Development of Optical Coherence Microscope Electronics

The optical coherence microscope is an optical system that takes depth-resolved en face images using low coherence interferometry. By implementing a fiber-based Michelson interferometer, the OCM system measures the light back-scattered from a plane within the sample. The location of this en face plane is governed by the optical path length set in the reference arm of the interferometer. A schematic of the optical coherence microscope (OCM) is shown in Figure 1-1.

Figure 1-1. Schematic of the optical coherence microscopy system.

Optical coherence microscopy has potential for biomedical application in its ability to image tissue regions that are inaccessible to conventional microscopes. The high light scattering properties of biological tissue renders such techniques as two-photon and confocal microscopy useless for imaging much beneath the surface layer of tissue. Optical coherence microscopy overcomes this limitation, allowing three-dimensional imaging of cells or groups of cells.

Project Goals

The purpose of this project is to improve the existing functionality and performance characteristics of the Optical Coherence Microscope (OCM) electronics. The

The original Printed Circuit Board (PCB) was created to drive a piezo device and demodulate the electronic signal from an optical detector (see figure above). Additional modifications have been made to improve the system and the major tasks have been undertaken:

1. Decrease Noise Floor
2. Increase Dynamic Range
3. Improve the Ability of the Piezo Drive CKT
4. Perform SNR Analysis at Each Stage
5. Perform Appropriate Integration/Test for the Final System

As a result of early experimentation, the following tasks have been undertaken to increase the functionality and performance of the OCM electronics system. They have been performed in this order.

• Re-organize the power regulation components, such that they will not interfere with sensitive electronics.
• Purpose: Attempt to Reduce Thermal Noise
• Replace the LM-741 op-amp with a more suitable device
• Purpose: Improve piezo driver characteristics (appropriate power, clean waveform)
• Match Piezo Driver Frequency to the Piezo Resonant Frequency through the addition or removal of circuit components (pot resistor)
• Purpose: Attempt to utilize full piezo range for better imaging
• Determine if existing circuitry can provide desired dynamic range
• Purpose: Learn if additional gain stage is necessary
• Perform a complete SNR analysis at each stage of the electronics
• Purpose: Determine other areas of noise generation
• Perform other Testing/Integration (as need be)

Please also refer to Publications for more resources.