Fiber Coupled Laser Diode Types

There are two main types of fiber coupled laser diode (LD).

• Single-mode fiber coupled laser diode. The core is usually several micrometers. (For example, the core is 6μm at a wavelength of 1μm and 9μm at a wavelength of 1.5μm)

• Multi-mode fiber coupled laser diode. It uses larger diameter fibers, which can handle greater optical power. The core is typically 62, 100, 200, 400, 800, or even 1000μm. In applications, the smaller the diameter, the easier it is to focus the light from the fiber to a small point using a lens or microscope objective.

Single-mode fiber coupled laser diode

Single-mode fiber coupled laser diode can be standard fiber (SMF) or polarization-maintaining fiber (PM). The difference is that in polarization-maintaining fiber, the fiber has a special cladding structure that allows the polarization of the light to be maintained along the length of the fiber.

Single-mode fiber coupled laser diode is typically packaged in what is known as a "butterfly" package. Its TEC cooler and thermistor are integrated into the package. This type of single-mode LD typically achieves output powers of several hundred mW, with a maximum of up to 1.5W.

Additionally, in the communication field, there are DIL packages and coaxial packages. Their power is usually <10mW.

Multi-mode fiber coupled laser diode

Multi-mode fiber coupled laser diode is based on broad area emitting laser diode chips and come in 4 types:

• Single emitter: The LD chip is isolated, assembled on a submount, and individually packaged in a semiconductor laser diode module, coupled to a 105/125μm multi-mode fiber, with a power of up to 15W.

• Multi-emitter: Multiple LD chips are individually isolated and optically coupled together in a multi-mode fiber. The output power can reach several hundred watts, while maintaining a small fiber size, such as 100 or 200um core diameter.

• Single bar: Multiple emitters assembled as a single bar in an LD module, coupled to a 200/240μm multi-mode fiber, with a power of up to 50W.

• Multi-bar: Multiple emitters assembled in a large water-cooled package, then coupled to a large diameter (600/800μm) multi-mode fiber, with power exceeding 100W.

In multi-mode fiber coupled laser diodes, attention needs to be paid to how the voltage and current of different types of LDs vary:

• Single emitter has a voltage level of 1.5V and a current of 15A.

• Multi-emitter is in series excitation. This means that the current does not change (usually a maximum of 15A), but the voltage increases with the number of emitters. (For a 60W LD, the voltage and current are 4.5V/15A)

• Single bar is parallel emitters. Therefore, the voltage does not change, but the current can easily reach 45 or 50A.

• Multi-bar is a series connection of multiple single bars. Therefore, its current (e.g., 45A) does not change, but the voltage increases with the number of bars.

These types of fiber coupled laser diodes are widely used in communication, sensing, and other technology fields requiring laser output.