4. Results and discussion
In Fig. 3 , three examples for the measured spectra of our double-mode ECDL at different grating angles are depicted. As
shown in Fig. 3 , the feasibility of a tunable double-mode ECDL is demonstrated. A manual coarse double-wavelength tuning range of 120 nm for the spectral range between 1470 nm and 1590 nm is obtained. The tuning range is limited by the gain bandwidth of the gain medium [13] . The both modes can be tuned independently. The peaks have the different intensities due to the reflection and transmission coefficient of the beam splitter and bandwidth of the
gain chip.
In Fig. 4, the measured gain bandwidth of the used gain chip is shown. This figure is obtained in a single-mode operation at different grating angles, i.e. just one laser beam path is open. In our previous work , we demonstrated a ultra-broadly coarse (170 nm)wavelength-tunable single-mode ECDL for the spectral range between 1451 nm and 1621 nm [14]. The reduction in tuning range of the double mode operation compared to the single-mode operation can be attributed to simultaneously oscillating and sharing the same gain medium of the both modes.
The fast fi ne tuning can be performed by scanning the external cavity length and/or the injected current. To observe the fine tuning behavior, the resolution of our monochromator is not