DESC:FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

Title: A COMPACT WIDE ANGLED ULTRA-VIOLET OPTICAL SYSTEM

APPLICANT DETAILS:
(a) NAME: BHARAT ELECTRONICS LIMITED
(b) NATIONALITY: INDIAN
(c) ADDRESS: Outer Ring Road, Nagavara, Bangalore-560045, Karnataka, India

PREAMBLE TO THE DESCRIPTION:
The following specification (particularly) describes the nature of the invention (and the manner in which it is to be performed):
A COMPACT WIDE ANGLED ULTRA-VIOLET OPTICAL SYSTEM

FIELD OF THE INVENTION:
This invention is related to the relates to the field of optical systems. The invention, more particularly, focuses on wide-angle ultraviolet (UV) optical systems optimized for operation in the solar blind UV region.

BACKGROUND OF THE INVENTION:
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Generally, the solar-blind ultraviolet (UV) region, characterized by its wavelength range of 200 nm to 280 nm, plays a crucial role in various applications due to its unique properties.
Ozone in the Earth's stratosphere absorbs UV radiation in this range, creating a solar blind area in the near-earth atmosphere. This distinctive feature is harnessed in technologies like solar-blind UV optical systems. These systems find applications in diverse fields such as missile approach warning, forest fire prevention, corona discharge detection and military scenarios, where the detection of specific UV signatures are critical. The solar-blind UV region thus emerges as a valuable domain for specialized optical systems and technologies, offering tailored solutions across environmental monitoring, defense, and safety sectors.
CN112162388A discloses a solar blind ultraviolet optical system with large relative aperture and large field of view, which is suitable for the technical field of optical instruments and comprises a first lens, a second lens, a third lens, a filter group, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are sequentially arranged from an object side to an image side at intervals along an optical axis; the first lens is a meniscus negative lens, the second lens is a double-concave negative lens, and the third lens is a double-convex positive lens; the fourth lens is a biconvex positive lens, the fifth lens is a biconvex positive lens, the sixth lens is a plano-concave negative lens, and the seventh lens is a meniscus positive lens. The optical system is suitable for an energy detection system in the solar blind ultraviolet spectral region.
CN 209070206U relates to a kind of big visual field UV warming lens optical systems of object lens of large relative aperture, and the system comprises the first negative power meniscus set gradually, the second negative power meniscus, optical filter, diaphragm, positive light coke biconvex lens, the first positive light coke plano-convex lens, positive light coke meniscus, negative power concave-convex lens, the second positive light coke plano-convex lens. .
CN 209070204U relates to a kind of big visual field UV warming lens systems, and the system comprises the negative power meniscus set gradually, the first negative power biconcave lens, positive light coke concave-convex lens, the first positive light coke plano-convex lens, the second positive light coke plano-convex lens, negative power plano-concave lens, diaphragm, the first positive light coke biconvex lens, negative power concave-convex lens, the second positive light coke biconvex lens and the second negative power biconcave lens.
CN211826686U discloses a super wide angle solar blind ultraviolet optical system belongs to the ultraviolet optics imaging field, include first negative focal power meniscus concave lens, first negative focal power biconcave lens, first group's light filter, second negative focal power biconcave lens, positive focal power meniscus convex lens, the second group light filter, first positive focal power biconvex lens, the diaphragm, third negative focal power biconcave lens, second positive focal power biconvex lens, third positive focal power biconvex lens, second negative focal power meniscus concave lens, fourth positive focal power biconvex lens along the optical axis direction from the object space to the image space in proper order
As disclosed in the available prior art CN112162388A, CN 209070206U, CN 209070204U covers FOV less than 120°, minimum of seven lenses with track length greater than 90mm and CN211826686U covers FOV of 210°, ten lenses with a track length of more than 138mm with degraded performance in extreme fields.

OBJECT/S OF THE INVENTION:
The primary object of the present invention is to overcome the drawbacks associated with prior art.
In an objective the present invention provides a wide-angled ultraviolet optical system that is particularly used in solar blind Ultraviolet regions. Furthermore, the optical system comprises a series of optical elements arranged in a specific manner, particularly, coaxially along the optical axis.

SUMMARY OF THE INVENTION:
In an aspect the present invention provides a compact wide angled ultra-violet optical system comprising:
a first negative power meniscus concave lens (L1),
a negative power biconcave lens (L2),
a first optical filter (F1),
a second negative power meniscus convex lens (L3),
a diaphragm (S),
a positive power meniscus lens (L4),
a negative power meniscus lens (L5),
a positive power biconvex lens (L6), and
a second optical filter (F2)

DETAILED DESCRIPTION OF DRAWINGS:
The advantages and features of the present disclosure will become better understood with reference to the following detailed description and claims taken in conjunction with the accompanying drawing, in which:
Fig. 1 illustrates an exemplary optical layout of the wide-angled solar blind UV optical system of based on various optical materials, lens types and optical filters.
Fig. 2 illustrates the graphical representation of Modular transfer function (MTF) of the disclosed optical system, MTF plots measure the performance and image resolution of the exemplary optical system
Fig. 3 illustrates the graphical representation of the performance of the exemplary optical system in the form of spot diagram for different field points.
Fig. 4 illustrates the graphical representation of Image distortion in percentage for each filed point and Field curvature plots the difference between distances of the real focus point to the theoretical focus point on the image detector for each field point.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative system and method of embodying the principles of the present disclosure. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION OF THE INVENTION:
The foregoing descriptions of specific embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiment was chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
The terms “a” and “an” herein do not denote a limitation of quantity but rather denote the presence of at least one of the referenced item.
The terms “having”, “comprising”, “including”, and variations thereof signify the presence of a component.
Figure 1 of the present invention illustrates a wide-angled ultraviolet optical system that is particularly used in solar blind Ultraviolet region. Furthermore, the optical system comprises a series of optical elements arranged in a specific manner, particularly, coaxially along the optical axis.
In one of preferred embodiment, the optical system as disclosed herein comprises a First Negative Power Meniscus Concave Lens L1, a Negative Power Biconcave Lens L2, a First Optical Filter F1, a Second Negative Power Meniscus Convex Lens L3, a Diaphragm S, a Positive Power meniscus Lens L4, a Negative Power meniscus Lens L5, a positive power biconvex lens L6, and a Second Optical Filter F2. Additionally, the system further comprises a Sensor/detector window and an Image Plane I.
In one of the implementations, the operating wavelength range of the disclosed invention can be within the range of 240nm - 280nm with a full Field of View >130 degrees. Furthermore, the f/# (pronounced as “F-number”) the ratio of the focal length, (f), of the lens to the effective aperture diameter is f/# 2 and image plane height of 25mm.
In one of the embodiments, the system adopts double gauss fisheye design form with stop at the Centre of the lens groups and the system image space is telecentric to have uniform relative illumination. In one of the implementations fused silica, sapphire, magnesium fluoride (MgF2), potassium bromide (KBr) and calcium fluoride (CaF2) are used for its superior ultraviolet transmission properties.
An example design of the disclosed optical system is listed in table-1 below. The system disclosed herein uses a total of six lenses with four standard lenses and two lenses having aspheric surfaces. The aspheric surfaces are chosen to be made on the sapphire material lenses for easing the fabrication challenges. The Two aspheric surfaces aide in for better correction of the spherical aberration and compactness of the system with track length of less the 70mm including image plane.
In one of the implementations the filters F1 & F2 are made of special glass materials. The first filter inherently has the property of absorbing wavelength band lower than a particular cut off wavelength band and acts as long-pass filter and second filter absorbs high wavelength than the designated band and acts as short-pass filter. These filters are also coated with dielectric sharp coatings to achieve the solar blind transmittance of 240 to 280 nm. The filter is a critical element in the system to reduce the noise that arises due to unwanted spectral band.
Figure 2 illustrates the polychromatic MTF plots, the MTF of the system is maintained at a minimum of 0.7 at 20lp/mm.
Figure 3 illustrates the spot diagram of the example UV system.
Figure 4 illustrates the field curvature and distortion of the system. The distortion of the system is within 50% and field curvature is also under control.
In one of the implementation, the invention discloses a specific set of parameters for the solar blind ultraviolet optical system, as detailed in the accompanying table 1:
S.NO Surface type Radius of curvature Thickness material
1 STANDARD 337.93 1.83 CAF2
2 STANDARD 20.41 9.03
3 STANDARD -50.65 1.80 CAF2
4 STANDARD 19.76 8.41
5 STANDARD Infinity 2.00 F_SILICA
6 STANDARD Infinity 5.81
7 STANDARD 15.04 8.89 SAPPHIRE
8 EVENASPH 56.22 1.56
9 STANDARD Infinity 2.00
10 STANDARD 17.24 2.83 F_SILICA
11 STANDARD -449.60 3.10
12 STANDARD -11.84 1.80 KBr
13 STANDARD -49.22 2.15
14 STANDARD 31.13 3.78 SAPPHIRE
15 EVENASPH -26.69 0.81
16 STANDARD Infinity 2.00 F_SILICA
17 STANDARD Infinity 1.37
18 STANDARD Infinity 5.27
19 STANDARD Infinity 5.55 F_SILICA
20 STANDARD Infinity 0.00

The even aspheric surfaces sag is defined by the below equation:

Where K is conic constant. C is curvature. r is normalized height of the surface from optical axis. a1, a2, a3, a4 ..etc. are aspheric coefficients
surface a2 a3 a4
8 3.73E-005 -2.645E-007 3.55E-009
15 1.118E-004 -7.08E-008 5.64E-010
,CLAIMS:We Claim:

1. A compact wide angled ultra-violet optical system comprising:
a first negative power meniscus concave lens (L1), a negative power biconcave lens (L2), a first optical filter (F1), a second negative power meniscus convex lens (L3), a diaphragm (S), a positive power meniscus lens (L4), a negative power meniscus lens (L5), a positive power biconvex lens (L6), and a second optical filter (F2), wherein the filters F1 & F2 are made of special glass materials, where first filter inherently has the property of absorbing wavelength band lower than a particular cut off wavelength band and acts as long-pass filter and second filter absorbs high wavelength than the designated band and acts as short-pass filter.
2. The wide-angle solar-blind ultraviolet optical system as claimed in claim 1, comprises sequentially along the optical axis direction, First Negative Power Meniscus Concave Lens L1, Negative Power Biconcave Lens L2, First Optical Filter F1, Second Negative Power Meniscus Convex Lens L3, Diaphragm S, Positive Power meniscus Lens L4, Negative Power meniscus Lens L5, and positive power biconvex lens L6. Sensor/detector window and Image Plane [I] progressing from an object space to an image space.
3. The wide-angle solar-blind ultraviolet optical system as claimed in claim 1, wherein the filters F1 and F2 are made up of a special materials, where the filter F1 absorbs radiation below a designated wave band and acts as long-pass filter and the filter F2 absorbs radiation above of a designated wave band and acts as short-pass filter, where the filters F1 and F2 are dielectrically coated to give sharp cut-off band.
4. The wide-angle solar-blind ultraviolet optical system as claimed in claim 1, wherein the lenses L1, L2, L3, L4, L5 and L6, and filter F1, F2 arranged sequentially along the optical axis direction, works for FOV >130 degrees, operating wavelength of 240nm to 280nm for detector height of 25mm.
5. The wide-angle solar-blind ultraviolet optical system as claimed in claim 1, wherein the lenses L1, L2, L3, L4, L5 and L6, and filter F1, F2 arranged sequentially along the optical axis direction, contrived to work at a low aperture ratio of 2, and compact in size with total track less than 70mm.
6. The wide-angle solar-blind ultraviolet optical system as claimed in claim 1, wherein the system uses the standard materials of fused silica, sapphire, Kbr MgF2 and CaF2 for its superior ultraviolet transmission properties.