Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1999-03-22
2000-11-07
Epps, Georgia
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359575, 359254, 359276, 359319, 385 10, 385 37, G02F 101, G02F 103, G02F 1295, G02B 518, G02B 634
Patent
active
061444804
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical arrangement and a method for processing an optical wave according to the preamble of appended claims 1 and 26 respectively.
BACKGROUND OF THE INVENTION
In many applications it is required that a guided optical wave be efficiently radiated out of an optical waveguide, and be split into a number of optical beams and simultaneously be focused at finite distances away from the optical waveguide. Here the guided optical wave can be produced by a semiconductor diode laser. In an optical interconnection system, for example, it is not only essential to produce an array of spots with uniform intensity, but also necessary to focus most optical power into the desired spots in order to reduce power loss and to suppress spurious light. In short, such optical devices must simultaneously provide the following functions: (1) radiating the guided optical wave out of the optical waveguide; (2) splitting the radiated optical wave into a number of optical waves; and (3) focusing the radiated optical wave(s) at a finite distance away from the optical waveguide.
It is well-known that a uniform grating coupler, which is fabricated on the surface of or into an optical waveguide, can be used to achieve function (1) stated in the previous paragraph, viz., it has the ability to radiate a guided optical wave out of an optical waveguide. However, such a simple device lacks the beam-splitting and beam focusing functions. For example, refer to Tamir and Peng, Appl. Phys. 14, p. 235, 1977.
A focusing grating coupler has been proposed in, for example, Ura et al, "Focusing grating for integrated optical-disk pickup device". The Transactions of IECE of Japan, Part C, vol. J68-C, No. 10, October 1985, pp. 803-810. Instead of having periodically positioned, rectilinear grating grooves as in a uniform grating coupler, a focusing grating coupler comprises a group of curved grating grooves, each of which being uniquely defined by the interference fringes between a guided optical wave and a spherical free-space optical wave. Such a focusing grating coupler enables a guided optical wave to be radiated out of an optical waveguide and simultaneously to be focused into a single spot, i.e. it possesses functions (1) and (3). However, it is unable to split the radiated optical wave into a number of optical waves. In other words, a focusing grating coupler cannot simultaneously produce more than one focusing spot. This problem remains to be solved.
In some other applications, such as a computer-generated hologram for use in an optical phase-matched filter, it is generally advantageous to introduce a continuous level phase modulation to an incoming optical wave. so far, most efforts have been concentrated on achieving different phase levels by utilizing a surface-relief stop-like structure (FIG. 1), usually fabricated using a standard lithography and etching technique. As the number of required phase levels increases, so do the number of lithographic masks and the number of etching steps. This indicates that it is difficult and costly to fabricate computer-generated holograms with a larger number of phase levels, because each new mask must be precisely aligned with the previously etched pattern and the height of each step must also be accurately controlled in order to provide the desired phase shift. Therefore, it is beneficial to establish a method which is able to provide multi-level or even continuous level phase shifts using only two-level (or binary) surface-relief structures.
Also in the prior art is a computer-generated guided-wave holographic structure proposed by Saarinen et al. (see for example, Saarinen et al, "Computer-generated guided-wave holography; application to beam splitting", Optics Letters, Vol. 17, No. 4, Feb. 15, 1992). In this device, both the incoming optical wave and the output optical waves are confined with the optical waveguide. The proposed holographic structure comprises a two-level surface relief with a mathematically synthesized geometric shape extending alon
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Larsson Anders
Li Ming
Epps Georgia
Lester Evelyn A.
LandOfFree
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