Multimode Semiconductor Laser Research Articles

Tunable single-mode fiber reflective grating filter

A single-mode fiber tunable reflective filter is demonstrated by translating a fan-shaped grating structure through the evanescent field of a side-polished fiber. Filter linewidths of about 1 nm were measured over tuning ranges in excess of 65 nm. Reflectivities as high as 88 percent were observed. Using the fiber filter as a feedback element, a multimode semiconductor laser was observed to oscillate in a single mode which could be discretely turned over a wavelength range of 26 nm.

Multimode effects in the spectral linewidth of semiconductor lasers

We present experimental results on the spectral linewidth of one longitudinal laser mode of multimode semiconductor lasers with different emission wavelengths and different wave guiding. The dependence of linewidth on mode power cannot be described by a single-mode theory (modified Schawlow-Townes formula), for all lasers. The observed power independent contribution to the linewidth as well as the slope of the linewidth versus optical power data show significant multimode effects. A theoretical model for the linewidth of a two-mode laser provides a qualitative description of the experimental results.

Laser phase noise effects in fiber-optic signal processors with recirculating loops

The power spectrum of the optical intensity at the output of a single-mode-fiber recirculating delay line driven by a multimode semiconductor laser is shown to exhibit a spectral structure with notches at zero frequency as well as at other multiples of 1/(loop delay). A theoretical model based on laser phase noise is suggested to explain the experimental data.

Single longitudinal mode control of semiconductor lasers by rectangular conical diffractor system for wavelength-division-multiplexing transmission

A new external feedback system named the rectangular conical diffractor (RCD), which is composed of a diffraction grating and a mirror, is designed. This system has advantages for wavelength-division-multiplexing transmission systems. By using this system in both single and multimode semiconductor lasers: 1) the oscillation wavelength of a semiconductor laser can be selected freely; 2) some semiconductor lasers oscillate at different wavelengths from one another simultaneously, and no interference exists between the oscillation wavelengths under the condition that each semiconductor laser is operated independently; and 3) the selected wavelength is stable against temperature variation of the lasers.

Design of nondispersion optical feedback system using diffraction grating for semiconductor laser multiple longitudinal modes control

The external optical feedback system with a diffraction grating and mirrors is designed as a light source system in wavelength division multiplexing transmission. This system can select not only oscillation center wavelength but also spectral range in semiconductor lasers by using an identical grating twice. Experimental results demonstrate selected oscillations of single and double longitudinal modes in a multimode semiconductor laser.