Shigeru Ohshima

Optical subcarrier multiplexing transmission for base station with adaptive array antenna

We propose utilizing a radio-over-fiber technique of optical subcarrier-multiplexing transmission for radio base stations (BSs) with adaptive array antennas. The proposed system can be constructed at low cost since only one optical transmitter and receiver is required for a center station and a BS. Moreover, relative phases among antenna branches are insensitive to equivalent length fluctuation of an optical fiber.

Optical cascade star network - A new configuration for a passive distribution system with optical collision detection capability

A new fiber-optic passive network configuration with novel star couplers is reported. The new optical network configuration, an Optical Cascade Star Network, optimizes contradictory requirements for network system size and cable cost, and matches the actual layout in offices or factories. The star coupler is novel in that the optical signal does not return to the source terminals. This feature enables cascade connection of star networks, the use of simple repeaters for system extension, and the easy support of carrier sense multiple access with collision detection (CSMA/CD) bus access procedure. Experimental results obtained from novel star couplers, optical transceivers with (CSMA/CD) bus compatibility, and a total network system are also discussed.

Small loss-deviation tapered fiber star coupler for LAN

A biconical tapered-fiber star coupler with a mixer rod was proposed to achieve small loss-deviation and low-excess loss. Design and fabrication techniques for this star coupler were minutely discussed, and a 100 × 100 star coupler was experimentally fabricated. The loss-deviation and average-excess loss for this star coupler was 0.37 and 3.2 dB, respectively.

A thermally stable Fabry-Perot tunable filter for 1 AA-spaced high-density WDM systems

A new tunable filter using two nonidentical Fabry-Perot etalons arranged on a single rotation stage has been demonstrated. The 3-dB passband, tuning range, and insertion loss were 0.2 AA, 1.2 nm, and 1.5 to 3 dB, respectively. The thermally induced wavelength deviation of the output was within 0.02 AA in the range of 0 to 50 degrees C. The sharp wavelength characteristics and the good temperature stability promised to operate FSK-DD stably where the wavelength spacing of FSK signals was 1 AA.<<ETX>>

Ultra-Dense WDM with over 100% Spectral Efficiency Using Co-polarized 40-Gb/s Inverse-RZ Signals

An inverse-RZ modulation scheme for dense WDM systems is proposed. Inverse-RZ signals have tolerances to chromatic dispersion and optical bandwidth limitation. The strongly pre-filtered inverse-RZ signals can be adapted to ultra-dense WDM systems, in which the spectral efficiencies are over 1.0b/s/Hz. We have confirmed the error-free transmission of pre-filtered and co-polarized 40-Gb/s inverse-RZ signals where the channel intervals were 37.5 GHz.

Frequency control techniques in coherent multichannel LAN's

This paper describes frequency control techniques for cold start and channel recognition functions in coherent multichannel local area networks. A Z-cut quartz etalon can be used to stabilize the optical transmitter frequencies. The capture range and the influence of humidity on a Fabry-Perot etalon are discussed. The frequency deviation of the optical transmitter was estimated to be less than /spl plusmn/1 GHz in the long term. A double AFC loop has been proposed for local LD frequency control. It showed a wide capture range of /spl plusmn/100 GHz. Coherent FDM receiver switching to the desired channel was demonstrated over a range from 0 to 40/spl deg/C in an experiment. >

Fast and precise wavelength switching of an SG-DBR laser for 1.07-b/s/Hz DVMM systems

Fast (<100-/spl mu/s) and precise (/spl plusmn/2-GHz) wavelength switching of an SG-DBR laser with fast feedback frequency control is confirmed by using 1.07-bit/s/Hz DWDM of 40-Gb/s pre-filtered inverse-RZ signals.

Wavelength Lock System Using a Quartz Etalon Supported at the Middle Point

This paper presents a wavelength lock system using a Z-cut quartz etalon supported at the middle point. The Z-cut quartz etalon possesses the cavity length modulation and the low temperature coefficient. We propose a Z-cut quartz etalon supported at the middle point in order to improve the modulation index and response time. The mechanism of the center supported Z-cut quartz etalon is described. We also show that the etalon possesses a high modulation index, a high Q factor, and a rapid response time in experimental results. A self-tuning dither oscillator realized by using quartz etalon is also described.

Analysis of Z-cut quartz etalon for wavelength stabilization

This paper presents an analysis of the cavity length modulation of a Z-cut quartz etalon for laser diode wavelength stabilization. The electrooptic effect, piezoelectric effect, photoelastic effect, and a mechanical circuit of the etalon were considered. Approximate equations that allow clear physical interpretation of the mechanical force, mechanical resonance frequency, and Q factor of the mechanical resonance were obtained. We also compared analysis and experimental results, and show that most of the experimental values were in accord with the calculated values.

Rapid, Precise, and Stable Control of Optical Frequency for SG-DBR LD Using Quartz Etalon

This paper presents rapid, precise, and stable control of optical frequency for sampled-grating distributed Bragg reflector (SG-DBR) laser diode (LD) using a Z-cut quartz etalon supported at the middle point. The optical frequency of SG-DBR LD was controlled by the mode-hop-free three-electrode control method. As a result, stable mode operation and wide continuous tuning range without mode hopping have been realized. A 0.2-ms optical frequency tuning speed with a 4.35-THz tuning range and a 130-MHz control error of the optical frequency was demonstrated. A 1.1-MHz Allan deviation was reached at an integration time of 12 times 103 s.