JPS5856490A - Laser diode system - Google Patents

Abstract

PURPOSE:To perform a laser diode system having excellent transmitting quality with less nose by disposing a laser diode and a detector oppositely at the prescribed distance from the optical axis of a lens at two lenses, disposing a translucent mirror at the middle of the lenses, disposing the optical fiber at the linearly symmetrical position with the detector at the optical axis, thereby constructing to allow the returning light from the fiber to be reflected on the mirror and to be incident into the detector. CONSTITUTION:In a laser diode LD, a detector D is opposed to two spherical lenses L1, L2 at the interval of 2l between the lenses. The diode LD and the detector D are isolated by h from the optical axis X-X' of the lenses L1, L2, an optical fiber F is disposed at the linearly symmetrical position with the detector D to the optical axis X-X', and the mirror surface of the translucent mirror M is disposed at the position just at the middle of the lenses L1 and L2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser diode system used for optical communications using laser diodes and optical fibers, and provides a laser diode system with low noise and excellent transmission quality. It is something that will be realized.

Figure 1 is a diagram showing a conventional laser diode system, in which the laser light from the laser diode LD is transmitted to the lens L.
It is made to enter the optical fiber F via l % L 2 and transmit the optical signal. However, the internally reflected light of the optical fiber F, as well as the return light from the point of incidence on the optical fiber F, the end of the optical fiber F, and the connecting surface return directly to the laser diode LD, distorting the oscillation spectrum of the laser diode LD, and causing As a result, a signal containing noise will be transmitted. However, since this returned light has a correlation with the optical signal transmitted from the laser diode LD,
This noise component can be removed as follows. That is, a mirror M is disposed between the lenses L1 and Lx, and the return light from the optical fiber F is reflected by the mirror M.
The noise component is extracted by a detector D through a lens L3, and is electrically reversed in phase and applied to the laser diode LD again. As a result, the component of the light returning to the laser diode LD is canceled out, making it theoretically possible to transmit a noise-free optical signal.

However, in reality, the return light from near-end positions such as the surface of the lens L2 near the mirror M and the entrance surface of the optical fiber F is too strong compared to the weak return light from the terminal end and connection point of the optical fiber F. Furthermore, it is impossible to accurately extract the actual noise component. Therefore, the effect of canceling the noise due to the antiphase component of the returned light cannot be obtained.

An object of the present invention is to solve such problems in the conventional method and to realize a device that can reliably extract each component of the returned light. To achieve this objective, the present invention
A laser diode and a detector are placed facing each other with two lenses in between, and the laser diode and detector are placed a certain distance away from the optical axis of the lens, and a semi-transparent glass is placed between the two lenses. A mirror is disposed, and an optical fiber is disposed at a position symmetrical to the detector with respect to the optical axis of the lens, so that the return light from the optical fiber is reflected by the mirror and enters the detector.

Next, an embodiment of a laser diode system according to the present invention will be described. FIG. 2 is a schematic diagram showing a first embodiment of the present invention. The laser diode LD faces the detector D with 2 f[i ball lenses L1 and L2 spaced apart from each other by a distance of 21. Further, the laser diode LD and the detector D are spaced by h from the optical axis XX' of the lenses L+ and L2, and the optical fiber F is arranged at a position symmetrical to the detector D with respect to the optical axis XX'. A mirror surface of a semi-transparent mirror M is placed exactly in the middle of the two lenses Ll and L2. Then lenses L+, L
When the distances from i to the output surface of the laser diode LD, the light receiving surface of the detector D, and the input surface of the optical fiber F are the focal lengths f of lenses L+ and L2, respectively, the output surface of the laser diode LD and the detector By tilting the light-receiving surface of D and the incident surface of optical fiber F by an angle δ with respect to the optical axis Reflection on the surface gives the best results.

This inclination angle δ can be determined using the ray matrix method as follows. That is, as shown in FIG. 3, the distance from the laser diode LD to the center of the lens L1 and the distance from the end face of the optical fiber F1 detector D to the center of the lens Lz are respectively A, and the distance between the centers of the lenses Ll and L2 is 2B, the focal length of lens L+, L2 is f, the distance from lens optical axis X-X' of laser diode LD is xl,
If the angle of inclination is θ1, the distance of the detector D and optical fiber F from the lens optical axis X-X" is x2, and the angle of inclination is θ2, then f=A, where・(1)B
If =x, then xz -h...(2) Also, θi
From -θ2... (3) 1, that is, θ+=6, so δ is as shown in equation (4), and the laser diode LD and optical fiber F are matched, and the optical fiber F and detector D are aligned with each other via mirror M. Furthermore, (1), (2), (3) above
, (4) expresses the optical path matching condition.

In this way, the optical signal transmitted from the laser diode LD is transmitted to the optical fiber F via the lenses I, +, and L2.
Transmitted with the best optical coupling efficiency. Moreover, the return light from the optical fiber F is reflected by the mirror M and enters the detector D, and the optical fiber F and the detector D are also in a positional relationship that provides the best optical coupling efficiency. Therefore, all the returning light components from the optical fiber F can be reliably received and detected by the detector D.

FIG. 4 is a diagram showing a second embodiment. This example is
Laser diode LD is 27! Two lenses separated by l, 1. ．． Opposing the detector D with L2 in between, the laser diode LD and the detector D connect the lenses I, +
, L2, an optical fiber F is arranged at a position that is a distance away from the optical axis x-x' of the optical axis x-x' and is line-symmetrical to the detector D with respect to the optical axis x-x', and is placed exactly in the middle of the two lenses L1 and Ll. The mirror surface of the semi-transparent mirror M is placed at the position. If the distance from the centers of lenses L+ and L2 to the end faces of laser diode LD, detector D, and optical fiber F is equal to the focal length of the lens 111f, then laser diode LD, detector D, and optical fiber F
The end face of the lens is formed into a surface that is inclined at an angle θC with respect to a plane perpendicular to the optical axis xx' of the lens. This angle θ0 is determined by the angle θ of the emitted light of the laser diode LD, as shown in the emission surface of the laser diode LI) in FIG.
l (same as θ1 in the first embodiment) is the prism angle for biasing, (θ1 +θ.) = na θ0
However, no is θo'' +10-101 from the above formula for the refractive index of the optical fiber.

In this case, losses due to reflection on the sloped finished surface can be prevented by applying an anti-refresh coating to the finished surface.

In this embodiment, in the case of l mi f, the end faces of the laser diode LD, optical fiber F, and detector D become θa=O as shown in FIG. As shown in the figure, the laser diode LD, optical fiber F
The inclination angle θ0 of the end face of the detector D is opposite to that in FIG. 4.

Since the return light from the optical fiber F can be effectively extracted in this way, by inverting its phase and applying it to the laser diode using a known method, optical transmission with less noise becomes possible.

Note that, as shown in FIG. 8, by providing a resonator such as an etalon in the laser diode LD itself, the oscillation frequency of the laser diode LD is further stabilized. In this figure, one of the light emitting surfaces S+ SSz at both ends of the laser diode LD is S! An etalon E is attached as a resonator. Then, only the signal with the oscillation frequency fO is reflected back into the laser diode LD by the spherical surface of the surface a of the etalon E, and the other noise components are reflected by the reflection 11m arranged diagonally in front of the etalon E. Remove by reflecting in the direction. Therefore, only the laser beam with the oscillation frequency f0 is emitted from the light emitting surface S2 and transmitted. The approximately spherical surface number a of the etalon E is formed on the same plane as the wavefront C, which is perpendicular to the light vector b, that is, the Gaussian beam, and is located on the same plane as the wavefront C. It is configured so that its dimensions are wavelength λ×n. Therefore, the surface a of the etalon E becomes almost spherical, and only the signal with the oscillation frequency fo is reflected on the same surface a as the wavefront, and a standing wave is generated L and fed back to the output surface S2. Only the signal resonates effectively and is emitted, 11:! Coupled with the fact that the return light described above can be effectively detected by the detector D, the transmission quality of the optical signal is further improved.

As is clear from the above embodiments, according to the present invention, a laser diode and a detector are placed facing each other with two lenses in between, and the laser diode and detector are placed at a certain distance from the optical axis of the lens. It is placed with only one side. Furthermore, a semi-transparent mirror is placed between the two lenses, and an optical fiber is placed at a position symmetrical to the detector with respect to the optical axis of the lens, so that the return light from the optical fiber is reflected by the mirror. The beam is configured to be incident on the detector. Therefore, the optical signal emitted from the laser diode is transmitted to the optical fiber with the best coupling efficiency, and the return light from the optical fiber is also incident on the detector and detected with excellent coupling efficiency, and the strength and weakness of the return light is detected. components are reliably detected by the detector. As a result, the signal transmission quality is significantly improved by inverting the phase of the return light that has a negative effect on the signal transmission quality and applying it to the laser diode.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a conventional laser diode system, Figs. 2 to 8 show embodiments of the laser diode system according to the present invention, and Fig. 2 shows the first embodiment. 3 is an explanatory diagram of its operation, FIG. 4 is a schematic diagram showing the second embodiment, FIG. 5 is an enlarged view of the emission surface of the laser diode, and FIG. 6 is an illustration of the second embodiment. FIG. 7 is a schematic diagram showing the case where l=f in the embodiment, FIG. 7 is a schematic diagram showing the case where e×f in the second embodiment, and FIG. 8 is a schematic diagram showing the third embodiment. In the figure, LD is a laser diode, Ll and Ll are lenses, F is an optical fiber, D is a detector, M is a mirror,
E is etalon and Al. Patent Applicant Fujitsu Limited Agent Patent Attorney Minoru Aoyagi Figure 1 Figure 3 Figure 4 Figure 6v! J Figure 7 Figure 8.

Claims (1)

[Claims] A laser diode and a detector are placed facing each other with two lenses in between, and the laser diode and detector are placed a certain distance away from the optical axis of the lens, and a semi-transparent glass is placed between the two lenses. A laser diode is configured such that a mirror is arranged and an optical fiber is arranged at a position symmetrical to the detector with respect to the optical axis of the lens, and the return light from the optical fiber is reflected by the mirror and enters the detector. system.