Method and apparatus for generation of coherent frequency combs
Embodiments of the invention provide apparatuses and methods for phase correlated seeding of parametric mixer and for generating coherent frequency combs. The parametric mixer may use two phase-correlated optical waves with different carrier frequencies to generate new optical waves centered at frequencies differing from the input waves, while retaining the input wave coherent properties. In the case when parametric mixer is used to generate frequency combs with small frequency pitch, the phase correlation of the input (seed) waves can be achieved by electro-optical modulator and a single master laser. In the case when frequency comb possessing a frequency pitch that is larger than frequency modulation that can be affected by electro-optic modulator, the phase correlation of the input (seed) waves is achieved by combined use of an electro-optical modulator and injection locking to a single or multiple slave lasers.
1. An apparatus for generating a frequency comb, the apparatus comprising:
an optical source operable to provide a first optical wave;
a wave splitter having an input port and at least two output ports, the input port being optically coupled to the optical source, wherein the wave splitter is operable to split the first optical wave into at least two separate second optical waves at the respective output ports, wherein the at least two second optical waves are characterized by respective first center frequencies separated from each other by a frequency spacing;
a set of slave laser sources, wherein each slave laser source is coupled to a respective output port of the wave splitter and operable to emit a respective third optical wave at a respective first center frequency via injection locking;
a wave combiner operable to combine the third optical waves emitted by the set of slave laser sources; and
a nonlinear optical medium optically coupled to the wave combiner and operable to input the third optical waves and to output a plurality of fourth optical waves characterized by respective second center frequencies separated from each other by the frequency spacing.
2. The apparatus of claim 1 wherein the optical source comprises:
a continuous wave optical source operable to provide a continuous optical wave; and
an optical modulator optically coupled to the continuous wave optical source and operable to transform the continuous optical wave into the first optical wave.
3. The apparatus of claim 1 wherein the first optical wave comprises a stream of optical pulses.
4. The apparatus of claim 1 wherein at least one second center frequency is different from any of the first frequencies.
5. A method of generating a frequency comb, the method comprising:
providing a first optical wave;
coupling the first optical wave into a nonlinear optical medium; and
transforming the first optical wave via the nonlinear optical medium into a plurality of second optical waves characterized by respective center frequencies separated from each other by a frequency spacing.
6. The method of claim 5 wherein the first optical wave comprises a stream of optical pulses.
7. The method of claim 6 wherein the first optical wave is characterized by a plurality of first center frequencies separated from each other by the frequency spacing.
8. The method of claim 5 wherein the first optical wave comprises a continuous optical wave characterized by a first center frequency and a first spectral linewidth.
9. The method of claim 8 comprising, after providing the first optical wave and before coupling the first optical wave into the nonlinear optical medium, modulating the first optical wave to transform the first optical wave into an optical wave characterized by a plurality of second center frequencies separated from each other by the frequency spacing.
10. The method of claim 9 wherein each of the plurality of second optical waves is characterized by a second spectral linewidth.
11. An apparatus for generating a frequency comb, the apparatus comprising:
an optical source operable to provide a first optical wave; and
a nonlinear optical medium optically coupled to the optical source and operable to receive the first optical wave and to output a plurality of second optical waves characterized by respective center frequencies separated from each other by a frequency spacing.
12. The apparatus of claim 1 wherein the nonlinear optical medium comprises at least one of a nonlinear optical fiber, a semiconductor waveguide, a nonlinear crystal, or a crystalline waveguide.
13. The apparatus of claim 1 wherein the first optical wave comprises a stream of optical pulses.
14. The apparatus of claim 13 wherein the first optical wave is characterized by a plurality of first center frequencies separated from each other by the frequency spacing.
15. The apparatus of claim 11 wherein the first optical wave comprises a continuous optical wave.
16. The apparatus of claim 15 wherein the first optical wave is characterized by a first center frequency and a first spectral linewidth.
17. The apparatus of claim 16 comprising an optical modulator optically coupled between the optical source and the nonlinear optical medium, wherein the optical modulator is operable to transform the first optical wave into an optical wave characterized by a plurality of second center frequencies separated from each other by the frequency spacing.
18. The apparatus of claim 17 wherein each of the plurality of second optical waves is characterized by a second spectral linewidth.
19. The apparatus of claim 17 wherein each second center frequency is different from the first center frequency.
20. The apparatus of claim 17 wherein the nonlinear optical medium comprises at least one segment characterized by a third-order susceptibility that is not less than about 1×10 −23 m 2 /V 2 measured at a frequency that is equal to one of the plurality of second center frequencies.