JP2014138291A - Wavelength-variable receiver and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength-variable receiver that allows wavelength-variable operation at high speed, maximally exploits characteristics of each PD constituting the wavelength-variable receiver, and is excellent in minimum reception sensitivity.SOLUTION: A wavelength-variable receiver according to the present invention includes: a plurality of light-receiving circuits photo-electric-converting signal light having different wavelength channels; a driving voltage source supplying a driving voltage to the plurality of light-receiving circuits; and a control circuit changing the driving voltage of the driving voltage source when a wavelength channel of signal light to be received is changed.

Description

  The present invention relates to a wavelength tunable receiver and a control method, and more particularly to an optical module in general, and more particularly to a control method of an optical receiver excellent in high-speed wavelength tunable operation.

  In recent years, with the rapid spread of the Internet, there has been a demand for increasing the capacity, sophistication, and economy of optical access systems. As a method for realizing such a system, research on PON (Passive Optical Network) has been advanced. PON means that multiple transmission lines from multiple users are concentrated on a single transmission line by an optical passive element such as an optical power splitter, so that the transmission line between the center device and the optical passive element is shared by multiple users. This is an optical access communication system that is advantageous for economy.

  Currently, in Japan, an economical optical access communication system GE-PON (Gigabit Ethernet (registered trademark) -PON) which shares a 1 Gbps class line capacity by time division multiplexing (TDM) with a maximum of 32 users has been introduced. ing. As a result, the FTTH service is provided at a realistic fee for the user and has rapidly spread.

  On the other hand, as a next-generation optical access system that can meet the needs for further increase in capacity, research on 10G-class 10G-EPON is underway, and IEEE standardization was completed in 2009. This system is a system capable of increasing the capacity while using the same transmission line portion as that of the existing GE-PON due to an increase in the bit rate of the optical transceiver. Also, depending on the service, such as high-definition video services, it may be necessary to increase the capacity exceeding the 10 Gbps class. However, further increase in the bit rate of the transceiver (40 or 100 Gbps class) significantly increases the cost of the transceiver. The problem was that it would not be a practical system.

  As means for realizing an economically large capacity, wavelength tunability is imparted to the optical transceiver so that optical transceivers in the station side apparatus can be added in stages according to the bandwidth requirement, and TDM is provided. And WDM: Wavelength Division Multiplexing (WDM) have been reported (see, for example, Non-Patent Document 1).

Japanese Patent Application No. 10-47630

S. Kimura, “WDM / TDM-PON Technologies for Future Flexible Optical Access Networks”, 15th OECC 2010, 6A1-1. R. Murano et al. “Tunable 2.5 Gb / s Receiver for Wavelength-Agile DWDM-PON”, OFC 2008 Post deadline paper. T.A. Tamanuki et al. , “High Density Packaged 4-channel Transceiver for Metro and Access Applications”, 2005 Electronic Components and Technology Conference, p. 1050.

  In such a system, an optical transmitter / receiver having wavelength tunability is required for the subscriber unit or the station side device. However, the higher the wavelength variable speed, the more functions such as protection can be given. Become. However, as for the optical receiver for wavelength tunable WDM / TDM-PON, only a device having a wavelength variable speed of about 1 s has been reported so far (for example, see Non-Patent Document 2), and a high-speed wavelength variable receiver. Realizing the above has been a serious problem for the wavelength-tunable WDM / TDM-PON.

  This is because there is no wavelength tunable filter that is small enough to be mounted in an optical receiver using a TO-CAN package or the like and capable of high-speed wavelength tunable operation (wavelength tunable speed 1 ms or less). On the other hand, after the wavelength multiplexed N-wave signal light is demultiplexed into one wave by the wavelength filter, the signal light is photoelectrically converted into an electric signal by PD (Photodiode) corresponding to each wavelength, and then the electric switch It is known that a wavelength tunable receiver can be configured by selecting and receiving an electrical signal corresponding to signal light having a desired wavelength (see, for example, Japanese Patent Application No. 10-47630).

  Such a wavelength tunable receiver is difficult to be miniaturized so that it can be accommodated in a TO-CAN package. However, since the variable speed of the electric switch corresponds to the wavelength variable speed, a commercially available 10 Gbps class electric switch is used for 30 ns. It is possible to achieve a wavelength variable speed that is extremely high. However, in such a configuration, since it is necessary to use the same number of PDs as the number of multiplexed wavelengths of signal light, the following problems arise.

  The PD needs to be driven by supplying a reverse bias voltage (Vpd). The optimum Vpd value is 1.5 to 3 V in the case of pin-PD, and if it exceeds 3 V, the reception band is saturated, so driving at 3.3 V or less is common.

  On the other hand, APD (Avalanche Photodiode) having an amplification function has a very high sensitivity compared with pin-PD, and thus is very advantageous for a repeaterless optical communication system such as PON, but Vpd is sufficiently amplified. In order to obtain the effect, for example, a high voltage of about 27V is required. Further, although the amplification effect is brought about by an increase in Vpd, the noise accompanying the amplification is also brought about at the same time. N (signal to noise) ratio cannot be obtained.

  On the other hand, it is known that the optimum driving voltage of APD has a variation of about 27V ± 0.3V even in the same production lot due to variations in manufacturing. Furthermore, since the APD material, structure, and manufacturing method differ depending on the manufacturer, the optimum Vpd value for APD varies greatly from about 26V to 28V.

  On the other hand, in the wavelength tunable receiver composed of the wavelength filter, N PDs, and electrical switches described above, the drive voltage Vpd to the N PDs is N for simplifying the circuit configuration and reducing the cost. In general, a single PD is connected in parallel to a single power supply circuit (see, for example, Non-Patent Document 3). Therefore, although the same Vpd value is given to each PD, as described above, the same reception band can be obtained if 3.3 V is supplied with pin-PD, so that the light receiving sensitivity is the same for each PD. It doesn't become a problem of variation.

However, when N APDs advantageous for high sensitivity are introduced into the wavelength tunable receiver capable of the high-speed wavelength tunable operation described above, the same Vpd value is given to each APD in this manner. The optimum Vpd value differs for each APD due to individual differences in the production lot or differences due to specifications for each manufacturer, and the minimum light receiving sensitivity (transmission speed 10 Gbps, code error rate 10 ⁻³ ) for each APD is, for example, −26. It has been a serious problem to have a large variation of -30 dBm. Furthermore, the wavelength tunable receiver has a fatal problem in practical use because the reception sensitivity differs greatly for each wavelength channel to be received.

  Accordingly, an object of the present invention is to provide a wavelength tunable receiver that can perform a wavelength tunable operation at high speed and that has a minimum reception sensitivity that maximizes the characteristics of each PD that constitutes the wavelength tunable receiver.

  The present invention supplies a driving voltage required for each photodiode in accordance with a predetermined wavelength channel of a wavelength table included in the control circuit.

Specifically, the wavelength tunable receiver of the present invention is:
A plurality of light receiving circuits that photoelectrically convert signal light of different wavelength channels;
A driving voltage source for supplying a driving voltage to the plurality of light receiving circuits;
And a control circuit that changes the drive voltage of the drive voltage source when the wavelength channel of the received signal light changes.

Specifically, the control method of the wavelength tunable receiver of the present invention is:
A control method of a wavelength tunable receiver in which a plurality of light receiving circuits receive signal light of different wavelength channels using a driving voltage supplied from one driving voltage source,
When the wavelength channel of the received signal light changes, a driving voltage control procedure for changing the driving voltage of the driving voltage;
A drive voltage supply procedure for supplying the drive voltage changed in the drive voltage control procedure to the plurality of light receiving circuits;
The light receiving circuit corresponding to the wavelength channel of the received signal light sequentially includes a light receiving procedure for photoelectrically converting the signal light input to the variable wavelength receiver.

In the wavelength tunable receiver of the present invention,
The control circuit may change the drive voltage of the drive voltage source according to a wavelength table in which the drive voltage is determined according to the wavelength channel of the signal light.

In the wavelength tunable receiver of the present invention,
In the wavelength table, a driving voltage may be determined according to the minimum light receiving sensitivity of each light receiving circuit that is different for each wavelength channel of the signal light.

In the wavelength tunable receiver of the present invention,
An electrical switch that selectively outputs an electrical signal from one of the plurality of light receiving circuits;
The control circuit may change the one light receiving circuit selected by the electric switch according to the wavelength channel of the received signal light.

In the wavelength tunable receiver of the present invention,
The light receiving circuit may be a pin photodiode or an avalanche photodiode.

  In the wavelength tunable receiver of the present invention, the signal light transmitted from the station side device may be received by the subscriber device using the wavelength tunable receiver.

  The above inventions can be combined as much as possible.

  According to the present invention, it is possible to provide a wavelength tunable receiver that can perform a wavelength tunable operation at a high speed and has a minimum reception sensitivity that maximizes the characteristics of each PD constituting the wavelength tunable receiver.

It is a figure which shows the structural example of the wavelength variable receiver which concerns on 1st Embodiment. It is a figure which shows the structural example of the wavelength variable receiver which concerns on 1st Embodiment. It is a flowchart explaining the operation | movement switched to the state which receives a different wavelength channel. It is a figure explaining the wavelength table which stored the wavelength channel. It is a figure explaining the code error rate characteristic at the time of using the drive voltage shown in FIG. It is a figure which shows the APD drive voltage and minimum light reception sensitivity in a light reception circuit. It is a figure which shows the structural example in the wavelength variable receiver which concerns on 2nd Embodiment. It is a figure which shows the structural example in the wavelength variable receiver which concerns on 3rd Embodiment. It is a figure which shows the drive voltage and minimum light receiving sensitivity in the light receiving circuit which concern on related technology. It is a figure explaining the code error rate characteristic at the time of using the drive voltage shown in FIG.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  The wavelength tunable receiver 1 according to the present embodiment includes a light receiving circuit, a drive voltage source 100, and a control circuit 70. The control method of the wavelength tunable receiver according to this embodiment includes a drive voltage control procedure, a drive voltage supply procedure, and a light reception procedure in order. The light receiving circuit is, for example, a pin photodiode or an avalanche photodiode.

  In the drive voltage control procedure, the control circuit 70 changes the drive voltage of the drive voltage source when the wavelength channel of the received signal light changes. In the drive voltage supply procedure, the drive voltage source 100 supplies the drive voltage changed in the drive voltage control procedure to the plurality of light receiving circuits. In the light receiving procedure, the light receiving circuit according to the wavelength channel of the received signal light photoelectrically converts the signal light input to the wavelength variable receiver.

(First embodiment)
Hereinafter, the wavelength tunable receiver 1 according to the first embodiment of the present invention will be described in detail with reference to FIG. In FIG. 1a, a wavelength tunable receiver 1 includes a wavelength filter 10, an APD 20 that is a light receiving circuit, a TIA (Transmimpance Amplifier) 30, a limiter amplifier 50, an electrical switch 40, a CDR (Clock Data Recovery) 60, a control circuit 70, and a wavelength control. The circuit 80 and the APD driving voltage source 100 are included.

  In the present embodiment, the wavelength tunable receiver 1 that selects and receives one wavelength of signal light in which four wavelengths are wavelength-multiplexed (number of wavelengths N = 4) will be described in detail. The same effect can be obtained with any integer. Hereinafter, the wavelength variable operation of the wavelength tunable receiver 1 will be described in detail.

  The wavelength multiplexed signal light (number of wavelengths N = 4) input to the input port 10-0 of the wavelength filter 10 is output to the output ports 10-1 to 10-4 for each wavelength channel by the wavelength filter 10. (Λ1 to λ4 are output to the output ports 10-1 to 10-4, respectively). The demultiplexed signal lights λ1 to λ4 of each wavelength are respectively incident on the APDs 20-1 to 20-4 and converted into electric signals. The electric signals e1 to e4 are amplified by the TIAs 30-1 to 30-4, respectively, and after the signal level is made constant by the limiter amplifier 50, one of the electric signals e1 to e4 is selected by the electric switch 40.

  In the present embodiment shown in FIG. 1a, an example in which the electrical signal e1 is selected is shown. The selected electrical signal e1 is input to the CDR 60, and the electrical signal e1 is identified and determined by a subsequent identification determination circuit (not shown).

  Here, the wavelength control circuit 80 sends a control signal S1 (signal light information to be received) to the control circuit 70. The control circuit 70 refers to the stored wavelength table (FIG. 3), and each optimum of the APD 20 corresponding to the wavelength channel or wavelength information (or both wavelength channel and wavelength information) of the signal light (λ1 to λ4) desired to be received. The drive voltage value (Vapd) is supplied to the APD 20, and the control circuit 70 sends a control signal S2 (switch control signal) to the electrical switch 40, so that the path of the electrical switch 40 can be received so as to receive the corresponding wavelength channel. Switch.

  Details of the wavelength variable operation will be described. The operation of switching from the state of receiving the wavelength channel ch1 (signal light λ1) shown in FIG. 1A to the state of receiving the wavelength channel ch3 (signal light λ3) shown in FIG. An example will be described using the flowchart shown in FIG. 2 and the wavelength table shown in FIG.

  In FIG. 1a, among the wavelength multiplexed signal lights (λ1 to λ4), the input port of the electrical switch 40 is set to 40-1, so that the wavelength channel ch1 (signal light λ1, wavelength channel ch1, wavelength 1577. 03 nm) is being received. For APD 20-1, a reverse bias voltage of 26.52 V is applied to Vapd by APD drive voltage source 100 based on information in the wavelength table (FIG. 3).

  Next, when the wavelength variable operation is performed so as to receive the wavelength channel ch3 by executing the drive voltage control procedure from this state, the following procedure is performed. First, a control signal S0 is sent to the wavelength tunable receiver 1 so that the wavelength control circuit 80 receives the wavelength channel ch3 from an upper communication network layer or the like (not shown).

  The wavelength control circuit 80 that has received the control signal S0 sends a control signal S1 for switching from the wavelength channel ch1 to the wavelength channel ch3 to the control circuit 70 (step S110). Based on the stored wavelength table shown in FIG. 3, the control circuit 70 sends a Vapd value of 26.44 V (control signal S3) corresponding to the wavelength channel ch3 to the APD drive voltage source 100. At the same time, a control signal S2 is sent to the route input port 40-3 to the electrical switch 40 (step S120).

  The APD drive voltage source 100 changes the Vapd value from 26.52V to 26.44V based on the control signal S3 received from the control circuit 70 (step S130). On the other hand, the electrical switch 40 refers to the information stored in the wavelength table from the control circuit 70 and sends the control signal S2 to the electrical switch 40, and switches the route input port from 40-1 to 40-3 ( Step S140). With this series of operations, the wavelength channel of the signal light received by the wavelength tunable receiver 1 is switched from ch1 (wavelength 1577.03 nm) to ch3 (wavelength 1578.69 nm).

  This state is shown in FIG. The APD drive voltage source 100 and the electric switch 40 keep the Vpad value and the route input port 40-3 as they are, respectively, until the control circuit 70 instructs to change to the next different wavelength channel (ch1, ch2, ch4). Hold. When there is a change instruction, the wavelength variable operation is performed based on the flowchart shown in FIG.

  In order to verify the effect of the present invention, the bit error rate (BER) characteristics of the variable wavelength receiver 1 shown in FIGS. 1a and 1b are compared. FIG. 4 shows a case where the wavelength tunable receiver 1 of the present embodiment is used. FIG. 9 shows a BER characteristic when the APD drive voltage value shown in FIG. 8 is used as a comparative example.

The BER characteristics shown in FIGS. 4 and 9 are graphs in which the measurement results for each wavelength channel are overwritten. As shown in FIG. 8, in the related art, the same APD drive voltage value is used for each APD 20, and therefore the optimum APD drive voltage value Vapd differs depending on the manufacturing lot or manufacturer. Therefore, when the APD 20 is driven at the same voltage value (27.0 V in the example of FIG. 8), the minimum light receiving sensitivity at a BER = 10 ^{−3 is} in the range of −28.0 to −31.0 dBm as shown in FIG. It differs greatly. Therefore, when the minimum light receiving sensitivity of the shipment inspection specification of the wavelength tunable receiver 1 is −30.0 dBm (BER = 10 ⁻³ ), the wavelength channels ch3 and ch4 are rejected, and the wavelength tunable receiver 1 fails to meet the specifications. It cannot be shipped, and the manufacturing yield of the wavelength tunable receiver 1 decreases.

  On the other hand, by applying the technique of the present invention described in the present embodiment, it is possible to receive each signal light by adjusting the optimum driving voltage value Vapd of each APD 20-1 to 20-4 for each wavelength channel. Therefore, as shown in FIGS. 4 and 5, the minimum light receiving sensitivity of each wavelength channel has a small variation range of −30.8 to −31.2 dBm, and the shipping inspection specification is sufficiently satisfied.

(Second Embodiment)
Hereinafter, the wavelength tunable receiver 1 according to the second embodiment of the present invention will be described with reference to FIG. The configuration of the wavelength tunable receiver 1 of the second embodiment shown in FIG. 6 is substantially the same as the configuration of the wavelength tunable receiver 1 of the first embodiment shown in FIGS. 1a and 1b. Different. In FIG. 1a and FIG. 1b, the limiter amplifier 50 is arranged with four (50-1 to 50-4) inserted between the TIA 30 and the electric switch 40, but in the second embodiment in FIG. The arrangement is different, and a single limiter amplifier 50 is inserted between the electrical switch 40 and the CDR 60.

  When the electrical distortion of the electrical switch 40 is small, such a configuration is possible because the limiter amplifier processing may be performed after passing through the electrical switch. The advantage of this configuration is that the configuration of the limiter amplifier 50 is simplified and the number of limiter amplifiers 50 may be a single number. Therefore, compared to the first embodiment, the power consumption, the cost, and the size can be reduced. It is advantageous.

(Third embodiment)
Hereinafter, the wavelength tunable receiver 1 according to the third embodiment of the present invention will be described with reference to FIG. The configuration of the wavelength tunable receiver 1 according to the third embodiment shown in FIG. 7 is substantially the same as the configuration of the wavelength tunable receiver 1 according to the first embodiment shown in FIGS. 1a and 1b. The difference is that the integrated module 200 is introduced.

  The wavelength tunable receiver integrated module 200 includes an AWG (Arrayed Waveguide Grating, 4ch APD array) monolithically integrated on a semiconductor substrate such as InP, and a 4ch TIA array on a heat sink such as a silicon terrace or AlN. (Or 4chTIA) is hybrid-integrated and mounted in the same module package.

  By adopting such a configuration, the wavelength tunable receiver 1 can be reduced in size and cost. Except for the introduction of the wavelength variable reception integrated module 200, the wavelength variable operation and its effect in the present embodiment are the same as those described in the first embodiment.

  The present invention can be applied to the information communication industry.

1: Variable wavelength receiver 10: Wavelength filter 10-0: Input port (wavelength filter side)
10-1, 10-2, 10-3, 10-4: input ports 20, 20-1, 20-2, 20-3, 20-4: APD
30, 30-1, 30-2, 30-3, 30-4: TIA
40: Electric switch 40-1, 40-2, 40-3, 40-4: Path input port (electric switch side)
50, 50-1, 50-2, 50-3, 50-4: Limiter amplifier 60: CDR
70: Control circuit 80: Wavelength control circuit 100: APD driving voltage source 200: Wavelength variable receiver integrated module S0, S1, S2, S3: Control signal

Claims (7)

A plurality of light receiving circuits that photoelectrically convert signal light of different wavelength channels;
A driving voltage source for supplying a driving voltage to the plurality of light receiving circuits;
When the wavelength channel of the received signal light changes, a control circuit that changes the drive voltage of the drive voltage source;
A tunable receiver comprising:   The variable wavelength receiver according to claim 1, wherein the control circuit changes the drive voltage of the drive voltage source according to a wavelength table in which the drive voltage is determined according to the wavelength channel of the signal light.   3. The wavelength tunable receiver according to claim 2, wherein in the wavelength table, a driving voltage is determined in accordance with a minimum light receiving sensitivity of each light receiving circuit which is different for each wavelength channel of the signal light. An electrical switch that selectively outputs an electrical signal from one of the plurality of light receiving circuits;
4. The wavelength tunable receiver according to claim 1, wherein the control circuit changes the one light receiving circuit selected by the electric switch according to a wavelength channel of received signal light. 5. .   The wavelength tunable receiver according to claim 1, wherein the light receiving circuit is a pin photodiode or an avalanche photodiode.   A subscriber unit that receives signal light transmitted from a station side device using the wavelength tunable receiver according to claim 1. A control method of a wavelength tunable receiver in which a plurality of light receiving circuits receive signal light of different wavelength channels using a driving voltage supplied from one driving voltage source,
When the wavelength channel of the received signal light changes, a driving voltage control procedure for changing the driving voltage of the driving voltage source;
A drive voltage supply procedure for supplying the drive voltage changed in the drive voltage control procedure to the plurality of light receiving circuits;
A light receiving circuit corresponding to the wavelength channel of the signal light to be received, a light receiving procedure for photoelectrically converting the signal light input to the wavelength variable receiver,
A method for controlling a wavelength tunable receiver having the following.

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