Axsun Technologies, Inc.

Excelitas Technologies Corp.

At+t Corp.

Coherent, Inc.

Micracor, Inc.

Goldberg, Brian

Kuznetsov, Mark E.

Johnson, Bartley C.

Larson, Noble G.

Mark E Kuznetsov

Dale C Flanders

Walid A Atia

Bartley C Johnson

Peter S Whitney

Petros Amestis Kotidis

James W Getz

Carlos R Melendez

Brian Goldberg

Aram Mooradian

Edward J Mallon

Mark R Malonson

Corrado Pietro Dragone

Ivan P Kaminow

Christopher C Cook

Noble G Larson

Yu Nathan Li

Steven C Fawcett

Ranko Galeb

Bart Ley C Johnson

Tunable VCSELs (TVCSELs) employing expanded material systems with expanded mechanical/optical design space for semiconductor DBR mirrors on GaAs substrates. One is the InGaAs/AlGaAsP material system. It adds indium In to decrease InGaAs H-layer bandgap for higher refractive index and higher DBR layer refractive index contrast. Adding phosphorus P gives independent control of bandgap and strain of AlGaAsP low refractive index L-layers. The tensile strain of AlGaAsP L-layer compensates compressive strain of InGaAs H-layer and lowers the cumulative strain of the multilayer DBR structure. Another option is the InGaAsN(Sb)/AlGaAsP material system, where both types of layers can be lattice matched to GaAs. It uses indium In and nitrogen N, and possibly antimony Sb, to get independent control of strain and bandgap, and thus refractive index, of dilute nitride InGaAsN(Sb) H-layers, with lower bandgap and higher refractive index than starting GaAs. Using expanded material system enables reliable DBR mirrors with higher reflectivity and spectral bandwidth and tunable VCSELs with wider tuning range.

Tunable VCSEL with strain compensated semiconductor DBR

A vertical cavity surface emitting laser (VCSEL) has a shortened overall laser cavity by combining the gain section with a distributed Bragg reflector (DBR). The overall cavity length can be contracted by placing gain structures inside the DBR. This generally applies to a number of semiconductor material systems and wavelength bands, but this scheme is very well suited to the AlGaAs/GaAs material system with strained InGaAs quantum wells as a gain medium, for example.

Tunable VCSEL with combined gain and DBR mirror

An optically pumped tunable VCSEL swept source module has a VCSEL and a pump, which produces light to pump the VSCEL, wherein the pump is geometrically isolated from the VCSEL. In different embodiments, the pump is geometrically isolated by defocusing light from the pump in front of the VCSEL, behind the VCSEL, and/or by coupling the light from the pump at an angle with respect to the VCSEL. In the last case, angle is usually less than 88 degrees. There are further strategies for attacking pump noise problems. Pump feedback can be reduced through (1) Faraday isolation and (2) geometric isolation. Single frequency pump lasers (Distributed feedback lasers (DFB), distributed Bragg reflector lasers (DBR), Fabry-Perot (FP) lasers, discrete mode lasers, volume Bragg grating (VBG) stabilized lasers can eliminate wavelength jitter and amplitude noise that accompanies mode hopping.

Optically pumped tunable VCSEL employing geometric isolation

Quantum well designs for tunable VCSELs are disclosed that are tolerant of the wavelength shift. Specifically, the active region has even number of substantially uniformly spaced (&#xbc; of the center wavelength in the semiconducting material) quantum wells.

Quantum well placement in a tunable VCSEL

A design and method for introducing asymmetric crystal strain to control polarization in a tunable VCSEL, either optically or electrically pumped. The invention is especially relevant to wafer- or die-bonded tunable VCSELs. Then, mechanical stress is applied to the half VCSEL device by asymmetric arrangement of metal bond pads.

Tunable VCSEL polarization control through dissimilar die bonding

A microelectromechanical systems (MEMS)-tunable vertical-cavity surface-emitting laser (VCSEL) in which the MEMS mirror is bonded to the active region. This allows for a separate electrostatic cavity that is outside the laser's optical resonant cavity. Moreover, the use of this cavity configuration allows the MEMS mirror to be tuned by pulling the mirror away from the active region. This reduces the risk of snap down. Moreover, since the MEMS mirror is now bonded to the active region, much wider latitude is available in the technologies that are used to fabricate the MEMS mirror. This is preferably deployed as a swept source in an optical coherence tomography (OCT) system.

OCT system with bonded MEMS tunable mirror VCSEL swept source

Real-time swept source OCT data is most often sampled using a specially cut hardware k-clock. The present invention involves mathematically resampling signals within an FPGA-based data acquisition board based on data sampled from a wide free spectral range reference interferometer. The FPGA can then multiply up the reference clock rate to achieve greater imaging depth. The Nyquist fold-over depth can thus be programmed from a standard reference to an arbitrary depth, much as PLL frequency synthesizer can produce many frequencies from a standard stable reference. The system is also capable of real-time performance.

Real time FPGA resampling for swept source optical coherence tomography

The present invention concerns the use of hybrid metal-dielectric optical coatings as the end reflectors of laser cavities and/or in the mirror structures used in other optical resonators, such as Fabry-Perot tunable filters, along with the use of such Fabry-Perot tunable filters in wavelength swept sources such as lasers. Hybrid metal-dielectric optical coatings have reflectivity spectra that can be broader than pure dielectric coatings, offer optical reflectivities higher than metal, as high as pure dielectric coatings, eliminate mirror transmission that can cause parasitic light reflections, and use fewer layers and thus have lower mass and higher mechanical resonant frequency for movable mirror applications An important characteristic of these coatings concerns the non-reflected light. Pure dielectric coatings offer high reflectivity, while the non-reflected portion of the light is transmitted by the coating to the substrate, for example. When metal is added to the optical coating, the non-reflected portion of the light is absorbed by the metal and is not transmitted to the substrate or outside the cavity. Hybrid metal-dielectric coatings have broader and more uniform spectral reflection. Tunable lasers with performance enhanced by the hybrid metal-dielectric coatings can be used in optical coherence tomography and spectroscopic analysis applications.

Dielectric-enhanced metal coatings for MEMS tunable filters

A frequency swept laser source for TEFD-OCT imaging includes an integrated clock subsystem on the optical bench with the laser source. The clock subsystem generates frequency clock signals as the optical signal is tuned over the scan band. Preferably the laser source further includes a cavity extender in its optical cavity between a tunable filter and gain medium to increase an optical distance between the tunable filter and the gain medium in order to control the location of laser intensity pattern noise. The laser also includes a fiber stub that allows for control over the cavity length while also controlling birefringence in the cavity.

Optical coherence tomography laser with integrated clock

An integrated swept wavelength optical source uses a filtered ASE signal with an optical amplifier and tracking filter. This source comprises a micro optical bench, a source for generating broadband light, a first tunable Fabry Perot filter, installed on the bench, for spectrally filtering the broadband light from the broadband source to generate a narrowband tunable signal, an amplifier, installed on the bench, for amplifying the tunable signal, and a second tunable Fabry Perot filter, installed on the bench, for spectrally filtering the amplified tunable signal from the amplifier. A self-tracking arrangement is also possible where a single tunable filter both generates the narrowband signal and spectrally filters the amplified signal. In some examples, two-stage amplification is provided. The use of a single bench implementation yields a low cost high performance system. For example, polarization control between components is no longer necessary.

Filtered ASE swept source for OCT medical imaging

An optical coherence analysis system comprising: a first swept source that generates a first optical signal that is tuned over a first spectral scan band, a second swept source that generates a second optical signal that is tuned over a second spectral scan band, a combiner for combining the first optical signal and the second optical signal for form a combined optical signal, an interferometer for dividing the combined optical signal between a reference arm leading to a reference reflector and a sample arm leading to a sample, and a detector system for detecting an interference signal generated from the combined optical signal from the reference arm and from the sample arm. In embodiments, the swept sources are tunable lasers that have shared laser cavities.

Integrated dual swept source for OCT medical imaging

An optical coherence analysis system comprising: a first swept source that generates a first optical signal that is tuned over a first spectral scan band, a second swept source that generates a second optical signal that is tuned over a second spectral scan band, a combiner for combining the first optical signal and the second optical signal to form a combined optical signal, an interferometer for dividing the combined optical signal between a reference arm leading to a reference reflector and a sample arm leading to a sample, and a detector system for detecting an interference signal generated from the combined optical signal from the reference arm and from the sample arm.

Growing community of inventors

Lexington, MA, United States of America

Mark E Kuznetsov