*2.2. Interrogator Design*

The previously presented AWG is the main component of the interrogator. To eliminate influences of the temperature on the optical properties of the AWG, it is fixed to an isothermal plate with a set temperature of 25 ◦C and regulated by a Peltier controller (MTD415L, Thorlabs). After polishing, a single-mode fiber is glued to the AWG polymeric input waveguide. At the other end of the fiber, a FC/APC connector is attached and is connected to a fiber port. The output waveguides face directly to a vertical CMOS linear image Sensor (iC-LFH1024, iC-Haus, Bodenheim, Germany). The sensor has a total of 1024 pixels, each with 600 μm height and 12.7 μm width. The output with its intensity maximum for a wavelength of 852.6 nm is positioned at pixel 407, the output with its intensity peak at a wavelength of 851.6 nm is positioned at pixel 486, and the third output with its intensity maximum at a wavelength of 850.6 nm is positioned at pixel 565, respectively. The descending order of wavelength at an increasing order of pixel number is simply because the CMOS linear image sensor is fixed up-side-down to the isothermal plate for easier connectorization. The CMOS linear image sensor is controlled and read-out by a microcontroller (Teensy 3.2, PJRC), that transmits its data via USB to a primary computer where they are processed further. The described components are placed in a lightproof aluminum casing. A schematic overview is shown in Figure 2.

**Figure 2.** Schematic (**a**) and photographic (**b**) overview of the AWG interrogator. The polymeric AWG (A) is connected with a single-mode fiber (B) at the input and fixed on an isothermal plate (C). The output waveguides end facets are attached directly to the vertical CMOS linear image sensor (D). The CMOS sensor is read-out by a microcontroller (E). The TEC controller (F) is also allocated within the system.
