T. Hoshida

Nonlinear photodetection scheme and its system applications to fiber-optic millimeter-wave wireless down-links

We report on our study on the nonlinear photodetection (NL-PD) scheme, which we have proposed and demonstrated as an extremely simple configuration for the optoelectronic millimeter-wave (MM-wave) mixing. The topics described in this paper are as follows: (1) advantageous optical MM-wave link architectures employing the NL-PD techniques; (2) operation principle of NL-PD; (3) detailed characterization of optoelectronic MM-wave mixer properties of a waveguide p-i-n photodiode; (4) experimental demonstration of NL-PD performance in analog and digital fiber-optic MM-wave transmission over a 30 km single-mode fiber; and (5) proposal of its possible applications to fiber-optic MM-wave wireless down-links, such as passive antenna base stations and coax-wireless-hybrid fiber-optic CATV systems.

Subharmonic hybrid mode-locking of a monolithic semiconductor laser

Performance of a subharmonically hybrid mode-locked (SH-ML) monolithic semiconductor laser is investigated. A 33-GHz passively mode-locked distributed Bragg reflector semiconductor laser is stabilized by the injection of an electrical signal with a subharmonic frequency of the laser cavity resonance. Systematic measurements on the phase noise, timing jitter, amplitude modulation, and locking bandwidth are performed for the second- and third-order SH-ML conditions, and the results are compared with the fundamental hybrid mode-locking (FH-ML) case. Low timing jitter of less than 0.6 ps, comparable to that under the FH-ML case, is achieved for the both SH-ML cases. The amplitude modulation imposed by the subharmonic driving frequencies is found to be very small (<-24 dBc) for the second-order SH-ML because of the sufficiently low modulation response of the laser at 16.5 GHz. The third-order SH-ML is found to exhibit a very unique locking characteristics, leading to a maximum locking bandwidth of 56 MHz that is even larger than that for the FH-ML case.

Extremely low-amplitude modulation in a subharmonically hybrid mode-locked monolithic semiconductor laser

Negligibly small amplitude modulation and sufficiently low timing jitter are achieved simultaneously in a passively mode-locked monolithic semiconductor laser stabilized by applying an electrical signal at the second subharmonic of the pulse repetition frequency. Nearly transform-limited 33 GHz pulse trains with 0.56 ps timing jitter and -23 dBc amplitude modulation are obtained with 23 dBm driving signals at 16.5 GHz. Detailed investigations are carried out on the dependence of the amplitude modulation and timing jitter on RF driving power for the second- and third-order subharmonic cases. The excellent amplitude modulation property of the second subharmonic case with the specific laser used in this work is ascribed to the frequency response characteristics of the device.

Broad-band millimeter-wave upconversion by nonlinear photodetection using a waveguide p-i-n photodiode

We propose and demonstrate the nonlinear photodetection technique for broad-band fiber-optic millimeter-wave distribution systems. An unmodulated millimeter-wave carrier and intermediate frequency (IF) signals on separate optical carriers are delivered to a single photodetector, where they are O/E converted and mixed simultaneously to generate radio frequency (RF) signals. It is demonstrated that a mixing bandwidth broader than 2 GHz and a spurious-free dynamic range higher than 90-dB/spl middot/Hz/sup 2/3/ are achieved for millimeter-wave frequency at 66 GHz. In the experiment, the nonlinear photodetection is realized by using a commercially available waveguide p-i-n photodiode under its saturation condition.

Generation of frequency/phase-modulated millimeter-wave subcarrier signals with a subharmonically hybrid mode-locked monolithic semiconductor laser

Novel methods are proposed and demonstrated for the generation of angle-modulated millimeter-wave optical signals; use of a monolithic semiconductor laser under subharmonic hybrid mode-locking conditions provides a compact and efficient scheme for frequency and phase modulation of subcarriers.

Passively Mode-Locked Semiconductor Lasers Stabilized by Subharmonic Electrical Injection and Their Application to Millimeter Wave Photonics

A review is presented, based on our experimental and theoretical works, of mode-locked monolithic semiconductor lasers with optical pulse train output stabilized by the subharmonic electrical injection and their performance in the millimeter wave photonic application. The following issues are emphasized: (1) the novel method of pulse train stabilization and its mechanism, (2) the application of a mode-locked semiconductor laser as an optical mm-wave oscillator and (3) the unique functionality in the compact optical mm-wave transmitter applications.

Millimeter-wave Upconversion By Nonlinear-photodetection Using A Carrier Generated From A remote Mode-locked Semiconductor Laser

We propose and demonstrate a scheme for upconversion of [F subcarrier signals with a millimeter-wave carrier using nonlinear photodetection and remote carrier supply. In a preliminary experiment, the former is realized by using ,a commercially available photodiode under its saturation condition, and the latter is provided by a suibharmonically hybrid mode-locked semiconductor laser. It is demonstrated that a 66-GHz carrier generated from the mode-llocked laser and 400-MHz subcarriers of IF laser output are successfully mixed after transmission over a 30-km non-dispersionshifted optical fiber.

Generation and RF Phase-Shifting of Millimeter-Wave Subcarriers Using a Hybrid Mode-Locked Monolithic Semiconductor Laser.

A method for generation and RF phase-shifting of millimeter-wave subcarrier signals using a single monolithic semiconductor laser device is proposed and demonstrated. Under fundamental or subharmonic hybrid mode-locking conditions, the optical cavity length of the laser is modulated by the thermo-optic effect in the passive waveguide section. As a result, the timing of the generated 33 GHz output optical pulse train was successfully varied over 10 ps, corresponding to phase-shifts over 2.7 and 5.3 rad for 33 and 66 GHz subcarriers, respectively. The mechanism of the RF phase-shift is explained by analogy with the injection-locked electrical oscillator.

Locking characteristics of a subharmonically hybrid mode-locked multisection semiconductor laser

Locking characteristics of a subharmonically hybrid mode-locked (SH-ML) semiconductor laser are investigated experimentally. The locking bandwidths under the second- and third-order SH-ML operation, as well as under fundamental hybrid mode-locking (FH-ML) condition, are characterized with a variety of microwave power and reverse bias voltage applied to the saturable absorber of the laser. Unique locking characteristics are observed for the third-order SH-ML where the locking bandwidth increases with increasing reverse bias, which is opposite to the FH-ML case. This leads to a locking bandwidth of 56 MHz, 2.3 times broader than that for the FH-ML under the shortest pulse condition.

Seamless integration of fiber optic networks and millimeter-wave wireless access using nonlinear photo-detection scheme

It would be attractive if the functionality of millimeter-wave (mm-wave) wireless transmitters could be integrated in an existing fiber optic access network for signal transmission of baseband and/or intermediate frequencies. It would be further desired if one were able to utilize the optical signals in the network without any O/E or E/O conversions. We have pointed out that such seamless integration of mm-wave wireless accessibility to a fiber optic system can be implemented by the mm-wave photonic methods such as the optical feeding technique of mm-wave signals from distant local oscillators and the optoelectronic mixing technique at the photo-detection stage in an antenna base station. Furthermore, we have proposed and demonstrated experimentally that the requirement on the base station components for the seamless integration can be drastically relaxed by employing a novel optoelectronic mixing technique called nonlinear photo-detection.