JPS58225744A - Semiconductor laser transmitting circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a beam splitter and to reduce loss to a main light signal, by using a polarized component which is not used for communication as a loop-back light signal in a duplicated semiconductor laser transmitting circuit. CONSTITUTION:The TM polarized component of a laser diode LD21 is polarized at right angled by a polarizer 25 and coupled with an optical fiber 15, and the TM polarized component of an LD22 enters and advances straight in the polarizer 25 and is coupled with the optical fiber 15 through the same route with the TM polarized component of the LD21. Therefore, the TM polarized components are transmitted to the optical fiber 15 through the polarizer 25 regardless of which of the LDs 21 and 22 is in use. A control circuit 13 detects a fault search signal during fault searching operation and then opens an optical switch 14. The TM polarized component transmitted through the optical fiber 15 is converted by a photodetecting element 10 into an electric signal, which is recovered into the light signal through a 3R circuit 11 and a light emitting element 12; and the light signal is returned to the terminal station through the optical fiber 5, thus sending the main signal back. Therefore, a beam splitter, etc., for extracting a loop-back signal are excluded from the main signal path and loss to the main signal is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention is capable of extracting a loopback signal and performing optical film folding without causing loss in the main signal. Automatic output control (APC)
) The present invention relates to a semiconductor laser transmitter circuit that can perform the following steps.

Prior Art and Problems In an optical fiber communication system, when a fault occurs in one of the many repeaters inserted in the transmission path, a repeater monitoring method to search for the faulty repeater is based on a method that searches for each valley repeater. A search signal having a unique frequency is sent from the terminal station, and each repeater is equipped with a filter that selectively passes the unique frequency.When the search signal is detected at the repeater, it is looped. A fault point locating method is generally used in which a faulty repeater is determined by backing up the signal and sending it back to the terminal station. In this case, as for the loopback method in the case of optical fiber cable system, especially optical submarine fiber cable system, it is difficult to accommodate an intervening counterpart made of metal conductor wire in the cable, so the main signal transmitted through optical fiber is looped. A positive signal folding method is used in which the signal is backed up, and an optical film folding method (two methods are used) in which the signal is folded back at the optical signal stage.

FIG. 1 shows a conventional optical film folding repeater monitoring system. In the figure, 1 is the receiving side optical fiber of the uplink, 2
3 is a transmitting optical fiber for the upper line, 4 is a receiving optical fiber for the downlink, and 5 is a transmitting optical fiber for the downlink, which transmits optical signals in opposite directions. A pair of fiber optic cables are shown including. In the repeater 2, an optical-to-electrical conversion element (6#'i) consisting of, for example, an avalanche photodiode (hereinafter abbreviated as APD) is installed.
7 is a 3R circuit of the upper 9 lines; 8 is an electro-optical conversion element (hereinafter referred to as a light emitting element) consisting of, for example, a laser diode (hereinafter abbreviated as LD); 9 is a beam splitter consisting of, for example, a half mirror; For example, lO is A
A photo-electrical conversion element (hereinafter referred to as a photodetector) consisting of a PD
, 11 is a 3R circuit of the lower line, 12 is an electro-optical conversion element (hereinafter referred to as a light emitting element) made of, for example, an LD, 13 is a control circuit, 14 is an optical switch, and 15 is a return optical fiber.

In FIG. 1, an optical signal transmitted through an optical fiber 1 is converted into an electrical signal by a light receiving element 6 and is input to a (3) 3Iζ circuit 7. The 3R circuit 7 receives the input signal, identifies the waveform, performs timing regeneration, and supplies the regenerated electrical signal to the light emitting element 8.

The light emitting element 8t converts the electrical signal into an optical signal and outputs it, and the output optical signal is transmitted to the optical fiber 3 via the beam sinter 9. Similarly, the optical signal transmitted through the optical fiber 4 is converted into an electrical signal by the light receiving element 10 and input to the 3R circuit 11, and the electrical signal reproduced by the 3R circuit 11 is converted into an optical signal by the light emitting element 12. The signal is transmitted to the optical fiber 5.

Now, when a fault search signal is sent to the repeater from a terminal station (not shown), it is detected from the output of the control circuit 13 Fi3R circuit 7 and the optical switch 14 is operated. As a result, a part of the optical signal from the light emitting element 8 passes through the beam sinter 9 and is transmitted to the light receiving element 10 via the return optical fiber 14.
The signal is added to the 3R circuit 11, the light emitting element 12, and sent back to the terminal station via the optical fiber 5, where the main signal is returned.

For this reason, in conventional transmitter circuits, in order to extract loopback signals for repeater monitoring, (4) a beam splitter is inserted in the path of the optical main signal, which increases the loss of the main signal. I couldn't avoid it.

OBJECT OF THE INVENTION The present invention attempts to solve the problems of the prior art, and its purpose is to loop back polarized components that are not used for communication purposes in a dual semiconductor laser transmission circuit. To provide a circuit type that can omit a beam splitter conventionally inserted into an optical main signal path to take out a loopback optical signal by using the optical signal as an optical signal for loopback, and can therefore reduce loss for the optical main signal. There is a particular thing.

Embodiment of the Invention FIG. 2 shows the configuration of an embodiment of the semiconductor laser transmitter circuit of the invention. This figure shows only the main parts related to loopback in the optical repeater, and the remaining parts are constructed in the same manner as in FIG. 1. In FIG. 2, the same parts as in FIG. 1 are indicated by the same numbers, 21.degree. 22 is an LD, 23 and 24 are lenses, and 25 is a polarizer.

The LDs 21 and LDs 22 are arranged such that the axes of their stripes, which are light emitting parts, are orthogonal to each other and their stripe surfaces are orthogonal to each other, and the forward light is directed to the lenses 23 and 24, respectively.
The signals are coupled so as to be input to mutually orthogonal surfaces of the polarizer 23 through the . When one of the LDs 21 and LD 22 is in use, the other is in a cold standby state, and serves as a backup and power source, forming a redundant transmission light source.

As shown in FIG. 3, the LD emits light along the stripe surface in the direction of the stripe axis. In Figure 3, 31 is L
D, 32 is a stripe, and 33 is an emitted light. L
The D light consists of TI polarized light whose electric field component is parallel to the stripe surface, and 1'M polarized light whose electric field component is perpendicular to the stripe surface. LD is light emitting diode (I, ED) and L7
In the IJD light emitting region where light is emitted, the TE polarizing tube T
M-polarized light has almost the same intensity, and in the LD light emitting region where light is emitted as a laser, ij:TE polarizing tube T
Although it is much larger for M-polarized light, its ratio shows a constant value determined by the characteristics of the LD. Usually TE for communication purposes
The polarized light component is used.

In FIG. 2, the light emitted from the LD 21 passes through the lens 23 and enters the polarizer section. The polarizer 25 causes the incident light to travel straight through the TE polarizing tube and transmits it to the optical fiber 3.

On the other hand, the light emitted from the LD 22 passes through the lens 24 and the polarizer 25.
However, since the LD 22 is arranged with its stripe surface rotated at right angles, the TI polarized light is polarized at right angles, and passes through the same path as the TE polarizing tube of LD 21 to the optical fiber 3.
transmitted to. Therefore, LD21.221j, polarizer 25
Both can be transmitted to the TE polarizing tube optical fiber 3 through the TE polarizing tube optical fiber 3, and a duplex transmission light source 'f can be constructed without using any switching means of the optical switching suit. Such a method of duplicating light sources is already known.

On the other hand, it is polarized at right angles by the TM polarization upper polarizer 25 of the LD 21 and coupled to the optical fiber 5. Also, the TM polarized light of the LD 22 enters the polarizer 25 and travels straight (,
The optical fiber 5 passes through the same path on the TM polarization of LD21.
is combined with Therefore, whichever of the LDs 21 and 22 is in use (7) is transmitted to the optical fiber 15 via the TM polarization polarizer 25. However, the optical switch 14 is normally closed and no further transmission of TM polarization occurs.

When searching for a fault, the control circuit 13 detects a fault searching signal and operates the optical switch 14 to open it. optical fiber 15
The 7'cTM polarized light component enters the light receiving element 10, is converted into an electrical signal, passes through the 3R circuit 11 and the light emitting element 12, is converted back into an optical signal, and is sent back to the terminal station via the optical fiber 5. The main signal is looped back.

According to the transmitting circuit shown in the embodiment of FIG. 2, a beam splitter or the like is not required in the main signal path for extracting the loopback signal in the duplicated transmitting light source.
Loss to the main signal can be reduced.

FIG. 4 shows the configuration of another embodiment of the semiconductor laser transmitter circuit of the present invention. In this figure, the same parts as in FIG. 2 are designated by the same numbers, and their operation is also the same as in FIG.

Reference numeral 41 added in FIG. 4 is a beam splitter consisting of a half mirror, 42 is a photodetector, (8) 43 and 44 are amplifiers, and 45 and 46 are LD drive circuits, which control the light in the LDs 21 and 22. It constitutes an automatic output control (APC) system that keeps the output constant.

In FIG. 4, a part of the TM polarized light output of the polarizer 23 is extracted by a beam splitter 41, inputted to a photodetector 42, and converted into an electrical signal. The electrical signals of the photodetector 42 are applied to amplifiers 43 and 44 and compared with reference voltages vR^ and vRB, respectively, and the difference signals are amplified to produce outputs, respectively, and the respective LDs
It is input to drive circuits 45 and 46. Now, for example, LD21
When is currently in use, the LD drive circuit j845 is in an operating state, and the LD drive circuit 45 generates a drive current in response to an input signal from the amplifier 43 to drive the LD 21. Also LD
When the LD 22 is currently in use, the LD drive circuit 46 is in an operating state, and the LD drive circuit 46 generates a drive current in response to an input signal from the amplifier 44 to drive the LD 22 . In either case, negative feedback control is performed so that the TM polarization detected by the soft detector 42 remains constant, and therefore the TI polarization color output, which has a constant relationship with the TM polarization, also becomes constant. In the circuit shown in Fig. 4, by using the TM polarization component as a loopback signal in the duplicated transmitting light source, the loss in the main signal path for extracting the loopback signal is not increased, and the extracted A-pc can be performed using part of the TM polarized light component.

In the embodiment shown in FIG. 2 or 4, if the TM polarization used for loopback or APC is insufficient, the stripe thickness t(0,1
Width w (about 0.5 to 1 μm) with a constant width (about 7 zm)
By gradually narrowing T, compared to the TE polarization component,
Since the M polarization component increases, this method allows the TM polarization component to be adjusted to a desired level. Or LD
By rotating VC within the stripe axis, the TM component of the polarizer output can be adjusted to a desired level.

Effects of the Invention As explained above, according to the present invention, in a dual semiconductor laser transmitting circuit configured by combining the output lights of two LDs via a polarizer, polarized light that is not used for communication purposes is By using the component as a loopback optical signal, there is no need to insert a beam splitter into the optical main signal path, and therefore loss to the optical main signal can be reduced. Furthermore, since APC can be performed using a part of the polarized light components that are not used for communication purposes, the optical main signal level can be stabilized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional optical film folding repeater monitoring system, FIG. 2 is a block diagram showing the configuration of an embodiment of the semiconductor laser transmitter circuit of the present invention, and FIG. 3 is the structure of the semiconductor laser. FIG. 4 is a block diagram showing the configuration of another embodiment of the semiconductor laser transmitter circuit of the present invention. l... Receiving side optical fiber of upper multi-line, 2... Repeater, 3... Transmitting side optical fiber of upper multi-line, 4... Receiving side optical fiber of lower multi-line, 5... Transmitting side optical fiber of lower multiple lines, 6...Receiving device, 7...3R of upper 9 lines
Circuit, 8... Light emitting element, 9... Beam splitter,
10... Light receiving (11) electron, 11... Downlink 3R circuit, ■... Light emitting element, 13... Control circuit, 14... Optical switch, 1
5... Optical fiber for folding, 21, 22... Semiconductor laser (LD), 23, 24... Lens, 25
... Polarizer, 31 ... Semiconductor laser (LD), 32
...stripe, 33...outgoing light, 41...beam splitter, 42...photodetector, 43.44
...Amplifier, 45°46...LD drive circuit. Patent Applicant: Fujitsu Ltd. Representative Patent Attorney Hisashi Tamamushi (3 others) (12)

Claims (2)

[Claims] (1) The optical signal of the bidirectional line transmitted through each receiving side optical fiber is converted into an electrical signal via an optical-to-electrical conversion means, and then converted back to an optical signal via an electrical-to-optical conversion means. In the optical repeater that sends out to each transmitting optical fiber, two semiconductor lasers are coupled via a polarizer, and the polarizer separates and extracts the TE polarized light component and the TM polarized light component on the same path. Duplicated electrical-to-optical conversion means outputs the polarized light component as an optical signal, and when a fault search signal is detected in the received optical signal of one line, the extracted TM polarizing tube fallback signal is used as the extracted TM polarization tube fallback signal of the other line. 1. A semiconductor laser transmitting circuit comprising: a folding means for applying a signal to an optical-to-electrical converting means. (2) The optical signal of the bidirectional line transmitted through each receiving side optical fiber is converted into an electrical signal via an optical-to-electrical conversion means, and then converted back to an optical signal via an electrical-to-optical conversion means. In the optical repeater that sends the TE polarized light and T to the respective transmitting optical fibers, two semiconductor lasers are coupled via a polarizer, and the TE polarized light and T
Duplicated electrical-to-optical conversion means separates and extracts the M-polarized tube and outputs it as a Tg-polarized tube optical signal; The optical signal output is stabilized by controlling the folding means used as a light tube fallback signal to the optical-to-electrical conversion means of the other line and the driving current to the semiconductor laser so that the output of the extracted 7IcTM polarized light is constant. 1. A semiconductor laser transmitting circuit characterized by comprising automatic output control means for controlling the output power.