[show abstract][hide abstract] ABSTRACT: Enhanced four-wave-mixing (FWM) effects have been observed with the help of large group-indices near the band edges in one-dimensional (1-D) silicon photonic crystal waveguides (Si PhCWs). A significant increase of the FWM conversion efficiency of about 17 dB was measured near the transmission band edge of the 1-D PhCW through an approximate 3.2 times increase of the group index from 8 to 24 with respect to the central transmission band region despite a large group-velocity dispersion. Numerical analyses based on the coupled-mode equations for the degenerated FWM process describe the experimentally measured results well. Our results indicate that the 1-D PhCWs are good candidates for large group-index enhanced nonlinearity devices even without having any special dispersion engineering.
[show abstract][hide abstract] ABSTRACT: We have demonstrated an actively Q-switched single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser by using an EDF saturable absorber modulated under an external laser pulse injection. A laser output of 1531.9 nm wavelength from a distributed-feedback laser diode was amplified with an EDF amplifier and modulated with an external electro-optical modulator, and the modulated signals were used as control pulses to saturate the EDF saturable absorber for the actively Q-switched ring-type fiber laser operation. Actively Q-switched 1542 nm wavelength laser pulses of 4.5 nJ pulse energy and of 4.0μs pulse width were achieved at a repetition rate of 100 Hz. When the Q-switched laser pulse energy was reduced to about 0.54 nJ by decreasing the gain-pump power used for exciting the ring cavity and the control-pulse beam power used for bleaching out the saturable absorber, the SLM laser pulses were achieved. Further improvement of the Q-switched SLM laser pulse output can be achieved simply by using an external laser amplifier and by shortening the cavity length with short pigtailed-fiber laser components, and thus the SLM laser pulses can be useful for various applications.
[show abstract][hide abstract] ABSTRACT: We propose a simple white-light interferometric method of measuring a one-dimensional rotation angle with use of an optical plane parallel plate of standard refractive index. The phase change of the interference pattern of the interferometer during the rotation of the flat plate of known refractive index and thickness placed in one of the interferometer's arms is used for determination of the rotation angle. This method has been demonstrated for an accurate angle measurement over the angle range from 0° to 40° within a maximum uncertainty of 0.057°.
[show abstract][hide abstract] ABSTRACT: This paper presents our recent achievement with a simple white-light
Mach-Zehnder (MZ) interferometric method to identify localized group
velocity dispersion (GVD) coefficient or group delay dispersion (GDD)
value of the nanostructured silicon waveguide devices (NSWDs).
Conventional methods of measuring the GVD of optical fibers or
waveguides are related to measurement of the total GVD of the entire
fibers or NSWDs. Recently time-resolved heterodyne detection technique
and the near-field scanning microscopy technique are demonstrated to
measure localized group delay of the photonic crystal waveguides (PhCWs)
devices, but the techniques have a limited group delay (GD) resolution
depending on laser pulse-width used for the measurement. It is
demonstrated that our white-light interferometric method can measure
very accurate GDD value up to 0.5 fs/nm resolution. This method has been
applied to determine not only the GVD or GDD profile of the entire NSWDs
but also that of their localized structural sections, such as grating
couplers and interface between the plain strip waveguide and single
line-defect (W1) PhCW.
[show abstract][hide abstract] ABSTRACT: We review the temporal dynamics of the laser output spectrum and polarization state of 1.55 μm wavelength single-mode (SM) vertical-cavity surface-emitting lasers (VCSELs) induced by external optical beam injection. Injection of an external continuous-wave laser beam to a gain-switched SM VCSEL near the resonance wavelength corresponding to its main polarization-mode output was critical for improvement of its laser pulse generation characteristics, such as pulse timing-jitter reduction, linewidth narrowing, pulse amplitude enhancement, and pulse width shortening. Pulse injection of pulse width shorter than the cavity photon lifetime into the SM VCSEL in the orthogonal polarization direction with respect to its main polarization mode caused temporal delay of the polarization recovery after polarization switching (PS), and its delay was found to be the minimum at an optimized bias current. Polarization-mode bistability was observed even in the laser output of an SM VCSEL of a standard circularly cylindrical shape and used for all-optical flip-flop operations with set and reset injection pulses of very low pulse energy of order of the 3.5~4.5 fJ.
[show abstract][hide abstract] ABSTRACT: We report on a simple and direct method of measuring localized chromatic
dispersion (CD) profiles of structured nanowaveguide devices using white-light
interferometry. Phase change in the interference fringe of a white-light interferometer
(WLI) caused by introducing a sample-under-test into one of the interferometer arms was
used to determine a spectral profile of its accurate CD coefficients. This method was
tested by measuring the spectral CD profiles of a localized silicon nanowaveguide and of
a nonmembrane-type photonic crystal waveguide (PhCW) excluding their optical coupling
sections. The measured local CD values of a 500-nm-wide single-line-defect (W1) PhCW
with a lattice period of 460 nm and the hole radius of 165 nm formed on 220-nm-thick
silicon layer of a silicon-on-insulator (SOI) wafer varied from 0.38 to 0.22
ps/(nm·cm) for a wavelength range from 1530 to 1570 nm. This method will be very
useful in determining the accurate CD profiles of nanophotonic waveguide
Journal of Lightwave Technology 12/2011; 30(1):43-48. · 2.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present experimental and numerical study of temporal characteristics of injection-locked polarization switching of a conventional-type 1.55-μm wavelength single-mode vertical cavity surface-emitting laser (VCSEL). Delayed recovery response of the main-mode of the VCSEL was observed when short and strong optical injection pulses of an orthogonal polarization to the VCSEL's main polarization-mode were applied. Numerical analysis based on a spin-flip model describes that the relatively long upper level lifetimes compared to a short injection-pulse width and long cavity photon lifetimes cause delayed recovery response of the main-mode of the VCSEL. An optimum bias current of the VCSEL was also observed for the shortest recovery time of its free-running polarization mode after the orthogonal polarization beam pulse injection.
[show abstract][hide abstract] ABSTRACT: We report a white-light Mach-Zehnder interferometry method for an accurate measurement of spectral distribution of the chromatic dispersion coefficient of very short optical waveguides over a wavelength range of 1520~1560 nm. The chromatic dispersion curve of a 7.6 mm long silicon nano-waveguide of 400 nm width and 250 nm height was successfully measured by confirming the method with standard single-mode fibers up to 3 cm length, for which its total chromatic dispersion is as small as 0.51 fs/nm. This method will be very useful for determination of chromatic dispersion profile of compact nanowaveguide devices.
[show abstract][hide abstract] ABSTRACT: Four-wave-mixing (FWM) efficiency of a silicon-based one-dimensional photonic crystal waveguide was measured along with its spectral profile of the group index. High FWM efficiencies were observed near the band edge compared to those at the middle sections of its transmission band despite its high dispersion effect.
[show abstract][hide abstract] ABSTRACT: All-optical set-reset flip-flop operations of conventional circular cylindrical-shaped 1.55-μm wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) have been demonstrated at a switching frequency of 1 GHz based on polarization bistability observed via injection current variation. The energy of set and reset pulses was lower than 4.5 fJ at a bias current of the VCSEL of 4 mA. Polarization bistable VCSELs will be useful for high-speed optical signal processing applications.
[show abstract][hide abstract] ABSTRACT: We introduce a new measurement method of the nonlinear coefficient (NC) of a highly nonlinear fiber based on a four-wave mixing (FWM) technique. The NC along with the fiber's zero-dispersion wavelength (ZDW) was determined from the precise measurement of the pump power dependent optimum pump frequency for peak FWM signal generation conditions. The measurement errors of the NC and ZDW values determined with this method were less than 4.6% and 0.051nm, respectively.
[show abstract][hide abstract] ABSTRACT: We report the effect of an external injection laser wavelength on reducing the timing jitter of optical pulses generated from gain-switched single-mode 1.5-μm vertical cavity surface emitting lasers (VCSELs). Simultaneous timing jitter reduction, pulse width shortening, and spectral linewidth narrowing without any peak power penalty were observed when the injection laser wavelength was tuned near the spectral peak of the free-running VCSELs spectrum operating in a continuous wave mode. The timing jitter was reduced up to 40% of that without any injection.
IEEE Journal of Quantum Electronics 10/2010; · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper reports demonstration of a new simple white-light interferometry method for continuous dispersion curves of the thermo-optic (TO) coefficients of optical samples. Phase shifts of the interference spectra of the white-light interferometer output are measured by changing temperature of an optical sample located in the one of the interferometer arms. A continuous dispersion curve of the TO coefficient of the sample materials over the full wavelength coverage region of the white light beam is obtained from the phase shift information with the temperature change. This new method is tested with a fused silica glass material of well-known optical properties to prove its accuracy by comparing the measured results with its known TO coefficient values. This continuous dispersion information of the TO coefficients of new optical materials will be useful for fabrication of the WDM signal processing devices or functional devices in multi-wavelengths.
[show abstract][hide abstract] ABSTRACT: We report a simple method of measuring the absolute values of the phase refractive index of an optical material of a flat plate shape over a wide spectral range at a single measurement run. A white-light interferometric technique with angle rotation of the optical plate sample located in one of the interferometer arms was used in this method. The validity of this method was proved by measuring the absolute phase refractive indices of flat plate samples of fused silica and BK7, and by comparing them with calculated values from their well-known Sellmeier dispersion formulas. The accuracy of this refractive index measurement method was within 0.002, which can be further improved by enhancing the angle measurement accuracy of the angle rotating stage used in this method.
[show abstract][hide abstract] ABSTRACT: We report experimental results on timing-jitter suppressed optical short pulse generation from a gain-switched single-mode vertical-cavity surface-emitting laser (VCSEL) at 1.55 μm wavelength with an external laser beam injection. The low timing-jittered optical short pulses are very useful for high-speed optical time-division-multiplexed (TDM) communications and signal processing. The obtained timing jitter and pulse duration from the VCSEL were less than 1 ps and 65 ps, respectively, at a pulse repetition rate of 1.6 GHz.
[show abstract][hide abstract] ABSTRACT: We report, for the first time to our knowledge, a novel and simple method for measuring continuous dispersion spectrum of unclamped linear electro-optic (EO) coefficient using a white-light interferometry. This method detects phase changes of the interference patterns with and without an applied electric voltage, and allows a simultaneous measurement of wavelength and polarization dependent EO coefficients of birefringent materials. Both of the unclamped EO coefficients, r(13) (T) and r(33) (T), of a congruent LiNbO(3) (LN) crystal have been measured simultaneously with the method, and their continuous dispersion curves have been also obtained.
[show abstract][hide abstract] ABSTRACT: We report the first experimental invetigation of the polarization-mode switching dynamics and injection-wavelength-dependent polarization-mode bistability of a 1.5-m wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) under external laser beam injection. An injection beam with polarization orthogonal to that of the stand-alone VCSEL caused polarization-mode instability and switching of the VCSEL output. By varying the optical injection detuning for fixed injection power observation was made of a novel form of polarization bistability which will have applications in a new type of all-optical flip-flop and signal processing scheme.
[show abstract][hide abstract] ABSTRACT: We propose two discrete fiber Raman amplifier schemes using Raman ring fiber oscillator, a two-stage scheme, and a forward pumping scheme, to reduce double Rayleigh backscattering noise at high gains over 20 dB. Both schemes have low noise characteristics compared to a previous scheme. Bit-error-rate measurements at 10 Gb/s show power penalty free operation for the two-stage scheme at a gain of 25 dB.