JP2008129295A - Optical communication device - Google Patents

Abstract

An optical communication device configured to prevent saturation of an output of a light receiving element when a VCSEL is employed as a light source for outputting information to be transmitted.
A VCSEL capable of irradiating modulated light modulated based on information to be transmitted and an incident end face on which the modulated light is incident. A part of the modulated light is incident on a core at the incident end face. An optical fiber arranged to reflect the remainder of the modulated light, a light receiving means for receiving the reflected light from the incident end face, and outputting a signal corresponding to the amount of the received light, and a level of the output signal output by the light receiving means Optical communication comprising signal level adjusting means for adjusting to a predetermined level and incident position adjusting means for adjusting the position of the modulated light on the incident end face based on the adjusted output signal adjusted by the signal level adjusting means Providing equipment.
[Selection] Figure 3

Description

  The present invention relates to an optical communication apparatus for performing information transmission using light as a medium, and more particularly to an optical communication apparatus adopting VCSEL (Vertical Cavity Surface Emitting Lasers) as a light source for irradiating modulated information.

  In recent years, optical communication devices for transmitting information are widely known and put into practical use. Such an optical communication device includes an LD (Laser Diode), a condenser lens, an optical fiber, and the like. These members are in a state where their relative positions are adjusted with high accuracy, and are arranged so that the light from the LD is condensed at the approximate center of the core of the optical fiber.

An example of such an optical communication device is disclosed in Patent Document 1 below. In the optical communication device described in Patent Document 1 below, reflected light from the incident end face of the optical fiber is received by a light receiving element (four-divided photodetector). Then, the relative positions of the LD, the condensing lens, and the optical fiber are adjusted so that the outputs of the respective light receiving areas of the quadrant photodetector have a predetermined relationship. As a result, the light transmission efficiency is improved by condensing the light from the LD at substantially the center of the core of the optical fiber, thereby improving the accuracy of signal transmission.
JP 2005-321669 A

  In the optical communication device described in Patent Document 1, an edge-emitter (edge light emission) type such as a Fabry-Perot LD or a DFB-LD (Distributed feedback-LD) is assumed as a light source for outputting information. These types of LDs are mounted inside the optical communication device so that only the P-polarized component is received by the four-divided photodetector.

  In recent years, some devices in the optical communication field employ a VCSEL as a light source for outputting information. The VCSEL has a high wavelength characteristic equivalent to that of the DFB-LD, emits a beam having a narrow emission angle and a substantially circular cross section. Such a beam characteristic can be said to facilitate the coupling between the optical fiber of the optical communication device and the condenser lens. Further, VCSEL has low power consumption, can be driven at high speed, and is inexpensive. In view of these merits, it can be said that the VCSEL is one of light sources suitable for the optical communication device described in Patent Document 1, for example.

  Here, the polarization characteristics of the beam irradiated by the VCSEL differ for each VCSEL (that is, there are individual differences in the VCSEL). In other words, the VCSEL includes a light emitting unit that emits a P-polarized component and an S-polarized component. And the position and number of the light emission parts which light-emit each component differ for every VCSEL. Therefore, when the VCSEL is employed in the optical communication device described in Patent Document 1, the polarization characteristics of the beam incident on the incident end face of the optical fiber (the ratio of the P-polarized component and the S-polarized component included in the beam) are also different for each VCSEL. Will be different. Further, the reflectances of the P-polarized component and the S-polarized component at the incident end face of the optical fiber are different. On the incident end face of the optical fiber, the P-polarized component is reflected by a minute amount, whereas the S-polarized component has a property of reflecting a much larger amount than the P-polarized component. Due to such a difference in reflectance of each polarization component, the amount of reflected light of the beam on the incident end face of the optical fiber varies for each VCSEL. This also means that the amount of light incident on the quadrant photodetector varies from one VCSEL to another.

  For example, when the beam irradiated by the VCSEL includes a large amount of P-polarized light component, the amount of light incident on the quadrant photodetector is small because the amount of light reflected on the incident end face of the optical fiber is small. For this reason, the output of the quadrant photodetector is low and does not saturate. However, for example, when the beam irradiated by the VCSEL includes a large amount of S-polarized light, the amount of reflected light on the incident end face of the optical fiber is large, so the amount of incident light on the quadrant photodetector is also large. For this reason, the output of the quadrant photodetector is also increased, and the output may be saturated.

  As described above, when the output of the four-divided photodetector is saturated, an error occurs in feedback control based on the output of the four-divided photodetector, and the relative position adjustment between the members cannot be performed.

  In view of the above circumstances, an object of the present invention is to provide an optical communication apparatus configured so that the output of a light receiving element is not saturated when a VCSEL is employed as a light source for outputting information to be transmitted.

  An optical communication apparatus according to one embodiment of the present invention for solving the above-described problem is an apparatus for performing information transmission using light as a medium. An optical communication apparatus according to an aspect of the present invention includes a VCSEL that can emit modulated light that is modulated based on information to be transmitted, an incident end surface on which the modulated light is incident, and the modulated light is incident on the incident end surface. An optical fiber arranged so that a part of the light enters the core and reflects the remainder of the modulated light, a light receiving means for receiving the reflected light from the incident end face, and outputting a signal corresponding to the received light amount, and a light receiving means And an incident position for adjusting the position of the modulated light on the incident end surface based on the adjusted output signal adjusted by the signal level adjusting means and the signal level adjusting means for adjusting the level of the output signal output by An optical communication apparatus comprising an adjusting unit.

  According to the optical communication apparatus configured in this way, even when a VCSEL is adopted as a light source for outputting information to be transmitted, the output signal from the light receiving means can be adjusted to a predetermined level. A situation in which the output of the light receiving means is saturated due to the difference does not occur.

  An optical communication apparatus according to another aspect of the present invention that solves the above problem is an apparatus for performing information transmission using light as a medium. An optical communication apparatus according to an aspect of the present invention includes a VCSEL that can emit modulated light that is modulated based on information to be transmitted, an incident end surface on which the modulated light is incident, and the modulated light is incident on the incident end surface. An optical fiber arranged so that a part of the light enters the core and reflects the remainder of the modulated light, a light receiving means for receiving the reflected light from the incident end face, and outputting a signal corresponding to the received light amount, and a light receiving means Is based on the output level adjusted by the signal level adjusting means and the signal level adjusting means for comparing the output signal output from the signal with a predetermined reference value and adjusting the level of the output signal to a level immediately before saturation. And an incident position adjusting means for adjusting the position of the modulated light on the incident end face.

  According to the optical communication apparatus configured in this way, even when a VCSEL is employed as a light source for outputting information to be transmitted, the output signal from the light receiving means can be adjusted to a level immediately before saturation. The situation in which the output of the light receiving means is saturated due to individual differences does not occur. Further, since the output signal from the light receiving means is at a level immediately before saturation, the output signal has a wide dynamic range. Since the incident position adjusting means can adjust the position of the modulated light using a signal having a wide dynamic range, the accuracy of the position adjustment is improved.

  The optical communication device may further include, for example, an operational amplifier capable of changing the amplification magnification. In this case, the signal level adjusting means adjusts the level of the output signal by changing the amplification magnification, for example. Such an operational amplifier may have an electronic volume, for example. In this case, the signal level adjusting means sets the amplification magnification by varying the internal resistance value of the electronic volume, for example. At this time, the signal level adjusting means sets the amplification magnification to a settable maximum value or minimum value, and then the amplification magnification is set so that the level of the adjusted output signal becomes the predetermined level. May be operable to vary step by step.

  The optical communication apparatus further includes, for example, level determination means for determining whether or not the level of the adjusted output signal is the predetermined level, and notification means for informing the determination result. Also good.

  The incident position adjusting means may include, for example, a condensing lens that condenses the modulated light to form a spot on the incident end face. In this case, the incident position adjusting means adjusts the spot position on the incident end face based on the adjusted output signal so that the spot center and the core center coincide.

  Further, the incident position adjusting unit may further include, for example, a condensing lens moving unit that moves the condensing lens. In this case, the incident position adjusting unit moves the spot position on the incident end surface in different first and second directions, for example, by moving the condensing lens by the condensing lens moving unit.

  Here, the light receiving means has, for example, four light receiving areas equally divided by two boundary lines corresponding to the first and second directions, and the spot center and the core center coincide with each other. It may be arranged so that the reflected light is incident on the intersection of the two boundary lines. In this case, the incident position adjusting means calculates the amount of deviation between the spot center and the core center based on, for example, the level of the output signal from each light receiving area. Then, the condensing lens is moved by the condensing lens moving means based on the calculated deviation amount.

  The optical communication apparatus further includes, for example, level determination means for determining whether or not all levels of the output signals from the respective light receiving areas have been adjusted to the predetermined level, and notification means for notifying the determination result. It may be provided.

  According to the present invention, it is possible to provide an optical communication apparatus configured so that the output of a light receiving element is not saturated even when a VCSEL is employed as a light source that outputs information to be transmitted.

  FIG. 1 is a diagram showing a configuration of an optical communication device 10 according to an embodiment of the present invention. The optical communication device 10 is used as an ONU (Optical Network Unit) that draws optical fiber communication into a subscriber's home. The optical communication device 10 is, for example, an optical communication device that supports bidirectional WDM (Wavelength Division Multiplexing) transmission, and transmits a wavelength of 1.3 μm as an upstream signal and 1.5 μm as a downstream signal using a single optical fiber. It is configured to receive a signal.

  The optical communication device 10 includes a VCSEL 1, a condenser lens 2, an optical fiber unit 3, a photodetector 4, and a drive system 5.

During optical communication, the VCSEL 1 emits a beam modulated by information to be communicated under the control of a communication control unit (not shown). In addition, the VCSEL 1 emits an unmodulated beam (continuous light) when adjusting the incident position of the beam on the optical fiber incident end face, which will be described later. The beam irradiated by the VCSEL 1 enters the condenser lens 2 and converges on the incident end face 3a of the optical fiber portion 3 by the power of the condenser lens 2 to form a spot (hereinafter referred to as “incident end face spot”). To do. Here, the incident end face spot is defined as a range having an intensity equal to or greater than 1 / e ² of the maximum intensity (where e is the base of natural logarithm) in the intensity distribution of the beam.

  In FIG. 1, the incident angle of the beam irradiated by the VCSEL 1 and incident on the incident end face 3a via the condenser lens 2 is shown to be larger than the actual angle. The corner is extremely small.

  FIG. 2 shows an enlarged view of the vicinity of the incident end face 3 a of the optical fiber portion 3. The optical fiber portion 3 has a core having a diameter r2 at the center thereof and a structure in which the core is covered with a clad. It is assumed that the center of the optical fiber portion 3 and the center of the core are the same. For convenience of explanation, the clad surface on the incident end face 3a is referred to as “clad surface 3b”, and the core surface is referred to as “core surface 3c”.

  As shown in FIG. 2, the incident end surface 3a has a step structure in which the core surface 3c protrudes from the clad surface 3b by a predetermined amount. This level difference protrudes in a direction perpendicular to the cladding surface 3b, and is processed so that the core surface 3c and the cladding surface 3b are substantially parallel. In the present embodiment, the step structure is formed on the incident end face 3a by using, for example, a well-known photolithography technique. The protruding amount of the step is a value smaller than λ / (4n), for example. Where λ is the wavelength of incident light and n is the refractive index of the medium. In the present embodiment, the incident end face 3a is processed so that the protruding amount is, for example, approximately λ / 8.

  When the VCSEL 1, the condensing lens 2 and the optical fiber unit 3 are in ideal positions, as shown in FIG. 2, the incident end surface spot has a diameter r1, and the center thereof is substantially coincident with the center of the core surface 3c. It is formed on the incident end face 3a. Since r1 is slightly larger than r2, when the incident end face spot is formed in this way, the beam at the center (on the core surface c) of the spot is incident on the core and propagates through the inside, and the incident end face spot The beam in the peripheral part (on the clad surface 3b) is reflected by the clad surface 3b. At this time, diffraction occurs due to the step structure on the incident end face 3a, and a diffracted wave is generated.

  Here, in the optical communication device 10, the VCSEL 1, the condensing lens 2, and the optical fiber unit 3 are arranged and configured so that the beam incident on the incident end surface 3 a from the condensing lens 2 is reflected in a direction different from the incident direction. The Further, when the incident end face spot center coincides with the center of the core surface 3c, the photodetector 4 guides the diffracted wave generated at the incident end face 3a to the center O which is the center of the photodetector 4 (hereinafter referred to as a spot (hereinafter referred to as a spot) (Referred to as “light receiving spot”).

  That is, each member of the VCSEL 1, the condensing lens 2, the optical fiber unit 3, and the photodetector 4 has the principal ray of the beam emitted from the VCSEL 1, the optical center of the condensing lens 2 and the optical center of the optical fiber unit 3 It is attached to the inside of the optical communication device 10 so as to be led to the center of the photodetector 4 through the optical communication device 10.

  However, since individual differences such as attachment errors and dead weights occur, the relative positions of the members of the VCSEL 1, the condensing lens 2, the optical fiber unit 3, and the photodetector 4 are not always as designed. Therefore, an adjustment operation for aligning the center of the incident end surface spot and the center of the core surface 3c, which will be described later, is performed.

  This adjustment work is performed, for example, at the stage of manufacturing the optical communication device 10. It is assumed that the optical communication device 10 is in a state where all the components other than the photodetector 4 are assembled at the stage of starting the adjustment work.

  The adjustment work is first executed under the control of the system controller 51 provided in the drive system 5. Here, FIG. 3 shows a circuit diagram of main parts of the photodetector 4 and the drive system 5.

  The drive system 5 has a biaxial actuator. According to FIG. 3, the biaxial actuator is configured by an X direction actuator driver 52x, an X direction actuator 53x, a Y direction actuator driver 52y, and a Y direction actuator 53y.

  The X-direction actuator driver 52x and the Y-direction actuator driver 52y drive the X-direction actuator 53x and the Y-direction actuator 53y, for example, by PWM (Pulse Width Modulation) control under the control of the system controller 51. The X direction actuator 53x and the Y direction actuator 53y are driven according to the duty of the pulses from the X direction actuator driver 52x and the Y direction actuator driver 52y, respectively.

  Here, the condenser lens 2 is installed so as to move in a predetermined direction in accordance with driving of the X-direction actuator 53x and the Y-direction actuator 53y. When the X-direction actuator 53x is driven, the condenser lens 2 moves in the X ′ direction in FIG. 1 in a plane perpendicular to the reference axis AX. Further, when the Y-direction actuator 53y is driven, the Y-direction actuator 53y moves in the Y ′ direction in FIG. 1 in a plane perpendicular to the reference axis AX.

  As the condenser lens 2 moves, the incident end face spot also moves. Hereinafter, of the moving directions of the incident end face spot, the directions corresponding to the respective movements of the condenser lens 2 in the X ′ direction and the Y ′ direction are referred to as an X direction and a Y direction, respectively. The X direction and the Y direction are orthogonal to each other. The X direction is a direction parallel to the up and down direction of FIG. The Y direction is a direction orthogonal to the paper surface of FIG.

  Further, as the incident end face spot moves, the light receiving spot formed by the photodetector 4 also moves. Of the movement directions of the light receiving spot, the directions corresponding to the movements of the incident end face spot in the X direction and the Y direction are referred to as the X ″ direction and the Y ″ direction, respectively (see FIG. 1).

  The system controller 51 has two ports connected to a pull-up resistor (not shown). These ports are connected to the ground via switches SW1 and SW2, respectively.

  Since each port is in a pulled-up state when the switches SW1 and SW2 are off, it detects an “H (high)” level signal. In addition, when the switches SW1 and SW2 are on, they are connected to the ground, so that an “L (low)” level signal is detected. The switches SW1 and SW2 can be turned on / off by, for example, operating a user operation key (not shown). The operator switches the on / off of the switches SW1 and SW2 to change the operation mode of the system controller 51 to any one of the wobbling feedback control mode, the four-divided photodetector position adjustment mode, the amplification magnification adjustment mode, and the real-time control mode. Can be set.

  When both the switches SW1 and SW2 are on (that is, when the inputs of both ports are “L” level signals), the system controller 51 controls each component to operate in the wobbling feedback control mode.

  When operating in the wobbling feedback control mode, the optical communication device 10 is attached to a predetermined jig (not shown). This jig is provided with a light receiving sensor. The optical communication device 10 is attached to a jig so that the light receiving sensor faces the other end surface of the optical fiber unit 3 (not shown, the end surface opposite to the incident end surface 3a). The light receiving sensor is connected to the system controller 51.

  The light receiving sensor irradiates the VCSEL 1, enters the optical fiber unit 3 through the condenser lens 2, and receives a beam emitted from the other end surface of the optical fiber unit 3. The system controller 51 receives the output of the light receiving sensor obtained by receiving the beam, performs wobbling feedback control based on the output, and wobbles the condenser lens 2 by the biaxial actuator. As a result, the position of the condenser lens 2 is adjusted. The detailed description of the wobbling feedback control can be referred to, for example, in Japanese Patent Application Laid-Open No. 2004-96299 filed by the present applicant.

  Further, the communication control unit for driving and controlling the VCSEL 1 is also provided with an APC (Auto Power Control) circuit. The APC circuit is connected to the light receiving sensor in addition to the VCSEL 1 and operates when the position adjustment by the wobbling feedback control is completed. Specifically, the APC circuit receives the output of the light receiving sensor and adjusts the drive current that flows through the VCSEL 1 so that the output becomes a predetermined value. In the present embodiment, the APC circuit adjusts the drive current so that the output of the light receiving sensor becomes 1 mW, for example, and this adjustment parameter is stored and held. Therefore, thereafter, the optical fiber output is 1 mW.

  Following adjustment of the drive current of the VCSEL 1, the operator temporarily fixes the photodetector 4. As shown in FIG. 3, the photodetector 4 is a quadrant photodetector in which the light receiving areas (4a, 4b, 4c, and 4d) are divided into four. The photodetector 4 amplifies the outputs of the light receiving areas 4a, 4b, 4c, and 4d by the operational amplifiers 41a, 41b, 41c, and 41d and outputs the amplified signals to the outside.

  In the temporary fixing, the photodetector 4 is mounted inside the optical communication device 10 and connected so that the output is input to the system controller 51. The photodetector 4 is positioned so that a beam (mainly composed of a diffracted wave) from the incident end face 3a is incident on the substantial center of the photodetector 4 in the temporary fixing stage in the previous wobbling feedback control mode.

  When each of the light receiving areas 4a, 4b, 4c, and 4d receives the beam, currents Ia, Ib, Ic, and Id corresponding to the received light amount are generated and supplied to the operational amplifiers 41a, 41b, 41c, and 41d. Electronic volumes DPa, DPb, DPc, DPd are connected to the operational amplifiers 41a, 41b, 41c, 41d, respectively. Here, “Rdpa”, “Rdpb”, “Rdpc”, and “Rdpd” are attached to the internal resistance values of these electronic volumes DPa, DPb, DPc, and DPd, respectively.

  The operational amplifiers 41a, 41b, 41c, and 41d each operate as an inverting amplifier, and the amplification magnification is determined by the internal resistance value of each electronic volume. The internal resistance value of each electronic volume varies according to the control of the system controller 51.

  Specifically, the system controller 51 adjusts the internal resistance value of each electronic volume using the count up / down designation signal and the clock pulse signal. The count up / down designation signal is input from the system controller 51 to the U / D terminal of each electronic volume, and the clock pulse signal is input from the system controller 51 to the CP terminal of each electronic volume.

  For example, when the clock pulse signal is input to the CP terminal while the count up / down designation signal input to the U / D terminal is at the “L” level, the electronic volume detects the internal resistance every time the rising edge of the clock pulse signal is detected. Decrease the value. For example, when the clock pulse signal is input to the CP terminal while the count up / down designation signal input to the U / D terminal is at the “H” level, the electronic volume detects the rising edge of the clock pulse signal. Increase internal resistance. That is, the internal resistance value of the electronic volume decreases according to the number of input pulses when the count up / down designation signal is at “L” level, and the number of input pulses when the count up / down designation signal is at “H” level. It increases according to.

  In addition, every time one clock pulse signal is input, the internal resistance value of the electronic volume increases or decreases by 1 kΩ. The maximum value of the internal resistance value is 100 kΩ, and the minimum value is 0Ω. That is, the internal resistance value of the electronic volume varies in 100 steps.

  The operational amplifiers 41a, 41b, 41c, and 41d amplify the input currents Ia, Ib, Ic, and Id at an amplification factor corresponding to the internal resistance value of each electronic volume, and output them as voltage signals A, B, C, and D, respectively. . For example, the voltage signal A output from the operational amplifier 41a is A = − (Ia × Rdpa). Similarly, the voltage signals B, C, and D output from the operational amplifiers 41b, 41c, and 41d are B = − (Ib × Rdpb), C = − (Ic × Rdpc), and D = − (Id × Rdpd), respectively. Become.

  The voltage signals A, B, C, and D are input to the system controller 51 as signals representing the amount of light received in each light receiving area. The system controller 51 performs A / D conversion on the input voltage signals A, B, C, and D, and processes them as digital signals.

  Here, if the light source is an LD, the beam incident on the incident end face of the optical fiber has a predetermined polarization (P-polarized light) component as described above. For this reason, the relationship between the amount of incident light and the amount of reflected light with respect to the incident end face is substantially the same for each LD. Accordingly, the amount of reflected light in this case becomes a specified amount when the drive current is adjusted, and the output of the quadrant photodetector (input to the system controller) does not vary.

  However, if the light source is a VCSEL, as described above, the beam incident on the incident end face of the optical fiber is a mixture of polarization components according to the individual difference of the VCSEL. For this reason, the relationship between the amount of incident light and the amount of reflected light with respect to the incident end face changes for each VCSEL. Therefore, the amount of reflected light in this case differs for each VCSEL even if the beam outputs of the VCSELs are aligned (even if the drive current of the VCSEL is adjusted as described above), and the output of the four-divided photodetector varies between optical communication devices. Depending on the optical communication device, since many S-polarized components are included in the beam, the output of the quadrant photodetector may be saturated for the reason described above.

  In order to solve such a problem, the following further adjustment work is performed.

  When the switch SW1 is turned on and the switch SW2 is turned off by the operator, the system controller 51 shifts to the 4-split photodetector position adjustment mode. When the system controller 51 shifts to the four-divided photodetector position adjustment mode, first, the count up / down designation signal is set to the “L” level, and for example, a clock pulse signal of 100 pulses is output. As a result, the internal resistance value of each electronic volume becomes the minimum value (0Ω), and the output of each operational amplifier also becomes zero.

  Next, the system controller 51 sets the count up / down designation signal to the “H” level and outputs a clock pulse signal of one pulse. Then, the voltage signals of the respective operational amplifiers are A / D converted, and their values (hereinafter referred to as “digital voltage signal values”) are detected. The internal resistance value of each electronic volume increases each time a clock pulse signal is input, and the amplification factor increases accordingly, so the output of each operational amplifier also increases.

  The system controller 51 outputs the clock pulse signal and detects the digital voltage signal value until the digital voltage signal value of the voltage signal A reaches a predetermined value (for example, a value corresponding to 1/2 of the power supply voltage of each operational amplifier). Run repeatedly. For example, when the digital voltage signal value is a value corresponding to the power supply voltage of the operational amplifier, the voltage signal from the operational amplifier is a signal that has reached the saturation level. Hereinafter, for convenience of explanation, the “value corresponding to the power supply voltage of the operational amplifier” is referred to as “saturation level”.

  In the wobbling feedback control mode, when the incident end surface spot center and the core surface 3c center are adjusted to substantially coincide with each other, when the digital voltage signal value of the voltage signal A reaches the predetermined value, the voltage signal B, The digital voltage signal values of C and D are also predetermined values. As described above, when all digital voltage signal values become predetermined values, an LED (Light Emitting Diode) indicator lamp 54 is turned on under the control of the system controller 51.

  By setting the amplification factor of each operational amplifier as described above, the voltage signal output from the photodetector 4 to the system controller 51 is not saturated, regardless of the amount of reflected light received in each light receiving area ( For example, 1/2 of the saturation level. That is, in the present embodiment, the amplification magnification is appropriately set so that the voltage signal from each operational amplifier is at the predetermined level. This makes it possible to provide an optical communication device 10 suitable for preventing saturation of the output of the photodetector 4 due to individual differences in the polarization characteristics of the VCSEL.

  When there is an error in position adjustment in the wobbling feedback control mode, each digital voltage signal value becomes a different value. In consideration of such a situation, for example, an adjustment mechanism (for example, an XY stage) capable of moving the photodetector 4 with high resolution may be provided in the optical communication device 10. In this case, the operator can easily finely adjust the position of the photodetector 4 by operating such an adjustment mechanism. The operator can check whether the photodetector 4 has been adjusted to an appropriate position by looking at the state of the LED indicator lamp 54.

  Further, an adjustment mechanism that automatically performs the fine adjustment may be provided in the optical communication device 10. In this case, the adjustment mechanism is an XY stage including a biaxial actuator, for example. This actuator is a stepping motor having a higher resolution than, for example, the X-direction actuator 53x, and can move the XY stage in two axes. The system controller 51 performs pulse adjustment of the stepping motor based on the feedback control, and adjusts the position of the photodetector 4 so that all digital voltage signal values become predetermined values.

  Next, when the switch SW1 is turned off and the switch SW2 is turned on by the operator, the system controller 51 shifts to the amplification magnification adjustment mode. When the system controller 51 shifts to the amplification magnification adjustment mode, first, the count up / down designation signal is set to the “H” level, and for example, a clock pulse signal of 100 pulses is output. Thereby, the internal resistance value of each electronic volume becomes the maximum value (100 kΩ), and the amplification factor of each operational amplifier is also maximized.

  When the internal resistance value of each electronic volume is set to the maximum value, the system controller 51 detects the digital voltage signal value of the voltage signal A. Then, the detected digital voltage signal value is compared with a predetermined reference value to determine whether or not the saturation level is reached. When the digital voltage signal value is greater than or equal to a predetermined reference value, the system controller 51 determines that the voltage signal A is a saturated signal (that is, a signal that reaches a saturation level) and decreases the amplification factor of the operational amplifier 41a. Specifically, the count up / down designation signal is set to the “L” level, and one clock pulse signal is output.

  After the output of the one-pulse clock pulse signal, the system controller 51 again detects the digital voltage signal value of the voltage signal A and determines whether or not the voltage signal A is a saturated signal. The system controller 51 repeats this series of processing until the detected digital voltage signal value becomes lower than the reference value (saturation level). When the digital voltage signal value is lower than the reference value, the voltage signal A is at a level just before saturation and becomes a signal with a wide dynamic range.

  Note that the outputs (voltage signals B, C, and D) of the other operational amplifiers are adjusted so as to have substantially the same level as the voltage signal A in the wobbling feedback control mode and the four-divided photodetector position adjustment mode. . For this reason, the system controller 51 sets the amplification factors of the other operational amplifiers to optimum values when the amplification factor of the operational amplifier 41a is set to the optimum value and the voltage signal A is adjusted to the optimum level. Consider it a thing. Accordingly, when the amplification factor of the operational amplifier 41a is set to the optimum value, the system controller 51 turns on the LED indicator lamp 54 and informs the operator that the amplification factor of each operational amplifier has been set to the optimum value. Inform.

  When the switch SW1 and the switch SW2 are turned off by the operator, the system controller 51 shifts to the real time control mode. This real-time control mode is a mode that is assumed to be always executed during optical communication after the optical communication device 10 is powered on, for example.

  The drive system 5 includes addition circuits 55x, 55y, 56x, 56y, and subtraction circuits 57x, 57y.

  Voltage signals A and D are input to the adder circuit 55x. The addition circuit 55x adds the voltage signals A and D and outputs an addition signal (A + D) to the subtraction circuit 57x. The voltage signals B and C are input to the adder circuit 56x. The addition circuit 56x adds the voltage signals B and C and outputs an addition signal (B + C) to the subtraction circuit 57x. The subtraction circuit 57 x calculates a difference between the addition signal (A + D) and the addition signal (B + C), generates a difference signal x, and outputs the difference signal x to the system controller 51.

  The voltage signals A and B are input to the adder circuit 55y. The addition circuit 55y adds the voltage signals A and B and outputs an addition signal (A + B) to the subtraction circuit 57y. The voltage signals C and D are input to the adder circuit 56y. The addition circuit 56y adds the voltage signals C and D and outputs an addition signal (C + D) to the subtraction circuit 57y. The subtraction circuit 57 y calculates a difference between the addition signal (A + B) and the addition signal (C + D), generates a difference signal y, and outputs the difference signal y to the system controller 51.

  In the real-time control mode, the system controller 51 causes the X direction actuator driver so that the outputs of the differential signals x and y are null (in other words, the levels of all voltage signals are substantially the same). 52x and Y direction actuator driver 52y are feedback-controlled. In addition, the condenser lens 2 is finely adjusted in the X ′ and Y ′ directions by this feedback control, and accordingly, the light receiving spot on the photodetector 4 is slightly moved in the X ″ and Y ″ directions. Tweaked. When the light receiving spot is finely adjusted and the output of each differential signal becomes null, the center of the incident end face spot and the center of the core surface 3c are substantially coincident.

  For example, even if the incident end face spot deviates from the core surface 3c during optical communication, since the optical communication apparatus 10 is in the real-time control mode, the positional deviation is appropriately corrected by the feedback control. A more detailed description of the real-time control can also be referred to, for example, Japanese Patent Application Laid-Open No. 2004-96299 filed by the present applicant, similarly to the wobbling feedback control.

  The above is the embodiment of the present invention. The present invention is not limited to these embodiments and can be modified in various ranges. For example, in the amplification magnification adjustment mode, the system controller 51 monitors only the digital voltage signal value of the voltage signal A. However, in another embodiment, all the digital voltage signal values may be monitored.

  In this embodiment, the internal resistance value of the electronic volume is varied every 1 kΩ, but in another embodiment, it may be varied by a finer value (for example, 0.1 kΩ). In this case, when the amplification magnification of the operational amplifier is adjusted in the amplification magnification adjustment mode, the digital voltage signal value from the operational amplifier can be made closer to the saturation level, and a signal with a wider dynamic range can be secured.

  Further, in this embodiment, the internal resistance value of the electronic volume is varied in the range of 0 to 100 kΩ, but in another embodiment, it may be varied in a wider range (for example, 0 to 500 kΩ). . In this case, for example, when the output of the light receiving area is significantly lower than the saturation level, the digital voltage signal value can be amplified with a high amplification factor to obtain a signal with a wider dynamic range.

It is the figure which showed the structure of the optical communication apparatus of embodiment of this invention. It is an enlarged view of the incident end face vicinity of the optical fiber part with which the optical communication apparatus of embodiment of this invention was equipped. The circuit diagram of the principal part of the photodetector with which the optical communication apparatus of embodiment of this invention was equipped, and a drive system is shown.

Explanation of symbols

1 VCSEL
DESCRIPTION OF SYMBOLS 2 Condensing lens 3 Optical fiber part 4 Photo detector 41a-41d Operational amplifier 5 Drive system 51 System controller 10 Optical communication apparatus

Claims (10)

In an optical communication apparatus for performing information transmission using light as a medium,
VCSEL (Vertical Cavity Surface Emitting Lasers) capable of emitting modulated light modulated based on information to be transmitted;
An optical fiber that has an incident end face on which the modulated light is incident, and is arranged so that a part of the modulated light is incident on the core and reflects the remainder of the modulated light at the incident end face;
A light receiving means for receiving reflected light from the incident end face and outputting a signal corresponding to the amount of light received;
Signal level adjusting means for adjusting the level of the output signal output from the light receiving means to a predetermined level;
An optical communication apparatus comprising: an incident position adjusting unit that adjusts the position of the modulated light on the incident end surface based on the adjusted output signal adjusted by the signal level adjusting unit. In an optical communication apparatus for performing information transmission using light as a medium,
A VCSEL capable of emitting modulated light modulated based on information to be transmitted;
An optical fiber that has an incident end face on which the modulated light is incident, and is arranged so that a part of the modulated light is incident on the core and reflects the remainder of the modulated light at the incident end face;
A light receiving means for receiving reflected light from the incident end face and outputting a signal corresponding to the amount of light received;
A signal level adjusting means for comparing the output signal output from the light receiving means with a predetermined reference value and adjusting the level of the output signal to a level immediately before saturation, which is a predetermined level;
An optical communication apparatus comprising: an incident position adjusting unit that adjusts the position of the modulated light on the incident end surface based on the adjusted output signal adjusted by the signal level adjusting unit. It further comprises an operational amplifier capable of changing the amplification factor,
The optical communication apparatus according to claim 1, wherein the signal level adjustment unit adjusts the level of the output signal by changing the amplification magnification.   4. The optical communication apparatus according to claim 3, wherein the operational amplifier has an electronic volume, and the signal level adjusting means sets the amplification magnification by changing an internal resistance value of the electronic volume.   The signal level adjustment means sets the amplification magnification to a settable maximum value or minimum value, and then varies the amplification magnification stepwise so that the level of the adjusted output signal becomes the predetermined level. The optical communication device according to claim 3, wherein the optical communication device is an optical communication device. Level determination means for determining whether or not the level of the adjusted output signal is the predetermined level;
The optical communication device according to claim 1, further comprising notification means for notifying the determination result.   The incident position adjusting means has a condensing lens that condenses the modulated light to form a spot on the incident end face, and determines the spot position on the incident end face based on the adjusted output signal. 6. The optical communication apparatus according to claim 1, wherein adjustment is performed so that a center coincides with the core center.   The incident position adjusting unit further includes a condensing lens moving unit that moves the condensing lens, and the spot position on the incident end surface varies depending on the movement of the condensing lens by the condensing lens moving unit. The optical communication apparatus according to claim 7, wherein the optical communication apparatus is moved in the first and second directions. The light receiving means has four light receiving areas equally divided by two boundary lines corresponding to the first and second directions, and the reflected light when the spot center coincides with the core center Is arranged to be incident on the intersection of the two boundary lines,
The incident position adjusting means calculates a deviation amount between the spot center and the core center based on the level of the output signal from each light receiving area, and based on the calculated deviation amount, the condenser lens moving means The optical communication apparatus according to claim 8, wherein the condenser lens is moved. Level determination means for determining whether or not the levels of the output signals from the respective light receiving areas are all adjusted to the predetermined level;
The optical communication device according to claim 7, further comprising notification means for notifying the determination result.

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