Millimeter Wave Imaging Using Up-Conversion Detection Method

with Glow Discharge Detector and Photoreceiver Combination

Arun Ramachandra Kurup

1 a

, Daniel Rozban

1 b

, Amir Abramovich

1 c

Yitzhak Yitzhaky

2 d

and Natan Kopeika

2 e

Department of Electrical and Electronic Engineering, Ariel University, Ariel, Israel

Department of Electro-Optics and Photonics Engineering, School of Electrical and Computer Engineering,

Ben-Gurion University of the Negev, Beer Sheva, Israel

Keywords: Millimeter Wave Imaging, Up-Conversion Detection, Glow Discharge Detector, Photoreceiver.

Abstract: This paper presents an advanced photonic detection system for high-resolution millimeter-wave (MMW)

imaging, utilizing an up-conversion detection method with a Glow Discharge Detector (GDD) and a

photoreceiver to capture detailed images of metallic objects. The system employs a 105 GHz MMW beam,

generated by a custom transmitter, which illuminates the object. Reflected MMW radiation is collected by a

large spherical mirror and directed to the GDD, where the MMW signal is up converted to an optical signal.

The GDD’s response to MMW incidence produces a measurable increase in light intensity, detected by a low-

noise photoreceiver equipped with a Si-PIN photodiode, enhancing the sensitivity and accuracy of the

detection process. The GDD-photoreceiver assembly is mounted on motorized linear stages, enabling precise

vertical and horizontal scanning in patterns, which facilitate the creation of grayscale MMW images. Data

acquisition is conducted through a dedicated platform that translates the detected signals into clear, high-

quality images. This system showcases significant advancements in photonic detection for MMW imaging,

offering enhanced resolution and sensitivity, which are advantageous for a range of applications.

1 INTRODUCTION

Millimeter wave (MMW) imaging has gained

significant attention across various fields, including

security screening, medical diagnostics, and

industrial inspection, due to its ability to penetrate

non-metallic materials and produce detailed images

(Siegel, 2002). However, traditional MMW imaging

systems often face limitations in resolution,

sensitivity, and operational complexity, which restrict

their effectiveness and application scope.

The advancement of affordable, durable, and

easy-to-use room-temperature sensors for MMW

applications is critical for the successful deployment

of MMW imaging systems. Conventional MMW

detectors, such as Schottky diodes, Golay cells, and

bolometers, often come with high costs and increased

https://orcid.org/0000-0002-5450-7582

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https://orcid.org/0000-0002-0060-3616

https://orcid.org/0000-0002-4974-9683

https://orcid.org/0000-0002-4729-0565

sensitivity to electrostatic discharge (ESD), making

them vulnerable to damage from high-power MMW

exposure (Rogalski and Sizov, 2011). In this context,

glow discharge detectors (GDDs) (Kopeika, 1975)

utilizing weakly ionized plasma (Hou and Shi, 2012)

have emerged as a promising alternative,

demonstrating superior sensitivity to MMW/THz

radiation alongside a faster response time. This

capability not only simplifies the detection system but

also significantly reduces costs, which is particularly

beneficial for applications involving imaging and

detector arrays (Rozban et al., 2008).

In our work, we focus on two fundamental

principles for MMW detection using GDDs: the

electrical current method, which measures changes in

bias current due to incident radiation, and the optical

up-conversion method (Haj Yahya et al., 2021).

Kurup, A. R., Rozban, D., Abramovich, A., Yitzhaky, Y. and Kopeika, N.

Millimeter Wave Imaging Using Up-Conversion Detection Method with Glow Discharge Detector and Photoreceiver Combination.

DOI: 10.5220/0013239100003902

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 13th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2025), pages 109-113

ISBN: 978-989-758-736-8; ISSN: 2184-4364

109

However, our primary emphasis is on the up-

conversion technique, which detects alterations in the

emitted light from the GDD when exposed to MMW

radiation (Aharon et al., 2016). By integrating a

photoreceiver with the GDD, we can accurately

measure these light intensity changes, taking

advantage of the rapid response time inherent in this

method (Aharon et al., 2019). The up-conversion

approach not only minimizes internal noise compared

to conventional electrical detection but also provides

a cost-effective solution for enhancing the

performance of MMW imaging systems. This

synergy between the GDD and photoreceiver is

pivotal in advancing our ability to capture high-

quality MMW images, thereby facilitating further

developments in THz applications.

This study introduces an innovative MMW

imaging system that addresses these limitations by

integrating a Glow Discharge Detector (GDD) with a

high-sensitivity photoreceiver, utilizing an up-

conversion detection method. By converting the

MMW signal into an optical signal, this system

enables the use of advanced optical components,

which offer enhanced sensitivity and bandwidth

compared to conventional electrical detectors.

At the core of the system is a 105 GHz MMW

source, which illuminates metal objects positioned in

the object plane. The collimated MMW beam, shaped

by an off-axis parabolic mirror and transmitted

through a horn antenna, is modulated by a 10 kHz

TTL pulse, providing precise control over the MMW

radiation. The GDD converts the MMW signal into

an optical signal, creating a measurable increase in

light intensity in response to MMW incidence. This

optical signal is then detected by a low noise

photoreceiver, significantly enhancing the sensitivity

and accuracy of signal capture.

The single GDD-photoreceiver assembly is

mounted on motorized linear stages (NRT100M from

Thorlabs) that enable precise raster scanning in both

vertical and horizontal directions. By moving in a

controlled, stepwise pattern, the system captures data

points across the object plane to construct an 8x8

grayscale MMW images. The flexibility in scanning

patterns allows for various levels of detail, with finer

grids providing higher image resolution and greater

detail for applications requiring in-depth MMW

analysis. Each captured data point is processed

through a dedicated data acquisition platform,

enabling the construction of detailed images that are

valuable for applications requiring rigorous MMW

analysis and imaging clarity.

This research demonstrates the effectiveness of

combining the up-conversion detection method with

the GDD-photoreceiver configuration in advancing

MMW imaging systems. Through enhanced detection

sensitivity and precise scanning capabilities, this

system overcomes key limitations of conventional

MMW imaging, opening new possibilities for high-

resolution imaging applications across multiple

domains.

2 EXPERIMENTAL SETUP

The experimental setup depicted in Figure 1 consists

of a millimeter wave source manufactured by

Virginia Diodes Inc. (VDI TX272), a quasi-optic

design based on an off-axis parabolic mirror (OPM),

a reflecting/imaging mirror, and a lock-in amplifier

(MFLI) from Zurich Instruments. The detection

circuit is comprised of a single Glow Discharge

Detector of type N523 from International Light Inc.

and a photoreceiver, which together serve as the

primary pixel/detector element.

The GDD is positioned in a head-on

configuration, providing a total detection cross-

section with an approximate diameter of 6 mm. The

effective detection area, where sensitivity is strongest

between the electrodes, has a diameter of about 3 mm,

which is at least twice the electrode separation.

The MMW source is capable of radiating signals

in the frequency range of 100 GHz, which are

modulated using a 10 kHz square wave with a peak-

to-peak amplitude of 5 V. The off-axis parabolic

mirror collects and collimates the MMW radiation

towards the metallic object placed in the object plane.

Reflected MMW radiation from the object is then

focused onto a spherical mirror, which projects the

radiation to the image plane where the detection

circuit is located.

Calibration and alignment of the GDD and

photoreceiver assembly are achieved using a laser to

ensure that the GDD is positioned at the reflective

focal length of the spherical mirror. The detection

circuit recognizes changes in the bias current of the

GDD due to the incidence of MMW radiation, while

the photoreceiver detects the resulting optical signal.

The signal output from the photoreceiver is connected

to the +V signal input of a lock-in amplifier (MFLI)

from Zurich Instruments, which operates at

frequencies of 500 kHz to 5 MHz and has a sampling

rate of 60 MSa/s.

The modulating signal is also routed to the

auxiliary input of the lock-in amplifier to facilitate

synchronous detection. The detected analog signal is

then processed by the lock-in amplifier for further

signal analysis and the generation of grayscale

PHOTOPTICS 2025 - 13th International Conference on Photonics, Optics and Laser Technology

110

images. The data acquisition is implemented using an

FFT-based algorithm incorporated into LabVIEW,

ensuring compatibility with the optical detection

system and enhancing the overall performance of the

imaging setup.

Figure 1: Schematic Diagram of the Experimental Setup for

MMW Imaging Using GDD and Photoreceiver.

2.1 Optimizing Detection for Improved

MMW Detection

To enhance the performance and accuracy of the

GDD and photoreceiver combination in our MMW

imaging system, specific modifications were made to

the experimental setup, addressing issues related to

ambient light interference and optimizing the

detection of MMW-induced optical signals. During

initial experiments, the photoreceiver experienced

saturation due to two main sources: ambient room

lighting and the high-intensity light emitted from the

GDD. To mitigate this interference, an optical long-

pass filter was introduced between the GDD and the

photoreceiver. This filter effectively blocks all visible

light wavelengths, thereby preventing ambient light

from reaching the photoreceiver and reducing

saturation issues.

2.2 Influence of MMW Radiation in

the NIR Spectrum

Experimental findings suggest that the GDD emits

light across a broad spectrum when interacting with

MMW radiation, with a notable increase in intensity

around the near-infrared (NIR) region, specifically

between 800 nm and 1000 nm (Kurup et al., 2021).

Preliminary research also showed that the MMW or

terahertz (THz) influence on the GDD emission

spectrum is strongest within this NIR range. In

contrast, almost no influence of the MMW/THz

radiation was observed in the visible spectrum,

particularly around 500 nm to 600 nm. This

observation justified the use of a long-pass NIR filter

to enhance the system's performance by isolating the

relevant signal range.

Figure 2: Photograph of the GDD-Photoreceiver Module

Integrated with a Near-Infrared (NIR) Filter.

By blocking visible wavelengths, the filter

reduces background illumination noise that originates

from both room lighting and the GDD's own bias

illumination. This results in a cleaner signal output

and enhances the signal-to-noise ratio (SNR) of the

photoreceiver, thus minimizing interference from

unwanted visible light sources. The filter also

contributes to a subtle increase in signal strength. Due

to back reflections from the filter body, a fraction of

the filtered light is directed back toward the GDD's

detection cross-section, effectively increasing the

detected signal level. This reflective effect, combined

with the noise reduction properties, results in higher

sensitivity and improved overall detector

performance for MMW or THz radiation. These

adjustments significantly improve the efficiency and

reliability of the GDD-photoreceiver assembly as a

pixel detector in our imaging system.

3 ENHANCING SIGNAL

QUALITY FOR OPTIMAL

DETECTION

In the initial stages of experimentation, we evaluated

the photoreceiver’s performance at the image plane

Millimeter Wave Imaging Using Up-Conversion Detection Method with Glow Discharge Detector and Photoreceiver Combination

111

position without an optical filter. Under standard

lighting conditions, including ambient room light and

the intense output from the Glow Discharge Detector

(GDD), the photoreceiver exhibited elevated noise

levels, resulting in suboptimal signal clarity. To

address this, preliminary tests were conducted in

complete darkness, where the photoreceiver’s

baseline performance was assessed.

To explore the impact of optical filtering, we

conducted tests in two configurations: with the filter

in a dark environment and with the filter in ambient

room light. The filter mitigated light interference

effectively, allowing for a significant reduction in

noise levels in both cases. Figure 3 and 4 presents the

signal acquisition data, highlighting the improved

signal detection level achieved with the optical filter

under varied lighting conditions.

Figure 3: Signal acquisition data for the GDD-

photoreceiver system with the optical filter under ambient

room light conditions.

Figure 4: Signal acquisition data showing the performance

of the GDD-photoreceiver system with the optical filter in

a dark environment.

For further signal enhancement, an SR445A

amplifier from Stanford Research Systems, Inc. was

introduced into the setup. This addition provided a

noticeable boost in the signal level as shown in Figure

5, proving beneficial for initial tests.

Figure 5: Waveform illustrating the enhanced signal output

from the GDD-photoreceiver system after the introduction

of the SR445A amplifier.

However, as we integrated a lock-in amplifier

(LIA) module from Zurich Instruments, the necessity

for the external amplifier diminished. The LIA’s high

sensitivity allowed it to reliably detect even minimal

signal outputs from the photoreceiver, effectively

enhancing the system’s ability to capture faint MMW

signals.

4 IMAGING RESULTS

In this section, we present the MMW imaging results

obtained from the experimental setup using a GDD-

photoreceiver combination. The object imaged was a

50 mm x 50 mm square metal plate with a thickness

of 2 mm and a 20 mm x 20 mm hollow square cutout

at its center, as shown in Figure 6, designed to

evaluate the system’s ability to capture distinct shapes

and internal structures. The imaging mirror utilized

had a 500 mm diameter, positioned with the object

and image distances both set to 2 meters, ensuring

that the MMW reflection would accurately project

onto the detection plane.

Figure 6: The square metal plate object used for imaging.

To optimize the performance, the setup underwent

meticulous optical alignment and calibration. Initial

trials involved refining the orientation and

positioning of the GDD-photoreceiver module within

PHOTOPTICS 2025 - 13th International Conference on Photonics, Optics and Laser Technology

112

the 8x8 scanning matrix, a configuration established

in the image plane to maximize resolution and

accuracy. Mounted on motorized linear stages, the

GDD-photoreceiver assembly could perform precise

vertical and horizontal raster scanning, enabling

detailed coverage of the target area. Using this

controlled scanning mechanism, the system produced

an 8x8 grayscale image, accurately capturing the

metal square's boundaries and internal hollow. The

iterative adjustments to positioning and scanning

patterns were essential in refining image clarity,

yielding well-defined and high-quality MMW

images. The final grayscale MMW images of the

square shape are presented in Figure 7. The image

processing steps significantly improved the clarity

and definition of the features within the MMW data,

allowing for a more precise representation of the

object's structure. This enhancement demonstrates the

effectiveness of the applied methods in refining the

imaging capabilities of the GDD-photoreceiver

system.

Figure 7: Final Grayscale MMW Image of the Square

Shape. The left image displays the original acquired MMW

data, while the right image illustrates the enhanced result

following image processing, showcasing improved clarity.

5 CONCLUSIONS

This study presents the design and implementation of

a novel millimeter wave imaging system that

leverages a Glow Discharge Detector coupled with a

high sensitivity photoreceiver. By employing an up-

conversion detection method, the system effectively

converts MMW signals into optical signals,

enhancing the detection capabilities in terms of

sensitivity and resolution. The integration of a long-

pass NIR optical filter between the GDD and

photoreceiver further improved the system’s signal-

to-noise ratio by filtering out visible light

interference, thus optimizing performance in ambient

light conditions. Additionally, the utilization of

motorized linear stages for controlled raster scanning

allowed the generation of detailed 8x8 grayscale

images, confirming the setup’s capability to capture

complex structures with high fidelity.

Overall, this MMW imaging system represents a

significant advancement in high-resolution imaging

for industrial, security, and scientific applications,

where precise detection of MMW radiation is

essential. Future work will focus on extending the

scanning resolution, exploring different object

geometries, and refining the data acquisition process

to broaden the system’s application range and

improve its performance further. submission.

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