Low-loss channel waveguides in a ring-resonator configuration have been fabricated; measured resu... more Low-loss channel waveguides in a ring-resonator configuration have been fabricated; measured results show a finesse of 16 and a coupling efficiency of 2%. Total losses, losses, were 0.05 + 0.01 dB/cm. including coupling, material, bending, and fabrication We report on the fabrication of a thin-film waveguide resonator with a finesse of 16. The device has extremely low loss (0.05 dB/cm) and maintains polarization. It makes possible a substantial improvement in the evaluation of the characteristics, particularly losses, of channel waveguides. Such a low-loss structure also offers an alternative to existing fiber-optic hybrid devices. The availability of ultra-low-loss, single-mode optical fibers and couplers has stimulated research in interferometric devices using fibers. Applications include acoustic and magnetic sensors,' temperature sensors, 2 and rotation sensors. 3-5 In such devices, the alignment, coupling, and polarization maintenances are critical. In the same applications, thin-film resonators could offer significant advantages.
We demonstrate a photonic integrated circuit using a novel monolithic integration platform combin... more We demonstrate a photonic integrated circuit using a novel monolithic integration platform combining InGaAsP gain elements and index matched amorphous silicon waveguide devices. The AWG based multi-frequency laser emits eight 100-GHz-spaced wavelengths near 1550 nm.
Abstract : We developed fabrication technology, advanced materials and design techniques to reali... more Abstract : We developed fabrication technology, advanced materials and design techniques to realize resonance enhanced modulators with ring-resonators. The devices are based on a lateral geometry with deeply etched waveguides in InP. ICP etching techniques and masks were developed to obtain sub-micrometer deep etched waveguides with nanometer residual sidewall roughness for low optical loss and high quality resonators. Ultra compact multi-mode interference (MMI) couplers are designed and fabricated for coupling of the ring-resonators with superior reproducibility and low excess loss. Design and test procedures were established for ring-resonators and resonance enhanced modulators. We developed three-step quantum wells in GalnAsP/InP for enhanced electro-optic coefficients. Measured electro-optic coefficient of the three-step quantum wells is nearly three times higher than the conventional rectangular quantum well at 1.55 micrometers. The enhanced electro-optic effect, combined with a low optical absorption coefficient alpha<1 /cm increases a modulator figure of merit by nearly 36 times, and decreases the power consumption by nearly one order of magnitude compared with a conventional quantum well design. MMI-coupled electro-refractive ring resonators have been fabricated using deeply etched InGaAsP/InP waveguides. We demonstrated the first electro-refractive ring-resonator modulators. RF-modulation with the ring resonator is demonstrated. Resonance enhanced modulation efficiency with the ring-resonance was confirmed.
The nonlinear magneto-optical Kerr-effect has been proposed as an ultrafast spectroscopic probe f... more The nonlinear magneto-optical Kerr-effect has been proposed as an ultrafast spectroscopic probe for the magnetic and electronic properties of ferromagnetic surfaces. The extension of our previous calculation of the linear (first-order) and nonlinear (second-order) magneto-optical susceptibilities by the inclusion of the complete nickel band structure and the dipole transition matrix elements leads to strongly improved agreement between theory and linear magneto-optical experiments. This electronic theory confirms the previous assertion that the nonlinear magneto-optical Kerr-effect should be observable and clearly shows that this effect contains detailed information about the electronic and magnetic surface properties (band structure, exchange interaction, spin-orbit coupling). We discuss possible geometries for experimental and technological applications.
A compact aneutronic fusion engine will enable more challenging exploration missions in the solar... more A compact aneutronic fusion engine will enable more challenging exploration missions in the solar system. This engine uses a deuterium-helium-3 reaction to produce fusion energy by employing a novel field-reversed magnetic field configuration (FRC). The FRC has a simple linear solenoidal coil configuration yet generates higher plasma pressures for a given magnetic field than other designs. Waste heat generated from bremsstrahlung and synchrotron radiation is recycled to maintain the fusion temperature. The charged reaction products, augmented by additional propellant, are exhausted through a magnetic nozzle. As an example, we present a mission to deploy the James Webb Space Telescope from LEO to an L2 halo orbit using a one MW compact aneutronic fusion rocket engine. The engine produces 20 N of thrust with an exhaust velocity of 55 km/s and has a specific power of 0.77 kW/kg. I.
Traditional thinking presumes that planetary defense is only achievable with years of warning, so... more Traditional thinking presumes that planetary defense is only achievable with years of warning, so that a mission can launch in time to deflect the asteroid. However, the danger posed by hard-to-detect small meteors was dramatically demonstrated by the 20 meter Chelyabinsk meteor that exploded over Russia in 2013 with the force of 440 kilotons of TNT. A 5-MW Direct Fusion Drive (DFD) engine allows rockets to rapidly reach threatening asteroids and deflect them using clean burning deuterium-helium-3 fuel, a compact field-reversed configuration, and heated by odd-parity rotating magnetic fields. This paper presents the latest development of the DFD rocket engine based on recent simulations and experiments as well as calculations for an asteroid deflection envelope and a mission plan to deflect an Apophis-type asteroid given just one year of warning. Armed with this new defense technology, we will finally have achieved a vital capability for ensuring our planet’s safety from impact thre...
NASA's JUNO mission will arrive at Jupiter in July 2016, after nearly five years in space. Si... more NASA's JUNO mission will arrive at Jupiter in July 2016, after nearly five years in space. Since operational costs tend to rise with mission time, minimizing such times becomes a top priority. We present the conceptual design for a 10MW aneutronic fusion engine with high exhaust velocities that would reduce transit time for a Jupiter mission to eighteen months and enable more challenging exploration missions in the solar system and beyond. __________________________________________________
The Direct Fusion Drive (DFD) is a nuclear fusion engine that produces both thrust and electric p... more The Direct Fusion Drive (DFD) is a nuclear fusion engine that produces both thrust and electric power. It employs a field reversed configuration with an odd-parity rotating magnetic field heating system to heat the plasma to fusion temperatures. The engine uses deuterium and helium-3 as fuel and additional deuterium that is heated in the scrape-off layer for thrust augmentation. In this way variable exhaust velocity and thrust is obtained.
Traditional thinking presumes that planetary defense is only achievable with years of warning, so... more Traditional thinking presumes that planetary defense is only achievable with years of warning, so that a mission can launch in time to deflect the asteroid. However, the danger posed by hard-to-detect small meteors was dramatically demonstrated by the 20 meter Chelyabinsk meteor that exploded over Russia in 2013 with the force of 440 kilotons of TNT. A 5-MW Direct Fusion Drive (DFD) engine allows rockets to rapidly reach threatening asteroids that and deflect them using clean burning deuterium-helium-3 fuel, a compact field-reversed configuration, and heated by odd-parity rotating magnetic fields. This paper presents the latest development of the DFD rocket engine based on recent simulations and experiments as well as calculations for an asteroid deflection envelope and a mission plan to deflect an Apophis-type asteroid given just one year of warning. Armed with this new defense technology, we will finally have achieved a vital capability for ensuring our planet’s safety from impact...
A compact aneutronic fusion engine will enable more challenging exploration missions in the solar... more A compact aneutronic fusion engine will enable more challenging exploration missions in the solar system. This engine uses a deuterium-helium-3 reaction to produce fusion energy by employing a novel field-reversed magnetic field configuration (FRC). The FRC has a simple linear solenoidal coil configuration yet generates higher plasma pressures for a given magnetic field than other designs. Waste heat generated from bremsstrahlung and synchrotron radiation is recycled to maintain the fusion temperature. The charged reaction products, augmented by additional propellant, are exhausted through a magnetic nozzle. As an example, we present a mission to deploy the James Webb Space Telescope from LEO to an L2 halo orbit using a one MW compact aneutronic fusion rocket engine. The engine produces 20 N of thrust with an exhaust velocity of 55 km/s and has a specific power of 0.70 kW/kg.
Presented here is a study of the nonlinear optical response of the surfaces of the noble metals. ... more Presented here is a study of the nonlinear optical response of the surfaces of the noble metals. Second harmonic generation is forbidden, in the dipole approximation, in centrosymmetric materials. Nonetheless, using pulsed lasers, it is readily observed in reflection. The signal originates in a narrow layer at the surface where the center of inversion is removed by the termination of the lattice. The goal is to go beyond the jellium model, and incorporate into the formulation of the response the nature of the electronic states at the surface, including both surface modified bulk states and intrinsic surface states. The foundation of the approach is the description of the three wave mixing phenomenon as a superposition of three step processes in which each step consists of an electronic transition between states of the system accompanied by the annihilation or creation of a photon. The symmetries of the wavefunctions determine how the strength of a particular mechanism depends on the...
Low-loss channel waveguides in a ring-resonator configuration have been fabricated; measured resu... more Low-loss channel waveguides in a ring-resonator configuration have been fabricated; measured results show a finesse of 16 and a coupling efficiency of 2%. Total losses, losses, were 0.05 + 0.01 dB/cm. including coupling, material, bending, and fabrication We report on the fabrication of a thin-film waveguide resonator with a finesse of 16. The device has extremely low loss (0.05 dB/cm) and maintains polarization. It makes possible a substantial improvement in the evaluation of the characteristics, particularly losses, of channel waveguides. Such a low-loss structure also offers an alternative to existing fiber-optic hybrid devices. The availability of ultra-low-loss, single-mode optical fibers and couplers has stimulated research in interferometric devices using fibers. Applications include acoustic and magnetic sensors,' temperature sensors, 2 and rotation sensors. 3-5 In such devices, the alignment, coupling, and polarization maintenances are critical. In the same applications, thin-film resonators could offer significant advantages.
We demonstrate a photonic integrated circuit using a novel monolithic integration platform combin... more We demonstrate a photonic integrated circuit using a novel monolithic integration platform combining InGaAsP gain elements and index matched amorphous silicon waveguide devices. The AWG based multi-frequency laser emits eight 100-GHz-spaced wavelengths near 1550 nm.
Abstract : We developed fabrication technology, advanced materials and design techniques to reali... more Abstract : We developed fabrication technology, advanced materials and design techniques to realize resonance enhanced modulators with ring-resonators. The devices are based on a lateral geometry with deeply etched waveguides in InP. ICP etching techniques and masks were developed to obtain sub-micrometer deep etched waveguides with nanometer residual sidewall roughness for low optical loss and high quality resonators. Ultra compact multi-mode interference (MMI) couplers are designed and fabricated for coupling of the ring-resonators with superior reproducibility and low excess loss. Design and test procedures were established for ring-resonators and resonance enhanced modulators. We developed three-step quantum wells in GalnAsP/InP for enhanced electro-optic coefficients. Measured electro-optic coefficient of the three-step quantum wells is nearly three times higher than the conventional rectangular quantum well at 1.55 micrometers. The enhanced electro-optic effect, combined with a low optical absorption coefficient alpha<1 /cm increases a modulator figure of merit by nearly 36 times, and decreases the power consumption by nearly one order of magnitude compared with a conventional quantum well design. MMI-coupled electro-refractive ring resonators have been fabricated using deeply etched InGaAsP/InP waveguides. We demonstrated the first electro-refractive ring-resonator modulators. RF-modulation with the ring resonator is demonstrated. Resonance enhanced modulation efficiency with the ring-resonance was confirmed.
The nonlinear magneto-optical Kerr-effect has been proposed as an ultrafast spectroscopic probe f... more The nonlinear magneto-optical Kerr-effect has been proposed as an ultrafast spectroscopic probe for the magnetic and electronic properties of ferromagnetic surfaces. The extension of our previous calculation of the linear (first-order) and nonlinear (second-order) magneto-optical susceptibilities by the inclusion of the complete nickel band structure and the dipole transition matrix elements leads to strongly improved agreement between theory and linear magneto-optical experiments. This electronic theory confirms the previous assertion that the nonlinear magneto-optical Kerr-effect should be observable and clearly shows that this effect contains detailed information about the electronic and magnetic surface properties (band structure, exchange interaction, spin-orbit coupling). We discuss possible geometries for experimental and technological applications.
A compact aneutronic fusion engine will enable more challenging exploration missions in the solar... more A compact aneutronic fusion engine will enable more challenging exploration missions in the solar system. This engine uses a deuterium-helium-3 reaction to produce fusion energy by employing a novel field-reversed magnetic field configuration (FRC). The FRC has a simple linear solenoidal coil configuration yet generates higher plasma pressures for a given magnetic field than other designs. Waste heat generated from bremsstrahlung and synchrotron radiation is recycled to maintain the fusion temperature. The charged reaction products, augmented by additional propellant, are exhausted through a magnetic nozzle. As an example, we present a mission to deploy the James Webb Space Telescope from LEO to an L2 halo orbit using a one MW compact aneutronic fusion rocket engine. The engine produces 20 N of thrust with an exhaust velocity of 55 km/s and has a specific power of 0.77 kW/kg. I.
Traditional thinking presumes that planetary defense is only achievable with years of warning, so... more Traditional thinking presumes that planetary defense is only achievable with years of warning, so that a mission can launch in time to deflect the asteroid. However, the danger posed by hard-to-detect small meteors was dramatically demonstrated by the 20 meter Chelyabinsk meteor that exploded over Russia in 2013 with the force of 440 kilotons of TNT. A 5-MW Direct Fusion Drive (DFD) engine allows rockets to rapidly reach threatening asteroids and deflect them using clean burning deuterium-helium-3 fuel, a compact field-reversed configuration, and heated by odd-parity rotating magnetic fields. This paper presents the latest development of the DFD rocket engine based on recent simulations and experiments as well as calculations for an asteroid deflection envelope and a mission plan to deflect an Apophis-type asteroid given just one year of warning. Armed with this new defense technology, we will finally have achieved a vital capability for ensuring our planet’s safety from impact thre...
NASA's JUNO mission will arrive at Jupiter in July 2016, after nearly five years in space. Si... more NASA's JUNO mission will arrive at Jupiter in July 2016, after nearly five years in space. Since operational costs tend to rise with mission time, minimizing such times becomes a top priority. We present the conceptual design for a 10MW aneutronic fusion engine with high exhaust velocities that would reduce transit time for a Jupiter mission to eighteen months and enable more challenging exploration missions in the solar system and beyond. __________________________________________________
The Direct Fusion Drive (DFD) is a nuclear fusion engine that produces both thrust and electric p... more The Direct Fusion Drive (DFD) is a nuclear fusion engine that produces both thrust and electric power. It employs a field reversed configuration with an odd-parity rotating magnetic field heating system to heat the plasma to fusion temperatures. The engine uses deuterium and helium-3 as fuel and additional deuterium that is heated in the scrape-off layer for thrust augmentation. In this way variable exhaust velocity and thrust is obtained.
Traditional thinking presumes that planetary defense is only achievable with years of warning, so... more Traditional thinking presumes that planetary defense is only achievable with years of warning, so that a mission can launch in time to deflect the asteroid. However, the danger posed by hard-to-detect small meteors was dramatically demonstrated by the 20 meter Chelyabinsk meteor that exploded over Russia in 2013 with the force of 440 kilotons of TNT. A 5-MW Direct Fusion Drive (DFD) engine allows rockets to rapidly reach threatening asteroids that and deflect them using clean burning deuterium-helium-3 fuel, a compact field-reversed configuration, and heated by odd-parity rotating magnetic fields. This paper presents the latest development of the DFD rocket engine based on recent simulations and experiments as well as calculations for an asteroid deflection envelope and a mission plan to deflect an Apophis-type asteroid given just one year of warning. Armed with this new defense technology, we will finally have achieved a vital capability for ensuring our planet’s safety from impact...
A compact aneutronic fusion engine will enable more challenging exploration missions in the solar... more A compact aneutronic fusion engine will enable more challenging exploration missions in the solar system. This engine uses a deuterium-helium-3 reaction to produce fusion energy by employing a novel field-reversed magnetic field configuration (FRC). The FRC has a simple linear solenoidal coil configuration yet generates higher plasma pressures for a given magnetic field than other designs. Waste heat generated from bremsstrahlung and synchrotron radiation is recycled to maintain the fusion temperature. The charged reaction products, augmented by additional propellant, are exhausted through a magnetic nozzle. As an example, we present a mission to deploy the James Webb Space Telescope from LEO to an L2 halo orbit using a one MW compact aneutronic fusion rocket engine. The engine produces 20 N of thrust with an exhaust velocity of 55 km/s and has a specific power of 0.70 kW/kg.
Presented here is a study of the nonlinear optical response of the surfaces of the noble metals. ... more Presented here is a study of the nonlinear optical response of the surfaces of the noble metals. Second harmonic generation is forbidden, in the dipole approximation, in centrosymmetric materials. Nonetheless, using pulsed lasers, it is readily observed in reflection. The signal originates in a narrow layer at the surface where the center of inversion is removed by the termination of the lattice. The goal is to go beyond the jellium model, and incorporate into the formulation of the response the nature of the electronic states at the surface, including both surface modified bulk states and intrinsic surface states. The foundation of the approach is the description of the three wave mixing phenomenon as a superposition of three step processes in which each step consists of an electronic transition between states of the system accompanied by the annihilation or creation of a photon. The symmetries of the wavefunctions determine how the strength of a particular mechanism depends on the...
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Papers by Gary Pajer