Table V.

Table comparing the bulk electromechanical and optomechanical strengths of some commonly used materials (adapted from Ref. [83]).

Material	EM coupling	OM coupling
Metric	$k_{\text{EM}}^2=\frac{e^2}{\epsilon c}$	$M=\frac{n^6{p}^3}{\rho v^3}\times {10}^{16}$
Units	%	s3/kg
Silicon	0	300
Quartz	1	17
GaAs	0.4	2000
GaP	0.2	630
GaN	1.3	1.3
GaPO4	1.7	500
AlN	7	0.2
LiNbO3	17	26
BaTiO3	60	1200

The electromechanical coupling coefficient ($k_{\text{EM}}^2$, material only) is defined in terms of the piezoelectric coefficient (e), the dielectric constant (ϵ), and the elastic coefficient (c). The optomechanical figure of merit (M) is defined (λ=1.55 μm) in terms of the refractive index (n), the photoelastic coefficient (p), density (ρ), and the speed of sound (v). Displayed values are based on the maximum piezoelectric and photoelastic coefficients for the materials.