Page 475 - Tunable Lasers Handbook

8 Tunable External-Cavity Semiconductor Lasers 435

Output mirror
Nd:YV04

W
Focusing lens nm
Laser diode lens
FlGu RE 5 3 Interference-filter-tuned extended-cavity laser used to pump intracavity-doubled
Nd:YVO,. (Reproduced with permission from Kitaoka et al. [ 1633.)

18.7 Injection Seeding
The optical parametric oscillator (OPO) is arguably the most widely tunable
coherent optical source. However, it is difficult to obtain narrow-bandwidth out-
put from an OPO. Use of dispersive elements in the OPO cavity complicates
tuning. An alternative is to use a tunable ECL as an injection-seeding source. A
1.55-ym grating ECL with a 150-kHz linewidth has been used to seed a lithium
niobate OPO [164]. The OPO was pumped at 1.064 pm with a Nd:YAG laser.
Seeding reduced the bandwidth of the signal from 50 GHz without seeding to
0.18 GHz with seeding. Seeding was obtained for injected signal wavelengths
from 1.526 to 1.578 pm, corresponding to an idler wavelength range of 3.20 to
3.51 pm. The authors noted that these limits could be extended with improved
cavity optics and a different seeding source. The tunable idler radiation is useful
for atmospheric spectroscopy because many species absorb in the 3- to 4-pm
atmospheric transmission window.

REFERENCES

1. Y. Tohmori. E Kano. H. Ishii. 1’. Yoshikuni, and Y. Kondo. ”Wide Tuning with Narrow
Linewidth in DFB Lasers with Superstmcture Grating (SSGL.’ Elecfron. Lerr. 29, 1350-135 1
(July 1993).
2. Y. C. Chung and Y. H. Lee. .‘Spectral Characteristics of Vertical-Cavity Surface-Emitting
Lasers xvith External Optical Feedback.’‘ Phoron. Technol. Leu. 3,597-599 (July 1991).
3. S. Jiang. Z. Pan, M. Dagenais, R. A. Morgan. and K. Kojima, “Influence of External Optical
Feedback on Threshold and Spectral Characteristics of Vertical-Cavity Surface-Emitting
Lasers,” Photon. Technol. Lerr. 6,3436 (Jan. 1991).
1. The internal quantum efficienq q,,, is defined as the ratio of the total carrier lifetime T~ to the
radiative lifetime T~.
5. C. H. Henry. “Theory of the Linewidth of Semiconductor Lasers,” IEEE J. Qziantiim Electron.
QE-18,259-264 (1982).
6. L. D. Westbrook. ”Dispersion of Linewidth-Broadening Factor in 1.5 bm Laser Diodes.” Elec-
fJ-On. Lerr. 21, 1018-1019 (1985).
7. K. Naganuma and H. Yasaka, “Group Delay and &Parameter Measurement of 1.3 pm Semi-
conductor Traveling-Wave Optical Amplifier Using the Interferometric Method,” IEEE J.
Qzianruni Electron. 2’7, 1280-1287 (1991 j.