Jungkwuen An

Grating-less, fiber-based oscillator that generates 25 nJ pulses at 80 MHz, compressible to 150 fs

We report a passively mode-locked fiber-based oscillator that has no internal dispersion-compensating gratings. This design, which we believe to be the first of its kind, produces 25 nJ pulses at 80 MHz with the pulses compressible to 150 fs. The pulses appear to be self-similar and initial data imply that their energy is further scalable.

Resolution enhancement of holographic printer using a hogel overlapping method

We propose a hogel overlapping method for the holographic printer to enhance the lateral resolution of holographic stereograms. The hogel size is directly related to the lateral resolution of the holographic stereogram. Our analysis by computer simulation shows that there is a limit to decreasing the hogel size while printing holographic stereograms. Instead of reducing the size of hogel, the lateral resolution of holographic stereograms can be enhanced by printing overlapped hogels, which makes it possible to take advantage of multiplexing property of the volume hologram. We built a holographic printer, and recorded two holographic stereograms using the conventional and proposed overlapping methods. The images and movies of the holographic stereograms experimentally captured were compared between the conventional and proposed methods. The experimental results confirm that the proposed hogel overlapping method improves the lateral resolution of holographic stereograms compared to the conventional holographic printing method.

Modulation efficiency of double-phase hologram complex light modulation macro-pixels

The modulation efficiency of the double-phase hologram macro-pixel that is designed for complex modulation of light waves is defined and analyzed. The scale-down of the double-phase hologram macro-pixel associated with the construction of complex spatial light modulators is discussed.

25 nJ passively mode-locked fiber laser at 1080 nm

We report a fiber laser that produces 25 nJ, sub-200 fs pulses, an energy 60% higher than previous reports. We attribute the improvement to increased pump power and spectral filtering by the oscillatorpsilas waveplates.

Electrically Driven Diffraction Grating Designed for Visible-Wavelength Region

We report on an electrically driven diffraction grating designed for visible light, where the refractive index of a liquid crystal (LC) was modulated periodically at an interval of 700 nm by applying an external dc bias to a metallic nanograting (NG). The LC-NG structure exhibited a maximum refractive index variation (Δn) of 0.088 and a diffraction efficiency (η) change of 0%-16% with a large diffraction angle of 64° for incident light of 633-nm wavelength. This approach, with the help of faster electronics, provides an opportunity of developing active holograms for real 3-D displays.

Holographic display with a FPD-based complex spatial light modulator

We demonstrate a holographic image reconstructed by a FPD-based complex spatial light modulator (SLM) which is composed of a phase-only SLM and a sheet of beam combiner. A complex SLM which modulates both amplitude and phase independently is necessary for a better image quality with reducing conjugate images. The two-phase encoding method is one of the most practical candidates for the complex SLM. The proposed complex SLM is presented in a phase-only LCD panel which can be manufactured in a conventional LCD process and it was used for generating different phases. The PAL (Parallel-Aligned nematic Liquid crystal) mode is used to modulate the phase without the amplitude change. The film-type beam combiner consists of a prism array and a grating made by a conventional fabrication process. The beam combiner plays a vital role to merge two pixels and to adjust effective complex modulation. In this paper, the holographic image by the proposed complex SLM is verified by the experimental and simulation work in a monochromatic reconstruction. This complex SLM can be scaled up and it is a promising candidate SLM for a large-size holographic 3D display.

Enhancement of the effective viewing window for holographic display with amplitude-only SLM

We propose the effective viewing window enhancement method for a holographic display with an amplitude-only SLM by using algorithmic approach. The basic concept is the superposition principle of holography. The multiple computer generated holograms (CGH) can be displayed on the SLM, and multiple 3D images are reconstructed at different positions within a viewing window simultaneously. In the experiments, we have implemented the holographic display using an amplitude-only SLM, a field lens, and laser light sources. We can observe the holographic 3D image in the frustum formed by the field lens through the viewing window located in the Fourier plane of the hologram. To enhance the effective viewing window, we generate multiple CGHs with an observer’s eye positions, and then overlap them to make the final CGH. Multiple 3D images can be reconstructed in different positions within the theoretical viewing window from the CGH displayed on SLM. This makes the enlargement of viewing zone that can observe the holographic images. The multiple holograms can be also made for enlargement of the viewing window along both horizontal and vertical direction (2D enlargement viewing zone). We confirmed that the experimental results and the simulation based on Rayleigh-Sommerfeld theory match well.

Ultra-slim coherent backlight unit for mobile holographic display

We propose slim coherent backlight unit for a mobile holographic display. This backlight unit consists of glass substrate for waveguide and two surface gratings produced by two-beam interference. The area of backlight illumination is 150 by 85 mm, and the thickness is 0.7 mm, which is thin compared to other conventional coherent backlight units. This backlight unit exhibits a total efficiency of 0.1%, preserving the collimation and a uniformity of 80% over the whole area. The proposed slim coherent backlight can be applied to a mobile holographic display.

An autocorrelator based on a Fabry-Perot interferometer

An autocorrelator based on a Fabry-Perot interferometer is proposed for ultrashort pulse measurement. Main features of this autocorrelator due to the superposition of multiple pulses were investigated experimentally and theoretically. It turns out that the signal from a Fabry-Perot interferometer can be used as an autocorrelator signal. This autocorrelator provides more compact setup with a much easier alignment than a conventional autocorrelator based on a Michelson interferometer.

Integrated Hologram Optical Head for Holographic Printer

We propose a compact holographic printer using RGB waveguide integrated optics. Our research reduces overall prototype size by 20 times, the number of optical components by 2 times, and improves the efficiency by 3 times.