Practical Application of Fiber Components Manufactured by Bonacom in Combined System of Photoacoustic Tomography and Optical Coherence Tomography  

 

Photoacoustic tomography (PAT) is a powerful noninvasive and nonionizing biomedical imaging modality that has attracted great attention in the last decade. It remotely measures photoacoustic (PA) signals with a 1550-nm laser on the surface of a sample by utilizing a fiber interferometer as an ultrasound detector.

Since the PA signal is strongly associated with the optical absorption properties of the sample, PAT can provide optically absorbed structural (i.e., vascular structure and internal organs), functional (blood oxygen concentration, blood flow, and hemodynamic change), and molecular (tumor and cancer cell) images of various biological tissues.However,PAT is less sensitive to the low-absorptive constituents in tissue, hence having difficulty in visualizing the tissue morphology.

 

Optical coherence tomography (OCT) is a high-resolution and noncontact imaging system that uses low-coherence interferometry. OCT is capable of having 2D and 3D tomograms of the internal microstructures of various biological samples, based on scattering and reflecting. The OCT signal is obtained from the interference between the beam back-reflected from the reference arm and the light back-scattered from the internal layers of the sample, which depends on intrinsic refractive index gradients. However, the OCT image is restricted in presenting the optical absorption property of the sample and in-depth imaging up to 2~5 mm due to the short mean free path of biological tissues.

 

Therefore, the combination of PAT and OCT can potentially provide valuable complementary information of structural and functional features of biological tissues.

 

The all-fiber-based combined PAT-OCT system is depicted in Figure 10. The system configuration is based on two fiber-based Mach-Zender interferometers; one for the noncontact PAT system (blue lines) and the other for the OCT system (red lines). The common fiber-optic probe, made up of a lensed single-mode fiber (SMF) and a large-core multimode fiber (MMF), is used for the common sample arm of two systems.

 

Figure 10. Schematic of the all-fiber-based dual modality of photoacoustic and optical coherence tomography with a miniature common probe. AOM: acousto-optic modulator; PC: polarization controller; BPD: balanced photodetector; C1-C4: fiber coupler, Cir1-Cir3: fiber circulator; Col: collimator; ND: neutral density filter; L1,2: lens; M: mirror; WDM: wavelength division multiplexer; MMF: multimode fiber.

 

For the heterodyne interferometer, a single frequency laser (SFL-1550, Thorlabs, Newton, NY, USA) with a wavelength of 1550 nm and maximum output power of 30 mW, is used. The output light from the source is coupled into a SMF and splits into reference and sample arms by a Bonacom’s 1x2 fiber coupler (C1,

BNFUC-1-55,Bonacom Technology Co.,LTD,Shenzhen,China ). In the reference arm, the beam is frequency modulated with an acousto-optic modulator (AOM; Fiber-Q FCAOM, Gooch & Housego, Ilminster,UK) and directed into the second Bonacom’s coupler (C 2,BNFUC-1-55 ) after passing through a polarization controller (FPC031,Thorlabs). The sample beam goes through a Bonacom’s circulator(Cir1,BNCIR-1-55-S) and a Bonacom’s wavelength division multiplexer (WDM;BNWDM-1310/1550) and is then focused onto the sample via the self-built lensed fiber.

 

The beam from the swept-source was coupled into a SMF and divided into the reference and sample arms of the Mach-Zender interferometer using a Bonacom’s 1x2 coupler (C 3,BNFUC-1-31).The sample arm of OCT shared the lensed SMF with the sample arm of the PAT system through the Bonacom’s WDM(WDM;BNWDM-1310/1550). In the reference arm, a Bonacom’s collimator(Col,BNCOL-31),a ND filter, a lens, and a Bonacom’s fiber mirror(M,BNFM-31) were used to match the optical path lengths of two arms. The light back-scattered from a sample was collected by the lensed fiber and recombined with the light reflected from the reference arm at a Bonacom’s 1x2 coupler (C 4,BNFUC-1-31).

  

The all-optical-fiber-based dual-modal PAT-OCT imaging system employ a compact common probe, which shares the sample arm of both a noncontact PAT sub-system and a swept-source OCT sub-system without any physical contact. As both PAT and OCT probe beams are guided into the same fiber-optics probe, it is possible to acquire the PAT and OCT signals at the same detection position.The MMF of the probe delivers the short pulses of a Nd:YAG laser to efficiently excite the PA signals. In addition, the fiber-optic design of the probe is compact, simple, flexible, cost-effective, robust, and stable. Further, it is free from electromagnetic interference. Thus, it can be beneficial for commercialization and clinical applications in fields requiring minimally invasive or endoscopic imaging.

 

Bonacom manufactures a variety of passive components for OCT systems application, e.g.:fused coupler,optical circulator, VOA(variable optical attenuator), isolator, in-line reflector,in-line-mirror, fiber collimator, WDM(Wavelength Division Multiplex), in-line polarizer, and polarization beam splitter(PBS) with broadband working wavelength at 1310nm,1550nm.

We also offer custom optical modules and subsystems by integrating multiple broadband components such as splitters, circulators, fixed and variable optical attenuators. These components are ideal choices for developing expanding global OCT interferometric systems. Contact Bonacom Technology to discuss your requirements.