High peak-power nanosecond pulses generated with DFB RW laser

Abstract

The generation of optical pulses with very high-peak power by gainswitching of a distributed-feedback (DFB) ridge-waveguide (RW) laser emitting at a wavelength of 1064 nm is demonstrated. With 4 ns-long pulses a peak power of 2.6 W is achieved at a repetition frequency of 250 kHz. The rise and fall times of the pulses are about 1.2 ns. The spectral full width at half maximum ranges between 30 and 40 pm for all powers, whereas the width enclosing 95% of the intensity increases from 90 to 450 pm from low to high power. The laser has a cavity length of 1 mm.Introduction: High-power diode lasers capable of generating spectrally stable nearly diffraction-limited optical pulses in the nanosecond range can be used in a variety of applications including free-space communications, metrology, material processing and frequency doubling. Gain switching, i.e. turning on and off the current injected into the active section of a diode laser, offers a simple, cost-effective and powerefficient possibility to generate optical pulses. Diffraction-limited emission is achieved by a proper design of the laser waveguide, so that only the fundamental transverse mode lases. Spectral stabilisation can be realised with Bragg gratings either in an external cavity configuration or integrated into the semiconductor chip. Both methods have their advantages and disadvantages. For example, internal Bragg gratings necessitate a more sophisticated chip technology. On the other hand, lasers with external Bragg gratings suffer from the long external round-trip time, such that during the onset of the pulse the spectral stabilisation fails. In [1] a slab-coupled optical waveguide laser emitting at 965 nm is reported, which is spectrally stabilised with an external fibre Bragg grating. A fibre-coupled power of 1.6 W (2.4 W emitted by the laser) was obtained with 35 ns-long pulses. The spectral full width at half maximum (FWHM) was 0.2 nm. A cavity as long as 5 mm was used. Lasers with Bragg gratings integrated into the chip can be realised either in a distributed Bragg reflector (DBR) or in a distributed feedback (DFB) configuration. DBR ridge-waveguide lasers emitting at 976 and 1064 nm were reported in [2] to generate optical pulses with pulse lengths between 4 and 48 ns. Stable pulses with a maximum peak power of 600 mW were obtained. In [3], a 1.8 mmlong DFB ridge-waveguide laser emitting at 976 nm having lateral Bragg gratings was used to generate 50 ns-long optical pulses with a peak power of 1.6 W. In this Letter, we demonstrate the generation of 4 ns-long optical pulses with a peak power of about 2.6 W at a repetition frequency of 250 kHz with a 1 mm-long DFB laser emitting at 1064 nm.

Wavelength stabilized ns-MOPA diode laser system with 16 W peak power and a spectral line width below 10 pm

“…A DFB laser as described in [10,11] is used as MO. The device has a ridge width of W RW = 5 μm and a length of L = 1 mm.…”