The document discusses approaches for developing a practical terahertz (THz) imaging system using a compact continuous wave (CW) transceiver. It describes how a THz transceiver can be integrated onto a single device using resonant tunneling diodes or photonic crystals to generate and detect THz signals. A single resonant tunneling diode was demonstrated to perform imaging by spatially modulating a transmitted signal and detecting the reflected signal. Efficient spatial sampling for imaging requires either moving a single transceiver or implementing an array of transceivers with beamforming, but arrays currently have limitations of cost and small imaging areas.

1. Navina Kleemann1
Towards Practical THz Imaging System
with Compact CW Transceiver
Arslan Ali
Master-Seminar THz Technology – SoSe23
arslan.ali@rub.de

2. Outline
■ Introduction
■ Integration of THz Transceiver for Imaging
■ A Single RTD Transceiver for Imaging
■ Spatial Sampling for Practical Imaging System
■ Summary
Towards Practical THz Imaging System with Compact CW Transceiver
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023

3. Outline
■ Introduction
■ Integration of THz Transceiver for Imaging
■ A Single RTD Transceiver for Imaging
■ Spatial Sampling for Practical Imaging System
■ Summary
Towards Practical THz Imaging System with Compact CW Transceiver
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023

4. Introduction
Terahertz (THz) Radiation
 submillimeter radiation.
 EM radiation that falls between the infrared and microwaves.
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Frequency (Hz)
Source: Singh, M.Koch, TU Braunschweig.

5. Introduction
Terahertz (THz) Radiation
 submillimeter radiation.
 EM radiation that falls between the infrared and microwaves.
Towards Practical THz Imaging System with Compact CW Transceiver
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Frequency (Hz)
Source: Singh, M.Koch, TU Braunschweig.

6. Introduction
Applications: security screening, medical imaging, etc.
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Source: Singh, K.R., Bandyopadhyay, A., & Sengupta, A. Low-Loss Metallic Waveguide for THz Applications.

7. Introduction
Imaging techniques that include the THz band
 two different approaches are generally applied :
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Pulse Imaging Continuous wave
Imaging

8. Introduction
Imaging techniques that include the THz band
 two different approaches are generally applied :
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Pulse Imaging Continuous wave
Imaging
- practical THz imaging system:
 includes a compact transceiver,
 and cost-effective spatial sampling method.

9. Introduction
Imaging techniques that include the THz band
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Pulse Imaging
- TDS, is mainstream for THz imaging applications.
- pulse duration of ps-order,
- thickness of thin layers.
- 3D imaging with tomography techniques.
- bulky source device
- complex TD data acquisition and costly.
[1] C. Wang, J. Y. Qin, W. D. Xu, M. Chen, L. J. Xie, and Y. B. Ying, “Terahertz imaging applications in agriculture and food engineering: A review,” Trans. ASABE, vol. 61, no. 2, pp. 411–424, 2018, https://elibrary.asabe.org/abstract.asp?aid=48880

10. Introduction
Imaging techniques that include the THz band
Towards Practical THz Imaging System with Compact CW Transceiver
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Continuous wave
Imaging
- a compact THz imaging system.
- THz waves ~ generated via both photonic and
electronic techniques.
- 3D imaging, CW signals ~ frequency sweep
- with coherent detection scheme
- synthetic pulses of high power.
[1] C. Wang, J. Y. Qin, W. D. Xu, M. Chen, L. J. Xie, and Y. B. Ying, “Terahertz imaging applications in agriculture and food engineering: A review,” Trans. ASABE, vol. 61, no. 2, pp. 411–424, 2018, https://elibrary.asabe.org/abstract.asp?aid=48880

11. Introduction
Imaging techniques that include the THz band
Towards Practical THz Imaging System with Compact CW Transceiver
4
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023
Pulse Imaging Continuous wave
Imaging
- TDS, is mainstream for THz imaging applications.
- pulse duration of ps-order,
- thickness of thin layers.
- 3D imaging with tomography techniques.
- bulky source device
- complex TD data acquisition and costly.
- a compact THz imaging system.
- THz waves ~ generated via both photonic and
electronic techniques.
- 3D imaging, CW signals ~ frequency sweep
- with coherent detection scheme
- synthetic pulses of high power.
[1] C. Wang, J. Y. Qin, W. D. Xu, M. Chen, L. J. Xie, and Y. B. Ying, “Terahertz imaging applications in agriculture and food engineering: A review,” Trans. ASABE, vol. 61, no. 2, pp. 411–424, 2018, https://elibrary.asabe.org/abstract.asp?aid=48880

12. Introduction
combination of electronic and photonic technique can realize a compact THz transceiver at different
frequency bands for various applications.
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[2] R. Safian, G. Ghazi, and N. Mohammadian, “Review of photomixing continuous-wave terahertz systems and current application trends in terahertz domain,” Opt. Eng., vol. 58, no. 11, pp. 1, 2019, doi: 10.1117/1.oe.58.11.110901

13. Introduction
combination of electronic and photonic technique can realize a compact THz transceiver at different
frequency bands for various applications.
- generate CW signals < or > 300-GHz band.
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[2] R. Safian, G. Ghazi, and N. Mohammadian, “Review of photomixing continuous-wave terahertz systems and current application trends in terahertz domain,” Opt. Eng., vol. 58, no. 11, pp. 1, 2019, doi: 10.1117/1.oe.58.11.110901

14. Outline
■ Introduction
■ Integration of THz Transceiver for Imaging
■ A Single RTD Transceiver for Imaging
■ Spatial Sampling for Practical Imaging System
■ Summary
Towards Practical THz Imaging System with Compact CW Transceiver
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023

15. Integration of THz Transceiver for Imaging
THz Sources and Detectors for Imaging System
Towards Practical THz Imaging System with Compact CW Transceiver
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- THz transceiver, including the source, detector, and interface components.
- electronic and photonic devices ~ configured to generate CW signals
- electronic devices ~ generate THz signals with DC bias,
- cost-effective. e.g. diodes
- THz detectors ~ photon detector & thermal detector.

16. Integration of THz Transceiver for Imaging
THz Sources and Detectors for Imaging System
Towards Practical THz Imaging System with Compact CW Transceiver
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- THz transceiver, including the source, detector, and interface components.
- electronic and photonic devices ~ configured to generate CW signals
- electronic devices ~ generate THz signals with DC bias,
- cost-effective. e.g. diodes
- THz detectors ~ photon detector & thermal detector.

17. Integration of THz Transceiver for Imaging
Integration of THz Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- quasi-optical configuration with a THz transceiver
- bulky.

18. Integration of THz Transceiver for Imaging
Integration of THz Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- quasi-optical configuration with a THz transceiver
- bulky.
[3] D. M. Mittleman, “Twenty years of terahertz imaging,” Opt. Exp., vol. 26, no. 8, pp. 9417, 2018, doi: 10.1364/oe.26.009417

19. Integration of THz Transceiver for Imaging
Integration of THz Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
Concept of simplifying a THz transceiver

20. Integration of THz Transceiver for Imaging
Integration of THz Transceiver
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
Concept of simplifying a THz transceiver

21. Integration of THz Transceiver for Imaging
Integration to a Single Device
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards
Practical THz Imaging System with
Compact CW Transceiver,"
- integration of devices ~ THz imaging is highly desirable
- production of convenient, compact, and potentially mass-producible
- cheap equipment.

22. Integration of THz Transceiver for Imaging
Integration of THz Transceiver
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- micro-structured all-intrinsic-si photonic-crystal technology
- integrated unit uses an unpatterned Si slab and monolithically integrates
- 1 2-Maxwell fisheye lenses ~ beam splitter
[4] K. Tsuruda, M. Fujita, and T. Nagatsuma, “Extremely low-loss terahertz waveguide based on silicon photonic-crystal slab,” Opt. Exp., vol. 23, no. 25, pp. 31977, 2015, doi: 10.1364/oe.23.031977

23. Integration of THz Transceiver for Imaging
Integration of THz Transceiver
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- packaging structures are compulsory to house fragile micro-structured Si units.
- a metal case,
- 4 waveguide parts are designed to join ~ coupling spikes of the integrated unit.

24. Outline
■ Introduction
■ Integration of THz Transceiver for Imaging
■ A Single RTD Transceiver for Imaging
■ Spatial Sampling for Practical Imaging System
■ Summary
Towards Practical THz Imaging System with Compact CW Transceiver
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023

25. A Single RTD Transceiver for Imaging
Another approach for Imaging Application
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- Resonant Tunneling Diode (RTD)
- transmitter and receiver simultaneously,
- reduced cost.
[5] L. Yi, R. Kaname, Y. Nishida, X. Yu, M. Fujita, and T. Nagatsuma, “Imaging applications with a single resonant tunneling diode transceiver in 300-GHz band,” in Proc. 2020 Int. Topical Meeting Microw. Photon. (MWP), 2020, pp. 120–123, doi: 10.23919/MWP48676.2020.9314482.

26. A Single RTD Transceiver for Imaging
Another approach for Imaging Application
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- transmitted signal ~ spatially modulated by an optical chopper at 1 kHz,
- transmitted to a mirror at 32.5 cm.
- reflected signal was output via the bias tee and a lock-in amplifier, A/D to digitalize the signals.

27. A Single RTD Transceiver for Imaging
Another approach for Imaging Application
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- mirror reflector ~ stage was moved toward the RTD module,
- detected phase differences.
- mirror reflector ~ shifted 3.5 mm, leads to clear periodical signal,
- oscillation frequency of the RTD.

28. A Single RTD Transceiver for Imaging
Another approach for Imaging Application
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- a 100-yen coin inside the envelope ~ imaged at a d = 20 cm
- conventional quasi-optic setup and a 2D moving stage.
- spatial resolution ∼1 mm

29. Outline
■ Introduction
■ Integration of THz Transceiver for Imaging
■ A Single RTD Transceiver for Imaging
■ Spatial Sampling for Practical Imaging System
■ Summary
Towards Practical THz Imaging System with Compact CW Transceiver
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023

30. Spatial Sampling - Practical Imaging System
Approach for Achieving Efficient Spatial Sampling
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- spatial sampling by moving a transceiver
- involves only one transceiver device
- extra efforts are required
- dense data sampling in a short time to realize RT THz imaging.

31. Spatial Sampling - Practical Imaging System
Approach for Achieving Efficient Spatial Sampling
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- array concept which involves multiple transceivers
- future trends,
- array system together with beam-forming technique,
- lead to a real-time imaging system.

32. Spatial Sampling - Practical Imaging System
Approach for Achieving Efficient Spatial Sampling
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- limitations: high cost and directional THz beam
- image a small area

33. Spatial Sampling - Practical Imaging System
Approach for Achieving Efficient Spatial Sampling
Towards Practical THz Imaging System with Compact CW Transceiver
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Source: L. Yi et al., "Towards Practical THz Imaging System with Compact CW Transceiver,"
- combination of a linear array with a quasi-optic system
- increase imaging speed while attaining a larger survey area.
[6] A. Rogalski and F. Sizov, “Terahertz detectors and focal plane arrays,” Opto-Electron. Rev, 2011, doi: 10.2478/s11772-011-0033-3.

34. Outline
■ Introduction
■ Integration of THz Transceiver for Imaging
■ A Single RTD Transceiver for Imaging
■ Spatial Sampling for Practical Imaging System
■ Summary
Towards Practical THz Imaging System with Compact CW Transceiver
PHOTONICS AND
TERAHERTZ
TECHNOLOGY
19.05.2023

35. Summary
■ THz imaging technology is developing rapidly, still not mature and difficult for large-scale
production.
■ Trade-offs betwaeen the imaging resolution and data acquisition.
■ Integration of the THz transceiver is a key aspect in realizing a compact practical imaging system.
■ RTD device exhibit potential for integration without the need for separate sources and detectors,
and coherent signal can be obtained directly.
■ Mechanical beam-scanning is an intermediate method for obtaining THz images in real-time.
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36. References
[1] C. Wang, J. Y. Qin, W. D. Xu, M. Chen, L. J. Xie, and Y. B. Ying, “Terahertz imaging applications in agriculture and food engineering: A
review,” Trans. ASABE, vol. 61, no. 2, pp. 411–424, 2018, https://elibrary.asabe.org/abstract.asp?aid=48880
[2] S. Wang and X. C. Zhang, “Pulsed terahertz tomography,” J. Phys. D. Appl. Phys., vol. 37, no. 4, 2004, doi: 10.1088/0022-3727/37/4/R01.
[3] D. M. Mittleman, “Twenty years of terahertz imaging,” Opt. Exp., vol. 26, no. 8, pp. 9417, 2018, doi: 10.1364/oe.26.009417
[4] K. Tsuruda, M. Fujita, and T. Nagatsuma, “Extremely low-loss terahertz waveguide based on silicon photonic-crystal slab,” Opt. Exp., vol.
23, no. 25, pp. 31977, 2015, doi: 10.1364/oe.23.031977
[5] L. Yi, R. Kaname, Y. Nishida, X. Yu, M. Fujita, and T. Nagatsuma, “Imaging applications with a single resonant tunneling diode transceiver in
300-GHz band,” in Proc. 2020 Int. Topical Meeting Microw. Photon. (MWP), 2020, pp. 120–123, doi: 10.23919/MWP48676.2020.9314482.
[6] A. Rogalski and F. Sizov, “Terahertz detectors and focal plane arrays,” Opto-Electron. Rev, 2011, doi: 10.2478/s11772-011-0033-3.
Towards Practical THz Imaging System with Compact CW Transceiver
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37. Questions
-
Towards Practical THz Imaging System with Compact CW Transceiver
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?
?
?

38. Thankyou for your
attention!
Master-Seminar THz Technology – SoSe23
RUHR
UNIVERSITÄT
BOCHUM