Headline Headline

1. Introduction Optical Coherence Tomography (OCT) is proven to be a non-invasive, high resolution (µm), medical optical imaging capable of providing cross-sectional and 3D images to visualize the structure of biological samples and internal organs.

2. Methods

A telecoms laser, with a wavelength coverage of ≈ 60 nm centered at 1540 nm, was optical characterized (lasing wavelength/SMSR) power using the setup shown in Fig. 3.

3. Results

9

Authors

Affiliations

References 1. J. Fujimoto and W. Drexler, Introduction to Optical Coherence Tomography in Optical Coherence Tomography and Applications. Springer, vol. 1 2. M. Bonesi, R.A. Leitgeb, W. Drexler, “Akinetic all-semiconductor programmable swept source at 1550 nm and 1310 nm with centimeters coherence length”, Opt. Express (2014) 3. J. Engelstaedter, B. Roycroft, F. Peters, B. Corbert, “Dynamic SMSR measurement of fast SG-DBR laser wavelength switching” IEEE Lasers and Electro-Optics, (2009)

Linear sweep of telecoms lasers for OCT applications

Carlos Reyes, Tomasz Piwonski, Stephen Hegarty, Brian Corbett, Brendan Roycroft 1 Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland

2 CAPPA – Centre for Advanced Photonics & Process Analysis, Cork Institute of Technology, Bishoptowns, Cork, Ireland

1 1,2 1,2 1 1

Objective To develop a tunable swept laser using telecoms laser technology that is able to create a linearly increasing sweep as a function of time, suitable for OCT.

Swept-source OCT (SS-OCT) requires a laser that is able to sweep over a wide wavelength range as a linear function of time. The axial resolution is defined by wavelength coverage.

• 5 section tunable laser allows

‘akinetic’ tunable mechanism • All-electronically tunable laser

without mechanical parts (Vernier tuning)

• Good wavelength coverage

• Tuning paths clearly identified

• Mode hopes in the borders

• Wavelength linearly increases

4. Conclusion

1

Figure 1. Basic structure of a SS-OCT system. DAQ : Data Acquisition

Figure 2. Swept laser performance

2

Figure 3. Experimental setup to characterize the optical performance of a tunable laser in terms of its lasing wavelength and SMSR. DAQ : Data Acquisition; V/I – Voltage to Current converter; PD: Photodiode TLS: Tunable Laser Source; TEC: Thermoelectric Controller; OSA: Optical Spectrum Analyzer

Figure 4. Multi-section laser composed of five sections: 2 mirrors, phase, gain and semiconductor optical amplifier (SOA)

Wavelength (nm)

Figure 6. Surface Plot of the Tuning Map

2

0 20

40 60

0 10

20 30

40 50

1580

1560

1540

1520

1500

Mirror 2 (mA) Mirror 1 (mA)

Wavelength (nm)

1510

1520

1530

1540

1550

1560

1570 3D Surface Plot • Wavelength levels are clear

• There are three main regions

• Perform tuning in Region 2

• Outstanding single mode operation

• Useful to increase OCT image quality

(4) 3000 points are found (5) 300 points are selected to build a linear sweep

(6) Automated algorithm to perform a linear sweep (7) 3 KHz sweep measurement

Funding was from the EU H2020 project PICCOLO, grant agreement 732111: ‘Multimodal highly-sensitive PhotonICs endoscope for improved in-vivo COLOn Cancer diagnosis and clinical decision support’.

3

∆𝑧 =2𝑙𝑛2

𝜋

𝞴2

∆𝞴

Axial Resolution:

5 No wavelength duplicates AC-RMS

0 10 20 30 40 50 60 100

50

0

Figure 9. No wavelength duplicates

6

Automated point finder algorithm

Figure 10. Automated Algorithm Amplitude

Sample # -1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0 5000 10000 15000 20000 25000 30000 35000 40000

Linear Filter Output 7

Figure 11. Linear Sweep

Figure 7. SMSR Map

SMSR Map

10 20 30 40 50 60 70

10

15

20

25

30

35

40

45

48.00

42.03

36.06

30.08

24.10

18.13

12.15

6.175

0.2

dB

Mirror 1 (mA)

Mir

ror

2 (

mA

)

3

Mirror 1

Phase

Gain

Mirror 2

SOA

Figure 5. Wavelength Tuning Map

10 20 30 40 50 60 70 1573

1565

1557

1549

1541

1533

1525

1517

1509

10

15

20

25

30

35

40

45

Mir

ror

2 (

mA

)

Mirror 1 (mA)

Laser’s Wavelength Tuning Map 1

A linear wavelength sweep can be obtained using a telecoms laser but its performance can be further improved by reducing the noise of the driver electronics and avoiding high noise transitions.

OCT 1560

1540

1520

60 40 20 0

20 40

60

Full 4D Scatter Plot AC-RMS

Figure 8. 4D Scatter Plot

Wavelength (nm)

4