Che-Chung Chou

Polymers for Electro‐Optical Modulation

Second‐order nonlinear optical (NLO) properties of polymeric materials have been attracting a lot of attention, especially for such potential applications as fast waveguides electrooptic (EO) modulation and frequency‐doubling devices. For these photonic applications, the performance of the NLO materials has to be optimized. This requires not only a fundamental knowledge of inter‐relationship between their chemical and NLO properties, but new technologies competitive or superior to existing ones as well. This review focuses on the synthesis of NLO polymers including chromophore design, and the comparison among comprehensive EO polymer systems. Moreover, characterization and device fabrication of electro‐optical polymer planar waveguides are also reported in this review.

Modulation-free laser frequency stabilization to molecular absorption using single acoustooptic frequency shifter

A modulation-free scheme for the laser frequency stabilization to molecular transitions is demonstrated in this letter. In this scheme, two diffracted beams of opposite order from a single acoustooptic frequency shifter were used to simultaneously probe the Doppler-broadened absorption of acetylene. A dispersion-like (DL) signal was obtained from the difference of the two absorption signals. By carefully balancing the two absorption signals, the deviation of the center of the DL signal from the center of Doppler-limited absorption can be less than 2.4 MHz. Using the DL signal as the error signal for frequency stabilization, we could lock a 1.53-/spl mu/m external-cavity diode laser with an estimated stability of 3.1/spl times/10/sup -10/.

Environment-noise-free optical heterodyne retardation measurement using a double-pass acousto-optic frequency shifter

We demonstrate an environment-noise-free optical heterodyne interferometer (OHI) based on a double-pass acousto-optic frequency shifter (AOFS) for phase retardation measurements. The OHI generates intermediate-frequency (IF) heterodyne beat signals for each orthogonal linear polarization mode of a birefringence sample. The phase differences of the IF signals are compared by using a wide-bandwidth lock-in amplifier. This scheme provides 20xa0dB rejection of common-mode environmental disturbances. Measurements of the half-wave voltage of an electro-optics modulator and the electro-optic coefficient of an LiNbO3 plate are demonstrated as application examples.

Diode Laser Frequency Locking to an Etalon With a Double-Pass Acousto-Optic Frequency Shifter

We demonstrate an optical heterodyne spectroscopy on the reflection of an etalon using a double-pass acousto-optics frequency shifter. The experiment setup is a modified Michelson interferometer using the double-pass acousto-optics frequency shifter as the beam splitter and one etalon as the end mirror. Without using frequency modulation, the dispersion-like signal of the etalon reflection was successfully observed and optimized. Using the dispersion-like signal as an error signal, we locked a 780-nm external cavity diode laser to one resonant mode of the etalon. The estimated relative stability was ~2.6 × 10-10 in 0.16-s integration time.

Optical heterodyne spectroscopy of acetylene saturated absorption in a hollow-core photonic crystal fiber

We demonstrated an optical heterodyne scheme based on single acousto-optic frequency shifter, to observe saturated absorption of acetylene ν₁+ν₂ band P(7) line.

Optical heterodyne phase detection and frequency stabilization of an external cavity diode laser by using single acousto-optic frequency shifter

We demonstrated an optical heterodyne scheme based on single acousto-optic frequency shifter, to detect laser phase variation. The signal was used in laser frequency stabilization, and the estimated stability was about 2.28 × 10−9.

Monitoring the active harmonically mode locking by using the internal second harmonic of a mode locker based on a laser diode

Internal second harmonic of a mode locker based on a laser diode was used to monitor our mode-locked fiber laser. The results indicated the laser diode played as a modulated mirror in the mode locking.

Fiber evanescent wave spectroscopy of acetylene molecules with the optical microfiber taper

We demonstrated the evanescent wave of an optical microfiber taper of μm level with the high sensitivity spectroscopic methods such as the difference spectroscopy and the optical heterodyne spectroscopy to observe the acetylene absorption transition.

Internal second harmonics of an injection-locked laser diode and its application to laser frequency stabilization

Features of internal second harmonics (ISH) originated from a laser diode injection-locked by a distribution feedback laser were experimentally observed. As an application of this injection-locked ISH, its frequency was locked to rubidium D2 line.