• Current Optics and Photonics
• /
• v.5 no.6
• /
• pp.711-720
• /
• 2021

A novel optical hybrid device that doubles the multilevel demodulation resolution by adding the optical interferometer with a waveguide crossover is proposed, theoretically analyzed and experimentally verified. We report two types of all-passive phase control schemes that will be referred to as a phase compensation scheme and a phase optimization scheme. We also apply the proposed phase control schemes to a 45° optical hybrid consisting of two parallel 90° optical hybrids together with the proposed phase control scheme for demodulating 8-level differential phase shift keying optical signals. Octagonal phase response with low wavelength sensitive excess loss of <0.8 dB over 31-nm-wide spectral range will be demonstrated in the InP-based material platform.

• Current Optics and Photonics
• /
• v.3 no.5
• /
• pp.401-407
• /
• 2019

Polymeric optical waveguide devices with Bragg gratings have been investigated, for implementing tunable lasers and wavelength filters used in wavelength-division-multiplexed optical communication systems. Owing to the excellent thermo-optic effect of these polymers, wavelength tuning is possible over a wide range, which is difficult to achieve using other optical materials. In this study the phase-mask technology, which has advantages over the conventional interferometeric method, was introduced to facilitate the fabrication of Bragg gratings in polymeric optical waveguide devices. An optical setup capable of fabricating multiple Bragg gratings simultaneously on a 4-inch silicon wafer was constructed, using a 442-nm laser and phase mask. During fabrication, some of the diffracted light in the phase mask was totally reflected inside the mask, which affected the quality of the Bragg grating adversely, so experiments were conducted to solve this issue. To verify grating uniformity, two types of wavelength-filtering devices were fabricated using the phase-mask lithography, and their reflection and transmission spectra were measured. From the results, we confirmed that the phase-mask method provides good uniformity, and may be applied for mass production of polymer Bragg-grating waveguide devices.

• Current Optics and Photonics
• /
• v.6 no.3
• /
• pp.323-331
• /
• 2022

Electro-optic modulator (EOM) takes a vital role in connecting the electric and optical fields. Here, we present a heterogeneously integrated EOM based on the lithium niobate-on-insulator (LNOI) platform. The key modulation waveguide structure is a field-enhanced slot waveguide formed by embedding silicon nanowires in a thin-film lithium niobate (LN), which is different from the previously reported LN ridge or etchless LN waveguides. Based on such slot structure, optical mode field area is reduced and enhanced electric field in the slot region can interact well with LN material with high Electro-optic (EO) coefficient. Therefore, the improvements in both aspects have positive effects on enhancing the modulation performance. From results, the corresponding EOM by adding such modulation waveguide structure achieves better performance, where the key half-wave-voltage-length product (V_𝜋L) and 3 dB EO bandwidth are 1.78 V·cm and 40 GHz under the electrode gap width of only 6 ㎛, respectively. Moreover, Lower V_𝜋L can also be achieved. With these characteristics, such field-enhanced waveguide structure could further promote the development of LNOI-based EOM.

• Current Optics and Photonics
• /
• v.3 no.2
• /
• pp.172-176
• /
• 2019

The work reports on the fabrication of an optical planar waveguide in the Nd:CNGG crystal by the 0.4-MeV hydrogen ion implantation with a fluence of $8.0{\times}10^{16}ions/cm^2$. The nuclear energy loss of the implanted hydrogen ions was derived by using SRIM 2013 code. The microscope image of the proton-implanted Nd:CNGG crystal cross section was captured by a metallographic microscope. The transmittance spectra were recorded before and after the ion implantation. The light intensity distribution of the planar waveguide at 632.8 nm was experimentally measured to validate its effect on one dimension confinement. The investigation shows that the proton-implanted Nd:CNGG waveguide is a candidate for an optoelectronic integrated device.

• Current Optics and Photonics
• /
• v.7 no.1
• /
• pp.83-89
• /
• 2023

This study reports a structure, based on a liquid-crystal (LC) core optical waveguide, for the switchable spatial control of linearly polarized light. The refractive indices of both left and right isotropic claddings in the waveguide are between the two principal-axis indices of the nematic liquid crystal (NLC). Numerical simulations demonstrate that the proposed structure can be operated in transmission mode or as an attenuator by controlling the on and off states of the applied voltage, whether the initial excitation is transverse electric (TE) linearly polarized light or transverse magnetic (TM) linearly polarized light. The design can also be used as an integrated optical polarizer, since only one type of linearly polarized light is always permitted to pass through the core zone of the NLC optical waveguide.

• Korean Journal of Optics and Photonics
• /
• v.16 no.1
• /
• pp.79-84
• /
• 2005

To increase the tolerance for passive fiber alignment, a single mode polymer waveguide with a large core structure is demonstrated. The large core waveguide is designed to have a mode profile comparable to that of a thermally expanded core (TEC) fiber, and it can be connected to a high-contrast waveguide through an adiabatic transition taper structure. From a waveguide with a rectangular core of 25 ${\times}$ 25 ${\mu}{\textrm}{m}$$^2$, a single mode propagation is observed when the index contrast is as low as 0.0005. A UV-cured injection molding method is used to fabricate the thick core structure. Due to the large mode size, the insertion loss of the device is below 0.5 dB until the lateral displacement of the TEC fiber is 4.5 ${\mu}{\textrm}{m}$. The low insertion loss is important for reproducible passive alignment.

• Korean Journal of Optics and Photonics
• /
• v.13 no.1
• /
• pp.21-26
• /
• 2002

In the conventional star coupler, a certain amount of loss should be expected because lateral diffraction is used for the power distribution. In this paper, we propose a new design of a low loss star coupler which employs UV-written tapered waveguides and an AWG based on the low loss star couplers, and investigate their various characteristics. The loss of the UV-written star coupler is lower than that of the conventional star coupler, and the AWG device based on the UV-written star couplers shows low loss characteristics.

• Korean Journal of Optics and Photonics
• /
• v.7 no.3
• /
• pp.280-286
• /
• 1996

This paper describes operation mechanism of a novel optical waveguide phase modulator with optical bistability characteristics by self electro-optic effect. The fabricated device structure is an optical waveguide modulator, using a refractive index change by an applied electric field, parallel integrated with SEED with an electrical bistability. GaAs/AlGaAs MQW is used as the core layer of the waveguide modulator and the absorption layer of SEED. The absorbed optical power in SEED changes the diode voltage and controls the optical power propagating through the waveguide phase modulator. Optical bistability of waveguide phase modulator is experimentally obtained by using electrical bistability of SEED. Compared to other waveguide modulators, the proposed one has an asset that the lowest optical power is required to generate optical bistability.

• Korean Journal of Optics and Photonics
• /
• v.22 no.5
• /
• pp.219-222
• /
• 2011

Integrated optical waveguide polarization converters are among the essential components for constructing various functional optical integrated circuits. The RM materials have been widely used in liquid crystal displays for fabricating waveplates. In this work, the polarization converters are fabricated by using a solution of Reactive Mesogen(RM) dissolved in liquid crystal(LC). In the middle of the polymer waveguide, a groove is defined by an oxygen plasma etching in a direction perpendicular to the optical waveguide. The solution of RM-LC is inserted to fill up the groove, and then liquid crystal is aligned in a certain direction by applying an electric field. After the alignment, RM materal is crosslinked by UV light so as to form a permanent waveplate. The phase retardation of the waveplate is determined by the width of the groove, and by the birefringence and the degree of alignment of the LC. Polarization conversion efficiency of 90% is obtained for the wavelength of 1550 nm.

• Current Optics and Photonics
• /
• v.6 no.1
• /
• pp.15-22
• /
• 2022

This paper describes the construction of a phase shifter with low loss and small volume. To construct it, we use the two graphene layers that are separated by a hexagonal boron nitride (hBN) and embedded in a silicon waveguide. The refractive index of the waveguide is adjusted by applying a bias voltage to the graphene sheet to create an optical phase shift. This waveguide is a compact device that only has a radius of 5 ㎛. It has a phase shift of 6π. In addition, the extinction ratio (ER) is 11.6 dB and the insertion loss (IL) is 0.031 dB. Due to its unique characteristics, this device has great potential in silicon on-chip optical interconnection and all-optical multiple-input multiple-output processing.