Wavelength-Tunable Lasers: Does the Tuner Degrade the Capacity Efficiency?

In a wavelength-tunable laser, some kind of adjustable optical bandpass filter such as a birefringent tuner is often used for adjusting the emission wavelength. As such a tuner introduces wavelength-dependent authority losses, one may wonder to which extent it reduces the faculty efficiency of the laser, and on which factors this force reduction depends. In a wavelength-tunable laser, some kind of adjustable optical bandpass filter such as a birefringent tuner is often used for adjusting the emission wavelength. As such a tuner introduces wavelength-dependent competence losses, one may wonder to which extent it reduces the ability efficiency of the laser, and on which factors this influence reduction depends. A tunable continuous-wave laser usually operates with a relatively narrow emission bandwidth. The issue is then to which extent the filter introduces losses in that narrow wavelength region. In principle, it could have virtually zero losses in some wavelength inte
rval and strong losses outside that interval. One might then expect that the potency efficiency of the laser is not affected at all, simply on account of there is no loss for the circulating light, having the true wavelength to be well transmitted. Of course, the energy may be reduced when forcing the laser to operate at some wavelength with low gain. All the more when not enforcing oscillation at an "inconvenient" wavelength, the power efficiency may be reduced if the laser doesn't "like" to emit with a narrow bandwidth. For example, spatial hole burning in the laser crystal may reduce the power efficiency when single-frequency operation is enforced. Other kinds of inhomogeneous saturation may also play a role, yet without single-frequency operation. Another occupation arises when the filter has no steep edge in its transmission spectrum. For example, consider the manipulate of an etalon as a tuner. The etalon shouldn't be very thick in order to select one
particular transmission window, however that window is then relatively broad. A resembling situation occurs when a prism pair is used to spatially disperse different wavelengths in some region of the laser resonator, and a knife edge is inserted in that region. The oscillation wavelength of the laser will then be a kind of compromise between minimum filter loss and maximum gain. Therefore, it does introduce significant loss for the oscillating wavelength, much though there would be some other wavelength nearby with still smaller losses. It can then be helpful to practice a filter with a steeper spectral transmission function. It is even imaginable that the insertion of such a narrowband filter in addition to the original tuner increases the output power by forcing the laser to operate where the loss is lower. Of course, one would then remove the first tuner, as it is not more required - except if the steeper filter is a thicker etalon, and the thinner one is required
to select the correct transmission window. Full text: http://computerandtechnologies.com/technology/news_2008-11-13-21-00-03-152.html