JP2001133612A - Optical element and optical communications equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform optical communication, even if of positional deviations of a light-emitting element and a light-receiving element. SOLUTION: An optical element (R-DOE) 16, which deflects a light beam from each VCSEL to a corresponding channel of an optical fiber array 14 and is capable of refraction and diffraction, is arranged between a VCSEL array 12 and the optical fiber array 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device and an optical communication device, and more particularly, to an optical communication device for transmitting and receiving data by optical communication and an optical device used for an optical communication device.

[0002]

2. Description of the Related Art Conventionally, by using wavelength division multiplexing (WDM) and time division multiplexing (TDM) in an optical fiber, an enormous amount of data can be transferred at high speed, for example, at a predetermined gigabyte or a predetermined terabyte per second. Optical communication is possible. In the case of a lower speed than this, the multimode optical fiber defines a part of the standard for Ethernet that performs communication with a predetermined number of giga hits per second [see. 1].

By the way, if the number of channels is increased by using a large bundle of multimode optical fibers,
The communication capacity of the LAN can be increased. And
Increasing the number of channels, wavelength division multiplexing,
Can be considered to increase the amount of communication per unit time.

[0004]

However, if the pitch on the side that emits light after wavelength division is different from the pitch of the channel of the optical fiber, an optical element for enabling optical communication between these two elements is provided. Is required.

The present invention has been made in view of the above facts, and proposes an optical element that enables optical communication even when the positions of a light emitting element and a light receiving element are shifted, and an optical communication device using the optical element. The purpose is to:

[0006]

In order to achieve the above object, an optical element according to the first aspect of the present invention is formed as a single unit and has a refraction characteristic and a diffraction characteristic. To reach a predetermined position after emission.

The optical element includes a light emitting element that emits a light beam and a light receiving element that is located at a position other than on the optical path where the light beam emitted from the light emitting element travels and receives the light beam. And can be used for an optical communication device having the following. That is, since the light receiving element is located at a position other than the optical path where the light beam emitted from the light emitting element travels, the light receiving element cannot receive the light beam as it is. Therefore, by using an optical element having the above refraction and diffraction characteristics, the light beam emitted by the light emitting element is made to reach the light receiving element by the refraction and diffraction characteristics. Therefore, optical communication can be performed even if the positions of the light emitting element and the light receiving element are shifted. Since the optical element according to the present invention has refraction and diffraction characteristics, a large diffraction effect can be obtained even when the light beam is largely deflected.

As described above, the light-receiving element is located at a position other than the optical path along which the light beam emitted from the light-emitting element travels, for example, by providing a plurality of light-emitting elements and a plurality of light-receiving elements. Each light receiving element is associated with each other one by one. When the pitch of each light emitting element is different from the pitch of each light receiving element, when a plurality of light emitting elements are provided and when one light receiving element is provided, one light emitting element is provided. In addition, it occurs when a plurality of light receiving elements are provided.

As described above, when a plurality of light-emitting elements and light-receiving elements are provided, and each light-emitting element and each light-receiving element are associated one-to-one, a plurality of optical elements are provided, and the plurality of optical elements is The light beam emitted from each light emitting element is made to reach a light receiving element that is associated with each emitting element on a one-to-one basis. Also, a plurality of light emitting elements are provided and one light receiving element is provided.
When a plurality of optical elements are provided, a plurality of optical elements are provided, and the plurality of optical elements cause light beams emitted from each of the plurality of light emitting elements to reach the light receiving element. Furthermore, when one light emitting element is provided and a plurality of light receiving elements are provided, a plurality of optical elements are provided, and the plurality of optical elements cause a light beam emitted from one light emitting element to reach each of the plurality of light receiving elements.

As will be described later, the optical element is formed by forming a Fresnel lens on the surface of a prism, for example, an incident surface on which light is incident (or an exit surface).
Can be configured.

The plurality of light emitting elements are VCSELs which are expected to play an important role in optical communication.
Arrays can be used. Here, VCSEL (Ve
rtical Cavity Surface Emitting Laser (Vertical Cavity Surface Emitting Laser) is a highly reflective 2
It has a number of reflecting mirrors and emits a laser in a direction perpendicular to the substrate. The wavelength of the emitted laser is determined by the optical confinement phase condition in the laser cavity known as the Fabry-Perot mode. VCSEL
Have a characteristic of a short resonator length and are excellent in a single wavelength property. Since the size of the element in the horizontal direction can be miniaturized, VCS
A plurality of ELs can be easily formed in an array, and can be driven at a low current because they are inexpensive and compact.
It can be easily configured according to the I standard.

Here, as described above, when the light receiving element is located at a position other than the optical path where the light beam emitted from the light emitting element travels, the light beam emitted by the light emitting element is transmitted to the light receiving element. The optical elements to be reached have refractive and diffraction characteristics for the following reasons.

[0013] Multi-wavelength radiation [see. 2] and recent improvements in their performance such as binary Fresnel lenses [see. 3] can be an optical element in the network.

[0014] David T. Neilson and E
ugen Scherfeld [see. 4] is WDM
Micro lens for MUX / DEMUX [see. 6] and optical communication [see. At the time of publication of the plane diffractive element of [5], an array-expander using a micro lens array and a telephoto system was proposed.

The optical element must be capable of simultaneously (i) deflecting and (ii) focusing the light beam on the light receiving element. The off-axis Fresnel lens has the ability to perform the above (i) deflection and (ii) focusing, but has a low diffraction efficiency especially at large deflection angles. On the other hand, analog gray scale lithography [see. Micro prism arrays fabricated using a technique referred to as [7] can increase the deflection angle.

The present inventor has conceived of a new type of optical element by combining the deflection effect by the prism and the diffraction effect by the off-axis Fresnel lens. That is, the present inventors have conceived a single optical element which has refraction and diffraction characteristics and allows incident light to reach a predetermined position after being emitted by the refraction and diffraction characteristics.

The present invention can be easily applied to various functions including data routing and WDM MUX / DEMUX, as well as adjusting the positional deviation between the light emitting element and the light receiving element.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a VCSE as a plurality of light emitting elements.
The concept of adjusting the element density (resolution) between the L array 12 and the optical fiber array 14 as a plurality of light receiving elements will be described. FIG. 1 shows a VCSEL array 1
2. Optical multiplexing including an optical fiber array 14 and a hybrid optical element (R-DOE) 16 disposed between the VCSEL array 12 and the optical fiber array 14 and capable of refracting and diffracting a light beam. A communication device is shown.

The pitch of the VCSEL array 12 is 15 μm. The pitch of each fiber as many as the number of VCSELs in the optical fiber array 14 is
250 μm for single mode optical fiber,
It is 400 μm for a multimode fiber. They communicate optically through space, but the pitch of the two arrays is mismatched. This mismatch increases as the channel (a pair of elements in optical communication) moves away from the central axis. Therefore, in the present embodiment, VCSE
Between the L array 12 and the optical fiber array 14, the light beam from each VCSEL is applied to the optical fiber array 14.
The optical element (R-DOE) 16 that deflects and deflects the light to the corresponding channel is disposed.

FIG. 2 shows three components 16A and 16B of the optical component (R-DOE) 16 which can be refracted and diffracted as optical components of the present invention.
16C is shown. The optical system element (R-DOE) 16
Is not constituted only by these three constituent elements. The components 16A and 16C are provided on the entrance surface 16S of the micro prism, as shown in FIG.
The lens 16F is formed by etching away the lens 16F. The Fresnel lens 16F is formed on the micro prism such that the optical axis of the Fresnel lens 16F is shifted from the central axis of the optical multiplex communication device. Therefore, hereafter, this Fresnel lens will be referred to as off-axis
Also called a micro Fresnel lens. Thus, the constituent elements 16A, 16C of the optical system element (R-DOE) 16
Is formed by forming a Fresnel lens on the prism, so that the refraction characteristics of the prism and the diffraction characteristics of the Fresnel lens can be used.

By the way, the pitch of the optical element (R-DOE) 16 that can be refracted and diffracted is determined by the VCSEL array 12.
The pitch is adjusted so as to be the same as the pitch.
When the light beam from the VCSEL passes through the Fresnel lens, the refraction characteristics of the prism and the Fresnel lens
Due to the diffractive properties of the lens, the light beam diffracts and generates a hologram along the optical axis (off-axis) of the Fresnel lens 16F, thereby simultaneously deflecting the light beam to each optical fiber of the optical fiber array 14. And it is focused. Further, since the optical system element (R-DOE) 16 through which the light beam passes is formed of a prism, the deflection of the light beam is further increased due to refraction in the prism. Thereby, the deflection angle can be increased.

FIG. 3 shows a schematic diagram of one component 16A of a refractive and diffractive optical element (R-DOE). According to Snell's theorem, the angle α of the prism must satisfy the following condition in order to avoid total reflection.

[0024]

(Equation 1)

Here, n is the refractive index of the prism.
For example, for glass, n is 1.5, so
α varies within the range of 42 ° to 90 °. If α is smaller than 42 °, the light beam is totally reflected in the prism. The deflection angle is determined by α, n, the wavelength, the offset of the Fresnel lens, and the focal length of the Fresnel lens. Note that all of the above parameters are adjusted in an actual system so that the light beam from each VCSEL is incident on the corresponding optical fiber. here,
Before specifying parameters at the device level, each deflection angle,
Determining the focal length from each VCSEL to each optical fiber is very important. Once these parameters are known, the prism and Fresnel lens can be designed. For how to calculate the total deflection angle and focal length,
This will be described with reference to FIGS.

As shown in FIG. 4, 2D (two-dimensional) VCS
The position of each VCSEL in the EL array is indicated by a symbol. Light emitted from each of these VCSELs must enter a corresponding optical fiber. For example, light from a VCSEL (denoted by (0,1)) located in row 1 and column 0 will have the same corresponding position in the optical fiber plane, ie, row 1
And column 0. Generally, VCSE
The position of L is indicated by coordinates (m, l). Pvx and Pvy are VCS in the x-axis direction and the y-axis direction, respectively.
This is the pitch of the EL array. Pfx and Pfy are the pitch of the fiber array in the x-axis direction and the y-axis direction, respectively. Therefore, the VCSEL at position (m, l)
For a set of fibers, m (Pfx-Pvx) and 1 (Pfy-Pvx) in the x-axis direction and the y-axis direction, respectively.
There is an offset of y). When m and l increase,
The offset of each VCSEL-fiber increases.

FIG. 5 shows parameters for specifying the total deflection angle required for light incident from the VCSEL at the position (m, l) to the corresponding fiber. Angle θm, l, φ
m and l are expressed by equations (2) and (3), respectively, and the focal length is expressed by equation (4). The beam waist on the fiber array surface is calculated using the equation (5).

[0028]

(Equation 2)

[0029]

(Equation 3)

[0030]

(Equation 4)

[0031]

(Equation 5)

However,

[0033]

(Equation 6)

[0034] And a is a single R-DOE channel
Beam spot size from VCSEL incident on the
is there.

N = 1.5, Z ₀ = 5.00 mm, Pfx =
Pfy = 400 μm, Pvx = Pvy = 15 μm, a = 10 μ
Consider the case where m and λ = 1 μm. Assuming a 15 × 15 array, the range of prism angles is 90 ° to 76 °.
Range (satisfies equation (1)), focal length is 5.0
0 mm to 8.00 mm. Then, the beam spot size is calculated from equation (5), and is adjusted to a value of 2 μm for each channel. This value is sufficient to concentrate the total optical power in the fiber core.

As described above, in the present embodiment,
Since the VCSEL array is used as the light emitting element of the optical communication device, the optical communication device can be configured inexpensively and compactly, can be driven with a low current, and has a VLSI.
It can be easily configured according to standards.

In this embodiment, the optical system element (R
-DOE) 16 is constructed by forming a Fresnel lens on a prism, so that the refraction characteristics of the prism and the diffraction characteristics of the Fresnel lens can be used, and therefore a large deflection A large diffraction effect can be obtained even at corners.

FIG. 6 shows a modification of the optical system element (R-DOE) 16 that can be refracted and diffracted. This modification is 1
A plurality of light beams of different wavelengths from one VCSEL array are focused on a single optical fiber 24. Each VCSEL is modulated with a different signal, and the light beam is transmitted over one optical fiber 24, thus this variant functions as a wavelength division multiplexing multiplexer system (WDM MUX).

FIG. 7 shows a 1 × 8 matrix waveguide switch array (which functions as a router as a whole (WDM
(DEMUX)) 26 shows an apparatus for transmitting a data stream. That is, an apparatus for distributing and transmitting one data stream to each of the plurality of optical fibers 24 is shown. The pitch number of the output channels of the waveguide switch array 26 is configured to be substantially equal to the pitch number of each optical fiber 24 of the optical fiber array 14. Thus, the output channels are arranged so as to be dense, that is, closer to each other, and thus the above-described pitch adjustment between the optical fiber array 14 and the waveguide switch array 26 is necessary. Therefore, an optical system element (R-DOE) 16 that can be refracted and diffracted is arranged on the output side of the waveguide switch array 26 to function as a deflection device.

Reference

[Outside 1]

[0041]

As described above, the present invention has a refraction characteristic and a diffraction characteristic, so that a large diffraction effect can be obtained even when light is largely deflected.

Further, the optical element according to the present invention uses an optical element having refraction and diffraction characteristics and causes the light beam emitted by the light-emitting element to reach the light-receiving element by the refraction and diffraction characteristics. Optical communication can be performed even if the positions of the element and the light receiving element are shifted.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating adjusting the element density (resolution) between a VCSEL array and a fiber optic array.

FIG. 2 shows an optical element (R-DOE) capable of refraction and diffraction.
It is a schematic diagram of.

FIG. 3 is a schematic diagram of constituent elements of a unit-type refractible and diffractive optical system element (R-DOE).

FIG. 4 is a diagram showing a common vertical axis of each VCSEL.

FIG. 5 is a diagram showing definitions of parameters for deflecting a light beam.

FIG. 6 is a diagram illustrating an example in which a refractible and diffractive optical system element (R-DOE) is applied for multi-wavelength coupling of a WDM system.

FIG. 7 is a diagram showing an example in which an optical system element (R-DOE) capable of refraction and diffraction is applied for a path switch of large deflection.

[Explanation of symbols]

 12 VCSEL array 14 Optical fiber array 16 Optical system element (R-DOE)

Claims (7)

[Claims] 1. A single optical element having a refraction characteristic and a diffraction characteristic and allowing incident light to reach a predetermined position after being emitted by the refraction characteristic and the diffraction characteristic. 2. The optical element according to claim 1, wherein the optical element is formed by forming a Fresnel lens on a surface of a prism. 3. A light-emitting element that emits a light beam, a light-receiving element that is located at a position other than on an optical path along which the light beam emitted from the light-emitting element travels, and receives the light beam; And a single optical element having a diffraction characteristic and allowing the light beam emitted by the light emitting element to reach the light receiving element by the refractive characteristic and the diffraction characteristic. 4. A light-emitting element and a plurality of light-receiving elements are provided, and each light-emitting element and each light-receiving element are associated with each other on a one-to-one basis. The optical communication device according to claim 3, wherein the light beam emitted from each of the elements is made to reach a light receiving element that is associated with each of the emitting elements on a one-to-one basis. 5. A light-emitting device comprising: a plurality of light-emitting elements; one light-receiving element; and a plurality of optical elements, wherein the plurality of optical elements transmit light beams emitted from each of the plurality of light-emitting elements to the light-receiving element. The optical communication device according to claim 3, wherein 6. A light-emitting device comprising: one light-emitting element; a plurality of light-receiving elements; a plurality of optical elements, wherein the plurality of optical elements receive light beams emitted from the one light-emitting element by the plurality of light-receiving elements. The optical communication device according to claim 3, wherein the optical communication device reaches each of the elements. 7. The optical communication device according to claim 3, wherein the optical element is formed by forming a Fresnel lens on a surface of a prism.