In this presentation, our technology development team explores the cutting-edge technology of Silicon Photonics MZ Modulator and its advantages in the optical networking industry. We will delve into the key benefits offered by MZ Modulators, including high working frequency, minimal frequency chirp, small wavelength dependence, and a high electro-optical coefficient. Join us on this journey of innovation and discover how MZ Modulators are transforming the landscape of optical networking. Moreover, GIGALIGHT is pushing the boundaries of optical networking devices and has released the advanced 400G DR4+ 10km optical modules recently which deliver high-performance solutions that meet the demands of the modern data-driven world. Embrace the future of optical networking with our series of silicon photonics optical modules. If you need any technical support don't hesitate to contact us at sales@gigalight.com and browse more products details on https://www.gigalight.com/

1. Module and System R&D Depar tment 2023

2. Silicon Photonics MZ
Working Principles
01
Silicon Photonics MZ
Quad Lock Point
02
Silicon Photonics High
and Low Temp MPD
Drift Compensation
03

4. Therefore, the optical signal can be modulated by controlling the
voltage.
When the optical path difference between two beams of light is an integer
multiple of the wavelength, they will interfere constructively.
When the optical path difference is half a wavelength multiplied by an
odd number, they will interfere destructively.
The input light wave is divided into two equal beams at a Y branch after
passing through a section of the optical path: they are transmitted
through two optical waveguides. The optical waveguides are made of
electro-optical materials whose refractive index varies with the magnitude
of the applied voltage, so that the two light signals arrive at the 2nd Y
branch respectively to produce a phase difference.
01/ Silicon Photonics MZ Working Principle
Based on Mach-Zehnder interferometer principle, its struture is as below:

5. 01/ Silicon Photonics MZ Working Principle
Ordinary silicon optical modules are mainly used for intensity modulation, as shown in the figure below:
Variation curve of MZM output power with modulation voltage
If the signal is loaded at the min point (marked 7 in the figure)
and the max point (marked 9 in the figure), the obtained signal is
an almost DC signal marked 10 and 12 in the figure, which is not
suitable for the intensity modulation scene;
If the signal is loaded at the quad point (marked 8 in the figure),
the modulated signal marked 11 in the figure can be obtained.
At this time, the optical power drops 3dB relative to the max
point, which is the best working point;
It can be seen from the figure that if the working point moves up
from the quad point, the output optical power will increase, and
the ER of the signal will decrease; if the working point moves
down from the quad point, the output power will decrease and
the ER will increase.
01
02
03

6. E m p o w e r i n g I n n o v a t i o n : H a r n e s s t h e p o w e r o f
a d v a n c e d m o d u l a t i o n c o d i n g a n d u n l e a s h n e w
p o s s i b i l i t i e s i n d a t a t r a n s m i s s i o n . O u r h i g h
e l e c t r o - o p t i c a l c o e f f i c i e n t e n a b l e s c u t t i n g - e d g e
a p p l i c a t i o n s a n d o p t m i z e d s y s t e m p e r f o r m a n c e .
S e a m l e s s I n t e g r a t i o n : E m b r a c e c o m p a t i b i l i t y
a n d s i m p l i c i t y . O u r S i l i c o n P h o t o n i c s M Z
M o d u l a t o r s e a m l e s s l y i n t e g r a t e s w i t h
e x i s t i n g f i b e r o p t i c i n f r a s t r u c t u r e , m a k i n g
a d o p t i o n a n d i n t e g r a t i o n h a s s l e - f r e e .
01/ Silicon Photonics MZ Working Principle
U n l e a s h t h e S p e e d : E x p e r i e n c e l i g h t n i n g - f a s t
d a t a t r a n s m i s s i o n w i t h o u r S i l i c o n P h o t o n i c s M Z
M o d u l a t o r , e n a b l i n g r a p i d c o m m u n i c a t i o n f o r
b a n d w i d t h - i n t e n s i v e a p p l i c a t i o n s .
S p e e d , S i z e , a n d S a v i n g s : S i l i c o n P h o t o n i c s
t e c h n o l o g y c o m b i n e s u n p a r a l l e l e d s p e e d ,
m i n i a t u r i z a t i o n , a n d c o s t - e f f e c t i v e n e s s .
M a x i m i z e e f f i c i e n c y , r e d u c e f o o t p r i n t , a n d
a c h i e v e s i g n i f i c a n t c o s t s a v i n g s i n y o u r
o p t i c a l n e t w o r k i n g s o l u t i o n s .

8. Each power-on process needs to lock the working point of the working voltage according to the following three-
step algorithm:
Input Optical
Singal
Output Optical
Singal
MPDI
Heater
MPDO
Control Circuitry
When the MZM has input light without modulation signal, scan the heater voltage 0-3.5V (step<0.05V), and
record the photocurrent of MPDO and MPDI. Among them, the state corresponding to the maximum value of
the photocurrent of MPDO/MPDI is that the MZM is in the state of minimum loss (peaking point);
Step 1
02/

9. 02/
Load the PAM4 electrical signal and adjust the heater voltage so that the photocurrent ratio of
MPDO/MPDI drops by 3dB compared to the maximum value. At this time, the corresponding
operating point of MZM is Q point, which is the operating point used by MZM.
Step 2-1
Due to temperature changes, mechanical vibrations, etc. may cause the operating point to drift, so the
modulator needs to be fine-tuned the heater to ensure that the MZM works at the preset operating point (in
actual work, it is not strictly required that the MZM work at the Q point, there may be ± 0.5dB selection space;
Step 2-2
The upward movement of the working point corresponds to an increase in output optical power, while the
ER of the signal decreases; the downward movement of the working point corresponds to a decrease in
output power and an increase in ER);
Step 2-3
In the follow-up work, the ratio of the photocurrent of MPDO/ photocurrent of MPDI is
continuously monitored so that it is near the set reference value.
Step 3

10. 0
20
40
60
80
100
120
140
0 1000 2000 3000 4000 5000
0
20
40
60
80
0 1000 2000 3000 4000 5000
0
20
40
60
80
0 1000 2000 3000 4000 5000
0
20
40
60
80
100
0 1000 2000 3000 4000 5000
Note that the different operating points of the rising edge and the falling edge will cause the polarity of the
optical signal to be different.
In the actual work of the optical module MZ modulator, we can scan to get a graph similar to the following figure, from
which one of the quad points can be selected as the working point.
02/

11. 02/
In actual work, as the external environment changes, the quad point curve will drift.
The following figure shows the scanning curves of two different temperature points, which need to be locked in real time:
according to the calibration of the initial scanning value.
Real-time Sampling is adjusted to ensure that the MZ modulator always works near the quad point.
S1
S2

13. 03/ Silicon Photonics High and Low Temp Drift Compensation
As shown in the figure below, we found that in addition to quad drifting left and right following environmental changes, the overall
sampling value of its corresponding MPD will also change to a certain extent with temperature changes.
Otherwise, the quad calibration point found earlier may not be locked to the real quad point at different temperatures, leading
directly to the difference in the ER extinction ratio.
Not all silicon photonics chips will exhibits this phenomenon, and it is only occasionally observed in some chips. This may be due to a
specific part of the manufacturing process that the MPD monitoring value to vary with temperature, and corresponding temperature
compensation needs to be done.
S2
S1

14. The main considerations in the actual debugging process are
high and low temperature changes and silicon photonics chips
may be affected by factors such as temperature during long-
term operation , to ensure real-time automatic locking
adjustment without affecting the normal working condition.
At present, our verification results on
and show that there is a relatively good
algorithm compensation solution for the problem of large
changes in the high and low temperature quad points of
individual silicon photonic chips.
The module with a large DR1 deviation has been measured,
and the result after compensation is as follows:
Temp℃
Before
Compensation
After
Compensation
ER/dB
TDECQ/
dB
ER/dB
TDECQ/
dB
0 5.6 3.2 4.33 2.47
37 4.22 2.11 4.36 2.03
70 3.86 2 4.62 1.63
01
02
03
04
The working point locking algorithm itself is not very
difficult. It is mainly to traverse and find points according
to a certain step.
03/ Silicon Photonics High and Low Temp Drift Compensation

15. GIGALIGHT News in Silicon Photonics
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communication operators, and cloud computing
service providers, GIGALIGHT with mature silicon
photonics integration technology, launched the 400G
QSFP-DD/QSFP112 DR4++ 10km silicon photonics
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16. GIGALIGHT SiPh Modules Series Ordering Information
Product Standard Trasmitter Receiver Reach
Optical
Interface
Case Operating
Temp(℃)
Max. Power
Consumption(W)
P/N

17. www.gigalight.com
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