Info
Info
News Article

Simplifying Laser Power Measurements For Telecoms

NIST's prototype carbon nanotube device is a silicon chip topped with circular mats of carbon nanotubes standing on end
NIST has demonstrated a chip-scale instrument made of carbon nanotubes that may simplify absolute measurements of laser power.

The device is especially suited to transmitting light signals used in optical fibres in telecommunications networks.



The circular patch of carbon nanotubes on a pink silicon backing is one component of NIST’s new cryogenic radiometer, shown with a quarter for scale. Gold coating and metal wiring has yet to be added to the chip. The radiometer will simplify and lower the cost of disseminating measurements of laser power. (Credit: Tomlin/NIST)

The prototype device, a miniature version of an instrument called a cryogenic radiometer, is a silicon chip topped with circular mats of carbon nanotubes standing on end.

NIST says the mini-radiometer builds on its previous work using nanotubes, the world's darkest known substance, to make an ultra efficient, highly accurate optical power detector.

"This is our play for leadership in laser power measurements," project leader John Lehman says. "This is arguably the coolest thing we've done with carbon nanotubes. They're not just black, but they also have the temperature properties needed to make components like electrical heaters truly multifunctional."

National metrology institutes around the world measure laser power by tracing it to fundamental electrical units. Radiometers absorb energy from light and convert it to heat. Then the electrical power needed to cause the same temperature increase is measured.

NIST researchers found that the mini-radiometer accurately measures both laser power (brought to it by an optical fibre) and the equivalent electrical power within the limitations of the imperfect experimental setup. The tests were performed at a temperature of 3.9 K, using light at the telecom wavelength of 1550nm.

The tiny circular forests of tall, thin nanotubes called VANTAs ("vertically aligned nanotube arrays") have several desirable properties. More importantly, they uniformly absorb light over a broad range of wavelengths and their electrical resistance depends on temperature.

The versatile nanotubes perform three different functions in the radiometer.

One VANTA mat serves as both a light absorber and an electrical heater, and a second VANTA mat serves as a thermistor (a component whose electrical resistance varies with temperature).

The VANTA mats are grown on the micro-machined silicon chip, an instrument design that is easy to modify and duplicate. In this application, the individual nanotubes are about 10nm in diameter and 150µm long.

By contrast, ordinary cryogenic radiometers use more types of materials and are more difficult to make. They are typically hand assembled using a cavity painted with carbon as the light absorber, an electrical wire as the heater, and a semiconductor as the thermistor.

Also, these instruments need to be modelled and characterised extensively to adjust their sensitivity, whereas the equivalent capability in NIST's mini-radiometer is easily patterned in the silicon.

NIST plans to apply for a patent on the chip-scale radiometer. Simple changes such as improved temperature stability are expected to greatly improve device performance.

Future research may also address extending the laser power range into the far infrared, and integration of the radiometer into a potential multipurpose "NIST on a chip" device.

More details of this work are described in the following articles:

"Carbon nanotube electrical-substitution cryogenic radiometer: initial results," by N.A. Tomlin et al in Optics Letters, Vol. 38, No. 2. Jan. 15, 2013.

NIST Tech Beat article, "Extreme Darkness: Carbon Nanotube Forest Covers NIST's Ultra-dark Detector," at www.nist.gov/pml/div686/dark_081710.cfm.

and

NIST Tech Beat article, "Prototype NIST Device Measures Absolute Optical Power in Fiber at Nanowatt Levels," at www.nist.gov/pml/div686/radiometer-122011.cfm.



AngelTech Live III: Join us on 12 April 2021!

AngelTech Live III will be broadcast on 12 April 2021, 10am BST, rebroadcast on 14 April (10am CTT) and 16 April (10am PST) and will feature online versions of the market-leading physical events: CS International and PIC International PLUS a brand new Silicon Semiconductor International Track!

Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

2021 is no different. Over the last few months interest in deep-UV LEDs has rocketed, due to its capability to disinfect and sanitise areas and combat Covid-19. We shall consider a roadmap for this device, along with technologies for boosting its output.

We shall also look at microLEDs, a display with many wonderful attributes, identifying processes for handling the mass transfer of tiny emitters that hold the key to commercialisation of this technology.

We shall also discuss electrification of transportation, underpinned by wide bandgap power electronics and supported by blue lasers that are ideal for processing copper.

Additional areas we will cover include the development of GaN ICs, to improve the reach of power electronics; the great strides that have been made with gallium oxide; and a look at new materials, such as cubic GaN and AlScN.

Having attracted 1500 delegates over the last 2 online summits, the 3rd event promises to be even bigger and better – with 3 interactive sessions over 1 day and will once again prove to be a key event across the semiconductor and photonic integrated circuits calendar.

So make sure you sign up today and discover the latest cutting edge developments across the compound semiconductor and integrated photonics value chain.

REGISTER FOR FREE

VIEW SESSIONS

Info
×
Search the news archive

To close this popup you can press escape or click the close icon.
×
Logo
×
Register - Step 1

You may choose to subscribe to the Compound Semiconductor Magazine, the Compound Semiconductor Newsletter, or both. You may also request additional information if required, before submitting your application.


Please subscribe me to:

 

You chose the industry type of "Other"

Please enter the industry that you work in:
Please enter the industry that you work in:
 
X
Info
X
Info
{taasPodcastNotification}
Live Event