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ABSTRACT: Terahertz (THz) generation was demonstrated from GaP rod-type waveguides via difference-frequency-mixing of near-infrared light using a collinear phase-matching condition. THz output peaks were observed, and appeared at frequencies corresponding to the fundamental and high-order waveguide modes. Interestingly, the position of the fundamental mode shifted to a higher frequency for a smaller waveguide cross-section, which is attributed to the waveguide confinement of the THz wave. The conversion efficiency was enhanced in the waveguide with a cross section of 200 mumtimes160 mum as compared to that in bulk GaP crystals
IEEE Photonics Technology Letters 03/2007; · 2.19 Impact Factor
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ABSTRACT: The characteristic of 80-ps mode-locked (ML) pulse-pumped gain, which results in a decline that changes from a linear gradient to a square-root gradient at introduced pump densities exceeding 10 dB, makes it difficult to develop pulse-pumped gains for high efficiency amplification. To overcome this disadvantage with pumping, we compared an 80-ps ML pulse and 4-ns Q-switched pulse in a straight waveguide. The amplification of the 4-ns pulse was linear and had a maximum gain of 23.3 dB at an introduced pump density of 1.4 W/μm<sup>2</sup> in a straight waveguide. The gain was more efficient than with the 80-ps pulse, which was limited by the optical damage threshold of the input antireflective coating (1.6 W/μm<sup>2</sup>). These high-gain operations should enable semiconductor Raman amplifiers to be used for detecting signals from chemical or biological materials, in addition to infrared light frequency selective amplification with wavelength-division multiplexing in optical communications.
IEEE Photonics Technology Letters 03/2004; · 2.19 Impact Factor
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ABSTRACT: GaP-AlGaP waveguide semiconductor Raman amplifiers (SRAs) tapered on both sides were fabricated by high-quality GaP-AlGaP liquid phase epitaxial growth using the temperature difference method with controlled vapor pressure (TDM-CVP), photolithography patterning, and reactive ion etching with PCl<sub>3</sub> gas. Although the finesse of the both-sides-tapered waveguide SRA is lower than previous values for straight or one-side-tapered waveguides, the CW-pumped gain was maximized, and a maximal gain of 4.2 dB was obtained. This letter presents the effect of tapered structures in SRA with CW pumping amplification.
IEEE Photonics Technology Letters 02/2004; · 2.19 Impact Factor
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ABSTRACT: High-power, frequency-tunable terahertz (THz) waves over the range from 0.3 to 7.5 THz were generated based on difference-frequency generation in GaP crystals using a YAG laser and an optical parametric oscillator. The THz-wave linewidth was estimated to 3.2 GHz and spatial distribution is discussed. We measured the absorption coefficient of the GaP as well as spectra of polytetrafluroethylene (PTFE) in the THz frequency region.
Compound Semiconductors: Post-Conference Proceedings, 2003 International Symposium on; 09/2003
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ABSTRACT: In this paper, we describe the detailed characteristics of frequency tunable THz-wave generation from GaP, in particular, small-angle noncollinear phase-matching properties. We use this frequency tunable THz-wave source to measure the spectra of macro-molecules such as polymers.
Compound Semiconductors, 2003. International Symposium on; 09/2003
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ABSTRACT: We have fabricated GaP-AlGaP tapered waveguide semiconductor Raman amplifiers, and analyzed the effect of tapering in pulse-pumped high-gain operation. The finesse measurement and 80-ps pulse pumped Raman amplification experiment were performed. Although the tapering has caused additional optical loss, the highest gain of 23 dB has been obtained for a tapered waveguide with input facet of 6.0 μm<sup>2</sup> and back facet of 2.9 μm<sup>2</sup> at averaged input power of 170 mW (peak power 26 W). It is shown that the optical loss of the pump light is more severe than the linear optical loss of the signal light when the gain is higher than 20 dB.
Journal of Lightwave Technology 02/2003; 21(1):170- 175. · 2.78 Impact Factor
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ABSTRACT: Semiconductor Raman amplifiers are useful for frequency selection in terahertz bandwidth and wavelength division multiplexing (WDM) systems with terabit capacity, as well as direct terabit optical communication systems. We have developed GaP-AlGaP Raman waveguides with micrometer-size cross sections. We have reduced residual optical loss of the waveguide by improvement of the fabrication process and realized a low-loss waveguide that is 10-mm long, which has a continuous wave (CW) Raman gain of 3.7 dB. Also, the time-gated amplification with 80-ps pulse pumping is performed and 20-dB gain is obtained. These performances are very suitable for light frequency selection in terahertz bandwidth and WDM optical communication systems
Journal of Lightwave Technology 05/2002; 20(4):705-711. · 2.78 Impact Factor
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ABSTRACT: The gain measurement of a semiconductor Raman amplifier with a
GaP-AlGaP waveguide structure pumped by a high-intensity pulse source
has been measured for use as a basis for the time gate amplification of
light. A gain of 10 dB has been obtained for a 5 mm long waveguide with
a back reflector. The gain measurement has also been performed for a
waveguide which has both faces antireflection coated. From this
measurement, it is confirmed that the gain is principally from backward
scattering rather than from forward scattering. It is shown that the
dominance of backward scattering limits the minimum gate time for the
time gate amplification of light
IEE Proceedings - Optoelectronics 11/1999; · 0.71 Impact Factor
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ABSTRACT: The intensity noise of a CW-operated semiconductor Raman laser
waveguide structure with Al<sub>x</sub>Ga<sub>1-x</sub>P cladding layers
has been measured and it has been found that the noise spectral
intensity in the frequency range 10 Hz-100 kHz was reduced to 34 dB
below that of the incident pump light under saturation conditions. This
effect has been interpreted as coupling between the pump light, the
first Stokes light and the second Stokes light, assuming a very small
contribution of nonlinear absorption
IEE Proceedings - Optoelectronics 09/1998; · 0.71 Impact Factor
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ABSTRACT: Raman amplification characteristics of the GaP-Al<sub>x</sub>Ga
<sub>1-x</sub>P heterostructure waveguide have been measured by fine
tuning the pump light frequency. The Raman gain and the Raman gain
bandwidth are 0.03×10<sup>-6</sup> W<sup>-1</sup> cm<sup>-1</sup>
and 23.5 GHz, respectively. The amplified signal light can be detected
even at the pump light power level of 10 mW. This result shows that the
semiconductor Raman amplifier is suitable for demodulators based on
light frequency discrimination in wideband optical communication systems
IEE Proceedings - Optoelectronics 05/1998; · 0.71 Impact Factor
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ABSTRACT: GaP-Al<sub>x</sub>Ga<sub>1-x</sub>P tapered waveguide
semiconductor Raman lasers have been cw-operated using a Ti sapphire
pump laser. The first Stokes output power is perfectly saturated and the
intensity noise level reduces over 30 dB. Also they are operated under
pumping by a laser diode. Also, the semiconductor Raman amplifier
characteristics are shown to be suitable for light frequency
discrimination in future THz band as well as WDM optical communication
systems
Compound Semiconductors, 1997 IEEE International Symposium on; 10/1997
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ABSTRACT: Low-threshold semiconductor Raman lasers with a tapered waveguide
structure with GaP core and Al<sub>x</sub>Ga<sub>1-x</sub>P cladding
layers have been operated in a quasi CW operation condition. It has been
found that the first Stokes light output power nearly perfectly
saturates when the pump power is increased, and this has been attributed
to lasing of the second Stokes light. This effect will be useful for
realising a low-noise light wave source
IEE Proceedings - Optoelectronics 05/1997; · 0.71 Impact Factor
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ABSTRACT: Low pump-power operation of GaP semiconductor Raman lasers with a
tapered waveguide structure is reported. The waveguides are both
laterally and vertically tapered and fabricated by the temperature
difference method under controlled vapour pressure with liquid-phase
epitaxy and an improved growth process, which has not caused any serious
increase of internal optical loss. The lowest threshold pump power of 55
mW has been achieved
IEE Proceedings - Optoelectronics 05/1996; · 0.71 Impact Factor
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ABSTRACT: A semiconductor Raman laser with a waveguide in which a pump beam
transmits with a fundamental mode, which can be used as an optical
heterodyne demodulator, is discussed. As a result of the improved growth
process and resonator construction, a threshold pump power as low as 300
mW has been achieved. The internal loss is discussed, and a
tapered-waveguide semiconductor Raman laser is fabricated as a method to
realise further lower pump power operation, and its lasing operation is
demonstrated
Optoelectronics [see also IEE Proceedings-Optoelectronics], IEE Proceedings J 01/1993;
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ABSTRACT: A waveguide structure semiconductor Raman laser for which the pump
beam is incident through a multilayer dielectric film transparent for
the pump light but highly reflective for the Stokes light is reported.
There is no need to open a window for pump beam introduction.
Accordingly, narrow waveguides with a width of 10 μm have been
fabricated and successful operation has been achieved using a
pulse-modulated pump beam from a CW-YAG laser, instead of a Q-switched
YAG laser used in the previous experiments. This structure is capable of
further reducing the size of the waveguide cross-section to realise very
low threshold operation necessary for use in wideband optical
communications
Optoelectronics [see also IEE Proceedings-Optoelectronics], IEE Proceedings J 01/1992;
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ABSTRACT: The authors describe the fundamental properties of the
GaP-Al<sub>x</sub>Ga<sub>1-x</sub>P heterostructure used for the
semiconductor Raman laser and the low threshold operation of the buried
heterostructure Raman laser, together with the first demonstration of
lasing by a new structure having a layer with an intermediate refractive
index for pump power introduction, which reduces the loss for the Stokes
field. They also describe the important applications of the
semiconductor Raman laser to optical-heterodyne demodulation, and
frequency difference mixing for frequency-tunable far-infra-red
generation, as one of the essential tools for very wideband optical
communication beyond 1 THz
Optoelectronics [see also IEE Proceedings-Optoelectronics], IEE Proceedings J 03/1990;
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ABSTRACT: This paper describes the first lasing experiment of the heterostructure semiconductor Raman laser with a GaP Raman active layer as thin as 15 ¿m and AlxGa1¿xP cladding layers for optical confinement, which should be a step towards realising a semiconductor Raman laser pumped by a semiconductor injection laser applicable to wideband optical communication. Also, the four-layer structure Raman laser is reported, by which the strain-induced optical anisotropy caused by the lattice mismatching can be reduced.
Optoelectronics [see also IEE Proceedings-Optoelectronics], IEE Proceedings J 09/1987;
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ABSTRACT: A frequency-tunable terahertz wave was generated from GaP crystals using an optical parametric oscillator as the pump source and a YAG laser 1.064 m as the signal source. By tuning the very small angle, in , between the pump and signal light beam directions, tunable terahertz waves over the frequency range from 0.5 to 3 THz were obtained. The THz frequency changed almost linearly with the angle in . The precise noncollinear phase matching condition is discussed. The pulsed peak power of the THz wave was as high as 480 mW at 1.3 THz. © 2003 American Institute of Physics.
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ABSTRACT: Time-gated Raman amplification in the GaP–AlGaP waveguide is investigated using mode-locked Ti–sapphire pump source with 80 ps pulse width. Logarithmic Raman gain linearly increases with increasing the pump power density as long as the gain is less than about 10 dB. However, with further increasing the pump power it becomes nearly proportional to the square root of the pump power density. This is due to the fact that the equivalent linewidth of the pump pulse is comparable to the spectral full width half maximum of the Raman gain coefficient 24 GHz. Another point is that the amplified pulse broadens as the waveguide length exceeds the optical length corresponding to the pump pulse width because Raman amplification occurs mainly due to backward scattering. © 2003 American Institute of Physics.
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ABSTRACT: Using a GaP Raman-based THz-wave (GRT) generator spectrometer in the frequency range 0.8–5 THz, we measured the terahertz (THz) wave absorption spectra of GaP crystals with carrier densities of 1010 and 1016 cm−3. We also investigated the temperature dependence from 20 to 300 K. In the lower-carrier-density GaP, the THz-wave absorption by phonons increased from 1.5 to 7 cm−1 as the THz frequency increased. In the higher-carrier-density GaP, absorption due to free carriers appeared below 2.5 THz. The THz-wave absorption decreased as a function of crystal temperature in each sample (α<2 cm−1 at 20 K). We also measured the temperature dependence of the THz-wave output from the GaP crystals. In each crystal, the THz-wave output was enhanced at 90 K, compared with room temperature, due to the decrease in the THz-wave absorption.
Journal of Physics and Chemistry of Solids 69:597-600. · 1.63 Impact Factor
