Spectral linewidth narrowing of broad-area blue diode bar in V-shape external Talbot cavity.

A 1-D linear array of 23 high-power broad-area laser diode (BALD) beams in the blue spectral region (447 nm) is combined employing a V-shape external Talbot cavity in Littrow configuration. A surface grating provides optical feedback via self-imaged diffractive coupling to the diode bar and induces all the emitters to lase at a common central wavelength. The external cavity reduces the spectral linewidth of the free-running laser diode bar from several nm to 20-50 pm (FWHM) with the power level of 11.8 W. The narrow spectrum of the external cavity stabilized laser can be tuned in the range of 3-4 nm by adjusting the tilt angle of the grating while the laser diode bar is operated in constant current mode at a temperature of 20°C.

Spectral linewidth narrowing of two broad-area blue laser diodes (445 nm) with a common external cavity.

Two watt-level broad-area laser diodes were simultaneously locked into a common external cavity made using a surface grating in a Littrow configuration. The spectral linewidth of the combined laser beam was narrowed down from over a nanometer to 10-15 pm (FWHM), and the output power was the sum of the power of the individually locked laser diodes. The spectrum of the combined laser beam can be tuned over a range of 2-3 nm by changing the tilt angle of the grating and varying the injection currents of each laser diode.

Phase-locking of arrays of weakly coupled semiconductor lasers.

In this paper we study the conditions for achieving almost perfect phase locking in large arrays of semiconductor diodes. We show that decayed non-local coupling of diode lasers can provide the necessary conditions for robust phase synchronization of an entire diode laser array. Perfect global coupling is known to allow for robust synchronization, however it is often physically impossible or impractical to achieve. We show that when diodes are coupled via the decayed non-local coupling layout, the dominant transverse mode of the laser array has a uniform phase across the lasers and can be stable. This state is robust to noise and frequency disorder and can be realized under periodic (fixed-intensity limit cycle) continuous-wave and chaotic behavior of lasers.

Spectral linewidth narrowing and tunable two-color laser operation of two diode laser arrays.

We propose and implement a common external cavity to narrow spectral linewidth of two broad-area laser diode arrays (LDAs) and align their center wavelengths. The locked center wavelength of two LDAs can be tuned in the range of ~10 nm by tuning the tilted angle of the diffraction grating. The output beams of two LDAs are spatially overlapped through the polarization beam splitter of the common external cavity, and the total output power equals the power of two LDAs. The center wavelength of each LDA can be independently tuned by shifting the corresponding fast-axis collimation lens. As a result, the high-power two-color LDA operation is demonstrated with the tunable wavelength difference of up to 2 nm (~1 THz).

Linewidth reduction of a broad-area laser diode array in a compound external cavity.

A compound external cavity is designed and implemented to achieve a homogeneous spectrum distribution of broad area laser diodes in an array and to narrow the spectral linewidth of the entire array. The compound external cavity is composed of an optical coupler and a Littrow external cavity with a telescope along the fast axis. The inhomogeneous distribution of individual laser diodes spectrum generated by the "smile" effect was reduced by the telescope. The effective transverse coupling among individual laser diodes in an array was enhanced by the optical coupler, which further reduced the spectrum inhomogeneous distribution of the entire array. The spectral linewidth of a 49-emitter laser array is reduced to 0.1 nm at the output power of 12.5 W.

Simultaneous injection locking of couples of high-power broad-area lasers driven by a common current source.

We experimentally demonstrate the simultaneous injection locking of pairs of high-power broad-area laser diodes in a 19-laser array driven by a common current source. Each pair is injection locked by use of a single-mode low-power semiconductor laser. The frequency and phase locking are verified bythe optical spectrum and the interference pattern between the injection-locked lasers. The influence of frequency detuning on the (simultaneous) injection behavior has been experimentally clarified. We validate a necessary condition for the injection locking of a broad-area laser array.