Enabling High-Speed Swept-Source OCT with Advanced Data Acquisition

Optical coherence tomography (OCT) has become an essential tool in modern medical imaging, with swept-source OCT (SS-OCT) emerging as a leading modality because of its superior imaging speed, depth penetration, and sensitivity. By employing swept laser sources, SS-OCT enables high-resolution, real-time visualization of tissue microstructures, making it particularly valuable in applications such as ophthalmology, cardiology, dermatology and dental imaging.

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Figure 1. Swept-source OCT offers performance benefits in a wide variety of applications.

A critical component at the core of the instrument is the data acquisition system. The digitizer, responsible for accurately capturing interferometric signals, directly affects image quality, imaging depth, and scan speed. As SS-OCT systems continue to push for higher scan speed, better axial resolution, and greater imaging depth, the demands placed on digitizers—such as sampling rate, bandwidth, dynamic range, and real-time processing—have become increasingly stringent.

This article will explore the key role of digitizers in enabling state-of-the-art SSOCT systems and explain why Teledyne digitizers, including the ADQ32 and ADQ35, provide the performance, flexibility, and advanced features required by SS-OCT instrument developers striving to build next-generation imaging solutions.

SS-OCT vs SD-OCT
Swept source OCT (SS OCT) offers major technical advantages over spectral domain OCT (SD OCT) because of its high speed swept laser source and single photodetector design, which deliver faster scan rates, deeper tissue penetration, and far less sensitivity roll off with depth.

Its longer operating wavelength (~1050 nm) improves imaging through scattering tissues and enables superior visualization of the choroid and deeper ocular structures. SS OCT also provides higher signal-to-noise performance and more stable phase information, making it especially powerful for high-density volumetric imaging and OCT angiography.



Table 1. Advantages of SS-OCT over SD-OCT.

Historically, swept lasers were the most expensive part of SS OCT systems. However, new semiconductor based tunable lasers (e.g., MEMS VCSELs) are being designed for low cost, high volume production, making SS-OCT instruments more competitive and affordable

SS-OCT Digitizer Requirements
Overall system performance is tightly constrained by the quality and capability of the digitizer. Developers are not simply looking for fast data acquisition; SS-OCT developers need digitizers that combine multi-GS/s sampling, low jitter, high analog bandwidth, and high ENOB performance for the accurate capture of GHz interferometric fringes. They also require deterministic timing, real-time k space linearization, and high throughput streaming to support real-time imaging pipelines. System performance is ultimately limited by the digitizer’s ability to acquire clean, precisely timed data at extremely high speeds.
Key developer requirements for SS-OCT digitizers typically include:

• 1 to 5 GSPS sampling rates to accurately capture rapidly swept interferometric signals. Imaging depth is proportional to digitizer sampling rate and laser coherence length. Increasing swept-source laser sweep rates, coherence length, and k-clock frequencies are driving the need for higher speed digitizer technology.
• Wide analog bandwidth (1 to 2 GHz) to support high-frequency fringe signals without distortion and k-clock frequencies in the range of 1 – 2 GHz.
• High dynamic range and low noise to preserve weak reflections from deeper tissue layers. 12-bit vertical resolution at up to 5 GSPS sampling rate.
• Real-time data handling, including peer-to-peer streaming and FPGA pre-processing, to avoid bottlenecks at high A-scan rates. Real-time streaming to CPU or GPU at gigabytes per second rates.
• Low-latency processing, enabling immediate image reconstruction or feedback.

Teledyne’s ADQ3-series digitizers meet and exceed these requirements.

ADQ3 Digitizer Series for SS-OCT
Up to 5 GSPS capability ensures that even the fastest swept lasers can be sampled with high fidelity, capturing high-frequency fringe frequencies and preserving axial resolution. This high sampling rate, combined with excellent analog front-end performance up to 2.5 GHz, allows developers to fully exploit the bandwidth of modern SS-OCT light sources without compromise.

An essential part of the digitizer solution is dedicated application-specific firmware. FWOCT is firmware developed by Teledyne SP Devices to map the sampled k-clock to the OCT signal in SS-OCT imaging systems and perform all the other signal processing steps to produce OCT images. The k-clock and OCT signal are connected to a dual-channel digitizer. The k-clock signal is sampled by the digitizer and then processed to find the desired OCT sampling points. For the selected points, the corresponding value of the OCT signal input is estimated with high precision. This has many advantages compared to direct-clocking approaches – see Digitizer for swept-source OCT (SS-OCT) - Teledyne SP Devices for more details.



Figure 2. Block diagram of a typical SS-OCT system with integrated digitizer.

Integrated firmware moves key processing steps—such as resampling (k-linearization), digital filtering, and potentially FFT preparation—onto the digitizer itself, and this has several advantages:

• Reduced host CPU/GPU load, enabling simpler system architecture.
• Lower data transfer bandwidth requirements, since data can be pre-processed before streaming.
• Deterministic, real-time performance, essential for high-speed imaging systems.
• Improved phase stability due to tightly controlled, hardware-level processing.

FWOCT Highlights

• Flexible k-clock support (4 – 2000 MHz) for use with a wide range of lasers.
• K-clock interpolation to support MZI-interferometers and low k-clock frequencies (4 – 2000 MHz k-clock supported).
• Programmable modes to select sampled k-clock points mapped to the OCT signal. For example, rising edge, rising and falling edge, or interpolated configuration with multiple points per k-clock period.
• High maximum OCT signal bandwidth (0 – 2000 MHz).
• Signal noise reduction by user-configurable FIR filters.
• Timing adjustments between the k-clock and OCT signal paths.
• FFT with flexible output formats – complex, squared magnitude, logarithmic.

• Background removal.
• Dispersion compensation.

Figure 3. ADQ35 digitizer with onboard real-time SS-OCT processing using FWOCT.

In contrast, many competing solutions rely heavily on software-based processing after acquisition, which introduces latency, increases system complexity, and can limit achievable imaging speeds.

Taken together, the combination of up to 5 GSPS capable hardware and dedicated FWOCT firmware provides a tightly integrated acquisition and processing platform. For these reasons, the ADQ3-series stand out as a leading choice for SS-OCT developers seeking to push the limits of speed, sensitivity, and real-time imaging capability.



Table 2. Selected performance figures for a number of ADQ3-series digitizers.

ADQ32, ADQ33, and ADQ35 are available in either PCIe format or with a USB 3.2 interface (see ADQ3-USB - Teledyne SP Devices) while ADQ36 is available in PXIe. For more information on Teledyne SP Devices SS-OCT solutions visit Digitizer for swept-source OCT (SS-OCT) - Teledyne SP Devices

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