JP2006268962A - Light emission reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emission reception device capable of switching gains with a simple configuration without providing a dedicated terminal for gain switching. <P>SOLUTION: The light emission reception device is provided with a semiconductor laser 8, a first photodiode 1 for receiving return light that is returned when forward light emitted from the semiconductor laser 8 is reflected by an optical disk, a second photodiode 11 for receiving backward light emitted from the semiconductor laser 8, and an amplifier circuit for converting a current signal generated by the first photodiode 1 into a voltage signal and amplifying the voltage signal. The amplifier circuit is provided with an operational amplifier 2, a first gain resistor 3 and a second gain resistor 4 connected in parallel with the operational amplifier 2, and a switching circuit 7 for switching the gain resistors, wherein switching between the first gain resistor 3 and the second gain resistor 4 is performed on the basis of a signal from the second photodiode 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light receiving and emitting device used for an optical disk pickup.

  An optical pickup device used for a CD, a DVD drive or the like usually includes a semiconductor laser, a photodiode, and a photoelectric conversion amplifier circuit that amplifies and outputs a signal from the photodiode.

  Hereinafter, the light emitting and receiving device used in the optical pickup device disclosed in Patent Document 1 will be described with reference to FIG.

  A semiconductor laser 21 is fixed on the silicon substrate 20, and a groove 22 and a reflection mirror 23 are provided on the inclined surface of the silicon substrate 20. The light emitted from the semiconductor laser 21 is raised perpendicularly to the surface of the silicon substrate 20 by the reflection mirror 23 and enters the optical disk (not shown) through the optical path 24.

  The signal light 25 reflected by the optical disk enters the first photodiode 26 and is converted into a current signal. Thereafter, the current signal is converted into a voltage signal by an amplifier circuit described later. Further, a second photodiode 27 for laser output monitoring for receiving backward light emitted from the semiconductor laser 21 is provided at the rear part of the semiconductor laser 21.

  From the above configuration, information recorded on the optical disk is read or information is recorded.

  Next, the light emitting / receiving device disclosed in Patent Document 2 will be described with reference to FIG.

  The semiconductor laser 8 is connected to a driving power source 9. When the light reflected by the optical disk (not shown) is received by the first photodiode 1, a charge corresponding to the amount of received light is generated to generate a photocurrent. This photocurrent is input to one of the input sections of the operational amplifier 2 that inverts and amplifies the input signal, and flows through the first gain resistor 3 that is connected to the input section and connected to the output section.

  When a photocurrent flows through the first gain resistor 3, a voltage is generated at both ends of the resistor. This voltage is fed back to the input of the operational amplifier 2, and the reference voltage of the reference voltage source 5 connected to the other input of the operational amplifier. In contrast, a voltage signal determined by the photocurrent and the resistance value of the gain resistor is output to the output terminal 6.

  Here, a second gain resistor 4 having a different resistance value is connected in parallel with the first gain resistor 3, and a switch for switching a path is provided between one end of these resistors and the output of the operational amplifier 2. The switch is switched by the switch circuit 7 that operates in response to the signal from the terminal 10.

  The switching of the gain resistance is mainly determined by the amount of light incident on the first photodiode 1, and specifically, when the optical disk is being recorded by the optical pickup device and when information is being reproduced from the optical disk. Switch with.

  For example, if the second gain resistor 4 having a low resistance flows during recording and the first gain resistor 3 having a high resistance flows during reproduction, the operational amplifier 2 is saturated by a large current flowing during recording. Can be prevented, and a wide dynamic range can be obtained.

Further, the backward light emitted from the semiconductor laser 8 is converted into a current signal by the second photodiode 11 and used as a power control signal of the driving power source 9.
JP-A-5-315699 JP 2000-124746 A

  In the configuration disclosed in Patent Document 2, a switch switching terminal must be secured.

  However, in recent optical pickup devices, an input terminal for a gain switching signal of an amplifier circuit is required to cope with a plurality of optical disks such as CD, DVD, Blu-ray, and the number of terminals is rapidly increasing. As shown in FIG. 4, an increase in the number of terminals leads to an increase in the size of the package, which is contrary to the demand for downsizing of optical components such as an optical pickup accompanying downsizing of the device. On the other hand, it is conceivable to expand the dynamic range of the operational amplifier, but the circuit becomes complicated and the circuit area increases.

  In view of the above problems, an object of the present invention is to provide a light receiving and emitting device capable of switching gains with a relatively simple configuration without increasing the number of terminals.

  In order to solve the above-described problems, a light receiving and emitting device according to the present invention includes a semiconductor laser, a first photodiode that receives a return light that is reflected by the forward light emitted from the semiconductor laser, and the semiconductor laser. A light receiving and emitting device comprising: a second photodiode that receives backward light emitted from the first photodiode; and an amplification circuit that converts a current signal generated by the first photodiode into a voltage signal and amplifies the voltage signal. The amplifier circuit includes at least an operational amplifier, a plurality of gain resistors, and a switch for switching the plurality of gain resistors, and the plurality of gain resistors have one end at one input of the operational amplifier and the other end at the output of the operational amplifier. And the gain resistor is switched based on a signal from the second photodiode. .

  It is preferable that the semiconductor laser outputs at least two lights having different powers according to a use mode, and the switch is switched according to the power of the emitted light emitted from the semiconductor laser.

  The light emitting and receiving device further includes a control circuit that controls a switching operation of the switch, and a signal generated by the second photodiode by backward light emitted from the semiconductor laser is input to the control circuit, and the second circuit It is preferable to operate the control circuit by a signal from the photodiode.

  Preferably, the light emitting and receiving device further includes a power source for driving the semiconductor laser, and controls an operation of the power source based on a signal from the second photodiode to control an output power of the semiconductor laser. .

  It is preferable to use a plurality of lasers that emit light of different wavelengths as the semiconductor laser.

  Preferably, at least two of the plurality of lasers are monolithically integrated.

  The first photodiode is preferably used in common for the plurality of lasers that emit light of different wavelengths.

  According to the light emitting / receiving device of the present invention, the gain switching operation can be controlled based on the signal from the photodiode that receives the backward light of the semiconductor laser, so there is no need to provide a dedicated terminal for gain switching, and the size of the device can be reduced. Can be planned.

  Hereinafter, a light emitting and receiving device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a light receiving and emitting device according to an embodiment of the present invention.

  Note that the specific arrangement of the semiconductor laser, the photodiode, and the like and the basic operation as the light emitting / receiving device are the same as those in the example shown in FIGS.

  A feature of the light emitting / receiving device in the present embodiment is that a signal from the second photodiode 11 that receives the backward light from the semiconductor laser 8 is used as a power control signal of the driving power source 9 and gain switching is performed. The point of feedback is to the control circuit 12 of the switch circuit 7.

  In a recordable optical disk such as CD-R, RW, DVD-R, RW, etc., the output of the semiconductor laser is different during reproduction and during recording. Generally, the gain is large during reproduction and the gain is small during recording. An amplifier circuit having a switching function is used. During reproduction and recording of CD-R, RW, DVD-R, RW, and the like, laser beams having different intensities are emitted from the semiconductor laser 8 toward the optical disc. At the same time, the semiconductor laser 8 also varies depending on the reproduction and recording. Intense backward light is emitted. The rear light is incident on the second photodiode 11 and converted into a current signal, and then converted into a gain switching control signal and input to the switch circuit 7 in the control circuit 12. Here, the threshold value of the gain changeover switch circuit 7 is set to an intermediate value between the input signal value at the time of reproduction and the input signal value at the time of recording, and is connected to the operational amplifier 2 in accordance with an input signal that differs between the reproduction time and the recording time. The gain resistor 3 and the gain resistor 4 are switched.

  The current Ipd generated by the light incident on the first photodiode 1 flows through the first gain resistor 3 (resistance value: R1) or the second gain resistor 4 (resistance value: R2) switched by the switch circuit 7. Thus, a voltage drop occurs, and a voltage given by Ipd × R1 or Ipd × R2 with respect to the reference voltage given by the reference voltage source 5 connected to the non-inverting input terminal of the operational amplifier 2 is output to the output terminal 6.

  Specifically, in CD, DVD, and next-generation DVD, the signal current at the time of reading is 3 to 9 mW, and at the time of recording is 100 to 250 mW. Further, the signal current of the back light is about 10 to 20 mW at the time of recording and about 0.5 to 2 mW at the time of reproduction. Therefore, by setting the threshold value of the gain changeover switch circuit 7 to 4 to 7 mW, the gain resistance during reproduction and recording can be switched.

As described above, according to the present embodiment, a gain switching signal can be generated using an existing circuit, so that a dedicated terminal is not necessary, and the light emitting and receiving device can be downsized.
Further, since the amount of light incident on the optical disk can be maintained because the back light is used, there is an advantage that the light use efficiency is not lowered.

  If there is no need to control the emitted light quantity of the laser with high accuracy, there may be a configuration in which the signal from the photodiode 11 is not fed back to the driving power source 9.

  In the present embodiment, the case where there is one semiconductor laser is shown. However, a plurality of CDs, DVDs, and next-generation DVDs may be provided, or a monolithic integrated configuration may be used. In this case, for example, a CD laser and a DVD laser may be monolithically integrated, and a next-generation DVD laser may be provided separately. Further, the recording laser and the reproducing laser may be modified separately or monolithically.

  In this case, if the first photodiode 1 and the second photodiode 11 are shared, the number of parts can be reduced and the apparatus can be further downsized.

  The arrangement and number of semiconductor lasers and photodiodes are not limited to those in this embodiment. For example, the first photodiode 1 and the second photodiode 11 may be formed on different substrates, or the semiconductor. The laser 8 may be provided on another substrate.

  Further, the first photodiode 1 and the second photodiode 11 may be divided.

  Further, the signal from the second photodiode 11 may not be directly fed back to the driving power source 9 and may be input to a separately provided power source driving IC (not shown).

  The light emitting / receiving device according to the present invention has a function of switching the gain according to the output power of the semiconductor laser, and can be used for an optical pickup device used for a next-generation DVD using a CD, a DVD, and blue light, Useful.

Circuit diagram of light emitting and receiving device in an embodiment of the present invention Schematic diagram showing the configuration of a conventional light emitting and receiving device Circuit diagram of conventional light emitting and receiving device Schematic diagram showing the configuration of an optical pickup device in the prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodiode 2 Operational amplifier 3 1st gain resistor 4 2nd gain resistor 5 Reference voltage source 6 Output terminal 7 Switch circuit 8 Semiconductor laser 9 Power supply for laser drive 10 Signal input terminal 11 Photodiode 12 Control circuit 20 Silicon substrate 21 Semiconductor Laser 22 Groove 23 Reflecting mirror 24 Optical path 25 Signal light 26 First photodiode 27 Second photodiode

Claims (7)

A semiconductor laser, a first photodiode for receiving return light reflected and returned from the forward light emitted from the semiconductor laser, and a second photodiode for receiving backward light emitted from the semiconductor laser; A light emitting / receiving device comprising an amplifier circuit for converting and amplifying a current signal generated by the first photodiode into a voltage signal,
The amplifier circuit includes at least an operational amplifier, a plurality of gain resistors, and a switch for switching the plurality of gain resistors,
The plurality of gain resistors are connected in parallel so that one end is connected to one input of the operational amplifier and the other end is connected to the output of the operational amplifier.
Switching between the gain resistors is performed based on a signal from the second photodiode. 2. The semiconductor laser according to claim 1, wherein the semiconductor laser outputs light having at least two different powers according to a use mode, and the switch is switched according to the power of the emitted light emitted from the semiconductor laser. Light emitting and receiving device. The light emitting and receiving device further includes a control circuit for controlling the switching operation of the switch,
The signal generated in the second photodiode by back light emitted from the semiconductor laser is input to the control circuit, and the control circuit is operated by a signal from the second photodiode. Item 3. The light emitting and receiving device according to Item 1 or 2. The light emitting / receiving device further includes a power source for driving the semiconductor laser,
4. The light receiving and emitting device according to claim 1, wherein an operation of the power source is controlled based on a signal from the second photodiode to control an output power of the semiconductor laser. 5. 5. The light receiving and emitting device according to claim 1, wherein a plurality of lasers that emit light having different wavelengths are used as the semiconductor laser. 6. The light emitting and receiving device according to claim 1, wherein at least two of the plurality of lasers are monolithically integrated. 7. The light receiving and emitting device according to claim 5, wherein the first photodiode is commonly used for the plurality of lasers emitting light of different wavelengths.

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