**7. References**


In conclusion, three tunable high-power narrow-spectrum red diode laser systems based on tapered semiconductor optical amplifiers in Littrow external-cavity are demonstrated. The epitaxial structruce and the geometry of these tapered devices are described, and the data on

For diode laser system A at 668 nm, an output power of 1.38 W is obtained with an injected current of 2.0 A, and the laser system is tunable from 659 to 675 nm with output power over 800 mW. This is to our knowledge the highest output power from a tunable diode laser system in this wavelength range. The spectral bandwidth of the output beam is less than

Both diode laser system B and C are tunable in a 20 nm range centered at 675 nm, and the spectral bandwidth of the output beam for both diode laser systems is less than 0.07 nm in their tunable ranges. The maximum output power is 1.25 W obtained from laser system B at the wavelength of 675.3 nm, and the maximum output power from laser system C is 1.05 W obtained at the wavelength of 675.6 nm. The beam quality factor *M*2 is 2.07 with the output power of 1.0 W for laser system B, and the *M*2 value is 1.13 with the output power of 0.93 W for laser system C. Laser system C is used as the pump source for the generation of UV light by single-pass frequency doubling in a BIBO crystal. An output power of 109 µW UV light at

The authors acknowledge the financial support of the European community through the

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**5. Conclusion** 

0.07 nm.

**6. Acknowledgment** 

**7. References** 

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**7** 

*Malaysia* 

**Doped Fiber Amplifier Characteristic** 

Siamak Emami1, Hairul Azhar Abdul Rashid2,

Sulaiman Wadi Harun1 and Harith Ahmad1

Seyed Edris Mirnia1, Arman Zarei1,

*1University of Malaya Malaysia, 2Multimedia University Malaysia,* 

**Under Internal and External Perturbation** 

Significant effort has been made in recent years to improve the Doped Fiber amplifier gain and noise figure. Extend the optical bandwidth of doped fiber amplifiers beyond the traditional 1550nm band, making the excellent EDFA characteristics available in a wider spectral region also was the main effort in optical amplifier fields. Several techniques have been developed to improve gain and shift the gain to the shorter wavelength region. In this chapter, the effects of external perturbation such as macro-bending and fiber length and internal perturbation such as transversal distribution profile and doped concentration on

A macro-bending approach is demonstrated to increase a gain and noise figure at a shorter wavelength region of EDFA. The conventional double-pass configuration is used for the EDFA to obtain a higher gain with a shorter length and lower pump power. The macrobending suppresses the ASE at longer wavelength to achieve a higher population inversion at shorter wavelengths. Without the bending, the peak ASE at 1530nm, which is a few times higher than the ASE at the shorter wavelength, would deplete the population inversion and

Macro-bending is introduced as a new method to increase gain flatness and bandwidth of EDFA in C-band region. Varying the bending radius and doped fiber length leads to the optimized condition with flatter and broader gain profile. Under the optimized condition, gain at shorter wavelengths is increased due to increment of population inversion which results in gain reduction in the longer wavelength regions. The balance of these two effects in the optimized condition has a significant result in achieving a flattened and broadened

This technique is also capable to compensate the fluctuation in operating temperatures due to proportional temperature sensitivity of absorption cross section and bending loss of the aluminosilicate EDF . This new approach can be used to design a temperature insensitive EDFA for application in a real optical communication system which operates at different environments but still maintaining the gain characteristic regardless of temperature variations. The effect of macro-bending on high concentration EDFA using optimized

doped fiber performance have been demonstrated (S.D.Emami et al., 2010).

**1. Introduction** 

suppresses the gain in this region.

gain profile.

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