Cold start control system and method for use in coherent lightwave communications system
AssigneeFujitsu Limited
InventorsHiroshi Onaka, Hideyuki Miyata, Takao Naito
Life of this patent
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Abstract
A cold start control system and method for use in a coherent lightwave communications system, in which received signal light is mixed with local light to obtain an IF signal. In the cold start control, the frequency of the local light and/or the frequency of the signal light is swept in the state of the system capable of detecting the IF signal and discrimination between the real/image states and relative correction are made, and then, an AFC operation is started.
Claims17
A cold start control system for use in a coherent lightwave communications system, comprising:
- optical detection means for mixing signal light and local light to output an intermediate-frequency signal having a center frequency;
- automatic frequency control means for controlling the intermediate-frequency signal from said optical detection means such that the center frequency of the intermediate-frequency signal is held constant;
- sweep means for monitoring one of a presence and an absence of the intermediate-frequency signal output from said optical detection means and sweeping at least one of a frequency of the signal light and a frequency of the local light;
- decision means for stopping the sweep of the frequency by said sweep means upon detecting that the intermediate-frequency signal is output from said optical detection means and determining a relative frequency position between the signal light and the local light, the relative frequency position being indicative of which one of the frequency of the signal light and the frequency of the local light is higher than the other one;
- correction means for correcting at least one of the frequency of the signal light and the frequency of the local light when the relative frequency position determined by said decision means is different from a predetermined relative frequency position;
- and
- automatic frequency control on/off control means for selectively switching said automatic frequency control means between an operating state and a nonoperating state, switching said automatic frequency control means from the nonoperating state to the operating state upon when one of the relative frequency position determined by said decision means is in agreement with the predetermined relative frequency position and said at least one of the frequency of the signal light and the frequency of the local light is corrected by said correction means.
A cold start control method for use in a coherent lightwave communications system in which received signal light is mixed with local light to obtain an intermediate-frequency signal having a center frequency, said cold start control method comprising the steps of:
- sweeping at least one of a frequency of the local light and a frequency of the signal light;
- determining a relative frequency position, indicative of which one of the frequency of the signal light and the frequency of the local light is higher than the other one, between the local light and the signal light when the intermediate-frequency signal is detected;
- correcting at least one of the frequency of the local light and the frequency of the signal light when the relative frequency position obtained in said step of determining a relative frequency is different from a predetermined relative frequency position;
- and
- starting automatic frequency control when the relative frequency position obtained in said determining step is one of in agreement with the predetermined relative frequency position and the correction of the frequency of said at least one of the frequency of the signal light and the frequency of the local light to be corrected is made in said correcting step.
Dependencies are inferred from the claim text.