THORLABS VEG200 Series User manual

Swept Source OCT
System Base Units
VEG200 Series
User Manual

Original User Manual – not translated

SS-OCT System Base Unit
Table of Contents
Chapter 1Introduction.....................................................................................................................1
1.1.Safety.......................................................................................................................... 2
1.2.Care and Maintenance .............................................................................................. 3
Optical Cleaning ............................................................................................................4
Fiber Cleaning Techniques Using the FBC1 .................................................................4
Using Extended Mode ..............................................................................................................4
Service ..........................................................................................................................5
Accessories and Customization ....................................................................................5
Chapter 2Setup................................................................................................................................6
2.1.Unpacking .................................................................................................................. 6
2.2.System Connections................................................................................................. 6
Base Unit Connections ..................................................................................................6
Internal Electrical Connections ......................................................................................7
Electrical Interfaces to Imaging Scanner .......................................................................7
2.3.Optical Interface to Imaging Scanner...................................................................... 7
2.4.System Installation.................................................................................................... 8
Chapter 3Description....................................................................................................................14
3.1.Tutorial ..................................................................................................................... 14
Theory ......................................................................................................................... 15
Thorlabs SS-OCT System Technology ....................................................................... 16
Nomenclature in OCT imaging .................................................................................... 18
3.2.SS-OCT Base Unit Components ............................................................................ 20
Base Unit .................................................................................................................... 20
PC with Graphical User Interface ................................................................................ 20
SDK ............................................................................................................................ 20
Imaging Scanner (Accessory) ..................................................................................... 22
OCT-Stand (Accessory) .............................................................................................. 23
Chapter 4System Operation.........................................................................................................25
4.1.Starting the System................................................................................................. 25
Turning on the Base Unit ............................................................................................ 25
Starting the Software ................................................................................................... 26
4.2.Basic Adjustments .................................................................................................. 27
Adjusting the Focus..................................................................................................... 27
Adjusting the Reference Length .................................................................................. 27
Adjusting the Polarization ............................................................................................ 29
Adjusting the Reference Light Intensity and Amplification ........................................... 30
4.3.Advanced Adjustments .......................................................................................... 31
Focus and Choice of Objective Lens ........................................................................... 31
Imaging through Refractive Media .............................................................................. 32
Reflecting Surfaces and Interfaces ............................................................................. 33
Rough Surfaces .......................................................................................................... 33
4.4.Shutting Down the System..................................................................................... 33
4.5.Example Images ...................................................................................................... 34
Chapter 5Imaging Artifacts..........................................................................................................36
5.1.Saturation and Non-Linearity ................................................................................. 36
5.2.Multiple Scattering .................................................................................................. 37
5.3.Phase Wrapping and Fringe Washout................................................................... 38

SS-OCT System Base Unit
5.4.Flipped Image .......................................................................................................... 39
5.5.Shadowing ............................................................................................................... 40
5.6.Image Distortion by Refractive Media ................................................................... 41
The Group Refraction Index ........................................................................................ 41
Measurement Depth in OCT Systems ......................................................................... 42
Distortions in the Image .............................................................................................. 43
Chapter 6Troubleshooting...........................................................................................................45
6.1.Changing the Input Fuses ...................................................................................... 46
Chapter 7Certifications and Compliance...................................................................................47
7.1.Declaration of Conformity Vega Series Base Units ............................................. 47
Chapter 8Warranty........................................................................................................................49
8.1.Lasers and Imaging Systems................................................................................. 49
8.2.Non-Warranty Repairs ............................................................................................ 49
8.3.Warranty Exclusions............................................................................................... 49
Chapter 9Specifications...............................................................................................................50
Chapter 10Mechanical Drawings...................................................................................................51
Chapter 11Regulatory.....................................................................................................................52
11.1.Waste Treatment is Your Own Responsibility............ Error! Bookmark not defined.
11.2.Ecological Background ................................................ Error! Bookmark not defined.
Chapter 12Thorlabs Worldwide Contacts....................................................................................53

SS-OCT System Base Unit Chapter 1: Introduction
Rev A, December 17, 2018 Page 1
Chapter 1 Introduction
ATTENTION
Please read the instruction manual carefully before operating the SS-OCT system. All
statements regarding safety and technical specifications will only apply when the unit is
operated correctly.
This equipment is intended for laboratory use only and is not certified for medical applications,
including but not limited to life support situations.
Refer to this manual whenever the following symbols are encountered on the SS-OCT system:
Attention symbol indicates that additional information is given in this manual.
Laser Safety symbol indicates that laser radiation is present.
Shock Warning symbol indicates there is possible danger of injury to users.
ATTENTION
Check the supply voltage of the system before plugging in the computer. Make sure the included
power cords for the base unit, computer, and monitor are connected to a properly grounded
outlet (100 – 240 VAC; 50 – 60 Hz).
Transportation and delivery may cause the SS-OCT system to be warm or cool upon receipt.
Please wait for the system to reach room temperature before attempting to operate.
Operate this system on a flat, dry, and stable surface only.
WARRANTY WARNING
Do not open the base unit, imaging scanner or PC. There are no user serviceable parts in this
product. Opening the device will void your warranty. Any modification or servicing of this
system by unqualified personnel renders Thorlabs free of any liability. This device can only be
returned when packed into the complete original packaging, including all foam packing inserts.
If necessary, ask for replacement packaging.
The following symbols are used on the device:
"ON" (power)
"OFF" (power)

Stand-by

Protective earth; protective ground

SS-OCT System Base Unit Chapter 1: Introduction
Page 2 MTN013142-D02
1.1. Safety
SHOCK WARNING – HIGH VOLTAGE
Before applying power to the system, make sure that the protective conductor of the three-
conductor mains power cord is correctly connected to the protective earth contact of the socket
outlet. Improper grounding can cause electrical shock resulting in severe injury or even death.
Make sure that the line voltage rating agrees with your local supply and that the appropriate
fuses are installed. Fuses should only be changed by qualified service personnel. Contact
Thorlabs for assistance. Do not operate without cover installed. Refer servicing to qualified
personnel.
ATTENTION
Do not obstruct the air-ventilation slots in the computer housing. Do not obstruct air-ventilation
into the bottom of the base unit or out of the exhaust fan on the rear of the unit.
Mobile telephones, cellular phones, or other radio transmitters are not to be used within the
range of three meters of this unit, since the electromagnetic field intensity may exceed the
maximum allowed disturbance values according to IEC 61000-6-1:2005.
The safety of any system incorporating the equipment is the responsibility of the assembler of
the system.
If equipment is used in a manner not specified by the manufacturer, the protection provided by
the equipment may be impaired.
LASER RADIATION WARNING
Laser emission may be emitted
a) from the scan lens of a scanner (intended use)
b) from the back of the base unit when the fiber cap is removed and the fiber disconnected
c) from the output of the fiber when the fiber is not connected to a scanner
Do not look into the optical output when the device is operating. The laser radiation is not visible
to the human eye and can cause serious damage to your eyesight.
The laser class information is also stated on the laser safety labels on the back of the housing.
Example given for class 1M LASER product:
INVISIBLELASERRADIATION

DONOTSTAREINTOBEAMORVIEW
DIRECTLYWITHOPTICALINSTRUMENTS

CLASS1MLASERPRODUCT

CLASSIFIED ACCORDINGTODINEN 60825‐1:2014

SS-OCT System Base Unit Chapter 1: Introduction
Rev A, December 17, 2018 Page 3
1.2. Care and Maintenance
Handle the system with care during transportation and unpacking. Banging or dropping the system can damage
the unit or lower system performance. If the system is mishandled during shipment, the optical components may
become misaligned, which could lead to a decrease in image quality. If this occurs, the system will need to be
realigned by qualified personnel. Please contact Thorlabs technical support for more information.
 Do not store or operate in a damp, closed environment.
 Do not store or operate on surfaces that are susceptible to vibrations.
 Do not expose to direct sunlight.
 Do not use solvents on or near the equipment.
 Keep away from dust, dirt, and air-borne pollutants (including cigarette smoke). The system is not
designed for outdoor use. Protect the equipment from rain, snow, and humidity.
 Do not expose to mechanical and thermal extremes. Protect the equipment from rapid variation in
temperature.
 Handle all connectors, both electrical and optical, with care. Do not use unnecessary force, as this may
damage the connectors.
 Handle the optical fiber with care. Mechanical stress can decrease performance and potentially destroy
the fiber. Continual bending of the optical fiber can cause damage. It is important, therefore, to keep
the optical fiber patch cable as straight as possible to minimize bending.
Note: The most common cause of low signal intensity is contamination of the fiber due to airborne pollutants.
To minimize exposure, avoid unnecessarily disconnecting the optical fiber patch cable. In addition, it is advisable
to check the fiber before making other adjustments to the optical system, such as changing the focus or optical
path length. Be sure to check the patch cord for a loose connection, and make sure that the fiber is kept as
straight as possible.
All lasers, especially lasers with resonator cavities that are defined by mechanical tolerances, are delicate
precision instruments and must be handled accordingly. The SS-OCT system is designed to withstand normal
transportation and operating conditions. Do not move the system while it is connected and in operation.

SS-OCT System Base Unit Chapter 1: Introduction
Page 4 MTN013142-D02
1.2.1. Optical Cleaning
Good performance and image quality of the OCT imaging system relies on clean optical connections. Whenever
using the Thorlabs OCT system, the following guidelines for optical fiber connection should be followed:
1) Always make sure that the light source is switched off when you clean the fiber.
2) Always inspect and clean the fiber end before plugging it into a receptacle.
3) Always cover the fiber end that is not in use with a fiber cap or dust protection cover.
The cleaning procedure sucess could be visualized using a fiber inspection scope.
Figure 1 Fiber Inspection Scope FS201
1.2.2. Fiber Cleaning Techniques Using the FBC1
This section details how to clean fiber bulkheads and fiber connectors using the FBC1 one-step cleaner.
Using Extended Mode
Figure 2 FBC1 Extended Mode
To use extended mode, pull the tip outward while simultaneously pushing down on the lock button. Extended
mode is useful for panels with multiple bulkhead connectors or other tight spaces.

SS-OCT System Base Unit Chapter 1: Introduction
Rev A, December 17, 2018 Page 5
Cleaning Fiber Bulkheads
Figure 3 Cleaning Fiber Bulkheads
Remove the guide cap completely from the device, and insert the tip of the cleaner into the bulkhead connector.
Push the case to start the cleaning process; a click indicates that the cleaning is complete.
Cleaning Fiber Connectors
Figure 4 Cleaning Fiber Connectors
Open the cover on the guide cap, and insert the fiber connector over the guide cap. Push the case to start the
cleaning process; a click indicates that the cleaning is complete.
1.2.3. Service
Only trained and approved Thorlabs personnel are allowed to service the system. Please contact Thorlabs
technical support for more information.
1.2.4. Accessories and Customization
The OCT base unit can easily be adapted for custom interfaces. To achieve the listed specifications however
this system should only be used with the accessories that Thorlabs provides. Any modification or maintenance
by unqualified personnel will render the warranty null and void, leaving Thorlabs free of liability. Please contact
Thorlabs technical support for questions on customization.

SS-OCT System Base Unit Chapter 2: Setup
Page 6 MTN013142-D02
Chapter 2 Setup
2.1. Unpacking
Carefully unpack the components from the transport boxes. Make sure that all components are delivered
according to the packing list included in the transport box. After unpacking, store the packing cartons and inserts.
You may need them in case of a service or upgrade of your OCT system.
2.2. System Connections
2.2.1. Base Unit Connections
All of the base unit connections are located in the rear (see Figure 5).
Figure 5 Rear View of Base Unit
A. Main Switch
B. SMA Connector for OCT SIGNAL to connect to Alazar Tech. ATS9351 or ATS9360
C. SMA Connector for DAQ k-CLOCK to connect to Alazar Tech. ATS9351 or ATS9360
D. USB Data Port to Connect PC (USB 2.0 Type B Interface)
E. Probe Fiber Receptacle (FC/APC)
F. Interlock (2.5mm Audio Jack)
G. Scanner Connection Port (LEMO, 19 Pin)
H. VHDCI Data Port to Connect to the NI PCIe-6351
I. Handheld Scanner or Auxiliary Connection Port (LEMO, 14 Pin)
J. SMA Connector for CWL Trigger to Connect to Alazar Tech. ATS9351 or ATS9360
o Note: This port remains unused in a default configuration.
K. SMA Connector for DAQ Trigger to Connect to Alazar Tech. ATS9351 or ATS9360
L. SMA Connector for SYNC Trigger to Connect to Alazar Tech. ATS9351 or ATS9360
M. Power Plug and Fuse Storage
A B C D E F G H
M L K JI

SS-OCT System Base Unit Chapter 2: Setup
Rev A, December 17, 2018 Page 7
2.2.2. Internal Electrical Connections
The USB connection to the PC is used for the control communication between the Software and Base Unit. The
acquisition and synchronization of the spectral information is using the SYNC Trigger connection.
2.2.3. Electrical Interfaces to Imaging Scanner
For the connection to a scanner application there are two different interfaces available:
 The scanner connection port is intended to be used together with dedicated Thorlabs imaging scanners
OCTG and OCTP.
 The auxiliary connection port is intended to be used together with the dedicated Thorlabs imaging
scanner OCTH and furthermore allows the use of a custom scanner. It hosts two analogue signals for
driving separate actuators (e.g. Galvanometer scanner), communication lines and supply voltages.
Imaging Scanner – Electrical Interfaces
Probe Connection Port Lemo ECG.2B.319.CLL
Auxiliary Connection Port Lemo ECA.1B.314.CLL
Table 1 Electrical Interfacess
Please contact Thorlabs’ tech support for information regarding the pin configuration.
2.3. Optical Interface to Imaging Scanner
The base unit incorporates one FC/APC fiber interface depending on the internal fiber architecture. If not
different due to customization, the single mode fiber used in the base units is given in Table 2:
Imaging Scanner - Optical Interface
Base Unit Series Fiber Plug / Receptacle Single Mode Fibe
r
V
ega FC/APC Corning SMF28e+
Table 2 Optical Interface

SS-OCT System Base Unit Chapter 2: Setup
Page 8 MTN013142-D02
2.4. System Installation
ATTENTION
Make sure the included power cords for the base unit, computer and monitor are connected to a
properly grounded outlet (100 – 240 VAC; 50 – 60 Hz).
Transportation and delivery may cause the OCT system to be warm or cool upon receipt. Please
wait for the system to reach room temperature before attempting to operate.
Operate this system on a flat, dry, and stable surface only.
1) Install the PC, monitor, mouse, and keyboard according to the documentation provided by the PC
manufacturer.
2) If applicable, assemble the OCT-Stand as described in the documents provided in the OCT-Stand
box.
3) If applicable, mount the scanner in the OCT-Stand by sliding the dove tail at the back of the scanner
into the dove tail slide of the OCT-Stand.
Figure 6 Mounting the Scanner into the Dove Tail Slide of the OCT-Stand
4) Connect the power supply plug to the socket of the base unit and connect the other end to an
electrical outlet.

SS-OCT System Base Unit Chapter 2: Setup
Rev A, December 17, 2018 Page 9
5) Attach the electric connection cable to the imaging scanner.
 Align the red dot of the plug to the alignment mark of the electric connection port of the scanner
(e.g. OCTG).
Figure 7 Plugging the Electrical Connector into the Scanner
 Push the connector into the plug until you hear a “click” sound.
Figure 8 Electrical Connector plugged into the Scanner

SS-OCT System Base Unit Chapter 2: Setup
Page 10 MTN013142-D02
6) Fiber connection to the imaging scanner:
ATTENTION
When installing the fiber, make sure that the fiber tip does not get contaminated by dust.
Do not touch the fiber tip!
 Remove the dust caps from one fiber end and from the FC/APC fiber connection at the imaging
scanner. Store these with the system packaging.
Figure 9 Fiber Connection to the Imaging Scanner
A) Slide the fiber tip into the center bore of the fiber connection.
B and C) The fiber needs to be rotationally oriented so that the alignment nose slides into the mating
part of the probe connector as shown in C.
NOTE: If the nose slide is not properly aligned, you will still be able to secure the fiber but
there will be significant light losses produced by this incorrect connection.
D) Secure the fiber connection by gently turning the lock cap clockwise.
A 
D  C 
B 

SS-OCT System Base Unit Chapter 2: Setup
Rev A, December 17, 2018 Page 11
7) Attach the electric connection cable to the base unit
 Align the red dot upwards, facing the alignment mark in the base unit.
 Push the connector into the plug until a “click” sound is heard.
Figure 10 Installing the Scanner Connection Cable at the Base Unit
8) Fiber connection to the base unit:
ATTENTION
When installing the fiber, make sure that the fiber tip does not get contaminated by dust.
Do not touch the fiber tip!
 Remove the dust caps from the fiber end and from the FC/APC fiber connection at the base unit.
The fiber should be installed in a similar fashion as at the scanner. Follow the steps indicated in
Figure 9 and make sure not to touch the fiber tip.
ATTENTION
The fiber is slightly longer than the interconnection cable to avoid stress to it. Please be careful
not to pull the loop of the fiber at the back of the base unit!
Figure 11 Fiber Connection to the Base Unit

SS-OCT System Base Unit Chapter 2: Setup
Page 12 MTN013142-D02
9) Signal, Trigger and USB connections at the Base Unit (see Figure 12):
 Attach the SMA cable labeled “k-CLOCK Signal” to the respective SMA port.
 Attach the SMA cable labeled “OCT Signal” to the respective SMA port.
 Attach the SMA cable labeled “DAQ Trigger” to the respective SMA port. NOTE: The CWLTrigger
output can be used as an alternative DAQ Trigger, but this will require modifications of parameters
for the data acquisition. By default the output is capped.
 Attach the SMA cable labeled “SYNC TRIGGER” to the respective SMA port. Make sure all the
SMA connections are secured tightly.
 Attach the VHDCI cable to the respective port which is labeled “Control”. Make sure both fastening
screws which are attached to the connector are bolted tightly.
 Connect the USB cable to the USB port and make sure the connection is tight.
Figure 12 Installation of the Electrical Connections at the Base Unit
10) Connections at the PC (see Figure 13):
 Identify both the ATS9351 or ATS9360 DAQ card, and the NI PCIe-6351 DAQ card at the back
of the PC (see Figure 13).
 Connect the VHDCI cable to the NI PCIe-6351 DAQ card. Make sure both fastening screws which
are attached to the connector are bolted tightly.
 Attach the SMA end of the cable labeled “ECLK” at the ATS9351 or ATS9360 card marked as
“ECLK”.
 Attach the SMA end of the cable labeled “CH B” to the respective SMA port of the ATS9351 or
ATS9360 card marked as “CH B”.
 Attach the SMA end of the cable labeled “TRIG IN” to the second SMA port from the left marked
as “TRIG IN”.
 Attach the SMA end of the cable labeled “AUX I/O” to the first SMA port from the left marked as
“AUX I/O”. Make sure all the SMA connections are secured tightly.
 The SMA port marked as “CH A” is not used!

SS-OCT System Base Unit Chapter 2: Setup
Rev A, December 17, 2018 Page 13
Figure 13 Connections of the Alazar (top) and NI DAQ (bottoms) Cards
15) Removing the protective cap off the scan objective:
Pull the protective cap off the scan objective. Do not rotate the protective cap, as this might loosen the
fit of the illumination tube. Do not touch the optical surface of the lens.
Figure 14 Protective Cap Removal

SS-OCT System Base Unit Chapter 3: Description
Page 14 MTN013142-D02
Chapter 3 Description
3.1. Tutorial
Fourier Domain Optical Coherence Tomography (FD-OCT) is based on low-coherence interferometry, which
utilizes the coherent properties of a light source to measure optical path length delays in a sample.
To obtain cross-sectional images with micron-level resolution using OCT, an interferometer is set up to measure
optical path length differences between light reflected from the sample and reference arms.
There are two types of FD-OCT systems, each characterized by its light source and detection schemes:
Spatially encoded Frequency Domain OCT (SeFD-OCT) and time encoded Frequency Domain OCT (TeFD-
OCT), also named Swept Source OCT (SS-OCT). In both types of systems, light is divided by a fiber coupler
into the sample and reference arms of an interferometer setup.
Back-reflected light, attributed to variations in the index of refraction within a sample, recouples into the sample
arm fiber and then combines with the light that has traveled a fixed optical path length along the reference arm.
The resulting interferogram is measured by either a spectrometer (SeFD-OCT) or balanced photodetectors (SS-
OCT).
The frequency of the interferogram measured by the sensor is related to the depth location of the reflector in
the sample. As a result, a depth reflectivity profile (A-scan) is produced by taking a Fourier transform of the
detected interferogram. 2D cross-sectional images (B-scans) are produced by scanning the OCT sample beam
across the sample; by doing so, a series of A-scans are collected to create the 2D image. Similarly, when the
OCT beam is scanned in a second direction, a series of 2D images is collected to produce a 3D volume dataset.
Figure 15 FD-OCT Signal Processing

SS-OCT System Base Unit Chapter 3: Description
Rev A, December 17, 2018 Page 15
3.1.1. Theory
The interference equation for the cross-correlated interference term is
~2 ∙  ∙
 ∙cos󰇛Δ󰇜
With the phase difference Δ being a function of the optical path length difference and the wavenumber
Δ   ∙ Δz
This optical amplification of a small sample intensity with a strong reference intensity allows the detection of
single photons from the sample and is the key to the outstanding sensitivity of OCT.
Due to the reflective character of the measurement modality the optical path length difference is twice the
distances in the image. The maximum imaging depth, and so twice optical path length difference, is defined by
the wavenumber spacing of the acquisition δ.
Δ 1
4∙
In Full-Range OCT setups the image depth could be doubled
The signal width has two limits,
 One limit for the signal width is given by the spectral distribution of the light source. For a fully used
light source being Gaussian shaped in  the equation is:
,, 2∙ln󰇛2󰇜
Δ
with:
Δ    ∙

 The other limitation for the signal width is given by the sampling. For a rectangular spectrum the FFT
results in a sinc function
,, 1.21∙

with:
   2∙Δ


  
A light source is not shaped in a way that the autocorrelation function is clean normally. Therefore the shape
should be apodized to get a clean point spread function. A good compromise between resolution and side lobe
suppression could be a Hanning window showing a signal width of:
, 2∙

In real mesurements the signal width is furthermore limited by noise, dispersion mismatch between sample- and
reference arm of the interferometer, and optical path length distribution of the imaging caused by aberration.

SS-OCT System Base Unit Chapter 3: Description
Page 16 MTN013142-D02
3.1.2. Thorlabs SS-OCT System Technology
Swept Source Optical Coherence Tomography (SS-OCT) technology uses a rapidly tuned broadband source
to illuminate the interferometer and records the information with a balanced detector. SS-OCT technology
measures the magnitude and time delay of reflected light in order to construct depth profiles (A-scans) of the
sample being imaged. Adjacent A-scans are then synthesized to create an image.
Advanced data acquisition and digital signal processing techniques are employed in the SS-OCT system to
enable real-time video rate OCT imaging. The 2D OCT images are analogous to ultrasound images and show
the cross-sectional structure view of the sample. The transverse and axial resolutions of the images are limited
by the focusing optics and spectral bandwidth of the light source respectively. The actual imaging depth into the
sample is highly dependent on the sample scattering properties at the measurement wavelength. The OCT
system also enables the generation of images similar to confocal microscopy by summing signals in the axial
direction. High-speed 3D OCT imaging provides comprehensive data that combines the advantages of surface
microscopy and structural OCT imaging in a single system.
At the heart of the SS-OCT system is a swept laser source that tunes the lasing wavelength over a broad
wavelength range, at hundreds of kilohertz repetition rate. Sample depth profile measurements are performed
at the high sweeping rate of the laser. The interference signals from the sample are collected using a high-
efficiency balanced detection scheme. Each sweep of the laser wavelength provides a depth scan at a sample
surface point that yields a depth dependent reflectivity profile along the direction of the laser illumination path.
The SS-OCT system utilizes the latest MEMS-VCSEL swept laser as the light source to perform Fourier domain
OCT measurements. The very short cavity length (on the level of a few micrometers) of the MEMS-VCSEL
cavity enables very long coherence length (≥100 mm) of the source when sweeping at very high speed (a few
hundreds of kHz). The very long coherence length of the MEMS-VCSEL swept laser supports the large depth
measurement range in OCT experiments, as its distinctive advantage compared to conventional short external
cavity (on the level of a few millimeters) based swept sources. The MEMS-VCSEL SS-OCT system is capable
of providing highly detailed, 2D cross-sectional imaging of a sample’s internal structure, as well as computer
generated 3D reconstruction of a volume near the sample surface. The internal structure of a sample can be
accurately mapped via computer generated tomographic images.
The VEG200 Series Swept Source OCT systems (Vega) provide simultaneous multiple imaging channels for
microscopic viewing of the sample. The en-face images, similar to those obtained from a conventional
microscope, can be acquired from the video camera channel while the cross-sectional images that show the
sample's internal structure are acquired from the OCT channel. Due to the novel data acquisition and signal
processing methods employed, real-time video-rate imaging speed has been achieved on both channels.
The system includes a high-speed MEMS-VCSEL swept laser with -10 dB spectral bandwidth larger than 100
nm, and an average output power greater than 20 mW, sweeping at ≥100000 A-scans per second. The swept
laser provides an A-scan trigger signal to be connected to the trigger input of the data acquisition device. The
laser also has a built-in monitoring interferometer that provides the real-time clock signals to be connected to
the external clock input of the data acquisition device. The main output of the laser is coupled into a fiber-based
Mach-Zehnder interferometer located inside the imaging module. The light is split into the sample and reference
arms using a broadband coupler.
In the reference arm of the interferometer, the light is reflected back into the fiber by a stationary mirror. In the
sample arm, the light is fiber-coupled into the imaging scanner, collimated, and then directed by the XY
galvanometric scanning mirrors towards the sample. A dichroic mirror is inserted into the beam path to reflect
the visible light from the sample onto a CCD camera that records the conventional microscope images of the
sample. The axial scans (A-scans) in the depth direction are performed at the sweeping frequency of the laser.
The transverse scan (B-scan) is controlled by the galvanometric scanning mirrors and determines the frame
rate of the OCT system. The light that exits the imaging scanner is focused onto the sample surface by an
objective.