function frequency = wavelength2frequency(wavelength, inputUnit)
% Convert wavelength to optical frequency.
% Supported units: m, nm.

c = physconst('LightSpeed');

switch lower(inputUnit)
    case 'm'
        wavelength_m = wavelength;
    case 'nm'
        wavelength_m = wavelength .* 1e-9;
    otherwise
        error('Unsupported input unit "%s". Use "m" or "nm".', inputUnit);
end

frequency = c ./ wavelength_m;

end