Phase noise compensation system, and method
AssigneeQinetiq Limited
InventorsDavid Arthur Orchard, Peter David Kightley, Malcolm David Macleod
Life of this patent
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Abstract
A system for compensating for phase noise, with particular application in lidar, includes a compensation interferometer that receives a signal from a source, and splits it into a first and second path, with a path length difference Δτ between them. Typically the path length is significantly less than that of the return distance to a target. The output of the compensation interferometer, which consists of phase noise generated in time Δτ is vectorially summed during a time similar to a signal flight time to a target, and the result used to reduce phase noise present on measurements of a target. It further includes means for selecting Δτ such that competing noise elements are reduced or optimised.
Claims19
A system comprising:
- a) a signal generator for providing a signal,
- b) a splitter for splitting the signal from the signal generator and directing it to a measurement path and a compensation path, wherein:
- i) the measurement path comprises a measurement interferometer having a splitter for splitting the signal into a first and a second part, the measurement interferometer being arranged to transmit the first part to a remote target, and to receive reflections therefrom, and to combine the received reflections with the second part in a measurement interferometer mixer, and
- ii) the compensation path comprises a compensation interferometer arranged to split its input signal into a first, delayed path, and a second, undelayed path, and to combine the first and second paths in a compensation interferometer mixer to produce an output bearing information pertaining to a phase difference between the two paths, the relative delay between the first and second paths being a predetermined time Δτ;
- c) a processor configured to calculate a phase compensation figure by digitally measuring a phase change across n successive passes through the compensation interferometer over a time nΔτ, where nΔτ is equal to n times the predetermined time Δτ, and subtracting the calculated phase compensation figure from the output of the measurement interferometer,
- wherein the system is arranged to calculate a range L/2 to the remote target based upon the compensated output from the measurement interferometer, said range giving a time delay τ to the received reflections as compared to the second part, and wherein the phase compensation figure is calculated under the condition that |τ−nΔτ|≤Δτ/2.
A method for compensating for phase noise in a LIDAR or radar, comprising the steps of:
- i) generating a signal;
- ii) splitting the signal into a measurement signal and a compensation signal and directing the measurement signal to a measurement path and directing the compensation signal to a compensation path;
- iii) transmitting a first part of the measurement signal in the measurement path to a remote target, and mixing returns from the remote target with a second part of the measurement signal in a measurement interferometer mixer to down-convert the returns;
- iv) passing the compensation signal into a compensation interferometer arranged to split its input signal into a first, delayed path, and a second, undelayed path, wherein a relative delay between the first and second paths being a predetermined time Δτ;
- v) calculating a phase compensation figure by measuring a phase change across n successive passes through the compensation interferometer over a time nΔτ, where nΔτ is equal to n times the predetermined time Δτ;
- vi) subtracting the calculated phase compensation figure from the down-converted output of the measurement interferometer mixer of step (iii);
- and
- vii) calculating a range L/2 to the target based upon the compensated output from the measurement interferometer, wherein said range giving a time delay τ to the received reflections as compared to the second part, and wherein the phase compensation figure is calculated under the condition that |τ−nΔτ|≤Δτ/2.
Dependencies are inferred from the claim text.