Takuo Tanemura

A novel type of multiple-wavelength focusing plasmonic coupler based on a nonperiodic nanoslit array is designed and experimentally demonstrated. An array of nanoslits patterned on a thin metal film is used to couple free-space light into surface plasmon polaritons (SPPs) and simultaneously focus different-wavelength SPPs into arbitrary predefined locations in the two-dimensional plane. We design and fabricate a compact triplexer on a glass substrate with an integrated silicon photodetector. The

A novel shape-adjustable narrowband optical filter utilizing stimulated Brillouin scattering in an optical fiber is proposed and demonstrated. In this scheme, binary-phase-shift-keying modulation is applied to the pump wave to broaden and shape the Brillouin gain spectrum. By choosing an appropriate modulation data pattern, we realized a flat-top steep-cutoff optical bandpass filter with a 3-dB bandwidth of 1.5 GHz and a 10-dB bandwidth of 2 GHz is realized. In addition, a tunable optical notch

We show that modulational instability may arise even in the normal group-velocity dispersion regime of an optical fiber when the fiber loss (gain) varies depending on the wavelength. A simple analytical expression for the instability gain is obtained, which reveals that the odd-order terms of the loss dispersion are responsible for this phenomenon. The instability gain is measured experimentally in an optical-parametric-amplification configuration. Large parametric gain is induced in a non-phase

The circular-birefringence fiber (CBF) or the so-called twisted fiber provides novel attractive potential for all-optical signal-processing applications. Unlike a standard nonpolarization-maintaining (non-PM) fiber, where the polarization dependence of chi <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(3)</sup> nonlinearity is averaged out by the residual birefringence, the CBF behaves as a perfectly isotropic fiber in terms of nonlinear wave prop

Highly efficient tunable wavelength conversion based on nondegenerate fiber four-wave mixing is demonstrated. We apply simultaneous phase modulation to the two pump waves so that stimulated Brillouin scattering is suppressed without affecting the generated idler wave. The signal light is converted from an arbitrary wavelength to another arbitrary one within the entire C-band with a conversion efficiency higher than -10 dB.

Optical buffering has been one of the major technical challenges in realizing optical packet switching (OPS) routers. While fiber-delay-line-based (FDL) buffers are the most practical and realistic solution to offer useful amount of capacity, the bulkiness of long FDLs and optical switches has been the main obstacle to practical implementation. This paper demonstrates a compact optical buffer with up to 750-ns capacity and 50-ns temporal resolution by using an InP integrated 1×16 optical phased-

We propose and demonstrate a simple scheme of a highly efficient polarization-independent wavelength converter utilizing the two-pump fiber optical parametric amplification. First, binary phase-shift-keying modulation is applied to two pump waves, which allows us to suppress stimulated Brillouin scattering without broadening the idler spectrum. Then, polarization states of the two pumps are aligned orthogonally to realize the wavelength conversion which is insensitive to the signal polarization.

An integrated semiconductor 1times5 InP-InGaAsP optical phased-array switch is fabricated and characterized. Using the carrier-induced refractive index change of InGaAsP waveguide, we achieve successful switching to five output ports with less than 60-mA current injection. Wide operating bandwidth covering the entire C-band (1520-1580 nm) and nanoseconds dynamic response are demonstrated, making it potentially applicable to large-capacity wavelength-multiplexed optical-packet-switching routers.

Cross-phase modulation in an optical fiber can lead to various types of modulational instability, such as polarization instability in a highly birefringent fiber and two-pump optical parametric amplification. We present unified analyses of such instabilities and clarify the general mechanisms behind them. By solving the generalized eigenvalue equation, we indicate the explicit conditions of inducing modulational instability. The eigenvector is also calculated, which allows us to explain underlyi

We derive explicit design rules of optical phased-array planar 1 × N switch to achieve small insertion loss, large extinction ratio, and non-dispersive waveguide structure required for wavelength-independent broadband operation. The minimum number of phase shifters and slab lengths were studied as a function of N and the optimized array shape was derived to minimize the optical path length. We show that the length depends nonlinearly on N, and may become significantly shorter compared with that

Proposes and demonstrates a novel method of suppressing spectral broadening of the idler wave, which is generated in fiber four-wave mixing (FWM) pumped by a continuous wave. In this scheme, binary-phase-shift-keying (BPSK) modulation of the pump wave broadens the pump spectrum so that the Brillouin threshold for the pump power is increased, whereas it never affects the spectrum of the idler wave. By the 2-Gb/s BPSK modulation of the pump wave, we achieve a FWM efficiency as high as 10 dB, maint

Polarization-independent all-optical wavelength conversion is demonstrated by using cross-phase modulation in a twisted fiber and subsequent optical filtering. By twisting a 1-km-long fiber at a rate of 15 turns/m and aligning the probe light to circular polarization, we reduce the polarization sensitivity successfully from 3.5 to 0.3 dB. Error-free operation with only 1-dB penalty is realized at 40 Gb/s with the input signal polarization scrambled. The demonstrated scheme also offers a novel fu

To meet the demand for continuous increase in data traffic, full usage of polarization freedom of light is becoming inevitable in the next-generation optical communication and datacenter networks. In particular, Stokes-vector modulation direct-detection (SVM-DD) formats are expected as potentially cost-effective method to transmit multi-level signals without using costly coherent transceivers in the short-reach links. For the SVM-DD formats to be practical, both the transmitter and receiver need

We show theoretically and experimentally that the polarization sensitivity of asymmetric nondegenerate fiber four-wave mixing can be eliminated by using circularly polarized pump waves in a twisted fiber. By twisting a fiber at 15 turns/m and aligning the pump waves to a circular state of polarization, we successfully reduce the polarization sensitivity from 5.8 dB to 0.9 dB. Although the polarization-mode dispersion (PMD) of the twisted fiber sets the limitation to the conversion bandwidth, its

Abstract Integrated phased‐array optical switches, having a high port‐count scalability and broad spectral coverage, can potentially be used as building blocks of large‐scale optical routers. In this article, recent works on monolithically integrated InP phased‐array switches and their applications to optical packet switching (OPS) are reviewed. After describing the theory of integrated phased‐array switches, experimental results on a single‐stage 1 × 16 switch, which features wavelength‐indepen