JP2858851B2 - Method for measuring characteristics of multi-beam semiconductor laser - Google Patents

Description

The present invention relates to a method for measuring characteristics of a multi-beam semiconductor laser.

(B) Conventional technology A so-called multi-beam semiconductor laser that emits a plurality of laser beams in the same direction has been developed by the present applicant and others. For example, IEICE Technical Review Vol.86, No.323, pp.75-79 ( 19
87) has been reported.

In such a multi-beam semiconductor laser, when a plurality of laser elements emitting each laser beam are simultaneously energized, the output characteristics of other laser elements change due to heat generated from each laser element. That is, in such a multi-beam semiconductor laser, it is important to measure not only the individual device characteristics of each laser device but also the device characteristics due to the thermal interaction at the time of simultaneous energization.

A method for measuring the thermal interaction of a conventional multi-beam semiconductor laser will be described with reference to FIG. In the figure, (1
1) is a multi-beam semiconductor laser having four laser elements formed monolithically and capable of emitting a laser beam independently from each element, and (12) is a light receiving element arranged in the laser beam emitting direction. , Four light receiving sections (12a) to (12
d). (13) is a lens disposed between the multi-beam semiconductor laser (11) and the light receiving element (12), which expands the beam interval of each laser beam to the corresponding light receiving sections (12a) to (12d). Make it incident. Here, the arrows in the drawings indicate the optical axes of the two outer laser beams among the four laser beams.

(14) is a jig having good thermal conductivity for fixing the multi-beam semiconductor laser (11), and (15) and (16) are jigs (14) described above.
A Peltier element and a heat sink, which are thermally connected to the multi-beam semiconductor laser (11) through the interface and control the temperature of the multi-beam semiconductor laser (11). (17) a driving unit for driving the multi-beam semiconductor laser (11),
(18) is a detection unit that detects the light output of each of the light receiving units (12a) to (12d) of the light receiving element (12).

The method of measuring thermal interaction using such a measurement system is performed in the following procedure.

i) First, the four laser elements i, k, l, m are operated independently, and the light output characteristics are measured. That laser element j, k, l, husband m s individual current _{I j, I k, I l} , energized and I _m, the light receiving portions (12a)
In (12d), the respective optical outputs _Pj , _Pk , _Pl , and _Pm are measured. Actually, P _j = P _k = P _l = P _m = P is set, and the current for obtaining such an output is measured. The temperature of the multi-beam semiconductor laser (11) at this time is set to T ° C.

ii) the temperature of the multi-beam semiconductor laser using a Peltier element (15) (11) raised [Delta] T ° C., the same current I _j and i) to each element, I _k, I _l, energized and I _m, each element The optical outputs P _j ′, P _k ′, P _l ′, and P _m ′ of the single operation are measured.

iii) From the obtained measured values, the temperature coefficient K _r (r = j, k, l, m) of each element is obtained according to the following equation.

K _r = (P _r −P _r ′) / ΔT iv) Assuming that the temperature of the multi-beam semiconductor laser (11) is T ° C., two elements r, s (r, s = j, k, l, by selecting the m) i) with the same current I _r, the operating voltage V _r 'and element r of elements r when energized the I _s at the same time, s of the light output P _sr, respectively measured P _rs.

v) From the obtained measured values, the element s is replaced with the element r
The thermal interaction C _{sr given} to

C _sr = (P _r −P _sr ) / K _r W _rs where W _sr = I _s V _s ′ −P _rs , and W _sr indicates the heat value of the element r.

(C) Problems to be Solved by the Invention However, in the conventional method, since a lens is used for the measurement system, it is necessary to adjust the optical axis, focus, and the like of the laser beam on the light receiving element. At this time, in such a multi-beam semiconductor laser, it is necessary to simultaneously adjust a plurality of laser beams, and the operation is complicated, which is not preferable particularly in automating the measurement.

Also, in such a conventional method, in order to increase the beam interval,
Requires an optical path length of 20 cm or more, and the measurement system becomes large.

By the way, when examining the thermal characteristics of each element for the purpose of mass production of such a multi-beam semiconductor laser, the thermal output C _sr and the temperature coefficient K _r are not separately obtained, but the optical output variation coefficient B by obtaining the _{sr (B sr = C sr K} r) is sufficient.

Also, a general semiconductor laser has a built-in light receiving element that emits a laser beam from one laser element in two directions and monitors one of the beams (in the present invention, this light receiving element is referred to as an internal light receiving element). Call). In such a multi-beam semiconductor laser, for example,
As disclosed in Japanese Patent Publication No. 354, a device having a light receiving element for individually monitoring a plurality of laser beams has been proposed.

Therefore, the present invention makes use of the internal light receiving element in such a multi-beam semiconductor laser to eliminate the need for complicated optical axis adjustment and the like, and facilitate the thermal interaction of the multi-beam semiconductor laser using the optical output variation coefficient. It is intended to provide a method that can be used for measurement.

(D) Means for Solving the Problems The present invention has N (N ≧ 2) laser elements each capable of emitting a laser beam in two directions, and individually separates the laser beams emitted in one direction. A method for measuring the characteristics of a multi-beam semiconductor laser having an internal light-receiving element for receiving light in the other direction, and using each laser beam emitted in the other direction as output light. Arranging an external light receiving element in the other laser beam emitting direction so as to receive all laser beams with a single light receiving section; and different elements r and s from the N laser elements.
Select, each element r, s respectively individually current I _r, by energizing the I _s, respectively internal light output p _r in the internal light receiving element to measure the p _s, respectively external light by the external light receiving element Measuring the outputs P _r , P _s , and simultaneously applying the currents I _r , I _s to the respective elements r, s, and measuring the terminal voltage V _s ′ of the element s, A step of measuring the internal light output p _sr of the element r and the internal light output p _rs of the element s in the light receiving element; and obtaining the light output variation coefficient B _sr given by the element s to the element r from the obtained measurement values. _{sr = (p r -p sr)} P r / P r W s ( _{where, W s = I s V s} ') , characterized in that it comprises a step of determining at the.

(E) Function According to the method of the present invention, the internal light receiving element built in the multi-beam semiconductor laser is used, and the external light receiving element that receives a plurality of output laser beams by a single light receiving unit is used. The light output variation coefficient of each laser element can be obtained.

(F) Embodiment FIG. 2 shows a multi-beam semiconductor laser used in the method of the present invention.

In the figure, (1) is a laser chip in which four laser elements j, k, l, m are monolithically formed, and each laser element emits a laser beam in two opposite directions as shown by arrows in the drawing. I do. (2) is an internal light receiving element arranged on an extension of one of the laser beams, and has four light receiving sections (2a) to (2d) for individually receiving each laser beam. (3) is an optical guide provided with optical waveguide grooves (3a) to (3d), which is provided between the laser chip (1) and the internal light receiving element (2), and separates the above one laser beam to cope therewith. To the light receiving section to be performed. (4) is a submount having one main surface and made of a material having good thermal conductivity. The laser chip (1), the internal light receiving element (2), and the light guide (3) are
Each of the submounts (4) is arranged on one main surface.
In the figure, the wiring of the laser chip (1) and the internal light receiving element (2) is omitted. Thus, in such a multi-beam semiconductor laser, of the laser beams emitted from the laser chip (1) in two directions, the laser beam emitted to the side opposite to the internal light receiving element (2) side becomes the output light. .

 Next, FIG. 1 shows a measuring system used in the method of the present invention.

In the figure, (5) is the multi-beam semiconductor laser shown in FIG. 2, (6) is an external light receiving element arranged in the output light emitting direction, and the multi-beam semiconductor laser (5)
And a single light receiving section (6a) for receiving all four laser beams output from the optical disk.

(7) is a jig having good thermal conductivity for fixing the multi-beam semiconductor laser (5), and (8) is thermally connected to the multi-beam semiconductor laser (5) via the jig (7). It is a heat sink. (9) is a drive unit capable of individually driving each laser element of the multi-beam semiconductor laser (5), and (10a) is each light-receiving element of the internal light-receiving element (2) built in the multi-beam semiconductor laser (4). A first detection unit for detecting the optical output of the unit, (10b) is the external light receiving element (5)
Is a second detection unit that detects the light output of the second detection unit.

Next, an embodiment of the method of the present invention using such a measurement system will be described.

i) First, the four laser elements j, k, l, and m are operated independently, and the light output characteristics are measured. That laser element j, k, l, m, respectively individually current _{I j, I k, I l} , energized and I _m, internal light output p _j obtained from the first detector (9), p _k, p _l, a p _m were respectively measured, at the same time the second detector (10) from the external light output _{P j, P k, P l} , P
Measure _m respectively. Actually, in order to simplify later calculations, the external light output is set to be constant, that is, P _j = P _k = P _l = P _m = P, and the internal light of the internal light receiving element (2) at this output is set. Output,
The current flowing through the laser element is measured.

ii) Two elements r, s (r, s = j, k, l, m) are selected from the four elements of the multi-beam semiconductor laser (4), and each element r, s is the same as i). and flowing current I _r, the I _s at the same time, measures a voltage V _s' of element s, each element r by the internal light receiving element (2), the internal optical output p _sr of s, and p _rs.

iii) Here, when the two elements are energized simultaneously, the element r
Is caused by the calorific value W _rs of the element s. If the thermal interaction that the element s gives to the element r is C _sr and ΔT = C _sr W _rs is defined, the following equation is established.

In _{(P r -P sr) / K} r = C sr W rs where difference P _r -P _sr external output of the time during the simultaneous energization alone energization element r is the external light output P _r at solely energized internal optical output p _r at each energization, with _{p sr, P r -P sr =} (p r -p sr) P r
/ p can be expressed as _r, therefore, the above equation can be expressed as follows.

(P _r −p _sr ) P _r / p _r K _r = C _sr W _rs The heating value W _rs of the element s at the time of simultaneous energization is the external light output P _s at the time of single energization and the internal light at each energization. Using the outputs p _s and p _rs , it can be expressed as follows.

W _rs = I _s V _s ′ −p _rs P _s / p _s Next, if the optical output variation coefficient of the element r resulting from the thermal interaction of the element s with the element _r is defined as B _sr = C _sr K _r ,
The optical output variation coefficient B _sr can be obtained from B _sr = C _sr K _r = (p _r −p _sr ) P _r / p _r W _rs .

For example, the optical output variation coefficient between adjacent elements of a multi-beam semiconductor laser (1) in which elements j, k, l, and m are arranged in this order is B _jk = (p _k −p _jk ) P _{k / p k W kj B kj =} (p j -p kj) P j / p j W jk B kl = (p l -p kl) P l / p l W lk B lk = (p k -p lk) P obtained from _{k / p k W kl B lm} = (p m -p lm) P m / p m W ml B ml = (p k -p ml) Pl / p l W lm. In addition, thermal interactions separated by two or more elements can be similarly obtained, and the method of the present invention can be applied regardless of the number of elements of the multi-beam semiconductor laser.

(G) Effects of the Invention According to the method of the present invention, a plurality of laser beams emitted from a multi-beam semiconductor laser are received by a single light receiving portion of a light receiving element, and the light output variation coefficient between the two elements is reduced. You can ask. Therefore, since it is not necessary to increase the laser beam interval using a lens, complicated adjustment work such as optical axis adjustment is not performed, and measurement can be performed easily.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a measurement system used in the method of the present invention, and FIG.
FIG. 3 is a sectional view of a main part of a multi-beam semiconductor laser used in the method of the present invention, and FIG. 3 is a schematic view showing a measuring system used in a conventional method.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01M 11/00

Claims (1)

(57) [Claims] An internal light receiving element for individually receiving each laser beam emitted in one direction, comprising N (N ≧ 2) laser elements capable of emitting a laser beam in two directions. A method for measuring the characteristics of a multi-beam semiconductor laser in which each laser beam emitted in the other direction is output light, wherein a single light-receiving part receives all laser beams in the other laser beam emission direction of the multi-beam semiconductor laser. placing the external light-receiving element in order to received, select different elements r, s from among the N number of laser elements, each individually current I _r, the I _s energizing each element r, s hand,
Each internal light output p _r in the internal light receiving element to measure the p _s, the external light-receiving element at each external optical output P _r, measuring a P _s, the respective elements r, s respectively above current I _r , _Is at the same time,
Measuring the terminal voltage V _s ′ of the element s and measuring the internal light output p _sr of the element r and the internal light output p _rs of the element s with the internal light receiving element; the optical output variation coefficient B _sr the element s has on the element _{r, B sr = (p r} -p sr) P r / P r W rs ( _{where, W rs = I s V s} ' -p rs P s / and ( _c ) determining a multi-beam semiconductor laser.