JPS63136839A - Tuning type optical receiver - Google Patents

Abstract

PURPOSE:To secure a necessary band width and to enable the transmission in high bit rate by using a circuit obtained by connecting plural tuning amplification circuits whose resonance frequencies are different in multistage. CONSTITUTION:A tuning amplification is formed by connecting an amplifier 2 to a tuning circuit consisting of the capacity component of a light receiving terminal 1 and an inductive element 4 and at least one tuning amplifier consisting of the tuning circuit 3 and the amplifier 2 is coutinously connected to the above-mentioned tuning amplifier in order that the resonance (tuning) frequency of the tuning circuit formed with the photodetector 1 including the capacity component and the inductive element and the resonance frequency of the respective tuning circuits 3 are adjusted to be a little different each other. The signal of the resonance (tuning) frequency of the tuning circuit formed with the photodetector 1 including the capacity component and the inductive element 4 is amplified in the amplifier 2 and also the signal of the frequency which is a little different from the above-mentioned one is tuned and amplified in the tuning circuit 3 and the amplifier 2 which are continuously connected. Moreover the signal of the frequency a little different from the former one is tuned and amplified in the tuning circuit 3 and the amplifier 2 which are continuously connected moreover.

Description

[Detailed Description of the Invention] [Summary] An optical receiver used in a coherent optical communication heterodyne detection method is equipped with a plurality of tuned amplifier circuits with different resonance frequencies connected in multiple stages to obtain the required bandwidth and achieve high Enables bit rate transmission.

[Industrial application field]

The present invention relates to a tunable optical receiver used in a coherent optical communication heterodyne detection method. More specifically, the present invention relates to a tunable optical receiver used in a coherent optical communication heterodyne detection method. More specifically, a plurality of tunable amplifier circuits with different resonance frequencies are connected in multiple stages to obtain the required bandwidth and enable high bit rate transmission. This invention relates to a tunable optical receiver.

Communication systems using coherent light are used to transmit large amounts of information at high speed. Particularly in those using a coherent optical communication heterogain detection method, the signal light and the local light are superimposed to form an intermediate frequency signal. For example, if the wavelength of the laser used as the signal light and the local light is adjusted to the order of 1 angstrom, the intermediate frequency will be approximately 10 GHz. Therefore, since the intermediate frequency itself is a very high frequency, a front end of an optical receiver that receives signal light is required to be capable of responding to an extremely high frequency range. If a reception circuit generally used for baseband transmission is used as a front end, an extremely wide band is required. If such a wideband receiving circuit is not used, it is necessary to configure an optical receiver that can pass only the signal spectrum that spreads around the intermediate frequency.

[Conventional technology]

The front end of the optical receiver is, for example, a high-impedance type consisting of a photodetector I, FETl0, and amplifier 2 as shown in Figure 4 (al), or a high-impedance type consisting of a light receiving element I, FETl0, and amplifier 2 as shown in Fig. A transimpedance type with a feedback resistor 5 connected to the gate, or a transimpedance type (
As shown in C), an LC open circuit or the like is used, which includes a coil 6 in parallel with the capacitive component of the light receiving element 1 to form a tuned circuit. The high-impedance type and transimpedance type have frequency characteristics that extend to the DC region, as shown in Figure 3 (bl).On the other hand, the LC-tuned type as a front end has a frequency characteristic that extends to the DC region.
It has frequency characteristics as shown in FIG. 3(C).

[Problem that the invention seeks to solve]

In this conventional method, the frequency characteristics of the high impedance type and transimpedance type are DC.
Since it extends over a wide range, it becomes possible to transmit signals in the intermediate frequency and required frequency bands without distortion, but in order to do so, it was necessary to design the frequency characteristics of the front end to have an extremely wide band. On the other hand, as a front end, L
When a C-tuned type is used, the frequency characteristic has extremely few flat parts. Therefore, when transmission is performed at a high bit rate, the amount of code interference in the output waveform becomes large, resulting in a problem that the S/N ratio decreases.

The present invention was created in view of these points, and an object of the present invention is to provide a same-open type optical receiver suitable for high-node rate transmission.

[Means for solving problems]

FIG. 1 shows a basic block circuit diagram of a tunable optical receiver of the present invention.

In the figure, 1 is a light receiving element including a capacitive component, and 2 is an amplifier. Further, 3 is a tuning circuit consisting of a parallel inductive element and a capacitive element, and 4 is an inductive element. An amplifier 2 is connected to a tuned circuit consisting of a capacitive component of the light receiving element and an inductive element 4 to form a tuned amplifier, and at least one of the tuned circuit 3 and the amplifier 2 is connected to the tuned amplifier 2.
Two tuned amplifiers are connected in cascade. The resonance (tuning) frequency of the tuning circuit formed by the light receiving element 1 including a capacitive component and the inductive element and the resonance frequency of each tuning circuit 3 are adjusted to be slightly different from each other.

Note that in the figure, the light receiving element 1 is illustrated isometrically as including a capacitive component.

[For production]

The amplifier 2 amplifies the signal at the resonant (tuned) frequency of the tuned circuit formed by the photodetector 1 containing a capacitive component and the inductive element 4, and the cascaded tuned circuit 3 and amplifier 2 amplify the signal at the resonant (tuned) frequency. Tuned amplification of signals of different frequencies. Furthermore, the cascade-connected tuning circuit 3 and amplifier 2 further tune and amplify signals of slightly different frequencies. With this, the overall frequency characteristic is as shown by the solid line in Figure 3(a).
It will have the required bandwidth.

〔Example〕

FIG. 2 shows an embodiment of the present invention, in which a bias resistor 7 is shown connected in series with a light receiving element l including a capacitive component.

By connecting the coil 4 in parallel to the bias resistor 7, a first tuned circuit 3 having a resonant frequency determined by the capacitive component of the light receiving element 1 and the inductive component of the coil 4 is formed. An amplifier 2 is connected to this first tuning circuit 3 to constitute a first tuning amplifier. The amplifier 2 is composed of two FETs 4.5, and has a source grounding circuit configuration using the FET 4 and a source follower circuit configuration using the FET 5, making it an amplifier with high input impedance and low output impedance.

This first tuned amplifier 10 has second and third tuned amplifiers having the same configuration.
Tuned amplifiers 12 and 14 are connected.

These tuned amplifiers 12 and 14 each include an LC tuned circuit 3 and an amplifier 2 having the same configuration as the amplifier 2 of the first tuned amplifier 10, and the resonant frequency of each of the LC tuned circuits 3 is The resonant frequency of the tuned circuit 3 of the tuned amplifier 10 of No. 1 is set as a reference, and is set to be slightly different from the resonant frequency of the tuned circuit 3 of the tuned amplifier 10. With such settings, the overall frequency characteristic of the tunable optical receiver of the present invention becomes as shown in FIG. 3(a). This frequency characteristic makes it possible to transmit signal spectrum components near intermediate frequencies necessary for high bit rate transmission. The above-mentioned overall frequency characteristics that enable this high bit rate transmission are determined by the first tuning amplifier 1.
The resonance frequency of 0 is used as a reference, but this is because the capacitance component of the light receiving element 1 takes a value unique to that element. Therefore, the resonant frequencies of the other tuned amplifiers are determined based on the resonant frequency of the first tuned amplifier 10 so as to obtain the above-mentioned overall frequency characteristics. In other words, each L
The capacitance value of the CC equivalent circuit capacitor and the inductance value of the coil are determined. For example, when the resonant frequency of the tuned amplifier 10 is set to the intermediate frequency flF, the inductance of the coil 4 is determined with respect to the capacitance of the light receiving element I. Then, the L of the tuned circuit 3 is set so that the resonant frequency of the tuned amplifier I2 is below the intermediate frequency fTF.
and C are determined, and the tuning circuit 3 is set so that the resonant frequency of the tuned amplifier I4 is above the intermediate frequency ftp.
The values of L and C are determined.

In the example shown in FIG. 2, a two-stage tuned amplifier circuit is used, but it is also possible to configure it with more stages. Also,
The present invention is not limited to an amplification element, and a similar BJT or the like can be used in place of the FET.

Moreover, if an intermediate frequency stage is constructed using a plurality of LC tuning circuits each having different frequency characteristics, an optical receiver with less circuit noise can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the overall frequency characteristics of each stage constituting the optical receiver are made such that the necessary signal spectrum near the intermediate frequency can be transmitted, and therefore high bit rate transmission is possible.

[Brief explanation of the drawing]

Fig. 1 is a principle block circuit diagram of the tunable optical receiver of the present invention, Fig. 2 is a circuit diagram of an embodiment of the present invention, Fig. 3 is a frequency characteristic diagram, Fig. 4 (al to (C1 is a conventional example) This is a circuit diagram. In Fig. 1, 1 is a light receiving element, 2 is an amplifier, 3 is an LC tuning circuit, and 4 is an inductive element (coil). [Ike JIIKB] Zhou He Murder and Figure 3

Claims (2)

[Claims] (1) a light receiving element (1) containing a capacitive component; a tuned amplifier circuit consisting of an inductive element (4) and an amplifier (2) that together with the light receiving element (1) constitute a tuned circuit; and a tuned amplifier circuit connected in series to the tuned amplifier circuit; A tunable optical receiver comprising at least one tunable amplifier circuit connected in parallel and including an inductive element and a capacitive element (3) resonating at a frequency different from the resonant frequency of the tunable amplifier circuit. (2) A bias resistor (7) is provided for applying a bias current to the light receiving element (1), and a coil (4) is connected in parallel to the bias resistor (7) to tune the light receiving element (1) including its capacitive component. A tunable optical receiver according to claim 1, characterized in that a circuit is constructed.