JP3545794B2 - Waveguide type optical signal detector - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a waveguide type optical signal detection element used for an optical pickup such as an optical disk memory and for performing focusing control of an optical disk.
[0002]
[Prior art]
Conventionally, various waveguide devices have been proposed, but most of them are functional elements such as a light source, a condensing path, a reflection / deflection path, a splitter, a photodetector, a demultiplexer, and an optical coupler on a slab waveguide. Are integrated.
As a specific configuration, for example, a buffer layer, a waveguide layer, and a clad layer are laminated on a substrate, and a prism coupler is bonded to the waveguide layer by an adhesive layer.
Among these waveguide devices, a type in which a reflective condenser and a split-type photodetector are arranged at the focal point thereof, and a pair of the reflective condensers 30a and 30a, as shown in FIG. 30b are arranged in parallel with each other symmetrically with respect to the optical axis of the guided light, and the photodetectors 16, 17 and 20, 21 of the split-type photodetectors are arranged at the focal point of each of the reflection type concentrators 30a, 30b (external light). (A prism coupler 5 is used as a coupler).
[0003]
This type of waveguide device has been proposed as a waveguide type optical signal detection element for detecting a focus error signal, a track error signal, and an RF signal in an optical pickup for recording / reproducing information on / from an optical disc. The optical specifications, that is, the focal length and NA, of the pair of reflective condensers arranged in parallel are the same. For example, as shown in the figure, if the detection signals from the photodetectors ₁₆ and ₁₇ are I ₁₆ and I ₁₇ , and the detection signals from the photodetectors ₂₀ and ₂₁ are I ₂₀ and I ₂₁ ,
The focus error signal is (I ₁₆ + I ₂₁ ) − (I ₁₇ + I ₂₀ )
The track error signal is (I ₁₆ + I ₁₇ ) − (I ₂₀ + I ₂₁ )
The RF signal is (I ₁₆ + I ₁₇ ) + (I ₂₀ + I ₂₁ )
Can be obtained by calculating respectively.
In the waveguide type optical signal detection device having this functional configuration, the detection sensitivity and the detection width (focus pull-in width) of the focus error signal were always constant.
[0004]
[Problems to be solved by the invention]
However, in the above-mentioned conventional waveguide type optical signal detecting element, the detection sensitivity and the detection width (focus pull-in width) of the focus error signal on the optical disk are always constant, and the demand is that the detection sensitivity is high and the detection width is wide. I couldn't respond. For example, when the position of the optical disk is greatly shifted due to disturbance or the like, the detection width is narrow, so that it exceeds the defocus detection area, and there is a problem that the defocus amount cannot be detected.
Therefore, the present invention is to solve the above-mentioned conventional problems and to provide a waveguide type optical signal detection element which can detect a focus error signal of an optical pickup with high sensitivity (high accuracy) and has a wide detection width. Is an issue.
[0005]
[Means for Solving the Problems]
The gist of the present invention is to provide a slab having at least a buffer layer formed on a substrate, a waveguide layer formed on the buffer layer, and a clad layer formed on the waveguide layer. Type waveguide, a prism coupler for coupling and exciting external light to the slab type waveguide, and a right half and a left half of the guided light provided in the slab type waveguide and including the vicinity of the optical axis of the guided light. A waveguide type including two waveguide-type reflection concentrators to be respectively taken in, and first and second split-type photodetectors provided near respective focal positions of the two waveguide-type reflection / concentrators. In the optical signal detecting element, the two waveguide-type reflection concentrators have different focal lengths, and are connected to the first differential amplifier and the first differential amplifier, respectively. and the adder, respectively against the said second split photodetector A second differential amplifier and the second adders, with the third differential amplifier are respectively connected to the first adder and the second adder and a third adder (Claim 1). In this waveguide type optical signal detection element, signals output from the first differential amplifier and the second differential amplifier are used as focus error signals and output from the third differential amplifier. Let the signal be a track error signal, and let the signal output from the third adder be an RF signal. Further, in this waveguide-type optical signal detection element, the difference signal in the second split-type photodetector normally disposed on the waveguide-type reflection / concentrator side having a shorter focal length is converted into a focus error signal. And when it exceeds the detection area of the second split-type photodetector, the first split-type photodetector disposed on the waveguide-type reflective collector with the longer focal length Is used as a focus error signal (claim 3).
Further, the present invention is characterized in that the waveguide type optical signal detecting element is used for an optical pickup for recording / reproducing information on / from an optical disk (claim 4).
[0006]
[Action]
In the waveguide-type optical signal detection device of the present invention, the two waveguide-type reflection concentrators have different focal lengths, so that the shift in the focus position of the guided light has high detection sensitivity but the detection angle range. Has a narrow split photodetector and a split photodetector having a low detection sensitivity but a wide detection angle range.
In the waveguide type optical signal detection device according to the present invention, the first differential amplifier and the first adder respectively connected to the first split type photodetector, and the second split type photodetector A second differential amplifier and a second adder respectively connected to the adder, a third differential amplifier and a third adder respectively connected to the first adder and the second adder A signal output from the first differential amplifier and the second differential amplifier is a focus error signal, a signal output from the third differential amplifier is a track error signal, The signal output from the third adder is used as an RF signal, and the signal is output from the second split-type photodetector that is normally disposed on the waveguide-type reflective collector with a shorter focal length. The difference signal is used as a focus error signal, and the detection area of the second split-type photodetector is used. If it exceeds, the difference signal of the first split-type photodetector arranged on the waveguide-type reflective collector with the longer focal length is used as a focus error signal, so that the focus detection sensitivity is reduced. It is possible to switch between two stages by using two waveguide type reflection concentrators having different focal lengths.
Therefore, when the waveguide type optical signal detection element is used in an optical pickup for recording / reproducing information on / from an optical disc, the defocus amount of the optical disc is usually small, and the focal length is shorter. High-sensitivity focus error detection is performed using a difference signal in the second split-type photodetector arranged on the waveguide-type reflective collector side as a focus error signal. When the defocus amount of the optical disk is large due to disturbance or the like, the difference signal of the first split-type photodetector arranged on the waveguide-type reflective collector with the longer focal length is used as a focus error signal. By using this, focus error detection with a wide detection width is performed.
[0007]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, a waveguide type optical signal detecting element 7 has a thermal oxide film 2 as a buffer layer on a silicon substrate 1 and a silicon oxynitride film 3 as a slab type waveguide layer thereon. A silicon oxynitride film 4 having a lower refractive index than the waveguide layer 3 is formed as a cladding layer on the nitride film 3 (hereinafter referred to as the waveguide layer 3). The prism coupler 5 is joined.
As shown in FIG. 2, waveguide-type reflection condensers 9a and 9b for reflecting the left half of the optical axis 10 of the guided light 8 coupled and excited by the prism coupler 5 to the waveguide layer 3 are arranged. Then, the guided light 14 is focused on the focal point 11. In addition, waveguide-type reflection concentrators 12 a and 12 b that reflect the right half of the optical axis 10 of the guided light 8 are arranged, and converge the guided light 18 to the focal point 13.
Behind the focal point 11, two photodetectors 16 constituting a first split-type photodetector are arranged so as to be substantially perpendicular to the optical axis component 15 of the guided light 14 toward the focal point 11 in the slab plane. And 17 are symmetrically juxtaposed with respect to the optical axis 15. Similarly, the two photodetectors constituting the second split-type photodetector are arranged behind the focal point 13 so as to be substantially perpendicular to the optical axis component 19 of the guided light 18 toward the focal point 13 in the slab plane. The vessels 20 and 21 are juxtaposed symmetrically with respect to the optical axis 19.
[0008]
Further, as shown in FIG. 5, the photodetectors 16 and 17 forming the first split type photodetector are connected to the differential amplifier 22, and the photodetector 20 forming the second split type photodetector. And 21 are similarly connected to a differential amplifier 23.
6, first stage amplifiers 34 and 35 may be provided before the differential amplifier 22 and first stage amplifiers 36 and 37 may be provided before the differential amplifier 23.
The arrangement of the waveguide-type reflection concentrators 9a and 9b and the waveguide-type reflection and concentrators 12a and 12b is not limited to the above-described embodiment, and the configuration shown in FIG. 3 or FIG. In the figure, the same members are given the same numbers.
In the above configuration, the left half of the guided light 8 coupled / excited to the waveguide layer 3 by the prism coupler 5 from the vicinity of the optical axis 10 is reflected by the waveguide-type reflection collectors 9a and 9b and collected at the focal point 11. Then, the right half of the guided light 8 from the vicinity of the optical axis 10 is reflected by the waveguide-type reflection collectors 12a and 12b and is focused on the focal point 13. As described above, when the external light is parallel light, the guided light 8 is separated and condensed at the focal point 11 and the focal point 13, and the signals obtained from the differential amplifiers 22 and 23 become zero.
[0009]
When the external light is divergent light, the condensing position of the guided light 8 is slightly shifted from the focal positions 11 and 13 in the traveling direction of the guided light 8. At this time, assuming that the shift amount of the light-collecting position with respect to the focus 11 is ΔZ ₁₁ and the shift amount of the light-collecting position with respect to the focus 13 is ΔZ ₁₃ , the focal lengths of the waveguide-type reflective light collectors 9 and 12 are different. ΔZ ₁₁ ≠ ΔZ ₁₃ . In this case, if the signals obtained by the differential amplifiers 22 and 23 are I ₂₂ and I ₂₃ (refer to FIG. 7, the signals from the photodetectors 16 and ₁₇ are I ₁₆ and I ₁₇ , respectively). I ₂₂ <I ₂₃ . Also, if the divergence angle θ of the divergent light is gradually increased, but I ₂₂ and I ₂₃ is increased both increment greater in I _23.
[0010]
Furthermore, if the external light is converged light is to be condensed position of the guided light 8 is shifted forward from the focal position 11 and 13, the shift amount [Delta] Z ₁₁ and [Delta] Z ₁₃ is an ΔZ ₁₁ ≠ ΔZ ₁₃ the signal _{I 22} by the differential amplifier 22, 23 _{', I 23'} is above the _{I 22, I 23} but code is reversed _{| I 22 '| <| I} 23' | a is, the convergent angle θ increases growth rate _| '| for who is _{large, | I 22' | I 23} <| I 23 '| also increases the difference.
As described above, this waveguide type optical signal detection element 7 (hereinafter referred to as sensor 7) has different detection sensitivities for detecting the parallelism and the divergence / convergence angle of the external light from the signals of the differential amplifiers 22 and 23. It has a function as a sensor, but when the divergence or convergence angle exceeds a predetermined value, the amount of light incident on the photodetectors 16 and 17 becomes zero, so that the angle detection functions of the photodetectors 16 and 17 are lost. Is In addition, since the detection angle range is narrowed when the detection sensitivity is increased, and the detection angle range is widened when the detection sensitivity is lowered, the sensor 7 detects the focusing signals I ₂₂ and I ₂₃ with the focusing error. It is suitable for applications such as an optical pickup that uses it as a signal and performs feedback control to a lens actuator.
[0011]
Therefore, when the objective lens position is in an on-focus state with respect to the optical disk, focusing control is performed by a high-sensitivity split-type photodetector. Focusing control is performed using the other split-type photodetector having a wide focus detection width. That is, after reaching the limit of the defocus detection width of the split type photodetector with high sensitivity, switching to focusing control by the split type photodetector with low sensitivity is performed.
Therefore, a case where the sensor 7 is used for a light source separated type optical pickup will be described. As shown in FIG. 8, light from a light source (LD) 38 enters a deflection beam splitter 40 via a collimator lens 39 . Light from an optical disk (optical information recording medium) 43 enters the prism coupler 5 of the sensor 7 via the objective lens 42 , the １ ／ λ plate 41 , and the deflection beam splitter 40 . The configuration of the sensor 7 is the same as that shown in FIG. 2, and the same members are denoted by the same reference numerals.
[0012]
Further, as shown in FIG. 9, a first differential amplifier 22 and a first adder 24 are connected to the photodetectors 16 and 17 constituting the first split type photodetector, Similarly, a second differential amplifier 23 and a second adder 25 are connected to the photodetectors 20 and 21 that constitute the photodetectors, and the first adder 24 and the second adder 25 The third differential amplifier 27 and the third adder 28 are connected.
In this configuration, the divergent light emitted from the light source 38 is collimated by the collimator lens 39 and is reflected by the deflection beam splitter 40 toward the optical disk 43 . This reflected light is converted into circularly polarized light by the λλ plate 41 , and collected on the recording surface of the optical disk 43 by the objective lens 42 . The condensed light reflected on the recording surface is converted into linearly polarized light by the λλ plate 41 via the objective lens 42, passes through the deflection beam splitter 40 and enters the prism coupler 5, The light is guided into the waveguide.
[0013]
Incidentally, the arrangement with respect to the track groove direction of the optical disk 43 of the sensor 7, as shown in FIG. 8, the y direction component of the sensor 7 is arranged to coincide with the track groove direction of the optical disc 43, at the time of on-track The sum signal I ₂₄ of the photodetectors 16 and 17 output from the first adder ₂₄ and the sum signal I ₂₅ of the photodetectors 20 and 21 output from the second adder 25 shown in FIG. a ₂₄ = _{I 25.} In FIG. 8, when the position of the condensed spot by the objective lens 42 deviates in the + y direction, I ₂₄ <I ₂₅ , and conversely, when the position deviates in the −y direction, I ₂₄ > I ₂₅ .
Therefore, as shown in FIG. 9, the track error signal (Tr) is output from the third differential amplifier 27 and is the sum signal I _{24 of the} photodetectors 16 and 17 and the sum signal I of the photodetectors 20 and 21. _{The 25} difference signal I ₂₇ (I ₂₅ −I ₂₄ ) is used, and the RF signal (pit signal) is the sum signal I ₂₈ of the I ₂₄ and I ₂₅ output from the third adder 28. Then, the focus error signal is a difference signal I ₂₂ between the photodetectors 16 and 17 output from the first differential amplifier 22 or a difference signal between the photodetectors 20 and 21 output from the second differential amplifier 23. the signal _{I 23} used.
[0014]
Further, as described above, the characteristics of the difference signal I ₂₂ of the first split photodetector of the photodetector 16 and 17, a focus error detection sensitivity photodetector 20 of the second split photodetector , lower than the difference signal I ₂₃ of 21, but the focus error detectable defocus range (focus pull width) wide. Therefore, when the near on-focus performs feedback control to the actuator using the difference signal I _23, when the optical disc 43 located by a disturbance or the like exceeds the detection area of the differential signals I ₂₃ largely deviated, the difference signal I ₂₂ Is switched to feedback control using. For example, as shown in FIG. 7, the difference signal _{I 23} is reached to Ith, a configuration for switching the feedback control of the difference signal _{I 22.}
[0015]
【The invention's effect】
As described above, in the waveguide-type optical signal detecting element according to the first aspect, the waveguide-type reflective condensers have different focal lengths and are connected to the first split-type photodetectors, respectively. said first differential amplifier and a first adder, a second differential amplifier which are respectively connected to the second division type optical detector and a second adder, said first adder and Since it has the third differential amplifier and the third adder respectively connected to the second adder, the configuration using a conventional device using a bulk optical system is difficult, that is, in the same detection device. Furthermore, two sensor functions having different sensitivities can be integrated without losing the characteristics of the waveguide element, and a compact configuration can be realized.
In the waveguide-type optical signal detection device according to claim 2 or 3, the signals output from the first differential amplifier and the second differential amplifier are used as a focus error signal, and the third differential amplifier is used as a focus error signal. A signal output from the amplifier is used as a track error signal, and a signal output from the third adder is used as an RF signal. The difference signal in the second split-type photodetector is used as a focus error signal, and when the detection signal exceeds the detection area of the second split-type photodetector, the waveguide type having a longer focal length is used. Since the difference signal of the first split-type photodetector arranged on the reflection / condenser side is used as a focus error signal, the focusing detection sensitivity can be reduced by two waveguide-type reflection / concentrators having different focal lengths. Switching to columns It can be.
Further, when the waveguide type optical signal detecting element is used in an optical pickup for recording / reproducing information on / from an optical disk, the optical disk may have a focus when the defocus amount of the optical disk is small. The difference signal in the second split-type photodetector disposed on the side of the waveguide-type reflective condenser with the shorter distance is used as a focus error signal, and when the defocus amount of the optical disk is large, the focal length The difference signal of the first split-type photodetector disposed on the side of the waveguide-type reflective collector that is longer is used as a focus error signal, so that the detection sensitivity of focusing can be reduced by using two waveguides having different focal lengths. By switching between two stages using the type reflection concentrator, it is possible to have both a high-precision focusing function and a wide focusing range.
[Brief description of the drawings]
FIG. 1 is a side view showing a waveguide type optical signal detection device according to an embodiment of the present invention.
FIG. 2 is a plan view showing a waveguide type optical signal detection device according to an embodiment of the present invention.
FIG. 3 is a plan view showing a waveguide type optical signal detection device according to another embodiment of the present invention.
FIG. 4 is a plan view showing a waveguide type optical signal detection device according to another embodiment of the present invention.
FIG. 5 is a configuration diagram showing a photodetector to which a differential amplifier is connected.
FIG. 6 is a configuration diagram showing a photodetector to which a differential amplifier and a first-stage amplifier are connected.
FIG. 7 is a characteristic diagram illustrating a relationship between a focus error signal and a disc position shift.
FIG. 8 is a schematic configuration diagram showing an optical disk and an optical pickup.
FIG. 9 is a configuration diagram showing an error signal detection circuit in the optical pickup.
FIG. 10 is a plan view showing a conventional waveguide type optical signal detection element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 Waveguide layer 4 Slab type waveguide 5 Prism coupler 9a, 9b Waveguide type reflection concentrators 12a, 12b Waveguide type reflection concentrators 16, 17 Construct a first split type photodetector Photodetectors 20 and 21 Photodetectors constituting second split type photodetector
43 optical disk

Claims (4)

At least a slab type waveguide having a buffer layer formed on a substrate, a waveguide layer formed on the buffer layer, a cladding layer formed on the waveguide layer, and a slab type waveguide. A prism coupler that couples and excites external light to the waveguide, and two waveguide-type reflectors that are provided in the slab waveguide and capture the right half and the left half of the guided light including the vicinity of the optical axis of the guided light, respectively. In a waveguide-type optical signal detection element including an optical device and first and second split-type photodetectors provided in the vicinity of respective focal positions of the two waveguide-type reflection condensers,
A first differential amplifier and a first adder , each of which has a different focal length and is connected to the first split photodetector ; A second differential amplifier and a second adder respectively connected to the second split type photodetector, and a third differential amplifier respectively connected to the first adder and the second adder A waveguide type optical signal detection device comprising an amplifier and a third adder . A signal output from the first differential amplifier and the second differential amplifier is used as a focus error signal, a signal output from the third differential amplifier is used as a track error signal, and the third adder is used. 2. The waveguide type optical signal detecting device according to claim 1, wherein the signal output from the optical signal is an RF signal. Normally, a difference signal in the second split-type photodetector disposed on the waveguide-type reflective collector with a shorter focal length is used as a focus error signal, and the second split-type photodetector When the detection area is exceeded, a difference signal of the first split-type photodetector arranged on the waveguide-type reflection / concentrator side having a longer focal length is used as a focus error signal. The waveguide type optical signal detection device according to claim 1 or 2, wherein: 4. The waveguide type optical signal detection device according to claim 1, wherein said waveguide type optical signal detection device is used in an optical pickup for recording / reproducing information on / from an optical disk. element.

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