JP2012173404A - Optical component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress connection loss caused by a change of temperature, in an optical component in which waveguide-type optical elements are butt connected, optimized to miniaturize a whole module, respectively having a plurality of optical waveguides, and having a different thermal expansion coefficient.SOLUTION: In an optical component, a first waveguide-type optical element 410 of a PLC or the like, and a second waveguide-type optical element 420 of a LN waveguide or the like are butt connected, and each waveguide-type optical element 410, 420 has a different thermal expansion coefficient. At reference temperature which is not room temperature, and more preferably at approximately middle temperature of a predetermined temperature range, adjustment is performed to align a position of a plurality of optical waveguides 411, 412 of the first waveguide-type optical element 410, and of a plurality of optical waveguides 421, 422 of the second waveguide-type optical element 420 to make them coincident.

Description

  The present invention relates to an optical component, and more particularly, to an optical component including a plurality of waveguide type optical elements.

There is a demand for an increase in communication traffic volume via the Internet and the like. Therefore, in a wavelength division multiplexing (WDM) system, an increase in transmission speed per channel and an increase in the number of wavelengths are required. Specifically, high transmission rates such as 40 Gbit / s and 100 Gbit / s are required for transmission in the WDM system. However, if the modulation symbol rate is increased for higher speed, there is a problem that the dispersion tolerance is rapidly deteriorated and the transmission distance is reduced. In addition, since the spread of the signal spectrum is increased, there is a problem that a filter band and a channel interval in wavelength division multiplexing (WDM) transmission must be increased. Thus, there is an increasing need for multilevel technology and multiplexing technology that increases the bit rate without increasing the symbol rate.

  Against this background, 40 Gbit / s or 100 Gbit / s ultra high speed transmission is actually realized or proposed per channel. As an example of such a multilevel modulator, an LN optical modulator in which an optical waveguide is formed on a lithium niobate (LN: LiNbO3) substrate using titanium (Ti) diffusion is promising. For example, DQPSK modulation for 40 Gbit / s And a 100 Gbit / s polarization multiplexed QPSK modulator are being developed.

  This LN modulator is an important optical component of an optical communication system, and its reliability is required to be improved. For high reliability, mounting technology that hermetically seals the LN modulator in a casing (package) has a great influence, and research is being advanced.

On the other hand, as shown in FIG. 6, a conventional example in which a modulator is configured by combining an LN substrate and a quartz lightwave circuit (PLC) composed mainly of SiO ₂ glass on a Si substrate is also reported. (See Patent Documents 1 and 2). In FIG. 6, the LN substrate 220 is used only for the phase shifter, and quartz-based PLCs 210 and 230 are used for the optical waveguide for routing. For this reason, the characteristics of the passive circuit with excellent PLC can be utilized while maintaining the excellent characteristics of the LN optical waveguide. For example, it is possible to reduce the size of the entire circuit or reduce the entire insertion loss.

  FIG. 7 is a perspective view of a conventional example in which a modulator is configured by combining an LN substrate and a quartz-based PLC. The modulator 300 includes an optical fiber 301 on the input side of an optical signal, a quartz PLC 302 having a two-stage Y branch, an LN substrate 303 having a plurality of phase shifters, and a two-stage coupler. It is composed of a quartz-based PLC 304 and an optical fiber 305 on the optical signal output side. These substrates can be connected by a UV adhesive after aligning the respective optical waveguides.

  We have already established mass productivity and reliability for the connection between PLC and optical fiber block, and such a connection technology between substrates is easily possible because the structure is similar to the above connection. I expect. The lightwave circuit on the PLC and LN substrate can use the ones with close mode field diameter values between the optical waveguides, and even if the shape of the LN optical waveguide is horizontally long, for example, the spot size conversion function is configured by the PLC. It has already been shown that connection can be made with low connection loss. In addition, as shown in the figure, the LN substrate and the PLC often have a structure that prevents reflection by connecting the waveguide with the end face inclined.

  In the above polarization multiplexing QPSK modulator, the connection between the PLC and the LN requires the connection of as many as eight optical waveguide arrays, and a technique for integrating them as small as possible is strongly desired.

  Further, as shown in FIG. 1 (corresponding to FIG. 5 of Patent Document 1), the first PLC board 31 and the third PLC board 33 are butt-connected to the second LN board 32 having the LN optical waveguide 34 (butt joint). ) Is also reported as prior art. Here again, PLCs 31 and 33, which have been proven as passive optical waveguides, and LN32, which has a track record of high-speed modulation function using the electro-optic effect, are combined to achieve higher functionality and multi-channels. There is a need for a technology that integrates the connection with a small size.

  In connecting the multi-array optical waveguides as described above, it is advantageous to narrow the array interval in order to optimize the entire module in a small size. In fact, in such a PLC-LN module, the array interval is set to be narrow, for example, several hundred microns or less, and the size of the module can be reduced.

JP 2003-207664 A JP 2003-121806 A

  However, there are problems as described below even in a state where the array interval is narrowly optimized in order to realize such a miniaturization. In the conventional technique, when waveguide type optical elements of different materials are butt-connected, a connection loss of the optical waveguide occurs due to a difference in thermal expansion coefficient. This problem will be described with reference to FIGS.

FIG. 2 is a diagram for explaining a shift in the position of the optical waveguide due to a temperature change. For example, it is assumed that at 25 ° C., the plurality of optical waveguides 211 and 212 of the PLC 210 and the plurality of optical waveguides 221 and 222 of the LN waveguide 220 are aligned and connected so as to coincide with each other. In this case, if there is a positive temperature change, for who LN than Si is large thermal expansion coefficient ^{(PLC: 2.5 × 10 -6 /K,LN:15.4×10} -6 / K) As shown in the lower diagram of FIG. 2, axial deviations δ1 and δ2 occur. When the PLC and the LN waveguide expand and contract so that the centers of the optical waveguides 211 and 212 of the PLC 210 coincide with the centers of the optical waveguides 221 and 222 of the LN waveguide 220 due to temperature changes, the axis deviations δ1 and δ2 The connection loss is also reduced.

  FIG. 3 is a diagram illustrating a calculation result of connection loss in an optical module in which PLCs are butt-connected to both ends of the LN waveguide. The calculation was performed according to the following equation, assuming that the core interval L0 of the optical waveguides 221 and 222 of the LN waveguide 220 at 25 ° C. was 4000 μm and the temperature range was −5 ° C. to + 75 ° C. The axial displacement δ1 = δ2, and the loss η was determined from the overlap of Gaussian beams. The coefficient “2” represents the contribution of loss from both end faces of the LN waveguide 220.

The loss, which was 0 dB at 25 ° C., has increased to a maximum of 0.5 dB at 75 ° C.

  The present invention has been made in view of such problems, and the purpose thereof is to match optical waveguides having different thermal expansion coefficients and opposed to waveguide-type optical elements each having a plurality of optical waveguides. In the optical components that are butt-connected, the increase in connection loss due to temperature change, which remains a problem even when the array interval is narrowly optimized in order to mount the module in a small size, is to be suppressed.

  In order to achieve such an object, according to a first aspect of the present invention, a first waveguide type optical element having a plurality of optical waveguides and a butt connection to the first waveguide type optical element are provided. An optical component comprising a second waveguide type optical element having a plurality of optical waveguides, wherein the first waveguide type optical element and the second waveguide type optical element have different thermal expansion coefficients. The positions of the plurality of optical waveguides of the first waveguide type optical element and the plurality of optical waveguides of the second waveguide type optical element coincide with each other at a reference temperature that is not room temperature. It is characterized by that.

  In addition, according to a second aspect of the present invention, in the first aspect, the reference temperature has a larger value of a difference between an upper limit or a lower limit of a predetermined temperature range between a room temperature and the upper limit or the lower limit. The difference is smaller than the larger value.

  According to a third aspect of the present invention, in the second aspect, the reference temperature is near the center temperature of the predetermined temperature range.

  According to a fourth aspect of the present invention, in the second or third aspect, the predetermined temperature range is −5 ° C. or higher and 75 ° C. or lower.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the first waveguide optical element is a PLC, and the second waveguide optical element is an LN waveguide. It is characterized by being.

  According to the present invention, in a hybrid optical module having waveguide-type optical elements having different thermal expansion coefficients and each having a plurality of optical waveguides, the optical waveguides facing each other at a reference temperature that is not room temperature coincide with each other. Connection loss can be suppressed by connecting to (alignment).

It is a figure which shows the conventional hybrid optical module. It is a figure for demonstrating the shift | offset | difference of the position of the optical waveguide by the temperature change in the conventional hybrid optical module. It is a figure which shows the calculation result of the connection loss in the conventional hybrid optical module by which PLC is butt-connected, respectively at the both ends of a LN waveguide. It is a figure for demonstrating the hybrid optical module by embodiment of this invention. It is a figure which shows the calculation result of the connection loss in the hybrid optical module by embodiment of this invention. It is a figure which shows the conventional hybrid module. It is a figure which shows the conventional hybrid module.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 4 is a view for explaining a hybrid optical module according to an embodiment of the present invention. For example, the first waveguide type optical element 410 such as a PLC and the second waveguide type optical element 420 such as an LN waveguide are connected to each other in the same manner as the conventional structure shown in FIG. However, in the present embodiment, the plurality of optical waveguides 411 and 412 of the first waveguide optical element 410 and the first optical waveguide 410 are arranged at a reference temperature that is not room temperature, more preferably near the center temperature of a predetermined temperature range. The difference is that alignment is performed with the plurality of optical waveguides 421 and 422 of the second waveguide type optical element 420.

  By performing alignment at a reference temperature that is not room temperature, the difference between the maximum temperature (upper limit) or minimum temperature (lower limit) at which the optical module is used and the adjusted temperature is suppressed, and as a result, connection loss is suppressed. can do. More preferably, the vicinity of the center temperature in a predetermined temperature range in which the optical module is used is set as the reference temperature. For example, a predetermined temperature range may be −5 ° C. or higher and 75 ° C. or lower. This temperature range is also specified in OIF (Optical Internetworking Forum) OIF-PMQ-TX-01.0, which is an international standardization promotion organization, and is the standard operating temperature range of modulators.

  Consider a case where the first waveguide type optical element 410 is a PLC and the second waveguide type optical element 420 is an LN waveguide. When the alignment reference temperature is set to 35 ° C. and the optical waveguide interval L1 of the LN waveguide at room temperature 25 ° C. is 4000 μm, the optical waveguide interval of the PLC that minimizes the connection loss is 4000.36 μm at room temperature. By aligning 35 ° C, which is not room temperature, as a reference temperature, a slight loss occurs near 25 ° C, but the maximum value of connection loss in the temperature range of -5 ° C to 75 ° C, for example, can be suppressed to 0.5 dB or less. FIG. 5 shows that this is the case.

  In the present embodiment, specific dimensions of the PLC and the LN waveguide are exemplified, but the same effect can be obtained by aligning at the reference temperature if the waveguide type optical elements of different materials are connected to each other. be able to. As a material for the waveguide type optical element, it can be applied to resin materials such as acrylic, epoxy, polyimide, and silicone, semiconductor materials such as silicon, InP, and GaAs, and dielectric materials such as KTN.

410 First waveguide type optical element 411, 412 Optical waveguide of first waveguide type optical element 410 420 Second waveguide type optical element 421, 422 Optical waveguide of second waveguide type optical element 420

Claims (5)

A first waveguide type optical element having a plurality of optical waveguides;
In an optical component comprising: a second waveguide type optical element having a plurality of optical waveguides connected to the first waveguide type optical element.
The first waveguide type optical element and the second waveguide type optical element are made of materials having different thermal expansion coefficients,
The positions of the plurality of optical waveguides of the first waveguide type optical element and the plurality of optical waveguides of the second waveguide type optical element coincide with each other at a reference temperature that is not room temperature. parts.   The reference temperature is characterized in that a larger value of differences between an upper limit or a lower limit of a predetermined temperature range is smaller than a larger value of differences between room temperature and the upper limit or the lower limit. The optical component according to 1.   The optical component according to claim 2, wherein the reference temperature is near the center temperature of the predetermined temperature range.   The optical component according to claim 2 or 3, wherein the predetermined temperature range is -5 ° C or higher and 75 ° C or lower.   5. The optical component according to claim 1, wherein the first waveguide optical element is a PLC, and the second waveguide optical element is an LN waveguide.

Images