Nec Corporation

Katsumi Emura

Makoto Shibutani

Minoru Shikada

Yoshihiko Suemura

Ikuo Mito

Toshihito Kanai

Junji Namiki

Naoki Shimosaka

Kouichi Minemura

An optical transmission system of an N : 1 or an N:N type is provided, in which there is no deterioration caused by beat noise between signals. A plurality of optical modulators are cascaded in an optical fiber transmission path having a light source and a plurality of light receivers connected to two respective ends of the optical fiber transmission path, and carrier waves having frequencies respectively different are applied to the optical modulators. This enables the light receivers to receive a radio frequency signal in which the carrier waves are frequency-multiplexed. The light receivers receive only the signal beam so that there is no occurrence of beat noise. In another arrangement, at the optical network terminal, a part of a signal beam is split and the split beam is intensity-modulated responsively to carrier waves by an optical modulator and, thereafter, is combined again to a passing beam. It is possible to obtain at the signal beam receiver a received signal in which carrier waves from respective optical network terminals are frequency-multiplexed. This prevents occurrence of inter-modulation distortion in the cascaded optical modulators.

Optical transmission system and optical network terminals used therein

In an optical network comprising terminator nodes (15(A1) etc) assigned with frequency bands for transmitting transmission signals subcarrier-frequency multiplexed on optical signals of a predetermined number of optical wavelengths from one node to at least another, the nodes are grouped into terminator node groups (11(A, B, C)), each assigned with selected wavelengths among the optical wavelengths except a specific wavelength specific thereto. One node group (11(A)) transmits outgoing signals of the selected wavelengths to an analog repeater node (17(A)) for supplying ingoing signals of the specific wavelength to a common optical coupler (13). Supplied as outcoming signals of various wavelengths with such outgoing signals of other node groups (11(B, C)) directed to the coupler, the repeater node supplies the one node group with incoming signals of the specific wavelength. Preferably, the repeater node comprises a photodetector detecting as send-in (receive-in) signals the transmission signals carried on the outgoing (outcoming) signals, bandbass filters for filtering the send-in (receive-in) signals into intermediate signals, frequency converters for the intermediate signals to produce send-out (receive-out) signals according to a demand assign scheme, and a light source producing the ingoing (incoming) signals carrying the send-out (receive-out) signals.

Optical network comprising node groups and an analog repeater node unit

A microcellular mobile radio communication system has a central base station and a plurality of radio base stations interconnected by a shared optical fiber transmission line. In the central and radio base stations, electrical radio signals are frequency-converted to frequencies assigned to the radio base stations and then converted into optical signals. In the central base station, the optical signals are combined for transmission through the optical fiber transmission line to the radio base stations. Alternatively, the frequency-converted electrical radio signals may first be combined and then converted into an optical signal for transmission. In the radio base stations, the electrical radio signals are converted to optical signals, which are combined and transmitted through the transmission line to the central radio station. In each radio base station, the frequency of the radio signal extracted from the received combined signal is frequency-converted to a frequency to be transmitted from its antenna, with the other signals filtered out. The central base station demodulates the received combined signal from the radio base stations into signals for the exchange office. The radio signals in different frequency bands assigned to each radio base station can simultaneously be transmitted through the shared optical fiber transmission lines between the radio and central base stations.

Microcellular mobile communication system

A cellular mobile communication system in which each of one or more cells is provided with a base radio station, and mobile terminals communicate with the base radio stations. Base radio stations (21, 22 and 23) are connected to a central base station (100) by optical fibers. The central base station is connected to a mobile switching center (50). Each of the base radio stations is provided with an O/E converter (201) and E/O converter (207). The O/E converter converts a optical signal containing speech signals and a call connection control signal into RF signals. The E/O converter (207) converts RF signals, received from a mobile terminal (11) via an antenna (204), into optical signals and transmits the optical signals to the central base station. The central base station comprises O/E converters (301-303) for converting optical signals from each base radio station into RF signals; receivers (401-403) for demodulating these RF signals; transmitters (406-408) for converting speech signals and a call connection control signal from the mobile switching center into RF signals; and E/O converters (304-306) for converting these RF signals into optical signals and transmitting the optical signals to a base radio station.

Mobile communication system

When a data transmission request is received in a node apparatus in an optical LAN system, the node apparatus receives a light of a wavelength assigned to a destinated node apparatus. Where the received light is not a modulated light, the received light will be modulated by a transmitting data, and where the received light is a modulated light, the received light is passed through the transmitting node apparatus without a further modulation.

Optical local area network system and node apparatus used in the same

In order to induce a flat frequency modulation response in a multi-electrode semiconductor laser which includes an active region and at least one phase control region with no active layer, a modulation current is applied to both of the active region and the phase control region. Further, an improved electrode arrangement for inducing a flat frequency modulation response in a multi-electrode semiconductor laser is present. The semiconductor laser includes three regions: an active region, a phase control region and a Bragg reflector region. Each of the active region, the phase control region and the Bragg reflector region being provided with an electrode for receiving an injection current, wherein the electrode provided for the active layer extends into the phase control region.

Method and electrode arrangement for inducing flat frequency modulation

A laser (21) is frequency modulated by an electrical modulating signal of a bit rate into a modulated signal of a first and a second modulated frequency. A combination of an optical mixer (27) and an optical detector (31) carries out optical heterodyne or homodyne detection on the modulated optical signal to produce a detected signal having a first and a second frequency component. A component separator (32) is for selecting only one of the components from the detected signal. A detector (33) detects the selected component to produce a demodulated electrical signal representative of the modulating signal. The laser is preferably a semiconductor laser. More preferably, the semiconductor laser is frequency modulated after the modulating signal is converted to a current of an mBnB code sequence. When the bit rate is below and above about 10 Mbit/second, either the modulating signal or the mBnB code sequence current is preferably used in frequency modulating the semiconductor laser after caused to pass through a high-pass and a low-pass filter, respectively.

Coherent optical communication system with FSK heterodyne or homodyne

An optical heterodyne detection pulse receiving system operates such that the light from a local oscillator and from a pulse modulated optical carrier are mixed, and a signal having an intermediate (difference) frequency is extracted. Pulse signal regeneration is effected by demodulating the intermediate frequency signal while maintaining a positive integer multiple of one-half the intermediate frequency signal synchronized with the repeating frequency of the pulse signal.

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Tokyo, Japan

Katsumi Emura