Gary Shambat | Stanford University (original) (raw)

Papers by Gary Shambat

Research paper thumbnail of Addition reaction and characterization of chlorotris(triphenylphosphine)iridium(I) on silicon(1 1 1) surfaces

Applied Surface Science, 2009

Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris... more Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris (triphenylphosphine) iridium (I), on hydrogen passivated Si (111) surfaces to form a self-assembled monolayer (SAM). The iridium complex was synthesized prior to chemical addition, for which modified reaction conditions were chosen. Following addition, the silicon surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The XPS results revealed that the surfaces consisted of the expected ...

Research paper thumbnail of Direct band Ge photoluminescence at 1.6 μm coupled to Ge-on-Si microdisk resonators

Germanium microdisks on silicon are fabricated and analyzed under various optical pumping conditi... more Germanium microdisks on silicon are fabricated and analyzed under various optical pumping conditions. WGMs are observed in transmission as well as PL via coupling to fiber tapers. It is concluded that heavy doping is required for lasing.

Research paper thumbnail of Direct band Ge photoluminescence near 1.6 mum coupled to Ge-on-Si microdisk resonators

Applied Physics Letters, 2010

We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium gr... more We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium grown on silicon. Resonators coupled to fiber tapers display clear whispering gallery modes in transmission and photoluminescence with quality factors limited by germanium's material absorption. Continuous wave pumping of the cavities resulted in a dominant heating effect for the cavity modes in both transmission and photoluminescence. Pulsed optical pumping proved to be more effective in minimizing heating, but was not sufficient to observe material gain or lasing. We believe that significantly higher doping levels are critical in order to achieve lasing at reasonable pump conditions.

Research paper thumbnail of Ultrafast direct modulation of a single-mode photonic crystal nanocavity light-emitting diode

Nature Communications, 2011

Low-power and electrically controlled optical sources are vital for next generation optical inter... more Low-power and electrically controlled optical sources are vital for next generation optical interconnect systems to meet strict energy demands. Current optical transmitters consisting of high-threshold lasers plus external modulators consume far too much power to be competitive with future electrical interconnects. Here we demonstrate a directly modulated photonic crystal nanocavity light-emitting diode (LED) with 10 GHz modulation speed and less than 1 fJ per bit energy of operation, which is orders of magnitude lower than previous solutions. The device is electrically controlled and operates at room temperature, while the high modulation speed results from the fast relaxation of the quantum dots used as the active material. By virtue of possessing a small mode volume, our LED is intrinsically single mode and, therefore, useful for communicating information over a single narrowband channel. The demonstrated device is a major step forward in providing practical low-power and integrable sources for on-chip photonics.

Research paper thumbnail of Tunable light sources in the visible and near infrared based on fiber taper coupled photonic crystal nanocavities

Photoluminescence at 1.53 um from Er: SiNx on silicon photonic crystal cavities was extracted via... more Photoluminescence at 1.53 um from Er: SiNx on silicon photonic crystal cavities was extracted via fiber tapers with 2.5 x greater collection efficiency compared to free space emission. Fibers were also used to demonstrate a 10 nm tuning range of 750 nm SHG emission from GaP cavities.

Research paper thumbnail of Fabrication and Analysis of Epitaxially Grown Ge$_{1-x}$Sn$_x$ Microdisk Resonator With 20-nm Free-Spectral Range

IEEE Photonics Technology Letters, 2011

Research paper thumbnail of Double-layer silicon photonic crystal fiber tip sensor

We describe a double-layer monolithic silicon photonic crystal (PC) fiber tip sensor. The PC is f... more We describe a double-layer monolithic silicon photonic crystal (PC) fiber tip sensor. The PC is fabricated using wafer-scale Si processing and epoxy bonding to the fiber. The sensor has sharper resonances and higher sensitivity to refractive index than previously-reported single-layer PC fiber tip sensors. The bonding technique enables batch production.

Research paper thumbnail of Nanobeam photonic crystal cavity quantum dot laser

Optics Express, 2010

The lasing behavior of one dimensional GaAs nanobeam cavities with embedded InAs quantum dots is ... more The lasing behavior of one dimensional GaAs nanobeam cavities with embedded InAs quantum dots is studied at room temperature. Lasing is observed throughout the quantum dot PL spectrum, and the wavelength dependence of the threshold is calculated. We study the cavity lasers under both 780 nm and 980 nm pump, finding thresholds as low as 0.3 uW and 19 uW for the two pump wavelengths, respectively. Finally, the nanobeam cavity laser wavelengths are tuned by up to 7 nm by employing a fiber taper in near proximity to the cavities. The fiber taper is used both to efficiently pump the cavity and collect the cavity emission.

Research paper thumbnail of Nonlinear optics in photonic crystal nanocavities: from light sources to quantum photonic interfaces

We demonstrate photonic interfaces between infrared and visible wavelength ranges by employing en... more We demonstrate photonic interfaces between infrared and visible wavelength ranges by employing enhanced nonlinear frequency conversion in photonic crystal cavities in GaP or GaAs. We first show resonantly enhanced second harmonic and sum frequency generation in GaP photonic crystal cavities. We then integrate these nonlinear frequency conversion elements with a single InAs quantum dot to produce a fast single photon source that is optically triggered at telecommunications wavelength. These frequency conversion techniques are critical for applications including light sources at wavelengths that are difficult to access with existing lasers, IR upconversion-based detectors, and photonic quantum interfaces between the fiber-optic networks and quantum emitters.

Research paper thumbnail of Optical fiber tips functionalized with semiconductor photonic crystal cavities

Applied Physics Letters, 2011

We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal cavities t... more We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal cavities to the facets of optical fibers. Passive Si cavities were measured via fiber taper coupling as well as direct transmission from the fiber facet. Active quantum dot containing GaAs cavities showed photoluminescence that was collected both in free space and back through the original fiber. Cavities maintain a high quality factor (2000-4000) in both material systems. This new design architecture provides a practical mechanically stable platform for the integration of photonic crystal cavities with macroscale optics and opens the door for novel research on fiber-coupled cavity devices.

Research paper thumbnail of Low power consumption electrically pumped photonic crystal membrane devices

A fabrication procedure for electrically pumping photonic crystal membrane devices using a latera... more A fabrication procedure for electrically pumping photonic crystal membrane devices using a lateral p-i-n junction has been developed and is described in this work. The lateral junction is optimized to efficiently inject current into a photonic crystal nanocavity. We have demonstrated electrically pumped lasing by using the lateral junction to pump a quantum dot photonic crystal nanocavity laser. Continuous wave lasing is observed at temperatures up to 150K, and a threshold of 181nA at 50K is demonstrated - the lowest threshold ever demonstrated in an electrically pumped laser. We have demonstrated electrical pumping of photonic crystal nanobeam light emitting diodes, and observe linewidth narrowing at room temperature.

Research paper thumbnail of Room temperature 16 mum electroluminescence from Ge light emitting diode on Si substrate

Optics Express, 2009

We report the room temperature electroluminescence (EL) at 1.6 µm of a Ge n+/p light emitting dio... more We report the room temperature electroluminescence (EL) at 1.6 µm of a Ge n+/p light emitting diode on a Si substrate. Unlike normal electrically pumped devices, this device shows a superlinear luminescence enhancement at high current. By comparing different n type doping concentrations, we observe that a higher concentration is required to achieve better efficiency of the device. Thermal enhancement effects observed in temperature dependent EL spectra show the capability of this device to operate at room temperature or above. These detailed studies show that Ge can be a good candidate for a Si compatible light emitting device. 2009 Optical Society of America OCIS codes: (160.4670) Optical materials; (230.3670) Light-emitting diodes.

Research paper thumbnail of Nanobeam Photonic Crystal Cavity Light-Emitting Diodes

We present results on electrically driven nanobeam photonic crystal cavities formed out of a late... more We present results on electrically driven nanobeam photonic crystal cavities formed out of a lateral p-i-n junction in gallium arsenide. Despite their small conducting dimensions, nanobeams have robust electrical properties with high current densities possible at low drive powers. Much like their two-dimensional counterparts, the nanobeam cavities exhibit bright electroluminescence at room temperature from embedded 1,250 nm InAs quantum dots. A small room temperature differential gain is observed in the cavities with minor beam self-heating suggesting that lasing is possible. These results open the door for efficient electrical control of active nanobeam cavities for diverse nanophotonic applications.

Research paper thumbnail of Ultra-low power fiber-coupled gallium arsenide photonic crystal cavity electro-optic modulator

Optics Express, 2011

We demonstrate electro-optic modulation in a GaAs laterally doped photonic crystal cavity diode w... more We demonstrate electro-optic modulation in a GaAs laterally doped photonic crystal cavity diode with ultra-low switching energy of several fJ/bit. A short non-radiative carrier lifetime allows fast switching with an upper threshold of 100 GHz.

Research paper thumbnail of Cavity-enhanced direct band electroluminescence near 1550 nm from germanium microdisk resonator diode on silicon

Applied Physics Letters, 2011

We electrically and optically characterize a germanium resonator diode on silicon fabricated by i... more We electrically and optically characterize a germanium resonator diode on silicon fabricated by integrating a germanium light emitting diode with a microdisk cavity. Diode current-voltage characteristics show a low ideality factor and a high on/off ratio. The optical transmission of the resonator features whispering gallery modes with quality factors of a few hundred. Direct band gap electroluminescence under continuous current injection shows a clear enhancement of emission by the cavity. At this stage, the pumping level is not high enough to cause linewidth narrowing and invert the material. A higher n-type activated doping of germanium is necessary to achieve lasing.

Research paper thumbnail of Fiber taper collection of photoluminescence at 1.54 µm from erbium doped silicon nitride photonic crystal cavities

Photoluminescence at 1.54 μm from Er-doped silicon nitride embedded in silicon photonic crystal c... more Photoluminescence at 1.54 μm from Er-doped silicon nitride embedded in silicon photonic crystal cavities was extracted with 2.5× greater collection efficiency compared to free space emission, with loaded Q values of up to 98% of the intrinsic Q.

Research paper thumbnail of Ultra-low Threshold electrically pumped quantum dot photonic crystal nanocavity laser

Nature Photonics, 2011

We demonstrate a quantum dot photonic crystal nanocavity laser electrically pumped by a lateral p... more We demonstrate a quantum dot photonic crystal nanocavity laser electrically pumped by a lateral p-i-n junction. Thresholds of 181 nA at 50 K and 287 nA at 150 K are observed, lower than any other laser.

Research paper thumbnail of Ge quantum well resonator modulators

The strong electroabsorption modulation possible in Ge/SiGe quantum wells promises efficient, CMO... more The strong electroabsorption modulation possible in Ge/SiGe quantum wells promises efficient, CMOScompatible integrated optical modulators. We demonstrate surface-normal asymmetric Fabry-Perot and microdisk resonator modulators employing Ge quantum wells grown on silicon.

Research paper thumbnail of Reconfigurable photonic crystal filters for multi-band optical filtering on a monolithic substrate

Many applications require the ability to image a scene in several different narrow spectral bands... more Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Absorption filters commonly used to generate RGB color filters do not have the flexibility and narrow band filtering ability. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. This paper extends the previous work in adjusting spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO2 and Si3N4 with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. It was found that individual layer fluctuations have a minor impact on filter performance, whereas hole taper produces a large peak shift. The results in this paper provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes.

Research paper thumbnail of Photonic crystal filters for multi-band optical filtering on a monolithic substrate

Many applications require the ability to image a scene in several different narrow spectral bands... more Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. We adjusted the spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO2 and Si3N4 with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. Our results provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes.

Research paper thumbnail of Addition reaction and characterization of chlorotris(triphenylphosphine)iridium(I) on silicon(1 1 1) surfaces

Applied Surface Science, 2009

Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris... more Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris (triphenylphosphine) iridium (I), on hydrogen passivated Si (111) surfaces to form a self-assembled monolayer (SAM). The iridium complex was synthesized prior to chemical addition, for which modified reaction conditions were chosen. Following addition, the silicon surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The XPS results revealed that the surfaces consisted of the expected ...

Research paper thumbnail of Direct band Ge photoluminescence at 1.6 μm coupled to Ge-on-Si microdisk resonators

Germanium microdisks on silicon are fabricated and analyzed under various optical pumping conditi... more Germanium microdisks on silicon are fabricated and analyzed under various optical pumping conditions. WGMs are observed in transmission as well as PL via coupling to fiber tapers. It is concluded that heavy doping is required for lasing.

Research paper thumbnail of Direct band Ge photoluminescence near 1.6 mum coupled to Ge-on-Si microdisk resonators

Applied Physics Letters, 2010

We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium gr... more We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium grown on silicon. Resonators coupled to fiber tapers display clear whispering gallery modes in transmission and photoluminescence with quality factors limited by germanium's material absorption. Continuous wave pumping of the cavities resulted in a dominant heating effect for the cavity modes in both transmission and photoluminescence. Pulsed optical pumping proved to be more effective in minimizing heating, but was not sufficient to observe material gain or lasing. We believe that significantly higher doping levels are critical in order to achieve lasing at reasonable pump conditions.

Research paper thumbnail of Ultrafast direct modulation of a single-mode photonic crystal nanocavity light-emitting diode

Nature Communications, 2011

Low-power and electrically controlled optical sources are vital for next generation optical inter... more Low-power and electrically controlled optical sources are vital for next generation optical interconnect systems to meet strict energy demands. Current optical transmitters consisting of high-threshold lasers plus external modulators consume far too much power to be competitive with future electrical interconnects. Here we demonstrate a directly modulated photonic crystal nanocavity light-emitting diode (LED) with 10 GHz modulation speed and less than 1 fJ per bit energy of operation, which is orders of magnitude lower than previous solutions. The device is electrically controlled and operates at room temperature, while the high modulation speed results from the fast relaxation of the quantum dots used as the active material. By virtue of possessing a small mode volume, our LED is intrinsically single mode and, therefore, useful for communicating information over a single narrowband channel. The demonstrated device is a major step forward in providing practical low-power and integrable sources for on-chip photonics.

Research paper thumbnail of Tunable light sources in the visible and near infrared based on fiber taper coupled photonic crystal nanocavities

Photoluminescence at 1.53 um from Er: SiNx on silicon photonic crystal cavities was extracted via... more Photoluminescence at 1.53 um from Er: SiNx on silicon photonic crystal cavities was extracted via fiber tapers with 2.5 x greater collection efficiency compared to free space emission. Fibers were also used to demonstrate a 10 nm tuning range of 750 nm SHG emission from GaP cavities.

Research paper thumbnail of Fabrication and Analysis of Epitaxially Grown Ge$_{1-x}$Sn$_x$ Microdisk Resonator With 20-nm Free-Spectral Range

IEEE Photonics Technology Letters, 2011

Research paper thumbnail of Double-layer silicon photonic crystal fiber tip sensor

We describe a double-layer monolithic silicon photonic crystal (PC) fiber tip sensor. The PC is f... more We describe a double-layer monolithic silicon photonic crystal (PC) fiber tip sensor. The PC is fabricated using wafer-scale Si processing and epoxy bonding to the fiber. The sensor has sharper resonances and higher sensitivity to refractive index than previously-reported single-layer PC fiber tip sensors. The bonding technique enables batch production.

Research paper thumbnail of Nanobeam photonic crystal cavity quantum dot laser

Optics Express, 2010

The lasing behavior of one dimensional GaAs nanobeam cavities with embedded InAs quantum dots is ... more The lasing behavior of one dimensional GaAs nanobeam cavities with embedded InAs quantum dots is studied at room temperature. Lasing is observed throughout the quantum dot PL spectrum, and the wavelength dependence of the threshold is calculated. We study the cavity lasers under both 780 nm and 980 nm pump, finding thresholds as low as 0.3 uW and 19 uW for the two pump wavelengths, respectively. Finally, the nanobeam cavity laser wavelengths are tuned by up to 7 nm by employing a fiber taper in near proximity to the cavities. The fiber taper is used both to efficiently pump the cavity and collect the cavity emission.

Research paper thumbnail of Nonlinear optics in photonic crystal nanocavities: from light sources to quantum photonic interfaces

We demonstrate photonic interfaces between infrared and visible wavelength ranges by employing en... more We demonstrate photonic interfaces between infrared and visible wavelength ranges by employing enhanced nonlinear frequency conversion in photonic crystal cavities in GaP or GaAs. We first show resonantly enhanced second harmonic and sum frequency generation in GaP photonic crystal cavities. We then integrate these nonlinear frequency conversion elements with a single InAs quantum dot to produce a fast single photon source that is optically triggered at telecommunications wavelength. These frequency conversion techniques are critical for applications including light sources at wavelengths that are difficult to access with existing lasers, IR upconversion-based detectors, and photonic quantum interfaces between the fiber-optic networks and quantum emitters.

Research paper thumbnail of Optical fiber tips functionalized with semiconductor photonic crystal cavities

Applied Physics Letters, 2011

We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal cavities t... more We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal cavities to the facets of optical fibers. Passive Si cavities were measured via fiber taper coupling as well as direct transmission from the fiber facet. Active quantum dot containing GaAs cavities showed photoluminescence that was collected both in free space and back through the original fiber. Cavities maintain a high quality factor (2000-4000) in both material systems. This new design architecture provides a practical mechanically stable platform for the integration of photonic crystal cavities with macroscale optics and opens the door for novel research on fiber-coupled cavity devices.

Research paper thumbnail of Low power consumption electrically pumped photonic crystal membrane devices

A fabrication procedure for electrically pumping photonic crystal membrane devices using a latera... more A fabrication procedure for electrically pumping photonic crystal membrane devices using a lateral p-i-n junction has been developed and is described in this work. The lateral junction is optimized to efficiently inject current into a photonic crystal nanocavity. We have demonstrated electrically pumped lasing by using the lateral junction to pump a quantum dot photonic crystal nanocavity laser. Continuous wave lasing is observed at temperatures up to 150K, and a threshold of 181nA at 50K is demonstrated - the lowest threshold ever demonstrated in an electrically pumped laser. We have demonstrated electrical pumping of photonic crystal nanobeam light emitting diodes, and observe linewidth narrowing at room temperature.

Research paper thumbnail of Room temperature 16 mum electroluminescence from Ge light emitting diode on Si substrate

Optics Express, 2009

We report the room temperature electroluminescence (EL) at 1.6 µm of a Ge n+/p light emitting dio... more We report the room temperature electroluminescence (EL) at 1.6 µm of a Ge n+/p light emitting diode on a Si substrate. Unlike normal electrically pumped devices, this device shows a superlinear luminescence enhancement at high current. By comparing different n type doping concentrations, we observe that a higher concentration is required to achieve better efficiency of the device. Thermal enhancement effects observed in temperature dependent EL spectra show the capability of this device to operate at room temperature or above. These detailed studies show that Ge can be a good candidate for a Si compatible light emitting device. 2009 Optical Society of America OCIS codes: (160.4670) Optical materials; (230.3670) Light-emitting diodes.

Research paper thumbnail of Nanobeam Photonic Crystal Cavity Light-Emitting Diodes

We present results on electrically driven nanobeam photonic crystal cavities formed out of a late... more We present results on electrically driven nanobeam photonic crystal cavities formed out of a lateral p-i-n junction in gallium arsenide. Despite their small conducting dimensions, nanobeams have robust electrical properties with high current densities possible at low drive powers. Much like their two-dimensional counterparts, the nanobeam cavities exhibit bright electroluminescence at room temperature from embedded 1,250 nm InAs quantum dots. A small room temperature differential gain is observed in the cavities with minor beam self-heating suggesting that lasing is possible. These results open the door for efficient electrical control of active nanobeam cavities for diverse nanophotonic applications.

Research paper thumbnail of Ultra-low power fiber-coupled gallium arsenide photonic crystal cavity electro-optic modulator

Optics Express, 2011

We demonstrate electro-optic modulation in a GaAs laterally doped photonic crystal cavity diode w... more We demonstrate electro-optic modulation in a GaAs laterally doped photonic crystal cavity diode with ultra-low switching energy of several fJ/bit. A short non-radiative carrier lifetime allows fast switching with an upper threshold of 100 GHz.

Research paper thumbnail of Cavity-enhanced direct band electroluminescence near 1550 nm from germanium microdisk resonator diode on silicon

Applied Physics Letters, 2011

We electrically and optically characterize a germanium resonator diode on silicon fabricated by i... more We electrically and optically characterize a germanium resonator diode on silicon fabricated by integrating a germanium light emitting diode with a microdisk cavity. Diode current-voltage characteristics show a low ideality factor and a high on/off ratio. The optical transmission of the resonator features whispering gallery modes with quality factors of a few hundred. Direct band gap electroluminescence under continuous current injection shows a clear enhancement of emission by the cavity. At this stage, the pumping level is not high enough to cause linewidth narrowing and invert the material. A higher n-type activated doping of germanium is necessary to achieve lasing.

Research paper thumbnail of Fiber taper collection of photoluminescence at 1.54 µm from erbium doped silicon nitride photonic crystal cavities

Photoluminescence at 1.54 μm from Er-doped silicon nitride embedded in silicon photonic crystal c... more Photoluminescence at 1.54 μm from Er-doped silicon nitride embedded in silicon photonic crystal cavities was extracted with 2.5× greater collection efficiency compared to free space emission, with loaded Q values of up to 98% of the intrinsic Q.

Research paper thumbnail of Ultra-low Threshold electrically pumped quantum dot photonic crystal nanocavity laser

Nature Photonics, 2011

We demonstrate a quantum dot photonic crystal nanocavity laser electrically pumped by a lateral p... more We demonstrate a quantum dot photonic crystal nanocavity laser electrically pumped by a lateral p-i-n junction. Thresholds of 181 nA at 50 K and 287 nA at 150 K are observed, lower than any other laser.

Research paper thumbnail of Ge quantum well resonator modulators

The strong electroabsorption modulation possible in Ge/SiGe quantum wells promises efficient, CMO... more The strong electroabsorption modulation possible in Ge/SiGe quantum wells promises efficient, CMOScompatible integrated optical modulators. We demonstrate surface-normal asymmetric Fabry-Perot and microdisk resonator modulators employing Ge quantum wells grown on silicon.

Research paper thumbnail of Reconfigurable photonic crystal filters for multi-band optical filtering on a monolithic substrate

Many applications require the ability to image a scene in several different narrow spectral bands... more Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Absorption filters commonly used to generate RGB color filters do not have the flexibility and narrow band filtering ability. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. This paper extends the previous work in adjusting spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO2 and Si3N4 with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. It was found that individual layer fluctuations have a minor impact on filter performance, whereas hole taper produces a large peak shift. The results in this paper provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes.

Research paper thumbnail of Photonic crystal filters for multi-band optical filtering on a monolithic substrate

Many applications require the ability to image a scene in several different narrow spectral bands... more Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. We adjusted the spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO2 and Si3N4 with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. Our results provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes.