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A multiple wavelength light source generates an output signal having a comb of accurately spaced apart frequencies with variable free spectral range in the C-band of optical fiber communication. The light source employs an electro-optical modulator (EOM) driven by a signal generator which modulates

A multiple wavelength light source generates an output signal having a comb of accurately spaced apart frequencies with variable free spectral range in the C-band of optical fiber communication. The light source employs an electro-optical modulator (EOM) driven by a signal generator which modulates with EOM with multiple modulation frequencies to widen the output spectrum of signal. The EOM has a crystal provided with a waveguide. The waveguide may be doped with a rare-earth metal to impart gain properties to equalize the intensities of the comb. In one preferred embodiment, Er, Yt or other doping elements provide the gain property to waveguides. The crystal is also provided with periodically poled structure, and this may be engineered so as to form domains of unequal widths to improve the efficiency of modulation. The output signal from the light source may be split and presented to a bank of filters to create a multiple signals, each signal having one of the spaced apart frequencies. The output signals may be used as channels to be modulated by data and then combined in dense wavelength division multiplexing system, or may be used as a soliton source in time-division multiplexed communication systems.

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What is claimed is: 1. A multi-frequency light source comprising: at least one laser configured to output a first light signal having a first frequency; an electro-optical modulator (EOM) comprising: a waveguide having a first and a second end, the waveguide extending along a light propagation dime

What is claimed is: 1. A multi-frequency light source comprising: at least one laser configured to output a first light signal having a first frequency; an electro-optical modulator (EOM) comprising: a waveguide having a first and a second end, the waveguide extending along a light propagation dimension; and a signal generator configured to apply a modulation signal to drive the EOM; a first mirror positioned in an optical path between the at least one laser and the first end of the waveguide, a second mirror positioned at the second end of the waveguide; wherein the waveguide includes a plurality of alternately poled optical domains, each optical domain having a width defined along the light propagation dimension, the plurality of optical domains collectively having a periodic width structure, and wherein the first mirror comprises a first number of alternating layers formed from a first material having a first index of refraction, and a second material having a second index of refraction, wherein the first and second indices of refraction either greater or less than an index of refraction of the waveguide. 2. The multi-frequency light source according to claim 1, wherein the width of the optical domains is at least about 0.5 and is less than about 3 millimeters. 3. The multi-frequency light source according to claim 1 wherein the first mirror having reflectivity of at least 80%. 4. The multi-frequency light source according to claim 1, wherein each layer is between 0.3-0.6 microns in thickness. 5. The multi-frequency light source according to claim 1, wherein the layers formed from the first material have a first thickness and the layers formed from the second material have a second thickness, the first and second thicknesses being different from one another. 6. The multi-frequency light source according to claim 1, wherein widths of the alternating layers increase in a direction away from the first end of the waveguide. 7. The multi-frequency light source according to claim 1, wherein the second mirror comprises a second number of alternating layers formed from a first material having a first index of refraction, and a second material having a second index of refraction, wherein the first and second indices of refraction fall on either side of an index of refraction of the waveguide. 8. The multi-frequency light source according to claim 1, wherein the periodic width structure has a periodicity of two and the waveguide comprises domains having alternating first and second widths along he light propagation dimension. 9. The multi-frequency light source according to claim 8, wherein the first and second widths are the same size. 10. The multi-frequency light source according to claim 8, wherein the first and second widths are of different size. 11. The multi-frequency light source according to claim 10, wherein the first width is at least twice as large as the second width. 12. The multi-frequency light source according to claim 10, wherein the first width is at least three times as large as the second width. 13. The multi-frequency light source according to claim 1, wherein the periodic width structure has a periodicity of six, each period of six comprising two repeated blocks of three domains each, the three domains having first, second and third widths. 14. The multi-frequency light source according to claim 13, wherein the second and third widths are the same, and are dissimilar from the first width. 15. The multi-frequency light source according to claim 1, wherein the periodic width structure has a periodicity of a number N and the waveguide comprises repeated blocks of domains having first through Nth widths which are all dissimilar to one another and wherein N>3. 16. The multi-frequency light source according to claim 1, wherein the modulation signal comprises multiple frequencies. 17. The multi-frequency light source according to claim 16, wherein the excitation signal comprises two frequencies, one of which is a multiple of the other. 18. The multi-frequency light source according to claim 16, wherein the modulation signal comprises three frequencies, two of which are multiples of a lowest of the three frequencies. 19. The multi-frequency light source according to claim 1, wherein the waveguide is formed by titanium doping a crystal. 20. The multi-frequency light source according to claim 19, wherein the titanium doped waveguide is doped with a gain medium. 21. The multi-frequency light source according to claim 20, wherein the gain medium comprises at least one from the group consisting of erbium and yttrium. 22. The multi-frequency light source of claim 1 comprising: a signal generator configured to apply a modulation signal to drive the EOM; and a duty cycle of the periodic structure being chosen to facilitate energy transfer to side harmonics of an output optical comb signal, and wherein the modulation signal comprises at least a first component and a second of the modulation signal applied simultaneously to drive the EOM. 23. The multi-frequency light source of claim 22, wherein the waveguide is provided with a plurality of alternately poled optical domains having a periodic width structure, and a duty cycle other than 50%. 24. The multi-frequency light source of claim 23, wherein the modulation signal comprises at least three frequency components of the modulation signal, wherein all components are applied simultaneously to drive the EOM. 25. A wavelength division multiplexed optical communication system including a multi-frequency light source comprising: at least one laser configured to output a first light signal having a first frequency; an electro-optical modulator (EOM) comprising: a waveguide having a first end and a second end, the waveguide extending between said first and second ends along a light propagation dimension; a signal generator configured to apply a modulation signal to drive the EOM; a first mirror positioned in an optical path between the at least one laser and the first end of the waveguide, a second mirror positioned at the second end of the waveguide; wherein the waveguide is provided with a plurality of alternately poled optical domains, each optical domain having a width defined along the light propagation dimension, the plurality of optical domains collectively having a periodic width structure, and wherein the first mirror comprises a first number of alternating layers formed from a first material having a first index of refraction, and a second material having a second index of refraction, wherein the first and second indices of refraction either greater or less than an index of refraction of the waveguide. 26. A time division multiplexed optical communication system including a multi-frequency light source comprising: at least one laser configured to output a first light signal having a first frequency; an electro-optical modulator (EOM) comprising: a waveguide having a first end and a second end, the waveguide extending between said first and second ends along a light propagation dimension; and a signal generator configured to apply a modulation signal to drive the EOM; a first mirror positioned in an optical path between the at least one laser and the first end of the waveguide, a second mirror positioned at the second end of the waveguide; wherein the waveguide is provided with a plurality of alternately poled optical domains, each optical domain having a width defined along the light propagation dimension, the plurality of optical domains collectively having a periodic width structure, and wherein the first mirror comprises a first number of alternating layers formed from a first material having a first index of refraction, and a second material having a second index of refraction, wherein the first and second indices of refraction either greater or less than an index of refraction of the waveguide. 27. A optical modulator sub-assembly comprising: an electro-optical modulator (EOM) comprising: a waveguide having a first end and a second end, the waveguide extending along a light propagation dimension between the first and second ends; a signal generator configured to apply a modulation signal to drive the EOM; a first mirror situated at the first end of the waveguide; and a second mirror situated at the second end of the waveguide; wherein the waveguide is provided with a plurality of alternately poled optical domains having a periodic width structure, and a duty cycle other than 50%, and wherein the first mirror comprises a first number of altemating layers formed from a first material having a first index of refraction, and a second material having a second index of refraction, wherein the first and second indices of refraction either greater or less than an index of refraction of the waveguide. 28. The optical modulator sub-assembly of claim 27, wherein the modulation signal is a multi-frequency modulation signal. 29. The optical modulator sub-assembly of claim 28, wherein the waveguide comprises a gain medium. 30. A optical device comprising: a first and a second optical cavities, the first and second optical cavities having respective, different lengths; a waveguide configured to receive light from a light source, wherein light received from the light source propagates along the waveguide; and an electro-optical modulator (EOM) configured to subject light propagating along the waveguide to multi-frequency modulation, the multi-frequency modulation generating light having at least first and second different frequencies, wherein the first optical cavity is configured to support oscillation of light having the first frequency and the second optical cavity is configured to support oscillation of light having the second frequency, and wherein a boundary of the first optical cavity is defined by a first layer of dielectric material and a boundary of the second optical cavity is defined by a second layer of different dielectric material, the first and second layers each having a respective different thickness. 31. The optical device of claim 30, wherein a boundary of the first optical cavity is defined by a first layer of dielectric material, having a first thickness of 0.3 to 0.6 micrometers, and a boundary of the second optical cavity is defined by a second layer of different dielectric material, the first and second layers each having a respective different thickness. 32. The optical device of claim 30, wherein an extent of the second cavity resides within the first cavity. 33. The optical device of claim 30, wherein first and second layers are layers of a chirped mirror. 34. The optical device of claim 30, wherein the waveguide is provided with a plurality of altemately poled optical domains having a periodic width structure, and a duty cycle other than 50%. 35. The optical device according to claim 30, wherein the waveguide is formed by titanium doping of a crystal. 36. The optical device according to claim 30, wherein the waveguide is doped with a gain medium. 37. The optical device according to claim 36, wherein the gain medium comprises at least one from the group consisting of erbium and yttrium. 38. The optical device according to claim 30, wherein the modulation signal comprises three frequencies, two of which are multiples of a lowest the of the three frequencies. 39. The optical modulator sub-assembly of claim 30, wherein the modulation signal is a multi-frequency signal, and the multi-frequency modulation signal comprises at least a first and a second modulation components having different frequencies applied simultaneously to the EOM. 40. The optical modulator sub-assembly according to claim 39, wherein the multi-frequency modulation signal consists of a first and a second modulation components having two frequencies, one of which is a multiple of the other, the first and the second modulation components being applied simultaneously to the OEM. 41. The optical modulator sub-assembly according to claim 39, wherein the multi-frequency modulation signal comprises three frequencies, two of which are multiples of a lowest the of the three frequencies. 42. The optical modulator sub-assembly according to claim 39, wherein the waveguide is formed by titanium doping of a crystal. 43. The multi-frequency light source according to claim 39, wherein the gain medium comprises at least one from the group consisting of erbium and yttrium. 44. The optical modulator sub-assembly of claim 39, wherein the waveguide is provided with a plurality of alternately poled optical domains having a periodic width structure, and a duty cycle other than 50% , the duty cycle being chosen to facilitate energy transfer to side harmonics of an output optical comb signal.