Alexander Ksendzov - Academia.edu (original) (raw)

Papers by Alexander Ksendzov

Proceedings of Spie the International Society For Optical Engineering, Jul 28, 2008

Modal filters are necessary to the proposed high-performance mid-infrared nulling interferometers... more Modal filters are necessary to the proposed high-performance mid-infrared nulling interferometers, because they can help achieve deeper interferometric nulls. Silver halide fibers of composition AgClxBr1-x(0<x<1) are leading candidates for these purposes, due to their high transparency in 4-20 mum spectral range. We have fabricated silver halide fibers with small cores and small differences between the refractive indices of the core and the clad. These operated as single mode fibers. An outer absorbing layer was applied to strip off cladding modes and reduce the minimum fiber length needed for modal filtering. Short sections of such fibers exhibited round and symmetrical optical field mode distributions with losses of 10-15dB/m at lambda=10.6mum. We have tested the modal filtering properties of such short fiber sections. We found that the presence of unsuppressed cladding modes at the output is the main factor limiting the fiber's performance as a modal filter. This effect can be mitigated by appropriate aperturing of the output. With a properly sized aperture, a 10.5 cm long fiber can suppress the power in nonfundamental modes by a factor larger than 17000. If an aperture is not used, the suppression is reduced by a factor of ~ 20.

Proceedings of Spie the International Society For Optical Engineering, 2008

This paper provides an overview of technology development for the Terrestrial Planet Finder Inter... more This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress with each of the testbeds is summarized.

We have built a miniature illuminator for Laser Doppler velocimeter on micromachined silicon opti... more We have built a miniature illuminator for Laser Doppler velocimeter on micromachined silicon optical bench utilizing a novel optical scheme. We used two intersecting coherent beams from the two opposing facets of semiconductor laser die to form a standing interference pattern needed for the particle detection and velocity measurement. Such devices are of interest to NASA for investigating wind patterns

High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength ... more High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength region are needed for coherent detection optical remote sensing applications. 2.05-µm Fabry Perot (FP) and distributed feedback (DFB) ridge waveguide lasers fabricated from epitaxially grown InGaAsSb/AlGaAsSb/GaSb and InGaAs/InP heterostructures are reported. This work is part of a NASA Earth Science Enterprise Advanced Technology Initiatives Program research effort to develop semiconductor laser reference oscillators for optical remote sensing from Earth orbit. In particular, local oscillators provide the frequency reference required for active spaceborne optical remote sensing concepts that use heterodyne (coherent) detection. The two most prominent Earth observation applications for this technology are Doppler LIDAR wind sensing and tropospheric carbon dioxide measurement by laser absorption spectrometry, the currently favored operational wavelength for both of which is 2.05 µm. Frequency-agile local oscillator (FALO) technology is critical in such applications because of the need to compensate for large platform-induced Doppler components that would otherwise compromise data reduction and interpretation. The semiconductor laserbased FALO option offers considerable scope for reduced mechanical complexity and improved frequency agility over equivalent crystal laser devices, while their potentially faster tuning ability holds significant potential for enhanced scanning versatility. To realize narrow linewidth operation in monolithic laser structures at the wavelength of interest at the high currents and output powers required for operation in an optical heterodyne receiver corrugation pitch-modulated distributed feedback (CPM-DFB) configuration is used. CPM-DFB lasers achieve narrow linewidth operation by suppressing gain nonlinearities inside the laser cavity that lead to linewidth re-broadening. CPM-DFB lasers utilize a grating segment of slightly different pitch to achieve added uniform light intensity along the laser cavity.

UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts V, 2011

ABSTRACT Arrays of single mode fibers can be used to form segmented pupils of almost arbitrary ge... more ABSTRACT Arrays of single mode fibers can be used to form segmented pupils of almost arbitrary geometry. Such pupil arrays can be used both for interferometric imaging, for example by non-redundant aperture masking or in direct imaging systems such as the phased array coronagraph. Achieving control over the optical coupling, phase and dispersion for fiber arrays of reasonable size is a technological challenge. Progress has been made using a monolithic block of single mode fibers, lens arrays and masks, and mirror arrays. On one testbed, arrays of up to 37 beamlets are being combined to form a single image. On a second testbed, control of dispersion between fibers of slightly different length is being evaluated. The combination of the techniques being demonstrated has a range of potential uses in astronomy. In this paper we discuss the initial testbed results.

The ability to observe and identify the presence of trace gases within an environment is a paramo... more The ability to observe and identify the presence of trace gases within an environment is a paramount capability needed to advance earth and planetary atmospheric research. Detection of trace levels of gases is also of interest in defense, industrial, security, medical, and environmental health applications. Current scientific objectives largely focus on identifying the presence of specific gases and isotopologues found in planetary atmospheres within our solar system. The presence and relative amounts of these gases allows scientists to deduce history of the planetary atmosphere and the likelihood that life has or could exist there. One challenge is accurately acquiring the data needed to make reliable conclusions when some of the target gas molecules are present in trace quantities of 10 parts per billion (ppb) or less. Laser gas spectrometers are effective ways of collecting in situ gas measurements, but their precision is directly proportional to the path length of the optical system. The Scanning Laser Infrared Molecular Spectrometer (SLIMS) is a novel solution that achieves very long effective path lengths, which yield ppb and sub-ppb measurements of trace gases. It can also accommodate multiple laser channels covering a wide range of wavelengths resulting in detection of more chemicals of interest. The mechanical design of the mirror cell allows for the large effective path length within a small footprint. The same design provides a robust structure which lends itself to being immune to some of the alignment challenges that similar cells face. The continued forward progress of the SLIMS project will rely on optimizing the optical paths and optical alignment geometries. Missions referred to in this document are for planning and discussion purposes only.

EPJ Web of Conferences, 2011

This paper provides an overview of technology development for the Terrestrial Planet Finder Inter... more This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. a e-mail: Peter.R.Lawson@jpl.nasa.gov This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly cited.

High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength ... more High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength region are needed for coherent detection optical remote sensing applications. 2.05-µm Fabry Perot (FP) and distributed feedback (DFB) ridge waveguide lasers fabricated from epitaxially grown InGaAsSb/AlGaAsSb/GaSb and InGaAs/InP hetero- structures are reported. This work is part of a NASA Earth Science Enterprise Advanced Technology Initiatives Program research effort to develop semiconductor laser reference oscillators for optical remote sensing from Earth orbit. In particular, local oscillators provide the frequency reference required for active spaceborne optical remote sensing concepts that use heterodyne (coherent) detection. The two most prominent Earth observation applications for this technology are Doppler LIDAR wind sensing and tropospheric carbon dioxide measurement by laser absorption spectrometry, the currently favored operational wavelength for both of which is 2.05 µm. Fre...

Optical Devices and Methods for Microwave/Millimeter-Wave and Frontier Applications, 1998

ABSTRACT This paper describes the design of infrared filters using methods drawn from microwave a... more ABSTRACT This paper describes the design of infrared filters using methods drawn from microwave and millimeter wave filters. Special note is made of approximations made in the infrared design, and ways to improve upon these approximations. Results from the design, manufacture and test of linear wedge filters built using microlithographic techniques and used in spectral imaging applications will be presented.

Advanced Microdevices and Space Science Sensors, 1994

ABSTRACT A new technology for infrared optical filters is presented. We have produced a band pass... more ABSTRACT A new technology for infrared optical filters is presented. We have produced a band pass filter consisting of a thin (12.4 micrometers ) Si wafer with cross-shaped metal patterns deposited on both sides. The crosses, with 6 micrometers arms, have been formed by direct-write electron- beam lithography on 1000 angstroms Al film. The filter is mounted on a 0.2 mm thick Si frame with 0.25 cm2 window, but it also can be bonded to detectors so that the filter and the detector temperature are the same. Due to the high index of refractive in Si, this filter is more tolerant to converging beams than interferometric filters made of metal meshes stretched in air that have been reported previously. When placed into an F/3 converging beam, the filter has a bandpass characteristic centered at 70 micrometers wavelength with width at half maximum (delta) (lambda) /(lambda) equals 7%. The transmission maximum is 44%. At present the band pass is limited by the non-uniformity of the available substrates. The out-of-band rejection need improving which can be achieved using additional non-interferometric filters with wider band pass made with similar technology. Another way of improving the performance is integrating the metal patterns onto the detector which will make it frequency selective. Extending the interference filter technology to shorter wavelengths is difficult due to the onset of absorption in the metal layers.

Infrared Technology XVII, 1991

ABSTRACT SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) dete... more ABSTRACT SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by MBE. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p(+) SiGe layers were grown using elemental boron, as the dopant source allows a low growth temperature. Good crystalline quality was achieved for boron-doped SiGe due to the reduced growth temperature. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited. HIP detectors with a 0.066 eV were fabricated and characterized using activation energy analysis, corresponding to a 18 micron cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 microns has been characterized with corresponding quantum efficiencies of 5 - 0.1 percent.

Miniaturized Systems with Micro-Optics and MEMS, 1999

We have built a miniature illuminator for Laser Doppler velocimeter on micromachined optical benc... more We have built a miniature illuminator for Laser Doppler velocimeter on micromachined optical bench utilizing a novel optical scheme. We used two intersecting coherent beams from the two opposing facets of semiconductor laser die to form a standing interference pattern needed for the particle detection and velocity measurement. Such devices are of interest to NASA for investigating wind patterns and dust loading on planets with atmosphere. They can be applied to other problems where the liquid or gas flux must be characterized without disturbing the flow. In addition, the small probe volume makes possible local flow characterization and profiling. The device fabrication, and the results of the fringe characterization and velocity measurements are presented and discussed.

Infrared Astronomical Instrumentation, 1998

Linear Variable Filters (LVFs or "wedge filters") have found increasing applicability in spectral... more Linear Variable Filters (LVFs or "wedge filters") have found increasing applicability in spectrally selective optical instruments. They serve as moderate resolution spectral discriminators in astronomical instruments and in reconnaissance equipment. They perform extremely well as "sliding out-of-band blocking filters" when used in conjunction with grating spectrometers.

Techniques and Instrumentation for Detection of Exoplanets V, 2011

ABSTRACT The last decade has seen great advances in interferometric nulling technology, propelled... more ABSTRACT The last decade has seen great advances in interferometric nulling technology, propelled at first by the SIM and KECK nulling programs and then by the Terrestrial Planet Finder Interferometer (TPF-I). In the infrared at N-band (using a CO2 laser at 10.6 micron wavelength) the first million to one nulls were reported on a KECK testbed in 2003. For TPF-I, nulls needed to be both deep and broadband, and a suite of testbeds was designed and built to study all aspects of achromatic nulling and system implementation, including formation flying technology. Also, observatory designs were drawn up and studied against performance models. Modeling revealed that natural variations in the alignment and control of the optical system produced an &quot;instability noise&quot; signal and this realization eventually led to a redesign of the layout to a rectangular formation. The complexity of the early TPF-I spacecraft design was mitigated by the infusion of ideas from Europe and produced the current X-Array design which utilizes simple reflectors to form the apertures together with a stretched three dimensional formation geometry. This paper summarizes the main achievements of the infrared nulling technology program including the development of adaptive nulling for broadband performance and the demonstration of starlight suppression by 100 million to one.

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT We demonstrate single-mode laterally coupled distributed-feedback diode lasers at 2.05 µ... more ABSTRACT We demonstrate single-mode laterally coupled distributed-feedback diode lasers at 2.05 µm employing low-loss etched gratings. Single-facet CW output exceeds 50 mW near room temperature with linewidth below 1 MHz over 10-ms observation times.

ISLC 2012 International Semiconductor Laser Conference, 2012

ABSTRACT We report on the phase noise properties of DFB lasers operating near 2.0 μm. Measured no... more ABSTRACT We report on the phase noise properties of DFB lasers operating near 2.0 μm. Measured noise spectra indicate intrinsic linewidths below 1 kHz. Less than 200 kHz effective linewidth is estimated for 5 ms measurement time.

Richard Lai, TRW Inc., Redondo Beach CA 90278

Semiconductor Science and Technology, 2011

We have demonstrated Fabry-Perot single spatial mode antimonide-based type-I quantum-well ridge w... more We have demonstrated Fabry-Perot single spatial mode antimonide-based type-I quantum-well ridge waveguide semiconductor diode lasers operating at 3.0-3.2 µm wavelength in continuous mode up to 333 K. Internal optical loss in narrow ridge devices was significantly reduced by using thick Si3N4 dielectric films for planarization. The fabricated lasers operate in CW mode at room temperature with output powers exceeding 5

This paper provides an overview of technology development for the Terrestrial Planet Finder Inter... more This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars.

Applied Physics Letters, 2012

ABSTRACT We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers design... more ABSTRACT We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers designed to operate at wavelengths near 2.05 μm. Second-order Bragg gratings were etched alongside narrow ridge waveguides to enable single-mode DFB operation in 2-mm-long laser diodes. At a heat-sink temperature of 10 °C, the lasers emit more than 40 mW continuous-wave in a single longitudinal mode, while increasing the current beyond 300 mA results in multimode operation due to spectral shifting of the laser gain with respect to the peak grating reflectivity. At −10 °C, we observe DFB operation at higher current, with single-facet emission exceeding 80 mW.

Proceedings of Spie the International Society For Optical Engineering, Jul 28, 2008

Modal filters are necessary to the proposed high-performance mid-infrared nulling interferometers... more Modal filters are necessary to the proposed high-performance mid-infrared nulling interferometers, because they can help achieve deeper interferometric nulls. Silver halide fibers of composition AgClxBr1-x(0<x<1) are leading candidates for these purposes, due to their high transparency in 4-20 mum spectral range. We have fabricated silver halide fibers with small cores and small differences between the refractive indices of the core and the clad. These operated as single mode fibers. An outer absorbing layer was applied to strip off cladding modes and reduce the minimum fiber length needed for modal filtering. Short sections of such fibers exhibited round and symmetrical optical field mode distributions with losses of 10-15dB/m at lambda=10.6mum. We have tested the modal filtering properties of such short fiber sections. We found that the presence of unsuppressed cladding modes at the output is the main factor limiting the fiber's performance as a modal filter. This effect can be mitigated by appropriate aperturing of the output. With a properly sized aperture, a 10.5 cm long fiber can suppress the power in nonfundamental modes by a factor larger than 17000. If an aperture is not used, the suppression is reduced by a factor of ~ 20.

Proceedings of Spie the International Society For Optical Engineering, 2008

This paper provides an overview of technology development for the Terrestrial Planet Finder Inter... more This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress with each of the testbeds is summarized.

We have built a miniature illuminator for Laser Doppler velocimeter on micromachined silicon opti... more We have built a miniature illuminator for Laser Doppler velocimeter on micromachined silicon optical bench utilizing a novel optical scheme. We used two intersecting coherent beams from the two opposing facets of semiconductor laser die to form a standing interference pattern needed for the particle detection and velocity measurement. Such devices are of interest to NASA for investigating wind patterns

High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength ... more High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength region are needed for coherent detection optical remote sensing applications. 2.05-µm Fabry Perot (FP) and distributed feedback (DFB) ridge waveguide lasers fabricated from epitaxially grown InGaAsSb/AlGaAsSb/GaSb and InGaAs/InP heterostructures are reported. This work is part of a NASA Earth Science Enterprise Advanced Technology Initiatives Program research effort to develop semiconductor laser reference oscillators for optical remote sensing from Earth orbit. In particular, local oscillators provide the frequency reference required for active spaceborne optical remote sensing concepts that use heterodyne (coherent) detection. The two most prominent Earth observation applications for this technology are Doppler LIDAR wind sensing and tropospheric carbon dioxide measurement by laser absorption spectrometry, the currently favored operational wavelength for both of which is 2.05 µm. Frequency-agile local oscillator (FALO) technology is critical in such applications because of the need to compensate for large platform-induced Doppler components that would otherwise compromise data reduction and interpretation. The semiconductor laserbased FALO option offers considerable scope for reduced mechanical complexity and improved frequency agility over equivalent crystal laser devices, while their potentially faster tuning ability holds significant potential for enhanced scanning versatility. To realize narrow linewidth operation in monolithic laser structures at the wavelength of interest at the high currents and output powers required for operation in an optical heterodyne receiver corrugation pitch-modulated distributed feedback (CPM-DFB) configuration is used. CPM-DFB lasers achieve narrow linewidth operation by suppressing gain nonlinearities inside the laser cavity that lead to linewidth re-broadening. CPM-DFB lasers utilize a grating segment of slightly different pitch to achieve added uniform light intensity along the laser cavity.

UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts V, 2011

ABSTRACT Arrays of single mode fibers can be used to form segmented pupils of almost arbitrary ge... more ABSTRACT Arrays of single mode fibers can be used to form segmented pupils of almost arbitrary geometry. Such pupil arrays can be used both for interferometric imaging, for example by non-redundant aperture masking or in direct imaging systems such as the phased array coronagraph. Achieving control over the optical coupling, phase and dispersion for fiber arrays of reasonable size is a technological challenge. Progress has been made using a monolithic block of single mode fibers, lens arrays and masks, and mirror arrays. On one testbed, arrays of up to 37 beamlets are being combined to form a single image. On a second testbed, control of dispersion between fibers of slightly different length is being evaluated. The combination of the techniques being demonstrated has a range of potential uses in astronomy. In this paper we discuss the initial testbed results.

The ability to observe and identify the presence of trace gases within an environment is a paramo... more The ability to observe and identify the presence of trace gases within an environment is a paramount capability needed to advance earth and planetary atmospheric research. Detection of trace levels of gases is also of interest in defense, industrial, security, medical, and environmental health applications. Current scientific objectives largely focus on identifying the presence of specific gases and isotopologues found in planetary atmospheres within our solar system. The presence and relative amounts of these gases allows scientists to deduce history of the planetary atmosphere and the likelihood that life has or could exist there. One challenge is accurately acquiring the data needed to make reliable conclusions when some of the target gas molecules are present in trace quantities of 10 parts per billion (ppb) or less. Laser gas spectrometers are effective ways of collecting in situ gas measurements, but their precision is directly proportional to the path length of the optical system. The Scanning Laser Infrared Molecular Spectrometer (SLIMS) is a novel solution that achieves very long effective path lengths, which yield ppb and sub-ppb measurements of trace gases. It can also accommodate multiple laser channels covering a wide range of wavelengths resulting in detection of more chemicals of interest. The mechanical design of the mirror cell allows for the large effective path length within a small footprint. The same design provides a robust structure which lends itself to being immune to some of the alignment challenges that similar cells face. The continued forward progress of the SLIMS project will rely on optimizing the optical paths and optical alignment geometries. Missions referred to in this document are for planning and discussion purposes only.

EPJ Web of Conferences, 2011

This paper provides an overview of technology development for the Terrestrial Planet Finder Inter... more This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. a e-mail: Peter.R.Lawson@jpl.nasa.gov This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly cited.

High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength ... more High power single mode, tunable, narrow linewidth semiconductor lasers in the 2.05-µm wavelength region are needed for coherent detection optical remote sensing applications. 2.05-µm Fabry Perot (FP) and distributed feedback (DFB) ridge waveguide lasers fabricated from epitaxially grown InGaAsSb/AlGaAsSb/GaSb and InGaAs/InP hetero- structures are reported. This work is part of a NASA Earth Science Enterprise Advanced Technology Initiatives Program research effort to develop semiconductor laser reference oscillators for optical remote sensing from Earth orbit. In particular, local oscillators provide the frequency reference required for active spaceborne optical remote sensing concepts that use heterodyne (coherent) detection. The two most prominent Earth observation applications for this technology are Doppler LIDAR wind sensing and tropospheric carbon dioxide measurement by laser absorption spectrometry, the currently favored operational wavelength for both of which is 2.05 µm. Fre...

Optical Devices and Methods for Microwave/Millimeter-Wave and Frontier Applications, 1998

ABSTRACT This paper describes the design of infrared filters using methods drawn from microwave a... more ABSTRACT This paper describes the design of infrared filters using methods drawn from microwave and millimeter wave filters. Special note is made of approximations made in the infrared design, and ways to improve upon these approximations. Results from the design, manufacture and test of linear wedge filters built using microlithographic techniques and used in spectral imaging applications will be presented.

Advanced Microdevices and Space Science Sensors, 1994

ABSTRACT A new technology for infrared optical filters is presented. We have produced a band pass... more ABSTRACT A new technology for infrared optical filters is presented. We have produced a band pass filter consisting of a thin (12.4 micrometers ) Si wafer with cross-shaped metal patterns deposited on both sides. The crosses, with 6 micrometers arms, have been formed by direct-write electron- beam lithography on 1000 angstroms Al film. The filter is mounted on a 0.2 mm thick Si frame with 0.25 cm2 window, but it also can be bonded to detectors so that the filter and the detector temperature are the same. Due to the high index of refractive in Si, this filter is more tolerant to converging beams than interferometric filters made of metal meshes stretched in air that have been reported previously. When placed into an F/3 converging beam, the filter has a bandpass characteristic centered at 70 micrometers wavelength with width at half maximum (delta) (lambda) /(lambda) equals 7%. The transmission maximum is 44%. At present the band pass is limited by the non-uniformity of the available substrates. The out-of-band rejection need improving which can be achieved using additional non-interferometric filters with wider band pass made with similar technology. Another way of improving the performance is integrating the metal patterns onto the detector which will make it frequency selective. Extending the interference filter technology to shorter wavelengths is difficult due to the onset of absorption in the metal layers.

Infrared Technology XVII, 1991

ABSTRACT SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) dete... more ABSTRACT SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by MBE. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p(+) SiGe layers were grown using elemental boron, as the dopant source allows a low growth temperature. Good crystalline quality was achieved for boron-doped SiGe due to the reduced growth temperature. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited. HIP detectors with a 0.066 eV were fabricated and characterized using activation energy analysis, corresponding to a 18 micron cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 microns has been characterized with corresponding quantum efficiencies of 5 - 0.1 percent.

Miniaturized Systems with Micro-Optics and MEMS, 1999

We have built a miniature illuminator for Laser Doppler velocimeter on micromachined optical benc... more We have built a miniature illuminator for Laser Doppler velocimeter on micromachined optical bench utilizing a novel optical scheme. We used two intersecting coherent beams from the two opposing facets of semiconductor laser die to form a standing interference pattern needed for the particle detection and velocity measurement. Such devices are of interest to NASA for investigating wind patterns and dust loading on planets with atmosphere. They can be applied to other problems where the liquid or gas flux must be characterized without disturbing the flow. In addition, the small probe volume makes possible local flow characterization and profiling. The device fabrication, and the results of the fringe characterization and velocity measurements are presented and discussed.

Infrared Astronomical Instrumentation, 1998

Linear Variable Filters (LVFs or "wedge filters") have found increasing applicability in spectral... more Linear Variable Filters (LVFs or "wedge filters") have found increasing applicability in spectrally selective optical instruments. They serve as moderate resolution spectral discriminators in astronomical instruments and in reconnaissance equipment. They perform extremely well as "sliding out-of-band blocking filters" when used in conjunction with grating spectrometers.

Techniques and Instrumentation for Detection of Exoplanets V, 2011

ABSTRACT The last decade has seen great advances in interferometric nulling technology, propelled... more ABSTRACT The last decade has seen great advances in interferometric nulling technology, propelled at first by the SIM and KECK nulling programs and then by the Terrestrial Planet Finder Interferometer (TPF-I). In the infrared at N-band (using a CO2 laser at 10.6 micron wavelength) the first million to one nulls were reported on a KECK testbed in 2003. For TPF-I, nulls needed to be both deep and broadband, and a suite of testbeds was designed and built to study all aspects of achromatic nulling and system implementation, including formation flying technology. Also, observatory designs were drawn up and studied against performance models. Modeling revealed that natural variations in the alignment and control of the optical system produced an &quot;instability noise&quot; signal and this realization eventually led to a redesign of the layout to a rectangular formation. The complexity of the early TPF-I spacecraft design was mitigated by the infusion of ideas from Europe and produced the current X-Array design which utilizes simple reflectors to form the apertures together with a stretched three dimensional formation geometry. This paper summarizes the main achievements of the infrared nulling technology program including the development of adaptive nulling for broadband performance and the demonstration of starlight suppression by 100 million to one.

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT We demonstrate single-mode laterally coupled distributed-feedback diode lasers at 2.05 µ... more ABSTRACT We demonstrate single-mode laterally coupled distributed-feedback diode lasers at 2.05 µm employing low-loss etched gratings. Single-facet CW output exceeds 50 mW near room temperature with linewidth below 1 MHz over 10-ms observation times.

ISLC 2012 International Semiconductor Laser Conference, 2012

ABSTRACT We report on the phase noise properties of DFB lasers operating near 2.0 μm. Measured no... more ABSTRACT We report on the phase noise properties of DFB lasers operating near 2.0 μm. Measured noise spectra indicate intrinsic linewidths below 1 kHz. Less than 200 kHz effective linewidth is estimated for 5 ms measurement time.

Richard Lai, TRW Inc., Redondo Beach CA 90278

Semiconductor Science and Technology, 2011

We have demonstrated Fabry-Perot single spatial mode antimonide-based type-I quantum-well ridge w... more We have demonstrated Fabry-Perot single spatial mode antimonide-based type-I quantum-well ridge waveguide semiconductor diode lasers operating at 3.0-3.2 µm wavelength in continuous mode up to 333 K. Internal optical loss in narrow ridge devices was significantly reduced by using thick Si3N4 dielectric films for planarization. The fabricated lasers operate in CW mode at room temperature with output powers exceeding 5

This paper provides an overview of technology development for the Terrestrial Planet Finder Inter... more This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars.

Applied Physics Letters, 2012

ABSTRACT We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers design... more ABSTRACT We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers designed to operate at wavelengths near 2.05 μm. Second-order Bragg gratings were etched alongside narrow ridge waveguides to enable single-mode DFB operation in 2-mm-long laser diodes. At a heat-sink temperature of 10 °C, the lasers emit more than 40 mW continuous-wave in a single longitudinal mode, while increasing the current beyond 300 mA results in multimode operation due to spectral shifting of the laser gain with respect to the peak grating reflectivity. At −10 °C, we observe DFB operation at higher current, with single-facet emission exceeding 80 mW.