Shizuoka University

Oscillating@with optical fiber

About fiber laser

An Er-doped single mode fiber works as a amplifier. A proper wavelength pumping-light oscillates a light. A fiber laser is a device that can get a laser beam by giving the amplifier feedback. Fig1 shows configuration of bulk laser such as a Ti:Sapphire laser ,and, Fig2 shows that of fiber laser. The difference between a bulk laser and a fiber laser is the medium of the way which lights pass through in the resonator. One is the air; the other is the optical fiber. The fiber laser has some advantages over the bulk laser because of the optical-fiber-medium. The advantages are as follow.
Advantages of fiber laser
(1) Small-sized device
A fiber laser is small device for obtaining laser .By rolling a fiber, the space which is needed for oscillating can be much smaller remaining the cavity which the light passes through appropriate length. On the other hand, a bulk laser needs a long strait line space to oscillate laser.
(2) Stability
Heat and vibration disturb stable oscillating of a bulk-laser, because they make bulk components slide from correct position. On the other hand, fiber laser is strong for heat and vibration, because it is assembled with connectors(called fiber couplers).
(3) High- reliability and Low-loss
Now optical communication is spreading. Low-loss optical fiber is important for a long distance light propagation. And, optical fibers for international communications are required to be highly reliable. For example a submarine cable, once it is laid in the bottom of the sea, it is difficult to repair. So, high- reliability and low-loss fiber is developed, and sold by various manufacturers. Fiber lasers are assembled from such excellent fibers.

Purpose

Assembling a fiber laser, we will get a compact, stable, and, reliable laser-oscillator.

Principle of fiber laser

Fig2 shows the configuration of fiber laser. We will use Erbium-doped-fiber (EDF). EDF is suitable for amplifying and oscillating, because of its high-gain, broad-bandwidth, and, low-noise. Fig3 shows energy level of Erbium. EDF is pumped by 980nm- wavelength-light, and, 1550nm-light is emitted. Pumping light is generated by Laser-diode (LD), and, coupled with EDF by using a WDM-coupler. Polarization beam splitter (PBS) picks up laser-output from resonator.

Aim

Fiber laser is a simply and stable device. Moreover it is a good femtosecond pulse source. Femotsecond laser is interesting for many applications, micromachining, and medical technologies. So various studies of fiber laser for getting higher power and much shorter femtosecond pulse are carried out. We aim to assemble a fiber laser that generates high-power and femtosecond pulse following those studies.