JP2008242364A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and stable optical module by attenuating light intensity with temperature using a general optical component. <P>SOLUTION: The optical module comprises an optical element 1 which varies in transmission loss at a certain wavelength with temperature, and a temperature control element 2 which varies the temperature of a body in proximity with the level of a current to be supplied, and the temperature control element 2 varies the temperature of the optical element 1 to vary the intensity of light transmitted through the optical element 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical module, and more specifically, is suitable for application to a light receiving optical module that receives incident light having an optimum intensity.

  In the field of optical communication or the like, a light receiving element is used as a receiver of an optical signal transmitted from a transmitter using an optical fiber as a medium. As a light receiving element, a pin photodiode (pinPD) and an avalanche photodiode (APD) are generally used. The pin PD has a function of converting an optical signal into an electric signal by converting irradiated photons into an electric current. On the other hand, the APD obtains an electric signal larger than that of the pin PD by further multiplying the converted current. In general optical communication, each base is connected with an optical fiber, and a transmitter and a receiver are connected to both ends of these optical fibers to propagate an optical signal.

  By the way, an optical signal propagating through a general optical fiber suffers a loss of about 0.3 dB per 1 km. Since transmitters and receivers are usually of the same type, the communication between bases with a short distance from each other has a small optical fiber loss due to the short optical fiber, and the intensity of the optical signal reaching the receiver is small. In communication between bases that are large and have a long distance from each other, the loss of the intensity of the optical signal is large because the optical fiber is long, and the intensity of the optical signal reaching the receiver is small.

  For example, when the distance between the bases is 10 km, the optical signal undergoes a loss of 0.3 × 10 = 3 dB by propagating through the optical fiber. Since the optical signal intensity from the transmitter is normally about +3 dB, the intensity of the optical signal incident on the receiver is 3-3 = 0 dBm. On the other hand, for example, when the distance between the bases is 80 km, the optical signal undergoes a loss of 0.3 × 80 = 24 dB by propagating through the optical fiber. In this case, the intensity of the optical signal incident on the receiver is 3-24 = -21 dBm.

  A pin PD or APD that receives light in a receiver exhibits a feature in efficiently converting a low-intensity optical signal or converting it into an electrical signal, but conversely, in the case of a strong optical signal, The saturation phenomenon of the electric signal intensity occurs, the signal is distorted, and the pin PD or APD is destroyed by Joule heat generated because the current exceeds the rated value. In particular, since the rated value of the light receiving intensity of APD is around 0 dBm, it is necessary to attenuate the intensity of the optical signal incident on the receiver in communication between bases having a short propagation distance.

  Therefore, in the conventional technique, an optical attenuator is inserted between the optical fiber and the receiver to attenuate the light intensity.

As a prior art document related to the optical element (FIG. 2) of the first embodiment described later, there is the following Patent Document 1.
Japanese Patent Application No. 2006-108218

  Since conventional optical modules have a mechanical drive as a means for attenuating light intensity, the characteristics become unstable due to the vibration of the optical module, and the optical module is fixed to stabilize the characteristics. There were problems such as the need for special parts.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an inexpensive and stable optical module by attenuating light intensity with temperature using a general-purpose optical component.

  The optical module of the first invention that solves the above problem comprises at least an optical element whose transmission loss for a certain wavelength varies with temperature, and a temperature control element that varies the temperature of an adjacent object with the intensity of an energized current, By changing the temperature of the optical element with a temperature control element, the intensity of light transmitted through the optical element is changed.

The optical module of the second invention is the optical module of the first invention.
The optical element and the light receiving element are spatially arranged so that light transmitted through the optical element is irradiated onto a light receiving surface of the light receiving element.

The optical module of the third invention is the optical module of the second invention.
A control mechanism for changing the temperature of the optical element by the temperature control element is connected so that the transmission loss in the optical element increases as the intensity of light incident on the optical element increases. is there.

Moreover, the optical module of the fourth invention is the optical module of any of the first to third inventions,
The wavelength of light incident on the optical element is constant.

The optical module of the fifth invention is the optical module of any of the first to fourth inventions,
The optical element has a dielectric multilayer film.

The optical module of the sixth invention is the optical module of any of the first to fourth inventions,
The optical module according to claim 1, wherein the optical element has an etalon filter.

The optical module of the seventh invention is the optical module of the sixth invention.
The etalon type filter is made of plastic.

The optical module of the eighth invention is the optical module of the sixth invention,
The etalon type filter is made of a compound semiconductor.

Moreover, the optical module of the ninth invention is the optical module of the sixth invention,
The etalon filter is characterized in that the transmission loss of the etalon filter is changed by changing the resonator length of the etalon filter due to thermal expansion of at least one substance constituting the etalon filter. It is what.

The optical module of the tenth invention is the optical module of the sixth invention.
The etalon type filter is characterized in that the transmission loss of the etalon type filter changes due to a temperature change of the refractive index of at least one substance constituting the etalon type filter.

The optical module of the eleventh aspect of the present invention is the optical module of any one of the second to tenth aspects of the invention,
A transmission unit made of a semiconductor laser is integrally formed in the optical module and has a transmission / reception function.

  According to the present invention, it is possible to stably and inexpensively realize a light receiving optical module that receives light with an optimum intensity of incident light by attenuating light intensity with temperature using a general-purpose optical component. it can.

  The optical module according to the present invention changes the intensity of light transmitted through the optical element by changing the temperature of the optical element in which the transmission loss with respect to a certain wavelength varies with temperature. Further, both are spatially arranged so that the light transmitted through the optical element is irradiated onto the light receiving surface of the light receiving element, and the light intensity incident on the light receiving element is made variable. Further, as the light intensity incident on the optical element becomes higher, a control mechanism for changing the temperature is connected so as to increase the transmission loss in the optical element, thereby limiting the light intensity incident on the light receiving element.

  Embodiments of an optical module according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a first embodiment of an optical module according to the present invention.

  As shown in FIG. 1, in the optical module of the first embodiment, the optical element 1 having the characteristic that the transmission loss with respect to light of a certain wavelength varies depending on the temperature is in thermal contact with the temperature control element 2. It is arranged. The optical element 1 is disposed in the optical module so that incident light having a certain wavelength is transmitted. Here, a cutout or a through hole 3 is provided in a part of the temperature control element 2 so that the transmitted light from the optical element 1 is not blocked by the temperature element 2. The temperature control element 2 changes the temperature of an adjacent object (optical element 1) depending on the strength of the current to be applied. That is, the temperature of the optical element 1 that is in thermal contact with the temperature control element 2 can be changed by adjusting the value of the current supplied to the temperature control element 2 to change the temperature of the temperature control element 2. .

  As the optical element 1, for example, an etalon type filter as shown in FIG. 2 can be used. The optical element 1 of the etalon type filter shown in FIG. 2 includes a plastic 11, an incident side reflection film 12, and an emission side reflection film 13, and the plastic 11 is divided into an incident side reflection film 12 and an emission side reflection film 13. It has a sandwiched structure.

  Here, the plastic 11 needs to have a transmittance of 90% or more with respect to incident light. For example, ZEONEX manufactured by ZEON Corporation has a permeability of 92% and can be used as the plastic 11.

In order to configure an etalon type filter, the incident side reflection film 12 and the emission side reflection film 13 have the same reflectance. Both reflectivities are about 1 to 10%. For example, a dielectric multilayer film is used for the reflection films 12 and 13. In the first embodiment, TiO ₂ and SiO ₂ are used as the dielectric multilayer film. The reflective films 12 and 13 were prepared by laminating 0.4 μm each of TiO ₂ and SiO ₂ with a sputter deposition apparatus.

The thickness of the plastic 11 changes with temperature. The resonator length of the etalon filter changes due to the thermal expansion of the plastic 11. The rate of change in thickness per unit temperature K of the plastic 11 is represented by the coefficient of thermal expansion, and the ZEONEX is about 5 × 10 ⁻⁵ / K.

As shown in FIG. 3, the etalon type filter has a property that the transmittance periodically increases and decreases with respect to the wavelength λ of the incident light, and the cycle is λ / 2. Assuming that the expansion coefficient of the plastic 11 constituting the etalon filter is 5 × 10 ⁻⁵ / K as described above, the plastic 11 has a thermal expansion of 7.5 × 10 ⁻⁴ with respect to a temperature change of 15 K. become. For example, when a plastic 11 having a thickness of 1000 μm is used, the thickness of the plastic 11 due to thermal expansion is 7.5 × 10 ⁻⁴ × 1000 μm = 0.75 μm. When the wavelength λ of incident light is 1.5 μm, the transmittance period of the etalon filter is shifted by one period due to a temperature change of 15K. In other words, the transmittance of the etalon filter can be adjusted to an arbitrary value between the maximum value and the minimum value by adjusting the temperature within a temperature change range of 15K.

  FIG. 4 shows the light transmission characteristics of the optical element 1. As shown in FIG. 4, the curve representing the transmittance measured at the reference temperature moves to the longer wavelength side as the temperature increases to the reference temperature + 10K and the reference temperature + 20K. When attention is paid to a certain wavelength indicated by a broken line, the transmittance decreases as the temperature increases. Therefore, it is possible to reduce the intensity of light transmitted through the optical element 1 by increasing the temperature of the optical element 1. Specifically, as shown in FIG. 4, the transmittance is 80% at a reference temperature of 25 ° C. for light having a wavelength of 1.55 μm. At 35 ° C., the transmittance is 50%, and at 45 ° C., the transmittance is 30%. With a temperature increase of 20 ° C., the transmittance is ½ or less, that is, the transmitted light intensity is attenuated by 3 dB or more. Similar effects can be obtained by changing the thickness of the etalon type filter, in other words, the resonator length, in other wavelength bands such as 1.3 μm and 1.6 μm other than 1.55 μm.

  In the above example, plastic is used as the etalon type filter. However, even if a semiconductor is used for the etalon type filter instead of plastic, the thermal expansion of the semiconductor and the refractive index of the semiconductor change with temperature. The same effect as when plastic is used can be expected.

For example, when a compound semiconductor such as GaAs or InP is used as the semiconductor, the rate of change of the refractive index due to the temperature change of the compound semiconductor is about 5 × 10 ⁻⁵ / K. If the change rate of the refractive index of the compound semiconductor composing the etalon filter is 5 × 10 ⁻⁵ / K, the change in refractive index of 5 × 10 ⁻⁴ occurs in the compound semiconductor with respect to the temperature change of 10K. become. This value corresponds to 5 × 10 ⁻⁴ μm, for example, when the wavelength λ of incident light is 1.5 μm, and the transmission characteristic curve in FIG. 3 is shifted along the 5 × 10 ⁻⁴ μm wavelength axis. become. The transmission loss of the etalon filter changes due to the temperature change of the refractive index of the compound semiconductor.

When plastic is used for the etalon type filter, plastic having a thermal expansion coefficient of 1 × 10 ⁻⁵ / K to 1 × 10 ⁻⁴ / K can be used. When a compound semiconductor is used for the etalon type filter, a compound semiconductor having a thermal expansion coefficient of 1 × 10 ⁻⁶ / K to 1 × 10 ⁻⁵ / K can be used. In addition, when using a change in refractive index due to temperature of a compound semiconductor, a compound semiconductor having a change in refractive index depending on temperature from 1 × 10 ⁻⁶ / K to 1 × 10 ⁻⁵ / K may be used for the etalon filter. it can.

  In the first embodiment, an example in which the light transmission characteristics of the optical element 1 move to the longer wavelength side as the temperature increases is shown. However, an optical element that moves to the shorter wavelength side as the temperature increases is described in the present invention. It can also be used for optical modules. Further, even when an optical element having a transmission characteristic that does not change monotonously with changes in temperature is used in the optical module of the present invention, the transmittance can be changed.

(Second Embodiment)
FIG. 5 is a diagram showing a second embodiment of the optical module according to the present invention. In FIG. 5, the same parts as those in FIG.

  As shown in FIG. 5, the optical module of the second embodiment includes an optical element 1, a temperature control element 2, and a light receiving element 21. Since the characteristics and functions of the optical element 1 and the temperature control element 2 are the same as those of the optical element 1 and the temperature control element 2 in the first embodiment (FIG. 1), detailed description thereof is omitted here. .

  The light receiving element 21 is spatially arranged so that the light transmitted through the optical element 1 is received by the light receiving surface of the light receiving element 21. That is, the optical element 1 and the light receiving element 21 are spatially arranged so that the light transmitted through the optical element 1 is irradiated onto the light receiving surface of the light receiving element 21. Therefore, by changing the temperature of the temperature control element 2 to change the transmission intensity of the light transmitted through the optical element 1, the intensity of the transmitted light exceeds the maximum rated value of the light reception intensity of the light receiving element 21 in the light receiving element 21. There can be no restriction.

  FIG. 6 shows an example in which the transmittance of the optical element 1 is changed with respect to the incident light intensity. By reducing the transmittance of the optical element 1 when the incident light intensity is high, it is possible to prevent the transmitted light intensity, that is, the received light intensity from exceeding the maximum rated value.

  For example, APD is used as the light receiving element 21. APD is destroyed when the light intensity is too high. A general APD operates normally in the range of -30 dBm to +5 dBm in received light intensity, and the maximum rated value of received light intensity is +5 dBm. On the other hand, in the optical module of the second embodiment, the incident light can be attenuated by 3 dB or more by the optical element 1 (etalon type filter). Therefore, when the incident light is strong, the incident light is reduced by, for example, 3 dB. By attenuating, it was possible to realize an APD that operates normally when the intensity of incident light is in the range of −30 dBm to +8 dBm. As the APD, an APD having a light receiving layer made of an InGaAsP material having sensitivity to light of 1.3 μm to 1.6 μm is used.

(Third embodiment)
FIG. 7 is a diagram showing a third embodiment of the optical module according to the present invention. In FIG. 7, the same parts as those in FIG.

  As shown in FIG. 7, the optical module according to the third embodiment includes an optical element 1, a temperature control element 2, a light receiving element 21, and a control mechanism 31. Since the characteristics and functions of the optical element 1, the temperature control element 2, and the light receiving element 21 are the same as those in the second embodiment, detailed description thereof is omitted here.

  In the optical module of the third embodiment, a control mechanism 31 is connected to the temperature control element 2 and the light receiving element 21. The control mechanism 31 monitors the light receiving current of the light receiving element 21 when the light transmitted through the optical element 1 is received by the light receiving element 21, and the temperature control element 2 is controlled so that the light receiving current does not exceed a predetermined value. Adjust the current value. That is, in the control mechanism 31, the temperature of the optical element 1 is changed by the temperature control element 2 so that the transmission loss in the optical element 1 increases as the intensity of light incident on the optical element 1 increases. As a result, the intensity of the transmitted light that has passed through the optical element 1 can be limited so that the light receiving element 21 does not exceed the maximum rated value of the light receiving intensity of the light receiving element 21.

  The control mechanism 31 compares a preset reference value (a voltage value corresponding to the reference light reception intensity) with a voltage value output from the light receiving element 21 in proportion to the light reception intensity, and determines the voltage value ( An analog feedback circuit that functions to change the temperature of the temperature control element 2 is used so that the transmittance of the optical element 1 decreases when the light reception intensity) is greater than the reference value (the reference light reception intensity). be able to. Further, as another control mechanism 31, a reference value (voltage value corresponding to the reference light reception intensity) stored in advance in memory is compared with a voltage value output from the light receiving element 21 in proportion to the light reception intensity. Programmed to change the temperature of the temperature control element 2 so that the transmittance of the optical element 1 decreases when the voltage value (the received light intensity) is greater than the reference value (the reference received light intensity). A digital feedback circuit can also be used.

(Fourth embodiment)
FIG. 8 is a view showing a fourth embodiment of the optical module according to the present invention. In FIG. 8, the same parts as those in FIG.

  As shown in FIG. 8, the optical module according to the fourth embodiment includes an optical element 1, a temperature control element 2, a light receiving element 21, a semiconductor laser 41, and a wavelength multiplexing / demultiplexing filter 42 in one casing 43. Is a single-fiber bidirectional optical module. Since the characteristics and functions of the optical element 1, the temperature control element 2, and the light receiving element 21 are the same as those in the second embodiment, detailed description thereof is omitted here.

  In this optical module, the wavelengths of the received light and the transmitted light are set to be different from each other. For example, 1.5 μm is used as the reception light wavelength, and 1.3 μm is used as the transmission light wavelength. The wavelength multiplexing / demultiplexing filter 42 has a characteristic of transmitting the wavelength of the received light and reflecting the wavelength of the transmitted light. The received light passes through the wavelength multiplexing / demultiplexing filter 42, is adjusted in transmittance (transmitted light intensity) by the optical element 1, and is incident on the light receiving element 21. On the other hand, the transmitted light is reflected by the wavelength multiplexing / demultiplexing filter 42 and emitted to the outside of the optical module along the same optical axis as the received light. As a result, it is possible to input received light and output transmitted light with a single optical fiber (not shown) connected to the optical module.

  The optical module according to the present invention is suitable for application to the optical input portion of a receiver for optical communication, but not only for a receiver, but also for adjustment of transmission light intensity and light intensity in the middle of a transmission path. It can also be used for adjustment and for a light emitting part or a light receiving part of an optical measuring instrument.

It is a figure which shows the 1st Embodiment example of the optical module which concerns on this invention. It is a figure which shows the optical element of an etalon type | mold filter. It is a figure explaining increase / decrease in the transmittance | permeability with respect to the incident light wavelength of an etalon type | mold filter. It is a figure explaining the transmittance | permeability of the optical module which concerns on this invention. It is a figure which shows the 2nd Example of the optical module which concerns on this invention. It is a figure explaining the transmittance | permeability and transmitted light intensity of the optical module which concerns on this invention. It is a figure which shows the example of 3rd Embodiment of the optical module which concerns on this invention. It is a figure which shows the example of 4th Embodiment of the optical module which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 2 Temperature control element 11 Plastic or semiconductor 12 Incident side reflective film 13 Outgoing side reflective film 21 Light receiving element 31 Control mechanism 41 Semiconductor laser 42 Wavelength multiplexing / demultiplexing filter 43 Case

Claims (11)

  It comprises at least an optical element whose transmission loss with respect to a certain wavelength changes depending on the temperature and a temperature control element that changes the temperature of an adjacent object with the intensity of the current to be passed. The temperature control element changes the temperature of the optical element. To change the intensity of light transmitted through the optical element. The optical module according to claim 1,
An optical module, wherein the optical element and the light receiving element are spatially arranged so that light transmitted through the optical element is irradiated onto a light receiving surface of the light receiving element. The optical module according to claim 2,
An optical module comprising a control mechanism for changing the temperature of the optical element by the temperature control element so that the transmission loss in the optical element increases as the intensity of light incident on the optical element increases. . The optical module according to any one of claims 1 to 3,
An optical module, wherein a wavelength of light incident on the optical element is constant. The optical module according to any one of claims 1 to 4,
An optical module, wherein the optical element has a dielectric multilayer film. The optical module according to any one of claims 1 to 4,
An optical module, wherein the optical element has an etalon filter. The optical module according to claim 6,
An optical module, wherein the etalon filter is made of plastic. The optical module according to claim 6,
An optical module, wherein the etalon filter is made of a compound semiconductor. The optical module according to claim 6,
The etalon filter is characterized in that the transmission loss of the etalon filter changes as the resonator length of the etalon filter changes due to thermal expansion of at least one substance constituting the etalon filter. And optical module. The optical module according to claim 6,
An optical module, wherein the etalon filter changes a transmission loss of the etalon filter due to a temperature change in a refractive index of at least one substance constituting the etalon filter. The optical module according to any one of claims 2 to 10, wherein
An optical module characterized in that a transmission unit made of a semiconductor laser is integrally formed in an optical module and has a function of transmission and reception.

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