OCT Selection Guide
OCT Systems Comparison
Thorlabs offers a wide variety of preconfigured Optical Coherence Tomography (OCT) imaging systems, as well as the option to design a complete system using components chosen to best meet the requirements of the application. The Telesto, Ganymede, and Callisto series are spectral domain OCT systems, and the Vega series are swept-source OCT systems. We encourage you to contact us directly at email@example.com or via our online request form to discuss specific imaging requirements.
Thorlabs' modular OCT systems consist of an OCT base unit, beam scanning system, scan lens kit, and user-selected accessories. As there are interdependencies among the various performance specifications in OCT systems, no single system can meet the needs of all applications. The purpose of OCT system design is to optimize key parameters while ensuring good overall system performance.
Choosing an OCT System
In all optical systems, including OCT systems, interrelationships exist among optical parameters. Significant performance parameters that are coupled in OCT systems include: axial resolution & imaging depth, lateral resolution & field of view, and A-Scan rate & field of view:
Immediately below is information about how our various preconfigured OCT systems compare when evaluated in terms of a single key parameter. Click the preconfigured OCT system name on the left of each bar to navigate to the related OCT series page for more details. Item numbers beginning with CAL, GAN, TEL, and VEG are members of the Callisto, Ganymede, Telesto, and Vega series OCT systems, respectively. A Selection Guide comparing the key specifications of all of our OCT base units is provided at the bottom of the page.
Center Wavelength and Bandwidth
Thorlabs currently offers OCT systems that operate with a center wavelength of 900 nm, 930 nm, 1300 nm, or 1325 nm. The center wavelength contributes to the actual imaging depth and resolution of the system. Shorter wavelength OCT systems, such as our 930 nm or 900 nm systems, are ideal for higher resolution imaging compared to systems with a center wavelength of 1300 nm. For imaging samples that have higher optical scattering properties, such as tissue, the longer wavelength systems are recommended. The longer center wavelength is not affected by scattering, and therefore, the light is able to penetrate deeper into the sample and return for detection.
The spectral bandwidth of the OCT light source is indirectly proportional to the axial (depth) resolution of the imaging system. Therefore, broadband light sources are used to provide high axial resolution.
A-Scan / Line Rate
A single depth profile (Intensity vs Depth) is called an A-Scan. A B-Scan, or two-dimensional cross-sectional image, is created by laterally scanning the OCT beam and collecting sequential A-scans. The speed with which a B-scan is collected depends on the A-Scan or Line rate. A-Scan rate and Sensitivity are coupled optical performance parameters; a higher A-Scan rate results in lower sensitivity.
For Spectral-Domain OCT systems (Ganymede, Telesto, and Callisto systems), the A-Scan rate is determined by the speed of the camera in the detection spectrometer. For Swept-Source OCT systems (Vega systems), the A-Scan rate is determined by the sweep speed of the swept laser source.
The sensitivity of an OCT system describes the largest permissible signal attenuation within a sample that can still be distinguished from the noise. In practice, higher sensitivity OCT systems are capable of providing higher contrast images. As the sensitivity of an OCT system can be increased by increasing the integration time, there is usually a tradeoff between A-scan rate and sensitivity.
The graphic to the right lists the imaging depths, in air, of our preconfigured OCT systems in descending order. The maximum imaging depth of an OCT system is strongly dependent on the design of the OCT system base unit. Imaging depth and axial resolution are coupled performance parameters, and each of our base units is optimized to provide a different balance between the two. For applications requiring greater depth or higher resolution, we offer custom configurations.
Please note that optical absorption and scattering effects of the specimen frequently limit the depth to which the light probe can penetrate. For an OCT system to provide valid measurements over the full quoted imaging depth range, the light probe must be able to penetrate the sample to a depth equal to the imaging depth.
In OCT, the axial (depth) resolution is dependent on different factors, and it varies inversely with imaging depth. The design of the base unit has a strong influence on the axial resolution of the OCT system. Other influences include the center wavelength and bandwidth of the optical source used to probe the sample and the index of refraction of the sample. Axial resolution improves as these increase. Axial resolution is coupled to imaging depth; improving one comes at the expense of the other.
The lateral resolution is dependent on the scan lens in the imaging probe. Each OCT base unit can be paired with one of several specially-designed OCT scan lens that offer a wide range of lateral resolutions. For specifications, see the individual OCT system presentations (links in the tables below). Lateral resolution and field of view are coupled parameters.
Field of View (FOV)
The length and width of the FOV are determined by the properties of the scan lens. Thorlabs offers several scan lens kits with different FOVs that have been specifically designed for OCT imaging applications. These scan lens options provide fields of view from 6 mm x 6 mm to 16 mm x 16 mm. Field of view and lateral resolution are inversely related; widening FOV worsens the lateral resolution. For specifications, see the individual OCT system presentations (links in the tables below).
Cross-Section of a Human Finger
OCT Cross-Sectional Image of a Human Finger.
Base Unit Selection Guide
Thorlabs offers a variety of OCT Imaging Systems to meet a range of application requirements. Significant performance characteristics, including axial resolution, A-Scan rate, and imaging depth, are entirely or strongly dependent on the design of the OCT base unit, while choice of scan lens kit determines other parameters, such as lateral resolution and field of view. The tables below present key performance parameters of our base units. For more information about our scan lens kits, click on the links in the tables below to navigate to the OCT system page of interest. We encourage you to contact us directly at firstname.lastname@example.org or via our online request form to discuss specific imaging requirements.
900 nm OCT Base Units
1300 nm OCT Base Units
Optical Coherence Tomography Tutorial
Optical Coherence Tomography (OCT) is a noninvasive optical imaging modality that provides real-time, 1D depth, 2D cross-sectional, and 3D volumetric images with micron-level resolution and millimeters of imaging depth. OCT images consist of structural information from a sample based on light backscattered from different layers of material within the sample. It can provide real-time imaging and is capable of being enhanced using birefringence contrast or functional blood flow imaging with optional extensions to the technology.
Thorlabs has designed a broad range of OCT imaging systems that cover several wavelengths, imaging resolutions, and speeds, while having a compact footprint for easy portability. Also, to increase our ability to provide OCT imaging systems that meet each customer’s unique requirements, we have designed a highly modular technology that can be optimized for varying applications.
Retina Cone Cells
OCT is the optical analog of ultrasound, with the tradeoff being lower imaging depth for significantly higher resolution (see Figure 1). With up to 15 mm imaging range and better than 5 micrometers in axial resolution, OCT fills a niche between ultrasound and confocal microscopy.
In addition to high resolution and greater imaging depth, the non-contact, noninvasive advantage of OCT makes it well suited for imaging samples such as biological tissue, small animals, and materials. Recent advances in OCT have led to a new class of technologies called Fourier Domain OCT, which has enabled high-speed imaging at rates greater than 700,000 lines per second.1
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. In OCT, to obtain cross-sectional images with micron-level resolution, 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: Spectral Domain OCT (SD-OCT) and Swept Source OCT (SS-OCT). In both types of systems, light is divided into sample and reference arms of an interferometer setup, as illustrated in Fig 2. SS-OCT uses coherent and narrowband light, whereas SD-OCT systems utilize broadband, low-coherence light sources. Back scattered light, attributed to variations in the index of refraction within a sample, is recoupled into the sample arm fiber and then combined with the light that has traveled a fixed optical path length along the reference arm. A resulting interferogram is measured through the detection arm of the interferometer.
The frequency of the interferogram measured by the sensor is related to depth locations of the reflectors 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. As the sample arm beam is scanned across the sample, 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 are collected to produce a 3D volume data set. With FD-OCT, 2D images are collected on a time scale of milliseconds, and 3D images can be collected at rates now below 1 second.
Spectral Domain OCT vs. Swept Source OCT
Spectral Domain and Swept Source OCT systems are based on the same fundamental principle but incorporate different technical approaches for producing the OCT interferogram. SD-OCT systems have no moving parts, and therefore, have high mechanical stability and low phase noise. Availability of a broad range of line cameras has also enabled development of SD-OCT systems with varying imaging speeds and sensitivities.
SS-OCT systems utilize a frequency swept light source and photodetector to rapidly generate the same type of interferogram. Due to the rapid sweeping of the swept laser source, high peak powers at each discrete wavelength can be used to illuminate the sample to provide greater sensitivity with little risk of optical damage.
FD-OCT Signal Processing
In Fourier Domain OCT, the interferogram is detected as a function of optical frequency. With a fixed optical delay in the reference arm, light reflected from different sample depths produces interference patterns with the different frequency components. A Fourier transform is used to resolve different depth reflections, thereby generating a depth profile of the sample (A-scan).
1V.Jayaraman, J. Jiang, H.Li, P. Heim, G. Cole, B. Potsaid, J. Fujimoto, and A. Cable, "OCT Imaging up to 760 kHz Axial Scan Rate Using Single-Mode 1310 nm MEMs-Tunable VCSELs with 100 nm Tuning Range," CLEO 2011 - Laser Applications to Photonic Applications, paper PDPB2 (2011).