[show abstract][hide abstract] ABSTRACT: Coupled modes of homogeneous coupled multi-core fiber are selectively excited and discriminated utilizing the difference of equivalent propagation angle. To quantatively evaluate the extinction ratio (selectivity) of adjacent modes, a new mode discrimination technique is developed by measuring the visibility of far-field patterns under small change of wavelength of the launching beam. The peak angles of discriminated far-field patterns show a strong correlation with the incident angle of the launching beam, which means that the coupled modes were selectively excited and discriminated.
[show abstract][hide abstract] ABSTRACT: Coupled modes of homogeneous coupled multi-core fiber are selectively excited and discriminated utilizing the difference of equivalent propagation angle. The mode conversion due to bending is investigated using far-field pattern observation.
Optical Communication (ECOC), 2011 37th European Conference and Exhibition on; 10/2011
[show abstract][hide abstract] ABSTRACT: The quadruple series coupled microring resonator (MRR) can realize a boxlike spectral response and lower adjacent channel crosstalk. Utilizing these features, we demonstrated the element of Optical Code Division Multiplexing (OCDM) coding circuit using two wavelength selective switches (WSSs) consisting of quadruple series coupled MRRs laid out in parallel topology and a phase shifter incorporated in the one arm between them. In addition, a digitally variable bandwidth filter was successfully demonstrated using the same circuit as the OCDM coder.
[show abstract][hide abstract] ABSTRACT: The shape of the filter response can be controlled by a combination of ring resonators, such as series coupling, parallel
coupling, and cascade topology. In particular series coupling is effective to realize box-like spectrum responses, which are
required for wavelength filtering in WDM systems for photonic networks. In this chapter, the transfer function of series-coupled
ring resonators is derived using the matrix method, and the optimum conditions for coupling coefficients to realize the box-like
filter response are described. In addition, the free spectral range (FSR) extension method using the Vernier effect in series-coupled
ring resonators with dissimilar radii will be discussed. Last, the transfer function of parallel-coupled ring resonators is
derived and an application to interleaving is introduced.
[show abstract][hide abstract] ABSTRACT: The temperature dependence of the resonant wavelength of vertically coupled microring resonator can be controlled via internal stress caused by the thermo-optic and photo-elastic effects. In the case of strong internal stress, a polarization-independent microring resonator can be realized by controlling the device surface temperature using a heater module; the temperature dependence of TE and TM polarizations are different due to the internal stress and thus manipulating temperatures, the resonant wavelengths for TE and TM can be equalized at a specific temperature. In this study, the UV trimming of polarization-independent wavelength was demonstrated using UV-sensitive SiON as a core material. The temperature dependence of TE polarization was almost athermalized and that of TM was made negative by controlling internal stress. As a result, the simultaneous realization of the UV trimming and the polarization-independent microring was made possible more easily than before; the UV trimming can be done at room temperature due to the athermalized resonant wavelength for TE polarization.
[show abstract][hide abstract] ABSTRACT: We discovered a photoluminescence phenomenon of SiON waveguide by the UV irradiation and investigated the luminescence spectrum by a conventional microscope and diffraction grating spectroscopy. It was shown from these measurements that the defect created by UV irradiation causes the UV sensitivity of SiON film after thermal annealing. Next, we measured the spectrum change of a microring resonator with SiON core via single point long time UV irradiation and multi point UV irradiation. As a result, we demonstrated a selective UV trimming of microring resonator combining thermal annealing and multi point UV irradiation.
Japanese Journal of Applied Physics 01/2010; 49(7). · 1.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: A microring resonator wavelength tunable filter utilizing the large electro-refractive effect in InGaAs/InAlAs FACQWs was proposed and demonstrated for the first time. The resonant wavelength shift of 0.9 nm was obtained at 13 V.
[show abstract][hide abstract] ABSTRACT: Perfect hitless wavelength selective switching was demonstrated using a microring resonator. The coupling efficiency between the busline and microring was manipulated by the micro-electro-mechanical systems (MEMS) structure to eliminte the through port loss in the OFF state. The measured results of extinction ratio at the drop and through ports were 23 and 5 dB, respectively, for TE polarization at the applied voltage of 45 V. The switching loss at the through port in the OFF state was nearly 0 dB. The resonant wavelength was shifted by 0.28 nm in the OFF state and after the wavelength shift, the resonator was switched on by applying the voltage of 45 V to the MEMS structure.
[show abstract][hide abstract] ABSTRACT: We propose a new type of optical fiber called homogeneous multi-core fiber (MCF) to drastically increase the transmission capacity of single fiber using the mode-division multiplexing. In this MCF, identical cores are closely arranged so that the cores are strongly coupled to each other to form coupled modes, each of which corresponds to a transmission channel. A novel mode multi/demultiplexer is proposed to discriminate each coupled mode. To rearrange cores to match the mode multi/demultiplexer, a hybrid configuration of coupled homogeneous with uncoupled heterogeneous multi-core is proposed. An example of hybrid configuration is designed so that the cross-talk becomes sufficiently small.
[show abstract][hide abstract] ABSTRACT: Electrostatic comb-drive micro actuator with submicron comb fingers was connected to silicon microring resonator to consist a wavelength-selective add-drop switch at 1.5 microm wavelength with variable coupling mechanism. A 500 nm wide 260 nm thick 63.4 microm long silicon microring waveguide was suspended in air with low-loss suspension arms. The air gap between the microring and the input/output waveguides was adjusted by the voltage applied to the comb actuator to vary the coupling efficiency. Transmittance from the input port to a drop port was varied 32.9dB by applying the voltages from 0V to 28.2V. At 28.2V, transmittance from the input port to a through port decreased by 7.83 dB from that at 0V, and 55% of the intensity was transmitted to the drop port. The full-width-half-maximum bandwidth of the dropped light was 0.5 nm, corresponding to a Q-value of 3150.
[show abstract][hide abstract] ABSTRACT: In this review, the fundamental characteristics of microring resonator filters using high index contrast (HIC) optical waveguides are introduced, and the recent progress in the hitless wavelength selective switch achieved by the author’s group is mainly described.
[show abstract][hide abstract] ABSTRACT: We propose a hitless wavelength selective switch using vertically series coupled microring resonator. The beam structure was designed to control the coupling efficiency with low driving voltage.
[show abstract][hide abstract] ABSTRACT: We have proposed and demonstrated the basic elements of a full matrix optical switching circuit (cross-connect circuit) using a hitless wavelength selective switch (WSS). The cross-connect circuits are made of a multi-wavelength channel selective switch consisting of cascaded hitless WSSs, and a multi-port switch. These switching elements are realized through the individual Thermo-Optic (TO) tuning of a series-coupled microring resonator, and can switch arbitrary wavelength channels without blocking other wavelength channels during tuning. We demonstrate a four wavelength selective switch using a parallel topology of double series coupled microring resonators and a three wavelength selective switch using a parallel topology of quadruple series coupled microring resonators. Since the spectrum shape of quadruple series coupled microring is much more box-like than the double series, a high extinction ratio of 39.0-46.6 dB and low switching cross talk of 19.3-24.5 dB were achieved.
[show abstract][hide abstract] ABSTRACT: We analyzed the dispersion characteristics of double-series-coupled microring resonator filter and found that the coupling efficiency between resonators for the zero third-order dispersion (Bessel-Thompson) filter is one-third of that of a flat passband (Butterworth) filter. By controlling the coupling efficiencies between waveguides, the flat-top group delay response (Bessel-Thompson filter response) was realized. However, under the symmetric arrangement of coupling efficiency, the Bessel-Thompson filter lost transmittance by 1.25 dB. Thus we found the optimum condition of coupling efficiencies for achieving zero third-order dispersion (flat-group delay) with unity transmittance is an asymmetric arrangement of coupling efficiencies.
Journal of Lightwave Technology 01/2008; 26(22):3694-3698. · 2.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper presents an analytic discussion of the optimal detuning combination of a hitless wavelength selective switch using individual thermo-optic tuning of a quadruple series coupled microring resonator. We found analytically that asymmetrically detuning the resonant wavelengths of two ring resonators closest to the input busline waveguide can reduce the extinction ratio and switching crosstalk compared with other combinations. The intuitive insight on the optimal combination to realize a low crosstalk OFF-state is derivable through a metaphor of the Vernier effect, i.e., it is equivalent to the optimal arrangement of series-coupled microring resonators with different ring radii to reduce the crosstalk. Large extinction ratio of 24.9 dB and small switching crosstalk of -28.6 dB were experimentally demonstrated.
Japanese Journal of Applied Physics 01/2008; 47:6733-6738. · 1.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: Plasma enhanced chemical vapor deposition (PE-CVD) silicon nitride (SiN) film was annealed with ultraviolet (UV) light for producing strained silicon. Stress increase of 700 MPa in 30-nm-thick SiN film was obtained after annealing time of 5 min using a low pressure mercury (Hg) lamp with irradiation power of 22 mW/cm2. The stress increase was found to be generated by not only the UV annealing but also thermal annealing. The behavior of stress increase can be described by a simple experimental formula including the UV and thermal annealing effects. And the stress increase in the thinner SiN film was calculated. The most useful method for obtaining larger stress increase was proposed.
Japanese Journal of Applied Physics 01/2008; 47:7081-7088. · 1.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this review, the fundamental characteristics of microring resonator filters using high index contrast (HIC) optical waveguides are introduced, and the recent progress in the hitless wavelength selective switch achieved by the author's group is mainly described.
Optical Fiber Communication and Optoelectronics Conference, 2007 Asia; 11/2007
[show abstract][hide abstract] ABSTRACT: We demonstrate the basic elements of a full matrix optical switching circuit using a hitless wavelength-selective switch (WSS). It is a multiwavelength channel-selective switch consisting of cascaded hitless WSS, and a multiport switch. These switching elements are based on the individual thermooptic tuning of double series-coupled microring resonators, and can switch arbitrary wavelength channels without blocking other wavelength channels during tuning. The fundamental switching operations, such as four switching states from a three-wavelength selection to a zero-wavelength selection and multiport switching characteristics, are successfully demonstrated