Using light-beam scanning technology based on a potassium tantalate niobate (KTa1-xNbxO3, KTN) single crystal, we constructed a wavelength-swept light source for industrial applications. The KTN crystal is placed in an external cavity as an electro-optic deflector for wavelength scanning without any mechanical operation. Cavity arrangement and mechanism elements are specially designed for long-term stability and environmental robustness. In addition, we updated the handling of the KTN crystal. We used a pair of thermistors for accurate temperature monitoring, and weakly irradiated the crystal with a 405-nm light during operation to achieve drift suppression. We selected a moderate repetition rate of 20 kHz to suit the practical application. The output of the light source was 6.2 mW in average power, 1314.5 nm in central wavelength, and 83.3 nm in bandwidth. The interference fringes of the light enable us to specify the thickness of a wafer sample by the peak positions of the point spread functions. We measured the thickness of a silicon wafer as 3651 μm in the optical path length using a reference quartz plate. The distribution of the obtained values is about 0.1 μm (standard deviation). We experimentally confirmed that this property persists continuously at least over 153 days. Our light source has a remarkable feature: extremely low timing jitter of the sweep. Thus, we can easily reduce the noise level by averaging several fringes, if necessary.
We have developed a highly stable electro-optic KTa1-xNbxO3 (KTN) deflector by enhancing electron transportation through KTN crystal. The amount of current is increased with 405-nm light irradiation to rapidly generate a stable refractive-index change, which induces deflection. The deflection angle is set at 160 mrad within tens of seconds and is kept at that angle for 3,000 hours. The developed deflector has been applied to a wavelength-swept light source to measure the thickness of Si wafers with a 3.6-mm optical length. The precision of 0.1-μm has been continuously achieved corresponding to the stability of the KTN deflector.
We have developed a wavelength-swept laser source with ultrahigh phase stability. Potassium tantalate niobate (KTa1-
xNbxO3, KTN) single crystal was employed as an electro-optic deflector for a high-speed wavelength sweep in the laser
cavity. A 200-kHz sweep rate was obtained with an average output power of 20 mW and a coherence length of 8 mm at
the wavelength range exceeding 100 nm. Since the electro-optic effect in KTN crystal has a fast response of more than
500 MHz, the deflection of a KTN deflector can follow the applied voltage precisely. Considering this advantage, we
demonstrated a swept source with ultrahigh phase stability in the 1.3 μm wavelength range as a result of the low-jitter
operation of the deflector. The standard deviation of measured timing jitters between adjacent A-lines was confirmed to
be less than 78 ps, which corresponds to a phase difference of 0.017 radians at a path difference of 1.5 mm of a
Michelson interferometer. The phase stability can be increased with an improved voltage source because the timing jitter
is still mainly caused by the voltage applied to KTN. In addition to realizing the phase stability of neighboring A-lines,
the long-term stable sweep was demonstrated by eliminating the refresh operation that was previously needed to prevent
output power decay. The ultrahigh phase stability we achieved makes our swept source promising for Doppler OCT and
polarization-sensitive OCT.
We are developing a new light source for swept-source OCT, namely, an external-cavity LD equipped with a KTN
electro-optic deflector. Being free from mechanical resonance, our 1.3-μm laser exhibits scanning range of almost 100
nm up to 200-kHz under a ±300 V deflector driving voltage. Using a semi-empirically derived equation, we find that
KTN's convex lens power degrades the coherence length, and this can be compensated with a cylindrical concave lens.
Such compensation was experimentally confirmed by observing reduction of elliptical beam divergence. OCT images of
a human fingernail are obtained using the swept source.
We present a new light source for the swept-source OCT, that is, an external-cavity LD incorporating an electro-optic
deflector. We use a KTN deflector that is unique in being very fast and simultaneously providing an appreciable
deflection caused by injected carriers. Particularly, high-speed and nearly linear to the applied voltage operation is
attained when KTN crystal is pre-charged. Our 1.3-μm Littman-Metcalf external-cavity laser exhibits static linewidth <
0.1 nm, and a 110-nm scanning range up to 150-kHz under a ±200 V sinusoidal driving voltage to the deflector. Being
free of mechanical resonance, the laser would hopefully realize a faster (in a separate study, deflector itself worked up to
400 kHz) and wavenumber-linear scan that is ideal for the swept-source OCT by designing the waveform of driving
voltage. And as for the resolving power of deflector, while our KTN deflector has only 35 spatial resolvable points, the
number of wavelength points for the swept source clearly exceeds to this limit, which we attribute to line narrowing
effect accompanied by the laser operation. Preliminary OCT images taken using the swept source are also presented.
Polymer optical waveguide devices are getting popular for next generation FTTH application. In order to accelerate the development of polymer optical devices, evaluation of waveguide characteristics should be speeded up. Polymer optical chip containing a combination of 45°-angled cut waveguide, Y-splitter and S-bend structures was designed and fabricated for simple evaluation of multimode waveguides. Input launching such as light source, mode scrambler was investigated for reliable measurement.
A new electroholography system is introduced that uses a liquid crystal display, a photorefractive crystal, and a time- sharing display method. By using the photorefractive crystal as a kind of screen through which the hologram is recreated, we can realize high quality, off-axis, and computer-generated holograms. The time sharing approach enables an electronic display device to display 3D objects clearly by breaking them into parts that are displayed in sequential frames. If the fames are cycled at a high enough speed, we see these parts as a single object due to the afterimage effect. This approach relaxes the strict dynamic range requirements that would normally be placed on the electronic display device. The photorefractive crystal suppresses the flicker caused by the time-sharing display method. This paper first describes the time-sharing method. Next, a new experimental 3D-TV system with a photorefractive crystal, strontium barium niobate, is demonstrated. This system confirms the exciting future of electroholography.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.