NOVEL IMAGE PROCESSING APPLICATIONS OF A BIREFRINGENT LENS IN THE INFRARED REGION

Authors

  • Pranati Mandal Ptu Roll No.- 1168657 Master Of Technology, Electronics And Communication, Punjab College Of Engineering & Technology , Lalru
  • Sandeep Kumar Assistant Professor , Electronics and Communication Engineering , PCET ,Lalru

Keywords:

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Abstract

The techniques for pre-specified modification of the imaging characteristics of an optical system received
considerable attention since the early days of systematic investigation of optical imagery [1 -2]. It was found that the
pupil function of any optical system plays an important role in this regard. The desired modification of the imaging
characteristics is usually implemented by using a mask on the pupil of the optical system. Extensive studies have been
carried out in this direction and the use of amplitude masks and phase masks have been reported [3-7]. Usually each
mask is dedicated to a specific purpose and on-line modification of such masks is not possible. At the same time,
synthesis of the pupil function for yielding a specific imaging characteristic is indeed a formidable task and remains
practically insolvable except for some limitingly terminal and simple cases.

It has been recognized that the polarization properties of light, if ingeniously used, offers additional flexibilities to the
optical designers that are unachievable by scalar wave properties alone [8-16]. The advantage of these polarizationbased optical systems is that their imaging properties can be continuously altered in situ. Polarization is used as a
parametric variable to introduce a variation in the complex amplitude of the pupil. Obviously, two degrees of freedom
due to two orthogonal states of variation are available to continually change the imaging properties of these systems by
varying the relative contributions of the two orthogonal components. However, fabrication and accurate alignment of
such masks are quite troublesome and a considerable loss of light due to absorption, scattering etc. takes place in the
masking element. Thus, a system, easily realizable, equally effective as well as free from the previously stated problems,
had long been a requirement. Optical systems fabricated with birefringent materials have this potential and this
motivated many researchers to investigate the behaviour of a birefringent lens made of a uniaxial crystal [17-26]. A
uniaxial birefringent lens sandwiched between two linear polarizers with its optic axis perpendicular to the lens axis
behaves like an ordinary lens with a radially varying complex filter at its pupil plane [17 -18]. Since the filter is
generated because of the interference phenomenon, the problem associated with the alignment is removed. The imaging
characteristics of the said system can be altered continuously just by changing the orientation of the any of the two
polarizers. This makes the proposed system more versatile.
The imaging characteristics of the proposed system under diffraction-limited condition were studied [17-21]. The
same system may be adapted either for enhanced resolution or for apodization just by rotating any polarizers included in
the system. This system behaves as a double focus lens in general and by varying the birefringent lens parameters it is
possible to change the separation between the two foci. The proposed system may be designed to obtain noticeably high
depth-of-focus compared to an identical ordinary lens [19]. The imaging characteristics of the proposed system in
presence of pre-specified on-axis and off-axis aberrations were studied [22-24]. It shows higher tolerance to the
aberrations than an identical conventional lens. The effect of polychromatic visible light on the performance of the
system was also investigated [25]. The study revealed that the focusing characteristics of the proposed system do not
change appreciably under polychromatic illumination from that under strictly monochromatic illumination. The need for
appropriate infrared imaging devices and components has been on the rise [27 -34]. The applications of proposed system
under monochromatic or polychromatic beam illumination in the infrared region have not been
explored till date. We study the viability of the proposed system considering crystal quartz as the birefringent lens
material in the infrared region. In this connection it may be mentioned that the coefficient of absorption for the crystal
quartz is less than 0.030 cm-1
in the region approximately from 190 nm to 2900 nm [35]. The infrared band is often
subdivided into smaller sections though the divisions are different for different applications [36]. We consider the range
of wavelengths for which infrared photography (700 nm to 900 nm) and short-wave infrared (SWIR) defence applications
(900 nm to 1700 nm) usually take place. The wavelength of around 1550 nm is used for mode rn fiber-optic
communication [37]. Thus the proposed system may find applications in multiple domains, such as SWIR defence and
surveillance purposes, infrared photography, medicine, archaeology, modern fiber-optic communication systems and
many other infrared imaging devices. The axial irradiance distribution function and the intensity point spread function
are considered as the image assessment parameters. The results show that all the above properties of the said system are
retained even under infrared illumination having large bandwidth.

Published

2015-06-25

How to Cite

Pranati Mandal, & Sandeep Kumar. (2015). NOVEL IMAGE PROCESSING APPLICATIONS OF A BIREFRINGENT LENS IN THE INFRARED REGION. International Journal of Advance Engineering and Research Development (IJAERD), 2(6), 517–533. Retrieved from https://ijaerd.com/index.php/IJAERD/article/view/897

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