feed optical fibre.

[mxhf]

All,

I would like to design a piece of optics that feeds and optical fibre. I have a fairly tight requirement that the fire need to be fed around F/#=3.5. Is there a way/operand etc. to constrain the F/#?

Also, in susch a system one want to image to pupil onto the fibre. Is there a specific way in optiland to set the fibre surface as conjugate to the pupil?

Any help would be much appreciated.

Max

[HarrisonKramer]

Hi @mxhf,

Thanks for the questions.

You can specify the F/# via the set_aperture method of Optic. You can also set the EPD, then optimize for a target effective focal length (f2).

To constrain the pupil onto the fibre, you can force the chief ray to a height of zero on the fibre surface via optimization. See the optimization examples in the docs.

Regards,
Kramer

[mxhf]

Dear Kramer, thank you so much for your reply. I believe the EPD won't work as I have a telescope+lens system? The EPD is set py the telescope aperture. Another way may be to set the marginal ray slope I suppose? Could you give guidance on how to do this and how to force the chief ray height? I have looked though the docs, I *believe* this is not covered? Max

…

--- my strawman design --- scale = 100 lens = optic.Optic() # add surfaces index_cnt = 0 lens.add_surface(index=index_cnt, thickness=np.inf) index_cnt += 1 lens.add_surface( index=index_cnt, thickness=-40*18*scale + 20, radius=-1440*scale, conic=-1, material="mirror", is_stop=True, ) index_cnt += 1 lens.add_surface( index=index_cnt, thickness=-1, radius=-8.6, conic=0, material="N-SF11", is_stop=False, ) index_cnt += 1 lens.add_surface( index=3, thickness=-4, radius=10.7, conic=0, is_stop=False, ) index_cnt += 1 lens.add_surface( index=index_cnt, thickness=-1, radius=-23, conic=0, material="N-SF11", is_stop=False, ) index_cnt += 1 lens.add_surface( index=index_cnt, thickness=0, radius=np.inf, conic=0, is_stop=False ) index_cnt += 1 fibre_aperture = EllipticalAperture( a=.1, b=.1 ) lens.add_surface(index=index_cnt, aperture=fibre_aperture) # set aperture lens.set_aperture(aperture_type="EPD", value=40*scale) # add field lens.set_field_type(field_type="angle") lens.add_field(y=0) lens.add_field(y=.1/3600. )#

On Tue, Dec 9, 2025 at 9:42 PM Kramer ***@***.***> wrote: Hi @mxhf <https://github.com/mxhf>, Thanks for the questions. You can specify the F/# via the set_aperture method of Optic. You can also set the EPD, then optimize for a target effective focal length (f2). To constrain the pupil onto the fibre, you can force the chief ray to a height of zero on the fibre surface via optimization. See the optimization examples in the docs <https://optiland.readthedocs.io/en/latest/gallery/optimization.html>. Regards, Kramer — Reply to this email directly, view it on GitHub <#410 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB2AZSTARTPPM2B5EYTXD534A4X4ZAVCNFSM6AAAAACOLTYQK6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTKMRRGI2TQMI> . You are receiving this because you were mentioned.Message ID: ***@***.*** com>

[HarrisonKramer]

Hi @mxhf,

You should be able to manually set the EPD, which will remain a constant, while also enforcing via optimization a target effective focal length. This allows you to constrain the F/#, which is simply the ratio of the two.

You can also enforce ray angles by using the real_N operand, which is the real ray direction cosine. You will need to supply the normalized field and pupil coordinates for either the marginal or chief ray, whichever you are using. See the code here. I'd also recommend looking at the optimization examples referenced above to see how it fits together.

Kramer