# NIR photopolymerization for VCSEL-to-fiber single mode connection

Nessim Jebali, Céline Molinaro, Julien Roul, Julie Jermann, Jean Baptiste

Doucet, Benjamin Reig, Véronique Bardinal

► To cite this version:

Nessim Jebali, Céline Molinaro, Julien Roul, Julie Jermann, Jean Baptiste Doucet, et al., NIR photopolymerization for VCSEL-to-fiber single mode connection. VCSEL Day 24 European Workshop, 2024, LAAS-CNRS, Sep 2024, Toulouse, France. hal-04974638

HAL Id: hal-04974638

https://laas.hal.science/hal-04974638v1

Submitted on 3 Mar 2025

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Distributed under a Creative Commons Attribution 4.0 International License
# NIR photopolymerization for VCSEL-to-fiber single mode connection

Nessim Jebaliª, Céline Molinaroᵇ,ᶜ, Julien Roulª, Julie Jermannᵇ,ᶜ,

Jean-Baptiste Doucetª, Benjamin Reigª, Olivier Sopperaᵇ,ᶜ and Véronique Bardinalª

ª Université de Toulouse, CNRS, 7 Avenue du Colonel Roche, 31400 Toulouse, France

ᵇ Université de Haute-Alsace, CNRS, IS2M UMR 7361, F-68100 Mulhouse, France

ᶜ Université de Strasbourg, F-67081 Strasbourg, France

E-mail: bardinal@laas.fr

Coupling VCSELs to optical fibers is a key issue for increasing their use in optical communications and instrumentation systems. However, tolerances on angular tilts and lateral misalignments are tight, especially in the case of single mode (SM) devices. Active alignment methods [1] as well as *in situ* fabrication by using 2-photon polymerization direct laser writing [2] were recently proposed to fabricate optical links between VCSELs and multimode fibers. An alternative solution consists in the creation between both parts a SM self-written waveguide (SWW) by exploiting near-infrared (NIR) photopolymerization (figure 1.a). The specificity of our method (NIR-SM-SWW) is to use a writing wavelength identical to that designed for single mode propagation in the fibers (850nm), leading to a single step NIR photopolymerization process directly transferable to 850nm SM-VCSEL to SM-fiber coupling. For best photochemical conditions, a coupling efficiency as high as 82% (i.e., -0.86 dB loss) was measured for a 300-µm-long SM optical link between two 780HP optical fibers (Figure 1.b) [3]. It is 35 times higher than the coupling measured in the air (2.3 %) and 16 times higher than the coupling measured in the polymer layer (5.06%) at the same distance, demonstrating the creation of a single mode link. A similar connection between a SM-VCSEL and a 780HP fiber has been recently experimentally demonstrated using this process (Figure 1.c).

<figure><img src="image_2.png" /><figcaption>**Fig. 1 (a)** Description of the steps of the NIR-SM-SWW process. (b) Coupling efficiency measurements for fiber-to-fiber distance of 300 µm for different connection configurations (air, polymer layer and SWW). (c) Self-coupling of SM-VCSEL to SM-fiber at 850nm.</figcaption></figure>

## References

[1] M. Grabherr, et al., “Advanced single-mode VCSEL fiber pigtail”, Proc. SPIE 12904, Vertical-Cavity Surface-Emitting Lasers XXVIII, 129040C (13 March 2024)

[2] P. Maier, et al., “3D-printed facet-attached optical elements for connecting VCSEL and photodiodes to fiber arrays and multi-core fibers”, Optics Express, Vol. 30, No. 26, December 19, 2022

[3] N. Jebali, et al., (2024), “Self-written single-mode optical link using a single near-infrared photopolymerization step”, [submitted]