JPS60192432A - Optical transmitter - Google Patents

Abstract

PURPOSE:To attain stable and accurate operation of an auxiliary function of an optical reception circuit at all times by driving two light emitting elements with a pulse signal of opposite phase mutually and coupling its optical output to the same light guide path to make the sum of optical power in the light guide path to be constant timewise independently of the state of an input pulse signal. CONSTITUTION:An input circuit 10 receives an input pulse signal 14 and outputs a drive pulse 16 in phase and a drive pulse 18 of opposite phase. At the rising of an input pulse signal 14, an opposite phase drive pulse 18 to a base of other transistor (TR) 2 descends, the TR2 is turned off, its collector current is cut off and a light emitting element 22 is turned off. Thus, when the input pulse signal 14 is at high level, only a light emitting element 20 is driven, and only the light of wavelength lambda1 is coupled to the light guide path 28. When the input signal 14 reaches a low level, only the light emitting element 22 is driven and only the light of wavelength lambda2 is coupled to the optical waveguide path 28. Since two beams of light of wavelengths lambda1, lambda2 are transmitted in a form of pulse, the information is transmitted digitally by the light of wavelength lambda1 (or lambda2).

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical transmitter in an optical communication system.

BACKGROUND OF THE INVENTION Conventionally, an optical receiving circuit in an optical communication system for transmitting digital signals has generally been configured to have an auxiliary function as shown in FIG. 1 or 2. That is, in the optical receiving circuit shown in FIG. 1, the electrical signal output from the photoelectric conversion circuit 2 including the light receiving element 1 is outputted as a signal output as it is, while the electrical signal is transmitted through the resistor R and the capacitor C. It is also supplied to one of the comparators 3 through a smoothing circuit consisting of. The other voltage of the comparator 3 is supplied with the reference voltage Vref. Comparator 3 determines that the optical signal has been interrupted for some reason and outputs an optical signal interruption detection signal when the voltage of the electrical signal smoothed by the smoothing circuit and made into a DC average voltage becomes lower than the reference voltage Vref. do. This makes it possible to detect breakage of the leading waveguide, failure of the light emitting element drive circuit, and the like.

In the circuit shown in FIG. 2, an electrical signal output from a photoelectric conversion circuit 2 including a light receiving element 1 is inputted to a variable gain amplifier 4, and also inputted to a smoothing circuit consisting of a resistor R and a capacitor C. Ru. The electric signal is smoothed by the smoothing circuit, converted into a DC average voltage, and then inputted to the DC amplifier 5. The output of the DC amplifier 5 is coupled to the gain control power of the variable gain amplifier 4. In this way, the variable gain amplifier 4 is automatically gain controlled according to the average DC voltage of the electric signal, and a signal with a stable output level is output from the variable gain amplifier 4 as a signal output due to the automatic gain control.

In the optical receiving circuit shown in FIG. 1 or 2 described above, in order to provide auxiliary functions such as an optical signal cutoff detection function or an automatic gain control function, the received electrical signal is smoothed and converted to an average DC voltage. This average DC voltage is used as the control voltage.

For this reason, compared to the time constant C-R of the smoothing circuit in Figures 1 and 2, the optical signal cutoff detection function and automatic gain control function are stable and accurate only for input signals with a sufficiently short pulse width. respond to. Particularly in pulse communication, for a signal that remains in an off state (extinguished state) for a long time, the output voltage of the smoothing circuit becomes zero, and the smoothing circuit cannot function normally. That is, in such a case, the optical receiver circuit with the optical signal interruption detection function will determine that the optical signal has been interrupted even though the optical signal has not been interrupted, and the automatic gain control function will Since the optical receiver circuit is adjusted to the maximum gain, when the next optical pulse signal is input, a signal with an abnormally high level will be output, and automatic gain control will not function.

OBJECTS OF THE INVENTION Therefore, it is an object of the present invention to provide an optical transmitter in which the auxiliary functions of the optical receiver circuit described above always operate stably and accurately.

Structure of the Invention By driving two light emitting elements with pulse signals having opposite phases to each other and coupling their optical outputs to the same optical waveguide,
The sum of optical powers within the optical waveguide remains constant over time, regardless of the state of the human-powered pulse signal. On the other hand, in the optical receiver circuit, a DC voltage proportional to the optical power in the optical waveguide is obtained through the photoelectric conversion circuit, and this is used as a control voltage to control the transmission speed and duty of the human-powered pulse signal. Regardless of the ratio, auxiliary functions such as the optical signal interruption detection function and the automatic gain control function can be operated stably and accurately, especially even in the case of completely DC signal transmission. Focusing on this, the inventor of the present application,
This completes the present invention.

That is, according to the present invention, a first light emitting element that emits light with a wavelength λ1, a second light emitting element that emits light with a wavelength λ2 different from the wavelength λ1, and light from the first and second light emitting elements. A light source characterized by comprising a leading wave path that combines and transmits outputs, and a drive circuit that receives a human pulse signal and drives the first (!: second light emitting element) in opposite phases to each other. A transmitting device is provided.

With the optical transmitter as described above, optical pulses with wavelengths λ1 and λ22, which are in opposite phases to each other, are transmitted through the same optical waveguide, and the sum of the optical powers of the optical pulses with these two wavelengths is always constant. ing.

Such an optical signal transmitted through the leading wavepath is split into two at the input section of the optical receiver, and one optical input is sent to an optical demultiplexer to receive only the optical signal with the first wavelength λ1. After taking it out, the photodetector is manually converted into a photoelectric signal to obtain a signal output.
The other optical input converts all of its optical power photoelectrically and performs auxiliary functions such as optical signal cutoff detection or gain control based on the output signal.

In this way, necessary information can be transmitted using the optical pulse signal of wavelength λ1, and auxiliary functions such as optical signal cutoff detection or gain control can be performed without being affected by the transmission speed or duty ratio of the optical pulse signal of wavelength λ1. It can be performed stably and accurately. .

Embodiments Hereinafter, embodiments of an optical transmitter of the present invention and an embodiment of an optical receiver that can be used in combination with the same will be described with reference to the accompanying drawings.

FIG. 3 is a circuit diagram of an optical transmitter according to the present invention. The illustrated device includes an input circuit 10 and a drive circuit 12. The input circuit 10 receives the input pulse signal 14, and
It outputs a drive pulse 16 of the same phase and a drive pulse 18 of opposite phase. This input circuit 10 can be constituted by, for example, a waveform shaping circuit, and obtains an in-phase drive pulse 16 from its non-inverted output, and obtains an anti-phase drive pulse 18 from its inverted output.

The drive circuit 12 also includes two NPN transistors T.
The two NPN transistors TRI and TR2 have their emitters commonly connected to each other to form a current switching type switch circuit.

In the current switching type switch circuit, the collector of one transistor TRI is connected to a voltage source via a forward-connected light emitting element 20 such as a light emitting diode or a semiconductor laser, and the collector of the other transistor TR2 is The emitters connected to the same voltage source via light emitting elements 22, such as light emitting diodes or semiconductor lasers, and whose commonly connected emitters are grounded via an isometric current source 24 and a resistor 26.

The in-phase drive pulse 16 is applied to the base of the transistor TR1, and the reverse-phase drive pulse 18 is applied to the base of the transistor TR2.

Furthermore, the light emitting elements 20 and 22 output light of wavelengths λ' and A2 having different lengths, and the light outputs are connected to the same leading waveguide 2B, such as an optical fiber, through a suitable optical coupler. (not shown).The two light emitting elements 20 and 22 are selected to have substantially equal light emission output when the same power is applied.

Furthermore, the two wavelengths λ1 and A2 correspond to the optical waveguide 28 used.
A combination is selected such that the wavelength dispersion characteristics and wavelength loss characteristics of the two wavelengths do not differ significantly between the two wavelengths at the transmission speed and transmission distance in that case.

For example, when using a quartz optical fiber as an optical waveguide, combinations such as [λ, = 1.2 μm band, λ2 = IJ μm band] or [λ+ = 1.3 μm band, λ2 = 1.5 μm band] are effective. To output light with a wavelength of 1.2 to 1.5 μm, for example, the oscillation wavelength should be set to 1.1 to 1.8 μm.
This can be achieved by using an InGaAsP semiconductor laser or an InGaAsP light emitting diode that can be varied within the range of , Ga with an emission wavelength of 0.8 to 019 μm
AItAs-based semiconductor laser and an emission wavelength of 1.1 to 1.
The light emitting element 2 is an 8 μm InGaAsP semiconductor laser.
It can also be used for 0 and 22 respectively.

Next, the operation will be explained. In the circuit configuration described above, when the human input pulse signal 14 is applied to the input circuit 10, when the input pulse signal 14 rises, the in-phase drive pulse 16 to the base of the transistor TRI also rises, and the base of the transistor TRI becomes forward biased. , transistor TR
I becomes conductive, and the collector current of the transistor TR1 flows through the light emitting element 20. As a result, the light emitting element 20 emits light, and an optical output having a wavelength λ is outputted to the optical waveguide 28.

When the human pulse signal 14 rises, the other transistor T
The negative phase drive pulse 18 to the base of R2 falls, the transistor TR2 is turned off, its collector current is cut off, and the light emitting element 22 is turned off.

Therefore, when the input pulse signal 14 is at a high level, only the light emitting element 20 is driven and only the light of wavelength λ1 is coupled to the leading waveguide 28.

Conversely, when the input pulse signal 14 falls, the in-phase drive pulse 16 also falls, the base of the transistor TR1 becomes reverse biased, and the transistor TRI is turned off. As a result, the light emitting element 20 extinguishes light, and light with the wavelength λ1 is no longer input to the optical waveguide 28. On the other hand, when the input pulse signal 14 falls, the opposite phase drive pulse 18 rises, the base of the transistor TR2 becomes forward biased, and the transistor T
R2 becomes conductive, the collector current of transistor TR2 flows through the light emitting element 22, and as a result, the light emitting element 22 emits light.
Optical output with wavelength A2 is output to optical waveguide 28.

Therefore, when the human pulse signal 14 becomes low level, only the light emitting element 22 is driven, and only the light of wavelength λ2 is coupled to the leading waveguide 28.

Thus, either one of the wavelengths λ1 and λ2 is always coupled to the optical waveguide 28, and the optical power propagating through the optical waveguide 28 is always maintained at a constant level. At the same time, the wavelength λ
, and λ2 are transmitted in a pulsed manner, so the wavelength λ1
(or λ2) can digitally transmit information.

1 Therefore, an optical signal with wavelength λ1 can be transmitted as a signal component in the optical waveguide, and the sum of the optical power propagating in the leading waveguide is temporally independent of the state of the input pulse signal 14. It becomes possible to maintain a constant power.

Note that although NPN type transistors were used in the above embodiments, it will be understood that PNP type transistors may also be used.

FIG. 4 is a circuit diagram showing an example of an optical receiving device that receives an optical signal transmitted by the optical transmitting device according to the present invention described above.

The optical signal including optical components of wavelengths λ1 and λ2 guided by the optical waveguide 28 is first separated by an optical splitter 30, and one of the signals is guided to an optical splitter 32 that extracts only the signal of wavelength λ. The output is coupled to a light receiving element 38 of a first photoelectric conversion circuit 36 including a DC amplifier 34 and subjected to photoelectric conversion, thereby reproducing the input pulse signal 14.

On the other hand, the other output of the optical splitter 30 is coupled to the light receiving element 42 of the second photoelectric conversion circuit 40 . The light receiving element 42 of the second optical-to-electrical conversion circuit 40 is selected to have approximately the same sensitivity to the wavelengths λ1 and λ2.

The light incident on the light receiving element 42 of this photoelectric conversion circuit 40 is
Since the optical power is not dependent on a human input signal and is constant over time, the photoelectric conversion circuit 40 is constituted by a DC amplifier.

The upper limit of the required frequency band is determined by how long the second photoelectric conversion circuit 40 detects the optical signal interruption state.
The output voltage of is input to a comparator 44 that compares it with a predetermined reference voltage ref, and the comparator 44 outputs a signal when the input voltage is higher than the reference voltage Vref and the optical signal is normally input. outputs a high level signal. On the other hand, if the input terminal voltage is lower than the reference voltage Vref due to a break in the optical waveguide, a failure in the light emitting element drive circuit, etc., a low level optical signal cutoff detection signal is output.

Note that the light receiving elements 38 and 42 may be of a photoconductive type or a photovoltaic type as long as they are sensitive to light of wavelength λ1 and wavelengths λ1 and λ2, respectively. The above example [λ, = 1
．． 2 μm band, λ2=1.3 μm band] and [λ+=1.
3μm band, λ2=1.5μm band], Ge photodiode, Ge avalanche photodiode, InGaAs pin photodiode or InG
A light receiving element such as an aAs avalanche photodiode is suitable.

In this way, regardless of the transmission speed, duty ratio, or code pattern of the human pulse signal 14, even in the case of transmitting a signal that continues only in an off state (quenching state),
An optical receiver having a stable and accurate optical signal interruption detection function can be obtained.

FIG. 5 is a circuit diagram showing another example of an optical receiver that receives the optical signal transmitted by the optical transmitter according to the invention described above. wavelength λ3 guided by the optical waveguide 28,
The optical signal containing the optical component of wavelength λ2 is first separated by an optical splitter 30, and one of the signals is guided to an optical splitter 32 that extracts only the signal of wavelength λ1, and the gain of the output can be controlled electronically. a first photoelectric conversion circuit 4 having a variable gain amplifier 46;
The input pulse signal 14 is coupled to the light receiving element 50 of No. 8 and subjected to photoelectric conversion, and the input pulse signal 14 is reproduced.

The other output of the optical splitter 30 is connected to a second photoelectric conversion circuit 40
is coupled to the light receiving element 42 of. This second photoelectric conversion circuit 40 and its light receiving element 42 are similar to the second photoelectric conversion circuit 40 and its light receiving element 42 in the example of FIG.
It has exactly the same characteristics as the photoelectric conversion circuit 40 and its light receiving element 42. The output voltage of the second photoelectric conversion circuit 40 is input to the gain control terminal of the variable gain amplifier 46.

In this way, the variable gain amplifier 46 is automatically gain controlled based on the photoelectric conversion voltage of the optically combined power of the wavelengths λ1 and λ2, which is not affected by the state of the input pulse signal I4 and is always constant, and the automatic gain control provides a stable output. A level signal is output from the variable gain amplifier 46 as a signal output.

In this way, stable and accurate automatic transmission can be achieved regardless of the transmission speed, duty ratio, or code pattern of the input pulse signal 14, even in the case of signal transmission in which the off state (quenching state) continues for a long time. An optical receiver capable of applying gain control is obtained.

5. It is also possible to configure an optical receiving device that combines the optical signal cutoff detection function and automatic gain control function described above, and
It will be clear that the photoelectric conversion voltage of the photosynthesized power of wavelengths λ1 and λ22 can also be used for other auxiliary functions.

As described in detail of the invention, the optical transmitter according to the present invention transmits a signal of a different wavelength in the guide wavepath in addition to the original optical pulse signal.
By transmitting optical pulse signals of opposite phases, the sum of optical power within the optical waveguide is kept constant over time. Therefore, by converting this optical power into a voltage in the optical receiver and using it as a control voltage, it is not affected by the transmission speed, duty ratio, or code pattern of the input pulse signal, and moreover, the off state (quenching state) can be maintained for a long time. Even in the case of time-continuous signal transmission, auxiliary functions such as a stable and accurate optical signal interruption detection function or an automatic gain control function can be performed stably and accurately.

6

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams of a conventional optical receiver;
The figure is a circuit diagram of an embodiment of an optical transmitter according to the present invention, and FIGS. 4 and 5 are circuit diagrams showing an example of an optical receiver that receives an optical signal transmitted by the optical transmitter according to the present invention. It is a diagram. (Reference numbers) 1: Photodetector, 2: Photoelectric conversion circuit, 3: Comparator, C: Capacitor, R: Resistor, 4: Variable gain amplifier, 5: DC amplifier, 10: Input circuit, 12: Drive circuit, TRI , TR2:) transistor 20: light emitting element with wavelength λ1, 22: light emitting element with wavelength λ2, 24: current source, 26: resistor, 28: optical waveguide, 30: optical splitter, 32: optical demultiplexer, 34: DC amplifier, 36: Photoelectric conversion circuit, 38: Photodetector, 40: Photoelectric conversion circuit, 42: Photodetector, 44: Comparator, 46; Variable gain amplifier, 48; Photoelectric conversion circuit, 50: Photodetector, Patent application Person: Sumitomo Electric Industries, Ltd. Agent: Patent attorney Masahiko Arai 9 Cancer

Claims (1)

Scope of Claims: (1) A first light emitting element that emits light with a wavelength λ1, a second light emitting element that emits light with a wavelength λ2 different from the wavelength λ1, and a combination of the first and second light emitting elements. It is equipped with an optical waveguide that combines and transmits optical output, and a drive circuit that receives an input pulse signal and drives the first and second light emitting elements in opposite phases, and has wavelengths λ1 that are opposite in phase to each other. and λ2 are transmitted through the optical waveguide so that the sum of the optical powers of the optical pulses of these two wavelengths is always constant. (2) The drive circuit is configured with a current switching type switch circuit composed of two transistors whose emitters are commonly coupled to each other, and the first light emitting element is connected to one of the transistors of the current switching type switch circuit. The second light emitting element is connected to the collector side of the other transistor, and drive pulse signals inverted from each other are supplied to the bases of the two transistors of the current switching type switch circuit. An optical transmitter according to claim 1, characterized in that the optical transmitter is configured as follows. −(
3) The optical transmitter according to claim 1 or 2, wherein the first and second light emitting elements are semiconductors. (4) The wavelength λ1 of the first light emitting element and the wavelength λ2 of the second light emitting element are selected so that the wavelength: dispersion characteristics and wavelength loss characteristics of the optical waveguide do not differ greatly between the two wavelengths. An optical transmitter according to any one of claims 1 to 3, characterized in that: (5) The optical transmitter according to claim 4, wherein the wavelength λ1 is around 1.2 μm, and the wavelength λ2 is around 1.3 μm. (6) The optical transmitter according to claim 4, wherein the wavelength λ1 is around 1.3 μm, and the wavelength λ2 is around 1.5 μm.