Hiromu Toba

Silica-based single-mode waveguides on silicon and their application to guided-wave optical interferometers

Low-loss silica-based single-mode waveguides and directional couplers are fabricated on silicon substrates. Their application to Mach-Zehnder interferometer type guided-wave devices is demonstrated. Optical switches or tunable optical couplers are fabricated using the thermooptic effect. Asymmetrical Mach-Zehnder interferometers are successfully applied to multi/demultiplexers for optical FDM transmission systems. >

Tunable gain equalization using a Mach-Zehnder optical filter in multistage fiber amplifiers

Tunable signal gain equalization is demonstrated in three-stage Er/sup 3+/-doped fiber amplifiers using a waveguide type Mach-Zehnder (MZ) optical fiber. A 29-channel multiplexed system is examined where signal wavelengths are positioned from 1.548 to 1.555 mu m. By adjusting the MZ transmittance with the external control current, tunable gain equalization is achieved at the output of each amplifier.<<ETX>>

Silica-based integrated optic Mach-Zehnder multi/demultiplexer family with channel spacing of 0.01-250 nm

A Mach-Zehnder (MZ) interferometer design is presented for application to wavelength-division multiplexed/frequency division multiplexed (WDM/FDM) systems. A variety of integrated-optic devices with low loss and low crosstalk, using silica-based waveguides, are demonstrated. MZ interferometers operate as multi/demultiplexers or frequency-selection switches. The channel spacing is determined by the waveguide arm length difference, and a spacing range of 1 GHz to 36 THz, corresponding to a wavelength spacing of 0.008-250 nm, is achieved. The devices for the WDM region have low fiber-to-fiber loss of 0.5 dB, and the devices for the FDM region have higher losses of 2-5 dB. Crosstalk of less than -15 dB was obtained for all the devices. A 5-GHz-spaced 16-channel frequency selection switch and a 10-GHz-spaced eight-channel multi/demultiplexer were also fabricated with a total loss of 5 dB and total crosstalk of -10 dB or less. >

A 100-channel optical FDM transmission/distribution at 622 Mb/s over 50 km

A 100-channel optical frequency-division multiplexing (FDM) transmission/distribution experiment at 622 Mb/s is demonstrated for a fiber length of 50 km. The feasibility of a polarization-insensitive waveguide frequency selection switch for 10-GHz intervals and a frequency-shift-keying (FSK) direct-detection scheme employing a Mach-Zehnder filter is verified. The demodulation circuit employs a Mach-Zehnder filter and a balanced receiver, which utilizes optical power more efficiently than the Fabry-Perot filter. No receiver sensitivity degradation is observed due to interchannel crosstalk of the 128-channel tunable waveguide frequency selection switch (FS-SW) or fiber four-wave mixing for transmissions over a 50-km-long nondispersion-shifted (NDS) fiber and a 26-km-long dispersion-shifted (DS) fiber. >

Optical FDM transmission technique

This paper surveys the present state of optical frequency-division multiplexing (optical FDM) technologies. Utilizing a broad optical frequency bandwidth up to several hundred terahertz, optical FDM is expected to find applications in large-capacity trunking and local distribution networks. The present state of the related technologies and the future prospects for these applications are discussed.

A four-channel optical waveguide multi/demultiplexer for 5-GHz spaced optical FDM transmission

A four-channel optical waveguide multi/demultiplexer for 5-GHz spaced optical FDM transmission is developed. The multi/demultiplexing principle is first presented, followed by the extinction ratio dependence on the power transfer ratio of the directional couplers, transmission loss of the waveguide, and birefringence of the waveguide. Experimental results are described for waveguides of high-silica glass fabricated on the silicon substrate by combination of flame hydrolysis and reactive ion etching. Their measured characteristics, such as frequency transmittance, loss, extinction ratio, and dependence of polarization and temperature are reported and evaluated. >

Multichannel amplification utilizing an Er/sup 3+/-doped fiber amplifier

An Er/sup 3+/-doped fiber amplifier for multichannel systems was studied from the viewpoint of clarifying the ultimate capacity of the applicable number of channels. In these experiments, 10-GHz spaced 100-channel common amplification was carried out in a 622-Mb/s frequency-shift-keying (FSK) direct detection scheme, together with measurement of the amplifier characteristics. Bit-error-rate measurements show that the power-penalty characteristics for 100-channel amplification are the same as for one-channel amplification. Based on the experimental results, possible channel capacity is discussed. There are two possible factors limiting channel capacity in multichannel amplification of fiber amplifiers: signal-gain bandwidth and amplifier noise. Calculations using the amplifier parameters obtained during the experiments reveal that signal gain bandwidth is the main factor limiting channel capacity in the amplifier used. >

Fully electrical 40-Gb/s TDM system prototype based on InP HEMT digital IC technologies

This paper presents a fully electrical 40-Gb/s time-division-multiplexing (TDM) system prototype transmitter and receiver. The input and output interface of the prototype are four-channel 10-Gb/s signals. The prototype can be mounted on a 300-mm-height rack and offers stable 40-Gb/s operation with a single power supply voltage. InP high-electron mobility transistor (HEMT) digital ICs perform 40-Gb/s multiplexing/demultiplexing and regeneration. In the receiver prototype, unitraveling-carrier photodiode (UTC-PD) generates 1 V/sub pp/ output and directly drives the InP HEMT decision circuit (DEC) without any need for an electronic amplifier. A clock recovery circuit recovers a 40-GHz clock with jitter of 220 fs/sub pp/ from a 40-Gb/s nonreturn-to-zero (NRZ) optical input. The tolerable dispersion range of the prototype within a 1-dB penalty from the receiver sensitivity at zero-dispersion is as wide as 95 ps/nm, and the clock phase margin is wider than 70/spl deg/ over almost all the tolerable dispersion range. A 100-km-long transmission experiment was performed using the prototype. A high receiver sensitivity [-25.1 dBm for NRZ (2/sup 7/-1) pseudorandom binary sequence (PRBS)] was obtained after the transmission. The 40-Gb/s regeneration of the InP DEC suppressed the deviation in sensitivity among output channels to only 0.3 dB. In addition, four-channel 40-Gb/s wavelength-division-multiplexing (WDM) transmission was successfully performed.

Design and performance of FSK-direct detection scheme for optical FDM systems

The authors describe the design and performance of an optical frequency-division-multiplexing (FDM) system that uses a frequency-shift-keying (FSK) direct detection scheme. This system utilizes a Mach-Zehnder type periodic filter as a channel selective filter and optical frequency discriminator. Requirement conditions for laser diode linewidth, frequency deviation, channel frequency spacing, detuning of optical filters, and signal power variance are discussed. These characteristics are experimentally confirmed using planar waveguide type filters. >

Lightwave synthesizer with lock-in-detected frequency references

The authors describe a lightwave synthesizer system based on the lock-in detected frequency references such as atomic or molecular spectra. This system uses two semiconductor laser diodes (LDs); one is a frequency-tunable master LD, and the other is a frequency-modulated tracking LD, used for stabilizing and tuning the master LD. The lightwave-frequency tuning of the master LD is controlled by a microwave synthesizer. This yields the same frequency stability and accuracy as the lock-in-detected frequency reference at anywhere in the tuning range. By using the 1535.39-nm absorption line of acetylene (C/sub 2/H/sub 2/) gas as the reference, tuning range of over 13 GHz with an absolute frequency stability of better than 10 MHz is demonstrated from distributed-Bragg-reflector LD. >