Masataka Shirasaki

Large angular dispersion by a virtually imaged phased array and its application to a wavelength demultiplexer

A new scheme that shows large angular dispersion is proposed and demonstrated. The key idea to this method is a virtually imaged phased array (VIPA). The angular dispersion of a VIPA is 10-20 times larger than those of common diffraction gratings, which have blaze angles of ~30 deg. With the VIPA, wavelength demultiplexing for 10 channels with 0.8-nm spacing is achieved. Low polarization-state dependence (~0.1 dB) is also confirmed.

Exact compensation for both chromatic dispersion and Kerr effect in a transmission fiber using optical phase conjugation

We propose a new method to compensate exactly for both chromatic dispersion and self-phase modulation in a transmission fiber, where the light intensity changes due to fiber loss and amplifier gain. This method utilizes optical phase conjugation (OPC). The pulse shape is precompensated before OPC by transmission through a fiber with large dispersion. A computer simulation demonstrates effective compensation for waveform distortion in a 40 Gb/s NRZ intensity-modulated light transmission.

Squeezing of pulses in a nonlinear interferometer

A symmetric nonlinear Mach–Zehnder interferometer containing a Kerr medium performs the operation of squeezing. The operation is performed by the interference of cotraveling waves, and the pump wave is removed. This mechanism is broadband. We analyze the operation of the interferometer and determine the degree of shot-noise reduction achieved in a balanced detector. A modification of the interferometer into a fiber ring reflector is described that accomplishes the squeezing and the pump separation.

Compact optical isolator for fibers using birefringent wedges

A new type of optical isolator for fibers is proposed in this paper. A birefringent wedge used to separate and combine the polarized light is developed, giving the isolator low forward loss and high isolation. The antire-flection process at the fiber endface reduces the forward loss and reflected return. A forward loss of 0.8 dB, a backward loss of 35 dB, and a reflected return of -32 dB were obtained. These characteristics were measured from fiber to fiber using multimode fibers with 50-/microm core diam at a wavelength of 1.3 microm. Details of the design, fabrication, and characteristics of this isolator are presented.

Compact polarization-independent optical circulator.

This paper introduces a compact polarization-independent optical circulator for communications using multimode optical fibers. This circulator consists of two pairs of rutile prisms used as polarization separators, a YIG Faraday rotator, a ring-shaped magnet, and a quartz halfwave plate. Insertion losses of 2.3 dB including fiber connection losses and isolations of 32 dB at a wavelength of 1.3 epsilonm were obtained using this circulator, and stabilization of the semiconductor laser was confirmed. Details on the design, fabrication, and characteristics of this circulator are presented.

Nonmechanical optical switch for single-mode fibers

This paper introduces a bistable nonmechanical optical switch for single-mode optical fibers. A l-input/2-output device for the l-microm wavelength range, the optical losses of the switch are independent of the polarization state in the input fiber. The insertion losses for the optical signal from the input fiber to the output fiber are 1.4 dB and the crosstalks are -28 dB at 1.3-microm wavelength. Switching is performed by a 20-microsec one-shot pulse with a maximum current of 500 mA. The voltage to switch the optical path is 5 V.

Magnetooptical 2×2 switch for single-mode fibers

An optical switch for single-mode fibers is presented in this paper. A novel polarizing prism is introduced to make the 2 input, 2 output optical switch insertion loss low and independent of the polarization state of the input fiber. This switch operates by one electric pulse with a voltage of only 2.5 V and a current of 35 mA. The insertion loss was 1.2 dB, its fluctuation for different input polarizations was within 0.03 dB, and the far-end crosstalk was −26 dB at a wavelength of 1.3 μm. The shock resistance of the switch was confirmed during an acceleration of 100 g.

Polarization and frequency control of a semiconductor laser with a new external cavity structure

A technique using a new external cavity structure to cause degeneration at the frequencies of two orthogonally polarized modes and to control the polarization and the frequency in a semiconductor laser has been devised. The phase difference between the polarizations in the gain medium can be canceled in a round trip through quarter‐wave plates set in the cavity. By rotating one of the quarter‐wave plates, orthogonally polarized laser beams can theoretically be made to oscillate at slightly different frequencies. Experimentally, two orthogonally polarized oscillations with rather large frequency differences occurred. The difference between the two frequencies alternated according to the quarter‐wave plate rotation. This phenomenon could be explained theoretically.

Bistable magnetooptic switch for multimode optical fiber

A bistable nonmechanical optical switch for multimode optical fiber is presented. It is a 2-input/2-output device for the 1-microm wavelength range. The optical characteristics are independent of the polarization state of incident light. The switch consists of Faraday rotators of thin plates of yttrium-iron-garnet single crystal, electromagnets whose cores are made of semihard magnetic material, halfwave plates of crystal quartz, polarizing prisms of rutile, and lenses. Switching is performed by one-shot 3-V 20-microsec pulses with a maximum current of 500 mA. The 1.5-dB insertion losses and -32-dB cross talk were obtained at a wavelength of 1.3 microm.

Quantum-noise reduction in a phase-sensitive interferometer using nonclassical light produced through Kerr media.

A phase-sensitive interferometer system is proposed. Quantum noise in this system is reduced by using nonclassical light that is produced by a simple squeezer with Kerr media. The noise in a balanced detector can be less than the noise attained by using an ordinary squeezed vacuum.