WO2002058287A1

WO2002058287A1 - Optical transmitter/receiver

Info

Publication number: WO2002058287A1
Application number: PCT/JP2002/000374
Authority: WO
Inventors: Takeshi Ota
Original assignee: Photonixnet Kabushiki Kaisha
Priority date: 2001-01-19
Filing date: 2002-01-21
Publication date: 2002-07-25
Also published as: JPWO2002058287A1

Abstract

An optical transmitter/receiver which can easily discriminate the re-attaching (connection) of an optical fiber without adversely affecting human eyes even when the optical fiber is disconnected from the optical transmitter/receiver body. A failure (O) to transmit an optical signal from the associated optical transmitter/receiver due to disconnected optical fiber is discriminated to change over a switch (8) and send a second reference voltage (10) to an automatic light output control mechanism (7), whereby power of a laser diode (5) is reduced. At the same time, a switch (3) allows the output of a low-frequency first dummy signal (S1) instead of a normal signal, and the associated optical transmitter/receiver also outputs the dummy signal (S1). When an optical fiber on one side is attached, the first dummy signal (S1) is detected and the optical transmitter/receiver sends a low-output second dummy signal (S2). When the optical fiber on the other side is correctly attached, the second dummy signal (S2) is detected at the associated optical transmitter/receiver to switch the transmission signal on the associated side to a normal signal (N) and change a laser diode output to a normal size.

Description

Description Optical transceiver Technical field

The present invention relates to an optical transceiver in an optical communication system using an optical fiber. The present invention relates to an eye-safe mechanism for preventing a laser beam from an optical transceiver from adversely affecting humans. Background art

FIG. 9 is a conceptual diagram showing a conventional optical fiber communication system. In FIG. 9A, the optical signal 105 transmitted from the optical transceiver 101 is transmitted to the optical transceiver 102 through the optical fiber 103. On the other hand, the optical signal 106 transmitted from the optical transceiver 102 is transmitted to the optical transceiver 101 through the optical fiber 104. Such an optical communication system is called a point-to-point system.

FIG. 9 (b) is a conceptual diagram showing a shared bus type optical communication system using the passive optical splitters 115. The optical signal transmitted from the optical transceiver 111 is split by the passive optical splitter 115, and then transmitted to the optical transceiver 112 or 114. On the other hand, the optical signals transmitted from the optical transceiver 112 or 111'4 are combined by the passive optical splitter 115 this time, and then transmitted to the optical transceiver 111. In actual operation, the optical transceivers 112 and 114 are controlled so as not to transmit optical signals at the same time by adopting a time division method. It is good to think that the passive optical splitter 1 15 has the function of concentrating the optical signal path.

FIG. 10 is a time chart showing how an optical signal is transmitted in a conventional optical fiber communication system. FIG. 10 (a) shows the state of optical signal transmission in the point-to-point optical fiber communication system shown in FIG. 9 (a). When there are no valid data 1 2 2 and 1 2 4, idle signals 1 2 1 and 1 2 3 are transmitted. That is, during normal operation, some optical signal is always exchanged between the two optical transceivers 101 and 102. On the other hand, FIG. 10 (b) is a time chart showing how an optical signal is transmitted in the shared bus type optical communication system shown in FIG. 9 (b). During the valid data period 125 and 126, there is a period during which no idle signal is transmitted and no optical signal is transmitted.

There is no problem when the optical transceiver as described above is properly connected by an optical fiber, but the optical transceiver 13 1 is not connected to the optical fiber as shown in Fig. 11 (a). In such a case, there has been a problem that the laser beam 132 from the optical transceiver 13 1 is emitted into free space and adversely affects the human eyes 133. Even if a cover is provided at the entrance of the optical fiber of the optical transmitter / receiver, one end of the optical fiber 13 4 is inserted into the optical transceiver 13 1 and the other end is inserted as shown in Fig. 11 (b). When the laser beam is released to free space, the optical signal 135, ie, the laser beam 133, is emitted to the free space, and there is a problem that the human eye 133 is adversely affected. Conventionally, the laser light output from the optical transceiver is limited to avoid these adverse effects, and the optical transceiver is designed so that even if the laser light is emitted into free space, it does not adversely affect human eyes. It was designed. The condition for preventing health damage to the human eye is called the I-Safe condition, and the mechanism for preventing health damage to the eye is called the eye-safe mechanism.

However, as the transmission speed of optical signals increases, unless high power laser light is used, it is becoming impossible to correctly receive optical signals attenuated by long-distance optical fiber transmission. Also, with the spread of wavelength multiplexing technology, the eye-safe problem has become more important. In wavelength multiplexing technology, optical signals of multiple wavelengths are combined into a single optical fiber.Even if individual optical signals meet the eye-safe condition, the bundled bundle of optical signals does not satisfy the eye-safe condition. Because there is.

As an eye-safe mechanism, an eye-safe mechanism has been proposed in which the operation of an optical amplifier is automatically stopped locally when an optical fiber is cut off, and is automatically restored when a cut-off portion is restored (Japanese Patent Laid-Open No. 6-204). No. 948 publication). Disclosure of the invention

The present invention relates to an optical transmission and reception method for an optical transceiver applied to a point-to-point optical communication system. The aim is to provide a mechanism that does not adversely affect the human eye even if the signal output is improved.

According to the present invention, in order to achieve the above object, a configuration as described in the claims is adopted. Here, a supplementary explanation will be given in connection with the claims. In order to solve the above problem, the optical transceiver of the present invention transmits a low-output first dummy signal (S 1) when no signal is received (0), and outputs the first dummy signal (S 1) When the second dummy signal (S 2) is transmitted, when the second dummy signal (S 2) is received, the high-output regular signal (N) is transmitted when the second dummy signal (S 2) is detected. When transmitting and receiving a normal signal (N), a high-output normal signal (N) is transmitted.

According to the above configuration, in the point-to-point optical transceiver for optical fiber communication, when the optical fiber is disconnected, the laser light is emitted into free space, which causes a health hazard to human eyes. Can be prevented. Also, when the optical fiber is reconnected correctly, the optical transceiver can automatically return to the normal transmission state. Furthermore, even if only one of the two optical fibers comes off, it is possible to prevent the laser light from being emitted into free space and causing a health hazard to human eyes.

It should be noted that the first dummy signal and the second dummy signal can be discriminated by changing the frequency or the like. Further, even when signals of the same frequency are used, discrimination can be performed by taking different sequences. For example, different envelopes may be used, one dummy signal may be intermittent, or an interrupt may be added. In short, it is only necessary that information indicating that a dummy signal is being received from the other party be included in its own dummy signal. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of a first embodiment of the optical transceiver of the present invention.

FIG. 2 is a time chart schematically showing the operation of the optical transceiver of the present invention. FIG. 3 is a diagram showing a transmission state and a reception state of the optical transceiver of the present invention.

FIG. 4 is a diagram illustrating the structure of the normal signal detector 14 and the dummy signal detector 15. Figure 5 shows a signal attenuated by an optical fiber and transmitted to the optical transceiver of the other party. It is a figure showing a situation.

Figure 6 is a signal level diagram showing the relationship between normal signals, dummy signals, and noise.

FIG. 7 is a block diagram showing a second embodiment of the optical transceiver of the present invention.

FIG. 8 is a schematic diagram showing the relationship between the waveforms of the normal signal and the dummy signal in the second embodiment of the optical transceiver of the present invention.

• Fig. 9 is a conceptual diagram showing the point-to-point-point method and the shared bus method.

FIG. 10 is a time chart showing signal paths in the point-in-point method and the shared bus method.

FIG. 11 is a schematic diagram showing that light from an open optical transceiver or an open optical fiber can adversely affect the human eye. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to examples.

[First embodiment]

FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, an electric signal is applied to an input terminal 1, passes through a signal switch 3, drives an LD driver (laser diode driver) 4, and drives a laser diode 5. The laser light (optical signal) 18 emitted from the laser diode 5 is modulated by an electric signal applied to the input terminal 1. The signal switching switch 3 is connected to the first dummy signal oscillator 2a and the second dummy signal oscillator 2b, and if a normal optical signal from the opposing optical transceiver is not detected as described later, it is input. A signal from the first dummy signal oscillator 2a or the second dummy signal oscillator 2b is transmitted as an optical signal 18 instead of the signal from the terminal 1. The oscillation frequencies of the first dummy signal oscillator 2a and the second dummy signal oscillator 2b are selected to be sufficiently lower than the frequency of a normal optical signal. For example, when a normal optical signal is 1 gigabit / second, the first dummy signal from the first dummy signal oscillator 2a is 1 MHz, and the second dummy signal from the second dummy signal oscillator 2a is 2 MHz. Select a value such as z. On the other hand, the optical signal 19 transmitted from the opposing optical transceiver through the optical fiber is photoelectrically converted by the photodetector 11 into a current signal. This current signal is converted into a voltage signal by a transimpedance amplifier 12, then converted into a digital electric signal by a post amplifier 13 having a waveform shaping function, and output from an output terminal 17.

A part 20 of the optical signal from the laser guide 5 is sent to a monitor 6 (photodiode) 6 where it is photoelectrically converted and sent to an automatic optical output control mechanism 7. The automatic optical output control mechanism 7 controls the optical signal output transmitted in accordance with either the first reference voltage 9 or the second reference voltage 10 selected by the output switching switch 8 to a constant value. The first reference voltage 9 defines the optical signal output during normal operation, and for example, a reference voltage is selected such that the laser light output is +6 dBm (4 mW). On the other hand, the second reference voltage 10 is a level that does not impair the human eye when the optical fiber is disconnected and the signal from the opposing optical transceiver is not correctly received, for example, — 6 dBm. (0.25 raW) is selected as the reference voltage.

FIG. 2 shows a case where the optical transceivers 31 and 32 as shown in FIG. 1 are connected to each other. FIG. 2A shows a state in which the two optical transceivers 31 and 32 are correctly connected by the optical fibers 33 and 34. FIG. 2B shows a state in which the two optical transceivers 31 and 32 are disconnected. FIG. 2 (c) shows the moment when only one optical fiber 34 of the two optical transceivers 31 and 32 that have been disconnected is reconnected. Figure 2 (d) shows the moment when one of the optical fibers 3 4 of the optical transceivers 3 1 and 3 2 is connected, and the other optical fiber 3 3 that was disconnected is reconnected. . FIG. 2 (e) is a diagram showing the behavior of the optical transceivers 31 and 32. When no signal is received (0), the first dummy signal S 1 (1 MHz signal) is transmitted, and when the first dummy signal S 1 is received, the second dummy signal S 2 (2 MHz) is received. z signal), and when the second dummy signal S 2 is received, the regular optical signal N (8 B / 10B code of 1 Gbps) is transmitted, and the regular signal N is received. In this case, the normal signal N is transmitted.

When properly connected, the optical transceivers 3 1 and 3 2 transmit a regular optical signal (1 Gbit / s) in high-power mode (+6 dBm), but the optical fiber connection is lost. If hand signal cannot be received, it switches to low power mode (_ 6 dBm), which is safe for human eyes, and the signal to be transmitted is switched to low-speed dummy signal S 1 (1 MHz) instead of regular optical signal. . Here, the reason why the low output light is transmitted without setting the optical signal to zero is to detect the restoration of the connection when the optical transceivers are reconnected. Reconnection cannot be detected if the optical signal is completely cut off.

However, if the normal signal is transmitted when the dummy signal S1 is received, the normal signal output from the optical transceiver 31 becomes the optical fiber when only one optical fiber is connected (Fig. 2 (c)). It is released to free space through 33. In order to prevent such a problem from occurring, in this embodiment, two types of dummy signals are prepared. In the case as shown in FIG. 2 (c), the optical transceiver 31 transmits the second dummy signal S2. This is because the optical transceiver 31 receives the first dummy signal S1. On the other hand, since the optical transceiver has not received any signal (0), it transmits the dummy signal S1. Further, when the other optical fiber 33 is connected as shown in FIG. 2D, the optical transceiver 32 receives the dummy signal S2 and starts transmitting the regular signal N. Next, the optical transceiver 31 that has begun to receive the normal signal N from the optical transceiver 32 also starts transmitting the normal signal N.

FIG. 3 is a time chart schematically showing the operation of the optical transceivers 31 and 32 as described above. When a correct connection is obtained, the optical transceivers 3 1 and 3 2 transmit a regular signal N, and when the connection is broken, output low-output low-frequency dummy signals S 1 and S 2. Referring back to FIG. 1, the mechanism for realizing the above behavior will be described. In FIG. 1, the output from the transimpedance amplifier 12 is sent not only to the post-amplifier 13 but also to the normal signal detector 14, the first dummy signal detector 15a and the second dummy signal detector 15 Also sent to b. The normal signal detector 14 detects a normal optical signal. On the other hand, the first dummy signal detector 15a and the second dummy signal detector 15b have a function of detecting a dummy signal (S1 or S2) from the opposing optical transceiver.

The structure of the normal signal detector 14 is shown in FIG. The normal signal detector 14 includes a band-pass filter 51a, an effective value detector 52a, a reference voltage 54a, and a voltage comparator 53a. After the input signal passes through the band-pass filter 5 1a, the RMS detector The signal is converted into a DC voltage corresponding to the effective value of the optical signal by 52a. The voltage comparator 53a compares this DC voltage value with the reference voltage 54a, and outputs a high-level digital signal when the effective value exceeds the reference voltage. The band-pass filter 51a has the characteristic of passing a normal signal N (8B / 110B code of l Gb ps).

The structure of the first dummy signal detector 15a is shown in FIG. 4 (b). The first dummy signal detector 15a includes a band-pass filter 51b, an effective value detector 52b, a reference voltage 54b, and a voltage comparator 53b. After passing through the low-frequency filter 51b, the input signal is converted to a DC voltage corresponding to the RMS value of the optical signal by the RMS detector. The voltage comparator 53b compares this DC voltage value with the reference voltage 54b, and outputs a high-level digital signal when the effective value exceeds the reference voltage.

The structure of the second dummy signal detector 15b is shown in FIG. 4 (c). The second dummy signal detector 15b comprises a band-pass filter 51c, an effective value detector 52c, a reference voltage 54c, and a voltage comparator 53c. After passing through the low-frequency filter 51c, the input signal is converted into a DC voltage corresponding to the effective value of the optical signal by the effective value detector 52c. The voltage comparator 53c compares this DC voltage value with the reference voltage 54c, and outputs a high-level digital signal when the effective value exceeds the reference voltage.

Figure 4 (d) shows the relationship between the passband characteristics of the bandpass filters 51a, 51b, and 51c and the normal signal N, the first dummy signal S1, and the second dummy signal S2. FIG. For the bandpass filter 51a, for example, a characteristic 57 that passes from 60 MHz (corresponding to 120 Mbps) to 62 MHz (corresponding to 1.25 Gbps) is selected. Also, as described above, the frequency of the first dummy signal S1 is 1 MHz, the frequency of the second dummy signal S2 is 2 MHz, and the band-pass filters 51 b and 51 c correspond to each other. Transmission characteristics 55 and 56 are defined respectively.

In FIG. 1, the output of the normal signal detector 14 is output to the signal detection terminal 21 and the OR of the output of the second dummy signal detector 15 b is obtained by the OR circuit 16. It is used for controlling the signal switching switch 3 and the output switching switch 8. 1st dam — The output of the signal detector 15a is used to control the signal changeover switch 3. Since the regular signal detector 14 has a function of detecting a normal signal, if the output of the regular signal detector 14 is high level, it may be determined that the optical fiber is correctly connected. so Wear. In addition, since the first dummy signal detector 15a can detect the first dummy signal S1, if the first dummy signal detector 15a is at a high level, only the connection of one of the optical fibers is restored. I can judge. If the second dummy signal 15b is at a high level, it can be determined that the connection of both optical fibers has been restored. If the outputs of the normal signal detector 14, the first dummy signal detector 15a, and the second dummy signal detector 15b remain low, the optical fiber was disconnected. It can be determined that it is in the state.

The OR circuit 16 outputs the logical sum of the outputs of the normal signal detector 14 and the second dummy signal detector 15b. When the output of the OR circuit 16 is at a low level, the output switching switch 8 selects the second reference voltage 10 and the automatic optical output control mechanism 7 sets the output of the laser diode 5 to the low output mode (−6 d B m). Also, when the output of the OR circuit 16 is at the one-level level, the signal switching switch 3 selects the second dummy signal oscillator 2 b and sends it to the LD driver 4, resulting in a low output (_ 6 dBm ) A low frequency (1 MHz or 2 MHz) dummy signal will be emitted from the optical transceiver.

When the connection of the optical fiber is restored, first, the first dummy signal S 1 is detected, the output of the first dummy signal detector 15 a becomes high, and the signal switch 3 is switched to the second dummy signal. Switched to output 2b output. As a result, if both optical fibers are correctly connected, the partner station will receive the second dummy signal S2, and the partner station will start transmitting the regular signal N. Then, since the normal signal N is detected in the own station, the output of the OR circuit 16 becomes high level, the signal changeover switch 3 selects the normal signal, and the output changeover switch 8 selects the first reference voltage 9. The normal signal N will be transmitted in the high power mode.

The first and second dummy signals are lower in frequency than the normal signal for the following reason. As shown in FIG. 5, it is assumed that the optical signal 36 is attenuated while propagating through the optical fiber 35 to become an optical signal 37. The optical signal 37 may fall to the lower limit signal level that can be received in the output mode. Here, when the optical fiber is disconnected, the optical transceivers 31 and 32 are switched to the low output mode. Then, even if the signal is at the lowest level that can be received in the high-power mode, the power is further reduced, so that even if the connection is restored, such a low-level signal cannot be detected.

However, compared to a regular signal (1 Gbit / s), a lower frequency (ΓΜ Η ζ or 2 For a dummy signal of MHz), the input conversion noise can be suppressed low by limiting the band of the signal detector. For this reason, it is possible to design a signal detector that can receive a dummy signal even if it cannot receive a normal signal. Figure 6 shows such a relationship. Figure 6 is a signal level diagram. Reference numeral 61 indicates the minimum reception level of the normal signal, and reference numeral 62 indicates the input-converted noise level when the band is 1 GHz (the band of the normal signal). Reference numeral 63 represents the lowest reception level of the dummy signal, and reference numeral 64 represents the input-converted noise level when the bandwidth is within 1 MHz. [Second embodiment]

FIG. 7 is a block diagram showing a second embodiment of the present invention. Dummy signal oscillators 23a and 23b for oscillating another dummy signal by replacing the dummy signal oscillators 2a and 2b are provided. Further, the normal signal detector 14, the first dummy signal detector 15a, and the second dummy signal detector 15b of the first embodiment (FIG. 1) are combined with the envelope filter 70, the gate 71, It has been replaced by a timer 72, a counter 73, a normal signal detection digital comparator 74a, a first dummy signal detection digital comparator 74c, and a second dummy signal detection digital comparator 74b. The output control of the laser beam is performed only for one reference voltage 9, and the reference voltage switching mechanism is removed.

In the present embodiment, the dummy signal is different from that of the first embodiment. Instead of oscillating a low-output dummy signal at a low frequency, a high-output pulse with a low duty ratio is used as the dummy signal as shown in Figs. 8 (b) and 8 (c). Fig. 8 (a) shows the waveform of the regular signal. As shown in Fig. 8, the peak value of the normal signal (the line shown as peak 1 in Fig. 8) and the peak value of the dummy signal (the line shown as peak 2 in Fig. 8) were selected at roughly the same level. ing. However, due to the low duty ratio, the effective value of the dummy signal (the line indicated as RMS-2 in Fig. 8) is lower than the effective value of the normal signal (the line indicated as RMS-1 in Fig. 8). Since the limit of the laser beam exposure to the human eye is specified by the integration value of a considerably long time, on the order of several hundred milliseconds, Figs. 8 (b) and 8 (c) Even a dummy signal as shown in Fig. 1 can prevent health damage to human eyes. As an example, the first dummy signal in Fig. 8 (b) has a pulse width of 6 // seconds and a pulse period of 100 周期 seconds, and the second dummy signal in Fig. 8 (c) has a pulse width of 3 seconds, The pulse period is set to 50 seconds. In each case, the duty ratio is set to 100: 6 (the time ratio at which light is emitted is 6%). Therefore, assuming that the normal signal output is +6 dBm (4 mW), the output is suppressed to 16 dBm (0.24 mW) when the dummy signal is output. In FIG. 7, the output of the post-amplifier 13 is applied to an envelope fill 73 and a counter 73 through a gate 71. The gate 71 is opened for a predetermined time by a signal from the timer 72. The counter 73 also has a latch function, and counts and latches a pulse count number for a predetermined time by a signal from a timer. In the evening, for example, a signal with a period of 1 millisecond is output.

The regular signal detection digit comparator 74a, the first dummy signal detection digital comparator 74c, and the second dummy signal detection digit comparator 74b are counted from the counter (latch) 73. The normal signal, the first dummy signal, and the second dummy signal are detected by comparing the number with the preset numerical value.

When a normal signal is received, it is always detected as high after passing through the envelope fill 70, so the output of the latch 73 during one millisecond is approximately zero. On the other hand, if the first dummy signal is received, after passing through the envelope 70, the counter 73 (latch) 73 counts a value near 10 within 1 millisecond. Similarly, when the second dummy signal is received, the count (latch) 73 counts a value near 5. The state of the received signal can be detected based on the count number.

In this embodiment, since the output limitation of the laser beam at the time of transmitting the dummy signal is performed by the waveform pattern of the dummy signal itself, the peak value control type automatic optical output control mechanism 24 has a reference voltage switching mechanism. There is no need to combine. However, it is necessary to control the output of the laser light according to the peak value of the laser light. Applicability of the invention

As described above, according to the present invention, in an optical transceiver for point-in-point optical communication, when an optical fiber is disconnected, a laser beam is emitted to free space and the human eye is healthy. Damage can be prevented. Also, when the optical fiber is reconnected correctly, the optical transceiver can automatically return to the normal transmission state.

Claims

The scope of the claims

1. An optical transmitter / receiver used to form a one-to-one optical communication system by connecting to an optical fiber,

In a state where nothing is received (0), the first dummy signal (S1) having a low output is transmitted,

When the first dummy signal (S 1) is received, a low-output second dummy signal (S 2) is transmitted,

When the second dummy signal (S 2) is detected, the 髙 output normal signal (N) 'is transmitted,

An optical transceiver that transmits a high-power regular signal (N) when the regular signal (N) is received.

2. The optical transceiver according to claim 1, wherein the first and second dummy signals are lower-frequency signals than normal signals.

3. The optical transceiver according to claim 1, wherein the transmission power is reduced by reducing a pulse duty ratio.

4. The optical transceiver according to claim 1, wherein the dummy signal identification is performed by changing the cycle of the first dummy signal and the second dummy signal.

5. In an optical transceiver used to form a one-to-one optical communication system by connecting to an optical fiber,

First dummy signal generation means;

Second dummy signal generating means;

Means for detecting a regular signal from the optical transceiver of the other party;

Means for detecting a first dummy signal from the optical transceiver of the other party;

Means for detecting a second dummy signal from the other party's optical transceiver; A normal signal, a first dummy signal, a second dummy signal switching means, and a transmission power changing means,

An optical transceiver that reduces transmission power when no signal is detected from a partner optical transceiver and when a first dummy signal is detected.

6. The optical transceiver according to claim 5, wherein the first and second dummy signals are lower-frequency signals than normal signals.

7. The optical transceiver according to claim 5, wherein the transmission power is reduced by reducing the duty ratio of the pulse.

8. The optical transceiver according to claim 5, wherein the dummy signal identification is performed by changing the cycle of the first dummy signal and the second dummy signal.