JP2010224189A - Optical module and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the power efficiency of a TO (thermo-optic) phase shifter in an optical control system using a PLC (planar lightwave circuit). <P>SOLUTION: An optical module includes: a planar lightwave circuit; a thermo-optic phase shifter for heating the planar lightwave circuit at a prescribed position; a photodetector for detecting optical output of optical signals which have passed through the planar lightwave circuit; and a control part for performing pulse width modulation control of the thermo-optic phase shifter so that the optical output detected by the photodetector gets close to a set value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical module and a control method thereof.

  In a DWDM (Dense Wavelength Division Multiplexing) optical communication system, the importance of an optical control device such as a PLC for controlling the wavelength is increasing. As a technique for controlling an optical device such as a PLC (Planar Lightwave Circuit), there is a TO (Thermo-Optic) heater driving system using a resistance heat source. Since most optical device materials have a temperature refractive index variation coefficient, the refractive index can be changed by changing the ambient temperature to achieve desired optical characteristics.

  Patent Document 1 is given as an example of controlling the optical module.

JP 2003-66388 A

  The TO heater driving method has advantages that it is easy to control stably because it uses heat, and there is a merit that the material is not selected, but the power efficiency of the refractive index fluctuation amount is worse than the EO (Electro-Optic) effect of the compound semiconductor. Therefore, relatively large electric power is required. In particular, since the temperature refractive index susceptibility of quartz glass material, which is a raw material of PLC, is 10 times as large as that of a compound semiconductor, power consumption when phase control is performed using a TO heater is as large as about sub-W. For this reason, it is necessary to prepare a dedicated analog drive circuit for the conventional TO heater control circuit, and power efficiency is deteriorated due to loss due to conversion of electric energy into heat generation of the circuit. Moreover, depending on the resistance value of the TO heater, it is necessary to supply a relatively high voltage such as 10V, but the optical MDL (optical module) uses only a standard power supply voltage such as 5.0V or 3.3V. It is necessary to generate a desired voltage with a DC-DC converter or the like. An additional circuit for voltage conversion is required, and the power is wastefully changed to heat for voltage conversion, which increases the power consumption and MDL size of the optical module. Therefore, in order to reduce the power consumption and size of the optical MDL in the light control system using the PLC, it is important to drive the TO phase shifter with efficient power.

  In a light control system using a PLC, a technique that can improve the power efficiency of the TO phase shifter is desired.

  An optical module according to an aspect of the present invention includes a planar optical waveguide circuit, a thermo-optic phase shifter that heats the planar optical waveguide circuit at a predetermined position, and optical detection that detects the optical output of the optical signal that has passed through the planar optical waveguide circuit. And a controller that performs pulse width modulation control of the thermo-optic phase shifter so that the light output detected by the photodetector approaches the set value.

  An optical module control method according to one aspect of the present invention includes a step of detecting an optical output of an optical signal that has passed through a planar optical waveguide circuit, and heating the planar optical waveguide circuit at a predetermined position so that the optical output approaches a set value. And a step of controlling the pulse width modulation of the thermo-optic phase shifter.

  In an optical control system using a PLC, a technique that can improve the power efficiency of a TO phase shifter is provided.

FIG. 1 shows a configuration of an optical module. FIG. 2A is a diagram for explaining PWM control. FIG. 2B is a diagram for explaining PWM control. FIG. 3A is a diagram for explaining PWM control. FIG. 3B is a diagram for explaining PWM control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an optical module according to this embodiment. The optical module includes PLCs (planar optical waveguide circuits) 2 and 3 formed on the substrate 1. A ring resonator 4 is further formed on the substrate 1 by PLC. The PLC 2 has a first input terminal IN1 and a second input terminal IN2. The PLC 3 has a first output terminal OUT1 and a second output terminal OUT2. The optical signal output from the second output terminal OUT2 is detected by the photodetector 7. As the photodetector 7, it is desirable to use a PD (photodiode) that detects light output. The optical module of the present embodiment can obtain a sufficient effect by PD without using an expensive device such as a wavelength dispersion detector.

  The optical module further includes a TO (Thermo-Optic) phase shifter 5 that realizes a phase shift of an optical signal by a heater. The TO phase shifter 5 generates an amount of heat in response to a control signal received from the control unit 6. This heat changes the temperature at a predetermined position of the optical waveguide forming the ring resonator 4. As a result, the phase of the optical signal in the ring resonator 4 is shifted by a controlled amount. The control unit 6 controls the TO phase shifter 5 by PWM (pulse width modulation) control based on the detection value of the optical output detected by the photodetector 7 so that the detection value approaches the set value.

  The ring resonator 4 receives a plurality of optical signals having wavelengths of λ1 to λn from the first input terminal IN1, and receives an optical signal of wavelength λ1 from the second input terminal IN2. The controller 6 adjusts the TO phase shifter so that the optical output detected by the photodetector 7 becomes the maximum value when such an optical signal is input. By such control, only the optical signal having the wavelength λ1 can be extracted from the first output terminal OUT1 from the plurality of optical signals input to the first input terminal IN1. Thus, by performing feedback control by combining a power control circuit using PWM and a light receiving circuit such as a PD, desired characteristics can be obtained in an optical circuit using a PLC.

  Hereinafter, the PWM control will be described. In recent optical INF_MDL (optical interface module), downsizing and power saving are strongly demanded. When a circuit like a TO heater is driven by a conventional analog control circuit, it is becoming increasingly difficult to reduce the size. The TO heater is an electric heater using a metal thin film, and can convert the applied electric power into heat to locally warm the optical device.

  On the other hand, techniques for reducing the power consumption of TO heaters are advancing. Therefore, if PWM control currently used for motor control etc. can be applied to the TO heater, the optical device can be controlled without generating wasteful power, and miniaturization and low power consumption are realized. I can do it.

  PWM is a digital control method that supplies two levels of voltage, a high voltage and a low voltage, by switching in time series. The average output is controlled by controlling the duty ratio indicating the ratio of the time during which the high voltage is supplied within a certain time. For example, in the control of the motor, a voltage as shown in FIG. 2B is applied. The horizontal axis represents time, and the vertical axis represents applied voltage. When the duty ratio is small as shown in FIG. 2B, the motor rotates at a low speed as shown in FIG. 2A. When the duty ratio of the applied voltage is large as shown in FIG. 3B, the motor rotates at a high speed as shown in FIG. 3A. Similarly to this motor, when the duty ratio is small, the temperature of the TO heater slightly increases, and conversely, when the duty ratio is large, the temperature of the TO heater increases more greatly. Thus, the control unit 6 can control the temperature of the TO heater by controlling the duty ratio.

  In PWM control, the average power is controlled by switching between a time zone in which the required maximum power is supplied in a time-series region and a time zone in which it is not supplied. The maximum voltage required is always constant and there is no voltage lost in the control switching circuit as in normal analog control. Therefore, power efficiency is greatly improved.

  In the conventional TO heater, since the drive voltage is particularly large as about 10V, it is difficult to use the PWM control as it is. However, in recent years, research and development of lower power and lower voltage TO heaters has progressed, and driving of TO heaters at 5.2V and 3.3V has come into the field of view. Therefore, in the present embodiment, the control unit 6 which is a circuit for driving the heater performs PWM control, so that the power consumption of the entire system can be reduced.

1 Substrate 2 PLC (planar optical waveguide circuit)
3 PLC (planar optical waveguide circuit)
4 ring resonator 5 TO (thermo-optic) phase shifter 6 control unit 7 detection unit

Claims (3)

A planar optical waveguide circuit;
A thermo-optic phase shifter that heats the planar optical waveguide circuit in place;
A photodetector for detecting an optical output of an optical signal that has passed through the planar optical waveguide circuit;
An optical module comprising: a controller that performs pulse width modulation control on the thermo-optic phase shifter so that the optical output detected by the photodetector approaches a set value. The optical module according to claim 1,
The planar optical waveguide circuit includes a ring resonator;
The predetermined position is set on the ring resonator. Detecting the optical output of the optical signal that has passed through the planar optical waveguide circuit;
And a pulse width modulation control of a thermo-optic phase shifter that heats the planar optical waveguide circuit at a predetermined position so that the optical output approaches a set value.

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