Since PMMA-BCP fairly absorption band extends from 350 nm to 450 nm, then polymer interaction with NH3 causes a refractive index shift at wavelengths around 1550 nm, given by [19]:��nPMMA?BCP(��,C)=F(��,��0)��(��0)vtSbpC(2)where ��0 is the absorption band central wavelength, F(��, ��0) is the proportionality factor between absorption and index changes, vt is the total number of BCP molecules per PMMA unit of volume, Sb is the reagent-analyte binding constant, p is the polymer permeability factor and C is the ammonia ambient concentration.Thus, a PMMA-BCP refractive index change determinates an effective index N change of mode propagating around the ring resonator. Microring resonant wavelength ��R is related to effective index by the following relation:��R=NLm(3)where m is the resonant mode order (m is an integer number) and L is the ring resonator length.

Effective index change implies a microring resonant wavelength shift (as schematically reported in Figure 2). Measuring the resonance wavelength shift around 1550 nm, it is possible to estimate Inhibitors,Modulators,Libraries the ammonia concentration in gaseous medium surrounding the sensor. The adoption of wavelengths around 1550 nm for optical sensing allows the additional advantage to use standard telecom equipments as lasers, photodetectors and so on.Figure 2.Proposed ammonia sensor operating principle.3.?Device SensitivityThe device sensitivity is one of the most important and critical aspect in sensor design and its theoretical estimation depends on a number of device Inhibitors,Modulators,Libraries geometrical and physical parameters.

Sensitivity of the designed sensor can be expressed as:����R��nc=����R��N��N��nc(4)where Inhibitors,Modulators,Libraries ��R is around 1550 nm and whose shift is measured to estimate the ammonia concentration, N is the ring mode effective Inhibitors,Modulators,Libraries index and nc is the cladding layer refractive index.Variation rate of N (as ��N/��nc) has been numerically estimated by a commercial mode solver [20] for bent waveguides based on Alternating Direction Implicit (ADI) method, by varying nc in a narrow range and observing the corresponding shift of N. Cilengitide The resonance wavelength incremental change (as a ratio between ����R and ��N) has been analytically estimated using the approach proposed in [21], obtaining the following formula:����R��N=[N(nc0,��R)��R??N?��|��=��R]?1(5)where nc0 is the PMMA-BMC refractive index before any interaction with ammonia.

In equation (5), N(nc0, ��r) and its derivative with respect to �� have been numerically estimated by ADI method. By eq. (5), it is possible to obtain the relationship:����R��nc=��N��nc[N(nc0,��R)��R??N?��|��=��R]?1(6)useful AZD9291 EGFR to make accurate estimations of the proposed sensor sensitivity. Thus, we have investigated the device sensitivity dependence on ridge height (h) and width (w), for different values of microring resonator radius (R) (see Figure 3 and and4).4). It can be observed the sensitivity as nearly independent from R, whereas it exhibits a quadratic dependence on w and h.