Technology

Below are descriptions of some of the novel photonic devices Praevium has developed.  We are constantly seeking unfulfilled applications that could benefit from a new photonic device!

Favorite Widely Tunable Vertical Cavity Lasers

Optical Spectrum of widely-tuned laser, showing lasing over 150 nm around 1310 nm, overlaid with continuously-tuned spectrum.

Optical spectrum of widely-tuned VCSEL, showing lasing over 150 nm around 1310 nm.

MEMS-VCSEL Schematic

Schematic of the mechanically-tunable vertical-cavity laser (MEMS-VCSEL).
The device is less than 1mm across.

Widest & Fastest Tunable 1310nm VCSEL to-date:

Widest tuning electrically-pumped 1060nm MEMS-VCSEL, producing high-quality ophthalmic images:

First Tunable 1060nm VCSEL:

 

State-of-the-art Light Sources for high resolution & meter-range 3-D imaging:

Praevium Research has recently developed record widely tunable Vertical Cavity Lasers (VCSELs) with tuning ranges of up to 150nm (see spectra at left) near 1310nm.
The 1050nm version stands out as one of the few tunable 1050nm laser sources available, with up to 100nm of tuning.
The single-mode nature of these sources results in extremely long coherence lengths (≥200 meters), enabling long-range 3-D imaging in addition to high-speed ophthalmic & endoscopic imaging.

Under NCI grant 2R44CA101067-05, in conjunction with commercial partner Thorlabs and academic partner MIT, these devices are being developed for emerging swept-source optical coherence tomography (SS-OCT) systems.

VCSELs provide an ideal source for OCT, as the combination of short cavity length and small mirror mass enable extremely high wavelength sweep rates needed for real-time volumetric imaging.
In addition, in contrast to other swept sources for OCT, truly single-mode operation enables narrow dynamic linewidth, which translates to long coherence length for deep imaging.

Praevium Research, Inc, in collaboration with MIT and Thorlabs, Inc., presented the first VCSEL/OCT results at a post deadline session at CLEO 2011 in Baltimore, MD, and more recently, featured the results in Electronics Letters (see links above).

In 2015 we published the first ophthalmic images taken with a new electrically-pumped MEMS-VCSEL. See the 2015 JLT paper for ophthalmic dye-free angiography and high-resolution images, measurements of the long coherence length and the benefits of spectral shaping with the Praevium-designed wide-band optical amplifier (BOA).

At OFC 2014 in San Francisco, Praevium demonstrated our first MEMS-VCSEL operating at 1550 nm.  This device is still in the prototyping phase, but initial results show C-band & L-band coverage with a tuning bandwidth >150 nm at up to 390 kHz sweep rate.

Tuning Spectrum of the prototype 1550nm MEMS-VCSEL.

Tuning spectrum of the prototype 1550nm MEMS-VCSEL with 170nm span.

Ultra-Broadband Superluminescent Diodes (SLD)

Spectrum of Thorlabs dual-SLED source, with 200nm of FWHM Bandwidth.

Praevium Research, under funding from the National Cancer Institute, has developed 1300nm superluminescent diodes with a combination of high power and broad optical bandwidth.  These advances have been enabled by fundamental materials and gain region design innovations.

Commercial devices sold by partner Thorlabs (part numbers LS2000BSLD1325) provide >10 mW fiber-coupled power in conjunction with >100 nm bandwidth in single devices and >170nm in coupled pairs.

Handpicked devices that are from time to time available on the Thorlabs website can provide >20mW fiber-coupled power, and in some cases >200nm bandwidth from a coupled pair.

Multi-Wavelength Laser Arrays for Spectroscopy

Butterfly packaged multi-wavelength source showing bonded lasers, waveguide array and combined coupled optical output

Packaged Multi-Wavelength Laser Array with multiple lasers coupled into a single fiber.

Optical spectrum of the MWS, showing each laser channel's optical characteristics.

Spectrum of each fiber-coupled laser.

Multi-wavelength source showing one of the lower-wavelength channels illuminating the access waveguide and fiber output.

A single channel illuminating the access waveguide and output fiber.

Near Infrared Spectroscopy has traditionally been accomplished using filtered white light sources and rotating gratings or detector arrays. This approach suffers from limited signal to noise ratio, high power consumption, and optical complexity.

Praevium, under funding from the US department of Agriculture and the National Cancer Institute, has developed miniaturized multi-wavelength laser arrays that offer essentially tunable radiation covering critical portions of the vis/NIR range (650-1700nm), at the output of a multi-mode optical fiber.

Such sources have increased signal to noise ratio relative to filtered white light, particularly in applications where high spatial resolution is required. Additionally, lasers can be high-speed modulated to obtain frequency domain as well as steady state measurements. Laser wavelengths can be customized to target a wide variety of specific applications, such as breast cancer detection, assessment of body hydration status, or quantification of agricultural constituents.

The multi-wavelength laser is not currently a commercial product. However, if you are interested in a funded development effort to customize these devices for a specific application, please contact us at info@praevium.com.

Wafer Bonding

Top-down SEM of laterally-bonded single-crystal waveguides

Top-down SEM of laterally-bonded single-crystal waveguides.

TEM of bonded interface, showing dislocation-free interface

TEM of the bonded interface.

Praevium scientists contributed to much of the early work on planar wafer bonding of GaAs to InP, which was driven in large part by the development of long-wavelength vertical cavity lasers. This work demonstrated atomically continuous GaAs/InP interfaces, low voltage current injection across such interfaces, and reliable, high power wafer-bonded VCSEL operation.

In recent years Praevium has developed a unique proprietary process for lateral wafer bonding of dissimilar semiconductors along cleaved facets, with excellent waveguide alignment.  GaAs/GaAs, InP/InP, and InP/GaAs bonded interfaces have been demonstrated. A number of devices, such as ultra-broadband superluminescent diodes and CWDM arrays have been demonstrated using this new technology.

Learn more by reading our Paper on Multi-Lateral Wafer Bonding.