JPH06302892A - Optical amplifier for obtaining optical output of constant polarization state - Google Patents

Abstract

PURPOSE:To provide a light amplifier made to obtain high output always having a fixed polarized state at an output end. CONSTITUTION:This light amplifier uses a combination of a polarization selective means such as a polarization filter 2 and a light output adjusting means such as an optical amplifing element 4 operating in a saturated amplification region. Because of different transmission factors at the polarization filter, depending on the polarization states of the respective pulses of input light 1, the respective pulses of filter output light 3 are different in amplitude. In this way, a pulse array uneven in height is inputted to the optical amplifier. At this time, if the input light quantity to the optical amplifier is above a threshold value of a saturated amplification region, a pulse array even in the amplitude and the polarization state can be obtained as output light 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical amplifier element used in an optical communication path using an optical fiber for transmitting an optical digital signal.

[0002]

2. Description of the Related Art FIG. 17 shows a typical usage example (one-way communication) of a conventional semiconductor optical amplifier device. In the figure,
Reference numeral 2001 denotes an optical transmitter for converting an electric signal into an optical signal, 20
Reference numeral 02 is a semiconductor optical amplification element that amplifies an optical signal by stimulated emission, 2003 is an optical receiver that converts an optical signal into an electric signal, 2004 is an optical fiber, and 2005 and 2006 are terminal devices that perform communication. The semiconductor optical amplification device 2002 is
Generally, an antireflection film is formed on the end face of a semiconductor laser, and a large amplification factor is obtained by injecting a large amount of current.

Generally, the polarization state of an optical signal transmitted through an optical fiber varies depending on the force applied to the optical fiber. On the other hand, the semiconductor optical amplifier device has a polarization state dependency in its amplification factor, which, together with the uncertainty of the polarization state of the optical signal in the optical fiber, hinders the provision of a stable transmission line. Was becoming. In order to remove such an instability factor, the amplification factor of the semiconductor optical amplification device 2002 is made polarization independent. For example, US Pat.
As disclosed in Japanese Patent No. 900,917, the input light is separated into two polarization state components, each of which is amplified and then multiplexed, and disclosed in Japanese Patent Application Laid-Open No. 1-257386. As described above, a polarization-independent optical amplifier is realized by a method of using a quantum well in which a biaxial (in-plane) tensile strain is introduced in a well portion in an active layer.

[0004]

However, even when the amplifying element of the above conventional example is used in the communication line as shown in FIG. 17, the polarization state of the light transmitted through the optical fiber is preserved. When the output of the optical amplifier is input to a polarization-dependent element for amplification, there is a drawback that the communication line has different transmission characteristics depending on the polarization state.

The drawbacks will be further described. In general optical communication (in principle, such as shown in FIG. 17), a semiconductor laser is used as a light emitting element in the optical transmitter 2001. The output light of the semiconductor laser is in a substantially linear polarization state. The optical signal transmitted through the optical fiber 2004 has its polarization direction rotated or its polarization state changed due to the disturbance applied to the optical fiber 2004. In this way, the optical signal transmitted while the polarization state changes due to the disturbance is input to the optical receiver 2003. As a component in the optical receiver 2003, for example, a wavelength filter having a waveguide or a photodetector, the characteristics of which differ depending on the polarization state of the input light (for example, in the wavelength filter, the transmission wavelength has a polarization state (T
E, TM) or the photodetector has different sensitivity depending on the polarization state)
The polarization state of the transmitted optical signal changes with time due to the disturbance applied to the fiber 2004, and the intensity of the received signal fluctuates accordingly, which has been an obstacle to establishing a stable communication line.

Therefore, an object of the present invention is to use an optical signal having a constant polarization state at the output end of the optical amplification element by using the polarization selection means and the optical amplification element operating in the saturation amplification region in combination. An optical amplifying device and a device and system using the same are provided.

[0007]

According to the present invention, an optical amplifying device is provided by using a polarization selecting means such as a polarization filter and an optical output adjusting means such as an optical amplifying element operating in a saturation amplification region in combination. The optical signal of a constant polarization state is always obtained at the output end of the.

That is, the optical amplifying device according to the present invention comprises a polarization filter means for transmitting only light of a fixed polarization component in an input optical signal, and an optical output adjusting means having a saturation characteristic in light input / output characteristics. And having.

Specifically, further, optical means for inputting input light to the polarization filter means, and optical means for inputting output light from the polarization filter to the optical output adjusting means,
The optical output adjusting unit has a unit for outputting the output light to the outside, the optical output adjusting unit is an optical amplifying element performing a saturation amplification operation, or the optical amplifying element is composed of a semiconductor optical amplifying element. Alternatively, the optical amplification element is composed of a fiber amplifier doped with rare earth, or the optical output adjusting means is composed of an optical amplification element performing a linear amplification operation and an optical amplification element performing a saturation amplification operation. The light output adjusting means and the polarization filter means may be integrated on the same substrate.

An optical receiver according to the present invention comprises the above optical amplifier, a photodetector having different performance depending on the polarization state, and a control circuit for processing an output signal from the photodetector. And This photodetector may be a waveguide type photodetector.

The optical receiver according to the present invention comprises the above optical amplifier, an optical bandpass filter having different performance depending on the polarization state of input light, a photodetector, and an output signal from the photodetector. It is characterized by comprising a control circuit for processing.

Further, in the optical communication system according to the present invention, a light emitting device whose output light is linearly polarized light, a control circuit for generating an optical signal in the light emitting device according to an input electric signal, and an output from the light emitting device. It is characterized in that it includes at least one optical transmission device including a polarization control device that converts the polarization state of the optical signal thus converted into circularly polarized light, and at least one optical reception device.

Further, the optical transmitter / receiver according to the present invention includes a light emitting device whose output light is linearly polarized light, a control circuit for generating an optical signal in the light emitting device according to an input electric signal, and an output from the light emitting device. A polarization control device for converting the polarization state of the generated optical signal into circularly polarized light, and the optical receiving device.

An optical communication system according to the present invention is characterized by including at least one or more of the above optical receiving device or optical transmitting / receiving device.

[0015]

Embodiment 1 FIG. 1 (a) is a drawing that best represents the features of Embodiment 1 of the present invention. In FIG. 1, 1 is the light that is input light transmitted through an optical fiber, and 2 is, for example, a polarizing plate. Is a polarization filter that transmits only a linear polarization component in a fixed direction, 3 is output light that has passed through the polarization filter 2, and 4
Is an optical amplifier 5 which is a so-called traveling wave type semiconductor laser amplifier in which an antireflection film is formed on the end face of the semiconductor laser, and 5 is output light from the optical amplifier 4. FIG. 3 schematically shows the input / output characteristics of the optical amplifier 4. Figure 3
_Indicates that the input light is amplified substantially linearly until the input light amount reaches a certain amount (P _inth ), and becomes constant output light when the input light amount is relatively strong (saturation region). In this embodiment,
So that the input light quantity to the optical amplifier 4 is in this saturation region,
The current injected into the optical amplifier 4 is adjusted.

Next, the operation of this embodiment will be described with reference to FIG. The input light 1 is transmitted through the optical fiber, its intensity is weakened, and the polarization state is not constant. Since only the intensity is shown in FIG. 2, the pulse train of the input light 1 with uniform amplitude is shown in the graph of FIG. When this pulse train is passed through the polarization filter 2, the transmittance varies depending on the polarization state of each pulse, so that the amplitude of each pulse of the filter output light 3 is different as shown in the graph of FIG.

The pulse train having the uneven heights is input to the optical amplifier 4 in the above operating state. At this time, if the amount of light input to the optical amplifier 4 is greater than or equal to P _inth shown in FIG. 3, the output light 5 of the optical amplifier 4 will be output as shown in the graph of FIG. (Not shown in FIG. 2) can be obtained.

Therefore, by placing such an optical amplifying device in front of the detector of the optical receiver, it is possible to stably receive the signal regardless of the polarization state of the signal transmitted through the optical transmission line.

Not limited to the discrete structure as shown in FIG.
As shown in FIG. 1B, a polarization filter section 2 ′ (for example, a rib type waveguide loaded with metal) and an optical amplification section 4 are provided on a common substrate.
′ (For example, a semiconductor laser structure having a rib type waveguide) may be integrated. In this case, it is not necessary to provide an optical means for inputting light from the former to the latter between the polarization filter unit 2'and the optical amplification unit 4 '.

[0020]

[Embodiment 2] Although Embodiment 1 is shown in a simplified configuration for explaining the basic concept, the value of P _inth of the optical input / output characteristics (FIG. 3) of the optical amplifier 4 is actually By changing the amount of pumping light to the optical amplifier 4 (in the case of the first embodiment, the amount of injected current because it is a semiconductor laser amplifier), its value (P
_inth ) can be changed. The intensity of the output (filter output light 3) of the polarization filter 2 largely depends on the polarization state of the input light to the polarization filter 2, and the filter output light 3 may be weak. In that case, P _{inth of the} optical amplifier 4
It is desirable to keep the value of. The P _inth value can be reduced by reducing the excitation amount (injection current amount), but in this case, the overall amplification factor is reduced. This embodiment has improved this point. FIG. 4 shows the embodiment of the second embodiment.

In FIG. 4, 1 is input light, 2 is a polarization filter, 3 is filter output light, 6A and 6B are first and second optical amplifiers having different characteristics, and 7A and 7B are first optical amplifiers 6A.
And the output light from the second optical amplifier 6B. The polarization filter 2 and the first and second optical amplifiers 6A and 6B may be the same as those in the first embodiment.

The first optical amplifier (1) is shown in FIGS. 5 (a) and 5 (b).
6A and the optical input / output characteristics of the second optical amplifier (2) 6B are shown. As can be seen from FIG. 5, the value of the input light power (P _inth ) at which the output light is saturated is set to be smaller in the optical amplifier (1) 6A (in the device of this embodiment, the optical amplifier 6A, The amount of current injected into 6B is adjusted).

With such a configuration (shown in FIGS. 4 and 5), the P _{inth of the} optical amplifier (1) 6A is small even if the output light 3 from the polarization filter 2 is weak, for example. A pulse train having the same amplitude and polarization is generated in the optical amplifier output light 7A (however, in this case, the amplitude is smaller than that of the input light 1, that is, not sufficiently amplified). By amplifying the pulse train having a small amplitude but a uniform amplitude by the optical amplifier (2) 6B, a pulse train having a large amplitude and a uniform size with respect to the input light 1 and a uniform polarization direction can be obtained. You can

In such operation, the optical amplifier (1) 6A
Is operating in saturation, and the optical amplifier (2) 6B is operating linearly.

It is also possible to reverse the operational relationship of this optical amplifier. In this case, the output light 3 of the polarization filter 2 is linearly amplified (in this state, the pulse train has the same polarization state but not the same amplitude), and thereafter,
An optical amplifier that is operating in saturation adjusts the amplitude and outputs the output light. By this operation, it is possible to generate a pulse train having a uniform amplitude and a uniform polarization state.

FIG. 6 shows a modification of this embodiment. Figure 6
Since the constituent members of (1) are the same as those in FIG. 4, the same numbers are attached. The configuration is such that the input light 1 is amplified by the optical amplifier (1) 6A,
The output light 7A is input to the polarization filter 2 and
Output light 3 is amplified by the optical amplifier (2) 6B, and output light 7B
To get At this time, the optical amplifier (1) 6A is made to perform a linear operation and the optical amplifier (2) 6B is made to perform a saturated operation, so that the same function is achieved. Regarding the combination of the two linear operation / saturation operation optical amplifiers and the polarization filter, the one in which the polarization filter is placed at the last stage and the one in which the saturation operation optical amplifier, the polarization filter, and the linear operation optical amplifier are arranged in this order The above function cannot be fully performed.

The optical amplifiers that perform saturation operation shown in the first and second embodiments are only required to be able to make the amplitudes of pulse trains having different amplitudes constant, and for example, optical bistable elements that have saturation characteristics in their optical input / output characteristics. Can be used.

The optical amplifiers shown in Examples 1 and 2 may be the polarization-independent optical amplifiers shown in the description of the conventional example.

[0029]

Third Embodiment FIG. 7 shows an example of using the optical amplifying device of the present invention. FIG. 7 shows the configuration of the optical receiver 16 used in the wavelength division multiplexing communication system. In FIG. 7, 10 is the optical amplification device shown in Embodiments 1 and 2, 11 is a waveguide type bandpass filter, 12 is a photodetector, 13 is a control circuit, and 14
Is an input light, and 15 is an output signal.

Next, the operation will be described. The optical signal transmitted through the optical fiber (not shown) becomes the input light 14 of the optical receiver 16, and the input light 14 is linearly polarized and aligned in the polarization direction by the optical amplifier 10 and has a constant amplitude. The pulse train is converted into a pulse train and input to the bandpass filter 11. Only a pulse train of a desired wavelength is extracted by the bandpass filter 11, inputted to the photodetector 12, and converted into an electric signal. The electric signal output from the photodetector 12 is input to the control circuit 13, is subjected to processing such as shaping, and the output signal 1
It is output as 5.

The waveguide type bandpass filter 11 is, for example, a phase shift type DFB-LD filter (Journal of the Institute of Electronics, Information and Communication Engineers CI, vol J73-CI, No5).
pp347-353 May 1990). The behavior of such a device is different between TE polarized light and TM polarized light. In the present embodiment, the polarization direction of the output light of the optical amplifying device 10 is the waveguide type bandpass filter 1.
It was adjusted so as to match the direction of the TE polarized wave of 1.

Although FIG. 7 does not show a coupling method among the optical amplifying device 10, the bandpass filter 11, the photodetector 12, etc., it goes without saying that an optical coupling means such as a lens is used. Nor.

[0033]

Fourth Embodiment FIG. 8 shows a case where the present invention shown in the first and second embodiments is applied to a receiver 2003 used in a conventional example (FIG. 17).

In this case, since it is not wavelength division multiplexing, the third embodiment
There is no bandpass filter 11 described in 1. The same members as those in the third embodiment are designated by the same reference numerals.

In this embodiment, the photodetector 12 is a waveguide type photodetector. As the waveguide type photodetector 12, there is one such as shown in US Pat. No. 4,360,246. Although the basic operation is the same as that of the third embodiment, a detailed description will not be given. However, an optical signal from the optical amplifying device 10 whose amplitude is uniform and whose polarization direction matches the TE direction of the waveguide type photodetector 12 is described. By making it output
We were able to maintain a stable reception condition at all times.

Although the coupling means between the optical elements is not shown as in the third embodiment, an optical coupling means such as a lens is used.

[0037]

Fifth Embodiment This embodiment provides a more stable communication line when the fourth embodiment is used.

For example, the optical receiver shown in the third or fourth embodiment is used as the optical receiver of the communication path shown in FIG. 17 shown in the conventional example, and the optical transmitter shown in FIG. 9 is used.
In FIG. 9, 18 is a control circuit, 19 is a light emitting device composed of, for example, a semiconductor laser, 20 is one for converting the polarization state of light such as a λ / 4 plate, 21 is an electric signal from a terminal device, 22 Is an optical signal.

In the optical transmitter 17 shown in FIG. 9, the control circuit 18 receives the electric signal 21 from the terminal device and the control circuit 18 controls the light emitting device 1.
9 is controlled to generate an optical signal. When a semiconductor laser, for example, is used for the light emitting device 19, the optical signal becomes a linearly polarized wave. The linearly polarized optical signal is passed through the polarization controller 20 to be circularly polarized. The circularly polarized optical signal 22 generated in the above process is transmitted through the optical fiber, and the optical receiver 16
To enter. Since the operation inside the optical receiver has been described in the third or fourth embodiment, it is omitted here.

By configuring as in this embodiment, the optical signal input to the optical receiver 16 is always circularly polarized. If such a mechanism is not adopted, the optical signal output from the transmitter becomes linearly polarized light, and depending on how external force is applied to the optical fiber on the way, the light transmitted through the polarization filter in the optical receiver 16 may be used. The amount of signal could be very low. Although the present embodiment has been described by being applied to the one-way optical communication system, this method can of course be applied to other forms of optical communication such as wavelength division multiplexing optical communication and bidirectional optical communication.

In this case, the optical amplifier inserted in the communication line is preferably the polarization-independent optical amplifier as shown in the conventional example.

[0042]

Sixth Embodiment This embodiment is a modification of the fifth embodiment. Similar to the fifth embodiment, the communication line having the configuration shown in FIG. 17 will be described as an example.

The optical transmitter 17 shown in FIG. 17 is used as the optical transmitter 2001 in FIG. A conventionally proposed polarization-independent optical amplifier is used as the optical amplification element in FIG. Further, as the optical receiver 2003 in FIG. 17, for example, the optical receiver 1 shown in FIG.
6 is used. The optical amplifying device 10 in the optical receiver 16 has the configuration of FIG. 1 of the first embodiment, and the optical amplifier 4 causes a conventionally proposed polarization-independent optical amplifier to perform a linear amplification operation.

With such a configuration, the light of the constant polarization state is always supplied to the waveguide type photodetector 12 having the polarization dependency which inputs the output light of the optical amplifying device 10 in the optical receiver 16. A signal is input and a stable communication line can be provided.

Like the fifth embodiment, the applicable range of the present embodiment can be applied to optical communication other than the mode shown here.

[0046]

[Embodiment 7] FIG. 12 shows a case where the optical amplifying device of the present invention is used in a bidirectional optical transmission system. In FIG.
Reference numeral 505 is an optical transceiver, and 502 is an optical amplifier, which is composed of, for example, the polarization-independent optical amplifier element described in the conventional example. Reference numeral 504 is an optical fiber.

The optical transceiver 505 has the structure shown in FIG. In FIG. 10, 31 is a control circuit and 32 is
Is a semiconductor laser, 33 is a polarization control device such as a λ / 4 plate, 34 is a photodetector having a polarization dependency in detection sensitivity, 3
Reference numeral 5 is the optical amplifying device shown in the first and second embodiments, 36 is an optical branching / merging element, and 37 is an optical signal input / output to / from the optical transceiver 30. With such a configuration, a stable bidirectional communication line can be provided. Although the polarization control device 33 is shown in FIG. 10, if the polarization control device 33 is not provided, it is possible to provide a transmission line having a significantly less polarization dependency than the conventional one, although the quality of the transmission line is slightly deteriorated. Further, although the optical amplification device 502 has been described as using the polarization-independent optical amplification element in the above description, it may be a semiconductor laser amplifier having polarization dependence. However, also in this case, the quality of the transmission line is slightly degraded.

[0048]

[Embodiment 8] FIG. 13 is a diagram showing a case where the present invention is used in a one-way N to N wavelength multiplex transmission system. In FIG. 13, 5
06 is an optical transmitter (# 1 to #N), 508 is an optical merging element,
509 is an optical branching element, 507 is an optical receiver (# 1 to #N)
Is. The same members as those in the other embodiments are designated by the same reference numerals (optical fiber 504, semiconductor optical amplifier device 50).
2). The optical transmitters # 1 to # N506- (1) to (N) are
It has the structure shown in FIG. 9, and the oscillation wavelengths of the semiconductor lasers are different from each other.

Optical receivers # 1 to #N 507- (1) to
(N) has the configuration shown in FIG. 7, for example.

The optical bandpass filter 11 is adjusted to pass only the wavelength of the optical transmitter #k corresponding to the optical receiver #k in which it is included. By doing so, from the optical transmitter #i 506- (i) to the optical receiver #i.
Light having a plurality of wavelengths passes through the transmission path to 507- (i) (formed by one transmission path optical fiber 504 and the semiconductor optical amplifier 502) to form a plurality of transmission paths equivalently. It will be. Since the transmission method of the transmission path of one wavelength constituted by the optical transmitter #i 506 (i) to the optical receiver #i 506- (1) is the same as that of the fourth embodiment, it is omitted here.

Further, in FIG. 13, the optical branching element 509
The optical bandpass filter 11 (bandpass filter in FIG. 7) in the optical receiver 507 becomes unnecessary by using as an optical demultiplexer.

[0052]

[Embodiment 9] FIG. 14 shows a case where the optical amplifying device of the present invention is used in a loop type optical LAN. In FIG. 14, 511 is a regenerator, 512 is a control station, 513 is a terminal device, 504 is an optical fiber, and 502 is a semiconductor optical amplifier. As the operation of the loop type LAN, a conventionally used method, for example, a token ring method can be used.

The regenerator 511 is generally a photodetector (O / E converter), a semiconductor laser (E / O converter),
The regenerative repeater is used as a preamplifier in which the semiconductor optical amplification device of the present invention is installed in front of a photodetector. By using the semiconductor optical amplifier device of the present invention in a repeater, it becomes possible to stabilize the input power to the photodetector.

[0054]

[Embodiment 10] FIG. 15 shows a case where the semiconductor optical amplifier device of the present invention is used in a bus type optical LAN. In FIG. 15, 514 is an optical branching / merging element, 515 is an optical transceiver, 516 is a terminal device, 502 is a semiconductor optical amplifier device, 5
Reference numeral 04 is an optical fiber.

The optical transceiver 515 is shown in FIG.
It is structured like.

The part of the bus type optical LAN is, for example, CSMA.
The / CD type communication method is used (of course, other token path, TDMA, etc. communication methods may also be used).

A communication request from the terminal device 516 is sent to the optical transceiver 515, and the control circuit 31 in the optical transceiver 515 drives the semiconductor laser 32 according to the communication system of the optical LAN to generate an optical pulse (optical digital signal). To send. The transmitted optical signal is sent to the optical branching / combining element 514 via the optical branching / combining element 36, and the signal is sent out onto the bus line. A semiconductor optical amplifier 502 is provided at an appropriate position on the bus line to transmit an optical signal to the APC.
Amplify. On the other hand, in the receiving process, the optical signal transmitted on the bus line is branched by the optical branching / coupling element 514 and input to the optical transceiver 515. Optical transceiver 515
The optical signal input to is branched by the optical branching / combining element 36, amplified by the semiconductor optical amplifier 35, received by the photodetector 34 via the bandpass filter 38, and converted into an electrical signal. The electric signal is shaped and reproduced by the control circuit 31, and is sent to the terminal device 516.

[0058]

[Embodiment 11] FIG. 16 shows a case where an optical branching element 517 having an amplifying function is installed in place of the optical branching / merging element 514 on the bus line of Example 10.

The optical branching / merging element 517 with a built-in optical amplification element is
For example, the semiconductor optical amplifier device of the present invention is provided at the input portions (3 places) of the optical branching / merging device. The transmission method is the same as that of the tenth embodiment, and therefore will be omitted here.

Further, in the present embodiment, a semiconductor optical amplifier device may be installed between the optical amplifier built-in optical branching elements 517 on the bus line, if necessary.

Although the examples in which the semiconductor optical amplifier device, the semiconductor laser, etc. shown in the third and fourth embodiments are applied to the optical communication system have been described above in the fifth to eleventh embodiments, the applicable optical communication system is this embodiment. The optical communication system using light as a medium for transmitting information is not limited to the example.
It can be used in the usage as shown in FIGS. In Examples 5 to 11, the example in which the optical amplification element operates in the APC is shown, but the constant current operation (constant gain operation) may be performed.

[0062]

As described above, the polarization selecting means and the optical output adjusting means such as an optical amplifier operating in the saturation region are provided.
An optical integrated circuit including a waveguide in an optical receiver connected to an optical communication line or an optical receiver in an optical transceiver by using it as a preamplifier of a waveguide type optical device (a plurality of waveguide type elements Is used), a stable communication path can always be provided even if the polarization state of light transmitted through an optical fiber changes.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention and a modified example thereof.

FIG. 2 is a diagram for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a diagram showing characteristics of the optical amplifier in FIG.

FIG. 4 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

5 is a diagram showing the characteristics of the optical amplifier in FIG.

FIG. 6 is a diagram showing a configuration of a modified example of the embodiment shown in FIG.

FIG. 7 is a diagram showing a configuration in which the present invention is applied to an optical receiver.

FIG. 8 is a diagram showing another configuration in which the present invention is applied to an optical receiver.

FIG. 9 is a diagram showing a configuration of an optical transmitter for making the present invention more effective.

FIG. 10 is a diagram showing a configuration in which the present invention is applied to an optical transceiver.

FIG. 11 is a diagram showing another configuration in which the present invention is applied to an optical transceiver.

FIG. 12 is a diagram for explaining bidirectional optical communication.

FIG. 13 is a diagram showing a configuration of N-to-N bidirectional optical communication.

FIG. 14 is a diagram showing a configuration of a loop type optical LAN.

FIG. 15 is a diagram showing a configuration of a bus type optical LAN.

FIG. 16 is a diagram showing a configuration of a bus type optical LAN.

FIG. 17 is a diagram showing a configuration of a conventional example.

[Explanation of symbols]

 2, 2'Polarization filter 4, 4 ', 6A, 6B Optical amplifier 10, 35, 502 Optical amplification device 11, 38 Bandpass filter 12, 34 Photodetector 13, 18, 31 Control circuit 16, 507 Optical receiver 17, 506 Optical transmitter 19 Light emitting device 20, 33 Polarization control device 30, 40, 505, 515 Optical transceiver 32 Semiconductor laser 36, 514 Optical branching / merging element 504 Optical fiber 508 Optical merging element 509 Optical branching element 511 Reproduction Repeater 513, 516 Terminal device 517 Optical branching element with built-in optical amplification element

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01S 3/094 3/103 H04B 10/16

Claims (17)

[Claims] 1. A polarization filter means for transmitting only light of a fixed polarization component in an input optical signal, and an optical output adjusting means having a saturation characteristic in light input / output characteristics. Optical amplifier. 2. Optical means for inputting the input light to the polarization filter means, optical means for inputting the output light from the polarization filter to the optical output adjusting means, and the optical output adjusting means. 2. The optical amplifying device according to claim 1, further comprising means for outputting the output light of the above. 3. The optical amplifying device according to claim 1, wherein the optical output adjusting means is an optical amplifying element performing a saturation amplification operation. 4. The optical amplifying device according to claim 3, wherein the optical amplifying element is a semiconductor optical amplifying element. 5. The optical amplifying device according to claim 3, wherein the optical amplifying element comprises a rare earth-doped fiber amplifier. 6. The optical amplifying device according to claim 1, wherein the optical output adjusting means comprises an optical amplifying element that performs a linear amplifying operation and an optical amplifying element that performs a saturated amplifying operation. 7. The optical amplifying device according to claim 6, wherein the polarization filter means, the optical amplifying element performing the saturation amplifying operation, and the optical amplifying element performing the linear amplifying operation are arranged in this order. . 8. The optical amplifying device according to claim 6, wherein the optical amplifying element performing the linear amplifying operation, the polarization filter means, and the optical amplifying element performing the saturated amplifying operation are arranged in this order. . 9. The optical output adjusting means and the polarization filter means,
The device is integrated on the same substrate.
The optical amplification device described. 10. The optical amplifying device according to claim 1 or 6, a photodetector having different performance depending on a polarization state, and a control circuit for processing an output signal from the photodetector. Optical receiver. 11. The optical receiver according to claim 10, wherein the photodetector is a waveguide type photodetector. 12. An optical communication system comprising at least one optical receiving device according to claim 10. 13. The optical amplifying device according to claim 1, an optical bandpass filter having different performance depending on a polarization state of input light, a photodetector, and an output signal from the photodetector. An optical receiving device comprising a control circuit. 14. An optical communication system comprising at least one optical receiving device according to claim 13. 15. A light emitting device whose output light is linearly polarized light, a control circuit for generating an optical signal in the light emitting device according to an input electric signal, and a polarization of the optical signal output from the light emitting device. An optical communication system comprising at least one optical transmitting device comprising a polarization control device for converting a state into circularly polarized light and at least one optical receiving device according to claim 10 or 13. 16. A light emitting device in which the output light is linearly polarized light, a control circuit for generating an optical signal in the light emitting device according to an input electrical signal, and a polarization of the optical signal output from the light emitting device. An optical transmission / reception device comprising a polarization control device for converting a state into circularly polarized light, and the optical reception device according to claim 10. 17. An optical communication system comprising at least one optical transmitter / receiver according to claim 16.