11:lO - lk25 M2.1

8W CW Front-Facet Power from 100 pm-aperture, AI-free, 0.98 ym Diode Lasers with Large Optical Cavity

L.J. Mawst, A. Bhattacharya, J. Lopez and D. Botez University of Wisconsin-Madison, Madison, WI

D.Z. Garbuzov, L. DeMarco and J.C. Connolly David Sarnoff Research Center, Princeton, NJ

M. Jansen, F. Fang and R.F. Nabiev Coherent Laser Group, Torrance, CA

Abstract: By increasing the optical-cavity thickness of InGaAs/InGaP/GaAs (A = 0.98 pm) lasers from 0.2 pm to 1 .O ym the internal loss decreases fivefold to - 1 Scm-1, and the transverse spot size doubles to 0.6 pm (FWHM). As a result, 100 pm-aperture devices emit up to 8.1W CW from their front facets.

High-power, wide-aperture, 0.96 - 0.98 pm diode lasers are needed for applications such as umping solid-state lasers, and medical therapy. There has been recent interest in AI-free 0.98 pm lasersf5 due to several advantages over InGaAdAlGaAs lasers: 1) ease of regrowth(s) for mode-stabilized structures; 2) significantly lower electrica1495 and thermal resistances; 3) and potential for improved reliability. We have recently reported596 on record performances (i.e. 3W CW front-facet power, and 61% CW wallplug efficiencys) from InGaAs/InGaP/GaAs (h = 0.96 pm) devices.

To further improve the devices' performance we have applied the lar e-optical-cavity concept798 for high-

confinement factor, r, by increasing the cavity length, L. Thus, large-optical-cavity (-1 ym) devices of large transverse spot size, and consequently high output power, are obtained8 with little penalty in threshold-current density or efficiency.

Fig. la shows the structure employed: SCH-SL-DQW InGaAs/InGaP/GaAs, where the thickness of the InGaAsP (Eg = 1.62eV) confinement layer, k, is varied above the "conventional" value of 0.2 ym4v5. The devices were grown by low-pressure MOCVD as previously described4; and were LR/HR coated: 3%/95%. Structures with = 0.6 pm have ai =3cm-1, a decrease of more than a factor of 2 compared to t, = 0.2 pm devices4.5. This appears to be due to reduced scattering loss at the confinementlcladding layers' interfaces, and reduced free-carrier absorption loss in the cladding layers. 1 mm-long devices mounted on diamond heatsinks provide up to 6W CW power at 18°C (Fig. 2). A peak wallplug efficiency, qp, of 51% is achieved at 1.7W, in good agreement with theoryg. The relatively small qp decrease with increasing power is a direct consequence of a low series resistance, Rs, value: 0.10.

Increasing b to 1.0 ym further decreases ai to 1.5cm-1, while r decreases to 2.5% compared to 4.6% for = 0.2 pm devices 495. As shown in Fig. lb, 94% of the mode energy resides in the confinement layer.

4"-long devices mounted on copper heatsinks provide up to 8.1 W CW power at 10°C (Fig. 3). qp is above 44% from 2W to 8.1W, with a maximum of 47% in the 3.5 - 4.8W range. The relative constancy of q is due to an extremely low Rs value: 0.050. The characteristic temperature, To, for these devices is -258K. The external differential quantum efficiency reaches values as high as 72%.

The 8.1W CW result represents the highest CW power ever reported from 100 pm-aperture diode lasers. It is 2.7 times higher that the best published data for 0.96-0.98 pm lasers~~*o, and well surpasses the best results from 100 pm-aperture GaAdAIGaAs devices

For both = 1.0 ym devices the power density at catastrophic-optical-mirror-damage (COMD) is =14.5MW/cm2. Applying nonabsorbing mirrors, such as Z I I S ~ ~ . ~ , on oxide-free facets should eliminate COMD and allow CW operation well above 1OW.

power operation. That is, if the internal loss coefficient, ai, is 52cm Q , one can offset decreases in optical

nonabsorbing mirrors11.

= 0.6 ym and

9

1. 2. 3 . 4. 5 . 6. 7.

9. a.

H. Asonen et a], lEEE J. Quantum Electron, a, 415 (1994). M. Ohkubo et al, IEEE J. Quantum Electron, 2 , 4 0 8 (1994). M. Sagawa et al, IEEE J. Select Topics Quantum EIectron, 1, 189 (1995). L.J. Mawst et al. Appl. Phys. Lett., a, 2901 (1995). A.V. Syrbu et al, Electron Lett. 2 , 3 5 2 (1996). A.V. Syrbu et al. Tech. Dig. CLEO ‘96 Conference, Paper C Tu C4, June 2-7 1996, Anaheim, CA. I.B. Petrescu-Prahova et al, IEICE Trans. Electron., E77-C, 1472 (1994). D.Z. Garbuzov et al, Tech. Dig. CLEO ’96 Conference, Paper C Tu CS, June 2-7, 1996, Anaheim, CA. D.P. Bour and A. Rosen, J. Appl. Phys., 46 2813 (1989).

10. D.F. Welch et al, Appl. Phys. Lett, 56, 10 (1990). 11. D.F. Welch et al, Electron Len, a, 115 (1988).

p- t “qv InGaP cladding layer - InGaAsP confinement layer (Eg = 1.62 eV)

(4 quantum.welI(75 A)

InGaAs I InGaP I GaAs A. = 0.966 prn; t c= 0.6 prn t

0 2 4 6 8 Current, A

Fig. 1. Al-free large-optical-cavity laser structure: (a) schematic representation; (b) field intensity profile for a confinement-layer thickness of 1.0 pm.

Fig2 CW light-cunent characteristic and wallplug efficiency for laser structure with = 0.6 pm;

1 mm; LH/HR : 3% / 95%.

1 I InGaAs / InGaP / GaAs

10

0 2 4 6 8 10 12 0

Current, A

- 60

-50 tj?

- 40 5 G .w 0

- 3 0 w M

a - 2 0 3 3 3

-10 g - 0

Fig. 3. CW light-current characteristic and wallplug efficiency for Iaser structure with = 1.0 pm; L = 4 mm; LHIHR: 3% I 95%.

10