Han Young Ryu

Absolute frequency measurement of an acetylene stabilized laser using a selected single mode from a femtosecond fiber laser comb

We performed an absolute frequency measurement of an acetylene stabilized laser utilizing a femtosecond injection locking technique that can select one component among the fiber laser comb modes. The injection locking scheme has all the fiber configurations. Femtosecond comb lines of 250 MHz spacing based on the fiber femtosecond laser were used for injection locking of a distributed feedback (DFB) laser operating at 1542 nm as a frequency reference. The comb injected DFB laser serves as a selection filter of optical comb modes and an amplifier for amplification of the selected mode. The DFB laser injection locked to the desired comb mode was used to evaluate the frequency stability and absolute frequency measurement of an acetylene stabilized laser. The frequency stability of the acetylene stabilized laser was measured to be 1.1 x 10(-12) for a 1 s averaging time, improving to 6.9 x 10(-14) after 512 s. The absolute frequency of the laser stabilized on the P(16) transition of (13)C(2)H(2) was measured to be 194 369 569 385.7 kHz.

Stable single-frequency fiber ring laser for 25-GHz ITU-T grids utilizing saturable absorber filter

A stable single-frequency fiber ring laser is proposed that operates in a single mode for more than an hour by incorporating unpumped erbium-doped fiber (EDF) as a saturable absorber filter and optimizing the length of EDF used as gain medium. This laser can be continuously tuned to 25-GHz spacing that precisely matches the ITU-T grids by temperature control of etalon filter. This laser had a signal-to-source spontaneous emission ratio higher than 70 dB, and lasing frequencies of 361 channels was matched to ITU-T grids with excellent flatness. Frequency offset from the ITU-T grid was less than 0.14 GHz. The linewidth and the relative intensity noise value was less than 1.3 kHz and 130 dB/Hz (above 250 kHz), respectively.

Optical frequency comb generator based on actively mode-locked fiber ring laser using an acousto-optic modulator with injection-seeding

We present an optical frequency comb generator (OFCG) based on a fiber ring laser that provides a bandwidth of over 1.8 THz with mode-locked pulse operation by external injection seeding. The OFCG was developed via a configuration with actively mode-locked fiber ring laser utilizing an acousto-optic modulator (AOM) with a carrier frequency of 150 MHz when an external seeding laser was injected into the fiber ring cavity. To our knowledge, our experimental device has the widest comb bandwidth ever reported for an OFCG based on a fiber ring loop adopting an AOM device, and ours is the first device that can operate with an actively mode-locked scheme.

Precision spectroscopy of Rb atoms using single comb-line selected from fiber optical frequency comb

We demonstrated the selection of a single comb-line from an optical frequency comb (OFC) of a mode-locked femtosecond fiber laser with a 250 MHz pulse repetition rate, and applied for precision spectroscopy of Rb atoms at 1529 nm. The single comb-line was selected from the fiber-OFC with a 1.5 GHz mode-spacing using spectral-mode-filtering and femtosecond laser injection-locking. When the repetition rate of the mode-locked femtosecond fiber laser was scanned over the range of 382.6 Hz at 250 MHz, we observed the double-resonance optical pumping spectra of the 5S(1/2)-5P(3/2)-4D(3/2) transition of Rb atoms using the selected comb-line of an OFC scanned over the range of 300 MHz at 196,037,213.8 MHz.

A discretely tunable multifrequency source injection locked to a spectral-mode-filtered fiber laser comb

We present a discretely tunable multifrequency source injection locked to an optical frequency comb (OFC) based on the spectral-mode-filtered femtosecond fiber laser. The spectral-mode-filtered OFC with a 1.5 GHz mode spacing, which is based on an femtosecond fiber laser (FSFL) with 250 MHz mode spacing, was achieved using the spectral-mode-filtering method with a Fabry–Perot cavity. With the spectral-mode-filtered OFC as the master laser and two distributed-feedback lasers as the slave lasers, we simultaneously selected and amplified the desired modes of the OFC using the IL technique. We generated the coherent multifrequency optical source to synthesize in the frequency range from gigahertz to terahertz.

Widely Tunable External Cavity Laser Diode Injection Locked to an Optical Frequency Comb

We report an ultrastable external cavity laser diode (ECLD) that can be selectively injection locked to an optical frequency comb (OFC) generated by acetylene stabilized laser (ASL) seeding. The carrier envelope offset (position) and repetition rate (mode spacing) of the OFC, which functions as the master oscillator, was stabilized to the ASL (1.1 × 10-12 at 1 s) and H-maser (2 × 10-13 at 1 s), respectively. The ECLD can be tuned over 70 nm in the 1.5-μm region and can be discretely locked to the comb modes with 25-GHz spacing over a 10-THz span. The frequency stability of the ECLD injection locked to the OFC reached as high as 1.1 × 10-12 for 1-s averaging time.

A multi-layer electro-optic field probe

We present a novel design method and sensing scheme for an electro-optic field probe using multi-stratified layers of electro-optic wafers. A serial stack of cascaded layers is found to be capable of enhancing the performance of interferometric electro-optic light modulation that utilizes the slopes of interference fringe patterns and field-induced electro-optic phase retardations within wafers. The absolute sensitivity of the probe is also characterized with a micro-TEM cell that generates electric fields distributions with accurate, calculable strength for use in probe calibration. The sensitivity of a multi-layered probe-per unit electro-optic wafer volume--was enhanced by 6 dB compared to that of a single-layer one.

A Fiber Ring Laser Dilatometer for Measuring Thermal Expansion Coefficient of Ultralow Expansion Material

A new type of measuring system for coefficient of linear thermal expansion (CTE) of ultralow expansion (ULE) material by using a fiber ring laser is introduced in this letter. The lasing frequency of the laser is stabilized to one of the transmission peaks of the etalon filter by controlling the resonant frequency of the tunable filter. The spacer of the (Fabry-Perot type) etalon filter is made of ULE material. We could measure the CTE of ULE by measuring the optical frequency change caused by the temperature change of the etalon spacer. The combined standard uncertainty is estimated as the value of plusmn36.6 ppb/degC in the temperature range from 5degC to 60degC.

A discretely tunable erbium-doped fiber ring laser with 273 Ch./spl times/50 GHz-spacing ITU-T grids in C-& L-band regions

We fabricated a wide-band discretely-tunable erbium-doped fiber laser with 50 GHz-spacing ITU-T grids in the C- and L-bands by incorporating a solid Fabry-Perot interferometer(SFPI) and a fiber Fabry-Perot(FFP) tunable filter. This laser was tunable over 111 nm with 273 channels.

CW visible standard source generated by second harmonic of injection locked DFB to optical frequency comb seeded with 13 C 2 H 2 stabilized laser

We demonstrate an ultra stable visible laser source generated by the second harmonic of selectively injection-locked distributed feedback (DFB) laser from frequency comb with acetylene stabilized laser seeding. For the second harmonics generation (SHG) of the injection-locked DFB laser, the periodically poled lithium niobate (PPLN) crystal was used. The frequency stability of this source was estimated to be 1.1×10−12 for a 1s averaging time.