JPS6343388A - External resonator type semiconductor laser device - Google Patents

Abstract

PURPOSE:To enlarge the temperature range in which the same axial mode is kept, by forming a base member, on which a semiconductor laser element and a reflecting member are placed, out of material having a linear expansion coefficient smaller than copper. CONSTITUTION:A semiconductor laser element 1 and a chip 2 forming a total reflection mirror 3 so as to feed back the backward outgoing beams of the element 1 to the element 1 are mounted onto a base plate 4. In such constitution, BeO, SiC, Si, etc. having a linear expansion coefficient smaller than copper are used as a material for the base plate 4. The linear expansion coefficient of the base plate 4 must be reduced in order to enlarged temperature range in which the same axial mode is maintained, and the temperature range in which the same axial mode is kept can be enlarged when the material having the linear expansion coefficient smaller than at least copper is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application This invention relates to an external cavity type semiconductor laser device that returns back emitted light from a semiconductor laser by an external reflecting member (mirror).

(B) Prior Art The oscillation axis mode of a conventional semiconductor laser is selected depending on the gain distribution of the laser medium and the transmission characteristics of the laser resonator. Figure 6 is a diagram showing the oscillation axis mode selectivity of a conventional semiconductor laser. The spectrum of the mode (fc) is shown above (ω and (b)
) are schematically shown in the superradiant state spectra superimposed on each other. Among the various axial modes of the laser, the one with a wavelength close to the peak of the gain distribution (large R value) gains the maximum gain and becomes the oscillation axial mode, but as the ambient temperature changes, the band gap of the semiconductor changes. The peak wavelength of the gain distribution changes toward longer wavelengths at a rate of 2 to 3 persons/dea. Furthermore, since the refractive index of the medium changes and the laser element itself also thermally expands, the effective optical length of the laser resonator changes, and as a result, each axial mode maintains a distance of about 3 people, while maintaining a distance of 0.7 people/year. It changes to the longer wavelength side at a rate of about deQ.

Therefore, when the temperature is raised beyond a certain state, the change range of the gain distribution is larger than the change range of the axial mode, so the emission wavelength changes continuously for a while, but mode hopping eventually occurs, and from then on, as shown in Figure 8. As shown in the figure, continuous changes and mode hopping are repeated, resulting in step-like changes. In addition, the wavelength changes depending on the current value used to drive the semiconductor laser, which has hindered its application as a light source for wavelength-multiplexed optical communications and high-resolution spectroscopy, which are expected in the future.

Therefore, SEC laser (Short Exter
nalCavity Laser diode) was invented, which returns the rear emitted light of the semiconductor laser to the semiconductor laser body using an external mirror.In this case, the oscillation axis mode is the same as the gain distribution of the normal laser The selection is made based on three factors: and the wavelength selectivity of the external resonator. Figure 7 schematically shows this situation in correspondence with Figure 6. Figure 7 (shows the gain distribution of the laser medium with respect to wavelength, , the figure (C) shows the resonance characteristics of the external resonator with respect to the wavelength, and the figure +cb shows the above (ω(b+
(C) shows the superradiant state spectrum superimposed. The envelope of the spectrum in the super radiant state differs from that shown in Figure 6 and has ripples as shown in Figure 7 (small).In this case, the temperature characteristics of the peak of the envelope are That is, since it can be controlled by changing the gap length between the semiconductor laser and the external mirror, mode hops can be suppressed and a single axial mode can be maintained over a wide temperature range.

An example of the characteristics of the oscillation wavelength with respect to temperature of this SEC laser is shown in Fig. 9. In the temperature range of △[, the same axial mode H is maintained, and in the temperature range of ∆T, as shown in Fig. 7 (d
) The axial mode sequentially obtains the maximum gain at the same peak of the spectrum envelope shown in ) and becomes the oscillation axial mode. In other words,
The oscillation wavelength is such that for every Δ, the oscillation axial mode shifts to an adjacent axial mode, causing a small mode hop, and for every Δ below, the oscillation axial mode shifts to the next peak of the envelope, producing a large mode hop. .

(c) Problems to be solved by the invention Conventional SEC lasers use GaAs on a GaAs substrate.
-Ga AI As -VSIS type semiconductor laser with -DH (double hetero) structure and Al as a total reflection mirror
2O3 coated GaAs chip and C
A predetermined external resonator is fixed to a mounting table made of u material at a distance equal to the distance between the emitting end face of the semiconductor laser and the reflecting surface of the mirror. FIG. 3 (Cu) shows the characteristics of the external cavity length of this SEC laser and the temperature range Δd shown in FIG. 9. In addition, the temperature coefficient dλ/dT of the peak wavelength of the spectrum envelope curve is shown in Figure 4 (
Cut').

By the way, as mentioned above, the temperature coefficient of the axial mode is 0.7 people/deQ. Therefore, dλ/dT is 50P
When L is smaller than 71, it becomes larger than the temperature coefficient of the axial mode, so a small mode hop occurs to the long wavelength side within the range below Δ, and when L is larger than 50, the temperature coefficient becomes smaller than the temperature coefficient of the axial mode. This results in a small mode hop to the wavelength side. Therefore, in order to maintain the coaxial mode completely as shown in Fig. 10, in other words, Δd =
In order to stay at △, l = 50. so that dλ/dT matches the temperature coefficient of the axial mode (0.7 persons/clec)'). It is necessary to set the temperature to a, but the ΔK in this case is only 35°C, as seen from Figure 3.

The present invention has been made in consideration of these circumstances, and it is an object of the present invention to provide an external cavity type semiconductor laser device that can further increase this Δt.

(D) Means for Solving Problems This invention provides a semiconductor laser device, a reflecting member for returning laser light emitted from one emission end facet of the semiconductor laser device to the semiconductor laser device, and a semiconductor laser device. An external cavity type semiconductor laser device comprising a mounting member for mounting and fixing an element and the reflecting member, the mounting member having a linear expansion coefficient smaller than that of copper. be.

The above mounting member uses Sl, SiC, or BeO as a constituent material.

(e) Effect The temperature coefficient of the gain distribution in Figure 7 (a) is 2 to 3 people/deg.
, the temperature coefficient of the axis mode for <b+ in the same figure is 0.7 people/de
g, and the temperature coefficient of the gain distribution is 3 to 4 times larger than that of the axial mode. Therefore, as shown in Fig. 7 (temperature coefficient dλ/(temperature coefficient of the peak wavelength of the small envelope), the smaller the IT and the smaller the difference from the temperature coefficient of the axial mode, the less likely mode hop will occur, the larger △T in Fig. 10. By the way, dλ/dT is the temperature coefficient of the gain distribution (2 to 3 people/
deg constant) and the resonance characteristics of the external resonator (Figure 7 (C))
Since the temperature coefficient dλ/dT of the peak wavelength λ is determined by the temperature coefficient dλ/dT, the smaller dλ/dT, the smaller the difference between dT/dT and the temperature coefficient of the axial mode.

Although the external resonator length changes due to the engraving of the mounting member due to temperature rise, the temperature coefficient dλ/dT of the peak wavelength λ of the resonance characteristics of the external resonator is generally (Tazushi, Lo is λ
expressed as an arbitrary external resonator length with 0 as the resonant wavelength),
The smaller the temperature coefficient dL/dT of the external resonator length, the more d
λ/dT becomes smaller.

Therefore, if a material with a coefficient of linear expansion smaller than that of copper is used for the mounting member, the difference between dλ/dT and the temperature coefficient of the axial mode will be smaller than when copper is used for the mounting member. ΔT in FIG. 10 increases correspondingly.

(f) Examples Hereinafter, the present invention will be described in detail based on examples shown in the drawings. Note that this invention is not limited to this.

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG. 2 is a side view of FIG. 1.

In these figures, 1 is QaA on a GaAs substrate.
VSIs with s -Ga AI AS -DH structure
2 is a Ga AS chip, 3 is a total reflection mirror formed by coating one surface of the Qa As chip 2 with Al2O3 so as to return the rear emitted light of the semiconductor laser 1 to the semiconductor laser 1, and 4 is a semiconductor A mounting plate on which the laser 1 and the GaAs chip 2 are installed, 5 is a lead wire for power supply to the semiconductor laser 1, la is the length of the semiconductor laser 1, Lb is the length of the chip 2, and L is the emission of the semiconductor laser 1. This is the distance from the end face to the reflective surface of the mirror 3 (external resonator length).

In such a configuration, in particular, Cu, Be○, and Si, which have a smaller coefficient of linear expansion than Cu, are used as the material for the mounting plate 4.
Using C and Sl, the dimensions of the mounting plate 4 are 1.5 mm
3.0mmX 1.0mm <thickness) and
La=Lb=250. ΔT (Fig. 10) and dλ/dT with respect to the external resonator length were measured. The measurement results are shown in FIGS. 3 and 4.

Temperature coefficient dT/ of the envelope peak wavelength shown in Figure 7 +d+
In order to make dT match the temperature coefficient of 0.7 in the axial mode, the mounting plate 4 must have a linear expansion coefficient of CD (linear expansion coefficient 17.0X10').
deg'), the external resonator length needs to be 50fim from Figures 3 and 4, and in this case, △
T=35℃, Si C line engraving coefficient 2.4×10
'deg-''), the external cavity length is set to 14.π
Therefore, ΔT=80°C. Furthermore, the linear expansion coefficients are 7.6x 10'deg' and 3.7x 1, respectively.
ΔT is also 48°C for Be O and Si C, which are 0'deg-'.

62° C. From these results, the relationship of 8T to the coefficient of linear expansion is shown in FIG.

Figure 5 shows that in order to increase the size of the 6-piece, it is necessary to reduce the linear expansion coefficient of the mounting plate 4, and it is also necessary to use a material with a linear expansion coefficient smaller than that of CO. It can be seen that the 6-piece can be made larger than before.

(G) Effects of the Invention According to this invention, it is possible to significantly expand the temperature range in which the coaxial mode is maintained, and a semiconductor laser that does not cause mode hops at all under normal usage conditions is provided. .

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2 is a side view of Fig. 1, and Fig. 3 shows the relationship between the external resonator length and the temperature range without large mode hops. graph, 4th
The figure is a graph showing the relationship between the external cavity length and the peak wavelength temperature fraction dλ/dT of the envelope of the axial mode spectrum.
FIG. 5 is a graph showing the relationship between the coefficient of linear expansion and the temperature range without mode hop, FIG. 6 is an explanatory diagram showing the selectivity of the oscillation axis mode of a conventional semiconductor laser, and FIG. 7 is an SEC according to the present invention. An explanatory diagram showing the selectivity of the oscillation axis mode of a semiconductor laser, Fig. 8 is a graph showing the temperature characteristics of the oscillation wavelength of a conventional semiconductor laser, and Fig. 9 shows the temperature characteristics of the oscillation wavelength of a general SEC semiconductor laser. FIG. 10 is a graph showing the temperature characteristics of the oscillation wavelength of the SEC semiconductor laser according to the present invention. 1... Semiconductor laser element, 2... Chip, 3... Mirror, 4...
・Placement plate, 5...Lead wire for power supply. Figure 1 Figure 2 line order) Tension coefficient (X70'deg-') Figure 6 → 2-3 people/deg Figure 7-1 2-3 people/deg -0,7 people/deg

Claims (1)

[Claims] 1. A mounting for mounting and fixing a semiconductor laser element, a reflecting member that returns laser light emitted from one emission end face of the semiconductor laser element to the semiconductor laser element, and the semiconductor laser element and the reflecting member. and a member;
An external cavity semiconductor laser device, wherein the mounting member has a linear expansion coefficient smaller than that of copper.