Noritaka Taguchi

Forward Brillouin scattering in holey fibers

Forward Brillouin scattering behavior of a holey fiber (HF) is investigated experimentally. The shear and longitudinal acoustic velocities are evaluated from measurements of forward and backward Brillouin scattering, respectively. Experimentally obtained results reveal that the acoustic velocity ratio, given as /spl alpha/ (=shear velocity V/sub S//longitudinal velocity V/sub L/), decreases as the ratio of the total air-hole area to fiber cross-sectional area becomes large. This means that increasing the air-hole area in an HFs cross section lowers the shear velocity with respect to the mixed tortional-radial (TR/sub 2m/) modes.

A predistortion-type equi-path linearizer designed for radio-on-fiber system

A predistortion-type equi-path linearizer is created for a radio-on-fiber system based on wide-band code division multiple access; its main benefit is its simple optical circuit configuration. Experiments show that the phase difference between the carrier and third-order intermodulation (IM3) component of the laser diodes (LDs) is shifted by around 90/spl deg/ from that of the RF amplifier. To our knowledge, this is the first report to describe this phase shift, which is observed with both Fabry-Perot and distributed-feedback LDs. To counter this shift, we use additional phase shifters. The proposed design places a pre-amplifier between the linearizer and LD for lower power consumption and better insertion gain at the linearizer. Experimental and calculated results agree well, and more than 20-dB improvement in the IM3 components is obtained over the bandwidth of 60 MHz. The linearizer works well in the temperature range of 10/spl deg/C to 40/spl deg/C with a simple control circuit.

Frequency multiplexing technique for relative-intensity-noise reduction

A 10 dB relative-intensity-noise reduction is achieved by a novel scheme that multiplexes local-oscillation frequency and intermediate frequencies. Simulations conducted to evaluate relative-intensity-noise levels match well the experimentally obtained data.

Distortion Reduction Filters for Radio-on-Fiber System

Three distortion reduction filters for radio-on-fiber systems are proposed and evaluated from the standpoint of improvements in in-band third order Intel-modulation (IM3) components (spurious components), insertion loss, temperature stability and so on. The basic filter configuration includes optical comb filter, RF (radiowave frequency) comb filter, and RF dual band rejection filter (DBRF). Experiments are conducted at 2 GHz band for frequency separation Δf=5 MHz and 100 MHz in the temperature range of -10°C to +50°C. These filters can reduce IM3 components even in the saturation region, unlike conventional linearizers. An optical comb filter can reduce IM3 components more than 20 dB and noise level around 10dB if its polarization controller is properly adjusted, but its insertion loss is large and stability against vibration is very poor. The proposed RF comb filter and RF-DBRF can reduce IM3 components by more than 20 dB and noise level by more than 3 dB. Their stability against vibration and temperature change is good, and insertion losses are 1-2 dB for Δf= 100 MHz.

Distortion Evaluation of Frequency-Converted Radio-on-Fiber System Employing RIN Reduction Technique

The distortion characteristics of a radio-over-fiber (ROF) system that uses the relative intensity noise (RIN) reduction technique is investigated in detail. The third-order intermodulation (IM3) and spurious free dynamic range (SFDR) characteristics of this system are measured using multi-reflection configurations. It is observed that the maximum deterioration in IM3 is 4 dB. However, SFDR is improved by 7 dB as CNR exceeds 12 dB. Moreover, we measure the adjacent channel leakage power ratio (ACLR) characteristics of this system in the multi-carrier transmission condition. The RIN reduction technique yields an ACLR improvement of 4.5 dB

Relative-intensity-noise reduction technique for frequency-converted radio-on-fiber system

A radio-on-fiber system is proposed that uses a frequency-multiplexing technique to reduce the relative intensity noise (RIN) caused by reflections at optical fiber connectors. It is based on the simultaneous transmission of IF and local oscillation (LO) frequency. Optimum LO frequency and optical modulation index that minimize RIN are investigated by experiments and calculations assuming the double and multiple reflection situations. The results agree well and RIN reduction of 17 dB is obtained in multiple reflection situations.