Mach-Zehnder Type Interferometer

OCT-Proven Clock for Swept Source Systems
Compact Design that Allows Subassembly Integration
Several Wavelengths Available

INT-MZI-1300

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Imaging Systems Overview

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Overview
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Operating Principles
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Item #	Wavelength Range^a	Detector Type	Free Spectral Range	Insertion Loss^a
INT-MZI-850	780 - 925 nm	Si/PIN	103.3 GHz ± 5%	<1.5 dB (Typ.), 3 dB (Max)
INT-MZI-1300	1225 - 1375 nm	InGaAs/PIN	103.3 GHz ± 5%	<0.7 dB (Typ.), 1 dB (Max)

For the interferometer

Features

For 850 nm or 1300 nm Center Wavelengths
Ideal for Swept Source Output Frequency Monitoring
Balanced Detection Output
Low Insertion Loss: <3 dB
Flat Wavelength Response
Integrated Signal Detection for Power Monitor and k-Clock Signals
Interferometer Power Supply Included

Thorlabs' Mach-Zehnder interferometer clock box subassemblies are designed to be used inside a swept source OCT system with a central wavelength of either 850 nm or 1300 nm. The internal fiber couplers are optimized for flat wavelength responses and coupling losses that have a very low polarization dependence, which make the output signals independent of input polarization changes. The clock box contains two detectors, providing a power monitor signal and a k-clock signal that monitors the output frequency of the swept source. Both outputs have a 200 MHz bandwidth, and the k-clock uses a balanced detection scheme to maximize rejection of common mode noise.

Although originally designed for OCT systems, this clock can also be used for other synchronization applications.
For more details on the clock, please see the Operating Principles Tab.

Note: Custom models are available with a choice of free spectral range and wavelength. Please contact Tech Support for more information.

Item #	INT-MZI-850	INT-MZI-1300
Optical Specifications
Interferometer Wavelength Range	780 - 925 nm	1225 - 1375 nm
Free Spectral Range	103.3 GHz ±5%	103.3 GHz ±5%
Fiber Type	Nufern 780-HP™	Corning SMF28™
Input/Output Connection	FC/APC Pigtail, 50 cm Long
Insertion Loss^a	<1.5 dB (Typ.), 3 dB (Max)	<0.7 dB (Typ.), 1 dB (Max)
Electrical Specifications
Detector Material/Type	Si/PIN	InGaAs/PIN
Detector Wavelength Range	320 - 1000 nm	800 - 1700 nm
Typical Responsivity (Max)	0.53 A/W	1.0 A/W
MZI Output Bandwidth (3dB)	DC - 200 MHz
Conversion Gain Power Monitor^b	30 V/W (±25%)	60 V/W (±25%)
Conversion Gain MZI Output^b	±30 V/W (±25%)	±60 V/W (±25%)
Saturation Power	100 mW @ 850 nm	50 mW @ 1300 nm
Maximum Input Power	250 mW (Photodiode Damage Threshold)
Electrical Outputs	SMA
Impedance	50 Ω
DC Offset	< ±5 mV
Power Supply	±12 V @ 250 mA (100/120/230 VAC, 50 - 60 Hz, Switchable)
General Specifications
Dimensions	120 mm x 80 mm x 16 mm

Includes connector losses of the Input and Output pigtail, measured at the central wavelength
Conversion gain measured with respect to the output power using a high impedance load, half value with a 50 Ω impedance.

Operating Principles

Rapidly swept laser sources typically use sinusoidal tuning elements to achieve the very fast optical frequency sweep speeds required for OCT imaging applications. Hence, accurate and reliable re-calibration of the OCT signal is required so that the final data points are equidistant in frequency. The Thorlabs swept source laser features a built-in Mach-Zehnder Interferometer (MZI) with balanced detector output that can be used for just this purpose. A frequency clock is derived from the zero crossings of the MZI interference fringe signal; these zero crossings are equally spaced in optical frequency (k-space). While this clock is intended for OCT applications, it can also be used in other synchronization applications.

MZI data
Figure 1: MZI Clock Signal

The schematic of the system is shown in figure 2 below. 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. Specially designed couplers are used to achieve a flat wavelength response for both the transmitted and the Power Monitor signal. (see figures 3 and 4 below). Both signals of the MZI are detected by an ultra-low noise amplified balanced photo detector.

Schematic diagram of INT-MZI-1300
Figure 2: Schematic of MZI Series Clock Box

graph of coupling ratio from input to output for INT-MZI-1300

Figure 3: Coupling Ratio for INT-MZI-1300 from Input to Output

graph of coupling ratio from input to power for MZI

Figure 4: Coupling Ratio for INT-MZI-1300 from Input to Power Monitor

Power Monitor Output

SMA Female

0 - 1.8 V (50 Ω) or 0 - 3.6 V (High Z)

Mach-Zehnder Interferometer Output

SMA Female

0 - 1.8 V (50 Ω) or 0 - 3.6 V (High Z)

Posted Comments:

ckdgus6819 (posted 2017-03-28 12:45:01.22)

Do you have 1500nm MZI clock box??

swick (posted 2017-03-30 03:21:23.0)

This is a response from Sebastian at Thorlabs. Thank you for the inquiry. We can offer customized version of our Mach-Zehnder Type Interferometers for different wavelengths. I will contact you directly to check your requirements in detail.

amahend (posted 2016-05-25 10:56:25.543)

Do you have similar product mach zehnder interferometer but the MZI output using optical connector (or remove the PD) so this can act as delay line interferometer?

besembeson (posted 2016-05-25 05:22:21.0)

Response from Bweh at Thorlabs USA: We don't have such a fiber based interferometer at this time. We could look into a custom solution according to your requirements. I will contact you.

jlow (posted 2012-11-01 13:17:00.0)

Response from Jeremy at Thorlabs: The MZI clock isn't designed for external clocking the DAQ card. Instead the MZI clock signals are acquired by the DAQ card simultaneously with the OCT signals. Then software is used to process the MZI clock signals and interpolate the zero-crossing to build the time-to-frequency conversion to perform a linear FFT. The number of raw clock points that comes out of the MZI is about 400-450 points. We recommend interpolating approximately 4x those points to perform a 2048 point FFT.

avle (posted 2012-10-24 02:06:41.657)

How many points per scan does the mzi clock generate when using the SL1325-P16 laser for external clocking?

Tyler (posted 2008-03-18 10:51:24.0)

Response from Tyler at Thorlabs to r93941013: Thank you for your interest in our product. The output of the MZI Clock Box can be used to trigger the data acquisition board. The output signal consists of a sinusoidal signal with zero crossings that are equally spaced in frequency.

r93941013 (posted 2008-03-16 21:49:52.0)

Hello, I am interested in this product. About the clock box, the MZI output signal could be directly used as the clock signal of data acquistion board? If not, the advanced calculation inplementation is required. Therefore, more input channel is essential fro frequency calibration. Waiting for more deailed response, thx. By the way, our primary application is swept source OCT application. Hsiang Chieh Lee National Taiwan University, Taiwan