Prabesh Dulal - Profile on Academia.edu (original) (raw)

Papers by Prabesh Dulal

Research paper thumbnail of Optimized Magneto-optical Isolator Designs Inspired by Seedlayer-Free Terbium Iron Garnets with Opposite Chirality

ACS Photonics, 2016

Simulations demonstrate that undoped yttrium iron garnet (YIG) seedlayers cause reduced Faraday r... more Simulations demonstrate that undoped yttrium iron garnet (YIG) seedlayers cause reduced Faraday rotation in silicon-oninsulator (SOI) waveguides with Ce-doped YIG claddings. Undoped seedlayers are required for the crystallization of the magneto-optical Ce:YIG claddings, but they diminish the interaction of the Ce:YIG with the guided modes. Therefore new magneto-optical garnets, terbium iron garnet (TIG) and bismuth-doped TIG (Bi:TIG), are introduced that can be integrated directly on Si and quartz substrates without seedlayers. The Faraday rotations of TIG and Bi:TIG films at 1550nm were measured to be +500 and-500°/cm, respectively. Simulations show that these new garnets have the potential to significantly mitigate the negative impact of the seedlayers under Ce:YIG claddings. The successful growth of TIG and Bi:TIG on low-index fused quartz inspired novel garnet-core waveguide isolator designs, simulated using finite difference time domain (FDTD) methods. These designs use alternating segments of positive and negative Faraday rotation for push-pull quasi phase matching in order to overcome birefringence in waveguides with rectangular cross-sections.

Research paper thumbnail of High-Gyrotropy Seedlayer-Free Ce:TbIG for Monolithic Laser-Matched SOI Optical Isolators

ACS Photonics

Monolithic optical isolators that provide modal (transverse electric, TE) and dimensional (500 nm... more Monolithic optical isolators that provide modal (transverse electric, TE) and dimensional (500 nm core) matching to on-chip lasers have been realized with "one step" seedlayer-free garnets. To date, seedlayer-free garnet claddings have required thinner (<340 nm) silicon-on-insulator (SOI) cores because mode-cladding interactions were too weak for laser-matched cores. However, laser matching is important because tapers and mode converters between the laser and the isolator can cause detrimental reflections prior to isolation. This paper reports the use of cerium-doped terbium iron garnet (Ce:TbIG) in a quasi-phase matched nonreciprocal mode conversion (NRMC) isolator that operates on both TE and TM modes without an external field. A key innovation presented here is a repeatable process for foundry-friendly sputter deposition of Ce:TbIG, which enables this high Faraday rotation material (−3200°/cm) to be synthesized in any isolator design that would benefit from one-step lithographical manufacturing. A proof-of-feasibility 500 nm SOI NRMC device is demonstrated with seedlayer-free Ce:TbIG that achieves an isolation ratio of 11 dB. With an optimal length, this NRMC design can provide greater than 30 dB isolation.

Research paper thumbnail of Monolithically-Integrated TE-mode 1D Silicon-on-Insulator Isolators using Seedlayer-Free Garnet

Scientific reports, Jan 19, 2017

The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are he... more The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are here realized to fill the 'missing link' in source-integrated near infrared photonic circuits. The isolators are simple 1D 2-element waveguides, where garnet claddings and longitudinal magnetic fields produce nonreciprocal mode conversion, the waveguide equivalent of Faraday Rotation (FR). Quasi-phase matched claddings are used to overcome the limitations of birefringence. Current experimental SOI isolators use nonreciprocal phase shift (NRPS) in interferometers or ring resonators, but to date NRPS requires TM-modes, so the TE-modes normally produced by integrated lasers cannot be isolated without many ancillary polarisation controls. The presented FR isolators are made via lithography and sputter deposition, which allows facile upscaling compared to the pulsed laser deposition or wafer bonding used in the fabrication of NRPS devices. Here, isolation ratios and losses of 11 dB and ...

Research paper thumbnail of Faraday Polarisation Rotation in Semiconductor Waveguides Incorporating Periodic Garnet Claddings

Nonreciprocal polarisation mode conversion is demonstrated in semiconductor waveguides with an al... more Nonreciprocal polarisation mode conversion is demonstrated in semiconductor waveguides with an alternating periodic upper cladding incorporating a segmented magneto-optic iron garnet fabricated with a novel lift-off process and crystallised by rapid thermal annealing.

Research paper thumbnail of Demonstration of Magnetooptic Latching Router for All-Optical Networking Applications

In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted... more In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted yttrium iron garnet (Bi:YIG) is presented. Experimentation shows that nearly 90° of rotation of the state of polarization of incident light occurs between material latching states upon application of an external magnetic field greater than 500 G. This amount of rotation is enough to cause sufficient routing at the output of an optical interferometer of Sagnac configuration, which is presented in this paper. Due to the high coercivity of the Bi:YIG, the material remains in its magnetized state for very long periods of time and is thus latched. Reversing
the applied magnetic field changes the state of the material, unlatching it. This capability has great importance for nonreciprocal all-optical devices requiring low power operation. In addition, having such control of the state of the nonreciprocal elements can allow for a wider diversification of small-scale and large-scale optical network design. A discussion of the experimental setup, the resulting measurement data, and its implication for future low power applications is presented.

Research paper thumbnail of Transmission Electron Backscatter Diffraction (tEBSD) analysis of Au Thin Films

Research paper thumbnail of Growth Parameters of Fully Crystallized YIG, Bi:YIG, and Ce:YIG Films With High Faraday Rotations

We report on the growth of thin films of yttrium iron garnet (YIG) on dielectric substrates. Such... more We report on the growth of thin films of yttrium iron garnet (YIG) on dielectric substrates. Such films have historically been challenging to grow due to either cracking or incomplete crystallization of the films. We have established the proper growth parameters by tuning seed layer thickness to an optimum of 45 nm. These films were then used as seed layers for growth of films of Bi:YIG and Ce:YIG. Bi:YIG films show a Faraday rotation of 1700 =cm, and Ce:YIG films show a Faraday rotation of 3700 =cm.

Research paper thumbnail of Quasi-Phase-Matched Faraday Rotation in Semiconductor Waveguides With a Magnetooptic Cladding for Monolithically Integrated Optical Isolators

Quasi-Phase-Matched Faraday Rotation in Semiconductor Waveguides With a Magnetooptic Cladding for Monolithically Integrated Optical Isolators

Research paper thumbnail of Laser Ionization Time of Flight Mass Spectrometry Study of Silicon Oxycarbide Glasses

Journal of the …, 2012

For the first time, a laser ionization time of flight mass spectrometry (LI-TOFS) characterizatio... more For the first time, a laser ionization time of flight mass spectrometry (LI-TOFS) characterization has been performed on silicon oxycarbide glasses obtained by pyrolysis of sol-gel precursors. This technique allows to desorb intermediate range mesounits from the network, and to determine their mass and atomic identity precisely. It is therefore complementary to all the other analysis typically performed on SiOC glasses as it leads to collect information on a length scale which is usually difficult to probe: the medium range. The results indicate the presence, in the SiOC glasses, of mixed silicon oxycarbide units together with pure silicate mesounits (SiO 2 and SiO 3 ). †

Research paper thumbnail of Optimized Magneto-optical Isolator Designs Inspired by Seedlayer-Free Terbium Iron Garnets with Opposite Chirality

ACS Photonics, 2016

Simulations demonstrate that undoped yttrium iron garnet (YIG) seedlayers cause reduced Faraday r... more Simulations demonstrate that undoped yttrium iron garnet (YIG) seedlayers cause reduced Faraday rotation in silicon-oninsulator (SOI) waveguides with Ce-doped YIG claddings. Undoped seedlayers are required for the crystallization of the magneto-optical Ce:YIG claddings, but they diminish the interaction of the Ce:YIG with the guided modes. Therefore new magneto-optical garnets, terbium iron garnet (TIG) and bismuth-doped TIG (Bi:TIG), are introduced that can be integrated directly on Si and quartz substrates without seedlayers. The Faraday rotations of TIG and Bi:TIG films at 1550nm were measured to be +500 and-500°/cm, respectively. Simulations show that these new garnets have the potential to significantly mitigate the negative impact of the seedlayers under Ce:YIG claddings. The successful growth of TIG and Bi:TIG on low-index fused quartz inspired novel garnet-core waveguide isolator designs, simulated using finite difference time domain (FDTD) methods. These designs use alternating segments of positive and negative Faraday rotation for push-pull quasi phase matching in order to overcome birefringence in waveguides with rectangular cross-sections.

Research paper thumbnail of High-Gyrotropy Seedlayer-Free Ce:TbIG for Monolithic Laser-Matched SOI Optical Isolators

ACS Photonics

Monolithic optical isolators that provide modal (transverse electric, TE) and dimensional (500 nm... more Monolithic optical isolators that provide modal (transverse electric, TE) and dimensional (500 nm core) matching to on-chip lasers have been realized with "one step" seedlayer-free garnets. To date, seedlayer-free garnet claddings have required thinner (<340 nm) silicon-on-insulator (SOI) cores because mode-cladding interactions were too weak for laser-matched cores. However, laser matching is important because tapers and mode converters between the laser and the isolator can cause detrimental reflections prior to isolation. This paper reports the use of cerium-doped terbium iron garnet (Ce:TbIG) in a quasi-phase matched nonreciprocal mode conversion (NRMC) isolator that operates on both TE and TM modes without an external field. A key innovation presented here is a repeatable process for foundry-friendly sputter deposition of Ce:TbIG, which enables this high Faraday rotation material (−3200°/cm) to be synthesized in any isolator design that would benefit from one-step lithographical manufacturing. A proof-of-feasibility 500 nm SOI NRMC device is demonstrated with seedlayer-free Ce:TbIG that achieves an isolation ratio of 11 dB. With an optimal length, this NRMC design can provide greater than 30 dB isolation.

Research paper thumbnail of Monolithically-Integrated TE-mode 1D Silicon-on-Insulator Isolators using Seedlayer-Free Garnet

Scientific reports, Jan 19, 2017

The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are he... more The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are here realized to fill the 'missing link' in source-integrated near infrared photonic circuits. The isolators are simple 1D 2-element waveguides, where garnet claddings and longitudinal magnetic fields produce nonreciprocal mode conversion, the waveguide equivalent of Faraday Rotation (FR). Quasi-phase matched claddings are used to overcome the limitations of birefringence. Current experimental SOI isolators use nonreciprocal phase shift (NRPS) in interferometers or ring resonators, but to date NRPS requires TM-modes, so the TE-modes normally produced by integrated lasers cannot be isolated without many ancillary polarisation controls. The presented FR isolators are made via lithography and sputter deposition, which allows facile upscaling compared to the pulsed laser deposition or wafer bonding used in the fabrication of NRPS devices. Here, isolation ratios and losses of 11 dB and ...

Research paper thumbnail of Faraday Polarisation Rotation in Semiconductor Waveguides Incorporating Periodic Garnet Claddings

Nonreciprocal polarisation mode conversion is demonstrated in semiconductor waveguides with an al... more Nonreciprocal polarisation mode conversion is demonstrated in semiconductor waveguides with an alternating periodic upper cladding incorporating a segmented magneto-optic iron garnet fabricated with a novel lift-off process and crystallised by rapid thermal annealing.

Research paper thumbnail of Demonstration of Magnetooptic Latching Router for All-Optical Networking Applications

In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted... more In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted yttrium iron garnet (Bi:YIG) is presented. Experimentation shows that nearly 90° of rotation of the state of polarization of incident light occurs between material latching states upon application of an external magnetic field greater than 500 G. This amount of rotation is enough to cause sufficient routing at the output of an optical interferometer of Sagnac configuration, which is presented in this paper. Due to the high coercivity of the Bi:YIG, the material remains in its magnetized state for very long periods of time and is thus latched. Reversing
the applied magnetic field changes the state of the material, unlatching it. This capability has great importance for nonreciprocal all-optical devices requiring low power operation. In addition, having such control of the state of the nonreciprocal elements can allow for a wider diversification of small-scale and large-scale optical network design. A discussion of the experimental setup, the resulting measurement data, and its implication for future low power applications is presented.

Research paper thumbnail of Transmission Electron Backscatter Diffraction (tEBSD) analysis of Au Thin Films

Research paper thumbnail of Growth Parameters of Fully Crystallized YIG, Bi:YIG, and Ce:YIG Films With High Faraday Rotations

We report on the growth of thin films of yttrium iron garnet (YIG) on dielectric substrates. Such... more We report on the growth of thin films of yttrium iron garnet (YIG) on dielectric substrates. Such films have historically been challenging to grow due to either cracking or incomplete crystallization of the films. We have established the proper growth parameters by tuning seed layer thickness to an optimum of 45 nm. These films were then used as seed layers for growth of films of Bi:YIG and Ce:YIG. Bi:YIG films show a Faraday rotation of 1700 =cm, and Ce:YIG films show a Faraday rotation of 3700 =cm.

Research paper thumbnail of Quasi-Phase-Matched Faraday Rotation in Semiconductor Waveguides With a Magnetooptic Cladding for Monolithically Integrated Optical Isolators

Quasi-Phase-Matched Faraday Rotation in Semiconductor Waveguides With a Magnetooptic Cladding for Monolithically Integrated Optical Isolators

Research paper thumbnail of Laser Ionization Time of Flight Mass Spectrometry Study of Silicon Oxycarbide Glasses

Journal of the …, 2012

For the first time, a laser ionization time of flight mass spectrometry (LI-TOFS) characterizatio... more For the first time, a laser ionization time of flight mass spectrometry (LI-TOFS) characterization has been performed on silicon oxycarbide glasses obtained by pyrolysis of sol-gel precursors. This technique allows to desorb intermediate range mesounits from the network, and to determine their mass and atomic identity precisely. It is therefore complementary to all the other analysis typically performed on SiOC glasses as it leads to collect information on a length scale which is usually difficult to probe: the medium range. The results indicate the presence, in the SiOC glasses, of mixed silicon oxycarbide units together with pure silicate mesounits (SiO 2 and SiO 3 ). †