Axial line scanning device for display and printing applications

Conventional two dimensional scanning methods operate by a two axis variable mirror system to deflect onel aser beam over the whole image field. Hence there occur two different deflection frequencies, one of which is the critical horizontal deflection frequency in the kHz regime and the other one is the uncritical vertical frequency of about 10OHz. The horizontal deflection frequency is difficult to achieve with mecanical means because precisely manufactured polygon mirrors must be employed to achieve a pointing stability good enough for printing and display applications. A number of devices have been developed recently to find alternatives to the conventional method. The axial line scanner intends to resolve this problem by utilizing a different scanning method: always one complete line is imaged in one scanning step and to obtain a complete two dimensional image it is thus just necessary to shift the lines vertically. The same concept could be applied in printing equipment where a rotating shaft is placed in front of the axial line scanner. To realize this concept it is neccessary to generate simultaneously a discrete number of points with equal beam characteristics and a fixed pitch. Furthermore these applications require an independant modulation of each channel's output power in order to generate intensity dependant effects. A system that fulfills all the requirements presented above can be developed as an integrated optic. LiNbO3 was chosen as host material because of it's superior electrooptical properties. With standard lithographical methods an array of Titanium indiffused waveguides has been manufactured. These waveguides have a nominal with of 3 mu m and operate in transversal single mode at the working vvavelength of 532 nm. According to the fact that Ti-diffused waveguides guide the light of both polarizations TF and TM the modulation itself can be realized by a phase-modulator which allows sufficiently fast modulation and in particular the smallest possible pitch between the waveguides. The system realized contains 32 waveguide channels with a pitch of 500 mu m. The radiation of a diode pumped solid state laser is coupled by aids of zylindrical lenses and microlens arrays into the waveguides. A ring resonator design was chosen as beamsource. Due to the large difference of the ordinary and the extraordinary refractive indices of LiNb03 the waveguide acts as a very high order waveplate with a small bandwidth, hence the single mode concept effectively avoids modulation problems attributed to this effect. There are several advantages of the axial line scanner to the mechanical technique: the system is fast and can be miniaturized. Attributed to it's all optical design the lifetime of this device is much higher since no mechanical degradation occurs. It can easily be scaled to a higher density allowing more distinct points and thus a higher resolution and the manufacturing process can be done by utilizing the standard equipment available in semiconductor processing environments.