JP2010231126A - Optical module and dispersion compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To flatten a transmission characteristic of a VIPA plate by applying the same control temperature to an optical filter and a VIPA plate. <P>SOLUTION: An optical module 10 includes: an optical filter 12 which has transmission characteristics having wavelength periodicity; an optical component 13 which includes a reflecting surface 13a for reflecting light with high reflectance and a transmission surface 13b having lower reflectance than the reflecting surface 13a and repeatedly reflects light emitted from the optical filter 12, in an internal region interposed between the reflecting surface 13a and the transmission surface 13b and emits diffracted output light through the transmission surface 13b; and a temperature control part 15 which controls temperatures of the optical filter 12 and the optical component 13. The temperature control part 15 applies the same control temperature to the optical filter 12 and the optical component 13 to flatten a transmission spectrum shape of output light emitted from the transmission surface 13b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical module and a dispersion compensation apparatus, and more particularly to an optical module that performs wavelength demultiplexing and a dispersion compensation apparatus that compensates for chromatic dispersion of light.

  Since the speed (group speed) at which an optical pulse propagates on an optical fiber varies depending on the wavelength of light, high-speed and large-capacity optical transmission causes chromatic dispersion in which the pulse waveform of the light becomes dull as the transmission distance increases. . The chromatic dispersion is defined as a difference in propagation time when two monochromatic lights having different wavelengths of 1 nm are propagated by 1 km, and the unit is ps / nm / km.

  In a system that performs optical transmission such as WDM (Wavelength Division Multiplex), when a pulse spread due to chromatic dispersion occurs, the reception level is significantly deteriorated, which has a harmful effect on the system. For this reason, it is necessary to perform dispersion compensation that equivalently cancels chromatic dispersion to zero so as to suppress chromatic dispersion generated during optical transmission.

  Dispersion compensation devices include dispersion compensation fiber (DCF) and dispersion compensation grating (DCG), but most of these are dispersion compensation (dispersion generated in an optical fiber transmission line). The amount of dispersion of the reverse sign is fixed.

  On the other hand, in a high-speed optical communication system of 40 Gbps or more, since the tolerance of chromatic dispersion (allowable tolerance of residual dispersion) is narrow and it is necessary to compensate with a more accurate dispersion value, variable dispersion compensation capable of arbitrarily adjusting the dispersion compensation amount It is essential to use a vessel. As a tunable dispersion compensator, an optical component called VIPA (Virtually Imaged Phased Array) has attracted attention in recent years.

  VIPA is a device that has a wavelength demultiplexing element (VIPA plate) with a highly reflective film deposited on both sides of a glass plate. By inputting a focused beam to the VIPA plate and making multiple reflections inside the glass plate, It is possible to perform wavelength demultiplexing without using a normal diffraction grating. Hereinafter, the basic concept of VIPA will be described with reference to FIGS.

FIG. 8 is a diagram showing a basic configuration of VIPA. The VIPA 50 includes a cylindrical lens 51 and a VIPA plate 52.
The cylindrical lens 51 is a lens that collects input light. The VIPA plate 52 includes a reflective surface 52a coated with a reflective film 5a having a reflectance of 100% or close to 100%, a transmissive surface 52b coated with a reflective film 5b with a reflectance of about 95 to 98%, a window (Irradiation window) 52c.

  FIG. 9 is a diagram for explaining an outline of the operation of the VIPA 50. The beam B1 collected by the cylindrical lens 51 is input from the window 52c of the VIPA plate 52. At this time, the optical axis Z of the beam B 1 has a small inclination angle θ with respect to the normal H of the VIPA plate 52.

  Assuming that the reflectance of the reflecting surface 52a is 100% and the reflectance of the transmitting surface 52b is 98%, 2% of the light beam B1 is emitted from the transmitting surface 52b to the outside with a beam diameter corresponding to the thickness of the glass plate. (The light emitted from the transmission surface 52b is a round beam (collimated beam) with a small divergence angle, and the beam diameter is the thickness of the glass plate), and the remaining 98% of the beam B1a is directed toward the reflection surface 52a. (The beam B1a travels toward the reflecting surface 52a while spreading slightly by the thickness of the plate inside the glass plate).

  Further, since the reflection surface 52a has a reflectivity of 100%, the beam B1a is totally reflected toward the transmission surface 52b (the beam B1a travels toward the transmission surface 52b while slightly spreading by the thickness of the plate inside the glass plate). Then, 2% of the beam B1a is emitted from the transmission surface 52b to the outside with a beam diameter corresponding to the thickness of the glass plate. At this time, the spot positions of the emitted lights of the beam B1 and the beam B1a are shifted by d.

  Similarly, the remaining 98% of the beam B1a is reflected toward the reflecting surface 52a. By repeating this, the beam input to the VIPA plate 52 through the cylindrical lens 51 is gradually reflected within the VIPA plate 52 while gradually spreading, and is separated from the transmission surface 52b by a certain distance d. Light will be emitted little by little.

  Light that is emitted from the transmission surface 52b by a predetermined distance d can be regarded as being emitted from virtual emission spots v1 to vn (shown up to v4 in FIG. 9) arranged in a staircase pattern. This behavior (called an image phased array) can be said to be the operation of an Echelon-type (staircase) diffraction grating, so that the emitted light is split and emitted.

  These virtual emission spots v1 to vn are arranged at a constant interval 2D along the normal H of the VIPA plate 52, where D is the thickness of the glass plate of the VIPA plate 52. Looking at the virtual exit spots v1 and v2, since the line segment pq = the line segment qr = D, the arrangement interval of the virtual exit spots v1 and v2 is 2D on the normal H of the VIPA plate 52, and the other virtual exits The arrangement interval of the spots is also arranged at the interval 2D.

  FIG. 10 is a diagram showing the interference conditions of the VIPA 50. It is assumed that there are m wavelengths (middle wavelengths) in the path t0 in the beam B2a with respect to the light emitted from the emission spot va. In this case, when the interference condition is satisfied in the beam B2b on the upper side of the beam B2a, the path t1 <the path t0, so that m wavelengths enter the beam B2b, the wavelength of the beam B2b is The wavelength needs to be shorter than the wavelength included in the beam B2a.

  In addition, when the interference condition is satisfied in the direction in which light is intensified in the beam B2c on the lower side of the beam B2a, since the path t0 <path t2, in order for m wavelengths to enter the beam B2c, the wavelength of the beam B2c is The wavelength needs to be longer than the wavelength included in the beam B2a.

  Therefore, the interference condition in which the light is strengthened with respect to the light emitted from the VIPA plate 52 is that the upper side has a short wavelength and the lower side has a long wavelength with respect to the optical axis, and from the VIPA plate 52 to the upper side of the optical axis. Short wavelength light is emitted and long wavelength light is emitted downward.

  FIG. 11 is a diagram showing the order of the diffracted light of the VIPA plate 52. From the intermediate emission point of the VIPA plate 52, the light of the m-th order of the diffraction order (positive or negative integer indicating the direction of light diffracted by the diffraction grating) is emitted.

  Further, m-1 order light is emitted from the upper emission point of the intermediate emission point, and m + 1 order light is emitted from the lower emission point. In this manner, light of various diffraction orders is emitted from the VIPA plate 52, but only the diffracted light of the order necessary for control is focused.

Next, reception degradation caused by chromatic dispersion on the optical network will be described. FIG. 12 is a diagram for explaining a state where chromatic dispersion occurs and normal reception cannot be performed. Signal light having data “0” and “1” flows through the optical fiber F0. Here, focusing on the spectrum of a 1-bit pulse, the spectrum of a pulse that constitutes 1 bit includes a plurality of wavelengths. The wavelength in the middle of the spectrum is λ _C , the long wavelength side is λ _L , the short wavelength side is λ _S , the speed of wavelength λ _C is V (λ _C ), the speed of wavelength λ _L is V (λ _L ), and wavelength λ _S Is V (λ _S ).

If these wavelengths λ _C , λ _L , λ _S are transmitted through the optical fiber F0 at the same speed and reach the receiver Rx (V (λ _C ) = V (λ _L ) = V (λ _S )) The corresponding 1-bit waveform is not distorted and can be normally identified.

However, when chromatic dispersion occurs due to an increase in transmission distance during high-speed optical transmission, the wavelength of the spectrum constituting one bit is V (λ _S )> V (λ _C )> V (λ _L ). Thus, a speed difference will occur. When such a speed difference occurs, distortion occurs in the transmission waveform of the corresponding 1 bit, and accurate bit identification cannot be performed in the receiver Rx.

  Next, dispersion compensation using the VIPA 50 will be described with reference to FIGS. 13 and 14 are diagrams for explaining VIPA type dispersion compensation. A condenser lens 53 and a reflection mirror 54 are disposed on the exit side of the VIPA plate 52. The emitted diffracted light is condensed on the reflection mirror 54 by the condenser lens 53.

The reflection mirror 54 has an aspherical shape and reflects light in various directions depending on the reflection position. Further, the reflection direction can be changed by the curve of the reflection mirror 54. Here, the beam having a short wavelength λ _S (referred to as beam λ _S ) is reflected so as to reach a location above the center of the VIPA plate 52, and the beam having a long wavelength λ _L (referred to as beam λ _L ) is Reflect the light so that it reaches a position below the center.

Then, as shown in FIG. 14, since the reflected beam λ _S reaches the upper point p1 of the VIPA plate 52 and is input again to the VIPA plate 52, the reflection is repeated many times inside the VIPA plate 52, so that the window The light is emitted from 52c. Further, the reflected beam λ _L reaches the point p2 on the lower side of the VIPA plate 52 and is input again. Therefore, the reflected beam λ _L is repeatedly reflected a small number of times inside the VIPA plate 52 and is emitted from the window 52c.

  As described above, the light reflected by the reflection mirror 54 reaches the VIPA plate 52, and the arrival position of the VIPA plate 52 differs depending on each wavelength. Therefore, there is a time difference between the multiple reflection inside the VIPA plate 52 and the return to the window 52c. Thus, a time difference (dispersion) can be generated for each wavelength (a group delay time can be generated).

In the above case, due to the chromatic dispersion, the short wavelength λ _S reaches the receiver Rx earliest and the long wavelength λ _L reaches the latest earliest, so that many delay times are generated for the short wavelength λ _S (short wavelength The light of λ _S is an image that is detoured before being emitted from the window 52c of the VIPA plate 52), and the delay time of the long wavelength λ _L is reduced (the light of the long wavelength λ _L is In this case, the chromatic dispersion generated on the optical transmission line is compensated.

  As a prior art, a dispersion compensation device using a VIPA is proposed in Patent Document 1. A technique for flattening the transmission band characteristics of VIPA using an etalon filter is proposed in Patent Document 2, and a technique for flattening using a spatial filter is proposed in Patent Document 3. However, in the method disclosed in Patent Document 2, it is necessary to add a temperature adjustment mechanism for adjusting the wavelength of the etalon filter, which causes problems that the device structure becomes complicated and the device volume increases. Moreover, the spatial filter shown in Patent Document 3 has a problem that it is technically difficult to manufacture.

Special table 2000-511655 gazette JP 2003-202515 A JP 2003-207618 A

  The transmission characteristics when light is transmitted through an optical device are generally required to have a wide spectrum of transmitted light and a flat transmission band. This is because, if the transmission band is not flat, the power of the frequency component that existed before the incidence is blocked and waveform distortion occurs (in addition, the transmission bandwidth does not cause crosstalk leakage of adjacent channels). It is also required that it should be as narrow as possible.)

  However, the VIPA plate 52 that constitutes the VIPA 50 does not have flat transmission characteristics. For this reason, if dispersion compensation is performed using the VIPA 50 as it is, there is a problem that transmission quality is deteriorated.

  FIG. 15 is a diagram showing the periodic filter characteristics of the VIPA plate 52. The vertical axis represents transmittance, and the horizontal axis represents wavelength. The VIPA plate 52 is a periodic filter, and light emitted from the VIPA plate 52 has wavelength periodicity.

  When wide band light (white light) is incident on the VIPA plate 52, the wavelength periodicity appears such that the emitted light from the VIPA plate 52 is transmitted and output in the order of λ1, λ2, λ3. Such a filter characteristic appears in the case of light emitted from an optical component such as a VIPA plate or an etalon in which a reflective film is provided on the front and back surfaces through a specific thickness and multiple reflections are made so that the light interferes internally.

  The optical path length of light passing through the VIPA plate 52 is proportional to the refractive index n of the glass plate of the VIPA plate 52 and the thickness D of the glass plate (optical path length ∝n × D), and the wavelength period T depends on the optical path length. To do.

  FIG. 16 is a diagram showing the transmission characteristics of the emitted light from the VIPA plate 52 at a single wavelength. The vertical axis represents transmittance, and the horizontal axis represents wavelength. The light emitted from the VIPA plate 52 has a round top shape characteristic having a peak near the center wavelength in each transmission band. Thus, since the transmission band of the VIPA plate 52 is not flat, the light transmitted through the VIPA plate 52 is substantially subjected to band limitation.

  The light emitted from the VIPA plate 52 has a round-top transmission characteristic, so that there is a difference in light level (transmittance) at a single wavelength within the transmission band, and the signal light pulse waveform differs greatly before and after passing through the VIPA plate 52. As a result, significant waveform distortion occurs.

  In addition, in a high-speed, large-capacity, long-distance optical communication system, when dispersion compensation is performed using such a dispersion compensator including the VIPA plate 52 in multiple stages, waveform distortion accumulates. Degradation of will become very large.

  On the other hand, the above-described conventional technique (Japanese Patent No. 3994737) employs a method of flattening the transmission spectrum of the VIPA plate 52 by using an etalon filter having a transmission property opposite to that of the VIPA plate 52. ing.

  In this case, it is necessary to adjust the transmission wavelength of the VIPA plate 52 and the transmission wavelength of the etalon filter so that the peak and bottom of the transmitted light spectrum cancel each other. To perform such wavelength adjustment, Temperature control is generally performed.

  However, the prior art (Japanese Patent No. 3994737) does not consider wavelength adjustment by temperature control and a temperature control mechanism. Even if temperature control is performed, normally, the transmission wavelength of the VIPA plate 52 and the transmission wavelength of the etalon filter do not coincide with each other, and the wavelength temperature coefficient indicating the wavelength change amount per 1 ° C. of the temperature change is also the VIPA plate 52. Since the etalon filter and the etalon filter are different from each other, it is conceivable to control them at different temperatures.

  However, if the VIPA plate 52 and the etalon filter are temperature-adjusted using separate temperature control mechanisms, the apparatus configuration becomes complicated, causing a problem in that the circuit scale, power consumption, and cost increase.

  The present invention has been made in view of the above points, and by the temperature control by the same temperature control mechanism, the transmission characteristics of the VIPA plate are flattened to improve transmission quality, reduce circuit scale and power consumption. An object of the present invention is to provide an optical module.

  Another object of the present invention is to provide a dispersion compensator that improves the transmission quality, reduces the circuit scale, and reduces power consumption by flattening the transmission characteristics of the VIPA plate by temperature control using the same temperature control mechanism. Is to provide.

  In order to solve the above problems, an optical module that performs wavelength demultiplexing is provided. The optical module includes an optical filter having wavelength-periodic transmission characteristics, a reflective surface that highly reflects light, and a transmissive surface that has a lower reflectance than the reflective surface, and is sandwiched between the reflective surface and the transmissive surface. An optical component that multiplex-reflects the light emitted from the optical filter and emits light diffracted through the transmission surface, and temperature control for controlling the temperature of the optical filter and the optical component. A part.

  Here, the temperature control unit applies the same control temperature to the optical filter and the optical component to flatten the transmission spectrum shape of the light emitted from the transmission surface.

  By applying the same control temperature to the optical filter and the VIPA plate to flatten the transmission characteristics of the VIPA plate, it becomes possible to improve transmission quality, reduce circuit scale and power consumption. .

It is a principle diagram of an optical module. It is a figure which shows the transmission spectrum shape of a VIPA board. It is a figure which shows a transmission spectrum shape. It is a figure which shows the adjustment operation of a transmission wavelength. It is a figure which shows the adjustment operation of a transmission wavelength. It is a figure which shows the adjustment operation of a transmission wavelength. It is a figure which shows the structure of a dispersion compensation apparatus. It is a figure which shows the basic composition of VIPA. It is a figure for demonstrating the operation | movement outline | summary of VIPA. It is a figure which shows the interference condition of VIPA. It is a figure which shows the order of the diffracted light of a VIPA board. It is a figure for demonstrating the state which chromatic dispersion arises and cannot perform normal reception. It is a figure for demonstrating VIPA type | mold dispersion compensation. It is a figure for demonstrating VIPA type | mold dispersion compensation. It is a figure which shows the periodic filter characteristic of a VIPA board. It is a figure which shows the transmission characteristic in the single wavelength of the emitted light of a VIPA board.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a principle diagram of an optical module. The optical module 10 is composed of a lens 11, an optical filter 12, and an optical component 13 (hereinafter referred to as VIPA plate 13), and is an optical module that performs wavelength demultiplexing.

The lens 11 collects input light and generates a condensed beam. The optical filter 12 is a filter having wavelength-periodic transmission characteristics, and filters and outputs the condensed beam.
The optical filter 12 is specifically an etalon filter (a structure in which two mirrors face each other in parallel, and selectively transmits only light of an integral multiple of a specific frequency, and does not pass other light. In the following, it is referred to as an etalon filter 12.

  The VIPA plate 13 includes a reflective surface 13a that highly reflects light (a surface coated with a reflective film 13-1 having a reflectance of 100% or near 100%) and a reflective film 13 that has a lower reflectance than the reflective surface 13a. -2 is provided with a transparent surface 13b coated.

  When the light beam emitted from the etalon filter 12 is incident on the window 13c, the light beam incident from the window 13c is multiple-reflected in the internal region sandwiched between the reflective surface 13a and the transmissive surface 13b, and passes through the transmissive surface 13b. The diffracted light is emitted. The etalon filter 12 and the VIPA plate 13 are bonded together with an adhesive 14.

  The temperature control unit 15 controls the temperature of the etalon filter 12 and the VIPA plate 13 and applies the same control temperature to the etalon filter 12 and the VIPA plate 13 so that the light is emitted from the transmission surface 13b of the VIPA plate 13. The transmission spectrum shape of the emitted light is flattened.

  FIG. 2 is a diagram showing the transmission spectrum shape of the VIPA plate 13. The vertical axis represents transmittance, and the horizontal axis represents wavelength. Depending on the configuration of the optical module 10, the transmission spectrum shape of the light emitted from the transmission surface 13 b of the VIPA plate 13 becomes a flat shape.

  Next, the operation of the optical module 10 for flattening the transmission spectrum from the VIPA plate 13 will be described in detail. FIG. 3 is a diagram showing a transmission spectrum shape. The vertical axis represents transmittance, and the horizontal axis represents wavelength. A transmission spectrum shape 1a of the VIPA plate 13 alone, a transmission spectrum shape 1b of the etalon filter 12 alone, and a transmission spectrum shape 1c of the emitted light of the VIPA plate 13 when these are added are shown.

  The temperature controller 15 applies a control temperature to the VIPA plate 13, variably adjusts the optical path length of the VIPA plate 13, and shifts the transmission wavelength of the VIPA plate 13 leftward or rightward. Further, a control temperature is applied to the etalon filter 12, the optical path length of the etalon filter 12 is variably adjusted, and the transmission wavelength of the etalon filter 12 is shifted leftward or rightward.

  By performing such temperature control, the peak wavelengths λ1 and λ2 of the round top spectral shape of the VIPA plate 13 are matched with the bottom wavelengths λ1 and λ2 of the spectral shape of the etalon filter 12, respectively.

  Then, the transmittance of the peak wavelength λ1 of the VIPA plate 13 and the transmittance of the bottom wavelength λ1 of the etalon filter 12 are added, so that the transmittance of the wavelength λ1 of the emitted light from the transmission surface 13b of the VIPA plate 13 is Flatten.

  Similarly, the transmittance at the wavelength λ2 of the emitted light from the transmission surface 13b of the VIPA plate 13 is obtained by adding the transmittance at the peak wavelength λ2 of the VIPA plate 13 and the transmittance at the bottom wavelength λ2 of the etalon filter 12. Is flattened.

  Here, normally, the transmission wavelengths of the VIPA plate 13 and the etalon filter 12 do not match, and the wavelength change amount (wavelength temperature coefficient) per 1 ° C. of temperature change is also different. However, as described above, if a separate temperature control mechanism is provided for each of the VIPA plate 13 and the etalon filter 12, an increase in circuit scale, power consumption, and cost can be achieved. It will cause.

  Therefore, in the optical module 10, by using a material having a wavelength temperature coefficient several times larger than that of the material of the VIPA plate 13 for the etalon filter 12, the VIPA plate 13 and the etalon filter 12 are controlled at the same temperature. The wavelength adjustment of the VIPA plate 13 and the wavelength adjustment of the etalon filter 12 are simultaneously performed to adjust the wavelengths of both.

  FIG. 4 is a diagram showing an operation for adjusting the transmission wavelength. The vertical axis represents transmittance, and the horizontal axis represents wavelength. In the graph g1, the transmission wavelength (peak wavelength λp) of the VIPA plate 13 completely coincides with the grid wavelength λg (wavelength of signal light) at a certain temperature, and the bottom wavelength λb of the etalon filter 12 controlled at the same temperature is It is assumed that the peak wavelength λp of the VIPA plate 13 does not match (in this state, the transmission spectrum shape of the VIPA plate 13 is not flattened).

  The grid wavelength is a wavelength used in a WDM network standardized by ITU-T (International Telecommunications Union-Telecommunications). In a WDM network, a plurality of different wavelengths are multiplexed and transmitted, so that signal wavelengths are recommended by ITU-T in order to avoid the influence of adjacent channels. Specifically, it is determined that the wavelength is set on a frequency grid arranged at intervals of 100 GHz (0.8 nm) with a frequency of 193.1 THz (1,552.525 nm) as a reference.

  In the graph g2, the control temperature is changed in order to match the bottom wavelength λb of the etalon filter 12 to the vicinity of the grid wavelength λg. In this case, the peak wavelength λp of the VIPA plate 13 deviates from the previously adjusted grid wavelength λg (shifts to the right), but the wavelength temperature coefficient is smaller than the substrate material of the etalon filter 12. Since it is a fraction of a wavelength, the wavelength shift can be suppressed to a range that has substantially no influence.

  As shown in the graph g3, when the grid wavelength λg, the bottom wavelength λb of the etalon filter 12, and the peak wavelength λp of the VIPA plate 13 substantially coincide with each other, the transmission spectrum of the grid wavelength λg in the transmitted light of the VIPA plate 13 is It becomes a flattened shape.

  In this way, by increasing the difference in wavelength temperature coefficient between the substrate materials of the VIPA plate 13 and the etalon filter 12 and adjusting the temperature by the same temperature control mechanism, the wavelength error is within the range of substantially no influence. Thus, the transmission spectrum characteristics of the VIPA plate 13 can be flattened.

  Next, the transmission wavelength adjustment operation will be described using specific numerical values. The VIPA plate 13 is made of BK7 borosilicate crown glass (Borosilicate Crown Glass), which is a representative optical glass. Optical glass material) is used, and the substrate material of the etalon filter 12 is silicon (Si). BK7 has a wavelength temperature coefficient of about 16 pm / ° C. at a wavelength of 1550 nm, and silicon has a wavelength temperature coefficient of about 82 pm / ° C. at a wavelength of 1550 nm (the wavelength temperature coefficient of the material of the etalon filter 12 is VIPA). About 5 times larger than the wavelength temperature coefficient of the material of the plate 13).

FIG. 5 is a diagram showing an operation for adjusting the transmission wavelength. The vertical axis represents the transmittance, and the horizontal axis represents the wavelength, and shows a state where there is a difference between the bottom wavelength of the etalon filter 12 and the peak wavelength of the VIPA plate 13. Before performing temperature control for flattening, the peak wavelength of the VIPA plate 13 is λ _V , and the bottom wavelength of the etalon filter 12 is λ _E.

First, the temperature control unit 15 performs temperature adjustment so that the peak wavelength λ _V of the VIPA plate 13 completely matches the grid wavelength λg (λ _V = λg). At this time, normally, the bottom wavelength λ _E of the etalon filter 12 does not coincide with the peak wavelength λ _V of the VIPA plate 13. It is assumed that there is a deviation between the peak wavelength λ _V of the VIPA plate 13 and the bottom wavelength λ _E of the etalon filter 12, and the deviation dλ is 80 pm (λg−λ _E = dλ = 80 pm).

FIG. 6 is a diagram showing an operation for adjusting the transmission wavelength. The vertical axis represents the transmittance, and the horizontal axis represents the wavelength, and shows a state where the bottom wavelength λ _E of the etalon filter 12 and the peak wavelength λ _V of the VIPA plate 13 are matched (the thin solid line before the wavelength shift, the wavelength shift) The back is indicated by a thick solid line).

The temperature control unit 15 applies the same control temperature to the etalon filter 12 and the VIPA plate 13 so that the bottom wavelength λ _E of the etalon filter 12 matches the peak wavelength λ _V of the VIPA plate 13.

In this case, the wavelength temperature coefficient of the material of the VIPA plate 13 is α _V , the wavelength temperature coefficient of the material of the etalon filter 12 is α _E (α _E > α _V ), the change amount of the control temperature is ΔT, and the control temperature change amount ΔT is When the change amount of the peak wavelength λ _V of the VIPA plate 13 when applied is Δλ _V and the change amount of the bottom wavelength λ _E of the etalon filter 12 when the control temperature change amount ΔT is applied is Δλ _E , 1) and (2) hold.

Δλ _E = Δλ _V + dλ (1)
ΔT = Δλ _E / α _E = Δλ _V / α _V (2)
Substituting dλ = 80 pm, α _E = 82 pm / ° C., and α _V = 16 pm / ° C. into equations (1) and (2) to obtain the control temperature change amount ΔT, ΔT = 1.2 ° C. Become. Therefore, the temperature control unit 15 further raises the bottom wavelength λ _E of the etalon filter 12 and the VIPA plate by raising the peak wavelength λ _V of the VIPA plate 13 by 1.2 ° C. further from the control temperature when the VIPA plate 13 matches the grid wavelength λg. The 13 peak wavelengths λ _V can be matched.

At this time, the peak wavelength λ _V of the VIPA plate 13 is shifted to the longer wavelength side by about 19 pm (= Δ = 1.2 × 16) than the grid wavelength λg, but the transmission spectrum shape of the emitted light from the VIPA plate 13 is flattened. Therefore, such a wavelength shift has no practical problem.

  Next, a dispersion compensation device to which the optical module 10 is applied will be described. FIG. 7 is a diagram showing the configuration of the dispersion compensation apparatus. The dispersion compensation apparatus 20 includes an optical input / output processing unit 21, a cylindrical lens 11 a (front lens), an etalon filter 12, a VIPA plate 13, a condenser lens 22 (back lens), a reflection mirror 23, and a temperature control unit 15. . In addition, the same code | symbol is attached | subjected to the component mentioned above, and description of those structures is abbreviate | omitted. Further, since the flattening control of the transmission spectrum shape of the VIPA plate 13 has been described above, the dispersion compensation operation will be described here.

  The optical input / output processing unit 21 separates optical paths so that input input light and output light after being internally processed (output light returned from the VIPA plate 13 after dispersion compensation) do not overlap. . In other words, the input light until reaching the VIPA plate 13 and the output light returned from the VIPA plate 13 are separated so as not to overlap.

  Specifically, the optical input / output processing unit 21 includes a circulator 21a and a collimator lens 21b. The circulator 21a has three ports P1 to P3. Light input from the port P1 is output from the port P2, and light input from the port P2 is output from the port P3.

  The light input to the port P1 of the circulator 21a is output from the port P2 and input to the optical fiber F. The light output from the optical fiber F becomes parallel light by the collimating lens 21b and travels toward the cylindrical lens 11a.

  The cylindrical lens 11 a condenses the light (input light) output from the light input / output processing unit 21 and enters the etalon filter 12, and the emitted light from the etalon filter 12 enters the window 13 c of the VIPA plate 13. To do.

  The diffracted light emitted after multiple reflection inside the VIPA plate 13 is condensed on the reflection mirror 23 by the condenser lens 22. The reflection mirror 23 reflects the outgoing light emitted from the transmission surface 13b and generates return light. The reflected return light reaches a predetermined portion of the transmission surface 13b necessary for providing a delay time difference for each wavelength via the condenser lens 22.

  The reflection mirror 23 is a 3D (3 Dimensional) mirror. For example, the 3D mirror 23 has a shape such that the shape in the y-axis direction continuously changes from concave to convex along the x-axis direction.

  Therefore, since the mirror inclination at the condensing position on the mirror surface (position in the y-axis direction) is different for each light wavelength, the reflection direction can be made different for each wavelength, and the optical path length is made different for each light wavelength. It is possible to make a difference in the incident time of the return light to the transmission surface 13b. Moreover, the optical path length difference (time difference) between wavelengths can be changed by adjusting the installation position of the 3D mirror 23 in the x-axis direction. Thus, by driving the 3D mirror 23, the amount of chromatic dispersion can be changed appropriately.

  The light that is multiple-reflected inside the VIPA plate 13 and emitted from the window 13c is dispersion-compensated by the control described above with reference to FIGS. 13 and 14, and the cylindrical lens 11a collimates the light after dispersion compensation (output light). The light is input to the collimating lens 21b. The collimating lens 21b collects parallel light and inputs it to the optical fiber F. The output light from the optical fiber F is input to the port P2 of the circulator, dropped to the port P3, and transmitted to the output path side.

  As described above, the etalon filter 12 made of a material having a larger wavelength temperature coefficient (a wavelength shift amount per unit temperature change) than the substrate material of the VIPA plate 13 is attached to the reflective surface 13 a side of the VIPA plate 13. By controlling the temperature of the VIPA plate 13 and the etalon filter 12 at the same temperature, the wavelength of the etalon filter 12 can be adjusted to a desired wavelength within the allowable range of the transmitted light wavelength shift of the VIPA plate 13. The transmission spectrum characteristics of the VIPA plate 13 can be flattened.

10 optical module 11 lens 12 optical filter (etalon filter)
13 Optical parts (VIPA plate)
13-1, 13-2 Reflective film 13a Reflective surface 13b Transmitted surface 13c Window 14 Adhesive 15 Temperature controller

Claims (8)

In an optical module that performs wavelength demultiplexing,
An optical filter having wavelength-periodic transmission characteristics;
A reflection surface that highly reflects light and a transmission surface that has a lower reflectance than the reflection surface, and multiple reflections of light emitted from the optical filter in an internal region sandwiched between the reflection surface and the transmission surface An optical component that emits light diffracted through the transmission surface;
A temperature control unit for controlling the temperature of the optical filter and the optical component;
With
The temperature control unit applies the same control temperature to the optical filter and the optical component, thereby flattening a transmission spectrum shape of light emitted from the transmission surface.
An optical module characterized by that. The temperature controller is
Applying the control temperature, changing the optical path length of the optical filter and the optical path length of the optical component, shift the respective transmission wavelength,
By matching a peak wavelength that is a wavelength located at the peak of the transmission spectrum shape of the optical component with a bottom wavelength that is a wavelength located at the bottom of the transmission spectrum shape of the optical filter, the transmission spectrum shape of the emitted light is Flatten,
The optical module according to claim 1.   The wavelength temperature coefficient of the material of the optical filter is larger than the wavelength temperature coefficient of the material of the optical component with respect to a wavelength temperature coefficient indicating a wavelength change amount per single temperature change. 2. The optical module according to 2. The temperature controller is
Applying the control temperature so that the peak wavelength matches the signal light wavelength;
When the control temperature is applied together with the optical component and the optical filter, and the difference between the peak wavelength and the bottom wavelength is dλ when the peak wavelength and the signal light wavelength coincide with each other,
The wavelength temperature coefficient of the material of the optical component is α _V , the wavelength temperature coefficient of the material of the optical filter is α _E (α _E > α _V ), the control temperature change amount is ΔT, and the control temperature change amount ΔT is applied. When the amount of change in the peak wavelength is Δλ _V , and the amount of change in the bottom wavelength when the control temperature change amount ΔT is applied is Δλ _E ,
Δλ _E = Δλ _V + dλ
ΔT = Δλ _E / α _E = Δλ _V / α _V
4. The optical module according to claim 3, wherein a control temperature change amount ΔT is obtained from the control temperature, and the currently applied control temperature is changed by ΔT. In a dispersion compensation device that compensates for chromatic dispersion of light,
A light input / output processing unit that separates an optical path between input light that has been input and output light that has been internally processed;
An optical filter having wavelength-periodic transmission characteristics;
An optical component provided with a reflective surface that highly reflects light and a transmissive surface having a lower reflectance than the reflective surface, and a window through which light is input and output is provided on the reflective surface side;
A movable reflection mirror that reflects the emitted light emitted from the transmission surface, generates return light, and reaches the predetermined position of the transmission surface again;
A pre-stage lens that is disposed between the light input / output processing unit and the optical filter and condenses the input light to enter the optical filter;
A rear-stage lens that is disposed between the optical component and the reflection mirror and condenses the emitted light on the reflection mirror;
A temperature control unit for controlling the temperature of the optical filter and the optical component;
With
The optical component causes the light beam emitted from the optical filter and incident on the window to be diffracted through the transmission surface by multiple reflection in an internal region sandwiched between the reflection surface and the transmission surface. The reflected light is emitted, and the return light that has reached the transmission surface is subjected to multiple reflection in the internal region, and dispersion-compensated light is emitted from the window as the output light,
The temperature control unit applies the same control temperature to the optical filter and the optical component, thereby flattening a transmission spectrum shape of light emitted from the transmission surface.
A dispersion compensator characterized by that. The temperature controller is
Applying the control temperature, changing the optical path length of the optical filter and the optical path length of the optical component, shift the respective transmission wavelength,
By matching a peak wavelength that is a wavelength located at the peak of the transmission spectrum shape of the optical component with a bottom wavelength that is a wavelength located at the bottom of the transmission spectrum shape of the optical filter, the transmission spectrum shape of the emitted light is Flatten,
The dispersion compensator according to claim 5.   The wavelength temperature coefficient of the material of the optical filter is larger than the wavelength temperature coefficient of the material of the optical component with respect to a wavelength temperature coefficient indicating a wavelength change amount per single temperature change. 6. The dispersion compensator according to 6. The temperature controller is
Applying the control temperature so that the peak wavelength matches the signal light wavelength;
When the control temperature is applied together with the optical component and the optical filter, and the difference between the peak wavelength and the bottom wavelength is dλ when the peak wavelength and the signal light wavelength coincide with each other,
The wavelength temperature coefficient of the material of the optical component is α _V , the wavelength temperature coefficient of the material of the optical filter is α _E (α _E > α _V ), the control temperature change amount is ΔT, and the control temperature change amount ΔT is applied. When the amount of change in the peak wavelength is Δλ _V , and the amount of change in the bottom wavelength when the control temperature change amount ΔT is applied is Δλ _E ,
Δλ _E = Δλ _V + dλ
ΔT = Δλ _E / α _E = Δλ _V / α _V
8. The dispersion compensation apparatus according to claim 7, wherein a control temperature change amount ΔT is obtained from the control temperature, and the currently applied control temperature is changed by ΔT.

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