JP2011028819A - Optical accumulation device and optical pickup apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical accumulation device that can reduce unnecessary radiation and suppress shortening of a lifetime of a semiconductor laser element and breakage of the element, and to provide an optical pickup apparatus including the same. <P>SOLUTION: The optical accumulation device 10 includes: a metal plate 14; a semiconductor laser element 16 that is fixed on the metal plate 14 and emits laser light La; a mirror 17 that is fixed on the metal plate 14 and reflects the laser light La emitted from the semiconductor laser element 16 toward a recording medium D; a hologram element 12 passing the laser light La reflected by the mirror 17 and deflecting returning light Lb that has been reflected by the recording medium D in a prescribed direction; a light-reception element 19 that is fixed on the metal plate 14 and receives the returning light Lb deflected in the prescribed direction; and a high-frequency superimposing circuit element 20 that is fixed on the metal plate 14 and supplying the semiconductor laser element 16 with a high frequency current. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical integrated device for recording information on a recording medium such as an optical disc or reproducing information recorded on the recording medium, and an optical pickup apparatus including the same.

A recording / reproducing apparatus for recording information on a recording medium such as an optical disc such as a CD (Compact Disc) or a DVD (Digital Versatile Disc), or reproducing information recorded on the recording medium, and an optical integrated device Optical pickup devices are widely used.
An optical integrated device generally includes a semiconductor laser element that emits laser light, a micromirror that reflects the laser light emitted from the semiconductor laser element toward a recording medium such as an optical disk, and the semiconductor laser element and the micromirror. And a substrate having a light receiving portion that receives return light from the recording medium and photoelectrically converts it into an electrical signal.
In general, an optical pickup apparatus is configured to include the above-described optical integrated device and a lens for focusing laser light emitted from the optical integrated device on a recording surface of a recording medium.

  By the way, a part of the return light from the recording medium may enter the semiconductor laser element without entering the light receiving portion. Usually, the semiconductor laser element oscillates in a single mode, and mode hopping occurs when a part of the return light enters the semiconductor laser element. As a result, the return light noise that the output light quantity of the semiconductor laser element changes greatly is generated.

  A high-frequency current having an amplitude of 20 mA to 30 mA or more at a frequency of 200 MHz or more is generated by an oscillation circuit, and this high-frequency current is superimposed on a direct current and supplied to the semiconductor laser element, thereby causing the semiconductor laser element to oscillate in multimode. There is a method for reducing the return light noise.

However, in this method, a high frequency component with respect to the oscillation frequency may become unnecessary radiation. Unwanted range radiation is radiation at a frequency subject to legal regulation, and the noise radiation level of the electronic device subject to regulation must be lower than the legal regulation value. In addition, it is required to use a frequency that has little influence on other devices, and it is necessary to ensure frequency accuracy.
The high frequency current generated by the oscillation circuit leaks to the supply line to the semiconductor laser element and the power supply line, and each line acts as a radiating antenna, thereby generating unnecessary radiation. Therefore, in order to reduce this unnecessary radiation, it is desirable to shorten the distance between the high frequency superimposing circuit and the semiconductor laser element as much as possible. By shortening this distance, the supply line to the semiconductor laser element serving as an antenna can be shortened, so that unnecessary radiation can be reduced. Further, a synergistic effect can be obtained because the driving loss is also reduced.
An example of means for reducing such unnecessary radiation is disclosed in Patent Document 1.

JP 2003-109237 A

  However, in the optical integrated device disclosed in Patent Document 1 and the optical pickup apparatus including the same, the distance between the high frequency superposition IC and the semiconductor laser element can be shortened, so unnecessary radiation in the supply line is reduced. Although it can be reduced, since the reduction effect is small with respect to unnecessary radiation leaked to the power supply line, further improvement is desired.

By the way, since the lifetime of the semiconductor laser element is extremely shortened when the element temperature rises, it is practically desirable to keep the junction temperature of the semiconductor laser element at about 100 ° C. or less.
In particular, when a recording / reproducing apparatus for recording information on a recording medium such as an optical disk or reproducing recorded information is used outdoors or on a vehicle, an optical pickup device used for this is, for example, − (minus). Since it is used in a wide temperature range of 30 ° C. to + (plus) 80 ° C., it is more important to suppress an increase in the junction temperature of the semiconductor laser element.

  However, in the optical integrated device disclosed in Patent Document 1 and the optical pickup device including the same, a semiconductor laser element, a high-frequency superposition IC, and a light receiving unit that are heat sources are integrated adjacent to each other. Therefore, the temperature of each element is likely to increase due to the influence of heat from each other. For this reason, if the output of the semiconductor laser element cannot be set to a desired value, or if the drive current passed to the semiconductor laser element is increased in order to obtain the desired output, the junction temperature of the semiconductor laser element rises and the lifetime is increased. May be shortened or the element may be destroyed, and further improvement is desired.

  Here, the reason why the lifetime of the semiconductor laser element is shortened or the element is destroyed will be described with reference to FIG. FIG. 11 is a diagram showing a semiconductor laser element in an equivalent circuit.

  As shown in FIG. 11, the semiconductor laser device 100 can be represented by a parallel circuit of an internal resistance R100 and a parasitic capacitance C100. Generally, the internal resistance R100 is in the range of 5Ω to 15Ω, and the parasitic capacitance C100 is in the range of 50 pF to 100 pF. When the AC resistance is calculated because the high-frequency superimposed current is AC, for example, when the parasitic capacitance C100 is 75 pF and the frequency is 400 MHz, the AC resistance of the parasitic capacitance C100 can be expressed by 1 / 2πfC, and thus becomes 5.3Ω. Since the AC resistances of the internal resistance R100 and the parasitic capacitance C100 are close to each other, even if a high frequency superimposed current is passed through the semiconductor laser element 100, a part of the high frequency superimposed current is the AC resistance of the internal resistance R100 and the parasitic capacitance C100. Depending on the ratio, it flows to the parasitic capacitance C100. For this reason, the high-frequency superimposed current flowing through the internal resistor R100, that is, the high-frequency superimposed current that contributes to light emission, decreases, and accordingly, a larger high-frequency superimposed current needs to flow through the semiconductor laser device 100. As a result, unnecessary radiation from the power supply line increases, the temperature of the high frequency superposition IC rises, the temperature of the semiconductor laser element rises due to the influence of this heat, and the element life is shortened or the element is destroyed. There was a case.

  The present invention has been made in view of the above problems, and includes an optical integrated device that can reduce unnecessary radiation and that can suppress the lifetime of the semiconductor laser element from being shortened or the element from being destroyed. An object of the present invention is to provide an optical pickup device.

In order to solve the above-described problems, the present invention provides the following optical integrated device and an optical pickup apparatus including the same.
1) a metal plate (14), a semiconductor laser element (16) fixed on the metal plate and emitting laser light (La), and the semiconductor laser element fixed on the metal plate and emitted from the semiconductor laser element A mirror part (17) for reflecting the laser light toward the recording medium (D), and the return light (Lb) reflected by the recording medium that transmits the laser light reflected by the mirror part in a predetermined direction. A hologram element (12) for receiving, a light receiving element (19) for receiving the return light fixed on the metal plate and deflected in the predetermined direction, and a semiconductor laser element fixed on the metal plate for the semiconductor laser element An optical integrated device (10) comprising: a high-frequency superimposed circuit element (20) for supplying a high-frequency current.
2) The high frequency superimposing circuit element includes an oscillation circuit (31) that oscillates a high frequency current and a high cut that passes the high frequency current oscillated by the oscillation circuit and removes higher harmonic components having a frequency higher than the high frequency current. A filter circuit (32); an output circuit (33) that outputs the high-frequency current that has passed through the high-cut filter circuit as an output current to the semiconductor laser element; and a current control signal that controls the output current is output to the output circuit. The optical integrated device according to 1), further comprising a reference current generating circuit (34).
3) further comprising a frequency divider circuit (61) for lowering the frequency of the high-frequency current oscillated by the oscillation circuit, the frequency divider circuit detecting an output pad (62) for detecting the lowered frequency; 2. The optical integrated device according to 2), further comprising an input pad (63) for externally controlling the frequency dividing circuit.
4) The output circuit is connected to the semiconductor laser element, and when the output current is output from the output circuit, the output current is output to the semiconductor laser element, and the output current is output from the output circuit. The optical integrated device according to 2), further comprising a protection circuit (65) for grounding the output side of the output circuit when the output circuit is not connected.
5) The high-frequency superposition circuit element includes an oscillation circuit (331) that oscillates a high-frequency current, a frequency divider (361) that lowers the frequency of the high-frequency current oscillated by the oscillation circuit, and the frequency divider circuit A high-cut filter circuit (32) that passes a high-frequency current having a low frequency and removes harmonic components having a frequency higher than the low-frequency, and the high-frequency current that has passed through the high-cut filter circuit as an output current. 1) Description comprising an output circuit (33) for outputting to a semiconductor laser element and a reference current generating circuit (34) for outputting a current control signal for controlling the output current to the output circuit. Optical integrated devices.
6) The semiconductor laser device includes a first conductivity type semiconductor substrate (41), a first conductivity type first clad layer (43) formed on the semiconductor substrate, and the first clad layer. An active layer (44) formed on the active layer, a second conductivity type second clad layer (45) formed on the active layer, and a second region formed on a predetermined region on the second clad layer. A second conductivity type ridge (49), a first conductivity type first current confinement layer (51) sequentially formed in a region different from the predetermined region on the second cladding layer, and a second current; The optical integration according to any one of 1) to 5), wherein the first current confinement layer has a carrier concentration lower than that of the second current confinement layer. device.
7) The optical integrated device according to any one of 1) to 6), a base unit (3) that holds the optical integrated device, and laser light emitted from the optical integrated device on the recording surface of the recording medium An optical pickup device (1) comprising a lens (2) for focusing.

  According to the present invention, it is possible to reduce unnecessary radiation, and it is possible to shorten the life of the semiconductor laser element and to suppress element destruction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view for explaining an embodiment of an optical integrated device according to the present invention and an optical pickup device including the same. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view for explaining an embodiment of an optical integrated device according to the present invention and an optical pickup device including the same. It is a typical perspective view for demonstrating the Example of the optical integrated device which concerns on this invention. It is a block diagram for demonstrating the high frequency superimposition IC of Example 1. FIG. FIG. 3 is a circuit diagram for explaining an output circuit in the high-frequency superposition IC according to the first embodiment. It is typical sectional drawing for demonstrating the Example of the semiconductor laser element in the optical integrated device which concerns on this invention. It is a block diagram for demonstrating the high frequency superimposition IC of Example 2. FIG. It is a block diagram for demonstrating the high frequency superimposition IC of Example 3. FIG. FIG. 6 is a circuit diagram for explaining a semiconductor laser protection circuit in a high frequency superposition IC of Example 3. It is a block diagram for demonstrating the high frequency superimposition IC of Example 4. FIG. It is the figure which showed the semiconductor laser element by the equivalent circuit.

  Embodiments of the present invention will be described with reference to FIGS.

<Example 1>
[Configuration of optical pickup device]
As shown in FIG. 1, an optical pickup device 1 emits a laser beam La serving as recording light or reproduction light toward an optical disc D, and receives an optical integrated device 10 that receives return light Lb reflected by the optical disc D; An objective lens 2 that focuses the laser light La emitted from the optical integrated device 10 on a recording surface (not shown) of the optical disc D; and a base portion 3 that holds the optical integrated device 10 and the objective lens 2. Configured.
In FIG. 1, the base portion 3 is shown only in the vicinity of the optical integrated device 10 for easy understanding.

[Configuration of Optical Integrated Device 10]
The optical integrated device 10 will be described with reference to FIGS. 2 and 3 together with FIG.

As illustrated in FIG. 1, the optical integrated device 10 includes a housing 11, a hologram element 12 fixed to the housing 11, and terminal groups 13 a and 13 b that protrude outward from the housing 11. Configured. The terminal groups 13a and 13b are connected to one end side of the flexible wires (or flexible wiring boards) Fa and Fb. The other ends of the flexible wires Fa and Fb are connected to an external circuit (not shown).
The casing 11 is formed by molding a material mainly composed of resin or ceramic.

  FIG. 2 shows the inside of the housing 11 of the optical integrated device 10, and the housing 11 and the groups 13a and 13b in FIG. 1 are omitted for easy understanding.

  As shown in FIG. 2, the optical integrated device 10 is fixed on a metal plate 14 having high thermal conductivity fixed to the base portion 3 (see FIG. 1) and a submount 15 fixed on the metal plate 14. The semiconductor laser element 16 that emits laser light La that becomes recording light or reproduction light, the micromirror 17 that reflects the laser light La emitted from the semiconductor laser element 16 toward the optical disk D, and the hologram that is reflected by the optical disk D A light receiving element 19 having a light receiving portion 18 that receives the return light Lb deflected by the element 12 and photoelectrically converts it to an electrical signal, and a high frequency superposition that performs high frequency modulation on the semiconductor laser element 16 to suppress return light noise. IC (sometimes referred to as a high-frequency superposition circuit element) 20.

  The micromirror 17 is formed by machining a glass material or etching a single crystal Si (silicon) material. It is desirable to form a metal film or a multilayer dielectric film on the reflection surface of the micromirror 17. Thereby, the reflectance of a reflective surface can be improved.

  Incidentally, a part of the return light Lb deflected by the hologram element 12 may be scattered and applied to the high frequency superposition IC 20. When such unnecessary light is irradiated onto the high frequency superimposing IC 20, the high frequency superimposing IC 20 may malfunction, and therefore, it is preferable to provide a light shielding film that shields unnecessary light inside the high frequency superimposing IC 20.

As shown in FIG. 3, the semiconductor laser element 16 and the submount 15 and the high frequency superposition IC 20 are electrically connected by a bonding wire 21. The high frequency superposition IC 20 and the terminal group 13a are electrically connected by a bonding wire 21. The light receiving element 19 and the terminal group 13b are electrically connected by a bonding wire 21.
In particular, it is desirable to shorten the distance between the semiconductor laser element 16 and the submount 15 and the high frequency superposition IC 20. By shortening the distance between the semiconductor laser element 16 and the submount 15 and the high frequency superposition IC 20, the length of the bonding wire 21 connecting them can be shortened. Can be made smaller. This makes it difficult for the bonding wire 21 to act as a radiating antenna, so that it is possible to suppress the occurrence of unnecessary radiation in the supply line to the semiconductor laser element 16.

  The ground of the high frequency superposition IC 20 and the ground of the light receiving element 19 are connected to the metal plate 14, and the ground of the semiconductor laser element 16 is connected to the metal plate 14 via the submount 15 and the high frequency superposition IC 20.

[Operation of optical pickup apparatus including optical integrated device]
An operation method of the optical pickup apparatus 1 including the optical integrated device 10 described above, for example, a reproduction method will be described with reference to FIGS.

A driving current obtained by superimposing a high frequency current on a direct current is supplied from the high frequency superposition IC 20 to the semiconductor laser element 16. Here, the reason why the high frequency current is superimposed on the direct current is to cause the semiconductor laser element 16 to oscillate in the multimode instead of the single mode, and the frequency of the high frequency current for the semiconductor laser element 16 to oscillate in the multimode is, for example, 200 MHz or higher.
The semiconductor laser element 16 oscillates in a multimode and emits laser light La when the drive current exceeds a threshold value.
The laser beam La emitted from the semiconductor laser element 16 is reflected toward the optical disc D by the micromirror 17 and focused on the recording surface (not shown) of the optical disc D by the objective lens 2.
The return light Lb reflected by the recording surface of the optical disk D passes through the objective lens 2, is deflected by the hologram element 12, and reaches the light receiving portion 18 of the light receiving element 19.
The return light Lb reaching the light receiving unit 18 is photoelectrically converted into an electric signal by the light receiving unit 18 and is output to the outside through the bonding wire 21, the terminal group 13b, and the flexible wire Fb.

According to the above-described optical integrated device and the optical pickup device including the same, the semiconductor laser element, the light receiving element, and the high-frequency superposition IC, each serving as a heat source, are respectively fixed to a metal plate having high thermal conductivity. When the element, the light receiving element, and the high frequency superposition IC are driven, heat generated from the element can be efficiently radiated to the metal plate.
Moreover, since the metal plate is being fixed to the base part 3, the heat of a metal plate can be efficiently radiated | emitted to a base part.
Therefore, when the semiconductor laser element, the light receiving element, and the high frequency superposition IC are driven, the heat generated from the elements can be efficiently radiated to the metal plate and the base portion. Even in the case of integration, it is possible to suppress an increase in the element temperature of the semiconductor laser element as compared with the conventional case. For example, the junction temperature of the semiconductor laser element can be maintained at about 100 ° C. or less.

Further, according to the above-described optical integrated device and the optical pickup device including the same, since the heat dissipation is improved as compared with the conventional one, the semiconductor laser element is less susceptible to the heat generated by the high frequency superposition IC. It is possible to shorten the distance between the element and the submount and the high frequency superposition IC.
By shortening the distance between the semiconductor laser element and the submount and the high frequency superposition IC, the length of the bonding wire for connecting them can be shortened, so that the impedance of the bonding wire is reduced according to the length. Can do. By reducing the impedance of the bonding wire, unnecessary radiation in the drive current supply line to the semiconductor laser element can be reduced.
In addition, since the metal plate has an impedance much lower than that of the bonding wire, it is possible to reduce unnecessary radiation leaked to the power supply line.

By the way, since the high frequency superposition IC 20 is disposed in the vicinity of the semiconductor laser element 16, the high frequency superposition IC 20 and the semiconductor laser element 16 have substantially the same element temperature. The high frequency superposition IC 20 is desirably designed to have a negative temperature coefficient because the high frequency current is controlled by its own element temperature. That is, it is desirable to design so that the higher the element temperature of the high frequency superposition IC 20 is, the smaller the output high frequency current is.
As a result, the higher the element temperature of the high-frequency superposition IC 20, the smaller the output high-frequency current, so that the increase in the element temperature of the semiconductor laser element 16 can be suppressed, and the shortening of the life and destruction of the semiconductor laser element 16 can be suppressed. can do.

Further, an LC circuit having, for example, a spiral coil may be formed in the high frequency superposition IC 20, and a drive current may be supplied to the semiconductor laser element 16 using this LC circuit.
As a result, unnecessary radiation is further reduced, and fluctuations in the frequency of the high-frequency current due to changes in the element temperature are reduced, so that a higher-accuracy high-frequency current can be supplied to the semiconductor laser element 16.

[About high frequency superposition IC]
Here, the above-described high-frequency superposition IC 20 will be described with reference to FIGS.

As shown in FIG. 4, the high frequency superposition IC 20 includes an oscillation circuit 31 having an inductance L1 and a parasitic capacitance C1 connected in parallel to each other inside the IC, a high cut filter circuit 32, an output circuit 33, a reference current generation circuit 34, and the like. It is equipped with.
The oscillation circuit 31 is connected to a high cut filter circuit 32. The high cut filter circuit 32 is connected to an output circuit 33. The output circuit 33 is connected to the anode of the semiconductor laser element 16 and the reference current generation circuit 34, respectively. Yes. The cathode of the semiconductor laser element 16 is grounded.

  By the way, the oscillation circuit of a high frequency superposition IC generally uses an RC oscillation circuit because the circuit is easy. The oscillation frequency f of the RC oscillation circuit is proportional to 1 / CR. Further, the resistance element inside the IC is formed by diffusing impurities into Si (silicon). A resistance obtained by diffusing impurities in Si has a low resistance accuracy in manufacturing, and has a poor temperature characteristic because it is a semiconductor. Therefore, the accuracy of the oscillation frequency is low and the change with respect to the environmental temperature is also large. In addition, in view of the above problems, it is conceivable to attach a resistance element having high accuracy and excellent temperature characteristics to the outside of the high frequency superposition IC. However, the wiring connecting the high frequency superposition IC and the resistance element becomes long. Unnecessary radiation is generated by the wiring.

  On the other hand, in the LC oscillation circuit, the oscillation frequency f is proportional to 1 / √2πLC. The inductance L and the capacitance C that determine the frequency are determined by their shapes. Since the inductance L and the capacitance C are formed by a semiconductor process, each shape processing accuracy is high and a change with respect to the environmental temperature is small. Therefore, the LC oscillation circuit has high oscillation frequency accuracy and little change with respect to the environmental temperature. In addition, since the LC oscillation circuit can obtain an oscillation waveform close to a sine wave compared to the RC oscillation circuit, the harmonic component is small and unnecessary radiation is also small.

The inductance L1 is, for example, a spiral coil in which Al (aluminum) wiring is formed in a spiral shape.
In general, the sheet resistance of Al wiring in an IC is high and the Q is low, so that it is difficult to oscillate stably. In the oscillation circuit, if the substantial load resistance is r and the mutual conductance of the transistors in the oscillation circuit is gm, it is desirable to satisfy the relational expression represented by r × gm> 2 in order to oscillate stably. Since the load in the oscillation circuit depends on the parallel resonance circuit of inductance, capacitance, and resistance, the resistance r at the resonance frequency is a relation of r = {L / (C × R)} = {Q / (ω × C)}. This is a substantial load resistance expressed by the equation. Here, L is the load of the oscillation circuit and is the inductance of the parallel resonance circuit for determining the oscillation frequency, C is the load of the oscillation circuit and is the capacitance of the parallel resonance circuit for determining the oscillation frequency, and R Is the resistance of the Al wiring in the inductance of the parallel resonance circuit for determining the oscillation frequency as a load of the oscillation circuit, and ω is the resonance frequency of the parallel resonance circuit, that is, the oscillation frequency.

  In Example 1, in order to obtain an inductance having a high Q, a large spiral coil was formed in multiple layers. For example, a spiral coil having a line width of 28 μm, a distance between lines of 2 μm, and an inner diameter of 164 μm was formed in two layers in four turns (total 8 turns). The outer diameter of the coil at this time is 400 μm.

When the sheet resistance of the Al wiring is 50 mΩ, the coil has an inductance of 16 nH and a resistance of 10Ω. The oscillation frequency is 400 MHz when the capacitance for determining the oscillation frequency is 10 pF in parallel with the inductance.
The substantial load resistance r at this time is 160Ω, and the necessary mutual conductance gm of the transistor in the oscillation circuit 31 is 12.5 mS or more.
As a result, a source current of several mA can be obtained with a MOS transistor having a gate length of 0.35 μm and a gate width of 100 μm.

As described above, the spiral coil is formed inside the high frequency superposition IC, and all the circuit elements are built in the high frequency superposition IC, so that there is no need to arrange a highly accurate resistance element or inductance element outside the high frequency superposition IC. It is possible to improve the accuracy of the oscillation frequency, reduce the temperature change, and reduce unnecessary radiation.
Since the spiral coil having the inductance L1 has a diameter of several hundred μm, it is desirable to use a nonmagnetic metal that does not affect the inductance L1 for the metal plate 14 to which the high frequency superposition IC 20 is fixed.

  The high cut filter circuit 32 is a circuit for suppressing harmonic components generated in the oscillation circuit 31. Since the semiconductor laser element 16 has a large parasitic capacitance that reduces the efficiency of the high-frequency superimposed current, harmonic components having a frequency higher than the oscillation frequency almost flow into the parasitic capacitance, and the efficiency does not contribute to the actual superposition. bad. In addition, since the harmonic component has a high frequency, it easily leaks from the output circuit that requires a large power supply current to the power supply line, and becomes a factor of increasing unnecessary radiation. For this reason, by providing the high-cut filter circuit 32 in the previous stage of the output circuit 33, the harmonic component generated in the oscillation circuit 31 can be removed by the high-cut filter circuit 32. Since the output circuit 33 amplifies only the component of the necessary fundamental frequency and supplies it to the semiconductor laser device 16, it is more efficient and can reduce unnecessary radiation.

As shown in FIG. 5, the output circuit 33 includes constant current circuits 36 and 37, a p-type MOS transistor 38, and an n-type MOS transistor 39.
An inverter circuit is formed by the p-type MOS transistor 38 and the n-type MOS transistor 39. The gates of the MOS transistors 38 and 39 are connected to the high cut filter circuit 32. The source of the p-type MOS transistor 38 is connected to one constant current circuit 36, and the source of the n-type MOS transistor 39 is connected to the other constant current circuit 37. The drains of the MOS transistors 38 and 39 are connected to the anode of the semiconductor laser element 16.
The constant current circuits 36 and 37 are connected to the reference current generation circuit 34, and the output currents of the MOS transistors 38 and 39 are controlled by the current control signal input from the reference current generation circuit 34 to the constant current circuits 36 and 37. The

The reference current generating circuit 34 has a negative temperature characteristic, and the characteristic is designed in accordance with the value of the high frequency superimposed current required depending on the temperature of the semiconductor laser element. In the equivalent circuit of the semiconductor laser device shown in FIG. 11, the internal resistance R100 decreases as the number of carriers increases as the temperature of the semiconductor laser device increases, and the driving current flows more easily through the internal resistance R100 than the parasitic capacitance C100. Efficiency is improved. That is, the necessary high-frequency superimposed current can be reduced as the temperature of the semiconductor laser element increases.
Therefore, even when the temperature of the semiconductor laser element rises, the high-frequency superimposed current flowing in the semiconductor laser element becomes small, so that the current consumption of the high-frequency superimposed IC can be reduced and the temperature rise of the high-frequency superimposed IC is suppressed. Can do.
In addition, since the high frequency superposition IC and the semiconductor laser element are arranged on a metal plate having high thermal conductivity, the element temperatures of the high frequency superposition IC and the semiconductor laser element are almost the same. The temperature of the element can also be suppressed.

[About semiconductor laser elements]
Next, the semiconductor laser device 16 described above will be described with reference to FIG.
FIG. 6A is a schematic cross-sectional view of the semiconductor laser device 16 described above, and FIG. 6B is a schematic cross-sectional view of a general semiconductor laser device shown as a comparative example.

As shown in FIG. 6A, the semiconductor laser device 16 includes an n-type semiconductor substrate 41, an n-type buffer layer 42, an n-type lower cladding layer 43, and a non-doped layer formed on the semiconductor substrate 41 sequentially. An MQW active layer 44 (hereinafter simply referred to as an active layer 44), a p-type upper cladding layer 45, and a p-type etching stop layer 46 are included.
The lower cladding layer 43, the active layer 44, and the upper cladding layer 45 form a double hetero structure.

The semiconductor substrate 41 and the buffer layer 42 are mainly composed of GaAs (gallium arsenide), for example. The lower cladding layer 43 and the upper cladding layer 45 are mainly composed of, for example, (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (aluminum, gallium, indium, phosphorus). The etching stop layer 46 is mainly composed of, for example, (In _0.5 Ga _0.5 ) P (indium gallium phosphorus). The active layer 44 is, for example, a double amount in which non-doped (In _0.53 Ga _0.47 ) P well layers and non-doped (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P barrier layers are alternately stacked. Has a child well structure.

  The semiconductor laser device 16 includes a p-type ridge 49 having a p-type upper cladding layer 47 and a p-type cap layer 48 sequentially formed on the etching stop layer 46, and an etching stop layer 46 on both sides of the ridge 49. N-type current confinement layers 51 and 52 sequentially formed thereon, a p-type contact layer 53 integrally formed on the ridge 49 and the current confinement layer 52, and a p-side formed on the contact layer 53 The electrode 54 and the n-side electrode 55 formed on the surface (the lower surface in FIG. 6) facing the surface on which the buffer layer 42 of the semiconductor substrate 41 is formed.

The upper cladding layer 47 has, for example, (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P as a main component. The cap layer 48 contains, for example, (In _0.5 Ga _0.5 ) P as a main component. The current confinement layers 51 and 52 are mainly composed of (Al _0.5 In _0.5 ) P (aluminum, indium, phosphorus), for example. The contact layer 53 is mainly composed of GaAs, for example. The p-side electrode 54 and the n-side electrode 55 are ohmic electrodes whose main component is Au (gold).
The above-described etching stop layer 46 is a layer for preventing the upper cladding layer 45, which is the lower layer of the etching stop layer 46, from being etched when the ridge 49 is formed by etching, and the laser oscillated in the active layer 44. In order to reduce the absorption loss of light, the thickness is preferably thin.

In Example 1, the thickness of the etching stop layer 46 was 3 nm.
In Example 1, Si (silicon) was used as an n-type carrier (dopant), and Zn (zinc) was used as a p-type carrier (dopant).
For example, when the n-type is the first conductivity type and the p-type is the second conductivity type, all the conductivity types of the above-described layers may be reversed. That is, the p-type may be the first conductivity type and the n-type may be the second conductivity type.
In Example 1, each carrier concentration, the buffer layer 42 1 × ¹⁰ 18 ^{cm -3,} the lower cladding layer 43 in 1 × ¹⁰ 18 ^{cm -3,} the upper cladding layer 45 5 × ¹⁰ 17 ^{cm -3,} The etching stop layer 46 is 1 × 10 ¹⁸ cm ⁻³ , the upper cladding layer 47 is 1 × 10 ¹⁸ cm ⁻³ , the cap layer 48 is 2 × 10 ¹⁸ cm ⁻³ , and the contact layer 53 is 2 × 10 ¹⁸ cm ⁻³ . did.

The current confinement layer 51 has an n-type carrier concentration lower than that of the current confinement layer 52. Assuming that the n-type carrier concentration of the current confinement layer 51 is n51 and the n-type carrier concentration of the current confinement layer 52 is n52, for example, n51 ≦ 1 × 10 ¹⁷ cm ⁻³ and n52 ≧ 1 × 10 ¹⁸ cm ⁻³ . Yes, and satisfies the relational expression of n51 <n52.

On the other hand, as shown in FIG. 6B, the semiconductor laser device 116 of the comparative example is different from the semiconductor laser device 16 of the first embodiment in the configuration of the n-type current confinement layer 150, and other components are the same as those of FIG. Since it is the same as the semiconductor laser device 16 of the first embodiment shown in a), the same components are denoted by the same reference numerals for easy understanding.
A general semiconductor laser element 116 shown as a comparative example has one current confinement layer 150. The current confinement layer 150 has, for example, (Al _0.5 In _0.5 ) P as a main component and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ .

In the semiconductor laser device 16, the region in the thickness direction where the ridge 49 is formed has a pn junction structure including a plurality of p-type layers above the active layer 44 and an n-type layer below the active layer 44. When a voltage is applied in the forward direction, a current flows and light is emitted from the active layer 44 at the pn junction.
On the other hand, in the region in the thickness direction where the current confinement layers 51 and 52 are formed, the n-type current confinement layers 51 and 52 are sandwiched between the p-type contact layer 53 and the p-type upper cladding layer 45. The p-type contact layer 53 and the n-type current confinement layers 51 and 52 are forward-biased when a voltage is applied in the forward direction, but the n-type current confinement is applied. Since the layers 51 and 52 and the upper cladding layer 45 are reversely biased, no current flows. The capacity C per unit area at this time is expressed by the following equation.

Here, q is an electric charge, εs is a relative dielectric constant of the n-type current confinement layer 51, ε0 is a vacuum dielectric constant, and Na and Nd are the p-type upper cladding layer 45 and the n-type current. The carrier concentration of the constriction layer 51, Vd is a diffusion voltage, and V is an applied voltage.
As can be seen from the above equation, C decreases as Nd and Na decrease.
Only by reducing the concentration of the n-type current confinement layer of the semiconductor laser element 116 of the comparative example, the capacitance C decreases, but the current confinement effect decreases.
On the other hand, the semiconductor laser device 16 of Example 1 is further provided with a current confinement layer 51 having an n-type carrier concentration as low as about 1/10 of the n-type confinement layer of the semiconductor laser device 116 of the comparative example. Therefore, the parasitic capacitance C100 can be reduced to about half of that of the semiconductor laser device 116 of the comparative example while maintaining the current confinement effect. For this reason, when a high-frequency superimposed current is applied to the semiconductor laser element 16, the reactive current flowing in the region in the thickness direction where the current confinement layer 51 is formed decreases, so that the high-frequency superimposed current applied to the semiconductor laser element 16 is reduced. It becomes possible to reduce. As a result, the temperature rise of the semiconductor laser element 16 itself can be suppressed and the current applied to the high frequency superposition IC 20 disposed on the same metal plate 14 can be reduced, so that the temperature rise of the semiconductor laser element 16 is further suppressed. can do.

<Example 2>
The optical integrated device according to the second embodiment and the optical pickup device including the same are different from the optical integrated device 10 according to the first embodiment and the optical pickup device 1 including the optical integrated device 10 in the circuit configuration of the high-frequency superposition IC. Since the components are the same as those in the first embodiment, only the circuit configuration of the high frequency superposition IC will be described with reference to FIG. FIG. 7 is a block diagram corresponding to FIG. 4, and the same components as those in FIG. 4 are denoted by the same reference numerals for easy understanding.

As shown in FIG. 7, the high frequency superposition IC 120 includes an oscillation circuit 31 having an inductance L1 and a parasitic capacitance C1 connected in parallel to each other inside the IC, a high cut filter circuit 32, an output circuit 33, a reference current generation circuit 34, and the like. And a frequency dividing circuit 61.
The inductance L1, the parasitic capacitance C1, the oscillation circuit 31, the high cut filter circuit 32, the output circuit 33, and the reference current generation circuit 34 are the same as those in the first embodiment, and the connections of these circuits are also the same as those in the first embodiment.

  The frequency dividing circuit 61 is connected to the oscillation circuit 31 and the high cut filter circuit 32 and has a function of reducing the frequency of the high-frequency current output from the oscillation circuit 31. The frequency dividing ratio of the frequency dividing circuit 61 is in the range of 1/10 to 1/100. The frequency dividing circuit 61 includes a test pad 62 and an input pad 63 for ON / OFF control of the frequency dividing circuit 61 from the outside. Although it is difficult to directly measure the oscillation frequency 200 MHz to 400 MHz of the high frequency superimposed current in the current IC tester, in the second embodiment, the high frequency superimposed current output from the oscillation circuit 31 is 1/10 to 1/100 in the frequency divider 61. The high frequency superimposed current thus divided can be detected by the current IC tester via the test pad 62. Then, the frequency of the high-frequency superimposed current can be calculated by dividing the frequency of the detected signal by the division ratio.

As a result, the high frequency superposition IC 120 can be inspected in the manufacturing process of the optical integrated device, so that the productivity and the yield can be improved.
Further, since the frequency dividing circuit 61 can be controlled ON / OFF from the outside via the input pad 63, the frequency dividing circuit 61 can be operated only when the frequency of the high frequency superimposed current is detected. For this reason, it is possible to suppress excessive current consumption when driving the semiconductor laser element.

<Example 3>
The optical integrated device of Example 3 and the optical pickup device including the same are different from the optical integrated device 10 of Example 1 and the optical pickup device 1 including the same in the circuit configuration of the high-frequency superposition IC 220. Since the components are the same as those in the first embodiment, only the circuit configuration of the high-frequency superposition IC 220 will be described here with reference to FIGS. FIG. 8 is a block diagram corresponding to FIG. 4, and the same components as those in FIG. 4 are denoted by the same reference numerals for easy understanding. FIG. 9 is a diagram showing a configuration of the semiconductor laser protection circuit 65 of FIG.

As shown in FIG. 8, the high frequency superposition IC 220 includes an oscillation circuit 31 having an inductance L1 and a parasitic capacitance C1 connected in parallel to each other inside the IC, a high cut filter circuit 32, an output circuit 33, and a reference current generation circuit 34. And a semiconductor laser protection circuit 65.
The inductance L1, the parasitic capacitance C1, the oscillation circuit 31, the high cut filter circuit 32, the output circuit 33, and the reference current generation circuit 34 are the same as those in the first embodiment, and the connections of these circuits are also the same as those in the first embodiment.

The semiconductor laser protection circuit 65 is connected to the output circuit 33 and the semiconductor laser element 16 and is a protection circuit for preventing electrostatic breakdown of the semiconductor laser element 16.
As shown in FIG. 9, the semiconductor laser protection circuit 65 (region surrounded by a broken line in FIG. 9) includes a p-type MOS transistor 66 and a resistance element 67.
The gate of the MOS transistor 66 is connected to the input side of the output circuit 33 and one end side of the resistance element 67. The source of the MOS transistor 66 is connected to the output side of the output circuit 33 and the anode of the semiconductor laser element 16. The drain of the MOS transistor 66, the other end of the resistance element 67, and the cathode of the semiconductor laser element 16 are grounded.

The resistance value of the resistance element 67 is in the range of 1 kΩ to 100 kΩ.
When the output circuit 33 is operating, a voltage having the same potential as that of the output circuit 33 is also applied to the gate of the MOS transistor 66, so that the MOS transistor 66 is turned off, and the high frequency superimposed current is supplied from the output circuit 33 to the MOS transistor 66. The semiconductor laser element 16 can be supplied without being affected by the transistor 66.
Further, when the output circuit 33 is not operating, the gate of the MOS transistor 66 is at the ground potential via the resistance element 67, so that the MOS transistor 66 is turned on. That is, since the semiconductor laser protection circuit 65 is in a short-circuit state, even when static electricity is generated, the static electricity can be released to the ground through the semiconductor laser protection circuit 65, so that electrostatic breakdown of the semiconductor laser element 16 is prevented. be able to.

<Example 4>
The optical integrated device according to the fourth embodiment and the optical pickup apparatus including the same are different from the optical integrated device 10 according to the first embodiment and the optical pickup apparatus 1 including the optical integrated device 10 in that the circuit configuration of the high-frequency superposition IC 320 is different. Since the components are the same as those in the first embodiment, only the circuit configuration of the high frequency superposition IC 320 will be described with reference to FIG. FIG. 10 is a block diagram corresponding to FIG. 4, and the same components as those in FIG. 4 are denoted by the same reference numerals for easy understanding.

As shown in FIG. 10, the high frequency superposition IC 320 includes an oscillation circuit 331 having an inductance L1 and a parasitic capacitance C1 connected in parallel to each other inside the IC, a frequency dividing circuit 361, a high cut filter circuit 32, an output circuit 33, A reference current generation circuit 34.
The oscillation circuit 331 is connected to the frequency dividing circuit 361, the frequency dividing circuit 361 is connected to the high cut filter circuit 32, the high cut filter circuit 32 is connected to the output circuit 33, and the output circuit 33 is a semiconductor laser element. The sixteen anodes and the reference current generating circuit 34 are connected.

By the way, when the frequency of the high-frequency superimposed current applied to the semiconductor laser element 16 is 400 MHz, for example, the spiral coil of the oscillation circuit 31 at that frequency is several hundred μm as described above, so the area of the high-frequency superimposed IC is large. turn into.
On the other hand, in the high frequency superposition IC 320 according to the fourth embodiment, the oscillation circuit 331 oscillates at a frequency twice as high as the high frequency superposition current applied to the semiconductor laser element 16 and is divided by ½ by the frequency division circuit 361. . Accordingly, since the oscillation circuit 31 oscillates at a frequency of 800 MHz, the inductance of the oscillation circuit 31 becomes 1/4. In general, since the inductance of the spiral coil is proportional to the square of the diameter, oscillation can be performed with a spiral coil having a half size. Therefore, the area of the high frequency superposition IC can be reduced, the integration degree of the high frequency superposition IC can be improved, and the manufacturing cost can be reduced.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

1_ optical pickup device, 2_ objective lens, 3_ base part,
10_Optical integrated device, 11_Case, 12_Hologram element, Terminal group_13a, 13b, 14_Metal plate, 15_Submount, 16_Semiconductor laser element, 17_Micromirror, 18_Light receiving part, 19_Light receiving element, 20_High frequency superposition IC, 21_ Bonding wire, D_optical disc, La_laser beam, Lb_return beam, Fa, Fb_flexible wire (flexible wiring board)

Claims (7)

A metal plate,
A semiconductor laser element that is fixed on the metal plate and emits laser light;
A mirror portion that is fixed on the metal plate and reflects the laser light emitted from the semiconductor laser element toward a recording medium;
A hologram element that transmits the laser light reflected by the mirror unit and deflects the return light reflected by the recording medium in a predetermined direction;
A light receiving element that receives the return light fixed on the metal plate and deflected in the predetermined direction;
A high-frequency superposition circuit element that is fixed on the metal plate and supplies a high-frequency current to the semiconductor laser element;
An optical integrated device comprising: The high-frequency superposition circuit element is
An oscillation circuit that oscillates a high-frequency current;
A high-cut filter circuit that passes the high-frequency current oscillated by the oscillation circuit and removes higher harmonic components having a frequency higher than that of the high-frequency current;
An output circuit that outputs the high-frequency current that has passed through the high-cut filter circuit to the semiconductor laser element as an output current;
A reference current generating circuit for outputting a current control signal for controlling the output current to the output circuit;
The optical integrated device according to claim 1, further comprising: A frequency dividing circuit that lowers the frequency of the high-frequency current oscillated by the oscillation circuit;
3. The optical integrated device according to claim 2, wherein the frequency dividing circuit includes an output pad for detecting the lowered frequency and an input pad for externally controlling the frequency dividing circuit. .   The output circuit and the semiconductor laser element are connected, and when the output current is output from the output circuit, the output current is output to the semiconductor laser element, and the output current is not output from the output circuit 3. The optical integrated device according to claim 2, further comprising a protection circuit for grounding an output side of the output circuit. The high-frequency superposition circuit element is
An oscillation circuit that oscillates a high-frequency current;
A frequency dividing circuit for lowering the frequency of the high-frequency current oscillated by the oscillation circuit;
A high-cut filter circuit that passes a high-frequency current having the frequency lowered by the frequency divider circuit and removes a harmonic component having a frequency higher than the lowered frequency; and
An output circuit that outputs a high-frequency current that has passed through the high-cut filter circuit as an output current to the semiconductor laser element;
A reference current generating circuit for outputting a current control signal for controlling the output current to the output circuit;
The optical integrated device according to claim 1, further comprising: The semiconductor laser element is
A first conductivity type semiconductor substrate;
A first conductivity type first cladding layer formed on the semiconductor substrate;
An active layer formed on the first cladding layer;
A second conductivity type second cladding layer formed on the active layer;
A ridge of a second conductivity type formed in a predetermined region on the second cladding layer;
A first conductivity type first current confinement layer and a second current confinement layer sequentially formed in a region different from the predetermined region on the second clad layer;
With
The optical integrated device according to claim 1, wherein the first current confinement layer has a carrier concentration lower than that of the second current confinement layer. The optical integrated device according to any one of claims 1 to 6,
A base for holding the optical integrated device;
A lens for focusing the laser beam emitted from the optical integrated device on the recording surface of the recording medium;
An optical pickup device comprising:

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