Research

Optical Metrology Lab

Research Lead: Prof. Gufran S. Khan

• Optical design

Design of freeform optics for non-imaging applications

The design of freeform and structured freeform optics have been introduced in various applications like ultra-short projection system, as optical front-end for VLC receiver systems, for uniform illumination for automobile headlamps etc. For projection system used freeform optics to generate optical surface for illumination of image modulator. Here, the non-uniform irradiance of LED is redistributed uniformly using structured freeform surfaces as a secondary optics. Freeform as optical front-end is used VLC receiver system to mitigate co-channel interference and improve SINR in indoor environment. Freeform mirror is used as LED collimator for automobile headlamps.

Multilayer dielectric grating for CPA

Multilayer dielectric grating comprising a dielectric mirror, top of that high index corrugation at the layer-air interface. Due to leaky mode resonance, grating can obtain 100% diffraction efficiency (for -1^st order).

• Optical metrology

A quantitative in-situ measurement scheme using Shack Hartmann wavefront sensor for aspheres and freeforms has been developed by his research team. The SHS offers the potential to be incorporated into the machine environment due to its less vibration sensitivity, compactness, simple principle of operation, and 3D shape measurement capability from slope data. It can

 

measure the slopes up to ~ 15 mrad in a single measurement. The SHS has the potential to be integrated on to the manufacturing platform for in-situ measurement process in order to develop the asphere and freeform surfaces within the required tolerances. It is used as a metrology tool for testing both the transmission as well as in reflection mode. The sensor can also be used for testing micro-optics, intraocular lenses, and laser beam characterization.

At present, the technique has been demonstrated for the fabrication and testing of a freeform surface within the accuracy of a wavelength (0.63 μm), which is good enough for the applications in IR optical systems. Further, a metrology technique suitable for an in-situ measurement in off-line using a scanning SHS in reflection mode has been developed. The results have been used as the feedback mechanism for corrective machining of freeform optics.

In recent future, the integration of the wavefront sensor, utilizing the scanning sub-aperture scheme along with the error feedback algorithm, with ultra-precision multi-axis machining platform for in-situ measurement in reflection mode will pave the way forward for the development of freeform optics with the precision required for imaging applications.

• Optical fabrication

 Ultra-precision SPDT

His lab has the facility of 5-axes ultra-precision SPDT with slow tool servo. Both freeform lenses and mirrors have been fabricated for applications like wavefront sensors, IR imaging, patterned illuminations etc. His team is working on fabricating grating structures on curved and freeform surfaces by ultra-precision machining slow tool servo for hyperspectral applications.  

Conventional optical workshop

In optical workshop, conventional optics are prepared using following steps (i) Curve generation and grinding Section, (ii) Polishing and Centering & Edging Section (iii) Metrology Section, and (iv) Coating and assembly Section. The Curve generation and grinding Section is equipped with slitting, trepanning, curve generation and rough grinding machines. The polishing section comprises four spindle machines and two spindle machine for polishing up to 12 inch optics. It also has centring and edging machine.