Optical Disc Drive Focus Error Signal Noise Reduction

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The astigmatic method for generating focus error signals in optical disc drives can be disrupted by the land/groove structure on optical discs, leading to noise in the focus error signal due to defocusing, which affects precise servo control, and existing solutions like the differential astigmatic method face challenges in balancing beam intensity and noise levels.

Innovation Solution

An optical disc drive configuration that includes a light source, beam dividing element, objective lens, astigmatism producing unit, and signal generation unit with sensors, where the intensity distribution of the main beam is adjusted to have a maximum intensity level within 70% of the pupil diameter, gradually decreasing to the peripheral portion, to reduce noise and maintain a suitable focus error signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the interval between beam spots of main beam and sub-beams is made extremely small to enable close sensor placement, then sensor placement is simplified, but defocus causes blurred main beam to enter sub-beam sensors creating noise

Engineering Contradiction:

Improvesensor placement complexityVSAvoidnoise in focus error signal

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by creating different intensity distributions for the main beam and sub-beams. The main beam has a specific intensity distribution pattern that differs from the sub-beams, allowing the system to distinguish between main beam and sub-beam signals even when they are closely spaced, thereby reducing noise while maintaining compact sensor placement

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If the intensity of sub-beam is increased to reduce noise from blurred main beam, then noise level decreases, but main beam intensity must be decreased which lowers RF signal level and fast recording performance

Engineering Contradiction:

Improvenoise levelVSAvoidRF signal level

Core Design Contradiction:

Object-affected harmful factorsVSPower

Solution Approach 1:

The patent changes the intensity distribution parameters of the main beam by introducing a specific intensity distribution pattern with a predetermined maximum intensity level position. This allows the main beam to have optimized intensity characteristics that maintain sufficient RF signal level while reducing noise interference with sub-beam sensors

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If the interval between beam spots is increased to reduce noise from blurred main beam, then noise level decreases, but effective angle of view of objective lens must be increased which causes unexpected aberrations

Engineering Contradiction:

Improvenoise levelVSAvoidaberration control

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration effectively suppresses noise levels in the focus error signal, allowing for precise focusing operations while maintaining a sufficient light amount and beam diameter for accurate recording and reproducing, even with defocusing issues.

Implementation Method 1

a beam dividing element that divides the light beam emitted by the light source into a main beam and a plurality of sub-beams

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

an objective lens that converges each of the main beam and the plurality of sub-beams onto a recording surface of an optical disc

Methodology Applied

Scientific EffectFocusing: Focusing

Implementation Method 3

an astigmatism producing unit that gives astigmatism to each of the main beam and the plurality of sub-beams which passed through the objective lens after reflecting from the recording surface of the optical disc

Methodology Applied

Scientific EffectAstigmatism:

Implementation Method 4

a signal generation unit that has sensors respectively provided for receiving the main beam and at least two of the plurality of sub-beams

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS8264922B2Optical disc drive having a mechanism to reduce the noise level of a focus error signal

Publication Date: 2012.09.11 KONICA MINOLTA INC

AI summary

There is provided an optical disc drive, which includes a light source emitting a light beam, a beam dividing element that divides the light beam into main and sub-beams, an objective lens, an astigmatism producing unit that gives astigmatism to the main and sub-beams, a signal generation unit that has sensors for the beams and generates a focus error signal based on output signals of the sensors; and an optical element that has a function of adjusting intensity distribution of the main beam such that the main beam incident on the optical disc has a predetermined intensity distribution where a maximum intensity level is positioned at a predetermined height within a range of 70% of a pupil diameter, the predetermined height is not equal to an optical axis, and an intensity of the main beam decreases gradually from the predetermined height to a peripheral portion of the pupil.