JPH0453013Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an output monitoring circuit for a semiconductor laser that emits three light beams.

[Prior art]

The semiconductor laser that emits three beams is 100 μm laterally from the semiconductor laser 10 as shown in Figure 3.
It is designed to emit three light beams P ₁ , P ₂ , and P ₃ that are lined up in a row. The spread angle θ of these monitoring light beams is approximately 10°, and the respective light beams P ₁ , P ₂ , and P ₃ are arranged horizontally in parallel at positions approximately 500 μm or more away from the light emitting part. The light beams are incident on each of the three light receiving elements 1A, 1B, and 1C corresponding to each light beam, and the light intensity of each light beam emitted by the semiconductor laser 10 is monitored.

[Problem that the invention attempts to solve]

In such a conventional three-beam semiconductor laser, the spread angle of each of the light beams P ₁ , P ₂ , and P ₃ is 10°, and the distance between the light emitting part and the light receiving element is approximately 500 μm or more. Therefore, each light receiving element 1A, 1B, 1C installed in parallel has a light beam.
Two or three light beams of P ₁ , P ₂ , and P ₃ are incident, and the light intensity of each light beam cannot be accurately monitored. Therefore, as shown in FIG. 4, it is also possible to avoid mixing of the respective light beams by using an array of light receiving elements and shortening the distance between the semiconductor laser 10 and the light receiving elements 1A, 1B, and 1C. However, the arrayed light receiving elements 1A, 1B, 1C
Since the crosstalk between each of them is as large as 1 to 2%, there are problems such as not being able to obtain good monitor characteristics.

On the other hand, Utility Application No. 168284 (Sho 58-74359)
The micro film of this issue is a semiconductor laser in which a cylindrical lens is placed between the semiconductor laser array and the photodetector array to prevent laser light from an adjacent semiconductor laser from leaking into the photodetector element. Array device is shown. However, in this case as well, it is difficult to align the semiconductor laser array, the cylindrical lens, and the photodetector array, to wire with wire bonds, and to fix the photodetector array.

In view of the above-mentioned problem, this invention has developed three
Light-receiving elements that receive each light beam from a book are arranged horizontally in parallel, and the light intensity of each light beam can be accurately monitored even when each light-receiving element receives two or three light beams. The purpose of the present invention is to provide a semiconductor laser monitor circuit that can be used.

[Means for solving problems]

The semiconductor laser monitoring circuit of the present invention monitors three light beams lined up in the horizontal direction by arranging light-receiving elements that separately receive the light beams of the semiconductor laser that emit the light beams in the same direction. , in a semiconductor laser monitor circuit in which each light receiving element receives two or three light beams, first and second light receiving elements weight the outputs of two light receiving elements located at both ends of the light receiving elements, respectively. and a weighting circuit of
An addition circuit that adds the outputs of the first and second weighting circuits, a first subtraction circuit that subtracts the output of the addition circuit from the output of the light receiving element located at the center, and a weighting circuit that weights the output of the subtraction circuit. a third weighting circuit, fourth and fifth weighting circuits that individually weight the output of the third weighting circuit, and a fourth weighting circuit that subtracts the output of the fourth weighting circuit from the output of the light receiving element located at one end. a third subtraction circuit that subtracts the output of the fifth weighting circuit from the output of the light receiving element located at the other end; and the light intensity of each light beam at the other end, and the output of the third weighting circuit is configured to be the light intensity of the central light beam.

[Effect]

Of the three light beams emitted in the horizontal direction, the light beams at both ends and part of the central light beam are mixed into each of the light receiving elements at both ends of the three light receiving elements arranged in the horizontal direction. and enter. The central light beam and a portion of the light beams on both sides are mixed and incident on the central light receiving element. The outputs of the light receiving elements located at both ends are respectively weighted and added by first and second weighting circuits, and the added outputs are subtracted from the output of the light receiving element located at the center by a first subtracting circuit. The weighted output represents the light intensity of the central light beam. The light intensity of each light beam at both ends is obtained by subtracting the output weighted by the fourth and fifth weighting circuits from the outputs of the light receiving elements located at both ends, which are calculated as the light intensity of the central light beam. represent.

Therefore, the light intensity of each of the three light beams can be correctly monitored.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof. FIG. 1 is a block diagram of a semiconductor laser monitor circuit according to the present invention. Prior to describing embodiments, the principle of monitoring the light intensity of a light beam using the output of a light receiving element according to the present invention will be explained. Third
As shown in the figure, the semiconductor laser emits three light beams P ₁ , P ₂ , and P ₃ arranged in the horizontal direction in two directions, one of which is directed toward a projection target such as an optical disk, and the other. Three light receiving elements 1A, 1B, 1C are arranged in parallel in the horizontal direction to monitor the light intensity.
directed towards.

And three light beams lined up horizontally
The light beams P ₁ , P ₃ at both ends of P 1 , _{P 2} , P ₃ are connected to the light receiving elements 1A, which are arranged in parallel in the horizontal direction and located at both ends.
1C, and a part of the light is incident on the light receiving element 1B located at the center. Further, the central light beam P ₂ is incident on the light receiving element 1B located at the center, and part of it is incident on the light receiving element 1B located at both ends.
It is incident on A and 1C.

Here, if the light intensity of each light beam is P ₁ , P ₂ , P ₃ as in the name of the light beam, and the output of the light receiving element that receives the light is L ₁ , L ₂ , L ₃ , then the neighboring light beams are It is thought that they mix with each other, and can be expressed as follows.

L ₁ =P ₁ +k ₁ P ₂ …(1) L ₂ =P ₂ +k ₂ P ₁ +k ₃ P ₃ …(2) L ₃ =P ₃ +k ₄ P ₂ …(3) However, k ₁ to k ₄ is a coefficient indicating the mixing ratio of the beam. Then, P ₂ is calculated using equations (1), (2), and (3). P ₂ = L ₂ −k ₂ L ₁ −k ₃ L ₃ /1−k ₁ k ₂ −k ₃ k ₄ …(4), and by substituting equation (4) into equations (1) and ( ₃ ) to find P ₁ and P 3, P ₁ = L ₁ − k ₁ P ₂ = L ₁ −k ₁ (L ₂ −k ₂ L ₁ −k ₃ L ₃ )/1−k ₁ k ₂ −k ₃ k ₄ …(5
) P ₃ = L ₃ −k ₄ P ₂ = L ₃ −k ₄ (L ₂ −k ₂ L ₁ −k ₃ L ₃ )/1−k ₁ k ₂ −k ₃ k ₄ …(6
) becomes. Therefore, if the coefficients k ₁ to _{k 4} are appropriately set using the method described later, the output L ₁ ,
The correct light intensity of each light beam P ₁ , P ₂ , P ₃ can be determined from L ₂ and L ₃ .

Now, in FIG. 1, the output signal P ₁ +k ₁ P ₂ of the light receiving element 1A into which the two light beams P ₁ and P ₂ located at one end and the center are mixed is transmitted to the second subtraction circuit N2 and the second subtraction circuit N2. The output signal P ₃ +k ₄ P ₂ of the light receiving element 1C mixed with the two light beams P ₃ and P ₂ at the other end and the center is input to the third weighting circuit Q1 and the third subtraction circuit N3. The output signal P 2 +k 2 P ₁ + _{k 3} of the light receiving element 1B is input to _the second weighting circuit Q2 and contains three light beams P ₁ , P ₂ , P _{3 .
P3} is input to the first subtraction circuit N1. The first and second weighting circuits Q1 and Q2 have coefficients k ₂ and k ₃
Output signal weighted by k ₂ P ₁ + k ₁ k ₂ P ₂ , k ₃ P ₃ +
k ₃ k ₄ P ₂ are each outputted and inputted to an adder circuit M.
The coefficients k ₁ and k ₄ indicate the mixing ratio of the central light beam to each of the light beams at both ends, which are incident on the light receiving elements 1A and 1C located at both ends, and the coefficients k ₂ ,
k ₃ indicates the mixing ratio of each beam at both ends to the central light beam incident on the light receiving element 1B located at the center.

The output signal k ₂ P ₁ +k ₁ k ₂ P ₂ +k ₃ P ₃ +k ₃ k ₄ P ₂ added and outputted by the adder circuit M is input to the first subtraction circuit N1. This first subtraction circuit N1
is from the output signal P ₂ +k ₂ P ₁ +k ₃ P ₃ of the light receiving element 2B in which the three beams at the center and both ends are mixed,
Output signal of adder circuit M k ₂ P ₁ +k ₁ k ₂ P ₂ +k ₃ P ₃ +k ₃
Subtract k ₄ P ₂ to get the output signal P ₂ +k ₂ P ₁ +k ₃ P ₃ −k ₂ P ₁
−k ₁ k ₂ P ₂ −k ₃ P ₃ −k ₃ k ₄ P ₂ , that is, P ₂ −k ₁ k ₂ P ₂
−k ₃ k ₄ P ₂ =(1−k ₁ k ₂ −K ₃ k ₄ )P ₂ is output and input to the third weighting circuit Q3. The third weighting circuit Q3 performs weighting of 1/( ₁ - _k1k2 - _k3k4 ), and the output signal _P2 of the third weighting circuit _Q3
is given to output terminal _T2 . The output signal P ₂ of the third weighting circuit Q3 is transmitted to the fourth weighting circuit Q4.
_{The output signal k 1 P 2} of this weighting circuit Q4 is input to the second subtracting circuit N
2 is entered. The second subtraction circuit N2 subtracts the output signal k 1 P ₂ of the fourth weighting circuit Q4 from the output signal P ₁ +k ₁ P ₂ of the light receiving element 1A to obtain P _{1 +} k ₁ P _2.
−k ₁ P ₂ = P ₁ , and output the output signal P ₁ to the output terminal
Giving T ₁ . Also, a third weighting circuit Q3
The output signal P ₂ of is input to the fifth weighting circuit Q5 and weighted with a coefficient k ₄ ,
The output signal k ₄ P ₂ of Q ₅ is input to the third subtraction circuit N3. The third subtraction circuit N3 is the light receiving element 1C.
from the output signal P ₃ +k ₄ P ₂ of the fifth weighting circuit Q
5 output signal k ₄ P ₂ is subtracted and P ₃ + k ₄ P ₂ − k ₄ P ₂ =
P ₃ and its output signal P ₃ is given to the output terminal T ₃ .

The semiconductor laser monitor circuit configured in this way is configured such that when three light beams P ₁ , P ₂ , and P ₃ aligned in a horizontal direction are emitted from the semiconductor laser 10 shown in FIG. It is detected by the light receiving elements 1A, 1B, and 1C which are arranged apart from the semiconductor laser 10, and each of the light receiving elements 1A, 1B, and 1C has (1), (2), and (3).
The outputs L ₁ , L ₂ , and L ₃ shown by each formula are output.

The output signals expressed by equations (1) and (3) of the light receiving elements 1A, 1B, and 1C located at both ends of the horizontal line are output from the first and second weighting circuits Q1 and 1C, respectively.
After being weighted by coefficients k ₂ and k ₃ in Q2,
The output signal of the adding circuit M is added by the adding circuit M, and the output signal of the light receiving element 1B located at the center is subtracted from the output signal shown by the equation (2), and the third weighting circuit Q3 calculates the output signal expressed by the equation (4). are weighted as shown in .

Then, by addition by the adder M and subtraction by the first subtracter N1, an output signal of the light beam P ₂ that is not mixed with the light beams P ₁ and P ₃ is obtained, and the output signal is sent to the output terminal.
Output to _T2 . This allows the light intensity of the centrally located light beam _P2 to be monitored correctly.

Further, the output signal of the third weighting circuit Q3 is transmitted to the fourth (or fifth) weighting circuit Q4 (or Q5).
The light receiving element _1A (or ₁
The output signal of the fourth (or fifth) weighting circuit Q4 (or Q5) is subtracted from the output signal of C) by the second (or third) subtraction circuit N2 (or N3) to obtain equation (5) [or The output signal shown in equation (6) is obtained.

Then, by subtraction by the second (or third) subtraction circuit N2 (or N3), an output signal of the light beam P 1 (or P 2 ) in which the light beam P ₂ is not mixed is obtained, and an output signal of the light beam P ₁ (or P ₂ ) is obtained from the output terminal T ₁ (or T ₃ ). As a result, the light intensities of the beams P ₁ and P ₃ located at both ends can be correctly monitored.

The coefficients k ₁ to _{k 4} are set so that, for example, only the central light beam P ₂ is emitted, and the outputs of the light receiving elements 1A and 1C located at both ends are both zero. , fifth weighting circuit Q4,Q
5 and set the coefficients k ₁ and k ₄ . In addition, the first (or second) weighting is applied so that only the light beam P ₁ (or P ₃ ) at one end (or the other end) is emitted, and the output of the light receiving element 1B located at the center becomes zero. Adjust the circuit Q1 (or Q2) to set the coefficient k ₂ (or k ₃ ).

FIG. 2 shows a block diagram of the monitor circuit shown in FIG. 1 as an actual circuit, and parts corresponding to those in FIG. 1 are given the same reference numerals.
In the figure, OP1, OP3, and OP5 are operational amplifiers as buffers, OP2, OP6, and OP7 are operational amplifiers for subtraction, and variable resistors are used for addition.
This is done by the resistance ratio of VR1, VR2, and resistor R1.
Weighting is performed by adjusting variable resistors VR1 to VR5.

For example, the output signals P ₁ of the light receiving elements 1A and 1C,
_P3 is an operational amplifier via variable resistors VR1 and VR2
Input to OP1. As a result, the voltage across resistor R1 is P ₁ , R ₁ / (VR1 + R1) + P ₃ R ₁ / (VR2
+R1), and weighting and addition are performed simultaneously.
The signal whose impedance has been converted by the operational amplifier OP1 is input to the operational amplifier OP2. This circuit is a subtraction circuit, and performs subtraction processing based on the resistance ratio of resistors _R2 to _R5 . Output signals P ₁ , P ₂ , and P ₃ are obtained by calculations based on the calculation contents described above.

〔effect〕

As described in detail above, according to the present invention, even if two or three light beams lined up laterally are mixed and received by each light receiving element, each output signal of the three light receiving elements will cause the beam to be centered. The output signal of the light receiving element located at one end is electrically corrected, and the output signal of the light receiving element located at one end is electrically corrected by the output signal of the light receiving element located at one end and the output signal of the light receiving element located at the other end. Furthermore, the output signal of the light receiving element located at the other end is electrically corrected by the output signal of the light receiving element located at the other end and the output signal of the light receiving element located at one end, so that each light beam The light intensity can be accurately monitored.

Therefore, there is no need to shorten the distance between the semiconductor laser and the light receiving element, which is extremely advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a semiconductor laser monitor circuit according to the present invention, FIG. 2 is an actual circuit diagram of the monitor circuit of FIG. 1, and FIGS. 3 and 4 are schematic diagrams of conventional semiconductor laser monitor circuits. FIG. P ₁ , P ₂ , P ₃ ... light beam, 1A, 1B, 1C
... Light receiving element, N1, N2, N3 ... Subtraction circuit,
Q1, Q2, Q3, Q4, Q5...Weighting circuit, M...Addition circuit, _T1 , _T2 , _T3 ...Output terminal.

Claims (1)

[Claims for Utility Model Registration] Three light beams lined up in the horizontal direction are emitted in the same direction by a semiconductor laser. Light receiving elements each receiving the light beams separately are arranged in parallel in the horizontal direction to monitor the two light beams. Alternatively, in a semiconductor laser monitor circuit in which each light receiving element receives three light beams, first and second weighting circuits weight the outputs of two light receiving elements located at both ends of the light receiving elements, respectively. an adder circuit that adds the outputs of the first and second weighting circuits, and a first adder circuit that subtracts the output of the adder circuit from the output of the light receiving element located at the center.
a subtraction circuit, a third weighting circuit that weights the output of the subtraction circuit, fourth and fifth weighting circuits that weight the output of the third weighting circuit separately, and a light receiving element located at one end. 4th from output
a second subtraction circuit that subtracts the output of the fifth weighting circuit, and a third subtraction circuit that subtracts the output of the fifth weighting circuit from the output of the light receiving element located at the other end; Each output of the subtraction circuit is
1. A semiconductor laser monitor circuit characterized in that the light intensity of each of the light beams at one end and the other end is taken as the light intensity, and the output of the third weighting circuit is made to be the light intensity of the central light beam.