Data-recordal using fibre lasers

Details Data-recordal using fibre lasers Data-recordal using fibre lasers

1995-04-21

1998-02-10

Reinhart, Mark J.

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

B41J 247

Patent

active

057174504

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to methods and apparatus for data-recordal (which term includes printing) using a laser beam, and relates especially, though not exclusively, to dye thermal transfer printing.
2. Description of the Prior Art
In dye thermal transfer printing, heat is applied to selected pixel areas of a dyesheet to cause dye to transfer to an adjacent dye receiver sheet to form a print.
Print speed is determined by the dye transfer rate which depends on the power of the heat source, and print resolution is determined by the spot size to which the source is able to be focused. For high speed and high resolution printing, therefore, a source of high radiance is required, and lasers have proved attractive.
Many different laser sources have been used, each having their own particular problems. For example, Nd:YAG lasers pumped by arc lamps suffer from being large, expensive, and inefficient, and require regular maintenance due to the short life of the lamps. Replacing the arc lamps by arrays of laser diodes can improve the size and performance of such lasers, but they remain expensive and somewhat inefficient.
Laser diodes may also be used as sources themselves, but produce highly divergent and asymmetrical beams of relatively low radiance.


SUMMARY OF THE INVENTION

The present invention aims to provide data-recordal apparatus having an alternative and advantageous laser source to those provided to date, and, from a first aspect, provides apparatus in which data-recordal is effected by a laser beam, wherein a fibre laser is provided as a laser beam source.
A fibre laser comprises, in essence, an optical fibre whose core (normally silica) is doped by a material suitable for causing lasing action (normally a rare earth metal, such as neodymium or erbium), and in which a resonant cavity is produced by, for example, providing dichroic mirrors at the fibre input and output ends to provide feedback gain at the lasing Wavelengths, whilst allowing pump light to be launched into the fibre input end and laser light to be emitted from the output end. As discussed in more detail below, the preferred form of the fibre laser is of a dual core type having an inner lasing core surrounded by a pump core which, in turn, is surrounded by an outer cladding. Preferably, the lasing core is doped with neodymium.
The fibre laser may be pumped by any convenient source, such as a laser diode or laser diode array, which may be end-coupled to the fibre laser by intermediate fibre optics or by geometrical multiplexing using appropriate multiplexing optics. Fibre coupling is simpler, and the fibre outputs may be butt coupled or imaged onto the fibre laser end. Where the fibre laser is dual core, the pump light is coupled into the pump core, and the lasing core is effectively side-pumped as the pump light travels down the pump core.
Fibre lasers have a number of significant advantages over prior art sources. They are less expensive than traditional solid-state Nd:YAG lasers, because it is far easier to fabricate a glass fibre than to grow a YAG crystal. Further, the efficiency of the fibre laser is greater, because the laser light is confined substantially to the fibre core, and so there is minimal sideways loss.
Moreover, when the fibre laser is end-pumped, the pump light is also confined to the core, and may be reflected back and forth by the mirrors, thereby allowing absorption of the pump light to take place during multiple passes of the light along the length of the fibre, and so increasing the source efficiency still further.
Another advantage of the present invention is that the fibre laser length, and thus the lasing core length and pump light path, may be set to suit desired power output and efficiency requirements, and the fibre laser may be coiled to provide a compact configuration easily locatable in what may be the restricted space of a printer.
A special advantage in the context of data recordal, and in particular printing, is that a fibre laser may follow a

REFERENCES:
patent: 5151714 (1992-09-01), Okino et al.

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