 -140.6 4 1.755 27.53 4 54.95 7 1.622 56.69 5 -1011.5 9.59 / / 6 39.4 7 1.754 37.66 7 121.34 14.33 / / 8 Infinity 19.7 Diaphragm / 9 31.81 5 1.622 56.69 10 140.6 3 / / 11 -28.233 4 1.755 27.53 12 312.42 6.9 / / 13 Infinity 2 1.516 64.12 14 Infinity 3.7 / /

[0050] Refer to figure 2 As shown, figure 2 It is the MTF diagram of the optical system in the wavelength range of 760nm~960nm. The MTF value reaches 0.7 at 80lp/mm. The MTF is close to the center field of view at the edge of the field of view, so that the energy on the entire image surface is evenly distributed, and the range of the full field of view is Can distinguish the details of the object very well, and the image is clearer.

[0051] Refer to image 3 As shown, image 3 It is the MTF diagram of the optical system in the wavelength range of 450nm to 700nm. The MTF value reaches 0.6 at 80lp/mm, which can meet the requirements of high-quality imaging lenses. The edge field of view is slightly lower than the center field of view. When using this band for imaging, the edge image is not as clear as the center field of view, and it does not affect the system's ability to detect targets. Within 0.7 field of view, the system's imaging quality and image surface uniformity are better.

[0052] Refer to Figure 4 As shown, Figure 4 It is a dot chart of the optical system in the wavelength range of 760nm~960nm. Its RMS radius is close to 1/4 wavelength. The various aberrations are well corrected to make the system a perfect image. The system basically reaches the diffraction limit and can be very good. Meet target detection needs.

[0053] Refer to Figure 5 As shown, Figure 5 It is a dot chart of the optical system in the wavelength range of 450nm to 700nm. The RMS radius is less than one wavelength. The primary aberrations of the system are well corrected. The advanced aberrations are small, and the residual aberrations have little effect on imaging. The optical system The image is clear in this band.

[0054] Refer to Image 6 As shown, Image 6 It is the secondary spectrum of the optical system in the full band. At 0.7 field of view, the secondary spectrum in the 450nm~700nm band is 0, which is good for correcting the secondary spectrum and chromatic aberration. The secondary spectrum in the 760nm~950nm band also approaches zero, and there is an advanced secondary spectrum, which does not affect the imaging characteristics of the system. In the entire wide-band range, the system has well corrected the secondary spectrum and chromatic aberration, and reached confocal after switching the band, eliminating the system's imaging quality degradation caused by focus shift.

[0055] Although the present invention has been disclosed as above in preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some changes and improvements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to those defined by the claims.