JP2009283859A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module exhibiting an improved reliability which can replace faulty semiconductor elements. <P>SOLUTION: The optical module has: a VCSEL array which is composed of several VCSEL elements, each including a p-type lower DBR; an active region and an n-type upper DBR constituting a resonator along with the lower DBR formed on a substrate; drive circuits 54 and 56 which drive a VCSEL element A with bias in the forward direction and drive a VCSEL element B next to it with bias in the reverse direction; a failure detecting circuit 52 which detects whether the VCSEL element A is faulty; and a switching circuit 58, which switches driving of the VCSEL element B from bias in the direction reverse to that of bias in the forward direction, when failure of the VCSEL element A is detected by the failure detecting circuit 52. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical module used as a light source for optical communication or optical information processing, and more particularly to an optical module using a surface emitting semiconductor laser element.

  In the technical fields such as optical communication and optical recording, interest in a light source of a surface-emitting semiconductor laser (Vertical-Cavity Surface-Emitting Laser: hereinafter referred to as VCSEL) is increasing. VCSELs are not available for edge-emitting semiconductor lasers that have low threshold currents, low power consumption, can easily obtain a circular light spot, and can be evaluated in a wafer state or two-dimensionally arrayed light sources. Has excellent features. Utilizing these features, it is expected to be used as a light source in the fields of optical communication and optical information processing. Thus, technologies relating to semiconductor light emitting devices using VCSELs are disclosed in several patent documents.

  Non-Patent Document 1 discloses a bidirectional communication in which a light-emitting element and a light-receiving element are monolithically formed by forming a receiving PD (photodiode) on the same substrate as a substrate on which a VCSEL that emits laser light is formed. A module is disclosed.

GaAs-based transceiver chip, Martin Stack, Fernandinaldi, Annual Port 2005, pp37-40, Optoelectronics Department, ULM University, Internet <http: // www-opto.e-technik.uni-ulm.de/forschung/jahresbericht/2005/ar2005.pdf>

  One of the failure modes of VCSEL is called death that causes the VCSEL to stop emitting light suddenly. In the case of an array light source in which a plurality of VCSELs are turned on at the same time, it is not a big problem if one VCSEL is killed. However, when optical communication is performed by modulating a single VCSEL, the VCSEL If this happens, it becomes a big problem in the communication field where high reliability is required. Although research has been conducted to elucidate the cause of the death of VCSELs, no measures have yet been found to prevent death. On the other hand, in the field of optical communication using a VCSEL that has a possibility of death, no effective measures have been taken to deal with the occurrence of failure in the VCSEL.

  The present invention solves such a problem, and an object of the present invention is to provide an optical module with improved reliability that can replace a failed semiconductor element.

  An optical module according to the present invention includes a second semiconductor multilayer film of a second conductivity type that forms a resonator together with at least a first semiconductor multilayer film of a first conductivity type, an active region, and the first semiconductor multilayer film. A semiconductor element array in which a plurality of semiconductor elements are formed on a substrate, a first semiconductor element among the plurality of semiconductor elements is driven with a forward bias, and a second semiconductor element adjacent to the first semiconductor element is A driving means for driving with a reverse bias, a detecting means for detecting an output signal of the second semiconductor element obtained in response to the light emission state of the first semiconductor element, and a second based on the detection result of the detecting means. Switching means for switching the driving of the semiconductor element from the reverse bias to the forward bias.

  Preferably, the detecting means compares whether or not the output signal from the second semiconductor element is equal to or lower than a threshold value, and the switching means is configured to compare the second semiconductor when the output signal is equal to or lower than the threshold value. The element drive is switched from reverse bias to forward bias. Preferably, each of the plurality of semiconductor elements includes a post serving as a laser light emitting unit, and the second semiconductor element receives reflected light or leakage light of light emitted from the post of the first semiconductor element, An electrical signal in response to the received light is output.

  Preferably, the drive means includes a forward bias drive circuit and a reverse bias drive circuit, and the switching means connects the forward bias drive circuit to a first semiconductor element, and the reverse bias drive circuit is a second bias drive circuit. The switching means connects the forward bias drive circuit to the second semiconductor element when the detecting means detects a failure of the first semiconductor element. Preferably, the posts of the plurality of semiconductor elements are arranged at equal intervals on the substrate, and the posts of the plurality of semiconductor elements are arranged symmetrically on the substrate. The plurality of semiconductor elements are, for example, surface emitting semiconductor laser elements.

  An optical communication system according to the present invention includes the optical module configured as described above, an optical fiber that transmits an optical signal emitted from the optical module, and a receiving module that receives an optical signal transmitted by the optical fiber.

  According to the present invention, the light emission state of the first semiconductor element is detected by the output signal of the second semiconductor element, and the driving of the second semiconductor element is switched from the reverse bias to the forward bias based on the detection result. Thus, continuous or continuous light emission can be obtained. As a result, it is possible to improve the reliability against a failure such as the death of the semiconductor element of the optical module.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an optical module according to an embodiment of the present invention. The optical module 10 according to this embodiment includes a metal disc-shaped stem 12, a submount 14 attached to the upper surface of the stem 12, a VCSEL array 16 mounted on the submount 14, and the submount 14. An integrated circuit chip 18 mounted on the stem 12, a cylindrical cap 20 connected to the stem 12, and lead terminals 22a, 22b, 22c made of a plurality of conductive metals attached to the bottom surface of the stem 12. Yes.

  A circular opening 20a is formed at the center of the upper surface of the cap 20, and a glass flat plate 20b is attached to the inside so as to close the opening 20a. The glass flat plate 20 b transmits the laser light emitted from the VCSEL array 16. The space formed on the stem 12 by the cap 20 and the glass flat plate 20b is preferably hermetically sealed to protect the VCSEL array 16 and the integrated circuit chip 18 from the external environment.

  The stem 12 is formed with a through hole (not shown) for inserting the lead terminals 22a to 22c. Each lead terminal is electrically insulated from the stem 12 by a coating made of glass or the like in the through hole. The lead terminals 22a to 22c lead to the internal space and are electrically connected to the VCSEL array 16 and the integrated circuit chip 18. For example, the lead terminal 22a is a terminal for inputting an input signal for driving the VCSEL element, the lead terminal 22b is a power supply terminal to the integrated circuit chip 18, and the lead terminal 22c is a common ground terminal.

  2 is a plan view of the VCSEL array shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along line AA of FIG. In the present embodiment, an example is shown in which two VCSEL elements are formed in the VCSEL array 16, but this is an example, and more VCSEL elements can be formed.

  As shown in FIG. 2, a VCSEL element A is formed on the left side, and a center line C passing through the substantially center of the rectangular semiconductor chip (substrate) constituting the VCSEL array 16 is formed on the left side. A VCSEL element B is formed. The basic configurations of the VCSEL elements A and B are the same, and the same reference numerals are assigned to the same configurations.

  As shown in FIG. 3, the VCSEL array 16 includes a p-type lower DBR (Distributed Bragg Reflector) formed of a semiconductor multilayer film including a p-type GaAs layer 102 and a plurality of AlGaAs pairs having different Al compositions on an insulating substrate 100. : Distributed Bragg reflector) 104, current confinement layer 106 made of p-type AlAs, active region 108 containing a quantum well active layer, n-type upper DBR 110 made of a semiconductor multilayer film containing a plurality of pairs of AlGaAs having different Al compositions A semiconductor layer including the n-type GaAs contact layer 112 is stacked. A cylindrical post (or mesa) P is formed by etching the stacked semiconductor layers.

  An interlayer insulating film 114 such as SiON or SiOx is formed on the entire surface of the substrate so as to cover the bottom, side and top of the post P, and then the interlayer insulating film 114 is used for making electrical contact with the VCSEL element. Contact hole holes 114a and 114b are formed. The contact hole 114a is an annular or ring-shaped opening that exposes the n-type contact layer 112 at the top of the post P, and the contact hole 114b is a circle for exposing the p-type lower DBR 104 at the bottom of the post. An arc opening (indicated by a broken line in FIG. 2).

  An annular n-side electrode 116 made of a conductive material is formed on the interlayer insulating film 114 at the top of the post P, and the n-side electrode 116 is ohmically connected to the contact layer 112 through a contact hole 114a. For the n-side electrode 116, for example, Au or Au / Ti laminate that is resistant to corrosion is used. An opening formed in the center of the annular n-side electrode 116 defines a laser light emission region. The opening in the emission region is preferably protected by the emission protection film 118. The emission protective film 118 may be the same insulating material as the interlayer insulating film 114. A p-side electrode 120 that is electrically connected to the lower DBR 104 through the contact hole 114b is formed at the bottom of the post P. The p-side electrode 120 is made of, for example, Au or Au / Ti.

  Lower DBR 104 and upper DBR 110 form a resonator structure, and current confinement layer 106 and active region 108 are interposed therebetween. The current confinement layer 106 includes an oxidized region 106a in which AlAs exposed on the side surface of the post P is selectively oxidized and a circular conductive region surrounded by the oxidized region, and current and light are contained in the conductive region. Do confinement. The center of this conductive region coincides with the center of the opening of the n-side electrode 116.

  A groove D passing through the center line C is formed in the substrate 100. The grooves D are preferably deep enough to reach the substrate 100, and the distance d is about 5 μm. By forming the groove D, the VCSEL element A and the VCSEL element B on the array are electrically insulated.

  As shown in FIG. 2, pad formation regions F are formed around the posts P of the VCSEL elements A and B, respectively. In the pad formation region F, an electrode pad 30 connected from the n-side electrode 116 via the wiring pattern 34 and an electrode pad 32 connected from the p-side electrode 120 via the wiring pattern 36 are formed. These electrode pads 30 and 32 are electrically insulated from the upper DBR by the interlayer insulating film 114. The VCSEL elements A and B configured in this way can emit a laser beam of, for example, 850 nm from the opening of the n-side electrode 116 in a direction perpendicular to the substrate by applying a forward bias current.

  FIG. 4 is a block diagram showing a configuration of a circuit formed on the integrated circuit chip. The integrated circuit chip 18 includes an amplifying circuit 50 that amplifies an electric signal from a VCSEL element operated as a light receiving element, a comparison between the electric signal amplified by the amplifying circuit 50 and a threshold value, and a VCSEL operated as a light emitting element. Fault detection circuit 52 for detecting whether or not an element has failed, forward bias drive circuit 54 for driving the VCSEL element with forward bias, reverse bias drive circuit 56 for driving the VCSEL element with reverse bias, and fault detection A switching circuit 58 that switches between forward bias and reverse bias drive of the VCSEL element based on an output from the circuit 52 is provided.

  In the present embodiment, the forward bias drive circuit 54 supplies a forward bias drive current sufficient to drive the VCSEL element in response to an input signal from the lead terminal 22a. The reverse bias drive circuit 56 provides a reverse bias voltage sufficient to operate the VCSEL element as a light receiving element, as will be described later.

  Next, the operation of the optical module of this embodiment will be described. As shown in FIG. 5A, the optical module drives the VCSEL element A with a forward bias and drives the VCSEL element B with a reverse bias during initial use, that is, during normal use. That is, the forward bias drive circuit 54 supplies a forward drive current to the electrode pads 30 and 32 of the VCSEL element A, and operates the VCSEL element A as a light emitting element. The reverse bias drive circuit 56 applies a reverse bias voltage to the electrode pads 30 and 32 of the VCSEL element B, and operates the VCSELB as a light receiving element.

  The operation at this time is shown in FIG. In the VCSEL device A, electrons are injected from the n-side electrode 116 and holes are injected from the p-side electrode 120. The injected electrons and holes are recombined in the active region 108, and light is generated. The generated light is amplified in the resonator formed by the lower DBR 104 and the upper DBR 110, and the light that has reached a certain light intensity level is emitted as a laser beam L from the center opening of the n-side electrode 116. At this time, although the laser beam is slight, it spreads in the lateral direction, and leakage light S is generated from the vicinity of the active region 108. The leaked light S passes through the interlayer insulating film 114 from the side surface of the post P and reaches the side surface of the post P of the adjacent VCSEL element B.

  When the leaked light S is incident on the active region 108 of the VCSEL element B, electron / hole pairs are generated in the active region 108 by the light. In addition to the leakage light S from the post P of the VCSEL element A, a part of the laser light L emitted from the VCSEL element A is reflected by the glass flat plate 20b and the reflected light is incident on the VCSEL element B. Also good. Since the VCSEL element B is biased in the reverse direction, electrons are attracted to the n-side electrode 116 biased to the positive side, and holes are attracted to the p-side electrode 120 biased to the negative side. In the element B, a minute current corresponding to the incident light is generated.

  The minute current generated in the VCSEL element B is amplified by the amplifier circuit 50 and then output to the failure detection circuit 52. The failure detection circuit 52 compares the amplified electric signal with a threshold value, and determines that the VCSEL element A has failed when the electric signal is smaller than the threshold value. If the VCSEL element A is dead, the VCSEL element B does not receive any leakage light S or reflected light, so that no electrical signal is output or the electrical signal is zero. In other words, when such an electrical signal is detected, it can be determined that the VCSEL element A has died. Thus, the VCSEL element B monitors the light emission state or failure of the VCSEL element A.

  The failure detection circuit 52 determines that the VCSEL element A has died when the output signal of the VCSEL element B is equal to or less than the threshold value or zero, and outputs the result to the switching circuit 58. In response to this, as shown in FIG. 5B, the switching circuit 58 switches the drive of the VCSEL element B from the reverse bias to the forward bias, thereby operating the VCSEL element B as a light emitting element.

  FIG. 7 is an explanatory diagram when the VCSEL element A fails, that is, when the VCSEL element B is operated as a light emitting element. When the VCSEL element A fails, no electron / hole pair due to the leaked light S is generated in the active region 108 of the VCSEL element B, and no current is generated. For this reason, the failure detection circuit 52 determines that the VCSEL element A has failed. The switching circuit 58 provides the forward bias current generated by the forward drive circuit 54 to the VCSEL element B in response to the failure of the VCSEL element A. Thereby, the VCSEL element B emits the modulated laser light L from the top of the post P.

  As described above, according to the present embodiment, by monitoring the light emission state of the VCSEL element A operated as the light emitting element by the adjacent VCSEL element B, it is possible to easily detect a failure such as the death of the VCSEL element A. In response to the failure of the VCSEL element A, the VCSEL element B can be operated as a light emitting element. Thereby, the optical module of the present embodiment can emit light continuously or continuously, and can be used for a light source of an optical communication system that apparently has improved operational life and requires high reliability. it can.

  Next, a modification of the present embodiment will be described. In the above embodiment, the groove D reaching the substrate is formed in order to electrically insulate the VCSEL element A and the VCSEL element B. However, the present invention is not limited to this, and the groove D1 is formed in the lower DBR 104 as shown in FIG. You may make it stop on the way. In this case, the p-side element region of the VCSEL element A and the VCSEL element B is common, but since the n-side element region is electrically separated, a desired bias voltage is applied to the n-side electrode 116, respectively. . Further, the substrate does not need to be insulative, a p-type GaAs substrate can be used, and a p-side electrode can be formed on the back surface of the substrate.

  In the above embodiment, the lower DBR is p-type and the upper DBR is n-type. However, the conductivity types may be opposite. Further, the number of VCSEL elements formed in the VCSEL array is not limited to two, and may be three or more. FIG. 9 is a schematic plan view showing a layout example of the VCSEL array. As shown in FIG. 9A, on the VCSEL array 16A, the posts P1, P2, and P3 of the three VCSEL elements are arranged at equal intervals L so as to form vertices of an equilateral triangle. For example, when the post P1 is used as a light emitting element, the post P2 is used as a light receiving element for monitoring the light emission state of the post P1, and when the post P1 fails, the post P2 used as the light receiving element is used as the light emitting element. The post P3 is used as a light receiving element for monitoring the light emission state of the post P2. When the post P2 fails, the post P3 is switched to the light emitting element.

  In FIG. 9B, the posts P1, P2, and P4 of the four VCSEL elements are arranged on the VCSEL array 16B so as to form a square apex. Also in this case, as described above, adjacent posts can be assigned to the light emitting element and the light receiving element, and the light emitting element can be switched each time a failure occurs from the posts P1 to P4.

  Furthermore, when simultaneously driving a plurality of VCSEL elements, the operation state of each VCSEL element is monitored by the plurality of VCSEL elements, and when one of the VCSEL elements fails, the VCSEL element that has detected the failure is designated as a light emitting element. You may make it switch to. For example, in FIG. 9B, the posts P1 and P3 may be simultaneously driven as light emitting elements, and the posts P2 and P4 may be used as light receiving elements for monitoring the light emission states of the posts P1 and P3.

  FIG. 10 is a diagram illustrating another example of the switching circuit of the present embodiment. 10A, the first drive circuit 59a supplies a forward bias drive current to the electrode pads 30 and 32 of the VCSEL element A by closing the switch SW1 of the switching circuit 58. The second drive circuit 59b applies a reverse bias voltage to the electrodes 30 and 32 of the VCSEL element B by causing the switch SW2 to perform the first selection.

  When a failure of the VCSEL element A is detected, the switch SW1 is opened and the first drive circuit 59a is disconnected from the VCSEL element A. The second drive circuit 59b supplies the forward bias drive current to the electrode pads 30 and 32 of the VCSEL element B by causing the switch SW2 to perform the second selection, and drives the VCSEL element B as a light emitting element. The first and second drive circuits 59a and 59b are not necessarily separate circuits, and the above operation may be realized by one drive circuit. Furthermore, in the above embodiment, as a method for detecting a failure of the VCSEL element, the electric signal output from the light receiving element is compared with the threshold value. However, the present invention is not limited to this, and determination of the failure of the VCSEL element using a microcomputer. May be performed.

  Furthermore, although the optical module in FIG. 1 illustrates a can-type package, the optical module is not limited to this and may be a ceramic package or a resin-encapsulated package. In the case of resin sealing, the resin uses a light transmitting material or includes a light transmitting window. In the above embodiment, the VCSEL array and the integrated circuit chip are mounted in the same package. However, the integrated circuit chip may be mounted in another package. Further, the optical module is not limited to the flat glass, and may be an uneven lens, a spherical lens, or the like arranged in the laser light emission region.

  Next, an optical communication system that provides an optical module according to the present embodiment is shown in FIG. The optical communication system 200 receives a transmission module 210 including the optical module of the present embodiment, a multimode optical fiber (MMF) 220 that transmits an optical signal transmitted from the transmission module 210, and an optical signal transmitted by the MMF 220. The receiving module 230 is included.

  The transmission module 210 normally transmits the laser light modulated by the VCSEL element A. When the VCSEL element B detects a failure of the VCSEL element A, the VCSEL element B is switched to the light emitting element, and the VCSEL element B transmits the laser light subjected to drive modulation. In this way, the optical module can be replaced even if one VCSEL element fails, so that the useful life of the optical module is effectively increased and the reliability of the optical communication system can be improved. .

  The embodiment described above is an exemplification, and the scope of the present invention should not be construed in a limited manner, and can be realized by other methods within the scope satisfying the constituent requirements of the present invention. Needless to say.

  The optical module according to the present invention can be used as a light source in various fields such as optical communication, optical devices, and optical systems.

FIG. 1 is a schematic cross-sectional view of an optical module according to an embodiment of the present invention. It is a top view of the VCSEL array shown in FIG. FIG. 3 is a cross-sectional view of the VCSEL array shown in FIG. 2 taken along line AA. It is a block diagram which shows the structure of the circuit formed in the integrated circuit chip of an optical module. FIG. 5A is a diagram for explaining a driving method for a VCSEL element in a normal state, and FIG. 5B is a diagram for explaining a driving method for the VCSEL element B when the VCSEL element A is in failure. It is operation | movement explanatory drawing when the VCSEL element A is a light emitting element and the VCSEL element B is a light receiving element at the normal time. It is operation | movement explanatory drawing of the VCSEL element B when the VCSEL element A fails. It is sectional drawing which shows the structure of the other VCSEL array of a present Example. It is a typical top view which shows the structure of the other VCSEL array of a present Example. It is a figure which shows the example of the other switching circuit of a present Example. It is a figure which shows the structural example of the optical communication system to which the optical module of a present Example is applied.

10: Optical module 12: Stem 14: Submount 16: VCSEL
18: integrated circuit chip 20: caps 22a, 22b, 22c: lead terminals 30, 32: electrode pads 34, 36: wiring pattern 50: amplifier circuit 52: failure detection circuit 54: forward bias drive circuit 56: reverse bias drive circuit 58 : Switching circuit 59a, 59b: drive circuit 200: optical communication system 210: transmission module 220: multimode optical fiber 230: reception module A, B: VCSEL element F: pad formation region

Claims (8)

A plurality of semiconductor elements including at least a first semiconductor multilayer film of the first conductivity type, an active region, and a second semiconductor multilayer film of the second conductivity type constituting a resonator together with the first semiconductor multilayer film are formed on the substrate. A semiconductor element array,
Driving means for driving a first semiconductor element of the plurality of semiconductor elements with a forward bias and driving a second semiconductor element adjacent to the first semiconductor element with a reverse bias;
Detecting means for detecting an output signal of the second semiconductor element obtained in response to the light emission state of the first semiconductor element;
Switching means for switching the driving of the second semiconductor element from the reverse bias to the forward bias based on the detection result of the detection means;
An optical module. The detecting means compares whether or not the output signal from the second semiconductor element is equal to or lower than a threshold value, and the switching means is configured to compare the second semiconductor element when the output signal is equal to or lower than the threshold value. The optical module according to claim 1, wherein the driving is switched from reverse bias to forward bias. The plurality of semiconductor elements each include a post serving as a laser light emitting portion, and the second semiconductor element receives reflected light or leakage light of light emitted from the post of the first semiconductor element, and receives the received light. The optical module according to claim 1, which outputs an electrical signal in response to. The drive means includes a forward bias drive circuit and a reverse bias drive circuit, and the switching means connects the forward bias drive circuit to a first semiconductor element, and connects the reverse bias drive circuit to a second bias circuit. 2. The semiconductor device according to claim 1, wherein the switching unit connects the forward bias drive circuit to the second semiconductor device when a failure of the first semiconductor device is detected by the detection unit. Light module. The optical module according to claim 1, wherein the posts of the plurality of semiconductor elements are arranged on the substrate at equal intervals. The optical module according to claim 5, wherein the plurality of semiconductor element posts are arranged line-symmetrically on the substrate. The optical module according to claim 1, wherein the plurality of semiconductor elements are surface-emitting type semiconductor laser elements. An optical module comprising: the optical module according to claim 1; an optical fiber that transmits an optical signal emitted from the optical module; and a receiving module that receives the optical signal transmitted by the optical fiber. Communications system.

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