JP2010040974A - Laser driving device and optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress variation in superposition amplitude of a laser driving current due to frequency characteristics of a laser driving system when spread spectrum plus high-frequency superposition is applied. <P>SOLUTION: The amplitude of a high-frequency signal included in a laser driving signal S10 to be input to a flexible board 46 is controlled in a direction where frequency characteristics of the laser driving system 3 are canceled. For example, the amplitude of a spread spectrum signal S2 generated by a spread spectrum signal generation unit 112 is controlled by a gain control unit 132 based upon power variation correction amount setting information J4. An amplitude control signal generation unit 134 generates an amplitude control signal S7 based upon a spread spectrum signal S6 and superposition amplitude setting information J5 from the gain control unit 132. A high-frequency superposition amplitude control unit 136 controls the amplitude of a high-frequency superposition signal S4 from a high-frequency superposition signal oscillation unit 116 based upon an amplitude control signal S7. The amplitude of the high-frequency superposition signal is controlled using the spread spectrum signal S2, so that a high-frequency superposition amplitude varies in synchronism with variation in oscillation frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser driving device (laser driving circuit) and an optical device such as an optical disk device (recording / reproducing device using an optical disk) using the laser driving device and a light emitting device using an optical fiber. More specifically, the present invention relates to a mechanism for driving a laser element (such as a laser diode) by a high frequency superposition method having a spread spectrum function.

  In an optical device such as an optical disk device or a light emitting device using an optical fiber, the laser element is driven by a so-called high-frequency superposition method in which a high-frequency current is superimposed on the drive current of the laser element as a countermeasure against return light or stable oscillation at low power. (Refer to Patent Document 1).

JP 2005-346874 A

  For example, the oscillation mode of a semiconductor laser is likely to change due to return light from a medium or optical component or a temperature change. This change in the oscillation mode is likely to occur particularly during a reproducing operation with a low output power, and noise is generated in the reproduced signal because the wavelength, polarization, power, and the like change. As a result, the servo operation may become unstable, and the error rate may deteriorate as the SNR of the reproduction signal decreases.

  Therefore, in the reproduction operation of the optical disc apparatus, the oscillation mode is stabilized by applying a high-frequency superposition method and superimposing a high-frequency signal on the drive current to oscillate the semiconductor laser in a pseudo multimode.

  Here, an example in which the high frequency superimposition method is applied in the playback mode of the optical disc apparatus has been shown, but it is also conceivable to apply the high frequency superposition method not only in the playback mode but also in the recording mode.

  In high-frequency superposition, the oscillation mode is stabilized by superimposing a high-frequency signal on the drive current to oscillate the semiconductor laser in a pseudo multimode. Usually, modulation is performed at a frequency of about 200 to 400 MHz with an amplitude that crosses the threshold current of the semiconductor laser. Usually, intermittent light emission is caused by the modulation current and the resonance frequency (relaxation vibration frequency) of the semiconductor laser itself.

  However, when the high frequency superposition method is applied, there is a problem that electromagnetic radiation interference (EMI: Electro Magnetic Interference) due to the high frequency superposition signal occurs. This occurs because high frequency superposition frequency and harmonics of n times (N> = 2 integer) of the fundamental wave easily radiate out of the system such as an optical pickup.

  In order to reduce this electromagnetic radiation interference, for example, measures such as electromagnetic shielding may be taken. Further, if measures such as connecting a filter to the output section or power supply of the superimposing circuit are taken, the circuit related to the high frequency superimposing method becomes large and expensive.

  On the other hand, Patent Document 1 applies a so-called spread spectrum method in which a frequency spectrum has a spread by using a modulation signal that is temporally frequency-modulated as a high-frequency superimposed signal. The peak level is lowered by adding a minute fluctuation to the high frequency superposition frequency and spreading the spectrum, that is, reducing the EMI by spreading the superposition frequency. Since the overall energy is the same due to the spread of the frequency spectrum, the level of unnecessary radiation is reduced as a result of the decrease in power at each frequency, and the level of unnecessary radiation is also reduced for harmonics due to the same effect. .

  However, when the high frequency superposition method combined with the spread spectrum method is applied to the inventor of the present application, the electromagnetic radiation interference is mitigated, but due to the frequency characteristics of the laser drive system, the high frequency superposition amplitude is increased in the drive current of the laser element. We found that there was a problem that fluctuated.

  The present invention has been made in view of the above circumstances, and suppresses fluctuations in the high frequency superposition amplitude of the laser drive current caused by the frequency characteristics of the laser drive system when applying the high frequency superposition method combined with the spread spectrum method. The purpose is to provide a mechanism that can do this.

  In one aspect of the present invention, a high-frequency signal to be superimposed on a drive signal for driving a laser element is generated, and the frequency of the high-frequency signal is modulated based on a spread signal that defines a change amount and a change period of the frequency of the high-frequency signal. A superposition frequency control unit, a high frequency superposition amplitude adjustment unit for adjusting the amplitude of a high frequency signal output from the superposition frequency control unit based on the amplitude control signal, and a high frequency signal output from the high frequency superposition amplitude adjustment unit are transmitted to the laser element. A transmission member is provided. That is, the high frequency superposition method combined with the spread spectrum method is applied.

  And an amplitude control unit that controls the amplitude of the high-frequency signal input to the transmission member in a direction that cancels out the frequency characteristics of the laser drive system including the laser element, the output stage of the high-frequency superimposed amplitude adjustment unit, and the transmission member. Shall.

  In the structure of the present invention, when the laser drive system has frequency characteristics and the high frequency superposition amplitude fluctuates when viewed as the drive current in the laser element unit due to the frequency characteristics of the laser drive system, The amplitude characteristic is adjusted in a direction to cancel the frequency characteristic. A function of changing the high frequency superposition amplitude so as to correspond to the change of the high frequency superposition frequency is realized.

  According to one aspect of the present invention, when a high-frequency superposition method combined with a spread spectrum method is applied, fluctuations in the high-frequency superposition amplitude of the laser drive current due to the frequency characteristics of the laser drive system are suppressed. As a result, the laser power fluctuation accompanying the spectrum spread is reduced as compared with the case where the present invention is not applied.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. When distinguishing each functional element according to the embodiment, an uppercase English reference such as A, B,... Is added and described, and when not particularly described, this reference is omitted. To describe. The same applies to the drawings.

<Recording and playback device>
FIG. 1 is a diagram illustrating a configuration example of a recording / reproducing apparatus (optical disk apparatus) which is an example of an optical apparatus. FIG. 1A is a diagram illustrating a configuration example of an optical pickup.

  The recording / reproducing apparatus 1 of the present embodiment includes, as a rotary servo system, a spindle motor 10 that rotates an optical disk OD (Optical Disk) on which information to be reproduced such as music is recorded, and a motor driver 12 that drives the spindle motor 10. The optical pickup 14 is provided.

  As the optical disk OD, in addition to a so-called reproduction-only optical disk such as a CD (compact disk) or a CD-ROM (Read Only Memory), a write-once optical disk such as a CD-R (Recordable) or a CD-RW (Rewritable). Such a rewritable optical disc may be used. Furthermore, it is not limited to a CD-based optical disk, but may be an MO (magneto-optical disk), a normal DVD (Digital Video or Versatile Disk), or a next-generation DVD using a blue laser with a wavelength of about 405 nm, for example. It may be a DVD-type optical disc. Further, it may be a so-called double density CD (DDCD; DD = Double Density), CD-R, or CD-RW in which the recording density is approximately double that of the current format while following the current CD format. .

  The recording / reproducing apparatus 1 includes a spindle motor control unit 30 and a pickup control unit 32. The spindle motor control unit 30 is an example of a rotation control unit (rotation servo system) that controls the motor driver 12. The pickup control unit 32 is an example of a tracking servo system and a focus servo system, and controls the radial position and the focal direction position of the light spot emitted from the optical pickup 14 with respect to the optical disc OD.

<Optical pickup>
As shown in FIG. 1A, the optical pickup 14 includes a semiconductor laser 41, a prism 42, a lens 43, a photodetector 44, and a drive current control unit 47 that is an example of a laser drive device. The semiconductor laser 41 emits a laser beam for recording additional information on the optical disc OD or reading information recorded on the optical disc OD. The prism 42 reflects the laser light from the semiconductor laser 41 toward the lens 43, and guides the reading light (reflected light) from the lens 43 to the photodetector 44. The lens 43 condenses the laser light reflected by the prism 42 onto the optical disc OD, and guides the reading light from the optical disc OD to the prism 42. The photodetector 44 converts the reading light into an electrical signal. The drive current control unit 47 includes a drive signal generation unit 48 and a high frequency superimposition processing unit 49. The drive current control unit 47 is configured by a laser drive IC as an example.

  Between the semiconductor laser 41 and the drive current control unit 47, signal wiring pattern-formed on the flexible substrate 46 as an example of a transmission member that transmits the laser drive signal S10 output from the drive current control unit 47 to the semiconductor laser 41. Connected through. The total length of the flexible substrate 46 varies depending on the arrangement of the drive current control unit 47 and the semiconductor laser 41, but has a length of about 20 to 50 mm, for example. From the output stage of the drive current control unit 47 (laser drive IC) to the semiconductor laser 41 is referred to as a laser drive system 3.

  The recording / reproducing apparatus 1 includes, as a recording / reproducing system, an information recording unit that records information via an optical pickup 14 and a recording / reproducing signal processing unit that is an example of an information reproducing unit that reproduces information recorded on an optical disc OD. 50. The recording / reproduction signal processing unit 50 and the optical pickup 14 are connected via a signal wiring pattern formed on a flexible substrate 51 as an example of a transmission member that transmits a signal. The total length of the flexible substrate 51 varies depending on the arrangement of the recording / reproducing signal processing unit 50 and the optical pickup 14, but has a length of about 100 mm, for example.

  The recording / reproducing apparatus 1 includes, as a controller system, a controller 62 and an interface unit that performs an interface function that is not illustrated. The controller 62 is configured by a microprocessor (MPU: Micro Processing Unit), and controls the operation of the servo system having the spindle motor control unit 30 and the pickup control unit 32 and the recording / reproduction signal processing unit 50. The interface unit has an interface (connection) function with a personal computer (hereinafter referred to as a personal computer) which is an example of an information processing apparatus (host apparatus) that performs various types of information processing using the recording / reproducing apparatus 1. A host IF controller is provided in the interface unit. The recording / reproducing apparatus 1 and the personal computer constitute an information recording / reproducing system (optical disc system).

<Recording / Signal Processing Unit>
The recording / playback signal processing unit 50 includes an RF amplification unit 52, a waveform shaping unit 53 (waveform equalizer; Equalizer), and an AD conversion unit 54 (ADC; Analog to Digital Converter) which is an example of an AD conversion circuit. .

  The RF amplifier 52 amplifies a minute RF (high frequency) signal (reproduced RF signal) read by the optical pickup 14 to a predetermined level. The waveform shaping unit 53 shapes the reproduction RF signal output from the RF amplification unit 52. The AD conversion unit 54 converts the analog reproduction RF signal output from the waveform shaping unit 53 into digital data.

  The recording / reproduction signal processing unit 50 includes a clock reproduction unit 55, a write clock generation unit 56, a digital signal processing unit 57 constituted by a DSP (Digital Signal Processor), and an APC control unit 58. The APC controller 58 supplies the optical pickup 14 with an APC signal that controls the light emission power of the laser element provided in the optical pickup 14 to be constant.

  The AD converter 54 converts the analog reproduction RF signal into digital reproduction RF data Din based on the AD clock CKad. The clock recovery unit 55 includes a data recovery type phase synchronization circuit (PLL circuit) that generates a clock signal locked to the reproduction RF data Din output from the AD conversion unit 54. The clock recovery unit 55 supplies the recovered clock signal to the AD conversion unit 54 as an AD clock CKad (sampling clock), or supplies it to other functional units. The write clock generator 56 generates a write clock for modulating data when recording on the optical disc OD based on a reference clock supplied from a crystal oscillator or the like.

  The digital signal processing unit 57 includes an ECC encoding unit and a modulation processing unit as recording functional units. The recording pulse from the digital signal processing unit 57 is supplied to the optical pickup 14. The digital signal processing unit 57 demodulates the reproduction RF data Din output from the AD conversion unit 54 and performs digital signal processing such as decoding digital audio data or digital image data.

  The digital signal processing unit 57 includes, for example, a data detection unit and a demodulation processing unit as a function unit for reproduction. The data detection unit performs processing such as PRML (Partial Response Maximum Likelihood) and detects digital data from the reproduction RF data Din. For example, in recent years, the recording density has been increased. When the performance of a recording / reproducing apparatus such as an optical disk or an optical pickup as a recording medium is determined, the shortest recordable wavelength is determined accordingly. If the recording density is increased without changing the given shortest wavelength, so-called intersymbol interference occurs in which the reproduction waveform of the adjacent code is superimposed and read out. In the conventional binarization method, proper reproduction is performed. It has become impossible to process. PRML is used as an example of a technique for solving such a problem in high density.

  The demodulation processing unit demodulates the digital data sequence and performs digital signal processing such as decoding digital audio data and digital image data. For example, the demodulation processing unit includes a demodulation unit, an error correction code (ECC) correction unit, an address decoding unit, and the like, and performs demodulation / ECC correction and address decoding. The demodulated data is transferred to the host device via the interface unit.

  Here, the recording / reproducing apparatus 1 of the present embodiment records and reproduces digital data output from the information source on the optical disc OD by the laser light emitted from the semiconductor laser 41. For this reason, the drive current control unit 47 modulates the optical output power according to the material and recording speed of the optical disc OD, and also outputs the optical output (optical light) of the laser light emitted from the semiconductor laser 41 (in the optical pickup 14). APC (Auto Power Control) control is performed to keep the intensity and light output power) at constant values. The drive current control unit 47 controls (on / off) the recording current of the laser beam for recording information on the optical disc OD in the recording mode. At this time, the drive signal generation unit 48 generates a predetermined laser drive signal based on the recording signal in the recording mode and in the reproduction mode, and supplies the laser drive signal to the high frequency superimposing processing unit 49. The high frequency superimposition processing unit 49 superimposes the high frequency superposition signal S8 from the built-in high frequency oscillation circuit on the laser drive signal S1. Then, the laser drive signal S10 on which the high-frequency signal is superimposed is supplied to the semiconductor laser 41 built in the optical pickup 14. The laser drive signal at the input point of the semiconductor laser 41 is S12.

<Problems of laser drive system>
2-8 is a figure explaining the problem of the laser drive system 3. FIG. Here, FIG. 2 is a diagram for explaining a laser driving method by high-frequency superposition. FIG. 3 is a diagram illustrating an example of a light emission waveform at the time of high frequency superposition. FIG. 4 is a diagram for explaining a change in the high-frequency superimposed spectrum due to spectrum spreading. FIG. 5 is a diagram for explaining a connection mode of the laser drive system. FIG. 6 is a diagram for explaining the frequency characteristics of the laser drive system. FIG. 7 is a diagram for explaining the reproduction power fluctuation accompanying the spectrum spread. FIG. 8 is a diagram for explaining fluctuation of the reproduction RF signal due to reproduction power fluctuation.

  For example, when a recording / reproducing optical disc OD is used, if the laser power is increased during reproduction, recorded data may be deteriorated. For this reason, generally, the laser power is increased during recording, but the laser power is kept low during reproduction. On the other hand, if the laser power is kept low, there is a concern that a stable oscillation output cannot be obtained.

  Therefore, so-called “high frequency superposition” is widely used in the reproducing operation of the recording / reproducing apparatus 1. In high-frequency superposition, the oscillation mode is stabilized by superimposing a high-frequency signal on the drive current to oscillate the semiconductor laser in a pseudo multimode. For example, as shown in FIG. 2, modulation is performed at a frequency of about 200 to 400 MHz with an amplitude that crosses over the threshold current Ith of the semiconductor laser. The semiconductor laser emits light intermittently as shown in FIG. 3 by the modulation current and the resonance frequency (relaxation vibration frequency) of the semiconductor laser itself.

  However, when high frequency superposition is performed, a problem of electromagnetic radiation interference due to the high frequency superposition signal occurs. As a circuit technique for reducing the electromagnetic radiation interference, there is a “spread spectrum method”. As shown in FIG. 4, the “spread spectrum method” lowers the peak level of the electromagnetic radiation component by spreading a spectrum by adding a minute fluctuation to the high frequency superimposed frequency.

  On the other hand, as shown in FIG. 5, in the laser drive system 3 from the output stage of the laser drive IC to the semiconductor laser 41, a high-frequency superimposition processing unit 49 (for example, constituted by a laser drive IC) that drives the semiconductor laser 41 and the semiconductor laser 41. Are connected via a flexible substrate 46, for example. The length of the flexible substrate 46 varies depending on the arrangement of the laser driving IC and the semiconductor laser 41, but has a length of about 20 to 50 mm, for example. Usually, the amplitude characteristic of the laser drive system 3 has frequency dependence as shown in FIG.

  This frequency characteristic is caused not only by the characteristics of the output stage of the laser drive IC, but also by the impedance characteristics of the flexible substrate 46 and the semiconductor laser 41, and has differences and individual differences depending on the design of the optical pickup 14.

  For this reason, when a high frequency superposition method combined with a spread spectrum method is applied, that is, when the high frequency superposition frequency is changed in order to perform the spread spectrum, the electromagnetic radiation interference is mitigated, but as shown in FIG. It has been found that due to the frequency characteristics of the system 3, the high frequency superimposed amplitude of the drive current of the semiconductor laser 41 also varies. As described above, in high frequency superimposition, modulation is performed with an amplitude across the threshold current Ith of the semiconductor laser 41. As a result, the light emission power also varies in the light emission waveform. As a result, the reproduction power fluctuates in synchronization with the change in the high frequency superposition frequency (spread spectrum signal S2).

  Such reproduction power fluctuation is superimposed on the information signal / servo error signal reproduced from the optical disk PD (media). For example, as shown in FIG. 8, it appears as fluctuations in the reproduction RF signal amplitude. As a result, problems such as an error rate deterioration and servo operation instability are caused.

  Furthermore, in recent years, an optical head compatible with three wavelengths of CD / DVD / next-generation DVD has been demanded. In such an optical head, since three semiconductor lasers 41 are connected to one laser drive IC, the flexible substrate 46 that connects the laser drive IC and each semiconductor laser 41 tends to be long. This leads to the deterioration of the frequency characteristics of the flexible substrate 46 and, consequently, the laser drive system 3, so that the reproduction power fluctuation accompanying the spectrum spread is likely to be manifested.

  Therefore, in the laser drive system 3 of the present embodiment, when a high frequency superposition method combined with a spread spectrum method is applied, the high frequency superposition amplitude in the semiconductor laser (laser element section) due to the frequency characteristics of the laser drive system 3 is applied. Make it possible to suppress fluctuations. The basic concept of this method is that the amplitude of the high frequency signal (high frequency superimposed amplitude) included in the laser drive signal S10 input to the transmission member (in this example, the pattern on the flexible substrate 46) is the frequency of the laser drive system 3. By adding a function of changing (controlling) the characteristic in a direction to cancel the characteristic, the power fluctuation due to spectrum spreading is reduced.

  In realizing the function of changing the high frequency superposition amplitude in the direction of canceling the frequency characteristic of the laser drive system 3, the frequency characteristic of the laser drive system 3 is canceled based on the spread spectrum signal when the high frequency signal is superimposed on the laser drive signal. A first method for changing the amplitude of the high-frequency superimposed signal in the direction, and a second method for controlling the frequency characteristic by filtering in a direction that cancels the frequency characteristic of the laser drive system 3 with respect to the laser drive signal superimposed with the high-frequency signal. It is conceivable to take any one of these methods or a combination thereof. Both are characterized in that when the high frequency superposition frequency changes, the fluctuation of the high frequency superposition amplitude caused by the frequency characteristic of the laser drive system 3 is canceled. Hereinafter, the first method and the second method will be specifically described.

<Laser Drive System: First Embodiment>
9 and 10 are diagrams for explaining a laser drive system 3X of a comparative example to which this embodiment is not applied. FIG. 11 is a diagram illustrating the laser drive system 3A according to the first embodiment.

  The laser drive system 3A according to the first embodiment applies the first method of changing the amplitude of the high frequency superimposed signal in accordance with the spread spectrum signal when the high frequency signal is superimposed on the laser drive signal.

  Specifically, in the laser drive systems 3A and 3X, the high frequency superimposition processing units 49A and 59X include a superposition frequency control unit 110 that determines the oscillation frequency of the high frequency superposition signal, and a high frequency superposition amplitude control unit 130 that determines the amplitude of the high frequency superposition signal. A superimposing unit 150 and a drive transistor 152 are included. The frequency and amplitude can be controlled from the outside, and are set by an IC external resistance value, a register setting, or the like.

  The superposition frequency and superposition amplitude controlled signal S8 output from the high frequency superposition amplitude control unit 130 are combined with the laser drive signal S1 from the drive signal generation unit 48 by the superposition unit 150. The laser drive signal S10 on which the high-frequency signal output from the superimposing unit 150 is superimposed is supplied to the semiconductor laser 41 via the drive transistor 152 and the flexible substrate 46.

  The superposition frequency control unit 110 changes the frequency of the high frequency signal superimposed on the laser drive signal S1 in accordance with the spread spectrum signal S2 (that is, by the spread spectrum technique). The amplitude of the spread high frequency superimposed signal S4 is changed according to the spread spectrum signal S2. As described above, the laser drive system 3A of the first embodiment changes the frequency and amplitude of the high-frequency signal to be superimposed on the laser drive signal S1 in accordance with the spread spectrum signal S2, thereby irradiating the laser light at each laser output power and The detection of reflected light is optimized.

  For example, at the time of reproduction, the drive signal generation unit 48 adjusts the laser emission power to the reproduction power level, generates the laser drive signal S1, and supplies the laser drive signal S1 to the superposition unit 150. The superimposing unit 150 superimposes the high frequency superimposed signal S8 supplied from the high frequency superimposed amplitude control unit 130 on the laser drive signal S1. At this time, the superposition frequency control unit 110 generates a spread spectrum signal S2 based on the modulation frequency setting information J1 and the spread frequency setting information J2 for spread spectrum, and further, a frequency obtained by combining the spread spectrum signal S2 and the superposition frequency setting information J3. The superposition frequency is controlled based on the control signal S3. The high frequency superimposed amplitude control unit 130 generates the amplitude control signal S7 using not only the superimposed amplitude setting information J5 but also the spread spectrum signal S2 generated by the superimposed frequency control unit 110, and based on the amplitude control signal S7. Thus, the amplitude of the high frequency superimposed signal S4 is controlled. As a result, the frequency and amplitude of the high frequency superimposed signal S8 superimposed on the laser drive signal S1 are controlled based on the spread spectrum signal S2.

  On the other hand, at the time of recording, recording data supplied from a host device such as a personal computer is supplied to the digital signal processing unit 57. The ECC encoding unit adds an error correction code to the recording data and supplies it to the modulation processing unit. The modulation processing unit modulates the recording data to which the error correction code is added and supplies the modulated recording data to the drive signal generation unit 48. The drive signal generator 48 performs pulse width modulation on the recording data modulated based on the recording command, generates a laser drive signal S1 having a recording power level, and supplies the laser drive signal S1 to the superimposing unit 150. The superimposing unit 150 superimposes the high frequency superimposing signal S8 from the high frequency oscillation circuit built in the high frequency superimposing processing unit 49 on the laser drive signal S1. At this time, the high frequency superimposition processing unit 49 performs control so as to vary the superposition frequency and amplitude of the high frequency superposition signal S8. For example, it is changed to a relatively small amplitude at a relatively high frequency for recording. The semiconductor laser 41 irradiates the optical disk OD with a laser beam via an optical lens based on the laser drive signal S12. A recording thin film of the optical disc OD is heated with laser light, and a mark with recorded information is formed by causing a predetermined thermal change.

  Hereinafter, the superposition frequency control unit 110 and the high frequency superposition amplitude control unit 130 will be described in detail. In the laser drive systems 3A and 3X, the superposition frequency control unit 110 is for the high frequency superimposition processing unit 49 having a spread spectrum function. The superposition frequency generation unit 112, the frequency control signal generation unit 114, and the high frequency superposition are performed. A signal oscillation unit 116 is included. The spread spectrum signal generator 112 is supplied with modulation frequency setting information J1 for spread spectrum and spread frequency setting information J2 for spread spectrum. The frequency control signal generation unit 114 is supplied with superposition frequency setting information J3.

  The spread spectrum signal generator 112 generates, for example, a triangular wave spread spectrum signal S2 based on the modulation frequency setting information J1 and the spread frequency setting information J2, and supplies the generated signal to the frequency control signal generator 114. The frequency control signal generation unit 114 synthesizes (superimposes) the spread spectrum signal S2 and the superimposed frequency setting information J3 to generate the frequency control signal S3 and supplies it to the high frequency superimposed signal oscillation unit 116. The high frequency superimposed signal oscillating unit 116 generates a high frequency superimposed signal S4 by oscillating at a frequency based on the frequency control signal S3, and supplies the generated signal to the high frequency superimposed amplitude control unit 130. As a result, the high frequency superimposed frequency of the high frequency superimposed signal S4 output from the high frequency superimposed signal oscillating unit 116 is modulated according to the spread spectrum signal S2.

  The amplitude of the spread spectrum signal S2 corresponds to the width at which the high frequency superposition frequency changes, and the period corresponds to the period at which the high frequency superposition frequency changes. Here, they are referred to as “spread frequency” and “modulation frequency”, respectively.

  Here, although an example of a triangular wave as the waveform of the spread spectrum signal S2, since the purpose of diffusing the spectrum of the high-frequency superposition signal may be any waveform including sinusoidal.

  In the laser drive system 3 </ b> A of the first embodiment, the high frequency superimposed amplitude control unit 130 includes a gain adjustment unit 132, an amplitude control signal generation unit 134, and a high frequency superimposed amplitude adjustment unit 136. The gain adjusting unit 132 is supplied with the spread spectrum signal S2 and the power fluctuation correction amount setting information J4 from the spread spectrum signal generating unit 112. The amplitude control signal generation unit 134 is supplied with the superimposed amplitude setting information J5. In the first embodiment, the gain control unit 132 and the amplitude control signal generation unit 134 include an amplitude control unit that controls the amplitude of the high-frequency signal superimposed on the drive signal S10 in a direction that cancels out the frequency characteristics of the laser drive system 3A. Composed.

  The gain adjusting unit 132 changes the amplitude of the spread spectrum signal S2 linearly or nonlinearly based on the power fluctuation correction amount setting information J4, and supplies the spread spectrum signal S6 after the amplitude change to the amplitude control signal generating unit 134. The amplitude control signal generation unit 134 combines (superimposes) the spread spectrum signal S6 and the superimposed amplitude setting information J5 to generate an amplitude control signal S7 and supplies it to the high frequency superimposed amplitude adjustment unit 136. The high frequency superimposed amplitude adjusting unit 136 adjusts the amplitude of the high frequency superimposed signal S4 supplied from the high frequency superimposed signal oscillating unit 116 based on the amplitude control signal S7, so that the high frequency superimposed amplitude adjusting unit 136 is based on the modulation frequency setting information J1 and the spread frequency setting information J2. The high-frequency superimposed signal S8 having the amplitude adjusted based on not only the superimposed amplitude setting information J5 but also the spread spectrum signal S2 is generated and supplied to the superimposing unit 150.

  The superimposing unit 150 synthesizes (superimposes) the high-frequency superimposing signal S8 and the laser driving signal S1 from the driving signal generating unit 48 (not shown) to generate the laser driving signal S10. The laser drive signal S10 is supplied to the semiconductor laser 41 via the drive transistor 152 and the flexible substrate 46.

  As described above, the laser drive system 3A of the first embodiment superimposes the spread spectrum signal S2 on the superimposed amplitude setting information J5 that is the source of the amplitude control signal S7 and inputs the superimposed signal to the high frequency superimposed amplitude adjusting unit 136. The spread spectrum signal S2 generated by the spread spectrum signal generator 112 is input not only to the high frequency superimposed signal oscillator 116 but also to the high frequency superimposed amplitude adjuster 136 as the amplitude control signal S7. The high frequency superimposed amplitude adjusting unit 136 changes the amplitude of the high frequency superimposed signal S4 (spread spectrum) in accordance with the spread spectrum signal S2, thereby generating a high frequency generated by the frequency characteristics of the laser drive system 3A when the high frequency superimposed frequency changes. The fluctuation of the superimposed amplitude is canceled out. That is, the power fluctuation accompanying the spectrum spread of the high frequency superimposed signal included in the laser drive signal S12 at the input point of the semiconductor laser 41 is reduced.

  For example, when the laser drive system 3A has a frequency characteristic in which the gain decreases at a high frequency, the amplitude is controlled so that the high frequency superimposed amplitude increases when the high frequency superimposed frequency increases. As a result, the high-frequency superimposed signal included in the laser drive signal S12 at the input point of the semiconductor laser 41, that is, the high-frequency superimposed signal input to the semiconductor laser 41 has a constant amplitude regardless of the high-frequency superimposed frequency. In this way, according to the mechanism of the first embodiment, the laser power can be kept constant even if spectrum spreading is performed.

  In addition, the laser drive system 3A of the first embodiment includes a gain adjustment unit 132 that changes the amplitude of the amplitude control signal S7 input to the high frequency superposition amplitude adjustment unit 136 based on the power fluctuation correction amount setting information J4. Yes. In other words, the gain adjustment unit 132 adjusts the amplitude of the spread spectrum signal S2 based on the power fluctuation correction amount setting information J4, and then superimposes it on the superimposed amplitude setting information J5 that is the source of the amplitude control signal S7. The signal is input to the superimposed amplitude adjustment unit 136.

  By providing the gain adjusting unit 132, it is possible to suppress power fluctuations even in different models / individuals. For example, the frequency characteristics of the laser drive system 3 have differences depending on the design of the optical pickup 14 (optical head) and individual differences. In other words, the magnitude of power fluctuations associated with spread spectrum has design differences and individual differences. Therefore, by adjusting the amount by which the high-frequency superimposed amplitude is changed according to the spread spectrum signal S2 based on the power fluctuation correction amount setting information J4, power fluctuation can be suppressed even in different models / individuals.

  By adjusting the amplitude of the amplitude control signal S7 input to the high frequency superimposed amplitude adjusting unit 136 by the gain adjusting unit 132, the amount of change in amplitude with respect to the frequency change of the high frequency superimposed signal is adjusted. As a result, the power fluctuation accompanying the spectrum spread is suppressed by optimizing and adjusting the gain with respect to the model difference / individual difference of the laser drive system 3A. Since the amplitude of the high frequency superimposed signal is controlled using the spread spectrum signal S2, the high frequency superimposed amplitude changes in synchronization with the change of the oscillation frequency.

  On the other hand, the laser drive system 3X of the comparative example to which the first embodiment is not applied does not include the gain adjustment unit 132 and the amplitude control signal generation unit 134, and the superimposition amplitude setting information J5 is directly input to the high frequency superposition amplitude adjustment unit 136. Supplied. As a result, the high frequency superimposed amplitude adjusting unit 136 adjusts the amplitude based only on the superimposed amplitude setting information J5, thereby performing spectrum spreading based on the modulation frequency setting information J1 and the spread frequency setting information J2, and also setting the superimposed amplitude setting. The high-frequency superimposed signal S8 whose amplitude is adjusted based on only the information J5 is output.

  For this reason, as described above, power fluctuations occur with spread spectrum. This is because the high-frequency superimposed amplitude adjustment unit 136 outputs a high-frequency superimposed signal S8 whose frequency changes according to the spread spectrum signal S2. Here, the amplitude is constant regardless of the change in frequency. On the other hand, the laser drive system 3X has a frequency characteristic such that the gain decreases as the frequency becomes higher. As a result, the high-frequency superimposed signal included in the laser drive signal S12 at the input point of the semiconductor laser 41, that is, the semiconductor The high frequency superimposed signal input to the laser 41 has a smaller amplitude as the frequency is higher. As described with reference to FIG. 7, this is because the high frequency superimposition is modulated across the threshold current of the semiconductor laser 41, and as a result, the reproduction power fluctuates according to the change of the high frequency superposition frequency.

  In the above description, the frequency characteristic of the laser drive system 3 has been described as having a characteristic in which the gain decreases at a high frequency. However, actually, the laser drive system 3 has various frequency characteristics depending on the characteristics of the semiconductor laser 41 and the flexible substrate 46. obtain. For example, a case where the gain increases at a high frequency can be sufficiently considered. In that case, when the amplitude control signal S7 is generated by superimposing the spread spectrum signal S2 with the superposition amplitude setting information J5 and supplied to the high frequency superposition amplitude adjustment unit 136, the amplitude is controlled to be small at a high frequency. A similar effect can be obtained.

<Laser Drive System: Second Embodiment>
12 and 13 are diagrams for explaining a laser drive system 3B of the second embodiment. The laser drive system 3B according to the second embodiment applies the second method of controlling the frequency characteristics by filtering the laser drive signal S10 on which the high frequency signal is superimposed.

  Specifically, in the laser drive system 3B, the superposition frequency control unit 110 and the high frequency superposition amplitude control unit 130 are the same as the laser drive system 3X of the comparative example. The filter processing unit 140 that changes the frequency characteristic of the laser drive signal S12 is provided between the high-frequency superposition amplitude control unit 130 and the superposition unit 150. That is, in the second embodiment, the filter processing unit 140 configures an amplitude control unit that controls the amplitude of the high-frequency signal superimposed on the drive signal S10 by the filter process in a direction that cancels the frequency characteristics of the laser drive system 3B. The

  The filter processing unit 140 includes a filter circuit 142 having a frequency characteristic opposite to the frequency characteristic of the laser driving system 3B. The amplitude characteristic of the laser driving system 3B has frequency dependence, and the frequency characteristic is caused not only by the characteristic of the output stage of the semiconductor laser 41 but also by the impedance characteristic of the flexible substrate 46 and the semiconductor laser 41. There are differences due to the design of the optical pickup 14 and individual differences. When the semiconductor laser 41 is changed or the length or material of the flexible substrate 46 is changed, the frequency characteristics are also changed.

  Therefore, the filter processing unit 140 prepares a plurality of filter circuits 142 having different frequency characteristics so that it can adapt to changes in these frequency characteristics, or a variable inductor circuit or varicap using an operational amplifier. It is preferable that one filter circuit 142 can be used to change the frequency characteristics.

  The laser drive system 3B_1 (high-frequency superimposition processing unit 49B_1) of the first example shown in FIG. 12 shows the former case, and the path selection switch 144 that switches the paths of the plurality of filter circuits 142 (FIL_1 to FIL_n) includes a filter. It is provided at the input / output of the circuit 142. The path selection switch 144 is supplied with frequency characteristic control information J11 for controlling the frequency characteristic.

  A laser drive system 3B_2 (high-frequency superimposition processing unit 49B_2) of the second example shown in FIG. 13 shows the latter case, and frequency characteristic control information J12 for controlling frequency characteristics is supplied to one filter circuit 142. ing.

  The frequency characteristic of the high-frequency superimposed signal S9 output from the filter processing unit 140 is realized by switching by the path selection switch 144 based on the frequency characteristic control information J11 or by changing the characteristic in the filter circuit 142 based on the frequency characteristic control information J12. .

  Therefore, the frequency characteristic control information J11, J12 has the same property as the superposition amplitude setting information J5 of the first embodiment, and the high frequency superposition superposed on the laser drive signal S10 based on the frequency characteristic control information J11, J12. The frequency characteristics of the signal, that is, the gain corresponding to the frequency can be adjusted. By providing the filter processing unit 140, the amount of change in amplitude with respect to the frequency change of the high-frequency superimposed signal is adjusted, so that power fluctuations can be suppressed even in different models and individuals. As a result, power fluctuations associated with spectrum spreading are suppressed by optimizing and adjusting the frequency characteristics of the high-frequency superimposed signal included in the laser drive signal S12 with respect to the model differences and individual differences of the laser drive system 3B.

  Here, in the case of the first example, the switching of the frequency characteristics is realized by selecting a plurality of filter circuits 142 with the path selection switch 144, so that the configuration itself is simple, but the characteristic change is a filter prepared in advance. Depending on the number of circuits 142, it is difficult to freely change the frequency characteristics, that is, the degree of freedom in changing the frequency characteristics is small. On the other hand, in the case of the second example, since the frequency characteristic is changed by one filter circuit 142 using a variable inductor circuit or a varicap, the circuit configuration is expected to be complicated, but the frequency characteristic can be freely changed. The degree is great.

  As described above, the laser drive system 3B of the second embodiment has a mechanism different from that of the first embodiment. However, the first embodiment is different in that a mechanism for suppressing power fluctuation accompanying spectrum spread is realized. It is the same. Due to the frequency characteristics of the filter circuit 142 when the high frequency superposition frequency changes, fluctuations in the high frequency superposition amplitude caused by the frequency characteristics of the laser drive system 3B are canceled out. That is, the power fluctuation accompanying the spectrum spread of the high frequency superimposed signal included in the laser drive signal S12 at the input point of the semiconductor laser 41 is reduced.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the above-described embodiment, the recording / reproducing apparatus (optical disk apparatus) that uses the optical disc PD as a recording medium (medium) is described as an example of the optical apparatus. However, the optical apparatus is not limited to the recording / reproducing apparatus. For example, it may be a light emitting device in an optical communication device using an optical fiber, and the same mechanism as in the above embodiment can be applied to this. In short, the mechanism of the above-described embodiment can be applied to any device that performs a combination of the spread spectrum method and the high-frequency superposition method in controlling the emission of laser light.

It is a figure which shows one structural example of the recording / reproducing apparatus (optical disc apparatus) which is an example of an optical apparatus. It is a figure explaining the structural example of an optical pick-up. It is a figure explaining the laser drive system by high frequency superposition. It is a figure which shows an example of the light emission waveform at the time of a high frequency superposition. It is a figure explaining the change of the superposition spectrum by spread spectrum. It is a figure explaining the connection aspect of a laser drive system. It is a figure explaining the frequency characteristic of a laser drive system. It is a figure explaining the reproduction power fluctuation accompanying spectrum spread. It is a figure explaining the fluctuation | variation of reproduction | regeneration RF signal by reproduction | regeneration power fluctuation | variation. It is FIG. (1) explaining the laser drive system of the comparative example which does not apply this embodiment. It is FIG. (2) explaining the laser drive system of the comparative example which does not apply this embodiment. It is a figure explaining the laser drive system of 1st Embodiment. It is a figure explaining the laser drive system of 2nd Embodiment (1st example). It is a figure explaining the laser drive system of 2nd Embodiment (2nd example).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Recording / reproducing apparatus (optical apparatus) 110 ... Superposition frequency control part 112 ... Spread spectrum signal generation part 114 ... Frequency control signal generation part 116 ... High frequency superposition signal oscillation part 130 ... High frequency superposition amplitude control part 132 DESCRIPTION OF SYMBOLS ... Gain adjustment part, 134 ... Amplitude control signal generation part, 136 ... High frequency superposition amplitude adjustment part, 14 ... Optical pick-up, 140 ... Filter processing part, 142 ... Filter circuit, 144 ... Path selection switch, 150 ... Superimposition part, 3 ... Laser drive system 41 ... Semiconductor laser (laser element) 46 ... Flexible substrate 47 ... Drive current controller (laser drive device) 48 ... Drive signal generator 49 ... High frequency superposition processor 50 ... Recording / reproduction signal Processing part

Claims (7)

A superposition frequency control unit that generates a high frequency signal to be superimposed on a drive signal for driving the laser element and modulates the frequency of the high frequency signal based on a diffusion signal that defines a change amount and a change period of the frequency of the high frequency signal;
A high frequency superimposed amplitude adjusting unit that adjusts the amplitude of the high frequency signal output from the superimposed frequency control unit based on an amplitude control signal;
A transmission member that transmits a high-frequency signal output from the high-frequency superimposed amplitude adjustment unit to the laser element;
An amplitude controller that controls the amplitude of the high-frequency signal input to the transmission member in a direction that cancels out the frequency characteristics of a laser drive system including the laser element, the output stage of the high-frequency superimposed amplitude adjustment unit, and the transmission member And a laser driving device. The laser drive device according to claim 1, wherein the amplitude control unit generates the amplitude control signal based on amplitude setting information and the diffusion signal and supplies the amplitude control signal to the high frequency superimposed amplitude adjustment unit. The amplitude control unit generates the amplitude control signal by combining a gain adjustment unit that changes the amplitude of the spread signal, the amplitude adjusted spread signal output from the gain adjustment unit, and the amplitude setting information. The laser driving device according to claim 2, further comprising an amplitude control signal generation unit. The amplitude control unit is a filter that controls the amplitude of the high-frequency signal input to the transmission member in a direction that cancels out the frequency characteristics of the laser drive system between the high-frequency superimposed amplitude adjustment unit and the transmission member. The laser driving device according to claim 1, further comprising a processing unit. The laser driving device according to claim 4, wherein the filter processing unit includes a plurality of filter circuits having different frequency characteristics and a switch for switching each filter circuit. The laser driving device according to claim 4, wherein the filter processing unit includes a filter circuit capable of changing a frequency characteristic. A laser element;
A superposition frequency control unit that generates a high-frequency signal to be superimposed on a drive signal for driving the laser element and modulates the frequency of the high-frequency signal based on a spread signal that defines a change amount and a change period of the frequency of the high-frequency signal; ,
A high frequency superimposed amplitude adjusting unit that adjusts the amplitude of the high frequency signal output from the superimposed frequency control unit based on an amplitude control signal;
A transmission member that transmits a high-frequency signal output from the high-frequency superimposed amplitude adjustment unit to the laser element;
An amplitude controller that controls the amplitude of the high-frequency signal input to the transmission member in a direction that cancels out the frequency characteristics of a laser drive system including the laser element, the output stage of the high-frequency superimposed amplitude adjustment unit, and the transmission member And an optical device.

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