JP2015154160A - Optical transmission/reception system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized, simple, and inexpensive optical transmission/reception system.SOLUTION: An optical transmission/reception system includes: N sets of multi-wavelength light sources 110 having M channels with a frequency interval ΔF; a periodic wavelength multiplexing element 130 for multiplexing N sets of M channel wavelength multiplex light to one set of M×N channel wavelength multiplex light; a periodic wavelength demultiplexing element 140 for demultiplexing the M×N channel wavelength multiplex light to N sets of M channel wavelength multiplex light; and N sets of multi-wavelength light receiving elements 150 for receiving M channel multi-wavelength light. Periods in the periodic wavelength multiplexing element 130 and periodic wavelength demultiplexing element 140 are made to be the same as the frequency interval ΔF in the multi-wavelength light sources 110.

Description

  The present invention relates to a configuration of an optical transmission / reception system using an optical module mainly applied to optical fiber communication. More particularly, the present invention relates to an optical transmission / reception system for performing telecom and datacom transmission using wavelength division multiplexing communication and a configuration of an optical circuit thereof.

  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. At present, in the standard for 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 (baud rate of 25 Gb / s per wave). . 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.

  When configuring 400 GbE at the bit rate (25 Gb / s) used in 100 GbE, the number of WDMs is 16 waves. As a proposal for the wavelength arrangement, a configuration in which 16 waves are continuously arranged while the frequency interval ΔF is maintained at 800 GHz is conceivable. However, since the overall frequency band becomes too wide, the sensitivity and dispersion frequency dependency in the optical transmission / reception system cannot be ignored. In addition, the wavelength required for the laser also becomes a wide band, making it difficult to manufacture with a single epitaxial wafer. Therefore, an increase in manufacturing cost due to an increase in component types becomes a problem.

  On the other hand, instead of continuously arranging 16 waves while maintaining ΔF = 800 GHz, a configuration in which ΔF is concentrated in a narrow band WDM such as 100 GHz or 200 GHz is also conceivable. In particular, a configuration that interleaves an 800 GHz multi-wavelength transceiver that has been technically established with the existing 100 GbE may be able to provide advantageous expandability in terms of economy. (For example, refer to Patent Document 1 and Non-Patent Document 1). These conventional techniques will be described below.

  FIG. 10A is a diagram showing a schematic configuration of a conventional interleave optical transmission / reception system disclosed in Patent Document 1. In FIG. FIG. 10A shows the configuration of only the receiving side (demultiplexing) of the optical transmission / reception system, and the description of the light receiving element after wavelength demultiplexing is omitted.

  FIG. 10A illustrates an operation of separating a WDM signal (1405) having a frequency interval of 100 GHz into four sets of WDM signals (1425, 1427, 1429, 1431) having a frequency interval of 400 GHz. Increased or decreased depending on the application.

  The receiving side of the optical transmission / reception system in FIG. 10A obtains a desired wavelength interleaving operation by connecting a plurality of wavelength filters (1200, 1210a, 1210b) in cascade.

  The first filter 1200 and the second filters 1210a and 1210b have filter characteristics at intervals of 100 GHz and 200 GHz, respectively.

  The operation in this configuration will be described. The input WDM signal (1405) with an interval of 100 GHz is separated for each even / odd channel (1415, 1417) by the first wavelength filter (1200). The even and odd channels are further separated by the subsequent second wavelength filters (1210a and 1210b), and finally the WDM signals (1425, 1427, 1429, and 1431) of one wavelength or plural wavelengths are respectively separated to the output channels of 4 channels. The By connecting a multi-wavelength light receiving element to each of these outputs, it is possible to receive each wavelength.

  FIG. 10B is a configuration diagram (cross-sectional view) of the wavelength filter (interleaver) used in FIG. As shown in FIG. 10B, the wavelength filter includes a circulator 1750 and a filter 1700 having a Fabry etalon resonator structure that performs a filter operation using a dielectric multilayer film.

  In the wavelength filter of FIG. 10B, for example, the wavelength filter 1700 can be set so that only the even-numbered channel is transmitted light 1802 and the odd-numbered channel is reflected light 1801 with respect to the wavelength-multiplexed input light 1800. In that case, a circulator (1750) is inserted to prevent the reflected light 1801 from returning to the input unit.

  Further, an optical system configuration as shown in FIG. 11A disclosed in Non-Patent Document 1 has also been proposed.

  The optical system configuration of FIG. 11A is a multiplexing / demultiplexing configuration of a WDM signal having a 200 GHz interval and a WDM signal having a 50 GHz interval. In FIG. 11A, the light source and the light receiving element are omitted.

  The optical system configuration in FIG. 11A is a configuration in which a 1 × 4 channel interleave filter and an AWG filter are connected in cascade.

  The light receiving operation will be described as an example. A WDM signal having an interval of 50 GHz is input from the left in FIG. 11A, and the four outputs from the interleave filter are separated into WDM signals having one wavelength or a plurality of wavelengths each having an interval of 200 GHz. The separated signals are further subjected to wavelength demultiplexing by a subsequent AWG filter. By connecting a light receiving element to each of these outputs, it is possible to receive each wavelength.

  FIG.11 (b) is a block diagram (circuit diagram) of the wavelength filter (interleaver) used for Fig.11 (a). This is an integrated optical circuit using a planar lightwave circuit (PLC). A multi-stage Mach-Zehnder interferometer is used.

  As shown in FIG. 11B, for example, after wavelength-multiplexed input light (common port) is transmitted through a plurality of interferometers, a wavelength separation signal is output from each port.

U.S. Pat.

T. Chiba et al., “Planar Wave-Guide Interleaving Filters”, Lasers and Electro-Optics Society, 2002. LEOS 2002. The 15th Annual Meeting of the IEEE, vol.1, pp.285-286 vol.1, 2002

  In the conventional optical transmission / reception system and optical circuit shown in FIG. 10, a two-stage wavelength filter is used when demultiplexing a WDM signal having a frequency interval of 100 GHz into a WDM signal having a frequency interval of 400 GHz. Each wavelength filter is composed of a spatial optical system component such as a dielectric multilayer film or a circulator. Therefore, there is a problem that the configurations of the optical multiplexing / demultiplexing system and the optical circuit are complicated and large.

  Further, in the optical system configuration shown in FIG. 11, the optical circuit is downsized by using a PLC. However, since a multi-stage Mach-Zehnder circuit is used, there is a limit to downsizing the chip size.

  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 and an optical circuit thereof that are small, simple, and economical.

  In order to achieve such an object, one aspect of the present invention is an M channel wavelength multiplexed light obtained by combining N sets of M channel multi-wavelength light sources having a frequency interval ΔF and the M channel. A periodic wavelength multiplexing element that multiplexes N sets of M-channel wavelength multiplexed light from each of a set of multi-wavelength light sources into a set of M × N channel wavelength-multiplexed light, and the M × N channel wavelength-multiplexed light Optical transmission / reception having a periodic wavelength demultiplexing element that demultiplexes into the N sets of M channel wavelength multiplexed light and N sets of multi wavelength light receiving elements that respectively receive the demultiplexed N sets of M channel multiwavelength light System.

  In one embodiment, the period of the periodic wavelength multiplexing element and the period of the periodic wavelength demultiplexing element are configured to be equal to the frequency interval ΔF of the multi-wavelength light source.

  In one embodiment, in the M-channel multi-wavelength light source, the frequency of adjacent sets is shifted by Δf as a whole, and N sets of interval products Δf × (N−1) are the wavelength components in the multi-wavelength light receiving element. It is smaller than the transmission band B of the wave element. The M-channel multi-wavelength light source has N sets of interval products Δf × (N−1) within 600 GHz.

  In one embodiment, the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element are arrayed waveguide gratings. The periodic wavelength multiplexing element and the periodic wavelength demultiplexing element may be integrated on the same substrate. The periodic wavelength multiplexing element and the periodic wavelength demultiplexing element have a port interval Δf, and the product of the port intervals Δf × (N−1) is the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element. Is less than half of the periodicity ΔF.

  In one embodiment, the periodic wavelength multiplexing element includes N input waveguides for inputting M-channel wavelength multiplexed light, input slab waveguides connected to the N input waveguides, and the input slabs. A monitor waveguide connected to the waveguide together with the N input waveguides for detecting and controlling the wavelength of the M-channel wavelength multiplexed light, and an output slab connected to the input slab waveguide by an array waveguide A waveguide, an output waveguide connected to the output slab waveguide, and a part of the output M × N channel wavelength multiplexed light connected to the output slab waveguide together with the output waveguide. And a loopback waveguide for re-input to the slab waveguide. The periodic wavelength multiplexing element includes a tap circuit that extracts a part of the M × N channel wavelength multiplexed light to which the output waveguide is connected, and is one of the extracted M × N channel wavelength multiplexed light. Is connected to the loopback waveguide.

  As described above, according to the optical transmission / reception system of one aspect of the present invention, there are N sets of M-channel multi-wavelength light sources having a frequency interval ΔF, and N sets of M-channel wavelength multiplexed light are used as one set of M × A periodic wavelength multiplexing element for multiplexing N-channel wavelength multiplexed light; a periodic wavelength demultiplexing element for demultiplexing M × N channel wavelength multiplexed light into N sets of M channel wavelength multiplexed light; and an M channel multi-wavelength It is configured to have N sets of multi-wavelength light receiving elements that receive light, and the period of the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element is set to be equal to the frequency interval ΔF of the multiwavelength light source. As a result, the existing WDM system can be expanded to a WDM having a higher density and a higher bit rate with a simple configuration.

  Furthermore, in the optical transmission / reception system of one embodiment of the present invention, since N sets of interval products Δf × (N−1) are smaller than the transmission band B of the wavelength demultiplexing element in the multiwavelength light receiving element, each multiwavelength light receiving element has a wavelength component. It is possible to use the same parts including wave characteristics. Therefore, the system can be further simplified and made economical.

  In the optical transmission / reception system of one embodiment of the present invention, 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 has an oscillation wavelength characteristic of the light source. The same parts can be used. Therefore, the system can be further simplified and made economical.

  In the optical transmission / reception system of one embodiment of the present invention, a PLC type arrayed waveguide diffraction grating (AWG) is applied to the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element. As a result, an optical circuit that is smaller and simpler than the conventional interleave type filter can be realized.

  Further, in the optical transmission / reception system of one aspect of the present invention, the product Δf × (N−1) of the port interval Δf of the periodic wavelength multiplexing element is set to half or less of the periodicity ΔF. As a result, as shown in the result of FIG. 5, the wavelength used can be near the center in the FSR, so that an optical circuit with low loss characteristics can be realized.

  In the optical transmission / reception system of one embodiment of the present invention, the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element are integrated on the same substrate, so that further miniaturization and economy of the optical circuit can be realized.

  In the optical transmission / reception system of one embodiment of the present invention, a monitor waveguide and a loopback waveguide can be added to the periodic wavelength multiplexing element without increasing the chip size or degrading the characteristics. The monitoring function of the wavelength and light intensity of the light source can be realized with a small and simple configuration.

  In the optical transmission / reception system of one embodiment of the present invention, the periodic wavelength multiplexing device can realize further miniaturization and economy of the optical circuit by integrating the tap circuit on the same substrate.

It is a block diagram of the optical transmission / reception system concerning one Embodiment of this invention. It is a figure which shows wavelength arrangement | positioning of the optical transmission / reception system concerning one Embodiment of this invention. It is a block diagram of the periodic wavelength multiplexing element in the optical transmission / reception system concerning one Embodiment of this invention. It is a block diagram of the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element in the optical transmission / reception system according to an embodiment of the present invention. It is a figure which shows the transmission spectrum of the periodic wavelength multiplexing element in the optical transmission / reception system concerning one Embodiment of this invention. It is a figure which shows wavelength arrangement | positioning of the multiwavelength light source concerning one Embodiment of this invention. It is a figure which shows the output spectrum from the periodic wavelength multiplexing element in the optical transmission / reception system concerning one Embodiment of this invention. It is a block diagram of the periodic wavelength multiplexing element in the optical transmission / reception system concerning one Embodiment of this invention. It is a block diagram of the periodic wavelength multiplexing element in the optical transmission / reception system concerning one Embodiment of this invention. It is a figure which shows the structure of the receiving side in the conventional optical transmission / reception system of an interleave system. It is a figure which shows the structure of the receiving side in the conventional optical transmission / reception system of an interleave system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
With reference to FIGS. 1 to 7, an optical transmission / reception system and an optical circuit thereof according to a first embodiment of the present invention will be described.
FIG. 1 is a configuration diagram of an optical transmission / reception system 100 of the present embodiment. In this system, N sets (110-1 to 110-N) of M-channel multi-wavelength light sources having a frequency interval ΔF and N sets of M-channel wavelength multiplexed lights are combined into one set of M × N channel wavelength-multiplexed lights. A periodic wavelength multiplexing element 130 that oscillates, a periodic wavelength demultiplexing element 140 that demultiplexes M × N channel wavelength multiplexed light into N sets of M channel wavelength multiplexed light, and a multi-wavelength light receiving multi-wavelength light of M channels. It is the structure which has N sets (152-1-150-N) of wavelength light receiving elements. The periodic wavelength multiplexing element 130 is connected to the periodic wavelength demultiplexing element 140 via the optical fiber 150.

  Each of the multi-wavelength light sources (110-1 to 110-N) includes M light sources 112 and a wavelength multiplexing element that wavelength-multiplexes M channel lights from the M light sources and outputs M channel wavelength multiplexed light. 114. 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 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 multiplexing device 130.

  Each of the multi-wavelength light receiving elements (150-1 to 150-N) receives a wavelength demultiplexing element 154 that wavelength-separates M channel wavelength multiplexed light and outputs M channel light, and M channel light. M light receiving elements 152 are provided. Each of the M light receiving elements 152 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 demultiplexed 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 respectively received by the M light receiving elements 152-11 to 152-M1.

  As the light source 112, a 1.3 μm band semiconductor laser is used, and the wavelength of the M × N channel is different. Each light source is integrated with an electroabsorption type modulation unit capable of performing a modulation operation with a data signal of 25 Gb / s.

Here, labels are given to the wavelengths in the N sets of multi-wavelength light sources. The wavelength of the first set of multi-wavelength light sources is M waves from λ ₁₁ to λ _M1 , and the wavelength of the second set of multi-wavelength light sources is M waves from λ ₁₂ to λ _M2 . Accordingly, the M-th set of wavelengths is M waves from λ _1N to λ _MN .

  The operation of the optical transmission / reception system of FIG. 1 will be briefly 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 propagates through the optical fiber 150 as an M × N channel wavelength division multiplexed signal. After propagation, the light is demultiplexed by the periodic wavelength demultiplexing element 140 into a wavelength group equivalent to each multi-wavelength light source (N sets of M-channel wavelength multiplexed signals), and then each multi-wavelength light receiving element (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) has a wavelength multiplexing number of 4 channels and each light source 112 has a modulation speed of 25 Gb / s, the total bit rate of each multi-wavelength light source is 100 Gb / s. Furthermore, by using four sets of multi-wavelength light sources (110-1 to 110-N; N = 4), a total bit rate of 400 Gb / s can be obtained from the periodic wavelength multiplexing element.

FIG. 2 shows the wavelength arrangement in this example. 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 present embodiment has a configuration assuming 400 GbE, which is an extension of 100 GbE. Considering the factors, the main parameters were set to the following numerical values.
M = 4
N = 4
ΔF = 800GHz
Δf = 100 GHz
B = 360GHz

  Therefore, in this configuration, each group has four-wave WDM at 100 GHz intervals, and the frequency interval for each group is 800 GHz. That is, in the proposed optical transmission / reception system, M × N WDM optical wavelengths are not necessarily arranged at the same frequency interval.

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

  Next, a configuration example of the periodic wavelength multiplexing element 130 and the periodic wavelength demultiplexing element 140 for realizing the above configuration will be described with reference to FIG. Here, the configuration will be described as a configuration diagram of the periodic wavelength multiplexing element 130, but the description as a periodic wavelength demultiplexing element is also possible by making the traveling direction of light symmetrical.

  The periodic wavelength multiplexing element shown in FIG. 3 is a PLC type arrayed waveguide diffraction grating (AWG) manufactured in an optical planar circuit (PLC) 300. The periodic wavelength multiplexing element includes an input waveguide (301-1 to 302-N), an output waveguide (310), an input slab waveguide 304, an output slab waveguide 308, and an arrayed waveguide 306. There are at least N input waveguides and at least one output waveguide.

  Here, as a circuit design condition, the period (free spectrum range, FSR) of the periodic wavelength multiplexing element 306 is configured to be equal to the frequency interval ΔF of the multi-wavelength light sources (110-1 to 110-N). Further, the interval (port interval) of the input waveguides (302-1 to 302-N) at the connection point with the input slab waveguide 304 is equal to Δf, and the input slab waveguide 304, the arrayed waveguide 306, the output slab waveguide The input light propagated through the waveguide 308 is configured to focus on the output waveguide 310 connected to the output slab waveguide.

Wavelengths from each set of multi-wavelength light sources (110-1 to 110-N) are input to the N input waveguides (302-1 to 302-N). 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 waveguide, and wavelength λ ₁₂ of the second set of multi-wavelength light sources is input to the second input waveguide. To M wave of λ _M2 is input. Therefore, the M waves of wavelengths λ _1N to λ _MN in the Nth set (N = 4) are input to the fourth input waveguide.

  Based on the above design conditions and input conditions, a set of M channel wavelength multiplexed light input to the N input waveguides (302-1 to 302-N) is output as an M × N channel WDM signal in the output waveguide 310. Is done.

  In this embodiment, since N = 4, there are four input waveguides. Since M = 4, 16 waves (4 × 4) of WDM signals are output from the output waveguide. Here, the port interval Δf of the periodic wavelength multiplexing element may be such that the product Δf × (N−1) is equal to or less than half of the FSR (ΔF). As a result, an optical circuit (periodic wavelength multiplexing element) having a low loss characteristic can be realized.

  FIG. 4 shows a circuit configuration of the periodic wavelength multiplexing element 430 and the periodic wavelength demultiplexing element 440 used in this embodiment. As shown in FIG. 4, the periodic wavelength multiplexing element 430 and the periodic wavelength demultiplexing element 440 may be integrated on the same PLC substrate 400. Thereby, miniaturization and economy of the optical circuit (periodic wavelength multiplexing element and periodic wavelength demultiplexing element) can be realized. The periodic wavelength combining element 430 includes N wavelength combining input waveguides 402, a wavelength combining input slab waveguide 404, a wavelength combining array waveguide 406, and a wavelength combining output slab waveguide 408. , And one output waveguide 410 for wavelength multiplexing. The periodic wavelength demultiplexing element 440 includes a single wavelength demultiplexing input waveguide 420, a wavelength demultiplexing input slab waveguide 418, a wavelength demultiplexing array waveguide 416, and a wavelength demultiplexing output slab waveguide. A waveguide 414 and N wavelength demultiplexing output waveguides 412 are included.

FIG. 5 shows a characteristic example of the fabricated 4 × 1 periodic wavelength multiplexing element. This element is a silica-based PLC on a silicon substrate, and the relative refractive index difference between the core and the clad is about 1%. The obtained characteristics have a low loss of 1.5 dB or less from λ ₁₁ to λ ₄₄ . Further, the frequency interval between adjacent groups (for example, the interval between λ ₁₁ and λ ₂₁ ) ΔF and the adjacent frequency interval within the same group (for example, the interval between λ ₂₁ and λ ₂₂ ) Δf are 800 GHz and 100 GHz, respectively, as designed. Was less than the measurement accuracy (± 4 GHz). In addition, regarding the characteristic difference (polarization dependence) in the two polarization directions of light, in FIG. 5, both polarization directions were overlaid, but the polarization dependence could not be identified (measured by frequency difference). It can be seen that it has good characteristics (below accuracy).

  Next, set wavelengths of the multi-wavelength light source 110 will be described 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, the number of channels M is 4, and 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 used is one in which each light source (M light sources 112) is integrated on the same substrate. Therefore, it is possible to collectively change all wavelengths of the multi-wavelength light source by adjusting the temperature for each substrate by temperature control means such as a Peltier element or a heater. 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 FIG. 6, the temperature of the same multi-wavelength light source is plotted on the horizontal axis and the oscillation wavelength is plotted on the vertical axis. According to this, four waves from λ ₁₁ to λ ₄₁ are obtained when the operating temperature is about 40 ° C., and the remaining wavelengths are obtained every time the temperature is increased, and from λ ₁₄ which is the longest wavelength at about 57 ° C. it is possible to generate a wavelength of lambda _44.

  Considering general laser performance, it is desirable to set the temperature control range within ± 20 ° C. That is, it is desirable that the frequency control range is within 600 GHz in total width.

  Therefore, in the M-channel multi-wavelength light source of the present embodiment, N sets of interval products Δf × (N−1) are set to 600 GHz or less. This makes it possible to use the same component. Therefore, the system can be further simplified and made economical.

  FIG. 7 shows an output spectrum waveform when it is input to the recursive wavelength multiplexing device in which the multi-wavelength light source is manufactured. In this experiment, since the same multi-wavelength light source is used as four sets of multi-wavelength light sources (using the wavelength adjustment shown in FIG. 6), the output spectrum of FIG. Is an overlay of the four output spectra obtained from

  As a result of the experiment, ΔF was 800 GHz, Δf was 100 GHz, and each lane could be allocated within the transmission band B (360 GHz) as shown in FIG.

  From the above results, according to the present embodiment, in the optical transmission / reception system as shown in FIG. 1, by setting the period of the periodic wavelength multiplexing element to a condition equal to the frequency interval ΔF of the multi-wavelength light source, The system can be expanded to a WDM with a higher density and a higher bit rate with a simple configuration.

  In this embodiment, the wavelength of the light source is set to the 1.3 μm band, but a 1.5 μm band which is a telecom wavelength may be used. The light source modulation unit is an electroabsorption type, but 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.

  Furthermore, in this configuration, since N sets of interval products Δf × (N−1) are smaller than the transmission band B of the wavelength demultiplexing element in the multiwavelength light receiving element, each multiwavelength light receiving element includes the same wavelength demultiplexing characteristics. It is possible to use these parts. Therefore, the system can be further simplified and made economical.

  In this embodiment, Δf is set to 100 GHz. However, if N waves in the same group are in the transmission band B, the above effect can be maintained even at 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 includes the same components including the oscillation wavelength characteristics of the light sources. Can be used. Therefore, the system can be further simplified and made economical.

  In this embodiment, a PLC type arrayed waveguide diffraction grating (AWG) is applied to the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element. As a result, an optical circuit that is smaller and simpler than the conventional interleave type filter can be realized.

  The 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.

  Further, by adding a temperature compensation function, that is, an athermal function, to the PLC of this embodiment, an optical circuit whose characteristics do not change even when the environmental temperature changes can be obtained. As a typical addition of the athermal function, there is a method of inserting a material having a thermal expansion coefficient symmetrical to the thermal expansion coefficient of the optical waveguide between the waveguides.

  In the present embodiment, the product Δf × (N−1) of the port interval Δf of the periodic wavelength multiplexing element is set to half or less of the periodicity ΔF. As a result, as shown in the result of FIG. 5, the wavelength used can be near the center in the FSR, so that an optical circuit with low loss characteristics can be realized.

  Furthermore, as shown in FIG. 4, the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element are integrated on the same substrate, so that further downsizing of the optical circuit can be realized.

(Second Embodiment)
Next, with reference to FIG. 8, an optical transmission / reception system and an optical circuit thereof according to a second embodiment of the present invention will be described. Since the configuration of the optical transmission / reception system of this embodiment is the same as the configuration shown in FIGS. The difference from the first embodiment is the circuit configuration of the periodic wavelength multiplexing element. FIG. 8 shows the configuration of the periodic wavelength multiplexing element in this example. The configuration of the periodic wavelength demultiplexing element is the same as that of the periodic wavelength multiplexing element described in FIG. 3 (the light traveling direction is symmetric with respect to FIG. 3).

  8 is a PLC-type AWG fabricated in the optical planar circuit PLC 800 as in the first embodiment, and includes an input waveguide 302, an output waveguide 310, an input slab waveguide 304, and an output. It comprises a slab waveguide 308 and an arrayed waveguide 306. There are at least N input waveguides and at least one output waveguide.

  Further, as one of the features of this embodiment, the periodic wavelength multiplexing element is connected to the input slab waveguide 304 and the monitor waveguide for detecting and controlling the wavelength of each multi-wavelength light source. A waveguide 802 is connected, and the output waveguide 310 is connected to the output slab waveguide 308, and a loopback waveguide 804 for re-inputting a part of the wavelength multiplexed light to be output to the output slab waveguide 308 is provided. Connected.

  A tap circuit 806 is inserted in the output portion of the periodic wavelength multiplexing element, and a part of the wavelength multiplexed light is connected to the loopback waveguide 804 via the connection waveguide 808. The tap circuit 806 is an optical component that can be configured with a directional coupler, a Y branch circuit, or the like. In this embodiment, 5% of the total intensity of wavelength multiplexed light is extracted and connected to the loopback waveguide 804.

  Basic circuit design conditions are the same as in the first embodiment. That is, the period of the periodic wavelength multiplexing element is configured to be equal to the frequency interval ΔF of the multi-wavelength light source. Further, the interval (port interval) of the input waveguide 302 at the connection point with the input slab waveguide 304 is equal to Δf, and the input light propagated through the input slab waveguide 304, the arrayed waveguide 306, and the output slab waveguide 308 is The output waveguide 310 connected to the output slab waveguide 308 is configured to be focused.

Further, the wavelengths from each set of multi-wavelength light sources (for example, 110-1 to 110-N (FIG. 1)) are input to the N input waveguides 302. 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 waveguide, and wavelength λ ₁₂ of the second set of multi-wavelength light sources is input to the second input waveguide. To M wave of λ _M2 is input. Therefore, the M waves of wavelengths λ _1N to λ _MN in the Nth set (N = 4) are input to the fourth input waveguide. The parameters in this embodiment are M = 4, N = 4, Δf = 100 GHz, and ΔF = 800 GHz.

  The design of the monitor waveguide 802 and the loopback waveguide 804, which is one of the characteristic structures of this embodiment, will be described.

  The number of monitor waveguides 802 is N for N sets of multi-wavelength light sources. Similar to the input waveguide 302, the interval (port interval) of the N monitor waveguides 802 at the connection point of the input slab waveguide 304 is set to Δf, and the monitor is sequentially arranged adjacent to the input waveguide 302. In this embodiment, the input waveguide 302 is disposed symmetrically at the center of the input slab waveguide in order to obtain low loss. Therefore, the monitor waveguide 802 is symmetrically disposed on both outer sides of the N input waveguides 302 as shown in FIG.

  The loopback waveguide 804 is disposed at a position that is Δf × N away from the connection point between the output slab waveguide 308 and the output waveguide 310.

  Based on the above design conditions and input conditions, as in the first embodiment, a set of M channel wavelength multiplexed light input to the N input waveguides 302 is output as an M × N channel WDM signal in the output waveguide 310. The In this embodiment, since N = 4, there are four input waveguides. Since M = 4, 16 waves (4 × 4) of WDM signals are output from the output waveguide.

  Further, as a feature of the present embodiment, a part of the wavelength multiplexed light returned from the loopback waveguide 804 to the output slab waveguide 308 is demultiplexed and then output to each monitor waveguide 802. The wavelength group output to each monitor waveguide has M channels at a frequency interval ΔF, which is equivalent to the wavelength group of each multi-wavelength light source. Therefore, it is possible to adjust (feedback control) the wavelength and light intensity of each multi-wavelength light source by monitoring the wavelength and light intensity from each monitor waveguide.

  The structure and function described above can be realized with almost no increase in the chip size of the AWG and almost no deterioration of the wavelength multiplexing / demultiplexing characteristics.

  As described above, according to this embodiment, by using the periodic wavelength multiplexing element as shown in FIG. 8, the existing WDM system can be expanded to a WDM with a high density and a high bit rate with a simple configuration. It becomes.

  In this embodiment, the input waveguide 302 is symmetrically arranged at the center of the input slab waveguide in order to obtain low loss. However, it may be at another position as long as it is within the FSR. For example, it is possible to connect each input waveguide to a position shifted by Δf × N. In that case, four monitor waveguides 802 are arranged adjacent to four input waveguides under the design conditions of this embodiment.

(Third embodiment)
Next, an optical transmission / reception system and its optical circuit according to a third embodiment of the present invention will be described with reference to FIG. Since the configuration of the optical transmission / reception system of this embodiment is the same as the configuration shown in FIGS. The difference from Embodiments 1 and 2 is the circuit configuration of the periodic wavelength multiplexing element. FIG. 9 shows the configuration of the periodic wavelength multiplexing element in this example. The configuration of the periodic wavelength demultiplexing element is the same as that of the periodic wavelength multiplexing element described in FIG. 3 (the light traveling direction is symmetric with respect to FIG. 3).

  The periodic wavelength multiplexing element in FIG. 9 is a PLC type arrayed waveguide diffraction grating (AWG) manufactured in an optical planar circuit (PLC) 900 as in the above embodiment. An input waveguide 302 and an output waveguide 310, an input slab waveguide 304 and an output slab waveguide 308, and an arrayed waveguide 306 are configured. There are at least N input waveguides 304 and at least one output waveguide 310.

  In the periodic wavelength multiplexing device, the input waveguide 302 is connected to the input slab waveguide 304 and the monitor waveguide 802 for detecting and controlling the wavelength of each multi-wavelength light source is connected as in the second embodiment. In addition, the output waveguide 310 is connected to the output slab waveguide 308, and a loopback waveguide 904 for re-inputting part of the output wavelength multiplexed light to the output slab waveguide 308 is connected.

  Further, as one of the features of the present embodiment, the output waveguide 310 is connected to the periodic wavelength multiplexing element, the output slab waveguide 308, and a tap circuit 906 that extracts a part of the output wavelength multiplexed light is provided. Connected to the output waveguide 310, 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 this embodiment, 5% of the total intensity of wavelength multiplexed light is extracted and connected to the loopback waveguide 904.

  Basic circuit design conditions are the same as those in the first and second embodiments. That is, the period of the periodic wavelength multiplexing element is configured to be equal to the frequency interval ΔF of the multi-wavelength light source. Further, the interval (port interval) of the input waveguide 302 at the connection point with the input slab waveguide 304 is equal to Δf, and the input light propagated through the input slab waveguide 304, the arrayed waveguide 306, and the output slab waveguide 308 is The output waveguide 310 connected to the output slab waveguide 308 is configured to be focused.

In addition, wavelengths from each set of multi-wavelength light sources (for example, 110-1 to 110-N (FIG. 1)) are input to the N input waveguides (302-1 to 302-N). 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 waveguide, and wavelength λ ₁₂ of the second set of multi-wavelength light sources is input to the second input waveguide. To M wave of λ _M2 is input. Therefore, M waves of wavelengths λ _1N to λ _MN of the Mth set (N = 4) are input to the fourth input waveguide. The parameters in this embodiment are M = 4, N = 4, Δf = 100 GHz, and ΔF = 800 GHz.

  The number of monitor waveguides 802 is N for N sets of multi-wavelength light sources. Similar to the input waveguide 302, the interval (port interval) of the N monitor waveguides 802 at the connection point of the input slab waveguide 304 is set to Δf, and the monitor is sequentially arranged adjacent to the input waveguide 302. In this embodiment, the input waveguide 302 is disposed symmetrically at the center of the input slab waveguide in order to obtain low loss. Therefore, the monitor waveguides 802 are symmetrically arranged on both outer sides of the N input waveguides 302 as shown 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 output waveguide 310.

  Based on the above design conditions and input conditions, as in the first embodiment, a set of M channel wavelength multiplexed light input to the N input waveguides 302 is output as an M × N channel WDM signal in the output waveguide 310. The In this embodiment, since N = 4, there are four input waveguides. Since M = 4, 16 waves (4 × 4) of WDM signals are output from the output waveguide.

  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 has M channels at a frequency interval ΔF, which is equivalent to the wavelength group of each multi-wavelength light source. Therefore, it is possible to adjust (feedback control) the wavelength and light intensity of each multi-wavelength light source by monitoring the wavelength and light intensity from each monitor waveguide.

  The structure and function described above can be realized with almost no increase in the chip size of the AWG and almost no deterioration of the wavelength multiplexing / demultiplexing characteristics.

  Further, since the tap circuit 906 is integrated on the same chip in this embodiment, the degree of integration can be improved without deterioration in size and characteristics as compared with the second embodiment.

  As described above, according to this embodiment, by using the periodic wavelength multiplexing element as shown in FIG. 9, the existing WDM system can be expanded to a WDM with a higher density and a higher bit rate with a simple configuration. It becomes.

DESCRIPTION OF SYMBOLS 100 Optical transmission / reception system 110 Multiwavelength light source 112 Light source 114 Wavelength multiplexing element 130 Periodic wavelength multiplexing element 140 Periodic wavelength demultiplexing element 150 Multiwavelength light receiving element 152 Light receiving element 154 Wavelength demultiplexing element 300,400,800,900 Light Planar circuit (PLC)
302, 402, 420 Input waveguide 304, 404, 418 Input slab waveguide 306, 406, 416 Array waveguide 308, 408, 414 Output slab waveguide 310, 410, 412 Output waveguide 802 Monitor waveguide 804, 904 Loop Back waveguide 806, 906 Tap circuit 808 Connection waveguide

Claims (8)

N sets of M-channel multi-wavelength light sources having a frequency interval ΔF,
M-channel wavelength multiplexed light that is multiplexed with the M channels, and N sets of M-channel wavelength multiplexed light from each of the N sets of multi-wavelength light sources are combined into one set of M × N channel wavelength-multiplexed light. A periodic wavelength multiplexing element;
A periodic wavelength demultiplexing element that demultiplexes the M × N channel wavelength multiplexed light into the N sets of M channel wavelength multiplexed light;
N sets of multi-wavelength light receiving elements for receiving the demultiplexed N sets of M-channel multi-wavelength light respectively;
The optical transmission / reception system, wherein a period of the periodic wavelength multiplexing element and a period of the periodic wavelength demultiplexing element are configured to be equal to the frequency interval ΔF of the multi-wavelength light source. The M-channel multi-wavelength light source is:
The frequency of the adjacent set is shifted by Δf as a whole,
2. The optical transmission / reception system according to claim 1, wherein N sets of interval products Δf × (N−1) are smaller than a transmission band B of a wavelength demultiplexing element in the multi-wavelength light receiving element. The M-channel multi-wavelength light source is:
The optical transmission / reception system according to claim 1, wherein N sets of interval products Δf × (N−1) are within 600 GHz. The optical transmission / reception system according to any one of claims 1 to 3, wherein the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element are arrayed waveguide gratings. The periodic wavelength multiplexing element and the periodic wavelength demultiplexing element have a port interval of Δf,
The product of the port interval Δf × (N−1) is equal to or less than half of the periodicity ΔF of the periodic wavelength multiplexing element and the periodic wavelength demultiplexing element. The optical transmission / reception system described. The periodic wavelength multiplexing element and the periodic wavelength demultiplexing element are:
The optical transmission / reception system according to claim 4, wherein the optical transmission / reception system is integrated on the same substrate. The periodic wavelength multiplexing element is:
N input waveguides for inputting the M-channel wavelength multiplexed light;
An input slab waveguide connected to the N input waveguides;
A monitor waveguide connected to the input slab waveguide together with the N input waveguides for detecting and controlling the wavelength of the M-channel wavelength multiplexed light;
An output slab waveguide connected by the input slab waveguide and the array waveguide;
An output waveguide connected to the output slab waveguide;
A loopback waveguide connected to the output slab waveguide together with the output waveguide for re-inputting a part of the output M × N channel wavelength multiplexed light to the output slab waveguide. The optical transmission / reception system according to claim 4. The periodic wavelength multiplexing element is:
The output waveguide is connected;
A tap circuit for extracting a part of the M × N channel wavelength division multiplexed light;
The optical transmission / reception system according to claim 7, wherein a part of the extracted M × N channel wavelength division multiplexed light is connected to the loopback waveguide.

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