JP6798676B2 - Optical transmitter and drive adjustment method for optical transmitter - Google Patents

Description

The present invention relates to an optical transmitter and a method for adjusting the drive of the optical transmitter.

Patent Document 1 below discloses an optical receiver capable of automatically controlling the identification level and the like according to an input signal. This optical receiver extracts an optical detector that converts an optical signal into an electric signal, an identification level automatic control circuit into which the electric signal is input, and a clock signal included in the electric signal, and supplies the clock signal to the identification level automatic control circuit. It is equipped with a clock extraction circuit.

JP-A-2002-141956

In order to realize a high-speed and large-capacity optical communication system, an optical multi-value transmission technique using a pulse amplitude modulation (PAM) method is being studied. For example, when optical multi-value transmission is performed using a quadrature pulse amplitude modulation signal (PAM4 signal) that is classified into four levels according to signal strength, first an electric signal (drive signal) for inputting the PAM4 signal to the optical modulator is performed. ). This electrical signal has a waveform with an amplitude corresponding to the level defined by the PAM4 signal. Next, by inputting an electric signal to the light modulator, the light modulator that receives the laser light outputs the modulated laser light (optical signal). The optical receiver receives this optical signal, demodulates it into an electric signal, and detects the level of the electric signal to carry out optical multi-value transmission using the PAM4 signal. In the case of the direct modulation type, an optical signal is output by directly inputting an electric signal to the laser element.

By the way, the relationship (modulation characteristic) between the amplitude of the electric signal input to the light modulator (or laser element) and the emission intensity of the light signal may vary depending on the type and the like. Therefore, depending on the variation in the modulation characteristics of the light modulator (or laser element), the theoretical emission intensity (output light intensity) and the actual emission intensity of the output optical signal according to the amplitude of the input electric signal There may be a gap between the and. Due to this deviation, the theoretical level and the actual level of the optical signal may differ. In this case, there is a problem that optical multi-value transmission is not accurately performed.

An object of the present invention is to provide an optical transmission device and a drive adjustment method for an optical transmission device that can improve the accuracy of optical multi-value transmission using a pulse amplitude modulation method.

The optical transmitter according to one aspect of the present invention includes a semiconductor laser, a drive circuit that outputs a drive signal having three or more different amplitude levels to the semiconductor laser, and three or more different amplitude levels based on the drive signal. It is provided with an amplitude control unit for selecting any of the above.

The optical transmitter according to another aspect of the present invention is an optical transmitter for optical multi-value transmission using a pulse amplitude modulation method, and includes an optical modulator that modulates laser light and outputs an optical signal. A selection signal input portion in which a selection signal is input indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the optical modulator, and an electric signal indicated by the selection signal. It is provided with an amplitude control unit that sets the amplitude of each level of the electric signal so that the difference in emission intensity between each level of the optical signal becomes a predetermined ratio based on the modulation characteristics of the optical modulator within the amplitude range. ..

The optical transmission device according to another aspect of the present invention is an optical transmission device for optical multi-value transmission using a pulse amplitude modulation method, and has a laser element and an amplitude range of an electric signal input to the laser element. , Based on the selection signal input portion where the selection signal is input indicating which of the plurality of predetermined amplitude ranges to select, and the modulation characteristics of the laser element within the amplitude range of the electric signal indicated by the selection signal. It is provided with an amplitude control unit that sets the amplitude of each level of the electric signal so that the difference in emission intensity between each level of the optical signal output from the laser element becomes a predetermined ratio.

The drive adjustment method according to another aspect of the present invention is a drive adjustment method for an optical transmitter including a semiconductor laser, a drive circuit that outputs drive signals having three or more different amplitude levels to the semiconductor laser, and a drive adjustment method. A step of selecting one of three or more different amplitude levels based on the drive signal.

The drive adjustment method according to another aspect of the present invention is a drive adjustment method of an optical transmitter for optical multi-value transmission using a pulse amplitude modulation method, which is input to an optical modulator that modulates laser light. Based on the step of reading a selection signal indicating which of a plurality of predetermined amplitude ranges to select the amplitude range of the electric signal, and the modulation characteristics of the optical modulator within the amplitude range of the electric signal indicated by the selection signal. The step includes setting the amplitude of each level of the electric signal so that the difference in emission intensity between the levels of the optical signal output from the optical modulator becomes a predetermined ratio.

The drive adjustment method according to another aspect of the present invention is a drive adjustment method of an optical transmission device for optical multi-value transmission using a pulse amplitude modulation method, and adjusts the amplitude range of an electric signal input to a laser element. , Output from the laser element based on the step of reading a selection signal indicating which of a plurality of predetermined amplitude ranges to select, and the modulation characteristics of the laser element within the amplitude range of the electrical signal indicated by the selection signal. The step includes setting the amplitude of each level of the electric signal so that the difference in emission intensity between the levels of the optical signal becomes a predetermined ratio.

According to the present invention, it is possible to provide an optical transmission device and a drive adjustment method for an optical transmission device that can improve the accuracy of optical multi-value transmission using a pulse amplitude modulation method.

FIG. 1 is a schematic configuration diagram showing an optical transmission device according to the first embodiment. FIG. 2A is a graph showing the modulation characteristics of the optical modulator in which the drive adjustment method according to the first embodiment is implemented. FIG. 2B is an eye pattern of an electric signal input to the light modulator. FIG. 2C is an eye pattern of an optical signal output from the optical modulator. FIG. 3A is a graph showing the modulation characteristics of the optical modulator in which the drive adjustment method according to the first embodiment is implemented. FIG. 3B is an eye pattern of an electric signal. FIG. 3C is an eye pattern of an optical signal. FIG. 4A is a graph showing the modulation characteristics of the optical modulator in which the drive adjustment method according to the first embodiment is implemented. FIG. 4B is an eye pattern of an electric signal. FIG. 4C is an eye pattern of an optical signal. FIG. 5A is a graph showing the modulation characteristics of the optical modulator in which the drive adjustment method according to the first embodiment is implemented. FIG. 5B is an eye pattern of an electric signal. FIG. 5C is an eye pattern of an optical signal. FIG. 6 is a flowchart illustrating a drive adjustment method of the optical transmission device according to the first embodiment. FIG. 7A is a graph showing the modulation characteristics of the optical modulator in which the drive adjustment method according to the first embodiment is not implemented. FIG. 7B is an eye pattern of an electric signal. FIG. 7C is an eye pattern of an optical signal. FIG. 8 is a schematic configuration diagram showing an optical transmission device according to a second embodiment.

[Explanation of Embodiments of the Invention]
First, the contents of the embodiments of the present invention will be listed and described.

One embodiment of the present invention comprises a semiconductor laser, a drive circuit that outputs a drive signal having three or more different amplitude levels to the semiconductor laser, and one of three or more different amplitude levels based on the drive signal. It is an optical transmission device including an amplitude control unit for selection.

Another embodiment of the present invention is a drive adjustment method for an optical transmitter including a semiconductor laser, a drive circuit that outputs drive signals having three or more different amplitude levels to the semiconductor laser, and a drive. It is a drive adjustment method including a step of selecting one of three or more different amplitude levels based on a signal.

In this optical transmitter and its drive adjustment method, any of three or more different amplitude levels is amplitude-controlled based on a drive signal output from the drive circuit to the semiconductor laser and having three or more different amplitude levels. Selected by department. As a result, the deviation between the theoretical emission intensity and the actual emission intensity in the optical signal can be suppressed, and the accuracy of optical multi-value transmission using the pulse amplitude modulation method can be improved.

Further, another embodiment of the present invention is an optical transmitter for optical multi-value transmission using a pulse amplitude modulation method, which is an optical modulator that modulates laser light and outputs an optical signal, and optical modulation. A selection signal input portion in which a selection signal is input indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the device, and an amplitude range of the electric signal indicated by the selection signal. Optical transmission including an amplitude control unit that sets the amplitude of each level of the electric signal so that the difference in emission intensity between each level of the optical signal becomes a predetermined ratio based on the modulation characteristics of the optical modulator inside. It is a device.

Further, another embodiment of the present invention is a drive adjustment method of an optical transmitter for optical multi-value transmission using a pulse amplitude modulation method, and is an electric signal input to an optical modulator that modulates laser light. Based on the step of reading a selection signal indicating which of a plurality of predetermined amplitude ranges to select the amplitude range of, and the modulation characteristics of the optical modulator within the amplitude range of the electric signal indicated by the selection signal. This is a drive adjustment method including a step of setting the amplitude of each level of an electric signal so that the difference in emission intensity between each level of the optical signal output from the optical modulator becomes a predetermined ratio.

In this optical transmitter and its drive adjustment method, the amplitude control unit reads out the selection signal set arbitrarily, and is based on the modulation characteristics of the light modulator within the amplitude range of the electric signal indicated by the set signal. Therefore, the amplitude of each level of the electric signal can be easily set so that the difference in emission intensity between the levels of the optical signal becomes a predetermined ratio. As a result, it is possible to suppress the deviation that occurs between the theoretical emission intensity and the actual emission intensity in the optical signal. Therefore, the accuracy of optical multi-value transmission using the pulse amplitude modulation method can be improved.

Another embodiment of the present invention is an optical transmission device for optical multi-value transmission using a pulse amplitude modulation method, in which a laser element and an amplitude range of an electric signal input to the laser element are predetermined. Output from the laser element based on the selection signal input portion where the selection signal indicating which of the multiple amplitude ranges to select is input and the modulation characteristics of the laser element within the amplitude range of the electric signal indicated by the selection signal. It is an optical transmission device including an amplitude control unit that sets the amplitude of each level of an electric signal so that the difference in emission intensity between each level of the optical signal is a predetermined ratio.

Further, another embodiment of the present invention is a drive adjustment method of an optical transmission device for optical multi-value transmission using a pulse amplitude modulation method, in which an amplitude range of an electric signal input to a laser element is set in advance. Light output from the laser element based on the step of reading a selection signal indicating which of a plurality of defined amplitude ranges to select, and the modulation characteristics of the laser element within the amplitude range of the electric signal indicated by the selection signal. This is a drive adjustment method including a step of setting the amplitude of each level of an electric signal so that the difference in emission intensity between each level of the signal becomes a predetermined ratio.

In this optical transmitter and its drive adjustment method, by reading out the selection signal set arbitrarily, each of the optical signals is based on the modulation characteristics of the laser element within the amplitude range of the electric signal indicated by the set signal. The amplitude of each level of the electrical signal can be easily set so that the difference in emission intensity between the levels becomes a predetermined ratio. As a result, it is possible to suppress the deviation that occurs between the theoretical emission intensity and the actual emission intensity in the optical signal. Therefore, the accuracy of optical multi-value transmission using the pulse amplitude modulation method can be improved.

[Details of Embodiments of the present invention]
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same reference numerals will be used for the same elements or elements having the same function, and duplicate description will be omitted.

(First Embodiment)
FIG. 1 is a schematic configuration diagram showing an optical transmission device according to the first embodiment. As shown in FIG. 1, the optical transmission device 1 is an indirect modulation type device used for optical multi-value transmission using a pulse amplitude modulation method (PAM method). Therefore, the optical transmission device 1 converts the input signal into a pulse amplitude modulation signal (PAM signal) and outputs an optical signal (output light) based on the PAM signal. In this embodiment, a quadrature pulse amplitude modulated signal (PAM4 signal) is used as the PAM signal. The optical transmitter 1 includes a laser element 2, an optical modulator 3, a selection signal input portion 4, an integrated circuit 5, and an external terminal 6.

The laser element 2 is a semiconductor laser. The laser element 2 outputs the laser light L1 directed to the light modulator 3. The upper limit of the emission intensity (output light intensity) of the laser beam L1 may be set by APC control. The laser element 2 may be on / off controlled by the integrated circuit 5.

The light modulator 3 is optically coupled to the laser element 2 and modulates the laser light L1 into an optical signal L2 according to the amplitude of the input electric signal and outputs the laser light L1 to the outside. As the light modulator 3, for example, an electric field absorption type optical modulator is used. The electric signal input to the light modulator 3 is a signal generated by the drive circuit unit 13 described later and converted from the PAM4 signal. Further, the optical signal L2 modulated by the light modulator 3 is a signal having an emission intensity corresponding to the level defined by the PAM4 signal. The relationship (modulation characteristics) between the amplitude of the electric signal input to the light modulator 3 and the emission intensity of the optical signal L2 output from the light modulator 3 is, for example, the type of the light modulator 3 and the light modulator 3 It changes depending on the bias voltage input to. This modulation characteristic is, for example, pre-measured data (modulation characteristic data) and is stored in the integrated circuit 5.

Here, light modulation using FIGS. 2 (a), 3 (a), 4 (a), and 5 (a) (hereinafter referred to as FIGS. 2 (a) to 5 (a)). The modulation characteristics of the vessel 3 will be described. 2 (a) to 5 (a) are graphs showing the modulation characteristics 21 of the optical modulator 3 to which the drive adjustment method described later is carried out. In FIGS. 2 (a) to 5 (a), the horizontal axis represents the amplitude (unit V) of the electric signal (drive signal) input to the light modulator 3, and the vertical axis is output from the light modulator 3. The emission intensity of the optical signal L2 (unit: dBm, also referred to as the amplitude of the optical signal L2) is shown. As shown in FIGS. 2A to 5A, the modulation characteristic 21 of the light modulator 3 has a region showing linearity and a region showing non-linearity. Specifically, when the amplitude of the electric signal is in the range of -1.5V to -0.5V, the modulation characteristic 21 is a linear region in which the amplitude of the electric signal and the emission intensity of the optical signal change proportionally. There is. On the other hand, when the amplitude of the electric signal is in the range of -2.5V to -1.5V and the range of -0.5V to 0.5V, the modulation characteristic 21 is proportional to the amplitude of the electric signal and the emission intensity of the optical signal. It is a non-linear region that does not change.

The selection signal input portion 4 has a plurality of terminals, and the selection signal indicating which of the plurality of predetermined amplitude ranges the amplitude range of the electric signal input to the optical modulator 3 is selected is This is the part to be input. This selection signal is, for example, a signal that is determined before shipment (manufacturing stage) of the optical transmitter 1 according to the variation in the modulation characteristics of the optical modulator 3, or is determined according to the user's design after shipment. It is a voltage signal input to at least one of a plurality of terminals in the selection signal input portion 4. The selection signal input to the selection signal input portion 4 is any of a plurality of predetermined amplitude ranges of the electric signal depending on the position or number of the input terminals or the combination of the positions and numbers of the terminals. Indicates whether is selected. Therefore, by changing the position or number of terminals to which the selection signal is input, the amplitude range of the electric signal indicated by the selection signal changes. In the first embodiment, any of the four signals of the first to fourth selection signals indicating the amplitude ranges of the electric signals different from each other is input to the selection signal input portion 4.

The amplitude range of the electric signal is the range of the voltage that the electric signal can have. The plurality of predetermined amplitude ranges are, for example, data appropriately set in the manufacturing stage, and are stored in the memory included in the integrated circuit 5.

The integrated circuit 5 is a chip that performs a designated operation and stores various data, and is electrically connected to an optical modulator 3, a selection signal input portion 4, and an external terminal 6. The integrated circuit 5 includes an amplitude control unit 11, a pulse amplitude modulation signal generation unit 12, and a drive circuit unit 13. The integrated circuit 5 may be composed of a single chip or a plurality of chips.

In the following, the amplitude control unit 11, the pulse amplitude modulation signal generation unit 12, and the drive circuit unit 13 of the integrated circuit 5 will be described with reference to FIGS. 2 to 5 as specific examples. 2 (b), 3 (b), 4 (b), and 5 (b) (hereinafter referred to as FIGS. 2 (b) to 5 (b)) are eye patterns of electric signals. Yes, FIGS. 2 (c), 3 (c), 4 (c), and 5 (c) (hereinafter referred to as FIGS. 2 (c) to 5 (c)) show the optical signal L2. It is an eye pattern.

The amplitude control unit 11 sets the light so that the difference in emission intensity between each level of the optical signal L2 becomes a predetermined ratio based on the modulation characteristics of the light modulator 3 within the amplitude range of the electric signal indicated by the selection signal. The amplitude of each level of the electric signal input to the modulator 3 is set. For example, the amplitude control unit 11 reads the selection signal from the selection signal input unit 4. Next, the amplitude range of the electric signal corresponding to the read selection signal is determined. Next, the range of light emission intensity that the optical signal L2 can take is acquired based on the modulation characteristics of the light modulator 3 corresponding to the determined amplitude range of the electric signal. Next, the amplitude control unit 11 divides the acquired emission intensity range into three so as to have a predetermined ratio. At this time, four division points (corresponding to each level of the optical signal L2) for dividing the range of the emission intensity into three are set. Then, the four amplitudes of the electric signal corresponding to the set four division points are acquired.

Here, an example of the function of the amplitude control unit 11 will be specifically described. First, the amplitude control unit 11 reads out the selection signal input to the selection signal input unit 4 and determines the amplitude range of the electric signal defined by the selection signal. For example, when the first selection signal is read out, the amplitude control unit 11 determines the amplitude range of the electric signal to be −2.5V to 0.5V as shown in FIG. 2A. Further, for example, when the second selection signal is read out, the amplitude control unit 11 determines the amplitude range of the electric signal to be −2.5V to −0.5V as shown in FIG. 3A. Similarly, for example, when the third selection signal is read out, the amplitude control unit 11 determines the amplitude range of the electric signal to be −1.5V to −0.5V as shown in FIG. 4A. For example, when the fourth selection signal is read out, the amplitude control unit 11 determines the amplitude range of the electric signal to −1.5V to −0.75V as shown in FIG. 5A.

Next, the range of the emission intensity of the optical signal L2 is determined based on the modulation characteristic 21 corresponding to the amplitude range determined by the read selection signal. For example, when the first selection signal is read out, the amplitude control unit 11 determines the range of the emission intensity of the optical signal L2 to be −20 dBm to −2 dBm as shown in FIG. 2 (a). Further, for example, when the second selection signal is read out, the amplitude control unit 11 determines the range of the emission intensity of the optical signal L2 to be −20 dBm to about −6 dBm, as shown in FIG. 3 (a). Similarly, for example, when the third selection signal is read out, the amplitude control unit 11 determines the range of the emission intensity of the optical signal L2 to be about -16 dBm to about -6 dBm as shown in FIG. 4 (a). Then, for example, when the fourth selection signal is read out, the amplitude control unit 11 determines the range of the emission intensity of the optical signal L2 to be about -16 dBm to -8 dBm as shown in FIG. 5 (a).

Next, the amplitude control unit 11 divides the determined range of emission intensity into three at a predetermined ratio. In the following drive adjustment method, the determined range of emission intensity is evenly divided. Therefore, for example, when the first selection signal is read out, the amplitude control unit 11 sets the point where the emission intensity of the optical signal L2 is −20 dBm in the modulation characteristic 21 as the division point indicating the 0th level, and modulates it. In the characteristic 21, the point where the emission intensity of the optical signal L2 is -14 dBm is set as the division point indicating the first level, and in the modulation characteristic 21, the point where the emission intensity of the optical signal L2 is -8 dBm is set as the division point indicating the second level. It is set as a point, and the point where the emission intensity of the optical signal L2 is -2 dBm in the modulation characteristic 21 is set as the division point indicating the third level. As a result, the emission intensity difference B4 between the 0th level and the first level, the emission intensity difference B5 between the first level and the second level, and the emission intensity difference B6 between the second level and the third level are -6 dBm, respectively. (See also FIG. 2 (c)). Then, the amplitude control unit 11 has an amplitude (-2.5V, -1.25V, -0.75V, and 0.5V) of each level of the electric signal corresponding to the division point indicating the first to third levels. (See also FIG. 2 (b)). Further, for example, when the second to fourth selection signals are read out instead of the first selection signal, the amplitude control unit 11 similarly divides the determined emission intensity range into four divisions to evenly divide the range into three. Points (ie, third to third levels) are set and the four amplitudes of the electrical signal corresponding to the set four division points are acquired (see FIGS. 3-5 for details).

The "predetermined ratio" is, for example, a ratio predetermined by a communication standard and is stored in the memory of the integrated circuit 5. Further, in the following, the amplitude of each level indicated by the electric signal set by the amplitude control unit 11 is also simply referred to as "amplitude information".

The pulse amplitude modulation signal generation unit 12 converts the signal input from the external terminal 6 into a signal suitable for the drive circuit unit 13. In the first embodiment, the pulse amplitude modulation signal generation unit 12 converts one or more modulation signals input from the external terminal 6 having a plurality of terminals into a PAM4 signal.

The drive circuit unit 13 generates and outputs an electric signal input to the light modulator 3. For example, first, the drive circuit unit 13 is input with the PAM4 signal output from the pulse amplitude modulation signal generation unit 12 and the amplitude information of the electric signal output from the amplitude control unit 11. By synthesizing the PAM4 signal and the amplitude information, the drive circuit unit 13 generates an electric signal having an amplitude corresponding to the level defined by the PAM4 signal, and outputs the electric signal to the light modulator 3. As a result, as described above, the light modulator 3 outputs an optical signal L2 having an emission intensity corresponding to the PAM4 signal input to the drive circuit unit 13. The drive circuit unit 13 outputs an electric signal having three or more (specifically, four) different amplitude levels according to the level of the input PAM4 signal to the optical modulator 3.

Next, the drive adjustment method of the optical transmission device 1 according to the first embodiment will be described with reference to FIG. FIG. 6 is a flowchart illustrating a drive adjustment method of the optical transmission device according to the first embodiment.

As shown in FIG. 6, as a first step, a selection signal indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the light modulator 3 is set ( Step S1). In step S1, the modulation characteristics of the optical modulator 3 vary from the amplitude ranges of a plurality of predetermined electric signals, and / or the magnitude of the applied bias voltage (hereinafter referred to as “characteristic variations, etc.”). In the plurality of terminals included in the selection signal input portion 4, the terminals to which the voltage signal is input are determined so that the selection signal can indicate an appropriate amplitude range according to the above.

Next, as a second step, the selection signal is read out (step S2). In step S2, it is read from the number and positions of terminals to which the voltage signal is input in the selection signal input portion 4 which of the plurality of predetermined amplitude ranges the selection signal is selected.

Next, as a third step, the difference in emission intensity between each level of the optical signal L2 is set to a predetermined ratio based on the modulation characteristic 21 of the light modulator 3 within the amplitude range of the electric signal indicated by the selection signal. The amplitude of each level of the electric signal is set in (step S3). For example, the amplitude control unit 11 selects one of the above three or more different amplitude levels based on the electric signal which is the drive signal. In step S3, the amplitude of each level of the electric signal is set so that the difference in emission intensity between each level of the optical signal L2 becomes equal (that is, the range of emission intensity is evenly divided) as described above. (See FIG. 2 (a) and the like). By going through these steps S1 to S3, the drive adjustment method of the optical transmission device 1 is completed.

Next, the operation and effect of the optical transmission device 1 in which the drive adjustment method according to the first embodiment is implemented will be described with reference to FIG. 7. FIG. 7A is a graph showing the modulation characteristics of the light modulator 3 to which the drive adjustment method has not been implemented. In FIG. 7A, the horizontal axis represents the amplitude (unit: V) of the electric signal, and the vertical axis represents the emission intensity (unit: dBm) of the optical signal L2. Further, FIG. 7B is an eye pattern of an electric signal, and FIG. 7C is an eye pattern of an optical signal L2.

As described above, the modulation characteristics of the optical modulator in the optical transmitter change due to, for example, variations in the characteristics of the optical modulator. Therefore, for example, when the amplitude differences B1 to B3 of the 0th level to the 3rd level of the electric signal are simply set evenly by using the optical modulator 3 without implementing the drive adjustment method, FIGS. 7A to 7A. As shown in (c), the emission intensity differences B4 to B6 of the 0th to 3rd levels of the optical signal L2 become uneven. In this case, a gap occurs between the eye pattern of the electric signal input to the light modulator 3 and the eye pattern of the optical signal L2 actually output from the light modulator 3, and the theoretical output optical signal is theoretically The emission intensity is different from the actual emission intensity. As a result, the theoretical level and the actual level of the output optical signal may differ depending on the amplitude of the electric signal input to the light modulator 3. For example, when an amplitude indicating the first level of an electric signal is input to the optical modulator 3, the optical signal L2 is actually the first, although the optical signal L2 theoretically indicates the first level. May show 2 levels. Therefore, if the drive adjustment method according to the first embodiment is not implemented, there is a problem that optical multi-value transmission is not accurately implemented depending on the modulation characteristics of the optical modulator.

On the other hand, when the drive adjustment method according to the first embodiment is implemented, as described above, the light modulator 3 stored in the integrated circuit 5 has a range of amplitudes of a plurality of predetermined electric signals. A selection signal indicating an amplitude range corresponding to variations in the characteristics of the above is input to the selection signal input portion 4. For example, when it is preferable that the modulation characteristic 21 within the amplitude range of the electric signal indicated by the selection signal is only in the linear region in view of the variation in the characteristics of the optical modulator 3, the selection signal input portion 4 has a third selection signal. Alternatively, a fourth selection signal is input. Then, based on the modulation characteristic 21 within the amplitude range of the electric signal indicated by the third selection signal or the fourth selection signal, the emission intensity differences B4 to B6 between the levels of the optical signal L2 are made equal to each other. The amplitude of each level of the electric signal is set. By arbitrarily setting the selection signal according to the optical modulator 3 in this way, each of the optical signals L2 is based on the modulation characteristic 21 of the optical modulator 3 within the amplitude range of the electric signal indicated by the selection signal. The amplitude of each level of the electrical signal can be easily set so that the difference in emission intensity between the levels becomes a predetermined ratio. This makes it possible to suppress the deviation that occurs between the theoretical emission intensity and the actual emission intensity in the optical signal L2. Therefore, according to the first embodiment, the accuracy of optical multi-value transmission using the pulse amplitude modulation method can be improved.

(Second Embodiment)
Hereinafter, the optical transmitter according to the second embodiment will be described. In the description of the second embodiment, the description overlapping with the first embodiment will be omitted, and the part different from the first embodiment will be described. That is, the description of the first embodiment may be appropriately used for the second embodiment to the extent technically possible.

FIG. 8 is a schematic configuration diagram showing an optical transmission device according to a second embodiment. As shown in FIG. 8, unlike the optical transmitter 1 of the first embodiment, the optical transmitter 1A does not include the laser element 2 and the light modulator 3, but instead includes the laser element 2A. It is a modulation type device. Therefore, the electric signal output from the drive circuit unit 13 in the integrated circuit 5 is directly input to the laser element 2A, and the optical signal L2A which is the modulated light is directly output from the laser element 2A. Therefore, the selection signal input to the selection signal input portion 4 indicates which of a plurality of predetermined amplitude ranges the amplitude range of the electric signal input to the laser element 2A is selected. The drive circuit unit 13 outputs an electric signal having three or more (four in the second embodiment) different amplitude levels to the laser element 2A according to the level of the input PAM4 signal.

In the integrated circuit 5 of the second embodiment, the amplitude control unit 11 determines the difference in emission intensity between each level of the optical signal L2A based on the modulation characteristics of the laser element 2A within the amplitude range of the electric signal indicated by the selection signal. The amplitude of each level of the electrical signal is set so as to have a predetermined ratio. Also in the second embodiment, the amplitude control unit 11 may select any of the above three or more different amplitude levels based on the electric signal which is the drive signal.

The drive adjustment method shown in the first embodiment can also be applied to the optical transmission device 1A according to the second embodiment. In other words, the drive adjustment method in the second embodiment includes steps S1 to S3 as in the first embodiment. In step S1 of the second embodiment, a selection signal indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the laser element 2A is set. In step S2 of the second embodiment, the selection signal is read out. In step S3 of the second embodiment, the difference in emission intensity between each level of the optical signal L2A is set to a predetermined ratio based on the modulation characteristics of the laser element 2A within the amplitude range of the electric signal indicated by the selection signal. , Set the amplitude of each level of the electrical signal.

From the above, even in the optical transmission device 1A in which the drive adjustment method according to the second embodiment is implemented, the selection signal is indicated by arbitrarily setting the selection signal according to the variation in the characteristics of the laser element 2A and the like. Based on the modulation characteristics of the laser element 2A within the amplitude range of the electric signal, the amplitude of each level of the electric signal can be easily set so that the difference in emission intensity between the levels of the optical signal L2A becomes a predetermined ratio. Therefore, in the second embodiment as well, the same effects as those in the first embodiment are exhibited.

The optical transmission device and the drive adjustment method thereof according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, the difference in emission intensity between the levels of the optical signals L2 and L2A does not necessarily have to be uniform.

Further, in the above embodiment, the PAM4 signal is used as the PAM signal, but the PAM8 signal having 8 values may be used, or the PAM16 signal having 16 values may be used.

Further, in the above embodiment, the selection signal input portion 4 does not have to have a plurality of terminals. For example, the selection signal input portion 4 may be an externally writable register. In this case, the amplitude control unit 11 may read the selection signal previously input to the register at the manufacturing stage. Further, the selection signal written in advance in the register may be changed by the user after shipment.

The drive adjustment method in the above embodiment may not be carried out again once the selection signal is determined. Further, when the selection signal input to the selection signal input portion 4 is changed, the drive adjustment method may be performed again.

1,1A ... Optical transmitter, 2,2A ... Laser element, 3 ... Optical modulator, 4 ... Selective signal input part, 5 ... Integrated circuit, 6 ... External terminal, 11 ... Amplitude control unit, 12 ... Pulse amplitude modulation signal Generation unit, 13 ... Drive circuit unit.

Claims (4)

An optical transmitter for optical multi-value transmission using a pulse amplitude modulation method.
An optical modulator that modulates laser light and outputs an optical signal,
A selection signal input portion in which a selection signal indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the light modulator is input.
The range of the emission intensity of the optical signal is determined based on the modulation characteristics of the light modulator within the amplitude range of the electric signal indicated by the selection signal, and the determined range of emission intensity is set to a predetermined ratio. an amplitude control unit for luminous intensity difference of the optical signals between divided, each level is further the divided is such that the predetermined ratio, setting the amplitude of each level of the electrical signal,
An optical transmitter equipped with. An optical transmitter for optical multi-value transmission using a pulse amplitude modulation method.
Laser element and
A selection signal input portion in which a selection signal indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the laser element is input.
Based on the modulation characteristics of the laser element within the amplitude range of the electric signal indicated by the selection signal, the range of the emission intensity of the optical signal output from the laser element is determined, and the emission intensity of the determined emission intensity is determined. range was divided into a predetermined ratio, and further wherein as luminous intensity difference of the optical signals between each divided level reaches a predetermined ratio, the amplitude control unit configured to set the amplitude of each level of the electrical signal An optical transmitter equipped with. It is a drive adjustment method of an optical transmitter for optical multi-value transmission using a pulse amplitude modulation method.
A step of reading a selection signal indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the light modulator that modulates the laser light.
A step of determining a range of emission intensity of an optical signal output from the light modulator based on the modulation characteristics of the light modulator within the amplitude range of the electric signal indicated by the selection signal .
A step of dividing the range of the emission intensity into a predetermined ratio,
A step of emitting intensity difference of the optical signals between the divided each level to a predetermined ratio, setting the amplitude of each level of the electrical signal,
Drive adjustment method including. It is a drive adjustment method of an optical transmitter for optical multi-value transmission using a pulse amplitude modulation method.
A step of reading a selection signal indicating which of a plurality of predetermined amplitude ranges is selected for the amplitude range of the electric signal input to the laser element, and
A step of determining a range of emission intensity of an optical signal output from the laser element based on the modulation characteristics of the laser element within the amplitude range of the electric signal indicated by the selection signal .
A step of dividing the range of the emission intensity into a predetermined ratio,
A step of emitting intensity difference of the optical signals between the divided each level to a predetermined ratio, setting the amplitude of each level of the electrical signal,
Drive adjustment method including.

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