Micro-Optics for High-Power Diode Lasers

The new array contains 200 lens elements spaced 48 μm apart. It is effectively double-sided: The entry side collimates the slow axis, the exit side the fast axis of the emitted light. (Source: Ingeneric)

At the Photonics West 2018, Ingeneric presented a new micro-optics module for the collimation of single-mode diode bars for the first time. It helps to exploit the improved brightness and open up new fields of application for laser manufacturers.

Single-mode bars can achieve high performances with their large numbers of single emitters. Also, the beam quality from single emitters is superior to that of broad stripe emitters, as each emitter gives off light in fundamental mode. To make best use of these advantages, an optical module needs to collimate the light beam separately for each emitter. The emitters are tightly packed, so it is necessary to use compact micro-optics with the finest structures. The new collimation module optimizes the utilization of the high performance available from single-mode diode bars, and this opens up potential new applications.

The new monolithic cylindrical lens array “C-SMDB” for single-mode bars achieves high degrees of collimation as it is produced with the process of precision glass molding. The array is effectively double-sided: The entry side collimates the slow axis, the exit side the fast axis of the emitted light.

The production accuracy of the micro-optics is subject to considerably higher demands than is the case with the optics for diodes with broad stripe emitters. The pitch between the individual lens elements on the slow-axis side, for example, must be maintained with extreme accuracy: For two hundred elements, the pitch has to be on average less than five nanometers. The center thickness should ideally be in the range of plus-minus two microns in order to achieve an optimal result.

Ingeneric uses the precision glass molding of the arrays to meet this challenge, a process which the company uses for other micro-optics in its product portfolio. With glass molding, high refractive-index glass very precisely takes on the shape of the pressing tool. The molds, manufactured to sub-micron precision, enable the arrays to be produced with exceptionally high accuracy and reproducibility. Ingeneric successfully manufactures arrays with minimal transition zones, highest filling factors and minimal pitch errors, even in large batches.

Dr. Stefan Hambücker, managing partner of Ingeneric, sees great potential for diode lasers: “For the single-mode bars, we are currently working to demonstrate their functionality and cost-effectiveness in new fields of application. That is why, in terms of optics, we are working very closely with the manufacturers of diode lasers. With high fill factors, excellent utilization of the surface area, extremely high contour accuracy and a good orientation of the surfaces to one another, the C-SMDB is exactly the right product to make the best use of the brightness.”

The new array has a design wavelength of 970 nm. The effective focal length (EFL) of the fast-axis collimation (FAC) is 600 μm with a numerical aperture of 0.8, the EFL of the slow-axis collimation (SAC) is 190 μm, and the pitch of the SAC is 48 μm. There are 200 lens elements on each part. The result is a back focal length (BFL) of 179 microns. (Source: Ingeneric)

Link: Optical Components, INGENERIC GmbH, Aachen, Germany

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