Directional Coupler based Polarization Beam Splitter using - - PowerPoint PPT Presentation

Directional Coupler–based Polarization Beam Splitter using dissimilar waveguides in InP Membrane on Silicon (IMOS)

Andreou S., Millan Mejia A.J., Smit M. K., Van der Tol J.J.G.M.

Content

• 1. Introduction
• InP Membrane On Silicon (IMOS)
• Polarization Beam Splitters (PBS)
• Slot waveguides
• 2. Coupled Mode Theory (CMT)
• 3. PBS structure
• 4. Simulation Results
• 5. Conclusions

InP Membrane On Silicon (IMOS)

• New photonic integration

platform

• Photonic Membrane technology
• InP Membrane: Optical layer
• Silicon: Electronics below
• High index contrast → high

confinement

• Light generation

Polarization Manipulation

• Polarization can add

functionalities to PICs

• Effective manipulation of

polarization states

• Various PBS’s
• Mach Zehnder
• Directional Coupler
• Mode evolution device

Slot waveguides

• Geometrical birefringence
• EM boundary conditions:
• TE mode is strongly

confined in the slot region (low index)

• TM mode changes very

slightly

• Normal waveguide

fabrication

• b

b

• a 0 a

x

ns nH nH nc nc

TE TM

Coupled Mode Theory (CMT)

• Power is evanescently

coupled from one waveguide to the other

• Two system modes: even

and odd

• Power is completely coupled

at 𝑴𝒅 =

𝝆 𝜸𝒇−𝜸𝒑

Coupled Mode Theory (CMT)

• If 𝜸𝒅𝒑𝒔𝒇𝟐 − 𝜸𝒅𝒑𝒔𝒇𝟑 ≠ 𝟏 total power transfer cannot be

achieved

• One of the two polarization states should be

completely transferred

5 10 15 20 25 30 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Length [um] Power in the two waveguides Core 1, β1  β2 Core 2, β1  β2 Core 1, β1 = β2 Core 2, β1 = β2

Effective indices

• TM is roughly the same, TE substantially differs
• For TM → Complete power transfer is possible
• For TE → Complete power transfer is not possible

200 220 240 260 280 300 320 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 Ridges width [nm] Neff

TE TM

300 320 340 360 380 400 420 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 Waveguide width [nm] Neff

TE TM

Normal waveguide Slot waveguide

PBS Structure

Bar, TE→ Cross, TM → Coupling Region Input → S-bend Length

Top View Coupling region cross section

• TE → even number of

crossings

• TM → odd number of

crossings

• S-bend contributions are

taken into account

SiO2

Ridge width Gap Slot width Waveguide width Membrane Thickness

Performance – FDTD Simulation

1.5 1.51 1.52 1.53 1.54 1.55 1.56 1.57 1.58 1.59 1.6

• 25
• 20
• 15
• 10
• 5

5 10 15 20 25 Wavelength [um] ERTE -TM [dB]

Bar Cross

Extinction ratio: 18 – 25dB for the whole C - band

Bar, TE→ Cross, TM → Input → 14μm

𝑴𝒅 [μm] TE 2.57 TM 5.4

Fabrication Error Tolerance

• Fabrication error: deviation

from design widths

• Extinction ratio >10dB for a

width deviation up to 30nm

• Acceptable for IMOS

platform

5 10 15 20 25 30

• 25
• 20
• 15
• 10
• 5

5 10 15 20 25 Fabrication error [nm] ERTE - TM [dB]

Bar Cross

Conclusions

• A 14 μm long PBS for membrane technology is

proposed and simulated

• The PBS exhibits high extinction ratio for the whole

C–band

• Fabrication comparable to normal waveguides
• The device has acceptable fabrication tolerances
• It can be used for polarization diverse applications