Frequency Conversion of a Wavelength Division Multiplexed Light Source

Abstract

A method for generating frequency converted laser radiation is disclosed. The disclosure provides a method enabling generation of a frequency converted wavelength division multiplexed light source that is easy to implement at low cost. Adjustment of the center frequency and the mode spacing in a frequency converted wavelength division multiplexed light source is also disclosed. A related method of use discloses generating pump laser radiation through combination of multiple pump sources in a wavelength division multiplexed arrangement; passing the pump laser radiation through the non-linear medium of a singly resonant, single-frequency optical parametric oscillator, wherein the pump laser radiation is continuous wave or pulsed, wherein the pulse duration in the latter case is longer than the time the optical parametric oscillation requires to reach its steady state; and coupling out the non-resonant idler or signal laser radiation from the optical parametric oscillator as usable frequency converted laser radiation. Moreover, the invention relates to a laser device for carrying out the method of the invention.

Claims

1. A method for generating frequency converted laser radiation, comprising the steps of: generating pump laser radiation comprised of a wavelength division multiplexed optical communication source; passing the pump laser radiation through the non-linear medium of a singly resonant, single-frequency optical parametric oscillator, wherein the pump laser radiation is continuous wave or quasi-continuous wave such that parametric oscillation is maintained; and coupling out the non-resonant idler or signal laser radiation from the optical parametric oscillator as usable frequency converted laser radiation.

2. Method of claim 1, wherein the spectrum of the usable frequency converted laser radiation coupled out from the optical parametric oscillator is a frequency converted replica of the spectrum of the pump laser radiation.

3. Method of claim 1, wherein the resonant linewidth of the singly resonant optical parametric oscillator is smaller than the linewidths of the individual optical communications channels contained in the pump laser radiation.

4. Method of claim 1, wherein the frequency of the usable frequency converted laser radiation is adjusted by changing the phase snatching conditions of the non-linear medium and/or changing the resonant frequency of the singly resonant, single-frequency optical parametric oscillator and/or changing the resonant mode of the singly resonant, single-frequency optical parametric oscillator and/or tuning the center frequency of the pump laser radiation.

5. Method of claim 1, wherein the optical spectrum of the usable frequency converted laser radiation is actively stabilized by electronic feedback to the spectrum of the pump laser radiation and/or to the resonant mode of the singly resonant optical parametric oscillator.

6. Method of claim 1, wherein said WDM source comprises a laser source further comprising a plurality of approximately equidistant narrow spectral lines, each of which is an information carrier.

7. Method of claim 6, wherein each information carrier is independently modulated in amplitude in order to independently encode information on that carrier.

8. Method of claim 6, wherein each information carrier is independently modulated in phase in order to independently encode information on that carrier.

9. Method of claim 6, wherein a single channel of the WDM source is maintained in the on state without amplitude modulation, in order to prevent a situation where amplitude modulation leaves all channels with zero power. Loss of power to the optical parametric oscillator for sufficient time will halt frequency conversion.

10. A laser device comprising: a pump laser source comprised of a wavelength division multiplexed optical communication source; a singly resonant, single frequency optical parametric oscillator comprising a non-linear medium located in an optical cavity, with the pump laser radiation passing through the non-linear medium, wherein the optical cavity is configured to be resonant at only a single cavity mode, wherein the pump laser radiation is continuous wave or quasi-continuous wave such that parametric oscillation is maintained; and an arrangement of one or more optical components configured to couple out the non-resonant idler or signal laser radiation from the optical parametric oscillator as usable frequency converted laser radiation.

11. Laser device of claim 10, wherein the pulse duration of the pump laser radiation is longer than a multiple of the round-trip time of the resonant signal or idler radiation in the optical cavity.

12. Laser device of claim 10, wherein the optical cavity is a bow-tie cavity.

13. Laser device of claim 10, wherein an etalon is located within the optical cavity in the beam path of the resonant signal or idler laser radiation and outside the beam paths of the pump laser radiation and the non-resonant idler or signal laser radiation.

14. Laser device of claim 10, wherein the non-linear medium is a periodically poled non-linear crystal.

15. Laser device of claim 10, wherein said WDM source comprises a laser source further comprising a plurality of approximately equidistant narrow spectral lines, each of which is an information carrier.

16. Laser device of claim 16, wherein each information carrier is independently modulated in amplitude and/or phase in order to independently encode information on that carrier.

17. Laser device of claim 16, wherein a single channel of the WDM source is maintained in the on state without amplitude modulation, in order to prevent a situation where amplitude modulation leaves all channels with zero power. Loss of power to the optical parametric oscillator for sufficient time will halt frequency conversion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The enclosed drawings disclose preferred embodiments of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.

[0023] FIG. 1 schematically illustrates an example laser device according to an embodiment of the invention as a block diagram.

[0024] FIG. 2 is a more detailed illustration of the example laser device of FIG. 1.

DETAILED DESCRIPTION

[0025] FIG. 1 schematically illustrates a laser device according to an embodiment of the invention. In one embodiment, the laser device comprises a pump laser source 11. In a further embodiment, the spectrum of the pump laser source 11 is a wavelength division multiplexed optical communications source.

[0026] In another embodiment, the pump laser radiation is provided to a singly resonant, single-frequency optical parametric oscillator 12. In the depicted embodiment, the optical parametric oscillator 12 has three outputs, namely a residual pump output 13, a resonant output 15 and a non resonant output 14.

[0027] In one example embodiment, the non-resonant (idler or signal) laser radiation is coupled out from the optical parametric resonator 12 as usable frequency converted laser radiation via output 14. The (idler or signal) laser radiation at the non-resonant output 14 has a spectrum which is the convolution of the spectrum of the pump laser radiation and the spectrum of the single resonant cavity mode of the optical parametric oscillator 12. In such case the single cavity mode spectrum is generally, though not necessarily, much narrower than the spacing between the spectral lines in the pump spectrum, thus the laser radiation at the non-resonant output 14 also is a wavelength division multiplexed optical communications source.

[0028] In the example embodiment of FIG. 2, a non-linear medium 21 (e.g., a periodically poled non-linear crystal) is placed inside a bow-tie cavity 23 that is resonant for either the signal or idler laser radiation. In one embodiment, an etalon 22 is placed in the cavity 23 outside the beam path of the pump laser radiation and the non-resonant (idler respectively signal laser radiation). In another, the cavity 23 is designed to be resonant at only one single cavity mode that matches the spectrum of the signal or idler laser radiation. In a further embodiment, the residual pump laser radiation and the non-resonant output beam paths (for coupling out the usable frequency converted laser radiation) are split using a dichroic filter 25. In other embodiments, the residual pump 13 and resonant output 15 are accessible to the user of the device as well. In a further embodiment, the pump laser radiation is continuous wave or quasi-continuous wave such that parametric oscillation is maintained.

[0029] In further embodiments, the wavelength division multiplexed optical communications source contained in the spectrum of the usable laser radiation at the non-resonant output 14 is frequency tuned by adjusting the phase matching conditions in the non-linear medium 21, for example, by heating, rotating, or shifting the medium. In one embodiment, the wavelength division multiplexed optical communication source contained in the radiation at the non-resonant output 14 is also tuned by adjusting the length of the cavity, for example, by using a piezoelectric transducer 24 carrying one of the cavity mirrors and/or by rotating the etalon 22.

[0030] In other embodiments, the wavelength division multiplexed optical communication source at the non-resonant output 14 can further be tuned by selecting a different cavity mode for oscillation, for example, by rotating the etalon 22 to such a degree that a cavity mode hop occurs. In further embodiments, the wavelength division multiplexed optical communication source at the output 14 is tuned by wavelength tuning of the pump laser source 11. In still further embodiments, the pump laser source 11 is wavelength tuned and the resonant mode of the cavity 23 does not change, so energy conservation causes the radiation at the non-resonant output 14 to change by the same amount of energy as the pump laser radiation.

[0031] Though the present invention has been depicted and described in detail above with respect to several exemplary embodiments, those of ordinary skill in the art will also appreciate that minor changes to the description, and various other modifications, omissions and additions may also be made without departing from either the spirit or scope thereof.