JPH04104131A - Semiconductor optical amplification device - Google Patents

Abstract

PURPOSE:To cancel the polarization dependency of a gain and to eliminate need to adjust the phase of signal light by rotating and polarizing signal light which is amplified by a semiconductor optical amplifier and amplifying it again by the same amplifier. CONSTITUTION:The signal light which has loss by being transmitted by a long optical fiber 12 from a transmitter 11 reaches the semiconductor optical amplification device 10 and is passed through an optical coupler 13 and amplified by the semiconductor optical amplifier 14. The amplified signal light is made incident on a Faraday rotator 15 through an isolator 111 and an optical coupler 17. The signal light which is rotated and polarized by the rotator 15 which is so fixed as to provide 45 deg. rotary polarization is reflected totally by a reflecting mirror 112 to travel through the same path with the incident light and made incident on the rotator 15 again and rotated and polarized by 90 deg. in total including the rotary polarization at the time of the incidence. The signal light is further passed through the optical couplers 17 and 13, amplified by the amplifier 14 again, and sent by a long fiber 18 through an isolator 111 and the coupler 17 to reach a receiver 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor optical amplifier device that controls the gain difference caused by the polarization of signal light.

[Conventional technology]

In recent years, along with the development of DFB-LDs (distributed feedback laser diodes) that oscillate in a dynamic single mode, the distance between repeaters in trunk optical communication systems has been lengthened, and capacity has been increased through high-speed direct modulation. . Of these, increasing the distance between repeaters requires increasing the output of DFB-LD and increasing the distance between repeaters.
Although efforts are being made to improve the performance of individual devices, such as increasing the sensitivity of aAs-APDs, there is a limit to the improvement in performance even after achieving high-speed direct modulation. For this reason, research on new optical communication systems using semiconductor optical amplification devices, optical fiber amplification devices, external modulators, and the like has recently been actively conducted. Among these, optical communication systems that use semiconductor optical amplifiers have some problems with their characteristics, but their structure and manufacturing method are similar to those of conventional semiconductor lasers, and there are technical problems in terms of packaging and reliability. It is an optical communication system that is very close to being put into practical use because of its foundation.

By the way, since a semiconductor optical amplifier normally used in a semiconductor optical amplifier device has a rectangular waveguide formed within the semiconductor optical amplifier to control the transverse mode, the gain of the signal light has polarization dependence. Furthermore, the polarization of the signal light varies depending on external conditions such as temperature, and it is extremely difficult to always maintain a constant polarization. Therefore, unless the gain difference caused by the polarization of the semiconductor optical amplifier is controlled, the output of the semiconductor optical amplifier will fluctuate as the polarization of the signal light changes, making it impossible to perform stable optical communication. In order to control the gain difference caused by the polarization of such a semiconductor optical amplifier, there are two types of semiconductor optical amplifier devices as described below.

One is a semiconductor optical amplifier device in which two semiconductor optical amplifiers are arranged in series and signal light is optically rotated by 90 degrees between the two semiconductor optical amplifiers. FIG. 3 shows a configuration diagram of a conventional semiconductor optical amplifier W30 using two semiconductor optical amplifiers 34a and 34b connected in series. A modulated signal output from a signal transmitter 31 including a semiconductor laser and a drive circuit is transmitted through a long optical fiber 32 and reaches a semiconductor optical amplifier 30 .

In the semiconductor optical amplifier 30, the loss of the signal light caused by transmission is amplified by the semiconductor optical amplifier 34a, and the Faraday rotator 35 is fixed to produce 90' optical rotation.
After the signal light undergoes optical rotation by 90 degrees, it enters the semiconductor optical amplifier 34b again and is amplified. The signal light that has been amplified twice in this way is transmitted through a long optical fiber 38 and reaches a receiving section 39, which constitutes a terminal station or a repeater.

In this way, it is possible to cancel out the gain difference caused by the polarization of the semiconductor optical amplifiers using two semiconductor optical amplifiers, to perform ultra-long distance optical fiber transmission, and to realize longer distances between repeaters. It is necessary that the inter-fiber gain of the two semiconductor optical amplifiers used and the gain difference due to polarization match accurately.

The other is a semiconductor optical amplification device in which a signal light is divided into two orthogonal components in advance, amplified by different semiconductor optical amplifiers, and then combined again. FIG. 4 shows a semiconductor optical amplifier 44 in which the signal light is divided in advance and different
FIG. 4 shows a configuration diagram of a semiconductor optical amplification device 40 that employs the method of amplification by a and 44b. The signal light transmitted from the transmitter 41 through the long optical fiber 42 and lost reaches the semiconductor optical amplifier 40 . In the semiconductor optical amplification device 40, the signal light is split into two by the optical coupler 43, and the - side of the light is divided into two by the polarizer 145 to convert only the linearly polarized component to the semiconductor optical amplifier 4.
4a, and the other light is amplified by Faraday rotator 45, which is fixed to produce 90° optical rotation.
After the light has been rotated, the polarizer 1 is
Only the linearly polarized light component orthogonal to the signal light that has passed through the signal light beam 45 is amplified by the semiconductor optical amplifier 44b. The signal light amplified and outputted by the semiconductor optical amplifier 44b is optically rotated back by 90'' by a Faraday rotator 46, then multiplexed again using an optical coupler 47, and further transmitted through a long optical fiber 48 to a receiver 49. In this way, the semiconductor optical amplifier 44a
, 44b, the semiconductor optical amplifier 40 without polarization dependence can be constructed in order to separately amplify and combine two orthogonal linearly polarized components, but the semiconductor optical amplifier 44a
It is necessary that the signal light outputted from the semiconductor optical amplifier 44b and the signal light outputted from the semiconductor optical amplifier 44b whose optical rotation is rotated back by 90° have the same phase when being combined.

[Problem to be solved by the invention]

In the conventional semiconductor optical amplifier device as shown in FIG. 3, which uses the two semiconductor optical amplifiers connected in series, two semiconductor optical amplifiers are used to cancel out the polarization dependence of the gain. It is necessary that the inter-fiber gain and the gain difference due to polarization match accurately. However, in general, the fiber-to-fiber gain of semiconductor optical amplifiers and the gain difference due to polarization vary depending on the individual elements, so it had the disadvantage that considerable selection was required to obtain two usable semiconductor optical amplifiers. .

In addition, in a semiconductor optical amplifier device as shown in Fig. 4, which adopts a method in which signal light is split in advance and amplified by different semiconductor optical amplifiers, the signal light output from one semiconductor optical amplifier and the signal light output from the other semiconductor optical amplifier are separated. It is necessary that the signal light outputted from the signal light beam whose optical rotation is rotated back by 90° be in phase with the signal light beam when being combined. However, since the phases of the two signal lights before being combined are usually not aligned, a phase adjustment part for the signal light is required, and a loss of about 6 dB is unavoidable in the two optical couplers, so semiconductor optical amplification This has the disadvantage that the gain as a device is significantly inhibited.

[Means to solve the problem]

The semiconductor optical amplifier device of the present invention includes a semiconductor optical amplifier and (4)
The semiconductor optical amplifier and the Faraday rotator are arranged in series, and the semiconductor optical amplifier and the Faraday rotator are arranged in series. It has a configuration in which reflective mirrors are arranged so that the signal light passes through it multiple times.

[Embodiment 1] FIG. 1 shows a semiconductor optical amplifier device 1 showing Embodiment 1 of the present invention.
0 is a configuration diagram. Long optical fiber 1 from transmitter 11
The signal light lost after being transmitted through the semiconductor optical amplifier 1
0, the signal passes through the optical coupler 13 and is amplified by the semiconductor optical amplifier 14. The amplified signal light is sent to isolator 1
11, the light enters the Faraday rotator 15 via the optical coupler 17. The signal light that has been optically rotated by the Faraday rotator 15 fixed to produce optical rotation of 45° is transmitted to the reflecting mirror 1.
12, the signal light passes through the same path as the incident light, enters the Faraday rotator 15 again, and undergoes optical rotation of 90'', including the time of incidence.The signal light further passes through optical couplers 17 and 13 and returns to the semiconductor optical amplifier 14. The input signal is input and amplified, and then passed through an isolator 111 and an optical coupler 17 to a long optical fiber 18.
is transmitted to the receiver 19. In two-layer amplification,
Since the signal lights are rotated by 90 degrees with respect to each other, the polarization dependence of the gain of the semiconductor optical amplifier 14 can be canceled out, and it is possible to obtain a semiconductor optical amplifier device that does not have polarization dependence. become.

Furthermore, during amplification, the signal light passes through only one path and is amplified by only one semiconductor optical amplifier 14, so unlike the case where the signal light is split into two, phase adjustment is required when combining the signals. do not. Note that the signal light once amplified by the semiconductor optical amplifier 14 is also input to the optical fiber 18 side when it is demultiplexed by the optical coupler 17, but the signal light that has undergone double layer amplification is about 1 Od. 'A sufficient strength difference of about B can be obtained, so
The receiver 19 can remove it as noise.

[Embodiment 2] FIG. 2 shows a semiconductor optical amplifier device 2 showing Embodiment 2 of the present invention.
0 is a configuration diagram. Long optical fiber 2 from transmitter 21
The signal light transmitted through the semiconductor optical amplifier 2 and lost is transmitted to the semiconductor optical amplifier 2.
0, the light passes through the isolator 121 and the optical coupler 23, and enters the Faraday rotator 25 where it is amplified by the semiconductor optical amplifier 24. The signal light that has been optically rotated by the Faraday rotator 25, which is fixed to produce optical rotation of 45 degrees, is totally reflected by the reflecting mirror 122 and enters the Faraday rotator again through the same path as the incident light. Total 90”
undergoes optical rotation. The signal light enters the semiconductor optical amplifier 24 again, is amplified, passes through the optical coupler 23, is transmitted through the long optical fiber 28, and reaches the receiver 29.

In this example, as in Example 1, it is possible not only to obtain a semiconductor optical amplifier device that does not require phase adjustment and has no polarization dependence, but also to reduce the number of optical couplers to one. It is possible to simplify the configuration and prevent a loss of about 3 dB of signal light caused by an optical coupler.

〔Effect of the invention〕

As explained above, the semiconductor optical amplifier device of the present invention includes a semiconductor optical amplifier, a Faraday rotator fixed to give optical rotation of (45°+n×1'80°), and a reflecting mirror, By rotating the signal light amplified by the amplifier by 90 degrees using a Faraday rotator and a reflecting mirror, and then amplifying it again by the same semiconductor optical amplifier, the gain can be changed without selecting the gain difference due to the polarization of the semiconductor optical amplifier. This has the effect of providing a semiconductor optical amplifier device that is polarization-independent and does not require phase adjustment of signal light.

Note that the semiconductor optical amplifier used in the examples is the same as that conventionally used, so a description of the semiconductor optical amplifier will be omitted.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a semiconductor optical amplifier device showing a first embodiment of the present invention, FIG. 2 is a block diagram of a semiconductor optical amplifier device showing a second embodiment of the present invention, and FIG. 3 is a block diagram of two semiconductor optical amplifiers connected in series. FIG. 4 is a block diagram of a conventional semiconductor optical amplifier using an amplifier. FIG. 4 is a block diagram of a semiconductor optical amplifier that employs a method in which signal light is divided in advance and amplified by different semiconductor optical amplifiers. 11.21.31.41...Transmitter, 12,22゜3
2.42.18, 28, 38.48... optical fiber,
13.23.43, 17.47... optical coupler, 14.
24.34a, 34b, 44a, 44b--Semiconductor optical amplifier, 15, 25.35, 45.46--Faraday rotator, 111.121--Isolator, 1j2,
122...Reflector, 19,29,39°49...Receiver, 145,146...Polarizer.

Claims (1)

[Claims] At least one semiconductor optical amplifier, a Faraday rotator fixed to give optical rotation of (45° + n x 180°) (n is an integer), and a reflecting mirror, and the optical system is amplified by the semiconductor optical amplifier. A semiconductor optical amplification device characterized in that signal light is rotated by 90 degrees using the Faraday rotator and the reflecting mirror, and is amplified again by the semiconductor optical amplifier.