JPH11202263A - Depolarizer and optical transmission/reception module provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an optical transmission/reception module possible to realize miniaturization, price-down and power consumption reduction. SOLUTION: This module is constituted so as to perform bidirectional communications through a one core optical fiber by providing a semiconductor laser element 1 for emitting linearly polarized light as signal light, photodiode(PD) 3 for receiving the signal light, and polarization branching element 11 for bisecting the incident light into orthogonal polarized components. In this case, a Cornu type depolarizer 16 is used as a depolarizer to be used for eliminating sensitivity changes caused by the polarizing characteristics of the PD 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a depolarizer used in an optical communication system for transmitting and receiving by sharing one optical fiber, and an optical transmitting and receiving module provided with the depolarizer.

[0002]

2. Description of the Related Art Optical communication devices have been developed with the increase in capacity and length of trunk systems. Currently, research and development of various transmission systems and devices for optical communication corresponding to them are being promoted for the spread of optical subscriber systems, but in order to promote the optical communication of subscriber systems,
Economicalization of optical communication devices has become a major issue.

In this regard, the optical line terminal (OSU: Opt)
ical Subscriber Unit) and a plurality of subscriber units (ONU: Optical Network)
Unit) and an optical star coupler (SC: Star)
One-to-many communication is performed using an optical coupler (SC).
A PDS (Passive Doub) that enables the construction of an economical system by achieving high reliability using an optical fiber and making one optical fiber both transmit and receive (bidirectional).
le Star) system is proposed by NTT (Nippon Telegraph and Telephone Corporation). FIG. 24 shows the system configuration of this PDS system. The details are described in the document "HP Design Symposium 95'p".
13-1 to 13-22 ", and will be briefly described here.

As shown in FIG. 24, in this PDS system, a TCM that performs two-way communication with one optical fiber is used.
(Time Compression Multipl
e), the OSU converts the signal to each ONU into a TDM (Time Division Multi).
iple), and is further converted into a TCM burst optical signal.

[0005] The converted optical signal is used as a downstream signal by OSU.
And is branched to each ONU by the SC. Conversely, signals transmitted from each ONU to the OSU are transmitted to TCM-TDMA (Time Div) allocated at different times.
The signal is converted into an optical signal, and transmitted to the OSU via the SC and the optical fiber as an upstream signal.

[0006] Both the OSU and the ONU which perform the conversion from electricity to light and the conversion from light to electricity use a common optical transmission / reception module.

As one conventional example of such an optical transmitting and receiving module, there is one described in Japanese Patent Application Laid-Open No. 7-104154 (hereinafter, referred to as a first conventional example). This first
In a conventional optical transmitting / receiving module, a holographic diffraction grating is used for an optical branching element to reduce the size and cost of the optical transmitting / receiving module.

[0008] The configuration and the operation will be described below with reference to FIG. Transmission signal light emitted from the light emitting element 102 mounted on the submount 101 supported by the stem 100 passes through the cover glass 104 attached to the package 103, and is subsequently formed on the emission surface side of the cover glass 104. After being divided into 0th order light and + 1st order light by the holographic diffraction grating 105, the condensing lens 10
6 and only the zero-order light is incident on the end face of the optical fiber 107.

On the other hand, the received signal light emitted from the optical fiber 107 is condensed by the condenser lens 106, then enters the holographic diffraction grating 105, where the 0th-order light and +1
Then, the light is divided into two lights and the next light, and then passes through the cover glass 104, and only the + 1st light enters the light receiving element 108. In addition,
Reference numeral 109 denotes a light receiving element for monitoring a signal light.

However, according to the first conventional example,
Since light use efficiency is low, there is a problem that it is difficult to reduce power consumption. That is, as described above, of the light branched (divided into two) by the holographic diffraction grating 105, only the 0th-order light is used at the time of transmission and only the + 1st-order light is used at the time of reception, so that the light use efficiency is low. Because.

In recent years, notebook personal computers and portable terminals using a battery as a power source have been widely used as terminal devices. However, there is a strong demand for low power consumption. In the first conventional example, since the energy consumption during transmission is particularly large, it is particularly important to suppress the loss.

To solve such a problem, there is an optical transceiver module described in Japanese Patent Application Laid-Open No. 4-156014 (hereinafter referred to as a second conventional example). In the second conventional example, as shown in FIG. 26, a method of reducing energy loss at the time of transmission by using polarization beam splitters 115a and 115b as optical branching elements is adopted.

In this case, if a single mode fiber (SMF) is used as the optical fiber, the received signal becomes unstable because the polarization plane of the received signal light transmitted through the SMF is not constant. In the example, the polarization cancelers 127a and 127b are provided between the SMF and the polarization beam splitters 115a and 115b, and the received signal light is made to have a random polarization to stabilize the received signal.

[0014]

However, the second conventional example has the following problems.

(1) As shown in FIG. 26, in the second conventional example, the optical transmitters 112a and 112b, the polarization beam splitters 115a and 115b, and the optical receivers 111a and 111b are used.
b and the optical elements such as the depolarizers 127a and 127b are connected to each other by optical fibers, and the optical fibers are present between the optical elements, which hinders miniaturization of the entire system.

(2) When an SMF is used as an optical fiber for coupling the optical fiber to each optical element, a troublesome adjustment operation is required because the core diameter is as small as 10 μm. As a result, the number of assembling steps increases, which hinders cost reduction.

(3) The optical fiber is a waveguide type component,
In order to reduce the light incident loss, it is necessary to match the light incident angle and the light collection size to the optical fiber. For example, SMF
In this case, the incident angle of light is NA = 0.1 and the condensing size is 10 μm.
In this case, the coupling efficiency can be maximized, but for that purpose, a lens is required between the optical fiber and each optical element for converting the incident angle and the size of the condensed light. As a result, the number of components of the optical system increases, and the number of assembling steps also increases, which hinders cost reduction.

(4) Misalignment between the optical fiber and each optical element occurs during manufacturing, which causes a decrease in coupling efficiency and a reduction in light use efficiency, which hinders reduction in power consumption.

(5) In the above publication, the depolarizer 127 is used.
The specific structures of a and 127b are not shown, but only that the light passing through the depolarizers 127a and 127b becomes a random polarization.

Here, random polarization means that various polarization (polarization) states such as linear polarization (polarization), circular polarization (polarization), and elliptical polarization (polarization) are uniform temporally and spatially. Means that the polarization state of the light at the position takes a random state at a certain moment. However, at present, an optical element that converts light having a specific polarization state into random polarization has not been developed.

On the other hand, as an optical element which is installed in front of a photodetector having a polarization characteristic and eliminates a change in sensitivity due to the polarization characteristic of the photodetector, a document “O plus E 1991/1” is used.
Moon, P142, "Polarization Characteristics and Depolarizers of Optical Equipment" (hereinafter referred to as reference materials), which is referred to as a depolarizer.

Here, the depolarizers 127a, 127
Although a depolarizer can be used for the purpose of 7b, in order to reduce the size, cost, and power consumption of the optical transmission / reception module, a depolarizer having a specification suitable for it is selected or optimized. The above-mentioned reference materials do not mention this point.

Therefore, even if this depolarizer is applied to the depolarizers 127a and 127b, it is unknown at present whether it is possible to reduce the size, cost and power consumption of the optical transceiver module. .

(6) Polarizing beam splitter 115a, 1
Reference numeral 15b denotes a cube formed by combining two right-angle prisms, and requires oblique polishing on the bonding surface. For this reason, the number of manufacturing steps increases, which hinders cost reduction. If the incident light is not a parallel light beam, the condition of the Brewster angle will not be satisfied, and the polarization splitting characteristics will be degraded.

The present invention has been made in view of the above situation, and from various viewpoints, a depolarizer capable of realizing miniaturization, low cost, and low power consumption, and an optical transmission / reception provided with the depolarizer. The purpose is to provide a module.

[0026]

The depolarizer of the present invention is a depolarizer that is installed in front of a photodetector having a polarization characteristic and is used to eliminate a change in sensitivity due to the polarization characteristic of the photodetector. Thus, the depolarizer is constituted by a cornew type depolarizer, thereby achieving the above object.

The depolarizer of the present invention is a cornew type depolarizer according to claim 1, wherein the plate-like right-rotating material and the left-rotating light have a thickness for rotating the polarization plane of the signal light by 45 degrees. And a bonding material, and the bonding plane is configured to be the optical axis, thereby achieving the above object.

Further, the depolarizer of the present invention is a depolarizer that is installed in front of a photodetector having a polarization characteristic and is used to eliminate a change in sensitivity due to the polarization characteristic of the photodetector, and is a flat polarizer. (2n-1) / 2λ wavelength plate (n is an integer) and a transparent plate having the same optical path length as the (2n-1) / 2λ wavelength plate, and the bonding plane is used as the optical axis of the optical system. Thereby, the above object is achieved.

The optical transmitting / receiving module of the present invention comprises:
An optical transmitter / receiver module for performing bidirectional communication using an optical fiber of a heart, a light emitting element that emits linearly polarized light as signal light, a light receiving element that receives signal light, and a polarization element that divides incident light into two orthogonal polarization components. And a depolarizer according to claim 1 or 2, wherein the signal light from the light emitting element passes through the polarization splitting element without branching, and after passing through the depolarizer, the signal light. Optically coupled to the fiber,
After passing through the depolarizer, the signal light from the optical fiber is split by the polarization splitting element and is incident on the light receiving element, thereby achieving the above object.

Further, the optical transceiver module of the present invention comprises:
An optical transmitter / receiver module for performing bidirectional communication using an optical fiber of a heart, a light emitting element that emits linearly polarized light as signal light, a light receiving element that receives signal light, and a polarization element that divides incident light into two orthogonal polarization components. 4. The depolarizer according to claim 3, further comprising: a branching element; and a depolarizer configured to rotate an optical axis of the (2n-1) / 2λ wave plate by 45 degrees with respect to an optical axis of the polarization branching element. The signal light from the light emitting element passes through the polarization splitting element without branching, passes through the depolarizer, and is optically coupled to the optical fiber, and the signal light from the optical fiber passes through the depolarizer. After passing through, the light is split by the polarization splitting element and is incident on the light receiving element, thereby achieving the above object.

Preferably, a lens is attached to the light incident surface and the light exit surface of the depolarizer.

Preferably, the polarization splitting element is made of a birefringent material.

Preferably, the polarization splitting element is constituted by a polarizing hologram optical element.

Preferably, the light emitting element and the light receiving element are formed on the same semiconductor substrate.

Preferably, the polarization splitting element is attached on the semiconductor substrate.

First, the details of the present invention will be described. The present inventors focused on a depolarizer as a means for solving the problem of the second conventional example, and made a selection as follows.

First, in order to achieve low power consumption, which is one of the specifications required for the optical transceiver module, the depolarizer needs to satisfy the following conditions.

(1) No power is consumed.

(2) High transmittance (light use efficiency).

(3) There is no deterioration of wavefront aberration.

Here, the wavefront aberration refers to an aberration which serves as a guide when the light is narrowed down by a condenser lens. In order to make the light incident on the transmission optical fiber efficiently, for example,
When SMF is used as the optical fiber, it is a necessary item because the light collection size must be 10 μm. In this case, the wavefront aberration of the entire optical system must be suppressed to less than the Marechal criterion (0.07λrms).

In order to reduce the size of the optical transceiver module, the depolarizer needs to be small.

Furthermore, in order to reduce the cost of the optical transceiver module, the depolarizer itself has to have the minimum necessary performance. That is, performance beyond necessity hinders cost reduction of the optical transceiver module.

Here, the minimum necessary performance of the depolarizer itself is that the light intensity of the light split by the polarization splitter and incident on the light receiving element is independent of the incident polarization state.

A depolarizer satisfying the above specifications was selected as follows.

First, in the PDS system, since a semiconductor laser (semiconductor laser element) is used as a light source, a monochromatic light depolarizer is a candidate. P149 of the above reference material
Describes a "monochromatic light depolarizer", in which the following are introduced as depolarizers that obtain temporal uniformity (function by time averaging).

(1) A structure in which a λ / 4 wavelength plate is rotated at a high speed, and a λ / 2 wavelength plate disposed immediately thereafter is rotated at twice the speed of the λ / 4 wavelength plate.

(2) An ADP element having a Pockels effect (linear electro-optic effect) and having a structure in which a sawtooth voltage is applied to the ADP element (FIG. 9 in the reference).

However, since these depolarizers consume power in order to obtain temporal uniformity, they are used as depolarizers of the optical transceiver module of the present invention for the purpose of reducing power consumption. Can not do.

Further, the above-mentioned reference material discloses that as a depolarizer for obtaining spatial uniformity (functioning by averaging the entire area of the incident light beam), the surface of the crystal plate is roughened and its refractive index is close to the average refractive index. An article covered with a transparent liquid (Figure 9 in the reference material) is introduced.

However, in this depolarizer, when a refractive index difference occurs between the crystal plate and the transparent liquid due to a temperature change, a wavefront aberration occurs, and the transmitted light cannot be converged by the condenser lens, and the coupling efficiency to the optical fiber is reduced. For this reason, it cannot be used as a depolarizer of the optical transceiver module of the present invention.

As another example of the depolarizer, for example,
There is a lotion-type depolarizer used in the spectroscopic device described in Japanese Utility Model Laid-Open No. 6-15004. The principle will be described below with reference to FIGS. 27 and 28.

As shown in FIG. 27, this depolarizer has two wedge-shaped (wedge-shaped) optical crystal plates 131 and 132.
And the optical axis of the first crystal plate 131 is in a direction parallel to the Y axis, and the optical axis of the second crystal plate 132 is in a direction parallel to the Z axis.

As shown in FIG. 28, when linearly polarized light oscillating in the direction of 45 degrees is incident on the Y axis, the first crystal plate 131
Then, a phase difference occurs between the two polarization components, and the polarization plane of both polarization components rotates in the second crystal plate 132. Since the crystal plates 131 and 132 are wedge-shaped, the two crystal plates 131 and 132
Since the thickness of the 132 differs for each X coordinate, the incident light spread in the X-axis direction is given a different phase difference and optical rotation angle for each incident point. If the spread of the incident light in the X-axis direction is large,
By averaging outgoing light in all apertures, the light intensity between two orthogonal polarization components can be equally divided into two.

However, in this depolarizer, when an extraordinary ray of the first crystal plate 131 is incident on the second crystal plate 132, it is refracted at the boundary surface, so that the transmittance (light use efficiency) is deteriorated. There are drawbacks. For this reason, it cannot be used as a depolarizer of the optical transceiver module of the present invention for the above-described reason.

From the above examination results, in the depolarizer manufactured by bonding the two wedge-shaped optical crystal plates 131 and 132, the crystal plate 1 is used to prevent refraction at the boundary surface.
It can be seen that the optical axes of 31 and 132 must be parallel to the incident light beam.

It can also be seen that in order to solve such a problem, a depolarizer having no wedge-shaped structure should be searched for.

The former example of the depolarizer includes a cornew type depolarizer, and the latter example of the depolarizer includes a lyo type depolarizer.

FIG. 29 shows a structure of a cornew type depolarizer. The depolarizer is manufactured by bonding a wedge-shaped left quartz plate 141 having a right-handed optical rotation and a wedge-shaped right quartz plate 142 having a left-handed optical rotation.
The optical axes of the right crystal plate 142 and the right crystal plate 142 are both configured to be parallel to the Z axis.

When linearly polarized light enters this polarizer, the first
In the left crystal plate 141, which is a crystal plate of the above, the plane of polarization rotates clockwise,
The polarization plane of the right crystal plate 142, which is the second crystal plate, rotates counterclockwise. Since both quartz plates 141 and 142 are wedge-shaped,
Since the thicknesses of the two quartz plates 141 and 142 are different for each Y coordinate, incident light spreading in the Y-axis direction is given a different optical rotation angle for each incident point.

If the spread of the incident light in the Y-axis direction is appropriate, by averaging the outgoing light over the entire aperture, the light intensity between two orthogonal polarization components can be equally divided into two. This cornew type depolarizer does not consume power, has a high transmittance (does not refract incident light), has no deterioration in wavefront aberration (has a uniform refractive index in an aperture), and is small in size. Therefore, the Cornu type depolarizer can be used as the depolarizer of the optical transceiver module of the present invention.

Next, the principle of operation of the optical transceiver module of the present invention using a cornew type depolarizer at the time of optical transmission will be described with reference to FIG. First, this optical transmission / reception module includes a semiconductor laser element (hereinafter, referred to as an LD) 151 as a light source, a first lens 152, a polarization beam splitter 153, a cornew type depolarizer 154, a second lens 155, an SMF 156, Third
Lens 157 and photodiode (hereinafter, PD
).

In the above configuration, the linearly polarized transmission signal light emitted from the LD 151 is converted into a parallel light beam by the first lens 152 and enters the polarization beam splitter 153.
Here, in this optical system, the positional relationship is adjusted so that the polarization plane of the transmission signal light becomes the P-polarized light of the polarization beam splitter 153. Therefore, the transmission signal light incident on the polarization beam splitter 153 is The light passes through the polarizing beam splitter 153 without being branched (reflected) by the surface.

Next, the transmission signal light is incident on the cornew type depolarizer 154. Here, since a parallel light beam is incident, no refracted light is generated, and the entire amount of light passes through the depolarizer 154 as it is. At this time, there is no optical path difference between the light beams forming the light flux. Therefore, the deterioration of the wavefront aberration is small, and it is easy to satisfy the Marechal criterion in the entire optical system. Accordingly, the transmission signal light is narrowed down to the diffraction limit by the second lens 155, and the SMF which is a low-loss optical fiber is used.
156.

Next, with reference to FIG. 31, the operation principle of the optical transmission / reception module having the above configuration at the time of optical reception will be described. The received signal light emitted from the SMF 156 is converted into a parallel light beam by the second lens 155 and is incident on a cornew type depolarizer 154. The received signal light is linearly polarized light or elliptically polarized light, but its polarization state is not constant depending on the laying state of the SMF 156 and the temperature.

However, when the received signal light passes through the cornew type depolarizer 154, the light intensity between the two orthogonal polarization components can be changed to the equally divided polarization state, so that the next polarization beam splitter 153 Half of the energy is reflected at the interface, and the reflected light is
The light is condensed at 57 and enters the PD 158.

Next, an outline of a lyo-type depolarizer will be described with reference to FIG. The lyo-type depolarizer is configured by laminating two birefringent crystal plates 161 and 162 so as to twist the optical axis by 45 °, and the thickness ratio is set to 1: 2. This thickness ratio is set such that the optical path difference between the ordinary ray and the extraordinary ray is equal to or longer than the coherent length of the light source. In FIG. 32, the crystal plates 161 and 162 are separated from each other, but this is for convenience of explanation, and they are actually manufactured without any gap.

Next, the operation principle of the lyo-type depolarizer will be briefly described. When the linearly polarized light indicated by the reference numeral a enters the first birefringent plate (crystal plate) 161, the incident light is separated into polarized light components of b and c. One of B and C is an ordinary ray and the rest is an extraordinary ray. The optical path difference L when passing through the first birefringent plate (crystal plate) 161 is set to be equal to or longer than the coherent length of the light source. Of course, the amplitude intensities of the polarized light components B and C are different, and are incident on the second birefringent plate 162.

Here, since the first birefringent plate 161 and the second birefringent plate 162 have an optical axis of 45 °, the polarization components B and C are each reduced by half to the second birefringent plate. In 162, the rays are equally distributed to the ordinary rays D, E, extraordinary rays, and G.

Now, assuming that the polarization direction of the ordinary ray is the X axis and the polarization direction of the extraordinary ray is the Y axis, the energy of the ordinary ray whose polarization plane is parallel to the X axis is the sum of d and e. Further, the energy of the extraordinary ray whose polarization plane is parallel to the Y axis is the sum of F and G. Both are naturally equal because they are the sum of equally distributed.

The reason why the sum of the two light energies is obtained is that the difference between the optical path lengths is equal to or longer than the coherent length, and the cross term disappears. Although it has been described that the light intensity between two orthogonally polarized light components can be equally divided into two for arbitrary linearly polarized light, the same applies to elliptically polarized light and circularly polarized light. The second birefringent plate 162 is the first birefringent plate 16
Since the thickness is twice as large as 1, the difference in optical path length is the same for the light of the four polarization planes. These are all longer than the coherent length. The thickness ratio need not be 1: 2, but the optical path difference of the four lights separated in this way must be equal to or longer than the coherent length.

Here, assuming that the light source is an LD, the coherent length is several tens of meters for a normal LD and several hundreds of meters for a DFB laser. Although it is possible to reduce the coherent length to several centimeters by changing to multimode, it is undecided which type of laser should be used for the LD of the PDS system.

For example, an LD having a coherent length of 10 cm
When rutile (TiO ₂ ) is used for the birefringent plate, the refractive index no for ordinary rays is 2.47 and the refractive index ne for extraordinary rays is 2.73 (thickness is 1310 nm). The thickness required for one birefringent plate 161 is 10 /
(2.73-2.47) = 38.5 cm, the thickness required for the second birefringent plate 162 is 38.5 × 2 = 77 cm, and such a birefringent plate is a crystal plate as shown in FIG. 1
It is not practical to manufacture 61,162.

When the polarization maintaining fibers 171 and 172 shown in FIG. 33 are used instead of the crystal plate, the difference in the refractive index is about 0.0003 (0.000262 for Furukawa Electric Co., Ltd., model number SP-13). Therefore, the length of the polarization maintaining fiber 171 corresponding to the first birefringent plate is 334 m, and the length of the polarization maintaining fiber 172 corresponding to the second birefringent plate is 667 m. By design, this type of depolarizer is used in fiber optic gyros and is in mass production.

However, the polarization maintaining fiber 17
Considering the transmission loss of 1,172, the transmittance (light use efficiency) is not good. For example, Furukawa Electric Co., Ltd., model number SP
・ In 13 the transmission loss is 3 dB / km, so the total length is 1
km, this depolarizer has a transmittance of only 50% and cannot be used as a depolarizer of the optical transceiver module of the present invention.

Here, the present inventors have repeated experiments and the like, and as a result, a plate-shaped right-rotating material and a left-rotating material having a thickness for rotating the polarization plane of the signal light by 45 degrees are bonded together. It has been found that if the bonding plane is adjusted to a plane including the optical axis of the optical fiber, a cornew type depolarizer capable of exhibiting the above-described effects can be formed.

FIG. 34 and FIG. 35 show this depolarizer. 34 is a side view of the depolarizer, and FIG.
Is a front view.

This depolarizer is made of the dextrorotatory material 18.
1 and the left-handed optical rotation material 182 are stuck up and down, and the bonding surface 183 is placed on the optical axis of the optical fiber. Therefore, the amount of light passing through the right-handed optical rotation material 181 and the left-handed optical rotation material 182 is the same. Becomes

In this depolarizer, when linearly polarized light enters, the right-rotating material 181 and the left-rotating material 182
Rotate the incident light by 45 ° in opposite directions, so that the equally divided outgoing lights are orthogonal to each other. This means that the light intensity between two orthogonal polarization components can be equally divided into two. Therefore, according to this bonding structure, it functions as a depolarizer.

For example, when quartz is selected as the optical rotation material, since the specific rotation is 4 ° / mm (1.31 μm), the required thickness is 11.25 mm, and it is possible to manufacture.

Next, with reference to FIG. 36, a description will be given of the operation principle of the optical transmission / reception module provided with the depolarizer at the time of optical transmission.

The linearly polarized transmission signal light emitted from the LD 151 is converted into a parallel light beam by the first lens 152 and enters the polarization beam splitter 153. In this optical system, since the positional relationship is adjusted so that the polarization plane of the transmission signal light becomes the P-polarized light of the polarization beam splitter 153, the transmission signal light incident on the polarization beam splitter 153 is branched (reflected) at the boundary surface. ) Without passing through the polarizing beam splitter 153.

Next, the transmission signal light is supplied to the depolarizer 15.
4 ′, a parallel light beam is incident, and the optical path length of the right-rotating material 181 and that of the left-rotating material 182 are set to be the same. And the deterioration of the wavefront aberration is small. Therefore, it is easy to satisfy the Marechal criterion in the entire optical system, and the transmission signal light is
The lens 155 allows the aperture to be reduced to the diffraction limit, and the coupling loss to the SMF 156 can be reduced.

Next, with reference to FIG. 37, the principle of operation of the optical transceiver module having the above-described depolarizer at the time of receiving light will be described.

The received signal light emitted from the SMF 156 is converted into a parallel light beam by the second lens 155, and is incident on the depolarizer 154 '. The received signal light is linearly polarized light or elliptically polarized light, but its polarization state is not constant depending on the laying state of the SMF 156 and the temperature.

However, the received signal light is supplied to the depolarizer 15.
After passing through 4 ′, the light intensity between the two orthogonal polarization components can be changed to the equally divided polarization state, so that the energy of 1 at the next boundary surface of the polarization beam splitter 153 is obtained.
/ 2 is reflected, the reflected light is condensed by the third lens 157, and is incident on the PD 158.

Next, when the light intensity between two orthogonal polarization components can be equally divided into two, the light intensity of the light split by the polarization splitting element, that is, the polarization beam splitter 153, and incident on the PD 158 is changed to the incident polarization. Prove to be state independent.

Now, in the above depolarizer 154 ', the coordinate axis on the depolarizer 154' is set to oxyz as shown in FIG. 38, and the coordinate axis on the polarization beam splitter 153 is set to oXYZ as shown in FIG.

Here, as shown in FIG. 40, it is assumed that the z axis and the z axis overlap, and the x axis is inclined by an angle δ with respect to the x axis. Now, in this optical system, it is assumed that linearly polarized light whose polarization plane is inclined by an angle θ with respect to the x-axis is incident on the depolarizer 154 ′, the electric field intensity is set to 1, and the time term is omitted. The electric field component in the polarizer coordinate system is represented by the following equations (1) to (4).

That is, the electric field components Ex right and Ey right of the light incident on the upper right rotatory material 181 are as follows: Ex right = cos (θ−π / 4) (1) Ey right = sin (θ−π) / 4)... (2)

On the other hand, the electric field components Ex left and Ey left of the light incident on the lower left rotatory material 182 are as follows: Ex left = cos (θ + π / 4) (3) Ey left = sin (θ + π / 4) (4) is represented by

When the above equations (1) to (4) are expressed in a coordinate system on the polarizing beam splitter 153, the following equations (5) to (5) are obtained.
Equation (8) is obtained.

EX right = cos δ · cos (θ−π / 4) + sin δ · sin (θ−π / 4) (5) EY right = −sin δ · cos (θ−π / 4) + cos δ · sin (θ− π / 4)… (6) EX left = cos δ · cos (θ + π / 4) + sin δ · sin (θ + π / 4)… (7) EY left = −sin δ · cos (θ + π / 4) + cos δ · sin (θ + π / 4) (8) Here, since only the X component is reflected at the boundary of the polarization beam splitter 153, the light incident on the PD 158 is EX right + EX left. Since the energy that can be detected by the PD 158 is energy, the square of the electric field is calculated to obtain (E
(X right + EX left) ² is the energy incident on the PD 158.

Now, assuming that the incident light is coherent light, the energy incident on the PD 158 is expressed by the following equation (9).

(EX right + EX left) ² = 1 + cos (2δ−2θ) (9) Accordingly, since the energy incident on the PD 158 depends on θ, the object of the present invention cannot be achieved.

However, the light passing through the right-handed rotatory material 181 and the light passing through the left-handed rotatory material 182 spatially overlap only at the condensing position of the third lens 157.
If D158 is slightly displaced from the above condensing position in the direction of the optical axis of the third lens 157, the energy of the light incident on the PD 158 is not the square of the amplitude sum but is the energy sum. That is, the cross terms disappear.

In the case where the incident light is incoherent light, the light passing through the right-handed rotating material 181 and the light passing through the left-handed rotating material 182 do not interfere with each other even if they are spatially overlapped. Therefore, in either case, EX right ² + EX left ² may be obtained.

Here, EX right ² = {1−sin (2δ−2θ)} / 2 (10) EX left ² = {1 + sin (2δ−2θ)} / 2 (11) ² + EX left ² = 1 and does not depend on δ or θ.

In order to cancel the above-mentioned sin (2δ−2θ) term of EX right ^{2 and} the sin (2δ−2θ) term of EX left ² , the light passing through the right-rotation material 181 and the left rotation The electric field strength of the light passing through the material 182 needs to be the same. This means that the right-rotating material 181 and the left-rotating material 1
An optical fiber, that is,
This means that it is placed on the optical axis of SMF156.

The transmittance is (EX right + EX left) ² /
(EX right + EY right + EX left + EY left) Since ² = 1/2, it is understood that 50% of the incident light energy is incident on the PD 157.

Not depending on the angle δ means that the depolarizer 154 ′ and the polarizing beam splitter 153 need not be adjusted around the Z axis. Also, the angle θ
Does not depend on the PD
157 means no change.

In this example, linearly polarized light is considered.
The same holds true for circularly polarized light and elliptically polarized light, since it holds for any linearly polarized light.

In the above example, the electric field intensity is uniformly set to 1 regardless of the location. However, the electric field intensity (energy) of the light actually emitted from the optical fiber is, as shown in FIG.
The distribution takes a rotationally symmetric distribution with respect to the optical axis of the optical fiber. In addition,
R in FIG. 41 indicates a distance from the optical axis.

Here, assuming that one light beam passes through the right-handed rotatory material 181, a light beam at a target position on the optical axis passes through the left-handed rotatory material 181 and has the same electric field intensity. Therefore, it can be seen that the above proof holds for these two rays.

Since this is true for all the light beams forming the light beam emitted from the optical fiber, the above explanation has been proved. Further, from the above proof, as shown in FIGS. 42 and 43, a rotatory material 191 having a thickness for rotating incident light by 90 ° and a transparent material having the same refractive index and temperature dependency of the refractive index. It can be seen that the configuration formed by 192 also functions as a depolarizer.

The Cornu depolarizer has a complicated proof because the rotation angle varies depending on the position of the light beam.
When a coherent light source is used as in the case of the depolarizer, it is necessary to shift the light receiving element from the focus position of the lens in the lens optical axis direction.

As described above, in the lyo-type depolarizer, the ordinary ray and the extraordinary ray spatially overlap with each other.
Since it cannot be spatially separated, it has to be separated in a topological manner, and there is a problem that the size is increased.

On the other hand, according to the present invention, the PD 15
By shifting 8 from the condensing position of the third lens 157 in the optical axis direction of the lens, the size can be reduced.

The operation of the present invention will be described below.

As described above, in the present invention, a Corneux type depolarizer is used as a depolarizer. When this Corneux type depolarizer is used for an optical transceiver module, the optical transceiver module is used for the above-described reason. Small size, low cost, and low power consumption can be achieved.

The optical transmitting / receiving module of the present invention comprises:
Since the optical transmitting and receiving module transmits and receives signal light by sharing the optical fiber, unlike the second conventional example, the following operation can be achieved.

(1) Since an optical fiber does not need to be used for coupling each optical element, the size of the optical transmitting / receiving module can be reduced.

(2) Since the number of parts can be reduced, the cost can be reduced.

(3) Since the coupling loss is suppressed, the power consumption can be reduced.

As described above, the cornew type depolarizer is obtained by laminating a plate-shaped right-rotating material and a left-rotating material having a thickness to rotate the polarization plane of signal light by 45 degrees.
This can be specifically realized by a configuration in which the bonding plane is adjusted to a plane including the optical axis of the optical fiber.

In particular, according to the configuration in which the birefringent material is used for the polarization splitting element, the polishing step can be omitted as compared with the polarization beam splitter, so that the cost can be reduced. In addition, since it can be used with convergent / divergent light, the light emitting element (L
D) and a light-receiving element (PD). For this reason, the size of the optical transceiver module can be reduced.

Further, according to the configuration in which the polarizing hologram optical element is used as the polarization splitting element, mass productivity can be improved, so that the cost can be reduced accordingly. Also in this case, since convergent / divergent light can be used, it can be arranged near a light emitting element or a light receiving element, and the optical transceiver module can be reduced in size.

Further, according to the configuration in which the light emitting element and the light receiving element are formed on the same semiconductor substrate, the alignment between the light emitting element and the light receiving element becomes unnecessary, and accordingly, the mass productivity of the optical transceiver module is improved. it can.

Further, according to the configuration in which a birefringent plate or a polarizing hologram optical element is bonded to a semiconductor substrate as a polarization splitting element, batch processing can be performed on a wafer-by-wafer basis. It becomes possible.

Here, since the depolarizer does not function unless the incident light is a parallel light beam, lenses are required before and after the depolarizer. However, the depolarizer has the above-described structure in which the lenses are bonded to and integrated with the entrance surface and the exit surface of the depolarizer. According to this, since it is not necessary to adjust the inclination of the lens and the depolarizer, it is possible to reduce the price in this respect as well.

When the light emitting element and the light receiving element are formed on the same semiconductor substrate, and the polarization splitting element is mounted thereon,
Unnecessary space can be eliminated, and downsizing can be achieved. In addition, since batch processing can be performed by a sticking process for each substrate, the cost can be reduced.

Further, the depolarizer to which the present invention is applied is not limited to the above-mentioned cornew type depolarizer, and a (2n-1) / 2λ wave plate (n
Is an integer), a (2n-1) / 2λ wavelength plate and a transparent plate having the same optical path length are attached to each other, and the plane is used as the optical axis of the optical system.
When the optical transmission / reception module is mounted on the optical transmission / reception module in a state where the optical axis of the (n-1) / 2 wavelength plate is rotated by 45 degrees with respect to the optical axis of the polarization splitting element, the above-described optical transmission / reception provided with a cornew type depolarizer It is possible to realize an optical transceiver module having the same operation as the module.

Also, with this depolarizer, the light intensity of the light incident on the light receiving element is independent of the incident polarization state, similarly to the above-mentioned cornew type depolarizer, but the proof and the fact that this depolarizer is mounted The operating principle of the optical transmitting and receiving module described above will be clarified later (Embodiment 6).

According to this depolarizer, unlike the above-mentioned cornew type depolarizer, oblique polishing is not required for the bonding surface, which is advantageous in reducing the cost.

[0125]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIGS. 1 to 7 show Embodiment 1 of the optical transceiver module of the present invention. First, a schematic configuration of the optical transceiver module will be described with reference to FIG. Inside the can package 12, an LD1 as a light source and a PD3 as a light receiving element are hermetically sealed. in addition,
The polarization splitting element 11 is attached to the window of the can package 12, and a lens 13, a cornew type depolarizer 16 and a lens 17 are mounted on the right side thereof. These optical components are housed in a can holder 18 and a receptacle holder 19. A receptacle 20 is held on the right side of the receptacle holder 19.

Next, the procedure for assembling the optical transceiver module will be described. First, the can package 12 is fixed to the can holder 18. This fixing is performed using screws, welding, or an adhesive.

Next, a product in which the lens 13, the depolarizer 16 and the lens 17 are integrated in another process (hereinafter referred to as a lens assembly) is placed in the can holder 18. Subsequently, while the LD 1 mounted on the can package 12 is turned on and the shape of the condensed beam condensed by the lens assembly is detected by an imaging means such as a camera (not shown), the lens assembly is placed in the can holder 18. At the optical axis direction (Fig. 1
(Z direction) to perform the adjustment work. Then, the lens assembly is fixed to the can holder 18 by welding or bonding at a position where the size of the focused beam is minimized.

Next, the can holder 18 on which the can package 12 and the lens assembly are fixed is mounted on the receptacle holder 1 on which the receptacle 20 is screwed, welded or bonded.
9, the can holder 18 is slid in a direction perpendicular to the optical axis direction (XY directions in FIG. 1) while monitoring the light output incident on the plug (optical fiber) 23 (see FIG. 2) inserted into the receptacle 20. To perform adjustment work. Then, the can holder 18 and the receptacle holder 19 are fixed by welding or bonding at a position where the light output is maximized. Through the above assembling steps, the optical transceiver module of the first embodiment is manufactured. The details of the optical transceiver module will be described later.

Next, the first embodiment will be described with reference to FIGS.
The operation of the optical transceiver module will be described. However,
FIG. 2 shows a transmission state in which the optical fiber 23 is inserted into the receptacle 20, and FIG. 3 shows the structure of the can package 12 in an enlarged manner.

The transmission signal light 22 emitted from the LD 1 is
The light is incident on the polarization splitting element 11 while diverging. The polarization splitting element 11 is made of a birefringent material. The optical axis of the polarization splitting element 11 is parallel to the paper surface as shown by the arrow in FIG. An angle of 45 ° (may be other than 45 °) with respect to the axis or the optical axis of the lens assembly).

Since the transmission signal light 22 incident on the polarization splitting element 11 is linearly polarized light (black circles in FIGS. 2 and 3) oscillating in the direction perpendicular to the plane of the drawing, the transmission signal light 22 does not split in the polarization splitting element 11. Pass through. The transmitted light becomes parallel rays by the lens 13 and enters the depolarizer 16.

The light incident on the depolarizer 16 is emitted with the light intensity equally divided between the two orthogonal polarization components according to the principle described above in operation. Since it has no birefringence, it has no effect.

The parallel light beam incident on the lens 17 is incident on the core of the optical fiber 23 in the ferrule 24 held in the sleeve 21 provided inside the receptacle 20 while being converged by the light condensing action of the lens 17. , Optical fiber 2
3. About 4% of the transmission signal light incident on the optical fiber 23 is reflected, and the reflected light travels in the opposite optical path in the reverse direction, is halved by the polarization splitter 11, and about 2% is LD.
It becomes return light returning to 1.

Depending on the communication system (for example, analog transmission), the return light may cause noise to the transmission light.
This problem can be easily solved by the means shown in FIG. 4 or FIG. 4 shows a means in which an AR coat 23 'is applied to the end face of the optical fiber 23, and FIG.
Shows a means in which oblique polishing 23 '' is applied to the end face of the substrate.

As a result of taking such measures, it was confirmed that the above-mentioned return light did not cause any problem in the PDS system.

Next, the operation in the reception state will be described with reference to FIGS. However, FIG.
Reference numeral 3 denotes a reception signal state inserted into the receptacle 20, and FIG.

The received signal light 25 emitted from the optical fiber 23 enters the lens 17 while diverging, is converted into parallel rays by this, and then enters the depolarizer 16.
The light incident on the depolarizer 16 is emitted by equally dividing the light intensity by two between two orthogonal polarization components according to the above-described principle, is incident on the lens 13, becomes convergent light by the condensing action of the lens 13, and becomes polarized light. The light enters the branch element 11. Of the light incident on the polarization splitting element 11, only a component that vibrates in a direction parallel to the paper surface (a short parallel line in FIG. 7 indicates the polarization direction) is split by the polarization splitting element 11. This split light 26 is P
It is incident on D3 and is converted into a received signal current.

Next, details of the above-mentioned optical components constituting the optical transceiver module of Embodiment 1 will be described.

First, the structure of the receptacle 20 is described in detail in the adapter of JIS C5973 “FC04 type single core optical fiber connector”.
The function of the optical fiber 2 inside the ferrule 24 in the plug (described in detail as a plug of JIS C5973 “FC04 type single core optical fiber connector”) is described.
3 is held in a specific position.

Incidentally, the configuration having the receptacle 20 as the optical transmitting / receiving module is called a receptacle type, and the configuration in which the optical fiber 23 directly exits from the optical transmitting / receiving module (corresponding to the first conventional example) is called the pigtail type. I have.
Although the receptacle type is shown in the first embodiment, it goes without saying that a pigtail type can also be manufactured.

The lens 13 is an aspheric lens 15 formed by a glass press as shown in FIG. 1 and the like, and is manufactured by being integrally formed with the metal lens barrel 14 at the time of pressing. In the first embodiment, the aspheric lens is used.
After passing through 1), the wavefront aberration (mainly spherical aberration) is deteriorated, so that the lens must be made aspherical and the aberration must be compensated.

Since the method of manufacturing the depolarizer 16 has been described in terms of operation, the description is omitted here.

As shown in FIG. 1 and the like, the lens 17 is a one-sided, one-sided convex lens, and is manufactured by polishing glass or pressing a glass. If the refractive index of this glass is the same as the refractive index of the depolarizer 16, reflection at the boundary does not occur, which is advantageous in terms of efficiency.

Next, a method of manufacturing a lens assembly will be described. First, prepare LD1 to be used in this process,
The light emitting point is aligned with the focal point of the lens 13. Next, the incident surface of the depolarizer 16 located on the left side in the drawing is brought into contact with the metal barrel 14 of the lens 13. When the parallel light emitted from the depolarizer 16 is observed with a camera having an analyzer, the focus of the camera lens is defocused, and when the analyzer is rotated, the right-handed material and the left-handed light of the depolarizer 16 are rotated. The plane where the materials are bonded can be observed.

The plane is set at 45 ° from the previous position.
When the depolarizer 16 is rotated and adjusted by moving the depolarizer 16 to the metal lens barrel 14 so that the focal point of the camera lens is adjusted to a focus point that appears as a just focus, the optical axis of the lens 13 and the bonding surface of the depolarizer 16 are aligned. be able to. Then, the outer shape of the lens 17 is adjusted to the outer shape of the depolarizer 16 and bonded by a resin adhesive or the like having a refractive index equal to these, thereby completing the lens assembly.

Next, a method of manufacturing the can package 12 will be described with reference to FIG. The stem 29 is composed of an eyelet 5 made of annealed copper and six leads 6 (electrodes) made of Kovar, of which five leads 6 are electrically insulated from the eyelet 5 by glass. It is fixed so that the end face comes out. The other one lead 6 is welded and fixed to the eyelet 5 so as to be able to make an electrical connection.

The eyelet 5 is provided with a convex portion.
The LD 1 is brazed and fixed to the side surface of the projection. A submount 4 made of ceramics is fixed to the upper surface of the convex portion of the eyelet 5 by brazing. Since ceramics cannot be brazed and fixed by nature, a metal film (eg, gold, titanium, platinum, etc.) is formed on the joint surface of the submount 4 by sputtering or the like, and then brazed and fixed.

On the upper surface of the submount 4, a PD 3 and a monitor PD 2 are fixed by brazing. The electrical connection between the semiconductor chip and the leads 6 is made by bonding wires 7
(For example, a gold wire or an aluminum wire). Since the number of semiconductor chips is three and each has two electrodes, six leads 6 are required. The lead 6 welded to the eyelet 5 of the first embodiment also has an action of connecting the can package 12 to an electric ground for electric shielding. In addition, it is better to use an amplifier (not shown) connected after the PD 3 as a semiconductor chip and mount the amplifier in the same can package 12, because it is more resistant to noise. In this case, the number of leads 6 increases or decreases.

The cap 30 comprises a Kovar cylindrical portion and a cover glass 8, and the cover glass 8 is made of a low melting glass 9
Thus, it is manufactured by fixing the opening at the end face of the cylindrical portion so as to be airtight.

Next, the stem 2 on which the semiconductor chip is mounted
The cap 30 is placed on 9 and seam welded them under a nitrogen atmosphere. Subsequently, the polarization splitting element 11 is
Then, the LD 1 is turned on to detect the light that has passed through the polarization splitting element 11, and the polarization splitting element 11 is rotated and adjusted around the optical axis of the LD 1 so that the amount of light is maximized. After the adjustment, the cap 30 and the polarization splitting element 11 are fixed with the adhesive 10, and the can package 12 is manufactured.

Although the LD 1 and the like are hermetically sealed by the can package 12 in the first embodiment, a ceramic package or the like may be used.

(Embodiment 2) FIGS. 8 and 9 show Embodiment 2 of the optical transceiver module of the present invention. The optical transmitting and receiving module of the second embodiment is different from the optical transmitting and receiving module of the first embodiment only in that a lotion prism is used for the polarization splitting element 11. Therefore, portions corresponding to those of the first embodiment are denoted by the same reference numerals and description thereof is omitted, and only different portions will be described below.

FIG. 8 shows the package 12 in the transmission state.
The transmission signal light emitted from the LD 1 is incident on the polarization splitter 11 while diverging. The polarization splitting element 11 includes a first triangular prism 28 made of a birefringent material (for example, quartz or the like) and a translucent material (glass).
A second triangular prism 27 made of is bonded to form a flat plate. The optical axis of the birefringent material 28 is parallel to the plane of the drawing and perpendicular to the optical axis of the optical fiber as indicated by the arrow in the polarization splitting element 11.

Since the transmission signal light incident on the polarization splitting element 11 is linearly polarized light (black circle in FIG. 8) vibrating in the direction perpendicular to the plane of the drawing, it passes through the first triangular prism 28 as an ordinary ray. Here, the refractive index of the second triangular prism 27 is the first
Is set to the same value as the ordinary light refractive index of the triangular prism 28. For this reason, the light incident on the second triangular prism 27 is not refracted at the boundary, but is
7, and propagates in the optical fiber via the same optical path as in the first embodiment.

FIG. 9 shows the can package 12 in the receiving state.
The received signal light emitted from the optical fiber enters the polarization splitter 11 while converging via the same optical path as in the first embodiment. Of the light incident on the polarization splitter 11, only the component that vibrates in the direction parallel to the paper surface (the short parallel line in FIG. 9 indicates the polarization direction) is transmitted to the second triangular prism 27 and the first triangular prism 28. Because of the difference in refraction,
The light is refracted at the boundary, becomes the branched light 26, enters the PD 3, and is converted into a received signal current.

In the third embodiment, the polarization splitting element 1
Although a Lochon-type prism is used for 1, a polarization splitting prism using another crystal such as a Glan-Thompson type can be used.

(Embodiment 3) FIGS. 10 to 13 show Embodiment 3 of the optical transceiver module of the present invention. The optical transceiver module of the third embodiment differs from the optical transceiver module of the first embodiment only in that a polarization hologram optical element is used for the polarization splitting element 11. Therefore, portions corresponding to those of the first embodiment are denoted by the same reference numerals and description thereof is omitted, and only different portions will be described below.

Here, as the polarizing hologram optical element to which the present invention is applied, those shown in FIGS. 10 and 11 are known. The polarizing hologram optical element shown in FIG. 10 uses a fine grating (birefringent grating) 40 of a wavelength or less, and the polarizing hologram optical element shown in FIG. 11 is a birefringent material (proton exchange region) 41. Is used.

These polarizing hologram optical elements are described in the document “O plus E March 1991, P86“ Polarizing hologram optical elements ””, and both polarizing hologram optical elements are parallel to the grating. It has a function of diffracting a linearly polarized light component that vibrates in a direction perpendicular to the grating without diffracting a linearly polarized light component that vibrates in the direction.

Next, the transmission operation and the reception operation of the optical transceiver module according to the third embodiment will be described with reference to FIGS.

FIG. 12 shows a can package 1 in a transmission state.
2, the transmission signal light emitted from the LD 1 is incident on the polarization splitting element 11, that is, the polarization hologram optical element 11, while diverging. The polarizing hologram optical element 11 is formed by forming a groove (lattice groove) 32 on the surface of a base material 31, and the groove 32 has a polarizing property. Groove 3
The direction of 2 is orthogonal to the paper surface.

In this configuration, since the transmission signal light incident on the polarizing hologram optical element 11 is linearly polarized light (black circle in FIG. 12) oscillating in the direction perpendicular to the plane of the drawing, the transmitting signal light is not diffracted by the groove 32 and is not polarized. The light passes through the optical element 11 and propagates in the optical fiber via the same optical path as in the first embodiment.

FIG. 13 shows a can package 1 in a receiving state.
2 is enlarged, and the received signal light emitted from the optical fiber converges via the same optical path as in the first embodiment,
The light enters the polarizing hologram optical element 11. Of the light incident on the polarizing hologram optical element 11, only a component that vibrates in a direction parallel to the paper surface (a short parallel line in FIG. 13 indicates the polarization direction) is diffracted by the groove 32.

The diffracted light becomes odd-order (± 1, ± 3,...) Higher-order diffracted light because the groove shape is rectangular, but the energy is distributed to ± 1st-order light by setting the groove depth. It is possible to The split lights 26 split in two directions are respectively P
The light enters D3, is converted into a current, is converted into a voltage signal by a current / voltage conversion circuit (not shown), and is added to become a reception signal.

As shown in FIGS. 12 and 13, in the optical transmitting / receiving module of the third embodiment, two PDs 3 are provided. These PDs have a U-shape when viewed from the optical axis direction of LD1. Mounted on mount 4.

(Embodiment 4) FIGS. 14 to 16 show an optical transceiver module according to Embodiment 4 of the present invention. In the optical transceiver module of Embodiment 4, the light emitting element LD1 and the light receiving element PD3 are formed on the same semiconductor substrate 33,
The point that the polarization splitting element 11 is mounted on the semiconductor substrate 33 is different from the optical transceiver module of the first embodiment. Therefore, portions corresponding to those of the first embodiment are denoted by the same reference numerals and description thereof is omitted, and only different portions will be described below.

FIG. 14 shows a can package 1 in a transmission state.
2, the transmission signal light emitted from the LD 1 formed on the semiconductor substrate 33 is incident on the polarization splitter 11 while diverging. The polarization splitting element 11 is made of a birefringent material, and its optical axis is parallel to the paper surface as shown by an arrow in the polarization splitting element 11, and is at 45 ° to the optical axis of the optical fiber (other than 45 °). ).

Since the transmission signal light incident on the polarization splitting element 11 is linearly polarized light oscillating in the direction perpendicular to the plane of the drawing, the transmission signal light passes through the polarization splitting element 11 without branching, passes through the same optical path as in the first embodiment, and Propagate inside.

The LD 1 of the fourth embodiment is a polarization control surface emitting laser element, which is described in the document “Optronics 1995 / NO1, P103“ Ultimate and widespread surface emitting laser ””.

FIG. 15 shows a can package 1 in a receiving state.
2 is enlarged, and the received signal light emitted from the optical fiber converges via the same optical path as in the first embodiment,
The light enters the polarization splitter 11. Of the light incident on the polarization splitting element 11, only a component that vibrates in a direction parallel to the paper surface is split by the polarization splitting element 11, becomes a split light 26, enters the PD 3 formed on the semiconductor substrate 33, and receives a received signal current. Is converted to

FIG. 16 shows the semiconductor substrate 33 and the polarization splitting element 11 in an enlarged manner.

(Embodiment 5) FIGS. 17 to 19 show Embodiment 5 of the optical transceiver module of the present invention. In the optical transceiver module of Embodiment 5, the LD1 as the light emitting element and the PD3 as the light receiving element are formed on the same semiconductor substrate 33,
Only the point that the polarization splitting element 11 is mounted on the semiconductor substrate 33 is different from the optical transceiver module of the third embodiment. Therefore, portions corresponding to those of the third embodiment are denoted by the same reference numerals, and description thereof will be omitted, and only different portions will be described below.

FIG. 17 shows a can package 1 in a transmission state.
2, the transmission signal light emitted from the LD 1 formed on the semiconductor substrate 33 is incident on the polarization splitter 11 while diverging. The groove of the polarization splitting element 11, that is, the groove of the polarizing hologram optical element 11 is perpendicular to the paper surface.

Since the transmission signal light incident on the polarizing hologram optical element 11 is linearly polarized light oscillating in the direction perpendicular to the plane of the drawing, it passes through the polarizing hologram optical element 11 without branching, and has the same optical path as in the first embodiment. Through the optical fiber.

The LD1 of the fifth embodiment is different from the LD1 of the fourth embodiment.
The polarization control surface emitting laser device used in the above.

FIG. 18 shows a can package 1 in a receiving state.
2 is enlarged, and the received signal light emitted from the optical fiber converges via the same optical path as in the first embodiment,
The light enters the polarizing hologram optical element 11. Of the light incident on the polarizing hologram optical element 11, only the component oscillating in a direction parallel to the paper is diffracted to form two branched lights 26, and the two PDs 3, P formed on the semiconductor substrate 33.
Each of them enters D3, is converted into a current, is converted into a voltage signal by a current-voltage conversion circuit (not shown), and is added to become a reception signal.

FIG. 19 shows the semiconductor substrate 33 and the polarizing hologram optical element 11 in an enlarged manner.

Next, a method of mounting the semiconductor substrate 33 and the polarization splitter 11 in the fourth and fifth embodiments will be described with reference to FIGS.

First, the semiconductor substrate 33 on which the LD and the PD are mounted and the substrate 34 on which the polarization splitting element is formed are rotated and adjusted, and as shown in FIG. Match. This rotation adjustment can be performed by causing the LD to emit light and adjusting so that the light intensity transmitted through the polarization splitter is maximized. It is also possible to adjust by aligning the markers and the like formed on each substrate.

In the fourth embodiment, a birefringent plate is used as the substrate 34, and in the fifth embodiment, a silicon substrate or the like on which a fine lattice is formed is used.

Next, as shown in FIG. 21, the bonded substrate 35 is cut into a predetermined size by a diamond cutter 36 or the like. After cutting, the polarization splitting element covering the electrode portion of the substrate 35 is removed by mechanical processing or chemical etching, brazed to a can package, wire-bonded between the electrodes, and a cap is welded. Thus, the structure shown in FIG. 14 or FIG. 17 is manufactured.

Although the above steps are performed for each wafer,
It is also possible to perform the process in units of bars (strips) obtained by cutting the wafer. In this case, if the polarization splitting element bar is cut out smaller than the semiconductor substrate bar, the step of removing the polarization splitting element covering the electrode portion of the substrate, which is necessary when the wafer is manufactured on a wafer basis, becomes unnecessary.

(Embodiment 6) Next, another example of a depolarizer to which the present invention is applied and an embodiment 6 of an optical transceiver module provided with this depolarizer will be described.

First, FIGS. 22 and 23 show a depolarizer used in the sixth embodiment. This depolarizer is a plate-like (2n-1) / 2λ wave plate (n is an integer).
0, the (2n-1) / 2λ wavelength plate 50 and the transparent plate 51 having the same optical path length are bonded together. In addition, the bonding plane is used as the optical axis of the optical system, and (2n−
1) The optical axis of the λ / 2 wavelength plate 50 is mounted on the optical transceiver module while being rotated by 45 degrees with respect to the optical axis of the polarization splitter.

The present inventors have found that this configuration makes it possible to form a depolarizer. The reason will be described below.

First, with reference to FIG. 38, FIG. 39 and FIG. 40, it will be proved below that the light intensity of the light split by the polarization splitting element and incident on the PD is independent of the incident polarization state. I do.

As shown in FIGS. 38 to 40, the coordinate axis on the depolarizer is oxyz, the coordinate axis on the polarization splitter is oXYZ, the z axis and the Z axis overlap, and the X axis is only an angle δ with respect to the x axis. Suppose you are leaning.

Now, as shown in FIG. 40, it is assumed that linearly polarized light whose polarization plane is inclined at an angle θ with respect to the x-axis is incident on the depolarizer, the electric field strength is 1, and the time term is cos.
Assuming that (ωt), the electric field component of the light ray in the depolarizer coordinate system is expressed by the following equations (12) to (15).

That is, the light incident on the (2n-1) / 2λ wave plate 50 is expressed as: Exw = cos θ · cos ωt (12) (13) On the other hand, the light incident on the transparent plate 51 is expressed as: ExC = cosθ · cosωt (14) EyC = sinθ · cosωt (15)

When these electric field components are represented by a coordinate system on the polarization splitting element, the light incident on the (2n-1) / 2λ wave plate 50 is expressed as: EXw = cosδ · cosθ · cosωt−sinδ · sinθ · cosωt ( 16) EYw = −sinδ · cosθ · cosωt−cosδ · sinθ · cosωt (17) On the other hand, the light incident on the transparent plate 51 is EXC = cosδ · cosθ · cosωt + sinδ · sinθ · cosωt (18) EYC = − sin δ · cos θ · cos ωt + cos δ · sin θ · cos (ωt) (19)

Reflected at the boundary of the polarization splitting element is X
Since it is only the component, the light incident on the PD is EXw + EX
C. Since the energy that can be detected by the PD is the square of the electric field, (EXw + EXC) ² becomes the energy incident on the PD. Here, assuming that the incident light is coherent light, (EXw + EXC) ² is given by the following (2)
0).

(EXw + EXC) ² = 2 (cosδ · cosθ · cosωt) ² (20) Therefore, the object of the present invention cannot be achieved because the angle θ depends.

However, the light passing through the (2n-1) / 2λ wavelength plate 50 and the light passing through the transparent plate 51 spatially overlap only at the condensing position of the lens. If the light is slightly displaced from the optical position in the direction of the optical axis of the lens, the energy of the light incident on the PD does not become the square of the sum of the amplitudes but becomes the energy sum.

If the incident light is incoherent light, (2
The light passing through the (n-1) / 2λ wavelength plate 50 and the light passing through the transparent plate 51 do not interfere with each other even if they overlap spatially. Therefore, in either case, EXw ² + EXC ² may be obtained.

EXw ² + EXC ² = 2 (cos δ ² · co
Since sθ ² + sin δ ² · sin θ ² ) cos ωt ^2, it is sufficient that δ = 45 ° so as not to depend on the angle θ. Here, ² cos δ · cos θ · si of EXw ²
nδ · sinθ term and ² cosδ · cosθ · of EXC ²
In order for the sin δ · sin θ term to cancel, (2n
-1) The electric field intensity of the light passing through the half-wave plate 50 and the light passing through the transparent plate 51 need to be the same.

This means that the bonding plane of the (2n-1) / 2λ wavelength plate 50 and the transparent plate 51 is placed on the optical axis of the optical fiber.

The transmittance is represented by the following equation (21).

(EXw + EXC) ² / (EXw + EYw + EXC + EYC) ² = 1/2 (21) Therefore, it can be seen that 50% of the incident light energy enters the PD.

Not depending on the angle θ means that the output of the PD does not change even if any linearly polarized light enters. In this example, linearly polarized light is considered. However, the same holds true for any type of linearly polarized light.

Further, in this example, the electric field intensity is uniformly set to 1 irrespective of the location, but the electric field intensity (energy) of the light actually emitted from the optical fiber is, as shown in FIG. Has a rotationally symmetric distribution with respect to the optical axis of.

Here, considering one light beam passing through the (2n-1) / 2λ wavelength plate 50, the light beam at a position symmetrical with the optical axis passes through the transparent plate 51, and the electric field intensity has the same value. Therefore, the above proof holds for these two rays. Since this proof is valid for all the light beams forming the light beam emitted from the optical fiber, the proof has been obtained in the above description.

Next, the transmission operation and the reception operation of the optical transceiver module of the sixth embodiment will be described with reference to FIGS. 36 and 37 described above.

First, as shown in FIG. 36, the linearly polarized transmission signal light emitted from the LD 151 is converted into a parallel light beam by the lens 152 and enters the polarization beam splitter 153. The polarization plane of the transmission signal light is polarized beam splitter 153
Since the positional relationship is adjusted so as to be P-polarized light, the transmission signal light incident on the polarization beam splitter 153 does not branch (reflect) at the boundary surface, and the polarization beam splitter 1
Go through 53. The transmission signal light is then incident on the depolarizer 154 'of the sixth embodiment, since the parallel light is incident and the (2n-1) / 2λ wavelength plate 50 and the transparent plate 51 have the same optical path length. There is no optical path difference between the light beams forming the light beam, and the wavefront aberration is less deteriorated.

Therefore, it is easy to satisfy the Marechal criterion in the entire optical system, the transmission signal light can be reduced to the diffraction limit by the lens, and the coupling loss to the SMF 156 can be reduced.

On the other hand, as shown in FIG.
The received signal light emitted from the SMF 156 is
Is converted into a parallel light beam, and enters the depolarizer 154 ′. The received signal light is linearly polarized light or elliptically polarized light, but its polarization state is not constant depending on the laying state of the SMF 156 and the temperature.

However, as described above, when the received signal light passes through the depolarizer 154 ′ and is reflected at the boundary surface of the next polarization beam splitter 153, half of the energy is reflected regardless of the polarization state. The light is condensed by the lens 157 and enters the PD 158.

The (2n-1) / 2λ wavelength plate 50 as described above can be easily manufactured from a birefringent material, a Fresnel rhombus, a liquid crystal, or the like. For example, assuming that the birefringent material is made of rutile, the refractive index n of the ordinary ray
Since o = 2.47 and the refractive index ne of the extraordinary ray ne = 2.73 (1310 nm in thickness), the thickness of the 1 / 2λ wavelength plate is 1
310 nm / 2 (ne-no) = 2519 nm,
Only a small amount of material is used, and miniaturization is possible.

The thickness of the transparent plate is 2519 × 2.47.
Any material and thickness that satisfies the optical path length of nm may be used, but when the lens is attached to the depolarizer, (2n-1)
The thickness must be equal to that of the / 2λ wavelength plate. For example, if the optical axis of rutile is parallel to the optical axis of the optical system (the optical axis of the optical fiber or the optical axis of the lens) and is made of a transparent plate, the temperature characteristics of the refractive index are the same, so there is no step. However, the characteristics are stable and it is convenient.

(Other Embodiments) In the present invention, it is possible to add the configuration of each of the above embodiments to the configuration of the optical transceiver module of the sixth embodiment, and it is needless to say that the present invention is not limited to the contents of the illustrated embodiment. It is.

[0211]

As described in claim 1 or claim 2, in the present invention, a cornew type depolarizer is used as a depolarizer, and when this cornew type depolarizer is used for an optical transmitting / receiving module, For the reasons described above, downsizing, low cost, and low power consumption of the optical transceiver module can be achieved.

The cornew type depolarizer can be specifically realized by the structure described in claim 2.

The above effects can also be achieved by using the depolarizer according to the third aspect.

Further, the optical transmitting / receiving module according to the fourth or fifth aspect of the present invention is an optical transmitting / receiving module for transmitting and receiving signal light by sharing one optical fiber, and therefore differs from the second conventional example. The following effects can be obtained.

(1) Since it is not necessary to use an optical fiber for coupling each optical element, the size of the optical transceiver module can be reduced.

(2) Since the number of components can be reduced, the cost can be reduced.

(3) Since the coupling loss is suppressed, power consumption can be reduced.

According to the optical transmission / reception module of the present invention, the lens is bonded to the entrance surface and the exit surface of the depolarizer to be integrated.
Since there is no need to adjust the tilt of the lens and depolarizer,
The price can be further reduced.

Further, according to the optical transmission / reception module of the present invention, since a birefringent material is used for the polarization splitting element, the polishing step can be omitted as compared with the polarization beam splitter. The price can be reduced. In addition, since convergent / divergent light can be used, it can be arranged near a light emitting element or a light receiving element, so that the optical transceiver module can be further reduced in size.

According to the optical transmission / reception module of the present invention, since a polarizing hologram optical element is used as the polarization splitting element, mass productivity can be improved.
The price can be further reduced. Also in this case, since convergent / divergent light can be used, it can be disposed near a light emitting element or a light receiving element, and the optical transceiver module can be further reduced in size.

According to the optical transmission / reception module of the ninth aspect, since the light emitting element and the light receiving element are formed on the same semiconductor substrate, there is no need to position the light emitting element and the light receiving element. Accordingly, the mass productivity of the optical transmission and reception module can be improved, so that the cost can be further reduced.

According to the optical transmission / reception module of the tenth aspect, since the polarization splitting element is bonded to the semiconductor substrate, batch processing can be performed on a wafer basis, and the cost can be further reduced. Becomes possible.

Further, in particular, according to the optical transmitting / receiving module according to the fifth aspect, unlike the cornew type depolarizer, oblique polishing is not required, which is advantageous in reducing the cost.

Further, according to the optical transmission / reception module of the present invention, it is not necessary to use an aspherical lens as a lens, so that it is possible to further reduce the cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing Embodiment 1 of an optical transceiver module of the present invention.

FIG. 2 is a sectional view showing a transmission state of the optical transceiver module of the first embodiment.

FIG. 3 is an enlarged sectional view showing a can package of the optical transceiver module of FIG. 2;

FIG. 4 is a sectional view showing a ferrule used in the optical transceiver module of the first embodiment.

FIG. 5 is a sectional view showing another example of the ferrule used in the optical transceiver module of the first embodiment.

FIG. 6 is a sectional view showing a receiving state of the optical transceiver module according to the first embodiment;

FIG. 7 is an enlarged sectional view showing a can package of the optical transceiver module of FIG. 6;

FIG. 8 is an enlarged cross-sectional view showing a can package in a transmission state, showing Embodiment 2 of the optical transceiver module of the present invention.

FIG. 9 is an enlarged cross-sectional view showing a can package in a receiving state, showing Embodiment 2 of the optical transceiver module of the present invention.

FIG. 10 is a diagram showing an example of a polarizing hologram optical element used in Embodiment 3 of the optical transceiver module of the present invention.

FIG. 11 is a diagram showing another example of the polarizing hologram optical element used in the optical transceiver module according to the third embodiment of the present invention.

FIG. 12 is an enlarged cross-sectional view showing a can package in a transmission state, showing Embodiment 3 of the optical transceiver module of the present invention.

FIG. 13 is an enlarged cross-sectional view showing a can package in a receiving state, showing Embodiment 3 of the optical transceiver module of the present invention.

FIG. 14 is an enlarged cross-sectional view showing a can package in a transmission state, showing Embodiment 4 of the optical transceiver module of the present invention.

FIG. 15 is an enlarged sectional view showing a can package in a receiving state, showing Embodiment 4 of the optical transceiver module of the present invention.

FIG. 16 is an enlarged cross-sectional view showing a semiconductor substrate and a polarization splitter according to a fourth embodiment of the present invention.

FIG. 17 is an enlarged cross-sectional view showing a can package in a transmission state, showing Embodiment 5 of the optical transceiver module of the present invention.

FIG. 18 is an enlarged cross-sectional view showing a can package in a receiving state, showing Embodiment 5 of the optical transceiver module of the present invention.

FIG. 19 is an enlarged cross-sectional view showing a semiconductor substrate and a polarization splitter according to a fifth embodiment of the optical transceiver module of the present invention.

FIG. 20 is a process chart showing a mounting method of the semiconductor substrate and the polarization splitter in the fourth and fifth embodiments.

FIG. 21 is a process chart showing a method for mounting a semiconductor substrate and a polarization splitting element in Embodiments 4 and 5.

FIG. 22 is a side view showing a depolarizer used in Embodiment 6 of the optical transceiver module of the present invention.

FIG. 23 is a front view showing a depolarizer used in Embodiment 6 of the optical transceiver module of the present invention.

FIG. 24 is a diagram showing a system configuration of a PDS system.

FIG. 25 is a diagram showing a first conventional example of an optical transceiver module.

FIG. 26 is a diagram showing a second conventional example of an optical transceiver module.

FIG. 27 is a side view of a lotion-type depolarizer.

FIG. 28 is a front view of a lotion-type depolarizer.

FIG. 29 is a perspective view showing a cornew type depolarizer.

FIG. 30 is a schematic diagram for explaining a transmission operation of the optical transceiver module using the Cornew type depolarizer shown in FIG. 29;

FIG. 31 is a schematic diagram for explaining a receiving operation of the optical transmitting and receiving module using the cornew type depolarizer shown in FIG. 29;

FIG. 32 is a perspective view showing a lyo-type depolarizer.

FIG. 33 is a perspective view showing a depolarizer using a polarization plane optical fiber.

FIG. 34 is a side view of the depolarizer of the present invention.

FIG. 35 is a front view of the depolarizer of the present invention.

FIG. 36 is a schematic diagram for explaining the transmission operation of the optical transceiver module of the present invention including the depolarizer shown in FIGS. 34 and 35.

FIG. 37 is a schematic diagram for explaining a receiving operation of the optical transceiver module of the present invention including the depolarizer shown in FIGS. 34 and 35.

FIG. 38 is a diagram showing a depolarizer coordinate system.

FIG. 39 is a view showing a polarization splitter coordinate system.

FIG. 40 is a diagram showing a relationship between a depolarizer coordinate system and a polarization splitter coordinate system.

FIG. 41 is a graph showing an electric field intensity distribution of light emitted from an optical fiber.

FIG. 42 is a side view showing another example of the depolarizer of the present invention.

FIG. 43 is a front view showing another example of the depolarizer of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 LD 2 PD for monitor 3 PD for signal detection 4 Submount 5 Eyelet 6 Lead 7 Bonding wire 8 Cover glass 9 Low melting glass 10 Adhesive 11 Polarization branching element (Polarizing hologram optical element) 12 Package 13 Lens 14 Metal barrel 15 Aspherical lens 16 Cornew type depolarizer 18 Can holder 19 Receptacle holder 20 Receptacle 21 Sleeve 22 Transmission signal light 23 Optical fiber 23 'AR coat 23' 'Oblique polishing 24 Fleur 25 Receive signal light 26 Branch light 27 second triangular prism 28 first triangular prism (birefringent material) 29 stem 30 cap 31 base material 32 groove 33 semiconductor substrate 50 (2n-1) / 2λ wavelength plate 51 transparent plate 151 LD 153 polarizing beam splitter 154, 154 'Depolarizer 156 SMF 181 Right-rotating material 182 Left-rotating material 183 Bonding surface

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/24 H04B 9/00 G

Claims (10)

[Claims] 1. A depolarizer which is installed in front of a photodetector having a polarization characteristic and is used to eliminate a change in sensitivity due to the polarization characteristic of the photodetector, wherein the depolarizer is a cornew type depolarizer. Depolarizer that is composed by. 2. The cornea-type depolarizer according to claim 1, wherein a plate-shaped right-rotating material and a left-rotating material having a thickness for rotating the polarization plane of the signal light by 45 degrees are bonded. A depolarizer configured so that the bonding plane is the optical axis. 3. A depolarizer which is installed in front of a photodetector having a polarization characteristic and is used to eliminate a change in sensitivity due to the polarization characteristic of the photodetector, wherein the depolarizer has a plate shape of (2n-1) / A depolarizer in which a 2λ wavelength plate (n is an integer), a (2n−1) / 2λ wavelength plate, and a transparent plate having the same optical path length are bonded, and the bonding plane is used as an optical axis of an optical system. 4. An optical transceiver module for performing bidirectional communication using a single optical fiber, comprising: a light emitting element that emits linearly polarized light as signal light; a light receiving element that receives signal light; And a depolarizer according to claim 1 or 2, wherein the signal light from the light emitting element passes through the polarization splitter without branching, and passes through the depolarizer. An optical transmitting / receiving module configured to be optically coupled to the optical fiber after passing therethrough, and that the signal light from the optical fiber passes through the depolarizer, is split by the polarization splitting element, and is incident on the light receiving element . 5. An optical transceiver module for performing bidirectional communication using a single optical fiber, comprising: a light emitting element that emits linearly polarized light as signal light; a light receiving element that receives signal light; 4. The depolarizer according to claim 3, wherein the polarization splitting element splits into two components.
1) a depolarizer obtained by rotating the optical axis of the λ / 2 wavelength plate by 45 degrees with respect to the optical axis of the polarization splitting element, and the signal light from the light emitting element is not split off the polarization splitting element. After passing through and passing through the depolarizer, it is optically coupled to the optical fiber.Signal light from the optical fiber passes through the depolarizer, is split by the polarization splitting element, and is incident on the light receiving element. Optical transceiver module configured as described above. 6. The optical transceiver module according to claim 4, wherein a lens is attached to a light incident surface and a light output surface of the depolarizer. 7. The optical transceiver module according to claim 4, wherein said polarization splitting element is made of a birefringent material. 8. The optical transceiver module according to claim 4, wherein said polarization splitting element is constituted by a polarizing hologram optical element. 9. The optical transceiver module according to claim 4, wherein said light emitting element and said light receiving element are formed on the same semiconductor substrate. 10. The optical transceiver module according to claim 9, wherein the polarization splitting element is attached on the semiconductor substrate.