Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-02-14
2002-06-18
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C359S569000
Reexamination Certificate
active
06408116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light guide path element including a grating for input-coupling or transmitting a light beam a light guide path by mean of a fine repetitive structure formed on the light guide path and a light receiving portion for receiving the light beam. The present invention also relates to an optical pickup for generating a focus error signal by using the light guide path element.
2. Description of the Prior Art
Recently, there has been largely developed an optical pickup including a light guide path element by utilizing the integrated circuit technique. An optical pickup of this kind is configured by a grating, a light receiving portion and a light guide path element, which are integrally formed on a substrate. The grating is used to establish an input-coupling or an output-coupling of the light beam between an external optical system and a light guide path element, thereby achieving the function of an optical pickup. Thus, a downsized, reliable optical pickup can be achieved.
However, the positioning of the light receiving portion in the integration process is a problem if an optical pickup for CD and/or DVD is configured by using the above-mentioned light guide path element. Generally, the optical pickup of that kind is configured such that the light beam reflected by an information storage medium is input-coupled with the light guide path element. A first light receiving portion is provided under the light guide path element to detect an RF signal and a tracking error, and a second light receiving portion is provided to detect a focus error. In such a configuration, in the case of focus error detection, a broadly-known technique such as the beam size method requires that a light quantity enough to differentiate the focus states of the respective beams is input-coupled with the light guide path element, thereby leading the light beams to the second light receiving portion. At the same time, in detecting the RF signal or the tracking error, in order to ensure the light quantity and stability, it is preferred that the guided light quantity after the input-coupling is as small as possible to increase the light quantity at the first light receiving portion.
Further, the second light receiving portion for use in the focus error detection is required to be arranged with a certain distance from the first light receiving portion for use in the tracking error detection, and hence the total area of the light guide path element necessarily becomes large. It becomes a bar to downsize the light guide path element and causes the increased cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a downsized, low-cost optical pickup including a light guide path element, in which the optical pickup function is achieved by a single light receiving portion.
It is another object of the present invention to provide the light guide path element to be used in the above-mentioned optical pickup.
According to one aspect of the present invention, there is provided a light guide path element for use in an optical pickup which irradiates a light beam emitted by a light source via an optical system onto an information storage medium and receives the light beam reflected therefrom, the light guide path element including: a waveguide layer for propagating the light beam; a grating for input-coupling a part of the light beam reflected by the information storage medium with the waveguide layer and for transmitting a remaining part of the light beam; and a light receiving portion for receiving light beam transmitted through the grating, wherein the waveguide layer, the grating and the light receiving portion are formed in a laminated manner to form a laminate structure, wherein the grating includes a first grating pattern adapted to an irradiation state of the light beam when the information storage medium and the optical system move away from each other by a predetermined distance to maximize a coupling efficiency with the waveguide layer, and a second grating pattern adapted to an irradiation state of the light beam when the information storage medium and the optical system approach each other by the predetermined distance to maximize a coupling efficiency with the waveguide layer, and wherein the light receiving portion includes a first light receiving area corresponding to the first grating pattern and a second light receiving area corresponding to the second grating pattern.
In accordance with the above invention, the light beam emitted by the light source is irradiated on the information storage medium via the optical system. The reflected light beam is irradiated by the light guide path element. Then, by the grating serving as the input-coupler to the waveguide layer, a part of the light beam is input-coupled with the waveguide layer while the remaining part is transmitted and received by the light receiving portion below. At this time, according to the positional relationship between the information storage medium and the optical system, an adjustment is made such that the coupling efficiency to the waveguide layer by the first grating pattern is maximized when the relative distance between the information storage medium and the optical system is increasing, and the coupling efficiency to the waveguide layer by the second grating pattern is maximized when the relative distance between the information storage medium and the optical system is decreasing. In the light receiving portion which is divided according to the respective grating patterns, the received light quantity becomes minimum when the respective coupling efficiencies are maximum.
Therefore, by taking the difference of the light receiving outputs of the respective light receiving areas, an S-shape curve characteristic can be obtained and a focus error signal can be readily produced. Thus, the focus error detection, which conventionally required a certain light path length to the light receiving portion, can be performed immediately below the grating. This can achieve the reduction of the light receiving portion area, and provide further downsized and low cost light-integrated optical pickup.
The first grating pattern and the second grating pattern may include a chirped, curved grating to be adapted to the irradiation state of the incident light beam. By this, when the light beam reflected by the information storage medium is irradiated on the grating, a necessary characteristic is applied to the light beam irradiated as a converging light by means of the chirped, curved grating pattern applied to the first and the second grating patterns, and then the light beam is input-coupled with the waveguide layer. Therefore, the coupling efficiency with the waveguide layer according to the positional relationship between the information storage medium and the optical system may be controlled with improved accuracy, and the focus error signal can be produced using a sharp S-shaped curve. This can achieve the downsizing and the performance improvement of the light integrated optical pickup.
The first grating pattern and the second grating pattern may be alternately arranged, and the light receiving portion may be divided into strip-like shape areas corresponding to the alternate arrangement of the first and the second grating patterns. By this, when the light beam reflected by the information storage medium is irradiated on the grating, the light beam passes through many strip-shaped areas. For example, since the odd-numbered and the even-numbered areas apply two different characteristics and the light receiving portion is divided in the same way, the focus error signal can be easily obtained. In addition, high light receiving performance can be obtained by maintaining high effective NA.
The light guide path element may further include a separation layer, formed in the laminated manner at the top of the laminate structure, for selectively reflecting and transmitting the light beam in accordance with a phase difference given to the light beam, and
Lee John D.
Pioneer Corporation
Song Sarah U.
Young & Thompson
LandOfFree
Light guide path element and optical pickup does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light guide path element and optical pickup, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light guide path element and optical pickup will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2893903