CEOI Emerging Technologies Workshop

Heterodyne Technologies

29th January 2008

Dave Matheson

Millimetre Technology

RAL Space Science and Technology Department

2

Contents

– Introduction

– Technology status

– EO opportunities

– Laser Heterodyne Radiometry - (Damien Weidmann, Kevin Smith)

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Introduction

• Frequency range:– ~200 to >3,000GHz:

• Rich in rotational and rotation-vibration transitions of molecular species • Dielectric materials that are partially transparent to the radiation

• Part of the spectrum still to be fully exploited:

– Technology and applications are still being invented and improved

• Why Heterodyne technology? - sensitive detection, arbitrarily fine spectral resolution

Frequency (GHz)

Cloud opaque in IR & near-IR limb-views

mm-wave limb spectra co-located 0.75mm limb imager

BT (K)

Results from the MARSCHALS airborne instrument, demonstrating mm wave observations of H2O & O3 through tropical cirrus

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Status of Heterodyne Technology

• Planar diode receivers have been demonstrated at all frequencies up to ~3THz:– Schottky diode mixer technology for room temperature operation

– Cryogenic mixers for lowest noise performance

• Air filled, single moded waveguide for critical technology (mixers, LO sources) :– circuits can now be accurately simulated and manufactured using non-linear design

software & CNC mills

• Generation of THz LO power remains tricky:– Development of receiver arrays will benefit from better LO technology

• Commercial availability of components & circuitry > ~300GHz is improving with time

IF Amplifier f1

f2

fnLocal Oscillator

Source

RF feedhorn

Spectrometer

mixer

2,000K

1,000K

500GHz 1,000GHz

amplifier

SIS

Diode mixercold temperature

diode mixerroom temperature

Indicative noise performance

-50

-40

-30

-20

-10

0

250 260 270 280 290 300 310 320 330 340 350

Frequency (GHz)

Transmission (dB)

USB

LSB

Queen’s University Belfast/ASTRIUM dielctric-free mm filter

RAL 380 GHz waveguide diode mixer

Indicative heterodyne radiometer performance

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Technology Trends

• Future instruments will require increased spectral coverage, lower resource requirements (mass and power), and receiver array

• This application demand is driving technology in directions that include the following:– Higher frequency components (mixers, harmonic multipliers) - above 1THz– More sophisticated components (Image reject sideband mixers, balanced mixers…) – New methods of THz power generation (for LOs):

• Quantum Cascade Lasers (QCL)• Photonic mixing (optical down conversion)

– Increased circuit integration:• Reduced mass, improved reliability, simpler interfaces, lower cost

– New concepts for building focal plane arrays - specifically, provision and injection of LO to drive multiple mixers

Prototype IRAM array technology (Huggard et al.)

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Technology Trends (Examples)

– Fixed tuned waveguide mixer cavity– Single 50micron thick GaAs circuit (filters and diodes)

340GHz Single Sideband Mixer (CEOI)

~200 GHz Integrated mixers

Integrated Mixer circuit

detail

Diode

region RF signal waveguide

LO waveguide

Frequency

Con

vers

ion

Loss

–Circuit design and simulation (Thomas et al.)

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Opportunities

• Investigation of processes linking atmospheric composition and climate• Future assimilation into operational systems used to forecast weather & air quality

• In the short/medium term:– STEAM-R, limb sounder focused on UT:

• Opportunity for UK involvement in Swedish funded contribution to PREMIER• CEOI studies to define instrument requirements and demonstrate novel SSB mixer

technology (Astrium, RAL, QU Belfast, SULA, )

– Aircraft radiometer designed to discriminate cirrus size components intermediate between those accessible in the IR and microwave:

• CEOI studies to demonstrate LO source and channel separating (filter) technology (Astrium, RAL, QUB)

• Linked studies with UKMO (FAAM) and ESA (aircraft demonstrator)

Earth Remote Sensing – Future Instrument Opportunities

Imagers, sounders Next generation GEO, LEO sounders (evolution of post EPS imagers and sounders)

Atmospheric bands up to ~900GHz (e.g., 220, 301, 462, 684, 875GHz)

Array receivers

Near time weather forecasting, cloud physics

Limb sounders e.g., ESA Explorer PREMIER

<400GHz for UTLS, frequencies up to ~3THz (inc. OH)

Atmospheric composition, climate change

STEAM Antenna and optics model (CEOI - Astrium)

Key capabilities • Passive monitoring of emissions and air quality – Occultation capability• Offers combination of high spectral & spatial resolutions at high sensitivity• Based on solid-state mid-IR quantum cascade lasers (QCLs)

Quantum Cascade Laser Heterodyne Radiometer (LHR)

Quantum cascade lasers as local oscillators- High power ( >10 mW )- Band engineering to tailor central wavelength from 4 to 150 m- Compact and robust for field deployment- High spectral purity (~ 1 MHz) - Continuously frequency tuneable (1% of central frequency)

Existing prototype developed at RAL- Operates at 9.7 m to target atmospheric ozone- Spectral resolution from 0.001 to 0.2 cm-1 set by electronic filters- 75 x 75 cm2 portable breadboard

Wide range of prospects- Ultra-compact packaging through optical integration- Extension to the far infrared and terahertz frequency range- Wide wavelength coverage with external cavity laser implementation- Heterodyne imaging through development of arrays of mixers- Development of heterodyne LIDAR

Spectra spanning 2 cm-1, Resolution 220 MHz DSB

Example high-resolution atmospheric spectra Retrieved O3 profile

Currently being implemented for CEOI Phase 1- Thermal and electro-magnetic shielding- Enhanced laser optical isolation- Frequency calibration investigation and active baseline correction- Absolute radiometric calibration- Further ground-based field deployment- Performance analysis for different viewing modes and various platforms types

Quantum Cascade Laser Heterodyne Radiometer (LHR)

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Summary

• THz and IR heterodyne technology and applications are still being invented

• Strong technology base in the UK in Industry, SMEs and Universities

• Excellent opportunity to exploit programmes proposed for EU/ESA GMES Sentinel and Eumetsat post-EPS satellite missions:

– KE applications, e.g., THz security imaging

• CEOI is supporting critical technology development:

– Aimed at PREMIER STEAM-R

– Cirrus aircraft instrument

• SSB Mixers, frequency multipliers, optical filters

• Associated ESA TRP/GSTP funding:

– Wideband spectrometer development, Cirrus aircraft instrument studies

THz security imaging, ThruVision