The combination of high brightness laser diodes and periodically poled (PP) waveguide crystals for the generation of blue light at the technically interesting wavelength of 488 nm is promising. Although PPKTP has a lower nonlinear coefficient compared to PPLN it is of interest for the use in such devices. Because of its higher photorefractive damage threshold, it is well suited for operation at room temperature. In this work, a DFB laser as well as a tunable external cavity enhanced broad area diode laser (ECDL) are used for second harmonic generation using a waveguide PPKTP crystal. Both lasers yield several hundred Miliwatts of diffraction limited light around a center wavelength of 976 nm with excellent spectral properties. The ECDL system is further tunable over a broad range of 40 nm. The PPKTP crystal has a length of 12 mm and the 4 μm x 8 μm waveguides are manufactured by ion exchange followed by a patented submount poling technique. By using a DFB laser diode as pump source a laser to waveguide coupling efficiency of more than 55% could be achieved. A maximum output power of 66.7 mW could be generated out of 220 mW infrared light inside the waveguide channel at room temperature. This results in a conversion efficiency of more than 260%/W.
Diode lasers provide a high degree of flexibility in signal shaping. Picosecond pulses with repetition rates from single shot to 80 MHz or arbitrary modulation formats with GHz bandwidth can be achieved through appropriate electrical drivers without changing the optical configuration. The limitations, however, of single mode diode lasers are low (mW) power levels and a lack of emission wavelengths between 470 and 630 nm. Optical amplification can extend single mode diode lasers to higher power levels where frequency doubling becomes a suitable option e.g. for producing green light at 530 nm. Ytterbium-doped fiber amplifiers (YDFA) show robust and stable operation at 1064 nm with amplifications of about 20 dB. We present a fiber amplified and frequency doubled diode laser that emits green picosecond pulses at variable repetition frequencies with an average output power of several milliwatts. Compared to existing semiconductor-amplified systems, higher stability at significantly smaller size and lower power consumption is achieved.
Quasi-phase matched (QPM) frequency conversion in ion exchanged potassium titanyl phosphate (KTP) waveguides can
be used for highly efficient single pass conversion of low power cw and quasi-cw lasers. Applications include frequency
doubling diode lasers for display and biomedical, pulsed sources for fluorescence and remote sensing, and recently KTP
waveguides have been used to generate photon pairs using both Type I and II down conversion for quantum information
science and technology (QUIST) applications.
In this paper, we will describe a nondestructive, all optical technique that can be used to assess the quality and modal
index of the ion exchanged waveguide before periodic poling. The structure of the waveguide is interrogated utilizing
Type II sum frequency generation (SFG) and is enabled by the fact that the ion exchange process results in waveguides
that can support both TE and TM optical modes. The results of this technique can be used to determine the uniformity of
the created waveguide and are used to determine the necessary period for a desired poling result. Furthermore, this
technique can be utilized to provide an in situ assessment of the poling for any QPM period without needing the laser
sources for the particular frequency conversion interaction. Experimental results will be reviewed.