Progress update: Compact measurement LED-based head
We have developed two concepts of miniature sensors based on LED-photodiode mid-IR optopair together with specific measuring algorithm that were used for determination of liquid composition by monolithic on-chip prototypes operating at 3.6 and 3.4 um wavelengths (see Fig.). Noise measurements in an immersion lens LED-photodiode pair (3.4 um) showed low LED output noise, the noise was less than that in the Black Body- photodiode pair. Reports on optical schematics and recommendations (D5.1 and D5.2) as well as the manufacturing and delivery of two samples of sensors (MS5) have been accomplished. Several aspects of the research results have been disclosed in two patents active in RF and in three scientific papers (DOI: 10.1002/pssa.202100456, 10.1134/S0030400X21090101, 10.1016/j.infrared.2021.103867).
Heterostructure LEDs and photodiodes produced by IoffeLED Ltd. were characterised and compared with other devices available in the market. Using specifications and measured parameters the LED drivers and the photodiode amplifiers have been developed and tested as well as drivers and control electronics for Thermo-Electric Coolers (TEC).
The delivered monolithic sensors (MS5) do not meet all project requirements so far, e.g. they are not adapted for measurements of solids due to mechanical (reliability) issues. Thus the nearest WP5 goal is to develop miniature ATR sensor head tolerant to mechanical stresses and appropriate for measuring of solids. Another issue to be solved is a heating (heatsinking) in LED-PD based sensor due to a LED operation that makes ground for measurement errors and uncertainties. The problem has been already partly solved by implementation of the abovementioned algorithm, however further study is of necessity. Thus near future research include design upgrade, precise temperature distribution measurements at different heatsinking conditions and improving correction accuracy in monolithic sensor constructions.