Ultra Stable Terahertz
Frequency Synthesizers and
Extremely Sensitive HEB
Detectors up to 70 THz.
Mikhail L. Gershteyn
President, Insight Product Co.
www.insight-product.com
Phone: (617) 965-8151
E-mail: InsightProduct@yahoo.com

• 1. Advancing frequency stabilization techniques to Terahertz range.
• 1.1 Applications of frequency stabilized sources.
• 1.1.1 Narrow band phenomena’s in Nature.
• 1.1.2 Narrow band systems technologies.
•
1.2 Stabilized sources in MMW and THz.
•
1.2.1 Comparison of Stabilized Sources.
• 1.2.2 THz synthesizers from Insight Product Co.
• 2. Superconducting Hot Electron Bolometer (HEB) Mixers &
Detectors
•
2.1 Applications of HEB Mixers & Detectors
•
2.2 Direct Detectors and Mixers
•
2.3 Comparison of Detectors & Mixers in THz area.
• 2.4 Superconducting Hot Electron Bolometer (HEB) detectors and mixers from
Insight Product
• 3. Conclusions
• 4. Acknowledgments

Applications of Synthesized
Sources
• Gas Spectroscopy
• Security: Gas detection systems
• Accessing water content in tissue
• Medical imaging: cancer tissue identification
• Heterodyne Receiving Systems
• Astrophysics
• Material characterization and testing
• NMR/ MRI, EPR, quantum computers
• Plasma diagnostics, Gyrotron cold testing
• Communications: high bandwidth channels

Naturally occurring physical narrow-band phenomena
• Absorption and emission spectrum of various molecules
• It is well know that each molecule has a distinctive frequency fingerprint of emitting and absorbing electromagnetic waves. There are very sharply, narrow-band frequency effects observed, called
“absorption lines”.
• Security Application : The THz absorption spectrum of various gases yields distinct regions of absorption which could be used to differentiate hazardous gases from benign ones.
• Applications: Air Monitoring
• Atmospheric Monitoring via satellite.
• Monitoring of emissions from Industrial Chemical Processing.
• Real-time monitoring of chemical processes in gas phase.
• Scientific Application: Gas Spectroscopy

Naturally occurring physical narrow-band phenomena II
• Resonance of mediums with minuscule absorption
• Mechanical resonance: quartz. Quartz vibrates because it basically does not absorb acoustic wave.
• Professor H. Frohlich’s concept: cell membranes participate in synchronized coherent high-frequency oscillations (10s of GHz up to 100s of GHz) : therefore dynamic biological functionality can be influenced by weak EM radiation at certain narrow-band frequency.
• Biological Coherence & Response to External Stimuli (Springer, 1988) edited by H. Frohlich
• First experimental demonstration of the effect of weak specific mm-wave frequencies on living organisms was obtained in the early 1970s by
Academician N. N. Devatkov et al. group in USSR.
• One of the latest reviews on the subject, entitled “Non-thermal Biological
Effects of Microwaves” (Microwave Review, November 2005) was published by Dr. Igor Y. Belyaev (Department of Genetics, Microbiology and
Toxicology, Stockholm University, Sweden)
• http://www.mwr.medianis.net/pdf/Vol11No2-03-IBelyaev.pdf
• Biomedical Applications : Millimeter Wave Therapy

Naturally occurring physical narrow-band phenomena III
• EPR (Electron Paramagnetic Resonance) and
NMR/DNP (Nuclear Magnetic Resonance/
Dynamic Nuclear Polarization)
• NMR enhancement by EPR
• Applications :
• Material characterization
• Medical Imaging
• Biological & Chemical Research.

Naturally occurring physical narrow-band phenomena IV
Frequency shift effects.
– Doppler effect: frequency change of EM coming from a moving source depending on the velocity of motion. Also the reflection of
EM against a moving target causing a frequency shift in reflected signal.
– Frequency shift is proportional to velocity over speed of light.
• ∆f/f= v/c
• General Applications : Motion detectors and velocity estimators.
• Security Applications : Intruder detection by motion.

Narrow band Systems in
Technology
• Systems in Technology and Science use narrow-band signals in order to achieve:
 high selectivity
 high frequency resolution
 high sensitivity
 high stability
 phase detection

Narrow band Systems in
Technology II
• Communications – we use synthesized sources to differentiate one channel from another and to inhibit interference. Also the narrow-frequency band allows the utilization of heterodyne receiving systems which offer exceptional sensitivity. This also enables broad receiving range with limited transmitted power.

Narrow band Systems in
Technology III
• Radars - Time for reflected signal to reach the sensor is used to calculate distance. Narrow band pulses are used to increase sensitivity, at the receiver end, and in Doppler shift radars to measure velocity. In FM (frequency modulation) radars the distance to the target if inferred from the change in frequency between reflected signal and current signal. In this case the frequency must be very accurately defined for every time point, so a narrow-banded time dependent signal is necessary.

Narrow band Systems in
Technology IV
• Selective receivers in Astrophysics and
Atmosphere Investigations
• We need to receive a signal in a certain frequency range corresponding to emission of various molecules in space.
Heterodyne receivers are used, since they yield excellent sensitivity. The heterodyne
LO (local oscillator) needs to have high frequency stability.

Narrow band Systems in
Technology V
• Imaging system for medical and security applications.
• In imaging systems, narrow-band signals together with heterodyne receiving technique increase the sensitivity of reception of the signal, expedite the frame rate, and boast resolution.
• An example in THz area, I’d like to refer to the latest results of Peter Siegel et al. (JPL)

Heterodyne Active Imager
Courtesy of Dr. Peter H. Siegel, JPL

Heterodyne Active Imager
Courtesy of Dr. Peter H. Siegel, JPL

Narrow band Systems in
Technology VI
• Systems for material characterization and plasma diagnostics :
• Narrow-band signal allows:
• a ) increased sensitivity
• b) selectivity by frequency
• c) phase measurements (especially relevant in plasma diagnostics)
• d) increased temporal resolution (faster measurements)
• e) introduce monitoring capability

Narrow band Systems in
Technology VII
• Gas absorption spectrometers and gas detectors.
• The natural absorption phenomena are narrow-banded.
• The typical “absorption line” width of any gas at a pressure of 1 Torr and standard temperature is 10-6
( ∆f/f) in the terahertz range.
• Therefore to match the “absorption line” we need to have a probing signal which has at least 10-6 ( ∆f/f) frequency stability (both long and short term stability).
• Security Application : Local atmosphere monitoring for specific known substances, biological agents, or gases.
• Monitoring of chemical reactions .
• Monitoring of technological processes .

Sources of frequency stable signal in THz range
• Synthesized frequency stable sources in microwaves (up to 20
GHz) are well developed and widely available. One of the latest reviews was written by Jack Browne.
Reference:
“Frequency Synthesizers Generate Clean Signals:
Frequency synthesizers come in many shapes and sizes, although the ultimate goal in any design is to generate stable output frequencies with minimal spurious and phase noise.
”
Jack Browne Microwaves & RF [Systems & Subsystems]
ED Online ID #10016 March 2005
( http://www.mwrf.com/Articles/Index.cfm?ArticleID=10016&pg=2 )

Sources of frequency stable signal in THz range II
• Lasers (C0
2 pumped)
• Pros : High output power (~10-100 mW) & high frequency stability (better than 300 KHz line).
• Cons : Fixed frequency, lacks tunability, limited possibility for frequency and phase modulation and manipulation, large bulky devices, available on only several specific frequencies.

Sources of frequency stable signal in THz range III
• Stabilized Quantum Cascade Lasers
(QCL)
• Pros : High output power (1-50 mW), good stability (less than 300 kHz)
• Cons : Small tuning bandwidth (~10 GHz),
Not available on all frequencies.

Sources of frequency stable signal in THz range IV
• Photo-mixers
• Pros: wide tunable bandwidth (several hundred GHz)
• Cons: low output power (1 microWatt at 1
THz, 0.1 microWatt at 3 THz), large bulky devices.

Sources of frequency stable signal in THz range III
• Direct Multiplier chains
• These devices use multipliers and amplifiers to go from microwave stable source (up to 20 GHz) to THz range.
• Pros: Solid-state, high frequency stability when input signal is from a frequency synthesizer, compact, commercially available, wide tunability
(~15%).
• Cons: Complex design. Amplifier and multi-cascaded chains (FEMs) are required to reach THz frequencies.
• Output power drops exponentially with increasing frequency.
• Low output power (1-2 microWatt at 1.25 THz)
• Do not go higher than 1.7 THz.
• Low efficiency (less than 0.5%)
• Multiple component spectrum of output signal with different harmonics.
• Possibility for frequency and phase modulation and manipulation is limited by what’s available in the driving microwave source.

Sources of frequency stable signal in THz range IV
• PLL (Phase-lock loop) Systems based on BWO (Backward
Wave Oscillator, a.k.a. “carcinotron” or “backward wave tube”)
• BWO by PLL locked to harmonic of microwave stable source.
• Pros : Wide tunability band (~20 %)
• Relatively high output power (2-8 milli-Watt at 1 THz)
• Possibility of quick frequency and phase modulation and manipulation.
• Simple (“one line”) output spectrum.
• Cons :
• Need high voltage power supply and magnet
• Do not go above 1.5 THz

Sources of frequency stable signal in THz range V
• Hybrid systems – PLL locked Sources plus
Multipliers (in development)
• PLL locked BWO sources (200-300 GHz) are multiplied to THz region.
• Pros: Wide tunability band.
• Possibility of quick frequency and phase modulation and manipulation.
• Projected cover from 1 up to 3 THz with power of about
10 microWatt.
• Cons: Need high voltage power splay and magnet.

Insight Product Synthesizers
(Insight FS) 36 GHz – 1.25 THz
• Typical Output Power (in milliWatt) and
Tuning Frequency Range.
• 370 - 535 GHz: 4-15 mW
• 526 - 714 GHz: 4-15 mW
• 667 - 857 GHz: 4-15 mW
• 789 - 968 GHz: 3-8 mW
• 882 - 1,111 GHz: 2-8 mW
• 1,034 – 1,250 GHz: 0.5-2 mW

Advantages:
 Extremely high frequency stability (up to 10 -11 = ∆f/f ).
 High output power (several mW at 1 THz).
 Each synthesizer covers a full waveguide band.
 Each synthesizer operates independently in free running mode as generator or with microwave signal generator as synthesizer.
 Insight FS provides several options for frequency and amplitude modulation (analog FM/AM modulation, frequency manipulation, pulses modulation).
 Insight FS are compact in size and controlled by IEEE, analog input, or manually.

“For millimeter-wave frequencies, Insight Product Co. (www.insight-product.com) offers a line of frequency synthesizers in full waveguide bands from 120 to 180 GHz, with output-power levels of 30 mW or more. Ideal for measurement and astronomy applications, these synthesizers can be equipped with optional AM and FM capabilities and GPIB remote control.”
March 2005, Microwaves & RF Journal

Schematics of direct vs. heterodyne detection
Courtesy of Drs. Peter H. Siegel and Robert J. Dengler, CALTECH & JPL
650 GHz: typical bolometer NEP @ 300 degrees K = 10 -11 W/Hz 2
650 GHz: typical mixer NEP @ 300 degrees K = 10 -15 - 10 -14 W/Hz 2

• Applications:
• Terahertz Spectroscopy
• Terahertz RadioAstronomy
• Remote sensing of Earth Atmosphere
• Active Terahertz Imaging
• Security Imaging and Monitoring

• Currently the following large-scale projects may benefit from HEB mixers:
• Large-scale government projects such as
SOFIA, FIRST, & ALMA.
• Astronomy projects: SMILES, EOS-MLS.
• Planetary science projects: ROSETTA,
Mars explorer.

• “Superconducting hot electron bolometer (HEB) mixers are the choice of device for the frequencies between 1.5 and 6 THz. They are complementary to SIS mixers which work as quantum noise limited detectors up to about 1 THz. An HEB consists of a niobiumnitride (NbN) superconducting bridge with nanometer or submicron dimensions, contacted by thick gold pads. THz radiation signals are coupled into the bridge through a lens and an on-chip antenna
(quasi optical). The heterodyne mixing process makes use of the resistive transition between the superconducting state and the normal state of the superconducting bridge, induced by the heating of THz radiation signals. Click for a schematic of the detector principle. To reach a high intermediate frequency (IF) bandwidth, an extremely thin NbN film with a high critical temperature is used, optimized for phonon cooling.
”
–SRON (Netherlands Institute for Space Research)

• HEB Mixers, Advantages
• Above about 1 THz Hot Electron
Bolometer mixers offer the best sensitivity and lowest noise of all the technology for the coherent detection of radiation.
• Wide converstion gain bandwidth and noise bandwidth ( both up to 4.5 GHz).
• Low Heterodyne source power (about 1 microW).

• Applications of Superconducting HEB
Detectors:
• Fast and/or wide range pulses of terahertz radiation for biological investigations, and real-time monitoring.
• Passive Imaging
• Active Imaging with short pulses

Schematic of Superconducting S.
HEB Mixer/Detector

Courtesy of Dr. Gregory Goltsman

Courtesy of Dr. Gregory Goltsman

S. HEB mixer System at .7-.9 THZ w/ components and LHe cryostat
• Quasioptical NbN mixers
• Hyper-hemispherical Si lens
• Mixer holder with SMA connector
• Bias-T adapter
• Cryogenically cooled HEMT amplifiers (four options)
• Liquid helium cryostats (3 options)
• Cryogenically cooled IR filter
• Teflon input cryostat window
• Room-temperature (RT) amplifiers (3 options)
• HEMT amplifier power supply
• RT amplifier power supply
• Mixer power supply

• 1 THz: ~800 ° K = Noise Temperature
• 2 THz: ~1,000 ° K = Noise Temperature
• 4 THz: ~1,200 ° K = Noise Temperature
• LO Power required < 1µW
• Bandwidth ~ 4.5 GHz

• 0.3 – 3.0 THz Detectors:
• NEP= 3-5*10 -13 W*Hz -0.5
; Response time=
50 ps
• NEP= 5-7*10 -14 W*Hz -0.5
; Response time=1 ns

• 0.1 – 30 THz Detectors:
• NEP= 1-2*10 -10 W*Hz -0.5
; Response time=
50 ps
• NEP= 6-8*10 -11 W*Hz -0.5
; Response time=1 ns

• 25 – 70 THz Detectors:
• NEP= 4-5*10 -12 W*Hz -0.5
; Response time=
50 ps
• NEP= 1-2*10 -12 W*Hz -0.5
; Response time=1 ns

• THz band synthesized sources and ultra sensitive detectors are well developed are commercially available.
• Most of the applications thus far lie in scientific research and government R&D.
• Technology is ready designing more widely used commercial applications, for security, medical imaging, air pollution monitoring, and biomedical therapy, and real-time monitoring of chemical and industrial processes.

• Special thanks to the following individuals:
• Dr. Peter H. Siegel for discussions, and materials.
• Dr. Gregory Goltsman for discussions, and materials.
• Dr. Lev I. Gershteyn for discussions.
• Arkady Gershteyn for discussions, and help with presentation of content.
• Matt Thomas, for organizing SURA conference.
© Insight Product Co. 2006