Fiber Collimators of Daheng Optics

 

Facing the ever-increasing market demand, Daheng New Epoch Technology Inc. (“Daheng Optics”) has developed a series of high-precision fiber collimators and fiber couplers of enhanced collimation performance, filling the blank of integrated coupling lenses in earlier days. Here is a brief introduction of the products.

 

GCX-L series triple-lens fiber collimator

 

In earlier days, the fiber collimators of Daheng Optics adopted a single-lens design. Due to restrictions of optical principles, the collimation effect was not ideal. Therefore, triple-lens fiber collimators of highly collimated beam spot have been designed. With better performance in eliminating spherical aberration, the new products have a smaller divergence angle and a relatively perfect wave phase difference lower than 1/8λ. The M2 factor tested is close to 1 (Gaussian beam). Of course, the value of the M2 factor is also related to the M2 factor of the original laser beam. Due to restrictions in optical design, the collimator works only on single mode fiber. Special consideration should be given to multimode fibers or fiber bundles with larger core diameters.

The triple-lens fiber collimators have the following features:

▲Broadband anti-reflection coating, calibration wavelength of 630nm, 660nm, 780nm and 1550nm

▲Effective focal length options of 6mm, 12mm and 15mm

▲Full divergence angle<=0.12°

▲Interface type: FC/PC or FC/APC

▲Exquisite stainless steel housing

Each fiber collimator will be individually calibrated before put in our storage, and M2-200S-FW@spiricon M2 measurement device is used in testing M2 factor value, which shall be kept within 1.3. The fiber interface is tightened in advance. Clients only need to connect the fiber pigtail to the interface of the collimator when using and there is no need to debug.

The broadband anti-reflection coating on lenses covering a range of 405nm-2µm can reduce the residual reflection on the lens surface with a high optical resistance. The typical value can reach 7.5J/cm² (10ns, 10Hz) at 1064nm. The high-precision stainless steel interface of the triple-lens collimator ensures outgoing alignment repeatability and facilitates the disassembly and replacement of fibers. Please note that the APC connector has an inclination angle and fiber with the same APC interface is required in debugging.

 

GCX-LF series aspherical fiber collimator

In order to simplify the assembly and process, Daheng Optics has further come up with a series of aspheric optical fiber collimators featuring a more compact structure and a more ideal collimation effect through single aspheric lens. Compared with earlier single-lens fiber collimators, the performance has been significantly improved. However, due to restrictions of the processing technology of aspheric lens, GCX-LF series are not applicable to high power laser. Tests prove that despite the low damage threshold, GCX-LF series collimator can still withstand relatively high laser energy, typically 5J/cm2 (10ns, 10Hz, 1064nm) under the condition of 1064nm.

▲Broadband anti-reflection coating and calibration wavelengths of 405nm, 532nm, 633nm, 780nm, 980nm, 1064nm and 1550nm

▲Effective focal length options of 4mm, 6mm, 11mm, 15mm and 18mm

▲Full divergence angle<=0.12°

▲Interface type: FC/PC, FC/APC, SMA

▲Exquisite stainless steel housing

Calibration is conducted on each fiber collimator that put in our storage and the optical fiber interface at the tail is fixed for client’s direct use under corresponding bands. Besides, clients have the option of conducting slight adjustment according to the actual waveband. For this purpose, a threaded hole is made in the collimator housing. Under certain circumstances when users are not able to choose the exact corresponding wavelength, the proximate band can be selected and fine-tuned to meet the application conditions.

For the above two series of collimators, the laser spot quality of some lenses are tested. The following is a typical laser spot diagram. The M2 factor of the laser source passing through the collimator is 1.27, which is basically the same as the laser itself, and the laser spot is basically of Gaussian distrubtion.

For detailed specifications of the above two types of optical fiber collimators, refer to website or consult sales staff of Daheng Optics. Please pay attention to the following before selecting our products:

• The full-angle divergence angle of the collimated laser spot approximately follows the formula：θ≈MFDf(180π)
• The theoretical beam waist diameter of the collimated laser spot approximately follows the formula：d≈4λ(fπ∙MFD)
• NA refers to the cone angle (half angle) range of the beam that the collimator receives, which is approximately D/2f. Generally, to avoid energy loss, the NA of the collimator should be higher than that of the fiber patch cord.
• The above collimators are all used under single-mode fiber conditions.
• Among our collimators, the triple-lens collimator can be used for higher damage thresholds, up to 7-10J/cm². However, the damage threshold of aspherical collimators is not recommended under high power circumstances. As the lens of aspherical collimators adopts a molding process, approximately 4-5J/cm² is OK.
• The standard GCX-LF series fiber collimators have M1.6 threaded holes in the housing. Before delivery, the product is adjusted according to the wavelength specified. After delivery, due to the difference in fiber connectors, clients can fine-tune by themselves to ensure the collimation of the outgoing beam. Currently the GCX-L series triple-lens collimators, adopting the bonding method, are not adjustable.

 

GCX-C series five-dimensional fiber coupler

The GCX-C series five-dimensional fiber couplers feature a compact structure, stable performance and precise five-dimensional adjustment in a very small space. The adjustment value in the X and Y directions is more than ±0.5mm, that in the Z direction is more than 2mm, and the pitch and yaw adjustment value is about ±4°. The product has a high coupling efficiency (70%) and good stability (<5%@72h). Calibration is conducted on each fiber coupler that put in our storage, but due to the diverse beam conditions of users, re-adjustment is necessary before using the device to obtain the best coupling effect. The coupling efficiency and stability of the product are closely related to the final debugging state. Please be sure to read carefully the instruction on debugging on our website.

• Broadband anti-reflection coating and calibration wavelengths of 405nm, 532nm, 780nm, 1550nm.
• Effective focal length: 6mm, 15mm, 18mm.
• Interface type: FC/PC, FC/APC, SMA
• Exquisite stainless steel housing

 

In order to obtain a compact structure and high coupling efficiency, aspheric lenses are also adopted as focusing lens in GCX-C series. The diagram below clearly shows the difference in focusing ability between spherical lens and aspheric lens.

Take a lens with a focal length of 30mm and a clear aperture of 9mm for example. With the same NA (numerical aperture) value, a lens with a smaller focal beam spot has a better coupling performance.

The following Diagram a shows the zemax simulated dispersed spot of an ordinary plano-convex lens, which is about 72µm. Diagram b shows the dispersed spot of an aspheric lens, which is approximately 0.22µm. It can be seen that for single lens, the focusing effect of the aspherical lens is far better than that of the ordinary spherical lens, so aspheric lens is adopted in small fiber couplers.

Diagram a

Diagram b

In theoretical simulation, the aspheric lens can achieve a coupling efficiency close to 99% under well-matched conditions. However, the coupling efficiency in the actual optical path is also affected by position tilting, offset, transmission loss, fiber connector loss, etc., which will reduce the actual coupling efficiency. The following diagrams show the effects of (a) lens focal length, (b) axial position deviation, (c) angle deviation and (d) lateral position deviation on coupling efficiency.