Lecture week 10

Directional coupler
Student: Luzian Lebovitz
Goal
The goal of this project is to make a directional coupler with defined power ratio for the two output
branches at the operating wavelength of λ = 1550 nm. In the first coupler design, power should be
equally split between two arms (50/50) with minimal overall losses, and in the second one there should
be 90/10 splitting of the power in the arms.
Milestones
1. Literature search. The first milestone is to familiarize with the theory behind direct coupling.
The most important is to answer to questions of which parameters are playing the crucial role.
2. Single mode waveguide. The design of a single mode Silicon waveguide (at λ = 1550 nm), using
the eigenmode solver of COMSOL. The material of the core is Silicon, while the cladding is SiO2.
3. Bending losses. The curvature for the coupling section should be evaluated so as little light as
possible is lost in the bending section. The structure should be symmetric, so one bending
radius optimization is needed.
a. NOTE: if you want, you could do asymmetric structure, but that would require 2 bend
loss calculation. However, if you have an idea and good reason to do it, you are
welcome to try!
4. Putting the things together. In the last step, the entire structure is put together, and the
coupling section length is changed so the power ratio can be plotted. Additional optimization
step requires for sweeping the distance between waveguides so the minimum coupling length
can be achieved. Reading out the power in the upper (lower) arm from this plot can reveal the
two desired coupling structures.
5. Convergence. The final structure should be tested with smaller mesh size.
6. 90/10 directional coupler. After the convergence test, the design should be adapted power
ratio in the two arms is 90%/10%.
7. Report and presentation. The results of the project should be summarized in the form of a
short report and 15 minutes presentation (10 minutes talk and 5 minutes for questions).
References

B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

Leuthold, J. (2014). Optics and Photonics (Script). Zurich.

Refractive Index: http://refractiveindex.info/?shelf=main&book=Si&page=Salzberg
Ring Resonator
Student: Pascal Stark
Goal
The goal of this project is to design and simulate a Silicon ring resonator for filtering purposes in a drop
configuration. The device should be optimized for an operating wavelength of 1550nm. In a second
step, a cascaded multi ring resonators device has to be designed. In this configuration, rings with
varying radius in series have to form an add/drop circuit with 50/50 power distribution. Fig. 2 shows
an implementation example.
Milestones
1. Literature search. The first milestone is to familiarize with the theory behind ring resonator.
The most important is to answer to questions of which parameters are playing the crucial role.
2. Single Mode Waveguide. Design a single mode Silicon waveguide (at λ = 1550 nm), using the
eigenmode solver of COMSOL. The material of the core is Silicon, while the cladding is air.
3. Ring Resonator. The ring resonating at 1550nm has to be designed for minimal radius with
minimal bending losses.
4. Single Ring Filter. The coupling between the waveguide and ring resonator has to be optimized
for > 20dB extinction ratio.
5. Cascaded Structure. An add/drop filter design with cascaded ring resonator in series has to be
designed. The power distribution should be optimized to 50/50.
6. Report and presentation. The results of the project should be summarized in the form of a
short report and 15 minutes presentation (10 minutes talk and 5 minutes for questions).
References

B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

Leuthold, J. (2014). Optics and Photonics (Script). Zurich.

Refractive Index: http://refractiveindex.info/?shelf=main&book=Si&page=Salzberg
Delay Interferometer (2 students)
Students: Sebastian and David Hug
Goal
The goal of this project is to design and simulate a delay interferometer for the purpose of verifying
the coherence of a light source. This project can be divided into two main work. One is the design and
optimization of the coupling, which should be implemented based on a direct coupling scheme.
Second, a delay line should be designed and optimized for a π-shift. Both designs should have minimal
losses and optimized for the operating wavelength of 1550nm.
Milestones
Milestones
1. Literature search. The first milestone is to familiarize with the theory behind Delay
Interferometers. Important is also the theory about direct coupling.
2. Single mode waveguide. The first milestone is to design a single mode Silicon waveguide (at λ
= 1550 nm), using the eigenmode solver of COMSOL. The material of the core is Silicon, while
the cladding is air. In both, the coupling scheme and the delay line, the waveguide dimension
are the same.
3. Bending losses for coupling. The curvature for the coupling section should be evaluated so as
little light as possible is lost in the bending section. The structure should be symmetric, so this
is needed to be done only once.
4. Bending losses for delay line. The curvature for the delay line should be optimized for minimal
loss of power. In addition, bending radius for the reference line should be optimized for
minimal losses as well.
5. Coupling scheme. The coupling design for splitting and combining the power has to be
designed. The splitting ratio should be 50/50 and the combining ratio 90/10. Additional
optimization step requires for sweeping the distance between waveguides so the minimum
coupling length can be achieved
6. Delay line. Based on the optimized curvature the delay line length should be designed for a πshift (wavelength of 1550nm). Do not forget the additional phase delay in the reference line!
7. Putting the things together. In the last step, the entire structure has to be assembled, and the
π-shift should be verified by calculating the extinction ratio on the output lines (> 10dB).
8. Convergence. The final structure should be tested for the mesh size.
9. Report and presentation. The results of the project should be summarized in the form of a
short report and 15 minutes presentation (10 minutes talk and 5 minutes for questions).
References

B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

Leuthold, J. (2014). Optics and Photonics (Script). Zurich.

Refractive Index: http://refractiveindex.info/?shelf=main&book=Si&page=Salzberg
Bragg Mirror
Student: Zhijian Pan
Goal
Goal of this project is to design a Bragg mirror with specified reflectivity R = 99% at the operating
wavelength of λ = 1550 nm. In the first design, only one wavelength will be considered. In the second
run, a range of wavelengths will be considered, so that 3dB (half of the power) reflectivity can be
achieved over range of wavelengths.
Milestones
1. Literature search. The first milestone is to familiarize with the theory behind the Bragg mirror.
The most important is to answer to questions which parameters are playing the crucial role.
2. Single mode waveguide (COMSOL). The following milestone is to design a single mode Silicon
waveguide (at λ = 1550 nm), using the eigenmode solver of COMSOL. The material of the core
is Silicon, while the cladding is SiO2.
3. Infinite Bragg mirror. The next milestone is to perform theoretical calculations of the infinite
Bragg mirror (2 physical dimensions are infinite), so the starting design points (number of
periods, filling factor and period) for COMSOL simulations could be chosen (see Figure 1).
4. COMSOL simulation of the mirror. Once the initial parameters are known, the Bragg mirror
should be simulated in COMSOL with the following goals:
a. Reflection coefficient of 99% for 𝜆𝑐 = 1550 nm
b. Reflection coefficient >3dB for 𝜆𝑐 ± 100 nm
5. Convergence test. The results should be tested for different mesh sizes.
6. Report and presentation. The results of the project should be summarized in the form of a
short report and 15 minutes presentation (10 minutes talk and 5 minutes for questions).
Λ
dSi
Figure 1: The Bragg mirror. The most important design parameters are the period (Λ), then thickness of the Si part (dSi), as well as
filing factor ff = dSi/Λ and number of periods N.
References

B. E. A. Saleh, M. C. (2007). Fundamentals of Photonics (2nd ed.). Wiley.

Leuthold, J. (2014). Optics and Photonics (Script). Zurich.

Refractive Index: http://refractiveindex.info/?shelf=main&book=Si&page=Salzberg