Sung-soo Park

AC-coupled burst-mode OLT SFP transceiver for gigabit ethernet PON systems

This letter presents a burst-mode optical line terminal transceiver for a gigabit ethernet passive optical network system. The transceiver package is compliant with small form-factor pluggable multisource agreement. The burst-mode receiver employs an ac-coupling between commercial transimpedance amplifier and limiting amplifier. The burst-mode receiver achieves sensitivity of -24.4 dBm at bit-error ratio 10/sup -12/ with pseudorandom bit sequence 2/sup 7/-1 data, overload of -1.5 dBm, and system dynamic range of 22.9 dB for preamble of 512 bits and guard time of 32 bits. Burst-mode penalty of 1.6 dB is also observed by experiment.

1.55-/spl mu/m DFB lasers utilizing an automatically buried absorptive InAsP layer having a high single-mode yield

We describe 1.55-/spl mu/m distributed feedback laser diodes (DFB LDs) having a single-mode (SM) yield as high as 80% and 93% for as-cleaved and antireflection/high reflection (AR/HR=3%/95%) coated devices, respectively. The high SM yield was achieved by introducing an automatically buried InAsP layer between a concave of InP corrugations and an overgrown layer. The use of the automatically buried InAsP layer implemented by a single step growth makes the device fabrication process much easier than that of conventional loss-coupled DFB LDs. Fabricated DFB LDs with AR/HR-coated facets showed a low threshold current of 8 mA (34 mA) and a high slope efficiency of 0.32 mW/mA (0.22 mW/mA) at 25/spl deg/C (85/spl deg/C). A sidemode suppression ratio better than 40 dB was obtained for the temperature range between -20/spl deg/C and 85/spl deg/C and the injection current range between 20 and 100 mA.

6.8 A pen-pressure-sensitive capacitive touch system using electrically coupled resonance pen

Capacitive touch systems for finger touch have become widely used in mobile devices such as smartphones, tablets, and so on. Beyond ordinary touch functions, some devices adopt an extra electromagnetic resonance (EMR) system [1] to support pens for advanced user experiences; these devices have been successfully commercialized for high-end devices [2]. Such devices offer a realistic and accurate pen-based drawing experience for consumers using a battreryless, light, and pressure-sensitive pen; this is possible because the EMR system excites a passive pen via magnetic coupling and senses the pens returning signal that contains coordinate and fine pen-pressure information. As shown in Fig. 6.8.1 (top), an EMR system, however, requires an additional costly sensor board made with a flexible printed circuit board beneath a display panel to find coordinates of the EMR pen via a magnetic field and a dedicated controller, and it also consumes excessive power. If a capacitive touch system could cover the function of the EMR system, it would be a cost-effective and compact solution in terms of re-utilizing an existing system without the additional sensor board and EMR controller. In this paper, a capacitive touch system sensing a passive pen with pen pressure as well as a finger is introduced as an alternative to an EMR system.

A Novel Growth Method of Freestanding GaN Using In situ Removal of Si Substrate in Hydride Vapor Phase Epitaxy

We demonstrate the freestanding GaN of 2 in. diameter and 400 µm thickness grown from Si substrate by hydride vapor phase epitaxy. To prevent the formation of cracks in the GaN layer during cooling, the Si substrate was removed at high temperature, which successfully suppressed the tensile stress evolution in GaN. The freestanding GaN exhibited high quality with FWHM of 65 arcsec in (0002) X-ray rocking curve and etch pit density of less than 1×106/cm2. It may be possible to fabricate high-quality freestanding GaN substrates of over 8 in. diameter using this method.

A two-step laterally tapered 1.55-/spl mu/m SSC DFB laser fabricated by using a nonselective grating process

We demonstrate a two-step laterally tapered 1.55-/spl mu/m spot size converter distributed feedback laser diode (SSC DFB LD) having a planar buried heterostructure-type active waveguide and a ridge-type passive waveguide fabricated by using a nonselective grating process. Unlike conventional SSC DFB LDs, where a selective grating is employed, this SSC DFB LD employed a nonselective grating over the entire device region in order to make its fabrication much simpler than that of the conventional SSC DFB LDs. The two-step laterally tapered SSC is effective in removing an unwanted wavelength peak originating from the SSC section having a multiquantum well and a grating under it. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far field pattern in horizontal and vertical directions of 13.4/spl deg/ and 19.5/spl deg/, respectively.

Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-mum spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 degC and 85 degC, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-mum wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3deg and 11.6deg, respectively

A Pen-Pressure-Sensitive Capacitive Touch System Using Electrically Coupled Resonance Pen

A touch system sensing pen-pressure of the proposed electrically coupled resonance (ECR) pen is implemented, which can replace costly digitizer system containing electro magnetic resonance (EMR) and capacitive touch system. The proposed system detects the location of the ECR pen and finger using proposed position sensor, and senses pen-pressure of ECR pen using proposed pen-pressure sensor. For the position sensor, to detect even small variation of the mutual capacitance on touch screen panel (TSP) of the pen, a simultaneous driving scheme is proposed with modified Hadamard matrix, resulting in highly increased dynamic range and SNR. In the proposed pen-pressure sensor, the resonant frequency of the ECR pen is measured by a frequency to voltage converter based sensor. The measured SNR for the pen position is 49 dB with 1 mm φ metal pillar, and 6.5-bit resolution is achieved for pen-pressure sensor in 6σ criteria.

Electronic Transport Mechanism for Schottky Diodes Formed by Au/HVPE a-Plane GaN Templates Grown via In Situ GaN Nanodot Formation

We investigate the electrical characteristics of Schottky contacts for an Au/hydride vapor phase epitaxy (HVPE) a-plane GaN template grown via in situ GaN nanodot formation. Although the Schottky diodes present excellent rectifying characteristics, their Schottky barrier height and ideality factor are highly dependent upon temperature variation. The relationship between the barrier height, ideality factor, and conventional Richardson plot reveals that the Schottky diodes exhibit an inhomogeneous barrier height, attributed to the interface states between the metal and a-plane GaN film and to point defects within the a-plane GaN layers grown via in situ nanodot formation. Also, we confirm that the current transport mechanism of HVPE a-plane GaN Schottky diodes grown via in situ nanodot formation prefers a thermionic field emission model rather than a thermionic emission (TE) one, implying that Poole–Frenkel emission dominates the conduction mechanism over the entire range of measured temperatures. The deep-level transient spectroscopy (DLTS) results prove the presence of noninteracting point-defect-assisted tunneling, which plays an important role in the transport mechanism. These electrical characteristics indicate that this method possesses a great throughput advantage for various applications, compared with Schottky contact to a-plane GaN grown using other methods. We expect that HVPE a-plane GaN Schottky diodes supported by in situ nanodot formation will open further opportunities for the development of nonpolar GaN-based high-performance devices.

A 10.1” 183-

A high-signal-to-noise ratio (SNR) inductor-free 3-D hover sensor is presented. This paper solved the low-signal component issue, which is the biggest problem in 3-D hover sensing. For this purpose, we propose a power- and cost-effective high-voltage driving technique in the self-capacitance sensing scheme (SCSS) and lateral resolution optimization of a touch panel. In addition, the huge panel offsets in the SCSS from both vertical panel capacitance (CSV) and horizontal panel capacitance (CSH) can effectively be eliminated by exploiting the panel’s natural characteristics, without using other costly resources. Therefore, in the proposed design, the total calibration block is minimized only for parasitic capacitance mismatches. Last, by adopting new driving scheme, two-phase simultaneous sensing is enabled to increase the SNR further. The proposed hover sensing system achieved a 39-dB SNR at a 1-cm hover point under a 240-Hz scan rate condition in noise experiments, while consuming 183

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