Optical modules and methods for making optical modules are described. The apparatus detects a frequency difference between at least one reference signal and an output signal, and generates a frequency error signal in response to the frequency difference. metal or paper strips, provides data records for a strip surface according to coordinates with information about a condition of the strip, its surface or anomalies. The formation of the titanium tantalum silicon nitride Nz) layer is compatible with integrated circuit fabrication processes.