THORLABS INT-MZI Series User manual

Mach - Zehnder - Interferometer
Clock Box
INT-MZI-xxx Series
Operation Manual
2018

2 INT-MZI-xxx
© 2018 Thorlabs
Version: 3.1
Date: 03. Dec. 2018

General Information 3
© 2018 Thorlabs
Table of Contents
1 General Information ................................................................................................................... 5
1.1 Safety ................................................................................................................................ 5
1.2 Ordering Codes and Accessories ...................................................................................... 5
2 Getting Started ........................................................................................................................... 5
2.1 Parts List ........................................................................................................................... 5
2.2 Optional Accessories ......................................................................................................... 6
2.3 Setting Up.......................................................................................................................... 6
2.4 First Operation ................................................................................................................... 6
3 Operating the INT-MZI-xxx ........................................................................................................ 7
3.1 General Principle of Operation .......................................................................................... 7
3.2 Optical Input and Output, Fiber Network ........................................................................... 7
3.3 Electrical Outputs .............................................................................................................. 9
3.3.1 Power Monitor .............................................................................................................................. 9
3.3.2 MZI Output ................................................................................................................................. 10
3.4 Detector Responsivity ..................................................................................................... 11
3.5 Mounting the INT-MZI-xxx series .................................................................................... 12
3.6 Recommendations .......................................................................................................... 13
4 Maintenance and Repair .......................................................................................................... 13
4.1 Cleaning .......................................................................................................................... 13
5 Appendix .................................................................................................................................. 14
5.1 Technical Data ................................................................................................................ 14
5.2 Mechanical Drawing ........................................................................................................ 15
5.3 Certifications and Compliances ....................................................................................... 16
5.4 Warranty .......................................................................................................................... 17
5.5 Copyright ......................................................................................................................... 17
5.6 Thorlabs “End of Life” Policy (WEEE) ............................................................................. 18
5.7 Thorlabs Worldwide Contacts ......................................................................................... 19

4 INT-MZI-xxx
© 2018 Thorlabs
We aim to develop and produce the best solution for your application in the field of
optical measurement technique. To help us to come up to your expectations and
develop our products permanently we need your ideas and suggestions. Therefore,
please let us know about possible criticism or ideas. We and our international
partners are looking forward to hearing from you.
Thorlabs
WARNING
Sections marked with this heading explain dangers that might result in personal
injury or death. Always read the associated information carefully before performing
the indicated procedure.
ATTENTION
Paragraphs preceded by this symbol in the manual explain hazards that could
damage the instrument and connected equipment or may cause loss of data.
NOTE
This manual also contains "NOTES" and "HINTS" written in this form.

General Information 5
© 2018 Thorlabs
1 General Information
The Thorlabs INT-MZI-xxx series MZI Clock Box is a subassembly to be used in swept
source OCT systems and other applications. It contains a fusion coupler network to
provide a Power Monitor signal as well as a k-Clock signal to monitor output power and
wavelength of a swept laser source. The used fusion couplers are optimized for flat
wavelength response and very low PDCR (polarization dependent coupling ratio change)
to make the Power Monitor signal nearly independent of input polarization changes.
The “Getting Started Quickly” section below gives an overview of how to set up the INT-
MZI-xxx series MZI Clock Box. Subsequent sections contain detailed information about
principle of operation, operating suggestions and technical specifications.
1.1 Safety
Attention
All statements regarding safety of operation and technical data in this instruction
manual will only apply when the unit is operated correctly as it was designed for.
Only with written consent from Thorlabs may changes to single components be
carried out or components not supplied by Thorlabs be used.
This precision device is only transportable if duly packed into the complete original
packaging. If necessary, ask for a replacement package.
1.2 Ordering Codes and Accessories
The following models of INT-MZI-xxx series are available:
INT-MZI-1300 MZI-Clock-Box, 1225-1375nm, FSR 103,3 GHz
INT-MZI-850 MZI-Clock-Box, 780-900nm, FSR 103,3 GHz
Different wavelength ranges can be ordered on request, as well as different Free Spectral
Ranges (FSR).
For the standard version, mounting holes are located on the small edges of the enclosure.
An alternative cover with four mounting holes as well as a customized cover can be
ordered on request.
Please refer to www.thorlabs.com for new models.
2 Getting Started
2.1 Parts List
Inspect the shipping container for damage. If the shipping container seems to be damaged,
keep it until you have inspected the contents and you have inspected the INT-MZI-xxx
mechanically and electrically.
Verify that you have received the following items within the package:
- INT-MZI-xxx
- LDS12B Power supply (12V, 250 mA), 100V, 120V, or 230V line voltage
- Operation manual

6 INT-MZI-xxx
© 2018 Thorlabs
2.2 Optional Accessories
Thorlabs offers a DC power supply cable to INT-MZI, the PDA-C-72. This cable has a
connector on one end and open wires at the other.
2.3 Setting Up
- If necessary, mount the unit on your optical table or application. The unit has four
tapped 6-32 mounting holes (see section 3.5 for details).
- Switch the power supply to your local main voltage (100 VAC, 120 VAC or 230 VAC),
see Figure 1.
Figure 1: Switchable power supply for 100 V. 120 V, or 230 V
- Plug the power connector cable into the DC INPUT.
- Plug the power supply into a 50-60 Hz, 100 VAC, 120 VAC, or 230 VAC outlet, turn
power supply on.
- Use coaxial cables with SMA connectors for Power Monitor and MZI Output.
2.4 First Operation
- Connect the INPUT pigtail to the optical source. Make sure that the connector of the
source is FC/APC style.
- Connect the OUTPUT pigtail to your application. Make sure that the connector is
FC/APC as well.
- The maximum output voltage swing of the Power Monitor output is +3,6 V for high
impedance loads (+1.8 V for 50  loads). The output signal should be below this
maximum output voltage to avoid saturation. Saturation of the Power Monitor output
may occur at optical input power > 50 mW.
- The maximum MZI-Output voltage swing is 3.6 V for high impedance loads (1.8 V for
50  loads). The MZI-Output signal should be below this maximum output voltage to
avoid saturation. Saturation of the MZI-Output may occur at optical input power >
50 mW.
NOTE
Please note, that the fiber connector style is FC/APC!
NOTE
To prevent saturation of the amplifier keep the optical input powers less than the saturation
power listed in specification.
ATTENTION
Refer to the specification and pay attention to the optical damage threshold! Exceeding
these values will permanently destroy the detectors!

Operating the INT-MZI-xxx 7
© 2018 Thorlabs
3 Operating the INT-MZI-xxx
3.1 General Principle of Operation
The Thorlabs INT-MZI-xxx series MZI Clock Box is a subassembly to be used in swept
source OCT systems and other applications. It contains a fusion coupler network and ultra-
low noise, high-speed transimpedance amplifiers with low output impedance to provide a
Power Monitor signal as well as a k-Clock signal to monitor both the output power and
wavelength of a swept laser source. The used couplers are optimized for flat wavelength
response and very low PDCR (polarization dependant coupling ratio change) to make the
Power Monitor signal nearly independent to input polarization changes.
The INT-MZI-xxx series is powered by the included external mains power supply (12 V,
250 mA) via a PICO M8 power connector.
Figure 2 shows the functional block diagram of the INT-MZI-xxx series MZI Clock Box.
Figure 2: Functional block diagram of the INT-MZI-xxx series
3.2 Optical Input and Output, Fiber Network
The INT-MZI-xxx MZI Clock Box subassembly is equipped with ~50 cm long INPUT and
OUTPUT pigtails with FC/APC connectors to be connected to your application. Model INT-
MZI-1300 uses Corning SMF28TM single mode fiber. Model INT-MZI-850 uses Nufern 780-
HPTM single mode fiber.
NOTE
FC/APC connectors are used for INPUT and OUTPUT pigtails!
Saturation of the electrical outputs may occur at optical input power > 50 mW. The optical
damage threshold is 250 mW. Exceeding this value may permanently destroy photo
detectors!
An internally fiber network is used to tap ~5% of the input light to generate Power Monitor
and k-Clock signals. The remaining light is transmitted to the Output pigtail. Insertion loss
(Input to Output) is less than 1 dB (model INT-MZI-1300), including connector losses. This
tap coupler is designed for nearly flat transmission wavelength response (see Figure 3).
The sophisticated design of the 50/50 fusion coupler provides a Power Monitor output
signal with flat wavelength response, which is nearly insensitive to input polarization
changes. Figure 4 shows the typical spectral behavior of the INT-MZI-1300 measured from
Input to Power Monitor output port.
INPUT
OUTPUT
95/5
50/50
50/50 50/50
MZI section
MZI Output
Power Monitor
INT-MZI-xxx
INPUT
OUTPUT
95/5
50/50
50/50 50/50
MZI section
MZI Output
Power Monitor
INT-MZI-xxx

8 INT-MZI-xxx
© 2018 Thorlabs
1200 1250 1300 1350 1400
0
20
40
60
80
100
INPUT --> OUTPUT (%)
Wavelength (nm)
Figure 3: INT-MZI-1300 coupling ratio from INPUT to OUTPUT
1200 1250 1300 1350 1400
0
1
2
3
4
INPUT --> POWER MONITOR (%)
Wavelength (nm)
Figure 4 : INT-MZI-1300 coupling ratio from INPUT to POWER MONITOR
The tapped light is split into the Power Monitor signal and the k-Clock signal. The k-Clock
signal is generated by an Mach-Zehnder interferometer section. Path length difference of
the MZI section is about 2 mm to achieve 100 GHz free spectral range. Figure 5 shows a
typical measurement of the MZI section.

Operating the INT-MZI-xxx 9
© 2018 Thorlabs
-200 -100 0 100 200
-30
-20
-10
0
Amplitude (dB)
Relative Frequency (GHz)
Figure 5: INT-MZI-1300 spectral behavior of the MZI section
Please note, that the INT-MZI-xxx can also operate outside the specified wavelength
range. It will generate expedient output signals, but Specifications cannot be guaranteed.
3.3 Electrical Outputs
The INT-MZI-xxx series has two output SMA connectors carrying monitoring signals of the
Power Monitor and the k-Clock signal (MZI Output).
3.3.1 Power Monitor
Power Monitor output delivers an output voltage proportional to optical input power. The
Power Monitor signal is detected by a photodiode and amplified by an ultra-low noise,
high-speed transimpedance amplifier. The maximum output voltage swing of the Power
Monitor output is +3,6 V for high impedance loads (+1.8 V for 50  loads). The output
signal should be below this maximum output voltage to avoid saturation. Saturation of the
Power Monitor output may occur at optical input power > 50 mW. The 3 dB bandwidth of
the Power Monitor output is typically in excess of 200 MHz. Figure 6 shows a typical
frequency response curve of the Power Monitor output of an INT-MZI-1300.
0 100 200 300 400 500 600 700
-30
-20
-10
0
Amplitude (dB)
Frequency (MHz)
Figure 6: INT-MZI-1300 POWER MONITOR frequency response

10 INT-MZI-xxx
© 2018 Thorlabs
3.3.2 MZI Output
MZI Output generates a periodical signal if the wavelength of the INPUT signal is changing.
This signal shows maxima and minima which are equally spaced in optical frequency
domain (k-space). The difference between two maxima is defined by the FSR, here 103.3
GHz (please refer to 5.1 Technical Data). As a practical application, the zero-crossing of
MZI Output signal can be used to detect (trigger) a change of input frequency, equal to the
FSR. For example, in OCT imaging applications rapidly swept laser sources are used,
typically with sinusoidal tuning elements, to achieve the required very fast optical
frequency sweep speed. As for this reason, a reliable and accurate recalibration of the
OCT signal is required in order to achieve data points equidistant in frequency.
The amplitude of MZI Output is proportional to optical input power. Both output signals of
the MZI section are fed into two well-matched photodiodes representing a balanced
detector; the balanced signal is amplified by an ultra-low noise, high-speed
transimpedance amplifier. The maximum output voltage swing of the MZI Output is 3,6 V
for high impedance loads (1.8 V for 50  loads). The output signal should be below this
maximum output voltage to avoid saturation. Saturation of the MZI Output may occur at
optical input power > 50 mW. The 3 dB bandwidth of the MZI Output is typically in excess
of 200 MHz. Figure 7 shows typical frequency response curves of the MZI Output for
model INT-MZI-1300.
0 100 200 300 400 500 600 700
-30
-20
-10
0
Amplitude (dB)
Frequency (MHz)
Figure 7: INT-MZI-1300 MZI OUTPUT frequency response