JPH0327633A - Laser diode driving system - Google Patents

Abstract

PURPOSE:To output an NRZ optical signal whose half value width is 100% by taking logic operation to a retarded NRZ signal and the original NRZ signal and inputting a signal whose half value width is increased by 100% or above to the driving circuit of a laser diode. CONSTITUTION:A variable delay circuit 1 retards an inputted NRZ electric signal for an optical time and is connected to the 2nd input terminal of an OR circuit 2. A laser diode LD 3 emits a coherent light with the strength responding to the current to be inputted, the output terminal of the circuit 2 is connected to an LD driving circuit 4 driving the LD 3. The circuit 4 is a differential current switching circuit, an NRZ signal is inputted to the base of one TR 1 and a voltage VREF1 being the center level of the NRZ signal inputted to the base of the TR 1 is fed to the base of other TR 2. A 3rd TR 3 is a TR to supply a bias current and the voltage VREF2 to set the bias current is applied to the base.

Description

[Detailed Description of the Invention] [Summary] Regarding a laser diode driving method for converting an NRZ digital electrical signal into an optical signal in an optical communication system, a laser capable of outputting an NRZ optical signal with a half width of 100% is provided. The purpose is to provide a diode drive system, and it is designed by using a variable delay circuit that inputs an NRZ electrical signal and outputs the signal with a variable delay, and by taking the logic between the output signal of the variable delay circuit and the original signal. , and a logic circuit that outputs an electrical signal with a half-width increased to 100% or more, and the output signal of the logic circuit is configured to be input to a laser diode drive circuit that converts the electrical signal into an optical signal.

[Industrial application field]

The present invention relates to a laser diode driving method for converting an NRZ (non-return-to-zero) digital electrical signal into an optical signal in an optical communication system.

In an optical signal transmitter of an optical communication system, a laser diode is driven by an electrical signal and converted into a coherent optical signal having the same waveform as the electrical signal.

[Conventional technology]

When driving a laser diode with an NRZ electrical signal,
Since the duty of the NRZ signal is 100%, the half-width (width of the signal waveform at half the height of the amplitude of the signal waveform with respect to the clock cycle width of the signal transmission path) is 100%.
It was driven by electrical signals.

[Problem to be solved by the invention]

FIG. 4 shows the relationship between the drive current of the laser diode and the optical output. Once the drive current I exceeds the threshold I lm, the light output increases approximately linearly above that point. Therefore, if a bias current corresponding to the threshold value is applied, an optical output having the same waveform as the electrical signal can be obtained.

However, in reality, in order to improve the extinction ratio and reliably eliminate light emission at the "0" level of the signal, the bias current I,
is the threshold current ■. It is set a little smaller than that, and is driven by a signal current based on that point. As a result, the half-width B of the optical output becomes smaller than the half-width A of the electrical signal.

In such a drive system, conventionally, the half width is 100%.
Since the laser diode was driven by the NRZ electric signal, there was a problem in that the half width of the optical output did not reach 100%. If the half-value width does not reach 100%, the duty when the signal data is "1" becomes small, and the cross point of the eye pattern waveform shifts, resulting in a waveform that does not conform to the optical signal standard.

It is an object of the present invention to provide a laser diode driving system capable of eliminating such conventional drawbacks and outputting an NRZ optical signal with a half width of 100%.

[Means to solve the problem]

In order to achieve the above object, the laser diode driving method of the present invention, as shown in FIG. A laser diode that converts the electrical signal into an optical signal by providing a logic circuit 2 that takes the logic between the output signal of the variable delay circuit 1 and the original signal and outputs an electrical signal whose half width is increased to 100% or more. It is characterized in that the output signal of the logic circuit 2 is manually input to the drive circuit 4 of No. 3.

[Effect]

The NRZ electric signal delayed by the variable delay circuit 1 and the original N
Based on the logic with the RZ electric signal, an electric signal whose half width has increased to 100% or more is input from the logic circuit 2 to the drive circuit 4 of the laser diode 3. Therefore, even if the half-width of the optical output is smaller than the half-width of the electrical signal, the half-width of the optical output can be made 100%. At this time, by changing the amount of delay of the NRZ electrical signal using the variable delay circuit 1, the half-width of the NRZ electrical signal inputted to the drive circuit 4 can be adjusted, and the half-width of the optical output can be made exactly 100%. .

〔Example〕

Examples will be described with reference to the drawings.

In FIG. 2, IO is an input terminal for the NRZ electrical signal, which is branched and connected to a known variable delay circuit 1 and a first input terminal of an OR circuit 2.

The variable delay circuit 1 delays the human-powered NRZ electric signal by an arbitrary time and outputs it, and its output terminal is connected to the second terminal of the OR circuit 2.
Connected to the input terminal ■.

3 is a laser diode (LD) that emits coherent light whose intensity corresponds to the current value manually applied, and the output terminal (■) of the OR circuit 2 is connected to a known LD drive circuit 4 for driving the LD 3. has been done.

In this embodiment, the LD drive circuit 4 is a differential current switching circuit, and has two transistors TR with the same characteristics.
I,TR2 is used. The NRZ signal is input to the base of one transistor TRI, and the NRZ signal input to the base of TRI is input to the base of the other transistor TR2. A voltage ■1l1,I, which is the center potential of , is applied.

Further, the third transistor TR3 is a transistor for supplying a bias current, and has a base voltage V1.0 for setting the bias current. ．． 2 is applied. This bias current I, is the threshold current I. of LD3.
It is slightly smaller than L, as shown in FIG.
The half-width B of the optical output waveform of D3 is slightly narrower than the half-width A of the electrical signal waveform.

In the embodiment configured in this way, the half width of the electrical signal is increased to 100% or more by the OR circuit 2, and L
Input to D drive circuit 4. Figure 3 is a time chart showing this state, and the signal that comes out to the output terminal (■) of the OR circuit 2 is the logical sum of the input signals to (■) of each input terminal, and as a result, the signal that comes out to the output terminal (■) of the OR circuit 2 is the The width increases for each range of "1", and the half width of the signal (2) at the output end becomes 100% or more.

The half-value width of the electrical signal input to the LD drive circuit 4 can be changed by adjusting the delay amount of the variable delay circuit 1. Then, while looking at the eye pattern waveform of the optical output signal from the LD 3, it is possible to adjust the waveform so that it is in the most desirable state, that is, the half width of the optical signal waveform is 100%.

Although an OR circuit is used as the logic circuit in the above embodiment, the exact same result can be obtained by using an AND circuit using logical product by taking negative logic.

〔Effect of the invention〕

According to the laser diode drive method of the present invention, it is possible to easily output an optical signal with a half-width of 100%, so it is an excellent method that can always stably obtain an optical signal with a good waveform that conforms to the standard. have an effect.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the present invention. Figure 2 is a circuit diagram of the embodiment, Figure 3 is a logic circuit input/output signal time chart, FIG. 4 is a drive current versus light output characteristic diagram. In the figure, ■...variable delay circuit, 2...logic circuit, 3...Laser diode, 4... Drive circuit. -21

Claims (1)

[Claims] A variable delay circuit (1) that inputs an NRZ electrical signal and outputs the signal with a variable delay, and a logic circuit between the output signal of the variable delay circuit (1) and the original signal. A logic circuit (2) that outputs an electrical signal with a half width increased to 100% or more is provided, and a drive circuit (4) for a laser diode (3) that converts the electrical signal into an optical signal is provided with the logic circuit (2). A laser diode drive method characterized by inputting the output signal of 2).