Interferometric distance measuring method with spectrally separable double chirp and device
In a distance-measuring method, chirped laser radiation with two separable radiation components is emitted to at least one target to be surveyed and via a local oscillator path, the radiation components having an opposite chirp as a time dependency of the modulated wavelengths (λ 1 , λ 2 ). After reception of the laser radiation scattered back from the target and passed via the local oscillator path, the laser radiation received is converted into signals and the distance to the at least one target is determined from the signals on the basis of interferometric mixing, separation of the radiation components being effected on the basis of their spectral characteristic.
1. A distance-measuring method comprising:
emitting a chirped laser radiation having two separable radiation components to at least one target to be surveyed and a local oscillator path, the radiation components having an opposite chirp;
receiving the laser radiation scattered back from the target and passed via the local oscillator path; and
determining at least one distance to the at least one target from the signals based on interferometric mixing, wherein the radiation components are chromatically separated on reception.
2. A distance-measuring method according to claim 1 , wherein the radiation components are emitted with a phase offset of the opposite chirps of 180°.
3. A distance-measuring method according to claim 1 , wherein the radiation components have different depths of modulation.
4. A distance-measuring method according to claim 1 , wherein the radiation components are separated on reception by discrimination of positive and negative frequencies around a modulation frequency.
5. A distance-measuring method according to claim 1 , wherein the radiation components are emitted with different average carrier wavelengths.
6. A distance-measuring method according to claim 5 , wherein the radiation components are separated on reception spectrally.
7. A distance-measuring method according to claim 1 , wherein one of the radiation components is emitted without modulation.
8. A distance-measuring method according to claim 1 , wherein, on determination of the at least one distance, a reference interferometer serves for taking into account or compensating nonlinearities in the production of the chirp.
9. A distance-measuring apparatus comprising:
a modulatable laser source for producing and for emitting laser radiation with two separable radiation components to a target to be surveyed;
a signal generator for modulation of the laser source of the radiation components with two opposite chirps; and
a receiver including:
a measuring interferometer consisting of a measuring arm and a local oscillator arm with at least one detector for receiving the laser radiation scattered back from a target; and
a mixer for carrying out a heterodyne interferometric mixing method, wherein the radiation components are chromatically separated on the receiver side.
10. A distance-measuring apparatus according to claim 9 , the mixer for carrying out a heterodyne interferometric mixing including a reference interferometer for taking into account or compensating nonlinearities in the production of the chirp.
11. A distance-measuring apparatus according to claim 9 , further comprising an acousto-optical modulator for raising the local oscillator of the measuring interferometer around a modulated frequency of the modulator.
12. A distance-measuring apparatus according to claim 11 , wherein the separation of the radiation components is achieved by discrimination of higher and lower frequencies around the modulation frequency.
13. A distance-measuring apparatus according to claim 9 , wherein the laser source has two laser diodes and with different average carrier wavelengths.
14. A distance-measuring apparatus according to claim 9 , wherein the laser source has two laser diodes and wavelengths of 1530 nm and 1540 nm.
15. A distance-measuring apparatus according to claim 9 , wherein the optical connections between components of the distance-measuring apparatus are in the form of single-mode fibres.
16. A distance-measuring apparatus according to claim 9 , wherein the detector has two detector units for spectrally separate reception of the radiation components.
17. A distance-measuring apparatus according to claim 9 , wherein the detector has a dielectric or dispersive element for chromatic separation of the back-scattered laser radiation into the radiation components.