JP6560020B2 - Optical transmitter and optical transmission system - Google Patents

Description

  The present invention relates to an optical transmitter and an optical transmission system, and more particularly to a technique for avoiding the influence of light output from an optical modulator during adjustment of the optical modulator.

  With the spread of the Internet, mobile phones, smartphones, etc., and the diversification and increase in capacity of services provided, the transmission capacity required for optical communication networks from the metro area to the backbone area is steadily increasing. . With an increase in transmission capacity in an optical communication network, miniaturization of an optical transmitter as a transmission apparatus is required in order to accommodate as many transmission apparatuses as possible in a station that handles the optical communication network.

  FIG. 1 is a block diagram schematically showing a configuration of a general optical transmitter 300. In the optical transmitter 300 shown in FIG. 1, the light L <b> 10 output from the variable wavelength light source 301 passes through the optical modulator 302 and is transmitted from the transmission terminal 305. The control circuit 303 adjusts and controls the optical modulator 302, and the optical modulator 302 performs intensity modulation and phase modulation of the input light, whereby the electrical signal generated by the electrical signal generation circuit 304 and input to the optical modulator 302. An optical signal L11 corresponding to the signal ES10 is transmitted. In order for intensity modulation and phase modulation to be appropriately performed in the optical modulator, it is necessary to detect the optimum point (operation optimum point) of the operating condition of the optical modulator. Further, since the optimal point of operation of the optical modulator drifts with time, it is required that the optical modulator be controlled so as to always maintain the state of the optimal point of operation. Many methods have been proposed as a method for controlling the operation optimum point of such an optical modulator (see, for example, Patent Documents 1 to 5).

  In general, when adjusting an optical modulator, it is necessary to first input light to the optical modulator and feed back the monitoring result of the light output from the optical modulator to a control circuit. As described above, since the adjustment of the optical modulator is performed in a state where light is input, light is output from the optical modulator during the period until the adjustment of the optical modulator is completed. Light output from the optical modulator during adjustment of the optical modulator is unnecessary light that is not intended in the optical transmission system. When such unnecessary light is transmitted to the optical transmission system, there is a possibility of some adverse effects on the optical transmission system. For this reason, the optical transmitter is required to have a function of preventing unnecessary light from being output during adjustment of the optical modulator.

  In order to realize such a function, an optical variable attenuator and a control circuit for controlling the optical variable attenuator are provided at the subsequent stage of the optical modulator, and a mechanism for blocking light output from the optical modulator under adjustment is provided. Has been introduced.

  Patent Document 3 proposes an optical module provided with an optical output reduction means for reducing the optical output to a predetermined value or less when the optical module is in an unstable state.

Japanese Patent No. 3591346 Japanese Patent No. 4397358 JP 2014-66968 A JP 2014-10187 A JP 2014-219571 A

  However, when the optical variable attenuator and the control circuit are provided in the subsequent stage of the optical modulator, the area on the mounting board is occupied by the optical variable attenuator and the control circuit, so that the optical transmitter can be reduced in size and simplified in configuration. Be inhibited. Further, since the optical output reduction means disclosed in Patent Document 3 includes a periodic signal reduction means, a second modulator extinction control means, etc., miniaturization of the optical transmitter and simplification of the configuration are hindered. .

  The present invention has been made to solve the above-described problems, and prevents the adverse effect of light output from an optical modulator during adjustment of the optical modulator while reducing the size and simplifying the configuration. An object of the present invention is to provide an optical transmitter and an optical transmission system that can be used.

Optical transmitter according to the present onset bright differs with wavelengths, and a light source which selectively outputs the light of the first wavelength and the light having the second wavelength, to modulate the light output from the light source to each other An optical modulator that outputs the modulated light; and a passive that blocks the light of the first wavelength and transmits the light of the second wavelength among the light output from the optical modulator. A wavelength selection unit that is an element; and a control unit that controls the light source and the light modulator. The control unit first causes the light source to output light of the first wavelength as an adjustment sequence . When the optimum point of the operating condition of the optical modulator is determined, the operating condition of the optical modulator is set based on the determined optimum point, and the light of the second wavelength is output to the light source after allowed to, as further fine adjustment sequence, the new optimum operating conditions of the optical modulator And setting an operating condition of the optical modulator based on the new optimum point, causing the optical modulator to output a second wavelength, and finally outputting the operation sequence from the optical modulator as an operation sequence. The light of the second wavelength is monitored, and the operating condition of the optical modulator is set based on the monitored result .

The optical transmission system according to the present onset Ming, an optical transmitter, and an optical receiver for receiving the transmitted light from said optical transmitter, said optical transmitter has a different wavelength from each other, the first A light source that selectively outputs light of a wavelength and light of a second wavelength, a light modulator that modulates light output from the light source and outputs the modulated light, the light source, and the light modulation A control unit that controls the optical modulator, wherein the control unit first outputs an optimum operating condition of the optical modulator when the light source outputs light of the first wavelength as an adjustment sequence. And after setting the operating condition of the optical modulator based on the determined optimum point and causing the light source to output the light of the second wavelength , the optical modulation is further performed as a fine adjustment sequence. Determine a new optimal point for the operating conditions of the optical modulator and Set based on a new optimum point, output the second wavelength to the optical modulator, and finally monitor the light of the second wavelength output from the optical modulator as an operation sequence, Based on the monitored result, an operating condition of the optical modulator is set, and the optical receiver is configured to output the first wavelength of the light output from the optical modulator of the optical transmitter. And a wavelength selection unit that is a passive element that transmits light of the second wavelength.

  According to the present invention, the light having the first wavelength output from the optical transmitter is determined while the light source outputs the light having the first wavelength and the optimum point of the operating condition of the optical modulator is determined. Blocked by the part. Since the wavelength selection unit is a passive element and does not require a control circuit used to control the wavelength selection unit, the area for the control circuit can be omitted. Moreover, the structure which provides a wavelength selection part can be implement | achieved comparatively easily. For this reason, the optical transmitter according to the present invention can prevent the occurrence of adverse effects due to light output from the optical modulator during adjustment of the optical modulator while reducing the size and simplifying the configuration.

It is a block diagram which shows the structure of a common optical transmitter roughly. It is a block diagram which shows roughly the structure of the optical transmitter which concerns on Embodiment 1 of this invention. 3 is a block diagram schematically showing a configuration of an optical modulator provided in the optical transmitter according to Embodiment 1. FIG. 3 is a flowchart illustrating an operation of the optical transmitter according to the first embodiment. 3 is a flowchart illustrating an operation of the optical transmitter according to the first embodiment. It is a block diagram which shows roughly the structure of the optical transmitter as a comparative example. 6 is a block diagram schematically showing a configuration of an optical transmitter as a modification of the first embodiment. FIG. It is a block diagram which shows roughly the structure of the optical transmitter which concerns on Embodiment 2 of this invention. It is a block diagram which shows roughly the structure of the optical transmitter which concerns on Embodiment 3 of this invention. It is a block diagram which shows roughly the structure of the optical transmitter which concerns on Embodiment 4 of this invention. FIG. 10 is a diagram schematically showing a configuration of a modulation selection function unit provided in an optical transmitter according to a fourth embodiment. It is a block diagram which shows roughly the structure of the optical transmission system which concerns on Embodiment 5 of this invention. It is a block diagram which shows roughly the structure of the optical transmission system which concerns on Embodiment 6 of this invention.

<< 1 >> Embodiment 1
<< 1-1 >> Configuration FIG. 2 is a block diagram schematically showing the configuration of the optical transmitter 1 according to Embodiment 1 of the present invention. As shown in FIG. 2, the optical transmitter 1 includes a variable wavelength light source 10 as a light source that selectively outputs light having a first wavelength and light having a second wavelength and having different wavelengths. And an optical modulator 20 that modulates the light output from the wavelength light source 10 and outputs the modulated light. In addition, the optical transmitter 1 includes a wavelength selection unit 60 that blocks light having the first wavelength and transmits light having the second wavelength among the light output from the optical modulator 20, and the variable wavelength light source 10. And a control circuit 30 as a control unit for controlling the optical modulator 20. The control circuit 30 determines (detects) the optimum point of the operating condition of the optical modulator 20 when the variable wavelength light source 10 outputs light of the first wavelength, and sets the operating condition of the optical modulator 20 to Based on the determined optimum point, the variable wavelength light source 10 is made to output light of the second wavelength. The optical transmitter 1 also includes an electric signal generation circuit 40 as an electric signal generation unit that supplies an electric signal ES based on transmission data to the optical modulator 20.

  The variable wavelength light source 10 is a light source that can change the wavelength of the output light L0. The optical modulator 20 modulates the light L0 output from the variable wavelength light source 10 based on the electrical signal ES generated by the electrical signal generation circuit 40, and converts the modulated light L1 into light based on the electrical signal ES. Output as a signal. The control circuit 30 outputs a signal I30 for controlling the wavelength of the light L0 output from the variable wavelength light source 10, and outputs a signal V30 for controlling the operating condition of the optical modulator 20. The wavelength selector 60 blocks light having a specific wavelength (a predetermined wavelength) and transmits light having a wavelength other than the specific wavelength. The optical signal L2 that has passed through the wavelength selector 60 is transmitted from the transmission terminal 50 to the optical receiver via the optical transmission path.

  FIG. 3 is a block diagram schematically showing the configuration of the optical modulator 20 provided in the optical transmitter 1 according to the first embodiment. As shown in FIG. 3, the optical modulator 20 includes an optical waveguide 21, an optical monitor unit 22, and a control IF (InterFace) unit 23 for controlling the optical waveguide 21. The light L0 output from the variable wavelength light source 10 is input to the optical modulator 20 and passes through the optical waveguide 21. The light monitoring unit 22 monitors the light L1 by monitoring a part of the light pL1 of the light L1 traveling from the optical waveguide 21 to the transmission terminal 50. The control circuit 30 reads the value M20 monitored by the optical monitor unit 22, and the operation condition of the optical waveguide 21, that is, the operation of the optical modulator 20, through the control IF unit 23 having a DC (direct current) terminal and electrodes. Adjust the conditions. The control circuit 30 performs feedback control, determines (detects) the optimum point of the operating condition of the optical modulator 20, and sets the operating condition of the optical modulator 20 based on the determined optimum point. When the operation condition of the optical modulator 20 is set to the optimum point, the optical modulator 20 is in the state of the optimum operation point.

  In the following description, the operating condition of the optical modulator 20 is the condition of the bias voltage BV applied to the optical modulator 20, and the optimum point of the operating condition of the optical modulator 20 is, for example, the optical modulator 20 This is an operating condition in the case where the light transmittance is maximum. The operating condition is not limited to the condition of the bias voltage BV, but may be determined by other adjustment values of the optical modulator 20, and other adjustment values of the bias voltage BV and the optical modulator 20. It may be determined by a combination of. Further, the optimum operation point of the optical modulator 20 is not limited to when the light transmittance of the optical modulator 20 is maximized. For example, when the light transmittance of the optical modulator 20 is minimized depending on the optical transmission system in which the optical modulator 20 is used and the modulation of the optical signal, the operation optimum point may be set. The optimal point of operation may be when the light transmittance is between the maximum value and the minimum value.

  The optical modulator 20 includes a signal modulation unit 24 that performs at least one of intensity modulation and phase modulation on the light L0 output from the variable wavelength light source 10 based on the electric signal ES generated by the electric signal generation circuit 40. Prepare. When the optical modulator 20 is in the state of the optimum operation point, the signal modulator 24 can appropriately perform phase modulation and intensity modulation.

<< 1-2 >> Operation FIG. 4 is a flowchart showing the operation of the optical transmitter 1 according to the first embodiment. FIG. 4 shows an adjustment sequence of the optical modulator 20. In the following description, reference is also made to FIGS.

  First, the control circuit 30 sends a light emission command signal I 30 to the variable wavelength light source 10. The control circuit 30 sets the wavelength of the light L0 output from the variable wavelength light source 10 to the adjustment wavelength λ1 as the first wavelength, and outputs the light of the adjustment wavelength λ1 from the variable wavelength light source 10 (step S1). ). The light having the adjustment wavelength λ <b> 1 is blocked by the wavelength selection unit 60. The adjustment wavelength λ1 is a wavelength that is not used during actual operation of the optical transmission system.

  Next, the control circuit 30 starts the adjustment of the optical modulator 20 using the light of the adjustment wavelength λ1, and determines the operation condition of the optical modulator 20 so that the optical modulator 20 is in the state of the optimum operation point. To do. The control circuit 30 operates the optical modulator 20 based on the intensity of the light of the adjustment wavelength λ1 output from the optical modulator 20 when the variable wavelength light source 10 outputs the light of the adjustment wavelength λ1. Set conditions. The control circuit 30 regards the operating condition of the optical modulator 20 when the intensity of the light of the adjustment wavelength λ1 output from the optical modulator 20 is maximized as the determined optimum point. This is because the light transmittance of the light modulator 20 is maximized when the intensity of the light of the adjustment wavelength λ1 output from the light modulator 20 is maximized. The control circuit 30 reads the intensity M20 of the light pL1 monitored by the light monitor unit 22 (step S2). At this time, the variable wavelength light source 10 outputs the light L0 having the adjustment wavelength λ1 with a constant intensity. Further, the light transmittance of the optical modulator 20 varies depending on the voltage value of the applied bias voltage BV. The control circuit 30 determines whether or not the light pL1 has the maximum intensity (step S3). When the intensity M20 of the light pL1 is the maximum (that is, when the intensity of the light L1 is the maximum) (YES in Step S3), the control circuit 30 sets the voltage value of the bias voltage applied to the optical modulator 20. Then, the adjustment sequence of the optical modulator 20 is completed. The control circuit 30 determines the detected voltage value as the optimum point of the operating condition. When the intensity M20 of the light pL1 is not the maximum (that is, when the intensity of the light L1 is not the maximum) (NO in step S3), the control circuit 30 sends the signal V30 to the control IF 23 and applies the bias voltage applied to the optical modulator 20 The voltage value of BV is changed by a predetermined value (step S4). The control IF unit 23 applies the bias voltage BV having the changed voltage value to the optical waveguide 21. The control circuit 30 performs the processes of steps S2 to S4 until the intensity of the light pL1 monitored by the light monitoring unit 22 is maximized.

  During steps S2 to S4 in FIG. 4, the light L0 output from the variable wavelength light source 10 passes through the optical waveguide 21 and is output from the optical modulator 20 as light L1. However, since the light L1 output from the optical modulator 20 is light having the adjustment wavelength λ1, it is blocked by the wavelength selector 60. For this reason, the light L1 output from the optical modulator 20 is not output from the transmission terminal 50 to the subsequent optical transmission system. In this way, it is possible to prevent the light L1 from being output from the optical transmitter 1 during the period in which the control circuit 30 adjusts the optical modulator 20.

  FIG. 5 is a flowchart showing the operation of the optical transmitter 1 according to the first embodiment. The flowchart shown in FIG. 5 includes a fine adjustment sequence of the optical modulator 20 (steps S6 to S8) and an operation sequence when the adjustment of the optical modulator 20 is completed and the optical transmitter 1 is operated in the optical transmission system ( Steps S9 to S12) are included. In the following description, reference is also made to FIGS.

  The control circuit 30 performs the operation shown in FIG. 5 after the adjustment sequence shown in FIG. 4 ends. When starting this operation, the control circuit 30 applies a bias voltage BV having a voltage value determined as the optimum point of the operating condition of the optical modulator 20 to the optical modulator 20.

  The control circuit 30 sends a wavelength change command signal I30 to the variable wavelength light source 10, and switches the wavelength of the light L0 output from the variable wavelength light source 10 from the adjustment wavelength λ1 to the operating wavelength λ2 (step S5). The control circuit 30 causes the variable wavelength light source 10 to output light having the operation wavelength λ2 as light having the second wavelength. The light having the operating wavelength λ <b> 2 passes through the wavelength selection unit 60 without being blocked by the wavelength selection unit 60. The operating wavelength λ2 is a wavelength used during actual operation of the optical transmission system.

  Here, the light transmittance of the optical modulator 20 has a wavelength characteristic. That is, the light transmittance of the light modulator 20 changes according to the wavelength. Since the wavelength of the light L0 output from the variable wavelength light source 10 has been changed from the adjustment wavelength λ1 to the operating wavelength λ2, the operation state of the optical modulator 20 is slightly different from the state of the optimum operation point. Therefore, the control circuit 30 performs fine adjustment of the optical modulator 20. The control circuit 30 operates the operating condition of the optical modulator 20 based on the intensity of the light of the operating wavelength λ2 output from the optical modulator 20 when the variable wavelength light source 10 outputs the light L0 of the operating wavelength λ2. Set. The control circuit 30 reads the intensity M20 of the light pL1 monitored by the optical monitor unit 22, thereby reading the intensity of the light L1 (step S6). Next, the control circuit 30 determines whether the intensity of the light pL1 is maximum (step S7). When the intensity of the light pL1 is maximum (that is, when the intensity of the light L1 is maximum) (YES in step S7), the control circuit 30 detects the bias voltage applied to the optical modulator 20, and The fine adjustment sequence of the modulator 20 is finished. The control circuit 30 determines the detected voltage value as a new optimum point of the operating condition. When the intensity of the light pL1 is not the maximum (that is, when the intensity of the light L1 is not the maximum) (NO in step S7), the control circuit 30 sends the signal V30 to the control IF unit 23 and applies the bias to the optical modulator 20 The voltage value of the voltage BV is changed (step S8). The control IF unit 23 applies the bias voltage BV having the changed voltage value to the optical waveguide 21. The control circuit 30 performs steps S6 to S8 until the intensity M20 of the light pL1 monitored by the light monitor unit 22 is maximized.

  When the fine adjustment sequence (steps S6 to S8 in FIG. 5) is performed, the operation sequence of the optical modulator 20 is already set in the vicinity of the new optimum point because the adjustment sequence shown in FIG. 4 is performed. ing. Therefore, the fine adjustment sequence of the optical modulator 20 is performed in a short time compared to the adjustment sequence. Even if fine adjustment of the optical modulator 20 is performed, the light output from the optical transmitter 1 to the subsequent optical transmission system can be minimized. The fine adjustment sequence (steps S6 to S8 in FIG. 5) is preferably executed, but can be omitted.

  After completion of the fine adjustment sequence, the optical modulator 20 performs intensity modulation and phase modulation (step S9), and outputs the light L1 as an optical signal of the operating wavelength λ2 based on the electrical signal ES generated by the electrical signal generation circuit 40. To do. Since the optical signal output from the optical modulator 20 is an optical signal having the operating wavelength λ2, the optical signal is not blocked by the wavelength selection unit 60 and passes through the wavelength selection unit 60. The optical signal L2 having the operating wavelength λ2 that has passed through the wavelength selector 60 is transmitted from the transmission terminal 50 to the subsequent optical transmission system. In this way, the operation of the optical transmission system is started. While the optical transmission system is in operation, the optimum point of operation of the optical modulator 20 varies (drifts) over time. The control circuit 30 monitors the light L1 as the optical signal output from the optical modulator 20 in order to follow the drift of the optimum operation point, and sets the operating condition of the optical modulator 20 based on the monitored result. . That is, the control circuit 30 reads the intensity M20 (that is, the intensity of the light L1) of the light pL1 monitored by the light monitoring unit 22 (step S10). If the intensity of the light pL1 is not the maximum (NO in step S11) ), The signal V30 is sent to the control IF unit 23 so that the intensity M20 of the light pL1 (that is, the intensity of the light L1) is maximized, and the voltage value of the bias voltage BV is changed (step S12). As described above, the control circuit 30 controls the operation condition of the optical modulator 20 so as to follow the fluctuation of the operation optimum point of the optical modulator 20 by the feedback control shown in steps S10 to S12.

<< 1-3 >> Comparative Example Next, a comparative example as a comparison target of the optical transmitter 1 according to Embodiment 1 will be briefly described. FIG. 6 is a block diagram showing a schematic configuration of an optical transmitter 1a as a comparative example. In FIG. 6, the same reference numerals as those shown in FIG. 2 are given to the same or corresponding elements as those shown in FIG. The optical transmitter 1a as a comparative example is provided with an optical variable attenuator 61 and an optical variable attenuator control circuit 62 for controlling the optical attenuator 61. The wavelength selector 60 is a passive element that does not require input of a control signal. This is different from the optical transmitter 1 according to the first embodiment including the above.

  The variable optical attenuator 61 attenuates the intensity of the light L1 output from the optical modulator 20. The optical variable attenuator control circuit 62 controls the optical variable attenuator 61 to control the optical attenuation amount of the optical variable attenuator 61. The optical variable attenuator control circuit 62 maximizes the attenuation amount of the optical variable attenuator 61 during the period when the optical modulator 20 is adjusted by the control circuit 30 and does not output the light L1 from the optical variable attenuator 61. And When the adjustment of the optical modulator 20 is completed, the optical variable attenuator control circuit 62 adjusts the attenuation amount of the optical variable attenuator 61 so that the optical signal L2 can be transmitted from the transmission terminal 50 with an arbitrary power. And

  The optical transmitter 1a of the comparative example uses the optical variable attenuator 61 and the optical variable attenuator control circuit 62 to prevent light from being output from the optical transmitter 1a during adjustment of the optical modulator 20. However, the area occupied by the optical variable attenuator 61 and the optical variable attenuator control circuit 62 is a factor that hinders downsizing of the apparatus. Moreover, since the optical transmitter 1a of the comparative example includes the optical variable attenuator control circuit 62 for controlling the optical variable attenuator 61, the configuration of the apparatus is complicated.

<< 1-4 >> Effect The optical transmitter 1 according to Embodiment 1 uses light of the adjustment wavelength λ <b> 1 when adjusting the optical modulator 20. The light of the adjustment wavelength λ1 is blocked by the wavelength selection unit 60. Further, since the wavelength selection unit 60 is a passive element and does not require a control circuit used for controlling the wavelength selection unit 60, an area for the control circuit is not necessary. As described above, the wavelength selection unit 60 of the optical transmitter 1 according to Embodiment 1 is a combination of the optical variable attenuator 61 and the optical variable attenuator control circuit 62 of the optical transmitter 1a of the comparative example shown in FIG. Therefore, the optical transmitter 1 according to the first embodiment can be downsized.

  In addition, the configuration in which the wavelength selection unit 60 that is a passive element is provided can be realized relatively easily. As described above, the wavelength selection unit 60 of the optical transmitter 1 according to Embodiment 1 is a combination of the optical variable attenuator 61 and the optical variable attenuator control circuit 62 of the optical transmitter 1a of the comparative example shown in FIG. Compared to the above, since the configuration is simplified, the configuration of the optical transmitter 1 according to Embodiment 1 can be simplified.

  Therefore, the optical transmitter 1 according to Embodiment 1 prevents the occurrence of adverse effects due to the light output from the optical modulator 20 during the adjustment of the optical modulator 20, while reducing the size and configuration of the apparatus. can do.

  Further, when the fine adjustment sequence shown in steps S6 to S8 in FIG. 5 is executed, the light transmittance of the light modulator 20 can be made closer to the maximum value. Since this fine adjustment sequence is completed in a short time and shifts to the operation sequence, the light of the operation wavelength λ2 output from the optical modulator 20 during the fine adjustment of the optical modulator 20 is very small. Therefore, the adverse effect on the system is small.

<< 1-5 >> Modification of First Embodiment FIG. 7 is a block diagram schematically showing a configuration of an optical transmitter 1b as a modification of the first embodiment. In FIG. 7, the same reference numerals as those shown in FIG. 2 are given to the same or corresponding elements as those shown in FIG. FIG. 7 shows an example of a configuration when the optical transmitter according to Embodiment 1 is applied to a general optical transmission system.

In the example shown in FIG. 7, ITLA (Integral Tunable Laser Assembly) is applied to the variable wavelength light source 10. An LN (lithium niobate, LiNbO ₃ ) modulator is applied to the optical modulator 20. The electric signal generation circuit 40 includes a signal processing LSI (Large Scale Integration) 41 and an electric signal amplifier 42. A band pass filter is applied to the wavelength selection unit 60. Since the band pass filter is a passive element, it does not require a control circuit used to control the band pass filter.

  The signal processing LSI 41 generates transmission data as an electrical signal ES0. The electric signal amplifier 42 amplifies the electric signal ES0 generated by the signal processing LSI 41 to generate an electric signal ES. The LN modulator 20 performs modulation based on the electric signal ES amplified by the optical L0 output from the ITLA 10, and for example, as an optical signal subjected to DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) modulation or the like. Outputs light L1. When adjusting the LN modulator 20, the control circuit 30 monitors the intensity of part of the light output from the LN modulator (for example, the optical power value and the photoelectrically converted current value).

  The ITLA specification is defined by OIF (Optical Internetworking Forum) -ITLA-MAS (Multi Source Agreement). The variable wavelength width of ITLA corresponds to L-band (1565 nm to 1625 nm) or C-band (1530 nm to 1565 nm), which is a wavelength band used in optical communication. In addition, the ITLA variable wavelength band can correspond to all the L-band and C-band wavelength bands (Full-band). The adjustment wavelength λ1 can be arbitrarily set in an optical transmission system to which the optical transmitter 1b is applied. For example, when the operation wavelength λ2 of the optical transmission system is C-band, the adjustment wavelength λ1 can be set to L-band. In this case, a band-pass filter is selected that blocks L-band light including the adjustment wavelength λ1 and transmits C-band light.

  It has been found that the adjustment wavelength λ1 is not included in the wavelength band used in the operation of the optical transmission system, and the light of the adjustment wavelength λ1 is output from the optical transmitter 1b without affecting the optical transmission system. In this case, the wavelength selection unit 60 can be omitted from the configuration of the optical transmitter 1b. However, a device such as an optical receiver connected to the optical transmitter 1b via the optical transmission path may be replaced with a device that is affected by the light having the adjustment wavelength λ1. Therefore, it is desirable to provide a wavelength selection unit like the optical transmitter 1b.

<< 2 >> Embodiment 2
FIG. 8 is a block diagram schematically showing the configuration of the optical transmitter 1c according to Embodiment 2 of the present invention. In FIG. 8, the same reference numerals as those shown in FIG. 2 are given to the same or corresponding elements as those shown in FIG. The optical transmitter 1c according to the second embodiment is different from the optical transmitter 1 according to the first embodiment in that the storage unit 70 is provided.

  The storage unit 70 stores in advance an adjustment value related to the wavelength characteristic of the light transmittance of the optical modulator 20. The adjustment value is, for example, a bias voltage offset value corresponding to a difference (change) in the light transmittance of the optical modulator 20 that occurs when the wavelength is changed from the adjustment wavelength λ1 to the operation wavelength λ2. By applying an offset to the bias voltage with this offset value, the difference in light transmittance corresponding to the difference in wavelength can be canceled. The adjustment value is not limited to a numerical value relating to the bias voltage, and may include a numerical value relating to other operating conditions. The storage unit 70 holds each adjustment value as a table.

  When the control circuit 30 switches from the adjustment wavelength λ1 to the operation wavelength λ2 and causes the variable wavelength light source 10 to output the light of the operation wavelength λ2, the optimal point determined for the light of the adjustment wavelength λ1 is stored in the storage unit 70. A new optimum point adjusted using the stored adjustment value is set as an operating condition of the optical modulator 20. The control circuit 30 refers to the table in the storage unit 70 (M30) and acquires the adjustment value V70 from the table. The control circuit 30 adjusts the operating condition of the optical modulator 20 using the acquired adjustment value V70. For this reason, the control circuit 30 can bring the optical modulator 20 into the state of the optimum operation point without performing the fine adjustment sequence of the optical modulator 20 (steps S6 to S8 shown in FIG. 5).

  The optical transmitter 1c according to the second embodiment has the light transmittance of the optical modulator 20 generated when the wavelength is changed from the adjustment wavelength λ1 to the operation wavelength λ2 after the adjustment sequence shown in steps S1 to S7 in FIG. Since the adjustment is performed using the offset value of the bias voltage corresponding to the difference (change amount), the light transmittance of the optical modulator 20 can be made closer to the maximum value. For this reason, the optical transmitter 1c according to Embodiment 2 can omit the fine adjustment sequence (steps S6 to S8 in FIG. 5).

  Except for the points described above, the optical transmitter 1c according to the second embodiment is the same as the optical transmitter 1 according to the first embodiment.

<< 3 >> Embodiment 3
FIG. 9 is a block diagram schematically showing a configuration of an optical transmitter 1d according to Embodiment 3 of the present invention. 9, components that are the same as or correspond to the components shown in FIG. 2 are assigned the same reference numerals as those shown in FIG. The optical transmitter 1 d according to the third embodiment is different from the optical transmitter 1 according to the first embodiment in that a fiber grating (fiber Bragg grating, FBG) 63 is provided instead of the wavelength selection unit 60.

  The fiber grating 63 is formed by subjecting the optical fiber 64 between the optical modulator 20 and the transmission terminal 50 to fiber grating processing. When the light L0 output from the optical modulator 20 is light having the adjustment wavelength λ1, the fiber grating 63 reflects the light having the adjustment wavelength λ1 and does not transmit the fiber grating 63. When the light L0 output from the optical modulator 20 is light having the operating wavelength λ2, the fiber grating 63 transmits light having the operating wavelength λ2. The fiber grating 63 does not require an area for providing the fiber grating. For this reason, the optical transmitter 1d according to Embodiment 3 prevents the light output from the optical modulator 20 being adjusted from being output from the optical transmitter 1d without changing the size of the apparatus. Thus, it is possible to prevent an adverse effect caused by unnecessary light.

  Except for the points described above, the optical transmitter 1d according to the third embodiment is the same as the optical transmitter 1 according to the first embodiment.

<< 4 >> Embodiment 4
FIG. 10 is a block diagram schematically showing the configuration of the optical transmitter 1e according to the fourth embodiment of the present invention. 10, components that are the same as or correspond to the components shown in FIG. 2 are assigned the same reference numerals as those shown in FIG. The optical transmitter 1e according to Embodiment 4 includes the modulation selection function unit 210 having both the optical modulation unit 25 and the wavelength selection unit 65, and the optical modulation unit 25 and the wavelength selection unit 65 are separately provided. This is different from the optical transmitter 1 according to the first embodiment.

  FIG. 11 is a diagram schematically showing a configuration of the modulation selection function unit 210 provided in the optical transmitter 1e according to the fourth embodiment. The modulation selection function unit 210 includes an optical modulation unit 25 and a wavelength selection unit 65. The light modulation unit 25 includes a light modulation waveguide 212 that modulates the light L0 output from the variable wavelength light source 10. The optical modulation unit 25 includes the optical monitor unit 22, the control IF unit 23, and the signal modulation unit 24 shown in FIG. The wavelength selection unit 65 is a grating, and is disposed on an optical waveguide through which the light L1 output from the light modulation unit 25 passes. The light modulator 25 and the wavelength selector 65 are formed on the same optical waveguide substrate 211.

  The wavelength selector 65 is a grating. When the light L0 input to the light modulation unit 25 is light with the adjustment wavelength λ1, the wavelength selection unit 65 reflects the light with the adjustment wavelength λ1 and does not transmit the light through the wavelength selection unit 65. When the light L0 input to the light modulation unit 25 is the light having the operating wavelength λ2, the wavelength selecting unit 65 transmits the light having the operating wavelength λ2. In the fourth embodiment, the light modulation waveguide 212 and the wavelength selection unit 65 are formed on the same optical waveguide substrate 211. Although the optical transmitter 1 according to the first embodiment includes the optical modulator 20 and the wavelength selection unit 60, the optical transmitter 1e according to the fourth embodiment needs to include the optical modulator 20 and the wavelength selection unit 60. There is no. Further, the optical transmitter 1e according to the fourth embodiment does not require an area for providing the fiber grating 63 as shown in the third embodiment. Therefore, the optical transmitter 1e according to the fourth embodiment can realize a smaller device than the optical modulators according to the first and fourth embodiments.

  Except for the points described above, the optical transmitter 1e according to the fourth embodiment is the same as the optical transmitter 1 according to the first embodiment.

<< 5 >> Embodiment 5
In the first to fourth embodiments, the light output from the optical modulator is prevented by preventing the light from being output from the optical transmitter during the adjustment of the optical modulator using the light of the adjustment wavelength λ1. The negative effect was avoided on the optical transmission system. On the other hand, the optical transmission system according to Embodiment 5 can prevent the adverse effect caused by the light output from the optical transmitter from occurring even when the light is output from the optical transmitter. .

  FIG. 12 is a block diagram schematically showing the configuration of the optical transmission system 200 according to Embodiment 5 of the present invention. 12, components that are the same as or correspond to the components shown in FIG. 2 are assigned the same reference numerals as those shown in FIG. The optical transmitter 1f of the optical transmission system 200 according to Embodiment 5 does not include the wavelength selection unit, and the wavelength selection unit 60a includes the optical receiver 4 that receives the optical signal transmitted from the optical transmitter 1f. This is different from the optical transmitter 1 according to the first embodiment.

  The optical transmission system 200 includes an optical transceiver 100 and an optical transceiver 100a. The optical transceiver 100 and the optical transceiver 100a are connected by optical transmission paths 110 and 120 such as optical cables so that optical communication is possible. Further, the optical transmission system 200 may include three or more optical transceivers capable of optical communication with each other.

  The optical transceiver 100 includes an optical transmitter 1 f and an optical receiver 2. The optical transmitter 1f includes a variable wavelength light source 10, an optical modulator 20, a control circuit 30, an electric signal generation circuit 40, and a transmission terminal 50. In addition, the optical receiver 2 includes a receiving terminal 80 that receives an optical signal transmitted from the opposing optical transceiver 100a (optical transmitter 3), a wavelength selection unit 60, and a reception processing unit 90 that performs processing of the optical signal. Prepare.

  The optical transceiver 100 a includes an optical transmitter 3 and an optical receiver 4. The variable wavelength light source 10a, the optical modulator 20a, the control circuit 30a, and the electrical signal generation circuit 40a provided in the optical transmitter 3 are the variable wavelength light source 10a, the optical modulator 20, and the control circuit 30 provided in the optical transmitter 1f, respectively. , And the function similar to the function of the electric signal generation circuit 40. The reception terminal 80a, the wavelength selection unit 60a, and the reception processing unit 90a provided in the optical receiver 4 are respectively the functions of the reception terminal 80, the wavelength selection unit 60, and the reception processing unit 90a provided in the optical receiver 2. Has the same function. The transmission terminal 50 and the reception terminal 80a are connected by the optical transmission line 110. The transmission terminal 50 a and the reception terminal 80 are connected by the optical transmission line 120.

  In the optical transmission system 200, the light L0 output from the variable wavelength light source 10 is modulated by the optical modulator 20. The modulated light L1 is output from the optical modulator 20 as an optical signal. The optical signal output from the optical modulator 20 is transmitted from the transmission terminal 50 and transmitted to the reception terminal 80a through the optical transmission path 110. When the optical signal received by the receiving terminal 80a is light having the adjustment wavelength λ1, the optical signal is blocked by the wavelength selector 60a. When the optical signal received by the receiving terminal 80a is light having the operating wavelength λ2, the optical signal L1 passes through the wavelength selector 60a, and the transmitted optical signal L2 is processed in the reception processor 90a.

  Similarly, in the optical transmission system 200, the light L0a output from the variable wavelength light source 10a is modulated by the optical modulator 20a. The modulated light L1a is output as an optical signal from the optical modulator 20a. The optical signal output from the optical modulator 20 a is transmitted from the transmission terminal 50 a and transmitted to the reception terminal 80 through the optical transmission path 120. When the optical signal received by the receiving terminal 80 is light having the adjustment wavelength λ1, the optical signal is blocked by the wavelength selector 60. When the optical signal received by the receiving terminal 80 is light having the operating wavelength λ2, the optical signal passes through the wavelength selection unit 60, and the transmitted optical signal L2a is processed in the reception processing unit 90.

  The wavelength selector 60a of the optical receiver 4 blocks the light having the adjustment wavelength λ1 used in the optical transmitter / receiver 100 out of the light output from the optical transmitter / receiver 100, and transmits the light having the operation wavelength λ2. For this reason, when the light of the adjustment wavelength λ1 is output from the optical transmitter 1f during the adjustment of the optical modulator 20, the light of the adjustment wavelength λ1 is blocked by the wavelength selection unit 60a. Since the wavelength selection unit 60 is a passive element, a control circuit for the wavelength selection unit 60 is not required. The wavelength selector 60 of the optical receiver 2 blocks light having the adjustment wavelength λ1 used in the optical transmitter / receiver 100a out of light output from the optical transmitter / receiver 100a and transmits light having the operating wavelength λ2. Let For this reason, when the light of the adjustment wavelength λ1 is output from the optical transmitter 3 during the adjustment of the optical modulator 20a, the light of the adjustment wavelength λ1 is blocked by the wavelength selection unit 60. Similarly to the wavelength selection unit 60, the wavelength selection unit 60a does not require a control circuit.

  As described above, when the optical modulator 20 is adjusted in the optical transceiver 100 and the light having the adjustment wavelength λ1 is output, the wavelength selection unit 60a blocks the light having the adjustment wavelength λ1. For this reason, during adjustment of the optical modulator 20 of the optical transceiver 100, it is possible to prevent light output from the optical modulator 20 from being input to the optical transceiver 100a. Further, it is possible to prevent light output from the optical modulator 20a from being input to the optical transceiver 100 even during adjustment of the optical modulator 20a of the optical transceiver 100a. Therefore, the optical transmission system according to the fifth embodiment has an adverse effect due to light output from the optical modulator during adjustment of the optical modulator while reducing the size and configuration of the optical transceiver included in the optical transmission system. Can be prevented.

  Except for the points described above, the optical transmitters 1f and 3 in the fifth embodiment are the same as the optical transmitter 1 according to the first embodiment.

  As described above, the optical transmitters 1f and 3 in the fifth embodiment use the light of the adjustment wavelength λ1 when adjusting the optical modulators 20 and 20a. The light having the adjustment wavelength λ1 is blocked by the wavelength selectors 60a and 60. In addition, since the wavelength selectors 60a and 60 are passive elements and do not require a control circuit used to control the wavelength selectors 60a and 60, an area for the control circuit is not necessary. Thus, since the wavelength selection units 60a and 60 of the optical transmitters 1f and 3 according to the fifth embodiment are small, the optical transceivers 100 and 100a according to the fifth embodiment can be miniaturized.

  In addition, the configuration in which the wavelength selectors 60a and 60 which are passive elements are provided can be realized relatively easily. Thus, since the optical transceivers 100 and 100a according to Embodiment 1 have a simplified configuration, the configuration of the optical transceivers 100 and 100a can be simplified.

  Therefore, the optical transmission system according to the fifth embodiment is output from the optical modulators 20 and 20a during the adjustment of the optical modulators 20 and 20a while reducing the size and the configuration of the optical transceivers 100 and 100a. It is possible to prevent the adverse effect of the light.

  In the above description, it is shown that the adjustment wavelength λ1 and the operation wavelength λ2 are used in the optical transceiver 100 and the optical transceiver 100a, respectively, but the present invention is not limited to this. In the optical transceiver 100 and the optical transceiver 100a, different adjustment wavelengths and operation wavelengths may be used.

<< 6 >> Embodiment 6
FIG. 13 is a block diagram schematically showing a configuration of an optical transmission system 200a according to Embodiment 6 of the present invention. In FIG. 13, the same reference numerals as those shown in FIG. 12 are given to the same or corresponding elements as those shown in FIG. The optical transmission system 200a according to the sixth embodiment is different from the optical transmission system 200 according to the fifth embodiment in that the wavelength selection units 60 and 60a are arranged in the optical transmission lines 110a and 120a, respectively.

  Since the optical transmission system 200a according to the sixth embodiment is constructed by including the wavelength selection units 60a and 60 that block the light of the adjustment wavelength λ1 on the optical transmission lines 110a and 120a, the existing system is modified. Thus, the present invention is particularly effective when an optical transmission system to which the present invention is applied.

  Except for the points described above, the optical transmission system 200a according to the sixth embodiment is the same as the optical transmission system 200 according to the fifth embodiment.

<< 7 >> Modifications The present invention is not limited to that described in the first to sixth embodiments. The present invention can be variously modified without departing from the spirit of the invention. For example, each of the embodiments can be combined with other embodiments as appropriate.

  1, 1a, 1b, 1c, 1d, 1e, 1f, 3 optical transmitters, 2, 2a, 4, 4a optical receivers, 10, 10a tunable light sources, 20, 20a optical modulators, 21, 21a optical waveguides, 22 optical monitor unit, 23 control IF unit, 24 signal modulation unit, 25 optical modulation unit, 30, 30a control circuit, 40, 40a electric signal generation circuit, 50, 50a transmission terminal, 60, 60a, 65 wavelength selection unit, 63 Fiber grating, 70 storage unit, 80, 80a reception terminal, 90, 90a reception processing unit, 100, 100a, 100b, 100c optical transceiver, 110, 110a, 120, 120a optical transmission line, 200, 200a optical transmission system, 210 A modulation selection function unit; 211 an optical waveguide substrate; and 212 an optical modulation waveguide.

Claims (10)

A light source that selectively outputs light of a first wavelength and light of a second wavelength having different wavelengths;
An optical modulator that modulates the light output from the light source and outputs the modulated light;
Of the light output from the optical modulator , a wavelength selection unit that is a passive element that blocks the light of the first wavelength and transmits the light of the second wavelength;
A control unit for controlling the light source and the light modulator;
With
The controller is
As an adjustment sequence, when causing the light source to output light of the first wavelength, determine the optimum point of the operating condition of the optical modulator,
After setting the operating condition of the light modulator based on the determined optimum point, and causing the light source to output light of the second wavelength ,
As a fine adjustment sequence, a new optimum point of the operating condition of the optical modulator is determined, the operating condition of the optical modulator is set based on the new optimum point, and a second wavelength is set in the optical modulator. Output
An optical transmitter characterized by monitoring light of the second wavelength output from the optical modulator as an operation sequence, and setting operating conditions of the optical modulator based on the monitored result .   The optical transmitter according to claim 1, wherein the operation condition of the optical modulator is a condition of a bias voltage applied to the optical modulator by the control unit.   The control unit operates the optical modulator based on the intensity of the light of the first wavelength output from the optical modulator when the light source outputs the light of the first wavelength. The optical transmitter according to claim 1, wherein a condition is set.   The optical modulator when the light intensity of the first wavelength output from the optical modulator is maximum when the control unit causes the light source to output light of the first wavelength. 4. The optical transmitter according to claim 1, wherein the operating condition is regarded as the determined optimum point. 5. An electric signal generator that generates transmission data as an electric signal;
The optical modulator modulates the light of the second wavelength output from the light source based on the electrical signal and outputs an optical signal of the second wavelength based on the electrical signal;
The optical transmitter according to claim 1, wherein the optical transmitter is provided. The optical transmitter according to any one of claims 1 to 5, wherein the wavelength selection unit is any one of a bandpass filter and a fiber grating. The optical modulator and the wavelength selection unit are formed on the same optical waveguide substrate,
The optical transmitter according to any one of claims 1 to 5, wherein the wavelength selection unit is a grating formed in the optical waveguide substrate. The control unit operates the optical modulator based on the intensity of the light of the second wavelength output from the optical modulator when the light source outputs the light of the second wavelength. The optical transmitter according to claim 1, wherein conditions are set. The optical modulator when the intensity of the light of the second wavelength output from the optical modulator is maximized when the control unit causes the light source to output light of the second wavelength The optical transmitter according to claim 1, wherein the operating condition is regarded as the new optimum point. An optical transmitter;
An optical receiver for receiving the light transmitted from the optical transmitter;
With
The optical transmitter is
A light source that selectively outputs light of a first wavelength and light of a second wavelength having different wavelengths;
An optical modulator that modulates the light output from the light source and outputs the modulated light;
A control unit for controlling the light source and the light modulator;
Have
The controller is
As an adjustment sequence, when causing the light source to output light of the first wavelength, determine the optimum point of the operating condition of the optical modulator,
After setting the operating condition of the light modulator based on the determined optimum point, and causing the light source to output light of the second wavelength,
As a fine adjustment sequence, a new optimum point of the operating condition of the optical modulator is determined, the operating condition of the optical modulator is set based on the new optimum point, and a second wavelength is set in the optical modulator. Output
As an operation sequence, the light of the second wavelength output from the optical modulator is monitored, and based on the monitored result, the operating condition of the optical modulator is set,
The optical receiver is a passive element that blocks the light of the first wavelength and transmits the light of the second wavelength among the light output from the optical modulator of the optical transmitter. Has a wavelength selector
An optical transmission system characterized by that.

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