GB2310555A

GB2310555A - Temperature insensitive regenerative optical receiver

Info

Publication number: GB2310555A
Application number: GB9703935A
Authority: GB
Inventors: Toshifumi Shine
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1996-02-26
Filing date: 1997-02-26
Publication date: 1997-08-27
Anticipated expiration: 2017-02-26
Also published as: JP2962219B2; FR2745452A1; GB2310555B; GB9703935D0; JPH09233028A

Abstract

The light-receiving apparatus comprises a light-receiving module 1 which converts an optical signal into an electrical signal. Amplifiers then amplify 2 and reshape 3 the electrical signal. Next, a timing circuit 7-9 and 11 extracts a clock signal from the amplified signal. Meanwhile, a delay line 6 adjusts the phase of the amplified signal to match that of the clock signal. Finally, a decision circuit 4 outputs a regenerated data signal based on the clock signal. The bandpass filter 9 and the delay line 6 are both surface acoustic wave (SAW) based devices, formed on substrates made of the same piezoelectric material. Both devices therefore have generally the same phase fluctuation characteristics with respect to ambient temperature change. Consequently, the light receiving sensitivity of the receiver is not adversely affected by temperature fluctuation. The apparatus can be used as part of a repeater system.

Description

A LIGHT-RECLIVING APPARATUS FOR USE IN F3ER OPTIC COMMUNICATION The present invention relates to a light-receiving apparatus and, more particularly, to a light-receiving apparatus having so-called 3R capabilities for use in fiber optic communication.

Some devices used for repeaters in conventional digital signal transmission systems have three basic capabilities; reshaping in which a distorted received waveform is amplified and shaped again into its original waveform, retiming in which phase information is regenerated from the received signal, and regenerating in which binary information is identified from the reshaped waveform by the regenerated phase information to regenerate a pulse signal (these capabilities are called the 3R capabilities).

In a light-receiving apparatus having the above-mentioned 3R capabilities, a light-receiving module converts a received optical signal into an electrical signal, which is amplified by an equalizing amplifier to a certain voltage level for reshaping and outputs a resultant signal. A timing circuit extracts a clock signal from the signal outputted from the equalizing amplifier. A delay line adjusts the phase of the clock signal and inputs the phase-adjusted clock signal in a decision circuit. The decision circuit, based on the phase-adjusted clock signal, regenerates the signal outputted from the above-mentioned amplifier as a data signal.

Normally, the phase of the clock signal outputted from the timing circuit is shifted from the phase of the signal directly outputted from the amplifier. Therefore, the delay line adjusts the phase of the clock signal so as to match that phase with the phase of the signal outputted from the amplifier.

However, in prior-art light-receiving apparatuses, the phase of the clock signal outputted from the timing circuit varies with the change in ambient temperature. This is because the characteristics of the bandpass filter in the timing circuit is temperature-dependent. The shifting of the clock-signal phase from a predetermined level deteriorates the light-receiving sensitivity of the light-receiving apparatus.

It is therefore an object of at least the preferred embodiment of the present invention to provide a light-receiving apparatus of whose light-receiving sensitivity will not be deteriorated by ambient-temperature change.

Accordingly, in a first aspect the present invention provides a light-receiving apparatus for use in fiber optic communication comprising: light-receiving means for converting a received optical signal into an electrical signal; amplifying means for amplifying said electrical signal outputted from said light-receiving means; timer means for extracting a clock signal from an amplified signal outputted from said amplifying means; delay means for adjusting a phase of said amplified signal outputted from said amplifying means; and means for regenerating a signal outputted from said delay means as a data signal based on said clock signal.

In a preferred embodiment of the present invention the light-receiving apparatus comprises a light-receiving section for receiving an optical signal and converting -he received optical signal into an electrical signal and an amplifier for amplifying the electrical signal outputted from the light-receiving section. A timing circuit has a bandpass filter to extract a clock signal from the amplified signal outputted from the amplifier. A delay line makes adjustment such that the phase of the amplified signal matches the phase of the extracted clock signal. The delay line has a phase fluctuation characteristic that is approximate to that of the bandpass filter against temperature change. Based on the above-mentioned clock signal, a decision circuit regenerates the signal outputted from the delay line as a data signal.

Each of the bandpass filter and the delay line can be constituted by a device based on SAW. Also, it is desired that each of these devices use a piezoelectric substrate made of a same material; for example, crystal, lithium niobate, or lithium tantalate.

In the above-mentioned novel light-receiving apparatus, constituting both the bandpass filter and the delay line by SAW devices using substrates of the same piezoelectric material causes the phase of the clock signal outputted from the bandpass filter and the phase of the data signal outputted from the delay line to present virtually the same fluctuation against ambient-temperature change. This prevents the light-receiving sensitivity of the light-receiving apparatus from being deteriorated by ambient-temperature change.

Preferred features of the present invention will now be described, purely by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a block diagram illustrating a constitution of a prior-art light-receiving apparatus; and FIG. 2 is a block diagram illustrating a constitution of a light-receiving apparatus practiced as one preferred embodiment of the present invention.

First, a prior-art light-receiving apparatus will be described for the purpose of comparison with the present invention. Referring to FIG. 1, an optical signal is converted by a light-receiving module 1 into an electrical signal. The preamplifier 2 amplifies the electrical signal.

An equalizing amplifier 3 further amplifies the signal outputted from the preamplifier 2 to a certain voltage amplitude, reshapes the amplified signal, and outputs the resultant signal. The signal outputted from the equalizing amplifier 3 is inputted in a decision circuit 4 and a timing circuit 5. The timing circuit 5 extracts a clock signal from the reshaped signal. The extracted clock signal is inputted in a delay line 10. The delay line 10 adjusts the phase of the clock signal. Based on the phase-adjusted clock signal, the decision circuit 4 regenerates the signal outputted from the equalizing amplifier 3 as a data signal and outputs the same. However, due to ambient-temperature change, the phase of the clock signal outputted from the delay line is shifted from the previously adjusted state, thereby deteriorating the light-receiving sensitivity of this light-receiving apparatus.

The following describes, by way of example, a constitution of a light-receiving apparatus practiced as one preferred embodiment of the present invention wherein the above-mentioned problem has been solved, with reference to FIG. 2.

The above-mentioned embodiment has a light-receiving module 1 for receiving an optical signal and converts the received optical signal into an electrical signal. The light-receiving module 1 is connected to a preamplifier 2, which is connected to an equalizing amplifier 3. A signal outputted from the equalizing amplifier 3 is inputted in a delay line 6 based on surface acoustic wave (hereinafter referred to as SAW) and a differential circuit 7. The differential circuit 7 is connected to a rectifying circuit 8, which is connected to a bandpass filter 9 constituted by a SAW filter, which is connected to a limiting amplifier 11 in series. The differential circuit 7, the rectifying circuit 8, the SAW bandpass filter 9, and the limiting amplifier 11 constitute a timing circuit. The SAW delay line 6 and the limiting amplifier 11 are connected to a decision circuit 4.

The above-mentioned delay line 6 and bandpass filter 9 are known devices, both being based on SAW. Each of these devices is fabricated by forming interdigital electrodes on a substrate of a same piezoelectric material to make the formed electrode function as the delay line or the bandpass filter. The piezoelectric material is crystal, lithium niobate (LiNbO3), lithium tantalate (tiTaO3) or the like.

The SAW delay line 6 and the SAW bandpass filter 9 may also be formed on a same substrate.

The following describes the operation of the above-mentioned embodiment. First, an optical signal is received by the light-receiving module 1 to be converted into an electrical signal. The optical signal is an optical pulse signal of 1.5-micron band, a bit rate of 300 megabits/second, and NRZ-coded, by way of example. The preamplifier 2 amplifies the electrical signal. The equalizing amplifier 3 further amplifies the amplified signal outputted from the preamplifier 2 to a certain voltage amplitude, reshapes the resultant signal, and outputs the same as data signals. One data signal outputted from the equalizing amplifier 3 is inputted in the differential circuit 7 which constitutes the timing circuit.

The differential circuit 7 and the rectifying circuit 8 perform waveform processing on the inputted signal. The resultant signal is then inputted in the SAW bandbass filter 9. The signal outputted from the SAW bandpass filter 9 is inputted in the limiting amplifier 11 to be outputted as a clock signal. The clock signal is then inputted in the decision circuit 4. On the other hand, the other data signal outputted from the equalizing amplifier 3 is inputted in the SAW delay line 6. The SAW delay line 6 adjusts the phase of the inputted signal to provide an optimum phase condition for the clock signal outputted from the limiting amplifier 11. The delay line thus operating may be adjusted either at the time of designing the same or at the time of assembling the same on the light-receiving apparatus. The decision circuit 4, based on the clock signal, regenerates the signal of which phase has been adjusted by the SAW delay line 6 and outputs the regenerated signal as a data signal.

The bandpass filter 9 and the delay line 6 are both based on SAW and are formed on the substrates made of the same piezoelectric material. Consequently, if the phase of the clock component outputted from the SAW bandpass philter 9 fluctuates due to ambient-temperature change, the phase of the signal outputted from the SAW delay line 6 fluctuates in generally the same direction and in generally the same manner. This maintains the pre-adjusted optimum phase condition of both the signals unchanged if an ambient-temperature change occurs, thereby preventing the light-receiving sensitivity of the light-receiving apparatus from being deteriorated.

While the presentation has been described in connection with a certain preferred embodiment, it is to be understood that the subjects matter encompassed by the present invention is not limited to the specific embodiment. On the contrary, it is intended to include all alternatives, modifications, and equivalents as can be included within the scope of the following claims.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

The text of the abstract filed herewith is repeated here as part of the specification.

The light-receiving apparatus has a bandpass filter and a delay line each based on surface acoustic wave (SAW). In operation, a light-receiving module converts an optical signal into an electrical signal. An amplifier amplifies the electrical signal.

A timing circuit extracts a clock signal from the amplified signal. Meanwhile, a delay line adjusts the phase of the amplified signal to that of the clock signal. A decision circuit regenerates a data signal based on the clock signal and outputs the regenerated data signal. The bandpass filter and the delay line are formed on the substrates made of the same piezoelectric material and use SAW, presenting generally the same phase fluctuation characteristic for ambient temperature change. Consequently, the lightreceiving sensitivity of the novel light-receiving apparatus will not be adversely affected by temperature fluctuation.

Claims

1. A light-receiving apparatus for use in fiber optic communication comprising: light-receiving means for converting a received optical signal into an electrical signal; amplifying means for amplifying said electrical signal outputted from said light-receiving means; timer means for extracting a clock signal from an amplified signal outputted from said amplifying means; delay means for adjusting a phase of said amplified signal outputted from said amplifying means; and means for regenerating a signal outputted from said delay means as a data signal based on said clock signal.

2. The light-receiving apparatus for use in fiber optic communication as claimed in Claim 1, wherein said timer means comprises a bandpass filter and the temperature variation of a phase fluctuation characteristic of said delay means is substantially equal to that of said bandpass filter.

3. The light-receiving apparatus for use in fiber optic communication as claimed in Claim 2, wherein said bandpass filter is a surface acoustic wave filter and said delay means is a surface acoustic wave delay line.

4. The light-receiving apparatus for use in fiber optic communication as claimed in Claim 3, wherein said bandpass filter and said delay line are formed from the same material.

5. The light-receiving apparatus for use in fiber optic communication as claimed in Claim 4, wherein said same material is selected from crystal, lithium niobate and lithium tantalate.

6. A light-receiving apparatus for use in fiber optic communication substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawings.