Optical communication device

An optical communication device includes a light source that emits a light beam and an optical fiber having a core and a cladding. The optical fiber has a light entrance face having a core region and a cladding region. The light beam emitted by the light source is converged by a converging lens on the core region and is transmitted through the optical fiber. The entrance face is configured to generate a light intensity distribution in light reflected by the light entrance face depending on a position where the light beam is incident on the entrance face, a converging lens arranged between the light source and the optical fiber.

BACKGROUND OF THE INVENTION

The present invention relates to an optical communication device for data communication by transmitting a laser beam, which is modulated in accordance with data to be transmitted, through an optical fiber.

An optical communication device generally includes a laser diode and a converging lens. The laser diode emits a laser beam which is modulated in accordance with data to be transferred. The modulated laser beam is converged by the converging lens on an entrance face of an optical fiber that is connected to the optical communication device. In particular, in the optical communication device known as an ONU (Optical Network Unit), a single optical fiber is used for two-way communication. For this purpose, a light receiving element and a WDM (Wavelength Division Multiplex) filter for separating light having different wavelengths are provided.

In order to efficiently transmit the laser beam through the optical fiber in such an optical communication device, the laser beam should be converged on the center of the core of the entrance face of the optical fiber. This requires very precise positioning of the laser diode and the converging lens against the optical fiber.

An example of a conventional method for positioning the laser diode and the converging lens against the optical fiber is disclosed in Japanese Patent Provisional Publication No. HEI 6-94947. According to the method disclosed in the publication, the light amount of the laser beam passed through the optical fiber is detected at an emerging end. The optical fiber is moved relative to the laser beam until the detected light amount exceeds a predetermined threshold value. When the detected light amount exceeds the predetermined threshold value (preferably, the light amount becomes its maximum value), it is determined that the laser beam emitted from the laser diode impinges on the center of the core of the optical fiber.

However, since it is difficult to visually distinguish the core of the entrance face of the optical fiber from the cladding, the position of the laser diode relative to the optical fiber must be first adjusted by trial and error until the laser beam enters the core of the optical fiber and can be detected on the other end of the optical fiber. This process is troublesome and time consuming.

When the positioning of the laser diode and the converging lens with respect to the optical fiber is achieved, the laser diode and the converging lens are fixed in the optical communication device by an adhesive, for example. However, since the adhesive contracts during a hardening process thereof, the proper alignment of the laser diode, the converging lens, and the optical fiber may be lost due to the contraction of the adhesive, which may worsen the positional relationship of the laser diode and/or the converging lens with respect to the optical fiber. Further, there is also a possibility that the positional relationship of the laser diode and/or the converging lens with respect to the optical fiber may change with time.

In the conventional optical communication device, however, once the laser diode and the converging lens are fixed to the device, it is impossible to re-adjust the positions thereof.

SUMMARY OF THE INVENTION

The present invention is advantageous in that an improved optical communication device that is free from the above defects.

According to an aspect of the invention, there is provided an optical communication device, which includes a light source that emits a light beam and an optical fiber having a core and a cladding. The optical fiber has a light entrance face having a core region and a cladding region. The light beam emitted by the light source is converged by a converging lens on the core region and is transmitted through the optical fiber. The entrance face is configured to generate a light intensity distribution in light reflected by the light entrance face depending on a position where the light beam is incident on the entrance face, a converging lens arranged between the light source and the optical fiber.

The optical communication device further includes a light receiving device, which has a light receiving surface that receives the reflected light that is a reflection of the light beam emitted by the light source and reflected by the entrance face of the optical fiber. The light receiving device outputs a signal corresponding to the light intensity distribution. The optical communication device further includes a beam spot moving structure that is controlled to move the beam spot on the entrance face, and a controller that controls the beam spot moving structure to move the beam spot on the entrance face such that the output signal of the light receiving device corresponds to a reference intensity distribution which is the intensity distribution when the incident position of the light beam is adjusted.

Optionally, the entrance face has a stepped structure in which the core region is formed to be stepped by a predetermined amount with respect to the cladding region. With this stepped structure, the reflected light is diffracted and a diffraction pattern is formed on the light receiving surface of the light receiving device.

According to the embodiments of the invention, a diameter of the beam spot formed on the light entrance face is greater than a diameter of a core region and smaller than a diameter of the cladding region.

Optionally, the light receiving device according to the embodiments is configured to output a signal corresponding to the light intensity distribution in a first direction and another signal corresponding to the light intensity distribution in a second direction that is different from the first direction.

Further optionally, the beam spot moving structure is capable of moving the beam spot on the entrance face of the optical fiber in a third direction and in a fourth direction which is different from the third direction, separately.

In a particular case, the first direction corresponds to the third direction, and the second direction corresponds to the fourth direction.

Alternatively, the first direction is different from each of the third and fourth directions, and the second direction is different from each of the third and fourth directions.

According to embodiments of the invention, the light receiving surface may include a plurality of light receiving areas, each of the light receiving areas being capable of detecting a light amount of light incident thereon. Further, the controller may include a determining system that determines whether the intensity distribution of the light incident on the light receiving surface of the light receiving device equals to the reference intensity distribution in accordance with the light amounts detected by the plurality of light receiving areas.

Optionally, the plurality of light receiving areas may include N×M areas arranged in matrix, where each of N and M is an integer greater than one.

Further optionally, at least one of N and M may be greater than 2, and wherein only four light receiving areas arranged in a 2×2 matrix are used from among the N×M light receiving areas.

In some embodiments, the beam spot moving structure is capable of moving the beam spot on the entrance face of the optical fiber in two different directions, separately, and directions in which the light receiving areas are arranged substantially coincide with the directions where the beam spot moving structure moves the beam spot.

In some embodiments, the beam spot moving structure is capable of moving the beam spot on the entrance face of the optical fiber in two different directions, separately, and directions in which the light receiving areas are arranged are different from the directions where the beam spot moving structure moves the beam spot.

In a particular case, the core region is protruded toward the light source with respect to the cladding region.

Optionally, the core region is protruded with respect to the cladding region by an amount less than λ/(4n), where λ is a wavelength of the light beam emitted by the light source and n is a refractive index of medium in which the light beam proceeds.

In a particular case, the core region is protruded with respect to the cladding region by an amount substantially equal to λ/(8n).

In some embodiments, the core region is parallel with the cladding region.

In some embodiments, the entrance face is substantially perpendicular to the optical axis of the optical communication device.

Alternatively, the entrance face is inclined with respect to a plane perpendicular to the optical axis of the optical communication device.

Optionally, the optical communication device may further include a beam splitter that allows at least a part of the light beam emitted by the light source toward the entrance face, the beam splitter directing at least a part of the reflected light toward the light receiving device.

Since the reflection light is used for adjusting the position of the beam spot on the entrance face of the optical fiber, the controller can control the beam spot moving structure to move the beam spot even when data is being transmitted.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, optical communication devices according to embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1schematically illustrates a configuration of an optical communication device10according to a first embodiment of the invention. The optical communication device10according to the present embodiment can be utilized, for example, as an optical network unit (ONU) that connects a terminal such as a subscriber's computer with an optical fiber network. The optical communication device10is designed with a wavelength division multiplexing (WDM) technology that transports bi-directional signal over a single optical fiber. The optical communication device10utilizes light of which wavelength is 1.3 μm for transmitting data and light of which wavelength is 1.5 μm for receiving data.

As shown inFIG. 1, the optical communication device10is provided with a laser diode LD, a converging lens2, a photo detector4, a controller5and an actuator6.

FIG. 2shows an enlarged side view of a beam incident end portion of the optical fiber3employed in the optical communication device10. As shown inFIG. 2, the optical fiber3has a core31and a cladding32, and the entrance face (i.e., the end face of the portion where the laser beam is incident)3ahas a core region3cand a cladding region3brespectively corresponding to the core31and the cladding32and have a circular shape. According to the embodiment, the core region3cis protruded with respect to a plane of the cladding region3bby an amount of λ/(8n) (where, λ is a wavelength of the laser beam emitted by the laser diode LD, and n is a refractive index of medium where the light proceeds) in a direction perpendicular to the plane of the cladding region3b. Since the light proceeds in the air, n can be considered as one, and thus the protruded amount is λ/8 in this embodiment. The plane of the core region3cand the plane of the cladding region3bare parallel with each other. This stepped structure can be formed with use of photolithography technology.

The laser diode LD emits a laser beam that is modulated in accordance with data to be transmitted through an optical fiber3, which is connected to the optical communication device10.

The converging lens2is placed in the optical path of the laser beam emitted from the laser diode LD, and converges the laser beam on the entrance face3aof the optical fiber3to form a beam spot thereon. A part of the laser beam incident on the entrance face3atransmits through the optical fiber3, while a remaining part of the laser beam is reflected by the entrance face3and enters the photo detector4. It should be noted that, for the sake of illustration, the incident angle of the laser beam with respect to the entrance face3ais exaggerated, and it is preferable that the incident angle is as small as possible, with allowing the reflection light to impinge on the photo detector4.

The converging lens2is configured to be movable in a first direction (X′ direction inFIG. 1) which is perpendicular to the optical axis of the converging lens2and on a plane including the optical axes of the converging lens2and the optical communication device10, and in a second direction (Y′ direction) which is perpendicular to the optical axis of the optical communication device10and perpendicular to the first direction by the actuator6. The controller5controls the actuator6to move the converging lens in accordance with the output of the photo detector4, which will be described in detail later. In accordance with the movement of the converging lens2in the X′ direction and in the Y′ direction, the beam spot moves on the entrance face3ain the X direction and the Y direction, respectively. The X and Y directions are parallel with the entrance face3aand perpendicular to each other.

As shown inFIG. 2, the beam spot formed on the entrance face3ahas a diameter r1slightly larger than a diameter r2of the core region3a. Therefore, when the center of the beam spot coincides with the center of the core region3c, a peripheral portion of the beam spot is incident on the cladding region3b.

With this configuration, when the laser beam is incident on the core region3cand the cladding region3bsimultaneously, a diffraction pattern is formed by the reflected light on the photo detector4. It should be noted that the protruded amount of the core region3cwith respect to the cladding region3bis set to less than λ/(4n), where n is a refractive index of medium. When the medium is air, n is considered to be one. In the present embodiment, the protruded amount is set to λ/8.

Generally, a beam spot size of the laser beam is defined as an area having an intensity greater than 1/e2of the peak intensity thereof (e being a base of natural logarithm). It is preferable that the diffraction pattern is formed with light having a relatively strong intensity. When the beam spot size is large, the diffraction pattern formed on the photo detector4is clear. However, even a portion of a beam having the intensity of 1/e2or lower with respect to the peak intensity, the diffraction pattern is formed on the photo detector4.

When the beam spot formed on the entrance face3ais larger, the pattern formed on the photo detector4becomes clearer, however the coupling efficiency becomes worse. When the beam spot is smaller, the pattern on the photo detector4becomes faint, while the coupling efficiency is improved. In the above embodiment, considering the balance between the diffraction pattern and the coupling efficiency, the diameter of the beam spot on the entrance face3ais slightly greater than the diameter of the core region3c. For example, the diameter of the beam spot is 11 μm and the diameter of the core region3cis 10 μm. The invention is not limited to this configuration, and even through the beam spot size is smaller than the size of the core region3c, the diffraction pattern may be formed on the photo detector4, and thus, the beam spot position on the entrance face3acan be adjusted.

According to the first embodiment, in order to make the laser beam reflected by the entrance face3aof the optical fiber3directly impinge on the photo detector4, the optical communication device10is configured such that the laser beam is incident on the entrance face3aat an incident angle other than 0°.

FIG. 3schematically shows a front view of the photo detector4. The photo detector4has a light receiving surface4a. The light receiving surface4ais divided into four light receiving areas A, B, C and D, which are divided by first and second boundary lines4band4c, crossing at a center O of the light receiving area4a. The directions in which the first and second boundary lines4band4cdivide the light receiving area (i.e., the directions in which4cand4bextend) will be referred to as an X″ direction and a Y″ direction, respectively.

In the first embodiment, the photo detector4is arranged such that, when the converging lens2is moved in the X′ direction and the beam spot shifts on the entrance face3ain the X direction, the intensity distribution on the light receiving area4achanges in the X″ direction, and when the converging lens2is moved in the Y′ direction and the beam spot shifts on the entrance face3ain the Y direction, the intensity distribution on the light receiving area4achanges in the Y″ direction. Each of the light receiving areas A, B, C and D, outputs a voltage corresponding to the received amount of light, which is input to the controller5. InFIG. 3, a circle drawn with broken lines represents an outline of the beam spot formed by the reflected light.

In this specification, directions are defined with reference to the X and Y directions in which the beam spot formed on the entrance face3amoves. InFIG. 1, when the entrance face3aof the optical fiber3is viewed from the laser diode LD side, the left-hand direction is defined as a positive X direction (indicated as X(+)), the right-hand direction is defined as a negative X direction (indicated as X(−)), an upper direction is a positive Y direction (indicated as Y(+)), and a lower direction is a negative Y direction (indicated as Y(−)).

According to the embodiment, a diffraction pattern is formed on the photo detector4. The intensity distribution across the diffraction pattern varies depending on a position of a beam spot on the entrance face3aof the optical fiber3. Specifically, based on the intensity distribution in the X direction, displacement of the beam spot on the entrance face3ain the X direction can be known, and based on the intensity distribution in the Y direction, displacement of the beam spot on the entrance face3ain the Y direction can be known. If the intensity distributions in X and Y directions when the center of the beam spot coincide with the center of the core31are known in advance, by moving the beam spot so that the intensity distributions in the X and Y directions coincide with the known distributions, the position of the beam spot can be adjusted.

FIGS. 4A–4Cshows a relationship between positions (in the X direction) on which a beam is incident on the entrance face3aof the optical fiber and intensity distribution of reflected beams on the light receiving area4aof the photo detector4(in the X″ direction).

It is assumed that when the beam spot is incident on the entrance face3aof the optical fiber3such that the center of the beam spot coincides with the center of the core region3c, the intensity distribution is substantially symmetrical with respect to the center O of the photo detector4as shown inFIG. 4B. The intensity distribution when the center of the beam spot coincides with the center of the core region3cwill be referred to as a reference distribution.

When the beam spot incident on the entrance face3aof the optical fiber3is shifted in X(−) direction, the intensity distribution of the diffraction pattern deforms as shown inFIG. 4A. When the beam spot incident on the entrance face3aof the optical fiber3is shifted in X(+) direction, the intensity distribution of the diffraction pattern deforms as shown inFIG. 4C. When the intensity distribution has the form as shown inFIG. 4AorFIG. 4C, by shifting the beam spot incident on the entrance face3aof the optical fiber3so that the intensity distribution coincides with the reference distribution, the center of the beam spot coincides with the center of the core region3c.

According to the embodiment, the position of the beam spot on the entrance face3aof the optical fiber3is controlled by making use of the above relationship of the position of the beam spot on the entrance face and the intensity distribution of the diffraction pattern on the light receiving area4aof the photo detector4.

Practically, the control of the position of the beam spot is performed as follows. As described above, the photo detector4has four light receiving areas A, B, C and D (seeFIG. 3), each detects the amount of light incident thereon. An integration value of the intensity distribution is considered to be an amount of light.

In the example shown inFIGS. 4A–4C, whether the intensity distribution coincides with the reference distribution can be determined by comparing the amount of light detected by the X″ (−) side light receiving areas B and C with the amount of light detected by the X″(+) side light receiving areas A and D. That is, if the amount of light detected by the X″(−) side light receiving areas B and C is greater than the amount of light detected by the X″ (+) side light receiving area A and D, it is considered that the beam spot is displaced on the X(−) side as shown inFIG. 4A.

If the amount of light detected by the X″(−) side light receiving areas B and C is smaller than the amount of light detected by the X″ (+) side light receiving area A and D, it is considered that the beam spot is displaced on the X(+) side as shown inFIG. 4C. Generally, from a difference between the light amounts detected by the X″ (−) side sensors and the light amounts detected by the X″(+) side sensors, whether the beam spot is shifted on the X(−) side or the X(+) side is known.FIG. 5is a graph showing a relationship of the difference between the light amounts detected by the X″(−) side sensors and detected by the X″(+) sensors and the shifting amount of the beam spot in the X direction.

A similar discussion applies with respect to the relationship of the beam spot position in the Y direction.FIG. 6is a chart showing the shift of the beam spot on the entrance face3aof the optical fiber3in the X and the Y directions, and the corresponding intensity distributions on light receiving surface4aof the photo detector4and outputs of the light receiving areas to be compared.

For example, in a case of the lower-right cell ofFIG. 6, the graphs (curves) show that the beam spot is displaced on the X(+) side and on the Y(−) side as indicated in the upper-right title cell and in the lower-left title cell. This judgment is made by comparing the outputs of the light receiving areas (B+C) with the outputs of the light receiving areas (A+D) for the shift in the X direction, and by comparing the outputs of the light receiving areas (A+B) with the outputs of the light receiving areas (C+D) for the shift in the Y direction. Please note that, for the sake of brevity, the value representing the detected light amount is denoted by the name of the light receiving area (e.g., the value detected by the light receiving area A is also represented as “A”).

In the example shown inFIG. 6, when the center of the beam spot coincides with the center of the core region3c, the intensity distributions on the X″(−) side and on the X″(+) side are the same, and the intensity distributions on the Y″ (−) side and on the Y″(+) side are the same. Therefore, B+C=A+D, and A+B=C+D. In other cases, i.e., the comparison results shows some difference between the detected light amounts, the controller5controls the actuator6so that the difference becomes zero.

It should be noted that, since the reflected light is used for adjusting the position of the beam spot on the entrance face3aof the optical fiber3, the controller5repeatedly or continuously executes the above-described position adjusting procedure even when the optical data is being transmitted.

In the above-described embodiment, the X direction is perpendicular to the Y direction. The photo detector4is arranged such that the differences between the light amounts corresponding to the intensity distributions in the X direction and in the Y direction are output (the boundary lines4band4ctend in Y and X directions, respectively). Then, the controller5controls the actuator6to move the converging lens2in the X direction and Y direction.

The invention need not be limited to the above structure. The X and Y directions may form another angle other than 90 degrees. The boundary lines4band4cneed not be perpendicular to each other. Further, the orientation of the boundary lines4band4cmay different from the X and Y directions.

FIG. 7shows an alternative arrangement of the photo detector4. The photo detector4is oriented such that the Y″ and X″ directions (i.e., the boundary lines4band4c) are rotated clockwise by 45 degrees at the center thereof. When the photo detector4is oriented in this way, the outputs A and C are compared to examine the intensity distributions for adjusting the position of the beam spot in the X direction, and the outputs B and D are compared to examine the intensity distributions for adjusting the position of the beam spot in the Y direction.

FIG. 8shows an optical communication device11according to a second embodiment. In the optical communication device11, an optical fiber3′ is used, which is configured such that the entrance face is inclined with respect to the central axis of the optical fiber3′. Specifically, the laser diode LD, the converging lens2and the optical fiber3′ are arranged so that the chief ray of the beam incident on the core of the optical fiber3′ proceeds substantially along the central axis of the optical fiber3′. With this arrangement, a coupling efficiency between the laser diode LD and the converging lens2with respect to the optical fiber3is improved.

FIG. 9shows an optical communication device12according to a third embodiment. In this embodiment, the laser diode LD, the converging lens2and the optical fiber3have a common optical axis (when the laser beam is incident on the core of the optical fiber3). With this configuration, the light reflected on the entrance face3aof the optical fiber returns the same optical path of the incident beam.

For directing the reflected light toward the photo detector4, a deflector having a polarization beam splitter8and λ/4 plate7is inserted between the entrance face3aof the optical fiber3and the converging lens2. Generally, the laser beam emitted by the laser diode is linearly polarized. An axis of polarization of the polarization beam splitter8is adjusted so that the beam emitted by the laser diode LD passes through the polarization beam splitter8. Since the λ/4 plate7is provided on the optical fiber side of the polarization beam splitter8, the beam passed through the deflector is incident on the entrance face3aof the optical fiber as a circular polarized beam. The reflected beam then passes through the λ/4 plate7again and enters the polarization beam splitter8as the linearly polarized beam. It should be noted that the axis of the polarization of the beam reflected by the entrance face3aand passed through the λ/4 plate7is perpendicular to the axis of the polarization emitted by the laser diode LD, and thus the reflected beam is deflected by the polarization beam splitter8toward the photo detector4.

Detection of the light amounts corresponding to the intensity distributions and adjustment of the incident position of the beam on the entrance face3ais similar to the above-described embodiments.

FIG. 10shows an optical communication device13according to a fourth embodiment. The optical communication device13is similar to the optical communication device12except that the deflector (i.e., the polarization beam splitter8and the λ/4 plate7) is arranged between the laser diode LD and the converging lens2. Due to this arrangement, the laser beam reflected on the entrance face3aof the optical fiber3passes through the converging lens2, and is once converged and then incident on the photo detector4as a diverging beam to project the diffraction pattern.

FIG. 11shows an optical communication device14according to a fifth embodiment. In the optical communication device14, a collimating lens9is employed. The laser beam emitted by the laser diode LD is collimated by the collimating lens9, and then converged by the converging lens2on the entrance face3aof the optical fiber3. In this embodiment, the deflector including the polarization beam splitter8and the λ/4 plate7is arranged between the collimating lens9and the converging lens2. Except for the above differences, the configuration of the optical communication device14is similar to the configuration of the third or fourth embodiment. It should be noted that the collimating lens9is sometimes provided integrally with the laser diode LD, and in such a case, the configuration of the fifth embodiment is particularly applicable. It should be noted that, similar to the third or forth embodiment, the deflector may be arranged between the laser diode LD and the collimating lens9, or between the converging lens2and the optical fiber3.

In the above-described embodiments, it is assumed that when the center of the beam spot on the entrance face3acoincides with the center of the core region3c, the intensity distribution of the diffraction pattern formed by the reflected light exhibits a symmetrical distribution both in the X″ direction and in the Y″ direction (or the directions where the intensity distribution changes as the converging lens2moves) with respect to the center O of the photo detector4(seeFIGS. 3 and 4B).

In practice, due to individual differences, the intensity distribution may deviate from the state shown inFIG. 4B. Further, due to variation over time, the intensity distribution may also deviate. In such a case, for example, even if a difference between (B+C) and (A+D) is zero, the center of the beam spot may not coincide with the center of the core region3c.

The above problem can be overcome by increasing or decreasing the outputs of the light receiving areas in accordance with the deviation. For example, in the X″ direction, (B+C) or (A+D) may be increased by a predetermined amount. Practically, this means that the difference between (B+C) and (A+D) equals the predetermined amount. Therefore, in order to deal with the deviation of the intensity distribution as described above, the controller5controls the actuator6so that the difference between the light amount on the positive side (X″(+) or Y″(+) direction) and the light amount of the negative side (X″(−) or Y″(−) direction) becomes the predetermined amount.

In the above-described embodiments, the photo detector4having four light receiving areas A–D is employed. The invention need not be limited to the configuration, and a photo detector having a plurality of light receiving areas may be employed. For example, N×M light receiving areas (each of N and M being an integer greater than one) may be arranged in a matrix (to form a grid pattern). In particular, when N and M are greater than two, even if the center of the diffraction pattern shifts due to individual differences and/or variation over time, appropriate four light receiving areas (arranged in 2×2) a center of which coincides with or is close to the center of the diffraction pattern formed by the reflected light can be selected, and the adjusting the beam position can be performed precisely.

In the above embodiment, the converging lens2is moved to adjust the incident position of the laser beam on the entrance face3aof the optical fiber3. It should be noted that the invention is not limited to such a configuration, and any other suitable measure can be used, which will be described with reference toFIG. 12.

FIG. 12shows an optical communication device15according to a sixth embodiment of the invention. The optical communication device15is similar to the optical communication device10shown inFIG. 1except that the converging lens2is not movable, that an transmission type deflector K is provided on the optical path from the laser diode LD to the entrance face3aof the optical fiber3, and that an actuator6K for driving the deflector K is provided instead of the actuator6.

In the configuration shown inFIG. 12, the deflector K is arranged between the converging lens2and the entrance face3aof the optical fiber3. The deflector K is a single or plurality of optical elements capable of varying the optical path of the laser beam passed therethrough so that a position of the beam spot formed on the entrance face3acan be controlled.

FIG. 13shows a cross sectional view of a variable angle prism20which is used for the transmission type deflector K.

The variable angle prism20has two glass plates21and22, and an accordion-foldable elastic cover23connecting the glass plate21and22. Each of the glass plates21and22has a sufficient size (area) so that the laser beam to be converged on the entrance face3acan pass therethrough. The glass plates21and22and the cover23enclose colorless liquid having a certain refractive index (e.g., Silicon oil). The glass plates21and22are held by glass holders24a,24b,24cand24d.

A distance between the glass holders24band24dis maintained with a plurality of spacers24edisposed therebetween. The glass holder24cis secured to an angle adjusting unit27, while the glass holder24ais movably held by the angle adjusting unit27. Specifically, the glass holder24aengages with a lead screw26of the angle adjusting unit27. The lead screw is can be rotated by the motor25through a gear train. As the motor25is driven to rotate the lead screw26, the glass holder24amoves in the direction of the rotational axis of the lead screw, thereby an angle θ formed between the glass plates21and22on a plane, is parallel with the rotation axis of the lead screw and perpendicular to the surfaces of the glass plates21and22. The plane along which the angel θ is defined will be referred to an axis of the variable angle.

As the deflector K (seeFIG. 12), a pair of variable angle prisms20may be employed with the orientation of the axes of variable angles differentiated from each other. For example, one of the axes of the variable angle is parallel with the X direction and the other parallel with the Y direction. With such a configuration, without moving the converging lens2, and only by changing the angle θ of each variable angle prism20, the beam position on the entrance face3acan be changed arbitrarily. Such a configuration which does not move the converging lens is particularly convenient when the converging lens cannot be moved (e.g., when the converging lens is formed integrally with the laser diode). When the pair of variable angle prisms20are employed, both prisms may be located on the same side (e.g., on the LD side or on the optical fiber side1). Alternatively, one of the variable angle prisms20may be arranged between the laser diode and the converging lens2, while the other may be located between the converging lens2and the optical fiber3.

The above-described structure of the variable angle prism is only an exemplary one of such a prism and various types of variable angle prism can be used as the deflector K.

It should be noted that, inFIG. 13, the variable angle prism20has only one axis of variable angle. It is possible to employ one variable angle prism having two axes of variable angles as the deflector K instead of two one-axis variable angle prisms.

Alternatively, the optical communication device may be configured such that the converging lens2and one-axis variable angle prism20are movably arranged to adjust the position of the beam spot on the entrance face3aof the optical fiber3.

The present disclosure relates to the subject matters contained in Japanese Patent Application No. 2002-326610 filed on Nov. 11, 2003, and Japanese Patent Application No. 2002-323494 filed on Nov. 7, 2003, which are expressly incorporated herein by reference in their