We present a photothermal reflectance microscopy for detecting local defects inside optical films. This technique employs CCD-based thermoreflectance microscopy, which measures temperature-dependent optical reflectivity changes of materials. For photothermal imaging, an 808 nm CW laser beam with sinusoidal modulation is used to heat absorbing defects in the transparent optical film. The thermo-optic response resulting from the laser beam absorption of defects in the material yields a periodic alteration in the reflectivity around the defects. Such a time-varying thermoreflectance signal is probed with a 636 nm LED, and the amplitude of this signal is detected using a homodyne lock-in detection scheme, permitting enhancement of the defect contrast. The feasibility of the proposed imaging system is demonstrated on an optical material having absorbing inclusions, showing that the variation of the normalized optical reflections clearly reveals the local distribution of the submicron-sized defects buried in the optical material.
We report a high-speed phase-sensitive optical coherence reflectometer (OCR) with a stretched supercontinuum source.
Firstly, supercontinuum source has been generated by injecting an amplified fiber laser pulses into a highly nonlinear
optical fiber. The repetition rate and pulse duration of the generated supercontinuum source are 10 MHz and 30 ps
respectively. The supercontinuum pulses are stretched into 70 ns pulses with a dispersion-compensating fiber (DCF).
This pulse stretching technique enables us to measure the spectral information in the time domain. The relationship of
time-wavelength has been measured by modified time-of-flight method. We have built a phase-sensitive OCR with this
stretched pulse source and a two-dimensional (2D) scanning system. The displacement sensitivity of our proposed
system has been investigated. We have demonstrated high-speed 2D imaging capability and single-point dynamics
measurement performance of our proposed system.
Two-photon microscopy is a very attractive tool for the study of the three-dimensional (3D) and dynamic processes in
cells and tissues. One of the feasible constructions of two-photon microscopy is the combination a confocal laser
scanning microscope and a mode-locked Ti:sapphire laser. Even though this approach is the simplest and fastest
implementation, this system is highly cost-intensive and considerably difficult in modification. Many researcher
therefore decide to build a more cost-effective and flexible system with a self-developed software for operation and data
acquisition. We present a custom-built two-photon microscope based on a mode-locked Yb<sup>3+</sup> doped fiber laser and
demonstrate two-photon fluorescence imaging of biological specimens. The mode-locked fiber laser at 1060 nm delivers
320 fs laser pulses at a frequency of 36 MHz up to average power of 80 mW. The excitation at 1060 nm can be more
suitable in thick, turbid samples for 3D image construction as well as cell viability. The system can simply accomplish
confocal and two-photon mode by an additional optical coupler that allows conventional laser source to transfer to the
scanning head. The normal frame rate is 1 frames/s for 400 x 400 pixel images. The measured full width at half
maximum resolutions were about 0.44 μm laterally and 1.34 μm axially. A multi-color stained convallaria, rat basophilic
leukemia cells and a rat brain tissue were observed by two-photon fluorescence imaging in our system.
We have demonstrated the high-speed confocal fluorescence lifetime imaging microscopy (FLIM) by analog mean-delay
(AMD) method. The AMD method is a new signal processing technique for calculation of fluorescence lifetime and it is
very suitable for the high-speed confocal FLIM with good accuracy and photon economy. We achieved the acquisition
speed of 7.7 frames per second for confocal FLIM imaging. Here, the highest photon detection rate for one pixel was
larger than 125 MHz and averaged photon detection rate was more than 62.5 MHz. Based on our system, we
successfully obtained a sequence of confocal fluorescence lifetime images of RBL-2H3 cell labeled with Fluo-3/AM and
excited by 4αPDD (TRPV channel agonist) within one second.
Confocal laser scanning microscopy (CLSM) has become the tool of choice for high-contrast fluorescence imaging in the
study of the three-dimensional and dynamic properties of biological system. However, the high cost and complexity of
commercial CLSMs urges many researchers to individually develop low cost and flexible confocal microscopy systems.
The high speed scanner is an influential factor in terms of cost and system complexity. Resonant galvo scanners at
several kHz have been commonly used in custom-built CLSMs. However, during the repeated illumination for live cell
imaging or 3D image formation, photobleaching and image distortion occurred at the edges of the scan field may be
more serious than the center due to an inherent property (e.g. sinusoidal angular velocity) of the scan mirror. Usually, no
data is acquired at the edges due to large image distortion but the excitation beam is still illuminated. Here, we present
the photobleaching property of CLSM with masked illumination, a simple and low cost method, to exclude the
unintended excitation illumination at the edges. The mask with a square hole in its center is disposed at the image plane
between the scan lens and the tube lens in order to decrease photobleaching and image distortion at the edges. The
excluded illumination section is used as the black level of the detected signals for a signal quantizing step. Finally, we
demonstrated the reduced photobleaching at the edges on a single layer of fluorescent beads and real-time image
acquisition without a standard composite video signal by using a frame grabber.
We constructed a passively mode-locked Er-doped fiber laser (PML-EDFL). It generates ~ 1.3 ps pulses at a repetition
rate of 12 MHz with an average output power of 0.7 mW. These pulses are amplified in a short Er-doped fiber amplifier
(EDFA) which is composed of low nonlinearity EDF. The average power of amplified pulse is about 15 mW. And its
pulse width is about 880 fs. An all-fiber supercontinuum (SC) is generated by putting the amplified fiber laser pulse at
the wavelength of 1. 56 &mgr;m into the highly nonlinear dispersion shifted fiber (HN-DSF) whose zero dispersion
wavelength is 1.537 &mgr;m and nonlinear coefficient is about 10.5/W/km at the input wavelength. The polarization state of
the generated SC spectra is well defined such that it can be properly controlled by the polarization controller. By using a
delayed pulsed method, we report an experimental study of the coherence of SC spectra generated through a HN-DSF.
In this paper, the strong dependence of the spectral coherence on the HN-DSF length is observed experimentally. And
optimal conditions for obtaining wide SC with high coherence are investigated in detail. We believed that our proposed
all-fiber laser based SC source with high coherence has many important applications in recently developed frequencydomain
measurement techniques such as optical coherence tomography (OCT), optical frequency domain imaging
(OFDI), optical frequency domain reflectometry (OFDR) and their instrumentation.
We developed the primary components applicable to HPCF links for short reach (SR) and very short reach (VSR)
data communication systems. We fabricated 4x4 HPCF fused taper splitter, HPCF pigtailed VCSEL and PIN
photodiode for high speed short reach communications and characterized back to back transmission performance of the
link composed of these components by measuring eye diagrams and jitters.
Adapting the fusion-tapering technique for glass optical fiber, we successfully fabricated a 4x4 HPCF fused taper
coupler. The HPCF with a core diameter of 200μm and an outer diameter of 230μm had step refractive index of 1.45
and 1.40 for the core and the clad. The optimized fusion length and tapering waist which make minimum insertion loss
of about 7dB and uniform output power splitting ratio with less than 0.5dB are 13mm and 150µm, respectively.
As a light source for VSR networks, we chose a vertical cavity surface emitting laser (VCSEL) and developed a
package with a HPCF pigtail. After positioning VCSEL and HPCF that made a minimum coupling loss, we glued the
HPCF inside ceramic ferrule housing. In HPCF-PIN PD packaging, we added a micro polymer lens tip onto the HPCF
ends to match the mode field area to the sensitive area of GaAs or InGaAs PIN PD. Coupling between a PIN PD chip
and the lensed HPCF was optimized with the radius of curvature of 156µm with a low coupling loss of 0.3dB, which is
compatible to conventional MMF-PD packaging. For 1.25 Gbps data rate, the eyes adequate to eye mask in gigabit
Ethernet were wide open after all HPCF transmission link and no significant power penalty was observed.