Optical waveguides – Temporal optical modulation within an optical waveguide
Reexamination Certificate
1999-09-20
2002-01-15
Spyrou, Cassandra (Department: 2872)
Optical waveguides
Temporal optical modulation within an optical waveguide
C385S002000, C385S008000, C385S040000, C385S045000, C359S246000, C359S249000
Reexamination Certificate
active
06339660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and a method for writing on imaging material. The device includes a radiation source for generating an electromagnetic radiation of such a wavelength that image information can be written to the imaging material using the wavelength. A waveguide is integrated with a substrate material and arranged as a modulator for modulating the radiation produced by the radiation source. The modulator includes an input capable of receiving a modulation signal which includes the image information.
2. Description of the Related Art
A device and a method of this type are described in the published international patent application WO 96/25009. This application describes a system for producing color images for rendering color or monochrome images, in particular for television and video applications and for printing, for example for printing on photo sensitive paper. The disclosed system for generating images includes waveguides which are integrated on a substrate in either monolithic or hybrid form. These integrated waveguides are implemented as modulators for modulating the intensity of the light guided in the waveguides with a modulation signal having wavelengths in the visible region of the spectrum. The modulated light exiting from the waveguide is transmitted to a device for deflecting the beam, such as a polygon mirror, which deflects the modulated lights to a photo sensitive surface—for example, photographic paper—so that the photo sensitive surface can be written line by line. They patent application also discloses that light of three wavelengths in the red, green and blue wavelength region of the visible spectrum are modulated with an integrated modulator and that the three modulated light beams are subsequently superimposed to form a color image. The disclosed image generating system therefore represents a color mixer capable of generating any desired color on the photo sensitive surface. Preferably, potassium titanyl phosphate, KTiOPO
4
, (KTP) is used as substrate material for the color mixer. This substrate material is particular suited for guiding single-mode the radiation in the entire spectral range of the visible light.
The integrated optical waveguide disclosed in WO 96/25009 is investigated in more detail in the dissertation “Untersuchung der physikalischen Eigenschaften ionenausgetauschter optischer Wellenleiter und Wellenleiterbauelemente in KTP” by J.-P. Ruske, Department for Physical, Astronomical and Technical Sciences of the Friedrich-Schiller University, Jena. The dissertation in particular discusses advantageous and disadvantageous waveguide properties. The dissertation investigates various effects causing a change in the effective index of refraction of the modes guided in the waveguide and change in the spontaneous polarization of the substrate material. The changes in the index of refraction and polarization cause changes in the phase of the radiation guided in the waveguide. Such phase changes are caused, in particular, by thermal, photo refractive and pyroelectric effects due to the optical power of the optical radiation guided in the waveguide. The absorption of the substrate material converts the guided light energy is into heat, causing the temperature of the waveguide region to increase. This heating then causes that changes in the index and refraction and polarization mentioned above. In addition, strain is produced in the substrate material, which also affects the phase of the guided radiation through photo elastic interactions. The changes in the index of refraction caused by the photo refractive effect are directly induced by the light. The effect of the investigated parameters on the waveguide properties is dependent on the power of the guided radiation. The dissertation, however, comes to the conclusion that the changes in the refractive index and phase do not significantly affect the operation of the integrated optical waveguides.
Based on the teaching of the WO 96/25009, it is the object of the present invention to improve the rendition of image information on an imaging material.
SUMMARY OF THE INVENTION
The present invention is based on the observation that writing on imaging material with an integrated waveguide implemented as a modulator poses particularly stringent requirements. The term “imaging material” includes many different materials suitable for rendering image information. For example, imaging materials can be recording materials for permanently recording image information, such as photographic paper, photographic or thermographic film or selenium drums, and projection materials, for example for television and video applications. Imaging materials have different properties, such as a specific sensitivity with respect to the absolute energy of a radiation, which can be used to generate on the imaging material a desired representation of image information. In particular with photographic recording material, the maximum and minimum attainable density of the recording material is predetermined by the recording material itself, as well as the resolvable density steps between that minimal and maximal density. The modulated radiation for recording should therefore advantageously be matched to the respective imaging material.
With the invention, modulation errors which occur when they radiation used to write on the imaging material is modulated, can be compensated or at least significantly reduced, so that image information can advantageously be rendered on imaging material with vibrant highlights and in high resolution. Modulation errors can be caused, for example, when the substrate material heats up. Other factors, for example, an unwanted rotations of the polarization in the radiation source itself, i.e., at the time the electromagnetic radiation is generated or when the supplied radiation is guided in the modulator—e.g., in a light waveguide—can also cause modulation errors. In any event, the modulation errors reduce the quality with which the image information is rendered on the imaging material as compared to the desired rendition of the image information.
According to an advantageous embodiment of the invention, a modulation errors signal is produced and used by the compensatior for compensating the modulation error. This modulation errors signal is produced by comparing a set-point information with an image of the radiation modulated by the modulator. The so determined modulation error can advantageously be used to compensate the modulation error more accurately. The set-point information may be predetermined and selected to allow a meaningful comparison with the image of the modulated radiation corresponding to an optimized modulation. The set-point information may, for example, include image information that is to be written on the imaging material.
According to another advantageous embodiment, an image signal is supplied to the compensator, wherein the image signal contains image information and the compensator generates the modulation signal in dependence of the image signal and the modulation error signal. In this way, the modulation error signal to be used to compensate the modulation error can be combined directly in the compensator with the image information This makes the control of the modulator with a modulation signal which includes the image information to be written on the imaging material, and the control information for compensating the modulation error less complex.
According to yet another advantageous embodiment of the invention, the device includes a evaluation means for processing the spectral composition of the modulated radiation. In this way, different error causes responsible for the modulation errors, in particular modulation errors at different frequencies, can be analyzed. The spectral composition of the modulated radiation can be analyzed simply by analyzing the image of the modulated radiation. To minimize distortion and other errors which can be introduced during an analysis of the spectral composition of modulat
Buchmann Frank
Ehbrecht Markus
Hebenstreit Jörk
AGFA-Gevaert AG
Assaf Fayez
Spyrou Cassandra
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