JP6825843B2 - Surface emitting semiconductor laser device and its failure detection method - Google Patents

Description

The present embodiment relates to a surface emitting semiconductor laser device and a failure detection method thereof.

Vertical Cavity Surface Emitting Laser (VCSEL) is a type of surface emitting laser diode that emits light in the direction perpendicular to the surface of the semiconductor substrate, and is a type of surface emitting laser diode that emits semiconductor thin films such as GaAs, InGaAs, and AlGaAs in the vertical direction. A pn junction is provided on the top and bottom of the cavity, and reflection mirrors are formed on the top and bottom to form a resonator, and the resonator multiplex reflects the light up and down to generate phase-matched light. For example, a VCSEL is mounted on an in-vehicle device and is used in an inter-vehicle distance measuring system for measuring an inter-vehicle distance with a vehicle in front.

Japanese Unexamined Patent Publication No. 2013-45845

In recent years, standards for safety functions (for example, functions such as fail-safe, anomaly detection, and safe stop) for all parts mounted on automobiles are being reviewed. In particular, many in-vehicle devices are electrically / electronically controlled, and not only high performance and high functionality but also ensuring safety is an important need.

ISO 26262, an international standard that systematically summarizes development methods and management methods for safe in-vehicle devices, has been established. When the VCSEL is used in an inter-vehicle distance measurement system or the like, it is desired to detect the failure (deterioration) of the VCSEL as soon as possible in order to avoid a serious systematic accident in advance.

The present embodiment provides a surface emitting semiconductor laser device capable of quickly detecting a failure of a VCSEL and a method for detecting the failure thereof.

According to one aspect of the present embodiment, the surface emitting laser diode, the plurality of photodiodes arranged around the surface emitting laser diode, and the variation in the light receiving level of each of the plurality of photodiodes are used. The present invention provides a surface emitting semiconductor laser device including a failure detecting circuit for detecting a failure of the surface emitting laser diode .

According to another aspect of the present embodiment, there is a failure detection method for a surface emitting semiconductor laser device including a surface emitting laser diode and a plurality of photodiodes arranged around the surface emitting laser diode. Therefore, a failure detection method is provided in which a failure detection circuit detects a failure of the surface emitting laser diode based on a variation in the light receiving level of each of the plurality of photodiodes.

According to the present embodiment, it is possible to provide a surface emitting semiconductor laser device capable of quickly detecting a failure of a VCSEL and a method for detecting the failure thereof.

It is sectional drawing of the surface light emitting type semiconductor laser apparatus which concerns on a basic technique. It is sectional drawing of the surface light emitting type semiconductor laser apparatus which concerns on embodiment. It is a bird's-eye view of the surface light emitting type semiconductor laser apparatus which concerns on embodiment. It is a top view of the surface light emitting type semiconductor laser apparatus which concerns on embodiment. FIG. 4 is a cross-sectional view taken along the line II shown in FIG. It is a graph which shows the change of the light receiving level of each of eight photodiodes provided in the surface emitting semiconductor laser apparatus which concerns on embodiment. It is a graph which shows the change of the light receiving level of each of eight photodiodes provided in the surface emitting semiconductor laser apparatus which concerns on embodiment, (a) when it does not have a feedback mechanism, (b) when it has a feedback mechanism. It is a top view which shows typically the opening of the VCSEL when the surface light emitting type semiconductor laser apparatus which concerns on embodiment breaks down. It is a top view which shows typically the arrangement example of the photodiode in the surface light emitting type semiconductor laser apparatus which concerns on embodiment. It is a flowchart which shows the operation example of the surface light emitting type semiconductor laser apparatus which concerns on embodiment. It is a circuit block diagram of the surface light emitting type semiconductor laser apparatus which concerns on embodiment. It is a graph which shows the state that the amount of change of the light receiving level of a specific photodiode provided in the surface emitting semiconductor laser apparatus which concerns on embodiment is far from the amount of change of the light receiving level of another specific photodiode, (a). When comparing one channel with the remaining channels, (b) When comparing two channels with the remaining channels. It is a specific example (basic circuit) of the circuit configuration shown in FIG. It is a specific example (compared with the average value of 8 pieces) of the circuit configuration shown in FIG. It is a specific example (compared with the diagonal position and the like) of the circuit configuration shown in FIG. It is a specific example of the circuit configuration shown in FIG. 11 (correcting eight initial values). It is a circuit block diagram of the main part of FIG. It is a specific example of the circuit configuration shown in FIG. 11 (correcting eight initial values). It is a top view which shows the power monitor photodiode provided in the surface light emitting type semiconductor laser apparatus which concerns on embodiment. It is a functional block diagram which shows the inter-vehicle distance measurement system which applied the surface-emitting type semiconductor laser apparatus which concerns on embodiment. It is a top view of the sensor module to which the surface emitting semiconductor laser apparatus which concerns on embodiment is applied. It is a top view in the case where a plurality of surface emitting semiconductor laser devices according to the embodiment are arranged on one PCB substrate.

Next, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings below, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the plane dimension, the ratio of the thickness of each layer, etc. are different from the actual ones. Therefore, the specific thickness and dimensions should be determined in consideration of the following explanation. In addition, it goes without saying that the drawings include parts having different dimensional relationships and ratios from each other.

Further, the embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and the embodiments of the present invention include materials, shapes, structures, and components of components. The arrangement etc. is not specified as the following. The embodiments of the present invention can be modified in various ways within the scope of the claims.

[Basic technology]
FIG. 1 shows a cross-sectional structure of a surface emitting semiconductor laser device according to a basic technique. Electrically, the laser emitting element and the light receiving element are formed above and below the common terminal arranged near the center, but optically, the semiconductor reflection that constitutes the resonator of the surface emitting laser unit. The feature is that a light receiving portion is formed in the mirror.

On the substrate 1, n-type multilayer film reflective layer 4, n-type clad layer 5, active layer 6, p-type clad layer 7, p-type spacer layer 8, p-type current block layer 9, p-type multilayer film reflective layer 10, The p-type contact layer 11 is laminated. Further, from a part of the n-type multilayer film reflective layer 4, the n-type clad layer 5, the active layer 6, the p-type clad layer 7, the p-type spacer layer 8, the p-type current block layer 9, and the p-type multilayer film reflective layer 10 Up to the p-type contact layer 11, a mesa region formed by mesa-etching in a cylindrical shape is formed.

An annular p-electrode 14 having an opening in the center is formed on the p-type contact layer 11 formed at the uppermost portion of the cylindrical mesa region. Further, a back surface electrode 15 is formed on the back surface of the substrate 1. The p-type current block layer 9 is composed of an oxidized annular high resistance region 9a and an unoxidized central low resistance region 9b. The emission direction of the laser beam is on the upper side as shown by the arrow in FIG.

In terms of an electric circuit, an n-type multilayer film reflective layer 4 to a p-type contact layer 11 constitute a laser element (VCSEL). Optically, it is composed of a resonator in which the active layer 6 is sandwiched between semiconductor reflection mirrors. The upper semiconductor reflective mirror is composed of a p-type multilayer film reflective layer 10, and the lower semiconductor reflective mirror is composed of an n-type multilayer film reflective layer 4.

Next, a configuration example of each layer is shown. First, as the substrate 1, for example, an N-type GaAs substrate (conductive substrate) is used. As an example, the N-type GaAs substrate is formed to have a thickness of 1000 Å and a carrier concentration of C (carbon) doping of 1 × 10 ^{18 to} 3 × 10 ¹⁹ cm ^-3 .

The n-type multilayer film reflective layer 4 is composed of an n-type DBR layer (n-type Bragg reflective layer), for example, an Al _0.16 Ga _0.84 As layer (low Al composition layer) having a thickness of 600 Å and a thickness. It is composed of 700 Å Al _0.92 Ga _0.16 As layer (high Al composition layer). Further, from the side in contact with the i-type multilayer film reflective layer 3, Al _0.16 Ga _0.84 As layer and Al _0.92 Ga _0.16 As layer are alternately laminated for 20 cycles. At this time, Si (silicon) is used as the n-type impurity, and the carrier concentration of the Si-doped is formed to be 2 × 10 ^{17 to} 5 × 10 ¹⁸ cm ^-3 .

The n-type clad layer 5 is composed of an Al _0.6 Ga _0.4 As layer having a thickness of 900 Å to 1500 Å, Si (silicon) is used as the n-type impurity, and the carrier concentration of Si-doped is 2. It is formed in × 10 ^{16 to} 5 × 10 ¹⁸ cm ^-3 .

The active layer 6 is an active layer having a quantum well structure (Quantum Well), and has a structure in which a well layer (well layer) is sandwiched between barrier layers (barrier layers) having a bandgap larger than that of the well layer. ing. This quantum well structure may be multiplexed instead of one, and in this case, it becomes MQW (Multi Quantum Well), that is, a multiple quantum well structure.

The active layer 6 is composed of, for example, a multiple quantum well structure in which undoped GaAs well layers and undoped AlGaAs barrier layers (barrier layers) are alternately laminated. First, an undoped Al _0.35 Ga _0.65 As barrier layer with a thickness of 150 Å is formed. Next, an undoped GaAs well layer having a thickness of 80 Å and an undoped Al _0.35 Ga _0.65 As barrier layer having a thickness of 100 Å are alternately and repeatedly formed on the barrier layer for 2 to 6 cycles. An undoped GaAs well layer having a thickness of 80 Å is laminated on this, and an undoped Al _0.35 Ga _0.65 As barrier layer having a thickness of 150 Å is laminated on the well layer. That is, both sides of the multiple quantum well structure are formed by a barrier layer composed of an undoped Al _0.35 Ga _0.65 As layer having a different thickness from the intermediate barrier layer.

The p-type clad layer 7 is composed of, for example, an Al _0.6 Ga _0.4 As layer having a thickness of 900 Å to 1500 Å. Further, carbon (C) is used as the p-type dopant, and the carrier concentration of the carbon doping is formed to be 1 × 10 ^{18 to} 3 × 10 ¹⁹ cm ^-3 .

The p-type spacer layer 8 is composed of, for example, an Al _0.92 Ga _0.16 As layer having a thickness of 700 Å. Further, carbon (C) is used as the p-type dopant, and the carrier concentration of the carbon doping is formed to be 1 × 10 ^{18 to} 3 × 10 ¹⁹ cm ^-3 .

The p-type current block layer 9 is composed of, for example, an Al _0.98 Ga _0.02 As layer having a thickness of 200 to 500 Å. Further, carbon (C) is used as the p-type dopant, and the carrier concentration of the carbon doping is formed to be 1 × 10 ^{18 to} 3 × 10 ¹⁹ cm ^-3 . Further, the p-type current block layer 9 is composed of a high resistance region 9a oxidized by the oxidation step and a low resistance region 9b not oxidized by the oxidation step. Here, the p-type current block layer 9 (high resistance region 9a, low resistance region 9b) constitutes a current constriction layer, and the injection carrier conducts mainly the low resistance region 9b sandwiched between the p-type high resistance regions 9a. Therefore, the current flowing through the surface-emitting semiconductor laser device is mainly narrowed to the low resistance region 9b. The region of the active layer 6 corresponding to the low resistance region 9b is the light emitting region.

The p-type multilayer film reflective layer 10 is composed of, for example, a p-type DBR layer (p-type Bragg reflective layer). Specifically, for example, it is composed of an Al _0.16 Ga _0.84 As layer (low Al composition layer) having a thickness of 600 Å and an Al _0.92 Ga _0.16 As layer (high Al composition layer) having a thickness of 700 Å. Will be done. Further, from the side in contact with the current block layer 9, the Al _0.16 Ga _0.84 As layer and the Al _0.92 Ga _0.16 As layer are alternately laminated for 19 cycles. At this time, C (carbon) is used as the p-type impurity, and the carrier concentration of the carbon doping is formed to be 1 × 10 ^{18 to} 3 × 10 ¹⁹ cm ^-3 .

The p-type contact layer 11 is composed of, for example, a GaAs layer having a thickness of 500 Å. Further, carbon (C) is used as the p-type dopant, and the carrier concentration of the carbon doping is formed to be 1 × 10 ^{19 to} 7 × 10 ¹⁹ cm ^-3 . By forming the p-type contact layer 11 with p-type GaAs that does not contain aluminum, the contact resistance of the p-electrode 14 can be reduced.

It is composed of an n-type clad layer 5, an active layer 6, a p-type clad layer 7, a p-type spacer layer 8, and a p-type current block layer 9 sandwiched between the n-type multilayer film reflective layer 4 and the p-type multilayer film reflective layer 10. The laminated structure constitutes the resonator region of the VCSEL.

As an example, the mesa diameter of the mesa region can be about 30 μm, and the diameter of the low resistance region 9b of the p-type current block layer 9 can be about 10 μm.

The DBR layer will be described. Taking the n-side multilayer film reflective layer 4 as an example, an interference phenomenon between reflected light from a plurality of interfaces composed of a first reflective film (low Al composition film) and a second reflective film (high Al composition film). The phase of the light reflected from different interfaces is shifted by 360 degrees to strengthen each other, and the intensity of the reflected light is extremely increased. In order to operate in this way, if the refractive index of the first reflective film is n1, the refractive index of the second reflective film is n2, and the wavelength of the laser light to be oscillated in the laser cavity is λ, the first reflection The film thickness is determined by λ / n1, and the film thickness of the second reflective film is determined by λ / n2.

[Embodiment]
Hereinafter, the surface emitting semiconductor laser device according to the embodiment will be described. In the following, the differences from the surface emitting semiconductor laser device according to the basic technology will be described.

(Outline of surface emitting semiconductor laser device)
FIG. 2 shows a cross-sectional structure of the surface emitting semiconductor laser device according to the embodiment. As shown in FIG. 2, this surface-emitting semiconductor laser device includes a VCSEL (surface emitting laser diode) and a plurality of photodiodes arranged around the VCSEL.

Further, a failure detection circuit for detecting a failure of the VCSEL based on the variation in the light receiving level of each of the plurality of photodiodes may be provided.

Further, the failure detection circuit may detect a failure based on the variation in the amount of change from the initial value of the light receiving level.

Further, the failure detection circuit may determine that the failure occurs when the light receiving level of the specific photodiode is lower than the light receiving level of the other specific photodiode by a predetermined ratio or more.

Further, even if the failure detection circuit determines that the failure occurs when the light receiving level of one of the eight photodiodes is lower than the light receiving level of the remaining seven photodiodes by a predetermined ratio or more. Good.

Further, even if the failure detection circuit determines that the failure occurs when the light receiving level of two of the eight photodiodes is lower than the light receiving level of the remaining six photodiodes by a predetermined ratio or more. Good.

Further, the failure detection circuit may compare the light receiving levels of the photodiodes arranged diagonally among the plurality of photodiodes.

Further, the failure detection circuit may compare the light receiving levels of adjacent photodiodes among a plurality of photodiodes.

Further, the failure detection circuit may send a failure detection signal when detecting a failure of the VCSEL.

Further, a feedback mechanism for keeping the power of the VCSEL constant may be provided.

Further, the VCSEL and the plurality of photodiodes may be manufactured by collectively growing crystals.

Further, a plurality of such VCSELs may be arranged on one PCB substrate.

(Details of surface emitting semiconductor laser device)
FIG. 3 is a bird's-eye view of the surface emitting semiconductor laser device according to the embodiment. As shown in FIG. 3, the VCSEL and the plurality of photodiodes are manufactured by collectively growing crystals. Specifically, an n-type multilayer film reflective layer 4, a resonator region 12, a p-type multilayer film reflective layer 10, and a p electrode 14 are formed on the substrate 1, and the n-type multilayer film reflective layers 4 to p electrodes 14 are formed. The central circular portion and the surrounding annular portion are divided. As described in the basic technique, the laser beam hv is irradiated from the opening AP of the VCSEL.

It is composed of an n-type clad layer 5, an active layer 6, a p-type clad layer 7, a p-type spacer layer 8, and a p-type current block layer 9 sandwiched between the n-type multilayer film reflective layer 4 and the p-type multilayer film reflective layer 10. The laminated structure constitutes the resonator region 12 of the laser element (VCSEL). Further, the n-type clad layer 5, the active layer 6, the p-type clad layer 7, the p-type spacer layer 8, and the p-type current block layer 9 sandwiched between the n-type multilayer film reflective layer 4D and the p-type multilayer film reflective layer 10D. The laminated structure composed of the diode constitutes the diode light receiving region 12D.

FIG. 4 is a plan view of the surface emitting semiconductor laser device according to the embodiment, and FIG. 5 is a sectional view taken along line II shown in FIG. As shown in FIGS. 4 and 5, the surrounding annular portions 4D, 12D, 10D, 14D may be divided into eight photodiodes PD1 to PD8. Here, the photodiodes PD1 and PD5, the photodiodes PD2 and PD6, the photodiodes PD3 and PD7, and the photodiodes PD4 and PD8 are arranged diagonally with the VCSEL in between. The case where the p electrode 14D is provided on the photodiodes PD1 and PD5 is illustrated. According to such a configuration, the lateral leakage of the laser beam hv can be received by each of the eight photodiodes PD1 to PD8, so that the failure of the VCSEL can be detected based on the variation in the light receiving level of each of them. Is possible.

(Change in light receiving level)
FIG. 6 is a graph showing changes in the light receiving level of each of the eight photodiodes PD1 to PD8 included in the surface emitting semiconductor laser device according to the embodiment. The vertical axis represents the current value flowing through each of the eight photodiodes PD1 to PD8, and the horizontal axis represents time. As shown in FIG. 6, the initial values of the current values flowing through each of the eight photodiodes PD1 to PD8 are almost the same. After that, the case where the current value flowing through the two photodiodes PD1 and PD5 is reduced by a predetermined ratio or more (for example, 20% or more) as compared with the other photodiodes is illustrated. In such a case, the individual controller (fault detection circuit) described later determines that the VCSEL has failed.

FIG. 7 is a graph showing changes in the light receiving level of each of the eight photodiodes PD1 to PD8 included in the surface emitting semiconductor laser apparatus according to the embodiment, and FIG. 7A is a graph showing the change in the light receiving level of each of the eight photodiodes PD1 to PD8. b) shows a case where a feedback mechanism is provided. The feedback mechanism is a mechanism that monitors the power of the VCSEL and keeps the power of the VCSEL at a constant value. As shown in FIG. 7A, when the feedback mechanism is not provided, a constant current flows through the VCSEL, so that only the current values flowing through the two failed photodiodes PD1 and PD5 decrease. On the other hand, as shown in FIG. 7B, when the feedback mechanism is provided, the current value flowing through the VCSEL is increased by the amount of the decrease in the current value flowing through the two photodiodes PD1 and PD5. As a result, the current value flowing through the remaining photodiodes PD1, PD3, PD4, PD6, PD7, and PD8 that have not failed increases by Δ, and the total amount of light is maintained at a constant value.

(Failure pattern)
FIG. 8 is a plan view schematically showing the opening AP of the VCSEL when the surface emitting semiconductor laser device according to the embodiment fails. As a result of experiments by the present inventors, it was found that a bright region and a dark region tend to appear symmetrically in the opening AP as shown in FIG. Specifically, the four regions DS1, DS2, DS3, and DS4 around the diamond-shaped region PH in the central portion of the opening AP are darker.

In such a case, it is desirable to determine that the VCSEL has failed earlier than to increase the current value by the feedback mechanism. Of course, there are various failure patterns. In order to avoid serious systematic accidents in advance, it is desirable to detect various failure patterns as soon as possible.

(PD placement example)
FIG. 9 is a plan view schematically showing an arrangement example of photodiodes in the surface emitting semiconductor laser device according to the embodiment. As shown in FIG. 9, eight photodiodes PD1 to PD8 may be arranged around the VCSEL at regular intervals. Here, the photodiodes PD1 and PD5, the photodiodes PD2 and PD6, the photodiodes PD3 and PD7, and the photodiodes PD4 and PD8 are arranged diagonally with the VCSEL in between, respectively. With such an arrangement, it is possible to accurately detect the diamond-shaped failure pattern as shown in FIG.

The method for detecting the failure pattern is not limited to this. That is, FIG. 9 illustrates a case where a failure is detected by focusing on two photodiodes arranged diagonally across the VCSEL, but for example, focusing on only one photodiode. You may detect the failure. Of course, the number and arrangement of the photodiodes are not limited to those shown in FIG. 9, and can be changed as appropriate.

(Operation example)
FIG. 10 is a flowchart showing an operation example of the surface emitting semiconductor laser device according to the embodiment. Here, too, the case where eight photodiodes PD1 to PD8 are arranged around the VCSEL at regular intervals will be described.

First, the individual controller, after storing the initial values of the eight respective light receiving level of the photodiode PD1～PD8 the memory (S1), eight variation of each of the light receiving level of the photodiode PD1~PD8 Δ ₁ calculating a ~Δ ₈ (S2). Variation Δ ₁ ~Δ ₈ is the difference between the received light level of the initial value and the current stored in the memory.

Then, the individual controller determines whether the variation of the amount of change Δ ₁ ~Δ ₈ exceeds a predetermined reference value (S4). There are various determination methods, and the determination method is not particularly limited. For example, a failure may be determined when the light receiving level of two photodiodes out of the eight photodiodes PD1 to PD8 is lower than the light receiving level of the remaining six photodiodes by a predetermined ratio or more. It is desirable that the two photodiodes are arranged diagonally with the VCSEL in between. Specifically, there are four sets of photodiodes PD1 and PD5, photodiodes PD2 and PD6, photodiodes PD3 and PD7, and photodiodes PD4 and PD8.

Here, the individual controller, if the variation in the change amount Δ ₁ ~Δ ₈ is determined to exceed the predetermined reference value (S4: YES), sends a failure detection signal to the microcomputer (not shown) (S4 → S5) .. On the other hand, if the variation in the change amount Δ ₁ ~Δ ₈ is determined not to exceed a predetermined reference value (S4: NO), to continue the failure detection processing (S4 → S2).

The same applies to the case where a feedback mechanism is provided. That is, when the power of the VCSEL falls below a certain value (S3: NO), the value of the current flowing through the VCSEL is increased to keep the power of the VCSEL at a constant value (S3 → S6 → S2). Even when such feedback control is performed, the light receiving level varies between the failed photodiode and the non-failed photodiode (see FIG. 7B). Therefore, as described above, it is possible to deliver a failure detection signal based on a variation in the receiving level of the variation _{Δ 1 ~Δ 8 (S3 → S4} → S5).

(Circuit configuration)
FIG. 11 is a circuit configuration diagram of the surface emitting semiconductor laser device according to the embodiment. Here, too, the case where eight photodiodes PD1 to PD8 are arranged around the VCSEL at regular intervals will be described. In the following description, each route of the eight photodiodes PD1 to PD8 will be referred to as ch (channel).

First, to convert the current of the eight photodiodes PD1~PD8 the voltage at the I / V conversion circuit 21 to 28, and amplifies the voltage by an amplifier circuit 31 to 38, the signal processing the amplified signal _S 1 to S ₈ To do. Specifically, it calculates the amount of change Δ ₁ ~Δ ₈ from the initial value by the arithmetic circuit 41 to 48, determining the variation of the amount of change Δ ₁ ~Δ ₈ in comparison determination unit 51.

Specifically, the comparison determination unit 51 may determine whether or not Δ _m / Σ (Δ remaining ch) exceeds a predetermined reference value a. m is a number for identifying each channel. For example, when Δ _m is Δ ₁ , Σ (Δ remaining ch) is Δ ₂ + Δ ₃ + Δ ₄ + Δ ₅ + Δ ₆ + Δ ₇ + Δ ₈ . When Δ _m / Σ (Δ remaining ch) exceeds a predetermined reference value a, as shown in FIG. 12 (a), the amount of change in the light receiving level of the specific photodiode PD _m Δ _m is the other specific value. of is far from the photodiode PDo amount of change in the received light level delta _o. Therefore, in such a case, the failure detection signal is transmitted from the comparison determination unit 51.

Alternatively, the comparison determination unit 51 may determine whether or not (Δ _m + Δ _n ) / Σ (Δ remaining ch) exceeds a predetermined reference value b. m and n are numbers for identifying each channel. For example, when Δ _m is Δ ₁ and Δ _n is Δ ₅ , Σ (Δ remaining ch) is Δ ₂ + Δ ₃ + Δ ₄ + Δ ₆ + Δ ₇ + Δ ₈ . When (Δ _m + Δ _n ) / Σ (Δ remaining ch) exceeds the predetermined reference value b, the amount of change in the light receiving level of the specific photodiodes PDm and PDn is as shown in FIG. 12 (b). Δ _m, Δ _n is far from the amount of change in the light receiving level of the other specific photodiode PDO delta _o. Therefore, in such a case, the failure detection signal is transmitted from the comparison determination unit 51.

Of course, the combination of m and n is not limited to a specific combination (1,5). When eight photodiodes PD1 to PD8 are arranged around the VCSEL at regular intervals, at least one set of (1,5) (2,6) (3,7) (4,8) is used. All you need is.

Further, the combination of m and n is not limited to the two diagonal combinations (1,5) (2,6) (3,7) (4,8), and any combination can be adopted. .. This makes it possible to determine the necessity of replacement, such as whether or not the failure is progressing.

(Specific example of circuit configuration: basic circuit)
FIG. 13 is a specific example of the circuit configuration shown in FIG. Hereinafter, the parts different from those in FIGS. 11 and 12 will be mainly described, and detailed description of the same parts will be omitted.

As shown in FIG. 13, the amplified signal _S 1 to S ₈ and time division MUX 61, the time division signals _{S 1,} S 2, · · ·, and the AD conversion to _{S 8} in one of the AD conversion circuit 62, the AD The converted digital signals D ₁ , D ₂ , ..., D ₈ may be signal-processed by the logic circuit 63. In the logic circuit 63, the changes in the light receiving level Δ _D1 , Δ _D2 , ···, Δ _D8 are calculated using the initial values, and the changes are based on the variations of the changes Δ _D1 , Δ _D2 , ···, Δ _D8. It is designed to send a failure detection signal. According to such a configuration, since a digital signal is processed, it is effective when performing a complicated calculation.

(Specific example of circuit configuration: Compare with the average value of 8)
FIG. 14 is a specific example of the circuit configuration shown in FIG. Hereinafter, the parts different from those in FIGS. 11 to 13 will be mainly described, and detailed description of the same parts will be omitted.

As shown in FIG. 14, the characteristics of the eight photodiodes PD1 to PD8 may be compared to determine whether or not there is a channel that deviates from the expected value. Specifically, the IV-converted value of each channel and the average value Ave of all channels are compared by the comparison circuits 71 to 78. By normalizing Σ (Δ remaining channels) to 1, the same function can be realized without using the AD conversion circuit 62. Therefore, it is useful when it is not appropriate to use the AD conversion circuit 62, such as when it is desired to realize it in a process without CMOS logic.

(Specific example of circuit configuration: Compare with diagonal position, etc.)
FIG. 15 is a specific example of the circuit configuration shown in FIG. Hereinafter, the parts different from those in FIGS. 11 to 14 will be mainly described, and detailed description of the same parts will be omitted.

As shown in FIG. 15, the characteristics of the two photodiodes may be compared by the comparison circuit 70. For example, the characteristics of PD1 and PD5, PD2 and PD6, PD3 and PD7, and PD4 and PD8 may be compared between the photodiodes arranged diagonally by the comparison circuit 70. Alternatively, the characteristics of the adjacent photodiodes PD1 and PD2, PD2 and PD3, ..., PD7 and PD8, PD8 and PD1 may be compared by the comparison circuit 70. According to such a configuration, it is possible to detect a diamond-shaped failure pattern as shown in FIG. 8 with a simple circuit configuration.

(Specific example of circuit configuration: Correct 8 initial values)
FIG. 16 is a specific example of the circuit configuration shown in FIG. Hereinafter, the parts different from those in FIGS. 11 to 15 will be mainly described, and detailed description of the same parts will be omitted.

As described above, in order to monitor the degree of decrease in the light receiving level of the eight photodiodes PD1 to PD8, it is necessary to store the eight initial values. Therefore, as shown in FIG. 16, after the voltage is amplified by the amplifier circuit 30, a repair process using a fuse may be performed to correct the offset _Vofs for each channel. For example, as shown in FIG. 17, the fuses Fuse 1 to 3 corresponding to the resistance ladders R1 to R3 may be provided, and the resistors RH and RL without fuses may be connected above and below the resistance ladders R1 to R3. According to such a circuit configuration, as shown in Equation 1, the resistance voltage divider (Rl / (Rh + Rl)) is trimmed by shorting the fuses Fuse 1 to 3, and the voltage divider voltage RES obtained by dividing the input voltage IN. Can be adjusted. As a result, it is possible to repair the variation of the eight initial values at the stage of shipping inspection or the like to obtain the same value.

(Specific example of circuit configuration: Correct 8 initial values)
FIG. 18 is a specific example of the circuit configuration shown in FIG. Hereinafter, the parts different from those in FIGS. 11 to 17 will be mainly described, and detailed description of the same parts will be omitted.

As shown in FIG. 18, a non-volatile memory 93 for storing initial values may be provided. For example, the initial value of the digital signal AD-converted by the AD conversion circuit 62 is input to the logic circuit 92. The logic circuit 92 stores the offset portion of each channel in the non-volatile memory 93. As a result, it is possible to repair the variation of the eight initial values at the stage of shipping inspection or the like to obtain the same value. There is also an effect that the comparison circuit 70 as shown in FIG. 16 is unnecessary.

(Feedback mechanism)
FIG. 19 is a plan view showing a power monitor photodiode PDm included in the surface emitting semiconductor laser device according to the embodiment. As shown in FIG. 19, apart from the eight photodiodes PD1 to PD8, a power monitor photodiode PDm for monitoring the power of the VCSEL may be provided. The VCSEL laser light hv1 to hv8 is received by each of the eight photodiodes PD1 to PD8, and the VCSEL laser light hvp is received by the power monitor photodiode PDm. This makes it possible to realize a feedback mechanism based on the current value flowing through the power monitor photodiode PDm.

(Inter-vehicle distance measurement system)
FIG. 20 is a functional block diagram showing an inter-vehicle distance measurement system to which the surface emitting semiconductor laser device according to the embodiment is applied. As shown in FIG. 20, this inter-vehicle distance measurement system includes a VCSEL chip 1A, an individual controller 110, a feedback controller 120, a microcomputer 130, an ECU (Engine Control Unit) 140, and a power monitor / photodiode PDm. To be equipped.

It is assumed that the chip 1A of the VCSEL includes not only the VCSEL but also eight photodiodes PD1 to PD8. The feedback controller 120 monitors the power of the VCSEL based on the value of the current flowing through the power monitor photodiode PDm, and keeps the power of the VCSEL constant. The individual controller 110 is an example of a failure detection circuit, and when a failure of the VCSEL is detected based on the variation in the light receiving level of each of the eight photodiodes PD1 to PD8, the failure detection signal is transmitted to the microcomputer 130. The microcomputer 130 can communicate with the VCSEL chip 1A, the individual controller 110, and the ECU 140, and performs various controls. The ECU 140 measures the inter-vehicle distance from the vehicle in front using the laser beam of the VCSEL, and notifies the microcomputer 130 of a signal such as the measurement result.

In such an inter-vehicle distance measurement system, not only high performance and high functionality but also ensuring safety is an important need. ISO 26262, an international standard that systematically summarizes development methods and management methods for safe in-vehicle devices, has been established.

Therefore, when the microcomputer 130 receives the failure detection signal, it is desirable that the microcomputer 130 determines that the signal such as the measurement result received from the ECU 140 is not valid. Alternatively, when the failure detection signal is received, the ECU 140 may be notified immediately to that effect. According to such a configuration, since the failure of the VCSEL can be detected at an early stage, it is possible to avoid a serious systematic accident in advance.

(Sensor module)
FIG. 21 is a plan view of a sensor module to which the surface emitting semiconductor laser device according to the embodiment is applied. As shown in FIG. 21, the VCSEL chip 1A is mounted on the PCB board 100. The VCSEL chip 1A is formed by forming a VCSEL and eight photodiodes PD1 to PD8 on a common substrate such as a gallium arsenide substrate. The size of the VCSEL chip 1A is, for example, about 200 to 300 μm. Electrode pads BP1 to BP8 and BPvc are formed on the surface of the chip 1A of the VCSEL in order to pass a current through the VCSEL and the eight photodiodes PD1 to PD8. The electrode pads BP1 to BP8, BPm, and BPvc are wire-bonded to the bonding terminals T1 to T8, Tm, and Tvc on the PCB substrate 100, respectively. Not limited to wire bonding, a method of connecting with patterned electrodes may be used. The PCB board 100 can be connected to a microcomputer 130, an ECU 140, or the like.

(Multi-chip)
FIG. 22 is a plan view when a plurality of surface emitting semiconductor laser devices according to the embodiment are arranged on one PCB substrate 100. As shown in FIG. 22, a plurality of VCSELs 11, 12, 13, ... May be arranged in a matrix on the PCB substrate 100. In this case, the photodiodes PD11, PD12, PD13, ... May be arranged in a matrix in the center between the VCSELs. According to such a configuration, failures of a plurality of VCSELs 11, 12, 13, ... Can be detected individually, and current values to be passed through the plurality of VCSELs 11, 12, 13, ... Are individually detected. Can be controlled.

As described above, according to the present embodiment, it is possible to provide a surface emitting semiconductor laser device capable of quickly detecting a failure of a VCSEL and a method for detecting the failure thereof.

In the present embodiment, VCSEL is exemplified as the surface emitting laser diode, but it is also possible to adopt a surface emitting laser diode other than VCSEL.

[Other embodiments]
As mentioned above, although described by embodiment, the discourses and drawings that form part of this disclosure should not be understood to limit the invention. This disclosure will reveal to those skilled in the art various alternative embodiments, examples and operational techniques.

As described above, it goes without saying that the present invention includes various embodiments not described here. Therefore, the technical scope of the present invention is defined only by the matters specifying the invention relating to the reasonable claims from the above description.

This embodiment can be applied to electronic devices in various fields such as automobiles, aircraft, ships, railways, rockets, medical devices, industrial machines, and robots.

1 ... Substrate 1A ... VCSEL chip 4,4D ... n-type multilayer film reflective layer 12 ... Resonator region 12D ... Diode light receiving region 10,10D ... p-type multilayer film reflective layer 14, 14D ... p electrodes 21-28 ... I / V conversion circuit 30, 31-38 ... Amplifier circuit 41-48 ... Arithmetic circuit 61 ... MUX
62 ... AD conversion circuit 63, 92 ... Logic circuit 70, 71-78 ... Comparison circuit 93 ... Non-volatile memory 110 ... Individual controller (fault detection circuit)
120 ... Feedback controller 130 ... Microcomputer 140 ... ECU
PD1 to PD8 ... Photodiode PDm ... Power monitor / photodiode hv ... Laser light

Claims (21)

Surface emitting laser diode and
A plurality of photodiodes arranged around the surface emitting laser diode ,
A surface-emitting semiconductor laser device including a failure detection circuit that detects a failure of the surface-emitting laser diode based on a variation in the light receiving level of each of the plurality of photodiodes . The surface-emitting semiconductor laser device according to claim 1, wherein the failure detection circuit detects a failure based on a variation in the amount of change from the initial value of the light receiving level. The surface emission according to claim 1, wherein the failure detection circuit determines that a failure occurs when the light receiving level of the specific photodiode is lower than the light receiving level of another specific photodiode by a predetermined ratio or more. Type semiconductor laser device. The failure detection circuit is characterized in that a failure is determined when the light receiving level of one of the eight photodiodes is lower than the light receiving level of the remaining seven photodiodes by a predetermined ratio or more. The surface emitting semiconductor laser apparatus according to claim 1. The failure detection circuit is characterized in that a failure is determined when the light receiving level of two photodiodes out of eight photodiodes is lower than the light receiving level of the remaining six photodiodes by a predetermined ratio or more. The surface emitting semiconductor laser apparatus according to claim 1. The surface emitting semiconductor laser device according to claim 1, wherein the failure detection circuit compares the light receiving levels of the photodiodes arranged at diagonal positions among the plurality of photodiodes. The surface emitting semiconductor laser device according to claim 1, wherein the failure detection circuit compares the light receiving levels of adjacent photodiodes among the plurality of photodiodes. The surface-emitting semiconductor laser device according to claim 1, wherein the failure detection circuit transmits a failure detection signal when a failure of the surface-emitting laser diode is detected. The surface emitting semiconductor laser device according to claim 1, further comprising a feedback mechanism for maintaining the power of the surface emitting laser diode at a constant value. The surface-emitting semiconductor laser diode according to claim 1, wherein the surface-emitting laser diode and the plurality of photodiodes are manufactured by collectively growing crystals. A surface emitting semiconductor laser device according to any one of claims 1 to 10, wherein a plurality of surface emitting semiconductor laser devices according to any one of claims 1 to 10 are arranged on one PCB substrate. A method for detecting a failure of a surface emitting semiconductor laser device including a surface emitting laser diode and a plurality of photodiodes arranged around the surface emitting laser diode.
A failure detection method, characterized in that a failure detection circuit detects a failure of the surface emitting laser diode based on a variation in the light receiving level of each of the plurality of photodiodes. The failure detection method according to claim 12, wherein the failure detection circuit detects a failure based on a variation in the amount of change from the initial value of the light receiving level. The failure detection according to claim 12, wherein the failure detection circuit determines that a failure occurs when the light receiving level of the specific photodiode is lower than the light receiving level of another specific photodiode by a predetermined ratio or more. Method. The failure detection circuit is characterized in that a failure is determined when the light receiving level of one of the eight photodiodes is lower than the light receiving level of the remaining seven photodiodes by a predetermined ratio or more. The failure detection method according to claim 12. The failure detection circuit is characterized in that a failure is determined when the light receiving level of two photodiodes out of eight photodiodes is lower than the light receiving level of the remaining six photodiodes by a predetermined ratio or more. The failure detection method according to claim 12. The failure detection method according to claim 12, wherein the failure detection circuit compares the light receiving levels of the photodiodes arranged diagonally among the plurality of photodiodes. The failure detection method according to claim 12, wherein the failure detection circuit compares the light receiving levels of adjacent photodiodes among the plurality of photodiodes. The failure detection method according to claim 12, wherein the failure detection circuit transmits a failure detection signal when a failure of the surface emitting laser diode is detected. The failure detection method according to claim 12, further comprising a feedback mechanism that keeps the power of the surface emitting laser diode at a constant value. The failure detection method according to claim 12, wherein the surface-emitting laser diode and the plurality of photodiodes are manufactured by collectively growing crystals.

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