A whole new class of optically pumped integrated optical lasers in LiNbO3 will be developed for a large spectrum of applications in advanced optical communication systems. Prototype of lasers of fixed emission wavelength, of tuneable lasers and of mode-locked lasers will be fabricated. Furthermore, the integration of laser and modulator on the same substrate will be demonstrated.
The research is concerned with a whole new class of optically pumped integrated optical lasers in lithium niobium oxide being developed for a large spectrum applications in advanced optical communication systems. It will involve prototype of lasers of fixed emission wavelength, of tuneable lasers and of mode locked lasers and the integration of a laser and modulator on the same substrate. The laser development is based on the erbium indiffusion technique.
The following results have been achieved:
erbium titanium lithium niobium oxide waveguide lasers, pumped by fibre pigtailed diode sources, have been demonstrated;
full wafer technology for the production of erbium titanium lithium niobium oxide lasers has been developed and used to produce amplifiers with comparable performance to laboratory devices.
By taking advantage of the excellent acoustooptical and electrooptical properties of lithium niobium oxide the feasibility of new laser devices with very attractive features can be demonstrated. The insertion of an acoustooptical wavelength filter in the cavity will permit laser tuneability and the insertion of an integrated broadband phase modulator will facilitate the generation of short optical pulses in the ps range. The cascading of a laser and an intensity modulator will yield high bit rate modulation without chirping.
The laser development is based on the erbium indiffusion technique, that is a simple and powerful tool allowing local erbium doping only where needed. The work is split into eight main activities:
- Quantitative numerical modelling of optical amplification and stimulated emission in Er-doped waveguide structures.
- Fabrication of low-loss single mode Ti-indiffused waveguides of optimised Er-concentration profile.
- Set up of a full wafer technology to improve the fabrication process uniformity, reproducibility and throughput.
- Development of dielectric end face mirrors to prepare laser cavities.
- Etching of holographically defined gratings into the waveguide surface to get DFB- and DBR- structures allowing the combination of lasers with further integrated optical devices on the same substrate.
- Combination of a laser with an intensity modulator on the same substrate.
- Development of two-stage acousto-optical wavelength filters to be incorporated in the laser cavity to fabricate tuneable sources.
- Integration of a phase modulator in the laser cavity to achieve mode locking as a means to generate ultra short pulses.
Key issues include the demonstration of:
- CW laser operation around 1.55 um wavelength.
- Tuning of laser emission wavelength in the range 1.53 um - 1.575 um.
- Laser mode-locking.
- Integration of laser and intensity modulator.
The new laser technology will significantly increase the potential of LiNbO3 as an attractive material for advanced telecommunication systems. Because of the excellent electro-optical and acousto-optical properties, circuits combining lasers, amplifiers, modulators and other active or passive devices will be possible. In particular, the externally modulated source will have different potential applications in high speed and analogue systems, whereas the tuneable source will have potential applications in WDM systems.