Tunable Lasers Handbook

8 Tunable External-Cavity Semiconductor Lasers

435

~ Filter Nd:YV04 KTP Output mirror

809

nrn /,,-,~ ~,,

532 nm

I Collimating Focusing lens 1064 nm

Laser diode lens

FIGURE 53

Interference-filter-tuned extended-cavity laser used to pump intracavity-doubled

Nd:YVO 4. (Reproduced with permission from Kitaoka et al. [163].)

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-~tm grating ECL with a 150-kHz linewidth has been used to seed a lithium

niobate OPO [164]. The OPO was pumped at 1.064 ~tm 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 lam, corresponding to an idler wavelength range of 3.26 to

3.51 ~tm. 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-~tm

atmospheric transmission window.

REFERENCES

1. Y. Tohmori, F. Kano, H. Ishii, Y. Yoshikuni, and Y. Kondo, "Wide Tuning with Narrow

Linewidth in DFB Lasers with Superstructure Grating (SSG)," Electron. Lett. 29, 1350-1351

(July 1993).

2. Y.C. Chung and Y.H. Lee, "Spectral Characteristics of Vertical-Cavity Surface-Emitting

Lasers with External Optical Feedback," Photon. Technol. Lett. 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. Lett. 6, 34-36 (Jan. 1994).

4. The internal quantum efficiency

]]int

is defined as the ratio of the total carrier lifetime x c to the

radiative lifetime 't r.

5. C.H. Henry, "Theory of the Linewidth of Semiconductor Lasers," IEEE J. Quantum Electron.

QE-18, 259-264 (1982).

6. L. D. Westbrook, "Dispersion of Linewidth-Broadening Factor in 1.5 ~tm Laser Diodes," Elec-

tron. Lett. 21, 1018-1019 (1985).

7. K. Naganuma and H. Yasaka, "Group Delay and m-Parameter Measurement of 1.3 lam Semi-

conductor Traveling-Wave Optical Amplifier Using the Interferometric Method," IEEE J.

Quantum Electron. 27, 1280-1287 ( 1991 ).