Ultraviolet to Infrared Picosecond Diode Laser Heads  Voted Top Ten at CLEO 2000

LDH 375 to 1550

Fibre coupling of LDH Series laser heads

The standard output of every laser head of the LDH Series is a collimated beam. However, all laser heads of the LDH-Series can also be coupled to optical fibres: multi mode, single mode or polarisation maintaining single mode with different connector types. For the majority of applications an angled FC/APC connector is recommended to prevent backreflections into the fibre that could interfere with the laser stability. Coupling of the laser into an optical fibre has the benefit that the elliptical beam shape is transformed into a round beam at the output of the fibre. For a single mode fibre, the resulting beam is even nicely gaussian shaped. However, fibre coupling also leads to a reduced output at the end of the fibre. Typical coupling efficiencies are around 40% for a single mode fibre and around 80% for a multi mode fibre. Upon request a collimator at the fibre output can also be provided.

	Possible fibre types	Typical coupling efficiency
	Single mode fibre with FC/PC connector FC/APC connector	>40%
	Polarisation maintining single mode fibre with FC/PC connector FC/APC connector	>40%
	Multi mode fibre with FC/PC connector FC/APC connector SMA connector	>80%

Connector types

• FC/APC connectors are recommended for the majority of applications. The output end of this fibre is cut by 8°, which minimizes backreflections into the fibre that might interfere with the laser stability.
• FC/PC connectors have a flat output end. They might be necessary if the fibre needs to be connected to a device that also has a FC/PC connector.
• SMA connectors are only suited for multi mode fibres due to their limited fixation accuracy. They have a flat output end.

Beam shape

Due to diffraction, the beam diverges rapidly after leaving the laser chip, typically at 30 degrees at the vertical (fast) axis by 10 degrees at the horizontal (slow) axis. This leads to an elliptical beam shape after the collimating optics with typical dimensions of 1.5 × 3.5 mm. The beam shape can be influenced using optical fibres or an anamorphotic beam shaper:

	Direct emission All lasers emit a collimated beam with an elliptical beam shape with typical dimensions of 1.5 × 3.5 mm.
	Behind a multi mode fibre In case of a multi mode fibre, the beam shape after the fibre is nearly round. A speckle pattern emerges by interference of multiple modes inside the fibre.
	Behind a single mode fibre In case of a single mode fibre, the beam shape after the fibre is a nice gaussian beam shape as only one mode is transmitted within the fibre