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More News about SS-OCT (2/2)

Swept laser source non-linearity and k-clock instability compensation

Swept source OCT lasers are non-linear. This non-linearity must be compensated to improve both resolution and sensitivity.

Non-linearity correction can be done in two ways:

Direct ADC clocking: the ADC capturing the OCT interference is clocked directly with a clock signal that contains the information of the laser source non-linearity.

Digital Resampling: The ADC capturing the OCT interference is clocked at constant sampling period. The digitized OCT interference is digitally non-linearly resampled in a way to compensate the non-linearities computed on the K-clock and acquired with a second ADC channel. K-clock can be easily generated with a Mach-Zehnder interferometer (MZI) connected to the same laser source.

Current solution is based on the resampling approach. If it requires an additional channel, on the other hand, it provides more flexibility, and simpler implementation of the OCT system. For instance, it is not required to generate a “dummy” K-clock out of the source sweep.  Besides, the digital resampling approach offers additional capabilities, such as:

-Compensation of the optical path difference between K-clock and OCT-signal

-Programmable maximum analysis depth. 

U5303A High-Speed Data Acquisition Card for SS-OCT: Product features and specifications 

Image clarity and high-resolution

Acquisition card signal integrity characteristics are critical to guarantee the best image quality. This unique solution offers:

  • A best in class signal noise ratio for a 12 bits resolution digitizer (57-58 dB typical)
  • Improved spurious free dynamic range (SFDR) thanks to x4 (SS2) or x2 (SS1) oversampling interpolation. For instance, with -SS2 option, artefacts are reduced by 14 dB due to interpolation.
  • Better phase stability thanks to accurate synchronization for A-scan triggers
  • SS1 option: ENOB = 9.3 (typical) at 100 MHz
  • SS2 option: ENOB = 9.1 (typical) at 410 MHz

Flexible SS-OCT analysis depth

To allow deep analysis, the system needs a high sampling rate. The new SS2 option doubles the sampling rate from 500 MS/s to 1GS/s, allowing:

-either to double the maximum analysis depth with same A-scan rate.

-or to double the image speed (double A-scan rate), keeping the same analysis depth.

In addition, the maximum analysis depth is programmable by selecting the effective sampling rate of the ADC card.

Key advantages of this approach are:

–           Flexibility from changing the A-scan rate.

–           Independency from K-clock frequency

–           Programmable through variable sampling rate (internal clock from 250 MHz up to 1 GHz).

Fast scan measurement and image restitution

3-D images are very long to acquire. The sustained scan rate is a crucial parameter to minimize unwanted samples movement in ophthalmic applications or to reduce the measurement time when the blood flow is stopped in cardio-vascular applications.

This solution enables up to 200 kHz A-scan rate (i.e. 200’000 A-scan per second), allowing fast acquisition of B-scans. The high scanning speed and fast image restitution are continuously guaranteed and not only for a limited period of time, thanks to:

–           Continuous mode with simultaneous OCT signal acquisition and image data readout (see Signal acquisition sequence)

–           Continuous acquisitions of B-scans without missing any trigger/data

–           Real time OCT processing on FPGA

–           U5303A sustained data throughput > 2 GB/s.

Related products:

U5303A PCIe 12-bit High-Speed Digitizer

To learn more about our SS-OCT solutions, please contact us at


About Acqiris SA

On August 1, 2017, Keysight PCIe-based digitizer group became a new company and returned to its original name: Acqiris, a leader in signal acquisition, enriched with the experience of Agilent and Keysight Technologies. The same team of dedicated specialists has been developing high quality signal acquisition products, bringing technical excellence to our customer unique application.

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