JP4345510B2 - Composite optical element for optical pickup and method for manufacturing the same - Google Patents

Description

  The present invention relates to a composite optical element for an optical pickup and a method for manufacturing the same.

  A so-called laser coupler is used as a composite optical element for an optical pickup of an optical disk recording / reproducing apparatus. As shown in FIG. 4, the optical element 44 for optical pickup has a laser element 31 disposed on a silicon semiconductor substrate 41 via a submount substrate 42, and faces the laser element 31 on the semiconductor substrate 41. A prism 33 is disposed via an adhesive layer (not shown), and a photodiode IC 40 including a plurality of photodiode elements 38 and 39 serving as light detection elements for signal detection is provided on the surface of the semiconductor substrate 41 immediately below the prism 33. Formed. The prism 33 has a mirror surface 34 of, for example, 45 ° that reflects laser light emitted from the laser element 31 and transmits return light reflected by an optical disc (not shown) that is an optical recording medium. The submount substrate 42 is formed of a silicon semiconductor substrate, and a photodiode element 45 for rear monitoring is formed on the rear surface of the submount substrate of the laser element 31. A signal processing IC for processing a signal detected by the photodiode IC 40 is further formed on the semiconductor substrate. 43 is an electrode pad.

  In this optical pickup composite optical element 44, the S-polarized laser light L1 emitted from the laser element 31 is reflected by the mirror surface 34 of the prism 33 and rises in the vertical direction, and a quarter-wave plate (not shown) and Return light L2, which is irradiated onto an optical disc (not shown) through an objective lens (not shown), reflected by the signal recording surface of the optical disc and converted into P-polarized light, passes through the same optical path from the prism mirror surface 34 into the prism 33. An RF (Radio Frequency) signal detected by the photodiode IC 40 by the incoming photodiode elements 38 and 39, that is, return light from the disk signal surface is detected, and the reproduced analog signal is read out.

  Since it is difficult to visually determine the optical characteristics, the optical pickup composite optical element 44 is assembled and then measured to determine whether there is any problem. Actually, in the optical pickup 44 on the user side, the applied current is controlled using the photodiode element 45 for rear monitoring so that the laser output becomes constant, and the laser output desired by the user is obtained. This control of the applied current is referred to as auto power control (hereinafter abbreviated as APC).

Patent Document 1 describes an optical pickup having a front monitor type polarizing prism, in which the transmittance and reflectance of the polarizing prism are specified.
Patent Document 2 discloses an optical pickup including a coating film having different reflectance or transmittance between a microprism and a plurality of light receiving elements.
Patent No. 3392206 JP-A-8-293127

  On the other hand, when measuring the optical characteristics after manufacturing the optical pickup composite element 44, if the APC function is added to the final measuring instrument, the tact (measurement time) at the time of measurement deteriorates. For this reason, the calculated coupling coefficients shown below are integrated to create a pseudo APC state, the applied current is corrected with the monitor output detected by the photodiode IC 40, and measured according to the laser output used on the user side. Was.

  Coupling coefficient = (monitor output obtained when the laser emits light at the rated output) / (set monitor output value)

Here, the set monitor output value corresponds to the laser output requested by the user, and is the monitor output from the photodiode IC40.
The monitor output obtained when the laser element emits light at the rated output is the monitor output from the photodiode IC 40 at the rated output of the composite optical element for optical pickup.

  Conventionally, the coupling coefficient is standardized by measurement. However, since the coupling coefficient is not stable, there has been a problem that a composite optical element for an optical pickup is defective.

  In view of the above, the present invention provides a composite optical element for an optical pickup that stabilizes a coupling coefficient and reduces the defect rate of the composite optical element for an optical pickup, and a method for manufacturing the same.

A composite optical element for an optical pickup according to the present invention includes a laser element that emits laser light, a light detection element for signal detection, and a mirror surface that is disposed on the light detection element and reflects and transmits the laser light. And the product of the value of S wave reflectance (%) and the value of P wave transmittance (%) of the mirror surface of the prism is set in a range of less than 2100 to 4000, and the S wave reflectance is 35%. The P-wave transmittance is set in the range of 60% to 80%.

In the composite optical element for an optical pickup according to the present invention, the product of the S wave reflectance (%) value and the P wave transmittance (%) value of the mirror surface of the prism is set in a range of less than 2100 to 4000 , and S By setting the wave reflectance in the range of 35% to 50% and the P wave transmittance in the range of 60% to 80%, the coupling coefficient can be stably defined within the optimum range. If the product of the S wave reflectance and the P wave transmittance is less than 2100, the laser is overloaded and the life of the laser element is shortened. If the product of the S wave reflectance and the P wave transmittance exceeds 4000, a problem of noise failure occurs. Further, if the S wave reflectance is less than 35%, the lifetime of the laser element is shortened for the above reason, and if it exceeds 50%, the problem of noise failure occurs for the above reason. If the P-wave transmittance is less than 60%, the life of the laser element is shortened for the above reason, and if it exceeds 80%, the problem of noise failure occurs due to the above reason.

The method of manufacturing a composite optical element for an optical pickup according to the present invention includes a step of placing a laser element that emits laser light on a semiconductor substrate via a submount substrate, and a signal detecting device formed on the surface of the semiconductor substrate. On the light detection element, there is a mirror surface that faces the laser element, reflects the laser light emitted from the laser element, and transmits the return light from the optical disk, and the value of the S wave reflectance (%) of the mirror surface a set P-wave transmittance product of the values of (%) in the range of less than 2100 to 4000, and the S-wave reflectivity is set to range from 35% to 50%, the 60% of P-wave transmittance ~ It has the process of arrange | positioning the prism set to 80%, It is characterized by the above-mentioned.

In the method of manufacturing a composite optical element for an optical pickup according to the present invention, the coupling coefficient is normalized by the product of the S wave reflectance (%) value and the P wave transmittance (%) value of the prism mirror surface. Thus, a composite optical element for an optical pickup having a stable coupling coefficient can be manufactured.

According to the composite optical element for an optical pickup according to the present invention, the coupling coefficient used for correcting the applied current for making the laser output constant can be stabilized, and the defect occurrence rate can be reduced.
In particular, the product of the value of S wave reflectance (%) and the value of P wave transmittance (%) on the mirror surface of the prism is set to a range of less than 2100 to 4000, and the S wave reflectance is 35% to 50%. By setting to the range and setting the P wave transmittance to the range of 60% to 80%, the coupling coefficient can be within the optimum range.

According to the method for manufacturing a composite optical element for an optical pickup according to the present invention, a composite optical element for an optical pickup having a stable coupling coefficient can be manufactured, and the manufacturing yield can be improved.
In particular, the product of the value of S wave reflectance (%) and the value of P wave transmittance (%) of the mirror surface of the prism is in the range of less than 2100 to 4000, and the S wave reflectance is in the range of 35% to 50%. By setting the P-wave transmittance in the range of 60% to 80%, the coupling coefficient can be kept within the optimum range.

Embodiments of the present invention will be described below with reference to the drawings.
1 and 2 show an embodiment of a composite optical element for an optical pickup according to the present invention. As shown in FIGS. 1 and 2, the composite optical element 14 for an optical pickup according to the present embodiment has a laser element 1 disposed on a silicon semiconductor substrate 10 via a submount substrate 11. Oppositely, the prism 3 is disposed on the semiconductor substrate 10 via an adhesive layer (not shown), and a plurality of photodiode elements 8 serving as light detection elements for signal detection are provided on the surface of the semiconductor substrate 10 immediately below the prism 3. And 9 is formed. The prism 3 and the semiconductor substrate 10 are connected by an adhesive layer 13. The prism 3 has a mirror surface 4 of, for example, 45 ° that reflects the laser light emitted from the laser element 1 and transmits the return light reflected by the optical disk 15 that is an optical recording medium. The submount substrate 11 is formed of a silicon semiconductor substrate, and a photodiode element 2 for rear monitoring is formed on the rear surface of the submount substrate of the laser element 1. The semiconductor substrate 10 is further formed with a signal processing IC for processing a signal detected by the photodiode IC12.

  In this optical pickup composite optical element 14, S-polarized laser light L 1, which is emitted from the laser element 1, is reflected by the mirror surface 4 of the prism 3 and rises in the vertical direction, and the quarter-wave plate 5 and the objective lens 6. The return light L2, which is irradiated onto the optical disk 15 through the optical disk 15 and reflected by the signal recording surface of the optical disk 15 and made P-polarized by the quarter-wave plate 5, enters the prism 3 from the prism mirror surface 4 through the same optical path, and is a photodiode. The RF signal, that is, the return light L2 from the disk signal surface, detected by the photodiode IC 12 comprising the elements 8 and 9 is detected, and the reproduced analog signal is read out.

  Factors that determine the coupling coefficient include the reflectance of the outgoing light and the transmittance of the return light at the prism mirror surface, and the amplification factor (gain) of the photodiode IC that is the light detection element. As will be described later, the coupling coefficient is controlled by normalizing the transmittance and reflectance of the mirror surface 4 of the prism 3.

First, when the S-polarized laser light L1 emitted from the laser element 1 is reflected by the prism mirror surface 4, the amount of laser light directed to the optical disk 15 is determined by the reflectance (Rs) of the mirror surface 4. Further, the laser light L 1 is reflected by the optical disk 15, and the P-polarized return light L 2 enters the prism 3 from the prism mirror surface 4. The amount of laser light entering the prism 3 is determined by the transmittance (Tp) of the mirror surface 4. (Unit is% for both Tp and Rs)
Therefore, the amount of light that enters the prism 3 is determined by Equation 1.
[Equation 1]
Rs x Tp

  Next, the laser beam L 2 that has entered the prism 3 enters the photodiode elements 8 and 9. The laser beam L2 incident on the photodiode elements 8 and 9 is converted into a photocurrent signal inside the photodiode IC 12, and further amplified by an amplifier and output. The amplification factor (gain) at this time is determined by the specific resistance PRH (Ω).

The monitor output obtained by the final photodiode elements 8 and 9 can be expressed by Equation 2.
[Equation 2]
(Rs x Tp) x PRH

  Here, the specific resistance PRH is controlled within a certain range with the accuracy allowed at present. Therefore, although the coupling coefficient can be determined by Equation 2, since the specific resistance PRH is in a certain range, it can be standardized by a value of Rs × Tp. As shown in FIG. 3, there is a correlation between the coupling coefficient and (Rs × Tp).

  FIG. 3 is a graph showing the relationship of transmittance (Tp) × reflectance (Rs) when the coupling coefficient (PIKa) is on the vertical axis and the prism mirror surface is 45 ° on the horizontal axis. As shown by the connecting line I, a proportional relationship can be derived between the product of the transmittance (Tp) and the reflectance (Rs) and the coupling coefficient. That is, by determining the range of the product of transmittance and reflectance, the coupling coefficient can be derived regardless of the PRH value.

In this embodiment, the optimum range of the coupling coefficient is determined by the product of the reflectance Rs and the transmittance Tp on the prism mirror surface from this correlation. When the optimum range of the coupling coefficient is obtained, the optimum range of Rs × Tp is Rs × Tp = 2100 to less than 4000. Furthermore, the optimum ranges of the reflectance Rs and the transmittance Tp at this time are Rs = 35 to 50% and Tp = 60 to 80%.
When Rs × Tp is less than 2100, the laser output decreases, so feedback is applied to output more, and a load is applied to the laser element, so that the life of the laser element 1 is shortened. When Rs × Tp exceeds 4000, the laser output increases, so feedback is applied to reduce the laser output, and noise defects are noticeable. This noise failure is so-called return light noise that occurs when a part of the return light reflected by the laser light disk is reflected again by the mirror surface of the prism and returns to the laser element.
In terms of S-wave reflectivity, if it is less than 35%, the lifetime of the laser element is shortened for the above reason, and if it exceeds 50%, a noise defect appears remarkably for the above reason .
Similarly, in terms of the P-wave reflectivity, if it is less than 60%, the lifetime of the laser element is shortened for the above reason, and if it exceeds 80%, a noise defect is remarkably exhibited for the reason described above.

Therefore, in the present embodiment, the product of the value of the S wave reflectance Rs and the value of the P wave transmittance Tp at the prism having the above-described conditions, that is, the mirror surface 4, is less than 2100 to 4000, and the S wave reflectance is A composite optical element for an optical pickup having a standardized coupling coefficient is provided by including the prism 3 having Rs of 35 to 50% and P wave transmittance Tp of 60 to 80%. Further, when manufacturing this composite optical element for an optical pickup, a coupling coefficient defined by the ratio between the set monitor output and the monitor output when the laser element is caused to emit light at the rated output is set to the mirror surface 4 of the prism 3. This is normalized by the product of the S wave reflectance Rs and the P wave transmittance Tp.

  According to the present embodiment, by defining Rs × Tp and Rs, Tp, it is possible to stabilize the coupling coefficient used for correcting the applied current for making the laser output constant, and the coupling coefficient is poor. The occurrence rate can be reduced. Thereby, the manufacturing yield of the composite optical element for optical pickup can be improved.

Incidentally, when the conventional monitor output was measured and standardized, the defect occurrence rate of the coupling coefficient (PIK) was 2.0%, but the transmittance and reflectance of the prism mirror surface of the present invention are It was possible to greatly improve the defective rate of coupling (PIK) when controlled and normalized to 0.6%.
The optical pickup uses a constant RF level, and the RF level is controlled by an applied current (actually, a monitor current detected by the rear monitor photodiode element 2 behind the laser element 1). This embodiment has an effect of stabilizing the laser output, that is, stabilizing the monitor current (stabilizing the RF level) by stabilizing the transmittance and reflectance of the prism 45 ° surface.

It is sectional drawing which shows one Embodiment of the composite optical element for optical pick-ups concerning this invention. It is an enlarged view of the principal part of the composite optical element for optical pick-ups concerning this invention. It is a graph which shows one Embodiment of the composite optical element for optical pick-ups which concerns on this invention. It is a side view which shows the conventional composite optical element for optical pick-ups.

1..Laser element, 2..Photodiode element for rear monitor, 3..Prism, 4..Mirror surface, 5..quarter wave plate, 6..Objective lens, 8, 9..Photodiode element 10..Silicon semiconductor substrate, 11..Submount substrate, 12..Photodiode IC, 13..Adhesive layer, 14..Composite optical element for optical pickup, 15, Optical disk, 31..Laser element, 33. ..Prism, 34..Mirror surface, 36..Recording medium, 38, 39..Photodiode element, 40..Photodiode IC, 41..Silicon semiconductor substrate, 42..Submount substrate, 43..Electrode pad , 44 .. Composite optical element for optical pickup, 45 .. Photodiode element

Claims (2)

A laser element that emits laser light, a light detection element for signal detection, and a prism that is disposed on the light detection element and has a mirror surface that reflects and transmits the laser light;
The product of the value of S wave reflectance (%) and the value of P wave transmittance (%) of the mirror surface of the prism is set in a range of less than 2100 to 4000,
The S wave reflectance is set in a range of 35% to 50%;
The composite optical element for an optical pickup, wherein the P wave transmittance is set in a range of 60% to 80%. Arranging a laser element that emits laser light on a semiconductor substrate via a submount substrate;
On the light detection element for signal detection formed on the surface of the semiconductor substrate, there is a mirror surface facing the laser element and reflecting the laser light emitted from the laser element and transmitting the return light from the optical disk. and, values and P-wave transmittance of S-wave reflectivity of the mirror surface (%) the product of the values of (%) set in the range of less than 2100 to 4000, and the S-wave reflectivity of 35% to 50% And a step of arranging a prism in which the P wave transmittance is set to 60% to 80%.
A method for producing a composite optical element for an optical pickup, comprising:

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