Prisms

I'm new to optical design and I'm greatful for optiland as a playground to learn. There are a lot of great examples/tutorials, but I didn't see any involving prisms so I thought I would share my experience in getting a 180 degree fold prism to work. I created a helper function that greatly simplifies accumulated thickness with persistent angle changes (it handles Z and Y computation) as well as offsets perpendicular to the local optical axis. TIR didn't seem to work so I added the mirror surfaces to the prism definition. Let me know if there is a way to fix that.

import numpy as np
import math
import matplotlib.pyplot as plt
from optiland.optic import Optic

WAVELENGTHS = (0.4861, 0.5876, 0.6563)  # F, d, C
EPD = 45
HALF_FOV = 2
 
def apply_system_spec(lens: Optic) -> Optic:
    """Apply the aperture, fields and wavelengths from the requirements."""
    lens.set_aperture(aperture_type="EPD", value=EPD)
    lens.fields.set_type("angle")
    for y in (0.0, 0.7 * HALF_FOV, HALF_FOV):
        lens.fields.add(y=y)
    for value in WAVELENGTHS:
        lens.wavelengths.add(value=value, is_primary=(value == 0.5876))
    return lens

yg=0
zg=0
rxg=0
idxg=0
lensg=None

def addSurface(prerotation=0, thickness=0, offset=0, rotation=0, *args, **kwargs):
    global yg, zg, rxg, idxg, lensg
    if lensg == None:
        lensg = Optic()
        lensg.surfaces.add(index=0, thickness=np.inf)
        idxg = 1
    print(f"Adding surface {idxg} at z={zg}, y={yg}, rx={rxg*180/math.pi}deg, parameters={args} {kwargs}")
    lensg.surfaces.add(*args, **kwargs, index=idxg, z=zg, y=yg, rx=rxg)
    rxg += prerotation
    zg += thickness * math.cos(rxg) + offset * math.sin(rxg)
    yg += thickness * math.sin(rxg) + offset * math.cos(rxg)
    rxg += rotation
    idxg += 1

# ThorLabs 2" diameter 500mm focal length achromatic doublet
def THOR_ACT508_500_A(flip=False):
    if flip:
        m1 = "N-SF2"
        m2 = "N-BK7"
        r1 = 471.2
        r2 = 182.1
        r3 = -382.5
    else:
        m1 = "N-BK7"
        m2 = "N-SF2"
        r1 = 382.5
        r2 = -182.1
        r3 = -471.2
    addSurface(thickness = 6.0, material=m1, is_stop=True, radius=r1)
    addSurface(thickness = 6.0, material=m2, radius=r2)
    addSurface(radius=r3)

# ThorLabs 60mm face right angle prism
def THOR_PS913(ccw=False):
    if ccw:
        stepAng = np.pi/4
    else:
        stepAng = -np.pi/4
    addSurface(thickness=42.42640687/2, rotation=stepAng, material="N-BK7")
    addSurface(material="mirror")
    addSurface(thickness=42.42640687, prerotation=stepAng, rotation=stepAng, material="N-BK7")
    addSurface(material="mirror")
    addSurface(thickness=42.42640687/2, prerotation=stepAng, material="N-BK7")

# Build the system
THOR_ACT508_500_A()
addSurface(thickness=240, offset=5)
THOR_PS913()
addSurface(thickness=200)
addSurface()

lengs = apply_system_spec(lensg)

fig,ax = lensg.draw(num_rays=10)
plt.show()