JP6499516B2 - Optical transmission / reception system - Google Patents

Description

  The present invention relates to an optical transmission / reception system, and more particularly to an optical transmission / reception system using an optical module mainly applied to optical fiber communication. The present invention further relates to an optical transmission / reception system and an optical circuit for performing optical communication (telecom) and information transmission (datacom) using, for example, wavelength division multiplexing.

  In recent years, the remarkable progress of optical fiber communication technology, particularly the data link market represented by communication between data centers, has dramatically increased the throughput of optical links. Currently, in a standard (100GBASE-LR4) with a transmission distance of 10 km in 100 Gigabit Ethernet (100 GbE), a configuration using wavelength division multiplexing (WDM) transmission using a single mode fiber is specified (25 Gb per wave). / S bit rate). In the future, the 400 Gigabit Ethernet (400 GbE) standard is drawing attention as a next-generation configuration for expanding the transmission capacity, and proposals for the physical configuration are being actively made at present.

  A frequency arrangement called LAN-WDM is applied to four-wave WDM transmission in the 10 GbE 10 km transmission specification. That is, the arrangement is four waves with a frequency interval ΔF of 800 GHz, and the use band (passband) B in each wavelength (lane) is 360 GHz. The center wavelength of each lane is designated as 129.56 nm for lane 0, 1300.05 nm for lane 1, 1304.58 nm for lane 2, and 1309.14 nm for lane 3, respectively. Since the number of fiber cores to be used has one core each for transmission and reception, there are a total of two cores.

  In 100 GbE, a modulation method using binary pulses, that is, intensity modulation using an NRZ code is used. On the other hand, in 400 GbE, application of a multi-level modulation method is assumed. As candidates for modulation schemes, pulse amplitude modulation (PAM) and discrete multitone (DMT) schemes are attracting attention. PAM can increase the number of transmission bits per symbol rate with a simple electric circuit. DMT divides an electric signal to be transmitted into a large number of subcarriers having different frequencies and assigns a modulation method such as quadrature amplitude modulation (QAM). Therefore, although an electric circuit becomes complicated, an optimum modulation signal for a transmission path is obtained. There is an advantage that it can be generated. However, in any of the multilevel modulation schemes, device performance is required to have higher linearity in the amplitude direction than NRZ.

  FIG. 11 shows a configuration of an optical transmission / reception system in 200 Gb / s transmission in which PAM modulation is applied to a 100 GbE optical module (optical subassembly) disclosed in Non-Patent Document 1. This optical transmission / reception system includes a multi-wavelength light source 110 that is a transmission optical subassembly that transmits a downstream optical signal, an optical fiber transmission line 113, and a multi-wavelength light receiving element 150 that is a reception optical subassembly that receives the downstream optical signal. Prepare. Each of the multi-wavelength light sources 110 includes N sets of signal sources 111-1 to 111 -N that generate digital electric signals, N sets of light sources 112-1 to 112 -N having different oscillation wavelengths, and the N sets of light sources. And a wavelength multiplexing element 114 for multiplexing the light from the light into a set of N-channel wavelength multiplexed light.

  Each of the multi-wavelength light receiving elements 150 includes a wavelength demultiplexing element 154 that demultiplexes the one set of N-channel wavelength multiplexed light into N sets of light, and N sets of N sets of light that respectively receive the demultiplexed N sets of light. The light receiving elements 152-1 to 152-N, N sets of amplifiers 153-1 to 153-N that respectively receive the photoelectrically converted signals, and receiving circuits 155-1 to 155-N.

  Here, a 1.3 μm band semiconductor laser is used as the light source 112. N-channel wavelengths are different. Each light source is integrated with an electro-absorption type modulator capable of high-speed modulation operation. As the amplifier 153, a limiting (LIM) type transimpedance amplifier (TIA) is used. The receiving circuit 155 has a waveform shaping function using a digital filter.

Labels are provided for the wavelengths in the N sets of light sources. At this time, the wavelength of the first set of light sources is λ _1, and the wavelength of the second set of light sources is λ ₂ . Similarly, the wavelength of the Nth set is λ _N.

  Hereinafter, an outline of the operation of the optical transmission / reception system of FIG. 11 will be described. The N-channel data signals output from the N sets of signal sources (111-1 to 111-N) are input to the light sources (112-1 to 112-N). Each N-channel optical signal output from the light source is input to the input port of the wavelength multiplexing element 114. The output propagates through the optical fiber transmission line 113 as an N-channel wavelength multiplexed signal.

  The waveform shown in FIG. 11 represents a single channel optical signal in the optical fiber transmission line 113. Since the data signal is a PAM system, it can be seen that a multi-valued waveform is obtained in the amplitude direction. After propagation in the optical fiber transmission line 113, the wavelength demultiplexing element 154 demultiplexes the signal into N channels, and the respective data signals are received by the light receiving elements (152-1 to 152-N). At this time, the data signal is received via the amplifier 153 and the receiving circuit 155.

  In the 100 GBASE-LR4 standard, the bit rate of the signal source 111 is 25 Gb / s, and the modulation method is NRZ. In the conventional optical transmission / reception system of FIG. 11, a bit rate of 50 Gb / s (28 Gbaud including an error correction code) and a modulation method of a 4-level PAM signal (PAM4) are applied. In this standard, since the number of channels N is N = 4, an optical transmission / reception system with a total of 200 Gb / s can be configured.

FIG. 12 shows a wavelength arrangement in a conventional optical transmission / reception system. The wavelength of the N channel is composed of N waves from λ ₁ to λ _N. Here, the frequency interval (for example, the interval between λ ₁ and λ ₂ ) between adjacent channels of the wavelength multiplexing element (or wavelength demultiplexing element) is Δf, and the 1 dB loss transmission band (passband) in each channel is B. .

  In the optical transmission / reception system shown in FIG. 11, for example, assuming 200 Gb / s transmission in which 100 GbE is expanded, the main parameters of the configuration take the following numerical values.

N = 4
Δf = 800 GHz
B = 360GHz or more

  In this case, the optical transmission / reception system has four-wave WDM and the channel frequency interval is 800 GHz. For passband B, B of the wavelength demultiplexing element used in this conventional example is 500 GHz or more. The arrayed waveguide grating (AWG) used in the wavelength demultiplexing element is designed so that the system does not lose even if the wavelength of the light source, wavelength multiplexing element, or center wavelength of the wavelength demultiplexing element varies slightly. Has been.

  FIG. 13 shows signal error rate characteristics (BER) in the optical transmission / reception system shown in FIG. In FIG. 13, the horizontal axis represents average received power, and the vertical axis represents BER. FIG. 13 shows the BER when the number of digital filter stages (Tap number) in the receiving circuit is used as a parameter and the value of the parameter is changed.

Yoshiyuki Doi et al., "Study of 200Gb / s transmission / reception configuration using Ethernet optical subassembly (4 waves 28Gbaud-PAM4)", IEICE, 2015 General Conference, B-10-58 Y. Doi et al. “Bidirectional 400-Gb / s transmission by 100GbE Optical Sub-Assemblies and a Cyclic Arrayed Waveguide Grating,” OFC2015, Th1G.5, 2015

In the optical transmission / reception system described above, when applied multilevel modulation such as PAM is used for the optical subassembly for 100 GbE, linearity is required for the device. Since the TIA of the separate receiving circuit performs the LIM operation for 100 GbE, there has been a problem that the received PAM signal is significantly deteriorated when the optical input is increased. As shown in the error rate characteristics in FIG. 13, it can be seen that the error rate rapidly deteriorates at an average received light power of −10 dBm or more. In the BCH method and 100GBASE-KP4 standard adopted as error rate correction (FEC), it is necessary to suppress the BER to less than 1 × 10 ⁻³ and 2 × 10 ⁻⁴ , respectively. In this configuration, since there is no optical attenuation function on the optical line, these values cannot be satisfied when the input is increased, and it is difficult to apply the optical transmission / reception system.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical transmission / reception system capable of optical transmission / reception even at high input.

In order to achieve the above object, the present invention is an optical transmission / reception system, in which N sets of light sources respectively emitting N sets of light having different oscillation wavelengths and the N sets of light are set as one set of N channels. A light source device having a wavelength multiplexing element that multiplexes and emits the wavelength multiplexed light; a wavelength demultiplexing element that demultiplexes the N-channel wavelength multiplexed light into the N sets of light; and the N sets of demultiplexed wavelengths . a light receiving device having a N sets of light receiving elements for receiving light, respectively, to feedback a signal indicating a signal intensity of the light to the light source side of the one of the light receiving elements of said N sets of light receiving elements, the signal When the intensity is larger than a preset value, the oscillation wavelength of the light source that emits light to the light receiving element is out of the preset transmission band in the wavelength multiplexing element or the wavelength demultiplexing element. The oscillation wavelength of the light source And a control to the control loop.

  Here, the optical signal emitted from the light source device may be a multilevel modulation signal.

  The light receiving device may include a limiting (LIM) type transimpedance amplifier (TIA) for amplifying an output from the light receiving element.

  The control loop may include a temperature control unit that controls the oscillation wavelength of each light source by adjusting the temperature individually or collectively for each light source.

  The light source device includes a periodic array waveguide diffraction grating that multiplexes the N sets of light into a set of N channel wavelength multiplexed light, and the light receiving device converts the N channel wavelength multiplexed light into N sets of light. It is also possible to have a periodic arrayed waveguide diffraction grating that demultiplexes into two.

  Each of the light source device and the light receiving device has a multiplexing / demultiplexing unit that multiplexes or demultiplexes light, and the signal of the signal intensity in the control loop is fed back via the multiplexing / demultiplexing unit. It may be.

  The multiplexing / demultiplexing unit may be a periodic array waveguide diffraction grating, and the periodic array waveguide diffraction grating may have a port for the feedback.

  According to the present invention, optical transmission / reception can be performed even at high input.

It is a block diagram which shows an example of the optical transmission / reception system concerning 1st Embodiment of this invention. It is a figure which shows the example of wavelength arrangement | positioning of the optical transmission / reception system concerning 1st Embodiment. In the optical transmission / reception system concerning 1st Embodiment, it is a figure for demonstrating the oscillation frequency shift amount with respect to light source temperature, and the attenuation amount given by a wavelength multiplexer and a splitter. It is a figure for demonstrating the temperature change dependence of the light source of an error rate characteristic in the optical transmission / reception system concerning 1st Embodiment. In the optical transmission / reception system concerning 1st Embodiment, it is a figure for demonstrating the dependence with respect to the attenuation amount given by the wavelength multiplexer and demultiplexer of an error rate characteristic. It is a block diagram which shows an example of the optical transmission / reception system concerning 2nd Embodiment of this invention. It is a figure which shows wavelength arrangement | positioning of the optical transmission / reception system concerning 2nd Embodiment. It is a block diagram which shows an example of the optical transmission / reception system concerning 3rd Embodiment. It is a figure which shows the example of wavelength arrangement | positioning of the optical transmission / reception system concerning 3rd Embodiment. In the optical transmission / reception system concerning 3rd Embodiment, it is a block diagram which shows an example of a 1st periodic wavelength multiplexing / demultiplexing element and a 2nd periodic wavelength multiplexing / demultiplexing element. It is a figure which shows the structure in the conventional optical transmission / reception system. It is a figure which shows the wavelength arrangement | positioning in the conventional optical transmission / reception system. It is a figure which shows the error rate characteristic in the conventional optical transmission / reception system.

  Hereinafter, first to third embodiments of the present invention will be described.

<First Embodiment>
First, the optical transmission / reception system 100 according to the first embodiment will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration example of an optical transmission / reception system 100. In this optical transmission / reception system 100, a case of 200 Gb / s transmission in which PAM modulation is applied to an optical subassembly for 100 GbE will be described.

  The optical transmission / reception system 100 includes a multi-wavelength light source (light source device) 110 that is a transmission optical subassembly that transmits a downstream optical signal, and a multi-wavelength light receiving element 150 that is a reception optical subassembly that receives the downstream optical signal. The optical fiber transmission line 113 is connected to a multiwavelength light source 110 and a multiwavelength light receiving element (light receiving device) 150.

  The multi-wavelength light source 110 includes N sets of signal sources 111-1 to 111 -N that generate digital electrical signals, N sets of light sources 112-1 to 112 -N having different oscillation wavelengths, and 1 set of N sets of light. And a wavelength multiplexing element 114 that multiplexes the set of N-channel wavelength multiplexed light.

  The multi-wavelength light receiving element 150 includes a wavelength demultiplexing element 154 that demultiplexes the N-channel wavelength multiplexed light into the N sets of light, and N sets of light receiving elements 152 that receive the demultiplexed N sets of light. 1 to 152-N, N sets of amplifiers 153-1 to 153-N for amplifying the photoelectrically converted signals, and N sets of receiving circuits 155-1 to 155-for receiving the amplified signals, respectively. N.

  In FIG. 1, the temperature control circuit 115-N receives the average received power information extracted by the light receiving element 152-N, and controls the oscillation wavelength of the light source 112-N based on the average received power information. ing. This control method will be described later.

  In FIG. 1, only the temperature control circuit 115-N and the average received power information 156-N are shown for simplification, but the same applies to all the other light sources 112-1 to 112-N-1. Are controlled by temperature control circuits 115-1 to 115 -N- 1 that receive average received power information 156-1 to 156 -N- 1 from the corresponding light receiving elements 152-1 to 152 -N- 1. It has become.

  In the following description, the description common to the signal sources 111-1 to 111-N is referred to by the signal source 111, and the description common to the light sources 112-1 to 112-N is referred to by the light source 112, and temperature control is performed. The description common to the circuits 115-1 to 115 N is referred to the temperature control circuit 115. The description common to the light receiving elements 152-1 to 152-N is referred to by the light receiving element 152, the description common to the amplifiers 153-1 to 153-N is referred to by the amplifier 153, and the receiving circuits 155-1 to 155- The description common to N is referred to by the receiving circuit 155. Further, the description common to the average received power information 156-1 to 156-N is referred to in the average received light power information 156.

  The control loop 105 feeds back a signal indicating the signal intensity of light in any one of the N sets of light receiving elements 152-1 to 152-N, and when the signal intensity is larger than a preset value. The oscillation wavelength of the light source that emits light to the light receiving element 152 is outside the transmission band preset in the wavelength multiplexing element 114 or wavelength demultiplexing element 154 (in this embodiment, as described later, outside the 1 dB transmission band) ), The oscillation wavelength of the light source 112 is controlled.

  As the light source 112, for example, a 1.3 μm band semiconductor laser is used. N-channel wavelengths are different. Each of the light sources 112-1 to 112-N is integrated with, for example, an electroabsorption type modulation unit capable of a 28 Gbaud PAM modulation operation.

  The amplifier 153 uses a LIM type TIA, and the receiving circuit 155 has a waveform shaping function using a digital filter.

The wavelengths in the N sets of light sources 112 are labeled. The wavelength of the _first light source is λ ₁ and the wavelength of the second light source is λ ₂ . Similarly, the wavelength of the Nth set is λ _N.

  Next, the operation of the above-described optical transmission / reception system 100 will be described again with reference to FIG.

  N-channel data signals output from the N sets of signal sources 111-1 to 111-N are input to the light sources 112-1 to 112-N, respectively. The N-channel optical signals output from the light sources 112-1 to 112 -N are respectively input to the input ports of the wavelength multiplexing element 114. The output of the wavelength multiplexing element 114 propagates in the optical fiber transmission line 113 as an N-channel wavelength multiplexed signal.

A waveform d shown in FIG. 1 shows a single-channel optical signal in the optical fiber 113. Since the data signal is a PAM system, it can be seen that a multi-valued waveform is obtained in the amplitude direction.
After propagating through the optical fiber 113, it is demultiplexed into N channels by the wavelength demultiplexing element 154, and each data signal is received by the light receiving elements 152-1 to 152-N. The reception circuits 155-1 to 155-N receive the received data signals via the amplifiers 153-1 to 153-N.

  Here, wavelength control by the temperature control circuit 115 connected to the light source 112 will be described. The average received power information 156 extracted from the light receiving element 152 in the multiwavelength light receiving element 150 is electrically fed back to the multiwavelength light source 110. The average light receiving power information 156 indicates the average value of the light intensity received by the light receiving element 152.

  The average received power information 156 is input to the temperature control circuit 115 connected to the light source 112 in the multi-wavelength light source 110, and the control temperature of the light source 112 is set. In this case, when the average received power information 156 is greater than a preset value, the temperature control circuit 115 determines that the oscillation wavelength of the light source 112 that emits light to the corresponding light receiving element 152 is the wavelength multiplexing element 114 or the wavelength component. The oscillation wavelength of the light source 112 is controlled so that the wave element 154 is outside the preset transmission band. Thereby, the oscillation wavelength of the light source 112N is changed by the control temperature. This point will be described in detail later.

  In the 100 GBASE-LR4 standard, the bit rate of the signal source 111 is 25 Gb / s, and the modulation method is NRZ.

FIG. 2 shows the wavelength arrangement in the optical transmission / reception system 100. The wavelength of the N channel is composed of N waves from λ ₁ to λ _N. In FIG. 2, the frequency interval (for example, the interval between λ ₁ and λ ₂ ) of adjacent channels of the wavelength multiplexing element 114 (or wavelength demultiplexing element 154) is Δf, and the transmission band (passband) in each channel is B And At this time, in the optical transmission / reception system 100 of the present embodiment, assuming 200 Gb / s transmission obtained by extending 100 GbE, main parameters take the following numerical values.

N = 4
Δf = 800 GHz
B = 30GHz

  According to these parameters, the optical transmission / reception system 100 has four-wave WDM and the channel frequency interval is 800 GHz.

  Note that the passband B of the wavelength demultiplexing element in the conventional example (see FIG. 11) is 500 GHz or more, whereas the passband B is 30 GHz in the optical transmission / reception system 100 of the present embodiment. The band is much narrower than the one (B = 50 GHz). In other words, the arrayed waveguide diffraction grating (AWG) used for the wavelength demultiplexing element 154 is suitable for the system even if the wavelength of the light source 112 and the center wavelength of the wavelength multiplexing element 114 or wavelength demultiplexing element 154 are slightly changed. Designed to give a big loss. In the optical transmission / reception system 100 of the present embodiment, the oscillation frequency of at least one of the N sets of light sources 112 is set to be at least outside the 1 dB transmission band of the wavelength multiplexing element 114 or wavelength demultiplexing element 154.

  Next, by using the optical transmission / reception system 100 described above, the light passes through the wavelength multiplexing element 114 and the wavelength demultiplexing element 154 when the control temperature to the single light source 112 is changed. The amount of light attenuation was measured.

  FIG. 3 shows the measurement result. In FIG. 3, df (GHz) indicates the shift amount of the oscillation frequency, and ATT (db) indicates the light attenuation amount. In FIG. 3, an AWG having a Gaussian transmission characteristic is used as the wavelength multiplexing element 114 and the wavelength demultiplexing element 154.

  From the measurement results shown in FIG. 3, it was found that when the control temperature of the light source 112 was changed twice, the oscillation frequency of the light source fluctuated by about 30 GHz and the attenuation amount was 8 dB or more.

  Furthermore, using this result, it was measured how the relationship between the average received power of the light receiving element and the error rate (BER) affects the control temperature of the light source 112. The measurement results are shown in FIG.

  FIG. 4 shows the relationship between the average received power of the light receiving element 152 and the error rate (BER) in association with the temperature change of the light source 112. In FIG. 4, the horizontal axis represents average received power, the vertical axis represents BER, and dT represents the temperature change amount of the light source 112. In FIG. 4, the number of TAPs in the receiving circuit 155 is fixed to 11 stages.

From the measurement results shown in FIG. 4, while the oscillation frequency is controlled (dT = 0) at the center of each passband of the wavelength multiplexing element 114 and wavelength demultiplexing element 154, the reception sensitivity is not affected even if the temperature varies. It turns out that it does not fluctuate greatly. Further, it was found that the reception sensitivity does not deteriorate with the increase of the temperature change amount dT but is accompanied by a slight improvement. This is thought to be due to the effect of single sidebanding (SSB) of the optical spectrum due to the increase in “dT”. For example, FIG. 5 shows the average received power at BER = 1 × 10 ⁻³ of the BCH system as sensitivity, and the horizontal axis expressed in attenuation.

  FIG. 5 shows the relationship between such attenuation and sensitivity. In FIG. 5, Pave represents an average value.

  From the results shown in FIG. 5, it was found that even if an attenuation amount of about 5 dB is given, for example, the sensitivity fluctuation is about 0.5 dB and becomes minute. From these results, even if an attenuation amount is given by setting the oscillation frequency of at least one of the light sources 112 to be at least outside the 1 dB transmission band of the wavelength multiplexing element 114 or the wavelength demultiplexing element 154, a waveform is obtained. It was found that the degradation was very small. Further, it was found that the optical transmission / reception system 100 that obtains an error rate below a desired FEC (Forward Error Correction) limit can be realized by giving an appropriate attenuation amount even at high optical input.

  Furthermore, in the optical transmission / reception system 100 of this embodiment, a multi-level modulation method such as PAM can be used for a limiting (LIM) type transimpedance amplifier (TIA) 153 known as an optical subassembly for 100 GbE. . As a result, it is possible to construct a system in which the bit rate is expanded simply and economically.

  Further, in the optical transmission / reception system 100 of the present embodiment, since the oscillation frequency of the light source 112 is performed by temperature control, it is possible to easily realize control of the amount of light attenuation.

(Modification)
In the optical transmission / reception system 100 of the present embodiment, the case where the above-described attenuation amount is controlled by the temperature control of the light source 112 has been described. However, the present invention is not limited to this, and for example, the wavelength multiplexing element 114 and the wavelength demultiplexing element 154 Even if temperature control by the temperature control circuit 115 described above is performed on at least one of them, it is possible to easily realize control of the light attenuation.

Second Embodiment
The optical transmission / reception system 100A according to the second embodiment will be described below with reference to FIGS. In the following description of the present embodiment, the symbols and the like used in the description of the first embodiment are used as they are unless otherwise specified.

  In the optical transmission / reception system 100 of the first embodiment, the number of the multi-wavelength light sources 100 and the multi-wavelength light receiving elements 150 is described as one, but this is not necessarily required. The optical transmission / reception system 100A of the present embodiment realizes optical communication similar to that of the first embodiment, but the number of the multi-wavelength light sources 100 and the multi-wavelength light receiving elements 150 is configured as N (N is integer).

  FIG. 6 is a diagram illustrating a configuration example of the optical transmission / reception system 100A according to the present embodiment.

  This optical transmission / reception system 100A is an M channel wavelength multiplexed light obtained by combining N sets of M wavelength (M is an integer) multi-wavelength light sources 110-1 to 110-N having a frequency interval ΔF and the M channels. A periodic wavelength multiplexing element 130 for multiplexing N sets of M channel wavelength multiplexed light from each of the N sets of multi-wavelength light sources 110-1 to 110-N into M × N channel wavelength multiplexed light; A periodic wavelength multiplexing / demultiplexing element 140 that demultiplexes the N channel wavelength multiplexed light into the N sets of M channel wavelength multiplexed light, and the N sets of M channel multi-wavelength light demultiplexed by the periodic wavelength demultiplexing element 140. N sets of multi-wavelength light receiving elements 150-1 to 150-N for receiving light are included. The optical transmission / reception system 100A is configured to transmit and receive the M × N channel wavelength division multiplexed light through the fiber 113 that connects the periodic wavelength multiplexing element 130 and the periodic wavelength multiplexing element 140. .

  The multi-wavelength light source 110-1 includes M light sources 112-1 to 112-M1 and a wavelength multiplexing element 114- that wavelength-multiplexes M channel light from these light sources and outputs M channel wavelength multiplexed light. 1. The multi-wavelength light sources 110-2 to 110-N are configured similarly to the multi-wavelength light source 110-1. For example, in the multi-wavelength light source 110-1, the frequency interval of the M channel lights from the M light sources 112-11 to 112-M1 is ΔF. The same applies to the multi-wavelength light sources 110-2 to 110-N.

  N sets of M channel wavelength multiplexed light from the N sets of multi-wavelength light sources 110-1 to 110 -N are wavelength-multiplexed into M × N channel wavelength multiplexed light by the periodic wavelength multiplexer 130.

  Although not shown in FIG. 6, each of the multi-wavelength light sources 110-1 to 110-N includes a signal source connected to an M channel light source (see FIG. 1).

  The multi-wavelength light receiving element 150-1 includes a wavelength demultiplexing element 154-1 that separates M channel wavelength multiplexed light and outputs M channel light, and M light receiving elements 152 that receive M channel light. -11 to 152-M1.

  Each of the M light receiving elements 152-1 to 152-M1 receives one of the M channel lights. For example, the wavelength demultiplexing element 154-1 of the multi-wavelength light receiving element 150-1 is one of N sets of M channel wavelength multiplexed light demultiplexed from the M × N channel wavelength multiplexed light by the periodic wavelength demultiplexing element 140. Are divided into M channel lights, and these M channel lights are received by M light receiving elements 152-11 to 152-M1, respectively.

  Similarly, in the multi-wavelength light receiving element 150-2, the wavelength demultiplexing element 154-2 includes N sets of M channels demultiplexed from the M × N channel wavelength multiplexed light by the second periodic wavelength multiplexing / demultiplexing element 140. One of the wavelength multiplexed lights is demultiplexed into M channel lights, and these M channel lights are respectively received by M light receiving elements.

  Although not shown in FIG. 6, the multi-wavelength light receiving elements 154-1 to 154-N include an amplifier and a receiving circuit connected to the M channel light receiving elements (see FIG. 1). In this embodiment, for example, an LIM type TIA is used as an amplifier, and the receiving circuit has a waveform shaping function by a digital filter.

  Further, temperature control circuits 115-1 to 115 -N are connected to the multi-wavelength light sources 110-1 to 110 -N, and average received power information 156-1 to 156 -N are extracted from the multi-wavelength light receiving elements. Is done.

  In FIG. 6, only the temperature control circuit 115-N that controls the oscillation wavelength of the light source by controlling the temperature of the light source 112 based on the average received power information 156-N is shown for the sake of simplification as in FIG. However, the average received power information 156-1 to 156-156 from the corresponding light receiving elements 152-1 to 152-N-1 is similarly applied to all the other multi-wavelength light sources 110-1 to 110-N-1. It is controlled by temperature control circuits 115-1 to 115-N-1 that receive N-1. Also in the present embodiment, this control is performed using the control loop 105 as in the first embodiment.

  In the following description, a description common to all light sources is referred to by the light source 112, and a description common to all temperature control circuits is referred to by the temperature control circuit 115. The description common to all the light receiving elements is referred to by the light receiving element 152, and the description common to all the average received power information is referred to by the average received light power information 156. The description common to all wavelength multiplexing elements is referred to by the wavelength multiplexing element 114, and the description common to all wavelength multiplexing elements is referred to by the wavelength multiplexing element 154.

  As the light source 112, a 1.3 μm band semiconductor laser is used, and the wavelength of the N channel is different. The light source 112 is integrated with an electroabsorption type modulation unit capable of 28 Gbaud PAM modulation.

Further, labels are assigned to the wavelengths in the N sets of multi-wavelength light sources 110-1 to 110-N. Wavelength of the first set of multi-wavelength light source 110-1 and M wave lambda _M1 from lambda _11, the wavelength of the second set of multi-wavelength light source 110-2 and M wave from λ ₁₂ λ _M2. Since wavelengths are similarly given to the third to Nth multi-wavelength light sources, for example, the wavelength of the Mth multiwavelength light source 110-M is M waves from λ _1N to λ _MN .

  Next, the operation of the optical transmission / reception system 100A will be described.

  The M-channel wavelength multiplexed signals output from the N sets of multi-wavelength light sources 110-1 to 110 -N are respectively input to the input ports of the periodic wavelength multiplexer 130. The output is an M × N channel wavelength multiplexed signal and propagates through the optical fiber 113. After propagation, the light is demultiplexed by the periodic wavelength demultiplexing element 140 into a wavelength group equivalent to each of the multi-wavelength light sources 110 (N sets of M-channel wavelength multiplexed signals), and then each of the multi-wavelength light receiving elements 150-1 to 150- In N, the light is demultiplexed into M channel lights by the wavelength demultiplexing element 154 and then received by the M light receiving elements 152.

  For example, when each multi-wavelength light source 110 is a PAM4 signal having a wavelength multiplexing number of 4 channels and each light source 112 has a modulation speed of 28 Gbaud, the total bit rate of each multi-wavelength light source is 200 Gb / s. Further, by using four sets of multi-wavelength light sources 110-1 to 110-N (for example, N = 4), a total bit rate of 800 Gb / s can be obtained from the periodic wavelength multiplexing / demultiplexing element 140.

  Wavelength control by the temperature control circuit 115 connected to each light source 110 will be described.

  Each average received power information 156 extracted from each multi-wavelength light receiving element 150 is electrically fed back to each multi-wavelength light source 150. Each average received power information 156 is input to each temperature control circuit 115 connected to each multi-wavelength light source 110, and the control temperature of each light source 112 is set collectively. Thereby, the oscillation wavelength of each light source 112 is changed by the control temperature.

  FIG. 7 shows an example of wavelength arrangement in the optical transmission / reception system 100A of the present embodiment.

The wavelength of the M × N channel is roughly divided into M groups of N channels. For example, the first group is composed of N waves from λ ₁₁ to λ _1N , and the subsequent second group is composed of N waves from λ ₂₂ to λ _2N .

Here, the frequency interval between adjacent groups (for example, the interval between λ ₁₁ and λ ₂₁ ) is ΔF, the adjacent frequency interval within the same group (for example, the interval between λ ₂₁ and λ ₂₂ ) is Δf, and the transmission band (passband) in each group ) Is B.

  The optical transmission / reception system 100A of the present embodiment applies 800 Gb / s transmission that is an extension of 100 GbE. Considering the factors, the main parameters are set as follows.

M = 4
N = 4
ΔF = 800GHz
Δf = 100 GHz
B = 360GHz

  According to this setting, each group has four-wave WDM at 100 GHz intervals, and the frequency interval for each group is 800 GHz. Therefore, in the optical transmission / reception system 100A of this embodiment, M × N WDM optical wavelengths are It is not always the same frequency interval.

  In this setting, the N sets of M-channel multi-wavelength light sources 110-1 to 110-N have the frequency of the adjacent sets shifted by Δf as a whole, and the N sets of interval products Δf × (N−1). ) Is smaller than the transmission band B of the wavelength demultiplexing element 154 in the multi-wavelength light receiving element 150.

  Both the periodic wavelength multiplexing element 130 and the periodic wavelength demultiplexing element 140 of this embodiment are PLC-type AWGs fabricated in an optical planar circuit (PLC). These elements 130 and 140 include an input / output channel waveguide and a wavelength division multiplex waveguide, an input / output slab waveguide and a wavelength division slab waveguide, and an arrayed waveguide. At this time, there are at least N input / output channel waveguides and at least one wavelength multiplexing waveguide.

  In this embodiment, since N = 4 is given, there are four input / output channel waveguides. Since M = 4 is given, 16 waves (4 × 4) of WDM signals are input / output from the wavelength multiplexing waveguide.

  At this time, the port interval Δf of the elements 130 and 140 may have a product Δf × (N−1) that is less than or equal to half of the FSR periodicity (free spectral range: FSR) ΔF. As a result, an optical circuit (periodic wavelength multiplexing element 130 and periodic wavelength demultiplexing element 140) having low loss characteristics can be realized.

  Next, the set wavelengths of the multi-wavelength light source 110 will be described again with reference to FIG. As described above, the frequency interval ΔF of the multi-wavelength light sources 110-1 to 110-N is 800 GHz, and the number of channels M is four. The value of the set N is 4.

  The M × N channels all have different oscillation wavelengths (oscillation frequencies), and the frequencies of adjacent sets are shifted by Δf as a whole. In order to make such wavelengths uniform, there is a method of preparing light sources having different compositions shifted by Δf, but in this embodiment, a method of using light sources having the same composition is adopted. That is, this is a method of adjusting the oscillation wavelength by adjusting the temperature.

  The multi-wavelength light source 110 is obtained by integrating each light source (in this embodiment, M light sources 112) on the same substrate. In this case, it is possible to change all the wavelengths of the multi-wavelength light source 110 at once by adjusting the temperature by temperature control means such as a Peltier element or a heater for each substrate. Since the wavelength variation due to temperature is about 15 GHz per 1 ° C., a temperature change of about 7 ° C. is sufficient to give Δf of 100 GHz.

  In consideration of general laser performance, the temperature control range is preferably set within ± 20 ° C. In other words, the frequency control range is preferably within 600 GHz in total width.

  In the M-channel multi-wavelength light source 110 of the present embodiment, N sets of interval products Δf × (N−1) are within 600 GHz. As a result, it is possible to use the same component, and thus it is possible to further simplify the system and reduce the cost.

  As described above, in the optical transmission / reception system 100A according to the present embodiment, conditions (parameters and the like) are set so that each period of the periodic wavelength multiplexing element 130 and the periodic wavelength demultiplexing element 140 is equal to the frequency interval ΔF of the multi-wavelength light source 110. ), The existing WDM system can be expanded to a higher density, higher bit rate optical transmission / reception WDM with a simple configuration. Even if an attenuation is given by setting the oscillation frequency of at least one of the light sources 112 to be at least outside the 1 dB transmission band of the wavelength multiplexing element 130 or wavelength demultiplexing element 140, the waveform deterioration is minute. If an appropriate amount of attenuation is given even at high optical input, it is possible to realize an optical transmission / reception system 100A that obtains an error rate below a desired FEC limit.

  Furthermore, in this embodiment, the optical transmission / reception system 100A can be realized by using a multilevel modulation method such as PAM for the existing optical subassembly for 100 GbE using the LIM type TIA. Therefore, it is possible to construct a system in which the bit rate is expanded simply and economically.

  In the present embodiment, since the oscillation frequency of the light source 112 is controlled by temperature control, it is possible to easily control the amount of light attenuation.

(Modification)
In the optical transmission / reception system 100A of this embodiment, the case where the above-described attenuation amount is controlled by the temperature control of the light source 112 has been described. However, the present invention is not limited to this, and for example, the wavelength multiplexing element 114 and the wavelength demultiplexing element 154 Even if temperature control by the temperature control circuit 115 described above is performed on at least one of them, it is possible to easily realize control of the light attenuation.

  In the present embodiment, the wavelength of the light source 112 is set to the 1.3 μm band, but a 1.5 μm band that is a telecom wavelength may be used. In addition, although the modulation unit of the light source 112 is an electroabsorption type, direct laser modulation may be used, or a modulator using an electro-optic crystal such as lithium niobate and a light source may be used in combination. Further, in this optical transmission / reception system 100A, since the N sets of interval products Δf × (N−1) are smaller than the transmission band B of the wavelength demultiplexing element 154 in the multiwavelength light receiving element 150, each multiwavelength light receiving element 150 has a wavelength component. It is possible to use the same parts including wave characteristics. Therefore, further simplification and cost reduction of the optical transmission / reception system can be achieved.

  In the present embodiment, Δf is set to 100 GHz. However, if the N waves in the same group are within the transmission band B, the above-described effects described in the present embodiment can be obtained with other values, for example, 75 GHz and 50 GHz.

  In this embodiment, since the M channel multi-wavelength light sources have N sets of interval products Δf × (N−1) within 600 GHz, each multi-wavelength light source 110 includes the same oscillation wavelength characteristics of the light source 112. Parts can be used. Therefore, further simplification and cost reduction of the optical transmission / reception system can be achieved.

  The above-described PLC of the present embodiment is a quartz waveguide on a silicon substrate, but the material of the substrate and the waveguide is not limited to silicon or quartz, and an organic polymer resin or the like can also be used.

  In the present embodiment, for the port interval Δf of the periodic wavelength multiplexing / demultiplexing elements (130, 140), the product Δf × (N−1) is set to half or less of the periodicity ΔF. Thereby, since the wavelength used can be near the center in the FSR, an optical circuit with low loss characteristics can be realized.

<Third Embodiment>
Next, an optical transmission / reception system 100B according to the third embodiment will be described with reference to FIGS. In the following description of the present embodiment, the reference numerals and the like used in the description of the first and second embodiments are used as they are unless otherwise specified.

  The optical transmission / reception system 100B of the present embodiment realizes optical communication similar to that of the first embodiment, but realizes a configuration in which the transmission / reception direction is different for each set of adjacent light sources or elements.

  FIG. 8 is a diagram illustrating a configuration example of the optical transmission / reception system 100B according to the present embodiment. In this optical transmission / reception system 100B, N sets (110-1 to 110-N) of M-channel multi-wavelength light sources having a frequency interval ΔF and N / 2 sets of M-channel wavelength multiplexed light to the first M × N / A first periodic wavelength multiplexing / demultiplexing element 131 for multiplexing the two-channel wavelength multiplexed light and demultiplexing the second M × N / 2 channel wavelength multiplexed light into N / 2 sets of M channel wavelength multiplexed light; Have Furthermore, the system 100B combines N / 2 sets of M channel wavelength multiplexed light with the second M × N / 2 channel wavelength multiplexed light, and the first M × N / 2 channel wavelength multiplexed light with N / N. Second periodic wavelength multiplexing / demultiplexing element 141 that demultiplexes two sets of M channel wavelength multiplexed light, and receives the first M × N / 2 channel wavelength multiplexed light and N / 2 sets of M channel multi wavelength light. N / 2 sets of multi-wavelength light receiving elements (150-1, 150-3, 150- (N-1)) and the second M × N / 2-channel wavelength multiplexed light into N / 2 sets of M channels. N / 2 sets of multi-wavelength light receiving elements (150-2, 150-4, 150-N) for receiving wavelength light.

  The first periodic wavelength multiplexing / demultiplexing element 131 is connected to the second periodic wavelength multiplexing / demultiplexing element 141 via the optical fiber 113.

  The multi-wavelength light source 110-1 is a wavelength multiplexing element 114 that wavelength-multiplexes M channel light from the M light sources 112-11 to 112-M1 and M channel wavelength multiplexed light from the M light sources. -1. For example, the frequency interval of the M channel lights from the M light sources 112-11 to 112-M1 of the multi-wavelength light source 110-1 is ΔF. The multi-wavelength light sources 110-2 to 110-N are configured similarly.

  N / 2 sets of M channel wavelength multiplexed light from the N sets of multi-wavelength light sources 110-1 to 110-N are converted into M × N / 2 channel wavelength multiplexed light in the first periodic wavelength multiplexing / demultiplexing element 131. Is multiplexed. The remaining N / 2 sets of M channel wavelength multiplexed light from the N sets of multi-wavelength light sources 110-1 to 110 -N are M × N / 2 channel wavelength multiplexed light in the second periodic wavelength multiplexing / demultiplexing element 141. Wavelength multiplexed.

  Although not shown in FIG. 8, each of the multi-wavelength light sources 110-1 to 110-N includes a signal source connected to an M channel light source.

  The multi-wavelength light receiving element 150-1 is a wavelength demultiplexing element 154-1 to 154-N that separates M channel wavelength-multiplexed light and outputs M channel light, and M number of light receiving M channel lights. Light receiving elements 152-11 to 152-M1. The multi-wavelength light receiving elements 150-2 to 150-N are similarly configured.

  Each of the M light receiving elements described above receives one of the M channel lights. For example, the wavelength demultiplexing element 154-1 of the multi-wavelength light receiving element 150-1 includes N sets of M channels demultiplexed from the M × N / 2-channel wavelength multiplexed light by the first periodic wavelength multiplexing / demultiplexing element 140. One of the wavelength multiplexed lights is demultiplexed into M channel lights, and these M channel lights are received by the M light receiving elements 152-11 to 152-M1, respectively. Similarly, the wavelength demultiplexing element 154-2 of the multi-wavelength light receiving element 150-2 includes N sets of M demultiplexed from the M × N / 2-channel wavelength multiplexed light by the second periodic wavelength multiplexing / demultiplexing element 140. One of the channel wavelength multiplexed lights is demultiplexed into M channel lights, and these M channel lights are respectively received by M light receiving elements.

  Although not shown in FIG. 8, the multi-wavelength light receiving elements 150-1 to 150-N include an amplifier and a receiving circuit connected to the M channel light receiving elements. As the amplifier, for example, a LIM type TIA is used, and the receiving circuit has a waveform shaping function by a digital filter.

  In the optical transmission / reception system 100B of the present embodiment, temperature control circuits 115-1 to 115-N are connected to the multi-wavelength light sources 110-1 to 110-N. Then, average received power information 156-1 to 156-N is extracted from each multi-wavelength light receiving element for monitoring (in FIG. 8, multi-wavelength light receiving elements 150-1 to 150-N).

  In FIG. 8, for simplification, the average reception extracted from the temperature control circuit 115-N connected to the Nth multiwavelength light source 110-N and the Nth monitor multiwavelength light receiving element 150-N. Only power information 156-N is shown.

  In the following description, a description common to all multi-wavelength light sources is referred to by the multi-wavelength light source 110, a description common to all light sources is referred to by the light source 112, and a description common to all temperature control circuits is temperature. Referenced by the control circuit 115. The description common to all the multi-wavelength light receiving elements is referred to by the multi-wavelength light receiving element 150, the description common to all the light receiving elements is referred to by the light receiving element 152, and the description common to all average received power information is Referenced by average received light power information 156. The description common to all wavelength multiplexing elements is referred to by the wavelength multiplexing element 114, and the description common to all wavelength multiplexing elements is referred to by the wavelength multiplexing element 154.

  As the light source 112, for example, a 1.3 μm band semiconductor laser is used, and the wavelength of the N channel is different. Each light source 112 is integrated with an electroabsorption type modulation unit capable of 28 Gbaud PAM modulation operation.

Labels are applied to the wavelengths in the N sets of multi-wavelength light sources 110. Wavelength of the first set of multi-wavelength light source 110-1 and M wave lambda _M1 from lambda _11, the wavelength of the second set of multi-wavelength light source 110-2 and M wave from λ ₁₂ λ _M2. Since wavelengths are similarly given to the third to Nth multi-wavelength light sources, for example, the wavelength of the Mth multiwavelength light source 110-M is M waves from λ _1N to λ _MN .

  Next, the operation of the optical transmission / reception system 100B will be described with reference to FIG. 8 again.

  The M-channel wavelength multiplexed signals output from the N sets of multi-wavelength light sources 110-1 to 110-N are respectively the first periodic wavelength multiplexing / demultiplexing element 131 or the second periodic wavelength multiplexing / demultiplexing element 141. Is input to the input port. The output is an M × N / 2 channel wavelength multiplexed signal and propagates through the optical fiber 113. After propagation, the first periodic wavelength multiplexing / demultiplexing element 131 or the second periodic wavelength multiplexing / demultiplexing element 141 is demultiplexed into a wavelength group equivalent to each multi-wavelength light source (N sets of M-channel wavelength multiplexed signals). After that, each of the multi-wavelength light receiving elements (150-1 to 150-N) is re-demultiplexed into M channel lights by the wavelength demultiplexing element 154 and then received by the M light receiving elements 152.

  For example, when each multi-wavelength light source 110 has a wavelength multiplexing number of 4 channels and each light source 112 has a modulation speed of 28 Gbaud, the total bit rate of each multi-wavelength light source is 200 Gb / s. Furthermore, by using four sets of multi-wavelength light sources (110-1 to 110-N; N = 4), a total bit rate of 800 Gb / s can be obtained from the periodic wavelength multiplexing / demultiplexing element. In this embodiment, since it is the optical transmission / reception system 100B by the single core fiber from which a transmission / reception direction differs for every adjacent group, the total bit rate of each direction is 400 Gb / s.

  Next, wavelength control by the temperature control circuit 115 connected to each light source 110 will be described.

  Each average received power information 156 extracted from each multi-wavelength light receiving element 150 for monitoring is electrically fed back to each multi-wavelength light source 110. The average received power information 156 is input to each temperature control circuit 115 connected to each multi-wavelength light source 110, and the control temperature of each light source 112 is set collectively. Thereby, the oscillation wavelength of each light source 112 is changed by the control temperature.

  FIG. 9 shows an example of wavelength arrangement in the optical transmission / reception system 100B of the present embodiment.

The wavelength of the M × N channel is roughly divided into M groups of N channels. For example, the first group is composed of N waves from λ ₁₁ to λ _1N , and the subsequent second group is composed of N waves from λ ₂₂ to λ _2N .

Here, the frequency interval between adjacent groups (for example, the interval between λ ₁₁ and λ ₂₁ ) is ΔF, the adjacent frequency interval within the same group (for example, the interval between λ ₂₁ and λ ₂₂ ) is Δf, and the transmission band (path) in each group (Band) is B.

  The optical transmission / reception system 100B of the present embodiment is configured to perform 400 Gb / s bidirectional transmission that is 100 GbE extended. Considering the configuration, the main parameters are set as follows.

M = 4
N = 4
ΔF = 800GHz
Δf = 100 GHz
B = 360GHz

  According to this setting, each group has four-wave WDM at 100 GHz intervals, and the frequency interval for each group is 800 GHz. Therefore, in the optical transmission / reception system 100B of this embodiment, M × N WDM optical wavelengths are It is not always the same frequency interval.

  In this setting, the N sets of M-channel multi-wavelength light sources 110-1 to 110-N have the frequency shift of the adjacent sets as a whole by Δf, and the N sets of interval products Δf × (N−1). ) Is smaller than the transmission band B of the wavelength demultiplexing element 154 in the multi-wavelength light receiving element 150.

  Next, configuration examples of the first periodic wavelength multiplexing / demultiplexing element 131 and the second periodic wavelength multiplexing / demultiplexing element 141 of the present embodiment will be described with reference to FIG.

  FIG. 10 is a diagram illustrating a configuration example of the first periodic wavelength multiplexing / demultiplexing element 131. In FIG. 10, the first periodic wavelength multiplexing / demultiplexing element 131 will be described. Similarly, the second periodic wavelength multiplexing / demultiplexing element 141 is similarly configured by making the traveling direction of light shown in FIG. 10 symmetrical. Can be explained.

  A periodic wavelength multiplexing / demultiplexing element 131 shown in FIG. 10 is a PLC type arrayed waveguide diffraction grating (AWG) fabricated in an optical planar circuit (PLC) 300. The periodic wavelength multiplexing / demultiplexing element 131 includes input / output channel waveguides 302-1 to 302-N, a wavelength division multiplexing waveguide 310, an input / output slab waveguide 304, a wavelength division multiplexing slab waveguide 308, and an array waveguide 306. It is configured with. At this time, there are at least N input / output channel waveguides and at least one wavelength multiplexing waveguide.

  In addition, the periodic wavelength multiplexing / demultiplexing element 131 has the input / output channel waveguide 302 connected to the input / output slab waveguide 304 and the wavelength of each multi-wavelength light source (multi-wavelength light sources 1 to 4 in FIG. 10). A monitor waveguide 802 for detecting and controlling is connected. Further, the periodic wavelength multiplexing / demultiplexing device 131 is connected to the wavelength division multiplexing slab waveguide 308 and the wavelength division multiplexing waveguide 310 is connected to the wavelength division multiplexing slab waveguide 308 again. Loopback waveguides 904 are connected.

  In FIG. 10, a periodic wavelength multiplexing / demultiplexing device 131 according to the present embodiment includes a wavelength multiplexing slab waveguide 308 connected to the wavelength multiplexing slab waveguide 308 and a tap circuit that extracts a part of the output wavelength multiplexing light. 906 is connected to the wavelength division multiplexing waveguide 310, and one of the tap circuits is connected to the loopback waveguide 904. The tap circuit 906 is an optical circuit that can be configured with a directional coupler, a Y branch circuit, or the like. In the example of FIG. 10, 5% of the total intensity of the wavelength multiplexed light is extracted and connected to the loopback waveguide 904. .

  Here, as a circuit design condition of the optical transmission / reception system 100B, the period (free spectrum range, FSR) of the periodic wavelength multiplexing / demultiplexing element 131 shown in FIG. 10 is the frequency of the multi-wavelength light sources 110-1 to 110-N. It is configured to be equal to the interval ΔF. The interval (port interval) between the input / output channel waveguides 302-1 to 302-N at the connection point with the input / output slab waveguide 304 is equal to Δf. The input light propagating through the input / output slab waveguide 304, the arrayed waveguide 306 and the wavelength division slab waveguide 308 is configured to focus on the wavelength division multiplexing waveguide 310 connected to the wavelength division slab waveguide 308. ing.

  Of the N input / output channel waveguides 302-1 to 302-N, the input / output channel waveguides 302-1 and 302-3 to 302- (N-1) have a multi-wavelength light source. 110-1 to 110-N having an odd number, that is, wavelengths from the multi-wavelength light sources 110-1 and 110-3 to 110- (N-1) are input.

In addition, the input / output channel waveguides 302-2 and 302-4 to 302-N, which have an even number among the N input / output channel waveguides, have multi-wavelength light receiving elements 150-1 to 150-N. Of these, the wavelengths having even numbers, that is, the wavelengths to the multi-wavelength light receiving elements 150-2 and 150-4 to 150-N are output. That is, M waves of wavelengths λ ₁₁ to λ _M1 of the first set of multi-wavelength light sources are input to the first input / output channel waveguide, and the second set of multi-wavelength light sources are input to the second input / output channel waveguide. M waves of wavelengths λ ₁₂ to λ _M2 are output to the wavelength light receiving element. M waves of wavelengths λ ₁₃ to λ _{M (N−1)} of the third set of multi-wavelength light sources are input to the third input / output channel waveguide, and the fourth input / output channel waveguide has Nth M waves of wavelengths λ _1N to λ _MN are output to a set (for example, N = 4) of multi-wavelength light receiving elements.

  Crosstalk between four-wave WDMs can be reduced by alternately connecting a multi-wavelength light source and a multi-wavelength light receiving element to N-number input / output channel waveguides having odd and even numbers. .

  In this embodiment, since N = 4, there are four input / output channel waveguides. Further, since M = 4, 16 waves (4 × 4) of WDM signals are input / output from the wavelength multiplexing waveguide when both directions are combined. Here, the port interval Δf of the periodic wavelength multiplexing / demultiplexing elements 131 and 141 may be such that the product Δf × (N−1) is half or less of the FSR periodicity (free spectrum range, FSR) ΔF. As a result, an optical circuit (periodic wavelength multiplexing / demultiplexing device) having low loss characteristics can be realized.

  In the present embodiment, the number of the monitor waveguides 802 shown in FIG. 10 is given to the N sets of multi-wavelength light sources described above, and thus N. Similar to the input / output channel waveguide 302 described above, the interval (port interval) of the N monitor waveguides 802 at the connection point of the input / output slab waveguide 304 is set to Δf, and adjacent to the input / output channel waveguide 302. Arrange in order. In this embodiment, the input / output channel waveguide 302 is symmetrically disposed at the center of the input / output slab waveguide 304 in order to obtain low loss. Therefore, the monitor waveguides 802 are symmetrically arranged on both outer sides of the N input / output channel waveguides 302 as shown in an example in FIG.

  The loopback waveguide 904 is disposed at a position that is Δf × N away from the connection point between the output slab waveguide 308 and the wavelength division multiplexing waveguide 310.

  Depending on the above design conditions and input conditions, a set of M-channel wavelength multiplexed light that is input to N / 2 of the N input / output channel waveguides 302-1 to 302-N becomes M in the wavelength multiplexed waveguide 310. X Output as N / 2 channel WDM signal.

  A part of the wavelength multiplexed light returned from the loopback waveguide 904 to the output waveguide slab waveguide 308 is demultiplexed and then output to each monitor waveguide 802. The wavelength group output to each monitor waveguide 802 has M channels at a frequency interval ΔF equivalent to the wavelength group of each multi-wavelength light source 110. From this point of view, the wavelength and light intensity of each multi-wavelength light source 110 can be adjusted by monitoring the wavelength and light intensity from each monitor waveguide 802. That is, the oscillation wavelength of the light source 112 can be controlled by feedback control based on the above-described wavelength and light intensity.

  Therefore, in the optical transmission / reception system 100B of this embodiment, the existing WDM system can be expanded to a high-density and high bit rate optical transmission / reception WDM with a simple configuration. Even if an attenuation is given by setting the oscillation frequency of at least one of the light sources 112 to be at least outside the 1 dB transmission band of the wavelength multiplexing element 114 or the wavelength demultiplexing element 154, the waveform deterioration becomes minute. . For this reason, if an appropriate amount of attenuation is given even at the time of high optical input, an optical transmission / reception system 110B that obtains an error rate below a desired FEC limit is realized.

  In the present embodiment, the optical transmission / reception system 100B can be realized by using a multilevel modulation method such as PAM for the existing optical subassembly for 100 GbE using the LIM type TIA. Therefore, it is possible to construct a system 100B with an expanded bit rate with simplification and low cost.

  Further, in the present embodiment, since the oscillation frequency of the light source 112 is controlled by temperature control, it is possible to easily control the amount of light attenuation.

  According to the optical transmission / reception system 100B of the present embodiment, by using a periodic wavelength multiplexing / demultiplexing device as shown in FIG. 10, it is possible to make an existing WDM system both simpler and higher in density and higher in bit rate. Extension to the directional optical transmission / reception WDM becomes possible.

(Modification)
In the optical transmission / reception system 100B of the present embodiment, the case where the above-described attenuation amount is controlled by the temperature control of the light source 112 has been described. However, the present invention is not limited to this, and for example, the wavelength multiplexing element 114 and the wavelength demultiplexing element 154 Even if temperature control by the temperature control circuit 115 described above is performed on at least one of them, it is possible to easily realize control of the light attenuation.

  In the above embodiment, the description has been given by taking an example in which the multi-wavelength light source 110 and the multi-wavelength light receiving element 150 are alternately connected to the odd-numbered and even-numbered ones of N input / output channel waveguides 302. Not limited to this. For example, the multi-wavelength light source 110 may be connected to the first to N / 2th of the N input / output channel waveguides, and the multi-wavelength light receiving element 150 may be connected to the remaining one.

DESCRIPTION OF SYMBOLS 100 Optical transmission / reception system 110 Multi-wavelength light source 111 Signal source 112 Light source 113 Optical fiber transmission line 114 Wavelength multiplexer 115 Temperature control circuit 130 Periodic wavelength multiplexer 131 First periodic wavelength multiplexer / demultiplexer 140 Periodic wavelength Wave element 141 Second periodic wavelength multiplexing / demultiplexing element 150 Multi-wavelength light receiving element 152 Light receiving element 153 Amplifier 154 Wavelength demultiplexing element 155 Receiver circuit 156 Average received power information 300, 800, 900 Optical planar circuit (PLC)
302 Input / output channel waveguide 304 Input / output slab waveguide 306 Array waveguide 308 Wavelength multiplexed slab waveguide 310 Wavelength multiplexed waveguide 802 Monitor waveguide 904 Loopback waveguide 906 Tap circuit

Claims (8)

An optical transmission / reception system,
A light source device having N sets of light sources that respectively emit N sets of light having different oscillation wavelengths, and a wavelength combining element that combines the N sets of light with one set of N-channel wavelength multiplexed light, and
A light receiving device having a N sets of light receiving element for receiving said N channels of wavelength-multiplexed light wherein the N sets the wavelength demultiplexing element for demultiplexing the optical the demultiplexed the N sets of light respectively,
A signal indicating the signal intensity of the light in any one of the N sets of light receiving elements is fed back to the light source side, and when the signal intensity is greater than a preset value, A control loop for controlling the oscillation wavelength of the light source so that the oscillation wavelength of the light source emitting light is outside the transmission band set in advance in the wavelength multiplexing element or the wavelength demultiplexing element. Optical transmission / reception system.   The optical transmission / reception system according to claim 1, wherein the optical signal emitted from the light source device is a multilevel modulation signal.   The optical transmission / reception system according to claim 1, wherein the light receiving device includes a limiting (LIM) type transimpedance amplifier (TIA) that amplifies an output from the light receiving element.   2. The optical transmission / reception system according to claim 1, wherein the control loop includes a temperature control unit that controls the oscillation wavelength of each light source by adjusting the temperature individually or collectively for each light source.   The light source device includes a periodic array waveguide diffraction grating that multiplexes the N sets of light into a set of N channel wavelength multiplexed light, and the light receiving device converts the N channel wavelength multiplexed light into N sets of light. 5. The optical transmission / reception system according to claim 1, further comprising a periodic arrayed waveguide diffraction grating that is demultiplexed into two. Each of the light source device and the light receiving device has a multiplexing / demultiplexing unit that multiplexes or demultiplexes light,
5. The optical transmission / reception system according to claim 1, wherein the signal having the signal strength in the control loop is fed back via the multiplexing / demultiplexing unit. 6. The multiplexing / demultiplexing unit is a periodic array waveguide diffraction grating,
The optical transmission / reception system according to claim 6, wherein the periodic array waveguide diffraction grating has a port for the feedback.   A light source device used in the optical transmission / reception system according to claim 1.