טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSassoon Eden
SubjectFlare in Interference-Based Hyperspectral Cameras
DepartmentDepartment of Electrical Engineering
Supervisors Professor Yoav Schechner
Dr. Avital Treibitz
Full Thesis textFull thesis text - English Version


Abstract

Hyperspectral cameras generally seek to resolve well defined, narrow spectral bands. Signal energy decreases as a pass-band narrows. Hence there is an important need for efficiency of light transfer, minimizing energy loss in the spectral band that passes to the detector. Meeting these two needs can be engineered using established theory and tools, based on {\em interference}. Recent technological developments enable such interference-based snapshot hyperspectral cameras (SHYCs) which are fast, compact, robust and modular making them suitable for imaging dynamic environments or for mounting on autonomous platforms, drones, etc. We point out a caveat in this design, of implication to snapshot hyperspectral Imagers, a stray light (flare) effect of significant magnitude. Stray light is formed inside imaging systems by internal reflections between the optical elements.

Contrary to traditional broad-band filters, which often absorb unwanted light, narrow band-pass interference filters reflect non-transmitted light. This is a source of very significant flare which biases hyperspectral measurements. The bias in any pixel depends on spectral content in other pixels. We present a theoretical image formation model for this effect, and quantify it through simulations and experiments. Lens flare in wide-band cameras is typically weak as it is mainly caused by second order lens reflections. Contrary to that, we show that flare induced by interference-based filters (FIIF) is caused by first order lens reflections. This yields contamination in the order of several percent over a wide range of wavelengths in the visible range,  for a camera lens consisting of 7 lens elements and high performance anti-reflective coating. We show that contrary to typical models, FIIF is highly non uniform spatially and spreads over large regions inside the field-of-view. In addition, we test deflaring of signals affected by FIIF.