FREQUENCY STABILIZATION OF AlGaAs LASERS BASED ON THE H2O AND Rb-D2 LINES

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FREQUENCY STABILIZATION OF AlGaAs LASERS BASED ON THE H2O AND Rb-D2 LINES

T. Tako, M. Ohtsu, H. Tsuchida

To cite this version:

T. Tako, M. Ohtsu, H. Tsuchida. FREQUENCY STABILIZATION OF AlGaAs LASERS BASED ON THE H2O AND Rb-D2 LINES. Journal de Physique Colloques, 1981, 42 (C8), pp.C8-83-C8-88.

�10.1051/jphyscol:1981810�. �jpa-00221705�

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CoZZoque C8, suppl6ment au n O l 2, Tome 42, de'cembre 2981 page C8-83

FREQUENCY STABILIZATION OF AlGaAs LASERS BASED ON THE H20 AND Rb-D2 LINES

T . Tako, M. Ohtsu and H . Tsuchida

Research Laboratory of Precision Machinery and EZectronics, Tokyo I n s t i t u t e o f Techno logy, 4259 Nagatsuta-cho, Midori-ku, Yokohama, ILznagma 227, Japan.

Abstract: Recent works on frequency stabilization of AlGaAs DH lasers based on absorption lines of H ₂ 0 vapor at 0.81

-

or 85%-D2 line at 0.78pm are reported. The minimum values of the square root of Allan variance are 1.0 x 10-11 and 1.4 x 10-l2 at 100s of averaging time, respectively.

$1. Introduction

Recently, spectral properties of semiconductor lasers have been improved. A stable single longitudinal and transversal mode oscillation has been obtained for AlGaAs double heterostructure

(DH) lasers and the spectral widths of these lasers have been

estimated to be narrower than 1 MHz by interferometric measurements 1)

.

The frequency stability as well as the spectral width is a very important factor for many applications, such as heterodyne-type optical communication, high resolution spectroscopy, precise metrology and so on.

There have been several reports on the frequency stabilization of semiconductor lasers by using a Fabry-Perot interferometer as a frequency reference. 2-7' In our previous workI7) the frequency of AlGaAs lasers was stabilized at the resonant frequency of a

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981810

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interferometer, which was controlled by a Lamb dip stabilized 633nm He-Ne laser. By controlling the injection current, the frequency stability of 2.lxl0-~ 2 q 2 2.0~10-l1 for lOmsl r 2 500s was obtained, where a and T represent the square root of the Allan variance and integration time, respectively.

Direct frequency locking of semiconductor lasers based on atomic or molecular lines is important for the use of frequency standards. Ohi reported the frequency stabilization of a PbSnTe laser to methane absorption lines in the v 4 band at about 7.7pm 8 1 and Yabuzaki et al. reported the frequency stabilization of a GaAlAs laser to the Cs-D2 line at 852.lnm. 9)

In this paper the frequency stabilization of AlGaAs lasers based on the absorption lines of water vapor and the hyperfine components of 8 5 ~ b - ~ 2 line are presented.

$2. Frequency stabilization based on H20 lines

H20 molecule has a vibration-rotation band (0,0,0)-(2,1,1) at 0.81

--

.

I , I I I

8150 8200 8250 8300 Fig. 1.

Wavelength (A)

A single mode AlGaAs DH laser CCSP type1')) was used. The threshold current was about 80 mA. The dependence of the laser frequency on the injection current was measured to be (-2.75) GHz/mA by using an interferometer. The laser frequency was tuned in the range of 822.5

-

-

An absorption cell of lOcm length with pure water drop was used at room temperature (the corresponding vapor pressure being about 20 Torr). The laser beam was focused on an APD after passing through the absorption cell. The first, second, and third

derivative signals of the transmission spectrum of H 0 vapor 2

was obtained by Synchronously detecting with a lock-in amplifier.

Figure 2 shows typical examples of records. The upper and lower traces represent the first and second derivative signals of the transmission spectrum, respectively. The lines marked (0)

correspond to that assigned by Baumann and Mecke and the lines marked (x) are unassigned. At present we have found several tens unknown lines.

L

120 125 130

Injection Current I (mA)

Fig. 2.

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Next, the frequency of AlGaAs DH lasers have been stabilized in refer to one of H20 absorption lines, P(O-l-l). The third derivative signal shown in Fig. 3 was used as a frequency dis- criminator. The square root of the Allan variance a 2 is shown at Curve A in Fig. 4. Curves A and B represent the stabilities of the free reunning laser and the stabilized laser by using a Fabry-Perot interferometer and a Lamb dip stabilized 633nm He-Ne laser for co~nparison.~) The value of a on curve A is better than that of curve B and is nearly proportional to T-~'~. The minimum value on this curve is

a = l x 1 0 -I1 at = 100s

I fm= 5 kHz

im"0.5 mAp-p

-

Fig. 4 Fig. 3

$ 3 . Freuquency stabilization to Rb-D2 line

Preliminary experiments are carried out on the frequency stabilization of another AlGaAs laser to a hyperfine component of Rb-DZ line at 780.0nm. Figure 5 represents the spectral profile

(the upper trace) and the first derivative (the lower trace) in case of linear absorption for a 85Rb cell without buffer gas at room temperature (the corresponding vapor pressure of Rb being

-loe5 Torr). Figure 6 represents the result on the freuqency stabilization to the F=3 components. The minimum value of0

PS

and is several times better than the results on the H20 stabilized laser in Fig. 4.

1 . _{6 2 63}

6 4 65

Injection Current I ( m A )

+ Frequency

62 63 6 4 6 5

Injection Current I ( m A 1

Fig. 5.

0 10-

1

1

Fig. 6.

The saturated absorption spectrum of Rb-D2 line was also observed as shown in Fig. 7 and the stabilization experiment to this spectrum is in progress.

I I I I

6 2 63 64 65

Injection Current I ( mA) Fig. 7.

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References

1) T. Takakura, K. Iga and T. Tako: Jpn. J. Appl. Phys. 19 (1980) L725.

2) Yu. A. Bykovskii, V. L. Velichanskii, I. G. Goncharov and V. A. Masrov: Sov. Phys.-Semicond. 4(1970) 580.

3) J. L. Picque and S. Roizen: Appl. Phys. Lett. 27 (1975) 340.

4) T. Okoshi and K. Kikuchi: Electron. Lett. 16(1980) 179.

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61 H. Tsuchida, S. Sanpei, M. Ohtsu and T. Tako: Jpn. J. Appl.

Phys. 19 (1980) L721.

7) H. Tsuchida, M. Ohtsu and T. Tako: Jpn. J. Appl. Phys. 20 (1981) L403.

8) M. Ohi: Jpn. J. Appl. Phys. 19(1980) L541.

9) T. Yabuzaki, T. Ibaragi, H. Hori, M. Kitano and T. Ogawa:

Jpn. J. Appl. Phys. 20(1981) L451.

10) W. Baumann and R. Mecke: Zeit. Physik. 81(1933) 445.

11) K. Aiki, M. Nakamura, T. Kuroda, J. Umeda, R. Ito, N. Chinone and M. Maeda: IEEE J. Quantum Electron., QE-14 (1978) 89.