ABSTRACT

We provide multi-watt class red, green, and blue lasers as a solid state light source solution for projectors and other display applications. Life tests demonstrated over 38,500 hours of actual operation for green and blue lasers. The test for red laser has passed 7,000 hours under acceleration test condition and is going on.

1. INTRODUCTION

Solid state light source based on semiconductor technology has a lot of attractive properties as a light source for projectors^1,2) such as long life and quick start. We provide multi-watt class red, green, and blue lasers as a solid state light source solution. The wavelengths of these red, green, and blue lasers are 639 nm, 532 nm, and 465 nm, respectively. The red (Model NECSEL-640-5000) is a direct-emitting laser diode with continuous wave output power of 5 W. Both green (Model NECSEL-532-3000) and blue (Model NECSEL-465-3000) are Necsel type laser diodes with output power of 3 W^3,4). This paper reviews the technology used for these laser product s and di scus ses the reliability based on measured life test data.

2. Laser structures and Life tests

This chapter reviews typical properties and life test results of each laser.

2.1 Green and blue lasers

Both green and blue are unique Necsel-type laser diodes with output power of 3 W shown in Fig. 1 [3,4].

The Necsel-type laser diode is an intra-cavity, frequency doubled type visible laser diode, which is composed with an infrared (IR) VCSEL (Vertical Cavity Surface Emitting Laser) array and a nonlinear optical crystal (PPLN：Periodically Poled Lithium Niobate) for blue of 465 nm and green of 532 nm. For both green and blue Necsel type laser diodes of the first generation, diamond was used as the submount material for excellent thermal conductivity. The life test result shown in Fig. 2 demonstrates that the laser output power is almost the same as the initial after 35,000 hours. This corresponds to over 10-year of use if it is used ten hours per day,seven days per week, and 50 weeks per year , which would be very typical for projection applications.

Generation 3 in Figs . 3 and 4 is the present product employing Cu-plated AlN as the submount material for matching of coefficients of thermal expansion with the GaAs die and copper cooling plate.

The life test result in Fig. 3 demonstrates that the laser output power is almost the same as the initial after 19,400 hours under the accelerated test condition of T_necsel = 50°C, corresponding to 38,800 hours for the rated temperature of Tnecsel = 40 °C.

The on-off test result in Fig.4 demonstrates that the laser output power is almost the same as the initial for the third generation after over 25,000 on-off cycles. Thermal stress was applied to confirm the stable operation at a variety of installation sites. The initial laser power level was set at 3 W. The temperature of T_necsel moved between 28 °C and 40 °C in one on-off cycle. Each on-off cycle has typically a 20-minute on-state to heat the laser by self-generating heat and a 20-minite off-state to cool the laser by forced air flow. The result shows that after over 25,000 on-off cycles, the laser output power is almost the same as the initial. This corresponds to over 14-year of use if these are used five times on-off per day, seven days per week, and 50 weeks per year, which would be very typical for cinema projection applications.

2.2 Red laser

Fig.5 shows di rec t emitting LD; (a) with collimation lens option, and (b) with fiber coupling option.

Fig.6 demonstrated that the laser output power is stable over 7,000 hours after some decrease during initial hundreds hours under an output power acceleration test condition of 6 W which is higher than the rated 5 W by 1 W. The acceleration factor is not discussed concretely here. However, it looks very promising to operate the laser much longer time at the rating of 5 W.

3. Conclusions

The life tests demonstrated over 38,500 hours of actual operation for both green and blue laser diodes. The test for red laser has passed 7,000 hours under acceleration test condition and is going on. We believe these reliable lasers are suitable for light sources for projectors and other displays.