JPH10290213A - Optical communication device, optical communication equipment, optical communication system and optical spectral analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength multiplex optical transmission technology which is excellent in mount performance and excellent in anti-fluctuation performance of a transmission wavelength and a reception wavelength due to a change in ambient temperature. SOLUTION: The system is made up of a wavelength multiplex optical transmitter 101 that multiplexes lights with a plurality of different wavelength bands, an optical fiber 102 that sends an optical signal L106 subject to wavelength multiplex, and an optical receiver 300 having an optical communication device 380 that extracts and demodulates the optical signal L106 propagated through the optical fiber 102 for each optical signal of each wavelength. The optical communication device 380 is of multi-stage configuration where (a) plurality of electric field absorbing modulation elements 36a, 36b,..., 36n connected in series and reverse bias voltages V1, V2,..., Vn higher toward the post-stages are applied to the electric field absorbing modulation elements 36a, 36b,..., 36n respectively with a reverse bias supply circuit 113.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical communication device, an optical communication apparatus, and an optical communication system used in a digital or analog optical communication system using an optical fiber.

[0002]

2. Description of the Related Art In an optical transmission system using an optical fiber as a main transmission medium, as one means for increasing the transmission capacity per core, a plurality of laser beams having different wavelengths are superimposed and the multiplexed light is obtained. There is a wavelength-division multiplexing optical transmission system for transmitting different signals simultaneously by transmitting signals through a single-core optical fiber.

In this wavelength multiplexed optical transmission, it is necessary for a receiving section to select an optical signal of a desired channel wavelength from an optical signal of another wavelength. If the selection of the desired optical signal is insufficient, the optical signal of another wavelength leaks, and the transmission characteristics deteriorate. Therefore, in order to maintain stable transmission characteristics, the stability of the wavelength of the transmission signal in the transmission section and the stability of the wavelength selection in the reception section, and the wavelength of the transmission signal and the signal selected in the reception section, The consistency with the wavelength is important.

[0004] In the optical transmission system, when the received light level fluctuates, the transmission characteristics fluctuate. When an optical fiber amplifier is used in a wavelength-division multiplexed optical transmission system, if the number of wavelengths of the multiplexed optical signal changes, the output level per wavelength generally changes. Transmission characteristics are affected.

Therefore, in an optical fiber amplifier used in a wavelength division multiplexing optical transmission system, the output level is usually monitored at a specific wavelength, and when the output level of the monitored wavelength fluctuates due to a change in the number of wavelengths, Control is performed such that the output level per wavelength is automatically maintained at a predetermined value by adjusting the excitation light power or the like.

Conventional optical receivers 1401, 21A, 21
, 21N are generally tunable optical filters 1402, 161a, 161 as shown in FIGS.
, 161n and the photodiode 64, the wavelength-multiplexed optical signals L106, L20a, L2
, L20n, and an optical signal of a desired wavelength is selected and demodulated.

Also, in a conventional optical fiber amplifier, as shown in FIG.
The monitor light is demodulated by a combination of the photodiode and the photodiode 64.

A conventional wavelength multiplexing optical transmitter 1700
, The transmission laser light sources 9a, 9b,..., 9n are transmitted by a laser light source driving circuit 805A as shown in FIG.
Is simply driven.

[0009]

However, in the transmission section of the conventional wavelength division multiplexing optical transmission system, the emission wavelength of the laser diode is deviated from the initial one due to a change in the ambient temperature, aging, and the like. When the transmission center wavelength of the optical filter for selecting the wavelength shifts due to a change in the ambient temperature or the like, there is a problem that light from a nearby wavelength leaks to deteriorate transmission characteristics.

In addition, by using an optical fiber amplifier in a wavelength division multiplexing transmission system, in a system having a function to stabilize the output for each wavelength based on a monitoring wavelength, the output stabilization control function when the monitoring wavelength itself is cut off. There was a problem that it would not be.

Also, the receiving section of the wavelength division multiplexing optical transmission system requires an optical branching means such as a coupler, an optical filter for the number of wavelengths corresponding to each wavelength, and a photodiode for the number of wavelengths, which is inferior in mountability. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has excellent mountability, excellent fluctuation resistance of a transmission wavelength and a reception wavelength due to a change in ambient temperature or the like. It is an object of the present invention to obtain an optical communication device, an optical communication apparatus, an optical communication system, and an optical spectrum analyzer according to a wavelength division multiplexing optical transmission technology capable of realizing an output stabilizing function that does not depend on a wavelength with high reliability.

[0013]

In order to achieve the above object, an optical communication device according to the present invention provides an optical wavelength multiplexing transmission system using an optical signal obtained by multiplexing lights of a plurality of different wavelengths. An optical communication device used for an optical signal, which is arranged in series along the traveling direction of the optical signal and absorbs an optical signal having a wavelength shorter than a wavelength corresponding to a reverse bias potential to be applied. A plurality of electroabsorption types that are capable of demodulating at the same time, transmitting optical signals having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, and applying a higher reverse bias potential toward a later stage. It has a modulation element.

According to the present invention, of the optical signals incident on the optical communication device, an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential is absorbed by the electro-absorption type modulation element. An optical signal having a longer wavelength than that passes through the electro-absorption type modulation element and enters a later-stage electro-absorption type modulation element. Of the optical signals incident on the latter electro-absorption modulator, those having a wavelength shorter than the wavelength corresponding to the reverse bias potential applied to the electro-absorption modulator are absorbed by the electro-absorption modulator. The optical signal having a longer wavelength is transmitted through the electro-absorption modulator, and is incident on the electro-absorption modulator further downstream.

An optical communication device according to the next invention is characterized in that
The two electroabsorption type modulation elements are arranged in front and behind.

According to the present invention, an optical signal having a shorter wavelength than a desired wavelength among optical signals incident on an optical communication device is absorbed by the preceding electroabsorption modulator, and an optical signal having a longer wavelength than that. Is transmitted through the preceding electro-absorption type modulation element and enters the latter electro-absorption type modulation element. Of the incident optical signals, an optical signal having a desired wavelength to be demodulated is absorbed by a subsequent electro-absorption modulator, and an optical signal having a longer wavelength is transmitted through the subsequent electro-absorption modulator.

An optical communication device according to the next invention is one in which a number of the electroabsorption type modulation elements corresponding to the number of multiplexed wavelengths are arranged before and after.

According to the present invention, of the optical signals incident on the optical communication device, an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential is absorbed by the electro-absorption modulation element. An optical signal having a longer wavelength than that passes through the electro-absorption type modulation element and enters a later-stage electro-absorption type modulation element. Of the optical signals incident on the latter electro-absorption modulator, those having a wavelength shorter than the wavelength corresponding to the reverse bias potential applied to the electro-absorption modulator are absorbed by the electro-absorption modulator. The optical signal having a longer wavelength is transmitted through the electro-absorption modulator, and is incident on the electro-absorption modulator further downstream.

An optical communication apparatus according to the next invention is used in an optical wavelength division multiplexing transmission system in which an optical signal obtained by multiplexing lights of a plurality of different wavelengths is split in a transmission path thereof. An optical communication device for receiving an optical signal, wherein the optical communication device is arranged in series along the traveling direction of the incident optical signal, and absorbs an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential. In addition to being capable of demodulation into an electric signal, it is also capable of transmitting an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, and a higher reverse bias potential can be applied to the subsequent stage than to the preceding stage. An optical communication device having a pair of front and rear electro-absorption modulation elements; and a reverse bias supply to which a pair of electro-absorption modulation elements can be applied with a higher reverse bias in a later stage than in a preceding stage. It is intended to and a circuit.

According to the present invention, an optical signal in which light of a plurality of different wavelengths is multiplexed is split into a plurality of signals, and the optical signals are converted into an optical communication device having a pair of front and rear electro-absorption modulation elements. Each of the optical signals is incident, and an optical signal of a desired wavelength is extracted and demodulated in each optical communication device.

An optical communication device according to another aspect of the present invention is an optical communication device for receiving an optical signal obtained by multiplexing light of a plurality of different wavelengths, and is arranged in series along the traveling direction of the incident optical signal. And an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential can be absorbed and demodulated into an electric signal, and the wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength can be demodulated. Optical communication device comprising three or more electroabsorption modulation elements capable of transmitting the optical signal of And a reverse bias supply circuit capable of applying a reverse bias of a higher potential toward a later stage so as to absorb one wavelength at a time.

According to the present invention, an optical signal in which light of a plurality of different wavelengths is multiplexed is demodulated by extracting one wavelength at a time by three or more stages of electroabsorption modulation elements.

An optical communication device according to the next invention is an optical communication device used as an optical fiber amplifier for amplifying an optical signal formed by multiplexing light of a plurality of different wavelengths, comprising: a rare earth-doped optical fiber; A pumping laser light source for exciting the rare-earth-doped optical fiber; light-synthesizing means for emitting light emitted from the pumping laser light source into the rare-earth-doped optical fiber to synthesize an optical signal propagating in the fiber; and the amplifier. Light branching means for branching a part of the light that can be emitted, and a wavelength shorter than a wavelength corresponding to the applied reverse bias potential, arranged in series along the traveling direction of the light branched by the light branching means. And can demodulate it into an electric signal by absorbing the optical signal of the same wavelength, and can transmit an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength. An optical communication device having a pair of front and rear electro-absorption modulation elements to which a higher reverse bias potential can be applied in a later stage, and a disconnection of an optical signal of a predetermined wavelength selected by the optical communication device is detected. And a reverse bias control that can apply a reverse bias of a higher potential to the pair of electro-absorption modulation elements in a later stage than in a preceding stage based on a detection result of the monitored wavelength slice detection circuit. A driving circuit for controlling the driving power of the laser light source for excitation according to a demodulated electric signal of the device for optical communication.

According to the present invention, out of the light branched from a part of the output optical signal, a monitor signal having a predetermined wavelength is extracted by the optical communication device having a pair of electro-absorption modulation elements. And demodulate.

An optical communication apparatus according to the next invention is an optical communication apparatus for receiving an optical signal obtained by multiplexing light of a plurality of different wavelengths, and is arranged in series along the traveling direction of the incident optical signal. And an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential can be absorbed and demodulated into an electric signal, and the wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength can be demodulated. An optical communication device including a pair of front and rear electro-absorption modulation elements capable of transmitting an optical signal of the same type and capable of applying a higher reverse bias potential to the latter stage than the former stage, and light transmitted through the optical communication device. A photodiode for receiving a signal; a wavelength variation detection circuit for detecting a wavelength variation of a received signal based on an output signal of the photodiode and a demodulated electric signal of the optical communication device; The pair of electric field absorption type modulator element based on a detection result of the length variation detection circuit is configured to and a reverse bias control circuit towards the stage after the preceding stage can apply a high reverse bias voltage.

According to this invention, the wavelength shift of the light emitted from the laser light source is detected, and the reverse bias potential applied to the pair of electroabsorption modulation elements of the optical communication device is controlled according to the shift amount. Controls the reception wavelength band.

An optical communication apparatus according to the next invention is an optical communication apparatus for transmitting an optical signal obtained by multiplexing light of a plurality of different wavelengths, wherein the plurality of lasers respectively emit optical signals of a plurality of different wavelengths. A light source, light branching means for branching a part of the multiplexed optical signal of each of the emitted lights of the laser light source, and are arranged in series along the traveling direction of the light branched by the light branching means, and are applied. Optical signal having a wavelength shorter than the wavelength corresponding to the reverse bias potential can be absorbed and demodulated into an electrical signal, and the optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength can be transmitted. A device for optical communication comprising a pair of front and rear electro-absorption modulation elements capable of applying a higher reverse bias potential at the rear stage than at the front stage and a pair of electro-absorption modulation devices at the rear stage of the front stage. of A reverse bias control circuit capable of applying a reverse bias of a high potential, a timing generation circuit for transmitting a timing signal to periodically adjust a wavelength band received by the optical communication device to each signal wavelength to the reverse bias control circuit; A signal light power information processing circuit capable of adjusting an output of each of the laser light sources based on a demodulated electric signal of light of each signal wavelength received by the optical communication device.

According to the present invention, a part of the output optical signal is branched, and the demodulated electric signal is periodically measured by the optical communication device. Stabilize the light wavelength and output level of the trusted laser light source.

An optical communication device according to the next invention is an optical communication device for transmitting an optical signal obtained by multiplexing light of a plurality of different wavelengths, wherein the plurality of lasers respectively emit optical signals of a plurality of different wavelengths. A light source, a plurality of variable optical attenuators respectively connected to the output units of the plurality of laser light sources, an optical branching unit for branching a part of an optical signal in which each emitted light of the laser light source is multiplexed; The optical signal is arranged in series along the traveling direction of the light branched by the means, and is capable of absorbing an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential and demodulating it into an electric signal. A pair of front and rear electro-absorption modulators capable of transmitting an optical signal having a wavelength corresponding to the reverse bias potential and a wavelength longer than the wavelength, and capable of applying a higher reverse bias potential in the subsequent stage than in the preceding stage. An optical communication device, a reverse bias control circuit capable of applying a reverse bias having a higher potential in the latter stage than in the former stage to the pair of electro-absorption modulation elements, and each transmission demodulated by the optical communication device. An attenuator control drive circuit for controlling the variable optical attenuator based on the signal power of the wavelength.

According to the present invention, a part of the optical signal to be output is branched, the demodulated electric signal is measured by the optical communication device, and the optical level of each signal wavelength periodically measured based on the signal is detected. The light output for each wavelength is flattened according to the light level.

An optical communication device according to the next invention has two different
An optical communication device for receiving an optical signal in which two wavelengths of light are multiplexed, the optical communication device being arranged in series along the traveling direction of the incident optical signal, and having a wavelength higher than the wavelength corresponding to the applied reverse bias potential. It is capable of absorbing an optical signal having a short wavelength and demodulating it into an electric signal, and transmitting a wavelength corresponding to the applied reverse bias potential and an optical signal having a wavelength longer than the wavelength. An optical communication device including a pair of electro-absorption modulation elements to which a bias potential can be applied, and a timing of a transmission signal based on a demodulated electric signal of a first wavelength demodulated by a preceding electro-absorption modulation element. A reverse bias information control circuit to be extracted;
A reverse bias control circuit capable of applying a higher reverse bias to the pair of electro-absorption modulation elements in the latter stage than in the preceding stage based on the timing signal extracted by the reverse bias information control circuit. It is.

According to the present invention, the optical signal of the wavelength λ1 modulated by the signal of the first transmission rate and the wavelength λ2 modulated by the signal of the second transmission rate corresponding to the multiplication of the first transmission rate An optical communication device demodulates an optical signal having a wavelength of λ1 from an optical signal obtained by multiplexing light of two wavelengths of an optical signal of (λ1 <λ2), extracts a timing of a transmission signal, and extracts a wavelength based on the timing. The optical signal of λ2 is demodulated.

[0033] An optical communication system according to the next invention comprises an encrypted optical signal transmitting apparatus for wavelength-multiplexing a plurality of different encrypted signals and transmitting the multiplexed optical signals as an optical signal. In an optical communication system including an encrypted optical signal receiving device that extracts a signal, the encrypted optical signal transmitting device encrypts and outputs a transmission signal by time division multiplexing with a plurality of wavelengths of light, and outputs the encrypted signal. The encrypted optical signal receiving device is arranged in series along the traveling direction of the incident optical signal, and absorbs an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential and demodulates the optical signal into an electric signal. It is possible to transmit an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, and a higher reverse bias potential can be applied to a later stage. An optical communication device comprising an electro-absorption type modulation element, and a pair of electro-absorption type modulation elements, based on a timing synchronized with the time division multiplexing timing of the encrypted optical signal transmitting apparatus, in a later stage than in a preceding stage. And a reverse bias control circuit capable of applying a high potential reverse bias.

According to the present invention, a reverse bias potential applied to an optical communication device is controlled based on predetermined encryption information to change an optical wavelength to be demodulated, thereby decoding an encrypted optical signal. I do.

An optical spectrum analyzer according to the next invention is a light spectrum analyzer for decomposing light composed of a plurality of wavelength components into a plurality of wavelength bands and measuring optical power in each wavelength band. Are arranged in series along and can absorb an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential and demodulate it into an electric signal. A plurality of electro-absorption modulators that can transmit an optical signal having a wavelength longer than the wavelength, and to which a higher reverse bias potential can be applied toward a later stage, and the electro-absorption modulator according to a resolution value, And a reverse bias control circuit that can apply a reverse bias of a higher potential toward the subsequent stage so that each stage can absorb one wavelength band at a time.

According to the present invention, an optical signal obtained by multiplexing a plurality of light beams having different wavelengths is converted into optical power in each wavelength band by using an n-stage electroabsorption modulation element.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a basic configuration and an operation principle of an optical communication device used in carrying out the present invention will be described below. In this device, as shown in FIG. 1, a first electro-absorption modulator 1 and a second electro-absorption modulator 2 in which the wavelength of light to be absorbed changes according to the applied reverse bias potential are applied to the light. The input optical fiber 3 and the electric signal output terminal 4 are connected to elements integrated in series in the traveling direction.

Then, as shown in FIG. 2, the reverse bias V2 applied to the second electro-absorption modulator 2 becomes larger than the reverse bias V1 applied to the first electro-absorption modulator 1. As described above, the reverse biases V1 and V2 are selected.

Each of the reverse biases V1,
V2 (V1 <V2) is calculated by the reverse bias control circuit 5
In a state where the light is applied to the first electro-absorption modulator 1 and the second electro-absorption modulator 2, respectively, when an optical signal L formed by multiplexing a plurality of lights of different wavelengths enters the optical communication device. Light having a wavelength shorter than the wavelength determined by the potential of the reverse bias V1 is absorbed by the first electro-absorption type modulation element 1. On the other hand, light having a wavelength longer than the wavelength determined by the potential of the reverse bias V1 passes through the first electro-absorption type modulation element 1.

The optical signal transmitted through the first electro-absorption modulator 1 at the first stage enters the second electro-absorption modulator 2 at the second stage, and the potential of the reverse bias V2 (V1
Light having a wavelength shorter than the wavelength determined by <V2) is absorbed by the second electro-absorption modulator 2. On the other hand, light having a wavelength longer than that wavelength passes through the second electro-absorption type modulator 2. That is, the second electro-absorption type modulation element 2
Accordingly, only the optical signal of the desired wavelength is demodulated.

Therefore, by setting the reverse bias potentials applied to the electro-absorption modulation elements 1 and 2 so as to absorb only the optical wavelength band to be demodulated, the conventional optical band-pass filter and the optical It has a function equivalent to that of a photoelectric conversion element that performs electrical conversion of a signal.

Next, embodiments of the present invention will be described in detail. In the following embodiments, the wavelengths λ1, λ2,..., Λk-1, λk, λk +
1,..., Λn−1, λn are λ1>λ2>.
>Λk> λk + 1>...>Λn−1> λn. Also,
In the embodiments, the same components or the same functions are denoted by the same reference numerals, and description thereof is omitted.

(Embodiment 1) FIG. 3 schematically shows an example of an optical communication device according to the present invention. The optical communication device 104 absorbs an optical signal of a predetermined wavelength out of the optical signal L106 incident on the device 104,
A first electroabsorption modulator 111 that transmits optical signals of other wavelengths, and an optical signal of a predetermined wavelength among optical signals L107 transmitted through the first electroabsorption modulator 111 absorbs an optical signal of another wavelength. The second electro-absorption type modulation element 112 that transmits the optical signal of

The optical communication device 104 is connected to an optical fiber 102 serving as a transmission path through which an optical signal L106 propagates. The electric signal S105 obtained by demodulating the optical signal L107 by the second electro-absorption modulator 112 is provided in the second electro-absorption modulator 112.
Are connected.

The optical communication device 104 includes the first
A reverse bias supply circuit 113 capable of applying a reverse bias of an appropriate potential is connected to each of the electroabsorption type modulation element 111 and the second electroabsorption type modulation element 112. By the reverse bias supply circuit 113, the first electro-absorption type modulator 111 and the second electro-absorption type modulator 112
Include bias supply lines (wirings) 108 and 109, respectively.
, Reverse biases V1 and V2 of an appropriate potential are applied.

FIG. 4 shows the optical communication device 1 shown in FIG.
The relationship between the wavelength of the incident light of No. 04 and the absorptance of the electroabsorption type modulation element is schematically shown. In the optical communication device 104 according to the present invention, the reverse bias V2 applied to the second electro-absorption modulator 112 is larger than the reverse bias V1 applied to the first electro-absorption modulator 111. Then, reverse biases V1 and V2 are selected, respectively.

Each of the reverse biases V1,
V2 (V1 <V2) is the first electroabsorption modulation element 11
In a state where the light is applied to the first and second electroabsorption modulation elements 112, light having a plurality of different wavelengths (λ1,..., Λn (where n is a natural number of 2 or more)) is applied to the optical communication device 104. When the multiplexed optical signal L106 is incident, light having a wavelength shorter than the wavelength determined by the potential of the reverse bias V1 (λk + 1,..., Λn (where k is a natural number of 2 or more and smaller than n)) Are absorbed by the first electro-absorption type modulation element 111. On the other hand, light having a wavelength (λ1,..., Λk) longer than the wavelength determined by the potential of the reverse bias V1 passes through the first electro-absorption modulation element 111.

The optical signal L107 (wavelength: λ1,..., Λk) transmitted through the first electroabsorption type modulation element 111 in the preceding stage is
The light is incident on the second electroabsorption type modulation element 112 at the subsequent stage. Of the incident light, the potential of the reverse bias V2 (V1 <V2)
Light having a wavelength (λk) shorter than the wavelength determined by the second electro-absorption modulator 112 is absorbed. On the other hand, light having a wavelength (λ1,..., Λk−1) longer than that wavelength passes through the second electro-absorption type modulation element 112. Therefore, only the optical signal of the desired wavelength (λk) is demodulated by the second electro-absorption type modulation element 112.

Here, the first electro-absorption modulation element 111
The wavelength of light that can be absorbed by the second electro-absorption type modulation element 112 depends on the applied potentials of the reverse biases V1 and V2. Therefore, by appropriately selecting the potentials of the reverse biases V1 and V2, an electric signal S105 corresponding to an optical signal having an arbitrary wavelength can be obtained.

The operation of the optical communication device 104 configured as described above is as follows. In other words, the optical signal L106 formed by multiplexing a plurality of lights of different wavelengths (λ1,..., Λn) propagates through the optical fiber 102 and enters the optical communication device 104.

The incident optical signal L106 is incident on the first electro-absorption type modulation element 111 in the device 104. The reverse bias supply circuit 113 applies a reverse bias V to the first electro-absorption type modulation element 111 so that all the light having a wavelength shorter than the wavelength λk of the optical signal to be demodulated can be absorbed.
1 is applied. Accordingly, the optical signal L106 (wavelength: λ1,...,
In λn), all optical signals having a wavelength shorter than λk are absorbed by the first electro-absorption modulator 111, while
λk and optical signals having a wavelength longer than λk all pass through the first electro-absorption modulator 111.

The optical signal L 107 (wavelength: λ 1,..., Λ k) transmitted through the first electro-absorption modulator 111 enters a second electro-absorption modulator 112 at a subsequent stage. The second electro-absorption modulator 112 has a reverse bias supply circuit 11
3, a reverse bias V2 that can absorb all of λk and light having a wavelength shorter than λk is applied. Since all the light having a wavelength shorter than λk has already been absorbed by the first electro-absorption modulator 111, of the optical signal L 107 incident on the second electro-absorption modulator 112, Only the second electroabsorption type modulation element 112 is absorbed. The absorbed optical signal having the wavelength λk is demodulated into an electric signal S105, and the electric signal S105 is output to the outside via the signal line 105. In the second electro-absorption type modulation element 112, all optical signals having a wavelength longer than λk are transmitted.

As described above in detail, according to the optical communication device 104, light having a wavelength shorter than an arbitrary wavelength selected by the applied reverse bias potential is absorbed.
And a pair of electro-absorption modulators that can transmit other wavelengths are provided, and these electro-absorption modulators include:
The reverse bias supply circuit 113 applies a reverse bias V applied to the subsequent electro-absorption modulation element 112 to the reverse bias V 1 applied to the preceding electro-absorption modulation element 111.
2 is applied with a reverse bias so as to have a higher potential.
Of the optical signal L106 incident on the optical signal L106, an optical signal having a shorter wavelength than the desired wavelength is absorbed by the preceding electro-absorption modulator 111, and an optical signal having a longer wavelength passes through the previous electro-absorption modulator 111. And the subsequent electro-absorption modulator 1
It is incident on 12. Of the incident optical signal L107,
An optical signal having a desired wavelength to be demodulated is absorbed by the subsequent electro-absorption modulator 112, and an optical signal having a longer wavelength passes through the latter electro-absorption modulator 112.

Therefore, by using the optical communication device 104 of the first embodiment as, for example, a receiver of an optical communication system, the transmission wavelength can be changed only by an electric means of adjusting the reverse bias potential. ,
By mechanically changing the transmission wavelength of the tunable optical filter, an optical signal of a desired wavelength is extracted from an optical signal obtained by multiplexing light of a plurality of wavelengths, and the extracted optical signal is photoelectrically converted by a photodiode. This has the effect that higher reliability can be obtained as compared with the conventional technique of obtaining an electric signal by using the conventional technique.

Note that the optical signal L106 formed by multiplexing light of a plurality of wavelengths is a signal obtained by multiplexing light of two different wavelengths, that is, an optical signal to be demodulated and an optical signal having a longer wavelength. Good.

(Embodiment 2) FIG. 5 schematically shows an example of an optical communication system according to the present invention. This optical communication system has a plurality of different wavelengths (λ1, λ2,.
λn), an optical fiber 102 that transmits the wavelength-multiplexed optical signal L106, and an optical signal L that has propagated through the optical fiber 102.
A branching unit 201 for branching the optical signal 106 into a plurality of transmission lines (optical fibers), and each of the branched optical signals L20a and L20
b,..., L20n are respectively incident on the optical receiver 21
, 21b,..., 21n.

Each of the optical receivers 21a, 21b,..., 21n
Are the optical communication devices 10 of the first embodiment, respectively.
4, and electrical signals S105a, S105b,..., 105 demodulated by the respective optical communication devices 104.
It has an electric signal processing unit 204 for performing the processing of n. Also, the optical communication device 104 has a first device in the device.
A reverse bias supply circuit 113 capable of applying a reverse bias of an appropriate potential is connected to each of the electroabsorption type modulation element 111 and the second electroabsorption type modulation element 112. Note that the configuration, operation, and the like of the optical communication device 104 and the reverse bias supply circuit 113 are the same as those in the first embodiment, and thus detailed description is omitted.

In the first optical receiver 21a, the reverse bias supply circuit 113 causes the first electro-absorption type modulation element 111 of the optical communication device 104 to transmit λ1
A reverse bias V having a potential capable of absorbing light having a shorter wavelength and transmitting light having a wavelength longer than λ1 and λ1.
1a is applied, and the second electroabsorption modulator 1
12, a reverse bias V2a having a potential capable of absorbing light having a wavelength shorter than λ1 and λ1 and transmitting light having a wavelength longer than λ1 is applied. Thus, in the first optical receiving device 21a, the optical signal L20a (wavelength: λ1, λ2,.
Only the optical signal of wavelength λ1 is extracted from λn).

In the second optical receiving device 21b, the reverse bias supply circuit 113 causes the first electro-absorption type modulation element 111 of the optical communication device 104 to apply λ2
A reverse bias V having a potential capable of absorbing light having a shorter wavelength and transmitting light having a wavelength longer than λ2 and λ2.
1b, and the second electroabsorption modulator 1
12, a reverse bias V2b having a potential capable of absorbing light having a wavelength shorter than λ2 and λ2 and transmitting light having a wavelength longer than λ2 is applied. Accordingly, in the second optical receiving device 21b, the optical signal L20b (wavelength: λ1, λ2,.
Only the optical signal of wavelength λ2 is extracted from λn).

As in the case of λ1 and λ2, in the n-th optical receiver 21n, the reverse bias supply circuit 113 causes the first electro-absorption type modulation element 111 of the optical communication device 104 to have a higher value than λn. A reverse bias V1n having a potential capable of absorbing light having a short wavelength and transmitting light having a wavelength longer than λn and λn is applied, and λn and λn are applied to the second electroabsorption modulator 112.
A reverse bias V2n having a potential capable of absorbing light having a shorter wavelength and transmitting light having a wavelength longer than λn is applied. Thereby, in the n-th optical receiver 21n,
Optical signal L20n obtained by multiplexing a plurality of lights of different wavelengths
Only the optical signal of wavelength λn is extracted from (wavelengths: λ1, λ2,..., Λn).

The operation of the optical communication system configured as described above is as follows. That is, in the wavelength division multiplexing optical transmission device 101, a plurality of different wavelengths (λ1, λ2,
.., Λn) are multiplexed. The multiplexed optical signal L
Reference numeral 106 denotes a light propagating through the optical fiber 102 and
1 and is branched by the branching means 201 into a plurality of transmission paths. The branched optical signals L20a and L20
, L20n are the respective optical receiving devices 21a, 21a
.., 21n.

Then, in the first optical receiving device 21a, only the optical signal of the wavelength λ1 is extracted and demodulated to obtain an electric signal S105a corresponding to the optical signal of the wavelength λ1. In the second optical receiving device 21b, only the optical signal of the wavelength λ2 is extracted and demodulated to obtain an electric signal S105b corresponding to the optical signal of the wavelength λ2. Similarly, the n-th
In the optical receiver 21n, only the optical signal of the wavelength λn is extracted and demodulated to obtain an electric signal S105n corresponding to the optical signal of the wavelength λn.

According to the second embodiment, the optical signal L106 in which light of different n wavelengths is multiplexed is branched into n signals, and the n optical signals L20a, L20b,..., L2
, 0n are respectively incident on n optical receiving devices 21a, 21b,..., 21n having the optical communication device 104 of the first embodiment, and the respective optical receiving devices 21a, 21b,.
Since the optical signals of wavelengths λ1, λ2,..., Λn are extracted and demodulated one by one at 21n, a plurality of light beams having different wavelengths are multiplexed by a combination of a plurality of optical filters and a plurality of photodiode modules. Compared to the conventional technique of discriminating and demodulating the optical signal obtained for each wavelength, the optical receiver can be configured by a single optical component, so that the optical receiver can be downsized, Since it is possible to reduce the number of fusion points of an optical fiber that requires a large amount of work time during manufacturing, there is an effect that manufacturing costs can be reduced.

(Embodiment 3) FIG. 6 schematically shows an example of an optical communication system according to the present invention. This optical communication system has a plurality of different wavelengths (λ1,.
1, λn) wavelength multiplexing optical transmitter 101
And an optical fiber 102 for transmitting the wavelength-multiplexed optical signal L106, and an optical communication device 380 for extracting and demodulating the optical signal L106 propagated in the optical fiber 102 for each optical signal of each wavelength. It is configured with the optical receiving device 300.

The optical communication device 380 has a multi-stage configuration in which a plurality of electro-absorption type modulation elements 36a, 36b,..., 36n are arranged in series.
, 36n via the bias supply lines 35a, 35b,..., 35n, respectively, by the reverse bias supply circuit 113, the higher the reverse bias potential V increases toward the subsequent stage.
1, V2,..., Vn are applied.

The reverse bias potential V1 applied to the first-stage electroabsorption modulator 36a is equal to the incident light signal L106.
(Wavelength: λ1,..., Λn-1, λn) is a potential that absorbs only the optical signal of the shortest wavelength λn and allows transmission of an optical signal having a wavelength longer than λn.

The reverse bias potential V2 applied to the second-stage electroabsorption modulator 36b is equal to the optical signal L37a (wavelength: λ) transmitted through the first-stage electroabsorption modulator 36a.
1,..., Λn−1), absorbs only the optical signal of the shortest wavelength λn−1 and has an optical signal 13 longer in wavelength than λn−1.
7b.

Similarly, the n-th stage electroabsorption modulator 3
6n is applied to the optical signal L that has passed through the (n−1) -th electroabsorption modulator (not shown).
37n-1 (wavelength: λ1) is a potential that absorbs only the optical signal of the shortest wavelength, that is, λ1, and transmits an optical signal having a wavelength longer than λ1.

The operation of the optical communication system configured as described above is as follows. That is, in the wavelength division multiplexing optical transmission device 101, a plurality of different wavelengths (λ1,.
−1, λn) are multiplexed. The multiplexed optical signal L106 propagates through the optical fiber 102 and enters the optical communication device 380 of the optical receiver 300.

Then, the first-stage electroabsorption modulator 3
6a, the incident light signal L106 (wavelength: λ1,.
−1, λn), only the optical signal of the shortest wavelength λn is extracted and demodulated to obtain an electric signal S105a corresponding to the optical signal of the wavelength λn. In the second-stage electroabsorption modulator 36b, the optical signal L37a (wavelength: λ1,..., Λ) transmitted through the first-stage electroabsorption modulator 36a.
n-1), only the optical signal of the shortest wavelength λn-1 is extracted and demodulated to obtain an electric signal S105a corresponding to the optical signal of the wavelength λn. In the n-th stage electroabsorption modulator 36n, the shortest wavelength of the optical signal L37n-1 (wavelength: λ1) transmitted through the (n-1) th stage electroabsorption modulator (not shown), that is, λ1 Is extracted and demodulated to obtain an electric signal S105n corresponding to the optical signal of wavelength λ1.

According to the third embodiment, the optical signal L106 in which the light of n different wavelengths is multiplexed is extracted and demodulated one by one by the n-stage electroabsorption modulation element. The conventional technology of discriminating and demodulating an optical signal obtained by multiplexing light of a plurality of different wavelengths by an apparatus including a plurality of devices each including a combination of a filter and a photodiode module and an optical branching unit for each wavelength. In comparison, the optical receiver can be configured with a single optical component, and the optical branching unit is not required, so that the components and the mounting space of the optical receiver can be reduced, and the optical receiver can be reduced in size. Can be achieved.

(Embodiment 4) FIG. 7 schematically shows an example in which an optical communication apparatus according to the present invention is applied to an optical spectrum analyzer. This optical spectrum analyzer 30
0a indicates a plurality of different wavelengths (λ1,..., Λn) that have entered through the optical fiber 102 and the signal light input unit 400.
−1, λn) is multiplexed into an optical signal L106,
Optical communication device 38 having the same configuration as in the third embodiment.
With 0, each optical signal in each wavelength band is extracted and demodulated. The optical spectrum analyzer 300a includes, in addition to the optical communication device 380, a reverse bias supply circuit 113 and an electric signal processing unit 20.
4 and an external interface unit 401 that can be connected to an external control device or the like (not shown). The configuration, operation, and the like of the optical communication device 380, the reverse bias supply circuit 113, and the electric signal processing unit 204 are as described in the above embodiments. Therefore, their description is omitted.

The external interface section 401 receives optical spectrum measurement condition information D 402 from an external control device or the like (not shown), and receives the electric signal processing section 20.
4, the measurement result information D33 of the optical spectrum is input. Further, the external interface unit 401 outputs the optical spectrum measurement result output information D403 to an external control device or the like (not shown), and outputs the reverse bias supply circuit 11
3 to output reverse bias control information D32.

The operation of the optical spectrum analyzer 300a configured as described above is as follows. That is,
The measured light (signal light) L106 is input to the optical spectrum analyzer 300a via the signal light input unit 400.
Further, based on the measurement condition information D402 regarding the wavelength resolution and the wavelength band input from an external control device or the like, the external interface unit 401 sends reverse bias control information D32 corresponding to the measured wavelength resolution and the wavelength band to the reverse bias supply circuit 113. Send.

The reverse bias supply circuit 113, based on the reverse bias control information D32, similarly to the third embodiment, has n stages of electroabsorption modulation elements 36a, 36b,.
6n, the reverse biases V1, V2,.
Is applied. n-stage electroabsorption modulators 36a, 36
b,..., 36n represent the applied reverse bias V
, V2,..., Vn, the optical power in the wavelength band corresponding to each of the electrical signals S105a, S105
b,..., S105n are transmitted to the electric signal processing unit 204.

The electric signal processing section 204 processes the transmitted electric signals S105a, S105b,..., S105n to generate measurement result information D33 and sends it to the external interface section 401. External interface unit 401
Converts the measurement result into a format according to the interface requested by the external side, and outputs the result to the outside as measurement result output information D403.

According to the fourth embodiment, an optical signal L106 obtained by multiplexing a plurality of lights of different wavelengths is converted into respective wavelengths by using n-stage electroabsorption modulation elements 36a, 36b,. Since the optical power is converted into the optical power in the band, the wavelength resolution and the measurement wavelength band can be controlled only by electrical control without providing a spectral means such as a diffraction grating. An optical spectral analyzer having excellent controllability can be obtained, the number of components can be reduced, and the optical spectral analyzer can be downsized.

(Embodiment 5) FIG. 8 schematically shows an example in which the optical communication device according to the present invention is applied to an optical fiber amplifier. This optical fiber amplifier includes a rare earth-doped optical fiber 501 for transmitting an optical signal L106 formed by multiplexing a plurality of lights having different wavelengths (λ1,..., Λn).
Optical multiplexing means 502 for synthesizing optical signal L106 and excitation laser light, excitation semiconductor laser 505 for emitting excitation laser light, and excitation semiconductor laser driving for controlling the excitation semiconductor laser 505 Control circuit 506
And an optical isolator 5 for blocking return light to the laser light source
03, a monitoring optical branching unit 504 for branching a part of the output light of the optical fiber amplifier, the optical communication device 104 having the same configuration as that of the first embodiment, and a monitoring optical branching unit 504. An input disconnection detection circuit 602 for monitoring the input of the light (optical signal for monitoring) extracted by the optical communication device 104, and a pair of electric fields of the optical communication device 104 based on the detection result of the input disconnection detection circuit 602. A reverse bias control circuit 601 for controlling a reverse bias potential applied to the absorption type modulation element. Note that the configuration, operation, and the like of the optical communication device 104 are the same as those in the first embodiment, and a detailed description thereof will be omitted.

The operation of the optical fiber amplifier configured as described above is as follows. That is, an optical signal L1 formed by multiplexing a plurality of lights of different wavelengths (λ1,..., Λn).
06 propagates through the rare earth-doped optical fiber 501 and is amplified. The optical signal L106 is multiplexed with the pumping laser light emitted from the pumping semiconductor laser 505 by the optical multiplexing means 502 and passes through the optical isolator 503. The light L510 that has passed through the optical isolator 503 is output to the outside, and a part of the light L510 is branched by the monitoring light branching unit 504. The split light L511
Is input to the optical communication device 104.

In the optical communication device 104, an optical signal of a predetermined first monitoring wavelength λk1 is extracted from the light L511 input to the device 104 and demodulated into an electric signal. The demodulated electric signal is input to the excitation semiconductor laser drive control circuit 506 and the monitoring signal input disconnection detection circuit 602 as monitoring signal level information D512.

The pumping semiconductor laser drive control circuit 506 controls the driving current I515 of the pumping semiconductor laser 505 based on the level information D512 of the input monitor signal so as to keep the output level per wavelength constant. I do. Thereby, the output level per wavelength of the optical signal output from the optical fiber amplifier is kept constant.

When the first monitoring wavelength λk1 is disconnected, it is detected by the input disconnection detection circuit 602, and the monitoring signal disconnection information D604 is transmitted from the input disconnection detection circuit 602 to the reverse bias control circuit 601. . In the reverse bias control circuit 601, of the light L511 branched by the monitoring light branching unit 504, a predetermined second monitoring wavelength λk
The reverse bias potential applied to the pair of electro-absorption modulation elements of the optical communication device 104 is controlled so that the second optical signal is demodulated as the monitoring signal. Similarly, when the second monitoring signal is interrupted, an optical signal of a predetermined third monitoring wavelength λk3 is used as the monitoring signal, and the output level per wavelength is kept constant. , Pumping semiconductor laser 5
The control of the drive current I515 of 05 is continued.

According to the fifth embodiment, out of the light L511 branched from a part of the output optical signal, the monitoring signal of a predetermined wavelength is transmitted to the optical communication system having a pair of electro-absorption modulation elements. The device 104 extracts and demodulates the signal, so that when the monitoring signal is fixed and the signal is interrupted, the output level control function is disabled. Even if the supervisory signal is interrupted, a signal of another wavelength can be newly set as the supervisory signal, so that even if the initial supervisory signal is interrupted, the control to keep the output level constant can be continuously performed. It is possible to achieve high reliability of the control function.

(Embodiment 6) FIG. 9 schematically shows an example of an optical communication apparatus according to the present invention. The optical communication device 300b has propagated in the optical fiber 102,
A light having the same configuration as that of the first embodiment for extracting and demodulating a signal of a predetermined wavelength λk from an optical signal L106 in which a plurality of lights of different wavelengths (λ1,..., Λk,. A communication device 104, an electric signal processing unit 204 that processes the demodulated electric signal S105, a photodiode 64 that receives the light L65 transmitted through the optical communication device 104, and a demodulation photoelectrically converted by the photodiode 64. A wavelength fluctuation detection circuit 62 that compares the signal S66 with the absorbed light level information D61 output from the electric signal processing unit 204 and detects the amount of wavelength fluctuation of the optical signal having the wavelength λk.
And the wavelength shift information D output from the detection circuit 62
69, a reverse bias control circuit 31 for controlling a reverse bias potential applied to the pair of electro-absorption modulation elements 111 and 112 of the optical communication device 104.

The operation of the optical communication apparatus configured as described above is as follows. That is, the optical communication device 10
Of the optical signal L106 input to 4, only the light having the wavelength λl is demodulated, and the light having a wavelength longer than λk is transmitted. The transmitted optical signal L65 is input to the photodiode 64 via the optical fiber 63. The absorbed light level information D61 obtained by processing the demodulated signal S66 of the transmitted light from the photodiode 64 and the electric signal S105 obtained by demodulating the light having the wavelength λk by the electric signal processing unit 204 is obtained by the wavelength fluctuation detection circuit 6
Sent to 2.

Generally, the light of the laser light source tends to shift to a longer wavelength due to aging. Accordingly, in the wavelength fluctuation detection circuit 62, the demodulation level of the optical signal having the wavelength λk is lowered, and the optical signal L transmitted through the optical communication device 104 is reduced.
When the demodulation level of 65 rises, the initial wavelength is λk
It is determined that the wavelength of the optical signal has been shifted to the longer wavelength side. On the other hand, when the demodulation level of the optical signal having the wavelength λk decreases and the demodulation level of the optical signal L65 transmitted through the optical communication device 104 does not change, the wavelength of the optical signal having the wavelength λk does not fluctuate. Is determined to have dropped.

When the wavelength fluctuation detecting circuit 62 recognizes that the wavelength of the optical signal of the wavelength λk has shifted to the longer wavelength side, the wavelength fluctuation detecting circuit 62
1, the wavelength shift information D69 is sent. In the reverse bias control circuit 31, the pair of electroabsorption modulation elements 111 and 112 of the optical communication device 104 are set so that the demodulation level of the shifted optical signal of the wavelength λk becomes the initial level according to the wavelength shift amount. To control the reverse bias potential applied to.

According to the sixth embodiment, the wavelength shift of the light emitted from the laser light source is detected, and according to the shift amount,
A pair of electro-absorption modulation elements 1 of the optical communication device 104
Since the receiving wavelength band is controlled by controlling the reverse bias potential applied to 11, 112, even in a communication system using wavelength-multiplexed light, even if the signal wavelength fluctuates, the system can respond to the wavelength fluctuation. The receiving wavelength band can be controlled at a higher speed than before, and deterioration of transmission characteristics due to a decrease in the S / N ratio can be prevented.

(Embodiment 7) FIG. 10 schematically shows an example of an optical communication system according to the present invention. This optical communication system includes an encrypted optical signal transmitting device 704 and an encrypted signal receiving device 705. The encrypted signal receiving device 705 extracts the predetermined signal from the encrypted optical signal L706 and demodulates the signal as described above. An optical communication device 104 having the same configuration as that of the first embodiment is used. Detailed description of the optical communication device 104 will be omitted.

The encrypted optical signal transmitting device 704 includes an encrypted signal generating device 701 for generating an encrypted signal, transmitting laser light sources 9a, 9b,..., 9n, and laser light sources 9a, 9b,. Drive circuit 805 for driving
, 9n, and a timing synthesizing means 804 for multiplexing optical signals emitted from the laser light sources 9a, 9b,..., 9n, and a timing generating circuit 71a for generating a timing signal used for encryption.

The encrypted signal receiving apparatus 705 includes an optical communication device 104, a reverse bias control circuit 72 for controlling a reverse bias potential applied to a pair of electroabsorption modulation elements 111 and 112 of the optical communication device 104, An electric signal processing unit 204 that processes the electric signal S78 demodulated by the optical communication device 104; and an encrypted optical signal transmission device 704.
And a timing generation circuit 71b synchronized with the timing generation circuit 71a.

The operation of the optical communication system configured as described above is as follows. That is, the signal S7 to be transmitted
, S75n are scrambled and encrypted by the encryption signal generator 701 in a time division manner in synchronization with the timing signal CLK sent from the timing generation circuit 71a. The encrypted electric signals S76a, S76b,..., S76n are sent to the laser drive circuit 805.

Transmission laser light sources 9a, 9b,..., 9n
Are driven by the drive currents I77a, I77b,..., I77n supplied from the laser drive circuit 805, and emit optical signals L78a, L78b,. The emitted optical signals L78a, L78b,..., L7
8n is synthesized by the photosynthesis means 804. The combined encrypted optical signal L706 is transmitted to the receiving side via the optical fiber 102.

The encrypted optical signal L706 sent via the optical fiber 102 is received by the optical communication device 104. The reverse bias control circuit 72 controls the reverse bias potential with predetermined encryption information in synchronization with the timing signal CLK sent from the timing generation circuit 71b, and changes the wavelength of light to be demodulated. Electric signal S78 decoded by optical communication device 104
Is sent to the electric signal processing unit 204.

According to the seventh embodiment, the reverse bias potential applied to the optical communication device 104 is controlled based on the predetermined encryption information to change the wavelength of the light to be demodulated. Since the optical signal L706 is decoded, a high-speed modulation / demodulation encryption communication system using wavelength multiplexing of light can be configured.

(Eighth Embodiment) FIG. 11 schematically shows an example of an optical communication apparatus according to the present invention. This optical communication device 800 includes transmission laser light sources 9a, 9b,.
, and a laser light source drive control circuit 805 for controlling the drive current and temperature of the transmission laser light sources 9a, 9b,.
A light combining means 804 for multiplexing the light emitted from the transmitting laser light sources 9a, 9b,..., 9n; an optical branching means 902 for branching a part of the wavelength-multiplexed optical signal L106;
Optical communication device 10 having the same configuration as in the first embodiment.
4, a reverse bias control circuit 801 for controlling a reverse bias potential applied to the optical communication device 104, and timing generation for generating a timing signal for periodically changing the reverse bias applied to the optical communication device 104 A circuit 806 and a signal light power information processing circuit 811 for sending the electric signal S105 demodulated by the optical communication device 104 to the laser light source drive control circuit are provided.

The operation of the optical communication device configured as described above is as follows. That is, the transmission laser light source 9
a, 9b,..., 9n, the optical signal L106 wavelength-multiplexed by the optical combining means 804 is
And a part thereof is branched by the optical branching unit 902 and sent to the optical communication device 104. The timing signal CLK is supplied from the timing generation circuit 806 to the reverse bias control circuit 801. The reverse bias potential applied to the optical communication device 104 is controlled in synchronization with the timing signal CLK,
A demodulated electric signal S105 of each signal wavelength is obtained.

The signal light power information processing circuit 811 monitors the fluctuation of the signal wavelength and the output level based on the demodulated electric signal S105 corresponding to the optical level of each signal wavelength measured periodically, and controls the laser drive current control. The signal S809 is output to the laser light source drive control circuit 805 to stabilize the light wavelengths and output levels of the transmission laser light sources 9a, 9b,..., 9n.

According to the eighth embodiment, a part of the output optical signal L106 is branched, and the demodulated electric signal S105 is periodically measured by the optical communication device 104. , 9n, and stabilizes the light wavelengths and output levels of the transmission laser light sources 9a, 9b,..., 9n. An optical communication system is configured.

(Embodiment 9) FIG. 12 schematically shows an example of an optical communication apparatus according to the present invention. This optical communication device includes transmission laser light sources 9a, 9b,.
, 1n, and the motorized variable light attenuators 1a, 1b,..., 1n, and the motorized variable light attenuators 1a, 1b,. Attenuator control drive circuit 901 for controlling, and transmission laser light sources 9a, 9b,.
A light combining means 804 for multiplexing the light emitted from 9n,
The optical branching unit 902 that branches a part of the wavelength-multiplexed optical signal L106, the optical communication device 104 having the same configuration as in the first embodiment, and the reverse bias potential applied to the optical communication device 104 are controlled. Reverse bias control circuit 8
01, and a timing generation circuit 806 for generating a timing signal for periodically changing the reverse bias applied to the optical communication device 104.

The operation of the optical communication device configured as described above is as follows. That is, the transmission laser light source 9
a, 9b,..., 9n, the optical signal L106 wavelength-multiplexed by the optical combining means 804 is
And a part thereof is branched by the optical branching unit 902 and sent to the optical communication device 104. The timing signal CLK is supplied from the timing generation circuit 806 to the reverse bias control circuit 801. The reverse bias potential applied to the optical communication device 104 is controlled in synchronization with the timing signal CLK,
A demodulated electric signal S105 of each signal wavelength is obtained.

The attenuator control drive circuit 901 detects the optical level of each signal wavelength periodically measured based on the demodulated electric signal S105, and flattens the optical output for each wavelength according to the optical level. , 1n for controlling the electric variable optical attenuators 1a, 1b,..., 1n.
1n.

According to the ninth embodiment, a part of the output optical signal L106 is branched, and the demodulated electric signal S105 is measured by the optical communication device 104. Since the optical level is detected and the optical output for each wavelength is flattened according to the optical level, the transmission device of the wavelength multiplexed optical communication system capable of controlling the flatness of the transmission wavelength at high speed is configured. Is done.

(Embodiment 10) FIG. 13 schematically shows an example of an optical communication apparatus according to the present invention. The optical communication apparatus 1000 includes an optical signal of wavelength λ1 modulated by a signal of a first transmission rate and a wavelength λ2 (λ) modulated by a signal of a second transmission rate corresponding to a multiple of the first transmission rate.
As a means for demodulating an optical signal of wavelength λ2 from an optical signal L1001 in which light of two wavelengths of an optical signal of 1 <λ2) is multiplexed, an optical communication device 104 having the same configuration as in the first embodiment is used. The optical communication device 104 includes a device 104 for optical communication, a reverse bias control circuit 801, an electric signal processing unit 204, and a reverse bias information control circuit 1012.

The operation of the optical communication apparatus configured as described above is as follows. That is, the received optical signal L1
001 is input to the optical communication device 104, and the shorter-wavelength λ1 modulated at the first transmission rate by the electro-absorption modulation element 111 in the preceding stage in the device 104.
Is demodulated. The obtained demodulated signal S1015 of the optical signal of the wavelength λ1 is used for the reverse bias information control circuit 1012.
Sent to

The reverse bias information control circuit 1012 extracts the timing of the transmission signal based on the received demodulated signal S1015, and sends a bias control signal S1011 relating to the extracted timing to the reverse bias control circuit 801. Based on the bias control signal S1011, the reverse bias applied to the subsequent electroabsorption modulation element 112 in the optical communication device 104 is modulated by the reverse bias control circuit 801, and the reverse bias corresponding to the multiple of the first transmission rate is modulated. 2
The optical signal of the wavelength λ2 modulated by the signal of the transmission speed is demodulated.

According to the tenth embodiment, the optical signal of wavelength λ1 modulated by the signal of the first transmission rate,
The optical communication device 104 converts an optical signal L1001 obtained by multiplexing two wavelengths of an optical signal of a wavelength λ2 (λ1 <λ2) modulated by a signal of a second transmission rate corresponding to the multiplication of the transmission rate of The optical signal having the wavelength λ1 is demodulated to extract the timing of the transmission signal.
Since the optical signal of wavelength 2 is demodulated, the bias of the optical signal of wavelength λ2 is modulated at a modulation frequency that is 1 / multiple of the transmission speed, the reception noise is reduced, and the S / N of reception is reduced.
The ratio is improved and the receiving sensitivity is increased.

Although the invention made by the inventor has been specifically described based on each embodiment, the present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the invention. It goes without saying that it is possible.

[0109]

As described above, according to the optical communication device of the present invention, the light having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential among the optical signals incident on the optical communication device. The signal is absorbed by the electro-absorption modulator, and an optical signal having a longer wavelength passes through the electro-absorption modulator and is incident on a later-stage electro-absorption modulator. Of the optical signals incident on the latter electro-absorption modulator, those having a wavelength shorter than the wavelength corresponding to the reverse bias potential applied to the electro-absorption modulator are absorbed by the electro-absorption modulator. Since an optical signal having a longer wavelength is transmitted through the electro-absorption type modulation element and is incident on an electro-absorption type modulation element at a further later stage, the optical communication device is used for a receiving apparatus of an optical communication system, for example. As a result, the transmission wavelength can be changed only by electrical means of adjusting the potential of the reverse bias,
By mechanically changing the transmission wavelength of the variable optical filter, an optical signal of a desired wavelength is extracted from an optical signal obtained by multiplexing light of a plurality of wavelengths, and the extracted optical signal is photoelectrically converted by a photodiode. This has the effect that higher reliability can be obtained as compared with the conventional technique of obtaining an electric signal by using the conventional technique.

According to the optical communication device of the next invention, of the optical signals incident on the optical communication device, the optical signal having a shorter wavelength than the desired wavelength is absorbed by the preceding electro-absorption type modulation element. An optical signal having a longer wavelength passes through the preceding electro-absorption modulator, and enters the latter electro-absorption modulator. Of the incident optical signals, an optical signal of a desired wavelength to be demodulated is absorbed by a subsequent electro-absorption modulator, and an optical signal having a longer wavelength passes through the subsequent electro-absorption modulator. By using this device for optical communication in, for example, a receiver of an optical communication system, the transmission wavelength can be changed only by electric means of adjusting the reverse bias potential, so that the transmission wavelength of the tunable optical filter is mechanically changed. The conventional technique of extracting an optical signal of a desired wavelength from an optical signal obtained by multiplexing light of a plurality of wavelengths by changing the optical signal, and photoelectrically converting the extracted optical signal by a photodiode to obtain an electric signal. In comparison with this, there is an effect that high reliability can be obtained.

According to the optical communication device of the next invention, of the optical signals incident on the optical communication device, the optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential is the electroabsorption type. The optical signal absorbed by the modulation element and having a longer wavelength than that is transmitted through the electro-absorption type modulation element and is incident on a later-stage electro-absorption type modulation element. Of the optical signals incident on the latter electro-absorption modulator, those having a wavelength shorter than the wavelength corresponding to the reverse bias potential applied to the electro-absorption modulator are absorbed by the electro-absorption modulator. Since an optical signal having a longer wavelength is transmitted through the electro-absorption type modulation element and is incident on an electro-absorption type modulation element at a further later stage, the optical communication device is used for a receiving apparatus of an optical communication system, for example. Thus, the transmission wavelength can be changed only by an electrical means of adjusting the potential of the reverse bias, so that light of a plurality of wavelengths is multiplexed by mechanically changing the transmission wavelength of the variable optical filter. Compared to the conventional technique of extracting an optical signal of a desired wavelength from an optical signal and photoelectrically converting the extracted optical signal by a photodiode to obtain an electric signal, An effect that Lai is obtained.

According to the optical communication apparatus of the next invention, an optical signal in which light of a plurality of different wavelengths is multiplexed is branched into a plurality of signals, and the optical signals are provided with a pair of front and rear electro-absorption modulators. In order to extract and demodulate an optical signal having a desired wavelength in each optical communication device, a plurality of optical filters and a plurality of photodiode modules are combined to generate a plurality of different wavelengths. Since the optical receiver can be composed of a single optical component, compared with the conventional technology of discriminating and demodulating an optical signal obtained by multiplexing the optical signals for each wavelength, the size of the optical receiver can be reduced. In addition to the above, it is possible to reduce the number of fusion points of the optical fibers that require a large amount of work time during manufacturing, so that the manufacturing cost can be reduced.

According to the optical communication apparatus of the next invention, an optical signal in which light of a plurality of different wavelengths is multiplexed is extracted and demodulated one wavelength at a time by three or more stages of electroabsorption modulation elements. Conventionally, an optical signal formed by multiplexing light of a plurality of different wavelengths is demodulated and demodulated for each wavelength by an apparatus including a plurality of devices in which an optical filter and a photodiode module are combined and an optical branching unit. Compared to the technology, the optical receiving device can be configured by a single optical component, and the optical branching unit is not required, so that the components and the mounting space of the optical receiving device can be reduced, and the optical receiving device can be reduced. Can be reduced in size.

[0114] According to the optical communication apparatus of the next invention, a monitor signal of a predetermined wavelength out of the light branched from a part of the output optical signal is provided with a pair of electro-absorption modulation elements. To extract and demodulate with an optical communication device,
If the monitoring signal is fixed and the signal is interrupted, the output level control function will not be possible. Since the monitoring signal can be set at the same time, the control for keeping the output level constant even when the initial monitoring signal is interrupted can be continuously performed, and the control function can be made highly reliable.

According to the optical communication apparatus of the next invention, the wavelength shift of the light emitted from the laser light source is detected, and the reverse shift applied to the pair of electro-absorption modulation elements of the optical communication device according to the shift amount. By controlling the bias potential to control the reception wavelength band, even in a communication system using wavelength-multiplexed light, even when the signal wavelength fluctuates,
The reception wavelength band according to the wavelength fluctuation can be controlled at a higher speed than before, and deterioration of the transmission characteristics due to a decrease in the S / N ratio can be prevented.

According to the optical communication apparatus of the next invention, a part of the output optical signal is branched, and the demodulated electric signal is periodically measured by the optical communication device. In order to stabilize the wavelength and output level of the light of the transmission laser light source, an optical communication system including a wavelength multiplexing transmission device having a fast response speed and output stabilization control function is configured.

According to the optical communication apparatus of the next invention, a part of the output optical signal is branched, and the demodulated electric signal is measured by the optical communication device. In order to detect the optical level and flatten the optical output for each wavelength according to the optical level, a transmission device of a wavelength multiplexed optical communication system capable of controlling the flatness of the transmission wavelength at high speed is configured. .

According to the optical communication apparatus of the next invention, the optical signal of the wavelength λ1 modulated by the signal of the first transmission rate and the signal of the second transmission rate corresponding to the multiplication of the first transmission rate Of the optical signal of wavelength λ2 (λ1 <λ2) modulated by
The optical communication device demodulates the optical signal of the wavelength λ1 from the optical signal in which the light of the wavelength is multiplexed, extracts the timing of the transmission signal, and demodulates the optical signal of the wavelength λ2 based on the timing. The bias of the optical signal of λ2 is modulated at a modulation frequency that is 1 / division of the transmission rate, so that the reception noise is reduced and the S / N ratio of reception is improved.
Receive sensitivity rises.

According to the optical communication system of the next invention, the reverse bias potential applied to the optical communication device is controlled based on the predetermined encryption information to change the wavelength of the light to be demodulated. In order to decode the encrypted optical signal, a high-speed modulation / demodulation encryption communication system using optical wavelength multiplexing can be configured.

According to the optical spectrum analyzer according to the next invention, an optical signal in which a plurality of lights of different wavelengths are multiplexed is converted into an optical power in each wavelength band by using an n-stage electro-absorption modulator. The wavelength resolution and the measurement wavelength band can be controlled only by electrical control without providing a spectroscopic means such as a diffraction grating. A spectral analyzer can be obtained, and the number of components can be reduced, so that the optical spectral analyzer can be downsized.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a basic configuration of an optical communication device according to the present invention.

FIG. 2 is a diagram for explaining the operation principle of the optical communication device according to the present invention.

FIG. 3 is a schematic block diagram illustrating an embodiment of an optical communication device according to the present invention.

FIG. 4 is a diagram schematically showing a relationship between a wavelength of incident light of the optical communication device shown in FIG. 3 and an absorptance of an electro-absorption type modulation element.

FIG. 5 is a schematic block diagram showing an embodiment of an optical communication system according to the present invention.

FIG. 6 is a schematic block diagram showing another embodiment of the optical communication system according to the present invention.

FIG. 7 is a schematic block diagram showing an example in which the optical communication device according to the present invention is applied to an optical spectrum analyzer.

FIG. 8 is a schematic block diagram showing an example in which the optical communication device according to the present invention is applied to an optical fiber amplifier.

FIG. 9 is a schematic block diagram illustrating an example of an optical communication device according to the present invention.

FIG. 10 is a schematic block diagram illustrating an example of an optical communication system according to the present invention.

FIG. 11 is a schematic block diagram illustrating an example of an optical communication device according to the present invention.

FIG. 12 is a schematic block diagram illustrating an example of an optical communication device according to the present invention.

FIG. 13 is a schematic block diagram illustrating an example of an optical communication device according to the present invention.

FIG. 14 is a block diagram illustrating a schematic configuration of a conventional optical receiving device.

FIG. 15 is a block diagram illustrating a schematic configuration of a conventional optical receiving device.

FIG. 16 is a block diagram illustrating a schematic configuration of a conventional optical receiving device.

FIG. 17 is a block diagram showing a schematic configuration of a conventional optical fiber amplifier.

FIG. 18 is a block diagram illustrating a schematic configuration of a conventional wavelength division multiplexing optical transmission device.

[Explanation of symbols]

1, 2, 36a, 36b, 36n, 111, 112 Electroabsorption type modulation element, 1a, 1b, 1n motorized variable optical attenuator, 3, 63, 102 optical fiber, 4 electric signal output terminals, 5, 31, 72, 601, 801 reverse bias control circuit, 9a, 9b, 9n laser light source for transmission,
21a, 21b, 21n Optical receiver, 35a, 35
b, 35n, 108, 109 bias supply line, 62
Wavelength fluctuation detection circuit, 64 photodiodes, 71a,
71b, 806 Timing generation circuit, 101 WDM optical transmitter, 104, 380 Optical communication device, 1
05 signal line, 113 reverse bias supply circuit, 201
Branching means, 204 electric signal processing unit, 300 optical receiving device, 300a optical spectrum analyzer, 300b, 8
00,1000 optical communication device, 400 signal light input unit,
401 external interface unit, 501 rare earth-doped optical fiber, 502 optical multiplexing means, 503 optical isolator, 504 monitor optical branching unit, 505 excitation semiconductor laser, 506 excitation semiconductor laser drive control circuit, 6
02 input disconnection detection circuit, 701 encryption signal generator,
704 encrypted optical signal transmission device, 705 encrypted signal reception device, 804 photosynthesis means, 805 laser drive circuit, 811 signal light power information processing circuit, 901 attenuator control drive circuit, 902 optical branching means, 1012 reverse bias information control circuit.

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Claims (12)

[Claims] 1. An optical communication device for use in an optical wavelength multiplexing transmission system using an optical signal in which light of a plurality of different wavelengths is multiplexed, wherein the optical communication device is connected in series along the traveling direction of the optical signal. An optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential is arranged and can be demodulated into an electric signal, and the wavelength corresponding to the applied reverse bias potential and longer than the wavelength can be absorbed. An optical communication device, comprising: a plurality of electro-absorption modulation elements capable of transmitting an optical signal of a wavelength and applying a higher reverse bias potential to a later stage. 2. The optical communication device according to claim 1, wherein the two electro-absorption modulation elements are arranged in front and behind. 3. The optical communication device according to claim 1, wherein a number of said electro-absorption modulation elements corresponding to the number of multiplexed wavelengths are arranged before and after. 4. An optical communication apparatus for receiving an optical signal which is used in an optical wavelength division multiplexing transmission system in which an optical signal formed by multiplexing light of a plurality of different wavelengths is split in a transmission path thereof. It is arranged in series along the traveling direction of the incident optical signal, and is capable of absorbing an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential and demodulating it into an electric signal. A pair of front and rear electro-absorption modulation elements capable of transmitting an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the applied wavelength, and capable of applying a higher reverse bias potential in the subsequent stage than in the preceding stage. And a reverse bias supply circuit capable of applying a reverse bias having a higher potential in the latter stage than in the former stage to the pair of electro-absorption modulation elements. Optical communication device. 5. An optical communication device for receiving an optical signal in which light of a plurality of different wavelengths is multiplexed, wherein the reverse bias is arranged and applied in series along the traveling direction of the incident optical signal. It can absorb an optical signal having a wavelength shorter than the wavelength corresponding to the potential and demodulate it into an electric signal, and can transmit an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, An optical communication device including three or more electro-absorption modulation elements to which a higher reverse bias potential can be applied to a further stage, and the electro-absorption modulation element capable of absorbing one wavelength at each stage. An optical communication device comprising: a reverse bias supply circuit capable of applying a reverse bias of a higher potential toward a later stage. 6. An optical communication device used as an optical fiber amplifier for amplifying an optical signal obtained by multiplexing light of a plurality of different wavelengths, comprising: a rare earth-doped optical fiber; and an excitation pumping the rare earth-doped optical fiber. A laser light source for excitation; a light synthesizing unit that causes light emitted from the excitation laser light source to enter the rare-earth-doped optical fiber and synthesizes with an optical signal that propagates in the fiber; and a part of light that can be emitted from the amplifier. An optical branching means for branching, and an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential, arranged in series along the traveling direction of the light branched by the optical branching means, and In addition to being capable of demodulation into a signal, it is capable of transmitting an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, and has a higher reverse bias in the latter stage than in the former stage. An optical communication device including a pair of electroabsorption modulators before and after which a potential can be applied; a monitoring wavelength disconnection detection circuit for detecting disconnection of an optical signal of a predetermined wavelength selected by the optical communication device; A reverse bias control circuit capable of applying a reverse bias having a higher potential in a subsequent stage than in a preceding stage to the pair of electroabsorption modulation elements based on a detection result of the monitoring wavelength cutoff detection circuit; and the optical communication device. An excitation laser light source driving circuit for controlling the driving power of the excitation laser light source in accordance with the demodulated electric signal of the optical communication device. 7. An optical communication device for receiving an optical signal in which light of a plurality of different wavelengths is multiplexed, wherein the reverse bias is arranged and applied in series along the traveling direction of the incident optical signal. It can absorb an optical signal having a wavelength shorter than the wavelength corresponding to the potential and demodulate it into an electric signal, and can transmit an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, Further, an optical communication device including a pair of front and rear electro-absorption modulation elements to which a higher reverse bias potential can be applied in the latter stage than in the former stage, and a photodiode that receives an optical signal transmitted through the optical communication device, A wavelength fluctuation detection circuit for detecting a wavelength fluctuation of a received signal based on an output signal of the photodiode and a demodulated electric signal of the optical communication device; and a detection result of the wavelength fluctuation detection circuit. The pair of electric field absorption type modulator elements based, optical communication device characterized by comprising a reverse-bias control circuit towards the subsequent stage can apply a reverse bias potential higher than the previous stage. 8. An optical communication device for transmitting an optical signal formed by multiplexing light of a plurality of different wavelengths, comprising: a plurality of laser light sources each emitting a plurality of optical signals of different wavelengths; An optical branching unit for branching a part of the multiplexed optical signal, and a wavelength corresponding to the applied reverse bias potential, which is arranged in series along the traveling direction of the light branched by the optical branching unit, and It can absorb an optical signal of a shorter wavelength and demodulate it into an electric signal, transmit a wavelength corresponding to the applied reverse bias potential and an optical signal of a wavelength longer than the wavelength, and furthermore, a later stage than the preceding stage. An optical communication device comprising a pair of front and rear electroabsorption modulators to which a higher reverse bias potential can be applied, and a pair of electroabsorption modulators having a higher reverse bias in the latter stage than in the former stage. To A possible reverse bias control circuit, a timing generation circuit for periodically transmitting a timing signal for adjusting a wavelength band received by the optical communication device to each signal wavelength to the reverse bias control circuit, and receiving by the optical communication device And a signal light power information processing circuit capable of adjusting the output of each of the laser light sources based on the demodulated electric signal of the light of each signal wavelength. 9. An optical communication apparatus for transmitting an optical signal obtained by multiplexing light of a plurality of different wavelengths, comprising: a plurality of laser light sources each emitting a plurality of optical signals having different wavelengths; A plurality of variable optical attenuators respectively connected to the output unit of the laser light source; an optical branching unit for branching a part of an optical signal obtained by multiplexing each output light of the laser light source; A wavelength that is arranged in series along the direction and that can absorb an optical signal of a shorter wavelength than the wavelength corresponding to the applied reverse bias potential and demodulate it into an electric signal, and that corresponds to the applied reverse bias potential And an optical communication device having a pair of front and rear electro-absorption modulation elements that can transmit an optical signal having a wavelength longer than the wavelength and that can be applied with a higher reverse bias potential in the latter stage than in the former stage. A reverse bias control circuit capable of applying a reverse bias having a higher potential in the latter stage than in the former stage to the pair of electroabsorption modulators, based on the signal power of each transmission wavelength demodulated by the optical communication device. An optical attenuator control drive circuit for controlling the variable optical attenuator. 10. An optical communication device for receiving an optical signal in which two different wavelengths of light are multiplexed, wherein the reverse bias is arranged and applied in series along the traveling direction of the incident optical signal. It can absorb an optical signal having a wavelength shorter than the wavelength corresponding to the potential and demodulate it into an electric signal, and can transmit an optical signal having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength, An optical communication device having a pair of electro-absorption modulators to which a higher reverse bias potential can be applied further to a later stage, and a demodulated electric signal of a first wavelength demodulated by the preceding electro-absorption modulator. A reverse bias information control circuit for extracting a timing of a transmission signal based on the transmission signal based on the timing signal extracted by the reverse bias information control circuit; And a reverse bias control circuit capable of applying a reverse bias having a higher potential in a subsequent stage than in a preceding stage. 11. An encrypted optical signal transmitting apparatus for wavelength-multiplexing a plurality of different encrypted signals and transmitting them as an optical signal, and an encrypted optical signal for decoding the optical signal and extracting a desired signal on the transmitting side. In an optical communication system including a signal receiving device, the encrypted optical signal transmitting device encrypts and outputs a transmission signal by time-division multiplexing with a plurality of wavelengths of light, and outputs the encrypted optical signal transmitting device. An optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential is arranged in series along the traveling direction of the incident optical signal, and can be demodulated into an electric signal and applied. A pair of electro-absorption modulation elements capable of transmitting an optical signal having a wavelength corresponding to the reverse bias potential and a wavelength longer than the wavelength, and to which a higher reverse bias potential can be applied toward a later stage; An optical communication device and, based on the timing synchronized with the time-division multiplexing timing of the encrypted optical signal transmitting apparatus, apply a reverse bias of a higher potential to the pair of electroabsorption modulation elements in the latter stage than in the former stage. An optical communication system, comprising: 12. An optical spectrum analyzer that decomposes light composed of a plurality of wavelength components into a plurality of wavelength bands and measures optical power in each wavelength band, wherein the optical spectrum analyzer is arranged in series along the traveling direction of the incident light, In addition, an optical signal having a wavelength shorter than the wavelength corresponding to the applied reverse bias potential can be absorbed and demodulated into an electric signal, and the light having a wavelength corresponding to the applied reverse bias potential and a wavelength longer than the wavelength can be demodulated. A plurality of electro-absorption modulation elements capable of transmitting a signal and to which a higher reverse bias potential can be applied toward a later stage, and absorbing one wavelength band in each of the electro-absorption modulation elements according to a resolution value. A reverse bias control circuit capable of applying a reverse bias of a higher potential toward a later stage so as to be able to perform the operation.