This paper presents frequency difference detector method which can be used in frequency locking the wavelength of a local VCO laser diode to the reference wavelength fed from OFDM network. The basic structure of the proposed frequency difference detec...
This paper presents frequency difference detector method which can be used in frequency locking the wavelength of a local VCO laser diode to the reference wavelength fed from OFDM network. The basic structure of the proposed frequency difference detector is based on the master-slave configuration. The optical signals from the reference master laser source and local slave VCO laser are heterodyned on a photo detector, resulting in the microwave output signal corresponding to the difference frequency between two input optical signals. The output electrical difference signal is then compared to the microwave reference frequency through the mixer and OP amplifier as a frequency difference detector. The final difference signal output is filtered and integrated by the integrating loop filter for the frequency locking, and it is delivered to the current source of local VCO laser diode causing its output wavelength change corresponding to the input difference signal.
Through experiments with the calculated parameters, we confirmed that the frequency difference detector simply develops an error component that is proportional to the frequency difference between heterodyned optical signals and a reference 1.5GHz microwave oscillator. The achieved locking range of the VCO laser diode is around ± 200 MHz.