We claim: 1. A waveguide device for operating as a stable optical amplifier or a waveguide laser in a room-temperature environment, the waveguide device comprising: a LiNbO.sub.3 substrate having a crystallographic z-axis; rare-earth ions incorporated into the LiNbO.sub.3 substrate, the rare-earth ions and LiNbO.sub.3 substrate forming a rare-earth-doped substrate; at least one metal diffused waveguide channel incorporated into the rare-earth-doped substrate, each metal-diffused waveguide channel being substantially parallel or nearly parallel to the crystallographic z-axis of the LiNbO.sub.3 substrate, the waveguide channel and the rare-earth-doped substrate forming a rare-earth-doped z-propagating waveguide; end facets formed on the rare-earth-doped z-propagating waveguide, the end facets substantially perpendicular to the axis of the waveguide; and wherein the rare-earth-doped z-propagating waveguide providing stable room-temperature operation as an optical amplifier or as a waveguide laser, both substantially free from photorefractive instability. 2. The waveguide device of claim 1 wherein the rare-earth ions are selected from one or more of the group consisting of Er.sup.3+, Nd.sup.3+, Yb.sup.3+, and Tm.sup.3+. 3. The waveguide device of claim 1 wherein the rare-earth ions are indiffused into the LiNbO.sub.3 substrate. 4. The waveguide device of claim 1 wherein the rare-earth ions are incorporated into the LiNbO.sub.3 substrate during formation of the LiNbO.sub.3 substrate. 5. The waveguide device of claim 1 wherein the metal channels are metals which increase the refractive index and form a waveguide, the metals being selected from one or more of the group consisting of Ti, Zn, Ni, and Cu. 6. The waveguide device of claim 1 wherein the metal channels are thermally diffused into the LiNbO.sub.3 substrate thereby forming optical waveguides. 7. The waveguide device of claim 1 wherein the z-propagating substrate has a modulator structure selected from the group consisting of an x-cut LiNbO.sub.3 plate and a y-cut LiNbO.sub.3 plate. 8. The waveguide device of claim 1 and further comprising a TE-TM polarization switching device formed on the z-propagating LiNbO.sub.3 substrate, the switching device allowing Q-switching, mode locking, or wavelength tuning of the waveguide device. 9. The waveguide device of claim 1 and further comprising a suitably-generated pump light injected into the rare-earth-doped waveguide exciting the rare-earth ions and enabling cw laser action and amplification of the rare-earth-doped waveguide device. 10. The waveguide device of claim 9 and further comprising mirrors mounted to the end facets of the waveguide device enabling laser action of the excited rare-earth ions free from impeding the injection of the pump light into the waveguide device. 11. The waveguide device of claim 1 and further comprising a modulator electrode structure fabricated on the surface of the substrate nearingly approximate the waveguide, and further comprising means for providing suitable switching voltages to the modulator electrodes. 12. The waveguide device of claim 10 wherein the modulator structure enables phase modulation and polarization switching of the guided optical modes. 13. The waveguide device of claim 10 and further comprising an attenuator absorbing or scattering either the TE or TM guided modes. 14. The waveguide device of claim 10 and further comprising pump light injected into the rare-earth-doped waveguide, wherein the waveguide laser simultaneously operates as a mode-locked and Q-switched laser or only as a mode-locked laser. 15. The waveguide device of claim 1 and further comprising a semiconductor saturable absorber connected to at least one or both, as required, of the waveguide facets enabling the waveguide laser to operate mode-locked, Q-switched, or simultaneously mode-locked and Q-switched. 16. The waveguide device of claim 9 and further comprising a guided signal light injected into the waveguide, the guided signal light having a predetermined wavelength to interact with the excited rare-earth dopants such that the signal light is amplified by the excited rare-earth dopant whereupon exiting the output face of the waveguide, the signal light is amplified to a greater optical power than when the signal light was presented at the input face of the waveguide device. 17. The waveguide device of claim 9 wherein the device is pumped with single or multiple wavelengths and lasing, in either cw, mode-locked, Q-switched, or combined mode-locked and Q-switched, at single or multiple wavelengths. 18. The waveguide device of claim 16 wherein the pump light is pumped with single or multiple wavelengths producing amplification of single or multiple injected signal light waves at various wavelengths. 19. The waveguide device of claim 9 and further comprising means for electro-optic tuning and adjustment of the output lasing wavelength by applying a suitable voltage to an electrode position on or nearingly adjacent to the waveguide channel or channels. 20. The waveguide device of claim 9 and further comprising a distributed Bragg reflector structure for providing the necessary feedback of the signal wave back into the waveguide laser cavity with the fabrication of the distributed Bragg reflector structure following from standard etching procedures forming shallow surface corrugations on the surface of the channel waveguides. 21. A method of forming a z-propagating waveguide, the method comprising: selecting an x-cut or y-cut LiNbO.sub.3 sample; depositing a rare-earth material on the LiNbO.sub.3 sample; incorporating ions of the rare earth material into the sample; delineating metal channels on the LiNbO.sub.3 sample; and incorporating the metal channels into the LiNbO.sub.3 sample. 22. The method of claim 21 and further comprising: positioning the LiNbO.sub.3 sample on a Pt pad; positioning the pad on an alumina pedestal; positioning the alumina pedestal in a furnace; subjecting the LiNbO.sub.3 sample, pad, and pedestal to a flowing oxygen atmosphere; and heating the alumina pedestal, Pt pad, LiNbO.sub.3 sample to a temperature in the range of approximately 1000.degree. C. to 1100.degree. C. for predetermined period of time. 23. The method of claim 21 wherein the rare-earth ions are selected from one or more of the group consisting of Er.sup.3+, Nd.sup..sup.3+, Yb.sup.3+, and Tm.sup.3+. 24. The method of claim 21 wherein the rare-earth ions are thermally indiffused into the LiNbO.sub.3 substrate. 25. The method of claim 21 wherein the rare-earth ions are incorporated into the LiNbO.sub.3 substrate during the growth of the bulk crystal. 26. The method of claim 21 wherein the metal channels are metals which increase the refractive index and form a waveguide, the metals being selected from one or more of the group consisting of Ti, Zn, Ni, and Cu. 27. The method of claim 21 wherein the metal channels are thermally diffused into the LiNbO.sub.3 substrate. 1. A waveguide device for operating as a stable optical amplifier or a waveguide laser in a room-temperature environment, the waveguide device comprising: a LiNbO.sub.3 substrate having a crystallographic z-axis; rare-earth ions incorporated into the LiNbO.sub.3 substrate, the rare-earth ions and LiNbO.sub.3 substrate forming a rare-earth-doped substrate; at least one metal diffused waveguide channel incorporated into the rare-earth-doped substrate, each metal-diffused waveguide channel being substantially parallel or nearly parallel to the crystallographic z-axis of the LiNbO.sub.3 substrate, the waveguide channel and the rare-earth-doped substrate forming a rare-earth-doped z-propagating waveguide; end facets formed on the rare-earth-doped z-propagating waveguide, the end facets substantially perpendicular to the axis of the waveguide; and wherein the rare-earth-doped z-propagating waveguide providing stable room-temperature operation as an optical amplifier or as a waveguide laser, both substantially free from photorefractive instability. 2. The waveguide device of claim 1 wherein the rare-earth ions are selected from one or more of the group consisting of Er.sup.3+, Nd.sup.3+, Yb.sup.3+, and Tm.sup.3+. 3. The waveguide device of claim 1 wherein the rare-earth ions are indiffused into the LiNbO.sub.3 substrate. 4. The waveguide device of claim 1 wherein the rare-earth ions are incorporated into the LiNbO.sub.3 substrate during formation of the LiNbO.sub.3 substrate. 5. The waveguide device of claim 1 wherein the metal channels are metals which increase the refractive index and form a waveguide, the metals being selected from one or more of the group consisting of Ti, Zn, Ni, and Cu. 6. The waveguide device of claim 1 wherein the metal channels are thermally diffused into the LiNbO.sub.3 substrate thereby forming optical waveguides. 7. The waveguide device of claim 1 wherein the z-propagating substrate has a modulator structure selected from the group consisting of an x-cut LiNbO.sub.3 plate and a y-cut LiNbO.sub.3 plate. 8. The waveguide device of claim 1 and further comprising a TE-TM polarization switching device formed on the z-propagating LiNbO.sub.3 substrate, the switching device allowing Q-switching, mode locking, or wavelength tuning of the waveguide device. 9. The waveguide device of claim 1 and further comprising a suitably-generated pump light injected into the rare-earth-doped waveguide exciting the rare-earth ions and enabling cw laser action and amplification of the rare-earth-doped waveguide device. 10. The waveguide device of claim 9 and further comprising mirrors mounted to the end facets of the waveguide device enabling laser action of the excited rare-earth ions free from impeding the injection of the pump light into the waveguide device. 11. The waveguide device of claim 1 and further comprising a modulator electrode structure fabricated on the surface of the substrate nearingly approximate the waveguide, and further comprising means for providing suitable switching voltages to the modulator electrodes. 12. The waveguide device of claim 10 wherein the modulator structure enables phase modulation and polarization switching of the guided optical modes. 13. The waveguide device of claim 10 and further comprising an attenuator absorbing or scattering either the TE or TM guided modes. 14. The waveguide device of claim 10 and further comprising pump light injected into the rare-earth-doped waveguide, wherein the waveguide laser simultaneously operates as a mode-locked and Q-switched laser or only as a mode-locked laser. 15. The waveguide device of claim 1 and further comprising a semiconductor saturable absorber connected to at least one or both, as required, of the waveguide facets enabling the waveguide laser to operate mode-locked, Q-switched, or simultaneously mode-locked and Q-switched. 16. The waveguide device of claim 9 and further comprising a guided signal light injected into the waveguide, the guided signal light having a predetermined wavelength to interact with the excited rare-earth dopants such that the signal light is amplified by the excited rare-earth dopant whereupon exiting the output face of the waveguide, the signal light is amplified to a greater optical power than when the signal light was presented at the input face of the waveguide device. 17. The waveguide device of claim 9 wherein the device is pumped with single or multiple wavelengths and lasing, in either cw, mode-locked, Q-switched, or combined mode-locked and Q-switched, at single or multiple wavelengths. 18. The waveguide device of claim 16 wherein the pump light is pumped with single or multiple wavelengths producing amplification of single or multiple injected signal light waves at various wavelengths. 19. The waveguide device of claim 9 and further comprising means for electro-optic tuning and adjustment of the output lasing wavelength by applying a suitable voltage to an electrode position on or nearingly adjacent to the waveguide channel or channels. 20. The waveguide device of claim 9 and further comprising a distributed Bragg reflector structure for providing the necessary feedback of the signal wave back into the waveguide laser cavity with the fabrication of the distributed Bragg reflector structure following from standard etching procedures forming shallow surface corrugations on the surface of the channel waveguides. 21. A method of forming a z-propagating waveguide, the method comprising: selecting an x-cut or y-cut LiNbO.sub.3 sample; depositing a rare-earth material on the LiNbO.sub.3 sample; incorporating ions of the rare earth material into the sample; delineating metal channels on the LiNbO.sub.3 sample; and incorporating the metal channels into the LiNbO.sub.3 sample. 22. The method of claim 21 and further comprising: positioning the LiNbO.sub.3 sample on a Pt pad; positioning the pad on an alumina pedestal; positioning the alumina pedestal in a furnace; subjecting the LiNbO.sub.3 sample, pad, and pedestal to a flowing oxygen atmosphere; and heating the alumina pedestal, Pt pad, LiNbO.sub.3 sample to a temperature in the range of approximately 1000.degree. C. to 1100.degree. C. for predetermined period of time. 23. The method of claim 21 wherein the rare-earth ions are selected from one or more of the group consisting of Er.sup.3+, Nd.sup..sup.3+, Yb.sup.3+, and Tm.sup.3+. 24. The method of claim 21 wherein the rare-earth ions are thermally indiffused into the LiNbO.sub.3 substrate. 25. The method of claim 21 wherein the rare-earth ions are incorporated into the LiNbO.sub.3 substrate during the growth of the bulk crystal. 26. The method of claim 21 wherein the metal channels are metals which increase the refractive index and form a waveguide, the metals being selected from one or more of the group consisting of Ti, Zn, Ni, and Cu. 27. The method of claim 21 wherein the metal channels are thermally diffused into the LiNbO.sub.3 substrate. 1. A waveguide device for operating as a stable optical amplifier or a waveguide laser in a room-temperature environment, the waveguide device comprising: a LiNbO.sub.3 substrate having a crystallographic z-axis; rare-earth ions incorporated into the LiNbO.sub.3 substrate, the rare-earth ions and LiNbO.sub.3 substrate forming a rare-earth-doped substrate; at least one metal diffused waveguide channel incorporated into the rare-earth-doped substrate, each metal-diffused waveguide channel being substantially parallel or nearly parallel to the crystallographic z-axis of the LiNbO.sub.3 substrate, the waveguide channel and the rare-earth-doped substrate forming a rare-earth-doped z-propagating waveguide; end facets formed on the rare-earth-doped z-propagating waveguide, the end facets substantially perpendicular to the axis of the waveguide; and wherein the rare-earth-doped z-propagating waveguide providing stable room-temperature operation as an optical amplifier or as a waveguide laser, both substantially free from photorefractive instability. 2. The waveguide device of claim 1 wherein the rare-earth ions are selected from one or more of the group consisting of Er.sup.3+, Nd.sup.3+, Yb.sup.3+, and Tm.sup.3+. 3. The waveguide device of claim 1 wherein the rare-earth ions are indiffused into the LiNbO.sub.3 substrate. 4. The waveguide device of claim 1 wherein the rare-earth ions are incorporated into the LiNbO.sub.3 substrate during formation of the LiNbO.sub.3 substrate. 5. The waveguide device of claim 1 wherein the metal channels are metals which increase the refractive index and form a waveguide, the metals being selected from one or more of the group consisting of Ti, Zn, Ni, and Cu. 6. The waveguide device of claim 1 wherein the metal channels are thermally diffused into the LiNbO.sub.3 substrate thereby forming optical waveguides. 7. The waveguide device of claim 1 wherein the z-propagating substrate has a modulator structure selected from the group consisting of an x-cut LiNbO.sub.3 plate and a y-cut LiNbO.sub.3 plate. 8. The waveguide device of claim 1 and further comprising a TE-TM polarization switching device formed on the z-propagating LiNbO.sub.3 substrate, the switching device allowing Q-switching, mode locking, or wavelength tuning of the waveguide device. 9. The waveguide device of claim 1 and further comprising a suitably-generated pump light injected into the rare-earth-doped waveguide exciting the rare-earth ions and enabling cw laser action and amplification of the rare-earth-doped waveguide device. 10. The waveguide device of claim 9 and further comprising mirrors mounted to the end facets of the waveguide device enabling laser action of the excited rare-earth ions free from impeding the injection of the pump light into the waveguide device. 11. The waveguide device of claim 1 and further comprising a modulator electrode structure fabricated on the surface of the substrate nearingly approximate the waveguide, and further comprising means for providing suitable switching voltages to the modulator electrodes. 12. The waveguide device of claim 10 wherein the modulator structure enables phase modulation and polarization switching of the guided optical modes. 13. The waveguide device of claim 10 and further comprising an attenuator absorbing or scattering either the TE or TM guided modes. 14. The waveguide device of claim 10 and further comprising pump light injected into the rare-earth-doped waveguide, wherein the waveguide laser simultaneously operates as a mode-locked and Q-switched laser or only as a mode-locked laser. 15. The waveguide device of claim 1 and further comprising a semiconductor saturable absorber connected to at least one or both, as required, of the waveguide facets enabling the waveguide laser to operate mode-locked, Q-switched, or simultaneously mode-locked and Q-switched. 16. The waveguide device of claim 9 and further comprising a guided signal light injected into the waveguide, the guided signal light having a predetermined wavelength to interact with the excited rare-earth dopants such that the signal light is amplified by the excited rare-earth dopant whereupon exiting the output face of the waveguide, the signal light is amplified to a greater optical power than when the signal light was presented at the input face of the waveguide device. 17. The waveguide device of claim 9 wherein the device is pumped with single or multiple wavelengths and lasing, in either cw, mode-locked, Q-switched, or combined mode-locked and Q-switched, at single or multiple wavelengths. 18. The waveguide device of claim 16 wherein the pump light is pumped with single or multiple wavelengths producing amplification of single or multiple injected signal light waves at various wavelengths. 19. The waveguide device of claim 9 and further comprising means for electro-optic tuning and adjustment of the output lasing wavelength by applying a suitable voltage to an electrode position on or nearingly adjacent to the waveguide channel or channels. 20. The waveguide device of claim 9 and further comprising a distributed Bragg reflector structure for providing the necessary feedback of the signal wave back into the waveguide laser cavity with the fabrication of the distributed Bragg reflector structure following from standard etching procedures forming shallow surface corrugations on the surface of the channel waveguides. 21. A method of forming a z-propagating waveguide, the method comprising: selecting an x-cut or y-cut LiNbO.sub.3 sample; depositing a rare-earth material on the LiNbO.sub.3 sample; incorporating ions of the rare earth material into the sample; delineating metal channels on the LiNbO.sub.3 sample; and incorporating the metal channels into the LiNbO.sub.3 sample. 22. The method of claim 21 and further comprising: positioning the LiNbO.sub.3 sample on a Pt pad; positioning the pad on an alumina pedestal; positioning the alumina pedestal in a furnace; subjecting the LiNbO.sub.3 sample, pad, and pedestal to a flowing oxygen atmosphere; and heating the alumina pedestal, Pt pad, LiNbO.sub.3 sample to a temperature in the range of approximately 1000.degree. C. to 1100.degree. C. for predetermined period of time. 23. The method of claim 21 wherein the rare-earth ions are selected from one or more of the group consisting of Er.sup.3+, Nd.sup..sup.3+, Yb.sup.3+, and Tm.sup.3+. 24. The method of claim 21 wherein the rare-earth ions are thermally indiffused into the LiNbO.sub.3 substrate. 25. The method of claim 21 wherein the rare-earth ions are incorporated into the LiNbO.sub.3 substrate during the growth of the bulk crystal. 26. The method of claim 21 wherein the metal channels are metals which increase the refractive index and form a waveguide, the metals being selected from one or more of the group consisting of Ti, Zn, Ni, and Cu. 27. The method of claim 21 wherein the metal channels are thermally diffused into the LiNbO.sub.3 substrate.