Byoung-Joon Seo

Electrooptic Polymer Ring Resonator Modulation up to 165 GHz

Modulation is demonstrated at 84, 111, 139, and 165 GHz resonances of a traveling-wave electrooptic polymer ring-resonator-based modulator. The modulation response is characterized throughout the W-band, illustrating the resonant response at 84 and 111 GHz. A traveling-wave analysis that includes the compound effect of microwave loss and optical/microwave velocity mismatch in a ring-resonator-based modulator is presented and shows a good agreement with experimental results. The ring modulator shows superior performance compared to the Mach-Zehnder modulator in the presence of these limitations when both structures have the same equivalent low-frequency Vpi

Isotropic left handed material at optical frequency with dielectric spheres embedded in negative permittivity medium

A possibility to realize an isotropic left handed material up to optical frequencies is theoretically investigated. The proposed homogeneous structure consists of dielectric spheres embedded randomly in a negative permittivity host medium. While the effective permittivity of the structure is negative over a wide frequency range due to the host medium, the negative effective permeability is obtained by spherical magnetic resonances of the dielectric spheres. Since this structure utilizes only magnetic resonance, both analytical and numerical simulation results show that it has higher fabrication tolerance, larger bandwidth and potentially less propagation loss than the previously proposed structure, i.e., the dielectric spheres embedded in the dielectric host.

Single-chip integrated electro-optic polymer photonic RF phase shifter array

This paper demonstrates a four-element integrated photonic radio-frequency (RF) phase shifter array in a single chip with an advanced configuration. These devices are integrated using electrooptic polymer materials and involve several novel technologies. Measurements of this configuration showed that our four outputs were independent and had highly linear RF phases over 360/spl deg/ with negligible RF power fluctuation at the modulation frequency of 20 GHz. This significant improvement is capable of removing one of the major problems in using this type of phase shifter architecture.

Side-chain electro-optic polymer modulator with wide thermal stability ranging from −46°Cto95°C for fiber-optic gyroscope applications

Electro-optic (EO) polymer modulators with a wide range of thermal stability from −46°Cto95°C for fiber-optic gyroscope applications are reported. The synthesized EO side-chain polymer used has a glass transient temperature (Tg) of 200°C and a large EO coefficient of 25.2pm∕V in a real device measurement. Mach–Zehnder (MZ) intensity and optical phase modulators are implemented based on this high-Tg side-chain EO polymer, exhibiting ∼3.75V half-wave voltage with 1.5cm interaction length and 2.3cm total length at 1.55μm wavelength. The optical fiber-to-lens insertion loss is ∼7.5dB in the MZ interferometers and ∼6dB in the straight waveguides. We examine the long-term thermal stability of these devices and demonstrate their ability to meet the strict requirements of various EO device applications, particularly fiber-optic gyroscopes.

Reduction of fiber chromatic dispersion effects in fiber-wireless and photonic time-stretching system using polymer modulators

We have investigated the general characteristics of the power penalty due to the fiber chromatic dispersion effects in both fiber-wireless and photonic time-stretching systems. Two different modulation schemes have been demonstrated to reduce this penalty using our novel polymer modulators incorporating a multimode interference (MMI) structure. A single-sideband (SSB) modulator configuration has almost completely eliminated this penalty without a bandwidth limit. A double-sideband (DSB) modulator configuration with an appropriate quadrature bias has also shown significant improvement in bandwidth limitations for a given fiber link length.

Photobleached refractive index tapers in electrooptic polymer rib waveguides

Photobleached refractive index tapers in electrooptic polymer rib waveguides, which act as two-dimensional optical mode transformers, are investigated. One taper method involves a discrete step mask-shifting scheme with a fixed intensity UV light source. A second method utilizes a gray-scale mask to precisely control the intensity of UV light reaching each portion of the taper. Using a gray-scale mask, adiabatic refractive index tapers can be inscribed into electrooptic polymer waveguides in a single fabrication step with no scanning parts. Optimized taper profiles are derived and applications for their incorporation into passive-to-active waveguide transitions are described.

Optical Signal Processor Using Electro-Optic Polymer Waveguides

We have investigated an optical signal processor using electro-optic polymer waveguides operating at a wavelength of 1.55 mum. Due to recent developments, many useful optical devices have become available such as optical filters, modulators, switches, and multiplexers. It will be useful to have a single optical device, which is reconfigurable to implement all of these functions. We call such a device an ldquooptical signal processor,rdquo which will play a similar role to digital signal processors in electrical circuits. We realize such an optical device in a planar lightwave circuit. Since the planar lightwave circuits are based on the multiple interference of coherent light and can be integrated with significant complexity, they have been implemented for various purposes of optical processing such as optical filters. However, their guiding waveguides are mostly passive, and the only viable mechanism to reconfigure their functions is thermal effects, which is slow and cannot be used for high-speed applications such as optical modulators or optical packet switches. On the other hand, electro-optic polymer has a very high electro-optic coefficient and a good velocity match between electrical and optical signals, thus, permitting the creation of high-speed optical devices with high efficiency. Therefore, we have implemented a planar lightwave circuit using the electro-optic polymer waveguides. As a result, the structure is complex enough to generate arbitrary functions and fast enough to obtain high data rates. Using the optical signal processor, we investigate interesting applications including arbitrary waveform generators.

True-time-delay element in lossy environment using EO waveguides

We investigate a photonic true time delay element in a lossy environment using electrooptic waveguides. Its principle is based on the ring resonator and the all-pass filter. In the lossy environment, it is known that the insertion loss depends on the delay time when using the conventional ring resonator. We add a by-pass waveguide to the ring resonator in order to compensate the resonant-dependent loss. As a result, we have a voltage-controlled photonic true time delay element with its insertion loss independent of the delay time.

Hybrid Lyot coronagraph for WFIRST: high-contrast broadband testbed demonstration

Hybrid Lyot Coronagraph (HLC) is one of the two operating modes of the Wide-Field InfraRed Survey Telescope (WFIRST) coronagraph instrument. Since being selected by National Aeronautics and Space Administration (NASA) in December 2013, the coronagraph technology is being matured to Technology Readiness Level (TRL) 6 by 2018. To demonstrate starlight suppression in presence of expecting on-orbit input wavefront disturbances, we have built a dynamic testbed in Jet Propulsion Laboratory (JPL) in 2016. This testbed, named as Occulting Mask Coronagraph (OMC) testbed, is designed analogous to the WFIRST flight instrument architecture: It has both HLC and Shape Pupil Coronagraph (SPC) architectures, and also has the Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to sense and correct the dynamic wavefront disturbances. We present upto-date progress of HLC mode demonstration in the OMC testbed. SPC results will be reported separately. We inject the flight-like Line of Sight (LoS) and Wavefront Error (WFE) perturbation to the OMC testbed and demonstrate wavefront control using two deformable mirrors while the LOWFS/C is correcting those perturbation in our vacuum testbed. As a result, we obtain repeatable convergence below 5 × 10−9 mean contrast with 10% broadband light centered at 550 nm in the 360 degrees dark hole with working angle between 3 λ/D and 9 λ/D. We present the key hardware and software used in the testbed, the performance results and their comparison to model expectations.

Dynamic testbed demonstration of WFIRST coronagraph low order wavefront sensing and control (LOWFS/C)

To maintain the required performance of WFIRST Coronagraph in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The LOWFS/C uses a Zernike wavefront sensor (ZWFS) with the phase shifting disk combined with the starlight rejecting occulting mask. For wavefront error corrections, WFIRST LOWFS/C uses a fast steering mirror (FSM) for line-of-sight (LoS) correction, a focusing mirror for focus drift correction, and one of the two deformable mirrors (DM) for other low order wavefront error (WFE) correction. As a part of technology development and demonstration for WFIRST Coronagraph, a dedicated Occulting Mask Coronagraph (OMC) testbed has been built and commissioned. With its configuration similar to the WFIRST flight coronagraph instrument the OMC testbed consists of two coronagraph modes, Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC), a low order wavefront sensor (LOWFS), and an optical telescope assembly (OTA) simulator which can generate realistic LoS drift and jitter as well as low order wavefront error that would be induced by the WFIRST telescope’s vibration and thermal changes. In this paper, we will introduce the concept of WFIRST LOWFS/C, describe the OMC testbed, and present the testbed results of LOWFS sensor performance. We will also present our recent results from the dynamic coronagraph tests in which we have demonstrated of using LOWFS/C to maintain the coronagraph contrast with the presence of WFIRST-like line-of-sight and low order wavefront disturbances.